Astronomy and Astrophysics – Astrophysics
Scientific paper
Mar 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997a%26a...319..459v&link_type=abstract
Astronomy and Astrophysics, v.319, p.459-469
Astronomy and Astrophysics
Astrophysics
28
Galaxies: Individual: Ngc 4449, Galaxies: Irregular, X-Rays: Galaxies
Scientific paper
X-ray emission (L_x_~2.5x10^39^erg/s) from the nearby, face-on Magellanic-type irregular galaxy NGC 4449 was detected with the ROSAT PSPC and HRI. The HRI resolves seven point sources located within the D_25_ ellipse of the galaxy. The most luminous source is a supernova remnant detected with an intrinsic luminosity of L_x_=4.7x10^38^erg/s. Another very luminous source (L_x_=3.1x10^38^erg/s) is located between two Hα shells. A source near the southern border of the galaxy (L_x_=1.7x10^38^erg/s) shows flux variations between the HRI and PSPC observations of a factor of two, no counterparts in other wavelengths and most likely is an X-ray binary. Two fainter sources (L_x_=1.2x10^38^erg/s and L_x_=0.8x10^38^erg/s) are positioned at the border of regions that show enhanced blue emission. The center of the galaxy was detected with a luminosity of L_x_=7x10^37^erg/s. Combining the spatial resolution of the HRI and the spectral capabilities of the PSPC indicates that the total X-ray emission of NGC 4449 is composed of resolved point sources (L_x_=1.4x10^39^erg/s), unresolved point sources (L_x_=2x10^38^erg/s), and extended emission possibly arising from a hot (T~3x10^6^K) gaseous component of the interstellar medium (L_x_=1.0x10^39^erg/s). The spectral and spatial findings indicate that most of the thermal emission originates from parts in the outer Hi disk and above it. The parameters and implications of a possible gaseous halo component are discussed. The NGC 4449 X-ray emission components are compared with those of the Magellanic Clouds which can be resolved in the contributing X-ray emission components. The NGC 4449 point source and extended emission components seem to reflect the LMC scaled for the different galaxy masses.
Pietsch Wolfgang
Vögler Alexander
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