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Galaxy Evolution: What Do We Need To Know?

Galaxy Evolution: What Do We Need To Know?. Eric M. Wilcots University of Wisconsin-Madison. A Few Questions. 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?.

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Galaxy Evolution: What Do We Need To Know?

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  1. Galaxy Evolution:What Do We Need To Know? Eric M. Wilcots University of Wisconsin-Madison

  2. A Few Questions • 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?

  3. The Evolution of the HI Content of Galaxies • 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…

  4. 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?

  5. Evolution of Galaxies in Clusters • Strength of red sequence in clusters decreases from z~0.4 to z~0.9 • Cluster luminosity function evolves (Gilbank et al 2008)

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

  7. 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.

  8. Evolution in density of damped Ly-alpha systems Rao et al. 2006 ApJ 636 610

  9. What We Need To Know…. • …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)

  10. ASKAP, 700-1800 MHz, with strawman 30 12m dishes with PAF, upgrade/expansion to 45. 5-sigma detections for all southern-hemisphere, “shallow” (1 yr) survey strawman, expansion FOV 30 deg2 – depends on success of PAF technology - N=600,000 Z=0.05 Johnston et al. 2007

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

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

  13. 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….

  14. NGC 891 – HI Halo (Oosterloo et al) Lowest contour ~ 5 x1018 cm-2

  15. Where’s the Halo??? NGC 5746 – Rand & Benjamin 2008

  16. Let’s Not Forget the Low Surface Brightness Universe • 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

  17. What We Need To Know…. • …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

  18. What is the impact of environment on the HI content of galaxies? • 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

  19. Tails 2

  20. 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

  21. 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

  22. Comparison with X-ray emission HI detections All members X-ray emission

  23. What We Need To Know…. • …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.

  24. Just how does a galaxy make stars? • This is mostly ALMA science since stars form out of molecular gas…. • but a little high resolution HI data might help…

  25. What We Need To Know…. • …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…

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