Modeling the Baryon Cycle in Low Mass Galaxy Encounters: the Case of NGC 4490 & NGC 4485

TL;DR

This paper presents the first detailed dynamical model of the low mass galaxy pair NGC 4490 & NGC 4485, showing how dwarf-dwarf interactions can redistribute baryons and influence their evolution in isolated environments.

Contribution

It introduces a hybrid N-body and test-particle simulation model that reproduces observed morphology and kinematics of a dwarf galaxy pair, revealing baryon redistribution mechanisms.

Findings

Repeated dwarf galaxy encounters can 'park' baryons at large distances.

The system is modeled as an 8:1 mass ratio encounter inducing a one-armed spiral.

Extended tidal features will evolve over ~5 Gyr, affecting baryon and gas dynamics.

Abstract

Discoveries of low mass galaxy pairs and groups are increasing. Studies indicate that dwarf galaxy pairs are gas rich in the field and exhibit elevated star formation rates, suggestive of interactions. Lacking are dynamical models of observed dwarf galaxy pairs to disentangle the physical processes regulating their baryon cycles. We present new optical data and the first detailed theoretical model of an observed tidal encounter between two isolated low mass galaxies, NGC 4490 & NGC 4485. This system is an isolated analog of the Magellanic Clouds and is surrounded by a ~50 kpc extended HI envelope. We use hybrid $N$-body and test-particle simulations along with a visualization interface $Identikit$ to simultaneously reproduce the observed present-day morphology and kinematics. Our results demonstrate how repeated encounters between two dwarf galaxies can "park" baryons at very large distances, without the aid of environmental effects. Our best match to the data is an 8:1 mass ratio encounter where a one-armed spiral is induced in the NGC 4490-analog, which we postulate explains the nature of diffuse starlight presented in the new optical data. We predict that the pair will fully merge in ~370 Myr, but that the extended tidal features will continue to evolve and return to the merged remnant over ~5 Gyr. This pre-processing of baryons will affect the efficiency of gas stripping if such dwarf pairs are accreted by a massive host. In contrast, in isolated environments this study demonstrates how dwarf-dwarf interactions can create a long-lived supply of gas to the merger remnant.