Modeling Dust and Starlight in Galaxies Observed by Spitzer and Herschel: The KINGFISH Sample

Interstellar dust and starlight are modeled for the galaxies of the project "Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel." The galaxies were observed by the Infrared Array Camera and the Multiband Imaging Photometer for Spitzer on Spitzer Space Telescope, and the Photodetector Array Camera and Spectrometer and the Spectral and Photometric Imaging Receiver on Herschel Space Observatory. With data from 3.6 to 500 μm, dust models are strongly constrained. Using a physical dust model, for each pixel in each galaxy we estimate (1) dust surface density, (2) dust mass fraction in polycyclic aromatic hydrocarbons (PAHs), (3) distribution of starlight intensities heating the dust, (4) total infrared (IR) luminosity emitted by the dust, and (5) IR luminosity originating in subregions with high starlight intensity. The dust models successfully reproduce the observed global and resolved spectral energy distributions. With the angular resolution of Herschel, we obtain well-resolved maps (available online) for the dust properties. As in previous studies, we find the PAH fraction q_(PAH) to be an increasing function of metallicity, with a threshold oxygen abundance Z/Z⊙ ≈ 0.1, but we find the data to be fitted best with q_(PAH) increasing linearly with log(O/H) above a threshold value of 0.15(O/H)⊙. We obtain total dust masses for each galaxy by summing the dust mass over the individual map pixels; these "resolved" dust masses are consistent with the masses inferred from a model fit to the global photometry. The global dust-to-gas ratios obtained from this study are found to correlate with galaxy metallicities. Systems with Z/Z⊙ ≳ 0.5 have most of their refractory elements locked up in dust, whereas in systems with Z/Z⊙ ≾ 0.3 most of these elements tend to remain in the gas phase. Within galaxies, we find that q_(PAH) is suppressed in regions with unusually warm dust with vL_v(70 μm) ≳ 0.4L_(dust). With knowledge of one long-wavelength flux density ratio (e.g., f₁₆₀/f₅₀₀), the minimum starlight intensity heating the dust (U_(min)) can be estimated to within ~50%, despite a variation in U_(min) of more than two orders of magnitude. For the adopted dust model, dust masses can be estimated to within ~0.2 dex accuracy using the f₁₆₀/f₅₀₀ flux ratio and the integrated dust luminosity, and to ~0.07 dex accuracy using the 500 μm luminosity vL_v(500 µm) alone. There are additional systematic errors arising from the choice of dust model, but these are hard to estimate. These calibrated prescriptions for estimating starlight heating intensity and dust mass may be useful for studies of high-redshift galaxies

High resolution IRAS maps and IR emission of M31; 2, diffuse component and interstellar dust

Large-scale dust heating and cooling in the diffuse medium of M31 is studied using the HiRes IRAS maps in conjunction with UV, optical (UBV) and the HI maps. A dust heating/cooling model is developed based on a radiative transfer model which assumes a `Sandwich' configuration of dust and stars and takes fully into account the effect of scattering of dust grains. The model is applied to a complete sample of 'cells' (small areas of size 2'\times 2'), generated from the above maps. The sample covers the M31 disk in the galactocentric radius range 2 --- 14 kpc, and includes only the cells for which the contribution of the discrete sources to the 60\mu m surface brightness is negligible (< 20\%). This effectively excludes most of the bright arm regions from our analysis. We find that: (1) The mean optical depth (viewed from the inclination angle of 77^\circ) increases with radius from \tau_V\sim 0.7 at r=2kpc outwards, reaches a peak of ~1.6 near 10kpc, and stays quite flat out to 14kpc, where the signal falls below the 5sigma level. (2) A correlation between \tau_V and HI surface density is suggested by the similarity between their radial profiles. Significant differences are found between the radial profiles of the H_2 gas (estimated from CO) and of the dust (from \tau_V), which are most probably due to the large uncertainty in the CO-to-H_2 conversion factor, and to the under-representation of H_2-rich regions in the sample of cells of diffuse regions. (3) The \tau_V / N(HI) ratio decreases with increasing radius in the disk of M31, with an exponential law fit yielding an e-folding scale length of 9.6\pm 0.4 kpc. (4) The optical depth adjusted for this gradient, \tau_{V,c}, is strongly and linearly correlated with N(HI) over one and a half order of magnitude of column density, indicating that at a give

