DUST EXTINCTION FROM BALMER DECREMENTS OF STAR-FORMING GALAXIES AT 0.75 ⩽<i>z</i>⩽ 1.5 WITH<i>HUBBLE SPACE TELESCOPE</i>/WIDE-FIELD-CAMERA 3 SPECTROSCOPY FROM THE WFC3 INFRARED SPECTROSCOPIC PARALLEL SURVEY

Abstract

Spectroscopic observations of Halpha and Hbeta emission lines of 128\nstar-forming galaxies in the redshift range 0.75&lt;z&lt;1.5 are presented. These\ndata were taken with slitless spectroscopy using the G102 and G141 grisms of\nthe Wide-Field-Camera 3 (WFC3) on board the Hubble Space Telescope as part of\nthe WFC3 Infrared Spectroscopic Parallel (WISP) survey. Interstellar dust\nextinction is measured from stacked spectra that cover the Balmer decrement\n(Halpha/Hbeta). We present dust extinction as a function of Halpha luminosity\n(down to 3 x 10^{41} erg/s), galaxy stellar mass (reaching 4 x 10^{8} Msun),\nand rest-frame Halpha equivalent width. The faintest galaxies are two times\nfainter in Halpha luminosity than galaxies previously studied at z~1.5. An\nevolution is observed where galaxies of the same Halpha luminosity have lower\nextinction at higher redshifts, whereas no evolution is found within our error\nbars with stellar mass. The lower Halpha luminosity galaxies in our sample are\nfound to be consistent with no dust extinction. We find an anti-correlation of\nthe [OIII]5007/Halpha flux ratio as a function of luminosity where galaxies\nwith L_{Halpha}&lt;5 x 10^{41} erg/s are brighter in [OIII]5007 than Halpha. This\ntrend is evident even after extinction correction, suggesting that the\nincreased [OIII]5007/Halpha ratio in low luminosity galaxies is likely due to\nlower metallicity and/or higher ionization parameters.\n