A spatially resolved map of the kinematics, star formation and stellar mass assembly in a star-forming galaxy at z = 4.9

A. M. Swinbank, T. M. Webb, J. Richard, R. G. Bower, R. S. Ellis, G. Illingworth, T. Jones, M. Kriek, I. Smail, D. P. Stark, P. Van Dokkum

Research output: Contribution to journalArticlepeer-review

81 Scopus citations


We present a detailed study of the spatially resolved kinematics, star formation and stellar mass in a highly amplified galaxy at z = 4.92 behind the lensing cluster MS 1358+62. We use the observed optical, near- and mid-infrared imaging from Hubble Space Telescope ACS & NICMOS and Spitzer IRAC to derive the stellar mass and the Gemini/NIFS IFU to investigate the velocity structure of the galaxy from the nebular [O ii]λλ3726.8,3728.9 emission. Using a detailed gravitational lens model, we account for lensing amplification factor 12.5 ± 2.0 and find that this intrinsically L* galaxy has a stellar mass of M* = 7 ± 2 × 108 M , a dynamical mass of Mdyn = 3 ± 1 × 109csc2(i) M (within of 2 kpc) and a star formation rate of 42 ± 8 M yr-1. The source-plane UV/optical morphology of this galaxy is dominated by five discrete star-forming regions. Exploiting the dynamical information we derive masses for individual star-forming regions of Mcl ∼ 108-9 M with sizes of ∼200 pc. We find that, at a fixed size, the star formation rate density within these H ii regions is approximately two orders of magnitude greater than those observed in local spiral/starburst galaxies, but consistent with the most massive H ii regions in the local Universe such as 30 Doradus. Finally, we compare the spatially resolved nebular emission-line velocity with the Lyα and UV interstellar medium (ISM) lines and find that this galaxy is surrounded by a galactic scale outflow in which the Lyα appears redshifted by ∼150 km s-1 and the UV-ISM lines blueshifted by ∼ -200 km s-1 from the (systemic) nebular emission. The velocity structure of the outflow mirrors that of the nebular emission suggesting the outflow is young (≲15 Myr), and has yet to burst out of the system. Taken together, these results suggest that this young galaxy is undergoing its first major epoch of mass assembly.

Original languageEnglish (US)
Pages (from-to)1121-1131
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Dec 2009


  • Galaxies: evolution
  • Galaxies: formation
  • Galaxies: high-redshift
  • Galaxies: individual: MS 1358+62arc

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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