How covariant is the galaxy luminosity function?

We investigate the error properties of certain galaxy luminosity function (GLF) estimators. Using a cluster expansion of the density field, we show how, for both volume and flux limited samples, the GLF estimates are covariant. The covariance matrix can be decomposed into three pieces: a diagonal term arising from Poisson noise; a sample variance term arising from large-scale structure in the survey volume; an occupancy covariance term arising due to galaxies of different luminosities inhabiting the same cluster. To evaluate the theory one needs: the mass function and bias of clusters, and the conditional luminosity function (CLF). We use a semi-analytic model (SAM) galaxy catalogue from the Millennium run N-body simulation and the CLF of Yang et al. (2003) to explore these effects. The GLF estimates from the SAM and the CLF qualitatively reproduce results from the 2dFGRS. We also measure the luminosity dependence of clustering in the SAM and find reasonable agreement with 2dFGRS results for bright galaxies. However, for fainter galaxies, L<L*, the SAM overpredicts the relative bias by ~10-20%. We use the SAM data to estimate the errors in the GLF estimates for a volume limited survey of volume V~0.13 [Gpc/h]^3. We find that different luminosity bins are highly correlated: for L<L* the correlation coefficient is r>0.5. Our theory is in good agreement with these measurements. These strong correlations can be attributed to sample variance. For a flux-limited survey of similar volume, the estimates are only slightly less correlated. We explore the importance of these effects for GLF model parameter estimation. We show that neglecting to take into account the bin-to-bin covariances can lead to significant systematic errors in best-fit parameters.Comment: 19 pages, 12 figures. Accepted for publication in MNRAS. Refs updated; Fig 6 added; Figs 7 and 10 improve

Using Cluster Abundances and Peculiar Velocities to Test the Gaussianity of the Cosmological Density Field

(Abridged) By comparing the frequency of typical events with that of unusual events, one can test whether the cosmological density distribution function is consistent with the normally made assumption of Gaussianity. To this end, we compare the consistency of the tail-inferred (from clusters) and measured values (from large-scale flows) of the rms level of mass fluctuations for two distribution functions: a Gaussian, and a texture (positively-skewed) PDF. Averaging the recent large-scale flow measurements, we find that observations of the rms and the tail at the 10 h^-1 Mpc scale disfavor a texture PDF at ~1.5 sigma in all cases. However, taking only the most recent measurement of the rms, that from Willick et al. (1997b), the comparison disfavors textures for low Omega_0=0.3, and disfavors Gaussian models if Omega_0=1 (again at ~1.5 sigma). Predictions for evolution of high temperature clusters can also be made for the models considered, and strongly disfavor Omega_0=1 in Gaussian models and marginally disfavor Omega_0=1 in texture models. Only Omega_0=0.3 Gaussian models are consistent with all the data considered.Comment: 34 pg incl. 8 embedded figures, LaTeX, aaspp4.sty, submitted to Ap

3D Spherical Analysis of Baryon Acoustic Oscillations

Baryon Acoustic Oscillations (BAOs) are oscillatory features in the galaxy power spectrum and are a standard rod to measure the cosmological expansion. These have been studied in Cartesian space (Fourier or real space) or in Spherical Harmonic (SH) space in thin shells. Future wide-field surveys will cover both wide and deep regions of the sky and thus require a simultaneous treatment of the spherical sky and of an extended radial coverage. The Spherical Fourier-Bessel (SFB) decomposition is a natural basis for the analysis of fields in this geometry and facilitates the combination of BAO surveys with other cosmological probes readily described in this basis. We present here a new way to analyse BAOs by studying the BAO wiggles from the SFB power spectrum. In SFB space, the power spectrum generally has both a radial (k) and tangential (l) dependence and so do the BAOs. In the deep survey limit and ignoring evolution, the SFB power spectrum becomes radial and reduces to the Cartesian Fourier power spectrum. In the limit of a thin shell, all the information is contained in the tangential modes described by the 2D SH power spectrum. We find that the radialisation of the SFB power spectrum is still a good approximation even when considering an evolving and biased galaxy field with a finite selection function. This effect can be observed by all-sky surveys with depths comparable to current surveys. We find that the BAOs radialise more rapidly than the full SFB power spectrum. Our results suggest the first peak of the BAOs in SFB space becomes radial out to l ~ 10 for all-sky surveys with the same depth as SDSS or 2dF, and out to l ~ 70 for an all-sky stage IV survey. Subsequent BAO peaks also become radial, but for shallow surveys these may be in the non-linear regime. For modes that have become radial, measurements at different l's are useful in practice to reduce measurement errors.Comment: 6 pages + Appendix. Astro-ph abstract is abridged. Updated with comments from anonymous referee. Corrected axes of Figure 2. Extended discussion of radialisation. Accepted for publication in Astronomy & Astrophysic

