Connecting Warm H2 Emission and Active Transformation within Compact Groups

Image Credit: NASA,ESA and the Hubble SM4 ERO Team

Michelle Cluver mcluver@aao.gov.au

CollaboratorsPhilip Appleton (NHSC/Caltech)Patrick Ogle (SSC/Caltech)Jesper Rasmussen (Dark Cosmology Centre, Copenhagen)Thomas Jarrett (IPAC/Caltech)Ute Lisenfeld (Universidad de Granada)Pierre Guillard (SSC/Caltech)Francois Boulanger (IAS, Orsay)Kevin Xu (NHSC/Caltech)Min Yun (UMass-Amherst)Lourdes Verdes-Montenegro (IAA, Granada)Thodoris Bitsakis (U. Crete)Vassilis Charmandaris (U. Crete)

Galaxy EvolutionHow do galaxies move from the blue sequence to

the red cloud?What are the characteristics of galaxies with

intermediate colours and what role does environment play?

Credit: T. Gonclaves

How do Galaxies Transform?

Schiminovich et al. (2007)

Transformation within Group Environments

S0 evolution significantly more dramatic in groups than in clusters (Wilman et al. 2009; Just et al. 2010); ram pressure stripping not dominant mechanism

Recent simulations show spirals in group environments strongly influenced by repetitive slow encounters, increasing mass of bulges and transforming into S0’s. 10-30% of stars and gas stripped during this process (Bekki and Couch 2011)

Shapley supercluster (Haines et al. 2011) quenching in S0/a before they reach dense core late-types are being transformed; quenching occurs before and after transformation to lenticular

HI-deficient, disturbed with inefficient ram-pressure stripping seen in NGC 2563 group (Rasmussen et al. 2012) and Pegasus I cluster(Rose et al. 2010)

Why Compact Groups?

Evolution is aggressive, but not too much

Compact Groups are high density environments, galaxies are strongly interacting

Relatively shallow gravitational potential well prolongs gravitational interactions (probe evolution in dense environment)

Transformation in Compact Groups

Hickson Compact Groups (HCGs); Hickson et al. (1982), 4+ members, median z ~ 0.03, median σ ~ 200 km/s

Galaxies are HI deficient: tidal interactions and ISM stripping lead to gas-poor systems (Verdes-Montenegro et al. 2001)

Negligible ram-pressure stripping from hot, tenuous medium: in most HI-deficient groups, diffuse X-rays detected in only 50%, insufficient to remove gas significantly

Galaxies appear to be undergoing rapid evolution onto the red sequence (Johnson et al. 2007, Walker et al. 2010)

(also Walker et al. 2012 – 174 galaxies in 37 HCGs)

Only similar in distribution to Coma Infall region

Bimodality of dusty/gas-rich and dust-free/gas-poor; suggests rapid evolution

Spitzer IRAC colours show tight trend

correlating with evolutionary stage

Johnson et al. (2007), Walker et al. (2010)42 galaxies in 12 HCGs

Transformation in Compact Groups

Warm Molecular Hydrogen Emission• Mid-IR emission from pure rotational H2

• direct detection of H2

• associated with starbursts, (U)LIRGs, AGN Genzel et al. 1998; Rigopoulou et al. 2002; Lutz et al. 2003

• Mechanisms:

• Far-UV induced pumping and/or collisional heating (PDRs associated with HII regions)

• hard X-rays heating regions in molecular clouds, H2 excited through collisions

• collisional excitation due to acceleration produced by shocks

Stephan’s Quintet: An HCG with dramatic H2 Line-Cooling

High velocity (~ 800 km/s) collision of NGC 7318b with intragroup medium: intergalactic shock wave (~35 kpc)

17.03μm: 0.3 - 2.1MJy/sr

Powerful, widespread shock-excited H2 emission

(Cluver et al. 2010a)

Stephan’s Quintet: An HCG with dramatic H2 Line-Cooling

• Dominates in mid-IR

H2 fits in gap in HI distribution : implies HI converted into hot plasma + H2

(Cluver et al. 2010a)

Optical (CFHT/Coelum) + X-ray (NASA/CXC/CfA/E.O’Sullivan)

Hubble WFC3 (comp) + Spitzer S(1) H2 (blue) Image credit: Robert Hurt, Michelle Cluver (SSC)

Origin of H2 and X-ray emissionHigh-speed collision with a multi-phase medium

creates multiple shocks (velocities)Low density HI hot plasma (X-rays)Denser clumps of HI forms H2

Slow MHD shocks (5-20 km/s) excite H2

Clouds of H2 are heated by turbulence in the hot gas i.e. the kinetic energy of shock fuels H2 emission.

Molecular gas is continuously excited by supersonic turbulence

See model of Guillard et al. (2009)

Ares I-X – bow shock forms collar of water droplets

Is Stephan’s Quintet unusual or just extreme?

