The Role of AGN in Galaxy Evolution

UNIVERSITÀ DEGLI STUDI “ROMA TRE” DIPARTIMENTO DI MATEMATICA E FISICA Scuola dottorale in Matematica e Fisica - XXIX Ciclo Tesi di Dottorato in Fisica The role of AGN in galaxy evolution A thesis submitted for the degree of Doctor of Phylosophy Author: Dr. Federica Ricci Supervisor: Prof. Fabio La Franca Co-supervisors: Dr. Francesco Shankar, Dr. Francesco Massaro Thesis coordinator: Prof. Roberto Raimondi A. A. 2014 - 2016 PREFACE Extragalactic astrophysics is less than a century old and yet the first observations of active galactic nuclei (AGN) were recorded serendipitously even earlier, even though these “nebulae” were thought to reside inside our own Milky Way Galaxy. As AGN continued to be discovered over the years it became clear that they were among the most energetic phenomena in the Universe. Now we know that AGN are extremely luminous, emitting radiation over the whole electromagnetic spectrum. For many decades these energetic engines, residing at the centre of almost every galaxy, were considered fascinating rare objects. Over the last decade, more and more fundamental questions rose up to drive the study of these astrophysical black holes (BH). The existence itself of this kind of objects is intriguing, as they represent one of the strongest implications of the theory of General Relativity, and their study can give us useful clues on strong gravity effects in action. The emission processes, which allow us to detect such a kind of sources, originate from accretion flows or relativistic jets. Both of these mechanisms take place in regions very close to the BH, thus allowing to study not only the physics of matter in extreme conditions, but also radiative effects and relativistic magneto-hydrodynamics. They are really like the most extreme laboratories that we could ever imagine and that we could never being able to build on our Earth. Moreover, as a matter of fact, the AGN are among the strongest ionizing sources available in the Universe and as such can deeply affect its history. The transition from the so called dark ages to an ionized Universe involves the cosmological transformation of neutral hydrogen, which mostly resides in the inter galactic medium, into an ionized state. Again, AGN are really important in this process since they could be used as probes to determine the end of reionization (McGreer et al., 2015). Nonetheless the global details of the hydrogen reionization are clear, still which astrophysical population has the leading contribution between AGN and star-forming galaxies is unclear and none of the ionizing population is able to complete alone reionization at z 6. Fi- È nally, the central BHs affect the formation and evolution of the structures they live in, like galaxies, groups and clusters, and therefore play a key role in a broader cosmological context. The tight link between BH activity and galaxy evolution has been indicated by several discoveries: • the observation of a supermassive BH (SMBH) in most of the nearby bulge-dominated galaxies (see e.g. Gebhardt et al. 2000, Ferrarese and Merritt 2000, Marconi and Hunt 2003 and references therein); iii iv • the growth of SMBH happens mainly during active phases, and therefore most local bulge galaxies should have passed an active phase in their lifetime (see Soltan 1982 and Marconi et al. 2004); • the evolution of active BHs (Ueda et al. 2003; Hasinger et al. 2005; La Franca et al. 2005) and of star-forming galaxies (Cowie et al. 1996; Franceschini et al. 1999) have a very similar shape. All these evidences push forward a linked growth of galaxies and AGN, in the so-called AGN/galaxy co-evolution scenario. Indeed the accretion of matter on the supermassive black holes and the related radiative and kinetic power outputs play an important role in the galaxy evolution, by suppressing/tuning the star formation and feeding the AGN itself (feedback; e.g. Silk and Rees, 1998; Fabian and Iwasawa, 1999; Croton et al., 2006; Cattaneo et al., 2009; Fabian, 2012, for a review). In this framework, it appears clear that the study of AGN evolution is very important to understand the evolution of the star formation rate and galaxies in the Universe (AGN/galaxy co-evolution). Moreover, the existence of the scaling relationships between the AGN BH mass and the bulge properties of galaxies, implies that the evolution of galaxies and the growth of SMBHs are intricately tied together. Thus, in order to obtain a clear picture of the AGN/galaxy co-evolution, it is important to accurately derive the shape and the evolution of both AGN luminosity and SMBH mass functions. There is still room to the realization of a complete BH mass census of AGN, as the reliable methods usually used to weigh SMBHs are really observationally challenging and yet far to be applied beyond the local Universe. Even a complete study of the local AGN population