EDP Sciences
Herschel: the first science highlights
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Issue
A&A
Volume 518, July-August 2010
Herschel: the first science highlights
Article Number L90
Number of page(s) 4
Section Letters
DOI https://doi.org/10.1051/0004-6361/201014596
Published online 16 July 2010
A&A 518, L90 (2010)

Herschel: the first science highlights

LETTER TO THE EDITOR

Herschel observations of the W43 ``mini-starburst''[*]

J. Bally1 - L. D. Anderson2 - C. Battersby3 - L. Calzoletti 4 - A. M. DiGiorgio5 - F. Faustini6 - A. Ginsburg7 - J. Z. Li8 - Q. Nguyen-Luong9 - S. Molinari10 - F. Motte11 - M. Pestalozzi12 - R. Plume13 - J. Rodon14 - P. Schilke15 - W. Schlingman16 - N. Schneider-Bontemps17 - Y. Shirley18 - G. S. Stringfellow19 - L. Testi20 - A. Traficante21 - M. Veneziani22 - A. Zavagno23

1 - Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 389 CASA, Boulder CO 80309-0389, USA
2 - Laboratoire d'Astrophysique de Marseille (UMR 6110 CNRS & Universitè de Provence), 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
3 - Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 389 CASA, Boulder CO 80309-0389, USA
4 - ASI Science Data Center, 00044 Frascati (Rome), Italy
5 - Istituto Fisica Spazio Interplanetario INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy
6 - ASI Science Data Center, 00044 Frascati (Rome), Italy
7 - Department of Astrophysical and Planetary Sciences, University of Colorado, UCB 389 CASA, Boulder CO 80309-0389, USA
8 - National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
9 - Laboratoire AIM, CEA/IRFU CNRS/INSU Université Paris Diderot, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
10 - Istituto Fisica Spazio Interplanetario INAF, via Fosso del Cavaliere 100, 00133 Roma, Italy
11 - Laboratoire AIM, CEA/DSM - CNRS Université Paris Diderot, DAPNIA/Service d'Astrophysique, Bât. 709, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France
12 - Dept. of Physics, University of Gothenburg, 412 96, Gteborg, Sweden
13 - Department of Physics and Astronomy, University of Calgary, 2500 University Drive NW, Calgary, AB T2N 1N4, Canada
14 - Laboratoire d'Astrophysique de Marseille (UMR 6110 CNRS & Université de Provence), 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France
15 - I. Physikalisches Instiut der Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
16 - Steward Observatory, University of Arizona, 933 North Cherry Ave., Tucson, AZ 85721, USA
17 - SAp-CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
18 - Steward Observatory, University of Arizona, 933 North Cherry Ave., Tucson, AZ 85721, USA
19 - Center for Astrophysics and Space Astronomy, University of Colorado, UCB 389 CASA, Boulder CO 80309-0389, USA
20 - European Southern Observatory, Karl Schwarzschild str. 2, 85748 Garching, Germany
21 - Dipartimento di Fisica, Universit di Roma 2 ``Tor Vergata'', Rome, Italy
22 - Dipartimento di Fisica, Universit di Roma 1 ``La Sapienza'', Rome, Italy
23 - Laboratoire d'Astrophysique de Marseille (UMR 6110 CNRS & Université de Provence), 38 rue F. Joliot-Curie, 13388 Marseille Cedex 13, France

