Search Publications
The Direct Detection of Lyman Continuum Emission from Star-forming Galaxies at z~3
Pettini, Max; Erb, Dawn K.; Shapley, Alice E. +2 more
We present the results of rest-frame UV spectroscopic observations of a sample of 14 z~3 star-forming galaxies in the SSA 22a field. These spectra are characterized by unprecedented depth in the Lyman continuum region. For the first time, we have detected escaping ionizing radiation from individual galaxies at high redshift, with 2 of the 14 objec…
Strong and Weak Lensing United. III. Measuring the Mass Distribution of the Merging Galaxy Cluster 1ES 0657-558
Bradač, Maruša; Schrabback, Tim; Jones, Christine +7 more
The galaxy cluster 1ES 0657-558 (z=0.296) is remarkably well suited for addressing outstanding issues in both galaxy evolution and fundamental physics. We present a reconstruction of the mass distribution from both strong and weak gravitational lensing data. Multicolor, high-resolution HST ACS images allow detection of many more arc candidates tha…
The Expansion Asymmetry and Age of the Cassiopeia A Supernova Remnant
Chevalier, Roger A.; Raymond, John C.; Dopita, Michael A. +7 more
HST images of the young supernova remnant Cas A are used to explore the expansion and spatial distribution of its highest velocity debris. ACS WFC images taken in 2004 March and December with Sloan F625W, F775W, and F850LP filters were used to identify 1825 high-velocity, outlying ejecta knots through measured proper motions of 0.35"-0.90" yr…
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…