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1.
CO isotopes are able to probe the different components in protostellar clouds. These components, core, envelope and outflow have distinct physical conditions, and sometimes more than one component contributes to the observed line profile. In this study, we determine how CO isotope abundances are altered by the physical conditions in the different components. We use a 3D molecular line transport code to simulate the emission of four CO isotopomers, 12CO   J = 2 → 1, 13CO J = 2 → 1  , C18O   J = 2 → 1  and C17O   J = 2 → 1  from the Class 0/1 object L483, which contains a cold quiescent core, an infalling envelope and a clear outflow. Our models replicate James Clerk Maxwell Telescope (JCMT) line observations with the inclusion of freeze-out, a density profile and infall. Our model profiles of 12CO and 13CO have a large linewidth due to a high-velocity jet. These profiles replicate the process of more abundant material being susceptible to a jet. C18O and C17O do not display such a large linewidth as they trace denser quiescent material deep in the cloud.  相似文献   

2.
We report the discovery of high-velocity dense gas from a bipolar outflow source near NGC 2068 in the L1630 giant molecular cloud. CO and HCO+ J =3→2 line wings have a bipolar distribution in the vicinity of LBS 17-H with the flow orientated roughly east–west and perpendicular to the elongation of the submillimetre dust continuum emission. The flow is compact (total extent ∼0.2 pc) and contains of the order of 0.1 M⊙ of swept-up gas. The high-velocity HCO+ emission is distributed over a somewhat smaller area <0.1 pc in extent.
A map of C18O J =2→1 emission traces the LBS 17 core and follows the ambient HCO+ emission reasonably well, with the exception of the direction towards LBS 17-H where there is a significant anticorrelation between the C18O and HCO+. A comparison of beam-matched C18O and dust-derived H2 column densities suggests that CO is depleted by up to a factor of ∼50 at this position if the temperature is as low as 9 K, although the difference is substantially reduced if the temperature is as high as 20 K. Chemical models of collapsing clouds can account for this discrepancy in terms of different rates of depletion on to dust grains for CO and HCO+.
LBS 17-H has a previously known water maser coincident with it but there are no known near-infrared, IRAS or radio continuum sources associated with this object, leading to the conclusion that it is probably very young. A greybody fit to the continuum data gives a luminosity of only 1.7 L⊙ and a submillimetre-to-bolometric luminosity ratio of 0.1, comfortably satisfying the criteria for classification as a class 0 protostar candidate.  相似文献   

3.
Near-infrared images in H2 line emission and submillimetre maps in CO J  = 3–2 emission illustrate the remarkable association between a molecular bow shock and the redshifted molecular outflow lobe in W75N. The flow lobe fits perfectly into the wake of the bow, as one would expect if the lobe represented swept-up gas. Indeed, these observations strongly support the 'bow shock' entrainment scenario for molecular outflows driven by young stars.   The characteristics of the bow shock and CO outflow lobe are compared with those of numerical simulations of jet-driven flows. These models successfully reproduce the bulge and limb-brightening in the CO outflow, although the model H2 bow exhibits more structure extending back along the flow axis. We also find that the size of the flow, the high mass fraction in the flow at low outflow velocities (low γ values) and the high CO/H2 luminosity ratio indicate that the system is evolved. We also predict a correlation, in evolved systems, between outflow age and the CO/H2 luminosity ratio.  相似文献   

4.
Maps are presented of 3 P 1→3 P 0[C  i ] and J =2→1 C18O line emission from the interstellar molecular cloud G35.2−0.74N. The maps are interpreted with reference to a previous model for the structure of the cloud in which opposing jets from a central object, embedded in a rotating interstellar disc, precess and drive a bipolar molecular outflow. The C18O emission traces the rotating interstellar disc, but the [C  i ] emission shows several features. An unresolved component is observed which probably results from dissociation of CO in the centre of the disc by UV radiation from the central source. Background [C  i ] emission is also observed which shares the rotation of the disc on larger scales. The C  i /CO ratio in these components is typically a few per cent. High-velocity [C  i ] emission, where C  i /CO is high (>0.1–0.4), is observed between the CO molecular outflow and the cavity exacavated by the jet. This material has probably been accelerated by the jet but dissociated by far-UV radiation propagating through the cavity. The C  i /CO ratio falls as the shocked outflow later sweeps up CO.  相似文献   

