arXiv subjects

Bhuvnesh Jain

Publications and source records attributed to Bhuvnesh Jain.

At least 73 records · Page 4Linked to original sources

arXiv2018

Probing Self-interacting Dark Matter with Disk Galaxies in Cluster Environments

Self-Interacting Dark Matter (SIDM) has long been proposed as a solution to small scale problems posed by standard Cold Dark Matter (CDM). We use numerical simulations to study the effect of dark matter interactions on the morphology of disk galaxies falling into galaxy clusters. The effective drag force on dark matter leads to offsets of the stellar disk with respect to the surrounding halo, causing distortions in the disk. For anisotropic scattering cross-sections of 0.5 and 1.0$\,\textrm{cm}^{2}\textrm{g}^{-1}$, we show that potentially observable warps, asymmetries, and thickening of the disk occur in simulations. We discuss observational tests of SIDM with galaxy surveys and more realistic simulations needed to obtain detailed predictions.

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arXiv2018

Splashback in galaxy clusters as a probe of cosmic expansion and gravity

The splashback radius is a physical scale in dark matter halos that is set by the gravitational dynamics of recently accreted shells. We use analytical models and N-body simulations to study the dependence of splashback on dark energy and screened modified gravity theories. In modified gravity models, the transition from screened to unscreened regions typically occurs in the cluster outskirts, suggesting potentially observable signatures in the splashback feature. We investigate the location of splashback in both chameleon and Vainshtein screened models and find significant differences compared with $Λ$CDM predictions. We also find an interesting interplay between dynamical friction and modified gravity, providing a distinctive signature for modified gravity models in the behavior of the splashback feature as a function of galaxy luminosity.

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arXiv2018

WFIRST Science Investigation Team "Cosmology with the High Latitude Survey" Annual Report 2017

Cosmic acceleration is the most surprising cosmological discovery in many decades. Testing and distinguishing among possible explanations requires cosmological measurements of extremely high precision probing the full history of cosmic expansion and structure growth and, ideally, compare and contrast matter and relativistic tracers of the gravity potential. This program is one of the defining objectives of the Wide-Field Infrared Survey Telescope (WFIRST), as set forth in the New Worlds, New Horizons report (NWNH) in 2010. The WFIRST mission has the ability to improve these measurements by 1-2 orders of magnitude compared to the current state of the art, while simultaneously extending their redshift grasp, greatly improving control of systematic effects, and taking a unified approach to multiple probes that provide complementary physical information and cross-checks of cosmological results. We describe in this annual report the activities of the Science Investigation Team (SIT) "Cosmology with the High Latitude Survey (HLS)" during the year 2017. This team was selected by NASA in December 2015 in order to address the stringent challenges of the WFIRST dark energy (DE) program through the Project's formulation phase. This SIT has elected to jointly address Galaxy Redshift Survey, Weak Lensing and Cluster Growth and thus fully embrace the fact that the imaging and spectroscopic elements of the HLS will be realized as an integrated observing program, and they jointly impose requirements on performance and operations. WFIRST is designed to be able to deliver a definitive result on the origin of cosmic acceleration. It is not optimized for Figure of Merit sensitivity but for control of systematic uncertainties and for having multiple techniques each with multiple cross-checks. Our SIT work focuses on understanding the potential systematics in the WFIRST DE measurements.

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arXiv2018

The Two-Halo Term in Stacked Thermal Sunyaev-Zel'dovich Measurements: Implications for Self-Similarity

The relation between the mass and integrated electron pressure of galaxy group and cluster halos can be probed by stacking maps of the thermal Sunyaev-Zel'dovich (tSZ) effect. Perhaps surprisingly, recent observational results have indicated that the scaling relation between integrated pressure and mass follows the prediction of simple, self-similar models down to halo masses as low as $10^{12.5} \, M_{\odot}$. Hydrodynamical simulations that incorporate energetic feedback processes suggest that gas should be depleted from such low-mass halos, thus decreasing their tSZ signal relative to self-similar predictions. Here, we build on the modeling of Vikram, Lidz, and Jain (2017) to evaluate the bias in the interpretation of stacked tSZ measurements due to the signal from correlated halos (the "two-halo" term), which has generally been neglected in the literature. We fit theoretical models to a measurement of the tSZ -- galaxy group cross-correlation function, accounting explicitly for the one- and two- halo contributions. We find moderate evidence of a deviation from self-similarity in the pressure -- mass relation, even after marginalizing over conservative miscentering effects. We explore pressure -- mass models with a break at $10^{14} \, M_{\odot}$, as well as other variants. We discuss and test for sources of uncertainty in our analysis, in particular a possible bias in the halo mass estimates and the coarse resolution of the Planck beam. We compare our findings with earlier analyses by exploring the extent to which halo isolation criteria can reduce the two-halo contribution. Finally, we show that ongoing third-generation CMB experiments will explicitly resolve the one-halo term in low-mass groups; our methodology can be applied to these upcoming data sets to obtain a clear answer to the question of self-similarity and an improved understanding of hot gas in low-mass halos.

