CosmoMIA: cosmic web-based redshift space halo distribution

Massive spectroscopic surveys will measure the redshift space distortion\n(RSD) induced by galaxy peculiar velocity to unprecedented accuracy. We develop\na new method to improve the RSD modeling and to carry out robust reconstruction\nof the 3D large scale peculiar velocity through galaxy redshift surveys, in\nlight of RSD. (1) We propose a mathematically unique and physically motivated\ndecomposition of peculiar velocity into three eigen-components of different\norigins, different scale dependences and different impacts on RSD. (2) This\ndecomposition has the potential to simplify and improve the RSD modeling. We\nderive a new formula for the redshift space power spectrum. Under the velocity\ndecomposition scheme, all high order Gaussian corrections and non-Gaussian\ncorrection of order $\\delta^3$ can be taken into account without introducing\nextra model uncertainties. We find that the leading order contribution $\\propto\n(1+f\\tilde{W}(k)u^2)^2$ differs from the Kaiser formula by a function\n$\\tilde{W}(k)\\leq 1$. We hence identify a significant systematic error causing\nunderestimation of the structure growth parameter $f$ by as much as $O(10%)$\neven at relatively large scale $k=0.1h/$Mpc. The velocity decomposition also\nreveals the three origins of the finger of God (FOG) effect. (3) The velocity\ndecomposition clarifies issues in peculiar velocity reconstruction through 3D\ngalaxy distribution. We discuss two possible ways to carry out the velocity\nreconstruction. Both use the otherwise troublesome RSD in velocity\nreconstruction as a valuable source of information. Both have the advantage to\nrender the reconstruction of a stochastic 3D field into the reconstruction of a\ndeterministic window function $W^s(k,u)$ of limited degrees of\nfreedom...[abridged]\n

The highly redshifted 21 cm line of neutral hydrogen has become recognized as\na unique probe of cosmology from relatively low redshifts (z ~ 1) up through\nthe Epoch of Reionization (z ~ 8) and even beyond. To date, most work has\nfocused on recovering the spherically averaged power spectrum of the 21 cm\nsignal, since this approach maximizes the signal-to-noise in the initial\nmeasurement. However, like galaxy surveys, the 21 cm signal is affected by\nredshift space distortions, and is inherently anisotropic between the\nline-of-sight and transverse directions. A measurement of this anisotropy can\nyield unique cosmological information, potentially even isolating the matter\npower spectrum from astrophysical effects. However, in interferometric\nmeasurements, foregrounds also have an anisotropic footprint between the\nline-of-sight and transverse directions: the so-called foreground "wedge".\nAlthough foreground subtraction techniques are actively being developed, a\n"foreground avoidance" approach of simply ignoring contaminated modes has\narguably proven most successful to date. In this work, we analyze the effect of\nthis foreground anisotropy in recovering the redshift space distortion\nsignature in 21 cm measurements at both high and intermediate redshifts. We\nfind the foreground wedge corrupts nearly all of the redshift space signal for\neven the largest proposed EoR experiments (HERA and the SKA), making\ncosmological information unrecoverable without foreground subtraction. The\nsituation is somewhat improved at lower redshifts, where the redshift-dependent\nmapping from observed coordinates to cosmological coordinates significantly\nreduces the size of the wedge. Using only foreground avoidance, we find that a\nlarge experiment like CHIME can place non-trivial constraints on cosmological\nparameters.\n

The observed density field in redshift space is directly affected by the radial motions generated from mass fluctuations outside the volumeoccupied by a given galaxy redshift survey. These motions introduce redshift space anisotropies which are more pronounced at larger distances from thesurvey's center, thus offering clues to the nature of mass fluctuations on super-survey scales. Furthermore, we note that all estimates of the growthfactor derived from redshift space distortions are based on relations which explicitly assume that the velocity field is generated by mass fluctuationsinside the survey volume. This may cause uncertainties in these estimates which are on the order of a few percent.

We have quantified the degree of nonlinearity and stochasticity of the clustering of biased objects using cosmological $N$-body simulations. Adopting the peaks and the halos as representative biasing models, we focused on the two-point correlation of the biased objects, dark matter and their cross-correlation. Especially, we took account of the effect of redshift-space distortion and attempted to clarify the scale dependence and the time dependence by analyzing the biasing factor and the cross-correlation factor. On small scales, stochasticity and nonlinearity become appreciable and strongly object-dependent, especially in redshift space due to the pair-wise velocity dispersion of the biased objects. Nevertheless, an approximation of deterministic linear biasing, $\delta_\mathrm{obj}\simeq b_\mathrm{obj} \delta_\mathrm{mass}$, works reasonably well even in the quasi-linear regime, $r \gtrsim 10\,h^{-1} \textrm{Mpc}$, and linear redshift-space distortion explains the clustering amplitudes in redshift space in this regime.

