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Sheth-Tormen mass function has been widely used to quantify the abundance of dark matter halos. It is a significant improvement over the Press-Schechter mass function as it uses ellipsoidal collapse in place of spherical collapse. Both of these mass functions can be written in a form that is universal, i.e., independent of cosmology and power spectrum when scaled in suitable variables. However, cosmological simulations have shown that this universality is approximate. In this paper, we investigate the power spectrum dependence of halo mass function through a suite of dark-matter-only N-body simulations of seven power-law models in an Einstein-de Sitter cosmology. This choice of cosmology and a power-law power spectrum ensures the self-similar evolution of dark matter distribution, allowing us to isolate the power spectrum dependence of mass function. We find that the mass function shows a clear non-universality. We present fits for the parameters of the Sheth-Tormen mass function for a range of power-law power-spectrum indices. We find a mild evolution in the overall shape of the mass function with the epoch. Finally, we extend our result to LCDM cosmology. We show that the Sheth-Tormen mass function with parameter values derived from a matched power-law EdS cosmology provides a better fit to the LCDM mass function than the standard Sheth-Tormen mass function. Our results indicate that an improved analytical theory is required to provide better fits to the mass function., 12 pages, 10 figures. This is a much expanded and upgraded version of 0908.2702. Accepted for Publication in the MNRAS

To investigate the effect of feedback from active galactic nuclei (AGN) on their surrounding medium, we study the diffuse X-ray emission from galaxy groups and clusters by coupling the Astrophysical Plasma Emission Code (APEC) with the cosmological hydrodynamic simulation involving AGN feedback. We construct a statistical sample of synthetic Chandra X-ray photon maps to observationally characterize the effect of AGN on the ambient medium. We show that AGN are effective in displacing the hot X-ray emitting gas from the centers of groups and clusters, and that these signatures remain evident in observations of the X-ray surface brightness profiles.

We present the conditional HI (neutral hydrogen) Mass Function (HIMF) conditioned on observed optical properties, $M_{\text{r}}$ ($r$-band absolute magnitude) and $C_{\text{ur}}$ ($u-r$ color), for a sample of 7709 galaxies from ALFALFA (40% data release - $\alpha.40$) which overlaps with a common volume in SDSS DR7. Based on the conditional HIMF we find that the luminous red, luminous blue and faint blue populations dominate the total HIMF at the high-mass end, knee and the low-mass end respectively. We use the conditional HIMF to derive the underlying distribution function of $\Omega_{\text{HI}}$ (HI density parameter), $p(\Omega_{\text{HI}})$, in the color-magnitude plane of galaxies. The distribution, $p(\Omega_{\text{HI}})$, peaks in the blue cloud at $M_{\text{r}}^{\text{max}}=$ $-19.25, C_{\text{ur}}^{\text{max}}=1.44$ but is skewed. It has a long tail towards faint blue galaxies and luminous red galaxies. We argue that $p(\Omega_{\text{HI}})$ can be used to reveal the underlying relation between cold gas, stellar mass and the star formation rate (SFR) in an unbiased way; that is the derived relation does not suffer from survey or sample selection., Comment: 5 pages, 3 figures, accepted for publication in MNRAS Letters

We present the neutral hydrogen mass ($M_{\text{HI}}$) function (HIMF) and velocity width ($w_{50}$) function (HIWF) based on a sample of 7857 galaxies from the 40% data release of the ALFALFA survey ($\alpha.40$). The low mass (velocity width) end of the HIMF (HIWF) is dominated by the blue population of galaxies whereas the red population dominates the HIMF (HIWF) at the high mass (velocity width) end. We use a deconvolution method to estimate the HI rotational velocity ($V_{\text{rot}}$) functions (HIVF) from the HIWF for the total, red, and blue samples. The HIWF and HIVF for the red and blue samples are well separated at the knee of the function compared to their HIMFs. We then use recent stacking results from the ALFALFA survey to constrain the halo mass ($M_{\text{h}}$) function of HI-selected galaxies. This allows us to obtain various scaling relations between $M_{\text{HI}} - w_{50} - V_{\text{rot}} - M_{\text{h}}$, which we present. The $M_{\text{HI}} - M_{\text{h}}$ relation has a steep slope ~2.10 at small masses and flattens to ~0.34 at masses larger than a transition halo mass, $\log_{10}(M_{\text{ht}} h^2_{70}/M_{\odot})=10.62$. Our scaling relation is robust and consistent with a volume-limited sample of $\alpha.40$. The $M_{\text{HI}} - M_{\text{h}}$ relation is qualitatively similar to the $M_{\text{star}} - M_{\text{h}}$ relation but the transition halo mass is smaller by ~1.4 dex compared to that of the $M_{\text{star}} - M_{\text{h}}$ relation. Our results suggest that baryonic processes like heating and feedback in larger mass halos suppress HI gas on a shorter time scale compared to star-formation., Comment: 17 pages, 11 figures, 2 tables, Accepted for publication in MNRAS

The Ly$\alpha$ forest decomposed into Voigt profile components allow us to study clustering properties of the intergalactic medium and its dependence on various physical quantities. Here, we report the first detections of probability excess of low-z (i.e z10^{14}$cm$^{-2}$ self-consistently or to the widespread of signal-to-noise ratio in the observed data., Comment: 23 pages, 14 figures. Submitted to MNRAS

In this study we quantify the properties of the gas and dark matter around active galactic nuclei (AGN) in simulated galaxy groups and clusters and analyze the effect of AGN feedback on the surrounding intra-cluster (group) medium. Our results suggest downsizing of AGN luminosity with host halo mass, supporting the results obtained from clustering studies of AGN. By examining the temperature and density distribution of the gas in the vicinity of AGN we show that due to feedback from the central engine, the gas gets displaced from the centre of the group/cluster resulting in a reduction of the density but an enhancement of temperature. We show that these effects are pronounced at both high and low redshifts and propose new observables to study the effect of feedback in higher redshift galaxies. We also show that the average stellar mass is decreased in halos in the presence of AGN feedback confirming claims from previous studies. Our work for the first time uses a fully cosmological-hydrodynamic simulation to evaluate the global effects of AGN feedback on their host dark matter halos as well as galaxies at scales of galaxy groups and clusters., Comment: 11 pages, 8 figures, Accepted for publication at Astrophysical Journal

