We develop a new code, the Hierarchical Bound-Tracing (HBT for short) code, to find and trace dark matter subhaloes in simulations based on the merger hierarchy of dark matter haloes. Application of ...this code to a recent benchmark test of finding subhaloes demonstrates that HBT stands as one of the best codes to trace the evolutionary history of subhaloes. The success of the code lies in its careful treatment of the complex physical processes associated with the evolution of subhaloes and in its robust unbinding algorithm with an adaptive source subhalo management. We keep a full record of the merger hierarchy of haloes and subhaloes, and allow growth of satellite subhaloes through accretion from its "satellite-of-satellites", hence allowing mergers among satellites. Local accretion of background mass is omitted, while rebinding of stripped mass is allowed. The justification of these treatments is provided by case studies of the lives of individual subhaloes and by the success in finding the complete subhalo catalogue. We compare our result to other popular subhalo finders and show that HBT is able to well resolve subhaloes in high density environment and keep strict physical track of subhaloes' merger history. This code is fully parallelized and freely available upon request to the authors.
We present a study on the stellar age and metallicity distributions for 1105 galaxies using the STARLIGHT software on MaNGA integral field spectra. We derive age and metallicity gradients by fitting ...straight lines to the radial profiles, and explore their correlations with total stellar mass M*, NUV-r colour and environments, as identified by both the large scale structure (LSS) type and the local density. We find that the mean age and metallicity gradients are close to zero but slightly negative, which is consistent with the inside-out formation scenario. Within our sample, we find that both the age and metallicity gradients show weak or no correlation with either the LSS type or local density environment. In addition, we also study the environmental dependence of age and metallicity values at the effective radii. The age and metallicity values are highly correlated with M* and NUV-r and are also dependent on LSS type as well as local density. Low-mass galaxies tend to be younger and have lower metallicity in low-density environments while high-mass galaxies are less affected by environment.
Simulating the evolution of the local universe is important for studying galaxies and the intergalactic medium in a way free of cosmic variance. Here we present a method to reconstruct the initial ...linear density field from an input non-linear density field, employing the Hamiltonian Markov Chain Monte Carlo (HMC) algorithm combined with Particle Mesh (PM) dynamics. The HMC+PM method is applied to cosmological simulations, and the reconstructed linear density fields are then evolved to the present day with N-body simulations. The constrained simulations so obtained accurately reproduce both the amplitudes and phases of the input simulations at various \(z\). Using a PM model with a grid cell size of 0.75 Mpc/h and 40 time-steps in the HMC can recover more than half of the phase information down to a scale k~0.85 h/Mpc at high z and to k~3.4 h/Mpc at z=0, which represents a significant improvement over similar reconstruction models in the literature, and indicates that our model can reconstruct the formation histories of cosmic structures over a large dynamical range. Adopting PM models with higher spatial and temporal resolutions yields even better reconstructions, suggesting that our method is limited more by the availability of computer resource than by principle. Dynamic models of structure evolution adopted in many earlier investigations can induce non-Gaussianity in the reconstructed linear density field, which in turn can cause large systematic deviations in the predicted halo mass function. Such deviations are greatly reduced or absent in our reconstruction.
Tidal disruption of stars by supermassive black holes at the centers of galaxies is expected to produce unique emission line signatures, which have not yet been explored adequately. Here we report ...the discovery of extremely strong coronal lines from Fe X up to Fe XIV in a sample of seven galaxies (including two recently reported cases), that we interpret as such signatures. This is the first systematic search for objects of this kind, by making use of the immense database of the Sloan Digital Sky Survey. The galaxies, which are non-active as evidenced by the narrow-line ratios, show broad emission lines of complex profiles in more than half of the sample. Both the high ionization coronal lines and the broad lines turn out to be fading on time scales of years in objects observed with spectroscopic follow-ups, suggesting their transient nature. Variations of inferred non-stellar continua, which have absolute magnitudes of at least -16 to -18 mag in the g band, are also detected in more than half of the sample. These extreme coronal line emitters reside in sub-L_* disk galaxies (-21.3 < M_i < -18.5) with small stellar velocity dispersions. The sample seems to form two distinct types based on the presence or absence of the Fe VII lines, with the latter having relatively low luminosities of O III, Fe XI, and the host galaxies. These characteristics can most naturally be understood in the context of transient accretion onto intermediate mass black holes at galactic centers following tidal disruption of stars in a gas-rich environment. We estimate the incidence of such events to be around 10^-5 per year for a galaxy with -21.5 < M_i < -18.5.
