Crazy heart: kinematics of the "star pile" in Abell 545

TL;DR

This study investigates the structure and complex internal kinematics of the star pile in Abell 545, revealing irregular velocity patterns that challenge its use as a straightforward dynamical tracer for the cluster's dark matter profile.

Contribution

It provides detailed spectroscopic analysis of the star pile, highlighting its irregular kinematics and questioning its suitability for dark matter studies.

Findings

The star pile has a flat luminosity profile and consistent color with elliptical galaxy outskirts.

Its velocity map is irregular with parts associated with an embedded nucleus.

The velocity pattern complicates using the entire star pile for dark matter profiling.

Abstract

We study the structure and internal kinematics of the "star pile" in Abell 545 - a low surface brightness structure lying in the center of the cluster.We have obtained deep long-slit spectroscopy of the star pile using VLT/FORS2 and Gemini/GMOS, which is analyzed in conjunction with deep multiband CFHT/MEGACAM imaging. As presented in a previous study the star pile has a flat luminosity profile and its color is consistent with the outer parts of elliptical galaxies. Its velocity map is irregular, with parts being seemingly associated with an embedded nucleus, and others which have significant velocity offsets to the cluster systemic velocity with no clear kinematical connection to any of the surrounding galaxies. This would make the star pile a dynamically defined stellar intra-cluster component. The complicated pattern in velocity and velocity dispersions casts doubts on the adequacy of using the whole star pile as a dynamical test for the innermost dark matter profile of the cluster. This status is fulfilled only by the nucleus and its nearest surroundings which lie at the center of the cluster velocity distribution.