We look at the contribution of different galaxy populations to the atomic hydrogen (HI) mass function (HIMF) and the HI density parameter, $\Omega_{\text{HI}}$, in the local Universe. Our analysis is based on a sample of 7857 HI-selected galaxies selected from a volume common to the SDSS and ALFALFA surveys (40$\%$ catalog -- $\alpha.40$). We define different populations of galaxies in the color(u-r)-magnitude($M_{\text{r}}$) plane and compute the HIMF for each of them. Additionally we compute the HIMF for dark galaxies; these are undetected in SDSS and represent $\sim 2\%$ of the total sample. We find that the luminous red population dominates the total HIMF for $\log_{10}(M_{\text{HI}}h^2_{70}/M_{\odot}) \geq 10.4$. The full red population -- luminous and faint -- represents about $\sim 17\%$ of the $\Omega_{\text{HI}}$ budget, while that of the dark population is $\sim 3\%$. The HIMF about the knee, $\log_{10}(M_{\text{HI}}h^2_{70}/M_{\odot}) \in [8,10.4]$, is dominated by the faint and luminous blue populations, the latter dominating at larger masses in this interval. Their total contribution to $\Omega_{\text{HI}}$ is $\sim 55-70\%$, the variation depending on the definition of population. The dominant populations at the low mass end, $\log_{10}(M_{\text{HI}}h^2_{70}/M_{\odot}) \leq 8.0$ are the faint blue and faint bluer populations, the latter's dominance being sensitive to its definition. The full blue (blue--bluer luminous and faint) population represents $\sim 80\%$ of $\Omega_{\text{HI}}$. A bimodal HIMF suggested by our results is however not seen since the amplitude of the HIMF of the luminous red population is small compared to that of the luminous blue population., Comment: 17 pages, 10 figures, 3 tables, Accepted in MNRAS

We compare the shapes and intrinsic alignments of galaxies in the MassiveBlack-II cosmological hydrodynamic simulation (MBII) to those in a dark matter-only (DMO) simulation performed with the same volume (100$h^{-1}$Mpc)$^{3}$, cosmological parameters, and initial conditions. Understanding the impact of baryonic physics on galaxy shapes and alignments and their relation to the dark matter distribution should prove useful to map the intrinsic alignments of galaxies from hydrodynamic to dark matter-only simulations. We find that dark matter subhalos are typically rounder in MBII, and the shapes of stellar matter in low mass galaxies are more misaligned with the shapes of the dark matter of the corresponding subhalos in the DMO simulation. At $z=0.06$, the fractional difference in the mean misalignment angle between MBII and DMO simulations varies from $\sim 28 \% - 12 \%$ in the mass range $10^{10.8} - 6.0 \times 10^{14} h^{-1}M_{\odot}$. We study the dark matter halo shapes and alignments as a function of radius, and find that while galaxies in MBII are more aligned with the inner parts of their dark matter subhalos, there is no radial trend in their alignments with the corresponding subhalo in the DMO simulation. This result highlights the importance of baryonic physics in determining the alignment of the galaxy with respect to the inner parts of the halo. Finally, we compare the ellipticity-direction (ED) correlation for galaxies to that for dark matter halos, finding that it is suppressed on all scales by stellar-dark matter misalignment. In the projected shape-density correlation ($w_{\delta+}$), which includes ellipticity weighting, this effect is partially canceled by the higher mean ellipticities of the stellar component, but differences of order $30-40\%$ remain on scales $> 1$ Mpc over a range of subhalo masses, with scale-dependent effects below $1$ Mpc., Comment: 15 pages, 17 figures, submitted to MNRAS, reference added

Simulations of the entire universe are by definition models of the largest and most complex physical system that exists. In carrying them out, simulators seek to discretize the matter (and radiation) in a model universe and follow their evolution from the Big Bang to the present day.

We investigate the properties of haloes, galaxies and black holes to z = 0 in the high-resolution hydrodynamical simulation MassiveBlack-II (MBII) which evolves a Λ cold dark matter cosmology in a comoving volumeVbox = (100 Mpc h−1)3. MBII is the highest resolution simulation of this size which includes a self-consistent model for star formation, black hole accretion and associated feedback. We provide a simulation browser web application which enables interactive search and tagging of the MBII data set and publicly release our galaxy catalogues. We find that baryons affect strongly the halo mass function (MF), with 20–33 per cent change in the halo abundance below the knee of the MF (Mhalo < 1013.2 M⊙ h−1 at z = 0) when compared to dark-matter-only simulations. We provide a fitting function for the halo MF out to redshift z = 11 and discuss its limitations. We study the halo occupation distribution and clustering of galaxies, in particular the evolution and scale dependence of stochasticity and bias finding reasonable agreement with observational data. The shape of the cosmic spectral energy distribution of galaxies in MBII is consistent with observations, but lower in amplitude. The Galaxy stellar mass function (GSMF) function is broadly consistent with observations at z ≥ 2. At z < 2, the population of passive low-mass (M* < 109 M⊙) galaxies in MBII makes the GSMF too steep compared to observations whereas at the high-mass end (M* > 1011 M⊙) galaxies hosting bright AGNs make significant contributions to the GSMF. The quasar bolometric luminosity function is also largely consistent with observations. We note however that more efficient AGN feedback is necessary for the largest, rarest objects/clusters at low redshifts.

