Marco Fatuzzo - Academia.edu (original) (raw)

Papers by Marco Fatuzzo

Physical Review Letters, 1993

... 2004 and references therein) has also provided an observational basis for studying planetary ... more ... 2004 and references therein) has also provided an observational basis for studying planetary stability in binary systems (eg, Harrington 1977; Pendleton & Black 1983; Rabl & Dvorak 1988; Holman & Wiegert 1999; David et al. 2003; Pilat-Lohinger et al. 2003; Musielak et al. ...

The Astrophysical Journal, 2002

The relativistic jets in AGNs are probably driven by the action of supermassive, spinning black h... more The relativistic jets in AGNs are probably driven by the action of supermassive, spinning black holes. There is very little direct evidence for this, however, since the nuclei of active galaxies are difficult to study. This is now changing with new, high-resolution multi-wavelength observations of nearby sources, such as Sgr A* at the Galactic center, and the nucleus of NGC 6251 (hereafter called NGC 6251*). In this paper, we explore the possibility that the radiative properties of the most compact region in NGC 6251* may be understood in the same sense as Sgr A*, though with some telling differences that may hint at the nature of jet formation. We show that observations of this object with ASCA, ROSAT, HST and VLBI together may be hinting at a picture in which Bondi-Hoyle accretion from an ambient ionized medium feeds a standard disk accreting at ∼ 4.0×10 22 g s −1 . Somewhere near the event horizon, this plasma is heated to > 10 11 K, where it radiates via thermal synchrotron (producing a radio component) and self-Comptonization (accounting for a nonthermal X-ray flux).

The Astrophysical Journal, 2006

This paper studies the dynamical evolution of young groups/clusters, with N = 100 − 1000 members,... more This paper studies the dynamical evolution of young groups/clusters, with N = 100 − 1000 members, from their embedded stage out to ages of ∼ 10 Myr. We use N -body simulations to explore how their evolution depends on the system size N and the initial conditions. Motivated by recent observations suggesting that stellar groups begin their evolution with subvirial speeds, this study compares subvirial starting states with virial starting states. Multiple realizations of equivalent cases (100 simulations per initial condition) are used to build up a robust statistical description of these systems, e.g., the probability distribution of closest approaches, the mass profiles, and the probability distribution for the radial location of cluster members. These results provide a framework from which to assess the effects of groups/clusters on the processes of star and planet formation, and to study cluster evolution. The distributions of radial positions are used in conjunction with the probability distributions of the expected FUV luminosities (calculated here as a function of cluster size N ) to determine the radiation exposure of circumstellar disks. The distributions of closest approaches are used in conjunction with scattering cross sections (calculated here as a function of stellar mass using ∼ 10 5 Monte Carlo scattering experiments) to determine the probability of disruption for newly formed solar systems. We use the nearby cluster NGC 1333 as a test case in this investigation. The main conclusion of this study is that clusters in this size range have only a modest effect on forming planetary systems. The interaction rates are low so that the typical solar system experiences a single encounter with closest approach distance b ∼ 1000 AU. The radiation exposure is also low, with median FUV flux G 0 ∼ 900 (1.4 erg s −1 cm −2 ), so that photoevaporation of circumstellar disks is only important beyond 30 AU. Given the low interaction rates and modest radiation levels, we suggest that solar system disruption is a rare event in these clusters.

The Astrophysical Journal, 2012

The presence of relativistic particles at the center of our galaxy is evidenced by the diffuse Te... more The presence of relativistic particles at the center of our galaxy is evidenced by the diffuse TeV emission detected from the inner ∼2 • of the Galaxy. Although it is not yet entirely clear whether the origin of the TeV photons is due to hadronic or leptonic interactions, the tight correlation of the intensity distribution with the distribution of molecular gas along the Galactic ridge strongly points to a pionic-decay process involving relativistic protons. In earlier work, we concluded that point-source candidates, such as the supermassive black hole Sagittarius A* (identified with the HESS source J1745-290), or the pulsar wind nebulae dispersed along the Galactic plane, could not account for the observed diffuse TeV emission from this region. Motivated by this result, we consider here the feasibility that the cosmic rays populating the Galactic Center (GC) region are accelerated in situ by magnetic turbulence. Our results indicate that even in a highly conductive environment, this mechanism is efficient enough to energize protons within the intercloud medium to the TeV energies required to produce the HESS emission.

