A multiwavelength study of embedded clusters in W5-east, NGC 7538, S235, S252 and S254-S258 (original) (raw)
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The structure and evolution of young stellar clusters
2006
We examine the properties of embedded clusters within 1 kiloparsec using new data from the Spitzer Space Telescope, as well as recent results from 2MASS and other ground-based near-infrared surveys. We use surveys of entire molecular clouds to understand the range and distribution of cluster membership, size and surface density. The Spitzer data demonstrate clearly that there is a continuum of star-forming environments, from relative isolation to dense clusters. The number of members of a cluster is correlated with the cluster radius, such that the average surface density of clusters having a few to a thousand members varies by a factor of only a few. The spatial distributions of Spitzer-identified young stellar objects frequently show elongation, low density halos, and sub-clustering. The spatial distributions of protostars resemble the distribution of dense molecular gas, suggesting that their morphologies result directly from the fragmentation of the natal gas. We also examine the effects of the cluster environments on star and planet formation. Although Far-UV and Extreme-UV radiation from massive stars can truncate disks in a few million years, fewer than half of the young stars in our sample (embedded clusters within 1 kpc) are found in regions of strong FUV and EUV fields. Typical volume densities and lifetimes of the observed clusters suggest that dynamical interactions are not an important mechanism for truncating disks on solar system size scales.
The formation and evolution of massive stellar clusters in IC4662
Astrophysics and Space Science, 2009
We present a multiwavelength study of the formation of massive stellar clusters, their emergence from cocoons of gas and dust, and their feedback on surrounding matter. Using data that span from radio to optical wavelengths, including Spitzer and Hubble ACS observations, we examine the population of young star clusters in the central starburst region of the irregular Wolf-Rayet galaxy IC 4662. We model the radio-to-IR spectral energy distributions of embedded clusters to determine the properties of their HII regions and dust cocoons (sizes, masses, densities, temperatures), and use near-IR and optical data with mid-IR spectroscopy to constrain the properties of the embedded clusters themselves (mass, age, extinction, excitation, abundance). The two massive star-formation regions in IC 4662 are excited by stellar populations with ages of ∼ 4 Ma and masses of ∼ 3 × 10 5 M (assuming a Kroupa IMF). They have high excitation and sub-solar abundances, and they may actually be comprised of several massive clusters rather than the single monolithic massive compact objects known as Super Star Clusters (SSCs). Mid-IR spectra reveal that these clusters have very high extinctions, A V ∼ 20 − 25 mag, and that the dust in IC 4662 is well-mixed with the emitting gas, not in a foreground screen.
Clustering Properties of Young Stellar Objects in the Massive Star Forming Region W49
American Astronomical Society, AAS Meeting #224, #223.07, 2014
Massive stars play a vital role in the star formation process, yet their own formation and their effects on subsequent generations of star formation is not well understood. To improve our understanding, we have begun a detailed study of massive and active star forming complexes in giant molecular clouds outside the Galactic Center. One of the main goals of this study is to identify and classify the Young Stellar Objects (YSOs) in each region by using Spitzer Space Telescope IRAC & MIPS data. Following this,YSO clusters will be identified based on spatial distributions of the detected sources. Studying clusters with different evolutionary stages will help us to understand the formation and evolution processes from beginning to end. This study will also provide significant information on how massive stars interact with their environment and how they affect the low-mass star formation in the cloud. Within this context, we present the initial results of our investigation on the star-forming complex W49 that is one of the youngest, most luminous and most massive star formation region in the Galaxy. We used a combination of Spitzer Space Telescope IRAC & MIPS data, Two Micron All Sky Survey (2MASS) and UKIRT Deep Infrared Sky Survey (UKIDSS) data to identify and classify the Young Stellar Objects (YSOs) and generated a final catalog with a photometry of sources containing more than 2 million sources within an area of size DeltalxDeltab = 2°.6 x 3°.4, centered at (l,b) = (42°.7,0°.04) over a wavelength range from 1.2 to 24 mum. With a preliminary source classification we identified thousands of YSO candidates. In addition, to understand the evolution of star formation in W49 we analyzed the distributions of YSOs to identify the clusters based on spatial distributions of the detected sources.
