XMM-Newton observations of the starburst merger galaxies NGC 3256 & NGC 3310

Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 05/2004; 352(4). DOI: 10.1111/j.1365-2966.2004.08025.x
Source: arXiv


We present XMM–Newton EPIC observations of the two nearby starburst merger galaxies NGC 3256 and NGC 3310. The broad-band (0.3–10 keV) integrated
X-ray emission from both galaxies shows evidence of multiphase thermal plasmas plus an underlying hard non-thermal power-law
continuum. NGC 3256 is well fitted with a model comprising two mekal components (kT= 0.6/0.9 keV) plus a hard power law (Γ= 2), while NGC 3310 has cooler mekal components (kT= 0.3/0.6 keV) and a harder power-law tail (Γ= 1.8). Chandra observations of both galaxies reveal the presence of numerous discrete sources embedded in the diffuse emission, which dominate
the emission above ∼2 keV and are likely to be the source of the power-law emission. The thermal components show a trend of
increasing absorption with higher temperature, suggesting that the hottest plasmas arise from supernova-heated gas within
the discs of the galaxies, while the cooler components arise from outflowing galactic winds interacting with the ambient interstellar
medium. We find no strong evidence for an active galactic nucleus in either galaxy.

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Available from: Timothy Roberts, Aug 15, 2013
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    ABSTRACT: We present XMM-Newton X-ray observations of the interacting galaxy pairs NGC 7771/7770 and NGC 2342/2341. In NGC 7771, for the first time we are able to resolve the X-ray emission into a bright central source plus two bright (LX > 1040 erg s−1) ultraluminous X-ray sources (ULXs) located either end of the bar. In the bright central source (LX ∼ 1041 erg s−1), the soft emission is well-modelled by a two-temperature thermal plasma with kT = 0.4/0.7 keV. The hard emission is modelled with a flat absorbed power-law (Γ ∼ 1.7, NH ∼ 1022 cm−2), and this together with a low-significance (1.7σ) ∼ 300 eV equivalent width emission line at ∼6 keV are the first indications that NGC 7771 may host a low-luminosity AGN. For the bar ULXs, a power-law fit to X-1 is improved at the 2.5σ level with the addition of a thermal plasma component (kT ∼ 0.3 keV), while X-2 is improved only at the 1.3σ level with the addition of a disc blackbody component with Tin ∼ 0.2 keV. Both sources are variable on short time-scales implying that their emission is dominated by single accreting X-ray binaries (XRBs). The three remaining galaxies, NGC 7770, NGC 2342 and NGC 2341, have observed X-ray luminosities of 0.2, 1.8 and 0.9 × 1041 erg s−1, respectively (0.3–10 keV). Their integrated spectra are also well-modelled by multi-temperature thermal plasma components with kT = 0.2–0.7 keV, plus power-law continua with slopes of Γ = 1.8–2.3 that are likely to represent the integrated emission of populations of XRBs as observed in other nearby merger systems. A comparison with other isolated, interacting and merging systems shows that all four galaxies follow the established correlations for starburst galaxies between X-ray, far-infrared and radio luminosities, demonstrating that their X-ray outputs are dominated by their starburst components.
    Full-text · Article · Jan 2005 · Monthly Notices of the Royal Astronomical Society
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    ABSTRACT: Molecular gas in the merging starburst galaxy NGC 3256 has been imaged with the Submillimeter Array at a resolution of 1'' x 2'' (170 x 340 pc at 35 Mpc). This is the first interferometric imaging of molecular gas in the most luminous galaxy within z=0.01. There is a large disk of molecular gas (r > 3 kpc) in the center of the merger with a strong gas concentration toward the double nucleus. The gas disk having a mass of ~3*10^9 Msun in the central 3 kpc rotates around a point between the two nuclei that are 850 pc apart on the sky. The molecular gas is warm and turbulent and shows spatial variation of the intensity ratio between CO isotopomers. High-velocity molecular gas is discovered at the galactic center. Its velocity in our line of sight is up to 420 km/s offset from the systemic velocity of the galaxy; the terminal velocity is twice as large as that due to the rotation of the main gas disk. The high-velocity gas is most likely due to a molecular outflow from the gas disk, entrained by the starburst-driven superwind in the galaxy. The molecular outflow is estimated to have a rate of ~10 Msun/yr and to play a significant role in the dispersal or depletion of molecular gas from the galactic center. A compact gas concentration and steep velocity gradient are also found around each of the twin nuclei. They are suggestive of a small gas disk rotating around each nucleus. If these are indeed mini-disks, their dynamical masses are ~10^9 Msun within a radius of 170 pc. Comment: Accepted for publication in ApJ
    Preview · Article · Mar 2006 · The Astrophysical Journal
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    Full-text · Article · May 2006 · Monthly Notices of the Royal Astronomical Society
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