Kinematics and line strength indices in the halos of the Coma Brightest Cluster Galaxies NGC 4874 and NGC 4889

TL;DR

This study examines the stellar kinematics and chemical line strength indices in the outer halos of the brightest cluster galaxies NGC 4874 and NGC 4889 in the Coma cluster, revealing their dynamic properties and chemical gradients to understand their formation history.

Contribution

It provides the most extended kinematic and line strength data for these galaxies' halos, offering new insights into their structure and evolution.

Findings

Stellar velocity and dispersion profiles extend to ~50-65 kpc.

Outer halo stars remain gravitationally bound to the galaxies.

Strong radial gradients in Mg and Fe line indices for NGC 4889.

Abstract

We investigate the stellar kinematics and line strength indices in the outer halos of brightest cluster galaxies (BCGs) in the Coma cluster to obtain the outer halo V_rot and sigma profiles and to derive constraints on the formation history of these objects. Methods: We analyzed absorption lines in deep, medium-resolution, long-slit spectra in the wavelength range ~ 4500 - 5900 Angstrom, out to ~50 kpc for NGC 4874 and ~65 kpc for NGC 4889, probing regions with a surface brightness down to mu_R ~24 mag/arcsec^2. Results: These data provide stellar velocity and velocity dispersion profiles along the major axes of both BCGs, and also along the minor axis of NGC 4889. The kinematic properties of NGC 4874 and NGC 4889 halos extend the previous relations of early-type galaxy halos to bright luminosities and indicate that the stars in the outer regions are still bound to these galaxies. For NGC 4889 we also determine Hbeta, Mg and Fe line strength indices, finding strong radial gradients for Mg and Fe. The current dataset for NGC 4889 is one of the most extended in radius, including both stellar kinematics AND line strength index measurements.