1807.11075
The theory of inflation
Martin
This article contains a concise review of the theory of inflation. Discuss its main theoretical aspects as well as its observational predictions. Also explain how the most recent astrophysical observations constrain the inflationary scenario.
1807.11461
3D cosmic shear: numerical challenges, 3d lensing random fields generation and Minkowski functionals for cosmological inference
Mancini, et al
Cosmic shear - the weak gravitational lensing effect generated by fluctuations of the gravitational tidal fields of the large-scale structure - is one of the most promising tools for current and future cosmological analyses. The spherical-Bessel decomposition of the cosmic shear field ("3D cosmic shear") is one way to maximize the amount of redshift information in a lensing analysis and therefore provides a powerful tool to investigate in particular the growth of cosmic structure that is crucial for dark energy studies. However, the computation of simulated 3D cosmic shear covariance matrices presents numerical difficulties, due to the required integrations over highly oscillatory functions. Present and compare two numerical methods and relative implementations to perform these integrations. Then show how to generate 3D Gaussian random fields in spherical coordinates, starting from 3D cosmic shear covariances. To validate the field-generation procedure, calculate the Minkowski functionals associated with the random fields, compare them with the known expectation values for the Gaussian case and demonstrate parameter inference from Minkowski functions from a cosmic shear survey. This is a first step towards producing fully 3D Minkowski functionals for a lognormal field in 3D to extract Gaussian and non-Gaussian information from the cosmic shear field, as well as towards the use of Minkowski functionals as a probe of cosmology beyond the commonly used 2pt statistics.
1807.11077
Prediction of astrometric microlensing events from Gaia DR2 proper motions
Klüter, et al
Astrometric gravitational microlensing is an excellent tool to determine the mass of stellar objects. Using precise astrometric measurements of the lensed position of a background source in combination with accurate predictions of the positions of lens and unlensed source it is possible to determine the mass of the lens with an accuracy of a few percent. Making use of the recently published Gaia DR2 catalogue, predict astrometric microlensing events by foreground stars with higher proper motion passing a background source in the next decades. Select roughly 148k high-proper-motion stars from Gaia DR2 with mu_tot>150 mas/yr as potential lenses. Then search for background sources close to their paths. Using the astrometric parameters of Gaia DR2, calculate the future positions of source and lens. With a nested-intervals algorithm, determine the date and separation of the closest approach. Using Gaia DR2 photometry, determine an approximate mass of the lens, which is used to calculate the expected microlensing effects. Predict 3914 microlensing events by 2875 different lenses between 2010 and 2065 with expected shifts larger than 0.1 mas between the lensed and unlicensed positions of the source. 513 of those are expected to happen between 2014.5-2026.5 and might be measured by Gaia. For 127 events, also expect a magnification between 1 mag and 3 mag.
1807.11940
Real-space computation of $E$/$B$-mode maps I: Formalism, compact kernels, and polarized filaments
Rotti, Huffenberger
Derive full-sky, real-space operators that convert between polarization Stokes Q/U parameters and the coordinate-independent scalar E/B modes that are widely used in CMB and cosmic shear analysis. Also derive real space operators that decompose the measured Stokes parameters into those corresponding to E-modes and B-modes respectively, without ever evaluating the scalar fields themselves. For all these real space operators, show that the kernels split naturally into angular and radial parts and show explicitly how the radial extent of these kernels depends on the targeted band-limit. The kernels can be interpreted either as a complex convolving beam or as a Green's function when they are expressed in terms of the forward or inverse rotation Euler angles. Show that an arbitrary radial function can produce E/B-like maps, provided it vanishes at the origin and the antipodal point. These maps are simply filtered versions of the standard E/B maps. Argue that it is possible to compute E/B maps in real space with a compactly-supported kernel, an approach that can guarantee the avoidance of known foreground regions and could be employed in a massively-parallel scheme at high-resolution. Show that the spin raising and lowering operators eth^2/\bar{eth}^2 are special cases of these generalized radial functions, and present their band limited version. The spatial structure of the real space operators provides great intuition of the E/B structure of polarized, filamentary galactic foregrounds. Predict a non-zero B-mode signature that is expected from polorized filaments in the sky. This paper is the first part in a series of papers that explore real-space computation of polarization modes and their applications.
