Galaxy Evolution:What Do We Need To

Know?Eric M. Wilcots

University of Wisconsin-Madison

How and when did galaxies accrete their gas?

Where and when did/do galaxies stop accreting gas?

How do galaxies lose their cool gas? How does star formation get started?

A Few Questions

Now have HI detections to z~0.2 (Verheijen, van Gorkom et al, Catinelli et al.)

This is fantastic, but there is lots of galaxy evolution beyond this…

The Evolution of the HI Content of Galaxies

Cosmic star formation history (Panter et al. 2007)

Want record of HI over redshift with large evolution in SFR – where, how, is gas going to stars?

• Strength of red sequence in clusters decreases from z~0.4 to z~0.9

• Cluster luminosity function evolves (Gilbank et al 2008)

Evolution of Galaxies in Clusters

Galaxy luminosity functions from Red Sequence Cluster Survey (Gilbank et al 2008)

Neutral gas density in Universe (from Lah et al. 2007). z=0 triangle is from HIPASS, large triangle is new GMRT measurement. High redshift points come from damped Ly-a measurements. Note large uncertainty in redshift range z = 0.1 – 1.5, corresponding to 2/3 age of Universe.

Rao et al. 2006 ApJ 636 610

Evolution in density of damped Ly-alpha systems

…the evolution of the HI content of galaxies to z~2…◦ Deep (~10ks) EVLA surveys of the HI content of

galaxies to z~0.5; push beyond z~0.5 (GMRT, ASKAP, MeerKAT)

What We Need To Know….

ASKAP, 700-1800 MHz, with strawman 30 12m dishes with PAF, upgrade/expansion to 45.

5-sigma detectionsfor all southern-hemisphere, “shallow” (1 yr) surveystrawman, expansion FOV 30 deg2 – depends on success of PAF technology - N=600,000

Z=0.05Johnston et al. 2007

ASKAP (cont.)Similar simulationfor a deep (1 yr)single pointing,N= 100,000

Z=0.2Johnston et al. 2007

• satellite accretion– 108 M worth of gas in Local Group for MWG

accretion – Accretion of gas-rich companions rare in the

nearby Universe – (e.g. Pisano & Wilcots 2003)

How Do Galaxies Get Their Gas?

• satellite accretion– 108 M worth of gas in Local Group for MWG

accretion – Accretion of gas-rich companions rare (e.g. Pisano

& Wilcots 2003)• Condensation of thermal instabilities in hot

halos – galactic “rain”?– NGC 891, head-tail clouds, etc– But….

How Do Galaxies Get Their Gas?

NGC 891 – HI Halo (Oosterloo et al)

Lowest contour ~ 5 x1018 cm-2

Where’s the Halo???

NGC 5746 – Rand & Benjamin 2008

• Halo Gas• Extended HI around galaxies

– Minchin et al (2003) – 4.2 x 1018 cm-2 in Centaurus– Westmeier, Braun, Thilker (2005) – 9 x 1017 cm-2

around M31• Ionization edges of galaxies – what is the true

extent of the HI disk?– N(HI) = 1.6 x 1017 cm-2 –optical depth at the Lyman

edge ~ 1 (Corbelli, Salpeter, & Bandiera 2001)• Goal: connect HI in emission around galaxies

to Lyman Limit Systems

Let’s Not Forget the Low Surface Brightness Universe

…the evolution of the HI content of galaxies from z~1 to z=0….

…the complete census of HI clouds/emission in the halos of nearby galaxies arising from the condensation of hot gas…◦ This requires surface brightness sensitivity (i.e.

high filling factor arrays) plus resolution

What We Need To Know….

Radio continuum sources more numerous in the outskirts of Red Sequence Clusters (Gladders)

Galaxy groups more active in the outskirts of clusters (Carlberg et al. 2002)

Galaxy transformation vs environment HI mass function varies with environment Optical luminosity function varies with

environment

What is the impact of environment on the HI content of galaxies?

Tails 2

The lore.. if halos get too big, gas does not coolBut.. at least some dry mergers are wet, and forming stars

Donovan, Hibbard, an Gorkom, 2007, AJ 134, 1118

HI in Galaxy Groups (Freeland et al. 2008)

Interaction rate much higher in spiral-dominated groups.

Spiral dominated/HI rich elliptical dominated/X-ray rich

“Unattached” HI clouds (merger remnants) more common in elliptical dominated groups

Conversion of neutral gas into hot gas takes place with the intragroup medium and not in individual galaxies

Comparison with X-ray emission

HI detections

All members

X-ray emission

• …the evolution of the HI content of galaxies from z~2 to z=0….

• …the complete census of HI clouds/emission in the halos of nearby galaxies arising from the condensation of hot gas…

• …the environmental impact statement…– e.g. A THINGS in and around clusters– Infall regions is where the action is– the Red Cluster Sequence survey will have 500

clusters; we have complementary HI data for <20.

What We Need To Know….

This is mostly ALMA science since stars form out of molecular gas….

but a little high resolution HI data might help…

Just how does a galaxy make stars?

• …the evolution of the HI content of galaxies from z~2 to z=0….

• …the accretion of gas onto galaxies…• …the complete census of HI clouds/emission

in the halos of galaxies arising from the condensation of hot gas…

• …the environmental impact statement…• …fine scale structure of the ISM in star-

forming galaxies…

What We Need To Know….