1509.06750
3D weak lensing with spin wavelets on the ball
Leistedt, McEwen, Kitching, Peiris
Construct the spin flaglet transform, a wavelet transform to analyse spin signals in 3D. Spin flaglets can probe signal content localised simultaneously in space and frequency and are separable so that their angular and radial properties can be controlled independently. They are particularly suited to analyzing of cosmo observations such as WL. Such observations have a unique 3D geometrical setting since they are natively made on the sky, have spin angular symmetries, and are extended in the radial direction by additional distance or redshift information. Flaglets are constructed in the harmonic space defined by the Fourier-Laguerre transform, previously defined for scalar functions and extended here to signals with spin symmetries. Thanks to various sampling theorems, both the Fourier-Laguerre and flageolet transforms are theoretically exact when applied to band-limited signals. In other words, in numerical computations, the only loss of information is due to the finite representation of floating point numbers. Develop a 3D framework relating the WL PS to covariances of flaglet coefficients. Suggest that the resulting novel flaglet WL estimator offers a powerful alternative to common 2D and 3D approaches to accurately capture cosmological information. While standard WL analyses focus on either real or harmonic space representations (i.e., correlation functions of Fourier-Bessel power spectra, respectively), a wavelet approach inherits the advantages of both techniques, where both complicated sky coverage and uncertainties associated with the physical modeling of small scales can be handled effectively. The codes to compute the Fourier-Laguerre and flaglet transforms are made publicly available.
1509.06756
Galaxy and mass assembly (GAMA): the wavelength dependence of galaxy structure versus redshift and luminosity
Kennedy et al
Study how the sizes and radial profiles of galaxies vary with wavelength, by fitting Sersic functions simultaneously to imaging in 9 optical and NIR bands. To quantify the wavelength dependence of effective radius, use the ratio R of measurements in two restframe bands. The dependence of service index on wavelength N is computed correspondingly. Vulcani+2014 have demonstrated that different galaxy populations present sharply contrasting behavior in terms of R and N. Study the luminosity dependence of this result. Find that at higher luminosities, early-type galaxies display a more substantial decrease in effective radius with wavelength, whereas late-types present a more pronounced increase in Sersic index. The structural contrast between types thus increases with luminosity. By considering samples at different redshifts, demonstrate that lower data quality reduces the apparent difference between the main galaxy populations. However, the conclusions remain robust to this effect. Show that accounting for different redshift and luminosity selections partly reconciles the size variation measured by Vulcani+ with the weaker trends found by other recent studies. Dividing galaxies by visual morphology confirms the behavior inferred using morphological proxies, although the sample size is greatly reduced. Finally, demonstrate that varying dust opacity and disc inclination can account for features of the joint distribution of R and N for late-type galaxies. However, dust does not appear to explain the highest values of R and N. The Bulge-disc nature of galaxies must also contribute to the wavelength-dependence of their structure.
1509.06758
Mapping stellar content to dark matter haloes. II. Halo mass is the main driver of galaxy quenching
Zu, Mandelbaum
Develop a simple yet comprehensive method to distinguish the underlying drivers of galaxy quenching, using the clustering and gg lensing of red and blue galaxies in SDSS. Building on the iHOD framework, consider two quenching scenarios: 1) a halo quenching model in which halo mass is the sole driver for turning off star formation in both centrals and satellite; and 2) a hybrid quenching model in which the quenched fraction of galaxies depends on their stellar mass while the satellite quenching has an extra dependence on halo mass. The two best-fit models describe the red galaxy clustering and lensing equally well, but halo quenching provides significantly better fits to the blue galaxies above 1e11 Msun/h^2. The halo quenching model also correctly predicts the average halo mass of the red and blue centrals, showing excellent agreement with the direct WL measurements of locally births galaxies. Models in which quenching is not tied to halo mass, including an age-matching model in which galaxy color depends on halo age at fixed M*, fail to reproduce the observed halo mass for massive blue centrals. Find similar critical halo masses responsible for the quenching of centrals and satellites (~1.5e12 Msun/h^2), hinting at a uniform quenching mechanism for both, e.g., the viral shock-heating of infalling gas. The success of the iHOD halo quenching model provides strong evidence that the physical mechanism that quenches star formation in galaxies is tied principally to the masses of their dark matter halos rather than the properties of their stellar components.
1509.06762
Strong bimodality in the host halo mass of central galaxies from galaxy-galaxy lensing
Mandelbaum, Wang, Zu, White, Henriques, More
Use gg lensing to study the DM haloes surrounding a sample of locally bright galaxies (LBGs) selected from SDSS. Measure mean halo mass as a function of the stellar mass and color of the central galaxy. Mock catalogues constructed from semi-analytic galaxy formation simulations demonstrate that most LBGs are the central objects of their halos, greatly reducing interpretation uncertainties due to satellite contributions to the lensing signal. Over the full stellar mass range, 10.3<log(M*/Msun)<11.6, find that passive central galaxies have haloes that are at least twice as massive as those of star-forming objects of the same stellar mass. The significance of this effect exceeds 3 sigma for log(M*/Msun)>10.7. Tests using the mock catalogues and on the data themselves clarify the effects of LBG selection and show that it cannot artificially induce a systematic dependence of halo mass on LBG color. The bimodality in halo mass at fixed stellar mass is reproduced by the astrophysical model underlying the mock catalogue, but the sign of the effect is inconsistent with recent, nearly parameter-free age-matching models. The sign and magnitude of the effect can, however, be reproduced by halo occupation distribution models with a simple (few-parameter) prescription for type-dependence.
1509.06877
The distribution function of the Galaxy's dark halo
Binney, Piffl
Starting from the hypothesis that the Galaxy's dark halo responded adiabatically to the infall of baryons, construct a self-consistent dynamical model of the Galaxy that satisfies a large number of observations, including measurements of gas terminal velocities and masers, the kinematics of a 180k giant stars from the RAVE survey, and star count data from the SDSS. The stellar disc and the dark halo are both specified by distribution functions (DFs) of the action integrals. The model is obtained by extending the work of Piffle Penoyre + Binney (2015) from the construction of a single model to a systematic search of model space. Whereas the model of PIffl+ violated constraints on the terminal-velocity curve, the model respects these constraints by adopting a long scale length R_d=3.6 kpc for the thin and thick discs. The models is, however, inconsistent with the measured optical depth for microlensing of bulge stars because it attributes too large a fraction of the density at R<~3 kpc to dark matter rather than stars. Moreover, it now seems likely that the thick disc's sale-length is significantly shorter than the model implies. Shortening this scale-length would cause the constraints from the rotation curve to be violated anew. Conclude that adiabatic compression of our Galaxy's dark halo can be ruled out.
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