The Strength of the 2175 Å Feature in the Attenuation Curves of Galaxies at 0.1 <  z ≲ 3

Abstract

We update the spectral modeling code MAGPHYS to include a 2175Å absorption feature in its UV-tonear-IR dust attenuation prescription. This allows us to determine the strength of this feature and the shape of the dust attenuation curve in ∼5000 star-forming galaxies at 0.1 < z 3 in the COSMOS field. We find that a 2175Å absorption feature of ∼1/3 the strength of that in the Milky Way is required for models to minimize residuals. We characterize the total effective dust attenuation curves as a function of several galaxy properties and find that the UV slopes of the attenuation curve for COSMOS galaxies show a strong dependence with star formation rate (SFR) and total dust attenuation (A V ), such that galaxies with higher SFR and A V have shallower curves and vice versa. These results are consistent with expectations from radiative transfer that attenuation curves become shallower as the effective dust optical depth increases. We do not find significant trends in the strength of the 2175Å absorption feature as a function of galaxy properties, but this may result from the high uncertainties associated with this measurement. The updated code is publicly available online.Corresponding author: A. J. Battisti andrew.battisti@anu.edu.au 1 We define attenuation to be a combination of extinction, scattering of light into the line of sight by dust, and geometrical effects due to the star-dust geometry. Extinction is the absorption and scattering of light out of the line of sight by dust, which has no dependence on geometry. Unlike extinction curves, the geometric effects in attenuation make it difficult to interpret the physical properties of dust from attenuation curves.

Revisiting Attenuation Curves: the Case of NGC 3351

“…The normalization 13 , R (V)=4.93 ± 0.37, is much larger than most extinction curves (typically with R(V)=3.1 or smaller, with few exceptions), and larger than the value found for many attenuation curves, including the SB one (R (V)=4.05±0.80 Calzetti et al 2000). However, this is consistent with the R (V) values found by Battisti et al (2020) for z>1 galaxies. When normalized to k(λ)/k(V)=1, the FUV slope in equation 8 is close to that of the MW extinction curve, and in-between those of the SB attenuation and SMC extinction curves (Figure 15, right).…”

Dependence of the IRX-β Dust Attenuation Relation on Metallicity and Environment *

“…Observations have shown that the IRX-β relation varies with stellar mass (Bouwens et al 2016(Bouwens et al , 2020Reddy et al 2018;Fudamoto et al 2020), infrared (IR) luminosity (Buat et al 2012;Casey et al 2014), age (Siana et al 2009;Reddy et al 2010;Shivaei et al 2015), redshift (Capak et al 2015;Pannella et al 2015), and intrinsic β 0 (β for a dust-free system; Boquien et al 2012;Reddy et al 2018;Schulz et al 2020). These variations are linked to the diversity of galaxies' attenuation curves, seen in previous studies (e.g., Kriek & Conroy 2013;Scoville et al 2015;Battisti et al 2020). The attenuation curve variations stem from two main sources: (a) different geometrical distributions of dust with respect to stars (and different dust optical depths), and (b) different dust grain properties, which affect the shape of the underlying extinction curve irrespective of the dust-star geometry (see the review by Salim & Narayanan 2020).…”

“…UV luminosity and β-To derive the UV continuum slope, β, and UV luminosity density (L ν ) at 1600 Å, we fit a power law to the photometry at rest-frame λ=1260-2600 Å, f λ ∝λ β (COSMOS and UDS have good rest-UV coverage with at least four photometric points in this range). We avoid the wavelength range of λ=1950-2400 Å, as it may potentially be affected by the 2175 Å UV bump, seen in the attenuation curve of highmetallicity galaxies at these redshifts (Scoville et al 2015;Battisti et al 2020;Shivaei et al 2020). Hereafter, νL ν at 1600 Å is referred to as UV luminosity, L(UV).…”

Investigating the delay between dust radiation and star-formation in local and distant quenching galaxies

“…) that can be used to handle the attenuation of old and young populations and thus change the effective attenuation law (e.g., Battisti et al 2020). The difference in dust geometry is therefore handled through this parameter.…”