Spitzer IRS low res spectroscopy (and photometry) of 23 HCGs

Intermediate HI depletion with visible signs of tidal interaction in 2+ galaxies dynamically active

Probe evolutionary sequence + connection of SQ

Sample covers 74 group members

HCG 40

Cluver et al. (2012, in prep)

IRAC Colour Evolution

74 galaxies in 23 groupsH2 enhanced (above star formation) -- 13

Star Forming

Early Types

Molecular Hydrogen Emission Galaxies (MOHEGs) defined using H2 divided by star formation indicator (Ogle et al. 2010)

9/13 are S0 (pec) type, 2 Sab (pec), 1 Sm

HCG 57A (Sb)– Disk spectrum

H2 Relative to Warm Dust Emission (24mm)

Trend confirms H2/PAH result and indicates limited AGN contamination

What is exciting H2?Star formation – ruled outX-rays – ruled outCosmic Rays – ruled outShocks

What produces shock excitation?AGN jets? Stochastic collisions:

Accretion? Viscous Stripping?

• Recent GBT + VLA observations reveal extended, faint emission; galaxies with largest HI deficiencies have more massive, diffuse HI component (Borthakur et al. 2010)

• Protracted gravitational interactions sea of material + disrupted disks• Galaxies pass through debris stochastic heating + viscous stripping

• Enhanced, excited H2 could be result of shock excitation as ISM interacts with tidal material – less

energetic version of what we see in Stephan’s Quintet

Death by Debris?

Specific Star Formation

H2-enhancement occurs at intermediate/low specific star

formation

IRAC colour acts as proxy for sSFR

A Green Valley Connection

In dynamically “old” groups~40% of late-type and ~50% of early-type lie in so-called “green valley”

Bitsakis et al. (2010)

In “dynamically old” groups>70% of early-types are

S0’s

How do you make an S0?

Ram Pressure Stripping (e.g. Gunn and Gott 1972)

Truncation of gas replenishment (e.g. Bekki 2002)

Tidal Encounters (e.g. Icke 1985)

Minor merging (e.g. Bekki 1998)

Slow encounters in groups builds bulge mass + gas stripping (Bekki and Couch 2011)

Compact Groups may be key

To what extent are galaxies pre-processed in a group environment

through:

Building bulge-dominated disksIntragroup HI stripping/heating

Group Environment

Other H2-enhanced show similar location in mid-IR colour

Interacting pair, triple, cluster or compact group shown as hollow circles

SINGS

Intragroup HI interacting with group galaxies could be

common mechanism

Disrupted star formation/accretion could

produce accelerated evolution

(seen in colour-colour plane)

Similar to ESO 137-001 in Norma Cluster?H2 tail due to ram-pressure stripping

(Sivanandam et al. 2010)

GAMA

ASKAP -- WALLABY

The tidal and dynamical processes influencing the evolution of galaxies in a group environment will

likely be key to understanding the role of environment in driving the evolution of galaxies

since z > 1.

K. Bekki

K. Bekki

25B (Sa)

6B (Sab)

15D (S0)

Morphology, Activity• 9/13 are S0 (pec) type, 2 Sab (pec), 1 Sm• 1 SF spectrum with SF colours (68C)• 1 AGN-dominated spectrum (56B)

Cluver et al. (2012)

• 68% HCG galaxies host AGN (Martinez et al. 2010)

BUT, low power

• low-luminosity LINERs or Sy2 (Coziol et al. 2004)

• ~3% broad-to-narrow-line AGN

• Shock excitation could be from gas falling back onto galaxies

• Velocity dispersion of gas/galaxies?• No enhancement in SFR (Iglesias-Paramo+ Vilchez 1999) overall relatively low (Bitsakis et al. 2011)

• Truncation of SF in early-types (de la Rosa et al. 2007)

H2 in the IGMHCG 40

HCG 91

Significant Cooling Pathway!

Power in shock-driven molecular hydrogen line cooling has implications for models of galaxy mergersgas accretion onto galaxiesaccretion onto massive halos in early structure formationstarburst driven winds (outflows) SNR(U)LIRGSAGN (jet interactions with ISM)

Strong warm H2 emission systems

+/- 30% local 3CR radio galaxies have dominant MIR H2 (often coupled with weak thermal continuum) - MOHEGS. Mechanical heating driven by jet interaction with host ISM (Ogle et al. 2007, 2010)

Seen in central cluster galaxies (Egami et al. 2006, Donahue et al. 2011)

Also in filaments in clusters (Johnstone et al. 2007) – “cooling flows”

Elliptical galaxies (Kaneda et al. 2008)

Taffy Galaxies (Peterson et al., ApJ in press)

LVL: Dale et al. (2009) < 11 Mpc 258 galaxies (dominated by spiral and irregular) HCG: Bitsakis et al. (2011) 135 galaxies in 32 HCGs

HCG 56

HCG 40

HCG 68

HCG 57

HCG 25

HCG 95