1,721,209 research outputs found
Particle energy cascade in the intergalactic medium
Full text linkWe study the development of high-energy (Ein <= 1 TeV) cascades produced by a primary electron of energy Ein injected into the intergalactic medium (IGM). To this aim we have developed the new code MEDEA (Monte Carlo Energy Deposition Analysis) which includes Bremsstrahlung and inverse Compton (IC) processes, along with H/He collisional ionizations and excitations, and electron-electron collisions. The cascade energy partition into heating, excitations and ionizations depends primarily not only on the IGM ionized fraction, xe, but also on redshift, z, due to IC on cosmic microwave background (CMB) photons. While Bremsstrahlung is unimportant under most conditions, IC becomes largely dominant at energies Ein >= 1 MeV. The main effect of IC at injection energies Ein <= 100 MeV is a significant boost of the fraction of energy converted into low-energy photons (hν < 10.2 eV) which do not further interact with the IGM. For energies Ein >= 1 GeV CMB photons are preferentially upscattered within the X-ray spectrum (hν > 104 eV) and can free stream to the observer. Complete tables of the fractional energy depositions as a function of redshift, Ein and ionized fraction are given. Our results can be used in many astrophysical contexts, with an obvious application related to the study of decaying/annihilating dark matter (DM) candidates in the high-z Universe
Simulating intergalactic quasar scintillation
Full text linkIntergalactic scintillation of distant quasars is sensitive to free electrons and therefore complements
Lyα 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 SMequ = 3.879, i.e. almost 40 times larger than that for the usually assumed
smooth IGM. This yields an average modulation index ranging from 0.01 (νs = 5 GHz) up to
0.2 (νs = 50 GHz); above νs 30 GHz the IGM contribution dominates over ISS modulation.
We compare our model with data from a 0.3≤z≤2 quasar sample observed at νobs =8.4 GHz.
For this high-frequency (10.92 ≤ νs ≤ 25.2), high-galactic-latitude sample ISS is negligible,
and IGM scintillation can reproduce the observed modulation with a 4 per cent 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–Zel’dovich data
recently obtained by Planck
Diffuse Galactic Gamma Rays at intermediate and high latitudes. I. Constraints on the ISM properties
No full textWe study the high latitude (vertical bar b vertical bar > 10 degrees) diffuse gamma-ray emission in the Galaxy in light of the recently published data from the Fermi collaboration at energies between 100MeV and 100GeV. The unprecedented accuracy in these measurements allows to probe and constrain the properties of sources and propagation of cosmic rays (CRs) in the Galaxy, as well as confirming conventional assumptions made on the interstellar medium (ISM). Using the publicly available DRAGON code, that has been shown to reproduce local measurements of CRs, we study assumptions made in the literature on atomic (HI) and molecular hydrogen (H2) gas distributions in the ISM, and non spatially uniform models of diffusion in the Galaxy. By performing a combined analysis of CR and gamma-ray spectra, we derive constraints on the properties of the ISM gas distribution and the vertical scale height of galactic CR diffusion, which may have implications also on indirect Dark Matter detection. We also discuss some of the possible interpretations of the break at high rigidity in CR protons and helium spectra, recently observed by P A M E L A and their impact on gamma-rays
The H I Content of Local Late-type Galaxies
No full textWe present a solid relationship between the neutral hydrogen (H I) disk mass and the stellar disk mass of late-type galaxies in the local universe. This relationship is derived by comparing the stellar disk mass function from the Sloan Digital Sky Survey and the H I mass function from the H I Parkes All Sky Survey (HIPASS). We find that the H I mass in late-type galaxies tightly correlates with the stellar mass over three orders of magnitude in stellar disk mass. We cross-check our result with that obtained from a sample of HIPASS objects for which the stellar mass has been obtained by inner kinematics. In addition, we derive the H I versus halo mass relationship and the dependence of all the baryonic components in spirals on the host halo mass. These relationships bear the imprint of the processes ruling galaxy formation, and highlight the inefficiency of galaxies both in forming stars and in retaining their pristine H I gas
Turbulent axion-photon conversions in the Milky Way TURBULENT AXION-PHOTON CONVERSIONS in the MILKY ... CARENZA, EVOLI, GIANNOTTI, MIRIZZI, and MONTANINO
