The circumgalactic medium of high redshift galaxies

We study the properties of the circumgalactic medium (CGM) of high-$z$ galaxies in the metal enrichment simulations presented in Pallottini et al. 2014. At $z=4$, we find that the simulated CGM gas density profiles are self-similar, once scaled with the virial radius of the parent dark matter halo. We also find a simple analytical expression relating the neutral hydrogen equivalent width (${\rm EW}_{\rm HI}$) of CGM absorbers as a function of the line of sight impact parameter ($b$). We test our predictions against mock spectra extracted from the simulations, and show that the model reproduces the ${\rm EW}_{\rm HI}(b)$ profile extracted from the synthetic spectra analysis. When compared with available data, our CGM model nicely predicts the observed ${\rm EW}_{\rm HI}(b)$ in $z\lesssim2$ galaxies, and supports the idea that the CGM profile does not evolve with redshift.Comment: 5 pages, 4 figures, accepted for publication in MNRAS Letter

Simulating intergalactic quasar scintillation

Intergalactic scintillation of distant quasars is sensitive to free electrons and therefore complements Ly$\alpha$ absorption line experiments probing the neutral intergalactic medium (IGM). We present a new scheme to compute IGM refractive scintillation effects on distant sources in combination with Adaptive Mesh Refinement cosmological simulations. First we validate our model by reproducing the well-known interstellar scintillation (ISS) of Galactic sources. The simulated cosmic density field is then used to infer the statistical properties of intergalactic scintillation. Contrary to previous claims, we find that the scattering measure of the simulated IGM at $z<2$ is \langle \mbox{SM}_{\equ}\rangle=3.879, i.e. almost 40 times larger than for the usually assumed smooth IGM. This yield an average modulation index ranging from 0.01 ($\nu_s=5$ GHz) up to 0.2 ($\nu_s=50$ GHz); above \nu_{s}\gsim30 GHz the IGM contribution dominates over ISS modulation. We compare our model with data from a $0.3\leq z\leq 2$ quasar sample observed at \nu_{\obs}=8.4 GHz. For this high frequency ($10.92\leq \nu_s \leq 25.2$), high galactic latitude sample ISS is negligible, and IGM scintillation can reproduce the observed modulation with a 4% accuracy, without invoking intrinsic source variability. We conclude by discussing the possibility of using IGM scintillation as a tool to pinpoint the presence of intervening high-$z$ groups/clusters along the line of sight, thus making it a probe suitably complementing Sunyaev-Zeldovich data recently obtained by \textit{Planck}.Comment: 14 pages, 13 figures, accepted for publication in MNRA

Un corpus di iscrizioni medievali della provincia di Viterbo: Metodologia d’analisi e alcune ri essioni sulla sua informatizzazione

Der Beitrag stellt einige methologische Überlegungen vor, die sich aus der Erstellung einer Datenbank zum Corpus der Inschriften des oberen Latium (Provinz Viterbo) aus dem 6.-12. Jahrhundert ergeben. Das Projekt ist Teil der Forschungs- und Editionsarbeiten des Centro italiano di studi sull’alto medioevo in Spoleto und der Arbeit am Corpus der Inscriptiones Medii Aevi Latini. Bei der Erstellung einer experimentellen Datenbank zur Analyse der etwa 100 Inschriften des Corpus ist ein Onlinedatenbank der Inschriften entstanden, die zu theoretischen und methodologischen Überlegungen anregten. Der Beitrag stellt die Kriterien vor, die bei Auswahl und Analyse des Corpus und der Organisation des Material sowohl als gedruckter Katalog wie als Datenbank angewendet wurden. Die Datenbank ist als Archivierungs- und Recherecheinstrument erstellt worden. Die Datenbank erlaubt es, zu jeder Inschrift ein Bild und zentrale Beschreibungsdaten zu erfassen. Die Beschreibungsdaten zu Text und Material folgen einem etablierten Schema. Diese formale Beschreibung ist besonders problemati- sch für die Paläographie der Inschriften im Corpus, die keine unabhängigen und homogenen Modelle besitzt, so daß es schwierig wird über Zeit und Raum stabile Klassikationsmerkmale zu entwickeln

