UR: Physical Properties of the Host Galaxies of Ca-rich Transients

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Yuxin Dong

Northwestern University

This guest post was written by Yuxin (Vic) Dong, a first-year astronomy PhD student at Northwestern University. She completed this research at Purdue University as her independent project under the guidance of Prof. Danny Milisavljevic.

Calcium-rich (Ca-rich) transients are a peculiar subclass of supernovae (SNe) that are known for their comparatively rapid evolution, modest peak luminosities, and strong nebular calcium emission lines. Their spectra strongly resemble those of stripped-envelope Type Ib/c SNe, pointing to a young and massive star origin which undergoes a core-collapse explosion. However, their remote location and large offsets from elliptical galaxies suggest a resemblance to Type Ia supernovae (Fig. 1), which are instead products of thermonuclear detonations of old white dwarfs. Given the origin of Ca-rich transients still remains unknown, we investigated the host environments of all known Ca-rich transients to place more stringent constraints on the progenitor systems of Ca-rich transients. Although Ca-rich transients make up only a small fraction of all SN events, knowing their progenitor systems of Ca-rich transients will be a key step in understanding their true roles in enriching galaxies and the intergalactic medium. 

Figure 1: Host galaxies for a subset of Ca-rich transients. The name of the SN and host galaxy are indicated on the top left-hand corner while the filter and survey are displayed on the top right-hand corner. All host galaxies are circled in yellow and transients in blue.

To model the stellar population properties of each host galaxy, we utilized both a parametric and a nonparametric model within the stellar-inference framework called Prospector to describe the star formation history (SFH) with different parameter assumptions and flexibilities. We estimated several galaxy parameters including integrated star formation rate, stellar mass, metallicity, and age. Using publicly available multi-wavelength observations of each host galaxy ranging from Far-UV to IR, we were able to construct the spectral energy distribution (SED) and examine the effect of stellar population properties on the shape of the SED and obtain a realistic mass distribution and age for the entire stellar population by analyzing the star formation rate as a function of time. Our work supports the notion that the population of Ca-rich transients do not come exclusively from core-collapse explosions and must either be only from white dwarf stars or a mixed population of white dwarf stars with other channels, potentially including massive star explosions.

Astrobite edited by: Mitchell Cavanagh

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