NGC 1600: Cluster or field elliptical?

Author(s): Smith, Rodney M.; Martinez, Vicent J.; Fernandez-Soto, Alberto; et al.

Source: ASTROPHYSICAL JOURNAL  Volume: 679   Issue: 1   Pages: 420-427   DOI: 10.1086/587454   Published: MAY 20 2008

A study of the galaxy distribution in the field of the elliptical galaxy NGC 1600 has been undertaken. Although this galaxy is often classified as a member of a loose group, all the neighboring galaxies are much fainter and could be taken as satellites of NGC 1600. 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. NGC 1600 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 neighboring galaxies has been measured from optical spectroscopic observations and shows that the mean radial velocity is approximately 85 km s(-1) less than that of NGC 1600, indicating that the center of mass could lie outside the galaxy. The velocity dispersion of the «group» is estimated at 429 +/- 57 km s(-1). The inferred mass of the system is therefore of the order of 10(14) M-circle dot, a value that corresponds to a large group. NGC 1600 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.