36 research outputs found
Nuevas técnicas para explotar cosmológicamente cartografiados de galaxias de forma óptima
Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Astrofísica y Ciencias de la Atmósfera, leída el 27/07/2017The emergence of the current cosmological model, which we know as Lambda Cold Dark Matter(ΛCDM), and the sophistication of the experiments with which we observe the Universe enabled the actual era of precision cosmology. This is because thedevelopment of technology together with the accurate predictions of multiple cosmological observables by ΛCDM opened the possibility of determining the properties of the Universe in detail. Nonetheless, there are still some challenges in this model, e.g. to unveil the nature of Dark Matter(DM) and to explain the cause behind the accelerated expansion of the universe. To enlighten these issues, tens of observatories and scientific instruments are built all over the world, and they will produce newer and preciser galaxy surveys. These future surveys will sample large volumes of the universe with unprecedented precision. The cosmological information extracted from them will no longer be dominated by statistical errors, and thus systematic errors will become the main source of uncertainty. These errors arise from an incorrect interpretation of the data and/or an imprecise modelling of the effect of observational techniques on the results. Moreover, they will have to be correctly accounted for in order to unbiasedly obtain cosmological information from future surveys and to fully exploit them...El desarrollo del modelo cosmológico actual, que denominamos Lambda Cold Dark Matter (ΛCDM), y la evolución de los experimentos con los que observamos el Universo iniciaron la actual era de la cosmología de precisión. Esto es debido a que ΛCDM realiza predicciones detalladas de diferentes observables en el universo cercano y lejano, lo que unido al progreso en la técnica, habilitó determinar detalladamente las propiedades del cosmos. Sin embargo, este modelo cuenta todavía con algunos problemas abiertos, como encontrar la naturaleza de la Materia Oscura (DM, Dark Matter) o descubrir qué produce la expansión acelerada del universo. En aras de solventarlos, decenas de observatorios astronómicos e instrumentos científicos se están construyendo por todo el mundo, y estos posibilitarán nuevos y más precisos cartografiados de galaxias. Estos futuros cartografiados mapearán con exquisito detalle grandes volúmenes cosmológicos, lo que les permitirá, al extraer información cosmológica de las observaciones, reducir al mínimo las incertidumbres estadísticas. Así, los errores sistemáticos se convertirán en la principal fuente de inexactitud, donde estos emergen de interpretar erróneamente los datos o de desconocer de forma específica el impacto de las técnicas observacionales en ellos. Además, estas inexactitudes deben ser correctamente modelados para no introducir sesgos al extraer parámetros cosmológicos de los cartografiados y aprovecharlos de forma óptima...Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu
Relativistic Angular Redshift Fluctuations embedded in Large Scale Varying Gravitational Potentials
We compute the linear order, general relativistic corrections to angular
redshift fluctuations (ARF), a new cosmological observable built upon
density-weighted two-dimensional (2D) maps of galaxy redshifts. We start with
an existing approach for galaxy/source counts developed in the Newtonian gauge,
and generalize it to ARF, modifying for this purpose a standard Boltzmann code.
Our calculations allow us identifying the velocity terms as the leading
corrections on large scales, emphasizing the sensitivity of ARF to peculiar,
cosmological velocity fields. Just like for standard 2D clustering, the impact
of gravitational lensing on ARF is dominant on small angular scales and for
wide redshift shells, while the signatures associated to gravitational
potentials are extremely small and hardly detectable. The ARF also present
interesting correlation properties to anisotropies of the Cosmic Microwave
Background (CMB): they are highly correlated to CMB lensing potential
fluctuations, while also exhibiting a significant (S/N-) {\em
anti-}correlation with the Integrated Sachs-Wolfe effect (ISW). This negative
ARFISW signal is quite complementary to the standard 2D
clusteringISW correlation, since the former appears mostly at higher
redshift () than the latter (, and the combination of
the two observables significantly increases the statistics testing the
null (no ISW) hypothesis. We conclude that ARF constitute a novel, alternative,
and potentially powerful tool to constrain the nature of Dark Energy component
that gives rise to the ISW.Comment: 25 pages, 7 figures, comments welcome
A neural network emulator for the Lyman- 1D flux power spectrum
The Lyman- offers a unique avenue for studying the distribution of
matter in the high redshift universe and extracting precise constraints on the
nature of dark matter, neutrino masses, and other CDM extensions.
