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Title: A LOW-METALLICITY MOLECULAR CLOUD IN THE LOWER GALACTIC HALO

We find evidence for the impact of infalling, low-metallicity gas on the Galactic disk. This is based on FUV absorption line spectra, 21 cm emission line spectra, and far-infrared (FIR) mapping to estimate the abundance and physical properties of IV21 (IVC135+54-45), a galactic intermediate-velocity molecular cloud that lies ∼300 pc above the disk. The metallicity of IV21 was estimated using observations toward the subdwarf B star PG1144+615, located at a projected distance of 16 pc from the cloud's densest core, by measuring ion and H I column densities for comparison with known solar abundances. Despite the cloud's bright FIR emission and large column densities of molecular gas as traced by CO, we find that it has a sub-solar metallicity of log (Z/Z{sub ☉}) = –0.43 ± 0.12 dex. IV21 is thus the first known sub-solar metallicity cloud in the solar neighborhood. In contrast, most intermediate-velocity clouds (IVC) have near-solar metallicities and are believed to originate in the Galactic Fountain. The cloud's low metallicity is also atypical for Galactic molecular clouds, especially in light of the bright FIR emission which suggest a substantial dust content. The measured I{sub 100{sub μm}}/N(H I) ratio is a factor of three below the average foundmore » in high latitude H I clouds within the solar neighborhood. We argue that IV21 represents the impact of an infalling, low-metallicity high-velocity cloud that is mixing with disk gas in the lower Galactic halo.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5] ;  [6]
  1. Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706 (United States)
  2. Department of Physics, University of Wisconsin-Whitewater, Whitewater, WI 53190 (United States)
  3. Argelander-Institut für Astronomie, Auf dem Hügel 71, D-53121 Bonn (Germany)
  4. National Radio Astronomy Observatory, Green Bank, WV 24944 (United States)
  5. Australian Astronomical Observatory, P.O. Box 296, Epping 1710 (Australia)
  6. Max-Planck-Institut für Radioastronomie (MPIfR), Auf dem Hügel 69, D-53121 Bonn (Germany)
Publication Date:
OSTI Identifier:
22270709
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 777; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABSORPTION SPECTRA; ASTRONOMY; ASTROPHYSICS; CARBON MONOXIDE; COMPARATIVE EVALUATIONS; DENSITY; DWARF STARS; HYDROGEN 1; MAPPING; METALS; MILKY WAY; ULTRAVIOLET RADIATION; VISIBLE RADIATION