J/MNRAS/289/225 SMC HI shells velocities (Staveley-Smith+ 1997)
An H I aperture synthesis mosaic of the Small Magellanic Cloud
Staveley-Smith L., Sault R.J., Hatzidimitriou D., Kesteven M.J.,
McConnell D.
<Mon. Not. R. Astron. Soc. 289, 225 (1997)>
=1997MNRAS.289..225S 1997MNRAS.289..225S (SIMBAD/NED BibCode)
ADC_Keywords: Magellanic Clouds ; H I data ; Radial velocities
Keywords: surveys - ISM: atoms - ISM: kinematics and dynamics -
galaxies: kinematics and dynamics - Magellanic Clouds -
radio lines: ISM
Abstract:
We present the results of a survey of neutral hydrogen emission in the
Small Magellanic Cloud (SMC) with the Australia Telescope Compact
Array (ATCA). The survey consists of a mosaic of 320 separate
pointings of the 375-m array, resulting in a resolution of 1.6arcmin
(28pc, for a distance of 60kpc) over a field of 20deg2. The rms
brightness temperature sensitivity is 1.4K, corresponding to an H I
column density sensitivity of 4x18cm-2 for each velocity channel
of width 1.6km/s. The HI distribution is complex and, on scales
≤1kpc, appears to be dominated by the effects of expanding H I
shells, which are probably driven by the combined effects of
supernovae and stellar winds from massive stars. The picture of the
SMC that arises from the current data seems to challenge the earlier
belief that the SMC consists of two or more spatially separate
structures with different systemic velocities. We find that the
observed multiple components are, in many cases, caused by the
combined effects of the numerous shells and supershells. Altogether,
we identify six supershells (defined here as those with radii greater
than 300pc) and 495 giant shells. For each of these, we measure
positions. radii, velocities and expansion rates, and derive ages and
kinetic energy requirements. The apparent age distribution of shells
is remarkably narrow, with a mean age of 5.4Myr and an intrinsic
dispersion of 2Myr. Southern shells appear to be older, on average, by
2.5Myr. The kinetic energy of the shells is a large fraction of the
gravitational binding energy of the SMC, implying that further
disintegration of the SMC will occur with time, and especially at the
next close passage with the Large Magellanic Cloud (LMC) or the
Galaxy, unless the SMC possesses a massive halo. Because of their
interferometric nature, the images presented here are insensitive to
structures of size ≥0.6°, and should not be used for deriving
total H I column densities
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1 57 501 List of positions, radii, expansion velocities,
ages and required wind luminosities for the
H I shells identified in the SMC
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Byte-by-byte Description of file: table1
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Bytes Format Units Label Explanations
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1- 3 I3 --- SSH97 SMC HI shell number
5- 6 I2 h RAh Right ascension (J2000)
8- 9 I2 min RAm Right ascension (J2000)
11- 12 I2 s RAs Right ascension (J2000)
14 A1 --- DE- Declination sign
15- 16 I2 deg DEd Declination (J2000)
18- 19 I2 arcmin DEm Declination (J2000)
21- 22 I2 arcsec DEs Declination (J2000)
24- 28 F5.1 arcmin Rad1 Shell angular radius
29 A1 --- u_Rad1 Uncertainty flag on Rad1
31- 33 I3 pc Rad2 Shell linear radius
35- 39 F5.1 km/s HV Central heliocentric velocity
40 A1 --- u_HV Uncertainty flag on HV
42- 45 F4.1 km/s Vexp Expansion velocity (1)
46 A1 --- u_Vexp Uncertainty flag on Vexp
48- 51 F4.1 Myr Age Dynamical age
53- 57 F5.2 [solLum.cm+3] log(Ls/n0) Required mechanical wind luminosity (2)
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Note (1): Expansion velocity (km/s) (half the width between the red-shifted and
blue-shifted peaks)
Note (2): Ls=1.5*105(rs/100pc)5(Ts/106yr)-3(no/1cm-3)L☉
where Ls is the wind velocity, Ts the dynamical age (in yr),
rs the radius (in pc) and no the ambient density
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Acknowledgements: Lister Staveley-Smith
(End) James Marcout, Patricia Bauer [CDS] 24-Oct-1997