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

TL;DR

This study uses 3D dust maps to assess how interstellar extinction affects the detectability of Galactic novae, suggesting that dust significantly obscures many novae and revising the estimated Galactic nova rate to around 30-40 per year.

Contribution

It introduces a novel application of 3D dust maps to quantify the impact of dust on nova detection and refines the Galactic nova rate estimate based on multiple survey comparisons.

Findings

Only about 48% of novae are detectable with current optical surveys.

Dust substantially reduces nova detection rates in the optical.

The tentative Galactic nova rate is estimated at around 40 per year.

Abstract

There is a longstanding discrepancy between the observed Galactic classical nova rate of $\sim 10$ yr$^{-1}$ and the predicted rate from Galactic models of $\sim 30$--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 ($\sim 48$\%) of novae are expected to be easily detectable ($g \lesssim 15$) 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 ASAS-SN, OGLE-IV, and the Palomar Gattini IR-survey in the context of our modeling, we find a tentative Galactic nova rate of $\sim 40$ yr$^{-1}$, though this could decrease to as low as $\sim 30$ 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.