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Quiescent Disks in Early Universe: Formation, Growth, and Evolution

Explore the formation, growth, and evolution of quiescent disk galaxies in the early universe, challenging traditional notions of spheroidal dominance in quenching star formation. Investigate the correlation between Sersic index and quenched fraction, with implications for merger scenarios and disk instabilities.

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Quiescent Disks in Early Universe: Formation, Growth, and Evolution

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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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