Observations of the outflow of gas from the nucleus of NGC 253 and its implications for the stellar population of the nucleus
The ionized gas in the central region of the nearby spiral galaxy NGC 253 was observed spectrographically. Between 15 and 25 arc seconds SE of the nucleus, the emission lines are resolved into two components; this result rules out a two-dimensional distribution of the gas and establishes that there is gas above the disk. From an argument based on the observed variation of the velocity with distance from center and on the similarity of the velocities of the ionized gas and of the H I observed in 21 cm absorption in front of the central radio source, it is concluded that the ionized gas observed along the minor axis at velocities lower than the systemic velocity is flowing out of the nucleus, rather than into the nucleus. Gas at velocity higher than the systemic velocity is also observed along the minor axis at 15 to 30 arcsec SE of the nucleus; there are several plausible interpretations for it. If this gas is outside the disk, it is either partaking in the same outflow as the gas at low velocities or it is falling on the disk; in this case, however, it cannot be pristine intergalactic material since it emits nitrogen lines, but it could be gas ejected from the nucleus and falling back on the plane. If the gas at high velocity is in the disk, then it is in an expanding arm located 2.2 kpc from the center and having a radial motion of 80 km s/sup -1/. This appears the most likely interpretation. The rate of mass loss from the nucleus is estimated to be greater than or equal to 10/sup -2/ M sub solar per year. The outflow of ionized gas is a transient phenomenon; otherwise it would deeplete the central region 150 pc in radius in 10/sup 9/ years. It is shown that 1000 O6 stars can produce the ionizing flux necessary to keep the gas ionized and the energy to accelerate it. An exotic explosive phenomenon does not appear necessary to account for the observations. 8 figures, 2 tables.
- Research Organization:
- Univ. of Texas, Austin
- OSTI ID:
- 6501777
- Journal Information:
- Astrophys. J.; (United States), Vol. 219:2
- Country of Publication:
- United States
- Language:
- English
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