MNRAS 000, 1–16 (2018) Preprint 1 July 2020 Compiled using MNRAS LATEX style file v3.0

The influence of angular momentum andenvironment on the H i gas of late-type galaxies

Chandrashekar Murugeshan,1,2? Virginia Kilborn,1,2 Thomas Jarrett,3

O. Ivy Wong,4,5,2 Danail Obreschkow,5,2 Karl Glazebrook,1,2

Michelle E. Cluver,1,6 and Christopher J. Fluke11Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia2ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (ASTRO 3D), Australia3Astronomy Department, University of Cape Town, Private Bag X3, Rondebosch 7701, Republic of South Africa4CSIRO Astronomy & Space Science, PO Box 1130, Bentley, WA 6102, Australia5ICRAR-M468, UWA, 35 Stirling Highway, Crawley, WA 6009, Australia6Department of Physics and Astronomy, University of the Western Cape,Robert Sobukwe Road, Bellville, South Africa

Accepted XXX. Received YYY; in original form ZZZ

ABSTRACTWe use high-resolution H i data from the WHISP survey to study the H iand angular momentum properties of a sample of 114 late-type galaxies. Weexplore the specific baryonic angular momentum – baryonic mass (jb−Mb)relation, and find that an unbroken power law of the form jb ∝M0.55±0.02

bfits the data well, with an intrinsic scatter of ∼ 0.13 ± 0.01 dex. We re-visit the relation between the atomic gas fraction, fatm, and the integratedatomic stability parameter q (the fatm − q relation), originally introducedby Obreschkow et al., and probe this parameter space by populating itwith galaxies from different environments, in order to study the influenceof the environment on their jb, fatm and q values. We find evidence thatgalaxies with close neighbours show a larger intrinsic scatter about thefatm − q relation compared to galaxies without close-neighbours. We alsofind enhanced SFR among the deviating galaxies with close neighbours. Inaddition, we use the bulge-to-total (B/T) ratio as a morphology proxy, andfind a general trend of decreasing B/T values with increasing disc stabilityand H i fraction in the fatm − q plane, indicating a fundamental link be-tween mass, specific angular momentum, gas fraction and morphology ofgalaxies.

Key words: galaxies: evolution– galaxies: fundamental parameters–galaxies: ISM– galaxies: kinematics and dynamics

1 INTRODUCTION

Galaxy evolution is governed by a range of inter-nal and external processes. The former include funda-mental properties such as mass and angular momen-tum, in conjunction with non-axisymmetric potentialsand feedback processes (see for example Jog 2002;Zasov & Zaitseva 2017; Genel et al. 2015). Externalprocesses are particularly prevalent in higher densityenvironments such as compact groups and clusters,where gas and stars can be redistributed in galaxiesdue to tidal interactions and ram pressure stripping(Gunn & Gott 1972; Fasano et al. 2000). This has beenshown to affect global properties of galaxies such astheir gas fractions (Davies & Lewis 1973; Giovanelli &

? E-mail:cmurugeshan@swin.edu.au

Haynes 1985; Solanes et al. 2001), star formation rate(see for example Lewis et al. 2002; Gomez et al. 2003),colour and morphology (Skibba et al. 2009). In addi-tion, there is a morphological trend with respect to theenvironment, wherein the fraction of redder and moreearly-type elliptical galaxies is observed to be higher indense environments such as clusters compared to thefield, where the fraction of disc-like star forming late-type galaxies is higher (morphology–density relation;Dressler 1980; Goto et al. 2003). Therefore, studyingthe effects of the various processes on the global prop-erties of galaxies is important for our understandingof how galaxies evolve. A particular focus of this workis to study the influence of angular momentum (an in-trinsic property) and that of the environment on theobservable properties of galaxies.

One of the key constituents of galaxies is their

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neutral atomic hydrogen (H i) gas. It is the H i gasthat is consequently converted to stars via a H2 phaseand drives the evolution of galaxies. The H i gas discis loosely bound to the gravitational potential of thegalaxy and typically more extended than the stellardisc (RH i ∼ 2−3Rd, where Rd is the optical disc scale-length, see for example Broeils & van Woerden 1994;Broeils & Rhee 1997; Verheijen & Sancisi 2001), whichleaves the H i gas susceptible to environmental pro-cesses (Hibbard & van Gorkom 1996). In addition,the H i gas is an excellent tracer of the rotation veloc-ity of galaxies out to large radii, thus enabling us toaccurately compute their angular momentum. High-resolution H i observations of galaxies, therefore, proveto be indispensable, as H i is a very good tracer of theeffects of both internal and external processes.

Peebles (1969) suggested that interacting darkmatter (DM) halos acquire their angular momen-tum (AM) from tidal torques during the protogalacticstages. The baryonic material that is eventually ac-creted by the DM halos then cools onto a centrifu-gally supported disc. This leads to the formation ofdiscs with well-defined scale lengths (see Fall & Efs-tathiou 1980; Mo et al. 1998 and references therein),bringing about the various disc scaling relations suchas the Tully-Fisher relation (Tully & Fisher 1977), themass-size relation (Verheijen & Sancisi 2001), the fun-damental plane of spiral galaxies (Shen et al. 2002)and various other H i scaling relations (Haynes &Giovanelli 1984; Chamaraux et al. 1986; Solanes etal. 1996; Verheijen & Sancisi 2001). Thus, AM alongwith mass becomes a fundamental underpinning prop-erty of galaxies.

The first empirical study of galactic stellar AMwas conducted by Fall (1983) who found a tight cor-relation between the stellar mass (M?) and the spe-cific stellar AM (j?) of the form j? = qMα

? , withα ≈ 2/3 for both spiral and elliptical galaxies, butwith the factor q about five times less for ellipticals.The ΛCDM model of the universe predicts this rela-tionship between mass and specific AM with an ex-ponent α = 2/3. Romanowsky & Fall (2012) revisitedthis relation with a larger sample of spiral and ellipti-cal galaxies and established the fact that, indeed themorphology of galaxies is related to their sAM. Thisgives a more physically motivated explanation to theobserved range of galaxies in the Hubble classification,in the sense that AM determines the morphology ofgalaxies (Sandage et al. 1970; Hernandez & Cervantes-Sodi 2006;). Similarly, a fundamental relation betweenmass, specific baryonic (cold gas + warm gas + stars)AM and the bulge mass fraction (β) was discoveredfor late-type galaxies by Obreschkow & Glazebrook(2014)[hereafter OG14]. Following this, the colour andmorphology of galaxies were also observed to be linkedto their AM (see for example Cortese et al. 2016; Sweetet al. 2018).

It is therefore important to understand both theevolution of AM in galaxies and the various pro-cesses that affect it. With the advancement in semi-analytic and hyrodynamical simulations over the pastfew decades, studies focusing specifically on the AMevolution of galaxies find that AM in galaxies can belost due to mergers (Hernquist & Mihos 1995; Lagos

et al. 2017), while it can be increased due to cold-mode accretion (see for example Danovich et al. 2015),galactic winds and fountains (Brook et al. 2012; De-Felippis et al. 2017 and references therein).

In terms of the connection between AM and theH i properties of galaxies, Zasov & Rubtsova (1989)found the first empirical evidence that the H i massof isolated disc galaxies strongly correlates with theirsAM. In a similar vain, Huang et al. (2012) find thatgalaxies with higher H i gas fractions reside preferen-tially in dark matter halos with high spin parameters.

Star formation in disc galaxies is induced viadisc instabilities that allow the H i gas to collapseto form molecular clouds, where eventually stars areformed. The local disc stability is often quantified bythe Toomre parameter

Q ≈ σκ

πGΣ

Where σ is the dispersion velocity of the gas in thedisc, κ is the epicyclic frequency and Σ is the gas sur-face density (Toomre 1964). A value of Q < 1 im-plies that the gas disc is unstable, promoting star for-mation and if Q > 1, the disc is said to be stable,restricting star formation. Many previous theoreticaland simulation studies showed the link between discstability and AM, where unstable disc galaxies werefound to re-distribute their AM and transform intospheroidal systems (Combes et al. 1990; Norman, Sell-wood & Hasan 1996; Mao & Mo 1998; Dutton & vanden Bosch 2012; Stevens et al. 2016).

Obreschkow et al. (2016)[hereafter O16] linkedthe atomic disc stability of galaxies to their sAMby introducing a parameter-free model predicting acorrelation between the atomic gas fraction fatm =1.35MH i/Mb and what they originally termed the“global stability” parameter q = jbσ/GMb, for ax-isymmetric disc galaxies in equilibrium. Here MH i isthe H i mass of the galaxy, jb is the specific bary-onic angular momentum, σ is the dispersion velocityof the Warm Neutral Medium (WNM), Mb is the to-tal baryonic mass and G is the universal gravitationalconstant. They find that a sub-sample of late-typegalaxies in THINGS (Walter et al. 2008), dwarf galax-ies part of LITTLE THINGS (Hunter et al. 2012),and a sub-sample of confusion-free HIPASS (Meyer etal. 2004) sources follow the model predictions consis-tently. It is worth noting, a priori, that the q parameterdoes not refer to the stability of any global mode, butto a local mode (Toomre instability of the atomic gas)that is integrated over the entire disc. For this reasonwe will term this parameter as the “integrated atomicstability parameter”(hereafter simply the stability pa-rameter), to avoid any confusion. Furthermore, q doesnot describe the actual current stability of the disc ora sub-component, but the hypothetical mean stabilityof a purely atomic disc with the same spin.

Lutz et al. (2017, 2018) show that a sample of iso-lated H i-excess galaxies follow the fatm − q relationconsistently and owe their excess H i gas fractions tohigher sAM. In a subsequent study testing the analyt-ical model of O16, Murugeshan et al. (2019) confirmthat AM regulates the H i gas fraction in H i-deficientspirals from low-density environments. Dzudzar et al.(2019) report that gas-rich galaxies that are part of

MNRAS 000, 1–16 (2018)

The influence of AM and environment on the HI gas of late-type galaxies 3

groups also follow the fatm−q relation, indicating thatthe sAM of galaxies is an important driver of their H igas even in group-like environments. Recently, Li etal. (2020) use a sample of galaxies from the VIVAsurvey (Chung et al. 2009) to study the behaviour ofa sub-sample of galaxies in the Virgo cluster on thefatm − q plane. They find that galaxies in their sam-ple lie consistently below the relation, indicating thatextreme environmental processes (such as ram pres-sure stripping) have removed significant fractions oftheir atomic gas without affecting their q values.

