Probing the Central Regions of Nearby Compact Elliptical Galaxies

TL;DR

This study uses high-resolution K-band spectroscopy to analyze the central stellar populations and chemical compositions of nearby compact elliptical galaxies, revealing complex chemical histories and potential intermediate age populations.

Contribution

It provides detailed spectroscopic insights into the central regions of compact ellipticals, highlighting non-solar chemical mixtures and age variations not previously characterized.

Findings

NGC 4486B and NGC 5846A have similar central stellar contents.

Both galaxies show non-solar chemical mixtures in their centers.

M32's chemical enrichment resembles the Galactic disk, not larger ellipticals.

Abstract

K-band spectroscopic observations recorded with NIFS+ALTAIR on Gemini North are used to probe the central arcsec of the compact elliptical galaxies NGC 4486B, NGC 5846A, and M32. The angular resolution of these data is ~0.1 arcsec FWHM. The central stellar contents of NGC 4486B and NGC 5846A are similar, in the sense that they occupy the same regions of the (Ca I, 12CO), (Na I, 12CO) and (13CO, 12CO) diagrams. The NGC 4486B and NGC 5846A observations depart from the sequence defined by solar neighborhood giants in the (Na I, 12CO) diagram, in a sense that is consistent with both galaxies having non-solar chemical mixtures. For comparison, the M32 data is consistent with a chemical enrichment history like that in the Galactic disk; M32 could not have formed from the stripping of a larger elliptical galaxy. The behaviour of the near-infrared line indices as a function of radius is also investigated. The radial gradients that are present in NGC 4486B and NGC 5846A at large radii break down or reverse within the central few tenths of an arcsec. Evidence is presented that the nuclear regions of NGC 4486B and NGC 5846A harbour intermediate age populations.