An Optical Spectrum of the Diffuse Galactic Light from BOSS and IRIS

TL;DR

This study presents a detailed optical spectrum of the diffuse Galactic light, correlating sky intensity with infrared dust emission, revealing stellar population differences and evidence for extended red emission in the southern Galactic hemisphere.

Contribution

It provides the first large-sample optical spectrum of DGL, incorporating dust self-absorption effects and identifying luminescence features like ERE, advancing understanding of dust and stellar contributions to Galactic light.

Findings

Spectral features match stellar spectra

Detected differences in DGL between hemispheres

Identified evidence for extended red emission

Abstract

We present a spectrum of the diffuse Galactic light (DGL) between 3700 and 10,000 A, obtained by correlating optical sky intensity with far-infrared dust emission. We use nearly 250,000 blank-sky spectra from BOSS/SDSS-III together with IRIS-reprocessed maps from the IRAS satellite. The larger sample size compared to SDSS-II results in a factor-of-two increase in signal to noise. We combine these data sets with a model for the optical/far-infrared correlation that accounts for self-absorption by dust. The spectral features of the DGL agree remarkably well with features present in stellar spectra. There is evidence for a difference in the DGL continuum between the regions covered by BOSS in the northern and southern Galactic hemisphere. We interpret the difference at red wavelengths as the result of a difference in stellar populations, with mainly old stars in both regions but a higher fraction of young stars in the south. There is also a broad excess in the southern DGL spectrum over the prediction of a simple radiative transfer model, without a clear counterpart in the north. We interpret this excess, centered at ~6500 A, as evidence for luminescence in the form of extended red emission (ERE). The observed strength of the 4000 A break indicates that at most ~7% of the dust-correlated light at 4000 A can be due to blue luminescence. Our DGL spectrum provides constraints on dust scattering and luminescence independent of measurements of extinction.