However, interpreting this observable requires accurate modelling of the
thermal and ionisation state of the intergalactic medium, and therefore
resorting to computationally expensive hydrodynamical simulations. In this
work, we build a neural network that serves as a surrogate model for rapid
predictions of the one-dimensional \lya flux power spectrum (),
thereby making Bayesian inference feasible for this observable. Our emulation
technique is based on modelling as a function of the slope and
amplitude of the linear matter power spectrum rather than as a function of
cosmological parameters. We show that our emulator achieves sub-percent
precision across the full range of scales ( to 4Mpc)
and redshifts ( to 4.5) considered, and also for three CDM
extensions not included in the training set: massive neutrinos, running of the
spectral index, and curvature. Furthermore, we show that it performs at the 1%
level for ionisation and thermal histories not present in the training set and
performs at the percent level when emulating down to
=8Mpc. These results affirm the efficacy of our emulation
strategy in providing accurate predictions even for cosmologies and
reionisation histories that were not explicitly incorporated during the
training phase, and we expect it to play a critical role in the cosmological
analysis of the DESI survey.Comment: 15 pages, 17 figure
Diffstar: A Fully Parametric Physical Model for Galaxy Assembly History
We present Diffstar, a smooth parametric model for the in-situ star formation
history (SFH) of galaxies. Diffstar is distinct from conventional SFH models
that are used to interpret the spectral energy distribution (SED) of an
observed galaxy, because our model is parametrized directly in terms of basic
features of galaxy formation physics. The Diffstar model assumes that star
formation is fueled by the accretion of gas into the dark matter halo of the
galaxy, and at the foundation of Diffstar is a parametric model for halo mass
assembly, Diffmah. We include parametrized ingredients for the fraction of
accreted gas that is eventually transformed into stars,
and for the timescale over which this transformation occurs,
some galaxies in Diffstar experience a quenching event at time and
may subsequently experience rejuvenated star formation. We fit the SFHs of
galaxies predicted by the IllustrisTNG (TNG) and UniverseMachine (UM)
simulations with the Diffstar parameterization, and show that our model is
sufficiently flexible to describe the average stellar mass histories of
galaxies in both simulations with an accuracy of dex across most of
cosmic time. We use Diffstar to compare TNG to UM in common physical terms,
finding that: (i) star formation in UM is less efficient and burstier relative
to TNG; (ii) galaxies in UM have longer gas consumption timescales, , relative to TNG; (iii) rejuvenated star formation is ubiquitous in UM,
whereas quenched TNG galaxies rarely experience sustained rejuvenation; and
(iv) in both simulations, the distributions of , , and share a common characteristic dependence upon halo
mass, and present significant correlations with halo assembly history.
[Abridged]Comment: 26 pages, 21 figure
Machine learning synthetic spectra for probabilistic redshift estimation: SYTH-Z
Photometric redshift estimation algorithms are often based on representative
data from observational campaigns. Data-driven methods of this type are subject
to a number of potential deficiencies, such as sample bias and incompleteness.
Motivated by these considerations, we propose using physically motivated
synthetic spectral energy distributions in redshift estimation. In addition,
the synthetic data would have to span a domain in colour-redshift space
concordant with that of the targeted observational surveys. With a matched
distribution and realistically modelled synthetic data in hand, a suitable
regression algorithm can be appropriately trained; we use a mixture density
network for this purpose. We also perform a zero-point re-calibration to reduce
the systematic differences between noise-free synthetic data and the
(unavoidably) noisy observational data sets. This new redshift estimation
framework, SYTH-Z, demonstrates superior accuracy over a wide range of
redshifts compared to baseline models trained on observational data alone.
Approaches using realistic synthetic data sets can therefore greatly mitigate
the reliance on expensive spectroscopic follow-up for the next generation of
photometric surveys.Comment: 14 pages, 8 figure
Consistent and simultaneous modelling of galaxy clustering and galaxy-galaxy lensing with Subhalo Abundance Matching
The spatial distribution of galaxies and their gravitational lensing signal
offer complementary tests of galaxy formation physics and cosmology. However,
their synergy can only be fully exploited if both probes are modelled
accurately and consistently. In this paper, we demonstrate that this can be
achieved using an extension of Subhalo Abundance Matching, dubbed SHAMe.
Specifically, we use mock catalogues built from the TNG300 hydrodynamical
simulation to show that SHAMe can simultaneously model the multipoles of the
redshift-space galaxy correlation function and galaxy-galaxy lensing, without
noticeable bias within the statistical sampling uncertainties of a SDSS volume
and on scales r = [0.6-30] Mpc/h. Modelling the baryonic processes in
galaxy-galaxy lensing with a baryonification scheme allows SHAMe's range of
validity to be extended to r = [0.1-30] Mpc/h. Remarkably, our model achieves
this level of precision with just five free parameters beyond those describing
the baryonification model. At fixed cosmology, we find that galaxy-galaxy
lensing provides a general consistency test but little additional information
on galaxy modelling parameters beyond that encoded in the redshift-space
multipoles. It does, however, improve constraints if only the projected
correlation function is available, as in surveys with only photometric
redshifts. We expect SHAMe to have a higher fidelity across a wider range of
scales than more traditional methods such as Halo Occupation Distribution
modelling. Thus it should provide a significantly more powerful and more robust
tool for analysing next-generation large-scale surveys.Comment: 14 pages, 7 figures. Submitted to MNRA
The cosmology dependence of the concentration-mass-redshift relation
The concentrations of dark matter haloes provide crucial information about
their internal structure and how it depends on mass and redshift -- the
so-called concentration-mass-redshift relation, denoted . We present
here an extensive study of the cosmology-dependence of that is based
on a suite of 72 gravity-only, full N-body simulations in which the following
cosmological parameters were varied: , ,
, , , , and
. We characterize the impact of these parameters on
concentrations for different halo masses and redshifts. In agreement with
previous works, and for all cosmologies studied, we find that there exists a
tight correlation between the characteristic densities of dark matter haloes
within their scale radii, , and the critical density of the Universe at
a suitably defined formation time. This finding, when combined with excursion
set modelling of halo formation histories, allows us to accurately predict the
concentrations of dark matter haloes as a function of mass, redshift, and
cosmology. We use our simulations to test the reliability of a number of
published models for predicting halo concentration and highlight when they
succeed or fail to reproduce the cosmological relation.Comment: 11 pages, 9 figure