Spiral Disk Opacity from Occulting Galaxy Pairs in the Sloan Digital Sky Survey

TL;DR

This study uses SDSS data to measure dust extinction in spiral galaxy disks through occulting pairs, finding no significant evolution in opacity up to redshift 0.2, but highlighting the need for higher resolution data.

Contribution

It demonstrates the effectiveness of SDSS spectral data in identifying occulting galaxy pairs for dust extinction studies and assesses the evolution of disk opacity over recent cosmic time.

Findings

Spiral disks show extinction to ~2 effective radii.

No evidence of recent evolution in disk opacity up to z=0.2.

SDSS spectral catalog is effective for finding occulting pairs.

Abstract

A spiral galaxy partially ovelapping a more distant elliptical offers an unique opportunity to measure the dust extinction in the foreground spiral. From the Sloan Digital Sky Survey DR4 spectroscopic sample, we selected 83 occulting galaxy pairs and measured disk opacity over the redshift range z = 0.0-0.2 with the goal to determine the recent evolution of disk dust opacity. The enrichment of the ISM changes over the lifetime of a disk and it is reasonable to expect the dust extinction properties of spiral disks as a whole to change over their lifetime. When they do, the change will affect our measurements of galaxies over the observable universe. From the SDSS pairs we conclude that spiral disks show evidence of extinction to ~2 effective radii. However, no evidence for recent evolution of disk opacity is evident, due to the limited redshift range and our inability to distinguish other factors on disk opacity such as the presence of spiral arms and Hubble type. Such effects also mask any relation between surface brightness and optical depth that has been found in nearby galaxies. Hence, we conclude that the SDSS spectral catalog is an excellent way to find occulting pairs and construct a uniform local sample. However, higher resolution than the SDSS images is needed to disentangle the effects of spiral arms and Hubble type from evolution since z = 0.2.