A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey

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Abstract

High-velocity clouds (HVCs) are neutral or ionized gas clouds in the vicinity of the Milky Way that are characterized by high radial velocities inconsistent with participation in the regular rotation of the Galactic disc. Previous attempts to create a homogeneous all-sky HI map of HVCs have been hampered by a combination of poor angular resolution, limited surface brightness sensitivity and suboptimal sampling. Here, a new and improved HI map of Galactic HVCs based on the all-sky HI4PI survey is presented. The new map is fully sampled and provides significantly better angular resolution (16.2 versus 36 arcmin) and column density sensitivity (2.3 versus 3.7 × 10^18 cm^-2 at the native resolution) than the previously available LAB survey. The new HVC map resolves many of the major HVC complexes in the sky into an intricate network of narrow HI filaments and clumps that were not previously resolved by the LAB survey. The resulting sky coverage fraction of high-velocity HI emission above a column density level of 2 × 10^18 cm^-2 is approximately 15 per cent, which reduces to about 13 per cent when the Magellanic Clouds and other non-HVC emission are removed. The differential sky coverage fraction as a function of column density obeys a truncated power law with an exponent of -0.93 and a turnover point at about 5 ×10^19 cm^-2. HI column density and velocity maps of the HVC sky are made publicly available as FITS images for scientific use by the community.
Original languageEnglish
Pages (from-to)289-299
JournalMonthly Notices of the Royal Astronomical Society
Volume474
Issue number1
DOIs
Publication statusPublished - 1 Feb 2018

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sky
angular resolution
sensitivity
neutral gases
ionized gases
Magellanic clouds
clumps
radial velocity
filaments
brightness
sampling
turnover
power law
exponents
gas

Cite this

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title = "A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey",
abstract = "High-velocity clouds (HVCs) are neutral or ionized gas clouds in the vicinity of the Milky Way that are characterized by high radial velocities inconsistent with participation in the regular rotation of the Galactic disc. Previous attempts to create a homogeneous all-sky HI map of HVCs have been hampered by a combination of poor angular resolution, limited surface brightness sensitivity and suboptimal sampling. Here, a new and improved HI map of Galactic HVCs based on the all-sky HI4PI survey is presented. The new map is fully sampled and provides significantly better angular resolution (16.2 versus 36 arcmin) and column density sensitivity (2.3 versus 3.7 × 10^18 cm^-2 at the native resolution) than the previously available LAB survey. The new HVC map resolves many of the major HVC complexes in the sky into an intricate network of narrow HI filaments and clumps that were not previously resolved by the LAB survey. The resulting sky coverage fraction of high-velocity HI emission above a column density level of 2 × 10^18 cm^-2 is approximately 15 per cent, which reduces to about 13 per cent when the Magellanic Clouds and other non-HVC emission are removed. The differential sky coverage fraction as a function of column density obeys a truncated power law with an exponent of -0.93 and a turnover point at about 5 ×10^19 cm^-2. HI column density and velocity maps of the HVC sky are made publicly available as FITS images for scientific use by the community.",
keywords = "ISM: clouds, Galaxy: halo, Galaxy: kinematics and dynamics, radio lines: ISM",
author = "Tobias Westmeier",
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A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey. / Westmeier, Tobias.

In: Monthly Notices of the Royal Astronomical Society, Vol. 474, No. 1, 01.02.2018, p. 289-299.

Research output: Contribution to journalArticle

TY - JOUR

T1 - A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey

AU - Westmeier, Tobias

PY - 2018/2/1

Y1 - 2018/2/1

N2 - High-velocity clouds (HVCs) are neutral or ionized gas clouds in the vicinity of the Milky Way that are characterized by high radial velocities inconsistent with participation in the regular rotation of the Galactic disc. Previous attempts to create a homogeneous all-sky HI map of HVCs have been hampered by a combination of poor angular resolution, limited surface brightness sensitivity and suboptimal sampling. Here, a new and improved HI map of Galactic HVCs based on the all-sky HI4PI survey is presented. The new map is fully sampled and provides significantly better angular resolution (16.2 versus 36 arcmin) and column density sensitivity (2.3 versus 3.7 × 10^18 cm^-2 at the native resolution) than the previously available LAB survey. The new HVC map resolves many of the major HVC complexes in the sky into an intricate network of narrow HI filaments and clumps that were not previously resolved by the LAB survey. The resulting sky coverage fraction of high-velocity HI emission above a column density level of 2 × 10^18 cm^-2 is approximately 15 per cent, which reduces to about 13 per cent when the Magellanic Clouds and other non-HVC emission are removed. The differential sky coverage fraction as a function of column density obeys a truncated power law with an exponent of -0.93 and a turnover point at about 5 ×10^19 cm^-2. HI column density and velocity maps of the HVC sky are made publicly available as FITS images for scientific use by the community.

AB - High-velocity clouds (HVCs) are neutral or ionized gas clouds in the vicinity of the Milky Way that are characterized by high radial velocities inconsistent with participation in the regular rotation of the Galactic disc. Previous attempts to create a homogeneous all-sky HI map of HVCs have been hampered by a combination of poor angular resolution, limited surface brightness sensitivity and suboptimal sampling. Here, a new and improved HI map of Galactic HVCs based on the all-sky HI4PI survey is presented. The new map is fully sampled and provides significantly better angular resolution (16.2 versus 36 arcmin) and column density sensitivity (2.3 versus 3.7 × 10^18 cm^-2 at the native resolution) than the previously available LAB survey. The new HVC map resolves many of the major HVC complexes in the sky into an intricate network of narrow HI filaments and clumps that were not previously resolved by the LAB survey. The resulting sky coverage fraction of high-velocity HI emission above a column density level of 2 × 10^18 cm^-2 is approximately 15 per cent, which reduces to about 13 per cent when the Magellanic Clouds and other non-HVC emission are removed. The differential sky coverage fraction as a function of column density obeys a truncated power law with an exponent of -0.93 and a turnover point at about 5 ×10^19 cm^-2. HI column density and velocity maps of the HVC sky are made publicly available as FITS images for scientific use by the community.

KW - ISM: clouds

KW - Galaxy: halo

KW - Galaxy: kinematics and dynamics

KW - radio lines: ISM

U2 - 10.1093/mnras/stx2757

DO - 10.1093/mnras/stx2757

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