Stima della massa di polvere di galassie ad alto redshift e suo utilizzo come tracciante evolutivo

In questa tesi, sfruttando la disponibilità di dati fotometrici sub-mm di ultima generazione, come quelli dell’interferometro ALMA, si è stimata l’emissione termica della polvere interstellare realizzando un codice numerico in IDL (i.e., Interactive Data Language) che permette di effettuare un fit single-temperature sui dati. Come funzione di fit, si è assunto il cosiddetto “corpo grigio”, che ben descrive la fisica dei grani di polvere. La temperatura di equilibrio della polvere è un parametro libero, del fit. Lo stesso procedimento è stato ripetuto prendendo come funzione di fit l’approssimazione otticamente sottile del corpo grigio, dato il suo largo impiego in letteratura. Confrontando i fit, quelli in approssimazione otticamente sottile risultano meno affidabili e danno una temperatura di best fit sistematicamente inferiore (di un fattore ∼ 1.7) a quella ottenuta nel caso non approssimato. Nota la temperatura di equilibrio della polvere, è stato possibile stimare la sua massa, assumendo che la polvere interstellare sia otticamente sottile alla sua stessa radiazione. Sotto questa assunzione, infatti, si ottiene una relazione tra la massa di polvere e il flusso osservato ad una lunghezza d’onda λ d tale che cada nel regime otticamente sottile. In questa sede si è presa λ_d = 230 μm da Gilli et al. (2014). Oltre alla massa di polvere, usando le curve di best fit, è stato possibile calcolare la luminosità infrarossa (λ rest = 8 − 1000 μm) e stimare il tasso di formazione stellare di ogni oggetto del campione (Kennicutt, 1999). Quest’ultimo, insieme alla massa della polvere e alla massa stellare, può dare vincoli cruciali riguardo la storia di formazione stellare delle galassie. La massa stellare degli oggetti del campione è stata prese da Fontana et al. (2006) e P. Santini (comunicazione privata). I risultati ottenuti sono stati confrontati con gli scenari di evoluzione proposti da Calura et al. (2016) e con lo scenario proposto da Mancuso et al. (2016b)

High-redshift Dusty Star-Forming Galaxies: a panchromatic approach to constrain massive galaxy evolution

The goal of this thesis is to investigate the early stages of massive galaxy evolution by defining an overall view of their physical properties combining the information extracted by all the details of their spectral behaviour. To this aim, I focused on the population of Dusty Star-Forming Galaxies at the Cosmic Noon ($zsim 2$). In my thesis project, I first deal with the modelling of the spatially-averaged time evolution of galaxy baryonic components, namely gas, stars, metals and dust, on the basis of a simple but effective approach that allows to solve analytically the equations that describe their evolution. Contrariwise to most of the analytic models on the market, the one developed during this PhD thesis self-consistently compute the metal and dust enrichment histories of the cold gas and stellar mass using as input the solutions for the evolution of the mass components. The solutions are coupled to specific prescriptions for parameter setting (inspired by extit{in-situ} galaxy-black hole co-evolution) and merger rates (based on numerical simulations) and, as such, reproduce the main statistical relationships followed by high-z massive star-forming galaxies and local ellipticals, that are thought to be their quiescent counterparts at $zsim0$. The analytic solutions are then exploited to interpret the spatially-averaged astrophysical properties of a pilot sample of (sub-)millimeter selected Dusty Star-Forming Galaxies in the multi-wavelength GOODS-S field and spectroscopically confirmed to be at the peak of Cosmic Star Formation History. Ultimately, they are used to disentangle the main physical processes regulating the evolution of these galaxies. The study highlights the importance of multi-wavelength broad-band and spectroscopic data to constrain dusty galaxy evolution at high-z and their role in the formation of spheroids, along with the need of a complete theoretical scenario that allows to self-consistently interpret the outcomes obtained from observational analyses. One possible framework is the one provided by the extit{in-situ} scenario for galaxy-black hole co-evolution, that has been used in this work to interpret the reconstructed panchromatic view combining spatially integrated (i.e. galaxy age, Star Formation Rate, stellar mass, dust mass, dust attenuation), spatially resolved (multi-wavelength sizes) and spectral (i.e. molecular gas content, kinematics and AGN/stellar driven outflows) properties of the aforementioned pilot sample of DSFG. The analysis is performed under specific requirements (e.g. spectroscopic measurement of galaxy redshift, complete sampling of galaxy multi-band emission) in order to unbiasedly constrain galaxy integral properties by performing an energy-balanced fit of the SED from the UV/optical to the radio band, including also galaxy X-ray emission, with the Code Investigating GALaxy Emission. Galaxy optical, far-infrared and radio sizes are measured from continuum maps at the highest spatial resolution currently available ($Delta hetalesssim1$ arcsec). CO spectral emission lines are extracted from publicly available data cubes in the Atacama Large Millimeter/sub-millimeter Array Archive and allow to measure the molecular gas content and to disentangle between a disk dominated configuration of the gaseous component and molecular outflows possibly driven by the central active nucleus. The multiple pieces of information coming from such a panchromatic study offer a clear description of the properties of individual galaxies and, once each of them is inscribed in the evolutionary context, offer a general view of the evolutionary mechanisms

