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Physical properties of the star-forming clusters in NGC 6334
Get PDFAims. We aim to characterise certain physical properties of high-mass star-forming sites in the NGC 6334 molecular cloud, such as the core mass function (CMF), spatial distribution of cores, and mass segregation.
Methods. We used the Atacama Large Millimeter/sub-millimeter Array (ALMA) to image the embedded clusters NGC 6334-I and NGC 6334-I(N) in the continuum emission at 87.6 GHz. We achieved a spatial resolution of 1300 au, enough to resolve different compact cores and fragments, and to study the properties of the clusters.
Results. We detected 142 compact sources distributed over the whole surveyed area. The ALMA compact sources are clustered in different regions. We used different machine-learning algorithms to identify four main clusters: NGC 6334-I, NGC 6334-I(N), NGC 6334-I(NW), and NGC 6334-E. The typical separations between cluster members range from 4000 au to 12 000 au. These separations, together with the core masses (0.1–100 M⊙), are in agreement with the fragmentation being controlled by turbulence at scales of 0.1 pc. We find that the CMFs show an apparent excess of high-mass cores compared to the stellar initial mass function. We evaluated the effects of temperature and unresolved multiplicity on the derived slope of the CMF. Based on this, we conclude that the excess of high-mass cores might be spurious and due to inaccurate temperature determinations and/or resolution limitations. We searched for evidence of mass segregation in the clusters and we find that clusters NGC 6334-I and NGC 6334-I(N) show hints of segregation with the most massive cores located in the centre of the clusters.
Conclusions. We searched for correlations between the physical properties of the four embedded clusters and their evolutionary stage (based on the presence of H I
THE STAR FORMATION REGION NGC 6334
Get PDFRESUMEN El complejo nebular NGC 6334 contiene varios ejemplos de núcleos de formación estelar extremadamente activa. Este se encuentra a una distancia de 1.62 kpc del Sol y tiene una masa total de más de 10 5 M . Las condiciones físicas que caracterizan cada uno de sus centros activos difieren significativamente de región a región, desde la fase más temprana que se pueda detectar milimétricamente hasta regiones HII bien desarrolladas. Las regiones más viejas están hacia el sur y las más jóvenes se alinean siguiendo un risco molecular. A lo largo deéste, no se aprecia ningún patrón que pueda correlacionar sus edades con su localización. ABSTRACT The bright nebular complex NGC 6334 contains some of the most active sites of massive star formation known in our Galaxy. It is located at a distance from the Sun of 1.62 kpc and has a total mass of a few 10 5 M . The physical characteristics of the active spots range widely, from well developed expanding HII regions to deeply embedded, still contracting, young objects detected only as millimeter sources, thus at their earliest observable stage of their evolution. The oldest optically visible round HII regions with central O-type stars are found in the southern parts, and the youngest along a molecular ridge. On the latter, no clear spatial evolutionary correlation is apparent. Key Words: H II regions -stars: formation PANORAMA OF THE COMPLEX NGC 6334 This optical emission nebula, also known as the "Cat's Paw", is one of the most complex natural star formation laboratories known in the Galaxy. It extends 32 × 40 across the sky and is at a distance from the Sun of 1.62 kpc INDIVIDUAL ACTIVE REGIONS NGC 6334 I, I(N), E The northeastern part of the molecular ridge of NGC 6334 is the best studied so far and includes two of the youngest regions ever detected. The thermal emission of the cold core I(N) has been detected only at λ > 200 µm and has a mass of ∼ 2200 M . With a prototrapezium system of five components detected only at 1.2 mm NGC 6334 II, IV and V The far-infrared source II coincides with the shell radio HII region D. The expansion of which seems to have triggered a new site for the formation of a small star cluster, seen embedded in a dense molecular clump on the western side of the shell. This scenario could well be an appropriate description for 7
[CI] 809 GHz Imaging of the NGC 6334 Complex
No full textWe present Antarctic Submillimeter Telescope and Remote Observatory (AST/RO) observations of submillimeter emissions from the NGC 6334 complex for both the 12[CI]3P2→3P1 fine-structure line of atomic carbon and the 12COJ=4→3 rotational transition of CO. We detected strong 12[CI]3P2→3P1 emission from the entire star-forming NGC 6334 complex, and present maps of 12[CI]3P2→3P1 emission and 12COJ=4→3 emission. Comparing these maps with archival ASCA data, we show that, to the south of NGC 6334, the [C I] emissions are likely to be associated with strong X-ray emissions from the FIR sources. However, the calculation using the X-ray dissociation region model shows that the majority of the [C I] emission can not arise from X-ray dissociation of the cloud. Alternatively, far-ultraviolet radiation produced in the photodissociation regions is expected to contribute to dissociate the carbon monoxide in the NGC 6334 complex
Millimeter multiplicity in NGC 6334 I and I(N)