The nature of the Lyman Alpha Emitter CR7: a persisting puzzle

The peculiar emission properties of the $z \sim 6.6$ Ly$\alpha$ emitter CR7 have been initially interpreted with the presence of either a direct collapse black hole (DCBH) or a substantial mass of Pop III stars. Instead, updated photometric observations by Bowler et al. (2016) seem to suggest that CR7 is a more standard system. Here we confirm that the original DCBH hypothesis is consistent also with the new data. Using radiation-hydrodynamic simulations, we reproduce the new IR photometry with two models involving a Compton-thick DCBH of mass $\approx 7 \times 10^6 \, \mathrm{M_{\odot}}$ accreting (a) metal-free ($Z=0$) gas with column density $N_H = 8 \times 10^{25} \, \mathrm{cm^{-2}}$, or (b) low-metallicity gas ($Z = 5 \times 10^{-3} \, \mathrm{Z_{\odot}}$) with $N_H = 3 \times 10^{24} \, \mathrm{cm^{-2}}$. The best fit model reproduces the photometric data to within $1 \sigma$. Such metals can be produced by weak star-forming activity occurring after the formation of the DCBH. The main contribution to the Spitzer/IRAC $3.6 \, \mathrm{\mu m}$ photometric band in both models is due to HeI/HeII $\lambda 4714, 4687$ emission lines, while the contribution of [OIII] $\lambda 4959, 5007$ emission lines, if present, is sub-dominant. Spectroscopic observations with JWST will be required to ultimately clarify the nature of CR7.Comment: Accepted for publication in MNRAS Letter

Scintillation in the InterGalactic Medium

The scintillation phenomenon consists in a light wave, coming from a compact enough source, that, passing through a ionized inhomogeneous medium, is subject to a random variation of the refraction index, and thus suffers multiple phase changes which lead to fluctuations in all the wave related quantities; the aim of this Thesis is to exploit the effects of this process when the light comes from a distant quasar and the random medium is given by the InterGalactic Medium, namely the baryon mass fraction of the universe laying between galaxies that is not locked up in stellar objects. The motivation that drives us toward this purpose is that either until now in this specific context a full investigation has not been developed in the literature, and either the IGM scintillation can, as we eventually show, be relevant in explaining some of the current discrepancies between theory and observations; furthermore this can prove to be a useful investigation tool, complementary to the ones available. To achieve the result proposed we have decided to employ the standard cosmological model, which gives the proper tools to analyze the environment we want to deal with, which is described in Chapter 1, and to numerically simulate the IGM, with the tools provided and depicted in Chapter 2. Next, in Chapter 3, we review the scintillation physical basis and its application to the InterStellar Medium, and then we naturally extend the ISM results to the IGM case. In Chapter 4 we expose and discuss the results of the simulation and finally, in Chapter 5, we apply our model to the simulation and analyze the behaviour of the IGM scintillation, confronting it with the observations. To conclude, in Chapter 6 we summarize the results obtained and the possible future developments

Missing cosmic metals revealed by X-ray absorption towards distant sources

The census of heavy elements (metals) produced by all stars through cosmic times up to present-day is limited to ~50%; of these only half are still found within their parent galaxy. The majority of metals is expelled from galaxies into the circumgalactic (or even more distant, intergalactic) space by powerful galactic winds, leaving unpleasant uncertainty on the amount, thermal properties and distribution of these key chemical species. These dispersed metals unavoidably absorb soft X-ray photons from distant sources. We show that their integrated contribution can be detected in the form of increasing X-ray absorption with distance, for all kinds of high-energy cosmic sources. Based on extensive cosmological simulations, we assess that $\sim$ 10\% of all cosmic metals reside in the intergalactic medium. Most of the X-ray absorption arises instead from a few discrete structures along the line of sight. These extended structures, possibly pin-pointing galaxy groups, contain million degree, metal-enriched gas, 100-1,000 times denser than the cosmic mean. An additional ~10% of cosmic metals could reside in this phase.Comment: Accepted for publication in Astronomy & Astrophysics. 9 pages, 4 figures, 1 tabl

