¹Viacheslav V. Klimenko, ¹Varsha P. Kulkarni, ²Monique C. Aller
The Astrophysical Journal, 1003, 129
Open Access Link to Article [DOI: 10.3847/1538-4357/ae5659]
¹Department of Physics & Astronomy, University of South Carolina, Columbia, SC 29208, USA
²Department of Biochemistry, Chemistry, & Physics, Georgia Southern University, Statesboro, GA 30458, USA

We present results from a mini-survey of dust spectral features arising in galaxies at redshifts 0.5 < z < 1.2 in our James Webb Space Telescope (JWST) mid-infrared spectra of physically unrelated background quasars. We analyze the JWST Mid-infrared Instrument Medium-Resolution Spectrometer spectra of five quasars presented in Klimenko et al. (Paper I) to determine the best-fit silicate mineralogies. Template profile fits to the 10 μm feature suggest the possible presence of crystalline silicates in three of the galaxies. This contrasts with the predominately amorphous silicate grains in the Milky Way diffuse interstellar medium (ISM). We also measure the extinction curves using existing data from UV to mid-IR. Combining our results with past Spitzer IRS studies, we find the following: (i) the 10 μm silicate peak optical depth (τ 10 diffuse ISM over the range A V =0.1–2.0, with τ 10 /A V ) is about 3 times stronger than expected for the local =0.17 ± 0.09. (ii) The relative strength of the UV bump is similar to that in the local ISM. However, the ratio τ 10 approaching the Galactic ISM value (∼0.1) at A V /A 2175 is larger (∼0.1–1), and appears to decrease with A ∼1.5–2. (iii) There is no significant correlation of τ R V . (iv) τ 10 is strongly correlated with the gas-phase Mg II V , 10 /A V with absorption strength for the quasar sightlines. Possible interpretations include that some quasar sightlines probe dust in the circumgalactic medium (CGM), and that dust grains may have been significantly reprocessed in the ISM and CGM under conditions that may differ from those in the local ISM.