Additionally, Romeo & Mogotsi (2018) discussthe role of AM and mass in regulating the local insta-bilities in galaxies, while a more generic stability pa-rameter that connects the sAM of individual disk com-ponents - such as cold (H2) and warm neutral medium(H i) as well as stars - to their individual fractions(H2, H i and stellar mass fractions) was introduced byRomeo (2020). All these studies show the importanceof AM in influencing star formation in disc galaxies,and how tightly it is linked to their global properties.

In this work, we extend previous studies that haveexplored the fatm−q parameter-space and populate itwith the largest sample of galaxies to date, for whichhigh-resolution H i data has been procured from theWesterbork H i Survey of Spiral and Irregular galaxies(WHISP; Swaters et al. 2002). Robust rotation curveshave been derived from 3D kinematic fitting to the H idata, which are then used to calculate precise valuesof their total baryonic AM. We examine the effects ofthe environment on the sample galaxies, probe theirstar formation properties, as well as study their mor-phology to establish a holistic understanding of theprocesses affecting their behaviour on the fatm − qplane. The results from this study are highly relevantfor the upcoming WALLABY H i survey (Koribalskiet al. 2020) using ASKAP, which has the potential toobtain high-resolution H i data for thousands of galax-ies. The WALLABY survey will have similar spatialand spectral resolutions as that of the WHISP sample.This study will therefore enable us to make predictionsand formulate expectations from the WALLABY sur-vey and other future large H i surveys such as the SKA,in the context of using H i as a tool to probe the AMin galaxies.

In Section 2, we present the sample and discussthe methods employed in our AM analysis, as well asthe different techniques used to probe the local en-vironment. We present the main results and the fol-lowing discussions in Section 3. Finally, we summarisethe main results in Section 4. We have assumed thefollowing cosmology for the current study: Ω = 0.27,Λ = 0.73 and H0 = 73 km s−1Mpc−1.

2 SAMPLE AND METHODS

2.1 The sample

The WHISP survey is one of the largest resolvedH i surveys to date, with high-resolution data avail-able for over 400 galaxies. The galaxies in the orig-inal WHISP sample were selected from the UppsalaGeneral Catalogue of Galaxies (UGC; Nilson 1973),and observed with the Westerbork Synthesis RadioTelescope (WSRT) with a synthesised beam ∼ 14′′ ×

14′′/sinδ. The target galaxies were required to haveD25 > 1.5′ (where D25 is the B-band isophotal di-ameter at 25 mag arcsec−2), with declinations northof 20oand additionally have H i peak flux densities> 100mJy.

For this work, we make use of the 30′′ resolu-tion data cubes (see Swaters et al. 2002), with typi-cal velocity resolutions of ∼ 5 km s−1. From the pri-mary sample, we selected galaxies with H i disc ra-dius spanning at least five resolution elements. Thisensures that there are enough resolution elements toaccurately fit 3D tilted-ring models to the galaxies andextract their kinematic properties. In addition, we se-lected only those galaxies with inclination angles be-tween 20oand 80o, to avoid highly face-on and edge-on systems. The final sample consists of 114 galaxies(listed in Appendix A ).

The stellar mass range for this sample varies be-tween 7 < logM?/M < 11.5. This is a wide range,spanning over five decades in stellar mass, includingdwarfs, irregulars and spiral galaxies. We compare theH i and stellar mass properties of our sample with thexGASS representative sample (Catinella et al. 2018).The xGASS survey is one of most sensitive single-dish extra-galactic H i surveys with H i detections forover 1000 nearby galaxies. It is an unbiased survey,in that, all galaxies within the stellar mass range9 < logM?/M < 11.5 and within the redshift range0.025 < z < 0.05 are observed until H i is detectedor a low gas-mass fraction (1.5 - 5%) is reached. Thismakes the xGASS sample a gold standard for com-paring the H i and stellar properties of nearby galax-ies such as those in the WHISP sample. To see if oursample spans uniformly in both H i and stellar mass,we plot the MH i −M? scaling relation alongside thexGASS galaxies for comparison, as shown in Fig. 1. Inaddition to the xGASS galaxies, we also plot the 16THINGS galaxies originally used by OG14 and O16in their study introducing the fatm − q relation. Wesee that our sample spans uniformly in both stellarand H i mass compared to the xGASS sample in thehigher-mass end (logM?/M > 9.0). While we donot have a good reference sample in the lower-massend (logM?/M < 9.0) to compare our sample galax-ies with, based on the fact that the WHISP galaxiesare H i selected, coupled with our size selection cri-teria means that the galaxies in the lower-mass endare likely to be biased towards gas-rich, low-mass spi-rals and/or dwarfs. Table. 1 lists some statistics forall three samples. Also shown in Fig. 2 is the H i gasfraction – stellar mass scaling relation for the WHISP,xGASS and THINGS samples. We list all the relevantproperties and derived quantities for our sample inTable. A1

2.2 Total baryonic mass (Mb) and specificbaryonic angular momentum (jb)

We perform 3D tilted-ring fitting (Rogstad etal. 1974) to the 30′′ resolution WHISP data cubesusing 3DBarolo (Di Teodoro et al. 2015) to modelthe galaxies and extract their kinematics. For everygalaxy, a list of best initial guesses for the center,systemic velocity, inclination (i), position angle (PA),maximum rotation velocity and dispersion velocity

MNRAS 000, 1–16 (2018)

4 C. Murugeshan et al.

Table 1. The range of stellar and H i mass of the xGASS, WHISP and THINGS sub-samples for comparison. Also included

are the mean and median of the masses.

Sample Sample size M? range Mean M? Median M? MH i range Mean MH i Median MH i

[M] [M] [M] [M] [M] [M]

WHISP 114 6.7 – 11.5 9.6 9.7 7.8 – 10.5 9.3 9.3

xGASS (detections 803 9.0 – 11.4 10.2 10.2 7.9 – 10.5 9.4 9.5only)

THINGS 16 9.1 – 10.9 10.3 10.4 8.3 – 10.1 9.5 9.6

7 8 9 10 11log(M?) [M]

8

8.5

9

9.5

10

10

log(M

HI)

[M

]

xGASS galaxies

WHISP

THINGS

Figure 1. The MH i − M? scaling relation for the cur-

rent WHISP sample (green squares) along with the xGASSrepresentative sample in the background (light blue cir-

cles) for comparison. THINGS galaxies used in the orig-

inal study by OG14 are indicated by the orange trian-gles. The xGASS sample’s stellar mass range is limited

to 9 < logM?/M < 11.5. Within this range, our sam-ple galaxies are observed to be uniformly spread in both

stellar and H i mass.

(σH i) are provided as input to the code. 3DBarolo

uses this information to generate model data cubeswhich are convolved with the synthesised beam of theinstrument. Following this, a χ2 minimisation is per-formed ring-by-ring between the observed and modeldata cubes and a best fit model is determined. Theoutput from the best fitting model encompasses a ro-bust rotation curve, σH i, i and PA values for everyring, as well as the H i surface density profile of thegalaxy. We make use of both the geometric and kine-matic parameters resulting from the fit to then cal-culate the H i mass, stellar mass and total angularmomentum within each ring.

Following the methods described in Murugeshanet al. (2019), we project the tilted-rings onto themoment-0 H i intensity maps to compute the H i masswithin each ring. To calculate the stellar mass, wemake use of the 2MASS (Skrutskie et al. 2006) Ks-band mosaics, after carefully masking foreground starsand performing a background sky subtraction. Thesum of the Ks magnitudes within each ring is thenconverted to a stellar mass following the relation de-scribed by Eq.3 in Wen et al. (2013) as follows

log10

(M?

M

)=(−0.498± 0.002) + (1.105± 0.001)

× log10

(vLv (Ks)

L

)

7 8 9 10 11log(M?) [M]

-2

-1

0

1

log(M

HI/M

?)

xGASS galaxies

WHISP

THINGS galaxies

Figure 2. The MH i/M? − M? scaling relation for the

WHISP sample (green squares). For comparison, also plot-ted is the xGASS sample (blue circles), while THINGS

galaxies are represented by the orange triangles. We ob-

serve that our sample spans uniformly in both M? andMH i/M?.

Where Lv is the luminosity, derived using theextinction-corrected Ks-band magnitude.

The total H i and stellar masses are computed bysumming their respective mass within each ring. Wethen compute the total baryonic mass using the rela-tion Mb = M? + 1.35(MH i +MH2), where MH i is thetotal H i mass, M? is the total stellar mass and MH2

is the H2 mass. The factor 1.35 accounts for the uni-versal 26% He fraction. Due to a lack of CO data forthe sample, we have assumed MH2/Mb ∼ 4% follow-ing the observations made by Obreschkow & Rawlings(2009) for a number of local late-type galaxies. The to-tal specific baryonic angular momentum is computedas

jb =

∑i(1.35MH i,i +M?,i)Vrot,iri∑

i(1.35MH i,i +M?,i)(1)

where ri is the radius of the ith ring and Vrot,i is therotation velocity corresponding to that ring. Followingthis, as mentioned in Section 1, we compute the atomicgas fraction and stability parameter as

fatm =1.35MH i

Mb; q =

jbσ

GMb

2.3 Probing the environment

In order to understand the influence of the en-vironment on our sample galaxies, we make use ofmethods that probe and quantify the effects of boththe very local (interacting pairs; close companions)

MNRAS 000, 1–16 (2018)

The influence of AM and environment on the HI gas of late-type galaxies 5

and intermediate environments (group to inter-groupregime) of the sample galaxies. Our sample consists ofisolated galaxies and those that are in pairs, tripletsand some that are part of groups. As such, environ-mental factors are likely to be playing an importantrole in re-distributing the H i gas in such systems. Tostudy the influence of close neighbours/companions onthe sample galaxies, we divided the sample into twofurther sub-samples – galaxies with close neighboursand those without. A galaxy is considered to havea close neighbour if one or more companion galax-ies are found within a projected distance of 200 kpcand ± 250 km s−1 in systemic velocity of the galaxy.We make use of NED’s1 environment search, and alsoexamine the H i image cubes to identify close neigh-bours.

