A Deep Search for a Strong Diffuse Interstellar Band in the Circumgalactic Medium

Abstract

We investigate the absorption signals of a strong diffuse interstellar band, DIB$\lambda 4430$, in the circumgalactic medium (CGM) traced by MgII absorption lines. To this end, we make use of approximately 60,000 MgII absorption line spectra within $0.4<z<1.0$ compiled from the Sloan Digital Sky Surveys and obtain composite spectra with uncertainties for absorption line measurements being a few m$\tilde{A}$. By using MgII absorption strength and dust reddening relation from the literature, we measure the DIB$\lambda 4430$ absorption strength as a function of $\mathrm{E}(\mathrm{B}-\mathrm{V})$ in the CGM, and compare the Milky Way DIB$\lambda 4430$ - $\mathrm{E}(\mathrm{B}-\mathrm{V})$ relation extrapolated down to the CGM $\mathrm{E}(\mathrm{B}-\mathrm{V})$ region. Our results show no detectable signals of DIB$\lambda 4430$ across the entire $\mathrm{E}(\mathrm{B}-\mathrm{V})$ range in the CGM traced by MgII absorption lines. This lack of detection of DIB$\lambda 4430$ in the CGM is inconsistent with the Milky Way signals by $\sim 5\ddot{I}ƒ$, indicating that the factors associated with different environments affect the abundance of the DIB$\lambda 4430$ carrier.

7 pages, 2 figures, comments and suggestions are welcome