High dense gas fraction in intensely star-forming dusty galaxies

Oteo, I., Zhang, Z-Y., Yang, C., Ivison, R. J., Omont, A., Bremer, M., Bussmann, S., Cooray, A., Cox, P., Dannerbauer, H., Dunne, Loretta ORCID: https://orcid.org/0000-0001-9880-2543, Eales, Stephen ORCID: https://orcid.org/0000-0002-7394-426X, Furlanetto, C., Gavazzi, R., Gao, Y., Greve, T. R., Nayyeri, H., Negrello, Mattia ORCID: https://orcid.org/0000-0002-7925-7663, Neri, R., Riechers, D., Tunnard, R., Wagg, J. and Werf, P. Van der 2017. High dense gas fraction in intensely star-forming dusty galaxies. The Astrophysical Journal 850 (2) , 170. 10.3847/1538-4357/aa8ee3

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Abstract

We present ALMA $J=3\mbox{--}2$ and VLA $J=1\mbox{--}0$ 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, ${z}_{\mathrm{spec}}=1.575$) and H-ATLAS J091043.1−000321 (SDP.11, ${z}_{\mathrm{spec}}=1.786$). In SDP.9 we have detected all $J=3\mbox{--}2$ 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 (${L}_{\mathrm{IR}}$) and dense line (${L}_{\mathrm{dense}}$) 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 ${L}_{\mathrm{IR}}\mbox{--}{L}_{\mathrm{dense}}$ 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.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Physics and Astronomy
Subjects:	Q Science > QB Astronomy
Publisher:	IOP Publishing
ISSN:	15384357
Date of First Compliant Deposit:	21 December 2017
Date of Acceptance:	12 September 2017
Last Modified:	07 May 2023 23:09
URI:	https://orca.cardiff.ac.uk/id/eprint/107726

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