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Abstract: A substantial fraction of the light emitted from young or star-forminggalaxies at ultraviolet to near-infrared wavelengths comes from the ionizedinterstellar medium in the form of emission lines and a nebular continuum. Athigh redshifts, star formation rates are on average higher and stellarpopulations younger than in the local Universe. Both of these effects act toboost the impact of nebular emission on the overall spectrum of galaxies. Evenso, the broadband fluxes and colours of high-redshift galaxies are routinelyanalyzed under the assumption that the light observed originates directly fromstars. Here, we assess the impact of nebular emission on broadband fluxes inJohnson-Cousins BVRIJHK, Sloan Digital Sky Survey griz and Spitzer IRAC-MIPSfilters as a function of observed redshift up to z=15 for galaxies withdifferent star formation histories. We find that nebular emission may accountfor a non-negligible fraction of the light received from high-redshiftgalaxies. The ages and masses inferred for such objects through the use ofspectral evolutionary models that omit the nebular contribution are thereforelikely to contain systematic errors. We argue that a careful treatment of thenebular component will be essential for the interpretation of the rest-frameultraviolet-to-infrared properties of the first galaxies formed, like the onesexpected to be detected with the James Webb Space Telescope.

Autor: E. Zackrisson, N. Bergvall, E. Leitet


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