Antitruncated Stellar Disks via Minor Mergers

TL;DR

This study uses hydrodynamic simulations of minor galaxy mergers to explain the formation of antitruncated stellar disks, showing that gas inflows and angular momentum transfer can produce observed surface brightness profiles.

Contribution

It demonstrates that minor mergers can naturally produce antitruncated disks through gas inflows and angular momentum transfer, aligning with observations.

Findings

Simulations reproduce observed broken exponential profiles.

Antitruncations are more common in earlier Hubble types.

Both gas inflows and angular momentum transfer are necessary.

Abstract

We use hydrodynamic simulations of minor mergers of galaxies to investigate the nature of surface brightness excesses at large radii observed in some spiral galaxies: antitruncated stellar disks. We find that this process can produce the antitruncation via two competing effects: (1) merger-driven gas inflows that concentrate mass in the center of the primary galaxy and contract its inner density profile; and (2) angular momentum transferred outwards by the interaction, causing the outer disk to expand. In our experiments, this requires both a significant supply of gas in the primary disk, and that the encounter be prograde with moderate orbital angular momentum. The stellar surface mass density profiles of our remnants both qualitatively and quantitatively resemble the broken exponentials observed in local face--on spirals that display antitruncations. Moreover, the observed trend towards more frequent antitruncation relative to classical truncation in earlier Hubble types is consistent with a merger-driven scenario.