We present phase-referenced VLBI observations of the radio continuum emission from , and the neutral hydrogen 21 cm absorption toward , the Ultra-Luminous Infrared Galaxy IRAS 17208–0014 .
The observations were carried out at 1362 MHz using the Very Long Baseline Array , including the phased Very Large Array as an element .
The high-resolution radio continuum images reveal a nuclear starburst region in this galaxy , which is composed of diffuse emission approximately 670 \times 340 pc on the plane of the sky , and a number of compact sources .
These sources are most likely to be clustered supernova remnants and/or luminous radio supernovae .
Their brightness temperatures range over ( 2.2–6.6 ) \times 10 ^ { 5 } K , with radio spectral luminosities between ( 1 - 10 ) \times 10 ^ { 21 } ~ { } { W~ { } Hz } ^ { -1 } .
The total VLBI flux density of the starburst region is \sim 52 mJy , which is about 50 % of the total flux density detected with the VLA at arcsecond resolution .
For this galaxy , we derive a massive star formation rate of \sim 84 \pm 13 ~ { } M { { } _ { \odot } } yr ^ { -1 } , and a supernova rate of \sim 4 \pm 1 yr ^ { -1 } .
H I absorption is detected in multiple components with optical depths ranging between 0.3 and 2.5 , and velocity widths between 58 and 232 km s ^ { -1 } .
The derived column densities , assuming T _ { s } = 100 ~ { } K , range over ( 10 - 26 ) \times 10 ^ { 21 } cm ^ { -2 } .
The H I absorption shows a strong velocity gradient of 453 km s ^ { -1 } across 0 \hbox to 0.0 pt { . } ^ { \prime \prime } 36 ( 274 pc ) .
Assuming Keplerian motion , the enclosed dynamical mass is about 2.3 \times 10 ^ { 9 } ~ { } ( { sin } ^ { -2 } i ) ~ { } M { { } _ { \odot } } , comparable to the enclosed dynamical mass estimated from CO observations .