- ID:
- ivo://CDS.VizieR/J/MNRAS/449/1769
- Title:
- Orion A North prestellar core properties
- Short Name:
- J/MNRAS/449/1769
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We employ SCUBA-2 (Submillimetre Common-User Bolometer Array 2) observations of the Orion A North molecular cloud to derive column density and temperature maps. We apply a novel, Hessian-based structural identification algorithm for detection of prestellar cores to these data, allowing for automated generation of the prestellar mass function. The resulting mass function is observed to peak at 1.39^+0.18^_-0.19_M_{sun}_, indicating a star-forming efficiency lower limit of ~14 per cent when compared with the Orion nebula Cluster initial mass function (IMF) peak. Additionally, the prestellar mass function is observed to decay with a high-mass power-law exponent {alpha}=2.53^+0.16^_-0.14_, indicating approximate functional similarity with the Salpeter IMF ({alpha}=2.35). This result, when combined with the results of previous investigations suggests a regional dependence of the star-forming efficiency.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/617/A77
- Title:
- Orion Bar Herschel/PACS CO maps
- Short Name:
- J/A+A/617/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- With Herschel, we can for the first time observe a wealth of high-J CO lines in the interstellar medium with a high angular resolution. These lines are specifically useful for tracing the warm and dense gas and are therefore very appropriate for a study of strongly irradiated dense photodissocation regions (PDRs). We characterize the morphology of CO J=19-18 emission and study the high-J CO excitation in a highly UV-irradiated prototypical PDR, the Orion Bar. We used fully sampled maps of CO J=19-18 emission with the Photoconductor Array Camera and Spectrometer (PACS) on board the Herschel Space Observatory over an area of ~110"x110" with an angular resolution of 9". We studied the morphology of this high-J CO line in the Orion Bar and in the region in front and behind the Bar, and compared it with lower-J lines of CO from J=5-4 to J=13-12 and ^13^CO from J=5-4 to J=11-10 emission observed with the Herschel Spectral and Photometric Imaging Receiver (SPIRE). In addition, we compared the high-J CO to polycyclic aromatic hydrocarbon (PAH) emission and vibrationally excited H_2_. We used the CO and ^13^CO observations and the RADEX model to derive the physical conditions in the warm molecular gas layers.
- ID:
- ivo://CDS.VizieR/J/A+A/632/A8
- Title:
- Orion Bar photon-dominated region water lines
- Short Name:
- J/A+A/632/A8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The ortho-to-para ratio (OPR) of water in the interstellar medium (ISM) is often assumed to be related to the formation temperature of water molecules, making it a potentially interesting tracer of the thermal history of interstellar gas. A very low OPR of 0.1-0.5 was previously reported in the Orion Bar photon-dominated region (PDR), based on observations of two optically thin H_2_^18^O lines which were analyzed by using a single-slab large velocity gradient (LVG) model. The corresponding spin temperature does not coincide with the kinetic temperature of the molecular gas in this UV-illuminated region. This was interpreted as an indication of water molecules being formed on cold icy grains which were subsequently released by UV photodesorption. A more complete set of water observations in the Orion Bar, including seven H_2_^16^O lines and one H_2_^18^O line, carried out using Herschel/HIFI instrument, was reanalyzed using the Meudon PDR code to derive gas-phase water abundance and the OPR. The model takes into account the steep density and temperature gradients present in the region. The model line intensities are in good agreement with the observations assuming that water molecules formed with an OPR corresponding to thermal equilibrium conditions at the local kinetic temperature of the gas and when solely considering gas-phase chemistry and water gas-grain exchanges through adsorption and desorption. Gas-phase water is predicted to arise from a region deep into the cloud, corresponding to a visual extinction of A_V_~9, with a H_2_^16^O fractional abundance of ~2x10^-7^ and column density of (1.4+/-0.8)x10^15^cm^-2^ for a total cloud depth of A_V_=15. A line-of-sight average OPR of 2.8+/-0.2 is derived. The observational data are consistent with a nuclear spin isomer repartition corresponding to the thermal equilibrium at a temperature of 36+/-2K, much higher than the spin temperature previously reported for this region and close to the gas kinetic temperature in the water-emitting gas.
