arXiv subjects

Y. P. Jing

Publications and source records attributed to Y. P. Jing.

At least 73 records · Page 4Linked to original sources

arXiv2009

Impacts of Source Properties on Strong Lensing by Rich Galaxy Clusters

We use a high-resolution $N$-body simulation to investigate the influence of background galaxy properties, including redshift, size, shape and clustering, on the efficiency of forming giant arcs by gravitational lensing of rich galaxy clusters. Two large sets of ray-tracing simulations are carried out for 10 massive clusters at two redshifts, i.e. $z_{\rm l} \sim 0.2$ and 0.3. The virial mass ($M_{\rm vir}$) of the simulated lens clusters at $z\sim0.2$ ranges from $6.8\times10^{14} h^{-1} {M_{\odot}}$ to $1.1\times 10^{15} h^{-1} M_{\odot}$. The information of background galaxies brighter than 25 magnitude in the $I$-band is taken from Cosmological Evolution Survey (COSMOS) imaging data. Around $1.7\times 10^5$ strong lensing realizations with these images as background galaxies have been performed for each set. We find that the efficiency for forming giant arcs for $z_{\rm l}=0.2$ clusters is broadly consistent with observations. The efficiency of producing giant arcs by rich clusters is weakly dependent on the source size and clustering. Our principal finding is that a small proportion ($\sim 1/3$) of galaxies with elongated shapes (e.g. ellipticity $ε=1-b/a>0.5$) can boost the number of giant arcs substantially. Compared with recent studies where a uniform ellipticity distribution from 0 to 0.5 is used for the sources, the adoption of directly observed shape distribution increases the number of giant arcs by a factor of $\sim2$. Our results indicate that it is necessary to account for source information and survey parameters (such as point-spread-function, seeing) to make correct predictions of giant arcs and further to constrain the cosmological parameters.(abridged)

astro-ph.CO↗

arXiv2009

Halo Occupation Distribution Modeling of Clustering of Luminous Red Galaxies

We perform Halo Occupation Distribution (HOD) modeling to interpret small-scale and intermediate-scale clustering of 35,000 luminous early-type galaxies and their cross-correlation with a reference imaging sample of normal L* galaxies in the Sloan Digital Sky Survey. The modeling results show that most of these luminous red galaxies (LRGs) are central galaxies residing in massive halos of typical mass M ~ a few times 10^13 to 10^14 Msun/h, while a few percent of them have to be satellites within halos in order to produce the strong auto-correlations exhibited on smaller scales. The mean luminosity Lc of central LRGs increases with the host halo mass, with a rough scaling relation of Lc \propto M^0.5. The halo mass required to host on average one satellite LRG above a luminosity threshold is found to be about 10 times higher than that required to host a central LRG above the same threshold. We find that in massive halos the distribution of L* galaxies roughly follows that of the dark matter and their mean occupation number scales with halo mass as M^1.5. The HOD modeling results also allows for an intuitive understanding of the scale-dependent luminosity dependence of the cross-correlation between LRGs and L_* galaxies. Constraints on the LRG HOD provide tests to models of formation and evolution of massive galaxies, and they are also useful for cosmological parameter investigations. In one of the appendices, we provide LRG HOD parameters with dependence on cosmology inferred from modeling the two-point auto-correlation functions of LRGs.

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arXiv2009

Effects of dark sectors' mutual interaction on the growth of structures

We present a general formalism to study the growth of dark matter perturbations when dark energy perturbations and interactions between dark sectors are present. We show that dynamical stability of the growth of structure depends on the type of coupling between dark sectors. By taking the appropriate coupling to ensure the stable growth of structure, we observe that the effect of the dark sectors' interaction overwhelms that of dark energy perturbation on the growth function of dark matter perturbation. Due to the influence of the interaction, the growth index can differ from the value without interaction by an amount within the observational sensibility, which provides a possibility to disclose the interaction between dark sectors through future observations on the growth of large structure.