Received 31 March 2010 / Accepted 5 May 2010

Abstract
Aims. To explore the infrared and radio properties of one of the closest Galactic starburst regions.
Methods. Images obtained with the Herschel Space Observatory at wavelengths of 70, 160, 250, 350, and 500 $\mu $m using the PACS and SPIRE arrays are analyzed and compared with radio continuum VLA data and 8 $\mu $m images from the Spitzer Space Observatory. The morphology of the far-infrared emission is combined with radial velocity measurements of millimeter and centimeter wavelength transitions to identify features likely to be associated with the W43 complex.
Results. The W43 star-forming complex is resolved into a dense cluster of protostars, infrared dark clouds, and ridges of warm dust heated by massive stars. The 4 brightest compact sources with $L > 1.5 \times 10^4~L_{\odot}$ embedded within the Z-shaped ridge of bright dust emission in W43 remain single at 4 $^{\prime\prime}$ (0.1 pc) resolution These objects, likely to be massive protostars or compact clusters in early stages of evolution are embedded in clumps with masses of 103 to $10^4~M_{\odot}$, but contribute only 2% to the $3.6 \times 10^6~L_{\odot}$ far-IR luminosity of W43 measured in a 16 by 16 pc box. The total mass of gas derived from the far-IR dust emission inside this region is $\sim$ $10^6~M_{\odot}$. Cometary dust clouds, compact 6 cm radio sources, and warm dust mark the locations of older populations of massive stars. Energy release has created a cavity blowing-out below the Galactic plane. Compression of molecular gas in the plane by the older H II region near G30.684-0.260 and the bipolar structure of the resulting younger W43 H II region may have triggered the current mini-star burst.

Key words: stars: protostars - stars: massive - H II regions - infrared: ISM - ISM: individual objects: W43

1 Introduction

The W43 ``mini-starburst'' region in the molecular ring near $l =30.8\hbox{$^\circ$ }$ is one of the most luminous star forming complexes in the Galaxy (Motte et al. 2003). Located at a distance of about 5.5 kpc at $V_{\rm LSR} \approx 85$ to 107 km s-1, W 43 contains a giant H II region powered by a cluster of OB and Wolf-Rayet stars emitting a Lyman continuum luminosity of about 1051 ionizing photons per second (Smith et al. 1978; Lester et al. 1985; Blum et al. 1999). The H II region is in contact with a 20 pc diameter giant molecular cloud (GMC) with a mass of about $10^6~M_{\odot}$ (Liszt 1995) and a total IR luminosity of $\sim$ $3.5 \times 10^6~L_{\odot}$ (Lester 1985). Motte et al. (2003) identified about 50 clumps with masses ranging from 40 to 4000 $M_{\odot}$ in 350 and 1100 $\mu $m maps of the dust continuum.

W43 may be a ``Rosetta Stone'' for studies of super-star cluster formation using Hi-GAL data. Comparison of the Hi-GAL data with ground based radio data and space based Spitzer images show that on-going star formation is confined to a Z-shaped region abutting the W43 H II region.

2 Observations

Images of four square degrees centered at l = 30$^\circ $, b = 0$^\circ $ at wavelengths of 70, 160, 250, 350, and 500 $\mu $m were obtained with the PACS (Griffin et al. 2010) and SPIRE (Poglitsch et al. 2010) instruments on the 3.5 m diameter telescope on the Herschel Space Observatory (Pilbratt et al. 2008) as part of the science demonstration program for the Hi-GAL Galactic Plane Survey (Molinari et al. 2010). Each Hi-GAL image was ``unsharp-masked'' to suppress diffuse Galactic emission by convolving with a $\sigma$ = 70 $^{\prime\prime}$ Gaussian to make a mask and subtracting this mask from the corresponding Hi-GAL image to enhance the visibility of small-sacle structure (<200 $^{\prime\prime}$ $\sim$6 pc).

3 Results

3.1 The W43 chimney: A young superbubble?

The Herschel images provide the first wide-field far-infrared views of the brightest portion of the Galactic plane near l = 30$^\circ $, allowing the investigation of the large-scale environment of the W43 mini-starburst complex (Fig. 1). W43 lies at the top of the most prominent cavity in the four square-degree l = 30$^\circ $ Herschel field. The cavity consists of an S-shaped ``hole'' in the dust emission bounded by a 6$^\prime$ radius curved ridge of dust extending from the left-side of W43 towards G30.772-0.209 and continuing to G30.684-0.260. Towards low-longitudes (right side of Fig. 1) the cavity is bounded by a 0.25$^\circ $-long vertical wall near l = 30.5. Most of the cavity interior is filled with faint free-free emission in the 20 cm MAGPIS VLA survey and the 5 GHz filled-aperture survey of Altenhoff et al. (1979). The cavity extends to at least Galactic latitude b = -0.6 where it becomes confused with the foreground H II region Sh2-67 at $V_{\rm LSR} = 18$ km s-1 ( $d \sim 400$ pc; Fich et al. 1990) excited by BD-02 4752, a B0.5V star with visual magnitude 10.5.

