Anomalous HI in NGC 2997

TL;DR

Deep HI observations of NGC 2997 reveal a thick, lagging disk and anomalous clouds, indicating ongoing gas accretion and galactic fountain activity, with implications for galaxy evolution and cosmological models.

Contribution

First detailed HI study of NGC 2997 identifying anomalous clouds and modeling the galaxy's thick, lagging HI disk, providing new insights into gas accretion processes.

Findings

Presence of a galactic fountain and intragalactic gas accretion.

Detection of anomalous velocity HI clouds with ~10^7 Msun.

Estimated extragalactic gas accretion rate of at least 1.2 Msun/yr.

Abstract

We present deep HI observations of the moderately inclined spiral galaxy, NGC 2997. The goal of these observations was to search for HI clouds in the vicinity of NGC 2997 analogous to the high velocity clouds of the Milky Way and gain insight into their origins. We find evidence for the presence of a galactic fountain as well as the accretion of intragalactic material, however we do not identify any large clouds of HI far from the disk of the galaxy. NGC 2997 has a thick, lagging HI disk that is modeled with a vertical velocity gradient of 18-31 km/s/kpc. Anomalous velocity HI clouds with masses of order 10^7 Msun, which cannot be explained by galactic fountain models allow us to estimate a lower limit to the accretion of extragalactic gas of 1.2 Msun/yr. The number and mass of these clouds have implications for cosmological simulations of large scale structure and the presence of dark matter halos. We have used values from the the literature to estimate a star formation rate of 5 +/- 1 Msun/yr and to derive a new distance to NGC 2997 of 12.2 +/- 0.9 Mpc using published Tully-Fisher relations.