ORIGIN(S) OF THE HIGHLY IONIZED HIGH-VELOCITY CLOUDS BASED ON THEIR DISTANCES
- Department of Physics, University of Notre Dame, 225 Nieuwland Science Hall, Notre Dame, IN 46556 (United States)
Previous Hubble Space Telescope and FUSE observations have revealed highly ionized high-velocity clouds (HVCs) or more generally low H I column HVCs along extragalactic sight lines over 70%-90% of the sky. The distances of these HVCs have remained largely unknown hindering from distinguishing a 'Galactic' origin (e.g., outflow, inflow) from a 'Local Group' origin (e.g., warm-hot intergalactic medium). We present the first detection of highly ionized HVCs in the Cosmic Origins Spectrograph spectrum of the early-type star HS 1914+7134 (l = 103 deg., b = +24 deg.) located in the outer region of the Galaxy at d {approx_equal} 14.9 kpc. Two HVCs are detected in absorption at v {sub LSR} = -118 and -180 km s{sup -1} in several species, including C IV, Si IV, Si III, Al II, C II, Si II, O I, but H I 21 cm emission is only seen at -118 km s{sup -1}. Within 17 deg. of HS 1914+7134, we found HVC absorption of low and high ions at similar velocities toward five extragalactic sight lines, suggesting that these HVCs are related. The component at -118 km s{sup -1} is likely associated with the outer arm of the Milky Way. The highly ionized HVC at -180 km s{sup -1} is possibly an HVC plunging at high speed onto the thick disk of the Milky Way. This is the second detection of highly ionized HVCs toward Galactic stars, supporting a 'Galactic' origin for at least some of these low H I column density HVCs.
- OSTI ID:
- 21301366
- Journal Information:
- Astrophysical Journal Letters, Vol. 709, Issue 2; Other Information: DOI: 10.1088/2041-8205/709/2/L138; Country of input: International Atomic Energy Agency (IAEA); ISSN 2041-8205
- Country of Publication:
- United States
- Language:
- English
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