Search Publications
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…
The Metagalactic Ionizing Radiation Field at Low Redshift
Shull, J. Michael; Giroux, Mark L.; Penton, Steven V. +2 more
We compute the ionizing radiation field at low redshift, arising from Seyferts, QSOs, and starburst galaxies. This calculation combines recent Seyfert luminosity functions, extrapolated ultraviolet fluxes from our IUE-AGN database, and a new intergalactic opacity model based on Hubble Space Telescope and Keck Lyα absorber surveys. At z=0 for AGNs …
Hubble Space Telescope Observations of the CFA Seyfert 2 Galaxies: The Fueling of Active Galactic Nuclei
Pogge, Richard W.; Martini, Paul
We present an investigation of possible fueling mechanisms operating in the inner kiloparsec of Seyfert galaxies. We analyze visible and near-infrared Hubble Space Telescope images of 24 Seyfert 2 galaxies from the CfA Redshift Survey sample. In particular, we are searching for the morphological signatures of dynamical processes responsible for tr…
Evidence for Large-Scale Structure at z ~ 2.4 from Lyα Imaging
Keel, William C.; Windhorst, Rogier A.; Cohen, Seth H. +1 more
The history of large-scale structure depends on cosmological parameters and on how merging unfolds among both galaxies and groups. There has been recent evidence for clustering among Lyα emitters, Lyman-break galaxies, and Lyman absorbers. We present deep, wide-field medium-band imaging in redshifted Lyα of fields surrounding regions selected to h…