arXiv subjects

Charling Tao

Publications and source records attributed to Charling Tao.

35 records · Page 2Linked to original sources

arXiv2016

The extended Baryon Oscillation Spectroscopic Survey (eBOSS): a cosmological forecast

We present a science forecast for the eBOSS survey, part of the SDSS-IV project, which is a spectroscopic survey using multiple tracers of large-scale structure, including luminous red galaxies (LRGs), emission line galaxies (ELGs) and quasars (both as a direct probe of structure and through the Ly-$α$ forest). Focusing on discrete tracers, we forecast the expected accuracy of the baryonic acoustic oscillation (BAO), the redshift-space distortion (RSD) measurements, the $f_{\rm NL}$ parameter quantifying the primordial non-Gaussianity, the dark energy and modified gravity parameters. We also use the line-of-sight clustering in the Ly-$α$ forest to constrain the total neutrino mass. We find that eBOSS LRGs ($0.6 0.6$), ELGs ($0.6<z<1.2$) and Clustering Quasars (CQs) ($0.6<z<2.2$) can achieve a precision of 1%, 2.2% and 1.6% precisions, respectively, for spherically averaged BAO distance measurements. Using the same samples, the constraint on $fσ_8$ is expected to be 2.5%, 3.3% and 2.8% respectively. For primordial non-Gaussianity, eBOSS alone can reach an accuracy of $σ(f_{\rm NL})\sim10-15$, depending on the external measurement of the galaxy bias and our ability to model large-scale systematic errors. eBOSS can at most improve the dark energy Figure of Merit (FoM) by a factor of $3$ for the Chevallier-Polarski-Linder (CPL) parametrisation, and can well constrain three eigenmodes for the general equation-of-state parameter (Abridged).

astro-ph.CO↗

arXiv2015

The Sloan Digital Sky Survey Reverberation Mapping Project: First Broad-line Hbeta and MgII Lags at z>~0.3 from six-Month Spectroscopy

Reverberation mapping (RM) measurements of broad-line region (BLR) lags in z>0.3 quasars are important for directly measuring black hole masses in these distant objects, but so far there have been limited attempts and success given the practical difficulties of RM in this regime. Here we report preliminary results of 15 BLR lag measurements from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project, a dedicated RM program with multi-object spectroscopy designed for RM over a wide redshift range. The lags are based on the 2014 spectroscopic light curves alone (32 epochs over 6 months) and focus on the Hbeta and MgII broad lines in the 100 lowest-redshift (z<0.8) quasars included in SDSS-RM; they represent a small subset of the lags that SDSS-RM (including 849 quasars to z~4.5) is expected to deliver. The reported preliminary lag measurements are for intermediate-luminosity quasars at 0.3<~z<0.8, including 9 Hbeta lags and 6 MgII lags, for the first time extending RM results to this redshift-luminosity regime and providing direct quasar black hole mass estimates over ~ half of cosmic time. The MgII lags also increase the number of known MgII lags by several-fold, and start to explore the utility of MgII for RM at high redshift. The location of these new lags at higher redshifts on the observed BLR size-luminosity relationship is statistically consistent with previous Hbeta results at z<0.3. However, an independent constraint on the relationship slope at z>0.3 is not yet possible due to the limitations in our current sample. Our results demonstrate the general feasibility and potential of multi-object RM for z>0.3 quasars.

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arXiv2015

DIVE in the cosmic web: voids with Delaunay Triangulation from discrete matter tracer distributions

We present a novel parameter-free cosmological void finder (\textsc{dive}, Delaunay TrIangulation Void findEr) based on Delaunay Triangulation (DT), which efficiently computes the empty spheres constrained by a discrete set of tracers. We define the spheres as DT voids, and describe their properties, including an universal density profile together with an intrinsic scatter. We apply this technique on 100 halo catalogues with volumes of 2.5\,$h^{-1}$Gpc side each, with a bias and number density similar to the BOSS CMASS Luminous Red Galaxies, performed with the \textsc{patchy} code. Our results show that there are two main species of DT voids, which can be characterised by the radius: they have different responses to halo redshift space distortions, to number density of tracers, and reside in different dark matter environments. Based on dynamical arguments using the tidal field tensor, we demonstrate that large DT voids are hosted in expanding regions, whereas the haloes used to construct them reside in collapsing ones. Our approach is therefore able to efficiently determine the troughs of the density field from galaxy surveys, and can be used to study their clustering. We further study the power spectra of DT voids, and find that the bias of the two populations are different, demonstrating that the small DT voids are essentially tracers of groups of haloes.

