The Microlensing Properties of a Sample of 87 Lensed Quasars

Gravitational microlensing is a powerful tool for probing the physical properties of quasar accretion disks and properties of the lens galaxy such as its dark matter fraction and mean stellar mass. Unfortunately the number of lensed quasars ($\sim 90$) exceeds our monitoring capabilities. Thus, estimating their microlensing properties is important for identifying good microlensing candidates as well as for the expectations of future surveys. In this work we estimate the microlensing properties of a sample of 87 lensed quasars. While the median Einstein radius crossing time scale is 20.6 years, the median source crossing time scale is 7.3 months. Broadly speaking, this means that on $\sim 10$ year timescales roughly half the lenses will be quiescent, with the source in a broad demagnified valley, and roughly half will be active with the source lying in the caustic ridges. We also found that the location of the lens system relative to the CMB dipole has a modest effect on microlensing timescales, and in theory microlensing could be used to confirm the kinematic origin of the dipole. As a corollary of our study we analyzed the accretion rate parameters in a sub-sample of 32 lensed quasars. At fixed black hole mass, it is possible to sample a broad range of luminosities (i.e., Eddington factors) if it becomes feasible to monitor fainter lenses.Comment: 31 pages, 7 figures, 2 tables, corrected typos in Table 2, revised version accepted for publication in Ap

Structural and dynamical uncertainties in modeling axisymmetric elliptical galaxies

Quantitative dynamical models of galaxies require deprojecting the observed surface brightness to determine the luminosity density of the galaxy. Existing deprojection methods for axisymmetric galaxies assume that a unique deprojection exists for any given inclination, even though the projected density is known to be degenerate to the addition of "konus densities" that are invisible in projection. We develop a deprojection method based on linear regularization that can explore the range of luminosity densities statistically consistent with an observed surface brightness distribution. The luminosity density is poorly constrained at modest inclinations (i > ~30 deg), even in the limit of vanishing observational errors. In constant mass-to-light ratio, axisymmetric, two-integral dynamical models, the uncertainties in the luminosity density result in large uncertainties in the meridional plane velocities. However, the projected line-of-sight velocities show variations comparable to current typical observational uncertainties.Comment: 20 pages, 8 Postscript figures, LaTeX, aaspp4.sty, submitted to MNRAS; paper w/figs (600 kb) also available at http://cfa-www.harvard.edu/~romanow/ell.mn.ps.gz GIF-format figures replaced by PostScrip

Gravitational Lensing Limits on Cold Dark Matter and Its Variants

Standard $\Omega_0=1$ cold dark matter (CDM) needs $0.27 < \sigma_8 < 0.63$ ($2\sigma$) to fit the observed number of large separation lenses, and the constraint is nearly independent of H_0=100h^{-1}\kms Mpc$^{-1}$. This range is strongly inconsistent with the COBE estimate of $\sigma_8=(2.8\pm0.2)h$. Tilting the primordial spectrum $\propto k^n$ from $n=1$ to 0.3 \ltorder n \ltorder 0.7, using an effective Hubble constant of 0.15 \ltorder \Gamma=h \ltorder 0.30, or reducing the matter density to 0.15 \ltorder \Omega_0 h \ltorder 0.3 either with no cosmological constant ($\lambda_0=0$) or in a flat universe with a cosmological constant ($\Omega_0+\lambda_0=1$) can bring the lensing estimate of $\sigma_8$ into agreement with the COBE estimates. The models and values for $\sigma_8$ consistent with both lensing and COBE match the estimates from the local number density of clusters and correlation functions. The conclusions are insensitive to systematic errors except for the assumption that cluster core radii are singular. If clusters with $\rho\propto(r^2+s^2)^{-1}$ have core radii exceeding $s = 15h^{-1}\sigma_3^2$ kpc for a cluster with velocity dispersion \sigma=10^3\sigma_3 \kms then the estimates are invalid. There is, however, a fine tuning problem in making the cluster core radii large enough to invalidate the estimates of $\sigma_8$ while producing several lenses that do not have central or ``odd images.'' The estimated completeness of the current samples of lenses larger than 5\parcs0 is 20\%, because neither quasar surveys nor lens surveys are optimized to this class of lenses.Comment: 27 pages, uuencoded compressed postscript file including figure

Microlensing Evidence That a Type 1 Quasar is Viewed Face-On

Using a microlensing analysis of 11 years of OGLE V-band photometry of the four image gravitational lens Q2237+0305, we measure the inclination i of the accretion disk to be cos i > 0.66 at 68% confidence. Very edge on (cos i < 0.39) solutions are ruled out at 95% confidence. We measure the V-band radius of the accretion disk, defined by the radius where the temperature matches the monitoring band photon emission, to be R_V = 5.8^+3.8_–2.3 × 10^15 cm assuming a simple thin disk model and including the uncertainties in its inclination. The projected radiating area of the disk remains too large to be consistent with the observed flux for a T α R ^–3/4 thin disk temperature profile. There is no strong correlation between the direction of motion (peculiar velocity) of the lens galaxy and the orientation of the disk