Intergalactic Space Research Articles

On the hadronic cascade scenario for extreme BL Lacs

The peculiar high-energy emission spectrum of the so-called extreme BL Lacs (EHBL) challenges the standard emission models of blazars. Among the possible solutions, the so-called hadronic cascade scenario assumes that the observed high-energy radiation is produced in the intergalactic space through photo-hadronic reactions by ultra-high energy cosmic rays (UHECR) with energies up to 1019−20 eV beamed by the blazar jet. Under the assumption – implicit in this model – that the intrinsic high-energy synchrotron self-Compton emission of the blazar does not substantially contribute to the observed γ-ray spectrum, we derive constraints to the basic physical quantities of the jet and we compare them with the requirements of the hadronic cascade scenario. We found that, for a plausible range of relativistic jet Doppler factors (δ = 10–50), the maximum achievable energy of the accelerated protons can exceed 2 × 1019 eV with jet powers of the order of ≈1044 erg s−1, parameters compatible with the requests of the hadronic scenario even if EHBL are embedded in magnetic fields of cosmic filaments. We also discuss the consequences of our results for the possibility that local EHBL contribute to the observed UHECR.

TeV GAMMA RAYS: OBSERVATIONS VERSUS EXPECTATIONS & THEORY

The scope of this paper is to discuss two important questions relevant for TeV γ-ray astronomy; the pursuit to reveal the origin of cosmic rays in our galaxy, and the opacity of the universe in γ-rays. The origin of cosmic rays stipulated the field of TeV astronomy in the first place, and led to the development of the atmospheric Cherenkov technique; significant progress has been made in the last decade through the detection of several supernova remnants, the primary suspects for harboring the acceleration sites of cosmic rays. TeV γ-rays propagate mostly unhindered through the galactic plane, making them excellent probes of processes in SNRs and other galactic sources. Key results related to the SNR origin of cosmic rays are discussed. TeV γ-ray spectra from extragalactic sources experience significant absorption when traversing cosmological distances. The opacity of the universe to γ-rays above 10 GeV progressively increases with energy and redshift; the reason lies in their pair production with ambient soft photons from the extragalactic background light (EBL). While this limits the γ-ray horizon, it offers the opportunity to gain information about cosmology, i.e. the EBL intensity, physical conditions in intergalactic space, and potentially new interaction processes. Results and implications pertaining to the EBL are given.

Probing the origin of cosmic rays with extremely high energy neutrinos using the IceCube Observatory

We have searched for extremely high energy neutrinos using data taken with the IceCube detector between May 2010 and May 2012. Two neutrino induced particle shower events with energies around 1 PeV were observed, as reported previously. In this work, we investigate whether these events could originate from cosmogenic neutrinos produced in the interactions of ultra-high energy cosmic-rays with ambient photons while propagating through intergalactic space. Exploiting IceCube's large exposure for extremely high energy neutrinos and the lack of observed events above 100 PeV, we can rule out the corresponding models at more than 90% confidence level. The model independent quasi-differential 90% CL upper limit, which amounts to $E^2 \phi_{\nu_e + \nu_\mu + \nu_\tau} = 1.2 \times 10^{-7}$ GeV cm$^{-2}$ s$^{-1}$ sr$^{-1}$ at 1 EeV, provides the most stringent constraint in the energy range from 10 PeV to 10 EeV. Our observation disfavors strong cosmological evolution of the highest energy cosmic ray sources such as the Fanaroff-Riley type II class of radio galaxies.