gr-qc↗

arXiv2009

Determine the galaxy bias factors on large scales using bispectrum method

We study whether the bias factors of galaxies can be unbiasedly recovered from their power spectra and bispectra. We use a set of numerical N-body simulations and construct large mock galaxy catalogs based upon the semi-analytical model of Croton et al. (2006). We measure the reduced bispectra for galaxies of different luminosity, and determine the linear and first nonlinear bias factors from their bispectra. We find that on large scales down to that of the wavenumber k=0.1h/Mpc, the bias factors b1 and b2 are nearly constant, and b1 obtained with the bispectrum method agrees very well with the expected value. The nonlinear bias factor b2 is negative, except for the most luminous galaxies with M<-23 which have a positive b2. The behavior of b2 of galaxies is consistent with the b2 mass dependence of their host halos. We show that it is essential to have an accurate estimation of the dark matter bispectrum in order to have an unbiased measurement of b1 and b2. We also test the analytical approach of incorporating halo occupation distribution to model the galaxy power spectrum and bispectrum. The halo model predictions do not fit the simulation results well on the precision requirement of current cosmological studies.

astro-ph.CO↗

arXiv2009

The velocity function in the local environment from LCDM and LWDM constrained simulations

Using constrained simulations of the local Universe for generic cold dark matter and for 1keV warm dark matter, we investigate the difference in the abundance of dark matter halos in the local environment. We find that the mass function within 20 Mpc/h of the Local Group is ~2 times larger than the universal mass function in the 10^9-10^13 M_odot/h mass range. Imposing the field of view of the on-going HI blind survey ALFALFA in our simulations, we predict that the velocity function in the Virgo-direction region exceeds the universal velocity function by a factor of 3. Furthermore, employing a scheme to translate the halo velocity function into a galaxy velocity function, we compare the simulation results with a sample of galaxies from the early catalog release of ALFALFA. We find that our simulations are able to reproduce the velocity function in the 80-300 km/s velocity range, having a value ~10 times larger than the universal velocity function in the Virgo-direction region. In the low velocity regime, 35-80 km/s, the warm dark matter simulation reproduces the observed flattening of the velocity function. On the contrary, the simulation with cold dark matter predicts a steep rise in the velocity function towards lower velocities; for V_max=35 km/s, it forecasts ~10 times more sources than the ones observed. If confirmed by the complete ALFALFA survey, our results indicate a potential problem for the cold dark matter paradigm or for the conventional assumptions about energetic feedback in dwarf galaxies.

astro-ph.CO↗

arXiv2009

A determination of dark matter bispectrum with a large set of N-body simulations

We use a set of numerical N-body simulations to study the large-scale behavior of the reduced bispectrum of dark matter and compare the results with the second-order perturbation theory and the halo models for different halo mass functions. We find that the second-order perturbation theory (PT2) agrees with the simulations fairly well on large scales of k<0.05 h/Mpc, but it shows a signature of deviation as the scale goes down. Even on the largest scale where the bispectrum can be measured reasonably well in our simulations, the inconsistency between PT2 and the simulations appears for the colinear triangle shapes. For the halo model, we find that it can only serve as a qualitative method to help study the behavior of Q on large scales and also on relatively small scales. The failure of second-order perturbation theory will also affect the precise determination of the halo models, since they are connected through the 3-halo term in the halo model. The 2-halo term has too much contribution on the large scales, which is the main reason for the halo model to overpredict the bispectrum on the large scales. Since neither of the models can provide a satisfying description for the bispectrum on scales of about 0.1h/Mpc for the requirement of precision cosmology, we release the reduced bispectrum of dark matter on a large range of scales for future analytical modeling of the bispectrum.

astro-ph.CO↗

arXiv2009

Intrinsic Ellipticity Correlation of SDSS Luminous Red Galaxies and Misalignment with their Host Dark Matter Halos

