Morphology of Mock SDSS Catalogues

We measure the geometry, topology and morphology of the superclusters in mock SDSS catalogues prepared by Cole et al.(1998). The mock catalogues refer to $\tau$CDM and \LCDM {\em flat} cosmological models and are populated by galaxies so that these act as biased tracers of mass, conforming with the correlation function measured using APM catalogue. We compute the Minkowski Functionals (MFs) for the cosmic density fields using SURFGEN (Sheth et al.2003) and use the available 10 realizations of $\tau$CDM to study the effect of cosmic variance in estimation of MFs and Shapefinders, which we find to be extremely well constrained statistics. Although all the mock catalogues of galaxies have the same two-point correlation function and similar clustering amplitude, the global MFs due to $\tau$CDM show systematically lower amplitude compared to those due to \LCDM; an indirect, but detectable effect due to nonzero, higher order correlation functions. The characteristic thickness (T), breadth (B) and length (L) of the superclusters are measured using the available 10 realizations of $\tau$CDM. While T$\le$B and T, B$\in$[1,17] h$^{-1}$Mpc, we find the top 10 superclusters to be as long as 90 h$^{-1}$Mpc, with the longest superclusters identified at percolation to be rare objects with their length as large as 150 h$^{-1}$Mpc. The $\tau$CDM superclusters are found to be significantly longer than those in \LCDM. Thickness (T), breadth (B), planarity (P) and mass/volume$-$weighted planarity and filamentarity of the superclusters are found to be useful to compare the two models (abridged).Comment: 23 Pages, 12 Figures, MNRAS Style. Minor modifications to the text. New references adde

Youth Involvement in Community Development: Implications and Possibilities for Extension

There is a need for Extension program/policy developers to better understand the role of youth in the community development process. While often seen as suited only for 4-H programs, youth can significantly contribute to a variety of Extension activities. Through active engagement, youth can take on ownership and become lifelong contributors to local well-being. This mixed-methods research reflects data from a survey of 418 Florida youth and 12 in-depth key informant interviews. The findings provide insights into the factors most directly shaping youth attitudes and involvement in their communities. From these, implications for applied use in Extension programs are presented

Can Baryonic Features Produce the Observed 100 Mpc Clustering?

We assess the possibility that baryonic acoustic oscillations in adiabatic models may explain the observations of excess power in large-scale structure on 100h^-1 Mpc scales. The observed location restricts models to two extreme areas of parameter space. In either case, the baryon fraction must be large (Omega_b/Omega_0 > 0.3) to yield significant features. The first region requires Omega_0 < 0.2h to match the location, implying large blue tilts (n>1.4) to satisfy cluster abundance constraints. The power spectrum also continues to rise toward larger scales in these models. The second region requires Omega_0 near 1, implying Omega_b well out of the range of big bang nucleosynthesis constraints; moreover, the peak is noticeably wider than the observations suggest. Testable features of both solutions are that they require moderate reionization and thereby generate potentially observable (about 1 uK) large-angle polarization, as well as sub-arc-minute temperature fluctuations. In short, baryonic features in adiabatic models may explain the observed excess only if currently favored determinations of cosmological parameters are in substantial error or if present surveys do not represent a fair sample of 100h^-1 Mpc structures.Comment: LaTeX, 7 pages, 5 Postscript figures, submitted to ApJ Letter

Measuring Feedback Using the Intergalactic Medium State and Evolution Inferred from the Soft X-ray Background

We explore the intergalactic medium (IGM) as a potential source of the unresolved soft X-ray background (XRB) and the feasibility to extract the IGM state and evolution from XRB observations. We build two analytical models, the continuum field model and the halo model, to calculate the IGM XRB mean flux, angular auto correlation and cross correlation with galaxies. Our results suggest that the IGM may contribute a significant fraction to the unresolved soft XRB flux and correlations. We calibrated non-Gaussian errors estimated against our $512^3$ moving mesh hydro simulation and estimate that the ROSAT all sky survey plus Sloan galaxy photometric redshift survey would allow a $\sim 10$ accuracy in the IGM XRB-galaxy cross correlation power spectrum measurement for $800<l<5000$ and a $\sim 20$ accuracy in the redshift resolved X-ray emissivity-galaxy cross correlation power spectrum measurement for $z\lesssim 0.5$. At small scales, non-gravitational heating, e.g. feedback, dominates over gravity and leaves unique signatures in the IGM XRB, which allows a comparable accuracy in the measurement of the amount of non-gravitational heating and the length scales where non-gravitational energy balances gravity.Comment: 17 pages, 5 figures. Will appear on ApJ May issu

Star formation history in the solar neighborhood: the link between stars and cosmology