Observations of the most distant bright quasars imply that billion solar mass supermassive black holes (SMBHs) have to be assembled within the first 800 million years. Under our standard galaxy formation scenario such fast growth implies large gas densities providing sustained accretion at critical or supercritical rates onto an initial black hole seed. It has been a long standing question whether and how such high black hole accretion rates can be achieved and sustained at the centers of early galaxies. Here we use our new MassiveBlack cosmological hydrodynamic simulation covering a volume (0.75 Gpc)3 appropriate for studying the rare first quasars to show that steady high density cold gas flows responsible for assembling the first galaxies produce the high gas densities that lead to sustained critical accretion rates and hence rapid growth commensurate with the existence of ~109 M ☉ black holes as early as z ~ 7. We find that under these conditions quasar feedback is not effective at stopping the cold gas from penetrating the central regions and hence cannot quench the accretion until the host galaxy reaches . This cold-flow-driven scenario for the formation of quasars implies that they should be ubiquitous in galaxies in the early universe and that major (proto)galaxy mergers are not a requirement for efficient fuel supply and growth, particularly for the earliest SMBHs.

Visualizing the high-redshift Universe is difficult due to the dearth of available data; however, the Lyman-alpha forest provides a means to map the intergalactic medium at redshifts not accessible to large galaxy surveys. Large-scale structure surveys, such as the Baryon Oscillation Spectroscopic Survey (BOSS), have collected quasar (QSO) spectra that enable the reconstruction of H I density fluctuations. The data fall on a collection of lines defined by the lines of sight (LOS) of the QSO, and a major issue with producing a 3D reconstruction is determining how to model the regions between the LOS. We present a method that produces a 3D map of this relatively uncharted portion of the Universe by employing local polynomial smoothing, a non-parametric methodology. The performance of the method is analysed on simulated data that mimics the varying number of LOS expected in real data, and then is applied to a sample region selected from BOSS. Evaluation of the reconstruction is assessed by considering various features of the predicted 3D maps including visual comparison of slices, probability density functions (PDFs), counts of local minima and maxima, and standardized correlation functions. This 3D reconstruction allows for an initial investigation of the topology of this portion of the Universe using persistent homology.

By combining optical and near-IR observations from the Hubble Space Telescope with NIR photometry from the Spitzer Space Telescope it is possible to measure the rest-frame UV-optical colours of galaxies at z=4-8. The UV-optical spectral energy distribution of star formation dominated galaxies is the result of several different factors. These include the joint distribution of stellar masses, ages, and metallicities, and the subsequent reprocessing by dust and gas in the ISM. Using a large cosmological hydrodynamical simulation we investigate the predicted spectral energy distributions of galaxies at high-redshift with a particular emphasis on assessing the potential contribution of nebular emission. We find that the average pure stellar UV-optical colour correlates with both luminosity and redshift such that galaxies at lower-redshift and higher-luminosity are typically redder. Assuming the escape fraction of ionising photons is close to zero, the effect of nebular emission is to redden the UV-optical 1500-V_w colour by, on average, 0.4 mag at z=8 declining to 0.25 mag at z=4. Young and low-metallicity stellar populations, which typically have bluer pure stellar UV-optical colours, produce larger ionising luminosities and are thus more strongly affected by the reddening effects of nebular emission. This causes the distribution of 1500-V_w colours to narrow and the trends with luminosity and redshift to weaken. The strong effect of nebular emission leaves observed-frame colours critically sensitive to the source redshift. For example, increasing the redshift by 0.1 can result in observed frame colours changing by up to ~0.6. These predictions reinforce the need to include nebular emission when modelling the spectral energy distributions of galaxies at high-redshift and also highlight the difficultly in interpreting the observed colours of individual galaxies without precise redshifts., 13 pages, 17 figures, accepted in MNRAS

We use a large dark matter simulation of a LambdaCDM model to investigate the clustering and environmental dependence of the number of substructures in a halo. Focusing on redshift z=1, we find that the halo occupation distribution is sensitive at the tens of percent level to the surrounding density and to a lesser extent to asymmetry of the surrounding density distribution. We compute the autocorrelation function of halos as a function of occupation, building on the finding of Wechsler et al. (2006) and Gao and White (2007) that halos (at fixed mass) with more substructure are more clustered. We compute the relative bias as a function of occupation number at fixed mass, finding a strong relationship. At fixed mass, halos in the top 5% of occupation can have an autocorrelation function ~ 1.5-2 times higher than the mean. We also compute the bias as a function of halo mass, for fixed halo occupation. We find that for group and cluster sized halos, when the number of subhalos is held fixed, there is a strong anticorrelation between bias and halo mass. Such a relationship represents an additional challenge to the halo model.

We examine predictions for the quasar luminosity functions (QLF) and quasar clustering at high redshift (z > 4.75) using MassiveBlack, our new hydrodynamic cosmological simulation which includes a self-consistent model for black hole growth and feedback. We show that the model reproduces the Sloan QLF within observational constraints at z >= 5. We find that the high-z QLF is consistent with a redshift-independent occupation distribution of BHs among dark matter halos (which we provide) such that the evolution of the QLF follows that of the halo mass function. The sole exception is the bright-end at z=6 and 7, where BHs in high-mass halos tend to be unusually bright due to extended periods of Eddington growth caused by high density cold flows into the halo center. We further use these luminosity functions to make predictions for the number density of quasars in upcoming surveys, predicting there should be ~119+-28 (~87+-28) quasars detectable in the F125W band of the WIDE (DEEP) fields of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) from z=5-6, ~19+-7 (~18+-9) from z=6-7, and ~1.7+-1.5 (~1.5+-1.5) from z=7-8. We also investigate quasar clustering, finding that the correlation length is fully consistent with current constraints for Sloan quasars (r_0~17 h^{-1} Mpc at z=4 for quasars above m_i = 20.2), and grows slowly with redshift up to z=6 (r_0~22 h^{-1} Mpc). Finally, we note that the quasar clustering strength depends weakly on luminosity for low L_BH, but gets stronger at higher L_BH as the BHs are found in higher mass halos.