We extend the real-space mapping method developed in Shi et at. (2016) so that it can be applied to flux-limited galaxy samples. We use an ensemble of mock catalogs to demonstrate the reliability of ...this extension, showing that it allows for an accurate recovery of the real-space correlation functions and galaxy biases. We also demonstrate that, using an iterative method applied to intermediate-scale clustering data, we can obtain an unbiased estimate of the growth rate of structure \(f\sigma_8\), which is related to the clustering amplitude of matter, to an accuracy of \(\sim 10\%\). Applying this method to the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7), we construct a real-space galaxy catalog spanning the redshift range \(0.01 \leq z \leq 0.2\), which contains 584,473 galaxies in the north Galactic cap (NGC). Using this data, we infer \(\fss\) at a median redshift \(z=0.1\), which is consistent with the WMAP9 cosmology at the \(1\sigma\) level. By combining this measurement with the real-space clustering of galaxies and with galaxy-galaxy weak lensing measurements for the same sets of galaxies, we are able to break the degeneracy between \(f\), \(\sigma_8\), and \(b\). From the SDSS DR7 data alone, we obtain the following cosmological constraints at redshift \(z=0.1\): $f=$$0.464^{+0.040}_{-0.040}\(, \)\sigma_8=0.769^{+0.121}_{-0.089}\(, and \)b=1.910^{+0.234}_{-0.268}\(, \)1.449^{+0.194}_{-0.196}\(, \)1.301^{+0.170}_{-0.177}\(, and \)1.196^{+0.159}_{-0.161}~\( for galaxies within different absolute magnitude bins \)^{0.1}{\rm M}_r-5\log h=-23,0, -22.0, -22,0, -21.0, -21.0, -20.0\( and \)-20.0, -19.0$, respectively.
Our research objective in this paper is to reconstruct an initial linear density field, which follows the multivariate Gaussian distribution with variances given by the linear power spectrum of the ...current CDM model and evolves through gravitational instability to the present-day density field in the local Universe. For this purpose, we develop a Hamiltonian Markov Chain Monte Carlo method to obtain the linear density field from a posterior probability function that consists of two components: a prior of a Gaussian density field with a given linear spectrum, and a likelihood term that is given by the current density field. The present-day density field can be reconstructed from galaxy groups using the method developed in Wang et al. (2009a). Using a realistic mock SDSS DR7, obtained by populating dark matter haloes in the Millennium simulation with galaxies, we show that our method can effectively and accurately recover both the amplitudes and phases of the initial, linear density field. To examine the accuracy of our method, we use \(N\)-body simulations to evolve these reconstructed initial conditions to the present day. The resimulated density field thus obtained accurately matches the original density field of the Millennium simulation in the density range 0.3 <= rho/rho_mean <= 20 without any significant bias. Especially, the Fourier phases of the resimulated density fields are tightly correlated with those of the original simulation down to a scale corresponding to a wavenumber of ~ 1 h/Mpc, much smaller than the translinear scale, which corresponds to a wavenumber of ~ 0.15 h\Mpc.
