Appleton P.N.,California Institute of Technology |
Guillard P.,California Institute of Technology |
Guillard P.,University Paris - Sud |
Boulanger F.,University Paris - Sud |
And 20 more authors.
Astrophysical Journal | Year: 2013
We present the first Herschel spectroscopic detections of the [O I] 63 μm and [C II] 158 μm fine-structure transitions, and a single para-H 2O line from the 35 × 15 kpc2 shocked intergalactic filament in Stephan's Quintet. The filament is believed to have been formed when a high-speed intruder to the group collided with a clumpy intergroup gas. Observations with the PACS spectrometer provide evidence for broad (>1000 km s-1) luminous [C II] line profiles, as well as fainter [O I] 63 μm emission. SPIRE FTS observations reveal water emission from the p-H 2O (111-000) transition at several positions in the filament, but no other molecular lines. The H2O line is narrow and may be associated with denser intermediate-velocity gas experiencing the strongest shock-heating. The [C II]/PAHtot and [C II]/FIR ratios are too large to be explained by normal photo-electric heating in photodissociation regions. H II region excitation or X-ray/cosmic-ray heating can also be ruled out. The observations lead to the conclusion that a large fraction the molecular gas is diffuse and warm. We propose that the [C II], [O I], and warm H 2 line emission is powered by a turbulent cascade in which kinetic energy from the galaxy collision with the intergalactic medium is dissipated to small scales and low velocities, via shocks and turbulent eddies. Low-velocity magnetic shocks can help explain both the [C II]/[O I] ratio, and the relatively high [C II]/H2 ratios observed. The discovery that [C II] emission can be enhanced, in large-scale turbulent regions in collisional environments, has implications for the interpretation of [C II] emission in high-z galaxies. © 2013. The American Astronomical Society. All rights reserved.
Bureau M.,University of Oxford |
Davis T.A.,University of Oxford |
Alatalo K.,University of California at Berkeley |
Crocker A.F.,University of Massachusetts Amherst |
And 19 more authors.
Proceedings of the International Astronomical Union | Year: 2010
The molecular gas content of local early-type galaxies is constrained and discussed in relation to their evolution. First, as part of the ATLAS 3D survey, we present the first complete, large (260 objects), volume-limited single-dish survey of CO in normal local early-type galaxies. We find a surprisingly high detection rate of 22%, independent of luminosity and at best weakly dependent on environment. Second, the extent of the molecular gas is constrained with CO synthesis imaging, and a variety of morphologies is revealed. The kinematics of the molecular gas and stars are often misaligned, implying an external gas origin in over a third of the systems, although this behaviour is drastically diffferent between field and cluster environments. Third, many objects appear to be in the process of forming regular kpc-size decoupled disks, and a star formation sequence can be sketched by piecing together multi-wavelength information on the molecular gas, current star formation, and young stars. Last, early-type galaxies do not seem to systematically obey all our usual prejudices regarding star formation, following the standard Schmidt-Kennicutt law but not the far infrared-radio correlation. This may suggest a greater diversity in star formation processes than observed in disk galaxies. Using multiple molecular tracers, we are thus starting to probe the physical conditions of the cold gas in early-types. © Copyright International Astronomical Union 2011.
Ahnen M.L.,ETH Zurich |
Ansoldi S.,University of Udine |
Antonelli L.A.,National institute for astrophysics |
Antoranz P.,University of Siena |
And 152 more authors.
Astronomy and Astrophysics | Year: 2016
During February-March 2014, the MAGIC telescopes observed the high-frequency peaked BL Lac 1ES 1011+496 (z = 0:212) in flaring state at very-high energy (VHE, E > 100 GeV). The flux reached a level of more than ten times higher than any previously recorded flaring state of the source. Aims. To describe the characteristics of the flare presenting the light curve and the spectral parameters of the night-wise spectra and the average spectrum of the whole period. From these data we aim to detect the imprint of the extragalactic background light (EBL) in the VHE spectrum of the source, to constrain its intensity in the optical band. Methods. We analyzed the gamma-ray data from the MAGIC telescopes using the standard MAGIC software for the production of the light curve and the spectra. To constrain the EBL, we implement the method developed by the H.E.S.S. collaboration, in which the intrinsic energy spectrum of the source is modeled with a simple function (≤ 4 parameters), and the EBL-induced optical depth is calculated using a template EBL model. The likelihood of the observed spectrum is then maximized, including a normalization factor for the EBL opacity among the free parameters. Results. The collected data allowed us to describe the night-wise flux changes and also to produce differential energy spectra for all nights in the observed period. The estimated intrinsic spectra of all the nights could be fitted by power-law functions. Evaluating the changes in the fit parameters, we conclude that the spectral shape for most of the nights were compatible, regardless of the flux level, which enabled us to produce an average spectrum from which the EBL imprint could be constrained. The likelihood ratio test shows that the model with an EBL density 1.07 (-0.20, +0.24)stat+sys, relative to the one in the tested EBL template, is preferred at the 4.6σ level to the no-EBL hypothesis, with the assumption that the intrinsic source spectrum can be modeled as a log-parabola. This would translate into a constraint of the EBL density in the wavelength range [0.24 μm, 4.25 μm], with a peak value at 1.4 μm of λFλ = 12.27+2.75 -2:29 nWm-2 sr-1, including systematics. © 2016 ESO.
