The COS/UVES Absorption Survey of the Magellanic Stream. III. Ionization, Total Mass, and Inflow Rate onto the Milky Way

Type Journal Article
Names Andrew J. Fox, Bart P. Wakker, Kathleen A. Barger, Audra K. Hernandez, Philipp Richter, Nicolas Lehner, Joss Bland-Hawthorn, Jane C. Charlton, Tobias Westmeier, Christopher Thom, Jason Tumlinson, Toru Misawa, J. Christopher Howk, L. Matthew Haffner,
Publication The Astrophysical Journal
Volume 787
Issue 2
Pages 147
Journal Abbreviation The Astrophysical Journal
Date June 1, 2014
DOI 10.1088/0004-637X/787/2/147
ISSN 0004-637X
Library Catalog
Abstract Dynamic interactions between the two Magellanic Clouds have flung large quantities of gas into the halo of the Milky Way. The result is a spectacular arrangement of gaseous structures, including the Magellanic Stream, the Magellanic Bridge, and the Leading Arm (collectively referred to as the Magellanic System). In this third paper of a series studying the Magellanic gas in absorption, we analyze the gas ionization level using a sample of 69 Hubble Space Telescope/Cosmic Origins Spectrograph sightlines that pass through or within 30° of the 21 cm emitting regions. We find that 81% (56/69) of the sightlines show UV absorption at Magellanic velocities, indicating that the total cross-section of the Magellanic System is ≈11,000 deg2, or around one-quarter of the entire sky. Using observations of the Si III/Si II ratio together with Cloudy photoionization modeling, we calculate the total gas mass (atomic plus ionized) of the Magellanic System to be ≈2.0 × 109 M ⊙ (d/55 kpc)2, with the ionized gas contributing around three times as much mass as the atomic gas. This is larger than the current-day interstellar H I mass of both Magellanic Clouds combined, indicating that they have lost most of their initial gas mass. If the gas in the Magellanic System survives to reach the Galactic disk over its inflow time of ~0.5-1.0 Gyr, it will represent an average inflow rate of ~3.7-6.7 M ⊙ yr-1, potentially raising the Galactic star formation rate. However, multiple signs of an evaporative interaction with the hot Galactic corona indicate that the Magellanic gas may not survive its journey to the disk fully intact and will instead add material to (and cool) the corona. Based on observations taken under programs 11520, 11524, 11541, 11585, 11598, 11632, 11686, 11692, 12025, 12029, 12038, 12172, 12204, 12212, 12248, 12263, 12264, 12275, 12533, 12536, 12569, 12593, and 12604 of the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Tags Galaxy: evolution, Galaxy: halo, ISM: ABUNDANCES, MAGELLANIC CLOUDS, quasars: absorption lines
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