Schönau-Berzdorf, Germany
Schönau-Berzdorf, Germany

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Schinnerer E.,MPI for Astronomy | Meidt S.E.,MPI for Astronomy | Colombo D.,MPI for Radioastronomy | Chandar R.,University of Toledo | And 9 more authors.
Astrophysical Journal | Year: 2017

The process that leads to the formation of the bright star-forming sites observed along prominent spiral arms remains elusive. We present results of a multi-wavelength study of a spiral arm segment in the nearby grand-design spiral galaxy M51 that belongs to a spiral density wave and exhibits nine gas spurs. The combined observations of the (ionized, atomic, molecular, dusty) interstellar medium with star formation tracers (H ii regions, young <10 Myr stellar clusters) suggest (1) no variation in giant molecular cloud (GMC) properties between arm and gas spurs, (2) gas spurs and extinction feathers arising from the same structure with a close spatial relation between gas spurs and ongoing/recent star formation (despite higher gas surface densities in the spiral arm), (3) no trend in star formation age either along the arm or along a spur, (4) evidence for strong star formation feedback in gas spurs, (5) tentative evidence for star formation triggered by stellar feedback for one spur, and (6) GMC associations being not special entities but the result of blending of gas arm/spur cross sections in lower resolution observations. We conclude that there is no evidence for a coherent star formation onset mechanism that can be solely associated with the presence of the spiral density wave. This suggests that other (more localized) mechanisms are important to delay star formation such that it occurs in spurs. The evidence of star formation proceeding over several million years within individual spurs implies that the mechanism that leads to star formation acts or is sustained over a longer timescale. © 2017. The American Astronomical Society. All rights reserved.

Becker J.K.,Ruhr University Bochum | Becker J.K.,Gteborgs University | Meli A.,Friedrich - Alexander - University, Erlangen - Nuremberg | Biermann P.L.,MPI for Radioastronomy | And 4 more authors.
Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment | Year: 2011

The high-peaked BL Lac object Pks2155-304 shows high variability at multiwavelengths, i.e. from optical up to TeV energies. A giant flare of around 1 h at X-ray and TeV energies was observed in 2006 [1]. In this context, it is essential to understand the physical processes in terms of the primary spectrum and the radiation emitted, since high-energy emission can arise in both leptonic and hadronic processes. In this contribution, we investigate the possibility of neutrino production in photo-hadronic interactions. In particular, we predict a direct correlation between optical and TeV energies at sufficiently high optical radiation fields. We show that in the blazar Pks2155-304, the optical emission in the low-state is sufficient to lead to photo-hadronic interactions and therefore to the production of high-energy photons. © 2010 Elsevier B.V. All rights reserved.

Biermann P.L.,MPI for Radioastronomy | Biermann P.L.,Karlsruhe Institute of Technology | Biermann P.L.,University of Alabama | Biermann P.L.,University of Bonn | And 5 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

The statistics of black holes and their masses strongly suggests that their mass distribution has a cut-off towards lower masses near 3 × 106 M⊙. This is consistent with a classical formation mechanism from the agglomeration of the first massive stars in the universe. However, when the masses of the stars approach 106 M⊙, the stars become unstable and collapse, possibly forming the first generation of cosmological black holes. Here, we speculate that the claimed detection of an isotropic radio background may constitute evidence of the formation of these first supermassive black holes, since their data are compatible in spectrum and intensity with synchrotron emission from the remnants. The model proposed fulfils all observational conditions for the background, in terms of single-source strength, number of sources, farinfrared and gamma-ray emission. The observed high-energy neutrino flux is consistent with our calculations in flux and spectrum. The proposal described in this paper may also explain the early formation and growth of massive bulge-less disc galaxies as derived from themassive, gaseous shell formed during the explosion prior to the formation of a supermassive black hole. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Biermann P.L.,MPI for Radioastronomy | Becker J.K.,Ruhr University Bochum | Caramete L.I.,MPI for Radioastronomy | Fraschetti F.,Ruhr University Bochum | And 3 more authors.
Nuclear Physics B - Proceedings Supplements | Year: 2011

Supermassive black holes in the centers of galaxies are very common. They are known to rotate, accrete, spin down and eject highly relativistic jets; those jets pointed at us all seem to show a spectrum with two strong bumps, one in the TeV photon range, and one in X-rays - ordered by the emission frequency of the first bump this constitutes the blazar sequence. Here we wish to explain this sequence as primary synchrotron emission of energetic electrons and protons, and secondary emission from interactions at the first strong shockwave pattern in the relativistic jet. With two key assumptions on particle scattering, this concept predicts that the two basic maximum peak frequencies νsyn,e,p scale with the mass of the central black hole as νe,p~MBH -1/2, of νsyn,p/νsyn,e=(mp/me)3, and the luminosities with the mass itself Le,p~MBH. Due to strong losses of the leptons, the peak luminosities are generally the same, but with large variations around equality. This model predicts large fluxes in ultra high energy cosmic rays, and also large neutrino luminosities. © 2011 Elsevier B.V.