The Astrophysical Journal, 2005

The EGRET supernova remnants (SNR's) are all expanding into nearby dense molecular clouds, poweri... more The EGRET supernova remnants (SNR's) are all expanding into nearby dense molecular clouds, powering a shock at the interface where protons and electrons accelerate to relativistic energies. A viable mechanism for the emission of γrays in these sources is the decay of neutral pions created in collisions between the relativistic hadrons and protons in the ambient medium. But neutral pion decay alone cannot reproduce the whole high-energy spectrum, particularly below 100 MeV. A pion-decay scenario thus requires a lepton population to "fill in" the lower part of the spectrum via bremsstrahlung emission. This population, however, is constrained by the SNR radio spectrum. Taking our cue from the behavior of Sgr A East, an energetic EGRET SNR at the Galactic center, we here examine the role played in these sources by secondary leptons-electrons and positrons produced in proton-proton scattering events and the ensuing particle cascades. We show that while secondary leptons cannot account for the γ-rays below 100 MeV, they can account for the hard radio spectra observed from the EGRET SNR's. Thus, it appears that both primary and secondary leptons may be important contributors to the overall broadband emission from these sources, but if so, must radiate most of their energy in different parts of the SNR-cloud environment. We show that shock acceleration in dense cores being overtaken by the expanding SNR shell can naturally lead to such a scenario.

The Astrophysical Journal, 2005

Recent analysis of data sets from two extensive air shower cosmic ray detectors shows tantalizing... more Recent analysis of data sets from two extensive air shower cosmic ray detectors shows tantalizing evidence of an anisotropic overabundance of cosmic rays towards the Galactic Center (GC) that "turns on" around 10 18 eV. We demonstrate that the anisotropy could be due to neutrons created at the Galactic Center through charge-exchange in proton-proton collisions, where the incident, high energy protons obey an ∼ E −2 power law associated with acceleration at a strong shock. We show that the normalization supplied by the gamma-ray signal from EGRET GC source 3EG J1746-2851 -ascribed to pp induced neutral pion decay at GeV energies -together with a very reasonable spectral index of 2.2, predicts a neutron flux at ∼ 10 18 eV fully consistent with the extremely high energy cosmic -2ray data. Likewise, the normalization supplied by the very recent GC data from the HESS air-Cerenkov telescope at TeV energies is almost equally-well compatible with the ∼ 10 18 eV cosmic ray data. Interestingly, however, the EGRET and HESS data appear to be themselves incompatible. We consider the implications of this discrepancy. We discuss why the Galactic Center environment can allow diffusive shock acceleration at strong shocks up to energies approaching the ankle in the cosmic ray spectrum. Finally, we argue that the shock acceleration may be occuring in the shell of Sagittarius A East, an unusual supernova remnant located very close to the Galactic Center. If this connection between the anisotropy and Sagittarius A East could be firmly established it would be the first direct evidence for a particular Galactic source of cosmic rays up to energies near the ankle.

Physical Review D, 1991

Resistive tearing is a primary candidate for flares occurring in stressed magnetic fields. Its po... more Resistive tearing is a primary candidate for flares occurring in stressed magnetic fields. Its possible application to the strongly magnetized environments ({ital H}{sub {ital z}}{similar to}10¹² G) near the surfaces of neutron stars motivates a quantum treatment of this process, which requires knowledge of the electrical conductivity Ï of a relativistic gas in a new domain, i.e., that of a low-density ({ital n}{sub {ital e}}) plasma in oblique electric ({bold E}=(0,{ital E}{sub {ital y}},{ital E}{sub {ital z}})) and magnetic fields. We derive the mathematical formalism for calculating Ï and present numerical results for the range of parameter values 10⁹â¤{ital H}{sub {ital z}}â¤10¹² G, {ital E}{sub {ital z}}/{ital H}{sub {ital z}}{approx lt}10⁻⁴, {ital E}{sub {ital y}}{approx lt}10⁻⁴{ital H}{sub {ital z}}²/{ital E}{sub {ital z}}, and 10²°â¤{ital n}{sub {ital e}}â¤10²⁵ cm⁻³. We find that Ï{similar to}{ital E}{sub {ital y}}²{ital E}{sub {ital z}n{ital e}}²/{ital H}{sub {ital z}}² over this range.

Monthly Notices of the Royal Astronomical Society: Letters, 2011

The diffuse TeV emission detected from the inner ∼ 2 • of the Galaxy appears to be strongly corre... more The diffuse TeV emission detected from the inner ∼ 2 • of the Galaxy appears to be strongly correlated with the distribution of molecular gas along the Galactic ridge.

