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Table 1.
Summary of model assumptions for SED fitting.
| Property | CIGALE | GRASILa | MAGPHYS |
|---|---|---|---|
| SFH | SFR(tgal) delayed+truncation (defined by Eq. (2)) with tgal = (8, 10, 12) Gyr; τ = (0.5, 1, 2, 4, 8) Gyr; rSFR = (0.01, 0.05, 0.1, 0.5, 1, 5, 10); agetrunc = (10, 100, 1000) Myrb. | SFR(tgal)=ν Mgas(tgal)k with primordial gas infall described as  ; k = 1; (NSS)cν = (0.3, 0.5, 0.8, 2.3, 8.0, 23.0) Gyr−1; (NSS)cτinf = (0.01, 0.1, 0.5, 1, 2, 5, 10) Gyr; (NSS)ctgal = (0.01, 0.02, 0.05, 0.1, 0.2, 0.5, 1, 2, 4, 7, 10, 13) Gyr. |
SFR(tgal)=exp(−γ tgal) with random bursts potentially occurring at all times with amplitude A = Mburst/Mconst, the ratio of the stellar masses in the burst and exponentially declining component; tgal ∈ [0.1, 13.5] Gyr; burst duration ∈[3, 30] Myr. |
| Geometry | None | Two geometries: (NSS) spheroid with King profiles for stars and dust, and (NSD) disk radial+vertical exponential profiles for stars and dust; GMCs are randomly embedded within each of these structural components; stellar radial scalelength (NSS)c Rgal = (0.04, 0.14, 0.52, 1.9, 7.2, 26.6) kpc; (NSD) inclination angle i such that cos(i)=(1, 0.8, 0.6, 0.4, 0.2, 0). | None |
| Stellar populations | Bruzual & Charlot (2003) SSPs with Chabrier (2003) IMF, and solar metallicity (Z = Z⊙). | Bruzual & Charlot (2003) SSPs with Chabrier (2003) IMF, and metallicities ranging from Z = 0.01 Z⊙ to Z = 2.5 Z⊙. | Bruzual & Charlot (2003) SSPs with Chabrier (2003) IMF, and metallicities ranging from Z = 0.02 Z⊙ to Z = 2 Z⊙. |
| Ionized gas? | Yesd | No | No |
| Dust attenuation | Modified starburst attenuation law with power-law slope ] = (−0.5, −0.4, −0.3, −0.2, −0.1, 0.0); normalization E(B−V) for stars younger than 10 Myr ∈[0.01,0.60] mag; differential E(B−V) factor E(B−V)old/E(B−V)young = (0.25, 0.50, 0.75); variable 0.2175 μm bump with strength of 0.0 (no bump), 1.5, 3.0 (Milky-Way-like). | Attenuation law as a consequence of geometry, grain opacities from Laor & Draine (1993) mediated over grain size distributions from 0.001 μm to 10 μm, and radiative transfer of the GMC and diffuse dust components. Free parameters are: Rgmc = (6.1, 14.5, 22.2, 52.2) pc; fmol = (0.1, 0.3, 0.5, 0.9); tesc = (0.001, 0.005, 0.015, 0.045, 0.105) Gyr. | Two-component (BC, ambient ISM) dust attenuation (Charlot & Fall 2000) as in Eq. (4) with μ∈[0,1], drawn from the probability density function p(μ)=1 − tanh(8μ − 6); ] parametrized according to the probability density function p( . Optical depth  is time-dependent as in Eq. (3). |
| Dust emission | Overall dust luminosity defined by energy-balance considerations with SED shape governed by the dust models of Draine et al. (2007); Draine et al. (2014). With the exception of one (α ≡ 2.0), parameters of these models are left to vary:qPAH = (0.47, 2.50, 4.58, 6.62)%; Umin = (0.10, 0.25, 0.50, 1.0, 2.5, 5.0, 10, 25); logγ = [−3.0,−0.3] in 10 steps. Dust emission is assumed to be optically thin; the DL07 models used in CIGALE have κabs = 0.38 cm2 g−1 at 850 μm. | Overall dust luminosity and SED shape governed by geometry, grain opacities from Laor & Draine (1993) mediated over grain size distributions from 0.001 μm to 10 μm, and radiative transfer of the GMC and diffuse dust components. The dust column is assumed to be proportional to the metallicity of the given SFH, and the consistent relation between extinction and emission ensures energy conservation. The same variable parameters for dust extinction govern dust emission through radiative transfer. Dust opacity κabs = 0.56 cm2 g−1 at 850 μm (Laor & Draine 1993). | Overall dust luminosity defined by energy-balance considerations with SED shape governed by four species of dust emitters in two environments (BC, ambient ISM), with both having PAH+hot+warm grains ( ,  ,  ,  ,  ,  ), but an additional cold-dust component for the ambient ISM ( ). In addition to ensuring unity ( ,  ) fixed parameters are:  ;  ; and  . Parameters left to vary are:  [0,1];  ;  [0,1];  [30,70] K;  [30,70] K;  [10,30] K. Dust emission is assumed to be optically thin; dust opacity κabs = 0.77 cm2 g−1 at 850 μm (Dunne et al. 2000). |
| Free parameters | 11 with SFH (tgal, τ, rSFR, agetrunc); dust attenuation (δ, normalization E(B−V), differential E(B−V), variable 0.2175 μm bump strength); dust emission (qPAH, Umin, γ). | 7 for NSS templates with SFH (tgal, τinf, ν); geometry (Rgal); dust attenuation (Rgmc, fmol, tesc); dust emission (same as for dust attenuation). 8 for NSD templates with the addition of galaxy inclination (viewing angle). | 12 with SFH (γ, tgal, A, Zstar); dust attenuation (μ, and  ); dust emission ( ,  ,  ,  ,  ,  ). |
Notes.
(a)
The parameter ranges for GRASIL are sampling points only; ultimately the best-fit parameters are interpolated so that essentially the entire range of parameters is covered making the symbol ∈ more appropriate (see text for more details).
(c)
For the NSD library: ν = (0.3, 0.9, 3, 9); τinf = (0.1, 0.5, 1, 5, 10) Gyr; tgal = (0.5, 1.25, 2, 5, 13) Gyr. Rgal = (0.1, 0.3, 1, 3, 10) kpc; Rgmc = (6.1, 13.1, 19.3, 28.1) pc; fmol = (0.1, 0.2, 0.5, 0.9); tesc = (0.001, 0.002, 0.005, 0.02, 0.05, 0.1) Gyr.
(d)
See Sect. 2.1 for details.
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