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Title: CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH

Abstract

The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (J{sub N} = 4{sub 3}-3{sub 2}), HC{sub 3}N (J = 5-4), N{sub 2}H{sup +} (J = 1-0), and SiO (J = 2-1, v = 0) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely strong CCS emission is detected. The CCS-to-N{sub 2}H{sup +} abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different V {sub LSR}. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few × 10{sup 5} yr because CCS is abundant only for a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is 0.4 × 10{sup 5} yr, is extremely high, about 70% inmore » the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.« less

Authors:
; ;  [1];  [2]; ; ; ; ; ; ;  [3]; ;  [4]; ;  [5];  [6];  [7];  [8];  [9];  [10] more »; « less
  1. National Astronomical Observatory, Mitaka, Tokyo 181-8588 (Japan)
  2. Graduate School of Natural Sciences, Nagoya City University, Mizuho-ku, Nagoya 467-8501 (Japan)
  3. Department of Physical Science, Osaka Prefecture University, Gakuen 1-1, Sakai, Osaka 599-8531 (Japan)
  4. Nobeyama Radio Observatory, Minamimaki, Minamisaku, Nagano 384-1305 (Japan)
  5. Department of Astronomy and Earth Sciences, Tokyo Gakugei University, Koganei, Tokyo 184-8501 (Japan)
  6. Laboratoire AIM, CEA/DSM-CNRS-Université Paris Diderot, IRFU/Service d'Astrophysique, CEA Saclay, F-91191 Gif-sur-Yvette (France)
  7. Center for Astronomy, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 310-8512 (Japan)
  8. Joint ALMA Observatory, Alonso de Crdova 3107 Vitacura, Santiago (Chile)
  9. Institute of Astrophysics and Planetary Sciences, Ibaraki University, Bunkyo 2-1-1, Mito 310-8512 (Japan)
  10. Solar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi 464-8601 (Japan)
Publication Date:
OSTI Identifier:
22365316
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal Letters; Journal Volume: 791; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; CLOUDS; COLLISIONS; EMISSION; LIFETIME; NITRILES; PROTOSTARS; SILICON OXIDES; STAR CLUSTERS; STAR EVOLUTION; STARS