H.E.S.S. discovery of VHEγ-rays from the quasar PKS 1510−089

The quasar PKS 1510-089 (z=0.361) was observed with the H.E.S.S. array of imaging atmospheric Cherenkov telescopes during high states in the optical and GeV bands, to search for very high energy (VHE, defined as E >= 0.1 TeV) emission. VHE \gamma-rays were detected with a statistical significance of 9.2 standard deviations in 15.8 hours of H.E.S.S. data taken during March and April 2009. A VHE integral flux of I(0.15 TeV < E < 1.0 TeV) = (1.0 +- 0.2 (stat) +- 0.2 (sys) x 10^{-11} cm^{-2}s^{-1} is measured. The best-fit power law to the VHE data has a photon index of \Gamma=5.4 +- 0.7 (stat) +- 0.3 (sys). The GeV and optical light curves show pronounced variability during the period of H.E.S.S. observations. However, there is insufficient evidence to claim statistically significant variability in the VHE data. Because of its relatively high redshift, the VHE flux from PKS 1510-089 should suffer considerable attenuation in the intergalactic space due to the extragalactic background light (EBL). Hence, the measured \gamma-ray spectrum is used to derive upper limits on the opacity due to EBL, which are found to be comparable with the previously derived limits from relatively-nearby BL Lac objects. Unlike typical VHE-detected blazars where the broadband spectrum is dominated by non-thermal radiation at all wavelengths, the quasar PKS 1510-089 has a bright thermal component in the optical to UV frequency band. Among all VHE detected blazars, PKS 1510-089 has the most luminous broad line region (BLR). The detection of VHE emission from this quasar indicates a low level of \gamma-\gamma absorption on the internal optical to UV photon field.

Radio continuum observations of the Leo Triplet at 2.64 GHz

Aims. The magnetic fields of the member galaxies NGC 3628 and NGC 3627 show morphological peculiarities, suggesting that interactions within the group may be caused by stripping of the magnetic field. This process could supply the intergalactic space with magnetised material, a scenario considered as a possible source of intergalactic magnetic fields (as seen eg. in the Taffy pairs of galaxies). Additionally, the plumes are likely to be the tidal dwarf galaxy candidates. Methods. We performed radio continuum mapping observations at 2.64 GHz using the 100-m Effelsberg radio telescope. We obtained total power and polarised intensity maps of the Triplet. These maps were analysed together with the archive data, and the magnetic field strength (as well as the magnetic energy density) was estimated. Results. Extended emission was not detected either in the total power or the polarised intensity maps. We obtained upper limits of the magnetic field strength and the energy density of the magnetic field in the Triplet. We detected emission from the easternmost clump and determined the strength of its magnetic field. In addition, we measured integrated fluxes of the member galaxies at 2.64 GHz and estimated their total magnetic field strengths. Conclusions. We found that the tidal tail hosts a tidal dwarf galaxy candidate that possesses a detectable magnetic field with a non-zero ordered component. Extended radio continuum emission, if present, is weaker than the reached confusion limit. The total magnetic field strength does not exceed 2.8 {\mu}G and the ordered component is lower than 1.6 {\mu}G.

EVIDENCE FOR SECONDARY EMISSION AS THE ORIGIN OF HARD SPECTRA IN TeV BLAZARS

We develop a model for a possible origin of hard very high energy spectra from a distant blazar. In the model, both the primary photons produced in the source and secondary photons produced outside the source contribute to the observed high energy $\gamma$-rays emission. That is, the primary photons are produced in the source through the synchrotron self-Compton (SSC) process, and the secondary photons are produced outside the source through high energy protons interaction with the background photons along the line of sight. We apply the model to a characteristic case was the very high energy (VHE) $\gamma$-ray emissions in distant blazar 1ES 1101-232. Assuming a suitable electron and proton spectra, we obtain excellent fits to observed spectra of distant blazar 1ES 1101-232. This indicated that the surprisingly low attenuation of high energy $\gamma$-rays, especially for the shape of the very high energy $\gamma$-rays tail of the observed spectra, can be explained by secondary $\gamma$-rays produced in interactions of cosmic-ray protons with background photons in the intergalactic space.

Do intergalactic magnetic fields imply an open universe?

The detection of magnetic fields at high redshifts, and in empty intergalactic space, supports the idea that cosmic magnetism has a primordial origin. Assuming that Maxwellian electromagnetism and general relativity hold, and without introducing any new physics, we show how the observed magnetic fields can easily survive cosmological evolution from the inflationary era in a marginally open Friedmann universe but fail to do so, by a very wide margin, in a flat or a marginally closed universe. Magnetic fields evolve very differently in open and closed Friedmann models. The existence of significant magnetic fields in the universe today, that require primordial seeding, may therefore provide strong evidence that the universe is marginally open rather than marginally closed.

