The HST Survey of BL Lac Objects: Gravitational Lens Candidates and Other Unusual Sources

Abstract

We present HST observations of seven unusual objects from the HST ``snapshot survey'' of BL Lac objects, of which four are gravitational lens candidates. In three cases a double point sources is observed: 0033+595, with 1.58 arcsec separation, and 0502+675 and 1440+122, each with $\sim 0.3$ arcsec separation. The last two also show one or more galaxies, which could be either host or lensing galaxies. If any are confirmed as lenses, these BL Lac objects are excellent candidates for measuring H${}_0$ via gravitational time delay because of their characteristic rapid, high amplitude variability. An additional advantage is that, like other blazars, they are likely superluminal radio sources, in which case the source plane is mapped out over a period of years, providing strong additional constraints on the lensing mass distribution. The fourth gravitational lens candidate is 1517+656, which is surrounded by three arclets forming an almost perfect ring of radius 2.4 arcsec. If this is indeed an Einstein ring, it is most likely a background source gravitationally lensed by the BL Lac object host galaxy and possibly a surrounding group or cluster. In the extreme case that all four candidates are true lenses, the derived frequency of gravitational lensing in this BL Lac sample would be an order of magnitude higher than in comparable quasar samples. We also report on three other remarkable BL Lac objects: 0138-097, which is surrounded by a large number of close companion galaxies; 0806+524, whose host galaxy contains an uncommon arc-like structure; and 1959+650, which is hosted by a gas rich elliptical galaxy with a prominent dust lane of $\sim 5\times 10^5{M}_{\odot }$.

arXiv comment29 pages in total, 12 figures

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Cited by in corpus (28)

• The HST Survey of BL Lacertae Objects. II. Host Galaxies
• Extreme synchrotron BL Lac objects
• The HST Survey of BL Lacertae Objects. I. Surface Brightness Profiles, Magnitudes, and Radii of Host Galaxies
• The Properties of the Radio-Selected 1Jy Sample of BL Lacertae Objects
• On the redshift of TeV BL Lac objects
• Binary quasars
• Supermassive Black Hole Masses of AGNs with Elliptical Hosts
• The Radio Structure of High-Energy Peaked BL Lacertae Objects
• The HST Survey of BL Lacertae Objects: Morphological Properties of Low redshift Host Galaxies
• BeppoSAX Spectral Survey of BL Lacs - new spectra and results
• Host Galaxies, Obscuration and Nuclear Structure of Three Nearby Compact Symmetric Objects
• X-ray spectral curvature of High Frequency Peaked BL Lacs: a predictor for the TeV flux
• Optical spectroscopy of Blazars for the Cherenkov Telescope Array
• Wide band X-ray and optical observations of the BL Lac object 1ES 1959+650 in high state
• The luminous host galaxies of high redshift BL Lac objects
• Near-Infrared Observations of BL Lacertae Host Galaxies
• Discovery of very high energy gamma-ray emission from the blazar 1ES 0033+595 by the MAGIC telescopes
• Discovery of Very High Energy Gamma Rays from 1ES 1440+122
• High-Resolution Radio Imaging of Gravitational Lensing Candidates in the 1 Jansky BL Lac Sample
• The nature of close companions of the BL Lac Objects 1ES 0502+675 and 1ES 1440+122
• Can Turbulence Dominate Depolarization of Optical Blazars?
• The Cluster-Scale Environment of PKS 2155-304
• PKS 0537-441: extended [O II] emission and a binary QSO?
• Clustering environment of BL Lac object RGB 1745+398
• The jet of the BL Lacertae object PKS 2201+044: MAD near-IR adaptive optics observations and comparison with optical, radio and X-ray data
• H1517+656: the Birth of a BL Lac Object?
• Detection of helicoidal motion in the optical jet of PKS 0521-365
• BL Lac objects with optical jets: PKS 2201+044, 3C 371 and PKS 0521-365