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arXiv2018

Cosmic Visions Dark Energy: Small Projects Portfolio

Understanding cosmic acceleration is one of the key science drivers for astrophysics and high-energy physics in the coming decade (2014 P5 Report). With the Large Synoptic Survey Telescope (LSST) and the Dark Energy Spectroscopic Instrument (DESI) and other new facilities beginning operations soon, we are entering an exciting phase during which we expect an order of magnitude improvement in constraints on dark energy and the physics of the accelerating Universe. This is a key moment for a matching Small Projects portfolio that can (1) greatly enhance the science reach of these flagship projects, (2) have immediate scientific impact, and (3) lay the groundwork for the next stages of the Cosmic Frontier Dark Energy program. In this White Paper, we outline a balanced portfolio that can accomplish these goals through a combination of observational, experimental, and theory and simulation efforts.

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arXiv2018

The ellipticity of galaxy cluster halos from satellite galaxies and weak lensing

We study the ellipticity of galaxy cluster halos as characterized by the distribution of cluster galaxies and as measured with weak lensing. We use monte-carlo simulations of elliptical cluster density profiles to estimate and correct for Poisson noise bias, edge bias and projection effects. We apply our methodology to 10,428 SDSS clusters identified by the redMaPPer algorithm with richness above 20. We find a mean ellipticity $= 0.271 \pm 0.002$ (stat) $\pm 0.031$ (sys) corresponding to an axis ratio $= 0.573 \pm 0.002$ (stat) $\pm 0.039$ (sys). We compare this ellipticity of the satellites to the halo shape, through a stacked lensing measurement using optimal estimators of the lensing quadrupole based on Clampitt and Jain (2016). We find a best-fit axis ratio of $0.56 \pm 0.09$ (stat) $\pm 0.03$ (sys), consistent with the ellipticity of the satellite distribution. Thus cluster galaxies trace the shape of the dark matter halo to within our estimated uncertainties. Finally, we restack the satellite and lensing ellipticity measurements along the major axis of the cluster central galaxy's light distribution. From the lensing measurements we infer a misalignment angle with an RMS of ${30^\circ \pm 10}^\circ$ when stacking on the central galaxy. We discuss applications of halo shape measurements to test the effects of the baryonic gas and AGN feedback, as well as dark matter and gravity. The major improvements in signal-to-noise expected with the ongoing Dark Energy Survey and future surveys from LSST, Euclid and WFIRST will make halo shapes a useful probe of these effects.

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arXiv2017

Implications of the Neutron Star Merger GW170817 for Cosmological Scalar-Tensor Theories

The LIGO/VIRGO collaboration has recently announced the detection of gravitational waves from a neutron star-neutron star merger (GW170817) and the simultaneous measurement of an optical counterpart (the gamma-ray burst GRB 170817A). The close arrival time of the gravitational and electromagnetic waves limits the difference in speed of photons and gravitons to be less than about one part in $10^{15}$. This has three important implications for cosmological scalar-tensor gravity theories that are often touted as dark energy candidates and alternatives to $Λ$CDM. First, for the most general scalar-tensor theories---beyond Horndeski models---three of the five parameters appearing in the effective theory of dark energy can now be severely constrained on astrophysical scales; we present the results of combining the new gravity wave results with galaxy cluster observations. Second, the combination with the lack of strong equivalence principle violations exhibited by the supermassive black hole in M87, constrains the quartic galileon model to be cosmologically irrelevant. Finally, we derive a new bound on the disformal coupling to photons that implies that such couplings are irrelevant for the cosmic evolution of the field.

