arXiv subjects

Adi Nusser

Publications and source records attributed to Adi Nusser.

At least 37 records · Page 2Linked to original sources

arXiv2019

Orbital decay of Globular Clusters in the galaxy with little dark matter

Recently, \cite{vanDokkum2018} have presented an important discovery of an ultra diffuse galaxy, NGC1052-DF2, with a dark matter content significantly less than predicted from its stellar mass alone. The analysis relies on measured radial velocities of 10 Globular Clusters (GCs), of estimated individual masses of a few $ \times 10^6 M_\odot$. This is about $1\%$ of the inferred mass of NGC1052-DF2 of $2\times 10^8 M_\odot$ within a half-light radius, $R_\mathrm{e}=2.2\, \mathrm{kpc}$. The large relative mass and the old age of these objects imply that they might be susceptible to orbital decay by dynamical friction. Using analytic estimates and N-body simulations of an isolated system matching the inferred mass profile of NGC1052-DF2, we show that orbits of the most massive GCs should already have decayed on a time scale of a few Gyrs. These findings should help in constraining mass profile and formation scenarios of NGC1052-DF2.

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arXiv2018

Abundance of peaks and dips in three-dimensional mass and halo density fields: a test for cosmology

Using cosmological N-body simulations, we study the abundance of local maxima (peaks) and minima (dips) identified in the smoothed distribution of halos and dark matter (DM) on scales of $10-100$s Mpcs. The simulations include Gaussian and local-type $f_{\rm NL}$ non-Gaussian initial conditions. The expression derived in the literature for the abundance (irrespective of height) of peaks for Gaussian fields is surprisingly accurate for the evolved halo and DM density fields for all initial conditions considered. Furthermore, the height distribution is very well fitted by a log-normal on quasi-linear scales. The abundance as a function of scale depends on the cosmological parameters ($H_0$ and background matter densities) through the shape of the power spectrum, but it is insensitive to the clustering amplitude. Further, the abundance in the smoothed halo distribution is substantially different in the non-Gaussian from the Gaussian simulations. The interpretation of this effect is straightforward in terms of the scale dependence of halo bias in non-Gaussian models. The abundance of extrema extracted from three-dimensional large galaxy redshift surveys could be a competitive probe of the cosmological parameters and initial non-Gaussianity. It breaks the degeneracy between $f_{\rm NL}$ and the clustering amplitude, making it complementary to counts of galaxy clusters and peaks in weak-lensing maps.

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arXiv2017

Velocity-Density Correlations from the cosmicflows-3 Distance Catalog and the 2MASS Redshift Survey

The peculiar velocity of a mass tracer is on average aligned with the dipole modulation of the surrounding mass density field. We present a first measurement of the correlation between radial peculiar velocities of objects in the cosmicflows-3 catalog and the dipole moment of the 2MRS galaxy distribution in concentric spherical shells centered on these objects. Limiting the analysis to cosmicflows-3 objects with distances of $100 \rm Mpc h^{-1}$, the correlation function is detected at a confidence level $> 4σ$. The measurement is found consistent with the standard $Λ$CDM model at $< 1.7σ$ level. We formally derive the constraints $0.32<Ω^{0.55}σ_8<0.48$ ($68\% $ confidence level) or equivalently $0.34<Ω^{0.55}/b<0.52$, where $b$ is the galaxy bias factor. Deeper and improved peculiar velocity catalogs will substantially reduce the uncertainties, allowing tighter constraints from this type of correlations.

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arXiv2017

Testing Lorentz invariance of dark matter with satellite galaxies

We develop the framework for testing Lorentz invariance in the dark matter sector using galactic dynamics. We consider a Lorentz violating (LV) vector field acting on the dark matter component of a satellite galaxy orbiting in a host halo. We introduce a numerical model for the dynamics of satellites in a galactic halo and for a galaxy in a rich cluster to explore observational consequences of such an LV field. The orbital motion of a satellite excites a time dependent LV force which greatly affects its internal dynamics. Our analysis points out key observational signatures which serve as probes of LV forces. These include modifications to the line of sight velocity dispersion, mass profiles and shapes of satellites. With future data and a more detailed modeling these signatures can be exploited to constrain a new region of the parameter space describing the LV in the dark matter sector.