Modeling the evolution of infrared luminous galaxies: the influence of the Luminosity-Temperature distribution

The evolution of the luminous infrared galaxy population is explored using a pure luminosity evolution model which incorporates the locally observed luminosity-temperature distribution for IRAS galaxies. Pure luminosity evolution models in a fixed $\Lambda$CDM cosmology are fitted to submillimeter (submm) and infrared counts, and backgrounds. It is found that the differences between the locally determined bivariate model and the single variable luminosity function (LF) do not manifest themselves in the observed counts, but rather are primarily apparent in the dust temperatures of sources in flux limited surveys. Statistically significant differences in the redshift distributions are also observed. The bivariate model is used to predict the counts, redshifts and temperature distributions of galaxies detectable by {\it Spitzer}. The best fitting model is compared to the high-redshift submm galaxy population, revealing a median redshift for the total submm population of $z=1.8^{+0.9}_{-0.4}$, in good agreement with recent spectroscopic studies of submillimeter galaxies. The temperature distribution for the submm galaxies is modeled to predict the radio/submm indices of the submm galaxies, revealing that submm galaxies exhibit a broader spread in spectral energy distributions than seen in the local IRAS galaxies.Comment: Accepted for publication in ApJ. Quality of several figures reduced due to size restriction

High resolution IRAS maps and IR emission of M31; 1, morphology and sources

The morphology of the IR emission and the properties of discrete FIR sources in M31 disk are studied using the HiRes maps from IRAS. Very thin and bright FIR arm segments are shown in these maps, which have similar structure as the HI gas but with much enhanced arm/inter-arm contrast, typically a factor of 5 on the 60\mum image. We identify 39 unconfused sources (excluding the nucleus) and 14 confused sources (7 pairs) at 60 \mum by direct Gaussian fittings to the image. IRAS colors of 10 bright isolated sources are studied, which are presumably representative of the discrete sources in general. The colors follow the well known anticorrelation between the 60micron/100micron flux ratio and the 12micron/25micron flux ratio. All sources coincide with optical HII regions. A comparison with H\alpha observations shows that the total luminosity (in the wavelength range 8 --- 1000\mum) associated with HII regions is 7.2\pm 2.9 \; 10^8L_sun, namely 30\pm 14\% of the total IR emission of M31. This luminosity translates into a present-day star formation rate of 0.36\pm 0.14 M_sun/yr, about an order of magnitude lower than that of the Milky Way Galaxy

Small scale variations of abundances of transiently heated grains in molecular clouds

IRAS images of a variety of fragments in nearby molecular clouds show that the energy distribution of their IR emission varies widely from cloud to cloud and from place to place within a given cloud. These variations at small scale are all the more unexpected since the colors of the IR emission of cold material differ very little at large scale: the colors of the cirrus emission above the 3kpc molecular ring are the same as those of the cirrus emission in the solar neighborhood. To quantitatively study these variations, 12, 60, and 100 microns brightnesses were obtained of small areas centered at different positions within the set of clouds and complexes. The range of observed 12/100 micron colors is given for each cloud. Variations by an order of magnitude are found in most clouds. Variations by a factor of 2 to 3 are observed within a cloud on scales as small as 0.5pc, the resolution of this study. It is concluded that large variations of the abundances of small particles with respect to those of the large grains responsible for the 100 micron emission are required to explain the observed color variations and that these abundances have to vary by large factors; an order of magnitude from cloud to cloud

