Astronomy and Astrophysics – Astronomy
Scientific paper
Jul 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995apj...447..171m&link_type=abstract
Astrophysical Journal v.447, p.171
Astronomy and Astrophysics
Astronomy
55
Galaxies: Individual Ngc Number: Ngc 5253, Galaxies: Ism, Galaxies: Kinematics And Dynamics, X-Rays: Galaxies
Scientific paper
A new ROSAT PSPC observation of the gas-rich dwarf galaxy NGC 5253 reveals an extended, soft X-ray source near the center of the galaxy. The pulse-height spectrum is well fit with a Raymond-Smith model for a thermal plasma at a temperature of (4.0±1.3) × 106 K for a foreground absorbing column of log NH = 21.4 cm-2. The X-ray luminosity between 0.1 and 2.4 keV is Lx = (6.5+5.8-1.6) × 1038 ergs s-1. Higher resolution X-ray imaging is needed to determine the contribution to Lx from point sources. However, we argue that hot interstellar gas produces most of the X-ray emission and investigate whether stellar winds and supernovae in the central starburst can heat the required mass of X-ray-emitting gas. We find the simplest superbubble model underpredicts Lx by a factor of 16 but show that a superbubble evolving in a clumpy ambient medium can easily reproduce the observed X-ray properties. Our model suggests the most recent burst is young (˜5 × 106 yr) and requires evaporating clouds or filaments to fill a small fraction of the nebula.
To provide additional insight into the dynamics of the interstellar medium (ISM) in NGC 5253, we present results from Hα imaging and follow-up high-resolution spectroscopy of the Hα emission line. The spectacular filaments extending from the galaxy in the Hα image do not show unusually high velocities; in the outer part of the nebula, the velocity of the gas producing the Hα emission shifts randomly by ±10-30 km s-1 over scales of ˜100-200 pc. The complex velocity field in the core can be interpreted as a slow, global expansion of the warm ionized medium coincident with the region of X-ray emission. We discuss the relation of the hot and warm phases of the ISM in NGC 5253 and draw analogies to giant H II regions and superwind galaxies.
Kennicutt Robert C. Jr.
Martin Crystal L.
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