It is thought that the chiral molecules of living material can induce circular polarization in light at levels much higher than expected from abiotic processes. We therefore obtained high quality imaging circular polarimetry of the martian surface during the favorable opposition of 2003 to seek evidence of anomalous optical activity. We used two narrow-band filters covering 43% of the martian surface, 15% of it in-depth. With polarization noise levels <0.1% (4.3 upper limits 0.2-0.3%) and spatial resolution 210 km, we did not find any regions of circular polarization. When data were averaged over the observed face of the planet, we did see a small non-zero circular polarization 0.02%, which may be due to effects associated with the opposition configuration though it is at the limit of the instrumental capability. Our observations covered only a small fraction of parameter space, so although we obtained a null result, we cannot exclude the presence of optical activity at other wavelengths, in other locations, or at higher spatial resolution.
We present images taken with the Wide Field Planetary Camera (WFPC-2) on the Hubble Space Telescope of 43 quasars selected from the 3CR radio catalog. The redshift range of the targets is large --- 0.3 < z < 2. These data were taken in the course of a large program that imaged 267 3CR radio galaxies and quasars using the HST in snapshot mode. Each quasar was centered on the Planetary Camera (PC1) and was imaged through the F702W filter (bandpass similar to Cousins R), typically for 5 and 10 minutes. Our analysis suggests that the quasar fuzz contributes from <5% to nearly 100% in the most extreme case (about 20% being typical) of the total light from the quasar, with 16 of the quasars (~40%) being unresolved according to the analysis of their light profiles (with only 7 being considered unresolved determined by PSF subtraction of the quasar images). Most of the host galaxies show twisted, asymmetric, or distorted isophotes. About 1/4 of the quasar hosts have close (within a few arc seconds) companions seen in projection and about 1/10 show obvious signs of tidal interactions with a close companion. We find that these sources exhibit a tendency for the principal axes of the radio and optical emission to align similar but perhaps weaker than that observed for radio galaxies.
We have used FORS1 at the ESO VLT to search for light echoes in imaging polarimetry from four historical supernovae in the face-on nearby spiral galaxy M83 (NGC 5236). No echoes were detected around our targets (SN 1923A, SN 1945B, SN 1950B and SN 1957D). This implies that the interstellar medium in their environs is rather tenuous (a few particles/cm^3), possibly as a result of previous supernova explosions that could have cleared the immediate vicinities of our targets. The merits and limitations of searching for light echoes in imaging polarimetry are discussed. From the photometry of the sources detected at the supernova locations, we estimate star cluster masses of 720, 400, 300 Mo for the cluster progenitors of SN 1957D, SN 1923A, and SN 1950B, respectively, and an upper limit of few tens of solar masses for SN 1945B.
We describe CCD observations and a numerical procedure which combine to be particularly effective in locating dust-lanes in elliptical galaxies. Application to 31 bright ellipticals shows that eight possess dust features while several others may do so. The technique also finds galaxies in the sample with compact and diffuse red nuclei, and of the present sample only 5/31 or ~ 15 percent show no colour gradients. Compact red nuclei are common in flat-spectrum radio ellipticals.
We report the results of Hubble Space Telescope near-infrared camera and multiobject spectrometer and Wide Field Planetary Camera 2 imaging of emission-line nebulae in the central galaxies of three clusters of galaxies purported to host massive cooling flows: Perseus (NGC 1275), Abell 2597, and PKS 0745-191. The spectral signature of vibrationally excited molecular hydrogen has been seen in every galaxy searched thus far that is central to a cluster cooling flow with an optical emission-line nebula. With the exquisite spatial resolution available to us with the Hubble Space Telescope, we have discovered that the vibrationally excited molecular hydrogen gas extends several kiloparsecs from the centers of Abell 2597 and PKS 0745-191, while the vibrationally excited molecular hydrogen in NGC 1275 appears to be mostly confined to its nucleus, with some extended emission less than 1 kpc from the center. The molecular hydrogen in Abell 2597 and PKS 0745-191 seems to be nearly cospatial with the optical emission-line filaments in those systems. There may be a tiny jet visible in the 1.6 μm image of PKS 0745-191. We also find significant dust absorption features in the 1.6 μm images of all three systems. The dust lanes are not strictly cospatial with the emission-line filaments, but are aligned with and perhaps intermingled with them. The morphology of the emission-line systems suggests that the presence of vibrationally excited molecular hydrogen is not purely an active galactic nucleus-related property of cluster "cooling flow" nebulae, and that the optical and infrared emission-line gas, that is, the ionized and vibrationally excited molecular gas, have similar origins, if not also similar energy sources. The infrared molecular hydrogen lines are much too bright to be generated by gas simply cooling from a cooling flow; furthermore, the gas, because it is dusty, likely did not condense from the hot intracluster medium (ICM). We examine some candidates for heating the nebulae, including X-ray irradiation by the ICM, UV fluorescence by young stars, and shocks. UV heating by young stars provides the most satisfactory explanation for the H2 emission in A2597; X-ray irradiation is energetically unlikely and strong shocks (v ≳ 40 km s-1) are ruled out by the high H2/Hα ratios. If UV heating is the main energy input, a few billion solar masses of molecular gas are present in A2597 and PKS 0745-191. UV irradiation models predict a significant amount of 1.0-2.0 μm emission line from higher excitation H2 transitions and moderate far-infrared luminosities (~1044 h-2 ergs s-1) for A2597 and PKS 0745-191. Even in the context of UV fluorescence models, the total amount of H2 gas and star formation inferred from these observations is too small to account for the cooling flow rates and longevities inferred from X-ray observations. We note an interesting new constraint on cooling flow models: the radio sources do not provide a significant amount of shock heating, and therefore they cannot counterbalance the cooling of the X-ray gas in the cores of these clusters.
We present UV images of 27 3CR radio galaxies with redshifts z < 0.1 that have been imaged with the Space Telescope Imaging Spectrograph (STIS) on board the Hubble Space Telescope (HST). The observations employed the NUV MAMA and broadband filters with peak sensitivity at 2200 Å. We find that the UV luminosities show approximately a factor of 10-100 higher dispersion than the optical. We compare the UV morphologies with optical V- and R-band WFPC2 snapshot survey images. We have found dramatic, complex, and extended UV emission from radio galaxies even at zero redshift. We find a diverse range of UV morphologies, some completely divergent from their visual morphology, which are reminiscent of the chaotic high-z radio galaxy structures seen in rest-frame UV. The UV morphologies show regions of star formation, jets, and possible scattered active galactic nucleus continuum. The UV emission is generally not aligned with the radio structure. We also detect the diffuse UV emission of the host galaxy. We propose that these are the same physical phenomena as observed at high redshift, but on a smaller spatial scale.
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