The COS/UVES absorption survey of the Magellanic stream. III. Ionization, total mass, and inflow rate onto the Milky Way
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Department of Astronomy, University of Wisconsin-Madison, 475 North Charter Street, Madison, WI 53706 (United States)
- Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States)
- Institut für Physik und Astronomie, Universität Potsdam, Haus 28, Karl-Liebknecht-Strasse 24/25, D-14476, Potsdam (Germany)
- Institute of Astronomy, School of Physics, University of Sydney, Sydney, NSW 2006 (Australia)
- Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)
- ICRAR, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009 (Australia)
- School of General Education, Shinshu University, 3-1-1 Asahi, Matsumoto, Nagano 390-8621 (Japan)
- Department of Physics and Astronomy, York University, 4700 Keele Street, Toronto, ON M3J 1P3 (Canada)
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 deg{sup 2}, 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 × 10{sup 9} M {sub ☉} (d/55 kpc){sup 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 {sub ☉} yr{sup –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.
- OSTI ID:
- 22356763
- Journal Information:
- Astrophysical Journal, Vol. 787, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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