We use the Evolution and Assembly of GaLaxies and their Environments (EAGLE) galaxy formation simulation to study the effects of baryons on the power spectrum of the total matter and dark matter distributions and on the velocity fields of dark matter and galaxies. On scales k ≳ 4 h Mpc−1 the effect of baryons on the amplitude of the total matter power spectrum is greater than 1 per cent. The back-reaction of baryons affects the density field of the dark matter at the level of ∼3 per cent on scales of 1 ≤ k/( h Mpc−1) ≤ 5. The dark matter velocity divergence power spectrum at k ≲ 0.5 h Mpc−1 is changed by less than 1 per cent. The 2D redshift space power spectrum is affected at the level of ∼6 per cent at $|\boldsymbol {k}|\gtrsim 1\,h\,{\rm Mpc}^{-1}$ (for μ > 0.5), but for $|\boldsymbol {k}|\le 0.4\,h\,{\rm Mpc}^{-1}$ it differs by less than 1 per cent. We report vanishingly small baryonic velocity bias for haloes: the peculiar velocities of haloes with M200 > 3 × 1011 M⊙ (hosting galaxies with M* > 109 M⊙) are affected at the level of at most 1 km s−1, which is negligible for 1 per cent-precision cosmology. We caution that since EAGLE overestimates cluster gas fractions it may also underestimate the impact of baryons, particularly for the total matter power spectrum. Nevertheless, our findings suggest that for theoretical modelling of redshift space distortions and galaxy velocity-based statistics, baryons and their back-reaction can be safely ignored at the current level of observational accuracy. However, we confirm that the modelling of the total matter power spectrum in weak lensing studies needs to include realistic galaxy formation physics in order to achieve the accuracy required in the precision cosmology era.

We present a unified model of dark matter and dark energy. The dark matter field is amodulus corresponding to a flat direction of supersymmetry, which couples, in a hybridtype potential, with the dark energy field. The latter is a light scalar, whose direction isstabilized by non-renormalizable terms. This quintessence field is kept ‘locked’ on top of afalse vacuum due to the coupling with the oscillating dark matter field. It is shown that themodel can satisfy the observations when we consider low-scale gauge-mediatedsupersymmetry breaking. The necessary initial conditions are naturally attained by theaction of supergravity corrections on the potential, in the period following the end ofprimordial inflation.

Redshift space distortions are an important probe of the growth of large-scale structure and for constraining cosmological parameters in general. As galaxy redshift surveys approach per cent level precision in their observations of the two point clustering statistics, it is timely to review what effects baryons and associated processes such as feedback may have on small-scale clustering in redshift space. Contrary to previous studies in the literature, we show using the large-volume Bahamas hydrodynamic simulations that the effect of baryons can be as much as 1 per cent in the $k \sim 0.1\, h\,$Mpc$^{-1}$ range for the monopole and 5 per cent for quadrupole, and that this could rise to as much as 10 per cent at $k \sim 10 \, h\,$Mpc$^{-1}$ in both measurements. For the halo power spectra, this difference can be as much 3-4 per cent in the monopole on scales of $0.05 \lt k \lt 0.3 \, h\,$Mpc$^{-1}$ for 10$^{13}\, h^{-1}$ M$_{\odot }$ haloes. We find that these deviations can be mitigated to the sub- per cent level in the both the monopole and quadrupole up to $k\sim 0.3\, h$ Mpc$^{-1}$ if the baryon corrected halo masses are used to calculate the redshift space power spectra. Finally, we use the cosmo-OWLS simulation suite to explore the changes in the redshift space power spectra with different feedback prescriptions, finding that there is a maximum of 15–20 per cent difference between the redshift space monopole and quadrupole with and without baryons at $k \sim 1\!-\!2\, h\,$Mpc$^{-1}$ within these models.