We probe the density of the intermediate envi-ronment of the sample galaxies using the projectednearest-neighbour density metric (ΣN [Mpc−2]). TheΣN values have been computed using the 2MASS Red-shift Survey (2MRS) catalogue (Huchra et al. 2012).The 2MRS catalogue contains measured spectroscopicredshifts for over 43,500 galaxies with Ks ≤ 11.75 magand |b| > 5o. Within these limits, the survey is com-plete to 97.6% and covers 91% of the entire sky. The2MRS is, however, a relatively shallow survey and themagnitude limits are based on the Ks-band magni-tudes. Therefore, the catalogue by virtue of the selec-tion criteria will be more sensitive to galaxies that areolder and redder. In-order to make the 2MRS cata-logue volume-limited for an unbiased measurement ofthe local densities, we employ the following two steps:

(i) We first make a velocity cut to the original2MRS catalogue, by selecting galaxies within the ve-locity range 200 – 8000 km s−1.

(ii) To this velocity-cut sample, we add an absoluteKs-band magnitude cut MK < −23.45, correspondingto the survey’s limiting apparent magnitude of 11.75mag at the highest velocity/redshift edge (8000 kms−1). This makes the 2MRS sample volume-limited.

Finally, we exclude galaxies in our WHISP sam-ple which have systemic velocities Vsys < 700 kms−1 to avoid peculiar velocity effects. This reduces ourWHISP sample size from 114 to 91. Since we haveimposed the above cuts to the original 2MRS cata-logue to make it volume-limited, the final referencecatalogue will not include many low-surface bright-ness galaxies within the volume, making the distribu-tion of galaxies in the final reference catalogue sparse.For this reason, following the justifications made byJanowiecki et al. (2019), we use the second nearest-neighbour density metric (Σ2) so that we are sensitiveto only the intermediate environment as otherwise theΣ3 and/or Σ5 metrics are likely to be probing large-scale structures. The Σ2 metric is defined as followsΣ2 = 2/πD2, where D is the projected distance to the2nd nearest-neighbour within ± 500km s−1. In ad-dition to the local environment densities, we use the2MRS group catalogue (Lu et al. 2016) to study the ef-

1 NASA/IPAC Extragalactic Database, http://ned.

ipac.caltech.edu/

8 9 10 11log(Mb) [M]

1.0

1.5

2.0

2.5

3.0

3.5

4.0

log(j b

)[k

pc

kms−

1 ]

Typical error

With close neighbours

W/O close neighbours

Best fit: α = 0.55± 0.02

ΛCDM: jb ∝M2/3b

Figure 3. Distribution of the total specific baryonic an-

gular momentum (jb) as a function of total baryonic mass

(Mb) for the 114 WHISP galaxies. The dotted lines showthe expected range of jb values based on ΛCDM predic-

tions. The solid dark gray line is the best fitting line to theentire sample with a slope α = 0.55 ± 0.02. The light grey

region is the 1σ intrinsic scatter of ∼ 0.13 ± 0.01 dex for

the full sample.

fects of group membership on the H i gas fraction andangular momentum properties of the sample galaxies.

3 RESULTS AND DISCUSSION

We now present the results from the study. Thiswork presents the largest sample of late-type galaxiesfor which accurate baryonic angular momentum (jb)has been computed to date. In the following subsec-tions we present the distribution of jb for our samplegalaxies and determine if the jb values vary with theirenvironment. Additionally, we examine the behaviourof galaxies in the fatm − q plane and study the in-fluence of the environment on their position in thisparameter-space. We also discuss the trends of otherglobal properties of the sample galaxies such as theirstar formation rate (SFR), star formation efficiency(SFE) and bulge-to-total (B/T) ratios in the fatm− qparameter-space.

3.1 The jb −Mb relation

In this section we discuss the distribution of jbas a function of Mb for our sample of 114 WHISPgalaxies. As described in Section 2.3, the sample wasfurther divided into two – those with close neighboursand those without. Fig. 3 shows the jb −Mb relationfor the full sample. We fit a linear regression2 of theform

log jb = α logMb + c

to the full sample as well as separately for the twosub-samples. For the full sample, we find a best fittingslope of α = 0.55±0.02 (dark grey line in Fig. 3) and a1σ intrinsic scatter∼ 0.13±0.01 dex (light grey shaded

2 Fitting was performed using Hyper-Fit, an R pack-age for fitting multi-dimensional data. See Robotham &Obreschkow 2015 for more details.

MNRAS 000, 1–16 (2018)

6 C. Murugeshan et al.

region in the plot). For the sample of galaxies withoutclose neighbours we find a slope of α = 0.54±0.04 andan intrinsic scatter ∼ 0.10 ± 0.02 dex. The sample ofgalaxies with close neighbours have a slope α = 0.56±0.03, but show a slightly larger intrinsic scatter of ∼0.14±0.02 dex. It is interesting to note that the slopesof the two sub-samples are statistically consistent witheach other, however, the larger observed scatter for thesample with close neighbours is possibly a result of theeffects of galaxy interactions on their jb values.

It is also worth noting that some galaxies withclose neighbours (indicated by the green squares inFig. 3), particularly in the higher baryonic mass end,have significantly low jb compared to galaxies with-out close neighbours of similar baryonic mass, indi-cating that past or ongoing interactions are likely tohave lowered their total specific baryonic AM. Manyof these outliers in the jb−Mb relation, located beyondthe 1σ scatter (light grey region), are also outliers inthe fatm − q relation (see Section 3.2), indicating astrong connection between specific AM and disc sta-bility. We discuss this further in Section 3.2.

OG14 derive a theoretical relation between jband Mb (based on the original prescriptions of Mo etal. 1998) for the local universe (assuming H = 70 kms−1Mpc−1) of the form

jb103kpc kms−1

= 1.96λfjf−2/3M

(Mb

1010M

)2/3

(2)

Where λ is the dimensionless halo spin parameter,fj = jb/jh is the fraction of sAM retained by thebaryons and is the ratio of the specific baryonic an-gular momentum (jb) and the specific angular mo-mentum of the halo jh. fM is the baryon mass frac-tion. OG14 assume λ ≈ 0.04 ± 0.02, fj ≈ 1 (withinabout 50%) and fM ≈ 0.05 for late-type galaxies and

show that the pre-factor 1.96λfjf−2/3M will vary be-

tween 0.14 and 1.3 in the local universe (for more de-tails see Section 4 in OG14). This range is shown bythe dotted lines in Fig. 3. We find that most galax-ies in our sample lie within the expected range of jbvalues for their mass, but the slope of the relation issignificantly lower than the expected slope of ∼ 2/3from the models of OG14. This can be explained byarguing that fjf

−2/3M is not a constant for galaxies of

all types and masses. In fact, Chowdhury & Chengalur(2017) examine five gas-rich dwarfs and find that theirjb is elevated compared to the model predictions forhigh-mass spirals. They suggest that this is primarilydue to the mass dependence of fM, which decreaseswith decreasing baryonic mass (see for example Crainet al. 2007).

In an independent study, Butler, Obreschkow &Oh (2017) come to a similar conclusion after analysingthe jb−Mb relation for 14 dwarf galaxies from the LIT-TLE THINGS survey. In addition, both Chowdhury &Chengalur (2017) and Kurapati et al. (2018) suggestthat fj is also likely to vary with mass based on prefer-ential ‘cold-mode’ accretion among low-mass systemscompared to high-mass galaxies that tend to accrete in‘hot-mode’. Many simulations allude to the fact thatcold-mode accretion is associated with high AM gas asopposed to hot-mode accretion, thereby boosting the

sAM of low-mass spirals (Pichon et al. 2011; Stewartet al. 2011; Danovich et al. 2015).

Furthermore, Posti et al. (2018) made an em-pirical study of the j? − M? relation (the Fall rela-tion) for late-type galaxies, that included dwarfs andhigh-mass spirals spanning over 5 decades in stellarmass. In this study, they find that their sample galax-ies follow an unbroken single power-law of the formj? ∝ M0.55±0.02

? , and point to the fact that this canbe explained by prescribing a biased collapse model(see for example Kassin et al. 2012; Dutton & van denBosch 2012), where fj decreases with decreasing mass.In addition, using a suite of cosmological zoom-in sim-ulations from the FIRE project, El-Badry et al. (2018)show that by introducing strong stellar feedback inlow-mass systems, fj can be reduced significantly inlow-mass galaxies.

Interestingly, the slope we derive for the jb −Mb

relation from our full sample (α = 0.55±0.02) matchesexactly with the best fitting slope of Posti et al. (2018),thus strengthening the argument in favour of variationin both fM and fj. Romanowsky & Fall (2012) in theirstudy of the j? − M? plane find a slope α ≈ 0.52for their sample when including both disc and bulgecomponents, again consistent with our findings.

In another study of the jb −Mb relation, Elson(2017) use 37 galaxies from the WHISP sample andfind a best fitting slope of α = 0.62±0.02, in disagree-ment with the best fitting slope for our full sample. Wesuspect the apparent discrepancy with the Elson studymay be due to two main reasons. Firstly, the massdistribution of the two samples are different. Elsonspecifically probe low-mass spirals (8 < logMb < 10[M]) in their study, while the baryonic mass rangefor our sample is 8 < logMb < 11.5 [M] with a sig-nificant fraction (50%) of galaxies in the high-mass(logMb > 10 [M]) end. To rule-out any biases intro-duced from the different methodologies employed inthe measurement of jb and Mb values in the two stud-ies, we also compared the jb and Mb values for an over-lapping sample of 26 WHISP galaxies and find a goodone-to-one correlation. We then fit a line to the jb−Mb

relation for these 26 common galaxies, and find a bestfitting line with slope α = 0.63± 0.05, consistent withthe results from the Elson study. We therefore believe,that the mass ranges probed in the two studies play animportant role in affecting the fitted slopes. Secondly,because our sample is size-selected (see Section 2.1),we may be naturally biased towards large high-spin,gas-rich systems, especially in the dwarf regime. As aconsequence, the slope of the jb −Mb relation (α) be-comes flatter due to this selection bias. A combinationof these reasons may explain the observed discrepancybetween the best fitting slopes of the two samples.

