I did my doctoral thesis on the large-scale structure of the Universe in the Institute of Space Sciences and a postdoc at the University of Pennsylvania. My focus was to compare data from large-scale surveys with standard cosmological theories with the objective of determining the best theories (and ruling out theories uncompatible with observations) and constraining the values of the different components of the Universe. This is my research keyword cloud, created with Scimeter

See my publications:

ADS publications  / astro-ph archive  / Download thesis

Summary

Physicists currently believe that the universe is composed basically of dark energy (70%) and dark matter (25%), both unknown components. The rest is made of known (baryonic) matter.

The standard cosmological model starts with Big Bang, followed by a rapid period of expansion of the universe called inflation. After that, tiny almost homogeneous fluctuations that conform the primordial universe, start to grow while universe expands now in a relatively slow rhythm. 380,000 years after the Big Bang, the temperature is low enough to make the universe become neutral after the recombination of atoms with electrons. Photons are almost free of interactions since then and reach us in the form of a Cosmic Microwave Background (CMB). We can measure the spatial anisotropy spectrum of CMB temperatures and compare it to the expected spectrum of acoustic oscillations. This comparison provides a direct geometrical test from which we can deduce that universe is flat or nearly flat. This can be explained if we introduce a new constituent in the universe apart from matter, the dark energy. Dark energy acts as anti-gravity that accelerates the expansion and is also observed through standard candles Supernovae Ia. Although there is a well motivated model that can explain observations, neither dark matter nor dark energy are known elements, so it is important to use the large amount of newly available data to obtain tighter constraints on the constituents of the universe, the evolution of growth perturbations, the expansion history, and also to explore other alternatives, such as modification of gravity.

I worked with data from the Sloan Digital Sky Survey and with simulations that were prepared for Dark Energy Survey, that is now ongoing. I mostly used Luminous Red Galaxies as my favourite tracer of dark matter. These galaxies are intrinsically bright and hence can be seen further away and trace a larger volume than normal galaxies. I studied the redshift space distortions that arise due to the peculiar motion of galaxies, when shifts in the light spectrum due to the movement of galaxies are confused with the shifts due to the expansion of the Universe. These distortions are one of the ways that cosmologists have to study directly the growth of perturbations in the space-time. I also worked on the Integrated Sachs Wolfe effect (ISW), another direct way to study the growth trough the evolution of gravitational potentials. ISW is detected when cross-correlating the remote cosmic microwave map with any more recent map that traces Large Scale Structure. Photons from the CMB can be modified when passing through the potential wells created by the large scale strucutre, if for example these potentials change with time. We can detect dark energy thanks to ISW, since we need a dark energy dominated universe to have an evolution of gravitational wells (although this could also be achieved by having a non-flat universe). Luminous Red Galaxies galaxies also allowed us to detect the baryon acoustic peak in the averaged correlation function, and we also detected it in the line-of-sight direction, which means a direct calculation of the Hubble constant! I also worked with photometric surveys (angular projections, photometric redshifts). I worked on modeling weak gravitational lensing as a way to also determine the dark matter in the Universe. Light from far away galaxies is bended when passing through all the dark matter between them and us. Finally, I was studying how to detect (or rule out) a type of modified gravity in dwarf (small) galaxies.