614 research outputs found
The circumgalactic medium of high redshift galaxies
We study the properties of the circumgalactic medium (CGM) of high-
galaxies in the metal enrichment simulations presented in Pallottini et al.
2014. At , 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 () of CGM absorbers as a function of the
line of sight impact parameter (). We test our predictions against mock
spectra extracted from the simulations, and show that the model reproduces the
profile extracted from the synthetic spectra analysis.
When compared with available data, our CGM model nicely predicts the observed
in 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 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 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 ( GHz) up to 0.2 ( GHz); above \nu_{s}\gsim30
GHz the IGM contribution dominates over ISS modulation. We compare our model
with data from a quasar sample observed at \nu_{\obs}=8.4
GHz. For this high frequency (), 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-
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 Ly 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 accreting (a) metal-free
() gas with column density ,
or (b) low-metallicity gas () with
. The best fit model reproduces the
photometric data to within . Such metals can be produced by weak
star-forming activity occurring after the formation of the DCBH. The main
contribution to the Spitzer/IRAC photometric band in
both models is due to HeI/HeII emission lines, while the
contribution of [OIII] 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 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) 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 (<1), (b) the true intergalactic
medium (IGM, 1<<10) and (c) the circumgalactic medium (CGM,
10<), 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 show log(O/H)+12=8.19, consistent with
observations. The total amount of heavy elements rises from
at z=6 to 8.05 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
(-Z) relation is in place for the diffuse phases: the IGM/voids have a
spatially uniform metallicity, Z~Zsun; in the CGM Z steeply rises
with density up to ~Zsun. In all diffuse phases a considerable
fraction of metals is in a warm/hot (T>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 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
at , with detailed
radiative transfer computations of dust/continuum, [CII] 158 m, and
Ly to clarify the relation between the galaxy properties and its
Ly emission. Althaea exhibits low () Ly escape
fractions and Equivalent Widths, EW 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 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
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-[CII] line velocity shift and Ly 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]
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
) 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 () for different SFR and Z values. We find that the [CII]
emission arises predominantly from PDRs: regardless of the galaxy properties,
% since, at these early epochs, the CMB temperature
approaches the spin temperature of the [CII] transition in the cold neutral
medium ( K). Our model predicts a high-z
[CII]-SFR relation consistent with observations of local dwarf galaxies
(). The [CII] deficit suggested by actual data
( 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 ().Comment: 9 pages, 6 figures, replaced with the version accepted for
pubblication in Ap
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