HELP: modelling the spectral energy distributions ofHerscheldetected galaxies in the ELAIS N1 field

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.

S2COSMOS: Evolution of gas mass with redshift using dust emission

“…In Appendix A, we compare the source catalogue from Driver et al (2018) made using the SED fitting code magphys (da Cunha et al 2008) to one created using the SED fitting routine CIGALE (Noll et al 2009, Boquien et al 2019 as part of the Herschel Extragalactic Legacy Project (HELP) database (Vaccari 2016;Ma lek et al 2018;Malek et al 2019;Shirley et al 2019;Oliver et al in prep.). This analysis shows that our choice of source catalogue is not likely to significantly impact the results of this study, and choosing the CIGALE catalogue over the Driver/magphys catalogue would not change our conclusions.…”

“…In this work, we make use of photometry and CIGALE data from the Herschel Extragalactic Legacy Project (HELP) database (Vaccari 2016;Ma lek et al 2018;Malek et al 2019;Shirley et al 2019;Oliver et al in prep.). HELP provides a homogenized, multi-wavelength database of all the fields observed by Herschel, covering 1270 square degrees over 23 different fields (Shirley et al 2019), including the COSMOS field.…”

“…To avoid over-dense photometry data causing forced SED fits, and to ensure that the deepest data are used, where there is photometry in similar bands for a given object, priority is given to the deepest observations. We refer the reader to Ma lek et al (2018) for details, but briefly, the 19 bands used in the CIGALE COSMOS fits are: ugriz, N921 (a narrow band filter on Suburu/HSC), yJK, IRAC1234, MIPS24, PACS100/160, SPIRE250/350/500. Again, note that not every source may have fluxes for all filters.…”

“…Unlike magphys, CIGALE offers the user a choice for the input parameters. We refer the reader to Ma lek et al (2018) for details, but briefly, the HELP consortium uses the Single Stellar Population (SSP) model of Bruzual & Charlot (2003), assuming a Chabrier (2003) IMF. They follow the dust attenuation curve of Charlot & Fall (2000) and dust emission is based on Draine & Li (2007), with AGN based on Fritz et al (2006).…”

“…The HELP photometry catalogue for the COSMOS field is based on the COSMOS2015 catalogue from Laigle et al (2016) (see Section 2.2.2 for a description of the COS-MOS2015 catalogue). The CIGALE catalogue we use was compiled by fitting every source within the HELP photometric catalogue for the COSMOS field that has at least four 'optical' and 'NIR' fluxes, where 'optical' bands are defined as ugrizy and N921, and 'NIR' bands are J and K (Ma lek et al 2018;Shirley et al 2019) Photometric redshifts are calculated as part of the HELP pipeline, using a Bayesian combination approach, which combines popular photometric redshift estimator templates to achieve the best estimate of the redshift, see Duncan et al (2018a) and Duncan et al (2018b). Spectroscopic redshifts are used, where possible, and are sourced from various different surveys compiled by the HELP consortium including: SDSS (Albareti et al 2017), PRIMUS (Cool et al 2013), zBRIGHT (Lilly et al 2007) and GAMA (Davies et al 2015).…”