The formation and evolution of massive stellar clusters in IC4662 (original) (raw)
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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 We used new deep JHK s photometry, along with unpublished deep Spitzer/IRAC mid-infrared photometry, complemented with optical HST/WFPC2 high spatial resolution photometry and X-ray Chandra observations, to constrain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.
IFS and IR Observations of Star Clusters in the Antennae
Symposium - International Astronomical Union
Over the past decade, it has become clear that interaction induced formation of compact young star clusters is a ubiquitous pheonomenon, and the understanding of this process is thought to also shed light on galaxy evolution in general, because these young clusters are widely believed to be the progenitors of a part of the globular cluster systems seen in local elliptical galaxies. We have observed the prototypical merger NGC 4038/4039 using near-infrared broad- and narrow band imaging, integral field spectroscopy and medium and high resolution spectroscopy. We find that all of the bright star clusters are young (<20 Myrs), but the “overlap region” hosts the youngest clusters (∼5 Myrs), while the nuclear starbursts started ∼100 Myrs ago. Photometric and dynamical masses range from 105 to a few x106M⊙. However, mass-to-light ratios vary from cluster to cluster and suggest differences in the contribution of low-mass stars. While clusters with a deficiency in low-mass stars are like...
Characterizing precursors to stellar clusters withHerschel
Astronomy & Astrophysics, 2011
Context. Despite their profound effect on the universe, the formation of massive stars and stellar clusters remains elusive. Recent advances in observing facilities and computing power have brought us closer to understanding this formation process. In the past decade, compelling evidence has emerged that suggests infrared dark clouds (IRDCs) may be precursors to stellar clusters. However, the usual method for identifying IRDCs is biased by the requirement that they are seen in absorption against background mid-IR emission, whereas dust continuum observations allow cold, dense pre-stellar-clusters to be identified anywhere. Aims. We aim to understand what dust temperatures and column densities characterize and distinguish IRDCs, to explore the population of dust continuum sources that are not IRDCs, and to roughly characterize the level of star formation activity in these dust continuum sources. Methods. We use Hi-GAL 70 to 500 μm data to identify dust continuum sources in the = 30 • and = 59 • Hi-GAL science demonstration phase (SDP) fields, to characterize and subtract the Galactic cirrus emission, and perform pixel-by-pixel modified blackbody fits on cirrus-subtracted Hi-GAL sources. We utilize archival Spitzer data to indicate the level of star-forming activity in each pixel, from mid-IR-dark to mid-IR-bright. Results. We present temperature and column density maps in the Hi-GAL = 30 • and = 59 • SDP fields, as well as a robust algorithm for cirrus subtraction and source identification using Hi-GAL data. We report on the fraction of Hi-GAL source pixels which are mid-IR-dark, mid-IR-neutral, or mid-IR-bright in both fields. We find significant trends in column density and temperature between mid-IR-dark and mid-IR-bright pixels; mid-IR-dark pixels are about 10 K colder and have a factor of 2 higher column density on average than mid-IR-bright pixels. We find that Hi-GAL dust continuum sources span a range of evolutionary states from preto star-forming, and that warmer sources are associated with more star formation tracers. Additionally, there is a trend of increasing temperature with tracer type from mid-IR-dark at the coldest, to outflow/maser sources in the middle, and finally to 8 and 24 μm bright sources at the warmest. Finally, we identify five candidate IRDC-like sources on the far-side of the Galaxy. These are cold (∼20 K), high column density (N(H 2) > 10 22 cm −2) clouds identified with Hi-GAL which, despite bright surrounding mid-IR emission, show little to no absorption at 8 μm. These are the first inner Galaxy far-side candidate IRDCs of which the authors are aware.
