Andre B. Fletcher

The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances*

We report data for I-band surface brightness fluctuation (SBF) magnitudes, (V-I) colors, and distance moduli for 300 galaxies. The survey contains E, S0, and early-type spiral galaxies in the proportions of 49 : 42 : 9 and is essentially complete for E galaxies to Hubble velocities of 2000 km s-1, with a substantial sampling of E galaxies out to 4000 km s-1. The median error in distance modulus is 0.22 mag. We also present two new results from the survey. (1) We compare the mean peculiar flow velocity (bulk flow) implied by our distances with predictions of typical cold dark matter transfer functions as a function of scale, and we find very good agreement with cold, dark matter cosmologies if the transfer function scale parameter Γ and the power spectrum normalization σ8 are related by σ8Γ-0.5 ≈ 2 ± 0.5. Derived directly from velocities, this result is independent of the distribution of galaxies or models for biasing. This modest bulk flow contradicts reports of large-scale, large-amplitude flows in the ~200 Mpc diameter volume surrounding our survey volume. (2) We present a distance-independent measure of absolute galaxy luminosity, and show how it correlates with galaxy properties such as color and velocity dispersion, demonstrating its utility for measuring galaxy distances through large and unknown extinction.

PMN J0134-0931: A gravitationally lensed quasar with unusual radio morphology

The radio-loud quasar J0134-0931 was discovered to have an unusual morphology during our search for gravitational lenses. In Very Large Array and MERLIN images, there are five compact components with a maximum separation of 07. All of these components have the same spectral index from 5 to 43 GHz. In a Very Long Baseline Array image at 1.7 GHz, a curved arc of extended emission joins two of the components in a manner suggestive of gravitational lensing. At least two of the radio components have near-infrared counterparts. We argue that this evidence implies that J0134-0931 is a gravitational lens, although we have not been able to devise a plausible model for the foreground gravitational potential. Like several other radio-loud lenses, the background source has an extraordinarily red optical counterpart.

The luminosity functions of embedded stellar clusters. 1: Method of solution and analytic results

We describe a method for computing the history of the luminosity function in a young cluster still forming within a molecular cloud complex. Our method, which utilizes detailed results from stellar evolution theory, assumes that clusters arise from the continuous collapse of dense cloud cores over a protracted period of time. It is also assumed that stars reaching the main sequence are distributed in mass according to a prescribed initial mass function (IMF). We keep track separately of the contributions to the luminosity function from the populations of protostars, pre-main-sequence stars, and main-sequence stars. We derive expressions for the fractional contribution of these populations to both the total number of stars produced and the total cluster luminosity. In our model, the number of protostars rises quickly at first, but then levels off to a nearly constant value, which it maintains until the dispersal of the cloud complex. The number fraction of protostars always decreases with time. Averaged over the life of the parent cloud, this fraction is typically a few percent. The protostar mass distribution can be expressed as an integral over the IMF.

The Gravitationally Lensed Radio Source MG 0751+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.

Metal enrichment, dust, and star formation in galaxies at high redshifts. II - Lyman-alpha emission from the Z = 2.465 absorber toward Q0836 + 113

QSO absorption systems with damped Ly-alpha lines have been suggested as the high-redshift progenitors of present-day galaxies. As part of a survey of element abundances and star formation rates in these systems, long-slit, 1.5 A resolution spectroscopic observations of the z(em) = 2.67 QSO 0836 + 113 were obtained. The detection of a narrow emission line centered in the black core of the damped Ly-alpha absorption line at z(abs) = 2.465 is reported. It is suggested that the Ly-alpha is from star-forming H II regions associated with the z = 2.465 galaxy. The implications of the detection on future observational studies are discussed, emphasizing the need for low detector noise and high S/N for the sky background. 43 refs.

MGC 2214+3550: A New Binary Quasar

We report the discovery of a binary quasar, MGC 2214+3550A,B, whose components have similar optical spectra at a redshift of z=0.88. The quasars are separated on the sky by 30 and have a magnitude difference of ΔmI=0.5 mag. The VLA radio map at 3.6 cm shows a single 47 mJy radio source with a core-jet morphology that is coincident with the brighter optical quasar A. Gravitational lensing is ruled out by the lack of radio emission from quasar B and the lack of any visible galaxies to act as the lens. We conclude that MGC 2214+3550A and B are physically associated. With a projected separation of 12.7 h−1 kpc (Ω0=1), MGC 2214+3550A,B is one of the smallest z>0.5 binary quasars.

The radio galaxy RC J1148+0455

Based on data from the MIT-GB-VLA 4850-MHz survey, we investigate the radio structure of RC J1148+0455 with a steep radio spectrum (α=−1.04) from the COLD catalog. The radio source consists of two components, each having a complex structure. We analyze an optical identification of the source by using 6-m telescope images. The centroid of the radio source falls on a group of eight galaxies at a 24m level in R.

Calibration Issues in the Search for Large-Scale Anisotropies in the 87 Green Bank and Parkes-Mit-Nrao Surveys

Until recently, there were no large scale radio surveys which were sensitive enough to have a sufficient number of sources to detect a dipole anisotropy. The 87 Green Bank (87GB) (Gregory and Condon, 1991) and Parkes-MIT-NRAO (PMN) (Griffith, 1993; Griffith et al., 1994, 1995; Wright et al., 1994) radio surveys are the first such efforts and are the most complete radio surveys to date. We would like to analyze the source counts in these surveys in order to test the isotropy of the sky distribution of extragalactic sources at cosmological redshifts. Of particular interest is a dipole anisotropy, which could arise from local motion with respect to the rest frame of extragalactic radio sources. Any detected anisotropy will give information about the source sky distribution at a redshift of z ∼ 1 (Condon, 1988), an epoch between the COBE observations at z ∼ 1000 and the local universe.

The Angular Size Distribution of 4741 Radio Sources in the MIT-VLA Snapshot Archive

The MIT all-sky and VLA snapshot surveys are described, and the scientific results to date are summarized. The largest angular size distribution is given for 4741 MIT-VLA sources, and a Monte-Carlo algorithm is proposed to model the cosmological evolution of jets in radio-loud AGN. Further progress requires compiling redshifts for a complete sub-sample.

Preliminary VLA Snapshots of Southern Radio Sources from the Parkes-MIT-NRAO (PMN) Survey

Selection criteria for 1800 MIT-VLA snapshots of PMN radio sources are described, and 6 new MG & PMN lens candidates are presented.