Spatial Variations of Galaxy Number Counts in the Sloan Digital Sky Survey. II. Test of Galactic Extinction in High Extinction Regions

TL;DR

This study tests the accuracy of the Schlegel, Finkbeiner, & Davis (1998) Galactic extinction map using galaxy counts from SDSS, confirming its reliability at low extinction but overestimation at higher extinction regions.

Contribution

It provides an empirical validation of the extinction map across different Galactic regions, highlighting its limitations in high extinction areas.

Findings

Map agrees with galaxy counts at low extinction

Overestimates reddening by up to 1.4 in high extinction regions

Results align with previous analyses of dark cloud complexes

Abstract

Galactic extinction is tested using galaxy number counts at low Galactic latitude obtained from five band photometry of the Sloan Digital Sky Survey. The spatial variation of galaxy number counts for low extinction regions of $E(B-V) < 0.15$ is consistent with the all-sky reddening map of Schlegel, Finkbeiner, & Davis (1998) and the standard extinction law. For higher extinction regions of $E(B-V) > 0.15$, however, the map of Schlegel et al.(1998) overestimates the reddening by a factor up to 1.4, which is likely ascribed to the departure from proportionality of reddening to infrared emissivity of dust. This result is consistent with the analysis of Arce & Goodman (1999) for the Taurus dark cloud complex.