NEBULAR ATTENUATION IN Hα-SELECTED STAR-FORMING GALAXIES AT z = 0.8 FROM THE NewHα SURVEY

We present measurements of the dust attenuation of Hα-selected emission-line galaxies at z = 0.8 from the NewHα narrowband survey. The analysis is based on deep follow-up spectroscopy with Magellan/IMACS, which captures the strong rest-frame optical emission lines from [O ii] λ3727 to [O iii] λ5007. The spectroscopic sample used in this analysis consists of 341 confirmed Hα emitters. We place constraints on the active galactic nucleus (AGN) fraction using diagnostics that can be applied at intermediate redshift. We find that at least 5% of the objects in our spectroscopic sample can be classified as AGNs and 2% are composite, i.e., powered by a combination of star formation and AGN activity. We measure the dust attenuation for individual objects from the ratios of the higher order Balmer lines. The Hβ and Hγ pair of lines is detected with S/N > 5 in 55 individual objects and the Hβ and Hδ pair is detected in 50 individual objects. We also create stacked spectra to probe the attenuation in objects without individual detections. The median attenuation at Hα based on the objects with individually detected lines is A(Hα) = 0.9 ± 1.0 mag, in good agreement with the attenuation found in local samples of star-forming galaxies. We find that the z = 0.8 galaxies occupy a similar locus of attenuation as a function of magnitude, mass, and star formation rate (SFR) as a comparison sample drawn from the SDSS DR4. Both the results from the individual z = 0.8 galaxies and from the stacked spectra show consistency with the mass–attenuation and SFR–attenuation relations found in the local universe, indicating that these relations are also applicable at intermediate redshift.