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Quiescent Disks in the Early Universe

Quiescent Disks in the Early Universe. Elizabeth J. McGrath, Aurora Y. Kesseli , Arjen van der Wel , Eric Bell, Guillermo Barro and the CANDELS Collaboration. Formation of the Red Sequence. Red sequence in place at z~2 Growth in quiescent population (red symbols) is dramatic since z~2

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Quiescent Disks in the Early Universe

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  1. Quiescent Disks in the Early Universe Elizabeth J. McGrath, Aurora Y. Kesseli, Arjen van der Wel, Eric Bell, Guillermo Barroand the CANDELS Collaboration

  2. Formation of the Red Sequence • 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) Bell et al. (2012)

  3. Search for a Quenching Parameter 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

  4. Quiescent Disks • Previous studies have found strong evidence for massive, quiescent disks, even without large central bulges (including spectroscopic confirmation of their quiescence): ACS NIC2 Model Residuals n=1.49 z=1.412 McGrath et al. (2007, 2008)

  5. 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. v z H Y J z = 1.6 WFC3 ACS

  6. Detailed Morphology Studies • Real galaxies aren’t as simple as pure disks or pure ellipticals. • By convention, Sersicn<2.5 = disk-like n>2.5 = spheroidal • With good data we can decompose an image of a galaxy into its subcomponents

  7. Point Spread Function • “Hybrid” PSF • Stacked stars within 2.5” • Central and outermost pixels replaced with TinyTim model • Drizzled in same manner as data Available at candels.ucolick.org or by email: emcgrath@colby.edu

  8. UVJ selection of quiescent galaxies at z > 1 a la Labbé et al. (2005); Wuyts et al. (2007); Williams et al. (2009) GOODS-S from CANDELS

  9. Quiescent Disks • Closer inspection of “high-Sersic”, massive, quiescent galaxies has revealed a number of disk-dominated galaxies. z = 0.90 n = 2.6 z = 1.29 n = 4.0 z = 1.61 n = 2.6 z = 1.68 n = 2.4 z = 1.69 n = 1.9 B/T = 0.25 B/T = 0.25 B/T = 0.33 B/T = 0.30 B/T = 0.19

  10. How common are these quiescent disks? • Results from Bruce et al. (2014) in the UDS + COSMOS: • 1<z<3, M*>1011Msun 29% of all quiescent galaxies have B/T < 0.5. Bruce et al. (2014)

  11. How common are Quiescent Disks? Time (Gyr) • Expanding the sample with CANDELS/ GOODS-S: • Defined to be disks if B/T < 0.5 • Redshift bins spaced equally in time. 10 5 4 3 Quiescent galaxies with M > 1010 Mo 30% are disk-dominated at z~2 EJM, Kesseli, et al., in prep.

  12. 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)

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