Issue |
A&A
Volume 667, November 2022
|
|
---|---|---|
Article Number | A70 | |
Number of page(s) | 17 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202243894 | |
Published online | 08 November 2022 |
PRUSSIC
I. A JVLA survey of HCN, HCO+, and HNC (1–0) emission in z ∼ 3 dusty galaxies: Low dense-gas fractions in high-redshift star-forming galaxies⋆
1
Faculty of Electrical Engineering, Mathematics and Computer Science, Delft University of Technology, Delft, The Netherlands
2
Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA, Leiden, The Netherlands
e-mail: m.rybak@tudelft.nl
3
Cosmic Dawn Center (DAWN), København, Denmark
4
DTU-Space, Technical University of Denmark, Elektrovej 327, 2800 Kgs. Lyngby, Denmark
5
Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
6
I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
7
Centro de Astrobiología (CAB), CSIC-INTA, Cra. de Ajalvir Km. 4, 28850 Torrejón de Ardoz, Madrid, Spain
8
European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
9
Max Planck Institute for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
10
SKA Observatory, Lower Withington Maccleseld, Cheshire, SK11 9FT, UK
Received:
28
April
2022
Accepted:
18
July
2022
Dusty star-forming galaxies (DSFGs) at redshift z ≥ 1 are among the most vigorously star-forming galaxies in the Universe. However, their dense (≥105 cm−3) gas phase – typically traced by HCN(1–0) – remains almost entirely unexplored: only two DSFGs have been detected in HCN(1–0) to date. We present the results of a Karl G. Jansky Very Large Array survey of the J = 1–0 transition of HCN, HCO+, and HNC(1–0) in six strongly lensed DSFGs at z = 2.5 − 3.3, effectively doubling the number of DSFGs with deep observations of these lines. We detect HCN(1–0) emission in one source (J1202+5354, 4.6 σ), with a tentative HCO+(1–0) detection in another (J1609+6045, 3.3σ). Spectral stacking yields strict upper limits on the HCN/FIR (≤3.6 × 10−4) and HCN/CO(1–0) ratios (≤0.045). The inferred HCN/FIR ratios (a proxy for the star-formation efficiency) are consistent with those in z ∼ 0 far-infrared-luminous starbursts. However, the HCN/CO ratios – a proxy for the dense-gas fraction – are a factor of a few lower than suggested by the two previous DSFG detections. Our results imply that most DSFGs have low dense-gas fractions. A comparison with theoretical models of star-forming galaxies indicates that the bulk of gas in DSFGs is at lower densities (≈102 cm−3), similar to ‘normal’ star-forming galaxies, rather than ultraluminous starbursts.
Key words: galaxies: high-redshift / galaxies: ISM / galaxies: star formation / submillimeter: general / radio lines: galaxies
© M. Rybak et al. 2022
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe-to-Open model. Subscribe to A&A to support open access publication.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.