Embedded Files
Dust opacity and FUV star formation rate measurements of disk galaxies over the past 6 billion years.
Dust opacity and FUV star formation rate measurements of disk galaxies over the past 6 billion years.
Disk opacity comes from dust in the galaxies and depends on the amount and properties of the dust and its relative spatial distribution. We probe the opacity of disks by comparing the light from galaxies at different inclination angles. For edge-on disks, the photons have to travel through more medium before we can observe them, so they are more likely to be scattered or absorbed by dust along the line of sight. So edge-on galaxies are dimmer than face-on galaxies in optical or UV wavelengths. We can use this inclination dependency to constrain the optical depth and also the clumpiness of the dust by fitting a simple radiative transfer model (Tuffs et al. 2004).
Ultra-violet attenuation has increased between z∼0 and z∼0.7, with the z∼0.7 sample being a factor of ∼3.4 more attenuated. A higher fraction of clumpy dust around nascent star-forming regions can explain the more substantial UV attenuation at z∼0.7 (Leslie et al. 2018a).
We also evaluated dust-corrected far ultraviolet (FUV) star formation rates (SFRs) from a hybrid mid-infrared (MIR) plus FUV relation, UV-slope, and from a radiative transfer based attenuation correction method. We assessed the performances of the attenuation correction methods by their ability to remove the dependency of the corrected SFR on inclination, as well as returning, on average, the expected population mean SFR. We find that combining MIR (rest-frame ∼13μm) and FUV luminosities gives the most inclination independent SFRs and reduces the intrinsic SFR scatter out of the methods tested (Leslie et al. 2018b).
Top left: Evolution of the fraction of SFR activity observed in FUV (FUV attenuation) for massive (log(M)>10.2) galaxies. Right: observed FUV-SFR as a function of galaxy inclination at z~0.1 (top) and at z~0.7 (bottom). Attenuation is inclination dependent and massive galaxies at z~0.7 suffer more attenuation. Blue lines show best fit Tuffs+2004 models. Grey bands are observational limits (Leslie+2018a)
In van der Giessen et al. 2022, we update the work of Leslie et al. 2018 by using multiwavelength fluxes from FUV to NIR, inclination, and other structural properties for two samples at 0.04<z<0.1 in SDSS and GAMA (13.5 Gyr after the Big Bang), and one at 0.6<z<0.8 in the COSMOS field (7 Gyr after the Big Bang). With this updated method we find that the optical depth and clumpiness are higher in galaxies at z~0.7, both by factor ~1.7.
We look at these average global dust properties in galaxies as a function of stellar mass, stellar mass surface density, the star-formation rate, specific star-formation rate, the star-formation main-sequence offset, and the star-formation rate surface density. We found that the optical depth increases with stellar mass and stellar mass surface density at both redshift ~0 and z~0.7. We found no clear trends in optical depth or clumpiness with the SFR, which could imply that the dust mass distribution is independent of the SFR. In turn, this would imply that the balance of dust formation and destruction is independent of the SFR.
Based on an analysis of the inclination dependence of the Balmer decrement, we found that reproducing the Balmer line emission requires not only a completely optically thick dust component associated with star-forming regions, as in the standard model, but an extra component of an optically thin dust within the birth clouds. This new component implies the existence of dust inside HII regions that attenuates the Balmer emission before it escapes through gaps in the birth cloud and we found it is more important in high-mass galaxies.
Our results imply that dust properties are dependent on global galaxy properties, redshift, and properties of HII regions. Future work with ALMA and JWST will better determine the dust structures of galaxies at higher redshift.
Google Sites
Report abuse