1. Galaxy Evolution At The Faint End Of The Luminosity Function Charles Liu and many COSMOS Team members City University of New York, College of Staten Island American Museum of Natural History, NY COSMOS Team Meeting, 7-10 June 2010

2. THE TAKEAWAY The ratio of very low-luminosity galaxies to higher-luminosity galaxies appears to have increased steadily from z=0.5 to the present. Why is this so? How long ago did this trend start? What does this tell us about galaxy formation and evolution?

5. Schechter Functions Number of galaxies per unit volume per unit luminosity Number of galaxies per unit volume per unit magnitude

6. SDSS

7. COMBO-17 (Wolf et al. 2003) Galaxy Luminosity Functions - the observational basis for GSMFs

8. M*,  * well studied; how about  ?

9. WHAT WE DID Using a sample of 80,820 COSMOS galaxies, we have derived detailed faint-end field galaxy luminosity functions (LFs), -18 > M(V) > -13, from 0 < z < 0.5 Our results are consistent with “every” LF from every other large survey (SDSS, 2dF, Combo-17, DEEP, VVDS, SRSS2, LCRS, etc.) - and paint a self- consistent picture of faint-end slope evolution that only COSMOS could do.

11. Examples of some faint z<0.5 galaxies in COSMOS

13. Luminosity Functions with Photometric Redshifts

14. Substantial Monte Carlo simulations are used to understand the systematic effects of using photometric redshifts on galaxy LF calculations. (Note: this – and possibly even more complex study – should be done on all high-z LF studies as well!)

18. The Result: Close focus on the faint-end slope of the luminosity function (not possible at z>1 yet)

21. Key Result: All galaxy spectral types (and thus the full galaxy population) have steepening faint end LF slopes from z=0.5 to the present.

22. Our results show significant steepening of the LF faint end (i.e.  ) in all galaxy spectral types from z=0.5 to the present day. Are large numbers of faint field galaxies being missed as redshift increases to 0.5? Or are we seeing clear evidence of evolution in the faint field galaxy population – something akin to “downsizing” at low redshift? Very interesting either way! Lots more work to do!

24. Galaxy Evolution At The Faint End Of The Luminosity Function Charles Liu and many COSMOS Team members City University of New York, College of Staten Island American Museum of Natural History, NY COSMOS Team Meeting, 7-10 June 2010

25. THE TAKEAWAY The ratio of very low-luminosity galaxies to higher-luminosity galaxies appears to have increased steadily from z=0.5 to the present. Why is this so? How long ago did this trend start? What does this tell us about galaxy formation and evolution?