86 research outputs found
Investigating the ISM of local Seyfert galaxies by modelling their CO SLED
No full textI will present a coherent multi-band analysis of the CO Spectral Line Energy Distribution (SLED) of two local Seyfert galaxies, NGC 34 and NGC 7130. These galaxies are prototypes of systems where the star formation and the accretion onto supermassive black holes coexist. The goal of the proposed study is to assess the impact of the two mechanisms on the physics of the molecular gas. We carried out our investigation by modelling the observed CO SLED, taking advantage of ALMA, Herschel, XMM and NuSTAR data. X-ray data analysis confirmed the presence (and allowed us to measure the power) of a heavily obscured AGN in both systems, whereas ALMA high resolution allowed us to scan the nuclear region, where the influence of the accretion could dominate, down to a spatial scale of ~ 100 pc for the CO(6–5) transition. We considered Photo-Dissociation Region (PDR), X-ray-Dominated Region (XDR) and shock models. PDRs are regions whose physics and chemistry are mainly dominated by far UV radiation produced by OB stars, while XDRs are influenced by the presence of X-ray photons, possibly due to an AGN. UV and X-ray radiation causes a different luminosity distribution over the CO rotational lines, since X-ray photons have a higher gas heating efficiency and are capable of penetrating at a larger column density of the gas than UV photons, causing the resulting CO SLEDs to be peaked at higher-J rotational transitions. Shock waves, originating from the supersonic injection of mass into the interstellar medium by stellar winds, supernovae and/or young stellar objects, can compress and heat the gas above T ~ 100 K, making the high-J CO rotational energy levels more populated. Both in NGC 7130 and in NGC 34, we found that the low-J transitions can be explained by PDRs, whereas the high rotational ladder requires the presence of a separate source of excitation, that we identified with X-ray heating due to the AGN. Hence, the observed CO SLED can be reproduced by adopting a composite PDR+XDR model, demonstrating that also the influence of the AGN is needed to reproduce the observed molecular emission (Pozzi et al. 2017, Mingozzi et al. 2018). Our study clearly indicates the capabilities offered by the current generation instruments at different wavelengths in shedding light on the properties of nearby galaxies, adopting the state-of-the-art physical modelling. The future exploitation of the data in the ALMA archive will allow us to enlarge the sample and place the results of NGC 34 and NGC 7130 on a more statistically significant context. Moreover, we intend to extend the analysis performed on the CO to other molecules, such as HCN, HCO+, for which we have already required and obtained APEX data (P.I. Francesca Pozzi), and we aim to obtain ALMA observations. These molecules, characterised by higher critical densities (log(n/cm-3) = 5 - 6) than CO, allow to trace a different parameter space of the giant molecular clouds, and their flux ratios permit to envisage the presence and strength of an AGN.</p
Gas-phase Metallicity of Local Active Galactic Nuclei in the GASP and MaNGA Surveys: The Role of Ram Pressure Stripping
No full textGrowing evidence in support of a connection between active galactic nuclei (AGN) activity and the ram pressure stripping (RPS) phenomenon has been found both observationally and theoretically in the past decades. In this work, we further explore the impact of RPS on the AGN activity by estimating the gas-phase metallicity of nuclear regions and the mass–metallicity relation of galaxies at z ≤ 0.07 and with stellar masses , either experiencing RPS or not. To measure oxygen abundances, we exploit Integral Field Spectroscopy data from the GASP and MaNGA surveys, photoionization models generated with the code Cloudy and the code Nebulabayes to compare models and observations. In particular, we build Cloudy models to reproduce line ratios induced by photoionization from stars, AGN, or a contribution of both. We find that the distributions of metallicity and [O iii ] λ 5007 luminosity of galaxies undergoing RPS are similar to the ones of undisturbed galaxies. Independently of the RPS, we do not find a correlation between stellar mass and AGN metallicity in the mass range , while for the star-forming galaxies we observe the well-known mass–metallicity relation between with a scatter mainly driven by the star formation rate and a plateau around . The gas-phase metallicity in the nuclei of AGN hosts is enhanced with respect to those of star-forming galaxies by a factor of ∼ 0.05 dex regardless of the RPS
Investigating the ISM of local Seyfert galaxies by modelling their CO SLED