Simulating cosmic metal enrichment by the first galaxies

We study cosmic metal enrichment via AMR hydrodynamical simulations in a (10 Mpc/h)$^3$ volume following the Pop III-Pop II transition and for different Pop III IMFs. We have analyzed the joint evolution of metal enrichment on galactic and intergalactic scales at z=6 and z=4. Galaxies account for <9% of the baryonic mass; the remaining gas resides in the diffuse phases: (a) voids, i.e. regions with extremely low density ($\Delta$<1), (b) the true intergalactic medium (IGM, 1<$\Delta$<10) and (c) the circumgalactic medium (CGM, 10<$\Delta<10^{2.5}$), the interface between the IGM and galaxies. By z=6 a galactic mass-metallicity relation is established. At z=4, galaxies with a stellar mass $M_*=10^{8.5}M_\odot$ show log(O/H)+12=8.19, consistent with observations. The total amount of heavy elements rises from $\Omega^{SFH}_Z=1.52\, 10^{-6}$ at z=6 to 8.05 $10^{-6}$ at z=4. Metals in galaxies make up to ~0.89 of such budget at z=6; this fraction increases to ~0.95 at z=4. At z=6 (z=4) the remaining metals are distributed in CGM/IGM/voids with the following mass fractions: 0.06/0.04/0.01 (0.03/0.02/0.01). Analogously to galaxies, at z=4 a density-metallicity ($\Delta$-Z) relation is in place for the diffuse phases: the IGM/voids have a spatially uniform metallicity, Z~$10^{-3.5}$Zsun; in the CGM Z steeply rises with density up to ~$10^{-2}$Zsun. In all diffuse phases a considerable fraction of metals is in a warm/hot (T>$10^{4.5}$K) state. Due to these physical conditions, CIV absorption line experiments can probe only ~2% of the total carbon present in the IGM/CGM; however, metal absorption line spectra are very effective tools to study reionization. Finally, the Pop III star formation history is almost insensitive to the chosen Pop III IMF. Pop III stars are preferentially formed in truly pristine (Z=0) gas pockets, well outside polluted regions created by previous star formation episodes.Comment: 23 pages, 18 figures, 3 tables, Accepted for publication in MNRA

Ly{\alpha} emission from galaxies in the Epoch of Reionization

The intrinsic strength of the Ly$\alpha$ line in young, star-forming systems makes it a special tool for studying high-redshift galaxies. However, interpreting observations remains challenging due to the complex radiative transfer involved. Here, we combine state-of-the-art hydrodynamical simulations of 'Althaea', a prototypical Lyman Break Galaxy (LBG, stellar mass $M_{\star}$$\simeq$ $10^{10}{\rm M}_{\odot})$ at $z=7.2$, with detailed radiative transfer computations of dust/continuum, [CII] 158 $\mu$m, and Ly$\alpha$ to clarify the relation between the galaxy properties and its Ly$\alpha$ emission. Althaea exhibits low ($f_\alpha< 1\%$) Ly$\alpha$ escape fractions and Equivalent Widths, EW $\lesssim 6$ Angstrom for the simulated lines of sight, with a large scatter. The correlation between escape fraction and inclination is weak, as a result of the rather chaotic structure of high-redshift galaxies. Low $f_\alpha$ values persist even if we artificially remove neutral gas around star forming regions to mimick the presence of HII regions. The high attenuation is primarily caused by dust clumps co-located with young stellar clusters. We can turn Althaea into a Lyman Alpha Emitter (LAE) only if we artificially remove dust from the clumps, yielding EWs up to $22$ Angstrom. Our study suggests that the LBG-LAE duty-cycle required by recent clustering measurements poses the challenging problem of a dynamically changing dust attenuation. Finally, we find an anti-correlation between the magnitude of Ly$\alpha$-[CII] line velocity shift and Ly$\alpha$ luminosity.Comment: published in MNRA

