The Accurate Census of Middle-aged Galaxies (Cosmology)

Thanks to the analysis of the latest data published in July by the European Lega-C observing program, astronomical observations of several thousand galaxies at a cosmic epoch between five and eight billion years ago are available for the first time, with sufficient accuracy to analyze the detailed characteristics of the populations of the stars they contain. Researchers from the National Institute of Astrophysics (INAF) are also part of the international collaboration. All the results on Astronomical Journal

The scientific results based on the analysis of the data produced by the latest release  of  Lega-C have just been published  , a real census of remote galaxies carried out with the Vimos  instrument  installed on the ESO Very Large Telescope in Chile between December 2014 and March 2018.

Thanks to Lega-C, astronomical observations of several thousand galaxies in a cosmic epoch between five and eight billion years ago are available for the first timewith a precision able to allow scientists to derive the detailed characteristics of the stellar populations present in the galaxies of the sample itself. These results allow us to study the even distant past of galaxies in greater detail than we can with galaxies in our cosmic neighborhood. The accurate measurements collected for the League-C sample of galaxies allow, for the first time, to directly compare the predictions of the theoretical models with observations at that particular interval in the history of the universe. In this way it is also possible to improve the models themselves and the understanding of the physics that govern the evolution of galaxies.

The study published today in the  Astronomical Journal  and led by Po-Feng Wu of the Institute of Astronomy and Astrophysics in Taipei (Taiwan), in which  Anna Gallazzi  and  Stefano Zibetti of INAF participated, shows that there is a good general agreement between the demographics of the observed galaxies and the data obtained in the simulations, regarding age and star formation processes. “It is an important step forward for the theoretical models used, especially if we consider that until a few years ago it was not even possible to reproduce the size of galaxies”, comments Gallazzi, INAF researcher in Florence and survey scientistof Lega-C. “The Lega-C data proved essential to achieve these results, thanks to the considerable progress made in reducing selection errors and systematic uncertainties that particularly affect the quantities involved in this study”.

The third and last release of Lega-C (DR3) data took place on July 31, 2021 and offers the entire scientific community a catalog of over 3000 galaxies  with direct spectroscopic measurements and some derived physical parameters. Compared to  releasesnot only increases the statistics (and therefore also the possibility of studying classes of rarer objects) but significantly improves the quality of the data reported which has allowed us to obtain measures that were not possible before and which are instead fundamental to know some properties of the populations of stars present in galaxies, such as their metallicity, or the abundance of heavy elements in their composition. “The DR3 also marks the beginning of full exploitation, not only by the collaboration but by the entire scientific community concerned, of spectroscopic measurements for a complete sample of intermediate redshift galaxies”, adds Stefano Zibetti, also he researcher of INAF in Florence and in the Lega-C team. «These represent a reference for a comparison both with simulations and with similar observations of the local universe. These data are also the ideal starting point for planning deep spectroscopic observations at intermediate redshift and in the distant universe with new generation instruments ».

Featured image: The evolution of three different galaxies as it emerges from the numerical simulation “Illustris-Tng”: each row of images represents each galaxy at different cosmic epochs, from 12.5 billion years ago (z = 5) to today, passing through the epoch where Lega-C observed (7.8 billion years ago, z = 1). The images of the upper panel represent the visible light of the stars, while the lower panels represent the distribution in gas. Credits: The Illustris Collaboration (2018)

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Provided by INAF

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