3,095 research outputs found
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
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Star Formation History since z = 1.5 as Inferred from Rest-Frame Ultaviolet Luminosity Density Evolution
We investigate the evolution of the universal rest-frame ultraviolet
luminosity density from z = 1.5 to the present. We analyze an extensive sample
of multicolor data (U', B, V = 24.5) plus spectroscopic redshifts from the
Hawaii Survey Fields and the Hubble Deep Field. Our multicolor data allow us to
select our sample in the rest-frame ultraviolet (2500 angstrom) over the entire
redshift range to z = 1.5. We conclude that the evolution in the luminosity
density is a function of the form (1+z)^{1.7\pm1.0} for a flat lambda cosmology
and (1+z)^{2.4\pm1.0} for an Einstein-de Sitter cosmology.Comment: 12 pages, 7 figs, 5 tables, submitted to A
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