48 research outputs found
Likelihood reconstruction method of real-space density and velocity power spectra from a redshift galaxy survey
No full textProperties of host haloes of Lyman-break galaxies and Lyman α emitters from their number densities and angular clustering
No full textInternational audienceWe explore empirical relations between three different populations of high-redshift galaxies and their hosting dark haloes employing the halo model approach. Specifically we consider Lyman-break galaxies (LBGs) at z~ 4 and at z~ 5, and Lyman α emitters (LAEs) at z~= 4.86, all from the Subaru Deep Field survey extending over an area of about 600 arcmin2. We adopt a halo occupation function (HOF) prescription to parametrize the properties of their hosting haloes and the efficiency of halo-dependent star formation. We find that the two LBG samples are well described by the halo model with an appropriate HOF. Comparing the model predictions with the observed number densities and the angular correlation functions for those galaxies, we obtain constraints on properties of their hosting haloes. A typical mass of hosting haloes for LBGs is 5 × 1011h-1 Msolar and the expected number of LBGs per halo is ~0.5 therefore there is an approximate one-to-one correspondence between haloes and LBGs. We also find an indication that the minimum mass of LBG hosting haloes decreases with time, although its statistical significance is not strong. We discuss the implications of these findings on the star formation history of LBGs. On the other hand, for LAEs, our simple HOF prescription fails to reproduce simultaneously the observed angular correlation function and the number density. In particular, a very high amplitude of the correlation function on scales larger than 120 arcsec cannot be easily reconciled by the HOF model; a set of parameters that account for this high correlation amplitude on large scales predict either excessive clustering on small scales or a much smaller number density than observed. While this difficulty might imply either that the distribution of LAEs within hosting haloes differs from that of dark matter, or that the strong large-scale correlation is due to the existence of an unusual, large overdense region, and so the survey region is not a representative of the z~ 5 Universe, the definite answer should wait for a much wider survey of LAEs at high redshifts
Bispectrum and nonlinear biasing of galaxies: perturbation analysis, numerical simulation and SDSS galaxy clustering
No full textWe consider nonlinear biasing models of galaxies with particular attention to a correlation between the linear and quadratic biasing coefficients, b(1) and b(2). We first derive perturbative expressions for b(1) and b(2) in halo and peak biasing models. We then discuss our computations of the power spectra and bispectra of dark matter particles and halos using N-body simulation data and of volume-limited subsamples of Sloan Digital Sky Survey (SDSS) galaxies, and determine their b(1) and b(2). We find that the values of those coefficients at linear regimes (k < 0.2 h Mpc(-1)) are fairly insensitive to the redshift-space distortion and the survey volume shape. The resulting normalized amplitudes of the bispectra, Q, for equilateral triangles are insensitive to the values of b(1), implying that b(2) indeed correlates with b(1). The present results explain the previous finding of Kayo et al. (2004, PASJ, 56, 415) for the hierarchical relation of three-point correlation functions of SDSS galaxies. While the relations between b(1) and b(2) are quantitatively different for specific biasing models, their approximately similar correlations indicate a fairly generic outcome of the biasing due to the gravity in primordial Gaussian density fields
Chasing unbiased spectra of the Universe
No full textInternational audienceThe cosmological power spectrum of the coherent matter flow is measured exploiting an improved prescription for the apparent anisotropic clustering pattern in redshift space. New statistical analysis is presented to provide an optimal observational platform to link the improved redshift distortion theoretical model to future real data sets. The statistical power as well as robustness of our method are tested against 60 realizations of 8h-3Gpc3 dark matter simulation maps mocking the precision level of upcoming wide-deep surveys. We showed that we can accurately extract the velocity power spectrum up to quasilinear scales of k∼0.1hMpc-1 at z=0.35 and up to k∼0.15hMpc-1 at higher redshifts within a couple of percentage precision levels. Our understanding of redshift space distortion is proved to be appropriate for precision cosmology, and our statistical method will guide us to a righteous path to meet the real world
Fitting the nonlinear matter bispectrum by the Halofit approach
No full textInternational audienceWe provide a new fitting formula of the matter bispectrum in the nonlinear regime calibrated by high-resolution cosmological N-body simulations of 41 cold dark matter (wCDM, w = constant) models around the Planck 2015 best-fit parameters. As the parameterization in our fitting function is similar to that in Halofit, our fitting is named BiHalofit. The simulation volume is sufficiently large () to cover almost all measurable triangle bispectrum configurations in the universe. The function is also calibrated using one-loop perturbation theory at large scales (). Our formula reproduced the matter bispectrum to within 10% (15%) accuracy in the Planck 2015 model at wavenumber and redshifts z = 0–3. The other 40 wCDM models obtained poorer fits, with accuracy approximating 20% at and (the deviation includes the 10%-level sample variance of the simulations). We also provide a fitting formula that corrects the baryonic effects such as radiative cooling and active galactic nucleus feedback, using the latest hydrodynamical simulation IllustrisTNG. We demonstrate that our new formula more accurately predicts the weak-lensing bispectrum than the existing fitting formulae. This formula will assist current and future weak-lensing surveys and cosmic microwave background lensing experiments. Numerical codes of the formula are available, written in Python (https://toshiyan.github.io/clpdoc/html/basic/basic.html#module-basic.bispec), C, and Fortran (http://cosmo.phys.hirosaki-u.ac.jp/takahasi/codes_e.htm)
Modeling the Anomaly of Surface Number Densities of Galaxies on the Galactic Extinction Map due to Their FIR Emission Contamination
No full textInternational audienceThe most widely used Galactic extinction map is constructed assuming that the observed far-infrared (FIR) fluxes come entirely from Galactic dust. According to the earlier suggestion by Yahata et al., we consider how FIR emission of galaxies affects the SFD map. We first compute the surface number density of Sloan Digital Sky Survey (SDSS) DR7 galaxies as a function of the r-band extinction, A r, SFD. We confirm that the surface densities of those galaxies positively correlate with A r, SFD for A r, SFD 100 μm/(νL) r . Then we search for the mean and rms values of y that fit the observed anomaly, using the analytical model. The required values to reproduce the anomaly are roughly consistent with those measured from the stacking analysis of SDSS galaxies. Due to the limitation of our statistical modeling, we are not yet able to remove the FIR contamination of galaxies from the extinction map. Nevertheless, the agreement with the model prediction suggests that the FIR emission of galaxies is mainly responsible for the observed anomaly. Whereas the corresponding systematic error in the Galactic extinction map is 0.1-1 mmag, it is directly correlated with galaxy clustering and thus needs to be carefully examined in precision cosmology
