Galaxies on the road to quenching

This thesis explores the properties of galaxies that reside in high density regions in the local Universe. The driving motivation is to shed light on how galaxies stop forming stars and the role played by the environment in this process. A wide variety of environmentallyrelated quenching mechanisms have been proposed and the smoking gun proving that these are actually transforming galaxies from being star forming to passive is the existence of a population of galaxies in transition with intermediate features. In this Thesis I will mainly focus on the properties of two population of galaxies: those that are forming stars at a reduced level compared to other galaxies at similar mass, and those that have recently and abruptly interrupted their star formation. The data exploited in this Thesis come from surveys which focus on different environments in the local Universe: the WIde-field Nearby Galaxy-cluster Survey (WINGS, Fasano et al. 2006) with its recent extension OmegaWINGS (Gullieuszik et al., 2015a, Moretti et al. submitted) and the Padova Millennium Galaxy and Group catalogue (PM2GC, Calvi et al. 2011). The Thesis starts with a characterization of the WINGS survey and then focuses on the new OmegaWINGS data, illustrating the most important aspects of the photometric and spectroscopic observations. I will describe in detail my personal contribution to the survey, from the data analysis to the redshift and velocity dispersion measurements, to the membership assignments. I will also present the complete galaxy catalog built from the combination of the two cluster surveys considered. While halo mass estimates are quite easily obtained for clusters, at the group regime it is less straightforward to derive robust measurements. I will then present a procedure I developed to compute halo masses from observable quantities for the PM2GC. My approach exploits mock galaxy catalogs extracted from the De Lucia & Blaizot (2007) semi-analytic model, run on the Millennium Simulation (Springel et al. 2005). Subsequently, I will discuss the methods adopted to compute the galaxy stellar properties, exploiting both spectroscopic and photometric information. Using the data from the WINGS+OmegaWINGS surveys, I will present an analysis of the ongoing Star Formation Rate (SFR) and the Specific Star Formation Rate (SSFR) - stellar mass (M∗) relations in field and cluster mass limited samples. I contrast trends in the different environments and, in clusters, at different clustercentric distances. The main result is that in clusters a population of galaxies with a reduced SFR is detected, named transition galaxies, which is much rarer in the field. The spatial location of these galaxies, together with the analysis of the star formation histories, colors and average ages, suggest that transition galaxies have had a reduced SFR for the past 2-5 Gyr. This is compatible with a strangulation scenario, even if other processes like ram pressure stripping can not be excluded. I characterize the properties of post starburst (PSB) galaxies, which are galaxies that abruptly interrupted their star formation sometimes during the past 2Gyr), the other a rapid truncation of the star formation activity (t∼0.1Gyr). Comparing the fraction of PSBs to the fraction of galaxies in transition, it appears that the short timescale star-formation quenching channel contributes two times more than the long timescale one to the growth of the passive population in clusters. The emerging picture is that ram pressure stripping is probably the most successful process affecting star formation in clusters, followed by strangulation. Other mechanisms might play a role, even though they most likely take place in lower density environments

From blue star-forming to red passive: galaxies in transition in different environments

Exploiting a mass complete (M_*>10^(10.25)M_sun) sample at 0.03<z<0.11 drawn from the Padova Millennium Galaxy Group Catalog (PM2GC), we use the (U-B)_rf color and morphologies to characterize galaxies, in particular those that show signs of an ongoing or recent transformation of their star formation activity and/or morphology - green galaxies, red passive late types, and blue star-forming early types. Color fractions depend on mass and only for M_*<10^(10.7)M_sun on environment. The incidence of red galaxies increases with increasing mass, and, for M_*<10^(10.7)M_sun, decreases toward the group outskirts and in binary and single galaxies. The relative abundance of green and blue galaxies is independent of environment, and increases monotonically with galaxy mass. We also inspect galaxy structural parameters, star-formation properties, histories and ages and propose an evolutionary scenario for the different subpopulations. Color transformations are due to a reduction and suppression of SFR in both bulges and disks which does not noticeably affect galaxy structure. Morphological transitions are linked to an enhanced bulge-to-disk ratio due to the removal of the disk, not to an increase of the bulge. Our modeling suggests that green colors might be due to star formation histories declining with long timescales, as an alternative scenario to the classical "quenching" processes. Our results suggest that galaxy transformations in star formation activity and morphology depend neither on environment nor on being a satellite or the most massive galaxy of a halo. The only environmental dependence we find is the higher fast quenching efficiency in groups giving origin to post-starburst signatures.Comment: 20 pages, 12 figures, accepted for publication in Ap

The star formation history of galaxies: the role of galaxy mass, morphology and environment