5.
The northern section of the molecular cloud complex NGC 6334 has been mapped in the CO and CS spectral line emission and in continuum emission at a wavelength of 1300 μm. Our observations highlight the two dominant sources, I and I(N), and a host of weaker sources. NGC 6334 I is associated with a cometary ultracompact H  ii region and a hot, compact core ≤10 arcsec in size. Mid-infrared and CH3OH observations indicate that it is also associated with at least two protostellar sources, each of which may drive a molecular outflow. For region I we confirm the extreme high-velocity outflow first discovered by Bachiller & Cernicharo and find that it is very energetic with a mechanical luminosity of 390 L⊙. A dynamical age for the outflow is ∼3000 yr. We also find a weaker outflow originating from the vicinity of NGC 6334 I. In CO and CS this outflow is quite prominent to the north-west, but much less so on the eastern side of I, where there is very little molecular gas. Spectral survey data show a molecular environment at position I which is rich in methanol, methyl formate and dimethyl ether, with lines ranging in energy up to 900 K above the ground state. NGC 6334 I(N) is more dense than I, but cooler, and has none of the high-excitation lines observed toward I. I(N) also has an associated outflow, but it is less energetic than the outflow from I. The fully sampled continuum map shows a network of filaments, voids and cores, many of which are likely to be sites of star formation. A striking feature is a narrow, linear ridge which defines the western boundary. It is unclear if there is a connection between this filament and the many potential sites of star formation, or if the filament existed prior to the star formation activity.  相似文献   

6.
We present SCUBA 850-μm, JCMT  CO( J =2→1)  , B -band imaging and VLA H  i observations of the NGC 7465/4/3 group of galaxies. The 850-μm emission associated with NGC 7465 extends to at least ∼2 R 25 and is well correlated with the H  i . We investigate a range of possible mechanisms by which dust beyond R 25 may be heated to give the observed extended submillimetre emission. By modelling the dust heating by stars in two extreme geometries, we fail to find any reasonable star formation scenario that is consistent with both the 850-μm and optical data. Furthermore, we do not detect any  CO( J =2→1)  emission coincident with the extended dust and atomic gas as would be expected if significant star formation were occurring. We show that shock-heating of dust via cloud–cloud collisions in the stripped interstellar medium of NGC 7465 could be sufficient to explain the extended 850-μm emission and lack of optical emission in the stripped gas, and suggest that cloud–cloud collisions may be an important dust heating mechanism in gas-rich systems.  相似文献   

7.
We have detected the   v = 1 → 0 S(1) (λ= 2.1218 μm)  and   v = 2 → 1 S(1) (λ= 2.2477 μm)  lines of H2 in the Galactic Centre, in a  90 × 27 arcsec2  region between the north-eastern boundary of the non-thermal source Sgr A East, and the giant molecular cloud (GMC)  M−0.02 − 0.07  . The detected  H2 v = 1 → 0  S(1) emission has an intensity of  1.6–21 × 10−18 W m−2 arcsec−2  and is present over most of the region. Along with the high intensity, the large linewidths  (FWHM = 40–70 km s−1)  and the  H2 v = 2 → 1 S(1)  to   v = 1 → 0 S(1)  line ratios (0.3–0.5) can be best explained by a combination of C-type shocks and fluorescence. The detection of shocked H2 is clear evidence that Sgr A East is driving material into the surrounding adjacent cool molecular gas. The H2 emission lines have two velocity components at ∼+50 and  ∼0 km s−1  , which are also present in the NH3(3, 3) emission mapped by McGary, Coil & Ho. This two-velocity structure can be explained if Sgr A East is driving C-type shocks into both the  GMC M−0.02 − 0.07  and the northern ridge of McGary et al.  相似文献   

8.
We present 450- and 800-μm images, made with the James Clerk Maxwell Telescope, of the NGC 2024 molecular ridge. The seven previously known compact cores, FIR1–7, have been detected, and FIR5 has been resolved into a compact object and an associated extended source to the east. The estimated masses of the dense cores vary between 1.6 and 5.1 M⊙ per 14-arcsec beam, assuming a dust temperature of 30 K and a dust opacity of κ800 μm = 0.002 m2 kg−1. A spectral index map made from the 450- and 800-μm images shows spatial variations, with the spectral index, α ( F ν ∝ να), being systematically lower towards the dense cores. We interpret this as evidence for a lower value of the frequency dependence of the dust opacity, β, towards the denser cores relative to the surrounding molecular material. This may indicate that grain growth is occurring in the cores, prior to planetesimal formation. By comparing the high-resolution 450-μm image with interferometer maps of the integrated CS(2–1) emission, the previously reported discrepancy between dust continuum emission and molecular line emission is found to be very localized. Depletion and temperature variations are discussed as possible explanations.  相似文献   

