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Register a new userThe VISTA Carina Nebula Survey II. Spatial distribution of the infrared-excess-selected young stellar population
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We performed a deep wide-field (6.76 deg^2) near-infrared survey with the VISTA telescope that covers the entire extent of the Carina nebula complex (CNC). The point-source catalog created from these data contains around four million individual objects down to masses of 0.1 M_sun. We present a statistical study of the large-scale spatial distribution and an investigation of the clustering properties of infrared-excesses objects, which are used to trace disk-bearing young stellar objects (YSOs). We find that a (J - H) versus (Ks - [4.5]) color-color diagram is well suited to tracing the population of YSO-candidates (cYSOs) by their infrared excess. We identify 8781 sources with strong infrared excess, which we consider as cYSOs. This sample is used to investigate the spatial distribution of the cYSOs with a nearest-neighbor analysis. The surface density distribution of cYSOs agrees well with the shape of the clouds as seen in our Herschel far-infrared survey. The strong decline in the surface density of excess sources outside the area of the clouds supports the hypothesis that our excess-selected sample consists predominantly of cYSOs with a low level of background contamination. This analysis allows us to identify 14 groups of cYSOs outside the central area. Our results suggest that the total population of cYSOs in the CNC comprises about 164000 objects, with a substantial fraction (~35%) located in the northern, still not well studied parts. Our cluster analysis suggests that roughly half of the cYSOs constitute a non-clustered, dispersed population.
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The Carina Nebula represents one of the largest and most active star forming regions known in our Galaxy with numerous very massive stars.Our recently obtained Herschel PACS & SPIRE far-infrared maps cover the full area (about 8.7 deg^2) of the Carina Nebula complex and reveal the population of deeply embedded young stellar objects, most of which are not yet visible in the mid- or near-infrared.We study the properties of the 642 objects that are independently detected as point-like sources in at least two of the five Herschel bands.For those objects that can be identified with apparently single Spitzer counterparts, we use radiative transfer models to derive information about the basic stellar and circumstellar parameters.We find that about 75% of the Herschel-detected YSOs are Class 0 protostars.The luminosities of the Herschel-detected YSOs with SED fits are restricted to values of <=5400 Lsun, their masses (estimated from the radiative transfer modeling) range from about 1 Msun to 10 Msun.Taking the observational limits into account and extrapolating the observed number of Herschel-detected protostars over the IMF suggest that the star formation rate of the CNC is about 0.017 Msun/yr.The spatial distribution of the Herschel YSO candidates is highly inhomogeneous and does not follow the distribution of cloud mass.Most Herschel YSO candidates are found at the irradiated edges of clouds and pillars.This provides support to the picture that the formation of this latest stellar generation is triggered by the advancing ionization fronts.The currently ongoing star formation process forms only low-mass and intermediate-mass stars, but no massive stars.The far-infrared fluxes of the famous object EtaCar are about a factor of two lower than expected from observations with the ISO obtained 15 years ago; this may be due to dynamical changes in the circumstellar dust in the Homunculus Nebula.
We present results of an infrared study of the molecular cloud Lynds 1340, forming three groups of low and intermediate-mass stars. Our goals are to identify and characterise the young stellar population of the cloud, study the relationships between the properties of the cloud and the emergent stellar groups, and integrate L1340 into the picture of the star-forming activity of our Galactic environment. We selected candidate young stellar objects from the Spitzer and WISE data bases using various published color criteria, and classified them based on the slope of the spectral energy distribution. We identified 170 Class II, 27 Flat SED, and Class 0/I sources. High angular resolution near-infrared observations of the RNO 7 cluster, embedded in L1340, revealed eight new young stars of near-infrared excess. The surface density distribution of young stellar objects shows three groups, associated with the three major molecular clumps of L1340, each consisting of less than 100 members, including both pre-main sequence stars and embedded protostars. New Herbig--Haro objects were identified in the Spitzer images. Our results demonstrate that L1340 is a prolific star-forming region of our Galactic environment in which several specific properties of the intermediate-mass mode of star formation can be studied in detail.
