Extinction in Star-Forming Disk Galaxies From Inclination-Dependent Composite Spectra

Abstract

Extinction in galaxies affects their observed properties. In scenarios describing the distribution of dust and stars in individual disk galaxies, the amplitude of the extinction can be modulated by the inclination of the galaxies. In this work we investigate the inclination dependency in composite spectra of star-forming disk galaxies from the Sloan Digital Sky Survey Data Release 5. In a volumelimited sample within a redshift range 0.065 − 0.075 and a r-band Petrosian absolute magnitude range -19.5 to -22 mag which exhibits a flat distribution of inclination, the inclined relative to face-on extinction in the stellar continuum is found empirically to increase with inclination in the g, r and i bands. Within the central 0.5 intrinsic half-light radius of the galaxies, the g-band relative extinction in the stellar continuum for the highly-inclined objects (axis ratio b/a = 0.1) is 1.2 mag, agreeing with previous studies. The extinction curve of the disk galaxies is given in the restframe wavelengths 3700 −8000Å, identified with major optical emission and absorption lines in diagnostics. The Balmer decrement, Hα/Hβ, remains constant with inclination, suggesting a different kind of dust configuration and/or reddening mechanism in the H II region from that in the stellar continuum. One factor is shown to be the presence of spatially non-uniform interstellar extinction, presumably caused by clumped dust in the vicinity of the H II region.

Characterizing Dust Attenuation in Local Star-forming Galaxies: Inclination Effects and the 2175 Å Feature

“…In the scenario in which a foreground-like dust component is dominating the attenuation, the optical depth is expected to behave according to t at lower b/a is evident, as seen in previous studies (e.g., Yip et al 2010;Chevallard et al 2013). For reference, if we assume the ionized gas experiences an extinction curve similar to the MW (R V =3.1), the values of 0.4 B l t = and 0.6 (∼68% and 95% upper boundary) correspond to A 1.07 V,gas = and 1.61, respectively (using Equation (3)).…”

“…Numerous optical and NIR studies have examined the influence that inclination has on the attenuation and observed galaxy properties by comparing more inclined galaxies to faceon galaxies, under the assumption that the intrinsic properties are independent of inclination (e.g., Disney et al 1989;Giovanelli et al 1994Giovanelli et al , 1995Masters et al 2003Masters et al , 2010Driver et al 2007;Unterborn & Ryden 2008;Maller et al 2009;Yip et al 2010). These studies find that the stellar continuum of edge-on galaxy disks suffers up to 1mag of additional attenuation in the B or g band, relative to face-on galaxies.…”

Probing star formation and ISM properties using galaxy disk inclination

“…Authors such as Yip et al (2010);Huizinga & van Albada (1992); Möllenhoff et al (2006); Masters et al (2010) and Conroy et al (2010) have all previously reported that galaxy size measurements (such as half-light or effective radius) are dependent on galaxy axis ratio b/a, with edge-on galaxies appearing larger at a fixed magnitude. Our local results are consistent with results from Möllenhoff et al (2006) who show that the B-band sizes increase by 10-40% from face-on to edge-on due to a reduction of the light concentration by centrally concentrated dust in local galaxies.…”

Effect of Inclination of Galaxies on Photometric Redshift

“…The effect of the inclination on disk galaxies is twofold: the reddening and the extinction on its spectral energy distribution, supported by many of the recent studies based on large samples of galaxies (e.g., Masters et al 2003Masters et al , 2010Driver et al 2007;Shao et al 2007;Bailin & Harris 2008;Unterborn & Ryden 2008;Padilla & Strauss 2008;Maller et al 2009;Yip et al 2010;Conroy et al 2010). If these effects are not corrected for, one would expect an impact on the derived properties of the galaxies.…”

“…We therefore encourage the interpolation to the actual data listed in Table 2 when higher-accuracy corrections are required. We choose Equation (6) for the purpose of a direct comparison with literature (e.g., Unterborn & Ryden 2008;Yip et al 2010), in which the powers of log 10 (b/a) have been considered. Only even integers are allowed in the power index because log 10 (b/a) is negative for all b/a values except unity.…”