A model for the infrared dust emission from forming galaxies

In the early epoch of galaxy evolution, dust is only supplied by supernovae (SNe). With the aid of a new physical model of dust production by SNe developed by Nozawa et al. (2003) (N03), we constructed a model of dust emission from forming galaxies on the basis of the theoretical framework of Takeuchi et al. (2003) (T03). N03 showed that the produced dust species depends strongly on the mixing within SNe. We treated both unmixed and mixed cases and calculated the infrared (IR) spectral energy distribution (SED) of forming galaxies for both cases. Our model SED is less luminous than the SED of T03 model by a factor of 2-3. The difference is due to our improved treatment of UV photon absorption cross section, as well as different grain size and species newly adopted in this work. The SED for the unmixed case is found to have an enhanced near to mid-IR (N-MIR) continuum radiation in its early phase of the evolution (age < 10^{7.25} yr) compared with that for the mixed case. The strong N--MIR continuum is due to the emission from Si grains, which only exist in the species of the unmixed dust production. We also calculated the IR extinction curves for forming galaxies. Then we calculated the SED of a local starbursting dwarf galaxy SBS 0335-052. Our present model SED naturally reproduced the strong N--MIR continuum and the lack of cold FIR emission of SBS 0335-052. We found that only the SED of unmixed case can reproduce the NIR continuum of this galaxy. We then made a prediction for the SED of another typical star-forming dwarf, I Zw 18. We also presented the evolution of the SED of LBGs. Finally, we discussed the possibility of observing forming galaxies at z > 5.Comment: MNRAS, in press. 18 pages, 15 figures. Abstract abridge

Infrared Spectral Energy Distribution Model for Extremely Young Galaxies

The small grain sizes produced by Type II supernova (SN II) models in young, metal-poor galaxies make the appearance of their infrared (IR) spectral energy distribution (SED) quite different from that of nearby, older galaxies. To study this effect, we have developed a model for the evolution of dust content and the IR SED of low-metallicity, extremely young galaxies based on Hirashita et al. (2002). We find that, even in the intense ultraviolet (UV) radiation field of very young galaxies, small silicate grains are subject to stochastic heating resulting in a broad temperature distribution and substantial MIR continuum emission. Larger carbonaceous grains are in thermal equilibrium at T \simeq 50 - 100K, and they also contribute to the MIR. We present the evolution of SEDs and IR extinction of very young, low-metallicity galaxies. The IR extinction curve is also shown. In the first few Myrs, the emission peaks at \lambda \sim 30-50um at later times dust self-absorption decreases the apparent grain temperatures, shifting the bulk of the emission into the submillimetre band. We successfully apply the model to the IR SED of a low metallicity (1/41 Z_\odot) dwarf galaxy SBS0335-052. We find the SED, optical properties and extinction of the star forming region to be consistent with a very young and compact starburst. We also predict the SED of another extremely low-metallicity galaxy, I Zw 18, for future observational tests. Some prospects for future observations are discussed.Comment: MNRAS in press, pages, 6 figures, using mn2e.cls. Abstract abridge

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

Exploring Galaxy Evolution from Infrared Number Counts and Cosmic Infrared Background

Recently reported infrared (IR) galaxy number counts and cosmic infrared background (CIRB) all suggest that galaxies have experienced a strong evolution sometime in their lifetime. We statistically estimate the galaxy evolution history from these data. We find that an order of magnitude increase of the far-infrared (FIR) luminosity at redshift z = 0.5 - 1.0 is necessary to reproduce the very high CIRB intensity at 140 um reported by Hauser et al. (1998). z \sim 0.75 and decreases to, even at most, a factor of 10 toward z \sim 5, though many variants are allowed within these constraints. This evolution history also satisfies the constraints from the galaxy number counts obtained by IRAS, ISO and, roughly, SCUBA. The rapid evolution of the comoving IR luminosity density required from the CIRB well reproduces the very steep slope of galaxy number counts obtained by ISO. We also estimate the cosmic star formation history (SFH) from the obtained FIR luminosity density, considering the effect of the metal enrichment in galaxies. The derived SFH increases steeply with redshift in 0 0.75. This is consistent with the SFH estimated from the reported ultraviolet luminosity density. In addition, we present the performance of the Japanese ASTRO-F FIR galaxy survey. We show the expected number counts in the survey. We also evaluate how large a sky area is necessary to derive a secure information of galaxy evolution up to z \sim 1 from the survey, and find that at least 50 - 300 deg^2 is required.Comment: 18 pages LaTeX, PASJ in press. Abstract abridge