Search Publications
Suppression of dwarf galaxy formation by cosmic reionization
Loeb, Abraham; Wyithe, J. Stuart B.
A large number of faint galaxies, born less than a billion years after the Big Bang, have recently been discovered. Fluctuations in the distribution of these galaxies contributed to a scatter in the ionization fraction of cosmic hydrogen on scales of tens of megaparsecs, as observed along the lines of sight to the earliest known quasars. Theoretic…
Spectral Statistics and Local Luminosity Function of a Complete Hard X-Ray Sample of the Brightest Active Galactic Nuclei
Ishisaki, Y.; Ueda, Y.; Miyaji, T. +2 more
We have measured the X-ray spectral properties of a complete flux-limited sample of bright active galactic nuclei (AGNs) from the HEAO-1 all-sky catalogs to investigate their statistics and provide greater constraints on the bright end of the hard X-ray luminosity function (HXLF) and the AGN population synthesis model of the X-ray background. Spec…
Extinction Columns and Intrinsic X-Ray Spectra of the Anomalous X-Ray Pulsars
Durant, Martin; van Kerkwijk, Marten H.
The X-ray spectra of anomalous X-ray pulsars have long been fit by smooth, empirical models such as the sum of a blackbody plus a power law. These reproduce the ~0.5-10 keV range well, but fail at lower and higher energies, grossly overpredicting the optical and underpredicting the hard X-ray emission. A poorly constrained source of uncertainty in…
Ages, metallicities and [α/Fe] ratios of globular clusters in NGC 147, 185 and 205
Afanasiev, V. L.; Sharina, M. E.; Puzia, T. H.
We present measurements of ages, metallicities and [α/Fe] ratios for 16 globular clusters (GCs) in NGC 147, 185 and 205 and of the central regions of the diffuse galaxy light in NGC 185 and 205. Our results are based on spectra obtained with the SCORPIO multislit spectrograph at the 6-m telescope of the Russian Academy of Sciences. We include in o…
Electron temperature of Titan's sunlit ionosphere
Coates, A. J.; Wahlund, J. -E.; Galand, M. +2 more
Titan's upper atmosphere is ionized by solar radiation and particle bombardment from Saturn's magnetosphere. The induced ionosphere plays a key role in the coupling of Titan's atmosphere with the Kronian environment. It also provides unique signatures for identifying energy sources upon Titan's upper atmosphere. Here we focus on observations from …
Low-energy (order 10 eV) ion flow in the magnetotail lobes inferred from spacecraft wake observations
Dandouras, I.; André, M.; Quinn, J. +4 more
Cold ionospheric ions with eV energies are common in the magnetosphere and can travel far out in the magnetotail. However, they are difficult to measure with conventional ion spectrometers mounted on spacecraft, since the potential of a sunlit spacecraft often reaches several tens of volts. In this paper we present two alternative methods of measu…
The near-infrared luminosity function of cluster galaxies beyond redshift one
Demarco, R.; Lidman, C.; Toft, S. +7 more
Aims.We determined the Ks band luminosity function (LF), and inferred the corresponding stellar mass function, of cluster galaxies at redshift z≃ 1.2, using near-infrared images of three X-ray luminous clusters at z=1.11,1.24,1.27.
Methods: .The composite LF was derived down to M*+4, by means of statistical background sub…
The Sunyaev-Zel'dovich Effect in a Sample of 31 Clusters: A Comparison between the X-Ray Predicted and WMAP Observed Cosmic Microwave Background Temperature Decrement
Zhang, Shuang-Nan; Lieu, Richard; Mittaz, Jonathan P. D.
The WMAP Q-, V-, and W-band radial profiles of temperature deviation of the cosmic microwave background (CMB) were constructed for a sample of 31 randomly selected nearby clusters of galaxies in directions of Galactic latitude b>30deg. The profiles were compared in detail with the expected CMB Sunyaev-Zel'dovich effect (SZE) caused b…
Vertical distribution of Galactic disk stars
Soubiran, C.; Siebert, A.; Bienaymé, O. +2 more
We used red clump stars to measure the surface mass density of the Galactic disk in the solar neighbourhood. High resolution spectra of red clump stars towards the NGP have been obtained with the ELODIE spectrograph at OHP for Tycho-2 selected stars, and nearby Hipparcos counterparts were also observed. We determined their distances, velocities, a…
Titan's damp ground: Constraints on Titan surface thermal properties from the temperature evolution of the Huygens GCMS inlet
Zarnecki, John C.; Lorenz, Ralph D.; Niemann, Hasso B. +2 more
A simple thermal model is developed to determine the temperature history of the inlet tube of the Huygens probe gas chromatograph mass spectrometer (GCMS) after its fortuitous emplacement on the surface of Saturn's moon Titan. The model parameters are adjusted to match the recorded temperature history of a nearby heater, taking into account heat l…