AAS 201st Meeting, January, 2003
Session 107. AGN
Oral, Wednesday, January 8, 2003, 2:00-3:30pm, 616-617

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[107.05D] Probing the innermost regions of luminous and ultra-luminous infrared galaxies: Sensitive VLBI continuum and HI absorption observations of the ULIRG IRAS17208-0014 and the LIRG NGC7674.

E. Momjian (U. of Kentucky/NRAO)

Very long baseline interferometry (VLBI) is one of the few techniques capable of revealing the highly obscured innermost regions of luminous and ultra-luminous infrared galaxies (LIRGs & ULIRGs) in the nearby universe. Observations at 21 cm show the uniqueness of VLBI measurements in revealing the details of the structure and the kinematics in the nuclear regions of these galaxies. Here, we present sensitive VLBI results on two galaxies, the ULIRG IRAS 17208-0014 and the LIRG NGC 7674.

The high resolution continuum images of IRAS 17208--0014 at 1.36 GHz reveal the details of the nuclear starburst region of this galaxy. Both diffuse and compact continuum emission are detected. The compact sources are more likely clustered luminous radio supernovae and supernova remnants. The results suggest a massive star formation rate of ~84 M\odot~{\rm yr}-1 and a supernova rate of ~4 {\rm yr}-1. A very wide HI absorption line is associated with this galaxy. This line is composed of several components with velocity widths between 58 and 232 km/s, and column densities on the order of 1020~T\rm s(K).

The image of NGC 7674 at 1.38 GHz and 20 mas resolution reveals previously undetected continuum structures in the nuclear region of this galaxy. At 11 \times 5 mas resolution, three compact sources can be seen in the central region with brightness temperatures ~108 K. One of these sources is a possible candidate to host an AGN. Several HI absorption features with optical depths \leq 0.4 are seen toward both compact and extended continuum sources.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.