The infrared-radio correlation of star-forming galaxies is strongly M_⋆-dependent but nearly redshift-invariant since z ∼ 4

¹ CEA, Irfu, DAp, AIM, Université Paris-Saclay, Université de Paris, CNRS, 91191 Gif-sur-Yvette, France
² INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
e-mail: ivan.delvecchio@inaf.it
³ Astronomy Centre, Department of Physics & Astronomy, University of Sussex, Brighton BN1 9QH, UK
⁴ Astrophysics, Department of Physics, Keble Road, Oxford OX1 3RH, UK
⁵ Department of Physics & Astronomy, University of the Western Cape, Private Bag X17, Bellville, Cape Town 7535, South Africa
⁶ Instituto de Astrofísica de Canarias (IAC), 38205 La Laguna, Tenerife, Spain
⁷ Universidad de La Laguna, Dpto. Astrofísica, 38206 La Laguna, Tenerife, Spain
⁸ MPI for Astronomy, Königstuhl 17, 69117 Heidelberg, Germany
⁹ Leiden Observatory, Leiden University, PO Box 9513 2300 RA Leiden, The Netherlands
¹⁰ Instituto de Física y Astronomía, Universidad de Valparaíso, Gran Bretaña 1111, Playa Ancha, Valparaíso, Chile
¹¹ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
¹² INAF – Osservatorio Astronomico di Cagliari, Via della Scienza 5, 09047 Selargius, CA, Italy
¹³ INAF – Istituto di Radioastronomia, Via P. Gobetti 101, 40129 Bologna, Italy
¹⁴ Department of Physics, University of Zagreb, Bijenička cesta 32, 10002 Zagreb, Croatia
¹⁵ Purple Mountain Observatory & Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, Nanjing, PR China
¹⁶ School of Astronomy and Space Science, University of Science and Technology of China, Hefei, Anhui, PR China
¹⁷ Núcleo de Astronomía, Facultad de Ingeniería y Ciencias, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
¹⁸ The Inter-University Institute for Data Intensive Astronomy (IDIA), Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa
¹⁹ School of Science, Western Sydney University, Locked Bag 1797, Penrith, NSW 2751, Australia
²⁰ South African Astronomical Observatory, PO Box 9 Observatory, 7935 Cape Town, South Africa
²¹ A&A, Department of Physics, Faculty of Sciences, University of Antananarivo, B.P. 906, Antananarivo 101, Madagascar
²² University of Padova, Department of Physics and Astronomy, Vicolo Osservatorio 3, 35122 Padova, Italy
²³ Laboratoire d’Astrophysique, EPFL, 1290 Sauverny, Switzerland
²⁴ Department of Physics and Electronics, Rhodes University, PO Box 94 Makhanda 6140, South Africa
²⁵ INAF – Osservatorio Astronomico di Bologna, Via P. Gobetti 93/3, 40129 Bologna, Italy

Received: 11 October 2020
Accepted: 22 January 2021

Abstract

Over the past decade, several works have used the ratio between total (rest 8−1000 μm) infrared and radio (rest 1.4 GHz) luminosity in star-forming galaxies (q_IR), often referred to as the infrared-radio correlation (IRRC), to calibrate the radio emission as a star formation rate (SFR) indicator. Previous studies constrained the evolution of q_IR with redshift, finding a mild but significant decline that is yet to be understood. Here, for the first time, we calibrate q_IR as a function of both stellar mass (M_⋆) and redshift, starting from an M_⋆-selected sample of > 400 000 star-forming galaxies in the COSMOS field, identified via (NUV − r)/(r − J) colours, at redshifts of 0.1 < z < 4.5. Within each (M_⋆,z) bin, we stacked the deepest available infrared/sub-mm and radio images. We fit the stacked IR spectral energy distributions with typical star-forming galaxy and IR-AGN templates. We then carefully removed the radio AGN candidates via a recursive approach. We find that the IRRC evolves primarily with M_⋆, with more massive galaxies displaying a systematically lower q_IR. A secondary, weaker dependence on redshift is also observed. The best-fit analytical expression is the following: q_IR(M_⋆, z) = (2.646 ± 0.024) × (1 + z)^{( − 0.023 ± 0.008)}–(0.148 ± 0.013) × (log M_⋆/M_⊙ − 10). Adding the UV dust-uncorrected contribution to the IR as a proxy for the total SFR would further steepen the q_IR dependence on M_⋆. We interpret the apparent redshift decline reported in previous works as due to low-M_⋆ galaxies being progressively under-represented at high redshift, as a consequence of binning only in redshift and using either infrared or radio-detected samples. The lower IR/radio ratios seen in more massive galaxies are well described by their higher observed SFR surface densities. Our findings highlight the fact that using radio-synchrotron emission as a proxy for SFR requires novel M_⋆-dependent recipes that will enable us to convert detections from future ultra-deep radio surveys into accurate SFR measurements down to low-M_⋆ galaxies with low SFR.