The Kiloparsec-scale Star Formation Law at Redshift 4: Widespread, Highly Efficient Star Formation in the Dust-obscured Starburst Galaxy GN20

Author(s)

Jacqueline A. Hodge, Dominik A. Riechers, Roberto Decarli, Fabian Walter, Chris Carilli, Emanuele Daddi, Helmut Dannerbauer

Abstract

We present high-resolution observations of the 880 μm (rest-frame FIR) continuum emission in the z = 4.05 submillimeter galaxy GN20 from the IRAM Plateau de Bure Interferometer (PdBI). These data resolve the obscured star formation (SF) in this unlensed galaxy on scales of 0.''3 × 0.''2 (~2.1 × 1.3 kpc). The observations reveal a bright (16 ± 1 mJy) dusty starburst centered on the cold molecular gas reservoir and showing a bar-like extension along the major axis. The striking anti-correlation with the Hubble Space Telescope/Wide Field Camera 3 imaging suggests that the copious dust surrounding the starburst heavily obscures the rest-frame UV/optical emission. A comparison with 1.2 mm PdBI continuum data reveals no evidence for variations in the dust properties across the source within the uncertainties, consistent with extended SF, and the peak star formation rate surface density (119 ± 8 M_⊙ yr^-1 kpc^-2) implies that the SF in GN20 remains sub-Eddington on scales down to 3 kpc². We find that the SF efficiency (SFE) is highest in the central regions of GN20, leading to a resolved SF law with a power-law slope of Σ_SFR ~ Σ _H2 ^{2.1+/- 1.0}, and that GN20 lies above the sequence of normal star-forming disks, implying that the dispersion in the SF law is not due solely to morphology or choice of conversion factor. These data extend previous evidence for a fixed SFE per free-fall time to include the star-forming medium on ~kiloparsec scales in a galaxy 12 Gyr ago.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Organisation(s)

Department of Astrophysics

External organisation(s)

National Radio Astronomy Observatory, Charlottesville, Max-Planck-Institut für Astronomie, Cornell University, National Radio Astronomy Observatory Socorro, Université Paris VII - Paris-Diderot

Journal

The Astrophysical journal Letters

Volume

798

No. of pages

6

ISSN

2041-8205

DOI

https://doi.org/10.1088/2041-8205/798/1/L18

Publication date

01-2015

Peer reviewed

Yes

Austrian Fields of Science 2012

103003 Astronomy, 103004 Astrophysics

Keywords

ASJC Scopus subject areas

Astronomy and Astrophysics, Space and Planetary Science

Portal url

https://ucrisportal.univie.ac.at/en/publications/d64832b5-7d06-4973-93bc-41ba4750b4c6