Young open clusters in the Galactic star forming region NGC 6357
Astronomy & Astrophysics, 2014
Context. NGC 6357 is an active star forming region with very young massive open clusters. These clusters contain some of the most massive stars in the Galaxy and strongly interact with nearby giant molecular clouds. Aims. We study the young stellar populations of the region and of the open cluster Pismis 24, focusing on their relationship with the nearby giant molecular clouds. We seek evidence of triggered star formation "propagating" from the clusters. Methods. We used new deep JHK s photometry, along with unpublished deep Spitzer/IRAC mid-infrared photometry, complemented with optical HST/WFPC2 high spatial resolution photometry and X-ray Chandra observations, to constrain age, initial mass function, and star formation modes in progress. We carefully examine and discuss all sources of bias (saturation, confusion, different sensitivities, extinction). Results. NGC 6357 hosts three large young stellar clusters, of which Pismis 24 is the most prominent. We found that Pismis 24 is a very young (∼1-3 Myr) open cluster with a Salpeter-like initial mass function and a few thousand members. A comparison between optical and infrared photometry indicates that the fraction of members with a near-infrared excess (i.e., with a circumstellar disk) is in the range 0.3-0.6, consistent with its photometrically derived age. We also find that Pismis 24 is likely subdivided into a few different subclusters, one of which contains almost all the massive members. There are indications of current star formation triggered by these massive stars, but clear age trends could not be derived (although the fraction of stars with a near-infrared excess does increase towards the Hii region associated with the cluster). The gas out of which Pismis 24 formed must have been distributed in dense clumps within a cloud of less dense gas ∼1 pc in radius. Conclusions. Our findings provide some new insight into how young stellar populations and massive stars emerge, and evolve in the first few Myr after birth, from a giant molecular cloud complex.
The structure and dynamics of young star clusters
2013
Homogeneous samples of photometric data, coupled with uniform methods of data analysis are essential to make statistical inferences based on the fundamental parameters of clusters. These studies can contribute to understanding the galactic disk, formation and evolution of clusters, molecular cloud fragmentation, star formation and evolution. In this work, we study a sample of young clusters viz. King 16, NGC 1931, NGC 637 and NGC 189 using photometric data from the Two Micron All Sky Survey (2MASS) (Skrutskie et al. 2006). The 2MASS covers 99.99 % of the sky in the near-infrared J (1.25 µm), H (1.65 µm) and Ks (2.16 µm) bands (henceforth Ks shall be refered to as K). Hence the 2MASS database has the advantages of being homogeneous, all sky (enabling the study of the outer regions of clusters where the low mass stars dominate) and covering near infrared wavelengths where young clusters can be well observed in their dusty environments. Dutra and Bica (2001) discovered 42 objects at in...
A Very Large Telescope/Naco Study of Star Formation in the Massive Embedded Cluster RCW 38
The Astronomical Journal, 2009
We present the results of high angular resolution adaptive optics (AO) near-infrared (JHK s ) observations of the deeply embedded massive cluster RCW 38 using NACO on the Very Large Telescope. Narrowband AO observations centered at wavelengths of 1.28 μm, 2.12 μm, and 2.17 μm were also obtained. The area covered by these observations is about 0.5 pc 2 , centered on the O-star RCW 38 IRS 2. We use the JHK s colors to identify young stars with infrared (IR) excess in this region. Through a detailed comparison to a nearby control field, we find that most of the 337 stars detected in all three IR bands are cluster members (∼317), with essentially no contamination due to background (likely due to the high cluster extinction of A V ∼ 15) or foreground sources. Five sources with three band detections have colors suggestive of deeply embedded protostars, while 53 sources are detected at K s only; their spatial distribution with respect to the extinction suggests they are highly reddened cluster members but their evolutionary status is unclear. Detectable K s -band excess is found toward 29% ± 3% of the stars. For comparison to a similar area of Orion Nebula Cluster observed in the near-IR, mass and extinction cuts are applied, and the excess fractions redetermined. The resulting excesses are then 25% ± 5% for RCW 38, and 42% ± 8% for Orion. RCW 38 IRS 2 is shown to be a massive star binary with a projected separation of ∼500 AU. Two regions of molecular hydrogen emission are revealed through the 2.12 μm imaging. One of these shows a morphology suggestive of a protostellar jet, and is clearly associated with a star only detected at H and K s , and previously identified as a highly obscured X-ray source. Three spatially extended cometary-like objects, suggestive of photoevaporating disks, are identified, but only one is clearly directly influenced by RCW 38 IRS 2. The structure of the inner core of RCW 38 is also characterized and compared to Orion and other clusters. A King profile provides a reasonable fit to the cluster radial density profile and a nearest-neighbor distance analysis shows essentially no subclustering.
