Modelling the spectral energy distribution of galaxies - V. The dust and PAH emission SEDs of disk galaxies

By C. Popescu, R. Tuffs, M. Dopita, J. Fischera, N. Kylafis, B. Madore. 2010

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We present a self-consistent model of the spectral energy distributions (SEDs) of spiral galaxies from the ultraviolet (UV) to the mid-infrared (MIR)/far-infrared (FIR)/submillimeter (submm) based on a full radiative transfer calculation of the propagation of starlight in galaxy disks. This model predicts not only the total integrated energy absorbed in the UV/optical and re-emitted in the infrared/submm, but also the colours of the dust emission based on an explicit calculation of the strength and colour of the UV/optical radiation fields heating the dust, and incorporating a full calculation of the stochastic heating of small dust grains and PAH molecules. The geometry of the translucent components of the model is empirically constrained using the results from the radiation transfer analysis of Xilouris et al. on spirals in the middle range of the Hubble sequence, while the geometry of the optically thick components is constrained from physical considerations with a posteriori checks of the model predictions with observational data. Following the observational constraints, the model has both a distribution of diffuse dust associated with the old and young disk stellar populations as well as a clumpy component arising from dust in the parent molecular clouds in star forming regions. In accordance with the fragmented nature of dense molecular gas in typical star-forming regions, UV light from massive stars is allowed to either freely stream away into the diffuse medium in some fraction of directions or be geometrically blocked and locally absorbed in clumps. These geometrical constraints enable the dust emission to be predicted in terms of a minimum set of free parameters: the central face-on dust opacity in the B-band τ f B , a clumpiness factor F for the star-forming regions, the star-formation rate SFR, the normalised luminosity of the old stellar population old and the bulge-to-disk ratio B/D. We show that these parameters are almost orthogonal in their predicted effect on the colours of the dust/PAH emission. In most practical applications B/D will actually not be a free parameter but (together with the angular size θ gal and inclination i of the disk) act as a constraint derived from morphological decomposition of higher resolution optical images. This also extends the range of applicability of the model along the Hubble sequence. We further show that the dependence of the dust emission SED on the colour of the stellar photon field depends primarily on the ratio between the luminosities of the young and old stellar populations (as specified by the parameters SFR and old) rather than on the detailed colour of the emissions from either of these populations. The model is thereby independent of a priori assumptions of the detailed mathematical form of the dependence of SFR on time, allowing UV/optical SEDs to be dereddened without recourse to population synthesis models. Utilising these findings, we show how the predictive power of radiative transfer calculations can be combined with measurements of θ gal , i and B/D from optical images to self-consistently fit UV/optical-MIR/FIR/submm SEDs observed in large statistical surveys in a fast and flexible way, deriving physical parameters on an object-by-object basis. We also identify a non-parametric test of the fidelity of the model in practical applications through comparison of the model predictions for FIR colour and surface brightness with the corresponding observed quantities. This should be effective in identifying objects such as AGNs or star-forming galaxies with markedly different geometries to those of the calibrators of Xilouris et al. The results of the calculations are made available in the form of a large library of simulated dust emission SEDs spanning the whole parameter space of our model, together with the corresponding library of dust attenuation calculated using the same model.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/98a475bfe061a3684cb97064030958b73149b29e

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Citations in the corpus

Modeling the Panchromatic Spectral Energy Distributions of Galaxies (2013, background): “…starlight (or simply the radiation field) to predict IR emission (Desert, Boulanger & Puget 1990; Silva et al. 1998; Devriendt, Guiderdoni & Sadat 1999; Popescu et al. 2000; Dale et al. 2001; Piovan, Tantalo & Chiosi 2006; Jonsson 2006; Draine & Li 2007; Groves et al. 2008; Popescu et al. 2011).”
RECONSTRUCTING THE STELLAR MASS DISTRIBUTIONS OF GALAXIES USING S4G IRAC 3.6 AND 4.5 μm IMAGES. II. THE CONVERSION FROM LIGHT TO MASS (2014, background): “So far, the effect of dust on UV-to-optical emission from late-type spiral disks has been well modeled assuming a mix of foreground screen and birth-cloud extinction (e.g. Popescu et al. 2011; da Cunha et al. 2008).”
Galaxy and Mass Assembly (GAMA): the star formation rate dependence of the stellar initial mass function (2011, methodology): “We explore several popular empirical dust models (Cardelli et al. 1989; Calzetti 2001; Fischera & Dopita 2005) along with radiative transfer model predictions of the effects of dust extinction (Popescu et al. 2000; Tuffs et al. 2004; Popescu et al. 2011).”
Dust spectral energy distributions of nearby galaxies: an insight from the Herschel Reference Survey (2014, methodology): “…transfer modeling of galaxies is a powerful tool to analyze the properties of dust in galaxies in a self-consistent way (e.g. Xilouris et al. 1999; Popescu et al. 2000; Alton et al. 2004; Bianchi 2008; Baes et al. 2010; MacLachlan et al. 2011; Popescu et al. 2011; de Looze et al. 2012b,a).”
Herschel-ATLAS: rapid evolution of dust in galaxies over the last 5 billion years (2010, background): “A strong test is to look at the effects of different κ on the attenuation–inclination relation in the optical as differing values of κ in the sub-mm will (for a fixed observed sub-mm flux) produce different values for the dust opacity in the optical–UV (see Popescu et al. 2011 for further details).”
EFFICIENT THREE-DIMENSIONAL NLTE DUST RADIATIVE TRANSFER WITH SKIRT (2011, background): “…spiral galaxy, which has always been a favorite class of galaxies for radiative transfer modellers, as the dust is clearly visible both in absorption and emission (e.g. Xilouris et al. 1997, 1998, 1999; Popescu et al. 2000, 2011; Misiriotis et al. 2001; Dasyra et al. 2005; Bianchi 2007, 2008).”
GALAXY AND MASS ASSEMBLY (GAMA): MID-INFRARED PROPERTIES AND EMPIRICAL RELATIONS FROM WISE (2014, background): “Bear in mind that the 24 μm warm dust emission is powered by the UV radiation fields from the massive stars inside the star-forming regions, while the 12 μm emission is mainly powered by the diffuse interstellar radiation fields (Popescu et al. 2011).”
Dust formation history of galaxies: A critical role of metallicity* for the dust mass growth by accreting materials in the interstellar medium (2012, background): “The lifetime of a star of initial mass m, expressed as τm , is taken from Raiteri et al. (1996). In this work, since its metallicity dependence is weak, we always take the lifetime of the case of the solar metallicity.”
MegaMorph - multiwavelength measurement of galaxy structure: complete Sersic profile information from modern surveys (2012, background): “Fully understanding the observed t ends will require careful consideration of both multi-wavelength bulgedisk decompositions and spatially-resolved models of dustattenuation (e.g., Popescu et al. 2011), constrained by spacebornUV & FIR/submm photometry.””