arXiv subjects

J. Anthony Tyson

Publications and source records attributed to J. Anthony Tyson.

63 records · Page 4Linked to original sources

arXiv1998

Detailed Mass Map of CL0024+1654 from Strong Lensing

We construct a high resolution mass map of the z=0.39 cluster 0024+1654, based on parametric inversion of the associated gravitational lens. The lens creates eight well-resolved sub-images of a background galaxy, seen in deep imaging with HST. Excluding mass concentrations centered on visible galaxies, more than 98% of the remaining mass is represented by a smooth concentration of dark matter centered near the brightest cluster galaxies, with a 35 h^{-1} kpc soft core. The asymmetry in the mass distribution is <3% inside 107 ~h^{-1} kpc radius. The dark matter distribution we observe in CL0024 is far more smooth, symmetric, and nonsingular than in typical simulated clusters in either Omega=1 or Omega=0.3 CDM cosmologies. Integrated to 107 h^{-1} kpc radius, the rest-frame mass to light ratio is M/L_V = 276\pm 40 h (M/L_V)_solar.

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arXiv1997

Improved Parameters and New Lensed Features for Q0957+561 from WFPC2 Imaging

New HST WFPC2 observations of the lensed double QSO 0957+561 will allow improved constraints on the lens mass distribution and hence will improve the derived value of H$_0$. We first present improved optical positions and photometry for the known components of this lens. The optical separation between the A and B quasar images agrees with VLBI data at the 10 mas level, and the optical center of the primary lensing galaxy G1 coincides with the VLBI source G' to within 10 mas. The best previous model for this lens (Grogin and Narayan 1996) is excluded by these data and must be reevaluated. Several new resolved features are found within 10\arcsec of G1, including an apparent fold arc with two bright knots. Several other small galaxies are detected, including two which may be multiple images of each other. We present positions and crude photometry of these objects.

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arXiv1997

The Mass distribution of the Most Luminous X-ray Cluster RXJ1347.5-1145 from Gravitational Lensing

Galaxy cluster mass distribution are potentially useful probes of $Ω_0$ and the nature of the dark matter. Large clusters will distort the observed shapes of background galaxies through gravitational lensing allowing the measurement of the cluster mass distributions. In this paper we describe weak statistical lensing measurements of the most luminous X-ray cluster known, RXJ1347.5-1145 at z=0.45. We detect a shear signal in the background galaxies at a signal-to-noise ratio of 7.5 in the radial range $120 \le r \le 1360 h^{-1}$ kpc. A mass map of the cluster reveals an 11$σ$ peak in the cluster mass distribution consistent with the position of the central dominant galaxy and 3 $σ$ evidence for the presence of a subcluster at a projected radius of 1.3 - 1.7 h^{-1} Mpc from the cluster center. In the range $120 \le r \le 1360 h^{-1}$ kpc mass traces light, and the azimuthally averaged cluster mass and light profiles are consistent with singular isothermal spheres with M(r<1 Mpc) = $1.7 \pm 0.4 \times 10^{15} M_\odot$. Assuming an isotropic velocity distribution function, the implied velocity dispersion is $σ= 1500 \pm 160 km s^{-1}$. The rest-frame mass-to-light ratio is $M/L_B = 200 \pm 50 h M_\odot/L_{B\odot}$. The lensing mass estimate is almost twice as high as a previously determined X-ray mass estimate.

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arXiv1996

The Mass distribution of the Cluster 0957+561 from Gravitational Lensing

Multiply gravitationally lensed objects with known time delays can lead to direct determinations of H$_0$ independent of the distance ladder if the mass distribution of the lens is known. Currently, the double QSO 0957+561 is the only lensed object with a precisely known time delay. The largest remaining source of systematic error in the H$_0$ determination results from uncertainty in the mass distribution of the lens which is comprised of a massive galaxy (G1) and the cluster in which it resides. We have obtained V-band CCD images from CFHT in order to measure the mass distribution in the cluster from its gravitional distorting effect on the appearance of background galaxes. We use this data to constuct a two-dimensional mass map of the field. A mass peak is detected at the $4.5σ$ level, offset from, but consistent with, the position of G1. Simple tests reveal no significant substructure and the mass distribution is consistent with a spherical cluster. The peak in the number density map of bright galaxies is offset from G1 similarly to the mass peak. We constructed an azimuthally averaged mass profile centered on G1 out to 2 \arcmin ($400 h^{-1}$ kpc). It is consistent with an isothermal mass distribution with a small core ($r_c \approx 5 \arcsec = 17 h^{-1}$ kpc). The inferred mass within 1 Mpc is consistent with the dynamical mass estimate but $2σ$ higher than the upper limits from a ROSAT X-ray study. We discuss implications for H$_0$ in a future paper.

