Interstellar Titanium in the Galactic Halo

Abstract

We present observations of Ti~II~$\lambda 3384$ absorption towards 15 distant stars in the Galactic halo and the Magellanic Clouds. These new data extend existing surveys of the distribution of Ti${}^{+}$ to larger distances from the plane of the Galaxy than sampled previously, allowing the scale height of titanium to be determined for the first time. We find $h_{T{i}^{+}}=1.5\pm 0.2$~kpc, a value which although greater than those of other tracers of neutral gas, is not as large as had been suspected. We interpret the extended distribution of Ti${}^{+}$ as an indication that its severe depletion in interstellar clouds in the disk is reduced at the lower densities prevailing in the halo. The data are consistent with a simple power-law dependence of the Ti abundance on the ambient density, with exponent $k\simeq -1$. If the model is correct, it implies that refractory elements like Ti are fully returned to the gas phase at distances beyond $\sim 1$ kpc from the plane of the Galaxy.

Accepted for publication in ApJ, due to appear 1 April 1995. 23 pages including 5 figures; uuencoded compressed postscript; RG0-212

Cited by in corpus (8)

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• Distances and Metallicities of High- and Intermediate-Velocity Clouds
• Chemical Abundances of the Damped Lya Systems at z>1.5
• The Extension of the Transition Temperature Plasma into the Lower Galactic Halo
• Spitzer Infrared Spectrographic point source classification in the Small Magellanic Cloud
• Evidence for Correlated Titanium and Deuterium Depletion in the Galactic ISM
• Interstellar Ti II in the Milky Way and Magellanic Clouds
• Dust in Hot Environments: Giant Dusty Galactic Halos