Iras 20050+2720: Anatomy of a Young Stellar Cluster
The Astronomical Journal, 2012
IRAS 20050+2720 is young star-forming region at a distance of 700 pc without apparent high-mass stars. We present results of our multi-wavelength study of IRAS 20050+2720 which includes observations by Chandra and Spitzer, and Two Micron All Sky Survey and UBVRI photometry. In total, about 300 young stellar objects (YSOs) in different evolutionary stages are found. We characterize the distribution of YSOs in this region using a minimum spanning tree analysis. We newly identify a second cluster core, which consists mostly of class II objects, about 10 from the center of the cloud. YSOs of earlier evolutionary stages are more clustered than more evolved objects. The X-ray luminosity function (XLF) of IRAS 20050+2720 is roughly lognormal, but steeper than the XLF of the more massive Orion Nebula complex. IRAS 20050+2720 shows a lower N H /A K ratio compared with the diffuse interstellar medium.
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...
The Interstellar Medium of Young Stellar Clusters from the Mid-Infrared Point of View
Arxiv preprint astro-ph/0003279, 2000
Effects of young stellar clusters on their gas and dust environment are probed using mid-infrared (MIR) wavelengths. The strong MIR [NeIII]/[NeII] ratios (∼ 5 to 10) reveal the presence of current massive stars less than 5 Myr. Using MIR line ratios along with optical and NIR data from the literature, composite SEDs are constructed for NGC 1569, NGC 1140 and II Zw40. The stellar SEDs are then used as input to a dust model to study the impact of the hard, penetrating radiation field on the dust components, particularly in low metallicity environments, where the destructive effects of the massive stellar clusters on the environments occur on global scales. For example, the smallest dust particles are destroyed over larger regions in the dwarf galaxies than in normal metallicity starbursts.
A multiwavelength study of embedded clusters in W5-east, NGC 7538, S235, S252 and S254-S258
Monthly Notices of the Royal Astronomical Society, 2014
We present Spitzer, near-IR (NIR) and millimetre observations of the massive star-forming regions W5-east, S235, S252, S254-S258 and NGC 7538. Spitzer data is combined with NIR observations to identify and classify the young population while 12 CO and 13 CO observations are used to examine the parental molecular cloud. We detect in total 3021 young stellar objects (YSOs). Of those, 539 are classified as Class I, and 1186 as Class II sources. YSOs are distributed in groups surrounded by a more scattered population. Class I sources are more hierarchically organized than Class II and associated with the most dense molecular material. We identify in total 41 embedded clusters containing between 52 and 73 per cent of the YSOs. Clusters are in general non-virialized, turbulent and have star formation efficiencies between 5 and 50 per cent. We compare the physical properties of embedded clusters harbouring massive stars (MEC) and low-mass embedded clusters (LEC) and find that both groups follow similar correlations where the MEC are an extrapolation of the LEC. The mean separation between MEC members is smaller compared to the cluster Jeans length than for LEC members. These results are in agreement with a scenario where stars are formed in hierarchically distributed dusty filaments where fragmentation is mainly driven by turbulence for the more massive clusters. We find several young OB-type stars having IR-excess emission which may be due to the presence of an accretion disc.
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.
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.
Discovery of a Young Massive Stellar Cluster Associated with IRAS Source 16177-5018
The Astronomical Journal, 2003
We report the discovery of a young massive stellar cluster embedded in an extended HII region, invisible at optical wavelengths where the extinction is A V ≈ 28 magnitudes, associated with the IRAS source 16177-5018. J, H and nbK imaging photometry combined with the K S 2MASS data show the presence of sources with infrared excess emission at 2.2 µm, concentrated in an area of about one square parsec around a massive young stellar object identified as the IRAS source. This object has a near-mid infrared spectral index betweem 2.2 and 25 µm α(IR) = d log(λF λ)/d logλ =4.78, characteristic of compact H II regions, with bolometric luminosity, inferred from the integrated near to far-infrared flux density of 2.8 × 10 5 L ⊙ , which corresponds to a ZAMS star of about 42M ⊙. From the color-magnitude diagram we were able to classify the majority of the cluster members as reddened massive stars earlier than spectral type B5.