can be hardly said to be unbiased versus a specific class of sources, the AGN2 which are among the most elusive AGN classes. These sources are enshrouded in some dusty opaque medium which happens to lie along our line of sight and blocks the direct view of the central engine (Antonucci, 1993). This dusty material does not allow us to directly probe the innermost region of the BH where the broad line region (BLR) resides, whose dynamics are often used in the so-called virial estimators to measure the central mass of the BH. The work performed in this thesis is inserted in this scientific framework. We have developed virial BH mass estimators that make use of the less affected by dust extinction NIR emission lines in combination with the intrinsic hard X–ray continuum luminosity of the AGN, which suffers less from galaxy starlight contamination. Such relations represent useful tools since they open the possibility to work also with obscured and low- luminosity AGN, allowing us to derive for the first time a virial measure of the AGN2 BH masses. We have started a systematic NIR spectroscopic campaign in order to observe a sample ( 40) of hard X–ray selected obscured and intermediate AGN (AGN2, AGN1.9 » and AGN1.8) from the Swift/BAT 70 month hard X–ray survey. We have observed the selected sources using the NIR spectrographs ISAAC at VLT and LUCI at LBT, and also using v the multiwavelenght spectrograph Xshooter at VLT. We found broad component in BLR emission lines (Pa¯ and He I) in 30% of our sources and, applying to them the NIR virial » estimator, we have been able to measure in a direct way the AGN2 BH masses, finding that AGN2 have on average lower BH masses and higher Eddington ratios with respect to AGN1 of same luminosity. Thanks to these measurements, we also started to investigate the connection between the BH masses of our sample of AGN2 and some properties of the host, such as the stellar velocity dispersion and the bulge luminosity, thus shedding light on the AGN/galaxy co-evolution scenario in a direct way also for these sources. This project is still ongoing as new data at LBT are being collected (13.5 hours proposal as PI accepted). A part of this thesis is dedicated to a project in which I have been involved during my PhD, which consists of optical identification of γ-ray emitting AGN. Due to their broad spectral energy distribution that goes up to gamma rays, AGN are also one of the main extragalactic populations that contribute significantly to the gamma ray diffuse back- ground emission. The Fermi satellite is performing an all-sky survey in the gamma-ray but still 1/3 of its sources are unidentified. These sources could be galactic dark matter or could have extragalactic origin. Our group has successfully applied two new association methods to recognize if there is a blazar counterpart within the positional uncertainty region of unidentified γ-ray sources (UGSs). Adopting these procedures, we identified γ-ray blazar and BL Lac candidates as possible counterparts for 40% of the UGSs listed » in the 2nd Fermi LAT catalog. Our methods are based on the infrared data of the WISE all-sky survey and on the low frequency radio observations performed with the Wester- bork Synthesis Radio Telescope. This optical blazar follow-up campaign answers to one of the main scientific objectives of the Fermi-NOAO Cooperative Arrangement, which is: “the study of the candidate counterparts, including redshift determination of previously unknown BL Lacs and high-redshift blazars”. Our successful campaign is still on-going, as new proposals have been accepted. Inside this campaign I have performed two runs of optical spectroscopic observations at the 4-meter class telescope SOAR, both in visit- ing and remotely. The study presented in this thesis is the analysis of the 2014 follow-up campaign performed both in the southern and northern hemispheres. As the aim of this thesis is to give a contribution inside the big AGN/galaxy picture pro- viding observational constraints on the influence of AGN on the evolution of galaxies, the thesis also presents an investigation carried out throughout cosmic time, starting from z 0 up to z 6. In this work we try to assess the true ionizing output of the entire AGN Æ » population in order to understand their cosmological role during the reionization. This study makes use of complete X–ray selected samples, including deep Chandra and COS- MOS data, together with a compilation of optical surveys. vi A general overview of our current theoretical understanding (or lack thereof) of the AGN phenomenon, their physical and observational characteristics, and their classifica- tion inside the unified model framework are summarized in Chapter1, while in Chapter 2 the main methods currently available to derive the AGN BH mass estimates are de- scribed.

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