We investigate the orientation correlation of giant elliptical galaxies by measuring the intrinsic ellipticity correlation function of 83,773 luminous red galaxies (LRGs) at redshifts 0.16 -- 0.47 from the Sloan Digital Sky Survey. We have accurately determined the correlation up to 30 $h^{-1}$Mpc. Luminosity dependence of the ellipticity correlation is also detected although the error bars are large, while no evidence is found for its redshift evolution between $z=0.2$ and $z=0.4$. Then we use a cosmological $N$-body simulation to examine misalignment between the central LRGs and their parent dark matter halos. Central and satellite galaxies are assigned to simulated halos by employing a halo occupation distribution model for the LRGs. The ellipticity correlation is predicted to have the same shape as but an amplitude about 4 times higher than our observation if the central LRGs are perfectly aligned with their host halos. This indicates that the central LRG galaxies are preferentially but not perfectly aligned with their host halos. With the assumption that there is a misalignment angle between a central LRG and its host halo which follows a Gaussian distribution with a zero mean and a width $σ_θ$, we obtain a tight constraint on the misalignment parameter, $σ_θ={35.4}^{+4.0}_{-3.3}$ deg. This type of intrinsic ellipticity correlation, if not corrected, can lead to contamination at 5% level to the shear power spectrum in weak lensing surveys of limiting magnitude $R_{AB}=24.5$ if the source central galaxies follow the same misalignment distribution as the LRGs.

astro-ph↗

arXiv2009

The distribution of ejected subhalos and its implication for halo assembly bias

Using a high-resolution cosmological $N$-body simulation, we identify the ejected population of subhalos, which are halos at redshift $z=0$ but were once contained in more massive `host' halos at high redshifts. The fraction of the ejected subhalos in the total halo population of the same mass ranges from 9% to 4% for halo masses from $\sim 10^{11}$ to $\sim 10^{12}\msun$. Most of the ejected subhalos are distributed within 4 times the virial radius of their hosts. These ejected subhalos have distinct velocity distribution around their hosts in comparison to normal halos. The number of subhalos ejected from a host of given mass increases with the assembly redshift of the host. Ejected subhalos in general reside in high-density regions, and have a much higher bias parameter than normal halos of the same mass. They also have earlier assembly times, so that they contribute to the assembly bias of dark matter halos seen in cosmological simulations. However, the assembly bias is {\it not} dominated by the ejected population, indicating that large-scale environmental effects on normal halos are the main source for the assembly bias.

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arXiv2009

The Gravitational Shear--Intrinsic Ellipticity Correlation Functions of Luminous Red Galaxies in Observation and in the $Λ$CDM Model

We examine whether the gravitational shear--intrinsic ellipticity (GI) correlation function of the luminous red galaxies (LRGs) can be modeled with the distribution function of a misalignment angle advocated recently by Okumura et al. For this purpose, we have accurately measured the GI correlation for the LRGs in the Data Release 6 (DR6) of the Sloan Digital Sky Survey (SDSS), which confirms the results of Hirata et al. who used the DR4 data. By comparing the GI correlation functions in the simulation and in the observation, we find that the GI correlation can be modeled in the current $Λ$CDM model if the misalignment follows a Gaussian distribution with a zero mean and a typical misalignment angle $σ_θ=34.9^{+1.9}_{-2.1}$ degrees. We also find a correlation between the axis ratios and intrinsic alignments of LRGs. This effect should be taken into account in theoretical modeling of the GI and intrinsic ellipticity--ellipticity correlations for weak lensing surveys.

