THE DEPENDENCE OF QUENCHING UPON THE INNER STRUCTURE OF GALAXIES AT 0.5 {<=} z < 0.8 IN THE DEEP2/AEGIS SURVEY
- Department of Astronomy and Astrophysics, 1156 High Street, University of California, Santa Cruz, CA 95064 (United States)
- Department of Physics and Astronomy, Elliot Building, 3800 Finnerty Road, University of Victoria, Victoria, BC V8P 5C2 (Canada)
- Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC V9E 2E7 (Canada)
- Harvard-Smithsonian Center for Astrophysics, 60 Garden State, Cambridge, MA 02138 (United States)
- Department of Astronomy, University of Michigan, 500 Church St., Ann Arbor, MI 48109 (United States)
- Racah Institute of Physics, Hebrew University, Jerusalem 91904 (Israel)
- National Optical Astronomical Observatories, 950 N. Cherry Avenue, Tucson, AZ 85719 (United States)
- Kavli Institute for the Physics and Mathematics of the Universe, University of Tokyo, Kashiwa 277-8582 (Japan)
- Department of Physics, Center for Astrophysics and Space Sciences, University of California at San Diego, 9500 Gilman Dr., La Jolla, San Diego, CA 92093 (United States)
- Center for Galaxy Evolution, Department of Physics and Astronomy, University of California, Irvine, 4129 Frederick Reines Hall, Irvine, CA 92697 (United States)
- School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD (United Kingdom)
- Department of Astronomy, University of California, Berkeley, CA 94720 (United States)
- Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
The shutdown of star formation in galaxies is generally termed 'quenching'. Quenching may occur through a variety of processes, e.g., active galactic nucleus (AGN) feedback, stellar feedback, or the shock heating of gas in the dark matter halo. However, which mechanism(s) is, in fact, responsible for quenching is still in question. This paper addresses quenching by searching for traces of possible quenching processes through their effects on galaxy structural parameters such as stellar mass (M {sub *}), M {sub *}/r {sub e}, surface stellar mass density ({approx}M {sub *}/r {sup 2} {sub e}), and Sersic index (n). We analyze the rest-frame U - B color correlations versus these structural parameters using a sample of galaxies in the redshift range 0.5 {<=} z < 0.8 from the DEEP2/AEGIS survey. In addition to global radii, stellar masses, and Sersic parameters, we also use 'bulge' and 'disk' photometric measurements from GIM2D fits to HST/ACS V and I images. We assess the tightness of the color relationships by measuring their 'overlap regions', defined as the area in color-parameter space in which red and blue galaxies overlap; the parameter that minimizes these overlap regions is considered to be the most effective color discriminator. We find that Sersic index (n) has the smallest overlap region among all tested parameters and resembles a step function with a threshold value of n = 2.3. There exists, however, a significant population of outliers with blue colors yet high n values that seem to contradict this behavior; they make up Almost-Equal-To 40% of n > 2.3 galaxies. We hypothesize that their Sersic values may be distorted by bursts of star formation, AGNs, and/or poor fits, leading us to consider central surface stellar mass density, {Sigma}*{sub 1kpc}, as an alternative to Sersic index. Not only does {Sigma}*{sub 1kpc} correct the outliers, but it also forms a tight relationship with color, suggesting that the innermost structure of galaxies is most physically linked with quenching. Furthermore, at z {approx} 0.65, the majority of the blue cloud galaxies cannot simply fade onto the red sequence since their GIM2D bulge masses are only half as large on average as the bulge masses of similar red sequence galaxies, thus demonstrating that stellar mass must absolutely increase at the centers of galaxies as they quench. We discuss a two-stage model for quenching in which galaxy star formation rates are controlled by their dark halos while they are still in the blue cloud and a second quenching process sets in later, associated with the central stellar mass buildup. The mass buildup is naturally explained by any non-axisymmetric features in the potential, such as those induced by mergers and/or disk instabilities. However, the identity of the second quenching agent is still unknown. We have placed our data catalog online.
- OSTI ID:
- 22086211
- Journal Information:
- Astrophysical Journal, Vol. 760, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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