Abstract We present a detailed structural and gas kinematic study of the star-forming complex W5-NW. A cloud–cloud collision scenario unravels with evidence of collision-induced star and cluster ...formation. Various signatures of cloud–cloud collision such as “complementary distribution” and “bridging features” are explored. At the colliding region, the two clouds have complementary morphologies, where W5-NWb has a filamentary key-like shape that fits into the U-shaped cavity in W5-NWa that behaves like a keyhole. The interaction region between the two clouds is characterized by bridging features with intermediate velocities connecting the two clouds. A skewed V-shaped bridging feature is also detected at the site of the collision. A robust picture of the molecular gas distribution highlighting the bridges is seen in the position–position–velocity diagram obtained using the SCOUSEPY algorithm. Star cluster formation with an overdensity of Class I and Class II young stellar objects is also seen towards this cloud complex, likely triggered by the cloud collision event.
Abstract
We present the results on the physical properties of filaments and dense cores in IC 5146, as a part of the TRAO FUNS project. We carried out on-the-fly mapping observations using the Taeduk ...Radio Astronomy Observatory (TRAO) 14 m telescope covering about 1 square degree of the area of IC 5146 using various molecular lines. We identified 14 filaments (24 in total, including sub-filaments) from the C
18
O (1–0) data cube and 22 dense cores from the N
2
H
+
(1–0) data. We examined the filaments’ gravitational criticality, turbulence properties, accretion rate from filaments to dense cores, and relative evolutionary stages of cores. Most filaments in IC 5146 are gravitationally supercritical within the uncertainty, and most dense cores are formed in them. We found that dense cores in the hubs show a systemic velocity shift of ∼0.3 km s
−1
between the N
2
H
+
and C
18
O gas. Besides, these cores are subsonic or transonic, while the surrounding filament gas is transonic or supersonic, indicating that the cores in the hubs are likely formed by the dissipation of turbulence in the colliding turbulent filaments and the merging is still ongoing. We estimated a mass accretion rate of 15–35
M
⊙
Myr
−1
from the filaments to the dense cores, and the required timescales to collect the current core mass are consistent with the lifetime of the dense cores. The structures of filaments and dense cores in the hub can form from a collision of turbulent converging flows, and mass flow along the filaments to the dense cores may play an important role in forming dense cores.
The CS molecule is known to be adsorbed onto dust in cold and dense conditions, causing it to be significantly depleted in the central region of cores. This study is aimed to investigate the ...depletion of the CS molecule using the optically thin molecular line observations. We mapped five prestellar cores, L1544, L1552, L1689B, L694-2, and L1197, using two molecular lines, (J = 2 − 1) and (J = 1 − 0) with the NRO 45 m telescope, doubling the number of cores where the CS depletion was probed using . In most of our targets, the distribution of emission shows features that suggest that the CS molecule is generally depleted in the center of the prestellar cores. The radial profile of the CS abundance with respect to directly measured from the CS emission and the Herschel dust emission indicates that the CS molecule is depleted by a factor of ∼3 toward the central regions of the cores with respect to their outer regions. The degree of the depletion is found to be even more enhanced, by an order of magnitude, when the contaminating effect introduced by the presence of CS molecules in the surrounding envelope that lie along the line of sight is removed. Except for L1197-which is classified as relatively the least evolved core in our targets, based on its observed physical parameters-we found that the remaining four prestellar cores are suffering from significant CS depletion at their central region, regardless of the relative difference in their evolutionary status.
"TRAO FUNS" is a project to survey the Gould Belt's clouds in molecular lines. This paper presents its first results on the central region of the California molecular cloud, L1478. We performed ...on-the-fly mapping observations using the Taeduk Radio Astronomy Observatory 14 m single-dish telescope equipped with a 16 multibeam array covering a ∼1.0 square degree area of this region using C 18 O ( 1 - 0 ) , mainly tracing low-density clouds, and a ∼460 square arcminute area using N 2 H + ( 1 - 0 ) , mainly tracing dense cores. CS ( 2 - 1 ) and SO ( 3 2 - 2 1 ) were also used simultaneously to map a ∼440 square arcminute area of this region. We identified 10 filaments by applying the dendrogram technique to the C 18 O data cube and 8 dense N 2 H + cores using FellWalker. Basic physical properties of filaments such as mass, length, width, velocity field, and velocity dispersion are derived. It is found that L1478 consists of several filaments with slightly different velocities. Particularly, the filaments that are supercritical are found to contain dense cores detected in N 2 H + . A comparison of nonthermal velocity dispersions derived from C 18 O and N 2 H + for the filaments and dense cores indicates that some of the dense cores share kinematics similar to those of the surrounding filaments, while several dense cores have different kinematics from those of their filaments. This suggests that the formation mechanism of dense cores and filaments can be different in individual filaments depending on their morphologies and environments.
