Study evolutionary status Study evolutionary status of dwarfs in the nearby of dwarfs in the nearby

Lynx-Cancer void. Lynx-Cancer void. Preliminary resultsPreliminary results

Pustilnik S.A. , Tepliakova A.L. Pustilnik S.A. , Tepliakova A.L. (SAO RAS)(SAO RAS)

Kniazev A.Y. (SAAO, Cape Town)Kniazev A.Y. (SAAO, Cape Town)

IntroductionIntroductionThe galaxy evolutionThe galaxy evolution versus the global versus the global

environmentenvironment

((clustersclusters, , groupsgroups, , voidsvoids)) is a long-studied is a long-studied problem.problem.

VoidsVoids are delineated byare delineated by luminous luminous ( (L > L*L > L*)) massive objectsmassive objects and populatedand populated by dwarfsby dwarfs.. The The galaxy densities and other parameters vary galaxy densities and other parameters vary significantly from one void to another.significantly from one void to another.

One expects that not only One expects that not only galaxy interactionsgalaxy interactions occur in voids much less frequentlyoccur in voids much less frequently, , but but also also DM halo and galaxy formation from density DM halo and galaxy formation from density perturbations can be somewhat retarded due to perturbations can be somewhat retarded due to the lower voidthe lower void mean gravitational potential. mean gravitational potential.

Motivation. Lynx-Cancer Motivation. Lynx-Cancer voidvoid

Despite the study galaxies in voids is an actual Despite the study galaxies in voids is an actual direction, not much is done so far. direction, not much is done so far. Almost all Almost all largelarge voids with D > 20-30 Mpc are quite distantvoids with D > 20-30 Mpc are quite distant! ! Due to selection effects one can see and study in Due to selection effects one can see and study in them only a small, brighter part of void galaxies them only a small, brighter part of void galaxies

(M_B < ~ --17), and those with strong emission-(M_B < ~ --17), and those with strong emission-line spectraline spectra.. More typical and fainter dwarfs More typical and fainter dwarfs (M_B=--12 to --16) remain largely unexplored. (M_B=--12 to --16) remain largely unexplored.

The only nearby large ‘the Local Void’ of Tully et The only nearby large ‘the Local Void’ of Tully et al. (2008) is close, but pretty empty.al. (2008) is close, but pretty empty.

A.Fairall (1998) described several small nearby A.Fairall (1998) described several small nearby voids (with sizes of D~10 Mpc) in Cetus, voids (with sizes of D~10 Mpc) in Cetus, Cepheus, Volans, MonocerosCepheus, Volans, Monoceros

Nearby voidsNearby voids

Lynx-Cancer voidLynx-Cancer void Pustilnik et al. (2003) described Lynx-Cancer void (with Pustilnik et al. (2003) described Lynx-Cancer void (with

`conditional’ center at RA~8.5 h, Dec~+30, D ~`conditional’ center at RA~8.5 h, Dec~+30, D ~1414 Mpc, Mpc,

with the total extent D ~> 10 Mpc). with the total extent D ~> 10 Mpc). The known to date void dwarf galaxy population The known to date void dwarf galaxy population

consists of ~50 objects with M_B down toconsists of ~50 objects with M_B down to -12 -12 (Pustilnik (Pustilnik & Tepliakova, in preparation).& Tepliakova, in preparation). The important The important advantage of this region is that it is well covered by the advantage of this region is that it is well covered by the SDSS images and spectra.SDSS images and spectra.

The project goalsThe project goalsComparative study of Comparative study of evolutionary statusevolutionary status of dwarfs in of dwarfs in

this voidthis void and in and in nearby denser structure elementsnearby denser structure elements. . Parameters:Parameters: 1. gas metallicity (HII regions O/H)1. gas metallicity (HII regions O/H),, 2. gas mass fraction2. gas mass fraction Mg/(Mg+M*),Mg/(Mg+M*), 3. ages of the oldest visible stellar population3. ages of the oldest visible stellar population

T_star. T_star.

Lynx-Cancer void Lynx-Cancer void cosmography.Icosmography.I

Lynx-Cancer void Lynx-Cancer void cosmography.IIcosmography.II

10-degree Declination slices in Lynx-10-degree Declination slices in Lynx-Cancer voidCancer void

Sample galaxies. ImagesSample galaxies. Images

Sample galaxies. Sample galaxies. PropertiesProperties

Observational dataObservational data Major part of this region is covered byMajor part of this region is covered by SDSS DR7. SDSS DR7.

This provides a) radial velocities for many dwarfs; b) This provides a) radial velocities for many dwarfs; b) five-filter good quality images with some photometry; five-filter good quality images with some photometry; c) small fractionc) small fraction of galaxies with spectra suitable for of galaxies with spectra suitable for O/H determination.O/H determination.

Own spectral survey with 6-m telescope (BTA) for Own spectral survey with 6-m telescope (BTA) for O/H O/H (in preparation). (in preparation).

Integrated HI parameters – partly from literature,Integrated HI parameters – partly from literature, the the restrest are from our are from our HI observations atHI observations at NRT (Nancay) NRT (Nancay) with J.-M. Martin (in preparation).with J.-M. Martin (in preparation).

