2025MNRAS.543.1429C

We investigate the absorption signals of one of the strongest diffuse interstellar bands, DIB$\lambda 4430$, in the circumgalactic medium (CGM) traced by Mg II absorption lines. To this end, we make use of approximately 60 000 Mg II 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 Mg II absorption strength and dust reddening relation from the literature, we measure the DIB$\lambda 4430$ absorption strength as a function of E(B - V) in the CGM, and compare the Milky Way DIB$\lambda 4430$ -E(B - V) relation extrapolated down to the CGM E(B - V) region. Our results show no detectable signals of DIB$\lambda 4430$ across the entire E(B - V) range in the CGM traced by Mg II absorption lines. This lack of detection of DIB$\lambda 4430$ 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$\lambda 4430$ carrier.