No full textUsing the Submillimeter Array (SMA), we have imaged the 1.3 mm continuum emission at the centers of the massive star-forming regions NGC 6334 I and I(N). In both regions, the SMA observations resolve the emission into multiple millimeter sources, with most of the sources clustered into areas only 10,000 AU in diameter. Toward NGC 6334 I, we find four compact sources: the two brightest (I-SMA1 and I-SMA2) are associated with previously known ammonia cores; I-SMA3 coincides with the peak of the compact H II region (NGC 6334 F), and I-SMA4 is a newly discovered object. While I-SMA3 exhibits a mixture of free-free and dust emission, the rest of the objects are dust cores. Toward NGC 6334 I(N), seven compact dust cores are found, one of which is associated with a faint centimeter source. With the exception of I-SMA3, none of the millimeter sources have infrared counterparts in Spitzer Space Telescope 3-8 mum images. Using a simple physical model for the dust continuum emission, we estimate that the mass of the interstellar material toward each of these compact objects is in the range of 3-66 Msolar. The total mass in the compact objects appears to be similar in I and I(N). The small size of these groups of sources suggest that these objects are proto-Trapezia forming in the centers of clusters of low- to intermediate-mass stars
HIRES Dust Imaging of the NGC 6334 Star Forming Complex
Get PDFWe present here our final report for the NASA grant "HIRES Dust Imaging of the NGC 6334 Star Forming Complex." This project was designed to study the photodissociation regions surrounding several OB stars in this cloud complex. NGC 6334 is unique in having at least seven distinct massive star forming regions in the same molecular cloud complex. The obvious advantage of studying young stars in the same molecular complex is that the stars all formed in the same global environment. Consequently, global factors like density waves, abundances, global magnetic field strength, and age of the parental molecular cloud cannot contribute to the differences among the star forming regions. Instead, the differences must arise only from local effects such as the mass, age, and UV fields of the individual stars. A study of NGC 6334 will greatly simplify the general problem of comparing different star formation regions by eliminating global effects
NGC 6334 and NGC 6357: Hα kinematics and the nature of the H II regions
No full textInternational audienceAims: NGC 6334 and NGC 6357 are amongst the most active, optically visible Galactic star-forming complexes. They are composed of several H ii regions that have a significant impact on their surrounding. The aim of this paper is to present a kinematic study of the optical H ii regions that belong to NGC 6334 and NGC 6357. Methods: We use Fabry-Perot interferometer observations of the Hα line, which cover NGC 6334 and NGC 6357. These observations allow us to analyse the Hα line profiles to probe the kinematics of the ionised gas of both regions. We complement the Hα observations with multi-wavelength data to specify the nature of the H ii regions. Results: We determine the dynamical nature of the optical H ii regions that belongs to NGC 6334 and NGC 6357. In NGC 6334, GUM 61 is an expanding wind shell-like H ii region, GUM 64b exhibits a champagne flow, GM1-24 is the Hα counterpart of two larger regions and H ii 351.2+0.5 is, in fact, composed of two H ii regions. In NGC 6357, H ii 353.08+0.28 and H ii 353.09+0.63 are probably stellar wind-shaped bubble H ii regions, while H ii 353.42+0.45 is a classical photo-ionised H ii region. We suggest that, at large scale, star-formation seems to be triggered where large/old H ii regions intersect. Inversely, stellar formation seems to have already started in the NGC 6334 north-east filament, irrespective of any evident external H ii region impact. While NGC 6357 shows more complicated kinematics, NGC 6334 is characterised by a more active stellar formation.The Hα data (FITS cubes) are only available at the CDS via anonymous ftp to http://cdsarc.u-strasbg.fr (ftp://130.79.128.5) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/587/A13
OB stars and YSO populations in the region of NGC 6334–NGC 6357 as seen with Gaia DR2
No full textInternational audienceAims. Our goal is to better understand the origin and the star-formation history of regions NGC 6334 and NGC 6357. We focus our study on the kinematics of young stars (young stellar objects and OB stars) in both regions mainly on the basis of the Gaia DR2 data.Methods. For both regions, we compiled catalogs of OB stars and young stellar objects from the literature and complemented them using VPHAS+ DR2 and Spitzer IRAC/GLIMPSE photometry catalogues. We applied a cross-match with the Gaia DR2 catalog to obtain information on the parallax and transverse motion.Results. We confirm that NGC 6334 and NGC 6357 are in the far side of the Saggitarius-Carina arm at a distance of 1.76 kpc. For NGC 6357, OB stars show strong clustering and ordered star motion with Vlon ∼–10.7 km s−1 and Vlat ∼3.7 km s−1, whereas for NGC 6334, no significant systemic motion was observed. The OB stars motions and distribution in NGC 6334 suggest that it should be classified as an association. Ten runaway candidates may be related to NGC 6357 and two to NGC 6334, respectively. The spatial distributions of the runaway candidates in and around NGC 6357 favor a dynamical (and early) ejection during the cluster(s) formation. Because such stars are likely to be ejected during a cluster’s formation, the fact that not as many such stars are observed towards NGC 6334 suggests different formation conditions than have been assumed for NGC 6357
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The Distribution and Properties of Cold Dust in NGC 6334