Full text linkThe Milky Way magnetic field can trigger conversions between photons and axionlike particles (ALPs), leading to peculiar features on the observable photon spectra. Previous studies considered only the regular component of the magnetic field. However, observations consistently show the existence of an additional turbulent component, with a similar strength and correlated on a scale of a few 10 pc. We investigate the impact of the turbulent magnetic field on the ALP-photon conversions, characterizing the effects numerically and analytically. We show that the turbulent magnetic field can change the conversion probability by up to a factor of two and may lead to observable irregularities in the observable photon spectra from different astrophysical sources
The galactic diffuse high energy neutrino flux
Full text linkWe calculate the diffuse high energy neutrino flux produced by the interactions of cosmic rays with the gas contained in our Galaxy. In order to quantify the role of uncertainties in the cosmic ray propagation models, we consider three different assumptions for the cosmic ray distribution in the Galaxy. We provide expectations for the spectrum and the angular dependence of the diffuse galactic neutrino flux. We compare our predictions with the isotropic flux required to explain the 54 HESE events observed by IceCube in four years data taking
Antiprotons from dark matter annihilation in the Galaxy: Astrophysical uncertainties
No full textThe latest years have seen steady progresses in weakly interacting massive particle dark matter (DM) searches, with hints of possible signals suggested both in direct and indirect detection. Antiprotons play a key role in this context, since weakly interacting massive particle annihilations can be a copious source of antiprotons, and the antiproton flux from conventional astrophysical sources is predicted with fair accuracy and matches the measured cosmic ray (CR) spectrum very well. Using the publicly available DRAGON code, we reconsider antiprotons as a tool to set constraints on DM models; we compare against the most up-to-date (p) over bar measurements, taking also into account the latest spectral information on the p and He CR fluxes. In particular, we probe carefully the uncertainties associated to both standard astrophysical and DM originated antiprotons, by using a variety of distinctively different assumptions for the propagation of CRs and for the DM distribution in the Galaxy. We find that the impact of the astrophysical uncertainties on constraining the DM properties of a wide class of annihilating DM models can be much stronger, up to a factor of similar to 50, than the one due to uncertainties on the DM distribution (similar to 2-6). Remarkably, even reducing the uncertainties on the propagation parameters derived by local observables, nonlocal effects can change our predictions for the constraints even by 50%. Nevertheless, current (p) over bar data can place tight constraints on DM models, excluding some of those suggested in connection with indirect and direct searches. Finally we discuss the impact of upcoming CR spectral data from the AMS-02 instrument on DM model constraints
Two-phase galaxy formation: the evolutionary properties of galaxies
Full text linkWe use our model for the formation and evolution of galaxies within a two-phase galaxy formation scenario, showing that the high-redshift domain typically supports the growth of spheroidal systems, whereas at low redshifts the predominant baryonic growth mechanism is quiescent and may therefore support the growth of a disc structure. Under this framework, we investigate the evolving galaxy population by comparing key observations at both low and high redshifts, finding generally good agreement. By analysing the evolutionary properties of this model, we are able to recreate several features of the evolving galaxy population with redshift, naturally reproducing number counts of massive star-forming galaxies at high redshifts, along with the galaxy scaling relations, star formation rate density and evolution of the stellar mass function. Building upon these encouraging agreements, we make model predictions that can be tested by future observations. In particular, we present the expected evolution to z = 2 of the supermassive black hole mass function, and we show that the gas fraction in galaxies should decrease with increasing redshift in a mass, with more and more evolution going to higher and higher masses. Also, the characteristic transition mass from a disc to bulge-dominated system should decrease with increasing redshift
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