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.

Highlights

  • Multi-wavelength data for extragalactic objects is a necessary precondition for a physical analysis of galaxies, as the full complexity of the galaxy is only seen when using different spectral ranges simultaneously

  • Summary of spectral energy distributions (SEDs) templates Each created SED template consists of five components (SFH, single stellar population, dust attenuation and emission, and the AGN component) which are spread over the entire grid of input parameters

  • All these parameters are default parameters used for all Herschel Extragalactic Legacy Project (HELP) fields

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Summary

Introduction

Multi-wavelength data for extragalactic objects is a necessary precondition for a physical analysis of galaxies, as the full complexity of the galaxy is only seen when using different spectral ranges simultaneously. Summary of SED templates Each created SED template consists of five components (SFH, single stellar population, dust attenuation and emission, and the AGN component) which are spread over the entire grid of input parameters The total time to fit all SEDs for ELAIS N1 was ∼6 h

Reliability check for SED fitting procedure and identification of outliers
Quality of the SED fits
Two χ2s criteria
Dust luminosity distribution for ELAIS N1
AGN contribution
Findings
Dust attenuation recipes
Full Text
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