Search Publications
Helicity Evolution in Emerging Active Regions
Pevtsov, Alexei A.; Maleev, Vasily M.; Longcope, Dana W.
We study the evolution of twist and magnetic helicity in the coronal fields of active regions as they emerge. We use multiday sequences of Solar and Heliospheric Observatory Michelson Doppler Interferometer magnetograms to characterize the region's emergence. We quantify the overall twist in the coronal field, α, by matching a linear force-free fi…
Empirically Determined Anisotropic Velocity Distributions and Outflows of O5+ Ions in a Coronal Streamer at Solar Minimum
Cranmer, S. R.; Kohl, J. L.; Frazin, R. A.
Empirical constraints on the O5+ velocity distributions and outflow speeds in a solar minimum equatorial streamer between 2.6 and 5.1 Rsolar are determined using a spectral synthesis code that includes O VI Doppler dimming. These constraints follow directly from UV spectra taken on 1996 October 12 with the Ultraviolet Coronag…
The Las Campanas Infrared Survey. IV. The Photometric Redshift Survey and the Rest-Frame R-Band Galaxy Luminosity Function at 0.5<=z<=1.5
McCarthy, Patrick J.; Martini, P.; Chen, Hsiao-Wen +6 more
We present rest-frame, R-band, galaxy luminosity function measurements for three different redshift ranges: 0.5<=z<=0.75, 0.75<=z<=1.0, and 1.0<=z<=1.5. Our measurements are based on photometric redshifts for ~3000 H-band-selected galaxies with apparent magnitudes 17<=H<=20 from the Las Campanas Infrared Survey. We show tha…
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 …