Using a cosmological galactic evolutionary approach to model the Milky Way, we calculate the star formation history (SFH) of the solar neighborhood. The good agreement we obtain with the observational inferences suggests that our physical model describes accurately the long term/large spatial trends of the local and global Milky Way SFH. In this model, star formation is triggered by disk gravitational instabilities and self-regulated by an energy balance in the ISM. The drivers of the SFH are the cosmological gas infall rate and the gas surface density determined by the primordial spin parameter. A LambdaCDM cosmology was used throughout.Comment: 8 pages, uses kluwer.cls. Invited talk, to appear in "New Quests in Stellar Astrophysics: The link between Stars and Cosmology", eds. M. Chavez, A. Bressan, A. Buzzoni & D. Mayya, Kluwer Academic Publisher

Numerical Analyses of Weakly Nonlinear Velocity-Density Coupling

We study evolution of various statistical quantities of smoothed cosmic density and velocity fields using N-body simulations. The parameter $C\equiv /( )$ characterizes nonlinear coupling of these two fields and determines behavior of bulk velocity dispersion as a function of local density contrast. It is found that this parameter depends strongly on the smoothing scale even in quasi-linear regimes where the skewness parameter $S_3$ is nearly constant and close to the predicted value by the second-order perturbation theory. We also analyze weakly nonlinear effects caused by an adaptive smoothing known as the gather approach.Comment: 22 pages, 4 figures, to appear in ApJ (558, Sep 10

The environment of active objects in the nearby universe

We study the galaxy environment of active galaxies, radio-loud and radio-quiet quasars in the redshift range $0.1\leq z\leq0.25$. We use APM galaxies in order to explore the local galaxy overdensity and the $b_J-R$ colour distribution of neighbouring galaxies of these target samples. For comparison, we perform similar analysis on samples of Abell clusters with X-ray emission, and samples of Abell clusters with richness R=1 and R=0. The projected cross-correlations show that the samples of quasars and active galaxies reside in regions of galaxy density enhancements lower than those typical of R=0 clusters. We also find that in the nearby universe the local galaxy overdensity of radio-loud and radio-quiet quasars are comparable. The analysis of the distribution of $b_J-R$ galaxy colour indexes suggests that the environment of quasars is not strongly dominated by a population of red galaxies, characteristic of rich Abell cluster, an effect that is more clearly appreciated for our sample of radio-loud quasars.Comment: 5 pages, 3 figures, to appear in MNRA

Origin and evolution of halo bias in linear and non-linear regimes

We present results from a study of bias and its evolution for galaxy-size halos in a large, high-resolution simulation of a LCDM model. We consider the evolution of bias estimated using two-point correlation function (b_xi), power spectrum (b_P), and a direct correlation of smoothed halo and matter overdensity fields (b_d). We present accurate estimates of the evolution of the matter power spectrum probed deep into the stable clustering regime (k~[0.1-200]h/Mpc at z=0). The halo power spectrum evolves much slower than the power spectrum of matter and has a different shape which indicates that the bias is time- and scale-dependent. At z=0, the halo power spectrum is anti-biased with respect to the matter power spectrum at wavenumbers k~[0.15-30]h/Mpc, and provides an excellent match to the power spectrum of the APM galaxies at all probed k. In particular, it nicely matches the inflection observed in the APM power spectrum at k~0.15h/Mpc. We complement the power spectrum analysis with a direct estimate of bias using smoothed halo and matter overdensity fields and show that the evolution observed in the simulation in linear and mildly non-linear regimes can be well described by the analytical model of Mo & White (1996), if the distinction between formation redshift of halos and observation epoch is introduced into the model. We present arguments and evidence that at higher overdensities, the evolution of bias is significantly affected by dynamical friction and tidal stripping operating on the satellite halos in high-density regions of clusters and groups; we attribute the strong anti-bias observed in the halo correlation function and power spectrum to these effects. (Abridged)Comment: submitted to the Astrophys.Journal; 19 pages, 9 figures LaTeX (uses emulateapj.sty

The Hierarchical Build-Up of Massive Galaxies and the Intracluster Light since z=1

We use a set of simulation-based models for the dissipationless evolution of galaxies since z=1 to constrain the fate of accreted satellites embedded in dark matter subhalos. These models assign stellar mass to dark matter halos at z=1 by relating the observed galaxy stellar mass function (GSMF) to the halo+subhalo mass function monotonically. The evolution of the stellar mass content is then followed using halo merger trees extracted from N-body simulations. Our models are differentiated only in the fate assigned to satellite galaxies once subhalos, within which satellites are embedded, disrupt. These models are confronted with the observed evolution in the massive end of the GSMF, the z~0 brightest cluster galaxy (BCG)-cluster mass relation, and the combined BCG and intracluster light (ICL) luminosity distribution -- all observables expected to evolve approximately dissipationlessly since z=1. The combined observational constraints favor a model in which the vast majority (>80%) of satellite stars from disrupted subhalos go into the ICL. Conversely, models that leave behind a significant population of satellite galaxies once the subhalo has disrupted are strongly disfavored, as are models that put a significant fraction of satellite stars into the BCG. Our results show that observations of the ICL provide useful and unique constraints on models of galaxy merging and the dissipationless evolution of galaxies in groups and clusters.Comment: 12 pages, 6 figures. Submitted to Ap