A Lower-Limit Flux for the Extragalactic Background Light

... A strict lower-limit flux for the evolving extragalactic background light (and in particular the cosmic infrared background) has been calculated up to redshift of 5. The computed flux is below the existing upper limits from direct observations, and in agreement with all existing limits derived from very-high energy gamma-ray observations. The corrected spectra are still in agreement with simple theoretical predictions. The derived strict lower-limit EBL flux is very close to the upper limits from gamma-ray observations. This is true for the present day EBL but also for the diffuse flux at higher redshift. If future detections of high redshift gamma-ray sources require a lower EBL flux than derived here, the physics assumptions used to derive the upper limits have to be revised. The lower-limit EBL model is not only needed for absorption features in AGN and other gamma-ray sources but is also essential when alternative particle processes are tested, which could prevent the high energy gamma-rays from being absorbed. It can also be used for a quaranteed interaction of cosmic-ray particles. The model is available online.Comment: 12 pages, 6 figures, accepted by A&

A strict lower-limit EBL: Applications on gamma-ray absorption

A strict lower limit flux for the extragalactic background light from ultraviolet to the far-infrared photon energies is presented. The spectral energy distribution is derived using an established EBL model based on galaxy formation. The model parameters are chosen to fit the lower limit data from number count observations in particular recent results by the SPITZER infrared space telescope. A lower limit EBL model is needed to calculate guaranteed absorption due to pair production in extragalactic gamma-ray sources as in TeV blazars.Comment: Comments: 4 pages, 2 figures, submitted to proceedings of "4th Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008

The ISO 170um Luminosity Function of Galaxies

We constructed a local luminosity function (LF) of galaxies using a flux-limited sample (S_170 > 0.195Jy) of 55 galaxies at z < 0.3 taken from the ISO FIRBACK survey at 170um. The overall shape of the 170-um LF is found to be different from that of the total 60-um LF (Takeuchi et al. 2003): the bright end of the LF declines more steeply than that of the 60-um LF. This behavior is quantitatively similar to the LF of the cool subsample of the IRAS PSCz galaxies. We also estimated the strength of the evolution of the LF by assuming the pure luminosity evolution (PLE): L(z) \propto (1+z)^Q. We obtained Q=5.0^{+2.5}_{-0.5} which is similar to the value obtained by recent Spitzer observations, in spite of the limited sample size. Then, integrating over the 170-um LF, we obtained the local luminosity density at 170um, \rho_L(170um). A direct integration of the LF gives \rho_L(170um) = 1.1 \times 10^8 h Lsun Mpc^{-3}, whilst if we assume a strong PLE with Q=5, the value is 5.2 \times 10^7 h Lsun Mpc^{-3}. This is a considerable contribution to the local FIR luminosity density. By summing up with other available infrared data, we obtained the total dust luminosity density in the Local Universe, \rho_L(dust)=1.1 \times 10^8 h Lsun Mpc^{-3}. Using this value, we estimated the cosmic star formation rate (SFR) density hidden by dust in the Local Universe. We obtained \rho_SFR(dust) \simeq 1.1-1.2 h \times 10^{-2} Msun yr^{-1} Mpc^{-3}$, which means that 58.5% of the star formation is obscured by dust in the Local Universe.Comment: A&A in pres

Infrared Spectral Energy Distributions of z~0.7 Star-Forming Galaxies

We analyze the infrared (IR) spectral energy distributions (SEDs) for 10micron < lambda(rest) < 100micron for ~600 galaxies at z~0.7 in the extended Chandra Deep Field South by stacking their Spitzer 24, 70 and 160micron images. We place interesting constraints on the average IR SED shape in two bins: the brightest 25% of z~0.7 galaxies detected at 24micron, and the remaining 75% of individually-detected galaxies. Galaxies without individual detections at 24micron were not well-detected at 70micron and 160micron even through stacking. We find that the average IR SEDs of z~0.7 star-forming galaxies fall within the diversity of z~0 templates. While dust obscuration Lir/Luv seems to be only a function of star formation rate (SFR; ~ Lir+Luv), not of redshift, the dust temperature of star-forming galaxies (with SFR ~ 10 solar mass per year) at a given IR luminosity was lower at z~0.7 than today. We suggest an interpretation of this phenomenology in terms of dust geometry: intensely star-forming galaxies at z~0 are typically interacting, and host dense centrally-concentrated bursts of star formation and warm dust temperatures. At z~0.7, the bulk of intensely star-forming galaxies are relatively undisturbed spirals and irregulars, and we postulate that they have large amounts of widespread lower-density star formation, yielding lower dust temperatures for a given IR luminosity. We recommend what IR SEDs are most suitable for modeling intermediate redshift galaxies with different SFRs.Comment: 12 pages, 11 figures, 2 tables, accepted for publication in Ap

The 2-850 micron SED of starforming galaxies

We present preliminary results on a study of the 2--850 micron SEDs of a sample of 30 FIRBACK galaxies selected at 170 micron. These sources are representative of the brightest ~10% of the Cosmic Infrared Background. They are a mixture of mostly local (z<~0.3) starforming galaxies, and a tail of ULIGs that extend up to z~1, and are likely to be a similar population to faint SCUBA sources. We use archival Spitzer IRAC and MIPS data to extend the spectral coverage to the mid-IR regime, resulting in an unprecended (for this redshift range) census of their infrared SEDs. This allows us to study in far greater detail this important population linking the near-IR stellar emission with PAH and thermal dust emission. We do this using a Markov Chain Monte Carlo method, which easily allows for the inclusion of ~6 free parameters, as well as an estimate of parameter uncertainties and correlations.Comment: 5 pages, 3 figures. Proceeding for the conference "Starbursts: From 30 Doradus to Lyman Break Galaxies", held in Cambridge (UK) in September, 200