Unveiling the physics behind the accelerating expansion of the Universe, which was discovered in 1998, is one of the most challenging tasks in modern sciences. In theory, the cosmic acceleration may result from the fact that approximately two thirds energy density of the Universe is provided by Dark Energy, a yet unknown energy component, or imply that general relativity, the most successful theory of gravity within the solar system established by Einstein, may need to be extended on cosmological scales. In principle, the scenarios of energy and modified gravity can yield identical cosmic expansion history, but predict different structure growth. Therefore, this dark degeneracy can be broken by studying the evolution history of the cosmic structure with large galaxy surveys. Galaxy surveys is one of the key probes for energy and gravity, which can be used to reconstruct the history of cosmic expansion and structure growth using baryonic acoustic oscillations (BAO) and redshift space distortions (RSD) respectively. BAO is a specific three-dimensional clustering pattern of galaxies due to interactions between photons and baryons in the early Universe. Back in the early cosmic epochs, photons scattered with electrons and electrons interacted with protons, making photons and protons (baryonic matter) glued together. There are two opposite forces exerting on this tightly coupled plasma: the pressure of photons and gravity acting on baryons. Similar to what happens to a vibrating spring vertically fixed on the ground, the photon-baryon plasma underwent Oscillations, propagating waves in the same way as the sound does. Therefore, this physical process is called Baryonic Acoustic Oscillations. The effect of the BAO is to push galaxies apart until at a specific time, called the cosmic recombination, when the temperature of the Universe becomes so low that no more photon-baryon interaction can happen. Since then, the separation among galaxies is frozen at a characteristic scale, which is about 150 Mpc depending on the energy content of the Universe, making it a standard ruler to be used to infer the expansion history of the Universe, thus BAO is one of the key probes for the nature of energy. RSD is another special three-dimensional clustering pattern of galaxies, but it is due to local motions of the galaxies under gravity. Suppose galaxies only co-move with the cosmic background without moving locally, the clustering of galaxies should be isotropic, in other words, there are same number of galaxy pairs along or across lines of sight of the observer. However, this is not the case in the real world. Galaxies move towards nearby galaxies due to gravity, thus they have velocities. As we infer galaxies positions from their line-of-sight velocities in astronomy, the peculiar velocities can distort galaxies positions, which results in a distortion, called Redshift Space Distortions, in the 3D clustering of galaxies. RSD plays a key role in cosmology as it can directly be used to infer the nature of gravity (remember the peculiar motion is caused by gravity!). The Baryonic Oscillation Spectroscopic Survey (BOSS) program, part of the Sloan Digital Sky Survey (SDSS)-III project, is the largest completed galaxy survey in the world. BOSS has enabled us to investigate energy and gravity to a unprecedented precision, which has implied a 3.5 sigma evidence for the dynamics of energy. Ongoing and forthcoming galaxy surveys including the extended Baryonic Oscillation Spectroscopic Survey (eBOSS), Dark Energy Spectroscopic Instrument (DESI) and Prime Focus Spectrograph (PFS), will be able to probe the Universe at higher redshifts with much higher precision, which will be providing key observational support for the study of cosmic acceleration.

We study a model in which dark matter couples to the Standard Model through a dilaton of a sector with spontaneously broken approximate scale invariance. Scale invariance fixes the dilaton couplings to the Standard Model and dark matter fields, leaving three main free parameters: the symmetry breaking scale f, the dilaton mass mσ, and the dark matter mass mχ. We analyze the experimental constraints on the parameter space from collider, direct and indirect detection experiments including the effect of Sommerfeld enhancement, and show that dilaton exchange provides a consistent, calculable framework for cold dark matter with f, mσ, mχ of roughly similar magnitude and in the range ∼ 1 − 10 TeV. Direct and indirect detection experiments, notably future ground-based gamma ray and space-based cosmic ray measurements, can probe the model all the way to dark matter mass in the multi-TeV regime. 1

Assuming a double-well bare potential for a self-interacting scalar field, with the Higgs vacuum expectation value, it is shown that non-perturbative quantum corrections naturally lead to ultra-light particles of mass $\simeq10^{-23}$eV, if these non-perturbative effects occur at a time consistent with the Electroweak phase transition. This mechanism could be relevant in the context of Bose Einstein Condensate studies for the description of cold Dark Matter. Given the numerical consistency with the Electroweak transition, an interaction potential for Higgs and Dark Matter fields is proposed, where spontaneous symmetry breaking for the Higgs field leads to the generation of ultra-light particles, in addition to the usual Higgs mechanism. This model also naturally leads to extremely weak interactions between the Higgs and Dark Matter particles.

We analyse the redshift space topology and geometry of the nearby Universe by computing the Minkowski functionals of the Updated Zwicky Catalogue (UZC). The UZC contains the redshifts of almost 20,000 galaxies, is 96% complete to the limiting magnitude m_Zw=15.5 and includes the Center for Astrophysics (CfA) Redshift Survey (CfA2). From the UZC we can extract volume limited samples reaching a depth of 70 hMpc before sparse sampling dominates. We quantify the shape of the large-scale galaxy distribution by deriving measures of planarity and filamentarity from the Minkowski functionals. The nearby Universe shows a large degree of planarity and a small degree of filamentarity. This quantifies the sheet-like structure of the Great Wall which dominates the northern region (CfA2N) of the UZC. We compare these results with redshift space mock catalogues constructed from high resolution N-body simulations of two Cold Dark Matter models with either a decaying massive neutrino (tauCDM) or a non-zero cosmological constant (LambdaCDM). We use semi-analytic modelling to form and evolve galaxies in these dark matter-only simulations. We are thus able, for the first time, to compile redshift space mock catalogues which contain galaxies, along with their observable properties, rather than dark matter particles alone. In both models the large scale galaxy distribution is less coherent than the observed distribution, especially with regard to the large degree of planarity of the real survey. However, given the small volume of the region studied, this disagreement can still be a result of cosmic variance.

