2018ApJ...865..145R

We present a new precision measurement of gas-phase abundances of S, O, N, Si, Fe, P, Al, Ca as well as molecular hydrogen (H₂) in the Leading Arm (region II, LA II) of the Magellanic Stream (MS) toward the Seyfert galaxy NGC 3783. The results are based on high-quality archival ultraviolet/optical/radio data from various different instruments (HST/STIS, FUSE, AAT, GBT, GB140 ft, ATCA). Our study updates previous results from lower-resolution data and provides for the first time a self-consistent component model of the complex multiphase absorber, delivering important constraints on the nature and origin of LA II. We derive a uniform, moderate α abundance in the two main absorber groups at +245 and +190 km s^–1 of α/H = 0.30 ± 0.05 solar, a low nitrogen abundance of N/H = 0.05 ± 0.01 solar, and a high dust content with substantial dust depletion values for Si, Fe, Al, and Ca. These α, N, and dust abundances in LA II are similar to those observed in the Small Magellanic Cloud (SMC). From the analysis of the H₂ absorption, we determine a high thermal pressure of P/k ≃ 1680 K cm^–3 in LA II, in line with the idea that LA II is located in the inner Milky Way halo at a z-height of <20 kpc, where it hydrodynamically interacts with the ambient hot coronal gas. Our study supports a scenario in which LA II stems from the breakup of a metal- and dust-enriched progenitor cloud that was recently (200-500 Myr ago) stripped from the SMC.