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arXiv2017

Fundamental Physics with the Hubble Space Telescope

Cosmology is intrinsically intertwined with questions in fundamental physics. The existence of non-baryonic dark matter requires new physics beyond the Standard Model of elemenatary-particle interactions and Einstein's general relativity, as does the accelerating expansion of the universe. Current tensions between various cosmological measurements may be harbingers of yet more new physics. Progress on understanding dark matter and cosmic acceleration requires long term, high-precision measurements and excellent control of systematics, demanding observational programs that are often outside the discovery/characterization mode that drives many areas of astronomy. We outline potential programs through which the Hubble Space Telescope (HST) could have a major impact on issues in fundamental physics in the coming years. To realize this impact, we suggest the introduction of a "HST Fundamental Physics" observational program that would be subject to a modified proposal and review process.

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arXiv2017

Tests of Gravity Theories Using Supermassive Black Holes

Scalar-tensor theories of gravity generally violate the strong equivalence principle, namely compact objects have a suppressed coupling to the scalar force, causing them to fall slower. A black hole is the extreme example where such a coupling vanishes, i.e. black hole has no scalar hair. Following earlier work, we explore observational scenarios for detecting strong equivalence principle violation, focusing on galileon gravity as an example. For galaxies in-falling towards galaxy clusters, the supermassive black hole can be offset from the galaxy center away from the direction of the cluster. Hence, well resolved images of galaxies around nearby clusters can be used to identify the displaced black hole via the star cluster bound to it. We show that this signal is accessible with imaging surveys, both ongoing ones such as the Dark Energy Survey, and future ground and space based surveys. Already, the observation of the central black hole in M~87 places new constraints on the galileon parameters, which we present here. $\mathcal{O}(1)$ matter couplings are disfavored for a large region of the parameter space. We also find a novel phenomenon whereby the black hole can escape the galaxy completely in less than one billion years.

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arXiv2017

Delensing Galaxy Surveys

Weak gravitational lensing can cause displacements, magnification, rotation and shearing of the images of distant galaxies. Most studies focus on the shear and magnification effects since they are more easily observed. In this paper we focus on the effect of lensing displacements on wide field images. Galaxies at redshifts 0.5--1 are typically displaced by 1 arcminute, and the displacements are coherent over degree-size patches. However the displacement effect is redshift-dependent, so there is a visible relative shift between galaxies at different redshifts, even if they are close on the sky. We show that the reconstruction of the original galaxy position is now feasible with lensing surveys that cover many hundreds of square degrees. We test with simulations two approaches to "delensing": one uses shear measurements and the other uses the foreground galaxy distribution as a proxy for the mass. We also estimate the effect of foreground deflections on galaxy-galaxy lensing measurements and find it is relevant only for LSST and Euclid-era surveys.

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arXiv2017

The Halo Boundary of Galaxy Clusters in the SDSS

Mass around dark matter halos can be divided into "infalling" material and "collapsed" material that has passed through at least one pericenter. Analytical models and simulations predict a rapid drop in the halo density profile associated with the transition between these two regimes. Using data from SDSS, we explore the evidence for such a feature in the density profiles of galaxy clusters and investigate the connection between this feature and a possible phase space boundary. We first estimate the steepening of the outer galaxy density profile around clusters: the profiles show an abrupt steepening, providing evidence for truncation of the halo profile. Next, we measure the galaxy density profile around clusters using two sets of galaxies selected based on color. We find evidence of an abrupt change in the galaxy colors that coincides with the location of the steepening of the density profile. Since galaxies are likely to be quenched of star formation and turn red inside of clusters, this change in the galaxy color distribution can be interpreted as the transition from an infalling regime to a collapsed regime. We also measure this transition using a model comparison approach which has been used recently in studies of the "splashback" phenomenon, but find that this approach is not a robust way to quantify the significance of detecting a splashback-like feature. Finally, we perform measurements using an independent cluster catalog to test for potential systematic errors associated with cluster selection. We identify several avenues for future work: improved understanding of the small-scale galaxy profile, lensing measurements, identification of proxies for the halo accretion rate, and other tests. With upcoming data from the DES, KiDS and HSC surveys, we can expect significant improvements in the study of halo boundaries.