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arXiv2009

Influence of baryonic physics on the merger time-scale of galaxies in N-body/hydrodynamical simulations

Following our previous work(Jiang et al.(2008)), in which we studied the merger time-scale of galaxies in a high-resolution cosmological hydro/N-body simulation, we investigate the potential influence of uncertainties in the numerical implementation of baryonic physics on the merger time-scale. The simulation used in the previous work suffers from the overcooling problem which causes the central galaxies of large halos too massive. This may result in a shortened merger time-scale compared to that in the real universe. We run a similar simulation, but the stellar mass is significantly reduced to model another extreme case of low stellar mass. Our result shows that the merger time-scale is little affected by the star formation recipes, except for the satellites in nearly radial orbits which show a 22 percent higher time-scale in the lower stellar mass case. Since the radial orbits only account for a small part of the satellites' orbits, the fitting formula in Jiang et al.(2008) is still applicable to a reasonable accuracy, nearly immune to the uncertainty in the baryonic physics.

astro-ph.CO↗

arXiv2009

Alignment between galaxies and large-scale structure

Based on the Sloan Digital Sky Survey DR6 (SDSS) and Millennium Simulation (MS) we investigate the alignment between galaxies and large-scale structure. For this purpose we develop two new statistical tools, namely the alignment correlation function and the cos(2theta)-statistic. The former is a two-dimensional extension of the traditional two-point correlation function and the latter is related to the ellipticity correlation function used for cosmic shear measurements. Both are based on the cross correlation between a sample of galaxies with orientations and a reference sample which represents the large-scale structure. Applied to the SDSS galaxy catalog the alignment correlation function reveals an overabundance of reference galaxies along the major axes of red, luminous (L > L*) galaxies out to projected separations of 60 Mpc/h. No alignment signal is detected for blue galaxies. The cos(2θ)-statistic yields very similar results. Starting from a MS semi-analytic galaxy catalog we assign an orientation to each red, luminous and central galaxy, based on the central region of the host halo. Alternatively, we use the orientation of the host halo itself. We find a mean projected misalignment between a halo and its central region of ~25 deg. Agreement with the SDSS results is good if the central orientations are used. Using the halo orientations overestimates the observed alignment by more than a factor of 2. The large volume of the MS allows to generate two-dimensional maps of the alignment correlation function which show the reference galaxy distribution to be flattened parallel to the orientations of red luminous galaxies with axis ratios of ~0.5 and ~0.75 for halo and central orientations,respectively. These ratios are almost independent of scale out to 60 Mpc/h.

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arXiv2008

Reconstructing the cosmic density field with the distribution of dark matter halos

We develop a new method to reconstruct the cosmic density field from the distribution of dark matter haloes above a certain mass threshold. Our motivation is that well-defined samples of galaxy groups/clusters, which can be used to represent the dark halo population, can now be selected from large redshift surveys of galaxies, and our ultimate goal is to use such data to reconstruct the cosmic density field in the local universe. Our reconstruction method starts with a sample of dark matter haloes above a given mass threshold. Each volume element in space is assigned to the domain of the nearest halo according to a distance measure that is scaled by the virial radius of the halo. The distribution of the mass in and around dark matter haloes of a given mass is modelled using the cross-correlation function between dark matter haloes and the mass distribution within their domains. We use N-body cosmological simulations to show that the density profiles required in our reconstruction scheme can be determined reliably from large cosmological simulations, and that our method can reconstruct the density field accurately using haloes with masses down to $\sim 10^{12}\msun$ (above which samples of galaxy groups can be constructed from current large redshift surveys of galaxies). Working in redshift space, we demonstrate that the redshift distortions due to the peculiar velocities of haloes can be corrected in an iterative way. We also describe some applications of our method.

