Mathematics – Logic
Scientific paper
Jan 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011aas...21733522w&link_type=abstract
American Astronomical Society, AAS Meeting #217, #335.22; Bulletin of the American Astronomical Society, Vol. 43, 2011
Mathematics
Logic
Scientific paper
The assembly modes via which galaxies develop their present-day mass and structure remain hotly debated. We explore this issue using one of the largest samples of massive galaxies (166 with stellar mass Mstar ≥ 5 × 1010 M&sun;) at z=1-3 with NICMOS F160W observations from the GOODS NICMOS Survey (GNS), along with complementary ACS, Spitzer, and Chandra data. Our findings are:
(1) The majority of the massive galaxies at z=2-3 have a disky structure (as characterized by the index of single-component Sersic profiles). Most are also compact with half-light radii less than 2 kpc. These massive galaxies at z=2-3 appear to be radically different in structure from their more massive descendants at z 0. Through artificial redshfiting experiments based on redshifted simulated NICMOS data of such massive z 0 elliptical, S0, and spiral galaxies, we show that most of this difference in structure is not due to cosmological or instrumental effects. This implies that significant structural evolution is needed to convert the massive z=2-3 systems into their z 0 elliptical and
S0 descendants, and places important constraints on the associated evolutionary mechanisms (e.g., major mergers and cold accretion).
(2) Using IR luminosities inferred from Spitzer detections, we find that over z=1-3, the mean star formation rate (SFR) rises substantially, even if AGN candidates are excluded. SFRs of several hundred solar masses per year or higher are common. The results imply a much higher average cold gas fraction than exists in z 0 galaxies.
(3) We identify AGN candidates using a variety of techniques (X-ray properties, IR power-law, and IR-to-optical excess) and classify about one-third of the massive galaxies at z=1-3 as AGN hosts. The AGN fraction rises with redshift and is 40% at z=2-3. A significant fraction of the AGN candidates have disky structures although they host massive black holes.
GOODS-NICMOS Collaboration
Jogee Sharda
Weinzirl Tim
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