Detection of cold atomic clouds in the Magellanic bridge.
KOBULNICKY H.A. and DICKEY J.M.
Abstract (from CDS):
We report a direct detection of cold atomic hydrogen in the Magellanic Bridge using 21 cm absorption spectroscopy toward the radio source B0312-770. With a maximum absorption optical depth of τ=0.10 and a maximum 21 cm emission brightness temperature of 1.4 K (NHI=1.2x1020 cm–2), this line of sight yields a spin temperature, Ts, between 20 and 40 K. H I 21 cm absorption and emission spectroscopy toward seven other low H I column density sight lines on the periphery of the LMC and SMC reveal absorption toward one additional background radio source behind the SMC with τ=0.03. The data have typical sensitivities of στ=0.005 to 0.070 in absorption and σTB=0.03 K in emission. These data demonstrate the presence of a cold atomic phase, which is probably accompanied by molecular condensations, in the tenuous interstellar medium of the Bridge region. Young OB stars observed in the Magellanic Bridge could form in situ from these cold condensations rather than migrate from regions of active star formation in the main body of the SMC. The existence of cold condensations and star formation in the Magellanic Bridge might be understood as a small-scale version of the mechanism that produces star formation in the tidal tails of interacting galaxies.