A Very High Velocity H I Cloud in the Direction of M31

Davies, R. D.

doi:10.1093/mnras/170.1.45p

Cited by 23 publications

(8 citation statements)

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“…Peak values of N HI are also similar to previous observations of Northern hemisphere IVCs and HVCs at this resolution (e.g. Davies 1975;Cohen & Mirabel 1979;Shaw et al 1996;Kennedy et al 1998), which range from ∼3-5×10…”

Section: Discussionsupporting

confidence: 88%

HI observations of the high-velocity cloud in the direction of M 92

Smoker

Roger

Keenan

et al. 2001

A&A

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Abstract. We present wide-field neutral hydrogen (H i) Lovell telescope multibeam, and Dominion Radio Astrophysical Observatory H i synthesis observations, of the high velocity cloud (HVC) located in the general direction of the globular cluster M 92. This cloud is part of the larger Complex C and lies at velocities between ∼-80 and −130 km s −1 in the Local Standard of Rest. The Lovell telescope observations, of resolution 12 arcmin spatially and 3.0 km s −1 in velocity, fully sampling a 3.1• RA-Dec grid, have found that this part of HVC Complex C comprises two main condensations, lying approximately north-south in declination, separated by ∼2• and being parallel to the Galactic plane. At this resolution, peak values of the brightness temperature and H i column density of ∼1.4 K and ∼5×1019 cm −2 are determined, with relatively high values of the full width half maximum velocity (FWHM) of ∼22 km s −1 being observed, equivalent to a gas kinetic temperature, in the absence of turbulence and geometric effects of ∼10 000 K. Each of these properties, as well as the sizes of the clouds, are similar in the two components. The DRAO observations, towards the Northern HVC condensation, are the first high-resolution H i spectra of Complex C. When smoothed to a resolution of 3 arcmin, they identify several H i intensity peaks with column densities in the range 4-7×10 19 cm −2 . Further smoothing of these data to 6 arcmin resolution tentatively indicates that parts of the HVC consist of two velocity components, of similar brightness temperature, separated by ∼7 km s −1 in velocity, and with FWHM velocity widths of ∼5−7km s −1 . No IRAS 60 or 100 micron flux is associated with the M 92 HVC. Cloud properties are briefly discussed and compared to previous observations of HVCs.

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Section: Discussionsupporting

confidence: 88%

HI observations of the high-velocity cloud in the direction of M 92

Smoker

Roger

Keenan

et al. 2001

A&A

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“…The only object in our sample that was known previously is Davies' Cloud (Davies 1975), which is at least 10 times brighter than the other features. Davies considered that it might be part of the Magellanic Stream rather than M31, but in our complimentary wide-field study of a 60 • × 30 • region centered on M31 (Braun et al (2003); see also Braun & Thilker 2003, in prep.…”

Section: H I Clouds Around M31mentioning

confidence: 78%

On the Continuing Formation of the Andromeda Galaxy: Detection of H i Clouds in the M31 Halo

Thilker

Braun²,

Walterbos

et al. 2004

ApJ

188

275

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Green Bank Telescope (GBT) λ21cm observations have revealed a faint, yet extensive H I cloud population surrounding the Andromeda Galaxy (M31). The newfound objects are likely analogs to the high-velocity H I clouds (HVCs) seen around the Milky Way. At least 20 discrete features are detected within 50 kpc of the M31 disk, with radial velocities that are comparable to those of outer disk rotation. In addition, a filamentary "halo" component of at least 30 kpc extent is concentrated at the M31 systemic velocity. Some of the discrete features are organized into elongated systems with velocity continuity, suggestive of tidal streams. The discrete population can be characterized by a steep power-law distribution of number versus H I mass in the range between 10 5 and 10 7 M ⊙ . The velocity line-width of discrete clouds is correlated with the cloud H I mass: such that if the clouds are gravitationally bound this implies a dark-to H I mass ratio of ∼ 100:1. Possible origins for the discrete and "halo" M31 features include: a Local Group "cooling flow", tidal debris from recent mergers or interactions, and the gaseous counterparts of low mass dark-matter halos.

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“…As our measurements are only over a sparse grid in this area, we do not know the size or mass of any cloud associated with this feature. One of the M31 HVCs, the Davies Cloud, has also been suspected of being part of the Stream because its mass would be an order of magnitude larger than the other M31 HVCs were it at the distance of M31 (Davies 1975;Westmeier et al 2008). The Davies Cloud does not have extraordinary kinematics and does not occupy an unusual location in Figure 10.…”

Section: Kinematics Of the Emissionmentioning

confidence: 99%

SENSITIVE 21 cm OBSERVATIONS OF NEUTRAL HYDROGEN IN THE LOCAL GROUP NEAR M31

Wolfe

Lockman

Pisano

2016

ApJ

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Very sensitive 21cm H I measurements have been made at several locations around the Local Group galaxy M31 using the Green Bank Telescope (GBT) at an angular resolution of 9. 1, with a 5σ detection level of N H I = 3.9 × 10 17 cm −2 for a 30 km s −1 line. Most of the H I in a 12 square degree area almost equidistant between M31 and M33 is contained in nine discrete clouds that have a typical size of a few kpc and H I mass of 10 5 M . Their velocities in the Local Group Standard of Rest lie between −100 and +40 km s −1 , comparable to the systemic velocities of M31 and M33. The clouds appear to be isolated kinematically and spatially from each other. The total H I mass of all nine clouds is 1.4 × 10 6 M for an adopted distance of 800 kpc with perhaps another 0.2 × 10 6 M in smaller clouds or more diffuse emission. The H I mass of each cloud is typically three orders of magnitude less than the dynamical (virial) mass needed to bind the cloud gravitationally. Although they have the size and H I mass of dwarf galaxies, the clouds are unlikely to be part of the satellite system of the Local Group as they lack stars. To the north of M31, sensitive H I measurements on a coarse grid find emission that may be associated with an extension of the M31 high-velocity cloud population to projected distances of ∼ 100 kpc. An extension of the M31 high-velocity cloud population at a similar distance to the south-east, toward M33, is not observed.

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A Very High Velocity H I Cloud in the Direction of M31

Cited by 23 publications

References 0 publications

HI observations of the high-velocity cloud in the direction of M 92

HI observations of the high-velocity cloud in the direction of M 92

On the Continuing Formation of the Andromeda Galaxy: Detection of H i Clouds in the M31 Halo

SENSITIVE 21 cm OBSERVATIONS OF NEUTRAL HYDROGEN IN THE LOCAL GROUP NEAR M31

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