The cosmic spectral energy distribution in the EAGLE simulation

Abstract

The cosmic spectral energy distribution (CSED) is the total emissivity as a function of wavelength of galaxies in a given cosmic volume. We compare the observed CSED from the UV to the submm to that computed from the EAGLE cosmological hydrodynamical simulation, post-processed with stellar population synthesis models and including dust radiative transfer using the SKIRT code. The agreement with the data is better than 0.15 dex over the entire wavelength range at redshift z = 0, except at UV wavelengths where the EAGLE model overestimates the observed CSED by up to a factor 2. Global properties of the CSED as inferred from CIGALE fits, such as the stellar mass density, mean star formation density, and mean dust-to-stellar-mass ratio, agree to within better than 20 per cent. At higher redshift, EA-GLE increasingly underestimates the CSED at optical-NIR wavelengths with the FIR/submm emissivity underestimated by more than a factor of 5 by redshift z = 1. We believe that these differences are due to a combination of incompleteness of the EAGLE-SKIRT database, the small simulation volume and the consequent lack of luminous galaxies, and our lack of knowledge on the evolution of the characteristics of the interstellar dust in galaxies. The impressive agreement between the simulated and observed CSED at lower z confirms that the combination of EAGLE and SKIRT dust processing yields a fairly realistic representation of the local Universe.

Infrared luminosity functions and dust mass functions in the EAGLE simulation

“…The EAGLE-SKIRT results do not reproduce the evolution seen in the GAMA data: the evolution in EAGLE-SKIRT is far too modest, which leads to a rapid build-up of a systematic underestimation of ∼ 0.4 dex. This finding is in agreement with our previous results on the CSED (Baes et al 2019). Indeed, we found that EAGLE-SKIRT increasingly underestimates the observed GAMA CSED, with the largest discrepancies found at farinfrared and submm wavelengths.…”

“…At the lowest redshifts, we believe that the Andrews et al (2017b) might be slightly overestimated, due to the peculiar shape of the MAGPHYS fits between 24 and 100 µm (see discussion in Sect. 3.5 of Baes et al 2019). The EAGLE-SKIRT data clearly underestimate the rapid evolution in the total infrared luminosity density: we obtain an evolution as (1 + z) 2.3 , where Le Floc'h et al (2005) and Rodighiero et al (2010) report a much stronger evolution as (1 + z) 3.9±0.4 and (1 + z) 3.8±0.4 , respectively.…”

“…Also shown on this plot is the observed HerMES CSED, as presented by Marchetti et al (2016). It is clear that the results of the two methods are completely compatible, which implies that the conclusions drawn by Baes et al (2019) are still fully valid.…”

“…Except in the UV, where the EAGLE-SKIRT CSED overestimated the observed values by up to an order of magnitude, we found an excellent agreement between the observed and simulated CSED in the Local Universe. At infrared wavelengths, the agreement was particularly satisfactory (see Baes et al 2019, Fig. 1), especially when the EAGLE-SKIRT CSED was compared to the HerMES CSED presented by Marchetti et al (2016).…”

“…Being a complex function of both the volume density of different galaxy populations and the different processes that shape the SED of a single galaxy, it is a fundamental observational characteristic of the Universe. In Baes et al (2019) we used the EAGLE-SKIRT database to generate the UV-submm CSED of the EAGLE simulation, and compared it to the observed GAMA CSED (Andrews et al 2017b). Except in the UV, where the EAGLE-SKIRT CSED overestimated the observed values by up to an order of magnitude, we found an excellent agreement between the observed and simulated CSED in the Local Universe.…”