RCW 49 at Mid‐Infrared Wavelengths: A GLIMPSE from the
                    <i>Spitzer Space Telescope</i>

Churchwell, E.; Whitney, B. A.; Babler, B.; Indebetouw, R.; Meade, M. R.; Watson, C.; Wolff, Michael; Wolfire, M. G.; Bania, T. M.; Benjamin, Robert A.; Clemens, D. P.; Cohen, Martin; Devine, K. E.; Dickey, John M.; Heitsch, Fabian; Jackson, James M.; Kobulnicky, Henry A.; Marston, A. P.; Mathis, J. S.; Mercer, E. P.; Stauffer, J. R.; Stolovy, S.

doi:10.1086/422504

Cited by 93 publications

(46 citation statements)

References 30 publications

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“…Similar emission from dust pillars is widely seen in IRAC images of other massive star-forming regions (e.g. Churchwell et al 2004Churchwell et al , 2009Reach et al 2004Reach et al , 2009Bowler et al 2009).…”

Section: General Properties Of the Extended Emission: Dust Pillarssupporting

confidence: 66%

Spitzer Space Telescope observations of the Carina nebula: the steady march of feedback-driven star formation

Smith¹,

Povich²,

Whitney³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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We report the first results of imaging the Carina nebula (NGC 3372) with the Infrared Array Camera (IRAC) onboard the Spitzer Space Telescope, providing a photometry catalogue of over 44 000 point sources as well as a catalogue of over 900 candidate young stellar objects (YSOs) based on fits to their spectral energy distributions (SEDs). We discuss several aspects of the extended emission, including the structure of dozens of dust pillars that result when a clumpy molecular cloud is shredded by feedback from massive stars. There are surprisingly few of the ‘extended green objects’ (EGOs) that are normally taken as signposts of outflow activity in Spitzer data, and not one of the dozens of Herbig‐Haro jets detected optically are seen as EGOs. EGOs are apparently poor tracers of outflow activity in strongly irradiated environments, due to the effects of massive star feedback. A population of ‘extended red objects’ tends to be found around late O‐type and early B‐type stars, some with clear bow‐shock morphology. These are dusty shocks where stellar winds collide with photoevaporative flows off nearby clouds. Finally, the relative distributions of O‐type stars, small star clusters and subclusters of YSOs as compared to the dust pillars show that while some YSOs are located within dust pillars, many more stars and YSOs reside just outside pillar heads. We suggest that pillars are transient phenomena, part of a continuous outwardly propagating wave of star formation driven by feedback from massive stars. As the pillars are destroyed, they leave newly formed stars in their wake, and these are then subsumed into the young OB association. The YSOs are found predominantly in the cavity between pillars and massive stars, arguing that their formation was in fact triggered. Altogether, the current generation of YSOs shows no strong deviation from a normal initial mass function (IMF). The number of YSOs is consistent with a roughly constant star‐formation rate over the past ∼3 Myr, implying that propagating star formation in pillars constitutes an important mechanism to construct unbound OB associations. These accelerated pillars may give birth to massive O‐type stars that, after several million years, could appear to have formed in isolation.

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Section: General Properties Of the Extended Emission: Dust Pillarssupporting

confidence: 66%

Spitzer Space Telescope observations of the Carina nebula: the steady march of feedback-driven star formation

Smith¹,

Povich²,

Whitney³

et al. 2010

Monthly Notices of the Royal Astronomical Society

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“…PAHs are most readily identified as broad lines in the mid-IR spectrum that have been seen in many H II regions and PNe. The observed survival of small dust grains in hostile environments is difficult to reconcile with models (Spitzer 1978), yet strong mid-IR PAH signals are observed in active star-forming regions including RCW 49 (Churchwell et al 2004). The spinning dust mechanism appears therefore to be still viable in such environments.…”

Section: Anomalous Dust Emissionmentioning

confidence: 99%

CBI limits on 31 GHz excess emission in southern H II regions

Dickinson

Davies

Bronfman

et al. 2007

Monthly Notices of the Royal Astronomical Society

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We have mapped four regions of the southern Galactic plane at 31 GHz with the Cosmic Background Imager. From the maps, we have extracted the flux densities for six of the brightest H ii regions in the southern sky and compared them with multifrequency data from the literature. The fitted spectral index for each source was found to be close to the theoretical value expected for optically thin free–free emission, thus confirming that the majority of flux at 31 GHz is due to free–free emission from ionized gas with an electron temperature of ≈7000–8000 K. We also found that, for all six sources, the 31‐GHz flux density was slightly higher than the predicted value from data in the literature. This excess emission could be due to spinning dust or another emission mechanism. Comparisons with 100‐μm data indicate an average dust emissivity of 3.3 ± 1.7 μK (MJy sr−1)−1, or a 95 per cent confidence limit of <6.1 μK (MJy sr−1)−1. This is lower than that found in diffuse clouds at high Galactic latitudes by a factor of ∼3–4. The most significant detection (3.3σ) was found in G284.3−0.3 (RCW 49) and may account for up to ≈30 per cent of the total flux density observed at 31 GHz. Here, the dust emissivity of the excess emission is 13.6 ± 4.2 μK (MJy sr−1)−1 and is within the range observed at high Galactic latitudes. Low‐level polarized emission was observed in all six sources with polarization fractions in the range 0.3–0.6 per cent. This is likely to be mainly due to instrumental leakage and is therefore an upper limit to the free–free polarization. It corresponds to an upper limit of ∼1 per cent for the polarization of anomalous emission.

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“…Fig. 3 shows a mosaic made from the 3.6 µm Spitzer IRAC images (Churchwell et al 2004) of the region towards the RCW49 complex. There we identify WR20a, WR20b and WR21a together with WR20aa and WR20c.…”

Section: The New O2 If*/wn6 Stars and The Westerlund 2 Clustermentioning

confidence: 99%

Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2

Roman-Lopes¹,

Barbá²,

Morrell³

2011

Monthly Notices of the Royal Astronomical Society

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In this paper we report the identification of two new Galactic O2 If*/WN6 stars (WR20aa and WR20c), on the outskirts of the massive young stellar cluster Westerlund 2. The morphological similarity between the near‐infrared spectra of the new stars with that of WR20a and WR21a (two of the most massive binaries known to date) is remarkable, indicating that probably they are also very massive stars. New optical spectroscopic observations of WR20aa suggest an intermediate O2 If*/WN6 spectral type. Based on a mosaic made from the 3.6 μm Spitzer IRAC images of the region including part of the RCW49 complex, we studied the spatial location of the new emission line stars, finding that WR20aa and WR20c are well displaced from the centre of Westerlund 2, being placed at ≈36 pc (15.7 arcmin) and ≈58 pc (25.0 arcmin), respectively, for an assumed heliocentric distance of 8 kpc. Also, very remarkably, a radius vector connecting the two stars would intercept the Westerlund 2 cluster exactly at the place where its stellar density reaches a maximum. We consequently postulate a scenario in which WR20aa and WR20c had a common origin somewhere in the cluster core, being ejected from their birthplace by dynamical interaction with some other very massive objects, perhaps during some earlier stage of the cluster evolution.

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RCW 49 at Mid‐Infrared Wavelengths: A GLIMPSE from the Spitzer Space Telescope

Cited by 93 publications

References 30 publications

Spitzer Space Telescope observations of the Carina nebula: the steady march of feedback-driven star formation

Spitzer Space Telescope observations of the Carina nebula: the steady march of feedback-driven star formation

CBI limits on 31 GHz excess emission in southern H II regions

Two O2 If*/WN6 stars possibly ejected from the massive young Galactic cluster Westerlund 2

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