scholarly journals Effect on dark matter exclusion limits from new silicon photoelectric absorption measurements

2021 ◽  
Vol 104 (6) ◽  
Author(s):  
B. von Krosigk ◽  
M. J. Wilson ◽  
C. Stanford ◽  
B. Cabrera ◽  
R. Calkins ◽  
...  
Keyword(s):  
Dark Matter ◽  
Photoelectric Absorption ◽  
Absorption Measurements

scholarly journals Constraints on Cold HI in the Halo of NGC 3079 from Absorption Measurements of Q0957+561

1999 ◽  
Vol 16 (1) ◽  
pp. 89-94 ◽  
Author(s):  
Judith A. Irwin ◽  
Lawrence M. Widrow ◽  
Jayanne English
Keyword(s):  
Dark Matter ◽  
Fractal Dimension ◽  
Parameter Space ◽  
Upper Limit ◽  
Observational Test ◽  
No Absorption ◽  
Absorption Measurements ◽  
Rule Out

AbstractWe perform the first observational test of dark matter in the form of cold (3 K) fractal clouds, as described by Pfenniger et al. (1994) and Pfenniger & Combes (1994). This is accomplished by probing for HI absorption in the halo of NGC 3079 against the background quasar, Q 0957+561, which is separated from the centre of NGC 3079 by 64 kpc, in projection. No absorption is detected to a limit of 3ΔTb/(–Tc) = 0·01. We have considered models for HI + H2 clouds characterised by the cloud radius and fractal dimension. Using the upper limit on absorption, we have ruled out a limited but interesting region of this parameter space. The observations do not rule out the possibility that all the dark matter could be hidden in the form of cold fractal clouds. By contrast, if the gas is diffuse with unity filling factors, then HI cannot constitute more than ∼ 10−5, by mass, of the galaxy's dark matter.

scholarly journals The absorption of monochromatic X-ray beams, of wave-length in the region 50 to 20 X -units, in lead, tin, copper, and iron

1935 ◽  
Vol 152 (876) ◽  
pp. 402-417 ◽  
Author(s):  
John Read ◽  
John Cunningham McLennan
Keyword(s):  
Absorption Coefficient ◽  
Atomic Number ◽  
Wave Length ◽  
Detailed Account ◽  
Photoelectric Absorption ◽  
Absorption Coefficients ◽  
X Ray ◽  
Method Of Measurement ◽  
Absorption Measurements

In a previous paper an account has been given of the measurement of the absorption of monochromatic X-ray beams of wave-length in the region 50 to 20 x -units, in carbon and aluminium. The relation of the measured coefficient of absorption to the wave-Iength did not differ from that predicted by the Klein-Nishina formula by more than 1%. The method used in that experiment has been improved, and used to measure the absorption coefficients of lead, tin, copper, and iron for similar monochromatic beams. Because lead has been used very extensively for absorption measurements the primary aim has been to measure as accurately as possible the dependence of its absorption coefficient on the wave-length of the radiation. It has not been possible to make such accurate measurements on tin, copper, and iron, but enough data has been obtained to determine the variation of the photoelectric absorption coefficient per electron with the atomic number of the absorbing element, with fair accuracy, for radiation in this region of wave-lengths. Since these absorption coefficients may find considerable application, it is considered well to give a more detailed account of the method of measurement, so that an independent judgment of their reliability may be made.

Existence of RNA 'dark matter' in doubt

Nature ◽  
2010 ◽  
Author(s):  
Melissa Lee Phillips
Keyword(s):  
Dark Matter

Constraints on the Clumpiness of Dark Matter Halos Through Heating of Disk Galaxies

2003 ◽  
Vol 10 ◽  
pp. 95-95
Author(s):  
E. Ardi ◽  
T. Tsuchiya ◽  
A. Burkert
Keyword(s):  
Dark Matter ◽  
Disk Galaxies ◽  
Dark Matter Halos
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