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A caveat:A caveat: LSB galaxies are rare objects among SDSS LSB galaxies are rare objects among SDSS spectral targets.spectral targets. Therefore the LSB dwarfs with Therefore the LSB dwarfs with knownknown velocitiesvelocities are underrepresented. HI blind are underrepresented. HI blind survey may help. But ALFALFA will cover only less survey may help. But ALFALFA will cover only less then a half of the respective sky sectionthen a half of the respective sky section

Lynx-Cancer void: some unusual Lynx-Cancer void: some unusual galaxiesgalaxies

First very low O/H galaxy BCG First very low O/H galaxy BCG HS 0822+3542HS 0822+3542 O/H=7.4, M_B~-12.9 (Kniazev et al. 2000) O/H=7.4, M_B~-12.9 (Kniazev et al. 2000)

LSB dwarf LSB dwarf SAO 0822+3545SAO 0822+3545 very blue, very blue, M_B~-13.3 M_B~-13.3 ( (at d~14 kpc), interacting with HS at d~14 kpc), interacting with HS 0822+3542. SDSS ugri colors vs PEGASE2 0822+3542. SDSS ugri colors vs PEGASE2 evolutionary tracks: no stars with T > 2-3 Gyr.evolutionary tracks: no stars with T > 2-3 Gyr. A A dwarf pairdwarf pair close to the void centerclose to the void center ( (Pustilnik et Pustilnik et al. 2003al. 2003))..

• DDO 68DDO 68 – a nearby dwarf (M_B=-15.3) with – a nearby dwarf (M_B=-15.3) with record low O/Hrecord low O/H (7 (7..1414, Pustilnik+05, Izotov+06). , Pustilnik+05, Izotov+06). SDSS ugri colors vs PEGASE2 SDSS ugri colors vs PEGASE2 T < 1 Gyr T < 1 Gyr ((Pustilnik etal. 2008). HI maps with GMRT: Pustilnik etal. 2008). HI maps with GMRT: recent merging of two very gas-rich objectsrecent merging of two very gas-rich objects ( (Ekta Ekta etal. 2008etal. 2008))..

• SDSS J0926+3343SDSS J0926+3343 – edge-on LSBD with M_B~- – edge-on LSBD with M_B~-12.9, O/H=7.12 and ugri colors 12.9, O/H=7.12 and ugri colors T ~1--3 Gyr. T ~1--3 Gyr. At D of only ~1.6 Mpc from DDO 68 (Pustilnik At D of only ~1.6 Mpc from DDO 68 (Pustilnik etal. 2009, MNRAS)etal. 2009, MNRAS)

Filaments, “groups”, pairsFilaments, “groups”, pairs

~80% of void ~80% of void dwarfs enter to dwarfs enter to pairs, or/and pairs, or/and belong to belong to filaments with filaments with lengths of 1-2 lengths of 1-2 Mpc. Groups are Mpc. Groups are rare. About 20% rare. About 20% of dwarfs look of dwarfs look like isolatedlike isolated

Summary of spectral dataSummary of spectral data

In total, for ~35 late-type dwarfs O/H is In total, for ~35 late-type dwarfs O/H is determined either by direct T_e method determined either by direct T_e method (with [OIII]4363 line), or by semi-empirical (with [OIII]4363 line), or by semi-empirical method of Izotov & Thuan (2007)method of Izotov & Thuan (2007)

For 17 of them: Zo/35 < Z < Zo/10For 17 of them: Zo/35 < Z < Zo/10 For 4 galaxies of these 17: 12+log(O/H) < For 4 galaxies of these 17: 12+log(O/H) <

7.35:7.35: SDSS J0926+3343 O/H=7.12SDSS J0926+3343 O/H=7.12 DDO 68 (J0956+2849) O/H=7.14DDO 68 (J0956+2849) O/H=7.14 SDSS J0812+4836 O/H=7.28 SDSS J0812+4836 O/H=7.28 SDSS J0737+4724 O/H~7.30SDSS J0737+4724 O/H~7.30------------------------------------------------------------------------------------------------------------------------------------------

-- [ … plus adjacent I Zw18 (J0934+5514) [ … plus adjacent I Zw18 (J0934+5514)

O/H=7.17 ]O/H=7.17 ]

DDO 68. SummaryDDO 68. Summary

DDO 68 summaryDDO 68 summary

Edge-on LSBDEdge-on LSBD SDSS SDSS J0926+3343J0926+3343

SDSS finding chart

SCORPIO slit position

2D spectrum of J0926+3343

BTA spectral resultsBTA spectral results

Spectra of HII regionsSpectra of HII regions « «aa» » andand « «bb» » with with SCORPIO. Estimates of O/H by classic SCORPIO. Estimates of O/H by classic T_e T_e method method give meangive mean value of value of 12+log(O/H)=7.12+-0.0212+log(O/H)=7.12+-0.02..