No full textI will present a coherent multi-band analysis of the CO Spectral Line Energy Distribution (SLED) of two local Seyfert galaxies, NGC 34 and NGC 7130. These galaxies are prototypes of systems where the star formation and the accretion onto supermassive black holes coexist. The goal of the proposed study is to assess the impact of the two mechanisms on the physics of the molecular gas. We carried out our investigation by modelling the observed CO SLED, taking advantage of ALMA, Herschel, XMM and NuSTAR data. X-ray data analysis confirmed the presence (and allowed us to measure the power) of a heavily obscured AGN in both systems, whereas ALMA high resolution allowed us to scan the nuclear region, where the influence of the accretion could dominate, down to a spatial scale of ~ 100 pc for the CO(6–5) transition. We considered Photo-Dissociation Region (PDR), X-ray-Dominated Region (XDR) and shock models. PDRs are regions whose physics and chemistry are mainly dominated by far UV radiation produced by OB stars, while XDRs are influenced by the presence of X-ray photons, possibly due to an AGN. UV and X-ray radiation causes a different luminosity distribution over the CO rotational lines, since X-ray photons have a higher gas heating efficiency and are capable of penetrating at a larger column density of the gas than UV photons, causing the resulting CO SLEDs to be peaked at higher-J rotational transitions. Shock waves, originating from the supersonic injection of mass into the interstellar medium by stellar winds, supernovae and/or young stellar objects, can compress and heat the gas above T ~ 100 K, making the high-J CO rotational energy levels more populated. Both in NGC 7130 and in NGC 34, we found that the low-J transitions can be explained by PDRs, whereas the high rotational ladder requires the presence of a separate source of excitation, that we identified with X-ray heating due to the AGN. Hence, the observed CO SLED can be reproduced by adopting a composite PDR+XDR model, demonstrating that also the influence of the AGN is needed to reproduce the observed molecular emission (Pozzi et al. 2017, Mingozzi et al. 2018). Our study clearly indicates the capabilities offered by the current generation instruments at different wavelengths in shedding light on the properties of nearby galaxies, adopting the state-of-the-art physical modelling. The future exploitation of the data in the ALMA archive will allow us to enlarge the sample and place the results of NGC 34 and NGC 7130 on a more statistically significant context. Moreover, we intend to extend the analysis performed on the CO to other molecules, such as HCN, HCO+, for which we have already required and obtained APEX data (P.I. Francesca Pozzi), and we aim to obtain ALMA observations. These molecules, characterised by higher critical densities (log(n/cm-3) = 5 - 6) than CO, allow to trace a different parameter space of the giant molecular clouds, and their flux ratios permit to envisage the presence and strength of an AGN.</p
Investigating the AGN-starburst connection in a nearby Seyfert galaxy with ALMA and multiwavelength data
No full textThe astrophysical context in which this thesis project lies concerns the comprehension of the mutual interaction between the accretion onto a Super Massive Black Hole (SMBH) and the Star Formation (SF), that take place in the host galaxy. This is one of the key topic of the modern extragalactic astrophysical research. Indeed, it is widely accepted that to understand the physics of a galaxy, the contribution of a possible central AGN must be taken into account.
The aim of this thesis is the study of the physical processes of the nearby Seyfert galaxy NGC 34. This source was selected because of the wide collection of multiwavelength data available in the literature. In addition, recently, it has been observed with the Atacama Large Submillimeter/Millimeter Array (ALMA) in Band 9. This project is divided in two main parts: first of all, we reduced and analyzed the ALMA data, obtaining the continuum and CO(6-5) maps; then, we looked for a coherent explaination of NGC 34 physical characteristics. In particular, we focused on the ISM physics, in order to understand its properties in terms of density, chemical composition and dominant radiation field (SF or accretion). This work has been done through the analysis of the spectral distribution of several CO transitions as a function of the transition number (CO SLED), obtained joining the CO(6-5) line with other transitions available in the literature. More precisely, the observed CO SLED has been compared with ISM models, including Photo-Dissociation Regions (PDRs) and X-ray-Dominated Regions (XDRs). These models have been obtained through the state-of-the-art photoionization code CLOUDY. Along with the observed CO SLED, we have taken into account other physical properties of NGC 34, such as the Star Formation Rate (SFR), the gas mass and the X-ray luminosity
Emissione di bremsstrahlung e applicazioni astrofisiche
No full textLa radiazione elettromagnetica è una singola entità, come si deduce dall’universalità delle leggi di Maxwell, nonostante lo spettro elettromagnetico sia caratterizzato da regioni a cui si associano nomi differenti. Questo implica l’esistenza di un meccanismo fondamentale comune alla base di tutti i processi di radiazione, che si identifica in una carica in moto non uniforme. Infatti una carica stazionaria ha un campo elettrico costante e un campo magnetico nullo, quindi non irradia; lo stesso vale per una carica in moto uniforme.
