Tidal streams in newly discovered M32 analogues: evidence for the stripping scenario

TL;DR

This paper reports the discovery of two compact elliptical galaxies with tidal streams, providing direct evidence for the tidal stripping process believed to form M32-type galaxies, and analyzes their properties and environments.

Contribution

The study presents newly discovered cE galaxies with tidal streams, offering direct observational evidence supporting the tidal stripping formation scenario for M32 analogues.

Findings

Evidence of tidal streams in two cE galaxies.

Structural parameters consistent with stripping origin.

Presence in small, young groups suggesting formation in dynamic environments.

Abstract

We present two newly-discovered compact elliptical (cE) galaxies, exhibiting clear evidence of tidal steams, and found during a search of SDSS DR7 for cE candidates. The structural parameters of the cEs are derived using GALFIT, giving effective radii, Re, of 388 and 263 parsecs, and B-band mean surface brightnesses within Re of 19.4 and 19.2 magnitudes per arcsec squared. We have re-analysed the SDSS spectra, which indicate that they possess young to intermediate-age stellar populations. These two cEs provide direct evidence, a "smoking gun", for the process of tidal stripping that is believed to be the origin of M32-type galaxies. Both are in small groups with a large spiral fraction, suggesting that we may be seeing the formation of such cE galaxies in dynamically young environments. The more compact of the galaxies is found in a small group not unlike the Local Group, and thus provides an additional model for understanding M32.