SDSS J0926+3343SDSS J0926+3343

SDSS J0926+3343 SDSS J0926+3343 is is one of two galaxies one of two galaxies with the record low with the record low O/H (of many O/H (of many thousands known to thousands known to date)date). . This is This is situatedsituated inside theinside the Lynx-Cancer void, at Lynx-Cancer void, at the distance ofthe distance of ~1.6 ~1.6 Mpc Mpc from DDO 68, from DDO 68, the next known the next known lowest O/H galaxy.lowest O/H galaxy.

Blue SDSS ugri Blue SDSS ugri colors for outer colors for outer regions of SDSS regions of SDSS J0926+3343, as J0926+3343, as compared with compared with PEGASE2 PEGASE2 evolutionary evolutionary tracks indicate tracks indicate ages of the oldest ages of the oldest stellar popul. of stellar popul. of ~1—3 Gyr~1—3 Gyr

Metal deficiency in void Metal deficiency in void dwarfsdwarfs

The basic relation The basic relation “O/H vs M_B” as “O/H vs M_B” as derived on the Local derived on the Local Volume groups and Volume groups and field dwarfs (van Zee field dwarfs (van Zee & Haynes 2006, the & Haynes 2006, the upper dashed line) and upper dashed line) and O/H, observed in void O/H, observed in void dwarfsdwarfs

The line shifted by 1 The line shifted by 1 mag (or ~0.2 dex on mag (or ~0.2 dex on O/H) better accounts O/H) better accounts for possible systematic for possible systematic lower O/H in the void lower O/H in the void

Several extremely low Several extremely low O/H dwarfs: very rare O/H dwarfs: very rare special casesspecial cases

Colors of dwarfs in the void. Colors of dwarfs in the void. SAO 0822+3545 (unknown SAO 0822+3545 (unknown

O/H)O/H)

Colors of dwarfs in the void. Colors of dwarfs in the void. SDSS J0737+4724 SDSS J0737+4724 (12+log(O/H)~7.3)(12+log(O/H)~7.3)

Colors of dwarfs in the void. Colors of dwarfs in the void. SDSS J0843+4025 SDSS J0843+4025

(12+log(O/H)=7.59)(12+log(O/H)=7.59)

Colors of dwarfs in the void. Colors of dwarfs in the void. SDSS J0859+3923 SDSS J0859+3923

(12+log(O/H)=7.57)(12+log(O/H)=7.57)

Colors of dwarfs in the void. Colors of dwarfs in the void. SDSS J0911+3136 SDSS J0911+3136

(12+log(O/H)=7.51)(12+log(O/H)=7.51)

ConclusionsConclusions About 50 dwarfs are currently found within the Lynx-Cancer About 50 dwarfs are currently found within the Lynx-Cancer

void. Their study allows much deeper probe of void galaxy void. Their study allows much deeper probe of void galaxy properties down to absolute magnitudes of M_B~-12.0 in properties down to absolute magnitudes of M_B~-12.0 in the volume of >~500 Mpc^3 and comparison with galaxies the volume of >~500 Mpc^3 and comparison with galaxies in more typical environments in the Local Volume. in more typical environments in the Local Volume.

• Our preliminary results indicate the sizable effect of void Our preliminary results indicate the sizable effect of void environment:environment:

* Late-type dwarfs in LC void are on mass * Late-type dwarfs in LC void are on mass more metal-deficient. Several outstanding more metal-deficient. Several outstanding void dwarfs are the most metal-poor known. void dwarfs are the most metal-poor known.

* Parameter M(HI)/L_B is enhanced for void * Parameter M(HI)/L_B is enhanced for void galaxies. galaxies.

* Several dwarf galaxies have outer colors * Several dwarf galaxies have outer colors consistent with the ages of the oldest consistent with the ages of the oldest visible stars of ~1--3 Gyr. visible stars of ~1--3 Gyr.

Prospects and future Prospects and future researchresearch The nearby voids are good places to address The nearby voids are good places to address

cosmologically related issues of N-body cosmologically related issues of N-body simulations of galaxies and their structures.simulations of galaxies and their structures.

It appears that the least evolved and “young” It appears that the least evolved and “young” galaxies favor the void environment => the galaxies favor the void environment => the way for hunting for local `cousins’ of high-way for hunting for local `cousins’ of high-redshift young galaxies!redshift young galaxies!

Number and spatial distribution of void Number and spatial distribution of void galaxies bears clues for CDM cosmology galaxies bears clues for CDM cosmology dwarf galaxy formation.dwarf galaxy formation.

LSB dwarfs are expected to be the main LSB dwarfs are expected to be the main population in voids, but currently are not well population in voids, but currently are not well represented. Need in means of their efficient represented. Need in means of their efficient selection and redshift/distance measurement. selection and redshift/distance measurement.

Our collaboratorsOur collaborators

We acknowledge the contribution to We acknowledge the contribution to the projectthe project

from J.-M.Martin (Obs. Paris, Nancay from J.-M.Martin (Obs. Paris, Nancay RT),RT),

Y.Lyamina (Rostov U.) and Y.Lyamina (Rostov U.) and E.Shaldenkova (SAI, Moscow)E.Shaldenkova (SAI, Moscow)

Thank you for Thank you for attention!attention!