astro-ph↗

arXiv2008

Environmental Effects on Real-Space and Redshift-Space Galaxy Clustering

Galaxy formation inside dark matter halos, as well as the halo formation itself, can be affected by large-scale environments. Evaluating the imprints of environmental effects on galaxy clustering is crucial for precise cosmological constraints with data from galaxy redshift surveys. We investigate such an environmental impact on both real-space and redshift-space galaxy clustering statistics using a semi-analytic model derived from the Millennium Simulation. We compare clustering statistics from original SAM galaxy samples and shuffled ones with environmental influence on galaxy properties eliminated. Among the luminosity-threshold samples examined, the one with the lowest threshold luminosity (~0.2L_*) is affected by environmental effects the most, which has a ~10% decrease in the real-space two-point correlation function (2PCF) after shuffling. By decomposing the 2PCF into five different components based on the source of pairs, we show that the change in the 2PCF can be explained by the age and richness dependence of halo clustering. The 2PCFs in redshift space are found to change in a similar manner after shuffling. If the environmental effects are neglected, halo occupation distribution modeling of the real-space and redshift-space clustering may have a less than 6.5% systematic uncertainty in constraining beta from the most affected SAM sample and have substantially smaller uncertainties from the other, more luminous samples. We argue that the effect could be even smaller in reality. In the Appendix, we present a method to decompose the 2PCF, which can be applied to measure the two-point auto-correlation functions of galaxy sub-samples in a volume-limited galaxy sample and their two-point cross-correlation functions in a single run utilizing only one random catalog.

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arXiv2008

Interactions, star formation and AGN activity

It has long been known that galaxy interactions are associated with enhanced star formation. In a companion paper, we explored this connection by applying a variety of statistics to SDSS data. In particular, we showed that specific star formation rates of galaxies are higher if they have close neighbours. Here we apply exactly the same techniques to AGN in the survey, showing that close neighbours are not associated with any similar enhancement of nuclear activity. Star formation is enhanced in AGN with close neighbours in exactly the same way as in inactive galaxies, but the accretion rate onto the black hole, as estimated from the extinction-corrected [O III] luminosity, is not influenced by the presence or absence of companions. Previous work has shown that galaxies with more strongly accreting black holes contain more young stars in their inner regions. This leads us to conclude that star formation induced by a close companion and star formation associated with black hole accretion are distinct events. These events may be part of the same physical process, for example a merger, provided they are separated in time. In this case, accretion onto the black hole and its associated star formation would occur only after the two interacting galaxies have merged. The major caveat in this work is our assumption that the extinction-corrected [O III] luminosity is a robust indicator of the bolometric luminosity of the central black hole. It is thus important to check our results using indicators of AGN activity at other wavelengths.

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arXiv2008

Interaction-induced star formation in a complete sample of 10^5 nearby star-forming galaxies

We investigate the clustering properties of a complete sample of 10^5 star-forming galaxies drawn from the SDSS DR4. On scales less than 100 kpc, the amplitude of the correlation function exhibits a strong dependence on the specific star formation rate of the galaxy. We interpret this as the signature of enhanced star formation induced by tidal interactions. We then explore how the average star formation rate in a galaxy is enhanced as the projected separation r_p between the galaxy and its companions decreases. We find that the enhancement depends strongly on r_p, but very weakly on the relative luminosity of the companions. The enhancement is also stronger in low mass galaxies than in high mass galaxies. In order to explore whether a tidal interaction is not only sufficient, but also necessary to trigger enhanced star formation in a galaxy, we compute background subtracted neighbour counts for the galaxies in our sample. The average number of close neighbours around galaxies with low to average values of SFR/M* is close to zero. At the highest specific star formation rates, however, more than 40% of the galaxies in our sample have a companion within a projected radius of 100 kpc. Visual inspection of the highest SFR/M* galaxies without companions reveals that more than 50% of these are clear interacting or merging systems. We conclude that tidal interactions are the dominant trigger of enhanced star formation in the most strongly star-forming systems. Finally, we find clear evidence that tidal interactions not only lead to enhanced star formation in galaxies, but also cause structural changes such as an increase in concentration.

