Modeling the Effects of Dust on Galactic Spectral Energy Distributions from the Ultraviolet to the Millimeter Band

Abstract

We present models of photometric evolution of galaxies in which the effects of a dusty interstellar medium have been included with particular care. A chemical evolution code follows the star formation rate, the gas fraction and the metallicity, basic ingredients for the stellar population synthesis. The latter is performed with a grid of integrated spectra of simple stellar populations (SSP) of different ages and metallicities, in which the effects of dusty envelopes around asymptotic giant branch (AGB) stars are included. The residual fraction of gas in the galaxy is divided into two phases: the star forming molecular clouds and the diffuse medium. The relative amount is a model parameter. The molecular gas is sub-divided into clouds of given mass and radius: it is supposed that each SSP is born within the cloud and progressively escapes it. The emitted spectrum of the star forming molecular clouds is computed with a radiative transfer code. The diffuse dust emission (cirrus) is derived by describing the galaxy as an axially symmetric system, in which the local dust emissivity is consistently calculated as a function of the local field intensity due to the stellar component. Effects of very small grains, subject to temperature fluctuations, as well as polycyclic aromatic hydrocarbons (PAH) are included.The model is compared and calibrated with available data of normal and starburst galaxies in the local universe, in particular new broad-band and spectroscopic ISO observations. It will be a powerful tool to investigate the star formation, the initial mass function (IMF), supernovae rate (SNR) in nearby starbursts and normal galaxies, as well as to predict the evolution of luminosity functions of different types of galaxies at wavelengths covering four decades.

Dusty star-forming galaxies at high redshift

“…Despite the relative lack of detailed data, detailed radiative transfer models and empirical template libraries have modeled the complex dust infrared emission from stars, molecular clouds and dust grains over a wide range of galaxy geometries and luminosities (Silva et al, 1998;Chary & Elbaz, 2001;Dale et al, 2001;Dale & Helou, 2002;Abel & Wandelt, 2002;Siebenmorgen & Krügel, 2007;Draine & Li, 2007). When discussing these models, it's important to keep in mind that the accuracy or applicability of these models cannot be tested with data since it simply does not exist in enough detail to disentangle effects of geometry, distribution, optical depth, etc.…”

“…It's also important to note that many have done work in this area, particularly modeling radiative transfer in local starburst populations to generate SEDs (Efstathiou & Rowan-Robinson, 1995;Efstathiou et al, 2000;Efstathiou & Siebenmorgen, 2009;Nenkova et al, 2002;Dullemond & van Bemmel, 2005;Piovan et al, 2006;Nenkova et al, 2008;Takagi et al, 2003;Fritz et al, 2006;Hönig et al, 2006;Schartmann et al, 2008), but here we try to focus on the techniques which have been most commonly employed for SED fitting of high-z dusty starbursts 11 . Silva et al (1998) developed the Grasil code to model galaxy emission by explicitly accounting for dust absorption and emission from the ultraviolet through to the far-infrared. They use stellar population synthesis models and a chemical evolution code to generate integrated spectra for simple stellar populations of different ages, metallicities, star formation rates, gas fractions, relative gas trapped in molecular clouds versus diffuse ISM, dust geometry and dust grain size distribution (small grains versus PAHs).…”

“…They use stellar population synthesis models and a chemical evolution code to generate integrated spectra for simple stellar populations of different ages, metallicities, star formation rates, gas fractions, relative gas trapped in molecular clouds versus diffuse ISM, dust geometry and dust grain size distribution (small grains versus PAHs). Chary & Elbaz (2001) use Grasil and the analysis of Silva et al (1998) to generate template SEDs for infrared-luminous galaxies out to moderately high redshifts (z ∼ 1) when measuring contributions of different galaxy populations to the CIB. Chary & Elbaz generate four SEDs with Grasil to fit data from nearby galaxies which each represent a different decade in infrared luminosity−Arp 220, NGC 6090, M 82, and M 51.…”

A dusty, normal galaxy in the epoch of reionization

“…As a final check, we fit self-consistent full UV to far-infrared SED models using the MAGPHYS 47 and GRASIL 48,49,50 codes. From these fits we derived the following lensing-corrected parameters: SFR = 10 +4 -2 M ⊙ yr -1 , log(M⋆/M ⊙ ) = 9.…”

A simple and general method for solving detailed chemical evolution with delayed production of iron and other chemical elements

“…The difficulty of building up a fast and accurate chemical evolution model -including chemical elements restored with a certain delay time from the star formation event -to couple with other population synthesis models, has represented an obstacle for developing a complete galaxy formation and evolution model for different groups in the past. Examples of works combining a chemical evolution model with the galaxy spectro-photometric evolution can be considered those of Brocato et al (1990); Bressan et al (1994); Gibson (1997); Silva et al (1998); Boissier & Prantzos (2000); Calura et al (2008); Cassarà et al (2015) for unresolved galactic stellar systems and Vincenzo et al (2016b) for resolved stellar systems.…”