Citation Formats

Nakamura, Fumitaka, Kawabe, Ryohei, Shinnaga, Hiroko, Sugitani, Koji, Tanaka, Tomohiro, Kimura, Kimihiko, Tokuda, Kazuki, Kozu, Minato, Okada, Nozomi, Hasegawa, Yutaka, Ogawa, Hideo, Nishitani, Hiroyuki, Mizuno, Izumi, Dobashi, Kazuhito, Shimoikura, Tomomi, Shimajiri, Yoshito, Yonekura, Yoshinori, Kameno, Seiji, Momose, Munetake, Nakajima, Taku, E-mail: fumitaka.nakamura@nao.ac.jp, and and others. CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH. United States: N. p., 2014. Web. doi:10.1088/2041-8205/791/2/L23.
Nakamura, Fumitaka, Kawabe, Ryohei, Shinnaga, Hiroko, Sugitani, Koji, Tanaka, Tomohiro, Kimura, Kimihiko, Tokuda, Kazuki, Kozu, Minato, Okada, Nozomi, Hasegawa, Yutaka, Ogawa, Hideo, Nishitani, Hiroyuki, Mizuno, Izumi, Dobashi, Kazuhito, Shimoikura, Tomomi, Shimajiri, Yoshito, Yonekura, Yoshinori, Kameno, Seiji, Momose, Munetake, Nakajima, Taku, E-mail: fumitaka.nakamura@nao.ac.jp, & and others. CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH. United States. doi:10.1088/2041-8205/791/2/L23.
Nakamura, Fumitaka, Kawabe, Ryohei, Shinnaga, Hiroko, Sugitani, Koji, Tanaka, Tomohiro, Kimura, Kimihiko, Tokuda, Kazuki, Kozu, Minato, Okada, Nozomi, Hasegawa, Yutaka, Ogawa, Hideo, Nishitani, Hiroyuki, Mizuno, Izumi, Dobashi, Kazuhito, Shimoikura, Tomomi, Shimajiri, Yoshito, Yonekura, Yoshinori, Kameno, Seiji, Momose, Munetake, Nakajima, Taku, E-mail: fumitaka.nakamura@nao.ac.jp, and and others. Wed . "CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH". United States. doi:10.1088/2041-8205/791/2/L23.
@article{osti_22365316,
title = {CLUSTER FORMATION TRIGGERED BY FILAMENT COLLISIONS IN SERPENS SOUTH},
author = {Nakamura, Fumitaka and Kawabe, Ryohei and Shinnaga, Hiroko and Sugitani, Koji and Tanaka, Tomohiro and Kimura, Kimihiko and Tokuda, Kazuki and Kozu, Minato and Okada, Nozomi and Hasegawa, Yutaka and Ogawa, Hideo and Nishitani, Hiroyuki and Mizuno, Izumi and Dobashi, Kazuhito and Shimoikura, Tomomi and Shimajiri, Yoshito and Yonekura, Yoshinori and Kameno, Seiji and Momose, Munetake and Nakajima, Taku, E-mail: fumitaka.nakamura@nao.ac.jp and and others},
abstractNote = {The Serpens South infrared dark cloud consists of several filamentary ridges, some of which fragment into dense clumps. On the basis of CCS (J{sub N} = 4{sub 3}-3{sub 2}), HC{sub 3}N (J = 5-4), N{sub 2}H{sup +} (J = 1-0), and SiO (J = 2-1, v = 0) observations, we investigated the kinematics and chemical evolution of these filamentary ridges. We find that CCS is extremely abundant along the main filament in the protocluster clump. We emphasize that Serpens South is the first cluster-forming region where extremely strong CCS emission is detected. The CCS-to-N{sub 2}H{sup +} abundance ratio is estimated to be about 0.5 toward the protocluster clump, whereas it is about 3 in the other parts of the main filament. We identify six dense ridges with different V {sub LSR}. These ridges appear to converge toward the protocluster clump, suggesting that the collisions of these ridges may have triggered cluster formation. The collisions presumably happened within a few × 10{sup 5} yr because CCS is abundant only for a short time. The short lifetime agrees with the fact that the number fraction of Class I objects, whose typical lifetime is 0.4 × 10{sup 5} yr, is extremely high, about 70% in the protocluster clump. In the northern part, two ridges appear to have partially collided, forming a V-shape clump. In addition, we detected strong bipolar SiO emission that is due to the molecular outflow blowing out of the protostellar clump, as well as extended weak SiO emission that may originate from the filament collisions.},
doi = {10.1088/2041-8205/791/2/L23},
journal = {Astrophysical Journal Letters},
number = 2,
volume = 791,
place = {United States},
year = {Wed Aug 20 00:00:00 EDT 2014},
month = {Wed Aug 20 00:00:00 EDT 2014}
}
  • We present the N{sub 2}H{sup +} (J = 1 → 0) map of the Serpens South molecular cloud obtained as part of the CARMA Large Area Star Formation Survey. The observations cover 250 arcmin{sup 2} and fully sample structures from 3000 AU to 3 pc with a velocity resolution of 0.16 km s{sup –1}, and they can be used to constrain the origin and evolution of molecular cloud filaments. The spatial distribution of the N{sub 2}H{sup +} emission is characterized by long filaments that resemble those observed in the dust continuum emission by Herschel. However, the gas filaments are typically narrower such that,more » in some cases, two or three quasi-parallel N{sub 2}H{sup +} filaments comprise a single observed dust continuum filament. The difference between the dust and gas filament widths casts doubt on Herschel ability to resolve the Serpens South filaments. Some molecular filaments show velocity gradients along their major axis, and two are characterized by a steep velocity gradient in the direction perpendicular to the filament axis. The observed velocity gradient along one of these filaments was previously postulated as evidence for mass infall toward the central cluster, but these kind of gradients can be interpreted as projection of large-scale turbulence.« less
