Volume 628, August 2019
|Number of page(s)||8|
|Published online||13 August 2019|
Neutral carbon and highly excited CO in a massive star-forming main sequence galaxy at z = 2.2⋆
Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército Libertador 441, Santiago, Chile
2 Service d’Astrophysique, CEA Saclay, France
3 Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
4 Universidad de La Laguna, Dpto. Astrofísica, 38205 La Laguna, Tenerife, Spain
5 INAF – Osservatorio di Astrofisica e Scienza dello Spazio, Via Gobetti 93/3, 40129 Bologna, Italy
6 Max-Planck-Institut für Astronomie, Königstuhl, 17, 69117 Heidelberg, Germany
7 Department of Astronomy, Cornell University, 220 Space Sciences Building, Ithaca, NY 14853, USA
8 SKA Organisation, Lower Withington Macclesfield, Cheshire SK11 9DL, UK
Accepted: 1 July 2019
We used the Plateau De Bure Interferometer to observe multiple CO and neutral carbon transitions in a z = 2.2 main sequence disk galaxy, BX610. Our observation of CO(7-6), CO(4-3), and both far-infrared (FIR) [CI] lines complements previous observations of Hα and low-J CO, and reveals a galaxy that is vigorously forming stars with UV fields (Log(GG0−1) ≲ 3.25); although less vigorously than local ultra-luminous infrared galaxies or most starbursting submillimeter galaxies in the early universe. Our observations allow new independent estimates of the cold gas mass which indicate Mgas ∼ 2 × 1011 M⊙, and suggest a modestly larger αCO value of ∼8.2. The corresponding gas depletion timescale is ∼1.5 Gyr. In addition to gas of modest density (Log(n cm3) ≲ 3) heated by star formation, BX610 shows evidence for a significant second gas component responsible for the strong high-J CO emission. This second component might either be a high-density molecular gas component heated by star formation in a typical photodissociation region, or could be molecular gas excited by low-velocity C shocks. The CO(7-6)-to-FIR luminosity ratio we observe is significantly higher than typical star-forming galaxies and suggests that CO(7-6) is not a reliable star-formation tracer in this galaxy.
Key words: galaxies: ISM / galaxies: star formation / galaxies: high-redshift / submillimeter: galaxies / photon-dominated region
The reduced spectra are only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (22.214.171.124) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/628/A104
© ESO 2019
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