The resolved scaling relations in DustPedia: Zooming in on the local Universe

We perform a homogeneous analysis of an unprecedented set of spatially resolved scaling relations (SRs) between ISM components and other properties in the range of scales 0.3-3.4 kpc. We also study some ratios: dust-to-stellar, dust-to-gas, and dust-to-metal. We use a sample of 18 large, spiral, face-on DustPedia galaxies. All the SRs are moderate/strong correlations except the dust-HI SR that does not exist or is weak for most galaxies. The SRs do not have a universal form but each galaxy is characterized by distinct correlations, affected by local processes and galaxy peculiarities. The SRs hold starting from 0.3 kpc, and if a breaking down scale exists it is < 0.3 kpc. By evaluating all galaxies at 3.4 kpc, differences due to peculiarities of individual galaxies are cancelled out and the corresponding SRs are consistent with those of whole galaxies. By comparing subgalactic and global scales, the most striking result emerges from the SRs involving ISM components: the dust-total gas SR is a good correlation at all scales, while the dust-H2 and dust-HI SRs are good correlations at subkpc/kpc and total scales, respectively. For the other explored SRs, there is a good agreement between small and global scales and this may support the picture where the main physical processes regulating the properties and evolution of galaxies occur locally. Our results are consistent with the hypothesis of self-regulation of the SF process. The analysis of subgalactic ratios shows that they are consistent with those derived for whole galaxies, from low to high z, supporting the idea that also these ratios could be set by local processes. Our results highlight the heterogeneity of galaxy properties and the importance of resolved studies on local galaxies in the context of galaxy evolution. They also provide observational constraints to theoretical models and updated references for high-z studies.Comment: 42 pages, 11 figures and 5 tables in the main text, 2 figures and 1 table in Appendix. Accepted for publication in A&

Emissione di Bremsstrahlung e applicazioni astrofisiche.

In ambiente astrofsico i principali meccanismi di produzione di energia sono associati a cariche elettriche in moto non uniforme. In generale è noto che cariche libere emettono radiazione elettromagnetica solamente se accelerate:una carica stazionaria ha campo elettrico costante e campo magnetico nullo, quindi non irradia, e lo stesso si ha per una carica in moto uniforme (difatti basta porsi nel sistema di riferimento solidale ad essa perchè si ricada nel caso precedente). In questo contesto si inserisce la radiazione di Bremsstrahlung, caratteristica dei plasmi astrofsici molto caldi e dovuta all'interazione coulombiana tra gli ioni e gli elettroni liberi del gas ionizzato. Data la piccola massa dell'elettrone, durante l'interazione lo ione non viene accelerato in maniera apprezzabile, quindi è possibile trattare il problema come quello di cariche elettriche negative decelerate dal campo coulombiano stazionario di un mare di cariche positive. Non a caso in tedesco la parola Bremsstrahlung signifca radiazione di frenamento". L'emissione di Bremsstrahlung è detta anche free-free emission poichè l'elettrone perde energia passando da uno stato non legato a un altro stato non legato. Questo processo di radiazione avviene nel continuo, su un intervallo di frequenze che va dal radio ai raggi gamma. In astrofsica è il principale meccanismo di raffreddamento per i plasmi a temperature elevate: si osserva nelle regioni HII, sottoforma di emissione radio, ma anche nelle galactic hot-coronae, nelle stelle binarie X, nei dischi di accrescimento intorno alle stelle evolute e ai buchi neri, nel gas intergalattico degli ammassi di galassie e nelle atmosfere di gas caldo in cui sono immerse le galassie ellittiche, perlopiù sottoforma di emissione X. La trattazione del fenomeno sarà estesa anche al caso relativistico che, per esempio, trova applicazione nell'emissione dei ares solari e della componente elettronica dei raggi cosmici. Infine la radiazione di Bremsstrahlung, oltre a permettere, solamente mediante misure spettroscopiche, di ricavare la temperatura e la misura di emissione di una nube di plasma, consente di effettuare una vera e propria "mappatura" del campo gravitazionale dei sistemi che hanno gas caldo

