Erratum: Arecibo imaging of compact high–velocity clouds

Burton, W. B.; Braun, Róbert; Chengalur, Jayaram N.

doi:10.1051/0004-6361:20010876

Cited by 6 publications

(12 citation statements)

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“…115.4 + 13.4 − 260 on the basis of dynamical stability and crossing-time arguments regarding the several cores observed with different systemic velocities, but embedded in a common diffuse envelope. The WSRT data for CHVC 125.3 + 41.3 − 205 likewise supported distances of several hundred kpc, based on a volume-density constraint stemming from the observed upper limit to the kinetic temperature of 85 K. Burton et al (2001) found evidence in Arecibo imaging of ten CHVCs for exponential edge profiles of the individual objects: the outer envelopes of the CHVCs are not tidally truncated and thus are likely to lie at substantial distances from the Milky Way. For plausible values of the thermal pressure at the core/halo interface, these edge profiles support distance estimates which range between 150 and 850 kpc.…”

Section: Galactic Halo Modelsmentioning

confidence: 60%

“…The column density distribution can then be expressed in an analytic form, containing a modified Bessel function of order 1 (e.g. Burton et al 2001). This analytic representation of the column-density distribution is then approximated by a Gaussian of the same halfwidth from, FWHM = 2.543h e .…”

Section: Model Descriptionmentioning

confidence: 99%

“…Simulated objects were considered detected if the peak brightness temperature exceeded the (2000) and Burton et al (2001), based on several different considerations. While few in number, they appear consistent with this distribution.…”

Section: Model Descriptionmentioning

confidence: 99%

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An all–sky study of compact, isolated high–velocity clouds

Heij

Braun²,

Burton

2002

A&A

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105

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Abstract.We combine the catalog of compact high-velocity H  clouds extracted by de Heij et al. (2002) from the Leiden/Dwingeloo Survey in the northern hemisphere with the catalog extracted by from the Parkes HIPASS data in the southern hemisphere, and analyze the all-sky properties of the ensemble. Compact high-velocity clouds are a subclass of the general high-velocity cloud phenomenon which are isolated in position and velocity from the extended high-velocity Complexes and Streams down to column densities below 1.5 × 10 18 cm −2 . Objects satisfying these criteria for isolation are found to have a median angular size of less than one degree. We discuss selection effects relevant to the two surveys; in particular the crucial role played by obscuration due to Galactic H . Five principal observables are defined for the CHVC population: (1) the spatial deployment of the objects on the sky, (2) the kinematic distribution, (3) the number distribution of observed H  column densities, (4) the number distribution of angular sizes, and (5) the number distribution of H  linewidth. Two classes of models are considered to reproduce the observed properties. The agreement of models with the data is judged by extracting these same observables from simulations, in a manner consistent with the sensitivities of the observations and explicitly taking account of Galactic obscuration. We show that models in which the CHVCs are the H  counterparts of dark-matter halos evolving in the Local Group potential provide a good match to the observables. The best-fitting populations have a maximum HI mass of 10 7 M , a power-law slope of the HI mass distribution in the range −1.7 to −1.8, and a Gaussian dispersion for their spatial distributions of between 150 and 200 kpc centered on both the Milky Way and M 31. Given its greater mean distance, only a small fraction of the M 31 sub-population is predicted to have been detected in present surveys. An empirical model for an extended Galactic halo distribution for the CHVCs is also considered. While reproducing some aspects of the population, this class of models does not account for some key systematic features of the population.

