Search Publications
The Evolution of the Star Formation Activity in Galaxies and Its Dependence on Environment
Aragón-Salamanca, Alfonso; White, Simon D. M.; Milvang-Jensen, Bo +16 more
We study how the proportion of star-forming galaxies evolves between z=0.8 and 0 as a function of galaxy environment, using the O II line in emission as a signature of ongoing star formation. Our high-z data set comprises 16 clusters, 10 groups, and another 250 galaxies in poorer groups and the field at z=0.4-0.8 from the ESO Distant Cluster Surve…
A New Cepheid Distance to the Maser-Host Galaxy NGC 4258 and Its Implications for the Hubble Constant
Stanek, K. Z.; Bersier, D.; Reid, M. J. +2 more
We present initial results from a time series BVI survey of two fields in NGC 4258 using the HST ACS. This galaxy was selected because of its accurate maser-based distance, which is anticipated to have a total uncertainty of ~3%. The goal of the HST observations is to provide an absolute calibration of the Cepheid distance scale and to measure its…
[Si II], [Fe II], [C II], and H2 Emission from Massive Star-forming Regions
Kaufman, Michael J.; Wolfire, Mark. G.; Hollenbach, David J.
We calculate the [Si II] 34.8 µm, [Fe II] 26.0 µm, and [C II] 158 µm infrared fine-structure emission that may arise from ionized gas (H II regions) and/or associated neutral gas (photodissociation regions [PDRs]) in massive star-forming regions. Assuming thermal pressure balance between an H II region and a PDR, the relative amo…
What Is the Total Deuterium Abundance in the Local Galactic Disk?
Jenkins, Edward B.; Moos, H. W.; Blair, William P. +14 more
Analyses of spectra obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, together with spectra from the Copernicus and interstellar medium absorption profile spectrograph (IMAPS) instruments, reveal an unexplained, very wide range in the observed deuterium/hydrogen (D/H) ratios for interstellar gas in the Galactic disk beyond…
The Hubble Constant: A Summary of the Hubble Space Telescope Program for the Luminosity Calibration of Type Ia Supernovae by Means of Cepheids
Panagia, N.; Saha, A.; Macchetto, F. D. +3 more
This is the final summary paper of our 15 yr program using the Hubble Space Telescope (HST) to determine the Hubble constant from the Cepheid-calibrated luminosity of Type Ia supernovae. Several recent developments have made it necessary to put the summary on H0 on a broader basis than we originally thought (see the four papers cited in…
Is the SMC Bound to the LMC? The Hubble Space Telescope Proper Motion of the SMC
van der Marel, Roeland P.; Kallivayalil, Nitya; Alcock, Charles
We present a measurement of the systemic proper motion of the Small Magellanic Cloud (SMC) made using the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST). We tracked the SMC's motion relative to four background QSOs over a baseline of approximately 2 yr. The measured proper motion is µW=-1.16+/-0.18 mas yr
A Statistical Study of Main and Residual Accelerations of Coronal Mass Ejections
Zhang, J.; Dere, K. P.
In this paper we present the results of a statistical study of the accelerations of coronal mass ejections (CMEs). A CME usually undergoes a multiphased kinematic evolution, with a main acceleration phase characterized by a rapid increase of CME velocity in the inner corona, followed by a relatively smooth propagation phase characterized by a cons…
A Long, Hard Look at the Low/Hard State in Accreting Black Holes
Wijnands, R.; Fabian, A. C.; Miller, J. M. +5 more
We present the first results of coordinated multiwavelength observations of the Galactic black hole GX 339-4 in a canonical low/hard state, obtained during its 2004 outburst. XMM-Newton observed the source for two revolutions, or approximately 280 ks; RXTE monitored the source throughout this long stare. The resulting data offer the best view yet …
Pixie Dust: The Silicate Features in the Diffuse Interstellar Medium
Tielens, A. G. G. M.; Chiar, J. E.
We have analyzed the 9.7 and ``18'' µm interstellar silicate absorption features along the line of sight toward four heavily extincted galactic WC-type Wolf-Rayet (WR) stars. We construct two interstellar extinction curves from 1.25 to 25 µm using near-IR extinction measurements from the literature, along with the silicate profiles of …
The Sloan Lens ACS Survey. II. Stellar Populations and Internal Structure of Early-Type Lens Galaxies
Treu, Tommaso; Bolton, Adam S.; Burles, Scott +2 more
We use HST images to derive effective radii and effective surface brightnesses of 15 early-type (E+S0) lens galaxies identified by the SLACS Survey. Our measurements are combined with stellar velocity dispersions from the SDSS database to investigate for the first time the distribution of lens galaxies in the fundamental plane (FP) space. Accounti…