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arXiv2017

Tests of Neutrino and Dark Radiation Models from Galaxy and CMB surveys

We analyze the ability of galaxy and CMB lensing surveys to constrain massive neutrinos and new models of dark radiation. We present a Fisher forecast analysis for neutrino mass constraints with the LSST galaxy survey and the CMB S4 survey. A joint analysis of the three galaxy and shear 2-point functions, along with key systematics parameters and Planck priors, constrains the neutrino masses to $\sum m_ν= 0.041\,$eV at 1-$σ$ level, comparable to constraints expected from Stage 4 CMB lensing. If low redshift information from upcoming spectroscopic surveys like DESI is included, the constraint becomes $\sum m_ν= 0.032\,$eV. These constraints are derived having marginalized over the number of relativistic species ($N_{\rm eff}$), which is somewhat degenerate with the neutrino mass. We also explore the gain by combining LSST and CMB S4, that is, using the five relevant auto- and cross-correlations of the two datasets. We conclude that advances in modeling the nonlinear regime and the measurements of other parameters are required to ensure a neutrino mass detection. Using the same datasets, we explore the ability of LSST-era surveys to test "nonstandard" models with dark radiation. We find that if evidence for dark radiation is found from $N_{\rm eff}$ measurements, the mass of the dark radiation candidate can be measured at a 1-$σ$ level of $0.162\,$eV for fermionic dark radiation, and $0.137\,$eV for bosonic dark radiation, for $ΔN_{\rm eff} = 0.15$. We also find that the NNaturalness model of Arkani-Hamed et al 2016, with extra light degrees of freedom, has a sub-percent effect on the power spectrum: even more ambitious surveys than the ones considered here will be needed to test such models.

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arXiv2016

Lensing Measurements of the Mass Distribution in SDSS Voids

We measure weak lensing mass profiles of voids from a volume-limited sample of SDSS Luminous Red Galaxies (LRGs). We find voids using an algorithm designed to maximize the lensing signal by dividing the survey volume into 2D slices, and then finding holes in this 2D distribution of LRGs. We perform a stacked shear measurement on about 20,000 voids with radii between 15-55 Mpc/h and redshifts between 0.16-0.37. We measure the characteristic radial shear signal of voids with a signal-to-noise of 7. The mass profile corresponds to a fractional underdensity of about -0.4 inside the void radius and a slow approach to the mean density indicating a partially compensated void structure. We compare our measured shape and amplitude with the predictions of Krause et al 2013. Voids in the galaxy distribution have been extensively modeled using simulations and measured in the SDSS. We discuss how the addition of void mass profiles can enable studies of galaxy formation and cosmology.

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arXiv2016

A Measurement of the Galaxy Group-Thermal Sunyaev-Zel'dovich Effect Cross-Correlation Function

Stacking cosmic microwave background (CMB) maps around known galaxy clusters and groups provides a powerful probe of the distribution of hot gas in these systems via the Sunyaev-Zel'dovich (SZ) effect. A stacking analysis allows one to detect the average SZ signal around low mass halos, and to extend measurements out to large scales, which are too faint to detect individually in the SZ or in X-ray emission. In addition, cross correlations between SZ maps and other tracers of large-scale structure (with known redshifts) can be used to extract the redshift-dependence of the SZ background. Motivated by these exciting prospects, we measure the two-point cross-correlation function between a catalog of $\sim 380,000$ galaxy groups (with redshifts spanning $z=0.01-0.2$) from the Sloan Digital Sky Survey (SDSS) and Compton-y parameter maps constructed by the Planck collaboration. We find statistically significant correlations between the group catalog and Compton-y maps in each of six separate mass bins, with estimated halo masses in the range $10^{11.5-15.5} M_\odot/h$. We compare these measurements with halo models of the SZ signal, which describe the stacked measurement in terms of one-halo and two-halo terms. The one-halo term quantifies the average pressure profile around the groups in a mass bin, while the two-halo term describes the contribution of correlated neighboring halos. For the more massive groups we find clear evidence for the one- and two-halo regimes, while groups with mass below $10^{13} M_\odot/h$ are dominated by the two-halo term given the resolution of Planck data. We use the signal in the two-halo regime to determine the bias-weighted electron pressure of the universe: $\langle b P_e \rangle= 1.50 \pm 0.226 \times 10^{-7}$ keV cm$^{-3}$ (1-$σ$) at $z\approx 0.15$.