Minimal cosmogenic neutrinos

The observed flux of ultra-high energy (UHE) cosmic rays (CRs) guarantees the presence of high-energy cosmogenic neutrinos that are produced via photo-hadronic interactions of CRs propagating through intergalactic space. This flux of neutrinos doesn't share the many uncertainties associated with the environment of the yet unknown CR sources. Cosmogenic neutrinos have nevertheless a strong model dependence associated with the chemical composition, source distribution or evolution and maximal injection energy of UHE CRs. We discuss a lower limit on the cosmogenic neutrino spectrum which depends on the observed UHE CR spectrum and composition and relates directly to experimentally observable and model-independent quantities. We show explicit limits for conservative assumptions about the source evolution.

Analytic calculations of the spectra of ultra-high energy cosmic ray nuclei. I. The case of CMB radiation

We present a systematic study of different methods for the analytic calculation of ultra-high energy nuclei diffuse spectra. Nuclei propagating in the intergalactic space are photo-disintegrated and decrease their Lorentz factor due to the interaction with Cosmic Microwave Background and extragalactic background light. We calculate the evolution trajectories in the backward time, that describe how atomic mass number A and Lorentz factor Γ change with redshift z. Three methods of spectra calculations are investigated and compared: (i) trajectory method, (ii) kinetic equation combined with trajectory calculations and (iii) coupled kinetic equations. We believe that these three methods exhaust at least the principal possibilities for any analytic solution of the problem. In the most straightforward method (i) only trajectory calculations are used to connect the observed nuclei flux with the production rate of primary (accelerated) nuclei A0. In the second method (ii) the flux (space density) of primary nuclei, and secondary nuclei and protons are calculated with the help of kinetic equation and trajectories are used only to determine the generation rates of these nuclei. The third method (iii) consists in solving the complete set of coupled kinetic equations, written starting with primary nuclei A0, then for A0-1 etc. down to the A of interest. The solution of the preceding equation gives the generation rate for the one which follows. An important element of the calculations for all methods is the systematic use of Lorentz factor instead of energy. We consider here the interaction of nuclei only with the Cosmic Microwave Background, this case is particularly suitable for understanding the physical results. In paper (II) of this series the extragalactic background light will be also included. Estimating the uncertainties of all methods discussed above, we conclude that the method of coupled kinetic equations gives the most reliable results.

NGC 3627: a galaxy-dwarf collision?

Group galaxies very often show distinct signs of interaction with both companion galaxies and the intragroup medium. X-ray observations are particularly helpful because they provide information on the temperatures and the densities of the hot gas in galaxies and intergalactic space. This can put important constraints on the nature and timescales of these interactions. We use the XMM-Newton X-ray observations of NGC 3627 in the Leo Triplet galaxy group to explain peculiar features visible in the polarized radio maps. We analyzed soft X-ray (0.2-1 keV) emission from NGC 3627 to study the distribution of the hot gas and its temperature in different areas of the galaxy. Any change throughout the disk can reflect distortions visible in the radio polarized emission. We also studied two bright point sources that are probably tightly linked to the evolution of the galaxy. We find an increase in the temperature of the hot gas in the area of the polarized radio ridge in the western arm of the galaxy. In the eastern part of the disk we find two ultra-luminous X-ray sources. We note a large hot gas temperature difference (by a factor of 2) between the two bar ends. The polarized radio ridge in the western arm of NGC 3627 is most likely formed by ram-pressure effects caused by the movement of the galaxy through the intragroup medium. To explain the distortions visible in the eastern part of the disk in polarized radio maps, the asymmetry of the bar, and the distortion of the eastern arm, we propose a recent collision of NGC 3627 with a dwarf companion galaxy.

