Radial dependence of the ratio of FeII to MgII equivalent widths in emission-line galaxies

The circumgalactic medium (CGM) plays a key role in galaxy evolution by regulating gas accretion, feedback, and metal enrichment, with its chemical evolution and metal distribution revealed through quasar absorption line studies. Using data from Sloan Digital Sky Survey extended Baryon Oscillation Spectroscopic Survey (SDSS/eBOSS), we constructed a dataset comprising 853 quasar-emission-line-galaxy (quasar-ELG) pairs with an impact parameter (d_̊m p) within 150 ̨pc. We then analyzed the variations in the ratio of the equivalent widths of the absorption line to the absorption line as a function of the impact parameter. To achieve this aim, we employed a spectral stacking method to generate median composite spectra in the rest frame of the foreground ELGs. Subsequently, we measured the equivalent widths of the ̊m r ̊m łambda2600) and ̊m r ̊m łambda2796) absorption lines in these composite spectra. Our results indicate that the equivalent width ratio of R (≡ W_ ̊m r ̊m łambda2600 /W_ ̊m r ̊m łambda2796) varies as R ∝ (-0. 64^) łog (d_ ̊m p ̨pc). Finally, we explored the potential causes and implications of this radial dependence.