27,510 research outputs found
Reionization and cosmic dawn astrophysics from the Square Kilometre Array: Impact of observing strategies
No full textInterferometry of the cosmic 21-cm signal is set to revolutionize our understanding of the epoch of reionization (EoR) and the cosmic dawn (CD). The culmination of ongoing efforts will be the upcoming Square Kilometre Array (SKA), which will provide tomography of the 21-cm signal from the first billion years of our Universe. Using a galaxy formation model informed by high-z luminosity functions, here we forecast the accuracy with which the first phase of SKA-low (SKA1-low) can constrain the properties of the unseen galaxies driving the astrophysics of the EoR and CD. We consider three observing strategies: (i) deep (1000 h on a single field); (ii) medium-deep (100 h on 10 independent fields); and (iii) shallow (10 h on 100 independent fields). Using the 21-cm power spectrum as a summary statistic, and conservatively only using the 21-cm signal above the foreground wedge, we predict that all three observing strategies should recover astrophysical parameters to a fractional precision of ∼0.1-10 per cent. The reionization history is recovered to an uncertainty of Δz ≾ 0.1 (1σ ) for the bulk of its duration. The medium-deep strategy, balancing thermal noise against cosmic variance, results in the tightest constraints, slightly outperforming the deep strategy. The shallow observational strategy performs the worst, with up to an ∼10-60 per cent increase in the recovered uncertainty. We note, however, that non-Gaussian summary statistics, tomography, as well as unbiased foreground removal would likely favour the deep strategy
Testing Verlinde's emergent gravity in early-type galaxies
No full textEmergent Gravity (EG) has been proposed to resolve the missing mass problem in galaxies, replacing the potential of dark matter (DM) by the effect of the entropy displacement of dark energy by baryonic matter. This apparent DM depends only on the baryonic mass distribution and the present-day value of the Hubble parameter. In this paper we test the EG proposition, formalized byVerlinde for a spherical and isolated mass distribution using the central dynamics (Sloan Digital Sky Survey velocity dispersion, σ) and the K-band light distribution in a sample of 4032 massive (M* ≳ 1010M O ̇) and local early-type galaxies (ETGs) from the SPIDER datasample. Our results remain unaltered if we consider the sample of 750 roundest field galaxies. Using these observations we derive the predictions by EG for the stellar mass-tolight ratio (M/L) and the initial mass function (IMF). We demonstrate that, consistently with a classical Newtonian framework with a DMhalo component or alternative theories of gravity as MOdified Newtonian Dynamics (MOND), the central dynamics can be fitted if the IMF is assumed non-universal and systematically changing with s. For the case of EG, we find lower, but still acceptable, stellar M/L if compared with the DM-based Navarro, Frenk & White (NFW) model and with MOND, but pretty similar to adiabatically contracted DM haloes and with expectations from spectral gravity-sensitive features. If the strain caused by the entropy displacement would be not maximal, as adopted in the current formulation, then the dynamics of ETGs could be reproduced with larger M/L
Concepts of Optimality and Their Uses
No full textLecture to the memory of Alfred Nobel, December 11, 1975allocation of resources;
The automorphism groups of the vertex operator algebras V+L: general case
No full textIn this article, we give a method of calculating the automorphism groups of the vertex operator algebras V+L associated with even lattices L. For example, by using this method we determine the automorphism groups of V+L for even lattices of rank one, two and three, and even unimodular lattices.
