3,593 research outputs found
Interstellar, intracluster and supercluster gas
Hot tenuous plasmas with temperatures in the range 1,000,000 to 3.10 to the 8th power K and densities of .000001 to .001 per cu cm are considered. The dominant radiation processes are thermal bremsstrahlung and collisional line excitation and all except the very hottest objects will have observable X-ray emissions lines. The most important unifying point is the angular scales involved. For the interstellar gas, structure ranging in size from about 10 ft to tens of degrees is expected
The Number Density of Intermediate and High Luminosity Active Galactic Nuclei at z~2-3
We use the combination of the 2 Ms Chandra X-ray image, new J and H band
images, and the Spitzer IRAC and MIPS images of the Chandra Deep Field-North to
obtain high spectroscopic and photometric redshift completeness of high and
intermediate X-ray luminosity sources in the redshift interval z=2-3. We
measure the number densities of z=2-3 active galactic nuclei (AGNs) and
broad-line AGNs in the rest-frame 2-8 keV luminosity intervals 10^44-10^45 and
10^43-10^44 ergs/s and compare with previous lower redshift results. We confirm
a decline in the number densities of intermediate-luminosity sources at z>1. We
also measure the number density of z=2-3 AGNs in the luminosity interval
10^43-10^44.5 ergs/s and compare with previous low and high-redshift results.
Again, we find a decline in the number densities at z>1. In both cases, we can
rule out the hypothesis that the number densities remain flat to z=2-3 at above
the 5-sigma level.Comment: 8 pages, Accepted by The Astrophysical Journal (scheduled for 10 Dec
2005
Are the virial masses of clusters smaller than we think?
The constraints that the available X-ray spectral and imaging data place on the mass distribution and mass to light ratio of rich clusters are considered. It was found for the best determined cases that the mass to light ratio is less than 125 h sub 50 at radii exceeding 1 h sub 50 Mpc. The mass to light ratio is approximately constant at radii exceeding 1 h sub 50 Mpc but may rise to values of roughly 200 h sub 50 in the central regions. The fraction of the total mass that is in baryons, primarily the hot X-ray emitting gas, is roughly 30% thus setting the mass to light ratio of the dark material to roughly 70. The model that fits the X-ray data for Coma is in good agreement with the observed optical velocity dispersion vs. radius data
An Early Bronze Age 'dagger grave' from Rameldry Farm, near Kingskettle, Fife
In February 2000, ploughing disturbed the capstone of a cist, located on the side of a prominent knowe at Rameldry Farm, near Kingskettle in central Fife. Excavation by Headland Archaeology Ltd on behalf of Historic Scotland revealed a short cist which contained the crouched inhumation of a man aged 40-50, who had suffered from arthritis, some tooth loss and possibly Paget's Disease. He had been buried wearing a garment adorned with six V-pelforated buttons. Five of these are of Whitby jet (including one with unique decoration including inlaid tin); the sixth is of the mineral lizardite, and has an enigmatic coating, possibly a glaze. Behind his shoulder was a dagger, of 'Milston type (East Kennet variant) it had had a fancy horn hilt and a scabbard lined with animal skin. The scabbard yielded two A MS radiocarbon dates, with a mean value of 2280-1970 cal Bc at 2
Faintest Galaxy Morphologies from WFPC2 Imaging of the Hawaii Survey Fields
We present very deep WFPC2 images in the F814W filter of two Hawaii
Survey fields, SSA13 and SSA22. Using these data with previous ground-based
imaging and spectroscopy, we compare the colors, star-forming properties and
morphologies of the faintest galaxies with a reference sample of bright nearby
galaxies and analyze the changes in field galaxy morphology with magnitude. Our
principal result is the identification of a new morphological class of
``chain'' galaxies at the faintest magnitudes. Based on limited spectroscopy,
we tentatively conclude that these are linearly organized giant star-forming
regions at and, if this is correct, that these are large galaxies
in the process of formation.Comment: 18 pages + 1 table of text as 1 LaTeX file (uses aastex style macros:
aaspp.sty, flushrt.sty) plus 1 uuencoded compressed tar file of 12 PostScript
figures (Figs. 3-9, 16-17, and 21-23). The remaining gray-scale plots are
available by anonymous ftp at
ftp://hubble.ifa.hawaii.edu/pub/preprints/plates To appear in the October
1995 Astronomical Journa
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