Il concetto di violenza nel passato e nella civilta di massa dei nostri tempi

In agreement with the title of this article, the essay is divided into two basic parts: one which is historical and the other philosophical. In the first part, the author examines at the beginning the classical latin etyma of the term uiolentia (uis, uiolare, uiolator, etc .. .. ). After that comes the acclaration of the philosophical concept of «violence» in Aristotle and Saint Thomas, and in continuation an indication of the application of the same concept to the field of ethics, and finally to the juridical field within classical roman law. In another sphere of considerations -ethical and political- the author points out the opinions of some characters which Plato introduces in his dialogues Gorgias and The Republic, due aboye all to the resonance which these works hace had in the history of the Western World until the present time. The subject of bloody violence, which is inherent to the action of the tyrannicide, is treated here briefly with references to the works of Cicero, John of Salisbury, Saint Thomas, Marsilius of Padua, Coluccio Salutati, Juan de Mariana, etc. Phenomena of midieval history suchaas the Crusades and the trials of the Inquisition could not be silenced in this case because both phenomena legitimized morally the use of violence directed towards infidels and heretics. The historical excursus on the topic of the legitimacy of violence in the hands of those who govern passes in successive orden, through Machiavelli, to the political literature on the areasson of state», jusnaturalism, etc ... To be underlined is the fact that since the end of the Eighteenth Century -and in an even much more important way in the realm of hegelian Idealism- the concept of violence has undergone a process of amplification as much within the field of Philosophy as within the experimental sciences: Darwin, Malthus and Hegel form the framework. This concept, which in Hegel's dialectic transformed itself into the dynamic principie of the antithesis, and which, therefore, affirmed the structure of the metaphysical movement of history, was passed on as a legacy to the successive hegelian trend, which was in itself so complex and so full of ramifications. The figure of Marx stands out in these pages not so much for his ties with the hegelian left, and with Feuerbach in particular, but rather because of one of the basic concepts of historical materialism -the struggle of the classes- which Marx underlined in his Communist Manifesto as the motivating force of history. The author then considers on the one hand the relationships which exist between the different european nationalisms of the last Century and the ones actually existing today, and, on the other, the Marxist ideology; he analyzes in passing the profound influence exercised by the Aufk/arung of the Eighteenth Century upon the deChristianization of man wrapped up first in his rationalism, and, later on, as a compensation, in new forms of religion and the cult of the world. From here on several names appear: Lenin, Stalin, Sorel, Mussolini, Hitler, etc., men who were very different one from the other and even opposed with regard to their respective political philosophies , but who set the pace for violence of a revolutionary and counter-revolutionary nature during short years or lasting decades. After a few more considerations, the first part of this essay ends with the author underlining the interest which experimental psychology and psycho-analysis have dedicated to the study of human aggressiveness and its mechanisms. In the second part of this work the author tries to establish gUidelines for the study of the relationships between the multiple phenomena of individual and collective violence in the present, and the mass civilization of our time. In the first place, the author makes a series of admonitions with relation to the words used: «violence-, .mass civilization- instead of «tnass society-, «civilization- instead ot «culture-, etc. He also recommends the need for not classifying en masse as a result of a reactionary mentality, the discontent which the intellectual contemplation of the present times produces in the observer, because if our state of animation could be termed as nothing else but «reactionary», then the same could be said to define a great part of the best literature of this Century, as well as the figurative arts of this modem age. The expression «mentality of violence- is applied in the historical context of cultural regression, from Friedrich Nietzsche to our day. After this, the author makes a summary description of the mental coordinates of massified man, as well as of certain particular features of the actual «organization- of culture, which is increasingly impregnated by political and economical ideas, in agreement with the fundamental methodology of historical materialism. The nucleus of these considerations is made up of a philosophical definition of the actual conditions of culture in Europe. This definition rests upon the conviction that the ideology of Marxism-Leninism, although it may by in a stage of partial historical modification, directs not only the political evolution of important sectors of , occidental society, but also that it has known how to model. thanks again to the coming-together of circunstances, the forma mentis of the contemporary intellectual. In the final part of the essay, the author dedicates special emphasis on the influence of Marxism upon wide sectors of modem Catholicism. He then adds several wamings in order to avoid , on the part of the reader, interpretations which might be inopportune or false

On the [CII]-SFR relation in high redshift galaxies

After two ALMA observing cycles, only a handful of [CII] $158\,\mu m$ emission line searches in z>6 galaxies have reported a positive detection, questioning the applicability of the local [CII]-SFR relation to high-z systems. To investigate this issue we use the Vallini et al. 2013 (V13) model, based on high-resolution, radiative transfer cosmological simulations to predict the [CII] emission from the interstellar medium of a z~7 (halo mass $M_h=1.17\times10^{11}M_{\odot}$) galaxy. We improve the V13 model by including (a) a physically-motivated metallicity (Z) distribution of the gas, (b) the contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic Microwave Background on the [CII] line luminosity. We study the relative contribution of diffuse neutral gas to the total [CII] emission ($F _{diff}/F_{tot}$) for different SFR and Z values. We find that the [CII] emission arises predominantly from PDRs: regardless of the galaxy properties, $F _{diff}/F_{tot}\leq 10$% since, at these early epochs, the CMB temperature approaches the spin temperature of the [CII] transition in the cold neutral medium ($T_{CMB}\sim T_s^{CNM}\sim 20$ K). Our model predicts a high-z [CII]-SFR relation consistent with observations of local dwarf galaxies ($0.02<Z/Z_{\odot}<0.5$). The [CII] deficit suggested by actual data ($L_{CII}<2.0\times 10^7 L_{\odot}$ in BDF3299 at z~7.1) if confirmed by deeper ALMA observations, can be ascribed to negative stellar feedback disrupting molecular clouds around star formation sites. The deviation from the local [CII]-SFR would then imply a modified Kennicutt-Schmidt relation in z>6 galaxies. Alternatively/in addition, the deficit might be explained by low gas metallicities ($Z<0.1 Z_{\odot}$).Comment: 9 pages, 6 figures, replaced with the version accepted for pubblication in Ap