- ID:
- ivo://CDS.VizieR/J/A+A/634/A115
- Title:
- Orion B9 dense cores H2D+ spectra
- Short Name:
- J/A+A/634/A115
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to determine the ortho-H_2_D^+^ properties (e.g. column density and fractional abundance with respect to H_2_) in a sample of dense cores in the Orion B9 star-forming filament, and to compare those with the previously determined source characteristics, in particular with the gas kinetic temperature, [N_2_D^+^]/[N_2_H^+^] deuterium fractionation, and level of CO depletion. We used the Atacama Pathfinder EXperiment (APEX) telescope to observe the 372GHz o-H_2_D+(1_1,0_-1_1,1_) line towards three prestellar cores and three protostellar cores in Orion B9. We also employed our previous APEX observations of C^17^O, C^18^O, N_2_H^+^, and N_2_D^+^ line emission, and 870 micron dust continuum emission towards the target sources. The o-H_2_D^+^(1_1,0_-1_1,1_) line was detected in all three prestellar cores, but in _nly one of the protostellar cores. The corresponding o-H_2_D^+^ abundances were derived to be ~(12-30)x10^-11^ and ~6x10^-11^. Two additional spectral lines, DCO^+^(5-4) and N_2_H^+^(4-3), were detected in the observed frequency bands with high detection rates of 100% and 83%. We did not find any significant correlations among the explored parameters, although our results are mostly consistent with theoretical expectations. Also, the Orion B9 cores were found to be consistent with the relationship between the o-H_2_D^+^ abundance and gas temperature obeyed by other low-mass dense cores. The o-H_2_D^+^ abundance was found to decrease as the core evolves. The o-H_2_D^+^ abundances in the Orion B9 cores are in line with those found in other low-mass dense cores and larger than derived for high-mass star-forming regions. The higher o-H_2_D^+^ abundance in prestellar cores compared to that in cores hosting protostars is to be expected from chemical reactions where higher concentrations of gas-phase CO and elevated gas temperature accelerate the destruction of H_2_D^+^. The validity of using the [o-H_2_D^+^]/[N_2_D^+^] abundance ratio as an evolutionary indicator, which has been proposed for massive clumps, remains inconclusive when applied for the target cores. Similarly, the behaviour of the [o-H_2_D^+^]/[DCO^+^] ratio as the source evolves was found to be ambiguous. Still larger samples and observations of additional deuterated species are needed to explore these potential evolutionary indicators further. The low radial velocity of the line emission from one of the targeted prestellar cores, SMM 7 (~3.6km/s versus the systemic Orion B9 velocity of ~9km/s), suggests that it is a chance superposition seen towards Orion B9. Overall, as located in a dynamic environment of the Orion B molecular cloud, the Orion B9 filament provides an interesting target system to investigate the deuterium-based chemistry, and further observations of species like para-H_2_D^+^ and D_2_H^+^ would be of particular interest.
- ID:
- ivo://CDS.VizieR/J/A+A/538/A137
- Title:
- Orion B9 dense cores maps
- Short Name:
- J/A+A/538/A137
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We aim to further constrain the properties and evolutionary stages of dense cores in Orion B9. The central part of Orion B9 was mapped at 350 micron with APEX/SABOCA. A sample of nine cores in the region were observed in C^17^O(2-1), H^13^CO^+^(4-3) (towards 3 sources), DCO^+^(4-3), N_2_H^+^(3-2), and N_2_D^+^(3-2) with APEX/SHFI. These data are used in conjunction with our previous APEX/LABOCA 870-micron dust continuum data. Many of the LABOCA cores show evidence of substructure in the higher-resolution SABOCA image.
