see also: recent NGC3603 papers in the literature
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ATCA radio imaging of the giant HII region NGC 3603
Anita Mücke (Universite de Montreal),
Bärbel Koribalski (ATNF),
A.F.J. Moffat (Universite de Montreal),
M.F. Corcoran (Goddard Space Flight Center),
I.R. Stevens (University of Birmingham)
Figure 1: 6 cm radio continuum emission of the HII region NGC 3603
(D = 6.1 kpc; 1' = 1.8 pc).
The image is dominated by a region approx. 2' x 2' in size, which contains
the brightest and most complex structures. To the north of that is a
fainter, extended area of emission, and to the west we find two
"mushroom-like" structures. Also visible are the three known proplyds
(see Paper I.) as well as at least one new proplyd (close to P3, see
below). The brightest emission (red) comes from the heads of the
gaseous pillars, well known from HST images. In general we find the
radio continuum and the Halpha emission in remarkable agreement.
The image was made using `uniform weighting' of the data, comprising five
6-km arrays with a total of about 60 h integration time. The measured
noise of about 0.4 mJy is a factor of 10 above the theoretical noise.
The original beam of 1.64" x 1.32" has been convolved to 2".
Figure 1b: Zoom-in to the "mushroom-like" structures
Figure 2: Similar to Fig. 1, but extended structure has been filtered
out (uvmin = 25 klambda), and a smaller region is shown.
Proplyd 4 is now clearly seen to the south-west of proplyd 3; it has an
extent of about 6" !! There are possibly 1 or 2 more proplyds towards
the south-east corner of the image. We also detected two stars in the
cluster ! The r.m.s. noise varies across the image, but is close to
0.4 mJy/beam near the stars and proplyds. The emission near the pillars
is not well cleaned, and a lot of the flux has been artificially broken
up into numerous blobs. I keep trying.
Figure 3: 6 cm radio continuum image of proplyd 4.
Anita Mücke (Universite de Montreal),
Bärbel Koribalski (ATNF),
A.F.J. Moffat (Universite de Montreal),
M.F. Corcoran (Goddard Space Flight Center),
I.R. Stevens (University of Birmingham)
(2002) ApJ 571, 366
Abstract.
Three cometary-shaped objects in the giant HII region NGC3603, originally
found and identified as proto-planetary disks (ProPlyDs) by Brandner et al.
2000) using HST+VLT in the optical and near-infrared, have been detected with
the Australia Telescope Compact Array (ATCA) in the radio continuum at 3 and
6 cm. All three ProPlyD-like objects are clearly resolved with an extent of a
few arcseconds. The integrated 6 cm fluxes are up to 1.3 times higher than
the 3 cm fluxes with spectral indices averaged over the whole clump between
alpha=0.1 and -0.5 (S_nu ~ nu^alpha), indicating non-thermal emission
for two of the three sources. We present spectral index maps, and show that
the sites of negative radio spectral indices are predominantly concentrated
in the direction of the tails in all three ProPlyD-like nebulae while positive
spectral indices are found in the region facing the ionizing star cluster. In
two of the three objects optically thin non-thermal (gyro-)synchrotron emission
appears to dominate on average, while the average spectrum of the third source
is in agreement with thermal bremsstrahlung or free-free absorbed
gyrosynchrotron radiation. All measured fluxes are at least one order of
magnitude higher than those predicted by Brandner et al. (2000). Upper limits
for mass loss rates due to photo-evaporation are calculated to be 10^-5
Msun/year and for electron densities to be 10^4 cm^-3. Due to the unexpectedly
large radio luminosities of the ProPlyD-like features a (proto-)stellar origin
of the non-thermal emission from a dust enshrouded star appears unlikely.
Instead we propose that magnetized regions within the envelope of the
ProPlyD-like nebulae exist with a total emitting volume much smaller than
the whole extent of the ProPlyD-like clump.
Headings: interstellar medium: HII regions: individual (NGC 3603) ---
stars: pre-main-sequence --- stars: early type, interferometry ---
stars: formation
Figure 1: Zoom-in of Figure 1 (see below) emphazising the
ProPlyds 1 and 2.
Figure 2: ATCA 3-cm radio continuum emission (green contours)
overlaid onto the HST image by Brandner et al. (2000).
North is to the top and East to the left.
Figure 3: ATCA 3-cm radio continuum emission of the proplyds
overlaid onto the HST image by Brandner et al. (2000).
Figure 4 and 5: HST (left) and VLT (right) images of NGC 3603.
Please note that orientation of the images is different
from those displayed above.