Search Publications
Difficulties with Recovering the Masses of Supermassive Black Holes from Stellar Kinematical Data
Emsellem, Eric; Merritt, David; Valluri, Monica
We investigate the ability of three-integral, axisymmetric, orbit-based modeling algorithms to recover the parameters defining the gravitational potential (mass-to-light ratio Υ and black hole mass M•) in spheroidal stellar systems using stellar kinematical data. We show that the potential estimation problem is generically underdetermin…
Galaxies at z~7-8: z850-Dropouts in the Hubble Ultra Deep Field
Bouwens, R. J.; Illingworth, G. D.; Thompson, R. I. +6 more
We have detected likely z~7-8 galaxies in the 144''×144'' Near-Infrared Camera and Multi-Object Spectrometer (NICMOS) observations of the Hubble Ultra Deep Field. Objects are required to be >=3 σ detections in both NICMOS bands, J110 and H160. The selection criteria for this sample are (z850
The Evolution of Disk Galaxies in the GOODS-South Field: Number Densities and Size Distribution
Jogee, S.; Dickinson, M.; Ferguson, H. C. +14 more
We examine the evolution of the sizes and number densities of disk galaxies using the high-resolution images obtained by the Great Observatories Origins Deep Survey (GOODS) with the Advanced Camera for Surveys on the Hubble Space Telescope. The multiwavelength images are used to classify galaxies based on their rest-frame B-band morphologies out t…
Ultraviolet Extinction Properties in the Milky Way
Gordon, Karl D.; Clayton, Geoffrey C.; Valencic, Lynne A.
We have assembled a homogeneous database of 417 ultraviolet (UV) extinction curves for reddened sight lines having International Ultraviolet Explorer spectra. We have combined these with optical and Two Micron All Sky Survey photometry, allowing estimates of the ratio of total-to-selective extinction, RV, for the entire sample. Fitzpatr…
Rotation of Jets from Young Stars: New Clues from the Hubble Space Telescope Imaging Spectrograph
Bacciotti, Francesca; Coffey, Deirdre; Eislöffel, Jochen +2 more
We report findings from the first set of data in a current survey to establish conclusively whether jets from young stars rotate. We observed the bipolar jets from the T Tauri stars TH 28 and RW Aur and the blueshifted jet from T Tauri star LkHα 321, using the Hubble Space Telescope Imaging Spectrograph. Forbidden emission lines show distinct and …
Relative Frequencies of Blue Stragglers in Galactic Globular Clusters: Constraints for the Formation Mechanisms
Djorgovski, S. G.; Rich, R. M.; Recio-Blanco, Alejandra +7 more
We discuss the main properties of the Galactic globular cluster (GC) blue straggler stars (BSSs), as inferred from our new catalog containing nearly 3000 BSSs. The catalog has been extracted from the photometrically homogeneous V versus (B-V) color-magnitude diagrams (CMDs) of 56 GCs, based on Wide Field Planetary Camera 2 images of their central …
Obscured Active Galactic Nuclei and the X-Ray, Optical, and Far-Infrared Number Counts of Active Galactic Nuclei in the GOODS Fields
Brandt, William N.; Van Duyne, Jeffrey; Chary, Ranga-Ram +12 more
The deep X-ray, optical, and far-infrared fields that constitute the Great Observatories Origins Deep Survey (GOODS) are sensitive to obscured active galactic nuclei (AGNs; NH>~1022 cm-2) at the quasar epoch (z~2-3), as well as to unobscured AGNs as distant as z~7. Luminous X-ray emission is a sign of accretion …
The Origins of X-Ray Emission from the Hot Spots of FR II Radio Sources
Hardcastle, M. J.; Birkinshaw, M.; Worrall, D. M. +1 more
We use new and archival Chandra data to investigate the X-ray emission from a large sample of compact hot spots of FR II radio galaxies and quasars from the 3C catalog. We find that only the most luminous hot spots tend to be in good agreement with the predictions of a synchrotron self-Compton model with equipartition magnetic fields. At low hot s…
The Formation of Dust Lanes: Implications for Galaxy Evolution
Yoachim, Peter; Dalcanton, Julianne J.; Bernstein, Rebecca A.
From a survey of edge-on disks, we find that disk galaxies show a sharp, mass-dependent transition in the structure of their dusty ISM. In more massive, rapidly rotating disks with Vc>120kms-1, we see the well-defined dust lanes traditionally associated with edge-on galaxies. However, in more slowly rotating, lower mass ga…
The Role of Magnetic Reconnection in the Observable Features of Solar Eruptions
Raymond, J. C.; van Ballegooijen, A. A.; Lin, J.
There are two competing classes of models for coronal mass ejections (CMEs): those that assume a preexisting magnetic flux rope and those that can make a flux rope during the eruption by magnetic reconnection. The present work is based on the model with a preexisting flux rope. We investigate the evolution of morphological features of the magnetic…