arXiv subjects

P. L. Schechter

Publications and source records attributed to P. L. Schechter.

22 records · Page 2Linked to original sources

arXiv1997

Groups of Galaxies in the Las Campanas Redshift Survey

A "friends-of-friends" percolation algorithm has been used to extract a catalogue of drho/rho = 80 density enhancements (groups) from the six slices of the Las Campanas Redshift Survey (LCRS). The full catalogue contains 1495 groups and includes 35% of the LCRS galaxy sample. A statistical sample of 394 groups has been derived by culling groups from the full sample which either are too close to a slice edge, have a crossing time greater than a Hubble time, have a corrected velocity dispersion of zero or less, or contain a 55 arcsec "orphan" (a galaxy with a "faked" redshift excluded from the original LCRS redshift catalogue due to its proximity --- i.e., within 55 arcsec --- of another galaxy). Median properties derived from the statistical sample include: line-of-sight velocity dispersion sigma_los = 164 km/s, crossing time t_cr = 0.10/H_0, harmonic radius R_h = 0.58/h Mpc, pairwise separation R_p = 0.64/h Mpc, virial mass M_vir = (1.90x10^13)/h M_sun, total group R-band luminosity L_tot = (1.40x10^11)/h^2 L_sun, and R-band mass-to-light ratio M/L = 153h M_sun/L_sun.

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arXiv1997

The Gravitationally-Lensed Radio Source MG0751+2716

We report the discovery of a new gravitationally lensed radio source. Radio maps of MG0751+2716 show four lensed images, which, at higher resolution, are resolved into long arcs of emission. A group of galaxies is present in optical images, including the principal lensing galaxy, with a much brighter galaxy just a few arcseconds away. We have measured the redshift of this brighter galaxy. No optical counterpart to the background source has been detected. Lens models that can readily reproduce the lensed image positions all require a substantial shear component. However, neither the very elongated lens nor the bright nearby galaxy are correctly positioned to explain the shear. Lens models which associate the mass with the light of galaxies in the group can produce an acceptable fit, but only with an extreme mass-to-light ratio in one of the minor group members.

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arXiv1996

The Las Campanas Redshift Survey Galaxy-Galaxy Autocorrelation Function

Presented are measurements of the observed redshift-space galaxy-galaxy autocorrelation function, xi(s), for the Las Campanas Redshift Survey (LCRS). For separations 2.0/h Mpc < s < 16.4/h Mpc, xi(s) can be approximated by a power law with slope of -1.52 +/- 0.03 and a correlation length of s_0 = (6.28 +\- 0.27)/h Mpc. A zero-crossing occurs on scales of roughly 30 - 40/h Mpc. On larger scales, xi(s) fluctuates closely about zero, indicating a high level of uniformity in the galaxy distribution on these scales. In addition, two aspects of the LCRS selection criteria - a variable field-to-field galaxy sampling rate and a 55 arcsec galaxy pair separation limit - are tested and found to have little impact on the measurement of xi(s). Finally, the LCRS xi(s) is compared with those from numerical simulations; it is concluded that, although the LCRS xi(s) does not discriminate sharply among modern cosmological models, redshift-space distortions in the LCRS xi(s) will likely provide a strong test of theory.

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arXiv1996

The Quadruple Gravitational Lens PG1115+080: Time Delays and Models

Optical photometry is presented for the quadruple gravitational lens PG1115+080. A preliminary reduction of data taken from November 1995 to June 1996 gives component ``C'' leading component ``B'' by 23.7+/-3.4 days and components ``A1'' and ``A2'' by 9.4 days. A range of models has been fit to the image positions, none of which gives an adequate fit. The best fitting and most physically plausible of these, taking the lensing galaxy and the associated group of galaxies to be singular isothermal spheres, gives a Hubble constant of 42 km/s/Mpc for Omega=1, with an observational uncertainty of 14%, as computed from the B-C time delay measurement. Taking the lensing galaxy to have an approximately E5 isothermal mass distribution yields H0=64 km/sec/Mpc while taking the galaxy to be a point mass gives H0=84 km/sec/Mpc. The former gives a particularly bad fit to the position of the lensing galaxy, while the latter is inconsistent with measurements of nearby galaxy rotation curves. Constraints on these and other possible models are expected to improve with planned HST observations.

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