Mock galaxy redshift catalogues from simulations: implications for Pan-STARRS1

We describe a method for constructing mock galaxy catalogues which are well suited for use in conjunction with large photometric surveys. We use the semi-analytic galaxy formation model of Bower et al. implemented in the Millennium simulation. We apply our method to the specific case of the surveys soon to commence with PS1, the first of 4 telescopes planned for the Pan-STARRS system. PS1 has 5 photometric bands (grizy), and will carry out an all-sky 3pi survey and a medium deep survey (MDS) over 84 sq.deg. We calculate the expected magnitude limits for extended sources in the two surveys. We find that, after 3 years, the 3pi survey will have detected over 10^8 galaxies in all 5 bands, 10 million of which will lie at redshift z>0.9, while the MDS will have detected over 10^7 galaxies with 0.5 million lying at z>2. These numbers at least double if detection in the shallowest band, y is not required. We then evaluate the accuracy of photometric redshifts estimated using an off-the-shelf photo-z code. With the grizy bands alone it is possible to achieve an accuracy in the 3pi survey of Delta z/(1+z)~0.06 for 0.25<z<0.8, which could be reduced by about 15% using near infrared photometry from the UKIDDS survey, but would increase by about 25% for the deeper sample without the y band photometry. For the MDS an accuracy of Delta z/(1+z)~0.05 is achievable for 0.02<z<1.5 using grizy. A dramatic improvement in accuracy is possible by selecting only red galaxies. In this case, Delta z/(1+z)~0.02-0.04 is achievable for ~100 million galaxies at 0.4<z<1.1 in the 3pi survey and for 30 million galaxies in the MDS at 0.4<z<2. We investigate the effect of using photo-z in the estimate of the baryonic acoustic oscillation scale. We find that PS1 will achieve a similar accuracy in this estimate as a spectroscopic survey of 20 million galaxies.Comment: 23 pages, 18 figures, accepted by MNRA

A New Method to Correct for Fiber Collisions in Galaxy Two-Point Statistics

In fiber-fed galaxy redshift surveys, the finite size of the fiber plugs prevents two fibers from being placed too close to one another, limiting the ability of studying galaxy clustering on all scales. We present a new method for correcting such fiber collision effects in galaxy clustering statistics based on spectroscopic observations. Our method makes use of observations in tile overlap regions to measure the contributions from the collided population, and to therefore recover the full clustering statistics. The method is rooted in solid theoretical ground and is tested extensively on mock galaxy catalogs. We demonstrate that our method can well recover the projected and the full three-dimensional redshift-space two-point correlation functions on scales both below and above the fiber collision scale, superior to the commonly used nearest neighbor and angular correction methods. We discuss potential systematic effects in our method. The statistical correction accuracy of our method is only limited by sample variance, which scales down with (the square root of) the volume probed. For a sample similar to the final SDSS-III BOSS galaxy sample, the statistical correction error is expected to be at the level of 1% on scales 0.1--30Mpc/h for the two-point correlation functions. The systematic error only occurs on small scales, caused by non-perfect correction of collision multiplets, and its magnitude is expected to be smaller than 5%. Our correction method, which can be generalized to other clustering statistics as well, enables more accurate measurements of full three-dimensional galaxy clustering on all scales with galaxy redshift surveys. (abridged)Comment: ApJ accepted. Matched to accepted version(improvements on systematics