We analyze the star formation history (SFH) of galaxies as a function of present-day environment, galaxy stellar mass and morphology. The SFH is derived by means of a non-parametric spectrophotometric model applied to individual galaxies at z ~ 0.04- 0.1 in the WINGS clusters and the PM2GC field. The field reconstructed evolution of the star formation rate density (SFRD) follows the values observed at each redshift (Madau & Dickinson 2014), except at z > 2 where our estimate is ~ 1.7x higher than the high-z observed value. The slope of the SFRD decline with time gets progressively steeper going from low mass to high mass haloes. The decrease of the SFRD since z = 2 is due to 1) quenching - 50% of the SFRD in the field and 75% in clusters at z > 2 originated in galaxies that are passive today - and 2) the fact that the average SFR of today's star-forming galaxies has decreased with time. We quantify the contribution to the SFRD(z) of galaxies of today's different masses and morphologies. The current morphology correlates with the current star formation activity but is irrelevant for the past stellar history. The average SFH depends on galaxy mass, but galaxies of a given mass have different histories depending on their environment. We conclude that the variation of the SFRD(z) with environment is not driven by different distributions of galaxy masses and morphologies in clusters and field, and must be due to an accelerated formation in high mass haloes compared to low mass ones even for galaxies that will end up having the same galaxy mass today.Comment: 16 pages, 10 figures. Published on MNRA

Erratum: “GASP. I. Gas Stripping Phenomena in Galaxies with MUSE” (2017, ApJ, 844, 48)

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VizieR Online Data Catalog: OmegaWINGS local clusters of galaxies redshifts (Moretti+, 2017)

Redshifts, magnitude/radial completeness, and memberships are given for the 17985 galaxies observed as part of the OmegaWINGS survey of local clusters of galaxies over 1 square degree. Redshifts have been measured using both absorption and emission lines features. The sample magnitude completeness is 80% at V=20. Thanks to the observing strategy, the radial completeness turned out to be relatively constant (90%) within the AAOmega field of view. The success rate in measuring redshifts is 95%, at all radii. Cluster members are flagged 1 or 2, depending on the cluster structure/secondary structure, and 0 if they are not cluster members. (1 data file)

