Intermediate Velocity Gas Detected Towards the NGC 6752 Globular Cluster
Abstract
We present medium resolution ultraviolet absorption measurements recorded with the HST-COS and FUSE spectrographs towards two post-AGB stars (UIT-1 and B1754) associated with the NGC 6752 globular cluster. We have detected intermediate velocity (IV) gas with Vlsr ∼ +38 km s-1 along the 3.9 kpc sight-line to the cluster in the absorption profiles of the CII, CII*, CIV, NI, OI, OVI, AlII, SiII, SiIV, SII, FeII and FeIII ions. The distance to this “multi-phase” IV gas lies in the 0.56-3.9 kpc range. We have fit the IV absorption profiles with models to determine column density values for the various ions. For the case of the highly ionized IV components the column density ratios of the SiIV, CIV, NV and OVI lines are most compatible with the predictions of ionization by turbulent mixing layers, shocks or halo SNRs. A gas-phase abundance analysis of the IV gas indicates that C, N, O, Al, Si and Fe appear to possess sub-solar metallicity values relative to that of sulfur. However, when the effects of element depletion onto interstellar dust in the halo is accounted for, the IVC gas probably has a value near to (or slightly less than) solar metallicity. The IV gas that is streaming away from the Galaxy is located within 3.9 kpc and its origin may well be linked to a galactic fountain in the disk. The IVC may be part of the trailing edge of the WE HVC complex, whose many constituent small clouds also possess positive velocities in this galactic direction.
- Publication:
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Publications of the Astronomical Society of the Pacific
- Pub Date:
- December 2012
- DOI:
- 10.1086/669043
- Bibcode:
- 2012PASP..124.1266W