arXiv subjects

T. J. Pearson

Publications and source records attributed to T. J. Pearson.

151 records · Page 9Linked to original sources

arXiv1999

CLASS B1152+199 and B1359+154: Two New Gravitational Lens Systems Discovered in the Cosmic Lens All-Sky Survey

The third phase of the Cosmic Lens All-Sky Survey (CLASS) has recently been completed, bringing the total number of sources imaged to over 15000 in the CLASS and JVAS combined survey. In the VLA observations carried out in March and April of 1998, two new candidate lensed systems were discovered: CLASS B1152+199 and B1359+154. B1152+199 is a 1.6 arcsecond double, with a background quasar at z=1.019 lensed by a foreground galaxy at z=0.439. The relatively flat radio spectra of the lensed images, combined with a previous ROSAT detection of the source, make B1152+199 a strong candidate for time delay studies at both radio and X-ray wavelengths. B1359+154 is a quadruply lensed quasar at z=3.235, with a maximum image separation of 1.7 arcseconds. As yet, the redshift of the lensing object in this system is undetermined. The steep spectral index of the source suggests that B1359+154 will not exhibit strong variability, and is therefore unlikely to be useful for determining the Hubble constant from measured time delays.

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arXiv1998

A new radio double lens from CLASS: B1127+385

We present the discovery of a new gravitational lens system with two compact radio images separated by 0.701+-0.001 arcsec. The lens system was discovered in the Cosmic Lens All Sky Survey (CLASS) as a flat spectrum radio source. Both radio components show structure in a VLBA 8.4 GHz radio image. No further extended structure is seen in either the VLA, MERLIN or VLBA images. Hubble Space Telescope (HST) WFPC2 images in F555W and F814W show two extended objects close to the radio components, which we identify as two lens galaxies. Their colours and mass-to-light ratios seem to favour two late-type spiral galaxies at relatively high redshifts (z_d>~0.5). Faint emission is also detected at positions corresponding to the radio images. A two-lens mass model can explain the observed VLBA structure. The best fit model has a reduced chi^2 of 1.1. The relative positions of the VLBA subcomponents are reproduced within 0.08 mas, the flux density ratios within 0.19. We also reproduce the position angle and separation of the two VLBA subcomponents in A and B within the observational errors, which we consider strong evidence for the validity of the lens model. Moreover, we find a surface density axis ratio of 0.74^{+0.10}_{-0.12} for the primary lens (G1), consistent with the surface brightness axis ratio of 0.69+-0.15. Also, the surface density position angle of 4.9^{+28.2}_{-22.4} degree of G1 compares well with the -6+-13 degree position angle of the surface brightness distribution. The errors indicate the 99 per cent confidence interval.

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arXiv1998

B2045+265: A New Four-Image Gravitational Lens from CLASS

We have discovered a new gravitational lens in the Cosmic Lens All-Sky Survey (CLASS). B2045+265 is a four-image system with a maximum separation of 1.9 arcsec. A fifth radio component is detected, but its radio spectrum and its positional coincidence with infrared emission from the lensing galaxy strongly suggests that it is the radio core of the lensing galaxy. This implies that the B2045+265 system consists of a flat-spectrum radio source being lensed by another flat-spectrum radio source. Infrared images detect the lensed images of the background source and the lensing galaxy. The lensed images have relative positions and flux densities that are consistent with those seen at radio wavelengths. Spectra of the system reveal a lens redshift of z_l=0.8673 and a source redshift of z_s=1.28. The image splitting and system redshifts imply that the projected mass inside the Einstein radius of the lensing galaxy is M_E=4.7x10^{11} h^{-1} M_sun. An estimate of the light emitted inside the Einstein radius gives a mass-to-light ratio in the rest frame B band of (M/L_B)_E = 20 h (M/L_B)_sun. Both the mass and mass-to-light ratio are higher than what is seen in nearby Sa galaxies. In fact, the implied rotation velocity for the lensing galaxy is two to three times higher than what is seen in nearby spirals. The large projected mass inside the Einstein ring radius may be the result of a significant amount of dark matter in the system, perhaps from a compact group of galaxies; however, it may also arise from a misidentification of the source redshift. A simple model of the gravitational potential of the lens reproduces the image positions well, but further modeling is required to satisfy the constraints from the image flux density ratios. With further observations and modeling, this lens may yield an estimate of H_0.

