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Published February 4, 2016 | Published + Submitted
Journal Article Open

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

Abstract

We present ALMA detections of the [NII] 205 μm and CO(12−11) emission lines, and the tentative detection of [CI] ^3P_1–^3P_0 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) × 10^(10)M_⊙, 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) pc^2)^(-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.

Additional Information

© 2016 ESO. Received: 13 November 2015. Accepted: 6 January 2016. Published online 04 February 2016. We thanks Roberto Decarli for his very useful suggestions, especially about the choices of axes for Fig. 4, and the anonymous referee for her/his very constructive comments. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2011.0.00957.S and ADS/JAO.ALMA#2012.1.00994.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The SPT is supported by the National Science Foundation through grant PLR- 1248097, with partial support through PHY-1125897, the Kavli Foundation and the Gordon and Betty Moore Foundation grant GBMF 947. J.D.V., K.C.L., D.P.M., and J.S.S. acknowledge support from the US National Science Foundation under grant No. AST-1312950.

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Submitted - 1601.01682v2.pdf

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