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

Journal
Date Issued
2015
Author(s)
Hodge, J. A.
•
Riechers, D.
•
•
Walter, F.
•
Carilli, C. L.
•
Daddi, E.
•
Dannerbauer, H.
DOI
Description
We thank John Hibbard, Mark Krumholz, Adam Leroy, Kartik Sheth, and an anonymous referee for helpful comments/discussions, and Roberto Neri, Sabine König, and Melanie Krips for help with data analysis. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Support for R.D. was provided by the DFG priority program 1573 “The physics of the interstellar medium.”
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 ΣSFR ~ Σ _H_2^2.1+/- 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.

Volume
798
Issue
1
Start page
L18
Uri
Url
Issn Identifier
2041-8205
Ads BibCode
2015ApJ...798L..18H
Rights
open.access
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