Physical Conditions in the Galactic Halos of the Milky way and NGC 3067

Details Physical Conditions in the Galactic Halos of the Milky way and NGC 3067 Physical Conditions in the Galactic Halos of the Milky way and NGC 3067

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995hst..prop.5892s&link_type=abstract

HST Proposal ID #5892

Computer Science

Hst Proposal Id #5892 Interstellar Medium

Scientific paper

We propose to conduct a detailed GHRS spectroscopic study of the metal absorption lines in the halo gas of the Milky Way and NGC 3067, using the quasar 3C 232 as a background source. Because 3C 232 is the only QSO metal-line system imaged in H I emission for which we can study metal-line ratios in detail, it provides a rare opportunity to measure abundances, grain depletions, and photoionizing radiation fields in halo gas. Discovered in 21-cm and Ca II absorption, the NGC 3067 absorption system has now been studied in 21-cm emission and absorption (VLA, Westerbork) and in UV absorption (IUE, HST/FOS) with 3 components spread over 160 kms. The H I cloud is almost certainly a tidal tail, pulled out of NGC 3067 some (10 kpc)h_75^-1 into the halo. We will measure column densities of Fe I and II, Mg I and II, S II, Mn II, Si II, C IV, Si IV, and perhaps C II and O I. These abundances and the H I emission characteristics can be used to determine metallicities and grain depletions in the halos of NGC 3067 and the Milky Way. The Fe I/Fe II and Mg I/Mg II ionization equilibrium, coupled with H I columns, will be used to set the metagalactic photoionizing radiation field and to model the thermal equilibrium of halo gas. The C IV/Si IV absorption can be used to diagnose the relative effects of photoionization and hot gas in these halo absorption systems. The depletion factors of Si, Mn, and Fe will be used to estimate the amount of grain disruption during the tidal encounter.

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