We investigate the formation and properties of galaxies hosting z∼ 6 quasars in the gigaparsec scale cosmological hydrodynamical simulation MassiveBlack, which includes a self-consistent model for star formation, black hole accretion and associated feedback. We select the host galaxies based on the sample of quasars in MassiveBlack brighter than the Sloan Digital Sky Survey magnitude limit in the redshift range 5.5 ≲z≲ 6.5. We find that quasar hosts in the simulation are compact gas-rich systems with high star formation rates (SFRs) of SFR ∼102–103 M⊙ yr−1 consistent with observed properties. We show that the star-forming gas in these galaxies predominantly originates from high-density cold streams which efficiently penetrate the halo and grow the galaxy at the centre. The ratio of molecular to total cold gas mass in these galaxies is Mmol/Mcold∼ 0.1, much larger than local galaxies of similar masses, indicating that star formation in high-redshift quasar host galaxies is more efficient than their local counterparts. We show that MassiveBlack predicts a deviation from the local MBH–σ and MBH–M* relations, implying that black holes are relatively more massive for a given stellar host at these redshifts.

We model the distribution of neutral Hydrogen (HI hereafter) in the post-reionization universe. This model uses gravity only N-Body simulations and an ansatz to assign HI to dark matter haloes that is consistent with observational constraints and theoretical models. We resolve the smallest haloes that are likely to host HI in the simulations, care is also taken to ensure that any errors due to the finite size of the simulation box are small. We then compute the smoothed one point probability distribution function and the power spectrum of fluctuations in HI. This is compared with other predictions that have been made using different techniques. We highlight the significantly high bias for the HI distribution at small scales. This aspect has not been discussed before. We then discuss the prospects for detection with the MWA, GMRT and the hypothetical MWA5000. The MWA5000 can detect visibility correlations at large angular scales at all redshifts in the post-reionization era. The GMRT can detect visibility correlations at lower redshifts, specifically there is a strong case for a survey at z=1.3. We also discuss prospects for direct detection of rare peaks in the HI distribution using the GMRT. We show that direct detection should be possible with an integration time that is comparable to, or even less than, the time required for a statistical detection. Specifically, it is possible to make a statistical detection of the HI distribution by measuring the visibility correlation, and, direct detection of rare peaks in the HI distribution at z = 1.3 with the GMRT in less than 1000 hours of observations.

We discuss the performance characteristics of using the modification of the tree code suggested by Barnes \citep{1990JCoPh..87..161B} in the context of the TreePM code. The optimisation involves identifying groups of particles and using only one tree walk to compute force for all the particles in the group. This modification has been in use in our implementation of the TreePM code for some time, and has also been used by others in codes that make use of tree structures. In this paper, we present the first detailed study of the performance characteristics of this optimisation. We show that the modification, if tuned properly can speed up the TreePM code by a significant amount. We also combine this modification with the use of individual time steps and indicate how to combine these two schemes in an optimal fashion. We find that the combination is at least a factor of two faster than the modified TreePM without individual time steps. Overall performance is often faster by a larger factor, as the scheme of groups optimises use of cache for large simulations., 16 pages, 5 figures; Accepted for publication in Research In Astronomy and Astrophysics (RAA)

Cosmological N-Body simulations are used for a variety of applications. Indeed progress in the study of large scale structures and galaxy formation would have been very limited without this tool. For nearly twenty years the limitations imposed by computing power forced simulators to ignore some of the basic requirements for modeling gravitational instability. One of the limitations of most cosmological codes has been the use of a force softening length that is much smaller than the typical inter-particle separation. This leads to departures from collisionless evolution that is desired in these simulations. We propose a particle based method with an adaptive resolution where the force softening length is reduced in high density regions while ensuring that it remains well above the local inter-particle separation. The method, called the Adaptive TreePM, is based on the TreePM code. We present the mathematical model and an implementation of this code, and demonstrate that the results converge over a range of options for parameters introduced in generalizing the code from the TreePM code. We explicitly demonstrate collisionless evolution in collapse of an oblique plane wave. We compare the code with the fixed resolution TreePM code and also an implementation that mimics adaptive mesh refinement methods and comment on the agreement, and disagreements in the results. We find that in most respects the ATreePM code performs at least as well as the fixed resolution TreePM in highly over-dense regions, from clustering and number density of haloes, to internal dynamics of haloes. We also show that the adaptive code is faster than the corresponding high resolution TreePM code., 18 pages, 11 figures. Accepted for publication in the MNRAS

N-Body simulations are an important tool in the study of formation of large scale structures. Much of the progress in understanding the physics of galaxy clustering and comparison with observations would not have been possible without N-Body simulations. Given the importance of this tool, it is essential to understand its limitations as ignoring these can easily lead to interesting but unreliable results. In this paper we study the limitations due to the finite size of the simulation volume. In an earlier work we proposed a formalism for estimating the effects of a finite box-size on physical quantities and applied it to estimate the effect on the amplitude of clustering, mass function. Here, we extend the same analysis and estimate the effect on skewness and kurtosis in the perturbative regime. We also test the analytical predictions from the earlier work as well as those presented in this paper. We find good agreement between the analytical models and simulations for the two point correlation function and skewness. We also discuss the effect of a finite box size on relative velocity statistics and find the effects for these quantities scale in a manner that retains the dependence on the averaged correlation function., Comment: 14 pages, 8 figures. Accepted for publication in the MNRAS

Maps of the large-scale structure of the Universe at redshifts 2-4 can be made with the Lyman-alpha forest which are complementary to low redshift galaxy surveys. We apply the Wiener interpolation method of Caucci et al. to construct three-dimensional maps from sets of Lyman-alpha forest spectra taken from cosmological hydrodynamic simulations. We mimic some current and future quasar redshift surveys (BOSS, eBOSS and MS-DESI) by choosing similar sightline densities. We use these appropriate subsets of the Lyman-alpha absorption sightlines to reconstruct the full three dimensional Lyman-alpha flux field and perform comparisons between the true and the reconstructed fields. We study global statistical properties of the intergalactic medium (IGM) maps with auto-correlation and cross-correlation analysis, slice plots, local peaks and point by point scatter. We find that both the density field and the statistical proper- ties of the IGM are recovered well enough that the resulting IGM maps can be meaningfully considered to represent large-scale maps of the Universe in agreement with Caucci et al., on larger scales and for sparser sightlines than had been tested previously. Quantitatively, for sightline parameters comparable to current and near future surveys the correlation coefficient between true and reconstructed fields is r > 0.9 on scales > 30 h^-1 Mpc. The properties of the maps are relatively insensitive to the precise form of the covariance matrix used. The final BOSS quasar Lyman-alpha forest sample will allow maps to be made with a resolution of ~ 30 h^-1 Mpc over a volume of ~ 15 h^-3 Gpc^3 between redshifts 1.9 and 2.3., 14 pages, 13 figures, 4 tables