The flattened and unbroken power-law we observefor our sample has important implications for cur-rent galaxy evolution models, particularly how differ-ent types of galaxies acquire, retain or lose their AM,and the effects of feedback processes on the fractionof baryons retained during galaxy formation. However,better statistical constraints of this relation would re-quire a larger and more homogeneous sample thanthat considered in this work, designed to study en-

MNRAS 000, 1–16 (2018)

The influence of AM and environment on the HI gas of late-type galaxies 7

vironmental effects, and not prone to any selectionbiases (e.g. size, mass, flux selected).

3.2 Effects of close neighbours

We now take a look at the effects of the local en-vironment on the H i gas, specific angular momentumand the stability parameter q of our sample galaxies,and how this affects their behaviour on the fatm − qrelation. Fig. 4 shows the relation colour-coded intogalaxies that have close neighbours (green squares)and those that do not (blue diamonds). Galaxies with-out close neighbours have an rms scatter of ∼ 0.13 dexabout the relation (note that this is smaller than therms scatter in the original work by O16, which was0.2 dex), while galaxies with close neighbours show anrms scatter of ∼ 0.22 dex, almost a factor of two com-pared to the sample without close neighbours. Thislarger scatter may be linked to galaxy-galaxy interac-tions and its effects on their jb and fatm values.

Interactions between galaxies tend to exert addi-tional tidal torques on their gas discs, which lowerstheir internal specific AM by spin-orbit interaction,leading to the funnelling of gas to their centres. Thecumulative effect of this is a net reduction of jb in bothinteracting galaxies (Barnes & Hernquist 1996), whichlowers their q value. Additionally, more massive galax-ies will tend to accrete H i gas from their less massivegas-rich companions, momentarily boosting their gasfractions, fatm (see for example Ellison et al. 2018).This will make the galaxy appear more H i rich for itsgiven stability parameter (q). Both these effects col-lectively move interacting galaxies to the left and/orabove the fatm − q relation. It has been shown thatinteracting pairs and galaxies with close companionsshow enhanced star formation, due to disc instabili-ties set by the external tidal perturbation (Ellison elal. 2008; Ellison et al. 2010; Patton et al. 2011; Scud-der et al. 2012). To test this, in Section 3.6 we alsoexamine if the SFR is elevated for those galaxies hav-ing close companions and deviating from the relation(see Fig. 9).

This is an important result of this study, and mo-tivates us to explore the use of the fatm − q relationas a diagnostic plot to identify galaxies having under-gone or currently undergoing tidal interactions. Thiswill become particularly important in high-density en-vironments such as clusters, where the two main gasstripping mechanisms – tidal and ram pressure strip-ping can be distinguished based on the location ofgalaxies on the fatm − q plane. Tidal interactions arelikely to move galaxies to the left of the relation, whilea fast gas stripping process like ram pressure, willmove the galaxies below the relation (Li et al. 2020).Upcoming large H i surveys such as WALLABY (Ko-ribalski et al. 2020), will enable us to populate thou-sands of galaxies on this diagnostic plot and allow usto study the effects of both tidal interactions and rampressure stripping on their fatm, jb and q values.

3.3 Effects of the intermediate environment

In this section we examine the effects of the inter-mediate environment on the H i gas fractions, angularmomentum and q values of the sample galaxies. We

0.01 0.1 1 10q

0.01

0.1

1

f atm

Obreschkow et al. (2016)40% scatterWith close neighboursW/O close neighboursTHINGSLITTLE THINGSMurugeshan et al. (2019)

Figure 4. The fatm − q relation for 114 WHISP galaxies.

Blue diamonds are WHISP galaxies with no close neigh-

bours and light green squares are galaxies in the WHISPsample with close neighbours (see Section 2.3). Galaxies

in the sample without close neighbours are seen to follow

the model very consistently (scatter ∼ 0.13 dex), whereasgalaxies with close neighbours are seen to have a larger

scatter (∼ 0.22 dex) about the relation with clear outliers.

The light grey region is the 40% empirical intrinsic scat-ter in the H i dispersion velocities (σH i) of galaxies. Also

plotted for reference is the original sample of THINGS and

LITTLE THINGS galaxies from O16 and the H i-deficientspiral galaxies from Murugeshan et al. (2019)

make use of the methods described in Section 2.3 toprobe the environment density of the sample galaxies.

We plot the jb values for our sub-sample of 91galaxies against their Σ2 density metric for three stel-lar mass bins as shown in Fig. 5. We find no correlationbetween jb and Σ2, indicating that the sAM of our cur-rent sample is not affected significantly by their inter-mediate environment. However, caution is warrantedas this result by no means implies that jb does notvary with environment in general. This may simplybe a selection effect, as our sample galaxies are drawnfrom the parent WHISP sample, which is heteroge-neous and does not include galaxies from cluster-likeenvironments, where interactions are more commonand more low sAM systems are observed.

Fig. 6 shows the fatm − q relation for the samplegalaxies, color coded by their Σ2 values. Interestingly,the intermediate environments do not seem to have aneffect on the stability of galaxies and their gas frac-tions. This indicates that in the group regime, unlessclose flybys and/or gas stripping is evident, galaxiesfollow the fatm − q relation consistently. It is also in-teresting to note that galaxies with close companionswhich are also outliers in the plot (deviating to the leftof the relation), are all isolated pairs and triplets resid-ing in relatively low-density environments. This againpoints to the fact that galaxies with close neighboursand undergoing gravitational interactions are most af-fected in terms of their disc stability and their positionin the fatm−q plane. However, it is worth noting thatin a recent work, Li et al. (2020) study the behaviourof cluster galaxies on the fatm − q plane. They makeuse of galaxies part of the VIVA survey (Chung et

MNRAS 000, 1–16 (2018)

8 C. Murugeshan et al.

-1.5 -1 -0.5 0 0.5log(Σ2) [Mpc−2]

2.2

2.5

2.8

3

3.2

3.5

3.8

4

log(j b

)[k

pc

km

s−1 ]

7.0 ≤ log(M?) < 9.0

9.0 ≤ log(M?) < 10.0

log(M?) > 10.0

Figure 5. The total specific baryonic AM (jb) is plot-

ted against the 2nd nearest-neighbour density Σ2 (for

a sub-sample 91 galaxies) for three stellar mass bins –7.0 ≤ log(M?) < 9.0 (blue triangles), 9.0 ≤ log(M?) < 10.0

(green squares) and log(M?) > 10.0 (orange diamonds).

The different lines show the rolling medians for the dif-ferent mass bins (blue dash-dot, green dash-dash and solid

orange respectively). The shaded regions show the 1σ scat-

ter about the rolling median. No trend between jb and Σ2

is observed for the galaxies in all three stellar mass bins.

0.01 0.1 1 10q

0.01

0.1

1

f atm

Obreschkow et al. (2016)

40% scatter

Our sample 0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

Σ2

[Mp

c−2 ]

Figure 6. The fatm − q relation for a sub-sample of

91 galaxies, color coded by their environment densities,

denoted by Σ2. Overall, no trend is observed in theparameter-space indicating that the intermediate environ-

ment of the sample galaxies does not have a significantimpact on their fatm and q. Most galaxies are from low- tointermediate-density environments. It is worth noting thatall galaxies that are clear outliers (to the left of the fatm−qrelation) are from low-density environments. These galax-

ies are in fact isolated interacting pairs and triplets.

al. 2009) and find that the galaxies are located belowthe relation, and are found to have significantly loweratomic gas fractions than expected for their q values,consistent with what semi-analytic simulations predict(Stevens et al. 2018). This can be explained by the fastgas-stripping associated with ram pressure in clusters,which strips off the H i gas in the outskirts, but doesnot affect the total specific baryonic angular momen-tum of the galaxy. The net result is a drastic reduction

in the atomic gas fraction while the q value remainsmore or less preserved. We reiterate that such drasticreductions in H i gas fractions are not observed in oursample as they are mostly from isolated or group-likeenvironments.

3.4 Group membership and halo mass effects

In this section we examine the behaviour of galax-ies in our sample on the fatm− q plane in the contextof their group membership. How do isolated centrals,galaxies in pairs/triplets and those part of groups be-have in this parameter space? To understand this, wemake use of the 2MRS group catalogue, published byLu et al. (2016) to identify isolated centrals, pairs,triplets and group galaxies in our sample. We firstidentify and cross-match galaxies in our sample andthose in the group catalogue, each of which is assigneda unique galaxy ID and a group ID. Using this groupID, we then extract the group membership and associ-ated halo mass details. This reduces our sample from114 to 63.

Fig. 7 shows a plot of the relation with the dif-ferent symbols indicating the different environmentsthe galaxies are part of, with isolated centrals, pairsand triplets and/or group galaxies represented by cir-cles, squares and triangles respectively. The halo massassociated with the galaxies are shown in the color-bar. Interestingly, we find that galaxies identified asisolated centrals (circles) and as pairs (squares) arethe ones deviating from the relation the most. Thosegalaxies identified to be part of groups are observedto follow the relation consistently, with a few excep-tions. However, it is worth noting that many galaxiesin the catalogue identified as isolated centrals by Luet al. (2016), do in fact have low surface brightnessdwarf-like companions detected in H i, missed possiblybecause the 2MRS is Ks-band selected. This observa-tion again indicates that galaxies tend to drift awayfrom the fatm − q relation due to the gravitationalinfluence of their close neighbours.

3.5 Relationship with stellar mass

Fig. 8 shows the fatm−q−M? plane, with the stel-lar masses indicated in the colour bar. A smooth trendin stellar mass is observed, wherein low stellar masssystems in the sample contain higher gas fractions andvice versa. This observed trend between fatm and M?

is simply the more commonly used MHI/M?−M? scal-ing relation (see Fig. 2), which can in fact be explainedwithin the framework of the fatm − q model. Galax-ies with larger q are more stable and so can retain alarger fraction of H i and vice versa. This is explainedby the dependence of q on the total baryonic mass ofgalaxies i.e. q ∝ jb/Mb ∼ M

−1/3b , where jb = kM

2/3b

and k is related to the halo spin parameter λ (Bullocket al. 2001). This leads to a relation between fatm andMb (see Section 3.2 in O16). Galaxies that are outliers(either H i-excess or H i-deficient for their stellar mass)on the traditional MHI/M? −M? scaling relation arein fact not outliers on the fatm − q plane (see Lutzet al. 2017; 2018; Murugeshan et al. 2019). Galaxieswith similar mass, but significantly varying H i gasfractions, are systems that have different specific an-gular momenta, which in turn is heavily dependent on

MNRAS 000, 1–16 (2018)

The influence of AM and environment on the HI gas of late-type galaxies 9

0.01 0.1 1 10q

0.01

0.1

1

f atm

Obreschkow et al. (2016)

40% scatter

Isolated Central

Pair

Group (N > 3)11.2

11.4

11.6

11.8

12.0

12.2

12.4

12.6

log(M

halo

)[M

]

Figure 7. The plot shows the fatm − q relation for a

sub-sample of 63 galaxies that are identified as isolatedcentrals, pairs and those belonging to triplets/groups, af-

ter cross-matching with the group catalogue by Lu et al.