Comprehensive comparison of models for spectral energy distributions from 0.1 μm to 1 mm of nearby star-forming galaxies

We have fit the far-ultraviolet (FUV) to sub-millimeter (850 μm) spectral energy distributions (SEDs) of the 61 galaxies from the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH). The fitting has been performed using three models: the Code for Investigating GALaxy Evolution (CIGALE), the GRAphite-SILicate approach (GRASIL), and the Multiwavelength Analysis of Galaxy PHYSical properties (MAGPHYS). We have analyzed the results of the three codes in terms of the SED shapes, and by comparing the derived quantities with simple “recipes” for stellar mass (M_(star)), star-formation rate (SFR), dust mass (M_(dust)), and monochromatic luminosities. Although the algorithms rely on different assumptions for star-formation history, dust attenuation and dust reprocessing, they all well approximate the observed SEDs and are in generally good agreement for the associated quantities. However, the three codes show very different behavior in the mid-infrared regime: in the 5–10 μm region dominated by PAH emission, and also between 25 and 70 μm where there are no observational constraints for the KINGFISH sample. We find that different algorithms give discordant SFR estimates for galaxies with low specific SFR, and that the standard recipes for calculating FUV absorption overestimate the extinction compared to the SED-fitting results. Results also suggest that assuming a “standard” constant stellar mass-to-light ratio overestimates M_(star) relative to the SED fitting, and we provide new SED-based formulations for estimating M_(star) from WISE W1 (3.4 μm) luminosities and colors. From a principal component analysis of M_(star), SFR, M_(dust), and O/H, we reproduce previous scaling relations among M_(star), SFR, and O/H, and find that M_(dust) can be predicted to within ∼0.3 dex using only M_(star) and SFR

NGC1377: An Extragalactic Proto-Starburst

NGC1377 is the archetype of a class of galaxies called nascent starbursts, selected by their very high infrared to radio continuum flux ratios and their high dust temperatures. This nearby galaxy is an ideal test case to refine the understanding of the mechanisms of the infrared-radio correlation of star-forming galaxies; to characterize the physical conditions of an embedded starburst at its very onset; and to gain a better knowledge of the activity of a class of ultraluminous galaxies sharing the main infrared-radio properties of NGC1377. We present new data on NGC1377 obtained as part of the Spitzer Infrared Nearby Galaxies Survey (SINGS) Legacy program and discuss briefly our interpretation of the combined optical, infrared and radio properties

AKARI-CAS --- Online Service for AKARI All-Sky Catalogues

The AKARI All-Sky Catalogues are an important infrared astronomical database for next-generation astronomy that take over the IRAS catalog. We have developed an online service, AKARI Catalogue Archive Server (AKARI-CAS), for astronomers. The service includes useful and attractive search tools and visual tools. One of the new features of AKARI-CAS is cached SIMBAD/NED entries, which can match AKARI catalogs with other catalogs stored in SIMBAD or NED. To allow advanced queries to the databases, direct input of SQL is also supported. In those queries, fast dynamic cross-identification between registered catalogs is a remarkable feature. In addition, multiwavelength quick-look images are displayed in the visualization tools, which will increase the value of the service. In the construction of our service, we considered a wide variety of astronomers' requirements. As a result of our discussion, we concluded that supporting users' SQL submissions is the best solution for the requirements. Therefore, we implemented an RDBMS layer so that it covered important facilities including the whole processing of tables. We found that PostgreSQL is the best open-source RDBMS products for such purpose, and we wrote codes for both simple and advanced searches into the SQL stored functions. To implement such stored functions for fast radial search and cross-identification with minimum cost, we applied a simple technique that is not based on dividing celestial sphere such as HTM or HEALPix. In contrast, the Web application layer became compact, and was written in simple procedural PHP codes. In total, our system realizes cost-effective maintenance and enhancements.Comment: Yamauchi, C. et al. 2011, PASP..123..852