Chandra observation of the NGC4449: analysis of the x-ray emission from a dwarf starburst galaxy

LK Summers, Ian Stevens, David Strickland, TM Heckman

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We present Chandra X-ray data on the nearby Magellanic irregular dwarf starburst galaxy NGC 4449. Contributions to the X-ray emission come from discrete point sources and extended diffuse emission. The extended emission has a complex morphology with an extent of similar to2.4 x 1.6 kpc down to a flux density of 1.3 x 10(-13) erg s(-1) cm(-2) arcmin(-2) . The best spectral fit to this emission is obtained with an absorbed, two-temperature model giving temperatures for the two gas components of 0.28 +/- 0.01 and 0.86 +/- 0.04 keV, a total mass content of similar to10(7) M-. compared with a galactic mass of several 10(10) M-. and a total thermal energy content of similar to2.5 x 10(55) erg, with an average energy injection rate for the galaxy of a few 10(41) erg s(-1) . Comparison of the morphology of the diffuse X-ray emission with that of the observed Halpha emission shows similarities in the two emissions. An expanding super-bubble is suggested by the presence of diffuse X-ray emission within what appears to be a cavity in the Halpha emission. The kinematics of this bubble suggest an expansion velocity of similar to220 km s(-1) and a mass injection rate of similar to0.14 M-. yr(-1), but the presence of a huge H i halo (r similar to 40 kpc) in NGC 4449 may prevent the ejection, into the intergalactic medium, of the metal-enriched material and energy it contains. The arcsecond resolution of Chandra has detected 24 X-ray point sources down to a completeness level corresponding to a flux of similar to2 x 10(-14) erg s(-1) cm(-2), within the optical extent of NGC 4449 and analysis of their spectra has shown them to be from at least three different classes of object. As well as the known supernova remnant in this galaxy, it also harbours several X-ray binaries and supersoft sources. The point source X-ray luminosity function, for the higher-luminosity sources, has a slope of similar to-0.51, comparable to those of other starburst galaxies.
Original languageEnglish
Pages (from-to)690-708
Number of pages19
JournalRoyal Astronomical Society. Monthly Notices
Issue number3
Publication statusPublished - 1 Jul 2003


  • galaxies : starburst
  • X-rays : galaxies
  • ISM : jets and outflows
  • galaxies : individual : NGC 4449


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