We examine the luminosity function (LF) of [OII] emission-line galaxies in the high-resolution cosmological simulation MassiveBlack-II (MBII). From the spectral energy distribution of each galaxy, we select a sub-sample of star-forming galaxies at $0.06 \le z \le 3.0$ using the [OII] emission line luminosity L([OII]). We confirm that the specific star formation rate matches that in the GAMA survey. We show that the [OII] LF at z=1.0 from the MBII shows a good agreement with the LFs from several surveys below L([OII])=$10^{43.0}$ erg/s while the low redshifts ($z \le 0.3$) show an excess in the prediction of bright [OII] galaxies, but still displaying a good match with observations below L([OII])=$10^{41.6}$ erg/s. Based on the validity in reproducing the properties of [OII] galaxies at low redshift ($z \le 1$), we forecast the evolution of the [OII] LF at high redshift ($z \le 3$), which can be tested by upcoming surveys such as the HETDEX and DESI. The slopes of the LFs at bright and faint ends range from -3 to -2 showing minima at z=2. The slope of the bright end evolves approximately as 1/(z+1) at z=2 while the faint end evolves as ~3/(z+1) at $0.6 \le z \le 2$. In addition, a similar analysis is applied for the evolution of [OIII] LFs, which is to be explored in the forthcoming survey WFIRST-AFTA. Finally, we show that the auto-correlation function of [OII] and [OIII] emitting galaxies shows a rapid evolution from z=2 to 1., Comment: 12 pages, 13 figures, 3 tables, accepted for publication in MNRAS

(Abridged for arXiv)We investigate the properties of halos, galaxies and blackholes to z=0 in the high resolution hydrodynamical simulation MassiveBlack-II (MBII) which evolves a LCDM cosmology in a comoving volume Vbox=100(Mpc/h)^3. MBII is the highest resolution simulation of this size which includes a self-consistent model for star formation, black hole accretion and associated feedback. We provide a simulation browser web application which enables interactive search and tagging of halos, subhalos and their properties and publicly release our galaxy catalogs. Our analysis of the halo mass function (MF) in MBII reveals that baryons have strong effects, with changes in the halo abundance of 20-35% below the knee of the MF (Mhalo < 10^13.2 Msun/h at z=0) when compared to fits based on dark matter only simulations. We provide a fitting function for the halo MF out to redshift z=11 and discuss how the onset of non-universality in the MF limits the accuracy of our fit. We study the halo occupation distribution and clustering of galaxies, in particular the evolution and scale dependence of stochasticity and bias finding reasonable agreement with observational data. The shape of the cosmic spectral energy distribution predicted by MBII is consistent with observations, but lower in amplitude. The Galaxy Stellar Mass Function (GSMF) function is broadly consistent with observations at z>=2. At z10^11 Msun) galaxies hosting bright AGNs make significant contributions to the GSMF. The quasar bolometric luminosity function is also largely consistent with observations. We note however that more efficient AGN feedback (beyond simple thermal coupling used here) is likely necessary for the largest, rarest objects/clusters at low redshifts., 26 pages, 25 figures. Submitted to MNRAS. High-resolution version and MBII galaxy catalogs can be found at http://mbii.phys.cmu.edu/data/

The intrinsic alignment of galaxy shapes with the large-scale density field is a contaminant to weak lensing measurements, as well as being an interesting signature of galaxy formation and evolution (albeit one that is difficult to predict theoretically). Here we investigate the shapes and relative orientations of the stars and dark matter of halos and subhalos (central and satellite) extracted from the MassiveBlack-II simulation, a state-of-the-art high resolution hydrodynamical cosmological simulation which includes stellar and AGN feedback in a volume of $(100{h^{-1}\mathrm{Mpc}})^3$. We consider redshift evolution from $z=1$ to $0.06$ and mass evolution within the range of subhalo masses, $10^{10} -6.0 \times 10^{14.0}{h^{-1}M_{\odot}}$. The shapes of the dark matter distributions are generally more round than the shapes defined by stellar matter. The projected root-mean-square (RMS) ellipticity per component for stellar matter is measured to be $e_\text{rms} = 0.28$ at $z=0.3$ for $M_{subhalo}> 10^{12.0}{h^{-1}M_{\odot}}$, which compares favourably with observational measurements. We find that the shapes of stellar and dark matter are more round for less massive subhalos and at lower redshifts. By directly measuring the relative orientation of the stellar matter and dark matter of subgroups, we find that, on average, the misalignment between the two components is larger for less massive subhalos. The mean misalignment angle varies from $\sim 30^{\circ}-10^{\circ}$ for $M \sim 10^{10} - 10^{14} {h^{-1}M_{\odot}}$ and shows a weak dependence on redshift. We also compare the misalignment angles in central and satellite subhalos at fixed subhalo mass, and find that centrals are more misaligned than satellites. We present fitting formulae for the shapes of dark and stellar matter in subhalos and also the probability distributions of misalignment angles., 18 pages, 18 figures, submitted to MNRAS

