Metallicity and Physical Conditions in the Magellanic Bridge

TL;DR

This study analyzes the metallicity and ionization state of the Magellanic Bridge's diffuse gas using UV spectra, revealing low metallicity and high ionization levels, and providing new insights into its physical conditions.

Contribution

First measurement of gas-phase metallicity in the Magellanic Bridge using UV spectra, showing it is significantly lower than current SMC metallicity and highly ionized.

Findings

Metallicity of the Bridge gas is [Z/H] ≈ -1.02 to -1.7.

The gas is approximately 70-90% ionized.

The density of the Bridge gas is less than 0.1 cm^-3.

Abstract

We present a new analysis of the diffuse gas in the Magellanic Bridge (RA>3h) based on HST/STIS E140M and FUSE spectra of 2 early-type stars lying within the Bridge and a QSO behind it. We derive the column densities of HI (from Ly\alpha), NI, OI, ArI, SiII, SII, and FeII of the gas in the Bridge. Using the atomic species, we determine the first gas-phase metallicity of the Magellanic Bridge, [Z/H]=-1.02+/-0.07 toward one sightline, and -1.7<[Z/H]<-0.9 toward the other one, a factor 2 or more smaller than the present-day SMC metallicity. Using the metallicity and N(HI), we show that the Bridge gas along our three lines of sight is ~70-90% ionized, despite high HI columns, logN(HI)=19.6-20.1. Possible sources for the ongoing ionization are certainly the hot stars within the Bridge, hot gas (revealed by OVI absorption), and leaking photons from the SMC and LMC. From the analysis of CII*, we deduce that the overall density of the Bridge must be low (<0.03-0.1 cm^-3). We argue that our findings combined with other recent observational results should motivate new models of the evolution of the SMC-LMC-Galaxy system.