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

TL;DR

This study searches for the diffuse interstellar band DIBλ4430 in the circumgalactic medium using SDSS spectra but finds no detectable signals, suggesting environmental factors influence DIB carrier abundance.

Contribution

First comprehensive search for DIBλ4430 in the CGM using large SDSS dataset, establishing non-detection and environmental dependence of DIB carriers.

Findings

No DIBλ4430 detection in the CGM across all E(B-V) values.

Results are inconsistent with Milky Way DIB-E(B-V) relation by ~5 sigma.

Environmental factors likely affect DIB carrier presence in the CGM.

Abstract

We investigate the absorption signals of a strong diffuse interstellar band, DIB$\lambda4430$, 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$\r{A}$. By using MgII absorption strength and dust reddening relation from the literature, we measure the DIB$\lambda4430$ absorption strength as a function of $\rm E(B-V)$ in the CGM, and compare the Milky Way DIB$\lambda4430$ - $\rm E(B-V)$ relation extrapolated down to the CGM $\rm E(B-V)$ region. Our results show no detectable signals of DIB$\lambda4430$ across the entire $\rm E(B-V)$ range in the CGM traced by MgII absorption lines. This lack of detection of DIB$\lambda4430$ in the CGM is inconsistent with the Milky Way signals by $\sim 5 \, \sigma$, indicating that the factors associated with different environments affect the abundance of the DIB$\lambda4430$ carrier.