- ID:
- ivo://CDS.VizieR/J/A+A/645/A27
- Title:
- Orion B in 18 molecular tracers maps
- Short Name:
- J/A+A/645/A27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Molecular hydrogen being unobservable in cold molecular clouds, the column density measurements of molecular gas currently rely either on dust emission observation in the far-IR or on star counting. (Sub-)millimeter observations of numerous trace molecules are effective from ground based telescopes, but the relationships between the emission of one molecular line and the H_2_ column density (NH_2_) is non-linear and sensitive to excitation conditions, optical depths, abundance variations due to the underlying physico-chemistry. We aim to use multi-molecule line emission to infer NH_2_ from radio observations. We propose a data-driven approach to determine NH_2_ from radio molecular line observations. We use supervised machine learning methods (Random Forests) on wide-field hyperspectral IRAM-30m observations of the Orion B molecular cloud to train a predictor of NH_2_, using a limited set of molecular lines as input, and the Herschel-based dust-derived NH_2_ as ground truth output. For conditions similar to the Orion B molecular cloud, we obtain predictions of NH_2_ within a typical factor of 1.2 from the Herschel-based estimates. An analysis of the contributions of the different lines to the predictions show that the most important lines are ^13^CO(1-0), ^12^CO(1-0), C^18^O(1-0), and HCO+(1-0). A detailed analysis distinguishing between diffuse, translucent, filamentary, and dense core conditions show that the importance of these four lines depends on the regime, and that it is recommended to add the N_2_H+(1-0) and CH_3_OH(2_0_-1_0_) lines for the prediction of NH_2_ in dense core conditions. This article opens a promising avenue to directly infer important physical parameters from the molecular line emission in the millimeter domain. The next step will be to try to infer several parameters simultaneously (e.g., NH_2_ and far-UV illumination field) to further test the method.
- ID:
- ivo://CDS.VizieR/J/A+A/604/A32
- Title:
- Orion BN-KL ALMA view
- Short Name:
- J/A+A/604/A32
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We wish to improve our understanding of the Orion central star formation region (Orion-KL) and disentangle its complexity. We collected data with ALMA during cycle 2 in 16GHz of total bandwidth spread between 215.1 and 252.0GHz with a typical sensitivity of 5mJy/beam (2.3mJy/beam from 233.4 to 234.4GHz) and a typical beam size of 1.7"x1.0" (average position angle of 89). We produced a continuum map and studied the emission lines in nine remarkable infrared spots in the region including the Hot Core and the Compact Ridge, plus the recently discovered Ethylene Glycol Peak. We present the data, and report the detection of several species not previously seen in Orion, including n- and i-propyl cyanide (C_3_H_7_CN), and the tentative detection of a number of other species including glycolaldehyde (CH_2_(OH)CHO). The first detections of gGg' ethylene glycol (gGg' (CH_2_OH)_2_) and of acetic acid (CH_3_COOH) in Orion are presented in a companion paper. We also report the possible detection of several vibrationally excited states of cyanoacetylene (HC_3_N), and of its ^13^C isotopologues. We were not able to detect the ^16^O^18^O line predicted by our detection of O_2_ with Herschel, due to blending with a nearby line of vibrationally excited ethyl cyanide. We do not confirm the tentative detection of hexatriynyl (C_6_H) and cyanohexatriyne (HC_7_N) reported previously, or of hydrogen peroxide (H_2_O_2_) emission. We report a complex velocity structure only partially revealed before. Components as extreme as -7 and +19km/s are detected inside the hot region. Thanks to different opacities of various velocity components, in some cases we can position these components along the line of sight. We propose that the systematically redshifted and blueshifted wings of several species observed in the northern part of the region are linked to the explosion that occurred ~500 years ago. The compact ridge, noticeably farther south displays extremely narrow lines (~1km/s) revealing a quiescent region that has not been acted by this explosion. This probably indicates that the compact ridge is either over 10,000 au in front of or behind the rest of the region. Many lines remain unidentified, and only a detailed modeling of all known species, including vibrational states of isotopologues combined with the detailed spatial analysis offered by ALMA enriched with zero-spacing data, will allow new species to be detected.
- ID:
- ivo://CDS.VizieR/J/A+A/610/A77
- Title:
- Orion Integral Filament ALMA+IRAM30m N2H+(1-0) data
- Short Name:
- J/A+A/610/A77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have investigated the gas organization within the paradigmatic Integral Shape Filament (ISF) in Orion in order to decipher whether or not all filaments are bundles of fibers. We combined two new ALMA Cycle 3 mosaics with previous IRAM 30m observations to produce a high-dynamic range N2H+ (1-0) emission map of the ISF tracing its high-density material and velocity structure down to scales of 0.009pc (or ~2000AU). From the analysis of the gas kinematics, we identify a total of 55 dense fibers in the central region of the ISF. Independently of their location in the cloud, these fibers are characterized by transonic internal motions, lengths of ~0.15pc, and masses per unit length close to those expected in hydrostatic equilibrium. The ISF fibers are spatially organized forming a dense bundle with multiple hub-like associations likely shaped by the local gravitational potential. Within this complex network, the ISF fibers show a compact radial emission profile with a median FWHM of 0.035pc systematically narrower than the previously proposed universal 0.1pc filament width. Our ALMA observations reveal complex bundles of fibers in the ISF, suggesting strong similarities between the internal substructure of this massive filament and previously studied lower-mass objects. The fibers show identical dynamic properties in both low- and high-mass regions, and their widespread detection in nearby clouds suggests a preferred organizational mechanism of gas in which the physical fiber dimensions (width and length) are self-regulated depending on their intrinsic gas density. Combining these results with previous works in Musca, Taurus, and Perseus, we identify a systematic increase of the surface density of fibers as a function of the total mass per-unit-length in filamentary clouds. Based on this empirical correlation, we propose a unified star-formation scenario where the observed differences between low- and high-mass clouds, and the origin of clusters, emerge naturally from the initial concentration of fibers.