astro-ph.CO↗

arXiv2015

Measuring Baryon Acoustic Oscillations from the clustering of voids

We investigate the necessary methodology to optimally measure the baryon acoustic oscillation (BAO) signal, from voids based on galaxy redshift catalogues. To this end, we study the dependency of the BAO signal on the population of voids classified by their sizes. We find for the first time the characteristic features of the correlation function of voids including the first robust detection of BAOs in mock galaxy catalogues. These show an anti-correlation around the scale corresponding to the smallest size of voids in the sample (the void exclusion effect), and dips at both sides of the BAO peak, which can be used to determine the significance of the BAO signal without any priori model. Furthermore, our analysis demonstrates that there is a scale dependent bias for different populations of voids depending on the radius, with the peculiar property that the void population with the largest BAO significance corresponds to tracers with approximately zero bias on the largest scales. We further investigate the methodology on an additional set of 1,000 realistic mock galaxy catalogues reproducing the SDSS-III/BOSS CMASS DR11 data, to control the impact of sky mask and radial selection function. Our solution is based on generating voids from randoms including the same survey geometry and completeness, and a post-processing cleaning procedure in the holes and at the boundaries of the survey. The methodology and optimal selection of void populations validated in this work have been used to perform the first BAO detection from voids in observations, presented in a companion paper.

astro-ph.CO↗

arXiv2015

nIFTy Cosmology: Galaxy/halo mock catalogue comparison project on clustering statistics

We present a comparison of major methodologies of fast generating mock halo or galaxy catalogues. The comparison is done for two-point and the three-point clustering statistics. The reference catalogues are drawn from the BigMultiDark N-body simulation. Both friend-of-friends (including distinct halos only) and spherical overdensity (including distinct halos and subhalos) catalogs have been used with the typical number density of a large-volume galaxy surveys. We demonstrate that a proper biasing model is essential for reproducing the power spectrum at quasilinear and even smaller scales. With respect to various clustering statistics a methodology based on perturbation theory and a realistic biasing model leads to very good agreement with N-body simulations. However, for the quadrupole of the correlation function or the power spectrum, only the method based on semi-N-body simulation could reach high accuracy (1% level) at small scales, i.e., r<25 Mpc/h or k>0.15 h/Mpc. Full N-body solutions will remain indispensable to produce reference catalogues. Nevertheless, we have demonstrated that the far more efficient approximate solvers can reach a few percent accuracy in terms of clustering statistics at the scales interesting for the large-scale structure analysis after calibration with a few reference N-body calculations. This makes them useful for massive production aimed at covariance studies, to scan large parameter spaces, and to estimate uncertainties in data analysis techniques, such as baryon acoustic oscillation reconstruction, redshift distortion measurements, etc.

astro-ph.CO↗

arXiv2015

The Sloan Digital Sky Survey Reverberation Mapping Project: Rapid CIV Broad Absorption Line Variability

We report the discovery of rapid variations of a high-velocity CIV broad absorption line trough in the quasar SDSS J141007.74+541203.3. This object was intensively observed in 2014 as a part of the Sloan Digital Sky Survey Reverberation Mapping Project, during which 32 epochs of spectroscopy were obtained with the Baryon Oscillation Spectroscopic Survey spectrograph. We observe significant (>4sigma) variability in the equivalent width of the broad (~4000 km/s wide) CIV trough on rest-frame timescales as short as 1.20 days (~29 hours), the shortest broad absorption line variability timescale yet reported. The equivalent width varied by ~10% on these short timescales, and by about a factor of two over the duration of the campaign. We evaluate several potential causes of the variability, concluding that the most likely cause is a rapid response to changes in the incident ionizing continuum. If the outflow is at a radius where the recombination rate is higher than the ionization rate, the timescale of variability places a lower limit on the density of the absorbing gas of n_e > 3.9 x 10^5 cm^-3. The broad absorption line variability characteristics of this quasar are consistent with those observed in previous studies of quasars, indicating that such short-term variability may in fact be common and thus can be used to learn about outflow characteristics and contributions to quasar/host-galaxy feedback scenarios.

