An illustration showing the evolution of the Universe from cosmic inflation to the present day. Small deviations of the initial fluctuations from a perfectly Gaussian distribution, known as primordial non-Gaussianity, may have left a mark on the formation of large-scale structure and on the distribution of objects such as quasars. The study uses this signal to extract information about the conditions of the early Universe from maps of galaxies and quasars.
An international team, led by researchers at Instituto de Astrofísica de Canarias (IAC), has developed a new method to extract information from the galaxy maps that trace the large-scale structure of the Universe and better understanding the physics of the early Universe right after the Big Bang. The study has been published in the journal "Astronomy & Astrophysics".
The current best knowledge about the early Universe sets that right after the Big Bang our Universe entered in an accelerated expansion phase, that lasted only a tiny fraction of second and multiplied the size of the Universe by a factor of 1026 which is the result of multiplying 26 times by 10. This paradigm is called cosmic inflation, and was proposed in the early 1980s. Cosmic inflation also predicts the formation of primordial fluctuations in the space-time energy distribution, that later would evolve until forming the galaxies that we can observe today. However, it is not yet clear which physical model better describes the inflationary process. To understand it, cosmologists are looking for a possible fingerprint of this initial phase of our Universe in the galaxies distribution that we observe today with maps of the Universe made with both ground-based and space telescopes.
The simplest physical models of inflation predicts the galaxies we observe nowadays should follow a distribution with a given statistical pattern. However, more complex models can induce changes in these patterns. Through what cosmologists call the primordial non-Gaussianity parameter, it is possible to get a fossil signal of the early Universe that remains in the cosmic web formed by galaxies. “To get strong conclusions about inflation we need to increase the precision of this parameter measurements, something that we try to achieve with the current generation of large-scale structure surveys” explains José R. Bermejo-Climent, researcher at Konkoly Observatory in Budapest and former researcher at IAC.
The scientists used for their study the Quaia quasar catalog obtained by Kate Storey-Fisher, researcher at Stanford, from the Gaia ESA satellite data. This mission has mapped our own Mikly Way for above 10 years, but it also allowed to observe very distant extragalactic objects like quasars. “Even if the Gaia mission was not originally designed to study the large-scale structure of the Universe, the telescope has observed above a million quasars, covering the largest volume of these objects ever sampled, and this allows us to trace precisely the matter distribution of the Universe” says Kate Storey-Fisher, coauthor of the article.
The novelty of this study is the development of a new technique to better take advantage of the catalogs information. This technique analyzes not only the changes in the density of galaxies along the observed sky footprint, but also how the redshift that estimates the distance to the same galaxies fluctuates. “The analyses of large-scale structure datasets can be improved If we add the angular redshift fluctuations as extra cosmological observable” says Carlos Hernández-Monteagudo, researcher at IAC. In particular, thanks to this new methodology, the researchers improved by 25% the measurement of the primordial non-Gaussianity parameter that is achieved with standard techniques. In this way, the scientists have put a measurement of this non-Gaussianity parameter that currently is the second tightest constraint obtained with galaxy catalogs, and the best one achieved with photometric dataset that do not measure directly the distance to galaxies.
In the future, the researchers plan to apply this novel method to the data from big galaxy surveys of this decade. “We are in an exciting era for cosmology, with experiments such as DESI, Euclid, LSST and SPHEREx, that will improve our understanding of the cosmological model thanks to datasets with an unprecedented volume and sensitivity, but also thanks to new analysis methods such as the one we have developed” adds José R. Bermejo-Climent.
The study counted also on the participation of Alba Crespo-Pérez (PhD student at IAC and ULL), Jorge Martin Camalich (researcher at the IAC and project lead for UNDARK, a European project funded by the European Union through the Widening programme), David Alonso (researcher at Oxford University) and Giulio Fabbian (researcher at Institut d’Astrophysique Spatiale).
Article: J. R. Bermejo-Climent, C. Hernández-Monteagudo, A. Crespo-Pérez, J. Martin Camalich, D. Alonso, G. Fabbian and K. Storey-Fisher. “Improving constraints on primordial non-Gaussianity from Quaia with a new cosmological observable: Angular redshift fluctuations’’, Astronomy & Astrophysics 710, A360. DOI: https://doi.org/10.1051/0004-6361/202659114
Contact:
José R. Bermejo-Climent, jose.bermejo [at] csfk.org (jose[dot]bermejo[at]csfk[dot]org)
Carlos Hernández-Monteagudo, chm [at] iac.es (chm[at]iac[dot]es)
