Measuring the stellar masses of z ∼ 7 galaxies with the spitzer ultrafaint survey program (Surfs up)

R. E. Ryan, R. E. Ryan, A. H. Gonzalez, B. C. Lemaux, M. Bradač, 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

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


We present Spitzer/IRAC observations of nine z′-band dropouts highly magnified (2 ≲ μ ≲ 12) by the Bullet Cluster. We combine archival imaging with our Exploratory program (SURFS UP), which results in a total integration time of ∼30 hr per Infrared Array Camera (IRAC) band. We detect (≳ 3σ) 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 ∼5 × 107 M·. The detected galaxy has an estimated magnification of μ = 12 ± 4, which implies this galaxy has an ultraviolet luminosity of-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 (SFR) of SFR ∼ 1.3 M· yr-1 and stellar mass of M ∼ 2.0 × 109 M·, which gives a specific star formation rate of sSFR ∼ 0.7 Gyr-1. If this galaxy had sustained this SFR 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 that the exponentially increasing model is unlikely. Finally, based on the intrinsic SFR, we estimate that this galaxy has a likely [C II] flux of 〈f [C II]〉 = 1.6 mJy.

Original languageEnglish (US)
Article numberL4
JournalAstrophysical Journal Letters
Issue number1
StatePublished - May 1 2014


  • galaxies: evolution
  • galaxies: formation
  • galaxies: high-redshift

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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