astro-ph.GA↗

arXiv2015

The Sloan Digital Sky Survey Reverberation Mapping Project: No Evidence for Evolution in the M-sigma Relation to z~1

We present host stellar velocity dispersion measurements for a sample of 88 broad-line quasars at 0.1 0.6) from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project. High signal-to-noise ratio coadded spectra (average S/N~30 per 69 km/s pixel) from SDSS-RM allowed decomposition of the host and quasar spectra, and measurement of the host stellar velocity dispersions and black hole (BH) masses using the single-epoch (SE) virial method. The large sample size and dynamic range in luminosity (L5100=10^(43.2-44.7) erg/s) lead to the first clear detection of a correlation between SE virial BH mass and host stellar velocity dispersion far beyond the local universe. However, the observed correlation is significantly flatter than the local relation, suggesting that there are selection biases in high-z luminosity-threshold quasar samples for such studies. Our uniform sample and analysis enable an investigation of the redshift evolution of the M-sigma relation free of caveats by comparing different samples/analyses at disjoint redshifts. We do not observe evolution of the M-sigma relation in our sample, up to z~1, but there is an indication that the relation flattens towards higher redshifts. Coupled with the increasing threshold luminosity with redshift in our sample, this again suggests certain selection biases are at work, and simple simulations demonstrate that a constant M-sigma relation is favored to z~1. Our results highlight the scientific potential of deep coadded spectroscopy from quasar monitoring programs, and offer a new path to probe the co-evolution of BHs and galaxies at earlier times.

astro-ph.GA↗

arXiv2015

Halo mass distribution reconstruction across the cosmic web

We study the relation between halo mass and its environment from a probabilistic perspective. We find that halo mass depends not only on local dark matter density, but also on non-local quantities such as the cosmic web environment and the halo-exclusion effect. Given these accurate relations, we have developed the HADRON-code (Halo mAss Distribution ReconstructiON), a technique which permits us to assign halo masses to a distribution of haloes in three-dimensional space. This can be applied to the fast production of mock galaxy catalogues, by assigning halo masses, and reproducing accurately the bias for different mass cuts. The resulting clustering of the halo populations agree well with that drawn from the BigMultiDark $N$-body simulation: the power spectra are within 1-$σ$ up to scales of $k=0.2\,h\,{\rm Mpc}^{-1}$, when using augmented Lagrangian perturbation theory based mock catalogues. Only the most massive haloes show a larger deviation. For these, we find evidence of the halo-exclusion effect. A clear improvement is achieved when assigning the highest masses to haloes with a minimum distance separation. We also compute the 2- and 3-point correlation functions, and find an excellent agreement with $N$-body results. Our work represents a quantitative application of the cosmic web classification. It can have further interesting applications in the multi-tracer analysis of the large-scale structure for future galaxy surveys.

astro-ph.CO↗

arXiv2014

The Sloan Digital Sky Survey Reverberation Mapping Project: Technical Overview

The Sloan Digital Sky Survey Reverberation Mapping project (SDSS-RM) is a dedicated multi-object RM experiment that has spectroscopically monitored a sample of 849 broad-line quasars in a single 7 deg$^2$ field with the SDSS-III BOSS spectrograph. The RM quasar sample is flux-limited to i_psf=21.7 mag, and covers a redshift range of 0.1 0.3, and will investigate the prospects of RM with all major broad lines covered in optical spectroscopy. SDSS-RM will provide guidance on future multi-object RM campaigns on larger scales, and is aiming to deliver more than tens of BLR lag detections for a homogeneous sample of quasars. We describe the motivation, design and implementation of this program, and outline the science impact expected from the resulting data for RM and general quasar science.

astro-ph.IM↗

arXiv2014

Weak lensing mass map and peak statistics in Canada-France-Hawaii Telescope Stripe 82 survey

