IAU Symposium Abstract S186-075T

HST Imaging Survey of Ultraluminous IR Galaxies

L. Colina1, K. Borne2, H. Bushouse3, R. Lucas4
1 Space Telescope Science Institute (colina@stsci.edu)
2 Hughes STX, NASA Goddard Space Flight Center (borne@xfiles.gsfc.nasa.gov)
3 Space Telescope Science Institute (bushouse@stsci.edu)
4 Space Telescope Science Institute (lucas@stsci.edu)

We present first results derived from a recent Hubble Space Telescope (HST) imaging survey of Ultraluminous Infrared Galaxies (log Lir > 12 Lsun, ULIRGs). To date we have obtained WFPC2 I-band (F814W) images for about 70 galaxies from our original sample of 160 ULIRGs. Fine structure is seen within a radius < 2" for each galaxy. In about 10% of the galaxies, the structure is smooth and centrally concentrated, suggestive of a bright nuclear energy source (AGN?). In about 90% of the galaxies, the sub-arcsecond morphology is chaotic and extended, suggestive of strong starburst activity. The disturbed morphologies that are seen on large (several kiloparsecs) scales among ULIRGs are continued down to the smallest scales in the nuclear regions (at HST resolution ~ 0.1 to 0.4 kiloparsecs). These morphological features, numerous bright clumps, shells, and bubbles, are similar to those seen in previous HST images of nearby strongly interacting galaxies, particularly the large star-forming regions seen in the Cartwheel Ring galaxy, the Antennae, and NGC 7252. The clumpy nature of the luminosity distribution (independent of obvious dust mottling) suggest that super star-forming complexes represent the typical mode for massive star formation among merger-induced starburst systems.