9.
Using the 13.7 m millimeter-wave telescope at the Qinghai Station of Purple Mountain Observatory, we have made observations of 13CO, C18O, HCO+ and N2H+ molecular lines towards IRAS 02232+6138. As the excitation density of the probe molecule increases from 13CO to HCO+, the size of the cloud core associated with IRAS 02232+6138 decreases from 2.40 pc to 0.54 pc, and the virial mass of the cloud core decreases from 2.2 × 103M to 5.1 × 102M. A bipolar molecular outflow is found towards IRAS 02232+6138. Using the power function n(r) ∝ r− to fit the spatial density structure of the cloud core, we obtain the power-law index  = 2.3 − 1.2; and we find that, as the probed density increases, the power function becomes more flat. The abundance ratio of 13CO to C18O is 12.4 ± 6.9, comparable with the values 11.8 ± 5.9 for dark clouds and the values 9.0–15.6 for massive cores. The abundance of N2H+ molecules is 3.5 ± 2.5 × 10−10, consistent with the value 1.0 − 5.0 × 10−10 for dark cloud cores and the value 1.2 − 12.8 × 10−10 for massive cores. The abundance of HCO+ molecules is 0.9 ± 0.5 × 10−9, close to the value 1.6 − 2.4 × 10−9 for massive cores. An increase of HCO+ abundance in the outflow region was not found. Combining with the IRAS data, the luminosity-mass ratio of the cloud core is obtained in the range 37–163(L/M). Based on the IRAS luminosity, it is estimated that a main-sequence O7.5 star is probably embedded in the IRAS 02232+6138 cloud core.  相似文献   

10.
We present VLA observations of the ( J , K )=(1, 1), (2, 2), (3, 3) and (4, 4) inversion transitions of NH3 toward the HW 2 object in Cepheus A, with 1-arcsec angular resolution. Emission is detected in the main hyperfine line of the first three transitions. The NH3(2, 2) emission shows a non-uniform 'ring' structure, which is more extended (3 arcsec) and intense than the emission seen in the (1, 1) and (3, 3) lines. A rotational temperature of ∼ 30–50 K and a lower limit to the mass of ∼ 1 ( X NH3/10−8)−1 M⊙ are derived for the ring structure. The spatio-kinematical distribution of the NH3 emission does not seem to be consistent with a simple circumstellar disc around the HW 2 thermal biconical radio jet. We suggest that it represents the remnant of the parental core from which both the inner 300-au (0.4 arcsec) disc, traced by the water maser spots previously found in the region, and the central object have formed. The complex velocity field of this core is probably produced from bound motions (similar to those of the inner disc) and from interaction with outflowing material.  相似文献   

11.
We discuss wide-field near-infrared (near-IR) imaging of the NGC 1333, L1448, L1455 and B1 star-forming regions in Perseus. The observations have been extracted from a much larger narrow-band imaging survey of the Taurus–Auriga–Perseus complex. These H2 2.122-μm observations are complemented by broad-band K imaging, mid-IR imaging and photometry from the Spitzer Space Telescope , and published submillimetre CO   J = 3–2  maps of high-velocity molecular outflows. We detect and label 85 H2 features and associate these with 26 molecular outflows. Three are parsec-scale flows, with a mean flow lobe length exceeding 11.5 arcmin. 37 (44 per cent) of the detected H2 features are associated with a known Herbig–Haro object, while 72 (46 per cent) of catalogued HH objects are detected in H2 emission. Embedded Spitzer sources are identified for all but two of the 26 molecular outflows. These candidate outflow sources all have high near-to-mid-IR spectral indices (mean value of  α∼ 1.4  ) as well as red IRAC 3.6–4.5 μm and IRAC/MIPS 4.5–24.0 μm colours: 80 per cent have [3.6]–[4.5] > 1.0 and [4.5]–[24] > 1.5. These criteria – high α and red [4.5]–[24] and [3.6]–[4.5] colours – are powerful discriminants when searching for molecular outflow sources. However, we find no correlation between α and flow length or opening angle, and the outflows appear randomly orientated in each region. The more massive clouds are associated with a greater number of outflows, which suggests that the star formation efficiency is roughly the same in each region.  相似文献   

