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?

 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…

Star formation directly seen in the rest-frame UV GALEX, Wyder et al GALEX, Schiminovich et al Wilson et al Bouwens et al Bunker et al Steidel et al Iwata et al Bouwens et al Wang, Cowie, & Barger 2006

Comparison of the FIR-determined star formation with the UV-determined star formation Directly measured FIR star formation Maximal corrections for missing EBL, if at z=1-3 Star formation rate density for a Salpeter IMF extending to 0.1 M(sun) x the cosmic time

 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?

Evolution of the FIR luminosity of the radio source population – downsizing? Barger, Cowie, Wang 2007

Strength of red sequence in clusters decreases from z~0.4 to z~0.9 Cluster luminosity function evolves (Gilbank et al 2008)

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-  measurements. Note large uncertainty in redshift range z = 0.1 – 1.5, corresponding to 2/3 age of Universe.

Rao et al ApJ 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)

 Current generation ALFA surveys will yield ~several x 10 4 galaxies to z~0.1, will characterize the local HI mass function very well. (Arecibo capable of going deeper, but confusion issues for high z, especially for blind surveys)

 ASKAP, MHz, with strawman 30 12m dishes with PAF, upgrade/expansion to sigma detections for all southern- hemisphere, “shallow” (1 yr) survey strawman, expansion FOV 30 deg 2 – depends on success of PAF technology - N=600,000 Z=0.05 Johnston et al. 2007

Similar simulation for a deep (1 yr) single pointing, N= 100,000 Z=0.2 Johnston et al. 2007

…the evolution of the HI content of galaxies to z~1… – Deep (3-10Ks) EVLA surveys of the HI content of galaxies to z~0.5; push beyond z~0.5 (GMRT, ASKAP, MeerKAT)

satellite accretion – 10 8 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)

satellite accretion – 10 8 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….

Lowest contour ~ 5 x10 18 cm -2

NGC 5746 – Rand & Benjamin 2008

Halo Gas Extended HI around galaxies – Minchin et al (2003) – 4.2 x cm -2 in Centaurus – Westmeier, Braun, Thilker (2005) – 9 x cm -2 around M31 Ionization edges of galaxies – what is the true extent of the HI disk? – N(HI) = 1.6 x cm -2 –optical depth at the Lyman edge ~ 1 (Corbelli, Salpeter, & Bandiera 2001) Goal: connect HI in emission around galaxies to Lyman Limit Systems

 …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

 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

The lore.. if halos get too big, gas does not cool But.. at least some dry mergers are wet, and forming stars Donovan, Hibbard, an Gorkom, 2007, AJ 134, 1118

Mulchaey & Zabludoff ~30% of the total HI is in the tidal material

 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

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.

 This is mostly ALMA science since stars form out of molecular gas….  but a little high resolution HI data might help…

…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…