We present empirical relations between the global dust reddening and other physical galaxy properties including the Halpha luminosity, Halpha surface brightness, metallicity and axial ratio for ...star-forming disc galaxies. The study is based on a large sample of ~22 000 well-defined star-forming galaxies selected from the Sloan Digital Sky Survey (SDSS). The reddening parameterized by color excess E(B-V) is derived from the Balmer decrement. Besides the dependency of reddening on Halpha luminosity / surface brightness and gas phase metallicity, it is also correlated with the galaxy inclination, in the sense that edge-on galaxies are more attenuated than face-on galaxies at a give intrinsic luminosity. In light of these correlations, we present the empirical formulae of E(B-V) as a function of these galaxy properties, with a scatter of only 0.07 mag. The empirical relation can be reproduced if most dust attenuation to the HII region is due to diffuse interstellar dust distributing in a disc thicker than that of HII regions. The empirical formulae can be incorporated into semi-analytical models of galaxy formation and evolution to estimate the dust reddening and enable comparison with observations more practically.
In order to adapt to the rapid development of green plant extract corrosion inhibitors, spinach extract (SPE) was selected as a corrosion inhibitor for Q235 steel in citric acid (CA) environment. SPE ...was extracted using a simple ethanol reflux method, and its main components, as well as their stability in CA, were confirmed through Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy (UV-Vis). The corrosion inhibition performance of SPE on Q235 steel in 0.5 mol/L CA solution was investigated using various methods including weight loss, dynamic potential polarization (PDP), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and contact angle measurements. Effects of temperature on the activation parameters (Ea, were studied by calculation. Results showed that chlorophyll was the main component of SPE, which exhibited good stability in a 0.5 mol/L CA solution. Furthermore, SP
Using a sample of galaxy groups selected from the Sloan Digital Sky Survey Data Release 7 (SDSS DR7), we examine the alignment between the orientation of galaxies and their surrounding large scale ...structure in the context of the cosmic web. The latter is quantified using the large-scale tidal field, reconstructed from the data using galaxy groups above a certain mass threshold. We find that the major axes of galaxies in filaments tend to be preferentially aligned with the directions of the filaments, while galaxies in sheets have their major axes preferentially aligned parallel to the plane of the sheets. The strength of this alignment signal is strongest for red, central galaxies, and in good agreement with that of dark matter halos in N-body simulations. This suggests that red, central galaxies are well aligned with their host halos, in quantitative agreement with previous studies based on the spatial distribution of satellite galaxies. There is a luminosity and mass dependence that brighter and more massive galaxies in filaments and sheets have stronger alignment signals. We also find that the orientation of galaxies is aligned with the eigenvector associated with the smallest eigenvalue of the tidal tensor. These observational results indicate that galaxy formation is affected by large-scale environments, and strongly suggests that galaxies are aligned with each other over scales comparable to those of sheets and filaments in the cosmic web.
There are mutually contradictory views in the literature of the kinematics and structure of high-ionization line (e.g. CIV) emitting regions in active galactic nuclei (AGNs). Two kinds of broad ...emission line region (BELR) models have been proposed, outflow and gravitationally bound BELR, which are supported respectively by blueshift of the CIV line and reverberation mapping observations. To reconcile these two apparently different models, we present a detailed comparison study between the CIV and MgII lines using a sample of AGNs selected from the Sloan Digital Sky Survey. We find that the kinematics of the CIV region is different from that of MgII, which is thought to be controlled by gravity. A strong correlation is found between the blueshift and asymmetry of the CIV profile and the Eddington ratio. This provides strong observational support for the postulation that the outflow is driven by radiation pressure. In particular, we find robust evidence that the CIV line region is largely dominated by outflow at high Eddington ratios, while it is primarily gravitationally bounded at low Eddington ratios. Our results indicate that these two emitting regions coexist in most of AGNs. The emission strength from these two gases varies smoothly with Eddington ratio in opposite ways. This explanation naturally reconciles the apparently contradictory views proposed in previous studies. Finally, candidate models are discussed which can account for both, the enhancement of outflow emission and suppression of normal BEL, in AGN with high Eddington ratios.