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arXiv2017

Speed from light: growth rate and bulk flow at z ~ 0.1 from improved SDSS DR13 photometry

Observed galaxy luminosities (derived from redshifts) hold information on the large-scale peculiar velocity field in the form of spatially correlated scatter, which allows for bounds on bulk flows and the growth rate of matter density perturbations using large galaxy redshift surveys. We apply this luminosity approach to galaxies from the recent SDSS Data Release 13. Our goal is twofold. First, we take advantage of the recalibrated photometry to identify possible systematic errors relevant to our previous analysis of earlier data. Second, we seek improved constraints on the bulk flow and the normalized growth rate f$σ_{8}$ at z ~ 0.1. Our results confirm the robustness of our method. Bulk flow amplitudes, estimated in two redshift bins with 0.02 < z$_{1}$ < 0.07 < z$_{2}$ < 0.22, are generally smaller than in previous measurements, consistent with both the updated photometry and expectations for the $Λ$CDM model. The obtained growth rate, f$σ_{8}$ = 0.48 +/- 0.16, is larger than, but still compatible with, its previous estimate, and closer to the reference value of Planck. Rather than precision, the importance of these results is due to the fact that they follow from an independent method that relies on accurate photometry, which is a top requirement for next-generation photometric catalogs.

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arXiv2016

Not a Copernican observer: biased peculiar velocity statistics in the local Universe

We assess the effect of the local large scale structure on the estimation of two-point statistics of the observed radial peculiar velocities of galaxies. A large N-body simulation is used to examine these statistics from the perspective of random observers as well as "Local Group (LG)-like" observers conditioned to reside in an environment resembling the observed universe within 20 Mpc. The local environment systematically distorts the shape and amplitude of velocity statistics with respect to ensemble-averaged measurements made by a Copernican (random) observer. The Virgo cluster has the most significant impact, introducing large systematic deviations in all the statistics. For a simple "top-hat" selection function, an idealized survey extending to $\sim 160h^{-1}\,{\rm Mpc}$ or deeper is needed to completely mitigate the effects of the local environment. Using shallower catalogues leads to systematic deviations of the order of $50$ to $200\%$ depending on the scale considered. For a flat redshift distribution similar to the one of the CosmicFlows-3 survey, the deviations are even more prominent in both the shape and amplitude at all separations considered $({\stackrel{<}{{}_\sim}} 100h^{-1}\,{\rm Mpc})$. Conclusions based on statistics calculated without taking into account the impact of the local environment should be revisited.

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arXiv2016

Performance study of Lagrangian methods: reconstruction of large scale peculiar velocities and baryonic acoustic oscillations

NoAM for "No Action Method" is a framework for reconstructing the past orbits of observed tracers of the large scale mass density field. It seeks exact solutions of the equations of motion (EoM), satisfying initial homogeneity and the final observed particle (tracer) positions. The solutions are found iteratively reaching a specified tolerance defined as the RMS of the distance between reconstructed and observed positions. Starting from a guess for the initial conditions, NoAM advances particles using standard N-body techniques for solving the EoM. Alternatively, the EoM can be replaced by any approximation such as Zel'dovich and second order perturbation theory (2LPT). NoAM is suitable for billions of particles and can easily handle non-regular volumes, redshift space, and other constraints. We implement NoAM to systematically compare Zel'dovich, 2LPT, and N-body dynamics over diverse configurations ranging from idealized high-res periodic simulation box to realistic galaxy mocks. Our findings are (i) Non-linear reconstructions with Zel'dovich, 2LPT, and full dynamics perform better than linear theory only for idealized catalogs in real space. For realistic catalogs, linear theory is the optimal choice for reconstructing velocity fields smoothed on scales > 5 Mpc/h. (ii) all non-linear back-in-time reconstructions tested here, produce comparable enhancement of the baryonic oscillation signal in the correlation function.

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arXiv2016

The Detailed Science Case for the Maunakea Spectroscopic Explorer: the Composition and Dynamics of the Faint Universe

MSE is an 11.25m aperture observatory with a 1.5 square degree field of view that will be fully dedicated to multi-object spectroscopy. More than 3200 fibres will feed spectrographs operating at low (R ~ 2000 - 3500) and moderate (R ~ 6000) spectral resolution, and approximately 1000 fibers will feed spectrographs operating at high (R ~ 40000) resolution. MSE is designed to enable transformational science in areas as diverse as tomographic mapping of the interstellar and intergalactic media; the in-situ chemical tagging of thick disk and halo stars; connecting galaxies to their large scale structure; measuring the mass functions of cold dark matter sub-halos in galaxy and cluster-scale hosts; reverberation mapping of supermassive black holes in quasars; next generation cosmological surveys using redshift space distortions and peculiar velocities. MSE is an essential follow-up facility to current and next generations of multi-wavelength imaging surveys, including LSST, Gaia, Euclid, WFIRST, PLATO, and the SKA, and is designed to complement and go beyond the science goals of other planned and current spectroscopic capabilities like VISTA/4MOST, WHT/WEAVE, AAT/HERMES and Subaru/PFS. It is an ideal feeder facility for E-ELT, TMT and GMT, and provides the missing link between wide field imaging and small field precision astronomy. MSE is optimized for high throughput, high signal-to-noise observations of the faintest sources in the Universe with high quality calibration and stability being ensured through the dedicated operational mode of the observatory. (abridged)

