arXiv subjects

N. K. Bhadari

Publications and source records attributed to N. K. Bhadari.

27 records · Page 2Linked to original sources

arXiv2022

Star-forming site RAFGL 5085: Is a perfect candidate of hub-filament system ?

To investigate the star formation process, we present a multi-wavelength study of a massive star-forming site RAFGL 5085, which has been associated with the molecular outflow, HII region, and near-infrared cluster. The continuum images at 12, 250, 350, and 500 $μ$m show a central region (having M$_{\rm clump}$ $\sim$225 M$_{\odot}$) surrounded by five parsec-scale filaments, revealing a hub-filament system (HFS). In the {\it Herschel} column density ($N({\rm{H}}_{2})$) map, filaments are identified with higher aspect ratios (length/diameter) and lower $N({\rm{H}}_{2})$ values ($\sim$0.1--2.4 $\times$10$^{21}$ cm$^{-2}$), while the central hub is found with a lower aspect ratio and higher $N({\rm{H}}_{2})$ values ($\sim$3.5--7.0 $\times$10$^{21}$ cm$^{-2}$). The central hub displays a temperature range of [19, 22.5]~K in the {\it Herschel} temperature map, and is observed with signatures of star formation (including radio continuum emission). The JCMT $^{13}$CO(J= 3--2) line data confirm the presence of the HFS and its hub is traced with supersonic and non-thermal motions having higher Mach number and lower thermal to non-thermal pressure ratio. In the $^{13}$CO position-velocity diagrams, velocity gradients along the filaments toward the HFS appear to be observed, suggesting the gas flow in the RAFGL 5085 HFS and the applicability of the clump-fed scenario.

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arXiv2022

Ionized filaments and ongoing physical processes in massive star-forming sites around l = 345.5 degree

Numerous research studies on dust and molecular filaments have been conducted in star-forming sites, but only a limited number of studies have focused on ionized filaments. To observationally study this aspect, we present an analysis of multi-wavelength data of an area of $\sim$74.6 arcmin $\times$ 55 arcmin around l = 345.5 degree. Using the 843 MHz continuum map, two distinct ionized filaments (i.e., IF-A (extent $\sim$8.5 arcmin) and IF-B (extent $\sim$22.65 arcmin)) hosting ionized clumps powered by massive OB stars are identified. Using the $^{13}$CO(2-1) and C$^{18}$O(2-1) line data, the parent molecular clouds of IF-A and IF-B are studied in a velocity range of [$-$21, $-$10] km s$^{-1}$, and have filamentary appearances. At least two cloud components around $-$18 and $-$15 km s$^{-1}$ toward the parent clouds of IF-A and IF-B are investigated, and are connected in velocity space. These filamentary clouds also spatially overlap with each other along the major axis, backing the filamentary twisting/coupling nature. Noticeable Class I protostars and massive stars appear to be observed toward the common zones of the cloud components. These findings support the collision of two filamentary clouds around 1.2 Myr ago. The existence of the ionized filaments seems to be explained by the combined feedback of massive stars. The molecular filaments associated with IF-A and IF-B favour the outcomes of the most recent model concerning the escape and the trap of the ionizing radiation from an O star formed in a filament.

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arXiv2022

Unraveling the observational signatures of cloud-cloud collision and hub-filament systems in W31

To understand the formation process of massive stars, we present a multi-scale and multi-wavelength study of the W31 complex hosting two extended HII regions (i.e., G10.30-0.15 (hereafter, W31-N) and G10.15-0.34 (hereafter, W31-S)) powered by a cluster of O-type stars. Several Class I protostars and a total of 49 ATLASGAL 870 $μ$m dust clumps (at d = 3.55 kpc) are found toward the HII regions where some of the clumps are associated with the molecular outflow activity. These results confirm the existence of a single physical system hosting the early phases of star formation. The Herschel 250 $μ$m continuum map shows the presence of hub-filament system (HFS) toward both W31-N and W31-S. The central hubs harbour HII regions and they are depicted with extended structures (with T$_{\text{d}}$ $\sim$ 25-32 K) in the Herschel temperature map. In the direction of W31-S, an analysis of the NANTEN2 $^{12}$CO(J = 1-0) and SEDIGISM $^{13}$CO(J = 2-1) line data supports the presence of two cloud components around 8 and 16 km s$^{-1}$, and their connection in velocity space. A spatial complementary distribution between the two cloud components is also investigated toward W31-S, where the signposts of star formation, including massive O-type stars, are concentrated. These findings favor the applicability of cloud-cloud collision (CCC) around $\sim$2 Myr ago in W31-S. Overall, our observational findings support the theoretical scenario of CCC in W31, which explains the formation of massive stars and the existence of HFSs.

