Dissertation committee:
Καλλιόπη Δασύρα, Επίκουρη Καθηγήτρια, Τμήμα Φυσικής, ΕΚΠΑ,
Δέσποινα Χατζηδημητρίου, Καθηγήτρια, Τμήμα Φυσικής, ΕΚΠΑ,
Νεκτάριος Βλαχάκης, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ,
Μανώλης Ξυλούρης, Διευθυντής Ερευνών, ΙΑΑΔΕΤ, Εθνικο Αστεροσκοπείο Αθηνών,
Θεοχάρης Αποστολάτος, Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ,
Μαρία Πετροπούλου, Επίκουρη Καθηγήτρια, Τμήμα Φυσικής, ΕΚΠΑ,
Στυλιανός Καζαντζίδης, Επίκουρος Καθηγητής, Τμήμα Φυσικής, ΕΚΠΑ
Summary:
Observational evidence suggests that the Star formation process in the universe peaked at 3.5 billion years after the Big Bang and declined in the last 10 billion years. While this decline can be partially associated with star formation itself, since stars consume gas and only return a small percentage of gas back to the galactic reserve, cosmological simulations cannot reproduce today’s galactic mass distribution in the high-mass branch. This hints at the existence of additional mechanisms negatively impacting star formation in high-mass galaxies.
The presence of supermassive black holes and their impact on their galactic host environment have been proposed as one of the main contributors to this negative feedback effect. As black holes grow in the center of the galaxies, it emits energy from its accretion disk either in the form of radiation pressure or as relativistic plasma jets. This energy can be coupled with the interstellar medium (ISM), affecting the molecular gas essential for forming new stars. Simulating this contribution in cosmological simulations succeeds in reproducing the expected mass distribution in the local universe.
Studies of hydrodynamic simulations of jets propagating through the ISM have shown that they can be a very efficient mechanism for providing this ISM-AGN coupling. Shocks produced from this jet-ISM interaction sweep large areas of a galaxy, heating and causing turbulence in the ISM as the jet percolates and breaks freely into intergalactic space.
This thesis aims to further investigate the jets as feedback mechanisms. In the first part, we focus on constructing and analyzing a radio-selected, multi-epoch, sample of galaxies observed in CO emission lines in the millimeter part of the electromagnetic spectrum to understand their molecular gas content in low and high redshift. This work utilizes a combination of ALMA observations, either as target observations or byproducts of calibration, and measurements from the literature. We detected CO emission in 35% of the sample radio galaxies, with molecular masses ranging from 1e7 1e10 solar masses) were not significantly lower with star-forming AGNs, suggesting that they are not entirely "red and dead". At higher redshifts, the observed radio galaxies had a significant amount of molecular gas, with about 1/4 of them having molecular gas amounts comparable to what simulations suggest for typical galaxy halos of that epoch. For the brightest sources, there is a consistency in molecular gas content across all epochs, suggesting that the interplay of inflows, star formation, and radio-mode feedback maintains a certain level of molecular gas.
Another goal of this survey was to lead to the detection of molecular outflows. In the second part of this thesis, we present a detailed kinematic analysis of one of the two sources with obvious kinematic deviations: the early-type galaxy NGC6328, which hosts the closest known Gigahertz Peaked radio Source (GPS) PKS1718-649. The data cubes for the re-calibrated CO(2-1) and CO(3-2) ALMA archival data revealed that the molecular gas had a highly complicated geometry that could not be estimated with any tool available in the literature. Thus, we created a novel accurate warped disk model that incorporates the evolution of the disk due to gravitational potential torques together with the effect of viscous forces. The fitting of the data and the model was done using a Bayesian framework on parameter and model estimation. This choice provided us the opportunity to combine multiple datasets (HI velocities, photometry, dust obscuration patterns) into a single probabilistic model, which resulted in a distribution of possible geometry and mass potential models. These models jointly point out the scenario of a highly warped molecular disk emerging from a merger incident estimated at 400-800 Myr ago. From the residuals of the fit, we detect two molecular outflows in the central 200 pc of the galaxy. The outflows, validated through gas excitation analysis and newly observed ionized gas outflows, have a total mass outflow rate of 3 solar masses per year and a kinetic power of 2-7e40 ergs per second, which suggests jet-driven outflows as the most plausible scenario for their acceleration. This adds NGC6328 to the catalog of sources, along with NGC1377, 4C 31.04, ESO 420-G13 and HE 0040−1105, where jet-induced outflows are detected but outside the current radio emission of the jet.
Motivated by this observation, we delved into various mechanisms and revisited the likelihood of a connection between published molecular outflows and jets. In the third part of this thesis, we conducted a meta-analysis encompassing a sample of 45 local galaxies with detected molecular outflows, augmented by the inclusion of galaxies NGC6328, NGC1377, 4C 31.04, and ESO 420-G13. Our analysis revealed that, for at least half of this extended sample, the jets align both energetically and geometrically with the observed outflows, positioning them as a significant or even dominant mechanism in driving these outflows.
Keywords:
active galaxies, black holes, star formation, jets, molecular outflows
