49 research outputs found
The impact of primordial black holes on the high redshift Universe
No full textRecent measurements of the cosmic X-ray and radio backgrounds (CXB/CRB, respectively), obtained with Chandra and ARCADE2, report signals in excess of those expected from known sources. Similarly, measurements of the near infrared background (NIRB) angular power spectrum on angular scales θ ≥ 1 arcmin exceeds by roughly two order of magnitudes predictions from known galaxy populations. The nature of the sources producing the CXB/CRB excesses, and the NIRB fluctuations remains unknown, suggesting the presence of a yet undiscovered population of emitters. Interestingly, the NIRB has been found to cross-correlate with the soft-X-ray background (SXB), possibly justified by X-ray emission from elusive, high redshift accreting black holes (BHs). In this context, the most recent James Webb Space Telescope (JWST) observations have revealed the presence of z ∼ 6-11 active galactic nuclei (AGN) powered by accreting MBHs (M_{BH} ∼ 10^{6-8} M_{sun}). The existence of these sources, along with supermassive black holes (SMBHs, M_{BH} ∼ 10^{8-10} M_{sun}) powering z ∼ 6-7.5 quasars, poses a puzzle for current theoretical models of BH formation and evolution. It is indeed still unclear both the nature of the seeds from which these SMBHs are formed and their ability to grow fast enough to assemble an SMBH in less than 1 Gyr (the age of the Universe at z ∼ 6). These results can be interpreted as requiring either massive (M_{BH} ∼ 10^{4-6} M_{sun}) seeds and/or less extreme BHs experiencing bursts of super-Eddington accretion. In this Thesis, we tackle the aforementioned puzzles by ascribing their solution to a population of accreting primordial black holes (PBHs). PBHs are black holes that are expected to have formed during the radiation dominated era from the collapse of overdense regions, and have been considered as potential dark matter (DM) candidates. In particular, the questions we would like to answer are:Can PBHs be the sources of the observed backgrounds excess?Can PBHs lead to the formation of SMBHs seeds?This thesis describes the PBH theoretical model we developed and presents the analysis we carried out to answer the aforementioned two open questions
Cosmic radiation backgrounds from primordial black holes
No full textRecent measurements of the cosmic X-ray and radio backgrounds (CXB/CRB,
respectively) obtained with Chandra and ARCADE2 report signals in excess of
those expected from known sources, suggesting the presence of a yet
undiscovered population of emitters. We investigate the hypothesis that such
excesses are due to primordial black holes (PBHs) which may constitute a
substantial fraction of dark matter (DM). We present a novel semi-analytical
model which predicts X-ray and radio emission due to gas accretion onto PBHs,
assuming that they are distributed both inside DM halos and in the
intergalactic medium (IGM). Our model includes a self-consistent treatment of
heating/ionization feedback on the surrounding environment. We find that (i)
the emission from PBHs accreting in the IGM is subdominant at all times (); (ii) most of the CXB/CRB emission
comes from PBHs in DM mini-halos () at early epochs
(). While a small fraction () of DM in the form
of PBHs can account for the total observed CXB excess, the CRB one cannot be
explained by PBHs. Our results set the strongest existing constraint on in the mass range . Finally, we comment on the implications of our results on the global
21cm signal.Comment: 13 pages, 10 figures, 2 tables. Accepted for publication in MNRA
Primordial Black Holes as Near-Infrared Background sources
No full textThe near infrared background (NIRB) is the collective light from unresolved
sources observed in the band 1-10 m. The measured NIRB angular power
spectrum on angular scales arcmin exceeds by roughly two
order of magnitudes predictions from known galaxy populations. The nature of
the sources producing these fluctuations is still unknown. Here we test
primordial black holes (PBHs) as sources of the NIRB excess. Considering PBHs
as a cold dark matter (DM) component, we model the emission of gas accreting
onto PBHs in a cosmological framework. We account for both accretion in the
intergalactic medium (IGM) and in DM haloes. We self consistently derive the
IGM temperature evolution, considering ionization and heating due to X-ray
emission from PBHs. Besides CDM, we consider a model that accounts for
the modification of the linear matter power spectrum due to the presence of
PBHs; we also explore two PBH mass distributions, i.e. a -function and
a lognormal distribution. For each model, we compute the mean intensity and the
angular power spectrum of the NIRB produced by PBHs with mass
1-. In the limiting case in which the entirety of DM
is made of PBHs, the PBH emission contributes <1 per cent to the observed
NIRB fluctuations. This value decreases to <0.1 per cent if current
constraints on the abundance of PBHs are taken into account. We conclude that
PBHs are ruled out as substantial contributors to the NIRB
Blue monsters : why are JWST super-early, massive galaxies so blue?
