Post on 24-Feb-2016
description
Elizabeth J. McGrath, Aurora Y. Kesseli,
Arjen van der Wel, Eric Bell, Guillermo Barro and the CANDELS Collaboration
QUIESCENT DISKS IN THE EARLY UNIVERSE
• Red sequence in place at z~2
• Growth in quiescent population (red symbols) is dramatic since z~2
• Galaxies evolve from mostly low Sersic index (open symbols) to higher Sersic (filled symbols)
FORMATION OF THE RED SEQUENCE
Bell et al. (2012)
• Strongest correlation is between Sersic index and quenched fraction for all redshift ranges.
• High Sersic = bulge dominated (?)• Consistent with merger formation scenario
SEARCH FOR A QUENCHING PARAMETER
Bell et al. (2012)
• Previous studies have found strong evidence for massive, quiescent disks, even without large central bulges (including spectroscopic confirmation of their quiescence):
QUIESCENT DISKS
McGrath et al. (2007, 2008)
n=1.49
z=1.412
ACS NIC2 Model Residuals
CANDELS
• Large area near-IR WFC3 survey.
• Particularly well-suited to the study of quenched or “passive” galaxies at z~2 that are essentially invisible at shorter, rest-frame UV wavelengths.
ACS WFC3
z = 1.6 v z Y J H
DETAILED MORPHOLOGY STUDIES
• Real galaxies aren’t as simple as pure disks or pure ellipticals.
• By convention, Sersic n<2.5 = disk-like n>2.5 = spheroidal
• With good data we can decompose an image of a galaxy into its subcomponents
POINT SPREAD FUNCTION
• “Hybrid” PSF• Stacked stars
within 2.5”• Central and
outermost pixels replaced with TinyTim model
• Drizzled in same manner as dataAvailable at
candels.ucolick.org
or by email: emcgrath@colby.edu
UVJ SELECTION OF QUIESCENT GALAXIES AT Z > 1
a la Labbé et al. (2005); Wuyts et al. (2007); Williams et al. (2009)
GOODS-S fromCANDELS
QUIESCENT DISKS
z = 1.29n = 4.0
z = 1.68n = 2.4
z = 1.69n = 1.9
z = 1.61n = 2.6
z = 0.90n = 2.6
• Closer inspection of “high-Sersic”, massive, quiescent galaxies has revealed a number of disk-dominated galaxies.
B/T = 0.30 B/T = 0.25 B/T = 0.25 B/T = 0.33 B/T = 0.19
• Results from Bruce et al. (2014) in the UDS + COSMOS:• 1<z<3, M*>1011 Msun
HOW COMMON ARE THESE QUIESCENT DISKS?
Bruce et al. (2014)
29% of all quiescent galaxies have B/T < 0.5.
• Expanding the sample with CANDELS/ GOODS-S:• Defined to be
disks if B/T < 0.5
• Redshift bins spaced equally in time.
HOW COMMON ARE QUIESCENT DISKS?
30% are disk-dominated at z~2
Quiescent galaxies
with M > 1010 Mo
EJM, Kesseli, et al., in prep.
10 5 4 3
Time (Gyr)
SUMMARY
• A significant fraction of quenched galaxies at high-z appear to be disk dominated.
• Spheroid formation may not be the trigger that quenches star-formation, but just an end result.
• (In)consistent with merger paradigm? • Compare number density of quiescent disks to
predictions from SAMs (e.g., Somerville et al. mock galaxy catalogs with B/T ratios).
• In-situ vs. ex-situ processes for star-formation quenching? • disk instabilities
• environment (e.g., halo quenching)