Search Publications
Far-Infrared and Submillimeter Emission from Galactic and Extragalactic Photodissociation Regions
Wolfire, Mark G.; Kaufman, Michael J.; Hollenbach, David J. +1 more
Photodissociation region (PDR) models are computed over a wide range of physical conditions, from those appropriate to giant molecular clouds illuminated by the interstellar radiation field to the conditions experienced by circumstellar disks very close to hot massive stars. These models use the most up-to-date values of atomic and molecular data,…
Heavy-Element Abundances in Blue Compact Galaxies
Thuan, Trinh X.; Izotov, Yuri I.
We present high-quality ground-based spectroscopic observations of 54 supergiant H II regions in 50 low-metallicity blue compact galaxies with oxygen abundances 12+logO/H between 7.1 and 8.3. We use the data to determine abundances for the elements N, O, Ne, S, Ar, and Fe. We also analyze Hubble Space Telescope (HST) Faint Object Spectrograph arch…
Hubble Space Telescope/NICMOS Observations of Massive Stellar Clusters near the Galactic Center
Rich, R. Michael; Serabyn, Eugene; Figer, Donald F. +3 more
We report Hubble Space Telescope (HST) Near-Infrared Camera and Multiobject Spectrometer (NICMOS) observations of the Arches and Quintuplet clusters, two extraordinary young clusters near the Galactic center. For the first time, we have identified main-sequence stars in the Galactic center with initial masses well below 10 Msolar. We pr…
The Spectral Energy Distributions of Low-Luminosity Active Galactic Nuclei
Ho, Luis C.
As a step toward elucidating the physical conditions in nearby active galaxies, this paper presents spectral energy distributions (SEDs) of a sample of seven low-luminosity active galactic nuclei (AGNs). SEDs for four objects are presented for the first time (NGC 4261, NGC 4579, NGC 6251, and M84); the data for the remaining three (M81, M87, and N…
A New Catalog of Photometric Redshifts in the Hubble Deep Field
Lanzetta, Kenneth M.; Yahil, Amos; Fernández-Soto, Alberto
Using the newly available infrared images of the Hubble Deep Field in the J, H, and K bands and an optimal photometric method, we have refined a technique to estimate the redshifts of 1067 galaxies. A detailed comparison of our results with the spectroscopic redshifts in those cases where the latter are available shows that this technique gives ve…
Hubble Space Telescope Observations of Superluminal Motion in the M87 Jet
Sparks, W. B.; Macchetto, F.; Biretta, J. A.
We present observations of the M87 jet made with the Faint Object Camera on board the Hubble Space Telescope at five epochs between 1994 and 1998. These observations reveal 10 superluminal features within the first 6" of the jet, with eight of these having apparent speeds in the range 4c-6c. Two additional features within the first arcsecond of th…
Keplerian Motion of Broad-Line Region Gas as Evidence for Supermassive Black Holes in Active Galactic Nuclei
Peterson, Bradley M.; Wandel, Amri
Emission-line variability data on NGC 5548 argue strongly for the existence of a mass of order 7×107 Msolar within the inner few light-days of the nucleus in the Seyfert 1 galaxy NGC 5548. The time-delayed response of the emission lines to continuum variations is used to infer the size of the line-emitting region, and these d…
The Mass Function of Young Star Clusters in the ``Antennae'' Galaxies
Fall, S. Michael; Zhang, Qing
We determine the mass function of young star clusters in the merging galaxies known as the ``Antennae'' (NGC 4038/9) from deep images taken with the Wide Field Planetary Camera 2 on the refurbished Hubble Space Telescope. This is accomplished by means of reddening-free parameters and a comparison with stellar population synthesis tracks to estimat…
Intrinsic Absorption Lines in Seyfert 1 Galaxies. I. Ultraviolet Spectra from the Hubble Space Telescope
Mushotzky, Richard F.; Crenshaw, D. Michael; Maran, Stephen P. +3 more
We present a study of the intrinsic absorption lines in the ultraviolet spectra of Seyfert 1 galaxies. The study is based on spectra from the Hubble Space Telescope and includes the Seyfert 1 galaxies observed with the Faint Object Spectrograph and Goddard High-Resolution Spectrograph at spectral resolutions of λ/Δλ~1000-20,000 with good signal-to…
SOHO/EIT Observations of the 1997 April 7 Coronal Transient: Possible Evidence of Coronal Moreton Waves
Michels, D. J.; Thompson, B. J.; Gurman, J. B. +7 more
We report observations obtained with the Extreme ultraviolet Imaging Telescope (EIT) on board SOHO of a large-scale coronal transient propagating across the disk of the Sun at a speed of 250 km s-1, in apparent association with a flare and coronal mass ejection. The observations consist of a series of images taken in the Fe XII 195 Å ba…