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Section: Galactic Halo Modelsmentioning

confidence: 60%

Section: Model Descriptionmentioning

confidence: 99%

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An all–sky study of compact, isolated high–velocity clouds

Heij

Braun²,

Burton

2002

A&A

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105

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“…The existence of a two-component gas structure is widely observed among HVCs and CHVCs (Cram & Giovanelli 1976;Wolfire et al 1995;Burton et al 2001;de Heij et al 2002;Braun & Burton 1999;Westmeier et al 2005). The 2D hydrostatic simulations of CHVCs by Sternberg et al (2002) are consistent with these observations.…”

Section: Evidence For Ram-pressure Interactionmentioning

confidence: 99%

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

Bekhti

Brüns

Kerp

et al. 2006

A&A

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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 with the Leading Arm of the Magellanic Clouds. The goal of our study is to learn more about the origin of the two CHVCs and to use them as probes for the structure and evolution of the Leading Arm. Methods. We have used the Parkes 64-m radio telescope and the Australia Telescope Compact Array (ATCA) to study the two CHVCs in the 21-cm line emission of neutral hydrogen. The observations with a single-dish and a synthesis telescope allow us to analyse both the diffuse, extended emission as well as the small-scale structure of the clouds. We present a method to estimate the distance of the two CHVCs.Results. The investigation of the line profiles of HVC 297+09+253 reveals the presence of two line components in the spectra which can be identified with a cold and a warm gas phase. In addition, we find a distinct head-tail structure in combination with a radial velocity gradient along the tail, suggesting a ram-pressure interaction of this cloud with an ambient medium. HVC 291+26+195 has only a cold gas phase and no head-tail structure. The ATCA data show several cold, compact clumps in both clouds which, in the case of HVC 297+09+253, are embedded in the warm, diffuse envelope. All these clumps have very narrow H i lines with typical line widths between 2 and 4 km s −1 FWHM, yielding an upper limit for the kinetic temperature of the gas of T max = 300 K. We obtain distance estimates for both CHVCs of the order of 10 to 60 kpc, providing additional evidence for an association of the clouds with the Leading Arm. Assuming a distance of 50 kpc, we get H i masses of 5.9 × 10 3 M and 4.0 × 10 4 M for HVC 291+26+195 and HVC 297+09+253, respectively.

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“…This system agrees with the Local Group system at about the one sigma level. Furthermore, analysis of high resolution images of sixteen of the CHVCs provide several independent, although indirect, indications of distances of between 150 and 850 kpc (Braun & Burton 2000;Burton et al 2001). …”

Section: Introductionmentioning

confidence: 99%

An automated search for compact high–velocity clouds in the Leiden/Dwingeloo Survey

Heij

Braun²,

Burton

2002

A&A

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Abstract.We describe an automated search through the Leiden/Dwingeloo H  Survey (LDS) for high-velocity clouds north of δ = −28• . From the general catalog we extract a sample of relatively small (less than about 8• ) and isolated high-velocity clouds, CHVCs: anomalous-velocity H  clouds which are sharply bounded in angular extent with no kinematic or spatial connection to other H  features down to a limiting column density of 1.5 × 10 18 cm −2 . This column density is an order of magnitude lower than the critical H  column density, ∼2 × 10 19 cm −2 , (e.g. Maloney 1993) where the ionized fraction is thought to increase dramatically due to the extragalactic radiation field. As such, these objects are likely to provide their own shielding to ionizing radiation. Their small angular size, of less than about 1• FWHM, might then imply substantial distances, since the partially ionized H  skin in a power-law ionizing photon field has a typical exponential scale-length of 1 kpc (e.g. Corbelli & Salpeter 1993). The automated search algorithm has been applied to the HIPASS and to the Leiden/Dwingeloo data sets. The results from the LDS are described here; Putman et al. (2002) describe application of this algorithm to the HIPASS material. We identify 67 CHVCs in the LDS which satisfy stringent requirements on isolation, and an additional 49 objects which satisfy somewhat less stringent requirements. Independent confirmation is available for all of these objects, either from earlier data in the literature or from new observations made with the Westerbork Synthesis Radio Telescope and reported here. The catalog includes 54 of the 65 CHVCs listed by on the basis of a visual search of the LDS data.

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Erratum: Arecibo imaging of compact high–velocity clouds

Cited by 6 publications

References 1 publication

An all–sky study of compact, isolated high–velocity clouds

An all–sky study of compact, isolated high–velocity clouds

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

An automated search for compact high–velocity clouds in the Leiden/Dwingeloo Survey

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