We present a weak lensing mass map covering ~124 square degrees of the Canada-France-Hawaii Telescope Stripe 82 Survey (CS82). We study the statistics of rare peaks in the map, including peak abundance, the peak-peak correlation functions and the tangential-shear profiles around peaks. We find that the abundance of peaks detected in CS82 is consistent with predictions from a Lambda-CDM cosmological model, once noise effects are properly included. The correlation functions of peaks with different signal-to-noise ratio (SNR) are well described by power laws, and there is a clear cross-correlation between the Sloan Digital Sky Survey III/Constant Mass galaxies and high SNR peaks. The tangential-shear profiles around peaks increase with peak SNR. We fit analytical models to the tangential-shear profiles, including a projected singular isothermal sphere (SIS) model and a projected Navarro, Frenk & White (NFW) model, plus a two-halo term. For the high SNR peaks, the SIS model is rejected at ~3-sigma. The NFW model plus a two-halo term gives more acceptable fits to the data. Some peaks match the positions of optically detected clusters, while others are relatively dark. Comparing dark and matched peaks, we find a difference in lensing signal of a factor of 2, suggesting that about half of the dark peaks are false detections.

astro-ph.CO↗

arXiv2012

Observational constraints on cosmic neutrinos and dark energy revisited

Using several cosmological observations, i.e. the cosmic microwave background anisotropies (WMAP), the weak gravitational lensing (CFHTLS), the measurements of baryon acoustic oscillations (SDSS+WiggleZ), the most recent observational Hubble parameter data, the Union2.1 compilation of type Ia supernovae, and the HST prior, we impose constraints on the sum of neutrino masses ($\mnu$), the effective number of neutrino species ($\neff$) and dark energy equation of state ($w$), individually and collectively. We find that a tight upper limit on $\mnu$ can be extracted from the full data combination, if $\neff$ and $w$ are fixed. However this upper bound is severely weakened if $\neff$ and $w$ are allowed to vary. This result naturally raises questions on the robustness of previous strict upper bounds on $\mnu$, ever reported in the literature. The best-fit values from our most generalized constraint read $\mnu=0.556^{+0.231}_{-0.288}\rm eV$, $\neff=3.839\pm0.452$, and $w=-1.058\pm0.088$ at 68% confidence level, which shows a firm lower limit on total neutrino mass, favors an extra light degree of freedom, and supports the cosmological constant model. The current weak lensing data are already helpful in constraining cosmological model parameters for fixed $w$. The dataset of Hubble parameter gains numerous advantages over supernovae when $w=-1$, particularly its illuminating power in constraining $\neff$. As long as $w$ is included as a free parameter, it is still the standardizable candles of type Ia supernovae that play the most dominant role in the parameter constraints.

astro-ph.CO↗

arXiv2012

Weak lensing measurement of galaxy clusters in the CFHTLS-Wide survey

We present the first weak gravitational lensing analysis of the completed Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). We study the 64 square degrees W1 field, the largest of the CFHTLS-Wide survey fields, and present the largest contiguous weak lensing convergence "mass map" yet made. 2.66 million galaxy shapes are measured, using a KSB pipeline verified against high-resolution Hubble Space Telescope imaging that covers part of the CFHTLS. Our i'-band measurements are also consistent with an analysis of independent r'-band imaging. The reconstructed lensing convergence map contains 301 peaks with signal-to-noise ratio ν>3.5, consistent with predictions of a ΛCDM model. Of these peaks, 126 lie within 3.0' of a BCG identified from multicolor optical imaging in an independent, red sequence survey. We also identify 7 counterparts for massive clusters previously seen in X-ray emission within 6 square degrees XMM-LSS survey. With photometric redshift estimates for the source galaxies, we use a tomographic lensing method to fit the redshift and mass of each convergence peak. Matching these to the optical observations, we confirm 85 groups/clusters with χ^2 reduced < 3.0, at a mean redshift = 0.36 and velocity dispersion <σ_c> = 658.8 km/s. Future surveys, such as DES, LSST, KDUST and EUCLID, will be able to apply these same techniques to map clusters in much larger volumes and thus tightly constrain cosmological models.

astro-ph.CO↗

arXiv2011

Astrophysical Constraints on Dark Matter

Astrophysics gives evidence for the existence of Dark Matter and puts constraints on its nature. The Cold Dark Matter model has become "standard" cosmology combined with a cosmological constant. There are indications that "Cold" Dark Matter could be "warmer" than initially discussed. This paper reviews the main information on the Cold/Warm nature of Dark Matter.

