John E. Hibbard NRAO-CV Interaction Driven Galaxy Evolution: The Fate of the Cold Gas “The Evolution of Galaxies through the Neutral Hydrogen Window”, Arecibo Observatory, Feb

Outline of Talk  Interactions happen locally  Two burning questions:  If gas rich galaxies merge to form spheroidals, what happens to the cold gas?  Are interactions any more important at higher redshift? Gas holds the answers!

Peculiar Galaxies: dynamically unrelaxed (non-equilibrium) forms Toomre Sequence of On-going Mergers (Toomre 1977) from Arp Atlas of Peculiar Galaxies (Arp 1966)

Morphologies (& Kinematics!) can be explained by galaxy-galaxy interactions Seminal Paper (1369 citations): Toomre & Toomre 1972

Mihos 2001, ApJ, 550, 94 Tidal forces drive large scale inflows and outflows

Simulated merger morphologies: J. Barnes, personal communication (see also Barnes & Hernquist 1992 ARAA)

5%-10% of population in local universe  In UGC, ~600 out of 9000 galaxies (~7%) with morphological descriptions including: disrupted, distorted, disturbed, interacting, eruptive, peculiar, bridge, loop, plume, tail, jet, streamer, connected (note, some are multiple systems, but not all need be interacting)  Total fraction that went through a peculiar phase = %peculiar *  T/  t peculiar

Fraction of galaxies with peculiar morphology increases strongly with L IR (~SFR) ACS Survey of IR Luminous Galaxies: A. Evans 2007 % Peculiar (Sanders & Mirabel 1996, ARAA): Log L IR =10-11: ~10% Log L IR =11-12: ~90% Log L IR >12: ~100%

Q1: When Gas-rich galaxies merge, what happens to the gas?  Interaction-driven inflows drive disk- wide star formation  leads to large central concentrations of cold gas

Models (w/o feedback) predict these dense gaseous concentrations will leave sharp spikes in luminosity profiles of remnants

But light profiles of likely merger remnants show no discrete feature identifying central burst population HST NICMOS of late-stage Toomre Sequence Rossa et al. 2007, AJ, 134, 2124 NGC2623NGC3256 NGC3921NGC7252

HST F702W of four E+A Wang et al. 2004, ApJ, 607, 258 EA2EA3 EA4EA5 Light profiles of likely merger remnants show no discrete feature identifying central burst population

Light profiles of likely merger remnants: luminosity enhancements are modest Ground-based K-band of Fine structure ellipticals Rothberg & Joseph, 2004 AJ, 128, 2098

Classic merger remnants NGC3921 and NGC7252 have post-burst spectra  Therefore had a sudden drop in SFR in past.  NGC7252: Peak SFR was M o /year (ULIG)  But….cold gas still rains in!! Fritz-v.Alvensleben & Gerhard 1994 A&A, 285, 775

NGC 3921: smooth light profile, but dynamically unrelaxed molecular gas Greys: HST F550W image (left); image-model (right): Schweizer 1996 Contours: OVRO CO(1-0): Yun & Hibbard 1999

NGC7252: HI streaming in from tidal tails  Tails must extend back into remnant, but HI ends abruptly  Gas is currently falling back into remnant at 1- 2 Mo/yr  Tails must extend back into remnant, but HI ends abruptly  Gas is currently falling back into remnant at 1- 2 Mo/yr  Yet body remains devoid of HI

Suggest some process removes cold gas - at least from more massive systems From HI Rouges Gallery ( Peculiar Early Types with HI outside Optical Body, arranged by decreasing HI content

Lower-luminosity systems may retain cold material, reforming gas disks From HI Rouges Gallery ( Peculiar Early Types with HI inside Optical Body, arranged by increasingly regular HI kinematics

Examples of low-z “quenching”? Springel, Di Matteo & Hernquist 2003 (also Li et al. 2006; Hopkins et al. 2005, 2006)

Q2: Are interactions any more important at higher redshift?  Should be for hierarchical cosmologies  Recent work suggest this is not the case

Recent claims: No evolution in merger fraction from z=0.2-1 Extended Groth Strip: Lotz et al. 2008, ApJ, 672, 177 (See also Bell et al. 2005, Wolf et al. 2005, Bundy et al. 2005) Fraction of total population Classfication by Gini-M20 indices Late Types Major Mergers Early types Late Types Early types Sanders & Mirabel 1996 ARAA

Evolution of star formation density since z~1 driven by SF in normal Hubble Types HUDF parallel fields: Menanteau et al. 2006, AJ, 131, 208 Late Types Peculiars Early types Classfication by eye Classfication by A-C indices Contribution to SFR density

Spirals Peculiar Compact Early-type undetected At z=1, SF dominated by “normal Hubble Types” Spitzer 24um & HST of GOODS-N: Melbourne, Koo & Le Floc’h 2005, ApJ, 632, L65 A class of galaxy not known locally (e.g. Ishida 2002 PhD Thesis): Normal Hubble type with SFR>50 Mo/year

Are interactions important at z<1.5?  Emerging Paradigm:  SFR evolution driven by same SF processes as locally, in morphologically normal galaxies  Higher SFR because galaxies are more gas-rich at higher-z e.g.: Daddi et al. 2008: 2 “disk” galaxies at z=1.5. SFR= Mo/yr, but M gas ~1E11 M o, so SF timescales more like “normal” disk galaxies (~10* lower SFE than ULIGs) PdB CO(2-1) of BzK galaxies: Daddi et al. 2008, ApJL, 673, L21

But…Can we trust classifications at higher redshift? Wang et al. 2004, ApJ, 607, 258 Also - Hibbard & Vacca 1997

Automated classifiers only sensitive to most extreme morphologies Taylor, 2005 PhD Thesis ASU See also: Conselice 2006 pM=pre-mergermM=minor merger M=major mergerMR=merger remnant pM M M M M MR Pre-Mergers (pM), minor Mergers (mM) & Merger Remnants (MR) occupy same morphological parameter space as normal Hubble Types. Only major mergers (M) stand out mM MR

Normal Hubble Types? M81/M82/NGC3077 VLA 12-pointing mosaic Yun et al. 1994

VLA HI: Mundell 2000WSRT HI: Swaters et al HI Tidal Debris

Non-peculiar morphological parameters does not mean morphologically Normal  True population of interacting/peculiar objects will be greater than derived optically  This will be even more true in the past, when galaxies were much more gas rich  Gas holds the clues  Locally: HI reveals dynamical nature  z=0-1: ALMA will image SFR, gas kinematics & morphology on sub-arcsec scales. Disks or multi- component?

ALMA CO(2-1) at z=1 (b=1.5km; 0.4”) SKA HI at z=1 (1.5”) “Normal” Spiral at z=1.08, SFR=30 Mo/yr “Normal” Elliptical at z=0.7, SFR=30 Mo/yr 5”x5” HUDF-S

What to do before SKA**?  Data volumes to be delivered by next- generation radio/mm instruments (EVLA, ALMA) are >>100x current capabilities  SKA will continue this trend  Number of Astronomers/grad students have not increased by similar factors  We have to give astronomers the tools to properly mine these immense datasets  (who is “we”?) **: the content of this page represents the personal viewpoint of the author, and in now way indicates opinions or policies of the NRAO