12.
1 INTRODUCTIONFor the behavior of a molecular cloud in subsonic collision with another, Mao et al. (1992)have obtained simplified one-dimension traveling wave solutions for a plane-parallel s1ab. Chang-ing the sign in the transformation of variables in their case, we have the fOllowing results,1 rP = 2 l W op -- 1, (1)1 r =v = -- j W -- ry 1. (2)2 {V(N M)' 2z 2t -- W 1. (2)In Eq. (1), p increases with increasing t. Instability is expected to occur in strongly perturbedmolecular…  相似文献   

13.
孙科峰  吴月芳 《天文学报》2002,43(4):353-358
^12CoJ=1-0成图观测表明在IRAS19282 1814附近存在着一个蓝向单极高速分子外流，计算了其基本参量并进行了分析，它的成协红外源IRAS19282 1814可能是大质量年轻星体，其IRAS波段色指数表明该源深埋于气体和尘埃物质之中，由60-100μm流量密度获得尘埃温度为30K,它的附近没有其他的源，所以IRAS19282 1814可能是外向流的驱动源。  相似文献   

14.
We present submillimetre observations of the   J = 3 → 2  rotational transition of 12CO, 13CO and C18O across over 600 arcmin2 of the Perseus molecular cloud, undertaken with the Heterodyne Array Receiver Programme (HARP), a new array spectrograph on the James Clerk Maxwell Telescope. The data encompass four regions of the cloud, containing the largest clusters of dust continuum condensations: NGC 1333, IC348, L1448 and L1455. A new procedure to remove striping artefacts from the raw HARP data is introduced. We compare the maps to those of the dust continuum emission mapped with the Submillimetre Common-User Bolometer Array (SCUBA; Hatchell et al.) and the positions of starless and protostellar cores (Hatchell et al.). No straightforward correlation is found between the masses of each region derived from the HARP CO and SCUBA data, underlining the care that must be exercised when comparing masses of the same object derived from different tracers. From the 13CO/C18O line ratio the relative abundance of the two species  ([13CO]/[C18O]∼ 7)  and their opacities (typically τ is 0.02–0.22 and 0.15–1.52 for the C18O and 13CO gas, respectively) are calculated. C18O is optically thin nearly everywhere, increasing in opacity towards star-forming cores but not beyond  τ18∼ 0.9  . Assuming the 12CO gas is optically thick, we compute its excitation temperature, T ex (around 8–30 K), which has little correlation with estimates of the dust temperature.  相似文献   

15.
Using MERLIN with 0.2-arcsec resolution we have observed neutral hydrogen absorption against the central region of the starburst galaxy NGC 3628. The central region resolves into ∼16 continuum components at 1.4 GHz. From comparison with published 15-GHz data, we infer that these components are supernova remnants, although three components may be consistent with a weak active galactic nucleus. Neutral hydrogen absorption is seen against the continuum emission with column densities ∼1022 cm−2. The absorption appears to be from two separate absorbing structures. Assuming a simple morphology, the main velocity structure can be attributed to a ring of neutral gas with a radius 130 pc rotating around a central starburst with a velocity gradient of 1270 km s−1 kpc−1. From simple assumptions, the mass interior to this ring is 0.9 × 109 M⊙. The second absorption structure may represent outflow from the starburst region or a large-scale galactic structure. Alternatively the absorption structure may be non-axisymmetric, such as a bar.  相似文献   

16.
恒星形成于分子云之中, 分子外向流是恒星形成正在进行的重要动力学特征, 也是研究和认识恒星形成的重要契入点. 利用紫金山天文台青海观测站德令哈13.7m毫米波望远镜, 采用5种分子谱线探针(包括12CO、13CO、C18O、HCO$^+$ $J=1-0$和CS $J=2-1$, J为角动量量子数), 对一个包含IRAS 19230+1506、IRAS 19232+1504和G050.3179--00.4186这3个源的大质量恒星形成复合体进行了成图观测研究. 通过对以上分子谱线数据并结合红外波段巡天数据的分析, 在这3个源中首次探测到了分子外向流活动, 并确定了分子外向流的中心驱动源. 最后对这3个源进行了分子外向流相关物理量参数的计算, 分析了这些物理量参数之间的关系, 结果表明分子外向流的性质与中心驱动源的性质息息相关.  相似文献   