The author was supported by the Japan Society for the Promotion of Science Research Fellowships for Young Scientists and COE grant of Hokkaido University
CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations
No full textPhysical processes can influence the formation and evolution of galaxies in diverse ways. It is essential to validate their incorporation into cosmological simulations by testing them against real data encompassing various types of galaxies and spanning a broad spectrum of masses and galaxy properties. For these reasons, in this second paper of the CASCO series, we compare the structural properties and dark matter content of early-type galaxies taken from the CAMELS IllustrisTNG cosmological simulations to three different observational datasets (SPIDER, ATLAS3D, and MaNGA DynPop), to constrain the value of cosmological and astrophysical feedback parameters, and we compare the results with those obtained comparing the simulation expectations with late-type galaxies. We consider the size-mass, internal DM fraction-mass, and internal DM mass-stellar mass relations for all the simulations, and search for the best-fit simulation for each set of observations. For SPIDER, we find values for the cosmological parameters in line with both the literature and the results obtained from the comparison between simulations and late-type galaxies; results for the supernovae feedback parameters are instead opposite with respect to the previous results based on late-type galaxies. For ATLAS3D, we find similar values as from SPIDER for the cosmological parameters, but we find values for the supernovae feedback parameters more in line with what we found for late-type galaxies. From MaNGA DynPop, we find extreme values for the cosmological parameters, while the supernovae feedback parameters are consistent with ATLAS3D results. When considering the full MaNGA DynPop sample, including both late- and early-type galaxies, no single simulation can reproduce the full variety in the observational datasets. The constraints depend strongly on the specific properties of each observational trend, making it difficult to find a simulation matching all galaxy types, indicating the existence of limitations in the ability of simulations in reproducing the observations.</p
CASCO: Cosmological and AStrophysical parameters from Cosmological simulations and Observations – I. Constraining physical processes in local star-forming galaxies
No full textWe compare the structural properties and dark matter content of star-forming
galaxies taken from the CAMELS cosmological simulations to the observed trends
derived from the SPARC sample in the stellar mass range , to provide constraints on the value of
cosmological and astrophysical (SN- and AGN-related) parameters. We consider
the size-, internal DM fraction-, internal DM mass- and total-stellar mass
relations for all the 1065 simulations from the IllustrisTNG, SIMBA and ASTRID
suites of CAMELS, and search for the parameters that minimize the
with respect to the observations. For the IllustrisTNG suite, we find the
following constraints for the cosmological parameters: , and , which are consistent within with the results
from the nine-year WMAP observations. SN feedback-related astrophysical
parameters, which describe the departure of outflow wind energy per unit star
formation rate and wind velocity from the reference IllustrisTNG simulations,
assume the following values: and
, respectively. Therefore, simulations
with a lower value of outflow wind energy per unit star formation rate with
respect to the reference illustrisTNG simulation better reproduce the
observations. Simulations based on SIMBA and ASTRID suites predict central dark
matter masses substantially larger than those observed in real galaxies, which
can be reconciled with observations only by requiring values of
inconsistent with cosmological constraints for SIMBA, or
simulations characterized by unrealistic galaxy mass distributions for ASTRID.Comment: 24 pages, 10 figures, 9 tables. Accepted by MNRAS for publication;
Added a reference to sec. 4.
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Galaxy formation from dry and hydro simulations
No full textAbstractThe effects of dry and wet merging on the Scaling Laws (SLs) of elliptical galaxies (Es) are discussed. It is found that the SLs, possibly established at high redshift by the fast collapse of gas-rich and clumpy stellar distributions in preexisting dark matter halos following the cosmological SLs, are compatible with a (small) number of galaxy mergers at lower redshift.</jats:p
Vitaal beleid : waardevolle rol voor leefstijlbeleid ouderen
No full textNederland vergrijst in snel tempo en daarom wordt het steeds belangrijker om oudere werknemers zo lang mogelijk vitaal en actief te houden. Leefstijlbeleid kan daaraa een belangrijke bijdrage leveren. TNO onderzocht samen met het Nederlands Instituut voor Sport en Bewegen (NISB) hoe het hier binnen Nederlandse organsiaties mee gesteld is. Vakmedi
The dichotomy of dark matter fraction and total mass density slope of galaxies over five dex in mass
No full textInternational audienceWe analyse the mass density distribution in the centres of galaxies across five orders of magnitude in mass range. Using high-quality spiral galaxy rotation curves and infrared photometry from SPARC, we conduct a systematic study of their central dark matter (DM) fraction (f_DM) and their mass density slope (α), within their effective radius. We show that lower mass spiral galaxies are more DM dominated and have more shallow mass density slopes when compared with more massive galaxies, which have density profiles closer to isothermal. Low-mass (||) gas-rich spirals span a wide range of f_DM values, but systematically lower than in gas-poor systems of similar mass. With increasing galaxy mass, the values of f_DM decrease and the density profiles steepen. In the most massive late-type gas-poor galaxies, a possible flattening of these trends is observed. When comparing these results to massive (||) elliptical galaxies from SPIDER and to dwarf ellipticals (dEs) from SMACKED, these trends result to be inverted. Hence, the values of both f_DM and α, as a function of M_*, exhibit a U-shape trend. At a fixed stellar mass, the mass density profiles in dEs are steeper than in spirals. These trends can be understood by stellar feedback from a more prolonged star formation period in spirals, causing a transformation of the initial steep density cusp to a more shallow profile via differential feedback efficiency by supernovae, and by galaxy mergers or AGN feedback in higher mass galaxies
- …
