A NICMOS search for obscured supernovae in starburst galaxies

Abstract

The detection of obscured supernovae (SNe) in near-infrared monitoring campaigns of starburst galaxies has shown that a significant fraction of SNe is missed by optical surveys. However, the number of SNe detected in ground-based near-IR observations is still significantly lower than the number of SNe extrapolated from the FIR luminosity of the hosts. A possibility is that most SNe occur within the nuclear regions, where the limited angular resolution of ground-based observations prevents their detection. This issue prompted us to exploit the superior angular resolution of NICMOS-HST to search for obscured SNe within the first kpc from the nucleus of strong starbursting galaxies. A total of 17 galaxies were observed in SNAPSHOT mode. Based on their FIR luminosity, we did not expect to detect fewer than ~ 12 SNe. However, no confirmed SN event was found. From our data we derived an observed nuclear SN rate <0.5 SN/yr per galaxy. The shortage of SN detections can be explained by a combination of several effects. The most important are: i) the existence of a strong extinction, A_V⪆ 11; ii) most SNe occur within the first 0.5 arcsec (which corresponds in our sample to about 500 pc) where even NICMOS is unable to detect SN events.

Based on observations made with the NASA/ESA Hubble Space Telescope associated with program 9726,

obtained at the Space Telescope Science Institute, which is operated by the Association of Universities

for Research in Astronomy, Inc., under NASA contract NAS 5-26555,

and on data obtained at the VLT through the ESO program 272.D-5043.