1,721,275 research outputs found
Neutrinos and the Lyman-α forest: myth or reality?
No full textI will review constraints on sterile and active neutrino masses that can be obtained using the Lyman-α forest
Lyman-α Forest and Cosmic Weak Lensing in a Warm Dark Matter Universe
Full text linkWe review the current state of the theory of large scale structure in a warm dark matter (WDM) cosmological model. In particular, we focus on the non-linear modelling of the matter power spectrum and on the mass function of dark matter haloes. We describe the results of N-body simulations with WDM and mention the effects that could be induced by baryonic physics. We also examine the halo model of large scale structure and its recently suggested modifications for a WDM cosmology, which account for the small scale smoothness of the initial matter density field and better fit the results of N-body simulations. Having described the theoretical models, we discuss the current lower limits on the WDM particle mass, m_w, which correspond to upper limits on the WDM temperature under the assumption that the particles are thermal relics. The best such constraints come from the Ly{\alpha} forest and exclude all masses below 3.3 keV at the 2{\sigma} confidence level. We finally review the forecasts for future lensing surveys, which will be of the same order of magnitude as the already existing constraints from the Ly{\alpha} forest data but explore a different redshift regime
The Lyman-beta forest as a cosmic thermometer
No full textWe present a comprehensive analysis of high resolution hydrodynamic simulations in terms of Lyman-alpha and Lyman-beta one dimensional flux power spectra ((P alpha alpha) and P-beta beta). In particular, we focus on the behaviour that the flux auto-power spectra and cross-power spectra (P-alpha beta) display when the intergalactic medium (IGM) thermal history is changed in a range of values that bracket a reference model, while cosmological parameters are kept fixed to best fit the cosmic microwave background data. We present empirical fits that describe at the sub-percent level the dependence of the power spectra on the thermal parameters. At the largest scales, the power spectra show a constant bias between each other that is set by the parameters describing the IGM thermal state. The cross-power spectrum has an oscillatory pattern and crosses zero at a scale which depends on T-0, the IGM temperature at the mean density, for reasonable values of the power-law index gamma of the IGM temperature-density relation (T = T-0(1 + delta)(gamma-1)). By performing a Fisher matrix analysis, we find that the power spectrum Po is more sensitive to the thermal history than P-alpha alpha alone, due to the fact that it probes denser regions than Lyman-a. When we combine the power and cross spectra the constraints on gamma can be improved by a factor similar to 4, while the constraints on T-0 improve by a factor of similar to 2. We address the role of signal-to-noise and resolution by mocking realistic observations and we conclude that the framework presented in this work can significantly improve the knowledge of the IGM thermal state, which will in turn guarantee better constraints on IGM-derived cosmological parameters
Novel constraints on noncold, nonthermal dark matter from Lyman-alpha forest data
Full text linkIn this paper, we present an efficient method for constraining both thermal and nonthermal dark matter (DM) scenarios with the Lyman-α forest based on a simple and flexible parametrization capable of reproducing the small-scale clustering signal of a large set of noncold DM (NCDM) models. We extract new limits on the fundamental DM properties through an extensive analysis of the high resolution, high redshift data obtained by the MIKE/HIRES spectrographs. By using a large suite of hydrodynamical simulations, we determine constraints on both astrophysical, cosmological, and NCDM parameters by performing a full Monte Carlo Markov chain analysis. We obtain a marginalized upper limit on the largest possible scale at which a power suppression induced by nearly any NCDM scenario can occur, i.e., α<0.03 Mpc/h (2σ C.L.). We explicitly describe how to test several of the most viable NCDM scenarios without the need to run any specific numerical simulations due to the novel parametrization proposed and due to a new scheme that interpolates between the cosmological models explored. The shape of the linear matter power spectrum for standard thermal warm DM models appears to be in mild tension (∼2σ C.L.) with the data compared to nonthermal scenarios. We show that a DM fluid composed by both a warm (thermal) and a cold component is also in tension with the Lyman-α forest, at least for large α values. This is the first study that allows us to probe the linear small-scale shape of the DM power spectrum for a large set of NCDM models