astro-ph.CO↗

arXiv2010

Offset between dark matter and ordinary matter: evidence from a sample of 38 lensing clusters of galaxies

We compile a sample of 38 galaxy clusters which have both X-ray and strong lensing observations, and study for each cluster the projected offset between the dominant component of baryonic matter center (measured by X-rays) and the gravitational center (measured by strong lensing). Among the total sample, 45% clusters have offsets >10". The >10" separations are significant, considering the arcsecond precision in the measurement of the lensing/X-ray centers. This suggests that it might be a common phenomenon in unrelaxed galaxy clusters that gravitational field is separated spatially from the dominant component of baryonic matter. It also has consequences for lensing models of unrelaxed clusters since the gas mass distribution may differ from the dark matter distribution and give perturbations to the modeling. Such offsets can be used as a statistical tool for comparison with the results of Lambda-CDM simulations and to test the modified dynamics.

astro-ph.CO↗

arXiv2008

Constraining Cosmological Parameters with Observational Data Including Weak Lensing Effects

In this paper, we study the cosmological implications of the 100 square degree Weak Lensing survey (the CFHTLS-Wide, RCS, VIRMOS-DESCART and GaBoDS surveys). We combine these weak lensing data with the cosmic microwave background (CMB) measurements from the WMAP5, BOOMERanG, CBI, VSA, ACBAR, the SDSS LRG matter power spectrum and the Type Ia Supernoave (SNIa) data with the "Union" compilation (307 sample), using the Markov Chain Monte Carlo method to determine the cosmological parameters. Our results show that the ΛCDM model remains a good fit to all of these data. For the dynamical dark energy model with time evolving EoS parameterized as w_{\DE}(a) = w_0 + w_a (1-a), we find that the best-fit model implying the mildly preference of Quintom model whose EoS gets across the cosmological constant boundary during evolution. Regarding the total neutrino mass limit, we obtain the upper limit, \sum m_ν< 0.471 eV (95% C.L.) within the framework of the flat ΛCDM model. Due to the obvious degeneracies between the neutrino mass and the EoS of dark energy model, this upper limit will be relaxed by a factor of 2 in the framework of dynamical dark energy models. For the constraints on the inflation parameters, we find that the upper limit on the ratio of the tensor to scalar is r<0.35 (95% C.L.) and the inflationary models with the slope n_s\geq1 are excluded at more than 2 σconfidence level. In this paper we pay particular attention to the contribution from the weak lensing data and find that the current weak lensing data do improve the constraints on matter density Ω_m, σ_8, \sum{m_ν}, and the EoS of dark energy.

astro-ph↗

arXiv2006

Probing for dynamics of dark energy and curvature of universe with latest cosmological observations

We use the newly released 182 Type Ia supernova data combined with the third-year Wilkinson Microwave Anisotropic Probe data (WMAP3) and large scale structure (LSS) information including SDSS and 2dFGRS to constrain the dark energy equation of state (EoS) as well as the curvature of universe $Ω_K$. Using the full dataset of Cosmic Microwave Background (CMB) and LSS rather than the shift parameter and linear growth factor, we make a Markov Chain Monte Carlo (MCMC) global fit, while paying particular attention to the dark energy perturbation. Parameterizing the EoS as $w_{DE}(a) = w_{0} + w_{1}(1-a)$, we find the best fit of ($w_0,w_1$) is ($-1.053,0.944$) and for $w_{DE}(a) = w_{0} + w_{1}\sin({3/2}π\ln(a))$, the best fit for ($w_0,w_1$) is ($-1.614,-1.046$). We find that a flat universe is a good approximation, namely, $|Ω_K|>0.06$ has been excluded by 2$σ$ yet the inclusion of $Ω_K$ can affect the measurement of DE parameters owing to their correlation and the present systematic effects of SNIa measurements.

astro-ph↗

arXiv2005

Negative Energies and a Constantly Accelerating Flat Universe

It has been shown that in the context of General Relativity (GR) enriched with a new set of discrete symmetry reversal conjugate metrics, negative energy states can be rehabilitated while avoiding the well-known instability issues. We review here some cosmological implications of the model and confront them with the supernovae and CMB data. The predicted flat universe constantly accelerated expansion phase is found to be in rather good agreement with the most recent cosmological data.

gr-qc↗