Evidence for an extended neutral Galactic halo

Abstract

view Abstract Citations (9) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Evidence for an Extended Neutral Galactic Halo Albert, C. E. ; Welsh, B. Y. ; Danly, L. Abstract Singly ionized titanium is the dominant ionization stage in H I regions and provides an excellent tracer of the neutral interstellar medium. Here we present new interstellar Ti II absorption line observations toward six halo stars located at absolute value of z greater than 1 kpc. Although the gas distribution is probably patchy, significant neutral gas does exist beyond 1 kpc from the Galactic plane and the projected column density, N(Ti II) sin (b), continues to increase out to the most distant star observed, at z = 8.7: kpc. Along this line of sight, the Ti II absorption is the strongest yet detected and also has the highest gas-phase abundance of titanium seen in interstellar gas. Ti II absorption observed toward halo stars may arise from a new component of the halo interstellar medium which contains low column density neutral gas over a wide velocity range and which may extend beyond several H I scale heights from the plane. The scale height of this component has yet to be determined, but could be well beyond several kpc, coincident with or even farther than the highly ionized gas observed in C IV and Si IV. Observations toward a large sample of extragalactic sources are needed to determine the actual scale height of neutral halo gas. Publication: The Astrophysical Journal Pub Date: December 1994 DOI: 10.1086/174989 Bibcode: 1994ApJ...437..204A Keywords: Abundance; Atomic Spectra; Early Stars; Galactic Halos; H I Regions; Interstellar Gas; Titanium; Ultraviolet Astronomy; Absorption Spectra; Astronomical Spectroscopy; Ionized Gases; Line Spectra; Astronomy; GALAXY: HALO; ISM: ABUNDANCES full text sources ADS | data products SIMBAD (7)