Experimental confirmation of the IsoRedShift at sunset and sunrise, with consequential absence of the universe expansion and related conjectures1

In this paper, we recall the mutation of the Minkowski spacetime for empty space into the covering isospacetime caused by physical media; we recall its experimental verifications via the isoredshift of laser light in a metal pipe containing air at pressure, as well as additional experimental verifications in other fields; and we present, apparently for the first time, experimental confirmations of Santilli's 1991 prediction of the isoredshift as the primary origin of the redness of direct Sunlight at Sunset and Sunrise without any appreciable relative motion between Earth and Sun, said isoredshift being proportional to the distance traveled by Sunlight in air. Absorption is dismissed as a source of said redness of the Sun because air predominantly absorbs red, as experimentally established, without dismissing minor contributions, e.g., for the shape (but not the shift) of wavelengths. The widely accepted conjecture that scattering is the origin of said redness of the Sun, without dismissing minor contributions, is shown to be inapplicable for direct Sunlight, to have no representational capability for the needed very large shifts (measured up to 200 nm), and to have been dismissed experimentally at the cosmological level with recent measurements via Hubble's telescope, as well as on Earth by recent scattering measurements by some of us. Since intergalactic spaces are far from being empty, and physical laws must be the same throughout the universe, the preceding experimental results are shown to be evidence for the absence of the expansion of the universe, the absence of the acceleration of the expansion, the absence of the big bang, and the elimination of the far reaching conjecture that space itself is expanding as needed, from Hubble's law, to prevent a return to the Middle Ages with Earth at the center of the universe. It is finally shown that the same experimental confirmations of Santilli isoredshift imply the absence of dark matter and dark energy since the universe is nowhere empty, with consequential universal validity of Santilli isospacetime and its Lorentz-Poincare-Santilli isosymmetry.

Indications for a pair-production anomaly from the propagation of VHEgamma-rays

In the recent years, the number of detected very high energy (VHE: E > 100 GeV) gamma-ray sources has increased rapidly. The sources have been observed at redshifts up to z = 0.536 without strong indications for the presence of absorption featuresin the energy spectra. Absorption is however expected due to pair-production processes of thepropagating photons with the photon bath in intergalactic space. Even though this photon density is not well known, lower limits can befirmly set by the resolved emission from galaxy counts. Using this guaranteed background light, we investigate the behaviour of theenergy spectra in the transition region from the optically thin to the optically thick regime. Among the sample of 50 energy spectra, 7 spectra cover the the range from optical depth τ < 1 to τ > 2. For these sources, the transition to τ > 2 takes place at widely different energies ranging from 0.4 TeV to 21 TeV. Consistently, in all of these sources,an upturn of the absorption-corrected spectrum is visible at this transition with a combined significance of 4.2 standard deviations. Given the broad range of energies and redshifts covered by the sample, source-intrinsic features are unlikely to explain the observed effect. Systematic effects related to observations have been investigated and found to be not sufficient to account for the observed effect.The pair-production process seems to be suppressed in a similar way as expected in the extension of the standard model by a light ( < neV) pseudoscalar (axion-like) particle.

Cosmic Rays in the Disk and Halo of Galaxies

We give a review of cosmic ray propagation models. It is shown that the development of the theory of cosmic ray origin leads inevitably to the conclusion that cosmic ray propagation in the Galaxy is determined by effective particle scattering, which is described by spatial diffusion. The Galactic Disk is surrounded by an extended halo, in which cosmic rays are confined before escaping into intergalactic space. For a long time cosmic ray convective outflow from the Galaxy (galactic wind) was believed to be insignificant. However, investigations of hydrodynamic stability and an analysis of ISM dynamics (including cosmic rays) showed that a galactic wind was emanating near the disk, and accelerating towards the halo, reaching its maximum velocity far away from the disk. Therefore convective cosmic ray transport should be important in galactic halos. Recent analysis of the gamma-ray emissivity in the Galactic disk of EGRET data, which showed that cosmic rays are more or less uniformly distributed in the radial direction of the disk, as well as the interpretation of soft X-ray emission in galactic halos, give convincing evidence of the existence of a galactic wind in star forming galaxies.

Photon-axion mixing and ultra-high energy cosmic rays from BL Lac type objects: Shining light through the Universe

Photons may convert into axion like particles and back in the magnetic field of various astrophysical objects, including active galaxies, clusters of galaxies, intergalactic space and the Milky Way. This is a potential explanation for the candidate neutral ultra-high-energy (E>10^18 eV) particles from distant BL Lac type objects which have been observed by the High Resolution Fly's Eye experiment. Axions of the same mass and coupling may explain also TeV photons detected from distant blazars.