(2016). Many galaxies identified as isolated centrals (cir-cles) in the group catalogue are observed to be isolated

pairs with small dwarf-like companions. In the plot, we ob-serve that isolated centrals and pairs (squares) deviate the

most from the relation, suggesting that interacting galaxies

are the ones most affected and drift away from the relation.

their formation and merger histories. Thus the AMof galaxies partly drive the observed scatter in theMHI/M?−M? scaling relation. This observation indi-cates that the fatm − q plane is a more fundamentaland physically motivated scaling relation compared tothe more traditional H i scaling relations connectingH i gas fraction and mass. The fatm − q parameter-space therefore can be used as a diagnostic plot todefine H i deficiencies in galaxies by measuring theiroffset in fatm for their given q values. This idea isintroduced in a novel work by Li et al. 2020.

3.6 Relationship with SFR and SFE

In this section we present results pertaining to thestar formation properties of our sample, such as theirSFR and SFE. The SFR of the galaxies are derivedfrom the WISE (Wright et al. 2010) W3 12µm fluxusing the relation from Cluver et al. (2017) and mea-surements as described in Jarrett et al. (2019).Mea-sured SFR is available for 86 of the original 114 galax-ies in our sample. Fig. 9 shows the fatm − q − SFRrelation for this sub-sample. We find that the major-ity of galaxies with close-neighbours which are devi-ating from the relation show elevated SFRs comparedto galaxies without close neighbours. This supportsour argument that galaxies that have interacted orare currently interacting, experience tidal forces thathave the overall effect of lowering their q values dueto a net reduction in jb (see Barnes & Hernquist 1996;Cox et al. 2008; Hopkins & Quataert 2010; Ellison etal. 2011 and references therein). A reduced q valuesets instabilities that funnel gas to the center lead-ing to enhanced star formation. This naturally movesinteracting galaxies to the left of the relation as ob-served in our case. Ellison et al. (2010) study the in-fluence of the local and intermediate environments on

0.01 0.1 1 10q

0.01

0.1

1

f atm

Obreschkow et al. (2016)

40% scatter

Our sample 7.5

8.0

8.5

9.0

9.5

10.0

10.5

log(M

?)

[M

]

Figure 8. Plot shows the fatm − q relation with the stel-

lar mass of the galaxies shown in the colour bar. A cleartrend between fatm and M? is observed, which is in fact

the more commonly used MHI/M? −M? scaling relation.This empirical relation between MHI/M? and M? can be

explained by the ability of galaxies with a given disc sta-

bility to retain a certain fraction of H i gas as predicted bythe models in O16

the SFR of galaxy pairs. They find that increased SFRis observed among galaxy pairs residing in low densityenvironments. This is likely due to the fact that galax-ies in low-density environments tend to typically havehigher gas fractions. Our results fit well under thisscenario, since we observe interacting pairs that arein low-density environments (based on their Σ2 val-ues; see Section 3.3) but are outliers on the fatm − qrelation, showing enhanced SFR.

In terms of the SFE of the galaxies, Fig. 10 showsthe trend for the sample. Overall, we observe thatgalaxies with higher q value have a lower SFE andvice versa. This observation agrees well with the pre-dictions of the original model proposed by O16. Galax-ies with a higher atomic disc stability prevent the H igas from collapsing to form stars and hence have alow SFE, as opposed to galaxies with a lower stabilitywhich will show higher SFE. In addition to our sam-ple, we have also included the 12 H iX galaxies (Lutz etal. 2017), which are some of the most H i-rich galax-ies in the local universe, and show that indeed theyhave very low SFE owing to their high sAM. Thus weshow evidence of the influence of the atomic stabil-ity of discs on the SFE of galaxies, for a large samplespanning more than four decades in stellar mass.

3.7 Relationship with B/T ratio

In this section we present the bulge-to-total(B/T) ratios of the galaxies in the sample and dis-cuss their trend on the fatm − q plane. The B/T val-ues for the sample have been derived using WISEW1 3.4µm mosaics following the methods describedin Jarrett et al. (2019). The use of the W1 mosaicsenable us to trace evolved stars without being af-fected by dust. The galaxies are fit with a series ofelliptical annuli, and their radial surface brightness isdetermined. The derived surface brightness profile isthen fit with a double Sersic profile consisting of a

MNRAS 000, 1–16 (2018)

10 C. Murugeshan et al.

0.01 0.1 1 10q

0.01

0.1

1

f atm

Obreschkow et al. (2016)

40% scatter

With close neighbours

W/O close neighbours0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

SF

R[M

yr−

1 ]

Figure 9. The fatm − q relation for a sub-sample of

86 WHISP galaxies for which SFR has been derived us-ing WISE W3 fluxes (Cluver et al. 2017 and Jarrett et

al. 2019). A majority of galaxies with close neighbours

(squares) and deviating from the relation, are seen to haveelevated SFRs, compared to galaxies without close neigh-

bours. This is in agreement with previous studies whichfind higher than average SFRs among galaxies that have

close companions (Ellison et al. 2008).

0.01 0.1 1 10q

0.01

0.1

1

f atm

Obreschkow et al. (2016)

40% scatter

Our sample

HIX galaxies (Lutz et al. 2017) −10.0

−9.8

−9.6

−9.4

−9.2

−9.0

log(

SF

E)

[yr−

1]

Figure 10. The fatm− q− SFE plane for a sub-sample 86WHISP galaxies. Observations nicely agree with the the-

oretical models, which predict that galaxies with higher

stability values will have a lower SFE and vice a versa.Also plotted are the H iX sample (Lutz et al. 2017) of H i-

excess galaxies. These galaxies are also observed to havelow SFE owing to their high sAM.

bulge and disk component. Robust fits were derivedfor 106 of the original sample of 114 galaxies. Fig. 11shows the fatm−q relation along with the B/T valuesfor this sub-sample. We observe that, overall, bulge-dominated galaxies have a low H i gas fraction (lowfatm) and q value. Galaxies with lower atomic sta-bility are expected to be more bulge-dominated. Thismay be driven by both an increase in mass, which de-creases the disc stability, and/or loss of specific AM,which makes the gas funnel to their centers, leadingto central star formation. On the other hand, galax-

0.01 0.1 1 10q

0.01

0.1

1

f atm

Obreschkow et al. (2016)

40% scatter

Our sample0.1

0.2

0.3

0.4

0.5

0.6

B/T

Figure 11. The fatm − q relation for a sub-sample of 106WHISP galaxies for which B/T values have been computed

usingWISE mosaics (Jarrett et al. 2019). Low-mass galax-

ies with higher gas fractions are typically seen to have lowerB/T values as opposed to the more evolved galaxies to-

wards the bottom of the plot, which, depending on their

merger histories evolve to become more bulgy due to lossof AM and build-up of mass over time. This presents a

scenario where the influence of both mass and angular mo-mentum on the gas fraction and the morphology of galaxies

is evidenced.

ies with a higher q value are likely to be low-massand/or high-spin systems, which resist the in-fall ofgas and likely to be more disky. Our study shows forthe first time how disk- and bulge-dominated galax-ies are distributed on the fatm − q plane. This is animportant secondary result showing the potential ofthis parameter-space in predicting not only the gasfraction for a given atomic disc stability, but also themorphology of galaxies.

4 SUMMARY

In this work, we have studied the angular mo-mentum and H i properties of galaxies as a functionof their environment, as well as other global proper-ties such as star formation and morphology. We haveshown that AM is an integral property of galaxies andan important driver of their evolution. We have ex-panded on the original work of O16 on the fatm − qrelation, and examined the influence of AM and en-vironment on late-type galaxies. We summarise themain results from this study below:

• We have measured precise specific baryonic an-gular momentum (jb) and baryonic mass (Mb) for asample of 114 WHISP galaxies. We find an unbrokenpower-law of the form jb ∝M0.55±0.02

b over four ordersof magnitude in Mb.• The sample was further divided into two sub-

samples – those with close neighbours and those with-out. We studied the behaviour of both sub-sampleson the fatm − q plane, and find that galaxies with-out close neighbours follow the model prediction verytightly, with an intrinsic scatter of only 0.13 dex, whilethe sub-sample of galaxies with close neighbours showa much larger scatter of 0.22 dex. We attribute this

MNRAS 000, 1–16 (2018)

The influence of AM and environment on the HI gas of late-type galaxies 11

larger scatter to the effects of past or ongoing interac-tions on the jb values of galaxies.• For the current sample, it is only their most local

environment (close neighbours) that affect their loca-tion on the fatm− q relation, while their intermediateenvironment (group regime) does not appear to affecttheir fatm, jb and q values.• Galaxies with close neighbours and deviating

from the fatm−q relation exhibit enhanced star forma-tion rates (SFR) compared to galaxies without closeneighbours. This highlights the effects of external tidalperturbations on the disc stability of galaxies. Tidalfields tend to exert additional external torques on theH i gas, which makes the gas lose its AM and funnel tothe centre to form stars, consequently enhancing theSFR.• We use the bulge-to-total ratio (B/T) as a proxy

for morphology and examine if the B/T values of thesample galaxies correlate on the fatm − q plane. Wefind evidence that, overall, galaxies with lower q andfatm values tend to have higher B/T values. This re-sult brings to light the importance of angular momen-tum and mass in determining not only the stability ofdiscs, but also their influence on the H i gas fractionsand morphology of galaxies. We show for the first time,a relation between atomic gas fraction, disc stabilityand the morphology of galaxies on the fatm− q plane.