Physical Review Letters, 1993

Physical Review Letters, 1993

... 2004 and references therein) has also provided an observational basis for studying planetary ... more ... 2004 and references therein) has also provided an observational basis for studying planetary stability in binary systems (eg, Harrington 1977; Pendleton & Black 1983; Rabl & Dvorak 1988; Holman & Wiegert 1999; David et al. 2003; Pilat-Lohinger et al. 2003; Musielak et al. ...

The Astrophysical Journal, 2002

The relativistic jets in AGNs are probably driven by the action of supermassive, spinning black h... more The relativistic jets in AGNs are probably driven by the action of supermassive, spinning black holes. There is very little direct evidence for this, however, since the nuclei of active galaxies are difficult to study. This is now changing with new, high-resolution multi-wavelength observations of nearby sources, such as Sgr A* at the Galactic center, and the nucleus of NGC 6251 (hereafter called NGC 6251*). In this paper, we explore the possibility that the radiative properties of the most compact region in NGC 6251* may be understood in the same sense as Sgr A*, though with some telling differences that may hint at the nature of jet formation. We show that observations of this object with ASCA, ROSAT, HST and VLBI together may be hinting at a picture in which Bondi-Hoyle accretion from an ambient ionized medium feeds a standard disk accreting at ∼ 4.0×10 22 g s −1 . Somewhere near the event horizon, this plasma is heated to > 10 11 K, where it radiates via thermal synchrotron (producing a radio component) and self-Comptonization (accounting for a nonthermal X-ray flux).

The Astrophysical Journal, 2006

This paper studies the dynamical evolution of young groups/clusters, with N = 100 − 1000 members,... more This paper studies the dynamical evolution of young groups/clusters, with N = 100 − 1000 members, from their embedded stage out to ages of ∼ 10 Myr. We use N -body simulations to explore how their evolution depends on the system size N and the initial conditions. Motivated by recent observations suggesting that stellar groups begin their evolution with subvirial speeds, this study compares subvirial starting states with virial starting states. Multiple realizations of equivalent cases (100 simulations per initial condition) are used to build up a robust statistical description of these systems, e.g., the probability distribution of closest approaches, the mass profiles, and the probability distribution for the radial location of cluster members. These results provide a framework from which to assess the effects of groups/clusters on the processes of star and planet formation, and to study cluster evolution. The distributions of radial positions are used in conjunction with the probability distributions of the expected FUV luminosities (calculated here as a function of cluster size N ) to determine the radiation exposure of circumstellar disks. The distributions of closest approaches are used in conjunction with scattering cross sections (calculated here as a function of stellar mass using ∼ 10 5 Monte Carlo scattering experiments) to determine the probability of disruption for newly formed solar systems. We use the nearby cluster NGC 1333 as a test case in this investigation. The main conclusion of this study is that clusters in this size range have only a modest effect on forming planetary systems. The interaction rates are low so that the typical solar system experiences a single encounter with closest approach distance b ∼ 1000 AU. The radiation exposure is also low, with median FUV flux G 0 ∼ 900 (1.4 erg s −1 cm −2 ), so that photoevaporation of circumstellar disks is only important beyond 30 AU. Given the low interaction rates and modest radiation levels, we suggest that solar system disruption is a rare event in these clusters.

The Astrophysical Journal, 2012

The presence of relativistic particles at the center of our galaxy is evidenced by the diffuse Te... more The presence of relativistic particles at the center of our galaxy is evidenced by the diffuse TeV emission detected from the inner ∼2 • of the Galaxy. Although it is not yet entirely clear whether the origin of the TeV photons is due to hadronic or leptonic interactions, the tight correlation of the intensity distribution with the distribution of molecular gas along the Galactic ridge strongly points to a pionic-decay process involving relativistic protons. In earlier work, we concluded that point-source candidates, such as the supermassive black hole Sagittarius A* (identified with the HESS source J1745-290), or the pulsar wind nebulae dispersed along the Galactic plane, could not account for the observed diffuse TeV emission from this region. Motivated by this result, we consider here the feasibility that the cosmic rays populating the Galactic Center (GC) region are accelerated in situ by magnetic turbulence. Our results indicate that even in a highly conductive environment, this mechanism is efficient enough to energize protons within the intercloud medium to the TeV energies required to produce the HESS emission.