Galaxies on the road to quenching

This thesis explores the properties of galaxies that reside in high density regions in the local Universe. The driving motivation is to shed light on how galaxies stop forming stars and the role played by the environment in this process. A wide variety of environmentallyrelated quenching mechanisms have been proposed and the smoking gun proving that these are actually transforming galaxies from being star forming to passive is the existence of a population of galaxies in transition with intermediate features. In this Thesis I will mainly focus on the properties of two population of galaxies: those that are forming stars at a reduced level compared to other galaxies at similar mass, and those that have recently and abruptly interrupted their star formation. The data exploited in this Thesis come from surveys which focus on different environments in the local Universe: the WIde-field Nearby Galaxy-cluster Survey (WINGS, Fasano et al. 2006) with its recent extension OmegaWINGS (Gullieuszik et al., 2015a, Moretti et al. submitted) and the Padova Millennium Galaxy and Group catalogue (PM2GC, Calvi et al. 2011). The Thesis starts with a characterization of the WINGS survey and then focuses on the new OmegaWINGS data, illustrating the most important aspects of the photometric and spectroscopic observations. I will describe in detail my personal contribution to the survey, from the data analysis to the redshift and velocity dispersion measurements, to the membership assignments. I will also present the complete galaxy catalog built from the combination of the two cluster surveys considered. While halo mass estimates are quite easily obtained for clusters, at the group regime it is less straightforward to derive robust measurements. I will then present a procedure I developed to compute halo masses from observable quantities for the PM2GC. My approach exploits mock galaxy catalogs extracted from the De Lucia & Blaizot (2007) semi-analytic model, run on the Millennium Simulation (Springel et al. 2005). Subsequently, I will discuss the methods adopted to compute the galaxy stellar properties, exploiting both spectroscopic and photometric information. Using the data from the WINGS+OmegaWINGS surveys, I will present an analysis of the ongoing Star Formation Rate (SFR) and the Specific Star Formation Rate (SSFR) - stellar mass (M∗) relations in field and cluster mass limited samples. I contrast trends in the different environments and, in clusters, at different clustercentric distances. The main result is that in clusters a population of galaxies with a reduced SFR is detected, named transition galaxies, which is much rarer in the field. The spatial location of these galaxies, together with the analysis of the star formation histories, colors and average ages, suggest that transition galaxies have had a reduced SFR for the past 2-5 Gyr. This is compatible with a strangulation scenario, even if other processes like ram pressure stripping can not be excluded. I characterize the properties of post starburst (PSB) galaxies, which are galaxies that abruptly interrupted their star formation sometimes during the past 2Gyr), the other a rapid truncation of the star formation activity (t∼0.1Gyr). Comparing the fraction of PSBs to the fraction of galaxies in transition, it appears that the short timescale star-formation quenching channel contributes two times more than the long timescale one to the growth of the passive population in clusters. The emerging picture is that ram pressure stripping is probably the most successful process affecting star formation in clusters, followed by strangulation. Other mechanisms might play a role, even though they most likely take place in lower density environments.L’obiettivo del lavoro presentato in questa tesi è la caratterizzazione osservativa delle proprietà delle galassie, per vincolarne gli scenari di formazione ed evoluzione. In particolare, mi sono concentrata nel determinare come l’ambiente in cui evolvono le galassie influisca sul processo di formazione stellare nelle regioni ad alta densità nell’Universo locale. Tra i diversi meccanismi proposti come responsabili del quenching, ovvero la tendenza delle galassie a smettere di produrre stelle, quelli relativi all’ambiente sembrano svolgere un ruolo cruciale. La prova che confermerebbe l’azione primaria di questi meccanismi dovrebbe essere l’esistenza, in ammassi e gruppi di galassie, di una popolazione di galassie in transizione con caratteristiche intermedie. Con lo scopo dunque di identificare questa nuova popolazione, mi concentrerò sullo studio delle proprietà di due particolari classi di galassie: quelle che stanno formando stelle ad un livello ridotto rispetto ad altre galassie di massa simile, e quelle che hanno recentemente, e molto probabilmente bruscamente, interrotto la loro formazione stellare. Utilizzerò i dati provenienti da diverse campagne osservative: la WIde-field Nearby Galaxy-cluster Survey (WINGS, Fasano et al. 2006) con la sua recente estensione OmegaWINGS (Gullieuszik et al., 2015a, Moretti et al. 2017), e il Padova Millennium Galaxy and Group catalogue (PM2GC, Calvi et al. 2011). La prima parte della tesi è riservata alla descrizione delle survey WINGS e OmegaWINGS. Particolare attenzione sarà dedicata alla presentazione degli aspetti più importanti delle osservazioni fotometriche e spettroscopiche di OmegaWINGS, in cui sono stata personalmente coinvolta. Descriverò in dettaglio il mio contributo alla survey, che va dall’analisi dei dati alle misurazioni di redshift e dispersione di velocità, all’individuazione delle galassie appartenenti agli ammassi. Presenterò dunque il catalogo completo costruito dalla combinazione delle due survey considerate. Mentre è relativamente facile ricavare una stima della massa di alone per gli ammassi, e più complicato ottenere misurazioni affidabili per i gruppi. Ho quindi sviluppato una procedura per derivare le masse di alone per i dati PM2GC da quantità osservabili, che descriverò in dettaglio. Tale procedura utilizza cataloghi di galassie estratti dai modelli semi analitici di De Lucia & Blaizot (2007), applicati alla Millennium Simulation (Springel et al. 2005). Successivamente, descriverò i metodi adottati per il calcolo delle propriet`a delle galassie, sfruttando le informazioni provenienti da osservazioni spettroscopiche e fotometriche. Utilizzando i dati WINGS+OmegaWINGS, discuterò l’analisi delle relazioni tra il tasso di formazione stellare (SFR), il tasso specifico di formazione stellare (SSFR) e la massa stellare di una galassia (M∗), nel campo e negli ammassi, in campioni limitati in massa. Confronterò gli andamenti nei diversi ambienti e, negli ammassi, a diverse distanze dal centro. Il risultato principale è l’individuazione di una popolazione di galassie in ammasso con SFR ridotta, denominate galassie in transizione, che è molto più rara nel campo. La distribuzione spaziale di queste galassie, insieme all’analisi della storia di formazione stellare, dei colori ed età medie, suggeriscono che le galassie in transizione abbiano avuto un SFR ridotta per circa 2-5 Gyr. Questo è compatibile con uno scenario di “strangulation”, anche se altri processi come la ram pressure stripping non possono essere esclusi. Successivamente caratterizzerò le proprietà delle galassie cosiddette post starburst (PSB), cioè galassie che hanno bruscamente interrotto la loro formazione stellare all’incirca 1 miliardo di anni fa e che presentano caratteristiche ben riconoscibili nei loro spettri (nessuna emissione e Hδ in assorbimento). Sfruttando un campione limitato in magnitudine apparente estratto dai dati WINGS + OmegaWINGS, presenterò la prima caratterizzazione completa di galassie PSB in ammasso e confronterò le loro proprietà con quelle di galassie passive (PAS) e con righe di emissione (EML). Il principale risultato riguarda il numero relativo di galassie PSB, che aumenta leggermente dalla periferia verso il centro degli ammassi e dall’ammasso meno luminoso/massiccio a quello più luminoso/massiccio. Le galassie PSB hanno proprietà, quali masse stellari, magnitudini, colori e morfologie, intermedie tra le PAS e EML, tipiche di una popolazione che è recentemente diventata passiva. L’analisi dello spazio delle fasi e dei profili di dispersione di velocità indicano anche che le PSB rappresentano una combinazione di galassie con diverse storie di accrescimento. In particolare, PSB con forte Hδ sono consistenti con l’essere state recentemente accresciute. Questa analisi suggerisce che, nel processo di accrescimento di una galassia su un ammasso, all’avvicinarsi alla regione virializzata, per effetto della ram pressure stripping (o di altre interazioni) viene indotto un rapido quenching, preceduto o meno da un forte episodio di formazione stellare; inoltre quest’effetto è più forte in ammassi più massicci. Descriverò successivamente la popolazione di PSB in sistemi più piccoli. Combinando i dati WINGS+OmegaWINGS ai dati PM2GC, mostrerò come la frazione di galassie PSB e l’efficienza del quenching dipendano dalla massa dell’alone e aumentino andando da galassie singole, a sistemi binari, gruppi e ammassi. Nei diversi ambienti, diversi meccanismi fisici sono probabilmente responsabili per la produzione di galassie PSB, ma tutti producono un troncamento della formazione stellare su brevi scale temporali. Mentre negli ammassi la ram presssure stripping sembra essere il candidato più probabile, l’interazione gravitazionale tra galassie potrebbe essere più efficiente nelle regioni a bassa densità. Dal confronto tra la frazione di PSB e di galassie in transizione, si può dedurre che il canale di quenching più rapido constribuisce circa due volte di più alla crescita della popolazione di galassie passive rispetto al canale di quenching più lento. Il quadro che emerge è che la ram pressure stripping è probabilmente il processo che maggiormente incide sul quenching della formazione stellare negli ammasi, seguito dalla strangulation. Altri meccanismi potrebbero influire, anche se probabilmente con effetto maggiore in ambienti a minore densità

