Nebular Attenuation in H\alpha-selected Star-forming Galaxies at z=0.8 from the NewH\alpha\ Survey

TL;DR

This study measures dust attenuation in H-alpha-selected star-forming galaxies at z=0.8, finding that their attenuation properties are similar to local galaxies, using spectroscopic data from the NewHalpha survey.

Contribution

First measurement of dust attenuation in H-alpha-selected galaxies at z=0.8 using Balmer line ratios, demonstrating consistency with local universe relations.

Findings

Median attenuation at H-alpha is 0.9 mag, similar to local galaxies.

Attenuation correlates with magnitude, mass, and SFR as in the local universe.

At least 5% of the sample are AGN, with 2% being composite sources.

Abstract

We present measurements of the dust attenuation of H\alpha-selected emission-line galaxies at z=0.8 from the NewH\alpha\ narrowband survey. The analysis is based on deep follow-up spectroscopy with Magellan/IMACS, which captures the strong rest-frame optical emission lines from [OII] \lambda 3727 to [OIII] \lambda 5007. The spectroscopic sample used in this analysis consists of 341 confirmed H\alpha\ emitters. We place constraints on the AGN fraction using diagnostics which can be applied at intermediate redshift. We find that at least 5% of the objects in our spectroscopic sample can be classified as AGN 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 H\beta\ and H\gamma\ pair of lines is detected with S/N>5 in 55 individual objects and the H\beta\ and H\delta\ 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 H\alpha\ based on the objects with individually detected lines is A(H\alpha)=0.9+-1.0 magnitudes, 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 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.