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arXiv2016

Goodness-of-fit analysis of the Cosmicflows-2 database of velocities

The goodness-of-fit (GoF) of the Cosmicflows-2 (CF2) database of peculiar velocities with the LCDM standard model of cosmology is presented. Standard application of the Chi^2 statistics of the full database, of its 4,838 data points, is hampered by the small scale nonlinear dynamics which is not accounted for by the (linear regime) velocity power spectrum. The bulk velocity constitutes a highly compressed representation of the data which filters out the small scales non-linear modes. Hence the statistics of the bulk flow provides an efficient tool for assessing the GoF of the data given a model. The particular approach introduced here is to use the (spherical top-hat window) bulk velocity extracted from the Wiener filter reconstruction of the 3D velocity field as a linear low pass filtered highly compressed representation of the CF2 data. An ensemble 2250 random linear realizations of the WMAP/LCDM model has been used to calculate the bulk velocity auto-covariance matrix. We find that the CF2 data is consistent with the WMAP/LCDM model to better than the 2 sigma confidence limits. This provides a further validation that the CF2 database is consistent with the standard model of cosmology.

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arXiv2016

Revisiting the NVSS number count dipole

We present a realistic modeling of the dipole component of the projected sky distribution of NVSS radio galaxies. The modeling relies on mock catalogs generated within the context of $Λ$CDM cosmology, in the linear regime of structure formation. After removing the contribution from the solar motion, the mocks show that the remaining observed signal is mostly (70\%) due to structures within $z\lesssim0.1$. The amplitude of the model signal depends on the bias factor $b$ of the NVSS mock galaxies. For sources with flux density, $ S> 15 \; \rm mJy$, the bias recipe inferred from higher order moments is consistent with the observed dipole signal at $2.12σ$. Flux thresholds above $20 \; \rm mJy$ yield a disagreement close to the $3σ$ level. A constant high bias, $b=3$ is needed to mitigate the tension to the $\sim 2.3σ$ level.

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arXiv2016

On Testing the Equivalence Principle with Extragalactic Bursts

An interesting test of Einstein's equivalence principle (EEP) relies on the observed lag in arrival times of photons emitted from extragalactic transient sources. Attributing the lag between photons of different energies to the gravitational potential of the Milky Way (MW), several authors derive new constraints on deviations from EEP. It is shown here that potential fluctuations from the large scale structure are at least two orders of magnitude larger than the gravitational potential of the MW. Combined with the larger distances, for sources at redshift $z\gtsim 0.5$ the {\it rms} of the contribution from these fluctuations exceeds the MW by more than 4 orders of magnitude. We provide actual constraints for several objects based on a statistical calculation of the large scale fluctuations in the standard $Λ$CDM cosmological model.

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arXiv2015

On methods of estimating cosmological bulk flows

We explore similarities and differences between several estimators of the cosmological bulk flow, $\bf B$, from the observed radial peculiar velocities of galaxies. A distinction is made between two theoretical definitions of $\bf B$ as a dipole moment of the velocity field weighted by a radial window function. One definition involves the three dimensional (3D) peculiar velocity, while the other is based on its radial component alone. Different methods attempt at inferring $\bf B$ for either of these definitions which coincide only for a constant velocity field. We focus on the Wiener Filtering (WF, Hoffman et al. 2015) and the Constrained Minimum Variance (CMV,Feldman et al. 2010) methodologies. Both methodologies require a prior expressed in terms of the radial velocity correlation function. Hoffman et al. compute $\bf B$ in Top-Hat windows from a WF realization of the 3D peculiar velocity field. Feldman et al. infer $\bf B$ directly from the observed velocities for the second definition of $\bf B$. The WF methodology could easily be adapted to the second definition, in which case it will be equivalent to the CMV with the exception of the imposed constraint. For a prior with vanishing correlations or very noisy data, CMV reproduces the standard Maximum Likelihood (ML, Kaiser 1988) estimation for $\bf B$ of the entire sample independent of the radial weighting function. Therefore, this estimator is likely more susceptible to observational biases that could be present in measurements of distant galaxies. Finally, two additional estimators are proposed.

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arXiv2015

Growth rate of cosmological perturbations at z ~ 0.1 from a new observational test

Spatial variations in the distribution of galaxy luminosities, estimated from redshifts as distance proxies, are correlated with the peculiar velocity field. Comparing these variations with the peculiar velocities inferred from galaxy redshift surveys is a powerful test of gravity and dark energy theories on cosmological scales. Using ~ 2 $\times$ 10$^{5}$ galaxies from the SDSS Data Release 7, we perform this test in the framework of gravitational instability to estimate the normalized growth rate of density perturbations f$σ_{8}$ = 0.37 +/- 0.13 at z ~ 0.1, which is in agreement with the $Λ$CDM scenario. This unique measurement is complementary to those obtained with more traditional methods, including clustering analysis. The estimated accuracy at z ~ 0.1 is competitive with other methods when applied to similar datasets.