- ID:
- ivo://CDS.VizieR/J/A+A/566/A45
- Title:
- Orion optical-depth and column-density maps
- Short Name:
- J/A+A/566/A45
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-resolution, high dynamic range column-density and color-temperature maps of the Orion complex using a combination of Planck dust-emission maps, Herschel dust-emission maps, and 2MASS NIR dust-extinction maps. The column-density maps combine the robustness of the 2MASS NIR extinction maps with the resolution and coverage of the Herschel and Planck dust-emission maps and constitute the highest dynamic range column-density maps ever constructed for the entire Orion complex, covering 0.01mag<A_K_<30mag, or 2x10^20^cm^-2^<N<5x10^23^cm^-2^. We determined the ratio of the 2.2{mu}m extinction coefficient to the 850{mu}m opacity and found that the values obtained for both Orion A and B are significantly lower than the predictions of standard dust models, but agree with newer models that incorporate icy silicate-graphite conglomerates for the grain population. We show that the cloud projected probability distribution function, over a large range of column densities, can be well fitted by a simple power law. Moreover, we considered the local Schmidt-law for star formation, and confirm earlier results, showing that the protostar surface density {Sigma}_*_ follows a simple law {Sigma}_*_{prop.to}{Sigma}_gas_^{beta}^, with {beta}~2.
- ID:
- ivo://CDS.VizieR/J/ApJS/144/47
- Title:
- Outer galaxy molecular cloud catalog
- Short Name:
- J/ApJS/144/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Five College Radio Astronomy Observatory (FCRAO) Outer Galaxy Survey (OGS) of ^12^CO(J=1-0) emission was carried out between 1994May and 1997September, using the FCRAO focal plane array QUARRY (Erickson et al. 1992, IEEE Trans. 40, 1), and initially described by Heyer et al. (1998ApJS..115..241H). The OGS covers the Galactic area 102.5<l<141.5, -3<b<54, and the velocity range -152km/s<vlsr<40km/s, at 45'' spatial resolution sampled every 50.22'', and 0.98km/s velocity resolution (1.39km/s for l<106) sampled every 0.81km/s. The typical sensitivity of the OGS at these resolutions is 0.6K (T*_R_ temperature scale). The catalog was generated in a two-phase object identification procedure. The first phase consists of grouping pixels into contiguous structures above a radiation temperature threshold of 0.8K; the second phase decomposes the first-phase objects by an enhanced version of the CLUMPFIND algorithm, using dynamic thresholding, and again with a threshold of 0.8K used for discrimination. Basic attributes of the clouds (coordinates, bounding boxes, integrated intensities, peak observed temperatures) are tabulated in the catalog. A two-dimensional elliptical Gaussian is fitted to the velocity- integrated map of each cloud; the major and minor axis sizes and major axis position angles thus derived are included in the catalog. To the spatially integrated emission line of each cloud, a Gaussian profile is fitted to measure the global linewidth. Model Gaussian clouds, truncated at 0.8K, are examined to determine the effects of biases on measured quantities, induced by truncation. Coupled with detailed analysis of the catalogued clouds, statistical corrections for the effects of truncation on measured sizes, linewidths, and integrated intensities are derived and applied, along with corrections for the effects of finite resolution on the measured attributes. The catalogued emission accounts for 76.4% of the total emission in the Outer Galaxy Survey. The deficit is shown to arise mainly from low-intensity emission on the periphery of larger objects, rather than from a large number of small and/or low-intensity features.
