High Dense Gas Fraction in Intensely Star-forming Dusty Galaxies

I. Oteo, R. J. Ivison, A. Omont, M. Bremer, S. Bussmann, A. Cooray, H. Dannerbauer, L. Dunne, S. Eales, C. Furlanetto, R. Gavazzi, T. R. Greve, H. Nayyeri, M. Negrello, R. Neri, D. Riechers, R. Tunnard, J. Wagg, P. Van der Werf

Research output: Contribution to journalArticle (Academic Journal)peer-review

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We present ALMA J=3{--}2 and VLA J=1{--}0 observations of the dense molecular gas tracers HCN, HCO+, and HNC in two lensed, high-redshift starbursts selected from the Herschel-ATLAS survey: H-ATLAS J090740.0-004200 (SDP.9, {z}{spec}=1.575) and H-ATLAS J091043.1-000321 (SDP.11, {z}{spec}=1.786). In SDP.9 we have detected all J=3{--}2 transitions and also HCN(1-0) and HCO+(1-0). In SDP.11 we have detected HCN(3-2) and HCO+(3-2). The amplification factors for both galaxies have been determined from subarcsecond-resolution CO and dust emission observations carried out with NOEMA and the SMA. The HNC(1-0)/HCN(1-0) line ratio in SDP.9 suggests the presence of photon-dominated regions, as happens in most local (U)LIRGs. The CO, HCN, and HCO+ spectral line energy distribution (SLEDs) of SDP.9 are compatible to those found for many local, IR-bright galaxies, indicating that the molecular gas in local and high-redshift dusty starbursts can have similar excitation conditions. We obtain that the correlation between total IR ({L}{IR}) and dense line ({L}{dense}) luminosity in SDP.9 and SDP.11 and local star-forming galaxies can be represented by a single relation. We argue that the scatter of the {L}{IR}{--}{L}{dense} correlation, together with the lack of sensitive dense molecular gas tracer observations for a homogeneous sample of high-redshift galaxies, prevents us from distinguishing differential trends with redshift. Our results suggest that the intense star formation found in some high-redshift, dusty, luminous starbursts is associated with more massive dense molecular gas reservoirs and higher dense molecular gas fractions.
Original languageEnglish
Pages (from-to)170
JournalAstrophysical Journal
Issue number2
Early online date28 Nov 2017
Publication statusPublished - 1 Dec 2017


  • galaxies: high-redshift
  • galaxies: ISM
  • galaxies: starburst
  • galaxies: star formation


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