The intrinsic alignment of galaxies with the large-scale density field is an important astrophysical contaminant in upcoming weak lensing surveys. We present detailed measurements of the galaxy intrinsic alignments and associated ellipticity-direction (ED) and projected shape ($w_{g+}$) correlation functions for galaxies in the cosmological hydrodynamic MassiveBlack-II (MB-II) simulation. We carefully assess the effects on galaxy shapes, misalignment of the stellar component with the dark matter shape and two-point statistics of iterative weighted (by mass and luminosity) definitions of the (reduced and unreduced) inertia tensor. We find that iterative procedures must be adopted for a reliable measurement of the reduced tensor but that luminosity versus mass weighting has only negligible effects. Both ED and $w_{g+}$ correlations increase in amplitude with subhalo mass (in the range of $10^{10} - 6.0\times 10^{14}h^{-1}M_{\odot}$), with a weak redshift dependence (from $z=1$ to $z=0.06$) at fixed mass. At $z \sim 0.3$, we predict a $w_{g+}$ that is in reasonable agreement with SDSS LRG measurements and that decreases in amplitude by a factor of $\sim 5$--18 for galaxies in the LSST survey. We also compared the intrinsic alignments of centrals and satellites, with clear detection of satellite radial alignments within their host halos. Finally, we show that $w_{g+}$ (using subhalos as tracers of density) and $w_{\delta+}$ (using dark matter density) predictions from the simulations agree with that of non-linear alignment models (NLA) at scales where the 2-halo term dominates in the correlations (and tabulate associated NLA fitting parameters). The 1-halo term induces a scale dependent bias at small scales which is not modeled in the NLA model., Comment: 25 pages, 27 figures, revised after referee comments, accepted for publication in MNRAS

We use zoom-in techniques to re-simulate three high-redshift (z > 5.5) halos which host 10^9 solar mass blackholes from the ~ Gpc volume, MassiveBlack cosmological hydrodynamic simulation. We examine a number of factors potentially affecting supermassive blackhole growth at high redshift in cosmological simulations. These include numerical resolution, feedback prescriptions and formulation of smoothed particle hydrodynamics. We find that varying the size of the region over which feedback energy is deposited directly, either for fixed number of neighbours or fixed volume makes very little difference to the accretion history of blackholes. Changing mass resolution by factors of up to 64 also does not change the blackhole growth history significantly. We find that switching from the density-entropy formulation to the pressure-entropy formulation of smoothed particle hydrodynamics slightly increases the accretion rate onto blackholes. In general numerical details appear to have small effects on the main fueling mechanism for blackholes at these high redshifts. We examine the fashion by which this occurs, finding that the insensitivity to simulation technique seems to be a hallmark of the cold flow feeding picture of these high-z supermassive blackholes. We show that the gas that participates in critical accretion phases, in these massive objects at z > 6~7 is in all cases colder, denser, and forms more coherent streams than the average gas in the halo. This is also mostly the case when the blackhole accretion is feedback regulated (z < 6), however the distinction is less prominent. For our resimulated halos, cold flows appear to be a viable mechanism for forming the most massive blackholes in the early universe, occurring naturally in LambdaCDM models of structure formation. Not requiring fine tuning of numerical parameters, they seem to be physically inevitable in these objects., 15 pages, 12 figures

The observed UV continuum slope of star forming galaxies is strongly affected by the presence of dust. Its observation is then a potentially valuable diagnostic of dust attenuation, particularly at high-redshift where other diagnostics are currently inaccesible. Interpreting the observed UV continuum slope in the context of dust attenuation is often achieved assuming the empirically calibrated Meurer et al. (1999) relation. Implicit in this relation is the assumption of an intrinsic UV continuum slope ($\beta=-2.23$). However, results from numerical simulations suggest that the intrinsic UV continuum slopes of high-redshift star forming galaxies are bluer than this, and moreover vary with redshift. Using values of the intrinsic slope predicted by numerical models of galaxy formation combined with a Calzetti et al. (2000) reddening law we infer UV attenuations ($A_{1500}$) $0.35-0.5\,{\rm mag}$ ($A_{V}$: $0.14-0.2\,{\rm mag}$ assuming Calzetti et al. 2000) greater than simply assuming the Meurer relation. This has significant implications for the inferred amount of dust attenuation at very-high ($z\approx 7$) redshift given current observational constraints on $\beta$, combined with the Meurer relation, suggest dust attenuation to be virtually zero in all but the most luminous systems., Comment: 6 pages, 4 figures, accepted in MNRAS

We investigate the evolution of the galaxy stellar mass function at high-redshift ($z\ge 5$) using a pair of large cosmological hydrodynamical simulations: {\em MassiveBlack} and {\em MassiveBlack-II}. By combining these simulations we can study the properties of galaxies with stellar masses greater than $10^{8}\,{\rm M_{\odot}}\,h^{-1}$ and (co-moving) number densities of $\log_{10}(��\, [{\rm Mpc^{-3}\,dex^{-1}}\,h^{3}])>-8$. Observational determinations of the galaxy stellar mass function at very-high redshift typically assume a relation between the observed UV luminosity and stellar mass-to-light ratio which is applied to high-redshift samples in order to estimate stellar masses. This relation can also be measured from the simulations. We do this, finding two significant differences with the usual observational assumption: it evolves strongly with redshift and has a different shape. Using this relation to make a consistent comparison between galaxy stellar mass functions we find that at $z=6$ and above the simulation predictions are in good agreement with observed data over the whole mass range. Without using the correct UV luminosity and stellar mass-to-light ratio, the discrepancy would be up to two orders of magnitude for large galaxies $>10^{10}\,{\rm M_{\odot}}\,h^{-1}$. At $z=5$, however the stellar mass function for low mass $, 7 pages, 4 figures, accepted in MNRAS

We use radiative transfer to study the growth of ionized regions around the brightest, z=8 quasars in a large cosmological hydrodynamic simulation that includes black hole growth and feedback (the MassiveBlack simulation). We find that in the presence of the quasar s the comoving HII bubble radii reach 10 Mpc/h after 20 My while with the stellar component alone the HII bubbles are smaller by at least an order of magnitude. Our calculations show that several features are not captured within an analytical growth model of Stromgren spheres. The X-ray photons from hard quasar spectra drive a smooth transition from fully neutral to partially neutral in the ionization front. However the transition from partially neutral to fully ionized is significantly more complex. We measure the distance to the edge of bubbles as a function of angle and use the standard deviation of these distances as a diagnostic of the isotropy of ionized regions. We find that the overlapping of nearby ionized regions from clustered halos not only increases the anisotropy, but also is the main mechanism which allows the outer radius to grow. We therefore predict that quasar ionized bubbles at this early stage in the reionization process should be both significantly larger and more irregularly shaped than bubbles around star forming galaxies. Before the star formation rate increases and the Universe fully reionizes, quasar bubbles will form the most striking and recognizable features in 21cm maps., 11 pages, 10 figures. Updated after referee report

