Dust in starburst nuclei and ULIRGs

Abstract

Aims. We provide a library of some 7000 SEDs for the nuclei of starburst and ultra luminous galaxies. Its purpose is to quickly obtain estimates of the basic parameters, such as luminosity, size and dust or gas mass and to predict the flux at yet unobserved wavelengths. The procedure is simple and consists of finding an element in the library that matches the observations. The objects may be in the local universe or at high z. Methods. We calculate the radiative transfer in spherical symmetry for a stellar cluster permeated by an interstellar medium with standard (Milky Way) dust properties. The cluster contains two stellar populations: old bulge stars and OB stars. Because the latter are young, a certain fraction of them will be embedded in compact clouds which constitute hot spots that determine the MIR fluxes. Results. We present SEDs for a broad range of luminosities, sizes and obscurations. We argue that the assumption of spherical symmetry and the neglect of clumpiness of the medium are not severe shortcomings for computing the dust emission. The validity of the approach is demonstrated by matching the SED of seven of the best studied galaxies, including M 82 and Arp 220, by library elements. In all cases, one finds an element which fits the observed SED very well, and the parameters defining the element are in full accord with what is known about the galaxy from detailed studies. We also compare our method of computing SEDs with other techniques described in the literature.

Dusty star-forming galaxies at high redshift

“…Siebenmorgen & Krügel (2007) describe a spherically symmetric radiative transfer model for dusty starburst nuclei and ULIRGs and argue that the symmetry assumption, and lack of accounting for dust clumpiness, does not significantly change a dusty galaxy's SED. They present a library of 7000 SEDs which can be fit to galaxies either locally or at high-z and accurately be used to measure luminosity, size, dust or gas mass.…”

“…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.…”

“…Constructed for solar-metallicity starbursts with duration ∼100 Myr and checked for consistency using local starbursts. Siebenmorgen & Krügel (2007) 7000 templates; spherically symmetric radiative transfer model accounting for a variety of star formation rates, gas fractions, sizes or dust masses. No accounting for dust clumpiness or asymmetry, although they argue it is insignificant.…”

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

“…The time-sequence of SEDs calculated by Efstathiou et al (2000) poses the interesting question: can we identify starbursts of different ages observationally (see section 8 below)? Subsequent work on radiative transfer models for starbursts includes the models of Takagi et al (2003), which includes distributed stars and dust satisfying a King law; the programme of Dopita et al (2005, Groves et al (2008) which incorporate detailed HII region physics; and the large library of parameterised models generated by Siebenmorgen & Krugel (2007).…”

Should we believe the results of ultraviolet–millimetre galaxy spectral energy distribution modelling?

“…One method is to perform radiative transfer calculations assuming some simple galaxy geometry (e.g. Silva et al 1998;Efstathiou et al 2000;Granato et al 2000;Popescu et al 2000;Tuffs et al 2004;Siebenmorgen & Krügel 2007;Groves et al 2008;Michałowski et al 2010a,b). Alternatively, one can take a more empirical approach and treat the FIR SED as a sum of modified blackbodies (e.g.…”