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

Abstract

We present measurements of the dust attenuation of H\\alpha-selected\nemission-line galaxies at z=0.8 from the NewH\\alpha\\ narrowband survey. The\nanalysis is based on deep follow-up spectroscopy with Magellan/IMACS, which\ncaptures the strong rest-frame optical emission lines from [OII] \\lambda 3727\nto [OIII] \\lambda 5007. The spectroscopic sample used in this analysis consists\nof 341 confirmed H\\alpha\\ emitters. We place constraints on the AGN fraction\nusing diagnostics which can be applied at intermediate redshift. We find that\nat least 5% of the objects in our spectroscopic sample can be classified as AGN\nand 2% are composite, i.e. powered by a combination of star-formation and AGN\nactivity. We measure the dust attenuation for individual objects from the\nratios of the higher order Balmer lines. The H\\beta\\ and H\\gamma\\ pair of lines\nis detected with S/N&gt;5 in 55 individual objects and the H\\beta\\ and H\\delta\\\npair is detected in 50 individual objects. We also create stacked spectra to\nprobe the attenuation in objects without individual detections. The median\nattenuation at H\\alpha\\ based on the objects with individually detected lines\nis A(H\\alpha)=0.9+-1.0 magnitudes, in good agreement with the attenuation found\nin local samples of star-forming galaxies. We find that the z=0.8 galaxies\noccupy a similar locus of attenuation as a function of magnitude, mass and SFR\nas a comparison sample drawn from the SDSS DR4. Both the results from the\nindividual z=0.8 galaxies and from the stacked spectra show consistency with\nthe mass -- attenuation and SFR -- attenuation relations found in the local\nUniverse, indicating that these relations are also applicable at intermediate\nredshift.\n