The growth and assembly of a massive galaxy at z ~ 2

TL;DR

This study investigates the stellar mass assembly of a massive galaxy at z ~ 2, revealing that satellite galaxies are likely to merge with the central galaxy, contributing to its growth and the formation of an extended stellar halo.

Contribution

It provides new insights into the assembly process of a massive galaxy at high redshift, highlighting the role of satellite mergers and stellar stripping.

Findings

Most satellite galaxies will merge with the central galaxy by z=0.

Star formation occurs mainly in surrounding low-mass satellites.

Stars and gas are being stripped from satellites, forming extended halos.

Abstract

We study the stellar mass assembly of the Spiderweb Galaxy (MRC 1138-262), a massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a brightest cluster galaxy. Nearby protocluster galaxies are identified and their properties are determined by fitting stellar population models to their rest-frame ultraviolet to optical spectral energy distributions. We find that within 150 kpc of the radio galaxy the stellar mass is centrally concentrated in the radio galaxy, yet most of the dust-uncorrected, instantaneous star formation occurs in the surrounding low-mass satellite galaxies. We predict that most of the galaxies within 150 kpc of the radio galaxy will merge with the central radio galaxy by z = 0, increasing its stellar mass by up to a factor of ~ 2. However, it will take several hundred Myr for the first mergers to occur, by which time the large star formation rates are likely to have exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the satellite galaxies are small, suggesting that stars and gas are being stripped and deposited at distances of tens of kpc from the central radio galaxy. These stripped stars may become intracluster stars or form an extended stellar halo around the radio galaxy, such as those observed around cD galaxies in cluster cores.