Decoding NGC 7252 as a blue elliptical galaxy

TL;DR

This paper shows that blue elliptical galaxies, often thought to be post-merger remnants, can appear as normal ellipticals at higher redshifts due to the faintness of merger features, impacting their classification.

Contribution

It demonstrates that deep imaging reveals merger features in NGC 7252, suggesting many high-redshift blue ellipticals may be undetected merger remnants in shallow surveys.

Findings

Deep imaging uncovers faint merger features in NGC 7252.

High-redshift blue ellipticals may be misclassified due to undetected merger signatures.

Shallow surveys may overlook merger history in blue elliptical galaxies.

Abstract

Elliptical galaxies with blue optical colours and significant star formation are hypothesised to be major merger remnants of gas-rich spiral galaxies or normal elliptical galaxies with a sudden burst of star formation. We present here a scenario in which blue elliptical galaxies identified in shallow imaging surveys may fail to recover faint features that are indicative of past merger activity using a nearby major merger remnant. Based on deep optical imaging data of the post-merger galaxy, NGC 7252, we demonstrate that the galaxy can appear as an elliptical galaxy if it is observed at higher redshifts. The main body and the low surface brightness merger features found at the outskirts of the galaxy are blue in the optical g - r colour map. We argue that the higher-redshift blue elliptical galaxies discovered in surveys as shallow as the SDSS or DECaLS may be advanced mergers whose defining tidal features fall below the detection limits of the surveys. This should be taken into consideration during the morphological classification of these systems in future and ongoing surveys.