The fatm−q plane is an important diagnostic plotthat links the atomic gas fraction and disc stabilityto the mass, angular momentum, star formation andmorphological properties of galaxies. Previous studieshave shown the importance of this parameter-space inunderstanding how H i-excess and H i-deficient galax-ies – both outliers on the MH i/M? −M? scaling rela-tion, in fact, follow the fatm − q relation consistently(Lutz et al. 2017, 2018; Murugeshan et al. 2019). Inaddition, Li et al. (2020) define a novel and morephysically motivated way to quantify H i deficienciesin galaxies based on their atomic gas fraction offsets(∆fq) in the fatm − q plane. In this work, we haveshown that tidally interacting galaxies tend to losetheir angular momentum and acquire lower q values,deviating to the left of the relation. Ram pressurestripped galaxies on the other hand have significantlylower fatm values for their disc stability (q) and areobserved to lie below the relation (Li et al. 2020).The fact that galaxies affected by tidal interactionsand ram pressure occupy very different spaces on thefatm− q plane will be particularly important in disen-tangling the effects of the two processes in high-densityenvironments, where both processes are prevalent.With upcoming high-resolution H i surveys such asWALLABY (Koribalski et al. 2020), which has the po-tential for homogeneous volume-limited observationsof thousands of galaxies from low- to high-density en-vironments, and (DINGO; Meyer et al. 2009) with thepotential to probe higher redshifts, we will be able tofully probe this parameter-space to study how galaxiesbehave as a function of both environment and redshift.

ACKNOWLEDGEMENTS

We thank the anonymous referee for their com-ments, which improved the overall quality of the

paper. CM is supported by the Swinburne Univer-sity Postgraduate Award (SUPRA). CM would liketo thank Robert Dzudzar, Luca Cortese and AdamStevens for the useful discussions.

DO is a recipient of an Australian Research Coun-cil Future Fellowship (FT190100083) funded by theAustralian Government.

KG and DO acknowledge the support of theAustralian Research Council through the DiscoveryProject DP160102235.

MEC is a recipient of an Australian ResearchCouncil Future Fellowship (FT170100273) funded bythe Australian Government.

We would like to thank the xGASS team for mak-ing the data publicly available.

This publication makes use of data products fromthe Two Micron All Sky Survey, which is a jointproject of the University of Massachusetts and theInfrared Processing and Analysis Center/ CaliforniaInstitute of Technology, funded by the National Aero-nautics and Space Administration and the NationalScience Foundation.

This research has made use of the NASA/IPACExtragalactic Database (NED), which is operated bythe Jet Propulsion Laboratory, California Institute ofTechnology, under contract with the National Aero-nautics and Space Administration.

This publication makes use of data products fromthe Wide-field Infrared Survey Explorer, which is ajoint project of the University of California, Los An-geles, and the Jet Propulsion Laboratory/CaliforniaInstitute of Technology, funded by the National Aero-nautics and Space Administration.

Parts of the results in this work make use ofthe colourmaps in the CMasher package (van derVelden 2020).

DATA AVAILABILITY

All data underlying this article is available within thearticle and enlisted in Table A1 in Appendix A

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ware, 5, 2004

APPENDIX A: PROPERTIES OF THESAMPLE GALAXIES

MNRAS 000, 1–16 (2018)

The influence of AM and environment on the HI gas of late-type galaxies 13

Table

A1.

The

gala

xy

sam

ple

.D

isth

egala

ctoce

ntr

icdis

tance

,Vsys

isth

esy

stem

icvel

oci

ty,i

isth

ein

clin

ati

on

an

gle

of

the

gala

xy,σH

iis

the

med

ian

of

the

Hi

dis

per

sion

vel

oci

tyco

mp

ute

dfr

om

the

3D

fit.

Th

eS

FR

valu

esare

borr

ow

edfr

om

Jarr

ett

etal.

2019,

whic

hh

ave

bee

nes

tim

ate

dusi

ngWISE

W3

flu

xes

.B

ulg

e-to

-tota

l(B

/T

)valu

esare

der

ived

usi

ngWISE

W1

3.4µ

mm

osa

ics.

Nam

eR

AD

EC

DVsys

iVmax

σH

ilo

g(M

?)

log(M

Hi)

log(M

H2)

log(M

b)

j bfatm

qlo

g(SFR

)B

/T

[J2000]

[J2000]

Mp

ckm

s−1

deg

km

s−1

km

s−1

[M

][M

][M

][M

]kp

ckm

s−1

[M

yr−

1]