In pursuit of giants - II. Evolution of dusty quiescent galaxies over the last six billion years from the hCOSMOS survey

International audienceThe physical mechanisms that link the termination of star formation in quiescent galaxies and the evolution of their baryonic components, stars, and the interstellar medium (ISM; dust, gas, and metals) are poorly constrained beyond the local Universe. In this work, we characterise the evolution of the dust content in 545 quiescent galaxies observed at 0.1 < z < 0.6 as part of the hCOSMOS spectroscopic redshift survey. This is, to date, the largest sample of quiescent galaxies at intermediate redshifts for which the dust, stellar, and metal abundances are consistently estimated. We analyse how the crucial markers of a galaxy dust life cycle, such as specific dust mass (Mdust/M⋆), evolve with different physical parameters, namely gas-phase metallicity (Zgas), time since quenching (tquench), stellar mass (M⋆), and stellar population age. We find morphology to be an important factor in the large scatter in Mdust/M⋆ (∼2 orders of magnitude). Quiescent spirals exhibit strong evolutionary trends of specific dust mass with M⋆, stellar age, and galaxy size, in contrast to the little to no evolution experienced by ellipticals. When transitioning from solar to super-solar metallicities (8.7 ≲ 12 + log(O/H)≲9.1), quiescent spirals undergo a reversal in Mdust/M⋆, indicative of a change in dust production efficiency. By modelling the star formation histories of our objects, we unveil a broad dynamical range of post-quenching timescales (60 Myr < tquench < 3.2 Gyr). We show that Mdust/M⋆ is highest in recently quenched systems (tquench < 500 Myr), but its further evolution is non-monotonic, as a consequence of different pathways for dust formation, growth, or removal on various timescales. Our data are best described by simulations that include dust growth in the ISM. While this process is prevalent in the majority of galaxies, for ∼15% of objects we find evidence of additional dust content acquired externally, most likely via minor mergers. Altogether, our results strongly suggest that prolonged dust production on a timescale of 0.5 − 1 Gyr since quenching may be common in dusty quiescent galaxies at intermediate redshifts, even if their gas reservoirs are heavily exhausted (i.e. cold gas fraction < 1 − 5%).Key words: galaxies: evolution / galaxies: formation / galaxies: IS

The resolved scaling relations in DustPedia : Zooming in on the local Universe

International audienceAims. We perform a homogeneous analysis of an unprecedented set of spatially resolved scaling relations (SRs) between interstellar medium (ISM) components, that is to say dust, gas, and gas-phase metallicity, and other galaxy properties, such as stellar mass (M star), total baryonic content, and star-formation rate (SFR), in a range of physical scales between 0.3 and 3.4 kpc. We also study some ratios between galaxy components: dust-to-stellar, dust-togas , and dust-to-metal ratios.Methods. We use a sample of 18 large, spiral, face-on DustPedia galaxies. The sample consists of galaxies with spatially resolved dust maps corresponding to 15 Herschel-SPIRE 500 µm resolution elements across the optical radius, with the morphological stage spanning from T = 2 to 8, M star from 2 × 10 9 to 1 × 10 11 M , SFR from 0.2 to 13 M yr −1 , and oxygen abundance from 12 + log(O/H) = 8.3 to 8.8. Results. All the SRs are moderate or strong correlations except the dust-Hi SR that does not exist or is weak for most galaxies. The SRs do not have a universal form but each galaxy is characterized by distinct correlations, affected by local processes and galaxy peculiarities. The SRs hold, on average, starting from the scale of 0.3 kpc, and if a breaking down scale exists it is below 0.3 kpc. By evaluating all galaxies together at the common scale of 3.4 kpc, differences due to peculiarities of individual galaxies are cancelled out and the corresponding SRs are consistent with those of whole galaxies. By comparing subgalactic and global scales, the most striking result emerges from the SRs involving ISM components: the dust-total gas SR is a good correlation at all scales, while the dust-H 2 and dust-Hi SRs are good correlations at subkiloparsec/kiloparsec and total scales, respectively. For the other explored SRs, there is a good agreement between small and global scales and this may support the picture where the main physical processes regulating the properties and evolution of galaxies occur locally. In this scenario, our results are consistent with the hypothesis of self-regulation of the star-formation process. The analysis of subgalactic ratios between galaxy components shows that they are consistent with those derived for whole galaxies, from low to high redshift, supporting the idea that also these ratios could be set by local processes. Conclusions. Our results highlight the heterogeneity of galaxy properties and the importance of resolved studies on local galaxies in the context of galaxy evolution. They also provide fundamental observational constraints to theoretical models and updated references for high-redshift studies

