## Found 60 talks archived in *Cosmology*

### Abstract

The standard cosmological model has been established and its parameters are now measured with unprecedented precision. However, there is a big difference between modelling and understanding. The next decade will see the era of large surveys; a large coordinated effort of the scientific community in the field is on-going to map the cosmos producing an exponentially growing amount of data. This will shrink the statistical errors. But precision is not enough: accuracy is also crucial. Systematic effects may be in the data but may also be in the model used in their interpretation. I will present a small selection of examples where I explore approaches to help the transition from precision to accurate cosmology. This selection is not meant to be exhaustive or representative, it just cover some of the problems I have been working on recently.

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Planck satellite provides for the first time the possibility to detect galaxy clusters using their Sunyaev-Zeldovich (SZ) effect signature covering the full sky (Planck Col XXIX, 2013). Planck SZ catalogs I and II include more than 1900 sources, of which 700 remain unknown. The study of the purity of these samples and the characterization of SZ sources is essential to perform cosmology with cluster counts. With this aim in mind, the IAC-Planck group is performing the optical validation and characterization of these samples through two long-term observing programs at Canary Island observatories, the ITP 13B15A and the large-term 15B-17A. In this talk we will present intermediate results of this validation program. Using photometric and spectroscopic information (mainly multi-object techniques) we estimate redshifts and dynamical masses in order to minimize the errors in the Msz-Mdyn scaling relation and the SZ clusters mass function which allow a better determination of cosmological parameters (mainly Omega_m, sigma_8 and neutrino mass) from Planck SZ survey.

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The cosmological large-scale structure encodes a wealth of information about the origin and evolution of our Universe. Galaxy redshift surveys provide a 3-dimensional picture of the luminous sources in the Universe. These are however biased tracers of the underlying dark matter field. I will discuss the different components which are relevant to model galaxy bias, ranging from deterministic nonlinear, over non-local, to stochastic components. These effective bias ingredients permit us to save computational time and memory requirements, to efficiently produce mock galaxy catalogues. These are useful to study systematics of survey, test analysis tools, and compute covariance matrices to perform a robust analysis of the data. Moreover, this description permits us to implement them in inference analysis methods to recover the dark matter field and its peculiar velocity field. I will show some examples based on the largest sample of luminous red galaxies to date based on the final BOSS SDSS-III data release.

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The Cosmic Microwave Background (CMB), the fossil light of the BigBang, is the oldest light that one can ever hope to observe in ourUniverse. The CMB provides us with a direct image of the Universe whenit was still an "infant" - 380,000 years old - and has enabled us to obtaina wealth of cosmological information, such as the composition, age,geometry, and history of the Universe. Yet, can we go further and learnabout the primordial universe, when it was much younger than 380,000years old, perhaps as young as a tiny fraction of a second? If so, thisgives us a hope to test competing theories about the origin of theUniverse at ultra high energies. In this talk I present the results from theWilkinson Microwave Anisotropy Probe (WMAP) satellite that Icontributed, and then discuss the recent results from the Plancksatellite (in which I am not involved). Finally, I discuss future prospectson ourquest to probe the physical condition of the very early Universe.

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I will present results from The X-Shooter Lens Survey (XLENS). With XLENS we are unambiguously separate the stellar from the dark-matter content in the internal region of lens early-type galaxies (ETGs) to understand their interplay and to probe directly their formation and dynamical evolution. We combine precise strong gravitational lensing and dynamical constraints on the mass distribution with high signal-to-noise spectroscopy in the entire rest-frame visible to the NIR.In this talk I will present results obtained on a sample of very massive lens ETGs from the SLACS Survey, with velocity dispersions greater than 250 km/s and redshift>0.1.

First I will show how to constrain the low mass end of the Initial Mass Function (IMF)directly from galaxy optical spectra using a new set of non-degenerate optical spectroscopic indices which are strong in cool giants and dwarfs and almost absent in main sequence stars (Spiniello et al., 2014a). I will present unambiguous evidence that the low-mass end of the IMF is not universal. Then, I will demonstrate that the combination of this SSP modelling with a fully self-consistent joint lensing+dynamics analysis (Barnabè et al. 2012) allows us to disentangle IMF slope variations from internal dark-matter variations and, for the first time ever, to contemporary put constrains on the IMF cutoff mass (Barnabè et al., 2013, Spiniello et al., in prep).

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Almost all cosmologists accept nowadays that the redshift of the galaxies is due to the expansion of the Universe (cosmological redshift), plus some Doppler effect of peculiar motions, but can we be sure of this fact by means of some other independent cosmological test? Here I will review some recent tests: CMBR temperature versus redshift, time dilation, the Hubble diagram, the Tolman or surface brightness test, the angular size test, the UV surface brightness limit and the Alcock-Paczynski test. Some tests favour expansion and others favour a static Universe. Almost all the cosmological tests are susceptible to the evolution of galaxies and/or other effects. Tolman or angular size tests need to assume very strong evolution of galaxy sizes to fit the data with the standard cosmology, whereas the Alcock-Paczynski test, an evaluation of the ratio of observed angular size to radial/redshift size, is independent of it.

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The standard model of cosmology is based on the Friedmann-Robertson-Walker (FRW) metric. Often written in terms of co-moving coordinates, this elegant and highly practical solution to Einstein's equations is based on the Cosmological principal and Weyl's postulate. But not all of the physics behind such symmetries has yet been recognized. We invoke the fact that the co-moving frame also happens to be in free fall to demonstrate that the FRW metric is apparently valid only for a medium with zero active mass. In other words, the application of FRW appears to require an equation-of-state rho+3p = 0, in terms of the total energy density rho and total pressure p. Though the standard model is not framed in these terms, the optimization of its parameters brings it ever closer to this constraint as the precision of the observations continues to improve. For example, the latest high-precision BAO measurements rule out the standard model at better than the 99.34% C.L. if the zero active mass condition is ignored.

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The extragalactic background light (EBL) is the second most energetic diffuse background that fills our Universe. It is produced by star formation processes and supermassive black hole accretion over the history of the Universe. Thus, it contains fundamental information about galaxy evolution and cosmology. Interestingly, it brings together classical astronomy and high energy astrophysics since gamma-rays from extragalactic sources such as blazars and gamma-ray bursts interact by pair-production with EBL photons. Therefore, it is also essential for extragalactic gamma-ray astronomy to understand precisely and accurately the EBL in order to interpret correctly high energy observations. In this talk, I will review the present EBL knowledge, and describe how we can extract information, such as the value of the expansion rate of the Universe, from the EBL. Finally, the latest all-sky Fermi-LAT catalog of hard sources (E>50 GeV), called 2FHL, and future directions of EBL research will also be discussed.

### Abstract

Current scientific cosmology hosts a plurality of scenarios that articulate in different ways the precision astronomy's observations. However, this palette of alternatives is not taken as the true scientific production. There is a monist tendency to think that scientific results should be represented by a single scenario. The present work seeks to undermine the attempts to justify that tendency and to show that even if a single and final stage is waiting, methodological pluralism also would be the best option to achieve it.

### Upcoming talks

- Dust in the Reionization Era: ALMA Observations of a z = 8.38 Gravitationally Lensed GalaxyDr. Ismael Perez Fournon, Dr. Alina StreblyanskaTuesday April 4, 2017 - 12:30
- Quantum Science and TechnologyProf. Ignacio CiracThursday April 20, 2017 - 10:30