  • We have made CO(J = 2-1) observations toward the H II region RCW 49 and its ionizing source, the rich stellar cluster Westerlund 2, with the NANTEN2 submillimeter telescope. These observations have revealed that two molecular clouds in velocity ranges of -11 to +9 km s{sup -1} and 11 to 21 km s{sup -1}, respectively, show remarkably good spatial correlations with the Spitzer IRAC mid-infrared image of RCW 49, as well a velocity structures indicative of localized expansion around the bright central regions and stellar cluster. This strongly suggests that the two clouds are physically associated with RCW 49. Wemore » obtain a new kinematic distance estimate to RCW 49 and Wd2 of 5.4{sup +1.1} {sub -1.4} kpc, based on the mean velocity and velocity spread of the associated gas. We argue that the acceleration of the gas by stellar winds from Westerlund 2 is insufficient to explain the entire observed velocity dispersion of the molecular gas, and suggest a scenario in which a collision between the two clouds {approx}4 Myr ago may have triggered the formation of the stellar cluster.« less
  • We present distributions of two molecular clouds having velocities of 2 and 14 km s{sup −1} toward RCW 38, the youngest super star cluster in the Milky Way, in the {sup 12}CO J = 1–0 and 3–2 and {sup 13}CO J = 1–0 transitions. The two clouds are likely physically associated with the cluster as verified by the high intensity ratio of the J = 3–2 emission to the J = 1–0 emission, the bridging feature connecting the two clouds in velocity, and their morphological correspondence with the infrared dust emission. The velocity difference is too large for the cloudsmore » to be gravitationally bound. We frame a hypothesis that the two clouds are colliding with each other by chance to trigger formation of the ∼20 O stars that are localized within ∼0.5 pc of the cluster center in the 2 km s{sup −1} cloud. We suggest that the collision is currently continuing toward part of the 2 km s{sup −1} cloud where the bridging feature is localized. This is the third super star cluster alongside Westerlund 2 and NGC 3603 where cloud–cloud collision has triggered the cluster formation. RCW 38 is the youngest super star cluster in the Milky Way, holding a possible sign of on-going O star formation, and is a promising site where we may be able to witness the moment of O star formation.« less
  • The Serpens South embedded cluster, which is located in the constricted part of a long, filamentary, infrared dark cloud, is believed to be in a very early stage of cluster formation. We present results of near-infrared (JHKs) polarization observations of the filamentary cloud. Our polarization measurements of near-infrared point sources indicate a well-ordered global magnetic field that is perpendicular to the main filament, implying that the magnetic field is likely to have controlled the formation of the main filament. On the other hand, the sub-filaments, which converge on the central part of the cluster, tend to run along the magneticmore » field. The global magnetic field appears to be curved in the southern part of the main filament. Such morphology is consistent with the idea that the global magnetic field is distorted by gravitational contraction along the main filament toward the northern part, which contains larger mass. Applying the Chandrasekhar-Fermi method, the magnetic field strength is roughly estimated to be a few x100 {mu}G, suggesting that the filamentary cloud is close to magnetically critical.« less
  • We present the results of CO (J = 3-2) and HCO{sup +} (J = 4-3) mapping observations toward a nearby embedded cluster, Serpens South, using the ASTE 10 m telescope. Our CO (J = 3-2) map reveals that many outflows are crowded in the dense cluster-forming clump that can be recognized as an HCO{sup +} clump with a size of {approx}0.2 pc and mass of {approx}80 M{sub sun}. The clump contains several subfragments with sizes of {approx}0.05 pc. By comparing the CO (J = 3-2) map with the 1.1 mm dust continuum image taken by AzTEC on ASTE, we findmore » that the spatial extents of the outflow lobes are sometimes anti-correlated with the distribution of the dense gas, and some of the outflow lobes apparently collide with the dense gas. The total outflow mass, momentum, and energy are estimated to be 0.6 M{sub sun}, 8 M{sub sun} km s{sup -1}, and 64 M{sub sun} km{sup 2} s{sup -2}, respectively. The energy injection rate due to the outflows is comparable to the turbulence dissipation rate in the clump, implying that the protostellar outflows can maintain the supersonic turbulence in this region. The total outflow energy seems only about 10% of the clump gravitational energy. We conclude that the current outflow activity is not enough to destroy the whole cluster-forming clump, and therefore star formation is likely to continue for several or many local dynamical times.« less