La diagnosi multidimensionale in Medicina Generale. Studio comparativo sull’uso di alcuni strumenti.

Sopo dello studio è stato sperimentare strumenti di valutazione multidimensionale della salute, già validati in ambito internazionale per sensibilizzare i MMG ad una nuova forma di semeiotica. Gli strumenti COOP, FSQ e DUHP sono stati somministrati da personale medico a pazienti in attesa negli ambulatori dei MMG nel Distretto di Correggio (Reggio Emilia). Gli strumenti hanno fornito informazioni su indicatori di salute e sono risultati graditi dai pazienti e dai medici

Radiation Environment in the ITER Neutral Beam Injector Prototype

We study the radiation environment in MITICA, the prototype of the ITER neutral beam injector, during deuterium operation. ITER is a scientific challenge: one of the several critical issues to solve is the compatibility to ionizing radiation of diagnostics components placed near the plasma vessel. In fact, non negligible fluxes of neutrons and photons are expected from deuterium-deuterium reactions, also from a major peripheral component such as the Neutral Beam Injector. After evaluating the results of Monte Carlo simulations on the expected environment, we determine the risk of malfunctions due to ionizing radiation in control and diagnostic electronics placed close to the injector vessel. The risk on different families of electronic devices is assessed, focusing separately on displacement damage, total ionizing dose, and single event effects

SLOW QUENCHING of STAR FORMATION in OMEGAWINGS CLUSTERS: GALAXIES in TRANSITION in the LOCAL UNIVERSE

The star formation quenching depends on environment, but a full understanding of what mechanisms drive it is still missing. Exploiting a sample of galaxies with masses {M}*\gt {10}9.8{M}☉ , drawn from the WIde-field Nearby Galaxy-cluster Survey (WINGS) and its recent extension OMEGAWINGS, we investigate the star formation rate (SFR) as a function of stellar mass (M{}*) in galaxy clusters at 0.04\lt z\lt 0.07. We use non-member galaxies at 0.02 * relation in the two environments, but detect a population of cluster galaxies with reduced SFRs, which is rare in the field. These transition galaxies are mainly found within the cluster virial radius (R200), but they impact on the SFR-M{}* relation only within 0.6R200. The ratio of transition to pure star-forming galaxies strongly depends on environment, being larger than 0.6 within 0.3R200 and rapidly decreasing with distance, while it is almost flat with M*. As galaxies move downward from the SFR-M{}* main sequence, they become redder and present older luminosity- and mass-weighted ages. These trends, together with the analysis of the star formation histories, suggest that transition galaxies have had a reduced SFR for the past 2-5 Gyr. Our results are consistent with the hypothesis that the interaction of galaxies with the intracluster medium via strangulation causes a gradual shut down of star formation, giving birth to an evolved population of galaxies in transition from being star forming to becoming passive