In previous attempts to measure cosmological parameters from the angular size-redshift (θ-z) relation of double-lobed radio sources, the observed data have generally been consistent with a static Euclidean universe, rather than with standard Friedmann models, and past authors have disagreed significantly as to what effects are responsible for this observation. These results and different interpretations may be due largely to a variety of selection effects and differences in the sample definitions destroying the integrity of the data sets, and inconsistencies in the analysis undermining the results. Using the VLA FIRST survey, we investigate the θ-z relation for a new sample of double-lobed quasars. We define a set of 103 sources, carefully addressing the various potential problems which, we believe, have compromised past work, including a robust definition of size and the completeness and homogeneity of the sample, and further devise a self-consistent method to assure accurate morphological classification and account for finite resolution effects in the analysis. Before focusing on cosmological constraints, we investigate the possible impact of correlations among the intrinsic properties of these sources over the entire assumed range of allowed cosmological parameter values. For all cases, we find apparent size evolution of the form l ∝ (1 + z) c with c ≈ −0.8 ± 0.4 which 1 ari@astro.columbia.edu 2 djh@astro.columbia.edu 3 bob@igpp.llnl.gov 4 rlw@stsci.edu is found to arise mainly from a power-size correlation of the form l ∝ P β (β ≈ −0.13 ± 0.06) coupled with a power-redshift correlation. Intrinsic size evolution is consistent with zero. We also find that in all cases, a subsample with c ≈ 0 can be defined, whose θ-z relation should therefore arise primarily from cosmological effects. These results are found to be independent of orientation effects, though other evidence indicates that orientation effects are present and consistent with predictions of the unified scheme for radio-loud active galactic nuclei. The above results are all confirmed by non-parametric analysis.Contrary to past work, we find that the observed θ-z relation for our sample is more consistent with standard Friedmann models than with a static Euclidean universe. Though the current data cannot distinguish with high significance between various Friedmann models, significant constraints on the cosmological parameters within a given model are obtained. In particular, we find that a flat, matter-dominated universe (Ω 0 = 1), a flat universe with a cosmological constant, and an open universe all provide comparably good fits to the data, with the latter two models both yielding Ω 0 ≈ 0.35 with 1σ ranges including values between ∼ 0.25 and 1.0; the c ≈ 0 subsamples yield values of Ω 0 near unity in these models, though with even greater error ranges. We also examine the values of H 0 implied by the data, using plausible assumptions about the intrinsic source sizes, and find these to be consistent with the currently accepted range of values. We dete...

A B S T R A C TWe investigate the effects of a variety of ingredients that must enter into a realistic model for disc galaxy formation, focusing primarily on the Tully±Fisher (TF) relation and its scatter in several wavebands. In particular, we employ analytic distributions for halo formation redshifts and halo spins, empirical star formation rates and initial mass functions, realistic stellar populations, and chemical evolution of the gas. Our main findings are as follows. (a) The slope, normalization and scatter of the TF relation across various wavebands are determined largely by the parent halo properties as dictated by the initial conditions, but are also influenced by star formation in the disc. (b) TF scatter in this model is due primarily to the spread in formation redshifts. The scatter can be measurably reduced by chemical evolution, and also by the weak anticorrelation between peak height and spin. (c) Multiwavelength constraints can be important in distinguishing between models that appear to fit the TF relation in I or K. (d) Assuming passive disc evolution, successful models seem to require that the bulk of disc formation cannot occur too early z . 2±3 or too late z , 0X2Y and are inconsistent with high values of V 0 . (e) A simple, realistic model with the above ingredients, and fewer free parameters than typical semi-analytic models, can reasonably reproduce the observed z 0 TF relation in all bands (B, R, I and K), as well as the observed B-band surface brightness±magnitude relation. In such a model, the nearinfrared TF relation at z 1 is similar to that at z 0Y while bluer bands show a markedly steeper TF slope at high redshift, consistent with limited current data. The remarkable agreement with observations suggests that the amount of gas that is expelled or poured into a disc galaxy may be small (though small fluctuations might serve to align B-band predictions better with observations), and that the specific angular momentum of the baryons should roughly equal that of the halo; there is little room for angular momentum transfer. In Appendix A we present analytic fits to stellar population synthesis models.

We calculate the normalized angular three-point correlation function (3PCF), q, as well as the normalized angular skewness, s 3 , assuming the small-angle approximation, for a biased mass distribution in flat and open cold-dark-matter (CDM) models with Gaussian initial conditions. The leading-order perturbative results incorporate the explicit dependence on the cosmological parameters, the shape of the CDM transfer function, the linear evolution of the power spectrum, the form of redshift distribution function, and linear and nonlinear biasing, which may be evolving. Results are presented for different redshift distributions, including that appropriate for the APM Galaxy Survey, as well as for a survey with a mean redshift of z ≃ 1 (such as the VLA FIRST Survey). Qualitatively, many of the results found for s 3 and q are similar to those obtained in a related treatment of the spatial skewness and 3PCF (Buchalter & Kamionkowski 1999), such as a leading-order correction to the standard result for s 3 in the case of nonlinear bias (as defined for unsmoothed density fields), and the sensitivity of the configuration dependence of q to both cosmological and biasing models. We show that since angular CFs are sensitive to clustering over a range of redshifts, the various evolutionary dependences included in our predictions imply -2that measurements of q in a deep survey might better discriminate between models with different histories, such as evolving vs. non-evolving bias, that can have similar spatial CFs at low redshift. Our calculations employ a derived equation-valid for open, closed, and flat models-for obtaining the angular bispectrum from the spatial bispectrum in the small-angle approximation.

