5 Conclusions

We have presented the discovery of SN 1999gw and SN 2001db obtained within the framework of a near-IR ( $\lambda \sim 2.1~\mu$m) search for obscured SNe in Luminous Infrared Galaxies. The spectroscopic follow-up of SN 2001db indicates that this was a type II SN, extinguished by $A_V \approx 4.6{-}6.7$. Interestingly, this SN, the first one to be discovered in the IR and spectroscopically confirmed, would have been missed by ordinary optical surveys.

Preliminary estimates of the SN rate indicate that the SN production in Luminous Infrared Galaxies is ${\sim} 10^{-11}~ (L_B/L_{\odot})~\rm yr^{-1}$, about an order of magnitude higher than expected by the relation between L_B and SN rate found in optical studies. This result confirms that optical surveys miss a significant fraction of the SNe, especially in obscured systems such as starburst galaxies. However, simple first order estimates, based on the far-IR luminosity, indicate that our near-IR survey is still largely incomplete, and that $\sim$80% of the SNe are missed. Some possible explanations for this issue are: 1) most SN are more obscured than A_V>30 mag; 2) the number of expected SNe as inferred from the $L_{\rm FIR}$ is overestimated because hidden AGNs dominated the luminosity; 3) most of the SNe occur in the nuclear region and the limited angular resolution prevents their discovery.

Acknowledgements

We are grateful to S. Mattila, P. Meikle and N. Panagia for useful comments. The near-IR survey partly presented in this paper is the result of the efforts of a larger collaboration that also includes V. Ivanov, A. Alonso-Herrero and N. Nagar. We thank the ESO staff, on La Silla and on Paranal, as well as the TNG staff for their help during the observations. We thank the ESO General Director for allocating Director Discretionary Time to this project. M. Della Valle and R. Maiolino are grateful to the Paranal and La Silla ESO observatories and to the ESO Santiago Science Office for their kind hospitality during this research program, within the framework of the Visiting Scientist Program. This work was partially supported by the the Italian Space Agency (ASI).