La radiazione di Bremsstrahlung, che avviene nel continuo, spaziando dal radio ai raggi gamma, fu scoperta negli anni ’30 del secolo scorso, in seguito all’osservazione che la perdita di energia che subisce un elettrone attraversando la materia non è data unicamente dalla ionizzazione: l’elettrone, accelerato dal nucleo ionizzato, irradia e, di conseguenza, viene frenato. Letteralmente “Bremsstrahlung“ significa “radiazione di frenamento” e in astrofisica rappresenta il principale meccanismo di raffreddamento di un plasma a temperature molto elevate; nel seguente elaborato tale plasma sarà considerato monoatomico e completamente ionizzato. Dall’analisi dello spettro di Bremsstrahlung
si possono rilevare la temperatura e la misura di emissione della nube di gas osservato, che consentono di ricavare la densità, la massa e la luminosità della nube stessa.
Nel capitolo 1 vengono riportate la descrizione di questo processo di radiazione e le principali formule che lo caratterizzano, illustrate in ambiente semiclassico (Bremsstrahlung termica) e in ambiente relativistico (Bremsstrahlung relativistica). Nel capitolo 2 segue
la trattazione di alcuni esempi astrofisici: le regioni HII; il gas intergalattico degli ammassi di galassie ed emettono principalmente nella banda X; le galassie Starburst; le binarie X; la componente elettronica dei raggi cosmici e i brillamenti solari; infine un accenno agli oggetti di Herbig-Haro
GASP XXVII: Gas-phase Metallicity Scaling Relations in Disk Galaxies with and without Ram Pressure Stripping
No full textExploiting the data from the GAs Stripping Phenomena in galaxies with MUSE (GASP) survey, we study the gas-phase metallicity scaling relations of a sample of 29 cluster galaxies undergoing ram pressure stripping and of a reference sample of (16 cluster and 16 field) galaxies with no significant signs of gas disturbance. We adopt the PYQZ code to infer the mean gas metallicity at the effective radius and achieve a well-defined mass-metallicity relation (MZR) in the stellar mass range with a scatter of 0.12 dex. At any given mass, reference cluster and stripping galaxies have similar metallicities, while the field galaxies with M⋆ 10.25 M⊙ show on average lower gas metallicity than galaxies in clusters. Our results indicate that at the effective radius, the chemical properties of the stripping galaxies are independent of the ram pressure stripping mechanism. Nonetheless, at the lowest masses, we detect four stripping galaxies well above the common MZR that suggest a more complex scenario. Overall, we find signs of an anticorrelation between the metallicity and both the star formation rate and the galaxy size, in agreement with previous studies. No significant trends are instead found with the halo mass, clustercentric distance, and local galaxy density in clusters. In conclusion, we advise a more detailed analysis of the spatially resolved gas metallicity maps of the galaxies, able to highlight effects of gas redistribution inside the disk due to ram pressure stripping
Exploring interstellar medium conditions in AGN and star forming galaxies with integral field spectroscopy
No full textThe interstellar medium (ISM), made up of ionised, neutral and molecular gas, and interstellar dust, is a fundamental ingredient of galaxy evolution. It is the “primary repository” of galaxies, where star formation (SF) takes place, depositing energy, momentum and chemical enriched material via stellar evolution events (e.g. stellar winds, supernova explosions). ISM properties can be largely influenced also by Active Galactic Nuclei (AGN) activity, that through outflows and jets is capable of heating, compressing and/or removing the gas (feedback). SF and AGN activities are part of the so-called galaxy baryon cycle, that encloses a variety of physical processes, driving and shaping galaxy formation and evolution. This Thesis aims at probing and interpreting ISM properties in different galaxy types, including star forming galaxies and AGN hosts, and in different conditions within a galaxy, through the use of integral field spectroscopy (IFS) and the comparison of the observed data with ionisation models. The use of ISM tracers from optical to submillimeter wavelengths allowed to explore the different processes that affect ISM conditions across both AGN and star forming galaxies, and to assess their impact on the evolution of their hosts. The results obtained represent also a unique test bench for the new generation of photoionisation models, given the unprecedented detail of the analysed data as well as some limitations of current models highlighted in this work
