Interstellar Absorption Towards Four Inner Galaxy Lower Halo Stars: Testing Kinematic Predictions of ISM Models

Details Interstellar Absorption Towards Four Inner Galaxy Lower Halo Stars: Testing Kinematic Predictions of ISM Models Interstellar Absorption Towards Four Inner Galaxy Lower Halo Stars: Testing Kinematic Predictions of ISM Models

May 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...180.2506t&link_type=abstract

American Astronomical Society, 180th AAS Meeting, #25.06; Bulletin of the American Astronomical Society, Vol. 24, p.766

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We analyze International Ultraviolet Explorer high-dispersion observations of interstellar absorption towards four distant (d > 6.3 kpc) inner Galaxy (2.3(deg) < l < 5.8(deg) ) lower halo (6.3(deg) < |b| < 12.3(deg) ) stars in order to test kinematic predictions of interstellar medium models. We concentrate on inner Galaxy stars in order to minimize the effects of Galactic rotation and thereby improve our ability to search for radial inflow or outflow that is predicted by some theories. For example, in the Galactic fountain model explored by Bregman (1980, Ap.J., 236, 577), supernova-heated gas buoyantly rises into the halo and moves radially outward before cooling into clouds that ballistically return to the galactocentric radius from which the fountain started. The rising gas may be too hot to be detected in absorption by the IUE, but the returning clouds could be detected and should show radial inflow. Other potential sources of inflow/outflow are expanding superstructures, a bar in the Galactic center, or a Galactic wind. The spectra, based on multiple IUE images, reveal strong and broad lines of neutral and highly ionized gas. Strong absorption by N V, C IV, and Si IV is seen toward each star. The presence of N V is significant because it traces 2 times \ 10({5) \ deg} K gas. Low and high ion absorption profiles towards three out of the four stars contain significant amounts of absorption at negative LSR velocities. If the rotation of gas in the disk and halo is circular and follows standard Galactic rotation curves, then absorption should only be detected at positive LSR velocities towards these stars, ignoring the effects of instrumental smearing and turbulence in the gas. The FWHM of the IUE is ~ 25 km s(-1) , and if the gas has a velocity dispersion of 25-30 km s(-1) , then the absorption profiles might be expected to extend from -30 km s(-1) to 100 km s(-1) . However, the observed profiles extend from -100 km s(-1) to 100 km s(-1) . We discuss some viable interpretations of the negative velocity gas.

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