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 1-3 2008
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
QuickTime™ and aYUV420 codec decompressor
are needed to see this picture.
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/tpeculiar
Fraction of galaxies with peculiar morphology increases strongly with LIR
(~SFR)
ACS Survey of IR Luminous Galaxies: A. Evans 2007
% Peculiar (Sanders & Mirabel 1996, ARAA):
Log LIR=10-11: ~10%
Log LIR=11-12: ~90%
Log LIR>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
NGC2623 NGC3256
NGC3921 NGC7252
HST F702W of four E+A
Wang et al. 2004, ApJ, 607, 258
EA2 EA3
EA4 EA5
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 ellipticalsRothberg & 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 300-500 Mo/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 1996Contours: OVRO CO(1-0): Yun & Hibbard 1999
NGC7252: HI streaming in from tidal tails
Tails must extend back into remnant, but HI ends abruptly
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 (www.nrao.edu/astrores/HIrogue): 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 (www.nrao.edu/astrores/HIrogue): 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)
QuickTime™ and a decompressor
are needed to see this picture.
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
SpiralsPeculiarCompactEarly-typeundetected
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=100-150 Mo/yr, but Mgas~1E11 Mo, 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-merger mM=minor merger
M=major merger MR=merger remnant
pMpM
pMpM
M M
M M
MR MR
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
mM
mM
mMMR
Normal Hubble Types?
M81/M82/NGC3077VLA 12-pointing mosaic
Yun et al. 1994
VLA HI: Mundell 2000WSRT HI: Swaters et al. 2002
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 cluesLocally: HI reveals dynamical naturez=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
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