Jacqueline Chen

Lensing Optical Depths for Substructure and Isolated Dark Matter Halos

Multiply imaged quasar lenses can be used to constrain the substructure mass fraction in galaxy-sized dark matter halos via anomalous flux ratios in lensed images. The flux ratios, however, can be affected both by the substructure in the lens halo and by isolated small-mass halos along the entire line of sight to the lensed source. While lensing by dark matter clumps near the lens galaxy is more efficient than elsewhere, the cumulative effect of all objects along the line of sight could be significant. Here we estimate the potential contribution of isolated clumps to the substructure lensing signal using a simple model motivated by cosmological simulations. We find that the contribution of isolated clumps to the total lensing optical depth ranges from a few percent to tens of percent, depending on assumptions and the particular configuration of the lens. Therefore, although the contribution of isolated clumps to the lensing signal is not dominant, it should not be neglected in detailed analyses of substructure lensing. For the currently favored ?CDM model, the total calculated optical depth for lensing is high, ? ~ 0.2-20, and could, therefore, naturally explain the high frequency of anomalous flux ratios in observed lenses. The prediction, however, is highly sensitive to the spatial distribution of substructure halos in the innermost regions of the lens halo, which is still very uncertain. Therefore, constraints on the properties of the substructure population or accurate cosmological constraints, such as the mass of the warm dark matter particle, are difficult?if not impossible?to derive at this point.

Constraining the Projected Radial Distribution of Galactic Satellites with the Sloan Digital Sky Survey

We use the Sloan Digital Sky Survey (SDSS) spectroscopic sample to constrain the projected radial distribution of satellites around isolated ~L* galaxies. We employ mock galaxy catalogs derived from high-resolution cosmological simulations to investigate the effects of interloper contamination and show that interlopers significantly bias the estimated slope of the projected radial distribution of satellites. We also show that the distribution of interlopers around galaxies is expected to be nonuniform in velocity space because galaxies are clustered and reside in crowded environments. Successful methods of interloper contamination correction should therefore take into account environments of the host galaxies. Two such new methods are presented, and the most reliable of them is used to correct for interloper contamination in analyses of the SDSS galaxy sample. The best-fit power-law slope of the interloper-corrected surface density distribution of satellites, ?(R) R?, in the volume-limited SDSS sample is ? -1.7 ? 0.1, independent of the galaxy and satellite luminosities. Comparison with ?CDM simulations shows that the radial distribution of the SDSS satellites is more concentrated than that of subhalos around galaxy-sized halos, especially at R < 100 h-1 kpc. The predicted dark matter radial distribution is somewhat more concentrated than the profile of the SDSS satellites, but the difference is not statistically significant for our sample.

Astrometric Perturbations in Substructure Lensing

In recent years gravitational lensing has been used as a means to detect substructure in galaxy-sized halos, via anomalous flux ratios in quadruply imaged lenses. In addition to causing anomalous flux ratios, substructure may also perturb the positions of lensed images at observable levels. In this paper we numerically investigate the scale of such astrometric perturbations using realistic models of substructure distributions. Substructure distributions that project clumps near the Einstein radius of the lens result in perturbations that are the least degenerate with the best-fit smooth macromodel, with residuals at the milliarcsecond scale. Degeneracies between the center of the lens potential and astrometric perturbations suggest that milliarcsecond constraints on the center of the lensing potential boost the observed astrometric perturbations by an order of magnitude compared to leaving the center of the lens as a free parameter. In addition, we discuss methods of substructure detection via astrometric perturbations that avoid full lens modeling in favor of local image observables and also discuss modeling of systems with luminous satellites to constrain the masses of those satellites.

Color dependence in the spatial distribution of satellite galaxies

Aims. We explore the color dependence of the radial profile of satellite galaxies around isolated parent galaxies. Methods. Samples of potential satellites selected from large galaxy redshift surveys are significantly contaminated by interlopers – objects not bound to the parent galaxy. We use the Sloan Digital Sky Survey to estimate the interloper fraction in samples of candidate satellite galaxies. Results. We show that samples of red and blue satellites have different interloper populations: a larger fraction of blue galaxies are likely to be interlopers compared to red galaxies. Both with and without interloper subtraction, the radial profile of blue satellites is significantly shallower than that of red satellites. In addition, while red and blue primaries have different interloper fractions, the slope of the corrected radial profiles are consistent after interloper correction. We discuss the implications of these results for galaxy formation models.

The galaxy cross-correlation function as a probe of the spatial distribution of galactic satellites

The spatial distribution of satellite galaxies around host galaxies can illuminate the relationship between satellites and dark matter subhalos and aid in developing and testing galaxy formation models. Previous efforts to constrain the distribution attempted to eliminate interlopers from the measured projected number density of satellites and found that the distribution is generally consistent with the expected dark matter halo profile of the parent hosts, with a best-fit power-law slope of ≈ -1.7 between projected separations ofxa0~

Statistics of Magnification Perturbations by Substructure in the Cold Dark Matter Cosmological Model

30,h^{-1}

Parity dependence in strong lens systems as a probe of dark matter substructure

xa0kpc andxa0

Distorted H I Gas in the Widely Separated Luminous Infrared Galaxy Arp 256

0.5, h^{-1}

Strong gravitational lensing probes of the particle nature of dark matter

xa0Mpc. Here, I use the projected cross-correlation of bright and faint galaxies to analyze contributions from satellites and interlopers together, using a halo occupation distribution (HOD) analytic model for galaxy clustering. This approach is tested on mock catalogs constructed from simulations. I find that analysis of Sloan Digital Sky Survey (SDSS) data gives results generally consistent with interloper subtraction methods between the projected separations of

BIASES IN THE GRAVITATIONAL LENS POPULATION INDUCED BY HALO AND GALAXY TRIAXIALITY

10,h^{-1}