A Deep Search for Diffuse Interstellar Band 4430Å in the Circumgalactic Medium

We investigate the absorption signals of one of the strongest diffuse interstellar bands, DIBλ4430, 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 mÅ. By using MgII absorption strength and dust reddening relation from the literature, we measure the DIBλ4430 absorption strength as a function of E(B-V) in the CGM, and compare the Milky Way DIBλ4430-E(B-V) relation extrapolated down to the CGM E(B-V) region. Our results show no detectable signals of DIBλ4430 across the entire E(B-V) range in the CGM traced by MgII absorption lines. This lack of detection of DIBλ4430 in the CGM is inconsistent with the Milky Way signals by ∼5 σ, indicating that the factors associated with different environments affect the abundance of the DIBλ4430 carrier.