Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aspc..276..268z&link_type=abstract
Seeing Through the Dust: The Detection of HI and the Exploration of the ISM in Galaxies, ASP Conference Proceedings, Vol. 276. E
Astronomy and Astrophysics
Astronomy
1
Scientific paper
Using the VLBA and the phase VLA, the extragalactic source 3C138 has been re-observed in the Galactic HI absorption line on December 2, 1999. These new observations are compared with the previous HI absorption line data of Faison et al. (1998). For both epochs, the spatial resolution is 20 mas and the velocity resolution is 0.49 km/s. The new data has a signal to noise ratio improvement of a factor of 2.5 due to increased dynamic range and bandpass stability. The spatial variations found by Faison et al. (1998) are confirmed, and for one of the velocity components (9.0 km/s), time variations at a level of 7 sigma (delta tau_max = -0.20+-0.03) are observed. These temporal variations can arise from motions in the ISM at the level of tens of km/s. An HI Zeeman observation suggests that large magnetic fields may be present (~400 microG); this result will be checked by future HI VLBI observations with the VLA, GBT and Arecibo, resulting in substantial improvements in sensitivity.
Brogan Crystal
de Pree Chris G.
Faison Michael D.
Goss William Miller
Zauderer Ashley B.
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