Census of Self-Obscured Massive Stars in Nearby Galaxies with Spitzer: Implications for Understanding the Progenitors of SN 2008S-Like Transients

TL;DR

This study systematically searches for self-obscured massive stars in four nearby galaxies using Spitzer IR data, revealing their rarity and short-lived dust-enshrouded phase, which informs understanding of their role as supernova progenitors.

Contribution

It introduces an innovative image subtraction method for identifying rare, dust-enshrouded massive stars in nearby galaxies using mid-IR data, expanding knowledge of their transient nature.

Findings

Self-obscured massive stars are very rare, about one per galaxy.

The dust-enshrouded phase is short-lived in massive star evolution.

Provides mid-IR catalogs for three galaxies.

Abstract

A new link in the causal mapping between massive stars and potentially fatal explosive transients opened with the 2008 discovery of the dust-obscured progenitors of the luminous outbursts in NGC 6946 and NGC 300. Here we carry out a systematic mid-IR photometric search for massive, luminous, self-obscured stars in four nearby galaxies: M33, NGC 300, M81, and NGC 6946. For detection, we use only the 3.6 micron and 4.5 micron IRAC bands, as these can still be used for multi-epoch Spitzer surveys of nearby galaxies (=<10 Mpc). We combine familiar PSF and aperture-photometry with an innovative application of image subtraction to catalog the self-obscured massive stars in these galaxies. In particular, we verify that stars analogous to the progenitors of the NGC 6946 (SN 2008S) and NGC 300 transients are truly rare in all four galaxies: their number may be as low as ~1 per galaxy at any given moment. This result empirically supports the idea that the dust-enshrouded phase is a very short-lived phenomenon in the lives of many massive stars and that these objects constitute a natural extension of the AGB sequence. We also provide mid-IR catalogs of sources in NGC 300, M81, and NGC 6946.