Search Publications
Binaries and the L Dwarf/T Dwarf Transition
Burgasser, Adam J.
High-resolution imaging has revealed an unusually high binary fraction among objects spanning the transition between the L dwarf and T dwarf spectral classes. In an attempt to reproduce and unravel the origins of this apparent binary excess, I present a series of Monte Carlo mass function and multiplicity simulations of field brown dwarfs in the v…
NICMOS Imaging of DRGs in the HDF-S: A Relation between Star Formation and Size at z ~ 2.5
Daddi, E.; Toft, S.; Rix, H. -W. +9 more
We present deep, high angular-resolution HST NICMOS imaging in the Hubble Deep Field South (HDF-S), focusing on a subset of 14 distant red galaxies (DRGs) at z~2.5 that have been preselected to have J-K>2.3. We find a clear trend between the rest-frame optical sizes of these sources and their luminosity-weighted stellar ages as inferred from th…
A Comparative Study between Eruptive X-Class Flares Associated with Coronal Mass Ejections and Confined X-Class Flares
Wang, Yuming; Zhang, Jie
We examine the two kinds of major energetic phenomena that occur in the solar atmosphere: eruptive and confined events. The former describes flares with associated coronal mass ejections (CMEs), while the latter denotes flares without associated CMEs. We find that about 90% of X-class flares are eruptive, but the remaining 10% are confined. To pro…
Evidence for a Population of High-Redshift Submillimeter Galaxies from Interferometric Imaging
Kohno, Kotaro; Wilner, David J.; Schinnerer, Eva +22 more
We have used the Submillimeter Array to image a flux-limited sample of seven submillimeter galaxies, selected by the AzTEC camera on the JCMT at 1.1 mm, in the COSMOS field at 890 µm with ~2" resolution. All of the sources-two radio-bright and five radio-dim-are detected as single point sources at high significance (>6 σ), with positions …
The White Dwarf Cooling Sequence of NGC 6397
Anderson, Jay; Dotter, Aaron; Rich, R. Michael +10 more
We present the results of a deep Hubble Space Telescope (HST) exposure of the nearby globular cluster NGC 6397, focussing attention on the cluster's white dwarf cooling sequence. This sequence is shown to extend over 5 mag in depth, with an apparent cutoff at magnitude F814W~27.6. We demonstrate, using both artificial star tests and the detectabil…
Probing the Dark Matter and Gas Fraction in Relaxed Galaxy Groups with X-Ray Observations from Chandra and XMM-Newton
Humphrey, Philip J.; Buote, David A.; Brighenti, Fabrizio +4 more
We present radial mass profiles within ~0.3rvir for 16 relaxed galaxy groups-poor clusters (kT range 1-3 keV) selected for optimal mass constraints from the Chandra and XMM-Newton data archives. After accounting for the mass of hot gas, the resulting mass profiles are described well by a two-component model consisting of dark matter, re…
Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17
Ford, H. C.; Demarco, R.; van der Wel, A. +13 more
We present a comprehensive mass reconstruction of the rich galaxy cluster Cl 0024+17 at z~=0.4 from ACS data, unifying both strong- and weak-lensing constraints. The weak-lensing signal from a dense distribution of background galaxies (~120 arcmin-2) across the cluster enables the derivation of a high-resolution parameter-free mass map.…
Suzaku Observations of Active Galactic Nuclei Detected in the Swift BAT Survey: Discovery of a ``New Type'' of Buried Supermassive Black Holes
Ueda, Yoshihiro; Terashima, Yuichi; Mushotzky, Richard +6 more
We present the Suzaku broadband observations of two AGNs detected by the Swift BAT hard X-ray (>15 keV) survey that did not have previous X-ray data, SWIFT J0601.9-8636 and SWIFT J0138.6-4001. The Suzaku spectra reveal in both objects a heavily absorbed power-law component with a column density of NH~=1023.5-1024
New Constraints on the Lyman Continuum Escape Fraction at z~1.3
Dickinson, Mark; Ferguson, Henry C.; Giavalisco, Mauro +8 more
We examine deep far-UV (1600 Å) imaging of the HDF-N and the HUDF to search for leaking Lyman continuum radiation from starburst galaxies at z~1.3. There are 21 (primarily sub-L*) galaxies with spectroscopic redshifts between 1.1<z<1.5, and none are detected in the far-UV. We fit stellar population templates to the galaxies' optic…
A Keck Survey for Gravitationally Lensed Lyα Emitters in the Redshift Range 8.5<z<10.4: New Constraints on the Contribution of Low-Luminosity Sources to Cosmic Reionization
Richard, Johan; Smith, Graham P.; Stark, Daniel P. +3 more
We discuss new observational constraints on the abundance of faint high-redshift Lyα emitters secured from a deep Keck near-infrared spectroscopic survey that utilizes the strong magnification provided by lensing galaxy clusters. In each of nine clusters, we have undertaken a systematic ``blind'' search for line emission with NIRSPEC in the J band…