Radial Profiles of Binary Fraction in Elliptical Galaxies

TL;DR

This study measures the radial binary star fraction profiles in 513 elliptical galaxies using spectral features, finding mostly flat profiles with little variation relative to galaxy centers.

Contribution

It applies a spectral method to a large galaxy sample to analyze binary fraction profiles, extending previous studies beyond the Milky Way.

Findings

Median binary fraction after correction is approximately flat across galaxies.

Binary fraction variation at 1 effective radius is less than 5% in most galaxies.

No significant correlation between binary fraction gradients and stellar population property gradients.

Abstract

The radial profile of binary fraction may vary with environment and is of significant importance for studying the formation mechanisms of binary stars and their dynamical evolution within globular clusters (GCs) and galaxies. However, existing studies remain limited to the Milky Way and its neighboring galaxies. Leveraging the method proposed by Zhang et al. for estimating the variation of binary fraction from integrated spectral features, we analyze a sample of 513 elliptical galaxies drawn from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey to measure their radial binary fraction profiles. Our results show that after accounting for the effect induced by radial variations in the stellar population (SP), the median SP-subtracted binary fraction, $r_{\rm b,sub}^{\rm med}$, becomes approximately flat. For nearly all elliptical galaxies in our sample, the variation in binary fraction relative to the galaxy center at $1R_e$ is less than 5%. No clear correlation is found between the binary fraction gradient and the gradients of SP properties. Moreover, we also compare differences between ultraviolet (UV) upturn and non-UV upturn galaxies. The overall binary fraction profiles and SP properties of the non-UV upturn galaxies in our sample are comparable to those of the UV upturn galaxies. This similarity may arise from the presence of residual star formation (RSF) in the non-UV upturn systems.