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Constraining Stellar Mass and Supermassive Black Hole Growth through Cosmic Times: Paving the way for the next generation sky surveys

Final Report Summary - COSMASS (Constraining Stellar Mass and Supermassive Black Hole Growth through Cosmic Times: Paving the way for the next generation sky surveys)

Understanding how galaxies form in the early universe and their subsequent evolution through cosmic time is a major goal of modern astrophysics. Panchromatic look-back sky surveys significantly advanced the field in the past decade, and we have recently entered an even more fruitful period - a 'golden age' of radio astronomy - with new facilities delivering an order of magnitude increase in sensitivity, such as the Karl G. Jansky Very Large Array (VLA), Australia Telescope Compact Array (ATCA) and Atacama Large Millimeter/submillimeter Array (ALMA).

The basis of the ERC project is provided by two unique, state-of-the-art radio sky surveys with the VLA and ATCA/GMRT that carry the potential to push to the next frontiers and reveal the mechanisms that shape galaxies over cosmic time. The ERC project was intended to focus on the growth of stellar and supermassive black-hole mass in galaxies throughout cosmic time, and this has been achieved as follows.

Over 850 hours of observations were taken with the VLA, ATCA, GMRT, PdBI/NOEMA and ALMA interferometers, and reduced, imaged, tested and analyzed. Eight verified and tested radio- and mm-continuum data-sets were released to the public (VLA-COSMOS 3 GHz Large Project, ATCA-XXL-S 2.1 GHz Pilot and Full projects, GMRT-XXL-N 610 MHz project, GMRT-COSMOS 325 and 610 MHz projects, ALMA-COSMOS observations of ASTEC/JCMT&ASTE SMGs). They set the basis for the science exploration of the project, important also for the preparation and success of surveys with future large facilities like ASKAP (Australian Square Kilometre Array Pathfinder).

We probed the contribution of various types of galaxies over cosmic time at faint, sub-micro-Jansky, radio levels, revealing the debated abundance of faint radio sources. Via direct determination, extrapolation, and modeling we found that radio source counts at sub-micro-Jansky levels are dominated by star-forming galaxies.

We explored star formation conditions at early cosmic times out to a redshift of about 6 in various ways and for the first time we derived the dust-unbiased cosmic star formation history since a red shift of 6 based on the VLA-COSMOS 3 GHz Large Project radio data.

We studied high-redshift starbursting galaxies (submillimeter galaxies or SMGs), and their role in galaxy formation and evolution through series of papers based on PdBI and ALMA intermediate resolution observations towards > 150 SMGs out to a redshift of about 5.5. We found that their radio- continuum sizes are surprisingly larger than their IR-continuum sizes, that they may reside in overdense environments, and that z>3 SMGs may be the progenitors of compact, z~2, red galaxies.

We explored radio sources associated with galaxies hosting supermassive black holes (active galactic nuclei or AGN), with different black-hole accretion modes, as well as their roles in galaxy evolution, and their relation to the cosmic star formation history. We found that i) the source of radio emission in high-accretors is predominantly star-formation related, ii) low-accretors reside in more massive haloes, iii) radio AGN have played an important role in the context of the so-called radio-mode feedback in galaxy evolution, iv) the radio AGN luminosity density peaks at a similar redshift as the star formation rate density.

In total eight ERC team members (four postdocs, three PhD students and PI) at the Department of Physics, Faculty of Science, University of Zagreb focused on the ERC project's science. A total of 61 refereed publications in astrophysical journals was published. Dissemination was extensively done via a) presentations at a number of astrophysical meetings, workshops and conferences, b) colloquia at institutes/universities, c) public presentations, d) TV, radio, magazine, and newspaper interviews, and an established astrophysics blog (in Croatian, https://astroucionica.hr).