A SUBSTANTIAL POPULATION OF MASSIVE QUIESCENT GALAXIES AT z similar to 4 FROM ZFOURGE

作者：Straatman Caroline M S^*; Labbe Ivo; Spitler Lee R; Allen Rebecca; Altieri Bruno; Brammer Gabriel B; Dickinson Mark; van Dokkum Pieter; Inami Hanae; Glazebrook Karl; Kacprzak Glenn G; Kawinwanichakij Lalit; Kelson Daniel D; McCarthy Patrick J; Mehrtens Nicola; Monson Andy; Murphy David; Papovich Casey; Persson S Eric; Quadri Ryan; Rees Glen; Tomczak Adam; Tran Kim Vy H; Tilvi Vithal

来源：Astrophysical Journal Letters, 2014, 783(1): L14.

DOI：10.1088/2041-8205/783/1/L14

• cosmology: observations
• galaxies: evolution
• galaxies: formation
• galaxies: high-redshift
• infrared: galaxies

We report the likely identification of a substantial population of massive M similar to 10(11) M-circle dot galaxies at z similar to 4 with suppressed star formation rates (SFRs), selected on rest-frame optical to near-IR colors from the FourStar Galaxy Evolution Survey (ZFOURGE). The observed spectral energy distributions show pronounced breaks, sampled by a set of near-IR medium-bandwidth filters, resulting in tightly constrained photometric redshifts. Fitting stellar population models suggests large Balmer/4000 angstrom breaks, relatively old stellar populations, large stellar masses, and low SFRs, with a median specific SFR of 2.9 +/- 1.8 x 10(-11) yr(-1). Ultradeep Herschel/PACS 100 mu m, 160 mu m and Spitzer/MIPS 24 mu m data reveal no dust-obscured SFR activity for 15/19(79%) galaxies. Two far-IR detected galaxies are obscured QSOs. Stacking the far-IR undetected galaxies yields no detection, consistent with the spectral energy distribution fit, indicating independently that the average specific SFR is at least 10x smaller than that of typical star-forming galaxies at z similar to 4. Assuming all far-IR undetected galaxies are indeed quiescent, the volume density is 1.8 +/- 0.7 x 10(-5) Mpc(-3) to a limit of log(10) M/M-circle dot %26gt;= 10.6, which is 10x and 80x lower than at z = 2 and z = 0.1. They comprise a remarkably high fraction (similar to 35%) of z similar to 4 massive galaxies, suggesting that suppression of star formation was efficient even at very high redshift. Given the average stellar age of 0.8 Gyr and stellar mass of 0.8x10(11) M-circle dot, the galaxies likely started forming stars before z = 5, with SFRs well in excess of 100 M-circle dot yr(-1), far exceeding that of similarly abundant UV-bright galaxies at z %26gt;= 4. This suggests that most of the star formation in the progenitors of quiescent z similar to 4 galaxies was obscured by dust.

• 出版日期2014-3-1