We present the results of a systematic search for molecular outflows in 68 Very Low Luminosity Objects (VeLLOs) from single-dish observations in CO isotopologues, finding 16 VeLLOs that show clear ...outflow signatures in the CO maps. Together with an additional three VeLLOs from the literature, we analyzed the outflow properties for these 19 VeLLOs, identifying 15 VeLLOs as proto-brown-dwarf (proto-BD) candidates and 4 VeLLOs as likely faint protostar candidates. The proto-BD candidates are found to have a mass accretion rate (∼10−8-10−7 M yr−1) lower than that of the protostar candidates ( 10−6 M yr−1). Their accretion luminosities are similar to or smaller than their internal luminosities, implying that many proto-BD candidates might have had either small accretion activity in a quiescent manner throughout their lifetimes, or be currently exhibiting relatively higher (or episodic) mass accretion than in the past. Outflows of many proto-BDs show strong trends of being less active if they are fainter or have less massive envelopes. The outflow forces and internal luminosities for more than half of the proto-BD candidates seem to follow the evolutionary track of a protostar with an initial envelope mass of ∼0.08 M , indicating that some BDs may form in less massive dense cores in a similar way to normal stars. But, because there also exists a significant fraction (about 40%) of proto-BDs with a much weaker outflow force than expected from the relations for protostars, we should not rule out the possibility of other formation mechanism for BDs.
Filaments are omnipresent in molecular clouds which are believed to fragment into cores. The detailed process of the evolution from filaments to cores depends critically on the physical conditions in ...the star forming region. This study aims at characterising gas motions using velocity structure and finding the dynamical importance of magnetic fields in the filament morphology. The plane-of-the-sky component of the magnetic field has been measured using optical polarization of the background stars. The orientation is found to be almost perpendicular to the filament implying its dynamical importance in the evolution of the cloud. Optical polarimetric results match very well with the sub millimetre polarization angles obtained in the inner core regions. The magnetic fields are found to have an orientation of 130° east with respect to north. The angular offset between the outflow axis and the magnetic field direction is found to be 25°. Values for parameters like the excitation temperature, optical depth and column densities have been derived using molecular lines. Optically thick lines show non-gaussian features. The non-thermal widths tell about the presence of turbulent motions whereas the C180 lines follow Gaussian features almost at all the locations observed in the filament.
Bright-rimmed clouds, located at the periphery of relatively evolved HIT regions, are considered to be the sites of star formation possibly triggered by the implosion caused due to the ionizing ...radiation from nearby massive stars. SFO 18 is one such region showing a bright-rim on the side facing the 0-type star, A Ori. A point source, IRAS 05417+0907, is detected towards the high density region of the cloud. A molecular outflow has been found to be associated with the source. The outflow is directed towards a Herbig-Haro object, HH 175. From the Spitzer and WISE observations, we show evidence of a physical connection between the molecular outflow, IRAS 05417+0907 and the HH object. The spectral energy distribution constructed using multi-wavelength data shows that the point source is most likely a highly embedded protostar.
ABSTRACT
Dust polarization observations at optical wavelengths help understand the dust grain properties and trace the plane-of-the-sky component of the magnetic field. In this study, we make use of ...published optical polarization data acquired with AIMPOL along with distances (d) and extinction (AV) data. We study the variation of polarization efficiency (P/AV) as a function of AV in the diffuse interstellar medium (ISM) and intracluster mediums (ICM) using the already published polarization data of six clusters. Among these clusters, NGC 2281, NGC 1664, and NGC 1960 are old; while Stock 8, NGC 1931, and NGC 1893 are young. We categorize stars towards each cluster into foreground, background, and cluster members by employing two clustering algorithms GMM and DBSCAN. Thus, classified field stars and cluster members are used to reveal the polarization properties of ISM and ICM dust, respectively. We find that the dust grains located in the diffuse ISM show higher polarization efficiencies when compared to those located in the ICM of younger clusters.
ABSTRACT
The region surrounding the well-known reflection nebula, NGC 7023, illuminated by a Herbig Be star, HD 200775, located in the dark cloud L1174 is studied in this work. Based on the distances ...and proper motion values from Gaia DR2 of 20 previously known young stellar object (YSO) candidates, we obtained a distance of 335 ± 11 pc to the cloud complex L1172/1174. Using polarization measurements of the stars projected on the cloud complex, we show additional evidence for the cloud to be at ∼335 pc distance. Using this distance and proper motion values of the YSO candidates, we searched for additional comoving sources in the vicinity of HD 200775 and found 20 new sources, which show low infrared excess emission and are of age ∼1 Myr. Among these, 10 YSO candidates and 4 newly identified comoving sources are found to show X-ray emission. Three of the four new sources for which we have obtained optical spectra show H α in emission. About 80 per cent of the total sources are found within ∼1 pc distance from HD 200775. Spatial correlation of some of the YSO candidates with the Herschel dust column density peaks suggests that star formation is still active in the region and may have been triggered by HD 200775.
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