Using a new large-scale (~ 0.75 Gpc)^3 hydrodynamic cosmological simulation we investigate the growth rate of supermassive black holes in the early universe (z > 4.75). Remarkably, we find a clear peak in the typical Eddington ratio at black hole masses of 4-8 * 10^7 solar masses (typically found in halos of ~7 * 10^11 to 10^12 solar masses), independent of redshift and indicative that most of BH growth occurs in the cold-flow dominated regime. Black hole growth is by and large regulated by the evolution of gas density. The typical Eddington ratio at a given mass scales simply as cosmological density (1+z)^3 and the peak is caused by the competition between increased gas density available in more massive hosts, and a decrease due to strong AGN feedback that deprives the black hole of sufficient gas to fuel further rapid growth in the high mass end. In addition to evolution in the mean Eddington ratio, we show that the distribution of Eddington ratio among both mass-selected and luminosity-selected samples is approximately log-normal. We combine these findings into a single log-normal fitting formula for the distribution of Eddington ratios as a function of (M_BH,z). This formula can be used in analytic and semi analytic models for evolving black hole populations, predicting black hole masses of observed quasars, and, in conjunction with the observed distribution of Eddington ratios, can be used to constrain the black hole mass function., 6 pages, 5 figures

We use radiative transfer to study the growth of ionized regions around the brightest, z = 8 quasars in a large cosmological hydrodynamic simulation that includes black hole growth and feedback (the MassiveBlack simulation). We find that in the presence of the quasars the comoving H IIbubble radii reach 10 Mpc h−1 after 20 Myr while with the stellar component alone the H II bubbles are smaller by at least an order of magnitude. Our calculations show that several features are not captured within an analytic growth model of Stromgren spheres. The X-ray photons from hard quasar spectra drive a smooth transition from fully neutral to partially neutral in the ionization front. However, the transition from partially neutral to fully ionized is significantly more complex. We measure the distance to the edge of bubbles as a function of angle and use the standard deviation of these distances as a diagnostic of the anisotropy of ionized regions. We find that the overlapping of nearby ionized regions from clustered haloes not only increases the anisotropy, but also is the main mechanism which allows the outer radius to grow. We therefore predict that quasar ionized bubbles at this early stage in the reionization process should be both significantly larger and more irregularly shaped than bubbles around star-forming galaxies. Before the star formation rate increases and the Universe fully reionizes, quasar bubbles will form the most striking and recognizable features in 21 cm maps.

Observations of the most distant bright quasars imply that billion solar mass supermassive black holes (SMBH) have to be assembled within the first eight hundred million years. Under our standard galaxy formation scenario such fast growth implies large gas densities providing sustained accretion at critical or supercritical rates onto an initial black hole seed. It has been a long standing question whether and how such high black hole accretion rates can be achieved and sustained at the centers of early galaxies. Here we use our new cosmological hydrodynamic simulation (MassiveBlack) covering a volume (0.75 \Gpc)^3 appropriate for studying the rare first quasars to show that steady high density cold gas flows responsible for assembling the first galaxies produce the high gas densities that lead to sustained critical accretion rates and hence rapid growth commensurate with the existence of ~10^9 solar mass black holes as early as z~7. We find that under these conditions quasar feedback is not effective at stopping the cold gas from penetrating the central regions and hence cannot quench the accretion until the host galaxy reaches M_halo > 10^{12} solar masses. This cold-flow driven scenario for the formation of quasars implies that they should be ubiquitous in galaxies in the early universe and that major (proto)galaxy mergers are not a requirement for efficient fuel supply and growth, particularly for the earliest SMBHs., 6 pages, 4 figures

The increasing size of cosmological simulations has led to the need for new visualization techniques. We focus on Smoothed Particle Hydrodynamical (SPH) simulations run with the GADGET code and describe methods for visually accessing the entire simulation at full resolution. The simulation snapshots are rastered and processed on supercomputers into images that are ready to be accessed through a web interface (GigaPan). This allows any scientist with a web-browser to interactively explore simulation datasets in both in spatial and temporal dimensions, datasets which in their native format can be hundreds of terabytes in size or more. We present two examples, the first a static terapixel image of the MassiveBlack simulation, a P-GADGET SPH simulation with 65 billion particles, and the second an interactively zoomable animation of a different simulation with more than one thousand frames, each a gigapixel in size. Both are available for public access through the GigaPan web interface. We also make our imaging software publicly available., Comment: 9 pages, 6 figures, Link to the Gigapan image: http://gigapan.org/gigapans/76215/ Link to the TimeMachine animation: http://timemachine.gigapan.org/wiki/Evolution_of_the_Universe Link to Gaepsi: http://web.phys.cmu.edu/~yfeng1/gaepsi

In the multi-fractal analysis of large scale matter distribution, the scale of transition to homogeneity is defined as the scale above which the fractal dimension of underlying point distribution is equal to the ambient dimension of the space in which points are distributed. With finite sized weakly clustered distribution of tracers obtained from galaxy redshift surveys it is difficult to achieve this equality. Recently we have defined the scale of homogeneity to be the scale above which the deviation of fractal dimension from the ambient dimension becomes smaller than the statistical dispersion. In this paper we use the relation between the fractal dimensions and the correlation function to compute the dispersion for any given model in the limit of weak clustering amplitude. We compare the deviation and dispersion for the LCDM model and discuss the implication of this comparison for the expected scale of homogeneity in the concordant model of cosmology. We estimate the upper limit to the scale of homogeneity to be close to 260 Mpc/h for the LCDM model. Actual estimates of the scale of homogeneity should be smaller than this as we have considered only statistical contribution to the dispersion in fractal dimension and we have ignored cosmic variance and contributions due to survey geometry and the selection function. We find that as long as non linear correction are insignificant, scale of homogeneity as defined above does not change with epoch. The scale of homogeneity depends very weakly on the choice of tracer of the density field. Thus the suggested definition of the scale of homogeneity is fairly robust.