17.
The central arcminute of the Perseus cooling flow galaxy, NGC 1275, has been mapped with the JCMT in 12CO(2–1) at 21-arcsec resolution, with detections out to at least 36 arcsec (12 kpc). Within the limits of the resolution and coverage, the distribution of gas appears to be roughly east–west, consistent with previous observations of CO, X-ray, Hα and dust emission. The total detected molecular hydrogen mass is ∼ 1.6 × 1010 M⊙, using a Galactic conversion factor. The inner central rotating disc is apparent in the data, but the overall distribution is not one of rotation. Rather, the line profiles are bluewards-asymmetric, consistent with previous observations in H  i and [O  iii ]. We suggest that the blueshift may be due to an acquired mean velocity of ∼ 150 km s−1 imparted by the radio jet in the advancing direction. Within the uncertainties of the analysis, the available radio energy appears to be sufficient, and the interpretation is consistent with that of Bo¨hringer et al. for displaced X-ray emission. We have also made the first observations of 13CO(2–1) and 12CO(3–2) emission from the central 21-arcsec region of NGC 1275 and combined these data with IRAM data supplied by Reuter et al. to form line ratios over equivalent, well-sampled regions. An LVG radiative transfer analysis indicates that the line ratios are not well reproduced by single values of kinetic temperature, molecular hydrogen density and abundance per unit velocity gradient. At least two temperatures are suggested by a simple two-component LVG model, possibly reflecting a temperature gradient in this region.  相似文献   

18.
We used the 13.7 m millimeter-wave telescope of the Qinghai Station of Purple Mountain Observatory at Delingha to carry out simultaneous mapping observations in the 12CO(J = 1 − 0), 13CO(J = 1 − 0) and CO18 (J = 1 − 0) lines towards 11 isolated star-forming molecular cores selected from the sample of Spitzer's c2d program. For all three lines, these sources were all observed to the positions of half the peak intensity of the 13CO(J = 1 − 0) line. The volume density, local thermodynamic equilibrium mass MLTE and virial mass MVIR were derived for each of the molecular cores. The obtained ratio of MVIR to MLTE is 0.85 ± 0.40 for the 13CO(J = 1 − 0) cores and 0.77 ± 0.35 for the CO18 (J = 1 − 0) cores. The density profiles of the cloud cores were also calculated.  相似文献   

19.
We investigate the morphology and kinematics of the interstellar medium in the environs of the open cluster Mrk 50, which includes the Wolf–Rayet star WR 157 and a number of early B-type stars. The analysis was performed using radio continuum images at 408 and 1420 MHz, and H  i 21-cm line data taken from the Canadian Galactic Plane Survey, molecular observations of the 12CO  ( J = 1 → 0)  line at 115 GHz from the Five College Radio Astronomy Observatory and available mid- and far-infrared (FIR) observations obtained with the Midcourse Space Experiment and IRAS satellites, respectively.
This study allowed the identification of the radio continuum and molecular counterpart of the ring nebula SG 13, while no neutral atomic structure was found to be associated. The nebula is also detected in the images in the mid- and FIR, showing the existence of dust well mixed with the ionized gas. We estimate the main physical parameters of the material linked to the nebula.
The interstellar gas distribution in the environs of Mrk 50 is compatible with a stellar wind bubble created by the mass loss from WR 157.
The distribution of young stellar object candidates in the region shows that the stellar formation activity may be present in the molecular shell that encircles the ring nebula.  相似文献   

20.
We present evidence for interaction between the supernova remnant (SNR) G357.7+0.3 and nearby molecular clouds, leading to the formation of wind-swept structures and bright emission rims. These features are not observed at visual wavelengths, but are clearly visible in mid-infrared mapping undertaken using the Spitzer Space Telescope . Analysis of one of these clouds, the bright cometary structure G357.46+0.60, suggests that it contains strong polycyclic aromatic hydrocarbon emission features in the 5.8 and 8.0 μm photometric bands, and that these are highly variable over relatively small spatial scales. The source is also associated with strong variations in electron density; a far-infrared continuum peak associated with dust temperatures of ∼30 K; and has previously been observed in the 1720 MHz maser transition of OH, known to be associated with SNR shock excitation of interstellar clouds. This source also appears to contain a young stellar object (YSO) within the bright rim structure, with a steeply rising spectrum between 1.25 and 24 μm. If the formation of this star has been triggered recently by the SNR, then YSO modelling suggests a stellar mass  ∼5–10 M⊙  , and luminosity   L YSO∼102–2 × 103 L⊙  .
Finally, it is noted that a further, conical emission region appears to be associated with the Mira V1139 Sco, and it is suggested that this may represent the case of a Mira outflow interacting with a SNR. If this is the case, however, then the distance to the SNR must be ∼half of that determined from CS   J = 2–1  and 3–2 line radial velocities.  相似文献   

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