1807.11488
Intracluster light: a luminous tracer for dark matter in clusters of galaxies
Montes, Trujillo
The bulk of stars in galaxy clusters are confined within their constituent galaxies Those stars do not trace the extended distribution of dark matter well as they are located in the central regions of the cluster's dark matter sub-haloes. A small fraction of stars is expected, however, to follow the global DM shape of the cluster. These are the stars whose extended spatial distribution results from the merging activity of galaxies and form the intracluster light (ICL). In this work, compare the bi-directional distribution of DM in massive galaxy clusters (as traced by gravitational lensing models) with the distribution of the ICL. To do that, use the exquisite data from the Hubble Frontier Fields Initiative. Using the Modified Hausdorff distance (MHD) as a way of quantifying the similarities between the mass and ICL distributions, find an excellent agreement (MHD~25 kpc) between the two components. This result shows that the ICL exquisitely follows the global DM distribution, providing an accurate luminous tracer of DM. This finding opens up the possibility of exploring the distribution of DM in galaxy clusters in detail using only deep imaging observations.
1808.00015
Detection of the milky way spiral arms in dust from 3d mapping
Rasaei Kh., Bailer-Jones, Hogg, Schultheis
Large stellar surveys are sensitive to interstellar dust through the effects of reddening. Using extinctions measured from photometry and spectroscopy, together with 3d positions of individual stars, it is possible to construct a 3d dust map. Present the first continuous map of the list distribution in the Galactic disk out to 7 kpc within 100 pc of the Galactic mid plane, using red clump and giant stars from SDSS APOGEE DR14. Use a non-parametric method based on Gaussian Processes to map the dust density, which is the local property of the ISM rather than an integrated quantity. This method models the dust correlation between points in 3d space and can capture arbitrary variations, unconstrained by a pre-specified functional form. This produces a continuous map without line-of-sight artifacts. The resulting map traces some features of the local Galactic spiral arms, even though the model contains no prior suggestion of spiral arms, nor any underlying model for the Galactic structure. This is the first time that such evident arm structures have been captured by a dust density map in the MW. The resulting map also traces some of the known giant molecular clouds in the Galaxy and puts some constraints on their distances, some of which were hitherto relatively uncertain.
1808.00357
Effects of neutrino mass and asymmetry on cosmological structure formation
Zeng, Yeung, Chu
Light but massive cosmological neutrinos do not cluster significantly on small scales, due to their high thermal velocities. With finite masses, cosmological neutrinos become part of the total matter field and contribute to its smoothing Structure formation in the presence of massive neutrinos is therefore impeded compared to that in the standard LCDM cosmology with massless neutrinos. Neutrinos' masses also distort the anisotropy power spectrum of CMB. Furthermore, a finite chemical potential mu for cosmological neutrinos, still allowed by current data, would have a nonn-neigligible impact on CMB and structure formation. Consistently evaluate effects of neutrino masses and chemical potentials on the matter PS by use of a neutrino-involved N-body sim, with cosmo parameters obtained from a MCMC refitting of CMB data. The results show that while a finite averaged neutrino mass m_nu tends to suppress the matter power spectrum in a range of wave numbers, the neutrino degeneracy parameters xi_i == mu_i/T (i=1,2,3) enhance the latter, leading to a large parameter degeneracy between m_nu and xi_i. Provide an empirical formula for the effects on the matter power spectrum in a selected range of wave numbers induced by m_nu and eta == set (sum_i xi^2_i. Observing a strong correlation between m_nu and eta, propose a single z-independent parameter m_nu - (4/3)eta^2 to characterize the neutrino effects on the matter power spectrum.
1808.00464
First constraints on fuzzy dark matter from the dynamics of stellar streams in the Milky Way
Amorisco, Loeb
Present a novel method to constrain the mass of ultra-light bosons as the DM using stellar streams formed by disrupting Globular Clusters in the Milky Way. The turbulent density field of Fuzzy Dark Matter (FDM) haloes results in perturbations and dynamical heating of thin streams. Using numerical simulations based on an effective model, explore the magnitude of this phenomenon and show that this is observable for the range of axion masses m_a that is interesting for alleviating the 'small-scale problems' of LCDM. Derive an analytical model for the thickening of thin stellar streams and obtain an early conservative lower limit for the boson mass of m_a>1.5e-22 eV, using pre-Gaia literature data for six MW streams and after marginalizing over physical parameters. This demonstrates the great promise for using this novel dynamical method as a full independent probe of FDM, to complement results based on Lyman-alpha forest data.
No comments:
Post a Comment