The intrinsic alignment of galaxy shapes with the large-scale density field is a contaminant to weak lensing measurements, as well as being an interesting signature of galaxy formation and evolution (albeit one that is difficult to predict theoretically). Here we investigate the shapes and relative orientations of the stars and dark matter of haloes and subhaloes (central and satellite) extracted from the MassiveBlack-II simulation, a state-of-the-art high-resolution hydrodynamical cosmological simulation which includes stellar and active galactic nucleus feedback in a volume of (100 h−1 Mpc)3. We consider redshift evolution from z = 1 to 0.06 and mass evolution within the range of subhalo masses, 1010–6.0 × 1014.0 h−1 M⊙. The shapes of the dark matter distributions are generally more round than the shapes defined by stellar matter. The projected root-mean-square ellipticity per component for stellar matter is measured to beerms = 0.28 at z = 0.3 for Msubhalo > 1012.0 h−1 M⊙, which compares favourably with observational measurements. We find that the shapes of stellar and dark matter are more round for less massive subhaloes and at lower redshifts. By directly measuring the relative orientation of the stellar matter and dark matter of subgroups, we find that, on average, the misalignment between the two components is larger for less massive subhaloes. The mean misalignment angle varies from ∼30° to 10° forM ∼ 1010–1014 h−1 M⊙ and shows a weak dependence on redshift. We also compare the misalignment angles in central and satellite subhaloes at fixed subhalo mass, and find that centrals are more misaligned than satellites. We present fitting formulae for the shapes of dark and stellar matter in subhaloes and also the probability distributions of misalignment angles.

We use zoom-in techniques to re-simulate three high-redshift (z ≥ 5.5) haloes which host 109 M⊙ black holes from the ∼Gpc volume, MassiveBlack cosmological hydrodynamic simulation. We examine a number of factors potentially affecting supermassive black hole growth at high redshift in cosmological simulations. We find insignificant differences in the black hole accretion history by (i) varying the region over which feedback energy is deposited directly, (ii) changing mass resolution by factors of up to 64, (iii) changing the black hole seed mass by a factor of 100. Switching from the density–entropy formulation to the pressure–entropy formulation of smoothed particle hydrodynamics slightly increases the accretion rate. In general numerical details/model parameters appear to have small effects on the main fuelling mechanism for black holes at these high redshifts. The insensitivity to simulation technique seems to be a hallmark of the cold flow feeding picture of these high-z supermassive black holes. We show that the gas that participates in critical accretion phases in these massive objects at z > 6–7 is in all cases colder, denser and forms more coherent streams than the average gas in the halo. This is also mostly the case when the black hole accretion is feedback regulated (z < 6), however, the distinction is less prominent. For our resimulated haloes, cold flows appear to be a viable mechanism for forming the most massive black holes in the early universe, occurring naturally in Λ cold dark matter models of structure formation, without requiring fine-tuning of numerical parameters.

We use zoom-in techniques to re-simulate three high-redshift (z ≥ 5.5) haloes which host 109 M⊙ black holes from the ∼Gpc volume, MassiveBlack cosmological hydrodynamic simulation. We examine a number of factors potentially affecting supermassive black hole growth at high redshift in cosmological simulations. We find insignificant differences in the black hole accretion history by (i) varying the region over which feedback energy is deposited directly, (ii) changing mass resolution by factors of up to 64, (iii) changing the black hole seed mass by a factor of 100. Switching from the density–entropy formulation to the pressure–entropy formulation of smoothed particle hydrodynamics slightly increases the accretion rate. In general numerical details/model parameters appear to have small effects on the main fuelling mechanism for black holes at these high redshifts. The insensitivity to simulation technique seems to be a hallmark of the cold flow feeding picture of these high-z supermassive black holes. We show that the gas that participates in critical accretion phases in these massive objects at z > 6–7 is in all cases colder, denser and forms more coherent streams than the average gas in the halo. This is also mostly the case when the black hole accretion is feedback regulated (z < 6), however, the distinction is less prominent. For our resimulated haloes, cold flows appear to be a viable mechanism for forming the most massive black holes in the early universe, occurring naturally in Λ cold dark matter models of structure formation, without requiring fine-tuning of numerical parameters.

The intrinsic alignment of galaxy shapes with the large-scale density field is a contaminant to weak lensing measurements, as well as being an interesting signature of galaxy formation and evolution (albeit one that is difficult to predict theoretically). Here we investigate the shapes and relative orientations of the stars and dark matter of haloes and subhaloes (central and satellite) extracted from the MassiveBlack-II simulation, a state-of-the-art high-resolution hydrodynamical cosmological simulation which includes stellar and active galactic nucleus feedback in a volume of (100 h−1 Mpc)3. We consider redshift evolution from z = 1 to 0.06 and mass evolution within the range of subhalo masses, 1010–6.0 × 1014.0 h−1 M⊙. The shapes of the dark matter distributions are generally more round than the shapes defined by stellar matter. The projected root-mean-square ellipticity per component for stellar matter is measured to beerms = 0.28 at z = 0.3 for Msubhalo > 1012.0 h−1 M⊙, which compares favourably with observational measurements. We find that the shapes of stellar and dark matter are more round for less massive subhaloes and at lower redshifts. By directly measuring the relative orientation of the stellar matter and dark matter of subgroups, we find that, on average, the misalignment between the two components is larger for less massive subhaloes. The mean misalignment angle varies from ∼30° to 10° forM ∼ 1010–1014 h−1 M⊙ and shows a weak dependence on redshift. We also compare the misalignment angles in central and satellite subhaloes at fixed subhalo mass, and find that centrals are more misaligned than satellites. We present fitting formulae for the shapes of dark and stellar matter in subhaloes and also the probability distributions of misalignment angles.