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arXiv1996

Galaxy Dark Matter: Galaxy-Galaxy Lensing in the Hubble Deep Field

In this Letter we present calibrated observations of the average mass of galaxies with 22< I < 25 in the Hubble Deep Field. We measure the mean mass profile using the statistical gravitational lens distortion of faint blue background galaxies, based on 2221 foreground-background pairs. The observed weak lensing distortion is calibrated via full 3-D simulations and other HST data on a foreground cluster of known mass. Inside a projected radius of 5 arcsec we find a 3σdetection of shear. Fitting to an isothermal mass distribution, we find a shear of 0.066^{+0.018}_{-0.019} at a radius of 2\arcsec\ (\sim 8 ~ h^{-1} kpc). The (1σ) limits on the parameters for the truncated isothermal model are σ_v =185^{+30}_{-35} km s^{-1}, r_{outer} \ge 15 ~ h^{-1} kpc, and r_{core}= 0.6^{+1.3}_{-0.6} ~ h^{-1} kpc. This corresponds to an average galaxy mass interior to 20 h^{-1} kpc of 5.9^{+2.5}_{-2.7}\times 10^{11} h^{-1} M_\odot. Inside 10 h^{-1} kpc, we find an average rest-frame V band mass-to-light ratio of 11.4^{+6.0}_{-6.7} h (M/L_V)_\odot.

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arXiv1996

Flickering Faint Galaxies: Few and Far Between

Optical variability in galaxies at high redshift is a tracer of evolution in AGN activity, and should provide a useful constraint on models of galaxy evolution, AGN structure, and cosmology. We studied optical variability in multiple deep CCD and photographic surveys of blank fields for galaxies with $B_j = 20 - 25$ mag. Weakly variable objects are far more common than strongly variable ones. For objects near $B_j = 22$, $0.74\% \pm 0.2 \%$ vary by 0.026~mag RMS or more, over a decade. This is small compared with previous claims based on photographic surveys, and also small compared with the fraction of bright quasars ($\approx 5\%$ at $B_j = 20$~mag) or Seyferts ($\approx 1-2\%$ for $B_j < 18$). The fraction of objects that vary increases slowly with magnitude. Detection probabilities and error rates were checked by simulations and statistical analysis of fluctuations of sample sky spots.

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arXiv1995

Unlensing Multiple Arcs in 0024+1654: Reconstruction of the Source Image

A unique reconstruction of the image of a high redshift source galaxy responsible for multiple long arcs in the z = 0.4 cluster 0024+1654 is obtained by inverse lensing. Deep B and I imaging with the Hubble Space Telescope (Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, under NASA contract NAS 5-26555) enables high resolution of the arcs due to strong gravitational lensing of the background source. The gravitational lens in the foreground cluster is thus used to obtain a magnified view of the distant source. Four strongly lensed images of the source lead to a unique reconstruction. Each of the long arcs, when unlensed, leads to the same reconstructed source image exhibiting a beaded ring-like morphology. The U luminosity of the ring alone is equivalent to a normal galaxy. This is likely a galaxy in formation.

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arXiv1995

A Catalog of Digital Images of 113 Nearby Galaxies

We present a digital catalog of images of 113 galaxies in this paper. These galaxies are all nearby, bright, large and well resolved. All images were recorded with charge coupled devices (CCDs) at the Palomar Observatory with the 1.5 meter telescope and at the Lowell Observatory with the 1.1 meter telescope. At Palomar we used the Thuan--Gunn g, r and i photometric bands to take 3 images each of 31 spiral galaxies; at Lowell we used the B_J and R bands (2 images per galaxy) of the photometric system by Gullixson et al. (1995) to observe 82 spirals and ellipticals. The galaxies were selected to span the Hubble classification classes. All data are photometrically calibrated with foreground stars removed. Important data on these galaxies published in the "Third Reference Catalog of Bright Galaxies" (RC3) are recorded in the FITS file headers. All files are available through anonymous FTP from ftp://astro.princeton.edu/, through WWW at http://astro.princeton.edu/~frei/galaxy_catalog.html, and Princeton University Press will soon publish the data on CD-ROM.

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arXiv1994

Detection of Lens Candidates for the Double QSO Q2345+007

Luminous objects associated with the 7.06\arcsec\ separation double quasar Q2345+007 have, until now, escaped detection. In this letter we present the results of the deepest known imaging of the region surrounding the quasar. The total exposure times were 47600 seconds in B$_j$ (101 frames) and 32160 seconds in R (82 frames). The frames came from CFHT, CTIO, and KPNO. We detect a B$_j$ = 25.0 mag galaxy (B$_j$ -- R = 0.5 mag) in close proximity to the fainter QSO image, possibly at $z = 1.49$ given by several absorption features in the QSO spectra. Furthermore, there is a 2.9$σ$ enhancement in the number density of faint galaxies ($24 \le$ B$_j$ $\le 28$, B$_j-$ R $ \le 1.5$) near the quasar and another 3.1$σ$ enhancement further away. These discoveries support the hypothesis that Q2345+007 is being lensed by one or more distant mass concentrations and may imply that compact ``clusters'' already exist at early epochs. We discuss several lens models for the system and the cosmological implications.

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