Linking Detectable Tidal Features to Stellar Halo Growth: An Integrated Analysis of the Outskirts of Massive Early-type Galaxies

Abstract

Motivated by the finding that massive galaxies with tidal features (GwT) are preferentially found in low-density environments, one wonders whether this trend arises from enhanced debris survivability or from more active mass-assembly histories. If driven by the latter, structural signatures, such as more developed stellar halos, should also form through cumulative accretion. To address this, we analyze azimuthally averaged surface-brightness profiles of 436 massive early-type galaxies from the DESI Legacy Imaging Survey, comparing the median-stacked profiles of galaxies with tidal features to those without. We find that, after resampling by stellar mass and environmental density, a subtle but systematic structural divergence emerges in the galaxy outskirts ($r>5\times r_{50}$). Specifically, the GwT population in the lower-density & higher-mass regime exhibits a relative intensity excess. This suggests that more developed stellar halos have formed, likely due to longer and/or more significant accretion events. In contrast, those in the higher-density & lower-mass regime show a relative deficiency in intensity, which is reasonable to interpret as a result of structural disruption from environmental effects rather than a lack of cumulative accretion. Our findings suggest that visible tidal features$-$particularly in massive systems within quiet environments$-$do not merely reflect recent stochastic accretion events but also hint at the long-term assembly history of galaxies. This work is a depth-limited study that offers a glimpse into an integrated analysis of tidal debris and stellar halos, thereby introducing a novel pathway to unravel the complex assembly histories of galaxies.