The MUSE view of He 2-10: No AGN ionization but a sparkling starburst
No full textWe study the physical and dynamical properties of the ionized gas in the prototypical HII galaxy Henize 2-10 using MUSE integral field spectroscopy. The large-scale dynamics are dominated by extended outflowing bubbles that are probably the result of massive gas ejection from the central star forming regions. We derived a mass outflow rate á out ~ 0.30 MâŠ(tm) yr-1, corresponding to mass loading factor η ~ 0.4, in the range of similar measurements in local luminous infrared galaxies. Such a massive outflow has a total kinetic energy that is sustainable by the stellar winds and supernova remnants expected in the galaxy. We studied the dust extinction, electron density, and ionization conditions all across the galaxy with a classical emission line diagnostic, confirming the extreme nature of the highly star forming knots in the core of the galaxy, which show high density and high ionization parameters. We measured the gas-phase metallicity in the galaxy, taking the strong variation of the ionization parameter into account, and found that the external parts of the galaxy have abundances as low as 12 + log (O/H) ~ 8.3, while the central star forming knots are highly enriched with super solar metallicity. We found no sign of AGN ionization in the galaxy, despite the recent claim of the presence of a supermassive active black hole in the core of He 2-10. We therefore reanalyzed the X-ray data that were used to propose the presence of the AGN, but we concluded that the observed X-ray emission can be better explained with sources of a different nature, such as a supernova remnant
CO excitation in the Seyfert galaxy NGC 7130
No full textWe present a coherent multiband modelling of the carbon monoxide (CO) spectral energy distribution of the local Seyfert galaxy NGC 7130 to assess the impact of the active galactic nucleus (AGN) activity on the molecular gas. We take advantage of all the available data from X-ray to the submillimetre, including ALMA data. The high-resolution (∼0.2 arcsec) ALMA CO(6–5) data constrain the spatial extension of the CO emission down to an ∼70 pc scale. From the analysis of the archival Chandra and NuSTAR data, we infer the presence of a buried, Compton-thick AGN of moderate luminosity, L_(2–10 keV) ∼ 1.6 × 10^(43) erg s^(−1). We explore photodissociation and X-ray-dominated-region (PDR and XDR) models to reproduce the CO emission. We find that PDRs can reproduce the CO lines up to J ∼ 6; however, the higher rotational ladder requires the presence of a separate source of excitation. We consider X-ray heating by the AGNs as a source of excitation, and find that it can reproduce the observed CO spectral energy distribution. By adopting a composite PDR+XDR model, we derive molecular cloud properties. Our study clearly indicates the capabilities offered by the current generation of instruments to shed light on the properties of nearby galaxies by adopting state-of-the-art physical modelling
Ionized Gas Outflows from the MAGNUM Survey: NGC 1365 and NGC 4945
No full textAGN feedback, acting through strong outflows accelerated in the nuclear region of AGN hosts, is invoked as a key ingredient for galaxy evolution by many models to explain the observed BH-galaxy scaling relations. Recently, some direct observational evidence of radiative mode feedback in action has been finally found in quasars at z >1.5. However, it is not possible to study outflows in quasars at those redshifts on small scales (≲100 pc), as spatial information is limited by angular resolution. This is instead feasible in nearby active galaxies, which are ideal laboratories to explore outflow structure and properties, as well as the effects of AGN on their host galaxies. In this proceeding we present preliminary results from the MAGNUM survey, which comprises nearby Seyfert galaxies observed with the integral field spectrograph VLT/MUSE. We focus on two sources, NGC 1365 and NGC 4945, that exhibit double conical outflows extending on distances >1 kpc. We disentangle the dominant contributions to ionization of the various gas components observed in the central ~5.3 kpc of NGC 1365. An attempt to infer outflow 3D structure in NGC 4945 is made via simple kinematic modeling, suggesting a hollow cone geometry
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