The resolved scaling relations in DustPedia : Zooming in on the local Universe

International audienceAims. We perform a homogeneous analysis of an unprecedented set of spatially resolved scaling relations (SRs) between interstellar medium (ISM) components, that is to say dust, gas, and gas-phase metallicity, and other galaxy properties, such as stellar mass (M star), total baryonic content, and star-formation rate (SFR), in a range of physical scales between 0.3 and 3.4 kpc. We also study some ratios between galaxy components: dust-to-stellar, dust-togas , and dust-to-metal ratios.Methods. We use a sample of 18 large, spiral, face-on DustPedia galaxies. The sample consists of galaxies with spatially resolved dust maps corresponding to 15 Herschel-SPIRE 500 µm resolution elements across the optical radius, with the morphological stage spanning from T = 2 to 8, M star from 2 × 10 9 to 1 × 10 11 M , SFR from 0.2 to 13 M yr −1 , and oxygen abundance from 12 + log(O/H) = 8.3 to 8.8. Results. All the SRs are moderate or strong correlations except the dust-Hi SR that does not exist or is weak for most galaxies. The SRs do not have a universal form but each galaxy is characterized by distinct correlations, affected by local processes and galaxy peculiarities. The SRs hold, on average, starting from the scale of 0.3 kpc, and if a breaking down scale exists it is below 0.3 kpc. By evaluating all galaxies together at the common scale of 3.4 kpc, differences due to peculiarities of individual galaxies are cancelled out and the corresponding SRs are consistent with those of whole galaxies. By comparing subgalactic and global scales, the most striking result emerges from the SRs involving ISM components: the dust-total gas SR is a good correlation at all scales, while the dust-H 2 and dust-Hi SRs are good correlations at subkiloparsec/kiloparsec and total scales, respectively. For the other explored SRs, there is a good agreement between small and global scales and this may support the picture where the main physical processes regulating the properties and evolution of galaxies occur locally. In this scenario, our results are consistent with the hypothesis of self-regulation of the star-formation process. The analysis of subgalactic ratios between galaxy components shows that they are consistent with those derived for whole galaxies, from low to high redshift, supporting the idea that also these ratios could be set by local processes. Conclusions. Our results highlight the heterogeneity of galaxy properties and the importance of resolved studies on local galaxies in the context of galaxy evolution. They also provide fundamental observational constraints to theoretical models and updated references for high-redshift studies

Demyelination as a rational therapeutic target for ischemic or traumatic brain injury

Previous research on stroke and traumatic brain injury (TBI) heavily emphasized pathological alterations in neuronal cells within gray matter. However, recent studies have highlighted the equal importance of white matter integrity in long-term recovery from these conditions. Demyelination is a major component of white matter injury and is characterized by loss of the myelin sheath and oligodendrocyte cell death. Demyelination contributes significantly to long-term sensorimotor and cognitive deficits because the adult brain only has limited capacity for oligodendrocyte regeneration and axonal remyelination. In the current review, we will provide an overview of the major causes of demyelination and oligodendrocyte cell death following acute brain injuries, and discuss the crosstalk between myelin, axons, microglia, and astrocytes during the process of demyelination. Recent discoveries of molecules that regulate the processes of remyelination may provide novel therapeutic targets to restore white matter integrity and improve long-term neurological recovery in stroke or TBI patients

New Analytic Solutions for Galaxy Evolution: Gas, Stars, Metals, and Dust in Local ETGs and Their High-z Star-forming Progenitors

We present a set of new analytic solutions aimed at self-consistently describing the spatially averaged time evolution of the gas, stellar, metal, and dust content in an individual star-forming galaxy hosted within a dark halo of a given mass and formation redshift. Then, as an application, we show that our solutions, when coupled to specific prescriptions for parameter setting (inspired by in situ galaxy-black hole coevolution scenarios) and merger rates (based on numerical simulations), can be exploited to reproduce the main statistical relationships followed by early-type galaxies and their high-redshift star-forming progenitors. Our analytic solutions allow one to easily disentangle the diverse role of the main physical processes regulating galaxy formation, quickly explore the related parameter space, and make transparent predictions on spatially averaged quantities. As such, our analytic solutions may provide a basis for improving the (subgrid) physical recipes presently implemented in theoretical approaches and numerical simulations and can offer a benchmark for interpreting and forecasting current and future broadband observations of high-redshift star-forming galaxies