Understanding the Links among the Magnetic Fields, Filament, Bipolar Bubble, and Star Formation in RCW 57A Using NIR Polarimetry

Eswaraiah, Chakali; Lai, Shih-Ping; Chen, Wen-Ping; Pandey, A. K.; Tamura, Motohide; Maheswar, G.; Sharma, Saurabh; Wang, Jia-Wei; Nishiyama, Shogo; Kwon, Jungmi; Purcell, Cormac; Magalhães, A. M.

doi:10.3847/1538-4357/aa917e

Cited by 16 publications

(14 citation statements)

References 129 publications

(259 reference statements)

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“…We note that, while many spherical or irregularly shaped classical H II regions or bubbles have been identified in our Galaxy (e.g., Churchwell et al 2006Churchwell et al , 2007Deharveng et al 2010;Simpson et al 2012), the observations of classical bipolar H II regions are still scarce; although our work has laid the foundations for the identification and investigation of a few more classical bipolar H II regions very recently (e.g. Xu et al 2017;Panwar et al 2017;Eswaraiah et al 2017).…”

Section: Introductionmentioning

confidence: 78%

Bipolar H II regions

Samal

Deharveng

Zavagno

et al. 2018

A&A

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Aims. We aim to identify bipolar Galactic H II regions and to understand their parental cloud structures, morphologies, evolution, and impact on the formation of new generations of stars. Methods. We use the Spitzer-GLIMPSE, Spitzer-MIPSGAL, and Herschel-Hi-GAL surveys to identify bipolar H II regions and to examine their morphologies. We search for their exciting star(s) using NIR data from the 2MASS, UKIDSS, and VISTA surveys. Massive molecular clumps are detected near these bipolar nebulae, and we estimate their temperatures, column densities, masses, and densities. We locate Class 0/I young stellar objects (YSOs) in their vicinities using the Spitzer and Herschel-PACS emission. Results. Numerical simulations suggest bipolar H II regions form and evolve in a two-dimensional flat- or sheet-like molecular cloud. We identified 16 bipolar nebulae in a zone of the Galactic plane between ℓ ± 60° and |b| < 1°. This small number, when compared with the 1377 bubble H II regions in the same area, suggests that most H II regions form and evolve in a three-dimensional medium. We present the catalogue of the 16 bipolar nebulae and a detailed investigation for six of these. Our results suggest that these regions formed in dense and flat structures that contain filaments. We find that bipolar H II regions have massive clumps in their surroundings. The most compact and massive clumps are always located at the waist of the bipolar nebula, adjacent to the ionised gas. These massive clumps are dense, with a mean density in the range of 105 cm−3 to several 106 cm−3 in their centres. Luminous Class 0/I sources of several thousand solar luminosities, many of which have associated maser emission, are embedded inside these clumps. We suggest that most, if not all, massive 0/I YSO formation has probably been triggered by the expansion of the central bipolar nebula, but the processes involved are still unknown. Modelling of such nebula is needed to understand the star formation processes at play.

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Section: Introductionmentioning

confidence: 78%

Bipolar H II regions

Samal

Deharveng

Zavagno

et al. 2018

A&A

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“…Given the ubiquity of the filamentary nature of the clouds, our proposition here in the HFS scenario better reflects the observations. Magnetic field observations of bipolar HII regions (Eswaraiah et al 2017) display an hourglass morphology closely following the bipolar bubble. The field strength itself suggests a magnetic pressure dominating the turbulent and thermal pressures.…”

Section: Arzoumanianmentioning

confidence: 95%

Unifying low- and high-mass star formation through density-amplified hubs of filaments