The Astrophysical Journal, 2005

The EGRET supernova remnants (SNR's) are all expanding into nearby dense molecular clouds, poweri... more The EGRET supernova remnants (SNR's) are all expanding into nearby dense molecular clouds, powering a shock at the interface where protons and electrons accelerate to relativistic energies. A viable mechanism for the emission of γrays in these sources is the decay of neutral pions created in collisions between the relativistic hadrons and protons in the ambient medium. But neutral pion decay alone cannot reproduce the whole high-energy spectrum, particularly below 100 MeV. A pion-decay scenario thus requires a lepton population to "fill in" the lower part of the spectrum via bremsstrahlung emission. This population, however, is constrained by the SNR radio spectrum. Taking our cue from the behavior of Sgr A East, an energetic EGRET SNR at the Galactic center, we here examine the role played in these sources by secondary leptons-electrons and positrons produced in proton-proton scattering events and the ensuing particle cascades. We show that while secondary leptons cannot account for the γ-rays below 100 MeV, they can account for the hard radio spectra observed from the EGRET SNR's. Thus, it appears that both primary and secondary leptons may be important contributors to the overall broadband emission from these sources, but if so, must radiate most of their energy in different parts of the SNR-cloud environment. We show that shock acceleration in dense cores being overtaken by the expanding SNR shell can naturally lead to such a scenario.

The Astrophysical Journal, 2005

Recent analysis of data sets from two extensive air shower cosmic ray detectors shows tantalizing... more Recent analysis of data sets from two extensive air shower cosmic ray detectors shows tantalizing evidence of an anisotropic overabundance of cosmic rays towards the Galactic Center (GC) that "turns on" around 10 18 eV. We demonstrate that the anisotropy could be due to neutrons created at the Galactic Center through charge-exchange in proton-proton collisions, where the incident, high energy protons obey an ∼ E −2 power law associated with acceleration at a strong shock. We show that the normalization supplied by the gamma-ray signal from EGRET GC source 3EG J1746-2851 -ascribed to pp induced neutral pion decay at GeV energies -together with a very reasonable spectral index of 2.2, predicts a neutron flux at ∼ 10 18 eV fully consistent with the extremely high energy cosmic -2ray data. Likewise, the normalization supplied by the very recent GC data from the HESS air-Cerenkov telescope at TeV energies is almost equally-well compatible with the ∼ 10 18 eV cosmic ray data. Interestingly, however, the EGRET and HESS data appear to be themselves incompatible. We consider the implications of this discrepancy. We discuss why the Galactic Center environment can allow diffusive shock acceleration at strong shocks up to energies approaching the ankle in the cosmic ray spectrum. Finally, we argue that the shock acceleration may be occuring in the shell of Sagittarius A East, an unusual supernova remnant located very close to the Galactic Center. If this connection between the anisotropy and Sagittarius A East could be firmly established it would be the first direct evidence for a particular Galactic source of cosmic rays up to energies near the ankle.

Physical Review D, 1991

Resistive tearing is a primary candidate for flares occurring in stressed magnetic fields. Its po... more Resistive tearing is a primary candidate for flares occurring in stressed magnetic fields. Its possible application to the strongly magnetized environments ({ital H}{sub {ital z}}{similar to}10¹² G) near the surfaces of neutron stars motivates a quantum treatment of this process, which requires knowledge of the electrical conductivity Ï of a relativistic gas in a new domain, i.e., that of a low-density ({ital n}{sub {ital e}}) plasma in oblique electric ({bold E}=(0,{ital E}{sub {ital y}},{ital E}{sub {ital z}})) and magnetic fields. We derive the mathematical formalism for calculating Ï and present numerical results for the range of parameter values 10⁹â¤{ital H}{sub {ital z}}â¤10¹² G, {ital E}{sub {ital z}}/{ital H}{sub {ital z}}{approx lt}10⁻⁴, {ital E}{sub {ital y}}{approx lt}10⁻⁴{ital H}{sub {ital z}}²/{ital E}{sub {ital z}}, and 10²°â¤{ital n}{sub {ital e}}â¤10²⁵ cm⁻³. We find that Ï{similar to}{ital E}{sub {ital y}}²{ital E}{sub {ital z}n{ital e}}²/{ital H}{sub {ital z}}² over this range.

Monthly Notices of the Royal Astronomical Society: Letters, 2011

The diffuse TeV emission detected from the inner ∼ 2 • of the Galaxy appears to be strongly corre... more The diffuse TeV emission detected from the inner ∼ 2 • of the Galaxy appears to be strongly correlated with the distribution of molecular gas along the Galactic ridge.

Physical Review Letters, 1993