High-velocity clouds

  title={High-velocity clouds},
  author={Bart P. Wakker},
▪ Abstract High-velocity clouds (HVCs) consist of neutral hydrogen (HI) at velocities incompatible with a simple model of differential galactic rotation; in practice one uses vLSR 90 km/s to define HVCs. This review describes the main features of the sky and velocity distributions, as well as the available information on cloud properties, small-scale structure, velocity structure, and observations other than in 21-cm emission. We show that HVCs contain heavy elements and that the more prominent… 

Do high-velocity clouds form by thermal instability?

We examine the proposal that the H i‘high-velocity’ clouds (HVCs) surrounding the Milky Way and other disc galaxies form by condensation of the hot galactic corona via thermal instability. Under the

Physical properties of two compact high-velocity clouds possibly associated with the leading arm of the Magellanic system

Aims. We observed two compact high-velocity clouds HVC 291+26+195 and HVC 297+09+253 to analyse their structure, dynamics, and physical parameters. In both cases there is evidence for an association

Detecting Dark Matter in High‐Velocity Clouds

Many high‐velocity H i clouds (HVCs) are now believed to be scattered throughout the Galactic halo on scales of tens of kiloparsecs. Some of these clouds appear to contain substantial H i masses (>

Distribution of the high-velocity clouds in the Galactic halo

Context. There is a connection between the kinematics and sky distribution of the high velocity clouds (HVCs) and the spatial velocity and orbital plane of the Magellanic Clouds (MCs) that allow us

Searching for stars in compact high-velocity clouds – II

ABSTRACT We address the hypothesis that High Velocity Clouds correspond to the “missing”dwarf galaxies of the Local Group predicted by cosmological simulations. To thisend, we present optical and

Global properties of the HI high velocity sky. A statistical investigation based on the LAB survey

Context. Since 1973, it has been known that some H i high velocity clouds (HVCs) have a core-envelope structure. Recent observations of compact HVCs confirm this, but more general investigations have

Searching for stars in compact high-velocity clouds – I. First results from VLT and 2MASS

We investigate the hypothesis that compact high-velocity clouds (CHVC) are the 'missing' dwarf galaxies of the Local Group, by searching them for populations of resolved stars. To this end we

The High-Velocity Gas toward Messier 5: Tracing Feedback Flows in the Inner Galaxy

We present FUSE and STIS E140M observations of the post-AGB star ZNG 1 in the globular cluster Messier 5 (l = 3.9°, b = + 47.7°; d = 7.5 kpc , z = + 5.3 kpc ). High-velocity absorption is seen in C


We present a catalog of high-velocity clouds (HVCs) from the Galactic All Sky Survey (GASS) of southern sky neutral hydrogen, which has 57 mK sensitivity and 1 km s−1 velocity resolution and was

On the Critical Ionization Velocity Effect in Interstellar Space and Possible Detection of Related Continuum Emission

Interstellar neutral hydrogen (HI) emission spectra manifest several families of linewidths whose numerical values (34, 13, and 6 km/s) appear to be related to the critical ionization velocities




We present the first complete catalogue of high-velocity clouds (HVCs), followed by a classification of these clouds into complexes and populations. The catalogue will form the basis for comparisons

Westerbork observations of high-velocity clouds. Discussion

Six high-velocity cloud fields were observed with 1' and 1 km s-1 resolution, using the Westerbork Synthesis Radio Telescope. The structures seen in earlier observations at 10' resolution break up

CO and IRAS detection of an intermediate-velocity cloud

In the course of a radio survey of high-Galactic-latitude clouds, CO emission was detected at the position l = 210.8 deg and b = 63.1 deg with an LSR velocity of -39 km/sec. This molecular cloud

Composition of Interstellar Clouds in the Disk and Halo. IV. HD 215733

In this paper we continue our investigation of diffuse clouds in the interstellar medium with an analysis of the line of sight toward the star HD 215733, located in the Galactic halo some 1700 pc

H I absorption limits and emission mapping for high-velocity clouds

Systematic emission and absorption surveys have been conducted for high-velocity H I in the direction of 63 bright continuum sources. High-velocity emisison is detected along 18 of these 63

Structure of the interstellar medium in the Magellanic Clouds

Using optical and UV observations, the internal gas structure of Magellanic Clouds (MCs) was examined for clues to the recent evolution of the Magellanic System and further signs of this collision


IRAS observations are used to look for infrared emission from dust in high-velocity clouds (HVCs). None of these clouds is detected. The upper limit that can be set on the IR emission per hydrogen

Are there really intergalactic hydrogen clouds in the Sculptor group

High-sensitivity 21 cm observations of the region of the Sculptor group of galaxies reveal at least 30 H I clouds distributed over only the southern sector of the group. These new data add two

Dynamics of the Outer Arm high-velocity cloud and the triaxiality of the Milky Way

Among high-velocity clouds of neutral hydrogen (HVCs) a so-called Outer Arm Cloud, often interpreted as a part of the general warp of the Milky Way disc, can be distinguished, which is located at 49°