An ALMA view of the interstellar medium of the z = 4.77 lensed starburst SPT-S J213242-5802.9

¹ European Southern Observatory, Karl Schwarzschild Straße 2, 85748 Garching, Germany
e-mail: mbetherm@eso.org
² Núcleo de Astronomía, Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
³ Cavendish Laboratory, University of Cambridge, JJ Thompson Ave, Cambridge CB3 0HA, UK
⁴ Dalhousie University, Halifax, Nova Scotia, Canada
⁵ Department of Astronomy, University of Florida, Gainesville, FL 32611, USA
⁶ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁷ Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547, USA
⁸ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁹ Infrared Processing and Analysis Center, California Institute of Technology, MC 220-6, Pasadena, CA 91125, USA
¹⁰ Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
¹¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
¹² Department of Astronomy and Department of Physics, University of Illinois, 1002 West Green Street, Urbana, IL 61801, USA
¹³ Department of Physiscs, Oxford University, Denis Wilkinson Building, Keble Road, Oxford, OX1 3RH, UK

Received: 13 November 2015
Accepted: 6 January 2016

Abstract

We present ALMA detections of the [NII] 205 μm and CO(12−11) emission lines, and the tentative detection of [CI] ³P₁–³P₀ for the strongly lensed (μ = 5.7 ± 0.5) dusty, star-forming galaxy SPT-S J213242-5802.9 (hereafter SPT2132-58) at z = 4.77. The [NII] and CO(12−11) lines are detected at 11.5 and 8.5σ levels, respectively, by our band 6 observations. The [CI] line is detected at 3.2σ after a reanalysis of existing band 3 data. The [CI] luminosity implies a gas mass of (3.8 ± 1.2) × 10¹⁰M_⊙, and, consequently, a very short depletion timescale of 34 ± 13 Myr and a CO luminosity to gas mass conversion factor α_CO of 1.0 ± 0.3 M_⊙ (K km s^-1 pc²)^-1. SPT2132-58 is an extreme starburst with an intrinsic star formation rate of 1100 ± 200 M_⊙/yr. We find a [CII]/[NII] ratio of 26 ± 6, which is the highest ratio reported at z > 4. This suggests that SPT2132-58 hosts an evolved interstellar medium (0.5 Z_⊙< Z < 1.5 Z_⊙), which may be dominated by photodissociation regions. The CO(2−1) and CO(5−4) transitions have lower CO to far-infrared ratios than local and high-redshift samples, while CO(12−11) is similar to these samples, suggesting the presence of an additional very excited component or an active galactic nucleus.