A Study of Massive and Evolved Galaxies at High Redshift

October 2014 • 2014ApJ...794...68N

Authors • Nayyeri, H. • Mobasher, B. • Hemmati, S. • De Barros, S. • Ferguson, H. C. • Wiklind, T. • Dahlen, T. • Dickinson, M. • Giavalisco, M. • Fontana, A. • Ashby, M. • Barro, G. • Guo, Y. • Hathi, N. P. • Kassin, S. • Koekemoer, A. • Willner, S. • Dunlop, J. S. • Paris, D. • Targett, T. A.

Abstract • We use data taken as part of Hubble Space Telescope (HST)/Wide Field Camera 3 (WFC3) observations of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) to identify massive and evolved galaxies at 3 < z < 4.5. This is performed using the strength of the Balmer break feature at rest-frame 3648 Å, which is a diagnostic of the age of the stellar population in galaxies. Using the WFC3 H-band-selected catalog for the CANDELS GOODS-S field and deep multi-waveband photometry from optical (HST) to mid-infrared (Spitzer) wavelengths, we identify a population of old and evolved post-starburst galaxies based on the strength of their Balmer breaks (Balmer break galaxies, BBGs). The galaxies are also selected to be bright in rest-frame near-IR wavelengths and hence massive. We identify a total of 16 BBGs. Fitting the spectral energy distribution of the BBGs shows that the candidate galaxies have average estimated ages of ~800 Myr and average stellar masses of ~5 × 10¹⁰ M _⊙, consistent with being old and massive systems. Two of our BBG candidates are also identified by the criteria that are sensitive to star-forming galaxies (Lyman break galaxy selection). We find a number density of ~3.2 × 10^-5 Mpc^-3 for the BBGs, corresponding to a mass density of ~2.0 × 10⁶ M _⊙ Mpc^-3 in the redshift range covering the survey. Given the old age and the passive evolution, it is argued that some of these objects formed the bulk of their mass only a few hundred million years after the big bang.

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Shoubaneh Hemmati

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