Search Publications
Detailed Structural Decomposition of Galaxy Images
Ho, Luis C.; Rix, Hans-Walter; Peng, Chien Y. +1 more
We present a two-dimensional fitting algorithm (GALFIT) designed to extract structural components from galaxy images, with emphasis on closely modeling light profiles of spatially well-resolved, nearby galaxies observed with the Hubble Space Telescope. Our algorithm improves on previous techniques in two areas: by being able to simultaneously fit …
The Observed Offset Distribution of Gamma-Ray Bursts from Their Host Galaxies: A Robust Clue to the Nature of the Progenitors
Bloom, J. S.; Djorgovski, S. G.; Kulkarni, S. R.
We present a comprehensive study to measure the locations of gamma-ray bursts (GRBs) relative to their host galaxies. In total, we find the offsets of 20 long-duration GRBs from their apparent host galaxy centers by utilizing ground-based images from Palomar and Keck and space-based images from the Hubble Space Telescope (HST). We discuss in detai…
A Hubble Space Telescope Census of Nuclear Star Clusters in Late-Type Spiral Galaxies. I. Observations and Image Analysis
Böker, Torsten; Ho, Luis C.; Shields, Joseph C. +4 more
We present new Hubble Space Telescope I-band images of a sample of 77 nearby late-type spiral galaxies with low inclination. The main purpose of this catalog is to study the frequency and properties of nuclear star clusters. In 59 galaxies of our sample, we have identified a distinct, compact (but resolved), and dominant source at or very close to…
A New Spectral Classification System for the Earliest O Stars: Definition of Type O2
Walborn, Nolan R.; Parker, Joel Wm.; Drissen, Laurent +7 more
High-quality, blue-violet spectroscopic data are collected for 24 stars that have been classified as type O3 and that display the hallmark N IV and N V lines. A new member of the class is presented; it is the second known in the Cyg OB2 association, and only the second in the northern hemisphere. New digital data are also presented for several of …
Hubble Space Telescope Evidence for an Intermediate-Mass Black Hole in the Globular Cluster M15. II. Kinematic Analysis and Dynamical Modeling
Gerssen, Joris; van der Marel, Roeland P.; Gebhardt, Karl +3 more
We have used the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope (HST) to obtain high spatial resolution spectroscopy of the central region of the dense globular cluster M15. The observational strategy and data reduction were described in Paper I of this series. Here we analyze the extracted spectra with a cross-correlati…
The Luminosity Function of Star Clusters in Spiral Galaxies
Larsen, Søren S.
Star clusters in six nearby spiral galaxies are examined using archive images from the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope (HST). The galaxies have previously been studied from the ground and some of them are known to possess rich populations of ``young massive clusters.'' Comparison with the HST images indica…
Deviations from the Local Hubble Flow. I. The Tip of the Red Giant Branch as a Distance Indicator
Méndez, Bryan; Davis, Marc; Moustakas, John +3 more
The properties of the velocity field in the local volume (cz<550 km s-1) have been difficult to constrain because of a lack of a consistent set of galaxy distances. The sparse observations available to date suggest a remarkably quiet flow, with little deviation from a pure Hubble law. However, velocity field models based on the distr…
The Halo Stars in NGC 5128. III. An Inner Halo Field and the Metallicity Distribution
Harris, William E.; Harris, Gretchen L. H.
We present new Hubble Space Telescope WFPC2 (V,I) photometry for field stars in NGC 5128 at a projected distance of 8 kpc from the galaxy center, which probes a mixture of its inner halo and outer bulge. The color-magnitude diagram shows an old red giant branch that is even broader in color than our two previously studied outer halo fields (at 21 …
Internal Dynamics, Structure, and Formation of Dwarf Elliptical Galaxies. I. A Keck/Hubble Space Telescope Study of Six Virgo Cluster Dwarf Galaxies
Geha, M.; van der Marel, R. P.; Guhathakurta, P.
Spectroscopy with the Keck II 10 m telescope and Echelle Spectrograph and Imager is presented for six Virgo Cluster dwarf elliptical (dE) galaxies in the absolute magnitude range -15.7<=MV<=-17.2. The mean line-of-sight velocity and velocity dispersion are resolved as a function of radius along the major axis of each galaxy, nearl…
Astrometry with the Hubble Space Telescope: A Parallax of the Fundamental Distance Calibrator RR Lyrae
McArthur, B. E.; Franz, O. G.; Bradley, A. J. +16 more
We present an absolute parallax and relative proper motion for the fundamental distance scale calibrator, RR Lyrae. We obtain these with astrometric data from FGS 3, a white-light interferometer on the Hubble Space Telescope. We find πabs=3.82+/-0.2 mas. Spectral classifications and VRIJHKT2M and DDO 51 photometry of the astr…