Monthly Notices of the Royal Astronomical Society, 2014
The galaxy cluster CLG0218.3-0510 at z=1.62 is one of the most distant galaxy clusters known, with a rich muti-wavelength data set that confirms a mature galaxy population already in place. Using very deep, wide area (20×20 Mpc) imaging by Spitzer MIPS at 24µm, in conjunction with Herschel 5-band imaging from 100-500µm, we investigate the dust-obscured, star-formation properties in the cluster and its associated large scale environment. Our galaxy sample of 693 galaxies at z ∼1.62 detected at 24µm (10 spectroscopic and 683 photo-z) includes both cluster galaxies (i.e. within r <1 Mpc projected clustercentric radius) and field galaxies, defined as the region beyond a radius of 3 Mpc. The star-formation rates (SFRs) derived from the measured infrared luminosity range from 18 to 2500 M /yr, with a median of 55 M /yr, over the entire radial range (10 Mpc). The cluster brightest FIR galaxy, taken as the centre of the galaxy system, is vigorously forming stars at a rate of 256±70 M /yr, and the total cluster SFR enclosed in a circle of 1 Mpc is 1161±96 M /yr. We estimate a dust extinction of ∼ 3 magnitudes by comparing the SFRs derived from [OII] luminosity with the ones computed from the 24µm fluxes. We find that the in-falling region (1-3 Mpc) is special: there is a significant decrement (3.5×) of passive relative to star-forming galaxies in this region, and the total SFR of the galaxies located in this region is lower (∼130 M /yr/Mpc 2 ) than anywhere in the cluster or field, regardless of their stellar mass. In a complementary approach we compute the local galaxy density, Σ 5 , and find no trend between SFR and Σ 5 . However, we measure an excess of starforming galaxies in the cluster relative to the field by a factor 1.7, that lends support to a reversal of SF-density relation in CLG0218.
A Spitzer/IRAC survey of massive star-forming regions
2005
We are conducting a survey of several regions of high-mass star formation to assess their content and structure. The observations include Spitzer observations, ground-based optical and near-IR imaging surveys, and optical and IR spectra of objects and locations in the molecular clouds. The goal of the survey is to gain a better understanding of the processes involved in high mass star formation by determining the characteristics of the stars detected in these regions and investigating the properties of the interstellar medium (ISM) environment in which these stars form. In this contribution, we present results on the identification and spatial analysis of young stars in three clusters, W5/AFGL 4029, S255, and S235. First we show how the IRAC data are used to roughly segregate young stars according to their mid-infrared colors, into two groups corresponding the SED Class I and Class II young stellar objects. Then using the IRAC data in combination with 2MASS, we show how more young stars can be identified. Finally, we examine the spatial distributions of young stars in these clusters and find a range of morphologies and of peak surface densities.
Spitzer, Near‐Infrared, and Submillimeter Imaging of the Relatively Sparse Young Cluster, Lynds 988e
The Astrophysical Journal, 2008
We present Spitzer images of the relatively sparse, low luminosity young cluster L988e, as well as complementary near-infrared (NIR) and submillimeter images of the region. The cluster is asymmetric, with the western region of the cluster embedded within the molecular cloud, and the slightly less dense eastern region to the east of, and on the edge of, the molecular cloud. With these data, as well as with extant Hα data of stars primarily found in the eastern region of the cluster, and a molecular 13 CO gas emission map of the entire region, we investigate the distribution of forming young stars with respect to the cloud material, concentrating particularly on the differences and similarities between the exposed and embedded regions of the cluster. We also compare star formation in this region to that in denser, more luminous and more massive clusters already investigated in our comprehensive multi-wavelength study of young clusters within 1 kpc of the Sun.