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arXiv · 1404.0316

Measuring the Stellar Masses of z~7 Galaxies with Spitzer Ultrafaint Survey Program (SURFS UP)

R. E. Ryan Jr.·A. H. Gonzalez B. C. Lemaux·M. Bradac·S. Casertano·S. Allen·B. Cain·M. Gladders·N. Hall·H. Hildebradt·J. Hinz·K. -H. Huang·L. Lubin·T. Schrabback·M. Stiavelli·T. Treu·A. von der Linden·D. Zaritsky
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Abstract

We present Spitzer/IRAC observations of nine $z'$-band dropouts highly magnified (2 3sigma) in both IRAC bands the brightest of these high-redshift galaxies, with [3.6]=23.80+-0.28 mag, [4.5]=23.78+-0.25 mag, and (H-[3.6])=1.17+-0.32 mag. The remaining eight galaxies are undetected to [3.6]~26.4 mag and [4.5]~26.0 mag with stellar masses of ~5x10^7 M_sol. The detected galaxy has an estimated magnification of mu=12+-4, which implies this galaxy has an ultraviolet luminosity of L_1500~0.3 L*_{z=7} --- the lowest luminosity individual source detected in IRAC at z>7. By modeling the broadband photometry, we estimate the galaxy has an intrinsic star-formation rate of SFR~1.3 M_sol/yr and stellar mass of M~2x10^9 M_sol, which gives a specific star-formation rate of sSFR~0.7 Gyr^-1. If this galaxy had sustained this star-formation rate since z~20, it could have formed the observed stellar mass (to within a factor of ~2), we also discuss alternate star-formation histories and argue the exponentially-increasing model is unlikely. Finally, based on the intrinsic star-formation rate, we estimate this galaxy has a likely [C II] flux of = 10^{-17} erg/s/cm2.

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R. E. Ryan Jr., A. H. Gonzalez B. C. Lemaux, M. Bradac, S. Casertano, S. Allen, B. Cain, M. Gladders, N. Hall, H. Hildebradt, J. Hinz, K. -H. Huang, L. Lubin, T. Schrabback, M. Stiavelli, T. Treu, A. von der Linden, D. Zaritsky. 2014-04-01. Measuring the Stellar Masses of z~7 Galaxies with Spitzer Ultrafaint Survey Program (SURFS UP). https://doi.org/10.1088/2041-8205%2F786%2F1%2Fl4

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