Galactic Extinction: How Many Novae Does It Hide and How Does It Affect the Galactic Nova Rate?

Abstract

There is a long-standing discrepancy between the observed Galactic classical nova rate of ∼10 yr−1 and the predicted rate from Galactic models of ∼30–50 yr−1. One explanation for this discrepancy is that many novae are hidden by interstellar extinction, but the degree to which dust can obscure novae is poorly constrained. We use newly available all-sky three-dimensional dust maps to compare the brightness and spatial distribution of known novae to that predicted from relatively simple models in which novae trace Galactic stellar mass. We find that only half (53%) of the novae are expected to be easily detectable (g ≲ 15) with current all-sky optical surveys such as the All-Sky Automated Survey for Supernovae (ASAS-SN). This fraction is much lower than previously estimated, showing that dust does substantially affect nova detection in the optical. By comparing complementary survey results from the ASAS-SN, OGLE-IV, and Palomar Gattini IR surveys using our modeling, we find a tentative Galactic nova rate of ∼30 yr−1, though this could be as high as ∼40 yr−1, depending on the assumed distribution of novae within the Galaxy. These preliminary estimates will be improved in future work through more sophisticated modeling of nova detection in ASAS-SN and other surveys.