First Results from the Arecibo Galactic H<scp>i</scp>Survey: The Disk/Halo Interface Region in the Outer Galaxy

Stanimirović, Snežana; Putman, Mary E.; Heiles, Carl; Peek, J. E. G.; Goldsmith, Paul F.; Koo, Bon‐Chul; Krčo, Marko; Lee, Jae‐Joon; Mock, Jeff; Müller, Erik; Pandian, J. D.; Parsons, Aaron; Tang, Yvonne; Werthimer, Dan

doi:10.1086/508800

Cited by 71 publications

(87 citation statements)

References 58 publications

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“…The distance was determined using the terminal velocity of the sources. b) Stanimirović et al (2006), using the Arecibo 300-m radio telescope, detected a number H i clouds distinctively separated from the Galactic disk towards the anti-center direction. Due to high intrinsic uncertainties, kinematic distances were not used, and the authors opted to use pressure equilibrium considerations to determine the distance.…”

Section: Comparison Between the Properties Of Different Samples Of H mentioning

confidence: 99%

Properties of extra-planar H I clouds in the outer part of the Milky Way

Dedes

Kalberla

2010

A&A

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Context. There is mounting evidence for an extra-planar gas layer around the Milky Way disk, similar to the anomalous H i gas detected in a few other galaxies. As much as 10% of the gas may be in this phase. Aims.We analyze H i clouds located in the disk-halo interface outside the solar circle to probe the properties of the extra-planar H i gas, which is following Galactic rotation. Methods. We use the Leiden/Argentine/Bonn (LAB) 21-cm line survey to search for H i clouds which take part in the rotation of the Galactic plane, but are located above the disk layer. Selected regions are mapped with the Effelsberg 100-m telescope. Two of the H i halo clouds are studied in detail for their small scale structure using the Westerbork Synthesis Radio Telescope (WSRT) and the NRAO Very Large Array (VLA) .Results. Data from the 100 m telescope allow for the parameterization of 25 distinct H i halo clouds at Galactocentric radii 10 kpc < R <15 kpc and heights 1 kpc < z < 5 kpc. The clouds have a median temperature of 620 K, column densities of N HI ∼ 10 19 cm −2 , and most of them are surrounded by an extended envelope of warmer H i gas. Interferometer observations for two selected regions resolve the H i clouds into several arc-minute sized cores. These cores show narrow line widths (FWHM ∼ 3 km s −1 ), they have volume densities of n > 1.3 cm −3 , masses up to 24 M , and are on average in pressure equilibrium with the surrounding envelopes. Pressures and densities fall within the expectations from theoretical phase diagrams (P vs. n h ). The H i cores tend to be unstable if one assumes a thermally bistable medium, but are in better agreement with models that predict thermal fragmentation driven by a turbulent flow.

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Section: Comparison Between the Properties Of Different Samples Of H mentioning

confidence: 99%

Properties of extra-planar H I clouds in the outer part of the Milky Way

Dedes

Kalberla

2010

A&A

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“…With the sensitivity of a single-dish radio telescope and resolution approaching that of a compact array, GALFA-H i is 2.5-80 times more sensitive to compact clouds than other large-area surveys (2.5: IGPS; Taylor et al 2003;Stil et al 2006b;McClureGriffiths et al 2005, 15:GASS/EBHIS; McClure-Griffiths et al 2009;Winkel et al 2010, 80: LAB;Kalberla et al 2005). Initial investigations of GALFA-H i data identified many compact clouds, both visually (Begum et al 2010;Stanimirović et al 2006) and through an automated algorithm (Hsu et al 2011).…”

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confidence: 99%

THE GALFA-H i COMPACT CLOUD CATALOG

Saul

Peek

Grcevich

et al. 2012

ApJ

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We present a catalog of 1964 isolated, compact neutral hydrogen clouds from the Galactic Arecibo L-Band Feed Array Survey Data Release One. The clouds were identified by a custom machine-vision algorithm utilizing the difference of Gaussian kernels to search for clouds smaller than 20 . The clouds have velocities typically between |V LSR | = 20 and 400 km s −1 , line widths of 2.5-35 km s −1 , and column densities ranging from 1 to 35 × 10 18 cm −2 . The distances to the clouds in this catalog may cover several orders of magnitude, so the masses may range from less than a solar mass for clouds within the Galactic disk, to greater than 10 4 M for high-velocity clouds (HVCs) at the tip of the Magellanic Stream. To search for trends, we separate the catalog into five populations based on position, velocity, and line width: HVCs; galaxy candidates; cold low-velocity clouds (LVCs); warm, low positive-velocity clouds in the third Galactic quadrant; and the remaining warm LVCs. The observed HVCs are found to be associated with previously identified HVC complexes. We do not observe a large population of isolated clouds at high velocities as some models predict. We see evidence for distinct histories at low velocities in detecting populations of clouds corotating with the Galactic disk and a set of clouds that is not corotating.

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“…Also, H i column densities which are known (typically 10 19 cm −2 ; Stanimirović et al 2006;Putman et al 2002), will be diluted by large unknown beam filling factors at the distance of NGC 2903 (234 = 10 kpc). We can say, however, that the MW's HVC Complex C, with a mass of 4.9 × 10 6 M at a distance of 10 kpc from the Sun (Thom et al 2008), should have been detected, provided it were separated in velocity from the bulk of the H i in NGC 2903 itself.…”

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Λcdm Satellites and H I Companions—the Arecibo Alfa Survey of NGC 2903

Irwin¹,

Hoffman²,

Spekkens³

et al. 2009

ApJ

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We have conducted a deep, complete H i survey, using Arecibo/Arecibo L-band Feed Array (ALFA), of a field centered on the nearby, isolated galaxy, NGC 2903, which is similar to the Milky Way in its properties. The field size was 150 kpc × 260 kpc and the final velocity range spanned from 100 to 1133 km s −1 . The ALFA beams have been mapped as a function of azimuth and cleaned from each azimuth-specific cube prior to forming final cubes. The final H i data are sensitive down to an H i mass of 2 × 10 5 M and column density of 2 × 10 17 cm −2 at the 3 σ 2 δ V level, where σ is the rms noise level and δ V is the velocity resolution. NGC 2903 is found to have an H i envelope that is larger than previously known, extending to at least three times the optical diameter of the galaxy. Our search for companions yields one new discovery with an H i mass of 2.6×10 6 M . The companion is 64 kpc from NGC 2903 in projection, is likely associated with a small optical galaxy of similar total stellar mass, and is dark matter dominated, with a total mass >10 8 M . In the region surveyed, there are now two known companions: our new discovery and a previously known system that is likely a dwarf spheroidal, lacking H i content. If H i constitutes 1% of the total mass in all possible companions, then we should have detected 230 companions, according to Λ cold dark matter (ΛCDM) predictions. Consequently, if this number of dark-matter clumps are indeed present, then they contain less than 1% H i content, possibly existing as very faint dwarf spheroidals or as starless, gasless dark-matter clumps.

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First Results from the Arecibo Galactic HiSurvey: The Disk/Halo Interface Region in the Outer Galaxy

Cited by 71 publications

References 58 publications

Properties of extra-planar H I clouds in the outer part of the Milky Way

Properties of extra-planar H I clouds in the outer part of the Milky Way

THE GALFA-H i COMPACT CLOUD CATALOG

Λcdm Satellites and H I Companions—the Arecibo Alfa Survey of NGC 2903

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