Suzaku Metal Abundance Patterns in the Outflow Region of M 82 and the Importance of Charge Exchange

Abstract We performed spectral analysis of Suzaku data of the galactic disk and outflow regions of the starburst galaxy M 82. Thermal modeling of the central disk regions requires at least three temperature components. The Ly $\beta $ line fluxes of O VIII and Ne X exceed those expected from a plasma in collisional ionization equilibrium. The ratios of the Ly $\beta/$ Ly $\alpha$ lines for O VIII and Ne X are higher than those of collisional ionization equilibrium, which may be caused by the process of charge exchange. In the outflow wind region, the spectra are well reproduced with two-temperature thermal models, and we have derived the metal abundances of O, Ne, Mg, and Fe in the outflow. The ratios of O $/$ Fe, Ne $/$ Fe, and Mg $/$ Fe are about 2, 3, and 2, respectively, relative to the solar value determined by Lodders (2003, ApJ, 591, 1220). Since there is no evidence of charge exchange in the outflow region, the metal abundances should be more reliable than those in the central region. This abundance pattern indicates that starburst activity enriches the outflow through SN II metal ejection into intergalactic space.

The Mind, Intergalactic Space, and Phi

Although counter-intuitive, many published papers have proved that scientific experiments are affected by the act of observation, as well as the mind being affected by local astronomical forces and factors, such as gravity, electromagnetism, spin, and orientation. This paper details the ability of the mind to filter out all of these local factors, and visualise experiments as if they were being undertaken in intergalactic space. In order to undertake this research both the mind and quantitative observation are required. As dowsing involves both it was adopted. The physical dimensions of simple geometric shapes were measured to compare to the dimensions of the same geometric shapes perceived “mentally” by the body’s senses. Global scaling has been demonstrated in these laboratory conditions with simple equations obeying power laws that involve the universal constant phi (φ) and no arbitrary constants. Examples are d = 0.5 * L ^ φ /2, Smax = 2 . r ^ φ, and a = φ * r ^ √φ. These formulae cannot be random results. The implications are (1) that phi forms part of the structure of space-time, (2) the important quantified discovery that the mind can interface with the fundamentals of space-time and the cosmos. The latter concept supports ancient Eastern philosophy, although it is alien to traditional western science.

Gas dynamics of a central collision of two galaxies: Merger, disruption, passage, and the formation of a new galaxy

Results of numerical simulations of a collision of the gaseous components of two identical disk galaxies during a head-on collision of the galaxies in the polar direction are presented. When the relative velocity of the galaxy collision is small, their gaseous components merge. At high relative velocities (100–500 km/s), the massive stellar components of the galaxies (Mg = 109M⊙) pass through each other nearly freely, leaving behind the gaseous components, which are decelerated and heated by the collision. If the overall gaseous component of the colliding galaxies is able to cool to the virial temperature during the collision, a new galaxy forms. At velocities V ≥ 500 km/s, the gaseous component does not have time to cool, and the gas is scattered into intergalactic space, supplying it with heavy elements produced in supernovae in the colliding galaxies. High-velocity (V ≥ 100 km/s) collisions of identical low-mass galaxies (Mg ≤ 109M⊙) whose mass is dominated by the mass of gas lead to the disruption of their stellar components. The overall gaseous component forms a new galaxy when V ≤ 500 km/s, and is scattered into intergalactic space if the velocity becomes higher than this. A galaxy collision increases the star-formation rates in the disk galaxies by nearly a factor of 100. Rotation of the colliding galaxies in the same direction increases the changes of the disruption of both the stellar and gaseous components of the galaxies. The merger of galaxies during their collision can explain the presence of gaseous disks rotating opposite to the rotation of the stellar component in some ordinary elliptical galaxies. Moreover, galaxy mergers can help explain the origin of a comparatively young stellar population in some elliptical galaxies.