Multipole expansion for 21cm Intensity Mapping power spectrum: forecasted cosmological parameters estimation for the SKA Observatory
Full text linkThe measurement of the large scale distribution of neutral hydrogen in the
late Universe, obtained with radio telescopes through the hydrogen 21cm line
emission, has the potential to become a key cosmological probe in the upcoming
years. We explore the constraining power of 21cm intensity mapping observations
on the full set of cosmological parameters that describe the CDM
model. We assume a single-dish survey for the SKA Observatory and simulate the
21cm linear power spectrum monopole and quadrupole within six redshift bins in
the range . Forecasted constraints are computed numerically through
Markov Chain Monte Carlo techniques. We extend the sampler \texttt{CosmoMC} by
implementing the likelihood function for the 21cm power spectrum multipoles. We
assess the constraining power of the mock data set alone and combined with
Planck 2018 CMB observations. We include a discussion on the impact of
extending measurements to non-linear scales in our analysis. We find that 21cm
multipoles observations alone are enough to obtain constraints on the
cosmological parameters comparable with other probes. Combining the 21cm data
set with CMB observations results in significantly reduced errors on all the
cosmological parameters. The strongest effect is on and ,
for which the error is reduced by almost a factor four. The percentage errors
we estimate are and , to
be compared with the Planck only results and
. We conclude that 21cm SKAO observations will provide a
competitive cosmological probe, complementary to CMB and, thus, pivotal for
gaining statistical significance on the cosmological parameters constraints,
allowing a stress test for the current cosmological model.Comment: 16 pages, 9 figure
On the degeneracy between baryon feedback and massive neutrinos as probed by matter clustering and weak lensing
No full textMassive neutrinos, due to their free streaming, produce a suppression in the matter power spectrum at intermediate and small scales which could be probed by galaxy clustering and/or weak lensing observables. This effect happens at scales that are also influenced by baryon feedback, i.e. galactic winds or Active Galactic Nuclei (AGN) feedback, which in realistic hydrodynamic simulations has also been shown to produce a suppression of power. Leaving aside, for the moment, the complex issue of galaxy bias, we focus here on matter clustering and tomographic weak lensing, we investigate the possible degeneracy between baryon feedback and neutrinos showing that it is not likely to degrade significantly the measurement of neutrino mass in future surveys. To do so, we generate mock data sets and fit them using the Markov Chain Monte Carlo (MCMC) technique and explore degeneracies between feedback parameters and neutrino mass. We model baryon feedback through fitting functions, while massive neutrinos are accounted for, also in the non-linear regime, using Halofit calibrated against accurate N-body neutrino simulations. In the error budget, we include the uncertainty in the modelling of non-linearities. For both matter clustering and weak lensing, we always recover the input neutrino mass within ∼0.25σ confidence level. Finally, we also take into account the intrinsic alignment effect in the weak lensing mock data. Even in this case, we are able to recover the right parameters: in particular, we find a significant degeneracy pattern between Mν and the intrinsic alignment parameter AIA
JWST high-z galaxy constraints on warm and cold dark matter models
Full text linkWe compare properties of high-redshift galaxies observed by JWST with
hydrodynamical simulations, in the standard cold dark matter model and in warm
dark matter models with a suppressed linear matter power spectrum. We find that
current data are not in tension with cold dark matter nor with warm dark matter
models with mWDM > 2 keV, since they probe bright and rare objects whose
physical properties are similar in the different scenarios. We also show how
two observables, the galaxy luminosity functions and the galaxy correlation
function at small scales of faint objects, can be promising tools for
discriminating between the different dark matter models. Further hints may come
from early stellar-mass statistics and galaxy CO emission.Comment: language editing; A&A in pres
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