SIMBAD references

We present, for the first time, a systematic study of quasar-associated 2175 Å dust absorbers using spectroscopic data from the Sloan Digital Sky Survey Data Release 16 (DR16). By analyzing the optical spectra and multiband magnitudes of 557,674 quasars in the redshift range of 0.7 ≤ z ≤ 2.4, we identify 843 absorbers that share the same redshifts as quasars and are believed to originate from dust in the quasar nuclei, the host galaxies, or their surrounding environments. These absorbers exhibit weak bump strengths (A_bump = 0.49 ± 0.15 μm^–1) and narrow widths (γ = 0.81 ± 0.14 μm^–1), while their peak positions span a broad range from x₀ = 4.2 to 4.84 μm^–1. Their average extinction curves resemble those of the Large Magellanic Cloud but exhibit a shallower slope. In broad-absorption-line quasars, the absorption bumps show systematic shifts in peak positions. Although further confirmation is needed, this may suggest environmental differences in dust grain properties. We find a statistically significant negative correlation between the bump strength and redshift, suggesting possible evolution in dust properties. These findings highlight the changing composition and physical conditions of dust in quasar environments, likely influenced by factors such as metallicity, radiation fields, and dust-processing mechanisms. Future studies incorporating ultraviolet and infrared data will be essential for refining the dust evolution models. Machine learning techniques and high-resolution spectroscopic follow-ups could enhance the sample completeness and provide deeper insights into the chemical properties of the dust absorbers.