The NGC 4013 tale: a pseudo-bulged, late-type spiral shaped by a major merger

TL;DR

This study models the formation of NGC 4013 through a recent gas-rich major merger, successfully reproducing its observed features and suggesting such mergers can produce late-type galaxies with pseudo-bulges.

Contribution

It demonstrates that a gas-rich major merger occurring 2.7-4.6 Gyr ago can explain NGC 4013's features, challenging the idea that pseudo-bulges form solely through secular evolution.

Findings

A gas-rich major merger reproduces NGC 4013's halo features and warp.

The model explains the galaxy's pseudo-bulge and thin/thick discs.

Minor mergers cannot account for the observed features.

Abstract

Many spiral galaxy haloes show stellar streams with various morphologies when observed with deep images. The origin of these tidal features is discussed, either coming from a satellite infall or caused by residuals of an ancient, gas-rich major merger. By modelling the formation of the peculiar features observed in the NGC 4013 halo, we investigate their origin. By using GADGET -2 with implemented gas cooling, star formation, and feedback, we have modelled the overall NGC 4013 galaxy and its associated halo features. A gas-rich major merger occurring 2.7-4.6 Gyr ago succeeds in reproducing the NGC 4013 galaxy properties, including all the faint stellar features, strong gas warp, boxy-shaped halo and vertical 3.6 mum luminosity distribution. High gas fractions in the progenitors are sufficient to reproduce the observed thin and thick discs, with a small bulge fraction, as observed. A major merger is able to reproduce the overall NGC 4013 system, including the warp strength, the red colour and the high stellar mass density of the loop, while a minor merger model cannot. Because the gas-rich model suffices to create a pseudo-bulge with a small fraction of the light, NGC 4013 is perhaps the archetype of a late-type galaxy formed by a relatively recent merger. Then late type, pseudo-bulge spirals are not mandatorily made through secular evolution, and the NGC 4013 properties also illustrate that strong warps in isolated galaxies may well occur at a late phase of a gas-rich major merger.