Galaxy Mass Assembly with VLT & HST and lessons for E-ELT/MOSAIC

TL;DR

This paper discusses how combining VLT and HST observations reveals that many distant disk galaxies underwent mergers, supporting a violent formation history, and highlights the potential of future ELT/MOSAIC observations for galaxy evolution studies.

Contribution

It demonstrates the effectiveness of combined 3D-spectroscopy and imaging in identifying merger histories of galaxies and provides insights into galaxy formation processes.

Findings

Half of the spiral progenitors at z=0.4-0.8 were in merger phases.

Methodological classifications align with kinematic data, confirming violent galaxy origins.

Nearby stellar streams are fossil remnants of ancient mergers.

Abstract

The fraction of distant disks and mergers is still debated, while 3D-spectroscopy is revolutionizing the field. However its limited spatial resolution imposes a complimentary HST imagery and a robust analysis procedure. When applied to observations of IMAGES galaxies at z=0.4-0.8, it reveals that half of the spiral progenitors were in a merger phase, 6 billion year ago. The excellent correspondence between methodologically-based classifications of morphologies and kinematics definitively probes a violent origin of disk galaxies as proposed by Hammer et al. (2005). Examination of nearby galaxy outskirts reveals fossil imprints of such ancient merger events, under the form of well organized stellar streams. Perhaps our neighbor, M31, is the best illustration of an ancient merger, which modeling in 2010 leads to predict the gigantic plane of satellites discovered by Ibata et al. (2013). There are still a lot of discoveries to be done until the ELT era, which will open an avenue for detailed and accurate 3D-spectroscopy of galaxies from the earliest epochs to the present.