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)