Kumar¹,

Palmeirim²,

Arzoumanian

et al. 2020

A&A

106

166

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Context. Star formation takes place in giant molecular clouds, resulting in mass-segregated young stellar clusters composed of Sun-like stars, brown dwarfs, and massive O-type(50–100 M⊙) stars. Aims. We aim to identify candidate hub-filament systems (HFSs) in the Milky Way and examine their role in the formation of the highest mass stars and star clusters. Methods. The Herschel survey HiGAL has catalogued about 105 clumps. Of these, approximately 35 000 targets are detected at the 3σ level in a minimum of four bands. Using the DisPerSE algorithm we detect filamentary skeletons on 10′ × 10′ cut-outs of the SPIRE 250 μm images (18′′ beam width) of the targets. Any filament with a total length of at least 55′′ (3 × 18′′) and at least 18′′ inside the clump was considered to form a junction at the clump. A hub is defined as a junction of three or more filaments. Column density maps were masked by the filament skeletons and averaged for HFS and non-HFS samples to compute the radial profile along the filaments into the clumps. Results. Approximately 3700 (11%) are candidate HFSs, of which about 2150 (60%) are pre-stellar and 1400 (40%) are proto-stellar. The filaments constituting the HFSs have a mean length of ~10–20 pc, a mass of ~5 × 104 M⊙, and line masses (M∕L) of ~2 × 103 M⊙ pc−1. All clumps with L > 104 L⊙ and L > 105 L⊙ at distances within 2 and 5 kpc respectively are located in the hubs of HFSs. The column densities of hubs are found to be enhanced by a factor of approximately two (pre-stellar sources) up to about ten (proto-stellar sources). Conclusions. All high-mass stars preferentially form in the density-enhanced hubs of HFSs. This amplification can drive the observed longitudinal flows along filaments providing further mass accretion. Radiation pressure and feedback can escape into the inter-filamentary voids. We propose a “filaments to clusters” unified paradigm for star formation, with the following salient features: (a) low-intermediate-mass stars form slowly (106 yr) in the filaments and massive stars form quickly (105 yr) in the hub, (b) the initial mass function is the sum of stars continuously created in the HFS with all massive stars formed in the hub, (c) feedback dissipation and mass segregation arise naturally due to HFS properties, and explain the (d) age spreads within bound clusters and the formation of isolated OB associations.

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“…Since these stars are not physically associated with LDN 1225 (located at ∼800 pc), we exclude them from further analyses. We also omitted 9 stars with NIR-excess ([J − H] ≥ 1.69 × [H − K]; see e.g., Eswaraiah et al 2013Eswaraiah et al , 2017 as their polarizations might be consisting of intrinsic components due to asymmetric distribution of material in their circumstellar disks. Remaining 238 stars are used in the further analyses.…”

Section: Polarimetric Observations Of Ldn 1225mentioning

confidence: 99%

Polarimetric and Photometric Investigation of the Dark Globule LDN 1225: Distance, Extinction Law, and Magnetic Fields

Eswaraiah

Lai²,

et al. 2019

ApJ

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We present the results based on the optical R-band polarization observations of 280 stars distributed towards the dark globule LDN 1225. Gaia data release 2 parallaxes along with the polarization data of ∼200 stars have been used to (a) constrain the distance of LDN 1225 as 830±83 pc, (b) determine the contribution of interstellar polarization (ISP), and (c) characterize the dust properties and delineate the magnetic field (B-field) morphology of LDN 1225. We find that B-fields are more organized and exhibit a small dispersion of 12 • . Using the 12 CO molecular line data from the Purple Mountain Observatory (PMO), along with the column density, dispersion in B-fields, we estimate B-field strength to be ∼56 ± 10 µG, magnetic to turbulence pressure to be ∼3 ± 2, and the mass-to-magnetic flux ratio (in units of critical value) to be < 1. These results indicate the dominant role of B-fields in comparison to turbulence and gravity in rendering the cloud support. B-fields are aligned parallel to the low-density parts (traced by 12 CO map) of the cloud, in contrast they are neither parallel nor perpendicular to the high-density core structures (traced by 13 CO and C 18 O maps). LDN 1225 hosts two 70 µm sources which seem to be of low-mass Class 0 sources. The total-to-selective extinction derived using optical and near-infrared photometric data is found to be anomalous (R V = 3.4), suggesting dust grain growth in LDN 1225. Polarization efficiency of dust grains follows a power-law index of −0.7 inferring that optical polarimetry traces B-fields in the outer parts of the cloud.

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Understanding the Links among the Magnetic Fields, Filament, Bipolar Bubble, and Star Formation in RCW 57A Using NIR Polarimetry

Cited by 16 publications

References 129 publications

Bipolar H II regions

Bipolar H II regions

Unifying low- and high-mass star formation through density-amplified hubs of filaments

Polarimetric and Photometric Investigation of the Dark Globule LDN 1225: Distance, Extinction Law, and Magnetic Fields

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Understanding the Links among the Magnetic Fields, Filament, Bipolar Bubble, and Star Formation in RCW 57A Using NIR Polarimetry

Cited by 16 publications

References 129 publications

Bipolar H II regions

Bipolar H II regions

Unifying low- and high-mass star formation through density-amplified hubs of filaments

Polarimetric and Photometric Investigation of the Dark Globule LDN 1225: Distance, Extinction Law, and Magnetic Fields

Contact Info

Product

Resources

About

Bipolar H II regions

Bipolar H II regions