HELP: modelling the spectral energy distributions of Herschel detected galaxies in the ELAIS N1 field

¹ Aix Marseille Univ. CNRS, CNES, LAM, Marseille, France
e-mail: Katarzyna.Malek@ncbj.gov.pl
² National Centre for Nuclear Research, ul. Ho˙za 69, 00-681 Warszawa, Poland
³ Astronomy Centre, Department of Physics and Astronomy, University of Sussex, Falmer, Brighton BN1 9QH, UK
⁴ Univ. Lyon, Univ. Lyon1, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon UMR5574, 69230 Saint-Genis-Laval, France
⁵ Leiden Observatory, Leiden University, 2300 RA Leiden, The Netherlands
⁶ School of Sciences, European University Cyprus, Diogenes Street, Engomi, 1516 Nicosia, Cyprus
⁷ Department of Physics and Astronomy, University of the Western Cape, Robert Sobukwe Road, Private Bag X17, 7535 Bellville, Cape Town, South Africa
⁸ INAF – Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁹ University of Hawaii, 2505 Correa Road, Honolulu, HI 96822, USA
¹⁰ Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa

Received: 29 March 2018
Accepted: 14 August 2018

Abstract

Aims. The Herschel Extragalactic Legacy Project (HELP) focuses on the data from ESA’s Herschel mission, which covered over 1300 deg² and is preparing to publish a multi-wavelength catalogue of millions of objects. Our main goal is to find the best approach to simultaneously fitting spectral energy distributions (SEDs) of millions of galaxies across a wide redshift range to obtain homogeneous estimates of the main physical parameters of detected infrared (IR) galaxies.

Methods. We perform SED fitting on the ultraviolet(UV)/near-infrared(NIR) to far-infrared(FIR) emission of 42 047 galaxies from the pilot HELP field: ELAIS N1. To do this we use the latest release of CIGALE, a galaxy SED fitting code relying on energy balance, to deliver the main physical parameters such as stellar mass, star formation rate, and dust luminosity. We implement additional quality criteria to the fits by calculating χ² values for the stellar and dust part of the spectra independently. These criteria allow us to identify the best fits and to identify peculiar galaxies. We perform the SED fitting of ELAIS N1 galaxies by assuming three different dust attenuation laws separately allowing us to test the impact of the assumed law on estimated physical parameters.

Results. We implemented two additional quality value checks for the SED fitting method based on stellar mass estimation and energy budget. This method allows us to identify possible objects with incorrect matching in the catalogue and peculiar galaxies; we found 351 possible candidates of lensed galaxies using two complementary χ²s criteria (stellar and infrared χ²s) and photometric redshifts calculated for the IR part of the spectrum only. We find that the attenuation law has an important impact on the stellar mass estimate (on average leading to disparities of a factor of two). We derive the relation between stellar mass estimates obtained by three different attenuation laws and we find the best recipe for our sample. We also make independent estimates of the total dust luminosity parameter from stellar emission by fitting the galaxies with and without IR data separately.