Search Publications
Globular Cluster Systems. I. V-I Color Distributions
Gebhardt, Karl; Kissler-Patig, Markus
We have compiled data for the globular cluster systems of 50 galaxies from the Hubble Space Telescope Wide Field Planetary Camera 2 archive, of which 43 are type S0 or earlier. In this paper, we present the data set and derive the V-I color distributions. We derive the first four moments of the color distributions, as well as a measure for their n…
The Star Formation History of the Local Group Dwarf Galaxy Leo I
Freedman, Wendy L.; Aparicio, Antonio; Gallart, Carme +2 more
We present a quantitative analysis of the star formation history (SFH) of the Local Group dSph galaxy Leo I, from the information in its Hubble Space Telescope [(V-I),I] color-magnitude diagram (CMD). It reaches the level of the oldest main-sequence turnoffs, and this allows us to retrieve the SFH in considerable detail. The method we use is based…
The Formation and Evolution of Candidate Young Globular Clusters in NGC 3256
Zepf, Stephen E.; Freeman, Kenneth C.; Sharples, Ray M. +2 more
We present images of the recent galaxy merger NGC 3256 obtained with the Wide Field Planetary Camera 2 of the Hubble Space Telescope in B and I filters. We show that there is a large population of more than 1000 compact, bright, blue objects in this galaxy within the 7 kpcx7 kpc region studied. These objects have sizes, colors, and luminosities li…
Simultaneous Multicolor Detection of Faint Galaxies in the Hubble Deep Field
Szokoly, Gyula P.; Szalay, Alexander S.; Connolly, Andrew J.
We present a novel way to detect objects when multiband images are available. Typically, object detection is performed in one of the available bands or on a somewhat arbitrarily co-added image. Our technique provides an almost optimal way to use all the color information available. We build up a composite image of the N passbands where each pixel …
Using HUBBLE SPACE TELESCOPE Imaging of Nuclear Dust Morphology to Rule Out Bars Fueling Seyfert Nuclei
Mulchaey, John S.; Regan, Michael W.
If active galactic nuclei (AGN) are powered by the accretion of matter onto massive black holes, how does the gas in the host galaxy lose the required angular momentum to approach the black hole? Gas easily transfers angular momentum to stars in strong bars, making them likely candidates. Although ground-based searches for bars in active galaxies …
A Keck High-Resolution Spectroscopic Study of the Orion Nebula Proplyds
O'Dell, C. R.; Henney, W. J.
We present the results of spectroscopy of four bright proplyds in the Orion Nebula obtained at a velocity resolution of 6 km s-1. After careful isolation of the proplyd spectra from the confusing nebular radiation, the emission-line profiles are compared with those predicted by realistic dynamic/photoionization models of the objects. Th…
Observations and Implications of the Star Formation History of the Large Magellanic Cloud
Cole, Andrew A.; Ballester, Gilda E.; Crisp, David +14 more
We present derivations of star formation histories based on color-magnitude diagrams of three fields in the LMC from HST/WFPC2 observations. One field is located in the LMC bar and the other two are in the outer disk. We find that a significant component of stars older than 4 Gyr is required to match the observed color-magnitude diagrams. Models w…
Optical and Radio Polarimetry of the M87 Jet at 0.2" Resolution
Perlman, Eric S.; Sparks, William B.; Macchetto, F. Duccio +2 more
We discuss optical (HST/WFPC2 F555W) and radio (15 GHz VLA) polarimetry observations of the M87 jet taken during 1994-1995. The angular resolution of both observations is ~0.2", which at the distance of M87 corresponds to 15 pc. Many knot regions are very highly polarized (~40%-50%, approaching the theoretical maximum for optically thin synchrotro…
The Star Formation History of I ZW 18
Aloisi, Alessandra; Tosi, Monica; Greggio, Laura
The star formation history in I ZW 18 has been inferred from Hubble Space Telescope Wide Field Planetary Camera 2 archival data. This is done by comparing the derived V, B-V and V, V-I color-magnitude diagrams and luminosity functions with synthetic ones, based on various sets of stellar evolutionary tracks. At a distance of 10 Mpc, the stars reso…
The Metallicity Distribution in the Halo Stars of NGC 5128: Implications for Galaxy Formation
Harris, William E.; Harris, Gretchen L. H.; Poole, Gregory B.
We have used the Hubble Space Telescope to obtain WFPC2 V, I photometry for stars in the halo of NGC 5128, the nearest giant elliptical galaxy. The resulting color-magnitude diagram (CMD) of this field, which lies ~21 kpc from the center of the galaxy, contains more than 10,000 stars and reaches almost 3 mag down the red giant branch (RGB). From t…