Reverse-engineering galaxy spectra to decode the IRX-β relation at intermediate redshift

In galaxies, different components interact with each other on various timescales. An example of such interaction is the interplay between young and as well evolved stars with dust. This complex interplay influences the total spectra of galaxies. Dust affects the shape of the spectral energy distribution (SED) like no other component, despite its low  contribution  to  the  overall mass  of the  baryonic  matter.  At  higher  redshifts,  the  challenging  measurements  of  FIR emission  are  overpowered  by  the  easily  available  rest-frame UV  emission. This in turn limits the wavelength range from which the physical properties are inferred, therefore, a correct understanding  of physical processes  that prevail at short wavelength domain,  like  dust attenuation,  becomes  critical. Observationally, many galaxies seem to follow what is known as the IRX-β relation, which links heavily-attenuated UV spectral slope (β) and the IR excess of galaxies characterised by the ratio between the IR (mainly dust)  and UV (mostly composed of young stars) luminosities (L(FIR)/L(UV)). However, this relation is not universal, and outliers for it are often encountered.

Understanding such relation and its connection to dust attenuation properties will help us uncover and understand the role of dust, and its attenuation at higher redshifts.

Our study used a unique dataset from the "VIMOS Public Extragalactic Redshift Survey" (VIPERS), which mapped in detail 24 deg2 of the sky sampling galaxies at redshift~0.7.    We use the robust Oii, Oiii, and Hβ line detections of our statistical sample from VIPERS to estimate the gas-phase metallicities at the redshift range 0.5<z<0.9. We derive key physical properties that are necessary to study galaxy evolution, such as the stellar masses and the star formation rates, from the SED fitting tool CIGALE.

We find a strong dependence of the IRX-β relation on gas-phase metallicity in our sample and dependencies on stellar properties of galaxies like stellar ages, stellar masses, and specific star formation rates. We have also checked morphological parameters, and we find that  the compactness of our sources characterised by the Sérsic indexes is also sensitive to the location on the IRX-β  plane.