Chris Simpson

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As part of a large exposure assessment and health-effects panel study, 33 trace elements and light-absorbing carbon were measured on 24-hr fixed-site filter samples for particulate matter with an aerodynamic diameter <2.5 microm (PM2.5) collected between September 26, 2000, and May 25, 2001, at a central outdoor site, immediately outside each subject's(More)
The age of the Universe depends on both the present-day Hubble Constant and on the history of cosmic expansion. For decelerating cosmologies such as Ωm= 1, the dimensionless product H0 t0 < 1 and modestly high values of the Hubble constant H0 > 70 would be inconsistent with a cosmic age t0 larger than 12 Gyr. But if ΩΛ > 0, then H0 t0 can take on a range of(More)
Using a complete, magnitude-limited sample of active galaxies from the Sloan Digital Sky Survey (SDSS) we show that the fraction of broad-line (Type 1) active galactic nuclei increases with luminosity of the isotropically-emitted [O III] narrow emission line. Our results are quantitatively in agreement with, and far less uncertain than, similar trends found(More)
We investigate the ability of the Space Infrared Telescope Facility ’s Infrared Array Camera to detect distant (z ∼ 3) galaxies and measure their photometric redshifts. Our analysis shows that changing the original long wavelength filter specifications provides significant improvements in performance in this and other areas. Subject headings: cosmology:(More)
We present the most accurate measurement to date of cosmological evolution of the near-infrared galaxy luminosity function, from the local Universe out to z ≃ 4. The analysis is based on a large and highly complete sample of galaxies selected from the first data release of the UKIDSS Ultra Deep Survey. Exploiting a master catalogue of Kand z-band selected(More)
An overview of the current status of the 8.2m Subaru Telescope constructed and operated at Mauna Kea, Hawaii, by the National Astronomical Observatory of Japan is presented. The basic design concept and the verified performance of the telescope system are described. Also given are the status of the instrument package offered to the astronomical community,(More)
We present quasi-simultaneous ASCA and RXTE observations of the most luminous known AGN in the local (z < 0.3) universe, the recently discovered quasar PDS 456. Multiwavelength observations have been conducted which show that PDS 456 has a bolometric luminosity of ∼ 10 erg s peaking in the UV part of the spectrum. In the X-ray band the 2-10 keV (rest-frame)(More)
We present HST/WFPC2 images, in narrow-band filters containing the [O III] 5007 and H +[N II] emissionlines and their adjacent continua, of a sample of seven Seyfert 2 galaxies selected on the basis of possessing either extended emission-line regions in ground-based observations or a hidden broad-line region in polarized light. Six of the galaxies have also(More)
We present multiband optical/infrared photometry of V4580 Sgr, the optical counterpart of the accretionpowered millisecond pulsar SAX J1808.4–3658, taken during the 1998 X-ray outburst of the system. The optical flux is consistent with emission from an X-ray–heated accretion disk. Self-consistent modeling of the X-ray and optical emission during the(More)