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arXiv2022

Simultaneous evidence of edge collapse and hub-filament configurations: A rare case study of a Giant Molecular Filament G45.3+0.1

We study multiwavelength and multiscale data to investigate the kinematics of molecular gas associated with the star-forming complexes G045.49+00.04 (G45E) and G045.14+00.14 (G45W) in the Aquila constellation. An analysis of the FUGIN $^{13}$CO(1-0) line data unveils the presence of a giant molecular filament (GMF G45.3+0.1; length $\sim$75 pc, mass $\sim$1.1$\times$10$^{6}$ M$_{\odot}$) having a coherent velocity structure at [53, 63] km s$^{-1}$. The GMF G45.3+0.1 hosts G45E and G45W complexes at its opposite ends. We find large scale velocity oscillations along GMF G45.3+0.1, which also reveals the linear velocity gradients of $-$0.064 and $+$0.032 km s$^{-1}$ pc$^{-1}$ at its edges. The photometric analysis of point-like sources shows the clustering of young stellar object (YSO) candidate sources at the filament's edges where the presence of dense gas and HII regions are also spatially observed. The Herschel continuum maps along with the CHIMPS $^{13}$CO(3-2) line data unravel the presence of parsec scale hub-filament systems (HFSs) in both the sites, G45E and G45W. Our study suggests that the global collapse of GMF G45.3+0.1 is end-dominated, with addition to the signature of global nonisotropic collapse (GNIC) at the edges. Overall, GMF G45.3+0.1 is the first observational sample of filament where the edge collapse and the hub-filament configurations are simultaneously investigated. These observations open up the new possibility of massive star formation, including the formation of HFSs.

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arXiv2021

Probing gas kinematics and PDR structure around O-type stars in Sh 2-305 HII region

We report an observational study of the Galactic HII region Sh 2-305/S305 using the [CII] 158 $μ$m line data, which are used to examine the gas dynamics and structure of photodissociation regions. The integrated [CII] emission map at [39.4, 49.5] km s$^{-1}$ spatially traces two shell-like structures (i.e., inner and outer neutral shells) having a total mass of $\sim$565 M$_\odot$. The inner neutral shell encompasses an O9.5V star at its centre and has a compact ring-like appearance. However, the outer shell is seen with more extended and diffuse [CII] emission, hosting an O8.5V star at its centre and surrounds the inner neutral shell. The velocity channel maps and position-velocity diagrams confirm the presence of a compact [CII] shell embedded in the diffuse outer shell, and both the shells seem to expand with $v_{\rm exp}\sim$1.3 km s$^{-1}$. The outer shell appears to be older than the inner shell, hinting that these shells are formed sequentially. The [CII] profiles are examined toward S305, which are either double-peaked or blue-skewed and have the brighter redshifted component. The redshifted and blueshifted components spatially trace the inner and outer neutral shell geometry, respectively. The ionized, neutral, and molecular zones in S305 are seen adjacent to one another around the O-type stars. The regularly spaced dense molecular and dust clumps (mass $\sim$10-10$^{3}$ M$_{\odot}$) are investigated around the neutral shells, which might have originated due to gravitational instability in the shell of collected materials.

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arXiv2021

Lynds Bright Nebulae: Sites of possible twisted filaments and ongoing star formation

The paper presents an analysis of multi-wavelength data of two Lynds Bright Nebulae (LBN), LBN 140.07+01.64 and LBN 140.77$-$1.42. The 1420 MHz continuum map reveals an extended Y-shaped feature (linear extent ~3.7 deg), which consists of a linear part and a V-like structure. The sites LBN 140.07+01.64 and AFGL 437 are located toward the opposite sides of the V-like structure, and LBN 140.77$-$1.42 is spatially seen toward the linear part. Infrared-excess sources are traced toward the entire Y-feature, suggesting star formation activities. Infrared and sub-millimeter images show the presence of at least two large-scale dust filaments extended toward the LBN sources. The Herschel maps, which are available only toward the northern and central parts of the Y-feature, display the presence of higher column density (> 2.4 X 10^{21} cm^{-2}) of materials toward the filaments. Using the 12CO(1-0) line data, the distribution of molecular gas at [-42.7, -34.4] km/s traces the cloud associated with the Y-feature, and confirms the existence of filaments. The large-scale filaments appear to be possibly spatially twisted. There is a hint of an oscillatory-like velocity pattern along both the filaments, favouring their proposed twisted nature. It is the first study showing the possible twisting of filaments, which is more prominent in the northern and central parts of the Y-feature. This possible twisting/coupling of the large-scale filaments appears to be responsible for the observed star formation (including known OB-stars). The proposed physical process and the energetics of OB-stars together seem to explain the origin of the ionized Y-feature.

