Search Publications
The Role of Polycyclic Aromatic Hydrocarbons in Ultraviolet Extinction. I. Probing Small Molecular Polycyclic Aromatic Hydrocarbons
Gordon, Karl D.; Witt, A. N.; Whittet, D. C. B. +6 more
We have obtained new Hubble Space Telescope/Space Telescope Imaging Spectrograph spectra to search for structure in the ultraviolet interstellar extinction curve, with particular emphasis on a search for absorption features produced by polycyclic aromatic hydrocarbons (PAHs). The presence of these molecules in the interstellar medium has been post…
A Survey of Far Ultraviolet Spectroscopic Explorer and Hubble Space Telescope Sight Lines through High-Velocity Cloud Complex C
Shull, J. Michael; Giroux, Mark L.; Collins, Joseph A.
Using archival Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST) data, we have assembled a survey of eight sight lines through high-velocity cloud Complex C. Abundances of the observed ion species vary significantly for these sight lines, indicating that Complex C is not well characterized by a single metallicity. Reli…
A Relation between Supermassive Black Hole Mass and Quasar Metallicity?
Hamann, Fred; Dietrich, Matthias; Warner, Craig
We analyze spectra for a large sample of 578 active galactic nuclei to examine the relationships between broad emission line properties and central supermassive black hole (SMBH) mass. We estimate SMBH masses by applying the virial theorem to the C IV λ1549 broad emission line. Although the FWHMs of C IV and Hβ appear nearly unrelated in individua…
The Oort Constants Measured from Proper Motions
Olling, Rob P.; Dehnen, Walter
The Oort constants describe the local spatial variations of the stellar streaming field. The classic way for their determination employs their effect on stellar proper motions. We discuss various problems arising in this procedure. A large, hitherto apparently overlooked, source of potential systematic error arises from longitudinal variations of …
Nascent Starbursts in Synchrotron-deficient Galaxies with Hot Dust
Helou, G.; Roussel, H.; Beck, R. +4 more
Three nearby galaxies that have abnormally high infrared-to-radio continuum ratios, NGC 1377, IC 1953, and NGC 4491, are investigated with a view to understanding the physical origin of their peculiarity. We review the existing data and present new radio continuum measurements along with near-infrared integral-field spectroscopy and molecular gas …
On the Assembly History of Early-Type Galaxies in the Hubble Deep Field-North
van Dokkum, Pieter G.; Ellis, Richard S.
We present deep Keck spectroscopy for a sample of I814<22.5 field early-type galaxies selected morphologically in the redshift range 0.56<=z<=1.02 in the Hubble Deep Field-North (HDF-N). Using velocity dispersions determined from the Keck spectra in conjunction with structural parameters measured from the deep WFPC2 images, we …
Molecular Gas and Dust at z=2.6 in SMM J14011+0252: A Strongly Lensed Ultraluminous Galaxy, Not a Huge Massive Disk
Downes, D.; Solomon, P. M.
We used the IRAM interferometer to detect CO (3-2), CO (7-6), and 1.3 mm dust continuum emission from the submillimeter galaxy SMM J14011+0252 at z=2.6. Contrary to a recent claim that the CO was extended over 6.6" (57 kpc), the new data yield a size of 2''×<=0.5" for the CO and the dust. Although previous results placed the CO peak …
Large Disklike Galaxies at High Redshift
van Dokkum, Pieter G.; Franx, Marijn; Labbé, Ivo +11 more
Using deep near-infrared imaging of the Hubble Deep Field-South with the Infrared Spectrometer and Array Camera on the Very Large Telescope, we find six large disklike galaxies at redshifts z=1.4-3.0. The galaxies, selected in Ks (2.2 µm), are regular and surprisingly large in the near-infrared (rest-frame optical), with face-on e…
The Effect of Proton Temperature Anisotropy on the Solar Minimum Corona and Wind
Raymond, John C.; Vásquez, Alberto M.; van Ballegooijen, Adriaan A.
A semiempirical, axisymmetric model of the solar minimum corona is developed by solving the equations for conservation of mass and momentum with prescribed anisotropic temperature distributions. In the high-latitude regions, the proton temperature anisotropy is strong and the associated mirror force plays an important role in driving the fast sola…
Chromospheric Evaporation and Warm Rain during a Solar Flare Observed in High Time Resolution with the Coronal Diagnostic Spectrometer aboard the Solar and Heliospheric Observatory
Brosius, Jeffrey W.
We present EUV light curves, Doppler shifts, and line-broadening measurements for a flaring solar active region obtained with the Coronal Diagnostic Spectrometer (CDS) aboard the NASA ESA Solar and Heliospheric Observatory (SOHO) under conditions of (1) comprehensive temporal coverage (including the quiescent preflare, impulsive, and gradual decli…