The radial velocities of selected dust clumps were measured using emission from the 98 GHz CS 2-1 transition (Shirley et al., in prep.) and with 13CO 1-0 data from the FCRAO Galactic Ring Survey (Jackson et al. 2006). In Figs. 1 and 3, CS radial velocities with 85 km s $^{-1} < V_{\rm LSR} < 107$ km s-1are shown in yellow; radial velocities outside this range are shown in blue and cyan. Radial velocities based on 13CO 1-0 are shown in with smaller yellow circles. The clouds located below W43, including the 6$^\prime$ radius ridge extending from the left side of W43 towards G30.772-0.209 and the wall near l = 30.5 are at $V_{\rm LSR} \approx
99$ to 107 km s-1. However, they appear to connect to the bright dust emission in W43. The larger radial velocities of these features compared to W43 may be due to acceleration by UV radiation and stellar winds. Although line-of-sight confusion by unrelated features is highly probable at l = 30$^\circ $, the preponderance of radial velocities similar to that of W43 make it likely that the Chimney is powered by massive young stars at a common distance of about 5.5 kpc. At this distance, the W43 Chimney is at least 70 pc long.

\begin{figure}
\par\includegraphics[width=7cm,clip]{14596fig1.eps}
\vspace*{-4mm}
\end{figure} Figure 1:

A color composite image showing the W43 starburst region and the superbubble bursting towards low Galactic latitudes at 70 $\mu $m (blue), 160 $\mu $m (green), and 500 $\mu $m (red) using ``unsharp-masked'' images as described in the text. Small red circles or dots mark the locations of 6 cm point sources. Large yellow circles mark locations where the radial velocity has been measured using mm-wavelength tracers; yellow indicates radial velocities within the velocity range $85 < V_{\rm LSR} < 107$ km s-1 measured using CS (Shirley et al., in prep.) or 13CO. Blue and cyan circles indicate LSR velocities outside this range. Small yellow circles mark the locations of 13CO clouds having similar radial velocities as W43. The numbers above each circle mark the LSR radial velocity in km s-1. Several regions discussed in the text are marked in cyan. Warm dust at 70 $\mu $m outlines the walls of the ``W43 Chimney'' (shown in blue line segments). A 0.1$^\circ $ interval corresponds to a linear scale of 9.6 pc at the assumed 5.5 kpc distance to W43.

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Infrared dark clouds (IRDCs) are seen in silhouette against background emission at wavelengths below 70 $\mu $m but are bright at wavelengths beyond 160 $\mu $m. The cometary IRDC G30.772-0.209 and its bright rims (Figs. 2 and 3) point towards G30.684-0.260 (IRAS 18456-0210). The 20 cm continuum and diffuse 24 $\mu $m Spitzer emission (not shown) indicate that massive stars are located just above G30.684-0.260. Figure 3 shows two concentrations of 6 cm mJy point-like radio sources in the MAGPIS survey (White et al. 2005; Helfand et al. 2006) that trace free-free emission from compact H II regions, ionized massive-star winds, or the brightest compact features in extended H II regions resolved by the VLA. The largest concentration is centered on W43 and a second group is located a few arcminutes below G30.684-0.260 around the UC H II region G30.667-0.332 embedded in a 13CO cloud at $V_{\rm LSR} = 89.4$ km s-1. While the upper portion of the Chimney is clearly powered by W43, the southern portion appears to contain an older group of massive stars which produce the compact 6 cm sources, a diffuse H II region, and several cometary clouds.

3.2 The W43 starburst region

The W43 region is shown in detail in Figs. 2 and 3. The 0.1$^\circ $ ($\sim$10 pc) long, Z-shaped W43 ridge of warm dust (red lines in Figs. 1 and 3) is the brightest source of far-IR, sub-mm, and mm emission in the l = 30$^\circ $ field, and one of the brightest in the entire Galaxy (Smith et al. 1978). At 70 $\mu $m, the Z-shaped ridge of bright dust emission contains a chain of about a dozen compact sources (<4 $^{\prime\prime}$ or 0.1 pc diameter) superimposed on the bright background of warm dust associated with the edges of the W43 H II region.

The Z-shaped ridge is situated at the ``waist'' of a bipolar H II region that breaks-out towards both positive and negative Galactic latitudes. While the high surface-brightness lobe of W43 breaking out above the bar of the Z is confined to a 4 by 10 pc region, below the Z the lobe extends to the cometary clump G30.772-0.209 about 11$^\prime$ ($\sim$19 pc) from the W43 central cluster. Filamentary 70 $\mu $m dust emission closely follows the radio continuum emission at 20 cm in the MAGPIS survey and presumably traces warm dust in photon-dominated regions (PDR) located just outside ionization fronts illuminated by W43's massive O and W-R stars. Ridges of colder dust seen absorption at 70 $\mu $m and below but in emission longward of 160 $\mu $m form arcs extending beyond the legs of the ``Z''. The curved ridge which peels off the high-longitude end of the ``Z'' is larger and forms a semi-circle of dust with a radius of about 6$^\prime$ (10 pc) and may be responsible for confining the eastern (low-latitude) lobe of the W43 H II region. This arc terminates in a prominent cometary clump, G30.772-0.209. A second chain of IRDCs extends from MM3 and wraps around the high-latitude side of the H II region, blocking its expansion in that direction.

\begin{figure}
\par\includegraphics[width=7.5cm,clip]{14596fig2.eps}
\vspace*{-2.5mm}
\end{figure} Figure 2:

A color composite image showing the W43 starburst region in the Spitzer$\mu $m (blue), and Hi-Gal 70 $\mu $m (green) and 250 $\mu $m (red).

Open with DEXTER

\begin{figure}
\par\includegraphics[width=7.5cm,clip]{14596fig3.eps}
\vspace*{-2.5mm}
\end{figure} Figure 3:

A color temperature image showing the W43 starburst region at 70 $\mu $m (blue), 160 $\mu $m (green), and 500 $\mu $m (red). Small white circles mark the 6 cm point sources. Black circles mark the brightest Motte et al. (2003) MM sources with their radial velocities. As in Fig. 1, yellow, blue, cyan, and red circles mark locations where radial velocites have been determined; the number above each circle give the LSR radial velocity.

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Table 1:   Properties of the brightest compact W43 sources.

G30.720-0.083 (= MM3 in Motte et al. 2003; 115 mJy at 6 cm) is the brightest compact H II region in the W43 complex. It is centered in a 1 pc radius IRDC seen in absorption at 70 $\mu $m and below and as a bright clump beyond 160 $\mu $m. Prominent ionization fronts wrap around the side facing W43's central cluster. G30.817-0.056 (= MM1) is located at the head of parsec-long cometary IRDC that faces the central part of the W43 H II region seen in silhouette at wavelengths less than 70 $\mu $m. MM1 is not detected at 6 and 20 cm and may thus be in an earlier state of evolution than MM3. It is likely a massive proto-star or cluster of proto-stars exhibiting OH, H2O, and CH3OH masers (see Motte et al. 2003). At 4 $^{\prime\prime}$ (0.1 pc) resolution at 70 $\mu $m, this and the other luminous sub-mm sources remain single and unresolved, implying that they are either isolated massive protostars, or clusters smaller than 0.1 pc.

The spectra of the four brightest compact sources, MM1 through 4 (Motte et al. 2003; marked in Fig. 2) peak in the SPIRE 160 $\mu $m filter (Table 1). These FIR sources contain massive stars or compact clusters smaller than 0.1 pc in radius. The contribution of mid-IR emission below 60 $\mu $m, and radiation that has escaped into the colder extended envelope (such as the 1 pc radius envelope around MM3) may raise the total luminosity of each to nearly $10^5~L_{\odot}$.

The unresolved emission from the 4 brightest MM sources provide about 2% of the total far-IR luminosity. The several dozen compact sources (Motte et al. 2003 listed 51) in the Z-shaped ridge may contribute an additional $\sim$6%. These compact sources probably represent massive stars with $L > 10^4~L_{\odot}$ in various stages of formation. MM1 is probably the youngest since it is the most luminous in the far-IR, is associated with masers, but lacks free-free emission. MM3 is more evolved since it is associated with the brightest compact H II region at 6 cm, but still highly embedded within the Z-shaped ridge. Masses for the brightest compact sources are estimated using the 500 $\mu $m fluxes since the sources are most likely to be optically thin and on the Rayleigh-Jeans tail of the spectrum. We use the dust opacities from Ossenkopf & Henning (1994; OH94) for the bracketing cases of MRN grains without and with thin ice mantles evolved for 105 years at densities of 106 cm-3. Dust temperatures listed in Table 1 were determined using grey body fits to the SEDs. The best-fit Robitaille (2006) models are consistent with the envelope masses in Table 1, imply stellar masses around 10 to 23 $M_{\odot}$ accreting at rates of around $10^{-3}~M_{\odot}$ yr-1. The beam-averaged envelope column densities range from N(H2) $\sim 2 \times 10^{22}$ cm-2 (MM4) to $\sim$ $ 1.6 \times 10^{22}$ cm-2 (MM1).

The Hi-GAL data provides the best estimate of the total luminosity of the W43 complex which peaks around 160 $\mu $m, implying a typical dust temperature of around 20 K. Summing the fluxes in a 600 $^{\prime\prime}$ by 600 $^{\prime\prime}$ (16 pc) box centered on W43 yields a total far-IR luminosity of $L_{\rm tot} = 3.6 \times 10^6~L_{\odot}$, within 10% of previous estimates (Lester et al. 1985). This is a lower limit since some radiation may escape to larger distances than the measurement box. Presumably, most of this luminosity is produced by the central WR+O cluster the massive stars traced by the 6 cm point sources and is reprocessed into the far-IR by the surrounding dust. Summing the total flux at 500 $\mu $m in this box, subtracting the background be averaging the surrounding annulus, assuming a grain temperature of 20 K, and a gas:dust ratio of 100 implies a total mass of $0.87{-}1.3 \times 10^6~M_{\odot}$ ( $3.7 \times 10^6~M_{\odot}$ for un-evolved MRN grains).

WR stars are post-main sequence states of the most massive stars ( $M > 60~M_{\odot}$) that have main-sequence lives of about 4 to 6 Myr. Thus, the age of the WR+O cluster in W43 is probably in this range. If massive stars have been forming at a constant rate over a 5 Myr period, the ratio of the luminosity of the 4 brightest objects, MM1 through 4, divided by the total luminosity of the region implies that the duration of the embedded massive protostar stage for such objects is $t_{\rm proto} \sim L_{\rm proto} / L_{\rm tot} < 10^5$ years.

4 Discussion

There are at least two locations in the ``W43 Chimney'' containing OB stars or associations; W43 and G30.684-0.260. Fich et al. (1990) have shown that G30.608-0.623 is likely to be associated with the foreground H II region Sh2-67. However, many molecular clouds associated with the dust rim surrounding this region have velocities similar to W43. Thus, these clouds are likely to be associated with the W43 chimney. Based on the dim 20 cm continuum, the large sizes of cometary clouds facing G30.684-0.260, and their location up to 20 pc away, the massive stars in this region (marked in part by the lower cluster of compact 6 cm sources in Figs. 1 and 3) must to be older than W43. Ionization fronts up to 40 pc away along the l = 30.5 wall appear to be illuminated from this direction (Fig. 1). Assuming a typical propagations speed of 5 km s-1 for a typical D-type I-front moving through the ISM, the age of this cluster is likely to be 5 to 10 Myrs. We hypothesize that as the expanding H II region powered by this group impacted denser gas toward the Galactic plane, it triggered the formation and gravitational collapse of the GMC that evolved into W43, giving birth to its oldest massive stars (the O and WR cluster). Subsequently UV radiation from the central O+WR cluster compressed the parent cloud towards both low- and high Galactic longitudes, triggering the formation of additional massive stars.

The bipolar morphology of the W43 H II region indicates that its evolution has been constrained by dense gas associated with the warm 70 $\mu $m to 500 $\mu $m dust emission located in the horizontal central bar of the Z-shaped ridge. As the H II region expandedabove and below the ridge, its pressure would have compressed it, possibly triggereing the current ``mini-starburst'' traced by the dozens of cores in the Z-shaped ridge.