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arXiv1997

The complex gravitational lens system B1933+503

We report the discovery of the most complex arcsec-scale radio gravitational lens system yet known. B1933+503 was found during the course of the CLASS survey and MERLIN and VLA radio maps reveal up to 10 components. Four of these are compact and have flat spectra; the rest are more extended and have steep spectra. The background lensed object appears to consist of a flat spectrum core (quadruply imaged) and two compact "lobes" symmetrically disposed relative to the core. One of the lobes is quadruply imaged while the other is doubly imaged. An HST observation of the system with the WFPC2 shows a galaxy with an axial ratio of 0.5, but none of the images of the background object are detected. A redshift of 0.755 has been measured for the lens galaxy.

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arXiv1997

The Caltech-Jodrell Bank VLBI Surveys

The Caltech-Jodrell Bank VLBI surveys of bright extragalactic radio sources north of declination 35 deg were carried out between 1990 and 1995 using the Mark-II system, achieving images with a resolution of about 1 mas at 5 GHz. The CJ1 survey (together with the older `PR' survey) includes 200 objects with 5 GHz flux density greater than 0.7 Jy; the CJ2 survey includes 193 flat-spectrum sources with 5 GHz flux density greater than 0.35 Jy; and we have defined a complete flux-density limited sample, CJF, of 293 flat-spectrum sources stronger than 0.35 Jy. We summarize the definition of the samples and the VLBI, VLA, MERLIN, and optical observations, and present some highlights of the astrophysical results. These include: (1) superluminal motion and cosmology; (2) morphology and evolution of the `compact symmetric objects' (CSOs); (3) two-sided motion in some CSOs; (4) the angular-size - redshift diagram; (5) misalignment of parsec-scale and kiloparsec-scale jets.

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arXiv1997

An Anomalous Component of Galactic Emission

We present results from microwave background observations at the Owens Valley Radio Observatory. These observations, at 14.5 and 32 GHz, are designed to detect intrinsic anisotropy on scales of 7'. After point source removal, we detect significant emission with temperature spectral index beta ~ -2 towards the North Celestial Pole (NCP). Comparison of our data with the IRAS 100 micron map of the same fields reveals a strong correlation between this emission and the infrared dust emission. From the lack of detectable H-alpha emission, we conclude that the signals are consistent either with flat-spectrum synchrotron radiation, or with free-free emission from T_e ~ 10^6 K gas, probably associated with a large HI feature known as the NCP Loop. Assuming beta = -2.2, our data indicate a conversion T_f/I_(100 micron) = 0.075*nu(GHz)^-2.2 K/(MJy/sr). The detection of such a component suggests that we should be cautious in any assumptions made regarding foregrounds when designing experiments to map the microwave background radiation.

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arXiv1997

Evidence for Ordered Magnetic Fields in the Quasar Environment

At a distance of 20 pc from the purported supermassive black hole powering quasars, temperatures and densities are inferred from optical observations to be ~10**4 K and ~10**4 cm**-3. Here we present Very Long Baseline Interferometry radio observations revealing organized magnetic fields on the parsec scale in the hot plasma surrounding the quasar OQ172 (1442+101). These magnetic fields rotate the plane of polarization of the radio emission coming from the core and inner jet of the quasar. The derived rotation measure (RM) is 40,000 rad m**-2 in the rest frame of the quasar. Only 10 mas (a projected distance of 68 pc) from the nucleus the jet absolute values of RM fall to less than 100 rad m**-2.

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