Abstract
Context. Dust attenuation shapes the spectral energy distribution of galaxies. It is particularly true for dusty galaxies in which stars experience a heavy attenuation. The combination of UV to IR photometry with the spectroscopic measurement of the Hα recombination line helps to quantify dust attenuation of the whole stellar population and its wavelength dependence. Aims. We want to derive the shape of the global attenuation curve and the amount of obscuration affecting young stars or nebular emission and the bulk of the stellar emission in a representative sample of galaxies selected in IR. We will compare our results to the commonly used recipes of Calzetti et al. and Charlot and Fall, and to predictions of radiative transfer models. Methods. We selected an IR complete sample of galaxies in the COSMOS 3D-HST CANDELS field detected with the Herschel satellite with a signal to noise ratio larger than five. Optical to NIR photometry is available as well as NIR spectroscopy for each source. We reduced the sample to the redshift range 0.6 < z < 1.6 to include the Hα line in the G141 grism spectra. We have used a new version of the CIGALE code to fit simultaneously the continuum and Hα line emission of the 34 selected galaxies. Results. Using flexible attenuation laws with free parameters, we are able to measure the shape of the attenuation curve for each galaxy as well as the amount of attenuation of each stellar population, the former being in general steeper than the starburst law in the UV-optical with a large variation of the slope among galaxies. The attenuation of young stars or nebular continuum is found on average about twice the attenuation affecting older stars, again with a large variation. Our model with power-laws, based on a modification of the Charlot and Fall recipe, gives results in better agreement with the radiative transfer models than the global modification of the slope of the Calzetti law.
Highlights
Modeling the spectral energy distribution (SED) of galaxies is a method commonly used to derive physical parameters useful to quantify galaxy evolution, the most popular ones being the star formation rate (SFR) and the stellar mass (Mstar)
We have analyzed a complete sample of 34 galaxies at intermediate redshift selected in IR with Herschel PACS and SPIRE detections, with an Hα line detection for each source from the 3D-HST survey
By fitting simultaneously UV to NIR broad band and Hα fluxes we have compared several dust attenuation recipes: the classical Calzetti et al (2000) and Charlot & Fall (2000) methods and flexible recipes modifying the slope of the effective attenuation curves
Summary
Modeling the spectral energy distribution (SED) of galaxies is a method commonly used to derive physical parameters useful to quantify galaxy evolution, the most popular ones being the star formation rate (SFR) and the stellar mass (Mstar). The attenuation law built by Calzetti and collaborators for nearby starburst galaxies (Calzetti et al 1994, 2000) is by far the most commonly used It is characterized by a grayer slope than both Milky Way and Large Magellanic Cloud extinction curves and by the lack of the so-called UV bump corresponding to the 2175 Å absorption feature. This recipe was originally built to be consistent with the properties of the nearby starburst galaxies analyzed by Calzetti et al (1994) but both recipes differ substantially in the visible to near-IR (NIR; Chevallard et al 2013; Lo Faro et al 2017; Malek et al 2018)
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