PRUSSIC

Astronomy and Astrophysics, vol. 679, pp. A119

Abstract

We present deep ALMA Band 3 observations of the HCN, HCO+, and HNC(4–3) emission in SDP.81, a well-studied z = 3.042, strongly lensed galaxy. These lines trace the high-density gas, which remains almost entirely unexplored in z ≥ 1 galaxies. Additionally, these dense-gas tracers are potentially powerful diagnostics of the mechanical heating of the interstellar medium. While the HCN(4–3) and HNC(4–3) lines are not detected, the HCO+(4–3) emission is clearly detected and resolved. This is the third detection of this line in a high-redshift star-forming galaxy. We find an unusually high HCO+/HCN intensity ratio of ≥2.2. Based on the modelling of the photodissociation region, the most likely explanation for the elevated HCO+/HCN ratio is that SDP.81 has low mechanical heating, making up less than 10% of the total energy budget, along with a sub-solar metallicity of Z ≈ 0.5 Z⊙. While such conditions might not be representative of the general population of high-redshift dusty galaxies, a lower-than-solar metallicity might significantly impact gas masses inferred from CO observations. In addition, we report the detection of CO(0–1) absorption from the foreground lensing galaxy and CO(1–0) emission from a massive companion to the lensing galaxy, approximately 50 kpc to the south-east.

Authors 9

1. Matus Rybak corresponding Aachen Leiden Observatory

   Leiden University · Leiden Observatory · Delft University of Technology

   Affiliation as printed

   Faculty of Electrical Engineering, Mathematics and Computer Science , Delft University of Technology , Mekelweg 4 , 2628 CD Delft , The Netherlands

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

   Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, Mekelweg 4, 2628 CD Delft, The Netherlands

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

2. Joshiwa van Marrewijk Aachen Leiden Observatory

   Leiden University · European Southern Observatory · Leiden Observatory

   Affiliation as printed

   European Southern Observatory , Karl-Schwarzschild-Straße 2 , 85748 Garching bei München , Germany

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

   European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

3. Jacqueline Hodge Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

4. P. Andreani

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory , Karl-Schwarzschild-Straße 2 , 85748 Garching bei München , Germany

   European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany

5. G. Calistro Rivera

   European Southern Observatory

   Affiliation as printed

   European Southern Observatory , Karl-Schwarzschild-Straße 2 , 85748 Garching bei München , Germany

   European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany

6. Luca Graziani

   Astronomical Observatory of Rome · Sapienza University of Rome · National Institute for Astrophysics

   Affiliation as printed

   Dipartimento di Fisica , Universitá di Roma La Sapienza , Piazzale Aldo Moro 2 , 00185 Roma , Italy

   INAF/Osservatorio Astronomico di Roma , Via di Frascati 33 , 00040 Monte Porzio Catone , Italy

   Dipartimento di Fisica, Universitá di Roma La Sapienza, Piazzale Aldo Moro 2, 00185 Roma, Italy

   INAF/Osservatorio Astronomico di Roma, Via di Frascati 33, 00040 Monte Porzio Catone, Italy

7. J. P. McKean

   University of Groningen · South African Radio Astronomy Observatory · University of Pretoria · Netherlands Institute for Radio Astronomy

   Affiliation as printed

   ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, NL-7991 PD Dwingeloo, the Netherlands

   Department of Physics, University of Pretoria, Lynnwood Road, Hatfield, Pretoria 0083, South Africa

   Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700AV Groningen, the Netherlands

   South African Radio Astronomy Observatory (SARAO), P.O. Box 443, Krugersdorp 1740, South Africa

8. S. Viti Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands

9. Paul P. van der Werf Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , The Netherlands

   Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands