John E. Hibbard

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Interaction Driven Galaxy Evolution The Fate of
the Cold Gas

• John E. Hibbard
• NRAO-CV

The Evolution of Galaxies through the Neutral
Hydrogen Window, Arecibo Observatory, Feb 1-3
2008
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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!

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Peculiar Galaxies dynamically unrelaxed
(non-equilibrium) forms
Toomre Sequence of On-going Mergers (Toomre 1977)
from Arp Atlas of Peculiar Galaxies (Arp 1966)
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Morphologies ( Kinematics!) can be explained by
galaxy-galaxy interactions
Seminal Paper (1369 citations) Toomre Toomre
1972
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Tidal forces drive large scale inflows and
outflows
Mihos 2001, ApJ, 550, 94
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Simulated merger morphologies J. Barnes,
personal communication (see also Barnes
Hernquist 1992 ARAA)
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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

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Fraction of galaxies with peculiar morphology
increases strongly with LIR (SFR)
Peculiar (Sanders Mirabel 1996, ARAA) Log
LIR10-11 10 Log LIR11-12 90 Log LIRgt12
100
ACS Survey of IR Luminous Galaxies A. Evans 2007
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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

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Models (w/o feedback) predict these dense gaseous
concentrations will leave sharp spikes in
luminosity profiles of remnants
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But light profiles of likely merger remnants show
no discrete feature identifying central burst
population
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Light profiles of likely merger remnants show no
discrete feature identifying central burst
population
HST F702W of four EA Wang et al. 2004, ApJ, 607,
258
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Light profiles of likely merger remnants
luminosity enhancements are modest
Ground-based K-band of Fine structure
ellipticals Rothberg Joseph, 2004 AJ, 128, 2098
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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 AA, 285, 775
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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
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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

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Suggest some process removes cold gas - at least
from more massive systems
From HI Rouges Gallery (www.nrao.edu/astrores/HIro
gue) Peculiar Early Types with HI outside
Optical Body, arranged by decreasing HI content
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Lower-luminosity systems may retain cold
material, reforming gas disks
From HI Rouges Gallery (www.nrao.edu/astrores/HIro
gue) Peculiar Early Types with HI inside Optical
Body, arranged by increasingly regular HI
kinematics
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Examples of low-z quenching?

• Springel, Di Matteo Hernquist 2003
• (also Li et al. 2006 Hopkins et al. 2005, 2006)

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Q2 Are interactions any more important at higher
redshift?

• Should be for hierarchical cosmologies
• Recent work suggest this is not the case

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Recent claims No evolution in merger fraction
from z0.2-1
Late Types
Late Types
Early types
Early types
Major Mergers
Classfication by Gini-M20 indices

• Fraction of total population

Extended Groth Strip Lotz et al. 2008, ApJ, 672,
177 (See also Bell et al. 2005, Wolf et al. 2005,
Bundy et al. 2005)
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Evolution of star formation density since z1
driven by SF in normal Hubble Types
Late Types
Peculiars
Early types
Classfication by eye
Classfication by A-C indices
Contribution to SFR density
HUDF parallel fields Menanteau et al. 2006, AJ,
131, 208
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At z1, SF dominated by normal Hubble Types
Spirals Peculiar Compact Early-type undetected
A class of galaxy not known locally (e.g. Ishida
2002 PhD Thesis) Normal Hubble type with SFRgt50
Mo/year
Spitzer 24um HST of GOODS-N Melbourne, Koo
Le Floch 2005, ApJ, 632, L65
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Are interactions important at zlt1.5?

• 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
  z1.5. SFR100-150 Mo/yr, but Mgas1E11 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
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ButCan we trust classifications at higher
redshift?
Wang et al. 2004, ApJ, 607, 258 Also - Hibbard
Vacca 1997
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Automated classifiers only sensitive to most
extreme morphologies
MR
MR
mM
pMpre-merger
mMminor merger
pM
pM
mM
M
M
Mmajor merger
MRmerger remnant
M
Pre-Mergers (pM), minor Mergers (mM) Merger
Remnants (MR) occupy same morphological parameter
space as normal Hubble Types. Only major mergers
(M) stand out
M
pM
MR
pM
mM
mM
MR
Taylor, 2005 PhD Thesis ASU See also Conselice
2006
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Normal Hubble Types?
M81/M82/NGC3077 VLA 12-pointing mosaic Yun et al.
1994
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HI Tidal Debris
VLA HI Mundell 2000
WSRT HI Swaters et al. 2002
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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
• z0-1 ALMA will image SFR, gas kinematics
  morphology on sub-arcsec scales. Disks or
  multi-component?

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HUDF-S
5x5
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What to do before SKA?

• Data volumes to be delivered by next-generation
  radio/mm instruments (EVLA, ALMA) are gtgt100x
  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?)

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