UG

C89

00h

09m

53.4

1s

25d55m

25.6

s62.6

4569.3

58.9

201

11.5

11.0

99.8

19.7

411.1

41222.2

20.0

60.0

21.0

30.7

6

UG

C94

00h

10m

25.9

s25d

49m

55s

62.9

4595.1

42.3

209

11.2

10.3

39.9

9.1

310.5

31359.5

90.3

20.1

n/a

0.4

5

UG

C232

00h24m

38.6

9s

33d

15m

22.2

s66.4

4845.3

47

145.9

13.8

10.6

39.9

39.3

610.7

62064.5

30.2

0.1

20.3

70.6

1U

GC

624

01h00m

36.4

1s

30d

40m

08.3

s65.5

4781.4

62.8

270.1

29.4

10.9

10.3

9.6

611.0

61905.7

0.2

40.1

11.1

0.8

9

UG

C731

01h10m

43.9

8s

49d

36m

07.9

s8.8

639.3

61.4

73.6

9.1

7.8

58.8

87.6

69.0

6296.6

90.8

80.5

4n

/a

0.4

7

UG

C1541

02h

03m

27.9

4s

38d

07m

01.0

s77.5

5658

55

228

16.4

10.9

510.0

99.6

511.0

52096.5

60.1

50.0

70.3

30.3

8U

GC

1550

02h

03m

44.8

s38d

15m

31s

79

5768.1

75

225.1

21.4

11.0

310.5

39.8

111.2

12872.9

20.2

80.0

9n/a

n/a

UG

C1886

02h

26m

00.4

9s

39d

28m

15.3

s66.7

4868.4

59.6

263.9

8.8

10.8

410.2

29.5

910.9

93056.6

80.2

30.0

60.2

90.8

4U

GC

1913

02h

27m

16.8

8s

33d

34m

45.0

s7.6

553.5

60.4

117.7

11.7

9.5

69.5

48.5

59.9

4743.2

80.5

30.2

3-0

.21

0.3

2

UG

C2080

02h

36m

27.8

8s

38d

58m

11.7

s12.4

903.6

23.3

145

5.3

9.7

59.6

98.7

110.1

11400.2

50.5

10.1

3-0

.12

0.2

UG

C2193

02h

43m

30.0

0s

37d

20m

28.8

s7.1

518.4

26.5

n/a

3.1

9.2

18.6

27.9

69.3

6347.0

10.2

50.1

3-0

.49

0.4

3U

GC

2487

03h

01m

42.3

7s

35d

12m

20.7

s67.8

4948.5

37

318.9

10.6

11.4

710.4

310.1

411.5

48719.6

20.1

0.0

60.4

10.5

1

UG

C2503

03h

03m

34.7

5s

46d

23m

10.9

s32.7

2388.6

63.3

252.6

7.6

10.8

89.8

79.5

610.9

62527.3

70.1

10.0

50.2

60.2

3

UG

C2800

03h

40m

02.4

6s

71d

24m

21.1

s16.1

1176.9

65.8

113.3

8.1

9.2

39.1

68.1

99.5

9649.4

80.5

0.3

2n

/a

0.0

7U

GC

2855

03h

48m

20.7

3s

70d

07m

58.4

s16.5

1200.9

67

217.3

17.6

10.5

59.5

39.2

310.6

3861.3

20.1

10.0

80.7

40.1

1

UG

C2916

04h

02m

33.8

6s

71d

42m

21.2

s61.9

4520.1

50.6

198

13

10.7

210.1

79.4

810.8

81839.5

20.2

60.0

70.5

80.6

2

UG

C3013

04h

23m

27.1

0s

75d

17m

44.1

s33.7

2462.7

41.9

211

10.9

10.7

39.9

29.4

310.8

31754.8

50.1

60.1

80.5

70.7

UG

C3205

04h

56m

14.8

8s

30d

03m

08.5

s49.2

3591.6

66.9

211.7

11.2

10.7

49.9

89.4

610.8

62179.0

50.1

80.0

80.0

30.0

5

UG

C3354

05h

47m

18.2

2s

56d

06m

44.5

s42.3

3087

69.3

185.9

18.7

10.3

39.9

59.1

510.5

51656.1

60.3

40.2

0.7

0.5

9

UG

C3371

05h

56m

38.6

0s

75d

18m

58.0

s11.2

816.6

50.7

81.1

6.9

8.4

78.9

17.7

79.1

7462.2

10.7

40.5

n/a

0.0

7U

GC

3382

05h

59m

47.7

3s

62d

09m

28.8

s61.6

4499.1

40.8

146.1

6.4

10.6

39.6

19.3

110.7

739.8

50.1

10.0

20.3

0.3

3

UG

C3384

06h

01m

37.0

0s

73d

07m

00.0

s14.9

1089.9

41.8

46.4

69.6

79.0

68.4

29.8

2262.5

70.2

40.0

6n

/a

0.4

8U

GC

3546

06h

50m

08.6

6s

60d

50m

44.9

s25.2

1841.4

54.5

202.4

10.7

10.4

9.3

99.0

810.4

8857.6

90.1

10.0

70.5

60.7

UG

C3574

06h

53m

10.4

4s

57d

10m

40.0

s19.8

1442.1

27.5

133.6

8.3

9.7

99.5

98.6

810.0

81130.3

0.4

30.1

8-0

.48

0.4

9U

GC

3580

06h

55m

30.8

6s

69d

33m

47.0

s16.5

1201.8

65.8

119.1

7.6

9.1

69.2

98.2

39.6

3691.3

10.6

10.2

8-0

.22

0.6

8U

GC

3642

07h

04m

20.3

0s

64d

01m

13.0

s61.7

4501.2

39

317.6

16.6

11.1

310.3

99.8

511.2

55457.1

50.1

80.1

20.5

20.7

6

UG

C3711

07h

10m

13.5

8s

44d

27m

26.3

s6

436.2

46.4

93

11.7

8.1

68.3

97.3

18.7

123.6

30.6

60.6

7-0

.96

0.2

5U

GC

3734

07h

12m

28.6

6s

47d

10m

00.1

s13.4

974.7

31.7

130.1

6.3

9.4

38.8

68.1

99.5

9320.8

0.2

50.1

2-0

.49

0.6

7U

GC

3993

07h

55m

43.9

7s

84d

55m

35.2

s59.8

4368

34.2

152.9

6.7

10.7

29.7

9.4

10.7

92058.3

70.1

10.0

5-0

.52

0.5

8

UG

C4256

08h

10m

15.1

8s

33d

57m

23.9

s72

5255.7

47

97.9

8.9

10.6

89.9

59.4

110.8

1534.5

70.1

90.0

21.1

80.1

8U

GC

4273

08h

12m

57.9

2s

36d

15m

16.7

s33.9

2472.6

66.2

158.2

7.5

10.1

9.4

88.8

510.2

51020.0

20.2

30.1

0.3

50.2

6U

GC

4284

08h

14m

40.1

2s

49d

03m

42.2

s7.5

548.4

57

103.2

11.3

8.8

9.2

18.0

89.4

8572.2

0.7

40.5

-0.7

70.2

2

UG

C4499

08h

37m

41.4

8s

51d

39m

08.6

s9.5

691.5

50

74.2

7.1

8.0

58.7

47.5

68.9

5198.7

0.8

20.3

6n

/a

0.1

9U

GC

4543

08h

43m

21.8

s45d

44m

10s

26.9

1961.4

61

50.9

7.5

9.3

79.4

68.4

29.8

2492.9

70.5

90.1

3-1

.41

0.1

4U

GC

4605

08h

49m

11.8

7s

60d

13m

16.0

s18.5

1347.9

78

190.9

19

10.2

59.6

79.0

110.4

11909.4

70.2

40.3

3-0

.26

0.3

8

UG

C4806

09h

09m

33.7

1s

33d

07m

24.7

s26.7

1948.2

69.7

173.4

13.8

9.8

89.7

58.8

10.2

947.4

90.4

70.1

90.0

80.0

2U

GC

4838

09h

12m

14.5

1s

44d

57m

17.4

s36

2627.7

38.9

112.5

910.3

89.9

59.1

810.5

8835.9

40.3

20.0

50.7

40.3

1

UG

C5079

09h

32m

10.1

1s

21d

30m

03.0

s7.5

550.2

65

198.2

910.3

19.1

98.9

810.3

81053.2

10.0

90.0

90.6

70.5

3

MNRAS 000, 1–16 (2018)

14 C. Murugeshan et al.

Table

A1

–continued

Nam

eR

AD

EC

DVsys

iVmax

σH

ilo

g(M

?)

log(M

Hi)

log(M

H2)

log(M

b)

j bfatm

qlo

g(SFR

)B

/T

[J2000]

[J2000]

Mp

ckm

s−1

deg

km

s−1

km

s−1

[M

][M

][M

][M

]kp

ckm

s−1

[M

yr−

1]

UG

C5251

09h

48m

36.0

5s

33d

25m

17.4

s20.3

1479

75.9

133.6

15.9

9.7

49.7

8.7

110.1

1993.8

90.5

20.2

80.0

60.4

7

UG

C5253

09h

50m

22.2

3s

72d

16m

43.1

s18.1

1323

47.7

n/a

11

10.3

89.8

89.1

610.5

61460.9

70.2

90.1

0.6

40.7

5

UG

C5316

09h

55m

40.6

s72d

12m

13s

14.5

1058.7

65.8

109.2

69.4

89.1

18.3

9.7

1067.8

70.3

50.2

9n

/a

n/a

UG

C5414

10h

03m

57.3

5s

40d

45m

24.9

s8.2

600.3

50.5

63.1

9.1

8.9

18.6

57.7

89.1

7194.7

20.4

0.2

8n

/a

0.0

6

UG

C5557

10h

18m

16.8

6s

41d

25m

26.6

s8.1

592.5

23

151.1

5.3

9.8

18.9

18.5

9.9

543.5

90.1

40.0

80.1

80.1

UG

C5589

10h

21m

47.5

9s

56d

55m

49.5

s15.8

1151.7

51.9

108.2

8.6

9.5

39.1

88.3

69.7

6598.6

0.3

60.2

1-0

.73

0.1

3

UG

C5685

10h

29m

19.9

4s

29d

29m

30.6

s18.6

1356

74.3

209.4

8.7

9.8

29.4

8.6

310.0

3945.3

40.3

20.1

80.0

60.4

8

UG

C5717

10h

32m

34.8

5s

65d

02m

27.9

s23.1

1687.2

62.6

n/a

6.2

9.5

29.6

78.6

110

1596.5

0.6

20.2

30.1

20.3

2U

GC

5721

10h

32m

17.2

7s

27d

40m

07.6

s7.4

537.3

63

82.1

9.9

8.1

78.9

37.7

49.1

4290.4

40.8

40.4

8-1

.68

0.2

6

UG

C5786

10h

38m

45.8

6s

53d

30m

12.2

s13.6

993.6

43.3

118.5

16.5

9.8

99.4

38.6

810.0

8414.4

80.3

0.1

30.6

90.4

9

UG

C5789

10h

39m

09.4

6s

41d

41m

12.0

s10.1

739.5

64

117.5

11.3

9.2

39.2

8.2

19.6

1589.5

30.5

30.3

8-0

.63

0.2

5U

GC

5829

10h

42m

41.9

1s

34d

26m

56.0

s8.6

629.4

52.5

45.2

8.7

8.8

68.9

77.9

39.3

2208.7

80.6

0.2

n/a

0.0

6

UG

C5960

10h

51m

20.7

4s

32d

45m

59.0

s8.8

645.3

66.6

81.4

16.5

8.1

88.6

27.4

88.8

8139.3

30.7

50.7

1-0

.91

0.4

7

UG

C5997

10h

53m

54.8

6s

73d

41m

25.3

s17.3

1263

69.3

145.5

10.1

9.6

59.5

38.5

99.9

81043.5

50.4

80.2

50.0

30.1

3U

GC

6128

11h

04m

02.9

s28d

02m

13s

18.9

1377

41.7

138.3

11.1

9.5

68.8

18.2

89.6

8260.9

90.1

80.1

4n/a

0.2

7

UG

C6161

11h

06m

49.1

9s

43d

43m

23.7

s10.4

756.6

55

76.4

9.1

8.1

38.8

17.6

39.0

3246.4

60.8

20.4

8-2

.05

0.1

5

UG

C6225

11h

11m

30.9

7s

55d

40m

26.8

s9.6

699.6

73.9

164.3

14.3

10.0

39.4

58.7

910.1

8587.6

60.2

50.1

30.4

4n

/a

UG

C6263

11h

14m

10.8

9s

48d

19m

06.7

s29.3

2137.5

54.4

n/a

7.6

10.5

99.7

9.2

910.6

81275.3

80.1

40.0

50.8

0.4

4

UG

C6283

11h

15m

52.0

1s

41d

35m

27.7

s9.9

719.4

75.7

99.5

10.2

8.8

19.0

17.9

39.3

3438.3

90.6

40.4

9-0

.88

0.7

2

UG

C6446

11h

26m

40.4

6s

53d

44m

48.0

s8.8

645.9

56.7

75.6

89.0

78.8

7.9

39.3

3347.5

60.4

0.3

n/a

0.2

4U

GC

6537

11h

33m

21.1

2s

47d

01m

45.1

s11.9

866.1

53

164.5

9.1

9.8

69.4

78.6

710.0

7814.1

60.3

30.1

50.1

90.0

8

UG

C6713

11h

44m

24.9

7s

48d

50m

06.7

s12.3

899.7

43.5

63.1

5.5

8.2

98.6

77.5

58.9

4258.6

50.7

30.3

8-2

.52

0.0

9U

GC

6778

11h

48m

38.1

9s

48d

42m

39.0

s13.3

967.8

59

145.8

12

10.1

19.4

8.8

310.2

3848.1

10.2

0.1

40.6

90.6

UG

C6786

11h

49m

09.4

6s

27d

01m

19.3

s24.7

1799.7

68

219.6

10.4

10.2

29.6

88.9

810.3

81389.2

80.2

60.1

40.1

90.7

8

UG

C6787

11h

49m

15.3

7s

56d

05m

03.7

s16.1

1176.9

63.9

246.6

13.6

10.2

59.4

48.9

510.3

51020.0

90.1

60.1

4-0

.12

0.7

3U

GC

6833

11h

51m

46.0

1s

38d

00m

54.4

s12.6

919.5

54.7

92.2

5.8

9.2

49.0

18.1

29.5

2440.1

80.4

20.1

8-1

.02

0.1

UG

C6840

11h

52m

07.0

1s

52d

06m

28.8

s14.3

1046.7

56.6

90.7

10.4

9.0

59.3

8.2

9.6

570.0

70.6

70.3

5-1

.38

0.3

6

UG

C6884

11h

54m

58.7

1s

58d

29m

37.1

s43.7

3190.2

52.2

71.4

7.6

10.4

99.8

49.2

310.6

3558.8

40.2

20.0

20.7

20.2

4U

GC

6930

11h

57m

17.3

5s

49d

16m

59.1

s10.7

777.6

31.1

111.7

88.0

58.9

47.7

49.1

3463.0

40.8

60.6

3-0

.57

0.2

5U

GC

7030

12h

03m

09.6

1s

44d

31m

52.8

s9.6

700.8

42.2

173.1

11.2

9.6

78.8

88.3

89.7

8323.8

0.1

70.1

40.3

30.4

UG

C7075

12h

05m

22.7

1s

50d

21m

10.6

s10.2

746.1

70.9

146.7

13.1

9.1

88.6

27.9

49.3

4158.3

20.2

60.2

20.2

90.0

8U

GC

7081

12h

05m

34.2

s50d

32m

21s

10.4

757.2

71.8

191.5

18

9.8

49.2

8.5

99.9

9613

0.2

20.2

7n

/a

n/a

UG

C7095

12h

06m

08.4

5s

49d

34m

57.7

s14.7

1075.2

73.3

185.4

10.2

9.9

29.2

58.6

610.0

6671.4

90.2

10.1

40.4

80.3

4

UG

C7166

12h

10m

32.5

8s

39d

24m

20.6

s13.6

995.7

33.6

102.1

8.4

10.2

49.3

48.9

310.3

3472.8

50.1

40.0

40.8

60.8

5U

GC

7256

12h

15m

05.0

6s

33d

11m

50.4

s14.9

1086.9

47

149.4

18.4

10.2

59.3

28.9

410.3

4412.1

50.1

30.0

8-0

.73

0.6

UG

C7261

12h

15m

14.4

4s

20d

39m

30.9

s11.9

870.6

38.7

58.7

7.5

8.9

99.0

28

9.4

252

0.5

60.1

8-0

.82

0.5

UG

C7323

12h

17m

30.1

8s

45d

37m

09.5

s6.9

506.4

46

84.2

8.5

9.0

78.7

27.9

9.3

230.6

40.3

60.2

3-1

.24

0.1

2U

GC

7399

12h

20m

38.1

1s

46d

17m

30.0

s7.1

520.2

57

91.1

7.9

8.4

48.6

97.6

9298.3

40.6

70.5

5-1

.25

0.1

8

MNRAS 000, 1–16 (2018)

