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