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تسجيل مستخدم جديدA wide-field CO survey towards the California Molecular Filament
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We present the survey of $^{12}$CO/$^{13}$CO/C$^{18}$O (J=1-0) toward the California Molecular Cloud (CMC) within the region of 161.75$^{circ} leqslant l leqslant$ 167.75$^{circ}$,-9.5$^{circ} leqslant b leqslant $-7.5$^{circ}$, using the Purple Mountain Observatory (PMO) 13.7 m millimeter telescope. Adopting a distance of 470 pc, the mass of the observed molecular cloud estimated from $^{12}$CO, $^{13}$CO, and C$^{18}$O is about 2.59$times$10$^{4}$ M$_odot$, 0.85$times$10$^{4}$ M$_odot$, and 0.09$times$10$^{4}$ M$_odot$, respectively. A large-scale continuous filament extending about 72 pc is revealed from the $^{13}$CO images. A systematic velocity gradient perpendicular to the major axis appears and is measured to be $sim$ 0.82 km s$^{-1}$ pc$^{-1}$. The kinematics along the filament shows an oscillation pattern with a fragmentation wavelength of $sim$ 2.3 pc and velocity amplitude of $sim$ 0.92 km s$^{-1}$, which may be related with core-forming flows. Furthermore, assuming an inclination angle to the plane of the sky of 45$^{circ}$, the estimated average accretion rate is $sim$ 101 M$_odot$ Myr$^{-1}$ for the cluster LkH$alpha$ 101 and $sim$ 21 M$_odot$ Myr$^{-1}$ for the other regions. In the C$^{18}$O observations, the large-scale filament could be resolved into multiple substructures and their dynamics are consistent with the scenario of filament formation from converging flows. Approximately 225 C$^{18}$O cores are extracted, of which 181 are starless cores. Roughly 37$%$ (67/181) of the starless cores have $alpha_{text{vir}}$ less than 1. Twenty outflow candidates are identified along the filament. Our results indicate active early-phase star formation along the large-scale filament in the CMC region.
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Aims. The process of gravitational fragmentation in the L1482 molecular filament of the California molecular cloud is studied by combining several complementary observations and physical estimates. We investigate the kinematic and dynamical states of
this molecular filament and physical properties of several dozens of dense molecular clumps embedded therein. Methods. We present and compare molecular line emission observations of the J=2--1 and J=3--2 transitions of 12CO in this molecular complex, using the KOSMA 3-meter telescope. These observations are complemented with archival data observations and analyses of the 13CO J=1--0 emission obtained at the Purple Mountain Observatory 13.7-meter radio telescope at Delingha Station in QingHai Province of west China, as well as infrared emission maps from the Herschel Space Telescope online archive, obtained with the SPIRE and PACS cameras. Comparison of these complementary datasets allow for a comprehensive multi-wavelength analysis of the L1482 molecular filament. Results. We have identified 23 clumps along the molecular filament L1482 in the California molecular cloud. All these molecular clumps show supersonic non-thermal gas motions. While surprisingly similar in mass and size to the much better known Orion molecular cloud, the formation rate of high-mass stars appears to be suppressed in the California molecular cloud relative to that in the Orion molecular cloud based on the mass-radius threshold derived from the static Bonnor Ebert sphere. Our analysis suggests that these molecular filaments are thermally supercritical and molecular clumps may form by gravitational fragmentation along the filament. Instead of being static, these molecular clumps are most likely in processes of dynamic evolution.
We analyze the gas mass distribution, the gas kinematics, and the young stellar object (YSO) content of the California Molecular Cloud (CMC) L1482 filament. We derive a Gaia DR2 YSO distance of 511$^{+17}_{-16}$ pc. We derive scale-free power-laws fo
r the mean gas line-mass (M/L) profiles; we calculate the gravitational potential and field profiles consistent with these. We present IRAM 30 m C$^{18}$O (1-0) (and other tracers) position-velocity (PV) diagrams that exhibit complex velocity twisting and turning structures. We find a rotational profile in C$^{18}$O perpendicular to the southern filament ridgeline. The profile is regular, confined ($rlesssim0.4$ pc), anti-symmetric, and to first order linear with a break at $rsim0.25$ pc. The timescales of the inner (outer) gradients are $sim$0.7 (6.0) Myr. We show that the centripetal force, compared to gravity, increases toward the break; when the ratio of forces approaches unity, the profile turns over, just before filament breakup is achieved. The timescales and relative roles of gravity to rotation indicate that the structure is stable, long lived ($sim$ a few times 6 Myr), and undergoing outside-in evolution. Moreover, this filament has practically no star formation, a perpendicular Planck plane-of-the-sky (POS) magnetic field morphology, and POS zig-zag morphology, which together with the rotation profile lead to the suggestion that the 3D shape is a corkscrew filament with a helical magnetic field. These results, combined with results in Orion and G035.39-00.33, suggest evolution toward higher densities as rotating filaments shed angular momentum. Thus, magnetic fields may be an essential feature of high-mass (M $sim10^5$ M$_{odot}$) cloud filament evolution toward cluster formation.
