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TheLockman Hole, or TheLockman Window, is an area of thesky in which minimal amounts of neutralhydrogengas are observed from the perspective of Earth. The Lockman Hole is a relatively clear window on distant objects, which makes it an attractive area of the sky for observational astronomy surveys. It is located near the pointer stars of theBig Dipper in theconstellationUrsa Major and is ~15 square degrees in size.[1][2]
The Lockman Hole is named after its discoverer, astronomerJay Lockman.
The Lockman Hole is located at aboutRA 10h 45m,Dec. +58° and is defined by a region of lowneutral hydrogen gas and dustcolumn density.[3] Column density is a commonly used measure in astronomy for the quantity of a givenchemical element ormolecule in a certain direction. In this region, the typical column density of neutral hydrogen isNH = 0.6 x 1020 cm−2.[4] This column density is moderately lower than typical values near the galactic poles, whereNH 1020 cm−2, and H I column densities ofNH > 1021 cm−2 are common at lowgalactic latitudes and towards H I clouds.[5]
The region around B1950.0 RA10h 45m Dec 57° 20′ has a minimumNH of 4.5 x 1019 cm−2.[3] There is a diffuse cloud covering half of the field.[3][6]
TheLockman Hole East is a subregion of the Lockman Hole centered at J2000.0 RA10h 52m Dec +57°.[7]
TheLockman Hole North-west (LHNW) is a region that appears about as wide as the moon centered at J2000.0 RA10h 34m Dec +57° 40′.,[8][9] with a column density ofNH = 5.72 x 1019 cm−2.[5]
Clouds of neutral hydrogen are ubiquitous in theMilky Way galaxy, and effectively absorbphotons that are energetic enough toionize hydrogen, which requires an energy of 13.6electron volts (in theextreme ultraviolet range). Even the relatively small amounts of hydrogen in the Lockman Hole absorb most radiation at and just above energies of 13.6 electron volts, but even so ittransmitsextreme ultraviolet andsoft x-rayradiation fromextragalactic objects to a greater degree than other areas of the sky.
Neutral hydrogen is also associated withdiffuse emission atinfrared wavelengths that can confuse observations of faint infrared sources.
The relatively clearfield of view offered by the Lockman Hole has allowed its use to view extremely distant regions of the universe. Observations by the Spectral and Photometric Imaging Receiver (SPIRE) instrument aboard theHerschel Space Telescope of the Lockman Hole have imaged thousands of extremely distantgalaxies that appear as they did 10–12 billion years ago.[10]
This field of view also contains hundreds ofastronomical X-ray sources, some of them supermassiveblack holes.TheChandra X-ray Observatory andROSAT have been used to study X-ray sources from the Lockman Hole.[4] Some 75 X-ray sources are observed with the PSPC ofROSAT.[4]
Detailed X-ray spectral analysis has been performed on 123 X-ray sources in the Lockman Hole using XMM-Newton.[11]
The diffuse X-ray background (XRB) has also been studied in the area.[12][13]
Active galactic nuclei have also been studied in the area, for example MBC2005.[11]
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