Panchromatic radiation from galaxies as a probe of galaxy formation and evolution

Abstract

Abstract. I review work on modelling the infrared and submillimetre SEDs of galaxies. The underlying physical assumptions are discussed and spherically symmetric, axisymmetric, and 3-dimensional radiative transfer codes are reviewed. Models for galaxies with Spitzer IRS data and for galaxies in the Herschel-Hermes survey are discussed. Searches for high redshift infrared and submillimetre galaxies, the star formation history, the evolution of dust extinction, and constraints from source-counts, are briefly discussed.Keywords. infrared galaxies, radiative transfer, star formation Early work on radiative transfer models for infrared sourcesDuring the 1960s and early 1970s very simplistic models began to be developed for infrared sources associated with circumstellar dust shells, HII regions and star-forming regions. These models assumed that the dust grain density n(r) and temperature T(r) have a power-law dependence on radius r and that the dust is optically thin. Scattering was neglected and so the emission was simply calculated as a sum of n(r)Q ν B ν (T (r)), integrated over r.The first complete solution of the spherically symmetric radiative transfer problem for an optically thick dust cloud was by Leung (1975). He used detailed grain properties and carried out a full solution of the moment equations, including anisotropic scattering. The grain temperature was solved for by assuming radiative balance. Yorke & Krugel (1977) modelled the dynamical evolution of an HII region, including the interaction between gas and dust. Radiative transfer was approximated by diffusion. These two papers marked a tremendous step forward in the quality of models for infrared sources. To take advantage of numerical techniques which had been used in modelling stellar atmospheres, Leung essentially assumed that the radiation field is isotropic through most of the cloud (the Eddington approximation).Rowan-Robinson (1980) carried out a numerical solution of the full radiative transfer equation. The intensity, I ν (θ, r), was calculated throughout the cloud using a grid of values in ν, r, θ. This showed that the Eddington approximation is a poor assumption throughout a dust cloud and revealed the phenomenon of sideways beaming of the radiation field at the inner edge of cloud. Viewed from a distance a dust cloud surrounding a star should show a ring of bright emission in the mid infrared, coming from the inner edge of the dust cloud. A second interesting phenomenon revealed by a full solution of the radiative transfer equation is that of back radiation onto the star. The dust cloud radiates at the star and so the net spectrum of emission emerging from the star is no longer a blackbody, but has absorption bands at the wavelengths of dust emission features (Rowan-Robinson 1982). Rowan-Robinson & Harris (1982 applied this code to all the bright circumstellar dust shells in the AFGL survey. 446at https://www.cambridge.org/core/terms. https://doi

Predicting the stellar and non-equilibrium dust emission spectra of high-resolution simulated galaxies with dart-ray

“…Indeed, farinfrared(FIR)/submm observations of spiral galaxies show that most of the dust emission luminosity is emitted longwards of 100 micron (see e.g. Sodroski et al 1997, Odenwald et al 1998, 2012, Bendo et al 2012) through grains situated in the diffuse ISM, which are generally located at very considerable distances from the stars heating the dust. In addition, infrared radiation shortwards of 100 µm is also known to have a significant contribution from small grains out of equilibrium with the radiation fields of low energy densities, the so-called stochastically heated grains.…”

Monolithic View of Galaxy Formation and Evolution

“…Thanks to this, the frontier for high-z objects has been continuously and quickly extended from z ∼ 4-5 [94,95], and z ∼ 6 [96,97] to z ∼ 10 [98-100]. According to the current view, first galaxies formed at z ∼ 10-20 [101] or even z ∼ 20-50 when DM haloes containing BM in cosmological proportions gave origin to the first sufficiently deep gravitational potential wells [102][103][104]. In addition to this, there is observational evidence for large and red galaxies already in place at very high redshift (see [105,106]).…”

Modelling galaxy spectra in presence of interstellar dust – III. From nearby galaxies to the distant Universe

“…In recent years the first epochs of galaxy formation have been continuously pushed back in time by the discovery of galaxy size objects at higher and higher redshifts, z∼4-5 (Madau et al 1996;Steidel et al 1999), z∼6 (Stanway, Bunker & McMahon 2003;Dickinson et al 2004) to z∼10 (Zheng et al 2012;Bouwens et al 2012;Oesch et al 2012), up to z∼10-20 according to the current view (Rowan-Robinson 2012). Furthermore, this high redshift Universe turned out to heavily obscured by copious amounts of dust (see for instance Shapley et al 2001;Carilli et al 2001;Robson et al 2004;Wang et al 2009;Micha lowski et al 2010), whose origin and composition are a matter of vivid debate ⋆ E-mail: letizia@lambrate.inaf.it (LPC); lorenzo.piovan@gmail.com (LP); cesare.chiosi@unipd.it (CC) (Gall, Andersen & Hjorth 2011a,b;Dwek, Galliano & Jones 2009;Draine 2009;Dwek & Cherchneff 2011).…”