Extragalactic background light inferred from AEGIS galaxy-SED-type fractions

Abstract

The extragalactic background light (EBL) is of fundamental importance both for understanding the entire process of galaxy evolution and for γ‐ray astronomy, but the overall spectrum of the EBL between 0.1 and 1000 μm has never been determined directly from galaxy spectral energy distribution (SED) observations over a wide redshift range. The evolving, overall spectrum of the EBL is derived here utilizing a novel method based on observations only. This is achieved from the observed evolution of the rest‐frame K‐band galaxy luminosity function up to redshift 4, combined with a determination of galaxy‐SED‐type fractions. These are based on fitting Spitzer Wide‐Area Infrared Extragalactic Survey (SWIRE) templates to a multiwavelength sample of about 6000 galaxies in the redshift range from 0.2 to 1 from the All‐wavelength Extended Groth Strip International Survey (AEGIS). The changing fractions of quiescent galaxies, star‐forming galaxies, starburst galaxies and active galactic nucleus (AGN) galaxies in that redshift range are estimated, and two alternative extrapolations of SED types to higher redshifts are considered. This allows calculation of the evolution of the luminosity densities from the ultraviolet (UV) to the infrared (IR), the evolving star formation rate density of the Universe, the evolving contribution to the bolometric EBL from the different galaxy populations including AGN galaxies and the buildup of the EBL. Our EBL calculations are compared with those from a semi‐analytic model, another observationally based model and observational data. The EBL uncertainties in our modelling based directly on the data are quantified, and their consequences for attenuation of very‐high‐energy γ‐rays due to pair production on the EBL are discussed. It is concluded that the EBL is well constrained from the UV to the mid‐IR, but independent efforts from IR and γ‐ray astronomy are needed in order to reduce the uncertainties in the far‐IR.

An empirical approach to the extragalactic background light from AEGIS galaxy SED-type fractions

“…Furthermore, discoveries of γ-rays from distant blazars (e.g., Aleksić et al 2011a,b,c) support the EBL specific intensity level derived from galaxy count and recent EBL models such as Gilmore et al (2011), Franceschini et al (2008, and Domínguez et al (2011a). We highlight that the EBL specific intensity calculated with our method matches lower limits from galaxy counts, which implies the highest transparency of the Universe to γ-ray allowed by standard physics (see Domínguez et al 2011c).…”

“…Furthermore, galaxy counts from very deep surveys taken with very sensitive instruments (Madau & Pozzetti 2000;Fazio et al 2004;Keenan et al 2010) should be considered as a good estimation of the true EBL from galaxies. On the other hand, different fully independent modelings based on different methodologies and galaxy data sets such as Franceschini et al (2008), Gilmore et al (2011), Domínguez et al (2011a) agree in the specific intensity level of the EBL. In particular, galaxy count data are in excellent agreement with our EBL estimations.…”

“…1 shows the local EBL, with its uncertainties, compared with direct and indirect observational data, and other EBL models. Other quantities such as EBL evolution † are discussed in Domínguez et al (2011a). Fig.…”

“…This will not be discussed in this proceedings paper but we refer the interested reader to Domínguez et al 2011a,b for a discussion about this.…”

“…On the other hand, there are phenomenological approaches in the literature that predict an overall EBL model (i.e., between 0.1 and 1000 µm and for any redshift). These are basically of the four kinds described in Domínguez et al (2011a) and enumerated here in Table 1. Generally, any EBL modeling is built from two main quantities: one describing the galaxy density evolution over time and another one describing the overall galaxy emission (stellar component plus absorption/re-emission by dust).…”