astro-ph↗

arXiv2007

Spatial and kinematic alignments between central and satellite halos

Based on a cosmological N-body simulation we analyze spatial and kinematic alignments of satellite halos within six times the virial radius of group size host halos (Rvir). We measure three different types of spatial alignment: halo alignment between the orientation of the group central substructure (GCS) and the distribution of its satellites, radial alignment between the orientation of a satellite and the direction towards its GCS, and direct alignment between the orientation of the GCS and that of its satellites. In analogy we use the directions of satellite velocities and probe three further types of alignment: the radial velocity alignment between the satellite velocity and connecting line between satellite and GCS, the halo velocity alignment between the orientation of the GCS and satellite velocities and the auto velocity alignment between the satellites orientations and their velocities. We find that satellites are preferentially located along the major axis of the GCS within at least 6 Rvir (the range probed here). Furthermore, satellites preferentially point towards the GCS. The most pronounced signal is detected on small scales but a detectable signal extends out to 6 Rvir. The direct alignment signal is weaker, however a systematic trend is visible at distances < 2 Rvir. All velocity alignments are highly significant on small scales. Our results suggest that the halo alignment reflects the filamentary large scale structure which extends far beyond the virial radii of the groups. In contrast, the main contribution to the radial alignment arises from the adjustment of the satellite orientations in the group tidal field. The projected data reveal good agreement with recent results derived from large galaxy surveys. (abridged)

astro-ph↗

arXiv2007

A fitting formula for the merger timescale of galaxies in hierarchical clustering

We study galaxy mergers using a high-resolution cosmological hydro/N-body simulation with star formation, and compare the measured merger timescales with theoretical predictions based on the Chandrasekhar formula. In contrast to Navarro et al., our numerical results indicate, that the commonly used equation for the merger timescale given by Lacey and Cole, systematically underestimates the merger timescales for minor mergers and overestimates those for major mergers. This behavior is partly explained by the poor performance of their expression for the Coulomb logarithm, \ln (m_pri/m_sat). The two alternative forms \ln (1+m_pri/m_sat) and 1/2\ln [1+(m_pri/m_sat)^2] for the Coulomb logarithm can account for the mass dependence of merger timescale successfully, but both of them underestimate the merger time scale by a factor 2. Since \ln (1+m_pri/m_sat) represents the mass dependence slightly better we adopt this expression for the Coulomb logarithm. Furthermore, we find that the dependence of the merger timescale on the circularity parameter εis much weaker than the widely adopted power-law ε^{0.78}, whereas 0.94*ε^{0.60}+0.60 provides a good match to the data. Based on these findings, we present an accurate and convenient fitting formula for the merger timescale of galaxies in cold dark matter models.

astro-ph↗

arXiv2007

Properties of Wide-separation Lensed Quasars by Clusters of Galaxies in the SDSS

We use high-resolution N-body numerical simulations to study the number of predicted large-separation multiply-imaged systems produced by clusters of galaxies in the SDSS photometric and spectroscopic quasar samples. We incorporate the condensation of baryons at the centre of clusters by (artificially) adding a brightest central galaxy (BCG) as a truncated isothermal sphere. We make predictions in two flat cosmological models: a LCDM model with a matter density $Ω_0=0.3$, and $σ_8=0.9$ (LCDM0), and a model favoured by the WMAP three-year data with $Ω_0=0.238$, and $σ_8=0.74$ (WMAP3). We found that the predicted multiply-imaged quasars with separation >10" is about 6.2 and 2.6 for the SDSS photometric (with an effective area 8000 deg$^2$) and spectroscopic (with an effective area 5000 deg$^2$) quasar samples respectively in the LCDM0 model; the predicted numbers of large-separation lensed quasars agree well with the observations. These numbers are reduced by a factor of 7 or more in the WMAP3 model, and are consistent with data at < 8% level. The predicted cluster lens redshift peaks around redshift 0.5, and 90% are between 0.3 and 1. We find that the BCG creates a central circular region, comparable to the Einstein ring of the BCG, where the central image disappears in the usual three-image and five-image configurations. If we include four image systems as an extreme case of five-image systems (with an infinitely demagnified central image), we find that 68% of the central images are fainter by a factor of 100 than the brightest image, and about 80% are within 1.5"of the BCG.

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