Gergely L.A.,University of Szeged | Biermann P.L.,MPI for Radioastronomy | Biermann P.L.,University of Bonn | Biermann P.L.,University of Alabama | And 3 more authors.
Classical and Quantum Gravity | Year: 2010

During post-Newtonian evolution of a compact binary, a mass ratio ν different from 1 provides a second small parameter, which can lead to unexpected results. We present a statistics of supermassive black hole candidates, which enables us first to derive their mass distribution, and then to establish a logarithmically even probability in ν of themass ratios at their encounter. In the mass ratio range ν ∈ (1/30, 1/3) of supermassive black hole mergers representing 40% of all possible cases, the combined effect of spin-orbit precession and gravitational radiation leads to a spin-flip of the dominant spin during the inspiral phase of the merger. This provides amechanism for explaining a large set of observations on X-shaped radio galaxies. In another 40% with mass ratios ν ∈ (1/30, 1/1000) a spin-flip never occurs, while in the remaining 20% of mergers with mass ratios ν ∈ (1/3, 1) it may occur during the plunge. We analyze the magnitude of the spin-flip angle occurring during the inspiral as a function of the mass ratio and original relative orientation of the spin and orbital angular momentum. We also derive a formula for the final spin at the end of the inspiral in this mass ratio range. © 2010 IOP Publishing Ltd.

Biermann P.L.,MPI for Radioastronomy | Biermann P.L.,University of Bonn | Biermann P.L.,University of Alabama | Biermann P.L.,University of Alabama in Huntsville | And 6 more authors.
Astrophysical Journal Letters | Year: 2010

One important prediction of acceleration of particles in the supernova caused shock in the magnetic wind of exploding Wolf-Rayet and red supergiant stars is the production of an energetic particle component with an E -2 spectrum at a level on the order of 1% of the full cosmic ray electron population. After allowing for transport effects, so steepening the spectrum to E -7/3, this component as cosmic ray electrons readily explains the WMAP haze from the Galactic center region in spectrum, intensity, and radial profile; this requires the diffusion timescale for cosmic rays in the Galactic center region to be much shorter than in the solar neighborhood: the energy for cosmic ray electrons at the transition between diffusion dominance and loss dominance is shifted to considerably higher particle energy. We predict that more precise observations will find a radio spectrum of ν-2/3, at higher frequencies ν-1, and at yet higher frequencies finally ν-3/2. © 2010. The American Astronomical Society. All rights reserved.

Biermann P.L.,MPI for Radioastronomy | Biermann P.L.,University of Alabama | Biermann P.L.,Karlsruhe Institute of Technology | Biermann P.L.,University of Alabama in Huntsville | And 4 more authors.
Astrophysical Journal | Year: 2013

We show that the large-scale cosmic-ray anisotropy at ∼10 TeV can be explained by a modified Compton-Getting effect in the magnetized flow field of old supernova remnants. Cosmic rays arrive isotropically to the flow field and are then carried along with the flow to produce a large-scale anisotropy in the arrival direction. This approach suggests an optimum energy scale for detecting the anisotropy. Two key assumptions are that propagation is based on turbulence following a Kolmogorov law and that cosmic-ray interactions are dominated by transport via cosmic-ray-excited magnetic irregularities through the stellar wind of an exploding star and its shock shell. A prediction is that the amplitude is smaller at lower energies due to incomplete sampling of the velocity field and also smaller at larger energies due to smearing. © 2013. The American Astronomical Society. All rights reserved.

Schinnerer E.,MPI for Astronomy | Weiss A.,MPI for Radioastronomy | Aalto S.,Chalmers University of Technology | Scoville N.Z.,California Institute of Technology
Astrophysical Journal | Year: 2010

Two selected regions in the molecular gas spiral arms in M51 were mapped with the Owens Valley Radio Observatory (OVRO) mm-interferometer in the 12CO(2-1), 13CO(1-0), C18O(1-0), HCN(1-0), and HCO+(1-0) emission lines. The CO data have been combined with the 12CO(1-0) data from Aalto et al. covering the central 3.5 kpc to study the physical properties of the molecular gas. All CO data cubes were short spacing corrected using IRAM 30 m (12CO(1-0): NRO 45 m) single-dish data. A large velocity gradient analysis finds that the giant molecular clouds (GMCs) are similar to Galactic GMCs when studied at 180 pc (120 pc) resolution with an average kinetic temperature of Tkin= 20(16)K and H2density of n(H2) = 120(240) cm-3when assuming virialized clouds (a constant velocity gradient dv/dr). The associated conversion factor between H2mass and CO luminosity is close to the Galactic value for most regions analyzed. Our findings suggest that the GMC population in the spiral arms of M51 is similar to those of the Milky Way and therefore the strong star formation occurring in the spiral arms has no strong impact on the molecular gas in the spiral arms. Extinction inferred from the derived H2column density is very high (AV about 15-30 mag), about a factor of 5-10 higher than the average value derived toward Hii regions. Thus, a significant fraction of the ongoing star formation could be hidden inside the dust lanes of the spiral arms. A comparison of MIPS 24 μm and Hα data, however, suggests that this is not the case and most of the GMCs studied here are not (yet) forming stars. We also present low (4."5) resolution OVRO maps of the HCN(1-0) and HCO+(1-0) emission at the location of the brightest 12CO(1-0) peak. © 2010. The American Astronomical Society.

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