J. B. Seamus Gallagher

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Using the Wide Field Planetary Camera 2 on the Hubble Space Telescope, we have obtained a deep color-magnitude diagram in V-and I-band equivalents for more than 2000 stars in a patch of the outer disk of the Large Magellanic Cloud (LMC). Aperture photometry is feasible from these data with good signal-to-noise for stars with V25 which allows us for the rst(More)
Sub-arcsecond images, taken in B, R, and Hα filters, and area spectroscopy obtained with the WIYN 3.5-m telescope provide the basis for an investigation of the unusual structures in the stellar body and ionized gas in and around the Perseus cluster central galaxy, NGC 1275. Our Hα filter is tuned to gas at the velocity of NGC 1275, revealing complex,(More)
Through a program of narrow band imaging, we have observed the changing structure of the Hα emission line around the nebular boundary advanced to the southwest at nearly the speed of light, implying that the nebula was created by an expanding wave of radiation originating in the explosion interacting with surrounding material. The expansion speed dropped to(More)
SMC in space and time: a project to study the evolution of the prototype interacting late-type dwarf galaxy Abstract. We introduce the SMC in space and time, a large coordinated space and ground-based program to study star formation processes and history, as well as variable stars, structure, kinematics and chemical evolution of the whole SMC. Here, we(More)
We have obtained high angular resolution, high signal-to-noise spectra of the Calcium triplet absorption lines on the photometric axes of the stellar spheroid in the polar disk galaxy NGC 4650A. Along the major axis, the observed rotation and velocity dispersion measurements show the presence of a kinematically de-coupled nucleus, and a flat velocity(More)
We present a systematic imaging survey of 37 nearby galaxies observed with the Hubble Space Telescope (HST) Wide Field and Planetary Camera 2 (WFPC2) in the mid-UV F300W filter, centered at 2930 A ˚ , as well as in the I-band (F814W) filter at 8230 A ˚. Eleven of these galaxies were also imaged in the F255W filter, centered at 2550 A ˚. Our sample is(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 with a(More)
Nearby (D≤ 100 Mpc) luminous blue starburst galaxies frequently show morphological evidence for recent involvement in mild collisions , or minor mergers where the disk survives. As a consequence UV-bright starbursts are preferentially seen in near face-on galaxies, and the postburst systems may become star-forming late-type galaxies. If this starburst(More)
We have used the Wide Field and Planetary Camera 2 (WFPC2) aboard the Hubble Space Telescope to obtain F 450W and F 814W (Band I-band) observations of the compact star cluster nuclei of the nearby, late-type, low-luminosity spiral galaxies NGC 4395, NGC 4242, and ESO 359-029. In addition, we analyze archival WFPC2 observations of the compact star cluster(More)
Irregular galaxies can be viewed as laboratories for studying the processes of star formation. This class of galaxy, unlike the more familiar spiral galaxies, forms stars without spiral arms and does so from a chemically less-evolved interstellar medium. In this article the problems associated with star formation in irregular galaxies are outlined and their(More)