Search Publications
The Morphological Mix of Field Galaxies to M I = 24.25 mag (b J approximately 26 mag) from a Deep Hubble Space Telescope WFPC2 Image
Keel, William C.; Driver, Simon P.; Windhorst, Rogier A. +3 more
We determine the morphological mix of field galaxies down to mI ~= 24.25 mag (mB ~ 26.0 mag) from a single ultradeep Hubble Space Telescope wide field planetary camera (WFPC2) image in both the V606 and the I814 filters. In total, we find 227 objects with mI <= 24.5 mag and classify these into three types: ellipticals (16%), early-type spirals …
Hubble Space Telescope Observations of the SN 1987A Triple Ring Nebula
Casertano, Stefano; Ballester, Gilda E.; Crisp, David +16 more
We have observed SN 1987A with the optically corrected WFPC2 on the Hubble Space Telescope both in emission lines and in the UV and optical continuum. The previously observed outer nebular structure is shown to be part of two closed unresolved loops. These loops were flash-ionized by the supernova itself. They are not caused by limb brightening of…
Hubble Space Telescope Imaging of Super Star Clusters in M82
O'Connell, Robert W.; Gallagher, John S., III; Hunter, Deidre A. +1 more
We describe high resolution V- and I-band images obtained with the HST Planetary Camera of the center of the prototype starburst galaxy M82. The deconvolved images reveal a remarkable complex of over 100 compact, luminous "super" star clusters, concentrated to the inner few 100 pcs of the galaxy. These clusters typically have half-peak intensity s…
Hubble Space Telescope Observations of Globular Clusters in M87 and an Estimate of H 0
Lucas, Ray A.; Whitmore, Bradley C.; Sparks, William B. +2 more
Hubble Space Telescope observations of over 1000 globular clusters in the central region of M87 have been made using the Wide Field and Planetary Camera 2. The limiting magnitude in V is 26 mag, more than 2 mag beyond the turnover of the luminosity function. The distribution is well fitted by a Gaussian profile with a mean of <m0
The Contribution of Late-Type/Irregulars to the Faint Galaxy Counts from Hubble Space Telescope Medium-Deep Survey Images
Driver, Simon P.; Windhorst, Rogier A.; Griffiths, Richard E.
We present a complete morphologically classified sample of 144 faint field galaxies from the HST Medium Deep Survey with 20.0 ≤ mI <22.0 mag. We compare the global properties of the ellipticals and early- and late-type spirals and find a nonnegligible fraction (13/144) of compact blue [(V - I) ≤ 1.0 mag] systems with r1/4 …
Multiwavelength Observations of Markarian 421 During a TeV/X-Ray Flare
Kafatos, M.; Takahashi, T.; Kondo, Y. +38 more
A TeV flare from the BL Lac object Mrk 421 was detected in May of 1994 by the Whipple Observatory air Cherenkov experiment during which the flux above 250 GeV increased by nearly an order of magnitude over a 2-day period. Contemporaneous observations by ASCA showed the X-ray flux to be in a very high state. We present these results, combined with …
The Size Distribution of Interstellar Dust Particles as Determined from Polarization: Spheroids
Martin, P. G.; Kim, Sang-Hee
We have determined the size distribution of polarizing interstellar dust grains based on electromagnetic scattering by spheroidal particles, extending our original work based on infinite cylinders. Shapes and alignment variants included the following: perfectly aligned oblate particles with axial ratios 1.414:1, 2:1, 4:1, and 6:1, picket fence pro…
Discovery of Cepheids in NGC 5253: Absolute Peak Brightness of SN IA 1895B and SN IA 1972E and the Value of H 0
Panagia, N.; Saha, A.; Labhardt, Lukas +4 more
Observations with the Hubble Space Telescope between 1993 May 31 and 1993 July 19 in 20 epochs in the F555W passband and five epochs in the F785LP passband have led to the discovery of 14 Cepheids in the Amorphous galaxy NGC 5253. The apparent V distance modulus is (m - M)_AV_ = 28.08 +/- 0.10 determined from the 12 Cepheids with normal amplitudes…
Testing Unified X-Ray/Ultraviolet Absorber Models with NGC 5548
Elvis, Martin; Mathur, Smita; Wilkes, Belinda
The bright Seyfert galaxy NGC 5548 shows absorption features in its X-ray and UV spectra. The large amount of optical/UV and X-ray monitoring data available for this object makes it an ideal candidate to test our model of a common X-ray/UV absorber. We show that the X-ray/UV absorption is caused by a highly ionized (2.2 < U < 2.8), high colu…
Detection of Compact Ultraviolet Nuclear Emission in LINER Galaxies
Filippenko, Alexei V.; Ho, Luis C.; Maoz, Dan +4 more
Low-ionization nuclear emission-line regions (LINERs), which exist in a large fraction of galaxies, may be the least luminous manifestation of quasar activity. As such, they may make possible the study of the AGN phenomenon in the nearest galaxies. The nature of LINERs has, however, remained controversial because an AGN-like nonstellar continuum s…