A deep, wide-field, near-infrared imaging survey was used to construct an extinction map of the southeastern part of the California Molecular Cloud (CMC) with $sim$ 0.5 arc min resolution. The same region was also surveyed in the $^{12}$CO(2-1), $^{1
3}$CO(2-1), C$^{18}$O(2-1) emission lines at the same angular resolution. Strong spatial variations in the abundances of $^{13}$CO and C$^{18}$O were found to be correlated with variations in gas temperature, consistent with temperature dependent CO depletion/desorption on dust grains. The $^{13}$CO to C$^{18}$O abundance ratio was found to increase with decreasing extinction, suggesting selective photodissociation of C$^{18}$O by the ambient UV radiation field. The cloud averaged X-factor is found to be $<$X$_{rm CO}$$>$ $=$ 2.53 $times$ 10$^{20}$ ${rm cm}^{-2}~({rm K~km~s}^{-1})^{-1}$, somewhat higher than the Milky Way average. On sub-parsec scales we find no single empirical value of the X-factor that can characterize the molecular gas in cold (T$_{rm k}$ $lesssim$ 15 K) regions, with X$_{rm CO}$ $propto$ A$_{rm V}$$^{0.74}$ for A$_{rm V}$ $gtrsim$ 3 magnitudes. However in regions containing relatively hot (T$_{rm ex}$ $gtrsim$ 25 K) gas we find a clear correlation between W($^{12}$CO) and A$_{rm V}$ over a large (3 $lesssim$ A$_{rm V}$ $lesssim$ 25 mag) extinction range. This suggests a constant X$_{rm CO}$ $=$ 1.5 $times$ 10$^{20}$ ${rm cm}^{-2}~({rm K~km~s}^{-1})^{-1}$ for the hot gas, a lower value than either the average for the CMC or Milky Way. We find a correlation between X$_{rm CO}$ and T$_{rm ex}$ with X$_{rm CO}$ $propto$ T$_{rm ex}$$^{-0.7}$ suggesting that the global X-factor of a cloud may depend on the relative amounts of hot gas within it.
We present results of a blind 21cm HI-line imaging survey of a galaxy overdensity located behind the Milky Way at $ell,b$ $approx$ 160 deg, 0.5 deg. The overdensity corresponds to a Zone-of-Avoidance crossing of the Perseus-Pisces Supercluster filame
nt. Although it is known that this filament contains an X-ray galaxy cluster (3C129) hosting two strong radio galaxies, little is known about galaxies associated with this potentially rich cluster because of the high Galactic dust extinction. We mapped a sky area of $sim$9.6 sq.deg using the Westerbork Synthesis Radio Telescope in a hexagonal mosaic of 35 pointings observed for 12 hours each, in the radial velocity range $cz = 2400 - 16600$ km/s. The survey has a sensitivity of 0.36 mJy/beam rms at a velocity resolution of 16.5 km/s. We detected 211 galaxies, 62% of which have a near-infrared counterpart in the UKIDSS Galactic Plane Survey. We present a catalogue of the HI properties and an HI atlas containing total intensity maps, position-velocity diagrams, global HI profiles and UKIDSS counterpart images. For the resolved galaxies we also present HI velocity fields and radial HI surface density profiles. A brief analysis of the structures outlined by these galaxies finds that 87 of them lie at the distance of the Perseus-Pisces Supercluster ($cz sim 4000 - 8000$ km/s) and seem to form part of the 3C129 cluster. Further 72 detections trace an overdensity at a velocity of $cz approx$ 10000 km/s and seem to coincide with a structure predicted from mass density reconstructions in the first 2MASS Redshift Survey.
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lar material (disk and envelope), and compare the star formation to that in the Orion A molecular cloud. We identify 59 candidate protostars based on the presence of compact submillimeter emission, complementing these observations with existing Herschel/SPIRE maps. Of our candidate protostars, 24 are associated with young stellar objects (YSOs) in the Spitzer and Herschel/PACS catalogs of 166 and 60 YSOs, respectively (177 unique), confirming their protostellar nature. The remaining 35 candidate protostars are in regions, particularly around LkHalpha 101, where the background cloud emission is too bright to verify or rule out the presence of the compact 70 micron emission that is expected for a protostellar source. We keep these candidate protostars in our sample but note that they may indeed be prestellar in nature. Our observations are sensitive to the high end of the mass distribution in Auriga-Cal. We find that the disparity between the richness of infrared star forming objects in Orion A and the sparsity in Auriga-Cal extends to the submillimeter, suggesting that the relative star formation rates have not varied over the Class II lifetime and that Auriga-Cal will maintain a lower star formation efficiency.
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