NGC1600 - Cluster or Field Elliptical?

TL;DR

This study investigates whether NGC1600 is a cluster or a field elliptical galaxy by analyzing galaxy distribution, X-ray emission, and velocity data, revealing it is more akin to a large isolated group than a typical cluster.

Contribution

The paper provides detailed observational evidence suggesting NGC1600 is a large, isolated galaxy group rather than a typical cluster or a simple field elliptical.

Findings

Galaxy density profile declines with radius

Velocity dispersion estimated at 429 km/s

Mass of the system is approximately 10^14 solar masses

Abstract

A study of the galaxy distribution in the field of the elliptical galaxy NGC1600 has been undertaken. Although this galaxy is often classified as a member of a loose group, all the neighbouring galaxies are much fainter and could be taken as satellites of NGC1600. The number density profile of galaxies in the field of this galaxy shows a decline with radius, with evidence of a background at approximately 1.3 Mpc. The density and number density profile are consistent with that found for other isolated early-type galaxies. NGC1600 appears as an extended source in X-rays, and the center of the X-ray emission seems not to coincide with the center of the galaxy. The velocity distribution of neighbouring galaxies has been measured from optical spectroscopic observations and shows that the mean radial velocity is approximately 85 km/s less than that of NGC1600, indicating that the centre of mass could lie outside the galaxy. The velocity dispersion of the `group' is estimated at 429 km/s. The inferred mass of the system is therefore of the order of 10^14 solar masses, a value that corresponds to a large group. NGC1600 therefore shares some similarities, but is not identical to, the `fossil clusters' detected in X-ray surveys. Implications of this result for studies of isolated early-type galaxies are briefly discussed.