The ``W43 Chimney'' may be similar to but much younger than the superbubble emerging from the Orion OB association (Bally 2008) or the one powered by the IC 1805 cluster in the W4 complex (Basu et al. 1999). The Lyman continuum radiation and total luminosity of the W43 complex implies that it contains the equivalent of about 50 O7 stars. When these stars explode, they may cause the Chimney to blow out of the Galaxy to drive a ``galactic fountain''.

5 Conclusions

Hi-GAL provides the first high resolution far-infrared view of the Galactic ISM. W43 contains about a dozen embedded massive protostars with $L > 10^4~L_{\odot}$ which contribute about 5% to 8% of the total luminosity, $L_{\rm tot} = 3.6 \times 10^6~L_{\odot}$ measured in a 16 pc diameter box. The youngest luminous (> $2 \times 10^4~L_{\odot}$) object, MM1 is located at the head of a comet-shaped IRDC pointing away from the W43 central cluster. MM3 is older since it is associated with the brightest compact H II region in W43. Compression of the Z-shaped filament by the bipolar W43 H II region may have triggered the formation of dozens of luminous sources.

The ``W43 Chimney'' is the most obvious giant cavity in the Hi-GAL fields and may represent a young 30 by 70 pc superbubble filled with diffuse 20 cm emission and rimmed by warm dust and molecular clouds having similar radial velocities as W43. Parsec-scale cometary clouds associated with G30.772-0.209 and G30.684-0.260 point to an older group of massive stars below W43 and associated with a cluster of compact 6 cm sources. Compression of clouds closer to the Galactic plane by this group may have triggered the initial burst of star formation in W43. W43 and this older group may be energizing the W43 Chimney.

Acknowledgements
The participation of J.B. and G.S.S are supported in part by NASA through an award issued by JPL/Caltech via NASA Grant #1350780. We thank the referee for making excellent suggestions for improving the text.

References

Footnotes

... ``mini-starburst''[*]
Herschel in an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.

All Tables

Table 1:   Properties of the brightest compact W43 sources.

All Figures

  \begin{figure}
\par\includegraphics[width=7cm,clip]{14596fig1.eps}
\vspace*{-4mm}
\end{figure} Figure 1:

A color composite image showing the W43 starburst region and the superbubble bursting towards low Galactic latitudes at 70 $\mu $m (blue), 160 $\mu $m (green), and 500 $\mu $m (red) using ``unsharp-masked'' images as described in the text. Small red circles or dots mark the locations of 6 cm point sources. Large yellow circles mark locations where the radial velocity has been measured using mm-wavelength tracers; yellow indicates radial velocities within the velocity range $85 < V_{\rm LSR} < 107$ km s-1 measured using CS (Shirley et al., in prep.) or 13CO. Blue and cyan circles indicate LSR velocities outside this range. Small yellow circles mark the locations of 13CO clouds having similar radial velocities as W43. The numbers above each circle mark the LSR radial velocity in km s-1. Several regions discussed in the text are marked in cyan. Warm dust at 70 $\mu $m outlines the walls of the ``W43 Chimney'' (shown in blue line segments). A 0.1$^\circ $ interval corresponds to a linear scale of 9.6 pc at the assumed 5.5 kpc distance to W43.

Open with DEXTER
In the text

  \begin{figure}
\par\includegraphics[width=7.5cm,clip]{14596fig2.eps}
\vspace*{-2.5mm}
\end{figure} Figure 2:

A color composite image showing the W43 starburst region in the Spitzer$\mu $m (blue), and Hi-Gal 70 $\mu $m (green) and 250 $\mu $m (red).

Open with DEXTER
In the text

  \begin{figure}
\par\includegraphics[width=7.5cm,clip]{14596fig3.eps}
\vspace*{-2.5mm}
\end{figure} Figure 3:

A color temperature image showing the W43 starburst region at 70 $\mu $m (blue), 160 $\mu $m (green), and 500 $\mu $m (red). Small white circles mark the 6 cm point sources. Black circles mark the brightest Motte et al. (2003) MM sources with their radial velocities. As in Fig. 1, yellow, blue, cyan, and red circles mark locations where radial velocites have been determined; the number above each circle give the LSR radial velocity.

Open with DEXTER
In the text


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