Bourdin H.,University of Rome Tor Vergata |
Arnaud M.,Laboratoire AIM |
Mazzotta P.,University of Rome Tor Vergata |
Pratt G.W.,Laboratoire AIM |
And 7 more authors.
Astronomy and Astrophysics | Year: 2011
Located at z = 0.203, A2163 is a rich galaxy cluster with an intra-cluster medium (ICM) that exhibits extraordinary properties, including an exceptionally high X-ray luminosity, average temperature, and a powerful and extended radio halo. The irregular and complex morphology of its gas and galaxy structure suggests that this cluster has recently undergone major merger events that involve two or more cluster components. In this paper, we study the gas structure and dynamics by means of spectral-imaging analysis of X-ray data obtained from XMM-Newton and Chandra observations. From the evidence of a cold front, we infer the westward motion of a cool core across the E-W elongated atmosphere of the main cluster A2163-A. Located close to a galaxy over-density, this gas "bullet" appears to have been spatially separated from its galaxy (and presumably dark matter component) as a result of high-velocity accretion. From gas brightness and temperature profile analysis performed in two opposite regions of the main cluster, we show that the ICM has been adiabatically compressed behind the crossing "bullet" possibly because of shock heating, leading to a strong departure of the ICM from hydrostatic equilibrium in this region. Assuming that the mass estimated from the Y X proxy best indicates the overall mass of the system and that the western cluster sector is in approximate hydrostatic equilibrium before subcluster accretion, we infer a merger scenario between two subunits of mass ratio 1:4, leading to a present total system mass of M500 1.9 × 1015 M. Additional analysis of the spatially-separated northern subcluster A2163-B does not show any evidence of strong interaction with the main cluster A2163-A, leading us to infer that the physical distance separating the northern subcluster and the main component is longer than the projected separation of these components. The exceptional properties of A2163 present various similarities with those of 1E0657-56, the so-called "bullet- cluster". These similarities are likely to be related to a comparable merger scenario. © 2011 ESO.
Boissier S.,Aix - Marseille University |
Boselli A.,Aix - Marseille University |
Voyer E.,Aix - Marseille University |
Bianchi S.,National institute for astrophysics |
And 8 more authors.
Astronomy and Astrophysics | Year: 2015
The Virgo direction has been observed at many wavelengths in recent years, in particular in the ultraviolet with GALEX. The far ultraviolet (FUV) diffuse light detected by GALEX offers interesting information on the large scale distribution of Galactic dust, owing to the GALEX FUV band sensitivity and resolution. Aims. We aim to characterise the ultraviolet large scale distribution of diffuse emission in the Virgo direction. A map of this emission may become useful for various studies by identifying regions where dust affects observations by either scattering light or absorbing radiation. Methods. We constructed mosaics of the FUV and near ultraviolet (NUV) diffuse emission over a large sky region (RA 12 to 13 h, Dec 0 to 20 deg) surrounding the Virgo cluster, using all the GALEX available data in the area. We tested for the first time the utilisation of the FUV diffuse light as a Galactic extinction E(B-V) tracer. Results. The FUV diffuse light scattered on cirrus reveals details about their geometry. Despite large dispersion, the FUV diffuse light correlates roughly with other Galactic dust tracers (coming from IRAS, Herschel, Planck), offering an opportunity to use the FUV emission to locate them in future studies with a better resolution (about 5 arcsec native resolution, 20 arcsec pixels maps presented in this paper) than for several usual tracers. Estimating the Galactic dust extinction on the basis of this emission allows us to find a smaller dispersion in the NUV-i colour of background galaxies at a given E(B-V) than with other tracers. The diffuse light mosaics obtained in this work are made publicly available. © 2015 ESO.