No full textNGC 6334 is a galactic star-forming region in Scorpius, heavily obscured by intervening dust. The region consists of several major sites of star formation known previously from far-infrared (IR) and radio-wavelength observations. We present images of NGC 6334 obtained at wavelengths of 850 and 450 μm with the Submillimeter Common-User Bolometric Array at the James Clerk Maxwell Telescope. These data highlight the distribution of dense cold dust, a particularly striking feature of which is a narrow ridge of emission passing between most of the star-forming centers. We use a clump-finding technique to quantify the distribution of dust emission throughout the region, and we obtain estimates of the sizes, masses, and temperatures of the clump ensemble under simple assumptions. Clump masses range from a minimum detectable of about 1 M ⊙, up to almost 3000 M ⊙. We find in particular that the ridge feature is characterized by a relatively narrow range of clump parameters as compared with the rest of NGC 6334, and we obtain a clump mass spectral index that lies between N(M) ∝ M–1.5 and M–1.0 for the high-mass clumps. The total mass of dust emitting at submillimeter wavelengths is about 16700 M ⊙ for an assumed temperature of 25 K; a significant fraction of this mass is contained within the ridge feature. These data are compared with recently published observations of NGC 6334 obtained at 1.2 mm wavelength using a direct-detection scanning technique, and with images obtained by the GLIMPSE-II and Mid-course Space Experiment missions at wavelengths from 3.3 to 21 μm in the near IR (NIR). The most massive compact submillimeter-wavelength regions in the north are invisible at these shorter wavelengths, and the NIR and mid-IR emission generally have little correspondence with the cool dust distribution. In this paper we use these data sets and supplementary millimeter-wavelength spectral line observations to investigate the star-forming sites in NGC 6334 and to speculate on the significance of the ridge of material seen in the submillimeter images
The new star forming site NGC 6334 IV (MM3)
No full textAims. The eastern part of the massive star forming region NGC 6334 IV is characterized by the presence of the
millimeter continuum sources MM3, MM4, and the optically thin HII region G351.24+0.65. Here we
study the star formation in this part of the cloud.
Methods. We imaged this region, here named NGC 6334 IV (MM3), at sub-arcsec resolution in , H2,
Br γ, and in the mid-infrared, from 8.9 to 12.7. In addition, we used IRAC/Spitzer and ISOCAM
images.
Results. From the analysis of the IRAC color-color and versus
Ks – [3.6] diagrams, we found 18 embedded
very young stellar objects within an area of 75\arcsec \times 75 \arcsec. One of these sources, IR-MM3
(IRS 8E), shows a very steep energy distribution with an infrared spectral index of and
. This protostar, which coincides with an OH maser source and with the continuum
millimeter source MM3, is the exciting source of two hydrogen molecular knots found in our
H2 image. Two sources (IRS 18, and 19) with infrared excess and a steep SED are probably
associated with the HII region G351.24+0.65. The IRAC and
ISOCAM images indicate the presence of extended PAH emission in the region.
Conclusions. We have discovered a new center of massive star formation in the giant molecular
cloud complex NGC 6334
Kinematics and Structure of Massive Star Formation in NGC 6334-V
Get PDFHow filamentary molecular clouds fragment into star-forming hub clusters remains an unresolved issue. This thesis focuses on the observational studies of the massive hub protocluster NGC 6334-V, which is embedded within the filamentary cloud NGC 6334. It delves deeply into the mechanisms operating at three distinct scales: compact structures present within the hub cluster, the sub-pc scales characterizing the filamentary accretions toward the cluster, and the pc scales dynamics defining the relationship between the cluster and the entire molecular cloud. The primary observational data used in this work consists of spectral-line ALMA observations with a spatial resolution of 1800 au, sensitive to both the 3 mm continuum emission and various molecular species. Moreover, low-resolution ancillary observations at larger scales and different wavelengths are also utilized to compare and connect the sub-pc and pc scale filamentary structures, as well as to search for ionized gas. High-resolution ALMA observations reveal 28 compact cores in the central hub cluster NGC 6334-V of which four show a detection of IR compact source counterparts. The existence of young high-mass cores suggest that cluster NGC 6334-V is in an early stage, and the observed segregation among the cores suggests that primordial segregation could be a potential formation scenario. The rotational temperature of CH3CCH varies widely, ranging from a few tens of kelvin up to 252K at the position of the hot core, with a measurement error of ≈20−50K. Utilizing dense gas tracers, particularly H13CO+, six prominent filaments were identified. The central cluster exhibits a distinctive widespread SiO emission, with an exceptionally narrow linewidth of less than 1.8 km s−1. The analysis of the SiO (2–1) line profile and spatial distribution reveals that 99.8% of SiO emission has a width of less than 10 km s−1 and 57% has a width of less than 1.8 km s−1. This emission reveals a tail-like structure along three filaments and suggests that the SiO emission in NGC 6334-V primarily results from low-velocity shocks. These shocks could originate from the encounter of filaments with the high-density central hub or from the confluence of an H II region behind the cluster. The morphological analysis of cluster NGC 6334-V on a large scale suggests a formation scenario based on the ionization injection process from cavities behind the cloud. In this scenario, ionized gas ejected from an unknown source behind the cloud hits the cloud from one side, effectively isolating source V from the rest of the NGC 6334 cloud and pushing the filaments to the opposite side while the accretion continues toward the center
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