Discovery of Five Candidate Analogs for $\eta\,$Carinae in Nearby Galaxies

TL;DR

This study reports the discovery of five objects in nearby galaxies with properties similar to $ ext{η}$ Carinae, providing insights into massive star evolution and potential superluminous supernova progenitors.

Contribution

It introduces five candidate analogs to $ ext{η}$ Carinae$ in nearby galaxies, expanding the sample for studying massive star eruptions and their link to superluminous supernovae.

Findings

Five $ ext{η}$ Car analogs identified in nearby galaxies.

Estimated rate of $ ext{η}$ Car-like events as a fraction of core-collapse supernovae.

Implication that eruptions are linked to the onset of carbon burning in massive stars.

Abstract

The late-stage evolution of very massive stars such as $\eta$ Carinae may be dominated by episodic mass ejections which may later lead to Type II superluminous supernova (SLSN-II; e.g., SN 2006gy). However, as long as $\eta$ Car is one of a kind, it is nearly impossible to quantitatively evaluate these possibilities. Here we announce the discovery of five objects in the nearby ($\sim4-8$ Mpc) massive star-forming galaxies M51, M83, M101 and NGC6946 that have optical through mid-IR photometric properties consistent with the hitherto unique $\eta$ Car. The Spitzer mid-IR spectral energy distributions of these $L_{bol}\simeq3-8\times10^{6} L_\odot$ objects rise steeply in the $3.6-8 \mu$m bands, then turn over between $8$ and $24 \mu$m, indicating the presence of warm ($\sim400-600$ K) circumstellar dust. Their optical counterparts in HST images are $\sim1.5-2$ dex fainter than their mid-IR peaks and require the presence of $\sim5-10 M_\odot$ of obscuring material. Our finding implies that the rate of $\eta$ Car-like events is a fraction $f=0.094$ ($0.040 < f < 0.21$ at $90\%$ confidence) of the core-collapse supernova (ccSN) rate. If there is only one eruption mechanism and SLSN-II are due to ccSN occurring inside these dense shells, then the ejection mechanism is likely associated with the onset of carbon burning ($\sim 10^3 - 10^4$ years) which is also consistent with the apparent ages of massive Galactic shells.