The Hubble sequence: just a vestige of merger events?

TL;DR

This study explores whether the Hubble sequence can be explained as remnants of galaxy merger events, showing that many present-day spirals may have formed through such processes around 6 billion years ago.

Contribution

It demonstrates that galaxy morphologies and kinematics at z=0.65 can be reproduced by gas models of major mergers, supporting the spiral rebuilding scenario as a formation pathway.

Findings

Anomalous starbursts are linked to local spirals.

Gas fractions in progenitors are generally above 50%.

Major mergers likely contributed to the formation of many present-day spirals.

Abstract

Abr: We investigate whether the Hubble sequence can be reproduced by the relics of merger events. We verify that, at zmed=0.65, the abundant population of anomalous starbursts is mainly linked to the local spirals. Their morphologies are dominated by young stars and are related to their ionised-gas kinematics. We show that both morphologies and kinematics can be reproduced by using gas modelling from Barnes' (2002) study of major mergers. Using our modelling to estimate the gas-to-stars transformation during a merger, we identify the gas fraction in the progenitors to be generally above 50%. All distant and massive starbursts can be distributed along a temporal sequence from the first passage to the nuclei fusion and then to the disk rebuilding phase. It confirms that the rebuilding spiral disk scenario is possibly an important channel for the formation of present-day disks in spirals. Because half of the present-day spirals had peculiar morphologies and anomalous kinematics at zmed=0.65, they could indeed be in major mergers phases 6 Gyrs ago, and almost all at z~1. It is time now to study in detail the formation of spiral disks and of their substructures, including bulge, disks, arms, bars, rings that may mainly originate from instabilities created during the last major merger.