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

The Effects of Massive Substructures on Image Multiplicities in Gravitati onal Lenses

Surveys for gravitational lens systems have typically found a significantly larger fraction of lenses with four (or more) images than are predicted by standard ellipsoidal lens models (50% versus 25-30%). We show that including the effects of smaller satellite galaxies, with an abundance normalized by the observations, significantly increases the expected number of systems with more than two images and largely explains the discrepancy. The effect is dominated by satellites with ~20% the luminosity of the primary lens, in rough agreement with the typical luminosities of the observed satellites. We find that the lens systems with satellites cannot, however, be dropped from estimates of the cosmological model based on gravitational lens statistics without significantly biasing the results.Comment: 23 pages, 7 figures, more discussion of sis vs sie and inclusion of uncorrelated contribution

Finding Gravitational Lenses With X-rays

There are $\sim 1$, 0.1 and 0.01 gravitationally lensed X-ray sources per square degree with soft X-ray fluxes exceeding $10^{-15}, 10^{-14}$ and $10^{-13} ergs/s cm^{-2}$ respectively. These sources will be detected serendipitously with the Chandra X-ray Observatory at a rate of 1--3 lenses per year of high resolution imaging. The low detection rate is due to the small area over which the HRC and ACIS cameras have the <1\farcs5 FWHM resolution necessary to find gravitational lenses produced by galaxies. Deep images of rich clusters at intermediate redshifts should yield one wide separation (\Delta\theta \gtorder 5\farcs0) multiply-imaged background X-ray source for every $\sim 10$, 30 and 300 clusters imaged to the same flux limits.Comment: 13 pages, including 5 figures, submitted to ApJ Letter

Redshifts of the Gravitational Lenses MG1131+0456 and B1938+666

The redshifts of the gravitational lens galaxies in MG1131+0456 and B1938+666 are 0.844 and 0.881 respectively. Both are early-type galaxies lying at the redshifts predicted by assuming that they are early-type galaxies with old stellar populations lying on the fundamental plane. We also find evidence for a foreground group of galaxies at z=0.343 near MG1131+0456. The source redshifts are predicted to be >1.8 in both systems, but they are so red that infrared spectra will be required to determine their redshifts.Comment: 10 pages, AASTeX Latex, including 1 JPEG and 2 postscript figures, submitted to Astronomical Journal Minor typos fixe

Discovery of Variability of the Progenitor of SN 2011dh in M51 Using the Large Binocular Telescope

We show that the candidate progenitor of the core-collapse SN 2011dh in M51 (8 Mpc away) was fading by 0.039 +- 0.006 mag/year during the three years prior to the supernova, and that this level of variability is moderately unusual for other similar stars in M 51. While there are uncertainties about whether the true progenitor was a blue companion to this candidate, the result illustrates that there are no technical challenges to obtaining fairly high precision light curves of supernova progenitors using ground based observations of nearby (<10 Mpc) galaxies with wide field cameras on 8m-class telescopes. While other sources of variability may dominate, it is even possible to reach into the range of evolution rates required by the quasi-static evolution of the stellar envelope. For M 81, where we have many more epochs and a slightly longer time baseline, our formal 3 sigma sensitivity to slow changes is presently 3 millimag/year for a M_V ~= -8 mag star. In short, there is no observational barrier to determining whether the variability properties of stars in their last phases of evolution (post Carbon ignition) are different from earlier phases.Comment: 17 pages, 5 figures, submitted to Ap