An enigmatic HI cloud

TL;DR

This paper reports the discovery and detailed analysis of an unusual HI cloud with a velocity gradient, exploring its possible nature as either a rotating dark galaxy or an expanding circumstellar envelope.

Contribution

It provides high-resolution observations of a peculiar HI cloud and discusses its potential classification as a dark galaxy or evolved star envelope based on its velocity structure.

Findings

Detected a velocity gradient of 1 km/s in the HI cloud

Morphology is elliptical with clumpy substructure

Possible association with a dark galaxy or AGB star envelope

Abstract

The discovery of an HI cloud with peculiar properties at equatorial coordinates (J2000) ra=07h49m, dec=04d30m is presented. The HI object was detected at 21cm using the 300-m NAIC Arecibo telescope. Subsequent follow-up high-resolution observations with the NRAO Very Large Array (VLA) telescope at L-Band revealed more details about its morphology. The most intriguing aspect of the object is the clear velocity gradient of 1 km/s, which is present in the data, an indication of either rotation or expansion. The gas appears to be cold, and its morphology is somewhat elliptical with clumpy substructure. Assuming disk rotation, the dynamical mass could be determined as a function of distance.Depending on the exact nature of the velocity gradient in the HI cloud, we can reach some preliminary conclusions about the nature of the object. Expansion would imply association with a circumstellar envelope of an evolved AGB star, while in the case of rotation, a comparison between the visible and the dynamical mass can lead to some preliminary conclusions. A common feature of those conclusions is the presence of a gravitational potential well, which is required to account for the rotation of the trapped HI gas. This potential well could be associated with a dark galaxy or some other exotic object.