Determination of the Baryon Density from Large Scale Galaxy Redshift Surveys

We estimate the degree to which the baryon density, $\Omega_{b}$, can be determined from the galaxy power spectrum measured from large scale galaxy redshift surveys, and in particular, the Sloan Digital Sky Survey. A high baryon density will cause wiggles to appear in the power spectrum, which should be observable at the current epoch. We assume linear theory on scales $\geq 20h^{-1}Mpc$ and do not include the effects of redshift distortions, evolution, or biasing. With an optimum estimate of $P(k)$ to $k\sim 2\pi/(20 h^{-1} Mpc)$, the $1 \sigma$ uncertainties in $\Omega_{b}$ are roughly 0.07 and 0.016 in flat and open ($\Omega_{0}=0.3$) cosmological models, respectively. This result suggests that it should be possible to test for consistency with big bang nucleosynthesis estimates of $\Omega_{b}$ if we live in an open universe.Comment: 23 Pages, 10 Postscript figure

The role of motivation to eat in the prediction of weight control behaviors in female and male adolescents

Objective: To examine whether motivation to eat variables predict changes in dieting and weight control behaviors in both gender groups over time. \ud Method: Greek adolescents (n=247), aged 14–18 years, completed questionnaires measuring different \ud dimensions of motivation to eat, dieting, healthy and unhealthy weight control behaviors. Dieting and weight \ud control behaviors were measured five months later. \ud Results: Compliance motivation positively predicted changes in dieting in males and a number of unhealthy \ud weight control behaviors in females. Coping motivation negatively predicted meal skipping in both genders \ud and was associated with a lower risk of vomiting in females. Social motivation positively predicted eating less \ud high fat food in males while pleasure motivation was associated with a reduced likelihood of eating more \ud fruits and vegetables in females and a reduced risk of fasting in males. \ud Conclusion: Intervention programs designed to facilitate healthy and circumvent unhealthy weight control \ud practices in adolescents should attend to gender differences in motivational factors shown to predict dieting \ud and weight control behaviors. For females it may be important to minimize compliance motivation whereas \ud for males, programs that foster social motivation to eat might be appropriate

Quantifying the coherent outflows of galaxies around voids in the SDSS DR7

We report the detection, with a high level of confidence, of coherent outflows around voids found in the seventh data release of the Sloan Digital Sky Survey (SDSS DR7). In particular, we developed a robust statistical test to quantify the strength of redshift-space distortions (RSD) associated with extended coherent velocity fields. We consistently find that the vector that joins void centers with galaxies that lie in shells around them is more likely to be perpendicular to the line-of-sight than parallel to it. This effect is clear evidence for the existence of outflows in the vicinity of voids. We show that the RSD exist for a wide range of void radius and shell thickness, but they are more evident in the largest voids in our sample. For instance, we find that the for galaxies located in shells within 2 h^-1 Mpc from the edge of voids larger than 15 h^-1 Mpc deviates 3.81sigma from uniformity. The measurements presented in this work provide useful information to constrain cosmological parameters, in particular Omega_m and Sigma_8.Comment: 4 pages, 1 figure, to appear in A&A Letter

Overweight status and psychological well-being in adolescent boys and girls: a multilevel analysis*

Background: Psychological distress and high body mass index (BMI) are linked in adults, especially in females. Effects of social position and behaviour, and whether obesogenic environments affect adolescents and adults equally are unresolved. The aim was to examine associations between psychological distress and being overweight in adolescents, by sex, accounting for social, lifestyle and contextual factors. Correlation of area-level variation in overweight status in adolescents and adults was investigated. Methods: Height, weight, General Health Questionnaire 12 (GHQ12) of psychological distress, physical activity, smoking, alcohol consumption, area deprivation and social class were available on 635 male and 618 female adolescents (13–15 years) from two cross-sectional population health surveys conducted in Scotland in 1998–99/2003–04. Multilevel logistic regression modelled overweight (including obese) status accounting for intraclass correlation of adolescents in households within postcode sector areas in health board regions. Univariable analysis examined effects of high (4 or more) GHQ12 score; multivariable analysis further allowed for covariates. Adult data were used to assess the importance of correlation between adolescent and adult area-level variation. Results: Univariably, there was significantly increased risk of being overweight associated with high GHQ12 score for girls but not boys; adolescent and adult area-level variation correlation did not impact. Results remained significant for girls in multivariable analyses (OR = 2.44, 95% confidence interval (CI): 1.33–4.50) and non-significant for boys (OR = 1.31, 95% CI: 0.56–3.05). Conclusions: Findings indicate being overweight is associated with psychological distress in adolescent girls, but not boys. Effects are not mediated by social, lifestyle or contextual factors