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arXiv2016

Tidal stripping as a test of satellite quenching in redMaPPer clusters

When dark matter halos are accreted by massive host clusters, strong gravitational tidal forces begin stripping mass from the accreted subhalos. This stripping eventually removes all mass beyond a subhalo's tidal radius, but the unbound mass remains in the vicinity of the satellite for at least a dynamical time t_dyn. The N-body subhalo study of Chamberlain et al. verified this picture and pointed out a useful observational consequence: measurements of subhalo correlations beyond the tidal radius are sensitive to the infall time, t_infall, of the subhalo onto its host. We perform this cross-correlation measurement using ~ 160,000 red satellite galaxies in SDSS redMaPPer clusters and find evidence that subhalo correlations do persist well beyond the tidal radius, suggesting that many of the observed satellites fell into their current host less than a dynamical time ago, t_infall < t_dyn. Combined with estimated dynamical times t_dyn ~ 3-5 Gyr and SED fitting results for the time at which satellites stopped forming stars, t_quench ~ 6 Gyr, we infer that for a significant fraction of the satellites, star formation quenched before those satellites entered their current hosts. The result holds for red satellites over a large range of cluster-centric distances 0.1 - 0.6 Mpc/h. We discuss the implications of this result for models of galaxy formation.

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arXiv2016

Cosmology from large scale galaxy clustering and galaxy-galaxy lensing with Dark Energy Survey Science Verification data

We present cosmological constraints from the Dark Energy Survey (DES) using a combined analysis of angular clustering of red galaxies and their cross-correlation with weak gravitational lensing of background galaxies. We use a 139 square degree contiguous patch of DES data from the Science Verification (SV) period of observations. Using large scale measurements, we constrain the matter density of the Universe as Omega_m = 0.31 +/- 0.09 and the clustering amplitude of the matter power spectrum as sigma_8 = 0.74 +/- 0.13 after marginalizing over seven nuisance parameters and three additional cosmological parameters. This translates into S_8 = sigma_8(Omega_m/0.3)^{0.16} = 0.74 +/- 0.12 for our fiducial lens redshift bin at 0.35 <z< 0.5, while S_8 = 0.78 +/- 0.09 using two bins over the range 0.2 <z< 0.5. We study the robustness of the results under changes in the data vectors, modelling and systematics treatment, including photometric redshift and shear calibration uncertainties, and find consistency in the derived cosmological parameters. We show that our results are consistent with previous cosmological analyses from DES and other data sets and conclude with a joint analysis of DES angular clustering and galaxy-galaxy lensing with Planck CMB data, Baryon Accoustic Oscillations and Supernova type Ia measurements.

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arXiv2016

Constraining the Mass-Richness Relationship of redMaPPer Clusters with Angular Clustering

The potential of using cluster clustering for calibrating the mass-observable relation of galaxy clusters has been recognized theoretically for over a decade. Here, we demonstrate the feasibility of this technique to achieve high precision mass calibration using redMaPPer clusters in the Sloan Digital Sky Survey North Galactic Cap. By including cross-correlations between several richness bins in our analysis we significantly improve the statistical precision of our mass constraints. The amplitude of the mass-richness relation is constrained to 7% statistical precision. However, the error budget is systematics dominated, reaching an 18% total error that is dominated by theoretical uncertainty in the bias-mass relation for dark matter halos. We perform a detailed treatment of the effects of assembly bias on our analysis, finding that the contribution of such effects to our parameter uncertainties is somewhat greater than that of measurement noise. We confirm the results from Miyatake et al. (2015) that the clustering amplitude of redMaPPer clusters depends on galaxy concentration, and provide additional evidence in support of this effect being due to some form of assembly bias. The results presented here demonstrate the power of cluster clustering for mass calibration and cosmology provided the current theoretical systematics can be ameliorated.

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arXiv2016

Lensing Measurements of the Ellipticity of LRG Dark Matter Halos

Lensing measurements of the shapes of dark matter halos can provide tests of gravity theories and possible dark matter interactions. We measure the quadrupole weak lensing signal from the elliptical halos of 70,000 SDSS Luminous Red Galaxies. We use a new estimator that nulls the spherical halo lensing signal, isolating the shear due to anisotropy in the dark matter distribution. One of the two Cartesian components of our estimator is insensitive to the primary systematic, a spurious alignment of lens and source ellipticities, allowing us to make robust measurements of halo ellipticity. Our best-fit value for the ellipticity of the surface mass density is $0.24 \pm 0.06$, which translates to an axis ratio of 0.78. We rule out the hypothesis of no ellipticity at the $4σ$ confidence level, and ellipticity < 0.12 (axis ratio > 0.89) at the $2σ$ level. We discuss how our measurements of halo ellipticity are revised to higher values using estimates of the misalignment of mass and light from simulations. Finally, we apply the same techniques to a smaller sample of redMaPPer galaxy clusters and obtain a $3σ$ measurement of cluster ellipticity. We discuss how the improved signal to noise properties of our estimator can enable studies of halo shapes for different galaxy populations with upcoming surveys.

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