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arXiv2021

ALMA discovery of a dual dense probably rotating outflow from a massive young stellar object G18.88MME

We report the discovery of a very dense jet-like fast molecular outflow surrounded by a wide-angle wind in a massive young stellar object (MYSO) G18.88MME (stellar mass $\sim$8 M$_{\odot}$) powering an Extended Green Object G18.89$-$0.47. Four cores MM1-4 are identified in the Atacama Large Millimeter/submillimeter Array (ALMA) 1.3 mm continuum map (resolution $\sim$0.$"$8) toward G18.88MME, and are seen at the center of the emission structure (extent $\sim$0.3 pc $\times$ 0.2 pc) detected in the ALMA map. G18.88MME is embedded in the core MM1 (mass $\sim$13-18 M$_{\odot}$), where no radio continuum emission is detected. The molecular outflow centered at MM1 is investigated in the SiO(5-4), HC$_{3}$N(24-23) and $^{13}$CO(2-1) lines. The detection of HC$_{3}$N in the outflow is rare in MYSOs and indicates its very high density. The position-velocity diagrams display a fast narrow outflow (extent $\sim$28000 AU) and a slower wide-angle more extended outflow toward MM1, and both of these components show a transverse velocity gradient indicative of a possible rotation. All these observed features together make G18.88MME as a unique object for studying the unification of the jet-driven and wind-driven scenarios of molecular outflows in MYSOs.

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arXiv2020

New insights in the HII region G18.88-0.49: hub-filament system and accreting filaments

We present an analysis of multi-wavelength observations of an area of 0.27 deg x 0.27 deg around the Galactic HII region G18.88-0.49, which is powered by an O-type star (age ~10^5 years). The Herschel column density map reveals a shell-like feature of extension ~12 pc x 7 pc and mass ~2.9 x 10^4 Msun around the HII region; its existence is further confirmed by the distribution of molecular (12CO, 13CO, C18O, and NH3) gas at [60, 70] km/s. Four subregions are studied toward this shell-like feature, and show a mass range of ~0.8-10.5 x 10^3 Msun. These subregions associated with dense gas are dominated by non-thermal pressure and supersonic non-thermal motions. The shell-like feature is associated with the HII region, Class I protostars, and a massive protostar candidate, illustrating the ongoing early phases of star formation (including massive stars). The massive protostar is found toward the position of the 6.7 GHz methanol maser, and is associated with outflow activity. Five parsec-scale filaments are identified in the column density and molecular maps, and appear to be radially directed to the dense parts of the shell-like feature. This configuration is referred to as a "hub-filament" system. Significant velocity gradients (0.8-1.8 km/s/pc) are observed along each filament, suggesting that the molecular gas flows towards the central hub along the filaments. Overall, our observational findings favor a global non-isotropic collapse scenario as discussed in Motte et al. (2018), which can explain the observed morphology and star formation in and around G18.88-0.49.

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arXiv2020

Star-forming sites IC 446 and IC 447: an outcome of end-dominated collapse of Monoceros R1 filament

We present an analysis of multi-wavelength observations of Monoceros R1 (Mon R1) complex (at d ~760 pc). An elongated filament (length ~14 pc, mass ~1465 Msun) is investigated in the complex, which is the most prominent structure in the Herschel column density map. An analysis of the FUGIN 12CO(1-0) and 13CO(1-0) line data confirms the existence of the filament traced in a velocity range of [-5, +1] km/s. The filament is found to host two previously known sites IC 446 and IC 447 at its opposite ends. A massive young stellar object (YSO) is embedded in IC 446, while IC 447 contains several massive B-type stars. The Herschel temperature map reveals the extended warm dust emission (at T_d ~ 15-21 K) toward both the ends of the filament. The Spitzer ratio map of 4.5 micron/3.6 micron emission suggests the presence of photo-dissociation regions and signature of outflow activity toward IC 446 and IC 447. Based on the photometric analysis of point-like sources, clusters of YSOs are traced mainly toward the filament ends. The filament is found to be thermally supercritical showing its tendency of fragmentation, which is further confirmed by the detection of a periodic oscillatory pattern (having a period of ~3-4 pc) in the velocity profile of 13CO. Our outcomes suggest that the fragments distributed toward the filament ends have rapidly collapsed, and had formed the known star-forming sites. Overall, the elongated filament in Mon R1 is a promising sample of the "end-dominated collapse" scenario, as discussed by Pon et al. (2011, 2012).

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