Bouchet et al. (1992) showed that in an open or closed Universe with only pressureless matter, gravitational instability from Gaussian initial conditions induces a normalized skewness, $S_3 \equiv \VEV{\delta^3} \VEV{\delta^2}^{-2}$, that has only a very weak dependence on the nonrelativistic-matter density. Here we generalize this result to a plethora of models with various contributions to the total energy density, including nonrelativistic matter, a cosmological constant, and other forms of missing energy. Our numerical results show that the skewness (and bispectrum) depend only very weakly ($\lesssim 2%$) on the expansion history. Thus, the skewness and bispectrum provide a robust test of gravitational instability from Gaussian initial conditions, independent of the underlying cosmological model.Comment: 11 pages, 1 Postscript figure, uses AASTeX, submitted to ApJ Letter

If the objects responsible for gravitational microlensing of Galactic-bulge stars are faint dwarfs, then blended light from the lens will distort the shape of the microlensing light curve and shift the color of the observed star during the microlensing event. In most cases, the resolution in current microlensing surveys is not accurate enough to observe this color-shift effect. However, such signatures could conceivably be detected with frequent followup observations of microlensing events in progress, providing the photometric errors are small enough. We calculate the expected rates for microlensing events where the shape distortions will be observable by such followup observations, assuming that the lenses are ordinary low-mass main-sequence stars in a rapidly rotating bar and in the disk. We adopt Galactic models consistent with observed microlensing timescale distributions, and consider separately the cases of self-lensing of the bulge, lensing of the bulge by the disk, and self-lensing of the disk, further differentiating between events where the source is a giant or a main-sequence star. We study the dependence of the rates for color-shifted microlensing events on the frequency of followup observations and on the precision of the photometry for a variety of waveband pairings. We find that for hourly observations in B and K with typical photometric errors of 0.01 mag, 28% of the events where a main-sequence bulge star is lensed, and 7% of the events where the source is a bulge giant, will give rise to a measurable color shift at the 95% confidence level. For observations in V and I, the fractions become 18% and 5%, respectively,

We performed an automated comparison of the FIRST radio survey with the APM optical catalog to find radio lobes with optical counterparts. Based on an initial survey covering ∼3000 square degrees, we selected a sample of 33 lens candidates for VLA confirmation. VLA and optical observations of these candidates yielded two lens systems, one a new discovery (J0816+5003), and one of which was previously known (J1549+3047). Two other candidates have radio lobes with galaxies superposed, but lack evidence of multiple imaging. One of our targets (J0958+2947) is a projected close pair of quasars (8 ′′ separation at redshifts 2.064 and 2.744). Our search method is highly efficient, with >5% of our observing targets being lensed, compared to the usual success rate of <1%. Using the whole FIRST survey, we expect to find 5-10 lenses in short order using this approach, and the sample could increase to hundreds of lensed lobes in the Northern sky, using deeper optical surveys and planned upgrades to the VLA. Such a sample would be a powerful probe of galaxy structure and evolution.

The parallax e †ect in ground-based microlensing (ML) observations consists of a distortion to the standard ML light curve arising from the EarthÏs orbital motion. This can be used to partially remove the degeneracy among the system parameters in the event timescale,In most cases, the resolution in t 0 . current ML surveys is not accurate enough to observe this e †ect, but parallax could conceivably be detected with frequent follow-up observations of ML events in progress, providing the photometric errors are small enough. We calculate the expected fraction of ML events where the shape distortions will be observable by such follow-up observations, adopting Galactic models for the lens and source distributions that are consistent with observed microlensing timescale distributions. We study the dependence of the rates for parallax-shifted events on the frequency of follow-up observations and on the precision of the photometry. For example, we Ðnd that for hourly observations with typical photometric errors of 0.01 mag, 6% of events where the lens is in the bulge, and 31% of events where the lens is in the disk (or B10% of events overall), will give rise to a measurable parallax shift at the 95% conÐdence level. These fractions may be increased by improved photometric accuracy and increased sampling frequency. While long-duration events are favored, the surveys would be e †ective in picking out such distortions in events with timescales as low as days. We study the dependence of these fractions on t 0 B 20 the assumed disk mass function and Ðnd that a higher parallax incidence is favored by mass functions with higher mean masses. Parallax measurements yield the reduced transverse speed, which gives both v8 , the relative transverse speed and lens mass as a function of distance. We give examples of the accuracies with which may be measured in typical parallax events. Fitting ML light curves, which may be shapev8 distorted (e.g., by parallax, blending, etc.), with only the three standard ML parameters can result in inferred values for these quantities that are signiÐcantly in error. Using our model, we study the e †ects of such systematic errors and Ðnd that, due primarily to blending, the inferred timescales from such Ðts, for events with disk lenses, tend to shift the event duration distribution by B10% toward shorter Events t 0 . where the lens resides in the bulge are essentially una †ected. In both cases, the impact parameter distribution is depressed slightly at both the low and high ends.

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