No full textThe recent James Webb Space Telescope tentative discovery of a population of super-early (redshift z > 10), relatively massive (stellar mass M* = 108-109M⊙) and evolved (metallicity Z ≈ 0.1 Z⊙) galaxies, which nevertheless show blue (β ≃ -2.6) spectra, and very small dust attenuation (AV ≲ 0.02), challenges our interpretation of these systems. To solve the puzzle, we propose two solutions in which dust is either (a) ejected by radiation pressure, or (b) segregated with respect to UV-emitting regions. We clarify the conditions for which the two scenarios apply, and show that they can be discriminated by ALMA observations, such as the recent non-detection of the 88μm dust continuum in GHZ2 (z ≃ 12) favouring dust ejection
S.P.Q.R. + Sicilia RoboCup 2005 Report
No full textInternational audienceThe Italian Robot Team SPQR+Sicilia is the result of a joint effort of two Italian research groups: S.P.Q.R. (Soccer Player Quadruped Robots, but also Senatus PopolusQue Romanus): the group of the Faculty of Engineering at University of Rome “La Sapienza” in Italy, that is involved in RoboCup competitions since 1998 in different leagues (Middle-size 1998-2002, Four-legged since 2001, Real-rescue-robots since 2003). The members of S.P.Q.R. are: Luca Iocchi (Team Leader), Daniele Nardi, Vittorio Amos Ziparo, Andrea Cherubini, Simone Elviretti, Francesca Giannone, Stefano La Cesa, Francesco Macr`ı, Luca Marchetti, Pier Francesco Palamara, Maria Sciannelli. SICILIA: the group of the Computer Science Department at University of Palermo that was involved in Middle-size RoboCup competitions in 1998-1999. The members of SICILIA are: Rosario Sorbello (Team Leader), Antonio Chella (Team Leader), Salvatore Maria Anzalone, Giuseppe Balistreri, Rosamaria Elisa Barone, Dario Cacca, Alessandro Cimino, Francesco Cinquegrani, Francesco Di Paola, Ivan Di Paola, Laura Mancuso, Luca Maria Benedetto Martorana, Sergio Orlando, Marco Palermo, Giovanni Reina, Carmelo Scozzola This paper presents the main development efforts of the team in 2005. In the following sections, before addressing the specific issues that have been developed during this year, we will briefly describe the features of the software architecture. Moreover, specific issues regarding the challenges will be reported in the last section
Total shunting and elective management of variceal bleeding
No full textA 20-year experience with treatment of esophageal varices in patients with cirrhosis is reported. Considering that total shunts are well tolerated immediately after operation (hospital mortality rate for all elective procedures being 6.4%), that they offer a good protection against rebleeding (rebleeding variceal rate of 7.6%), and that they offer the same long-term survival as given by other shunts (5- and 10-year survival rates of 57% and 31%, respectively), the authors affirm that these kinds of shunts are still useful in well selected cases. Late follow-up results of a prospective randomized trial of elective mesocaval shunts compared to portacaval shunt have shown no significant differences in operative mortality, rebleeding rates, encephalopathy rates, or survival. Based on this information, the authors currently use portacaval shunt as their operation of choice
Teamwork Design Based on Petri Net Plans
No full textThis paper presents a design of cooperative behaviors through Petri Net Plans, based on the principles provided by Cohen and Levesque's Joint Commitments Theory. Petri Net Plans are a formal tool that has proved very effective for the representation of multi-robot plans, providing all the means necessary for the design of cooperation. The Joint Commitment theory is used as a guideline to present a general multi-robot Petri Net Plan for teamwork, that can be used to model a wide range of cooperative behaviors. As an example we describe the implementation of a robotic-soccer passing task, performed by Sony AIBO robots. © 2009 Springer Berlin Heidelberg
High redshift radio background from primordial black holes
No full textThe discovery of gravitational waves from black hole mergers detected by the LIGO/VIRGO interferometers have been brought renew interest to the field of primordial black holes (PBHs). These objects have many fields of application.
They can be used to probe primordial inhomogeneities, the properties of the early Universe and they are considered possible non-baryonic Dark Matter candidates.
PBHs are formed by gravitational collapse of overdense regions in the early Universe, during the radiation dominated era.
The presence of a population of Black Holes accreting at high redshift could be used to investigate unclear results obtained by observational experiments such as EDGES or ARCADE2. These results revealed, respectively, an anomalous amplitude in the 21cmabsorption signal at z = 17 and an extragalactic radio excess over the CMB at redshift z = 0. In this thesis we model the accretion of PBHs in dark matter halos to compute their radio emission, with the final aim to understand whether the EDGES and ARCADE2 results can be explained by a radio background of PBHs.
To compute the radio emission from PBHs we proceed as follows. Given a dark matter halo of mass M_H at a given redshift, we first compute the expected number of PBHs for given value of f_DM (namely the fraction of dark matter that can be explained through PBHs) and PBHs mass (we assume M = 30 M_sun). For each PBH, we compute its accretion rate considering the Bondi-Hoyle Littleton prescription according to which the accretion rate depends on the gas density distribution and the sound speed in the gas surrounding the black hole. Given the accretion rate, the bolometric luminosity (Lbol epsilon ˙M c2, where epsilon is the radiative efficiency) can be converted into an X-Ray luminosity through bolometric corrections (L_X = 0.3 Lbol ). Finally, we adopt the Fundamental Plane relation to compute the radio emission starting from the X-Ray luminosity.
The main results of our work are the following:
• for fDM = 0.05 ( fDM = 1) we find that the expected radio luminosity of
DM halos with 10^8 < M_H/M_sun < 10^10 at redshift z = 10 is 10^32 < L_rad/erg/s < 10^36
(10^32 < L_rad/ergs < 10^36);
• At z = 17 our model predicts a radio background intensity from accreting
PBHs (4x10^(-21) < I21,PBH < 9x10^(-18)[erg/scm^2srHz]) depending on the
choice of parameters ( f_DM, epsilon);
• By taking into account the radio background expected from accreting
PBHs, we find that these sources can only explain <=30% of the EDGES
signal.
We discuss possible improvements of the model that can be further constrained through ARCADE2 data