The influence of AM and environment on the HI gas of late-type galaxies 15

Table

A1

–continued

Nam

eR

AD

EC

DVsys

iVmax

σH

ilo

g(M∗)

log(M

Hi)

log(M

H2)

log(M

b)

j bfatm

qlo

g(SFR

)B

/T

[J2000]

[J2000]

Mp

ckm

s−1

deg

km

s−1

km

s−1

[M

][M

][M

][M

]kp

ckm

s−1

[M

yr−

1]

UG

C7483

12h

24m

11.1

7s

31d

31m

19.0

s17.2

1254

78.7

103.1

12.2

9.4

9.0

68.2

49.6

3551.4

0.3

60.3

6-0

.48

0.5

6

UG

C7559

12h

27m

05.1

5s

37d

08m

33.3

s3

218.1

56.6

42

8.1

6.6

77.7

66.5

47.9

433.8

10.8

90.7

3n/a

0.0

5

UG

C7603

12h

28m

44.1

1s

22d

49m

13.6

s8.7

637.5

74.3

69.2

88.6

88.8

67.7

99.1

9297.2

20.6

40.3

6-1

.85

0.1

3U

GC

7608

12h

28m

44.2

0s

43d

13m

26.9

s7.4

538.5

32

54.7

6.2

7.0

88.6

57.4

28.8

2151.8

10.9

30.3

3n

/a

n/a

UG

C7690

12h

32m

26.8

9s

42d

42m

14.8

s7.4

537.3

48

47.7

6.8

8.7

48.4

67.6

9122.9

60.3

90.2

-1.7

20.2

4U

GC

7766

12h

35m

57.6

5s

27d

57m

36.0

s11.1

807.6

68

125.9

9.4

9.9

59.8

98.9

110.3

11346.1

20.5

10.1

4-0

.24

0.0

8

UG

C7861

12h

41m

52.7

s41d

16m

26s

8.5

621.3

42.2

45.6

58.7

38.7

97.7

69.1

6153.1

90.5

70.1

2n/a

n/a

UG

C7916

12h

44m

25.1

4s

34d

23m

11.5

s8.3

607.5

67.2

39.9

9.3

8.1

78.5

67.4

48.8

392.5

10.7

30.2

9n

/a

0.1

3U

GC

7971

12h

48m

22.8

7s

51d

09m

52.9

s6.4

468.3

37

42.6

7.2

8.1

88.2

27.2

8.6

69.2

20.5

60.2

9n

/a

0.0

8

UG

C7989

12h

50m

26.5

8s

25d

30m

02.9

s16.5

1206.9

49.9

232.1

10.6

11.0

19.7

59.6

711.0

72579

0.0

70.0

50.1

60.4

7

UG

C8403

13h

21m

56.4

s38d

44m

05s

13.4

975.6

51.9

125.3

11

9.3

89.1

38.2

59.6

5525.0

60.4

10.3

n/a

n/a

UG

C8699

13h

45m

08.7

1s

41d

30m

12.2

s34.6

2527.8

72.1

190.9

9.5

10.2

69.4

28.9

610.3

6930.8

90.1

60.0

9n

/a

0.5

7

UG

C8700

13h

45m

19.2

s41d

42m

45s

35.3

2574.9

75

247.1

14.4

10.6

89.4

79.3

410.7

4924.8

30.0

70.0

6n

/a

0.8

7

UG

C8709

13h

46m

23.6

7s

43d

52m

20.4

s33

2410.8

74

200.6

11.9

10.4

110.0

19.2

210.6

21926.5

80.3

30.1

30.5

80.2

6U

GC

8863

13h

56m

16.6

7s

47d

14m

08.5

s24.6

1794.3

65

209.9

10

10.3

69.2

69.0

310.4

3870.2

50.0

90.0

8-0

.22

0.7

3

UG

C9211

14h

22m

32.1

7s

45d

23m

01.9

s9.4

686.4

57.3

57.8

5.7

88.6

97.5

18.9

1216.6

0.8

20.3

6n/a

0.2

8

UG

C9366

14h

32m

46.8

5s

49d

27m

28.4

s29

2115.6

63.5

229.4

12.1

10.7

19.6

79.3

810.7

81191.1

70.1

0.0

61.0

40.2

2U

GC

9648

14h

58m

59.6

s53d

55m

24s

46.3

3378.3

65.2

135.4

9.3

9.8

89.4

28.6

710.0

7954.6

50.3

0.1

8n

/a

n/a

UG

C9753

15h

09m

46.7

3s

57d

00m

00.7

s10.6

772.5

75.7

136.4

9.5

9.3

58.7

8.0

99.4

9269.2

20.2

20.1

90.0

50.8

2

UG

C9797

15h

15m

23.3

2s

55d

31m

02.5

s46.5

3392.4

49.6

198

10

10.7

10.3

59.5

310.9

33817.0

30.3

60.1

0.7

30.5

7U

GC

9969

15h

39m

37.0

9s

59d

19m

55.0

s34.5

2518.8

63.7

286.7

710.8

9.8

69.4

910.8

93287.6

20.1

30.0

70.8

20.2

1

UG

C10310

16h

16m

18.3

5s

47d02m

47.1

s9.8

716.4

47.3

64.5

5.8

8.5

28.6

47.5

98.9

9207.4

90.6

10.2

9-1

.62

0.0

6U

GC

10359

16h

20m

58.1

6s

65d23m

26.0

s12.5

910.5

49.3

129.8

6.5

9.6

69.5

48.5

99.9

91344.0

40.4

80.2

1-0

.20.6

3

UG

C10445

16h

33m

47.6

2s

28d59m

05.2

s13.2

963.6

56.8

65.6

8.8

8.6

99.0

37.9

19.3

1358.7

0.7

10.3

6-0

.62

0.1

7

UG

C10470

16h

32m

39.2

0s

78d11m

53.4

s18.7

1362.9

46.4

119.8

8.2

10.3

39.7

69.0

910.4

91151.0

30.2

50.0

70.6

0.6

1U

GC

10502

16h

37m

37.6

9s

72d22m

28.8

s59

4310.1

32.7

206.1

5.5

10.4

9.9

39.1

910.5

91584.6

30.3

0.0

5n/a

0.0

3U

GC

10564

16h

46m

21.9

9s

70d21m

31.7

s15.5

1129.8

71.2

84.1

10.3

8.4

49.2

68.0

69.4

6516.0

30.8

50.4

3-1

.18

0.0

8

UG

C11124

18h

07m

27.5

0s

35d33m

48.0

s22.1

1614

49.5

81.7

9.2

9.2

99.2

88.2

89.6

8511.6

80.5

40.2

3n

/a

0.0

2U

GC

11218

18h

19m

46.4

1s

74d34m

06.1

s20.3

1485

63

179.1

10.2

10.3

39.4

49.0

210.4

2871.7

50.1

40.0

80.6

50.1

UG

C11670

21h

03m

33.5

8s

29d53m

50.9

s10.7

779.4

66.5

162.7

10.5

9.9

58.7

88.6

110.0

1451.6

70.0

80.1

1-0

.14

0.8

6

UG

C11852

21h

55m

59.3

1s

27d53m

54.3

s80.2

5853.9

65

157.6

10

10.5

210.4

69.4

910.8

83643.8

0.5

10.1

10.5

0.7

UG

C11861

21h

56m

24.0

0s

73d15m

38.6

s20.3

1482

54

146.2

9.6

10.2

79.6

910.4

1225.5

90.2

10.1

10.4

40.0

5U

GC

11909

22h

06m

16.1

7s

47d15m

04.4

s15.1

1105.8

76

152.2

18.5

9.4

29.4

58.4

49.8

3454.9

40.5

60.2

9-0

.43

0.0

4

UG

C11951

22h

12m

30.1

2s

45d19m

42.5

s14.8

1078.8

71.4

121.1

13

9.2

78.9

58.1

19.5

1243.7

70.3

80.2

3-0

.49

0.2

1U

GC

12043

22h

27m

50.5

2s

29d05m

45.5

s13.8

1008.6

70.9

90.8

10.7

8.7

8.9

47.8

59.2

5388.1

10.6

60.5

4-1

.22

0.0

8U

GC

12082

22h

34m

10.8

2s

32d51m

37.8

s11

802.5

48.4

51.8

6.5

8.4

28.8

57.7

29.1

1219.2

80.7

40.2

5n

/a

0.0

7U

GC

12212

22h

50m

30.3

3s

29d08m

18.4

s12.1

886.5

46.1

106.9

7.9

8.4

8.5

87.5

18.9

1343.5

80.6

40.7

8n

/a

0.0

6U

GC

12732

23h

40m

39.8

6s

26d14m

11.1

s10.2

747.6

36.3

91.5

6.6

9.2

69.2

58.2

59.6

5595.3

30.5

40.2

n/a

0.1

2

MNRAS 000, 1–16 (2018)

16 C. Murugeshan et al.

This paper has been typeset from a TEX/LATEX file pre-

pared by the author.

MNRAS 000, 1–16 (2018)