The peculiar velocities of galaxies distort the clustering pattern anisotropically in redshift space. This effect on the statistics of isodensity contours is examined by linear theory. The statistics considered in this paper are the three- and two-dimensional genus of isodensity contours, the area of isodensity contours, the length of isodensity contours in the 2-dimensional slice and the level crossing statistics on the line. We find that all these statistics in redshift space as functions of density threshold of contours have the same shape as in real space. The redshift space distortion affects only amplitudes of these statistics. The three-dimensional genus and the area hardly suffer from the redshift space distortion for $0 \leq \Omega b^{-5/3} \leq 1$, where $b$ is a linear bias parameter. The other statistics are defined in one- or two-dimensional slices of the sample volume and depend on the direction of these slices relative to the line of sight. This dependence on direction of these statistics provides a way to determine the density parameter of the universe.

Forward modeling the galaxy density within the Effective Field Theory of Large Scale Structure (EFT of LSS) enables field-level analyses that are robust to theoretical uncertainties. At the same time, they can maximize the constraining power from galaxy clustering on the scales amenable to perturbation theory. In order to apply the method to galaxy surveys, the forward model must account for the full observational complexity of the data. In this context, a major challenge is the inclusion of redshift space distortions (RSDs) from the peculiar motion of galaxies. Here, we present improvements in the efficiency and accuracy of the RSD modeling in the perturbative LEFTfield forward model. We perform a detailed quantification of the perturbative and numerical error for the prediction of momentum, velocity and the redshift-space matter density. Further, we test the recovery of cosmological parameters at the field level, namely the growth rate f, from simulated halos in redshift space. For a rigorous test and to scan through a wide range of analysis choices, we fix the linear (initial) density field to the known ground truth but marginalize over all unknown bias coefficients and noise amplitudes. With a third-order model for gravity and bias, our results yield < 1 % statistical and < 1.5 % systematic error. The computational cost of the redshift-space forward model is only ∼ 1.5 times of the rest frame equivalent, enabling future field-level inference that simultaneously targets cosmological parameters and the initial matter distribution.

view Abstract Citations (4) References (34) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Mass Segregation in Dark Matter Models Campos, A. ; Yepes, G. ; Klypin, A. ; Murante, G. ; Provenzale, A. ; Borgani, S. Abstract We use the moments of counts of neighbors as given by the generalized correlation integrals, to study the clustering properties of dark matter halos (DHs) in cold dark matter (CDM) and cold + hot dark matter (CHDM) models. We compare the results with those found in the CfA and SSRS galaxy catalogs. We show that if we apply the analysis in redshift space, both models reproduce equally well the observed clustering of galaxies. Mass segregation is also found in the models: more massive DHs are more clustered compared with less massive ones. For example, at 3h-1 Mpc in real space, the number of neighbors in excess of random increases ∼3 times when the mass of halos increases by ∼100. In redshift space, this mass segregation is reduced by a factor ∼2-3 due to the peculiar velocities. Observational catalogs give an indication of luminosity and size segregation, which is consistent with the predictions of the models. Because the mass segregation is smaller in redshift space, it is suggestive that the real luminosity or size segregation of galaxies could be significantly larger than what it is found in redshift catalogs. Publication: The Astrophysical Journal Pub Date: June 1995 DOI: 10.1086/175766 arXiv: arXiv:astro-ph/9502018 Bibcode: 1995ApJ...446...54C Keywords: COSMOLOGY: DARK MATTER; COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE; COSMOLOGY: THEORY; GALAXIES: CLUSTERS: GENERAL; Astrophysics E-Print: 13 pages including 9 figures (220 KB) in uuencoded compressed Postscript format. To appear in The Astrophysical Journal, June 10. Latex file and figures available at ftp://astrohp.ft.uam.es/pub/preprints/masseg full text sources arXiv | ADS |

We present an emulator that accurately predicts the power spectrum of galaxies in redshift space as a function of cosmological parameters. Our emulator is based on a second-order Lagrangian bias expansion that is displaced to Eulerian space using cosmological N-body simulations. Redshift space distortions are then imprinted using the non-linear velocity field of simulated particles and haloes. We build the emulator using a forward neural network trained with the simulations of the BACCO project, which covers an eight-dimensional parameter space including massive neutrinos and dynamical dark energy. We show that our emulator provides unbiased cosmological constraints from the monopole, quadrupole, and hexadecapole of a mock galaxy catalogue that mimics the BOSS-CMASS sample down to non-linear scales ($k\sim 0.6{h\, {\rm Mpc}^{-1}}$). This work opens up the possibility of robustly extracting cosmological information from small scales using observations of the large-scale structure of the universe.