Properties of mid- to far-infrared dust emission in the nearby superwind galaxy M82

AbstractUsing the reconstructed imaging data obtained with the Infrared Camera (IRC) on board AKARI, mid-infrared (MIR; 5-30 μm) emission characteristics of the superwind galaxy M82 are studied. The MIR images at four wavelengths (7, 11, 15, and 24 μm) show extended (out to distances of 4 kpc) emission mainly from polycyclic aromatic hydrocarbons (PAHs). The MIR SED of M82 halo is surprisingly constant. Using far-infrared imaging data obtained by Herschel/SPIRE, we reveal that the PAH abundance relative to the big (sub-micron sized) grains radially increases by about a factor of three. These results imply that PAHs may be formed in small and dense molecular clumps in the halo and efficiently supplied to the intergalactic space by the galactic superwind.

The origin of intergalactic stars in galaxy clusters

The paper analyzes possible origins of stars located in intergalactic space that are not bound to specific galaxies, which comprise 15–50% of all stars in galaxy clusters. Some such stars can form in streams of intergalactic gas flowing around gas-rich disk galaxies moving in the cluster. Others may be the products of the decay of young, low-mass, spheroidal galaxies after the loss of their gaseous components during an initial burst of star formation. The decay of low-mass disk galaxies moving at high speeds after they have lost their gaseous components due to the pressure of the incident flow of dense intergalactic gas is possible in the cluster core. The largest fraction of intergalactic stars are probably produced by the partial disruption of galaxies as a result of close passages, collisions, or mergers. Collisions of low-mass, gas-rich galaxies are especially good suppliers of intergalactic stars. Both stars from decaying stellar components of galaxies and stars arising in the gaseous components of colliding galaxies can be supplied to the intergalactic medium. The merger of galaxies harboring supermassive black holes in their nuclei could lead to the partial or total disruption of these galaxies during the deceleration of the binary black hole that is formed during the merger. An enhanced density of intergalactic stars is observed in the cores of galaxy clusters, underscoring the role of galaxy collisions in the formation of the intergalactic stellar population, since the frequency of galaxy collisions grows with their density.

Spectropolarimetry of the Superwind Filaments of the Starburst Galaxy M 82: Kinematics of Dust Outflow

Spectropolarimetry results for the starburst galaxy M 82 are presented. The optical emission lines of the filaments in the energetic outflow (``superwind'') from the nuclear starburst region of M 82 are substantially polarized. The H$\alpha$ polarization degrees and angles measured by our study are consistent with previous narrowband imaging polarimetry data. The polarized emission lines are redshifted with respect to the emission lines in the total light and systemic motion of the galaxy. The emission line intensity ratios [N II]$/$H$\alpha$ and [S II]$/$H$\alpha$ in the polarized light are similar to those of the nuclear star-forming region. In addition, the electron density $N_{\rm e}$ derived from the [S II]$\lambda$6731$/\lambda$6717 line ratio of the polarized light is $\sim\ $600–1000 cm$^{-3}$ at a distance of more than 1 kpc from the nucleus, whereas the $N_{\rm e}$ derived from the total light are less than 300 cm$^{-3}$. These facts strongly suggest that the emission from the nuclear starburst of M 82 is scattered by dust grains entrained and transported outward by the superwind. A simple hollow biconical outflow model shows that the velocity of the outflowing dust grains, $v_{\rm d}$, ranges from 100 to 200 km s$^{-1}$ near the nucleus, decreases monotonically with the distance from the nucleus, and reaches $\sim\ $10 km s$^{-1}$ at around 1 kpc. The motion of the dust is substantially slower than that of both ionized gas ($v_{{\rm H}\alpha}$$\sim\ $ 600 km s$^{-1}$) and molecular gas ($v_{\rm CO}$$\sim\ $ 200 km s$^{-1}$) at the same distance from the nucleus of M 82. This indicates that dust grains in the superwind are kinematically decoupled from both gas components at large radii. Since the dust velocity $v_{\rm d}$ is much less than the escape velocity of M 82 ($v_{\rm esc}$$\approx$ 170 km s$^{-1}$ at 1.5 kpc from the nucleus), most of the dust entrained by the superwind cannot escape to intergalactic space, and may fall back into the galaxy disk if there is no additional acceleration mechanism (such as radiation pressure).