(abbreviated) We investigate the spatial structure and spectral energy distribution of an edge-on circumstellar disk around an optically invisible young stellar object that is embedded in a dark cloud in the Carina Nebula. Whereas the object was detected as an apparently point-like source in earlier infrared observations, only the superb image quality (FWHM ~0.5) of our VLT / HAWK-I data could reveal, for the first time, its peculiar morphology. It consists of a very red point-like central source that is surrounded by a roughly spherical nebula, which is intersected by a remarkable dark lane through the center. We construct the spectral energy distribution of the object from 1 to 870 microns and perform a detailed radiative transfer modeling of the spectral energy distribution and the source morphology. The observed object morphology in the near-IR images clearly suggests a young stellar object that is embedded in an extended, roughly spherical envelope and surrounded by a large circumstellar disk with a diameter of ~5500 AU that is seen nearly edge-on. The radiative transfer modeling shows that the central object is a massive (10-15 Msun) young stellar object. The circumstellar disk has a mass of about 2 Msun. The disk object in Carina is one of the most massive young stellar objects for which a circumstellar disk has been detected so far, and the size and mass of the disk are very large compared to the corresponding values found for most other similar objects.
We present [Fe II] 1.64 {mu}m imaging observations for jets and outflows from young stellar objects (YSOs) over the northern part (~ 24x45) of the Carina Nebula, a massive star forming region. The observations were performed with IRIS2 of Anglo-Australian Telescope and the seeing was ~1.5+-0.5. Eleven jet and outflow features are detected at eight different regions, and are named as Ionized Fe Objects (IFOs). One Herbig-Haro object candidate missed in Hubble Space Telescope H{alpha} observations is newly identified as HHc-16, referring our [Fe II] images. IFOs have knotty or longish shapes, and the detection rate of IFOs against previously identified YSOs is 1.4 %, which should be treated as a lower limit. Four IFOs show an anti-correlated peak intensities in [Fe II] and H{alpha}, where the ratio I([Fe II])/I(H{alpha}) is higher for longish IFOs than for knotty IFOs. We estimate the outflow mass loss rate from the [Fe II] flux, using two different methods. The jet-driving objects are identified for three IFOs (IFO-2, -4, and -7), for which we study the relations between the outflow mass loss rate and the YSO physical parameters from the radiative transfer model fitting. The ratios of the outflow mass loss rate over the disk accretion rate are consistent for IFO-4 and -7 with the previously reported values (10^-2-10^+1), while it is higher for IFO-2. This excess may be from the underestimation of the disk accretion rate. The jet-driving objects are likely to be low- or intermediate-mass stars. Other YSO physical parameters, such as luminosity and age, show reasonable relations or trends.
We present a multi-wavelength study of the young stellar population in the Cygnus-X DR15 region. We studied young stars forming or recently formed at and around the tip of a prominent molecular pillar and an infrared dark cloud. Using a combination of ground based near-infrared, space based infrared and X-ray data, we constructed a point source catalog from which we identified 226 young stellar sources, which we classified into evolutionary classes. We studied their spatial distribution across the molecular gas structures and identified several groups possibly belonging to distinct young star clusters. We obtained samples of these groups and constructed K-band luminosity functions that we compared with those of artificial clusters, allowing us to make first order estimates of the mean ages and age spreads of the groups. We used a $^{13}$CO(1-0) map to investigate the gas kinematics at the prominent gaseous envelope of the central cluster in DR15, and we infer that the removal of this envelope is relatively slow compared to other cluster regions, in which gas dispersal timescale could be similar or shorter than the circumstellar disk dissipation timescale. The presence of other groups with slightly older ages, associated with much less prominent gaseous structures may imply that the evolution of young clusters in this part of the complex proceeds in periods that last 3 to 5 Myr, perhaps after a slow dissipation of their dense molecular cloud birthplaces.
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