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arXiv2015

The clustering of radio galaxies: biasing and evolution versus stellar mass

We study the angular clustering of $\sim 6\times 10^5$ NVSS sources on scales $\gtrsim 50 h^{-1}$ Mpc in the context of the $Λ$CDM scenario. The analysis partially relies on the redshift distribution of 131 radio galaxies, inferred from the Hercules and CENSORS survey, and an empirical fit to the stellar to halo mass (SHM) relation. For redshifts $z\lesssim 0.7$, the fraction of radio activity versus stellar mass evolves as $f_{_{\rm RL}}\sim M_*^{α_0+α_1 z}$ where $α_0=2.529{\pm0.184}$ and $α_1=1.854^{+0.708}_{-0.761}$. The estimate on $α_0$ is largely driven by the results of Best et al. (2005), while the constraint on $α_1$ is new. We derive a biasing factor $b(z=0.5)=2.093^{+0.164}_{-0.109}$ between radio galaxies and the underlying mass.The function $b(z)=0.33z^2+0.85 z +1.6$ fits well the redshift dependence. We also provide convenient parametric forms for the redshift dependent radio luminosity function, which are consistent with the redshift distribution and the NVSS source count versus flux.

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arXiv2014

Re-examination of Large Scale Structure and Cosmic Flows

Comparison of galaxy flows with those predicted from the local galaxy distribution ended as an active field after two analyses came to vastly different conclusions 25 years ago, but that was due to faulty data. All the old results are therefore suspect. With new data collected in the last several years, the problem deserves another look. For this we analyze the gravity field inferred from the enormous data set derived from the 2MASS collection of galaxies, and compare it to the velocity field derived from the well calibrated SFI++ Tully-Fisher catalog. Using the "Inverse Method" to minimize Malmquist biases, within 10,000 km/s the gravity field is seen to predict the velocity field to remarkable consistency. This is a beautiful demonstration of linear perturbation theory and is fully consistent with standard values of the cosmological variables.

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arXiv2014

Dynamics of The Tranquil Cosmic Web

The phase space distribution of matter out to $\sim 100 \rm Mpc$ is probed by two types of observational data: galaxy redshift surveys and peculiar motions of galaxies. Important information on the process of structure formation and deviations from standard gravity have been extracted from the accumulating data. The remarkably simple Zel'dovich approximation is the basis for much of our insight into the dynamics of structure formation and the development of data analyses methods. Progress in the methodology and some recent results is reviewed.

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arXiv2014

Large-scale peculiar velocities through the galaxy luminosity function at z ~ 0.1

Peculiar motion introduces systematic variations in the observed luminosity distribution of galaxies. This allows one to constrain the cosmic peculiar velocity field from large galaxy redshift surveys. Using around half a million galaxies from the SDSS Data Release 7 at z ~ 0.1, we demonstrate the applicability of this approach to large datasets and obtain bounds on peculiar velocity moments and $σ_{8}$, the amplitude of the linear matter power spectrum. Our results are in good agreement with the $Λ$CDM model and consistent with the previously reported ~ 1% zero-point tilt in the SDSS photometry. Finally, we discuss the prospects of constraining the growth rate of density perturbations by reconstructing the full linear velocity field from the observed galaxy clustering in redshift space.

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arXiv2014

Tracing the cosmic velocity field at z ~ 0.1 from galaxy luminosities in the SDSS DR7

Spatial modulations in the distribution of observed luminosities (computed using redshifts) of ~ 5 $\times$ 10$^5$ galaxies from the SDSS Data Release 7, probe the cosmic peculiar velocity field out to z ~ 0.1. Allowing for luminosity evolution, the r-band luminosity function, determined via a spline-based estimator, is well represented by a Schechter form with M$^{\star}$(z) - 5log$_{10}$h = -20.52 - 1.6(z - 0.1) $\pm$ 0.05 and $α^{\star}$ = -1.1 $\pm$ 0.03. Bulk flows and higher velocity moments in two redshift bins, 0.02 < z < 0.07 and 0.07 < z < 0.22, agree with the predictions of the $Λ$CDM model, as obtained from mock galaxy catalogs designed to match the observations. Assuming a $Λ$CDM model, we estimate $σ_{8}$ $\approx$ 1.1 $\pm$ 0.4 for the amplitude of the linear matter power spectrum, where the low accuracy is due to the limited number of galaxies. While the low-z bin is robust against coherent photometric uncertainties, the bias of results from the second bin is consistent with the ~ 1% magnitude tilt reported by the SDSS collaboration. The systematics are expected to have a significantly lower impact in future datasets with larger sky coverage and better photometric calibration.

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