2MASS wide field extinction maps

We present a 8 deg x 6 deg, high resolution extinction map of the Pipe nebula using 4.5 million stars from the Two Micron All Sky Survey (2MASS) point source catalog. The use of NICER, a robust and optimal technique to map the dust column density, allows us to detect a Av = 0.5 mag extinction at a 3-sigma level with a 1 arcmin resolution. We find for the Pipe nebula a normal reddening law, E(J-H) = (1.85 +/- 0.15) E(H-K). We measure the cloud distance using Hipparchos and Tycho parallaxes, and obtain ~130 pc. This, together with the total estimated mass, 10^4 Msun, makes the Pipe the closest massive cloud complex to Earth. We compare the NICER extinction map to the NANTEN 12CO observations and derive with unprecedented accuracy the relationship between the near-infrared extinction and the 12CO column density and hence (indirectly) the 12CO X-factor, that we estimate to be 2.91 10^20 cm^-2 K^-1 km^-1 s in the range Av <- [0.9, 5.4] mag. We identify ~1500 OH/IR stars located within the Galactic bulge in the direction of the Pipe field. This represents a significant increase of the known numbers of such stars in the Galaxy. Our analysis confirms the power and simplicity of the color excess technique to study molecular clouds. The comparison with the NANTEN 12CO data corroborates the insensitivity of CO observations to low column densities (up to approximately 2 mag in Av), and shows also an irreducible uncertainty in the dust-CO correlation of about 1 mag of visual extinction.

We present a near-infrared extinction map of a large region (approximately 2200 deg^2) covering the Orion, the Monoceros R2, the Rosette, and the Canis Major molecular clouds. We used robust and optimal methods to map the dust column density in the near-infrared (NICER and NICEST) towards ~19 million stars of the Two Micron All Sky Survey (2MASS) point source catalog. Over the relevant regions of the field, we reached a 1-sigma error of 0.03 mag in the K-band extinction with a resolution of 3 arcmin. We measured the cloud distances by comparing the observed density of foreground stars with the prediction of galactic models, thus obtaining d_{Orion A} = (371 +/- 10) pc, d_{Orion B} = (398 +/- 12) pc, $d_{Mon R2} = (905 +/- 37) pc, $d_{Rosette} = (1330 +/- 48) pc, and $d_{CMa} = (1150 +/- 64) pc, values that compare very well with independent estimates.

\n We present a near-infrared extinction map of a large region (approximately 2200 deg2) covering the Orion, the Monoceros R2, the Rosette, and the Canis Major molecular clouds. We used robust and optimal methods to map the dust column density in the near-infrared (<sc>Nicer </sc>and <sc>Nicest</sc>) towards ~19 million stars of the Two Micron All Sky Survey (2MASS) point source catalog. Over the relevant regions of the field, we reached a 1-σ error of 0.03 mag in the K-band extinction with a resolution of 3arcmin. We measured the cloud distances by comparing the observed density of foreground stars with the prediction of galactic models, thus obtaining dOrionA = (371 ± 10) pc, dOrionB = (398 ± 12) pc, dMonR2 = (905 ± 37) pc, dRosette = (1330 ± 48) pc, and dCMa = (1150 ± 64) pc, values that compare very well with independent estimates. \n

Dust extinction is one of the most reliable tracers of the gas distribution in the Milky Way. The near-infrared (NIR) Vista Variables in the Vía Láctea (VVV) survey enables extinction mapping based on stellar photometry over a large area in the Galactic plane. We devise a novel extinction mapping approach, XPNICER, by bringing together VVV photometric catalogues, stellar parameter data from StarHorse catalogues, and previously published X percentile and PNICER extinction mapping techniques. We apply the approach to the VVV survey area, resulting in an extinction map that covers the Galactic disc between 295° ≲ l ≲ 350° and −2° ≲ b ≲ 2°, and the Galactic bulge between −10° ≲ b ≲ 5°. The map has 30 arcsec spatial resolution and it traces extinctions typically up to AV ∼ 10–20 mag and maximally up to AV ∼ 30 mag. We compare our map to previous dust-based maps, concluding that it provides a high-fidelity extinction-based map, especially in its ability to recover both the diffuse dust component of the Galaxy and moderately extincted giant molecular cloud regions. The map is especially useful as independent, extinction-based data on the Galactic dust distribution and applicable for a wide range of studies from individual molecular clouds to the studies of the Galactic stellar populations.

We have performed the submillimeter and millimeter observations in CO lines\ntoward supernova remnant (SNR) IC443. CO molecular shell is well coincident\nwith the partial shell of the SNR detected in radio continuum observations. The\nbroad emission lines and three 1720-MHz OH masers were detected in CO molecular\nshell. The present observations have provided further evidence in support of\nthe interaction between the SNR and the adjoining molecular clouds (MCs). The\ntotal mass of the MCs is 9.26*10^{3} sun masses. The integrated CO line\nintensity ratio I(CO(3-2))/I(CO(2-1)) for the whole molecular cloud is between\n0.79 and 3.40. The average value is 1.58, which is much higher than previous\nmeasurements of individual Galactic MCs. Higher line ratios imply that shocks\nhave driven into the MCs. We conclude that high I(CO(3-2))/I(CO(2-1)) is\nidentified as one good signature of SNR-MCs interacting system. Based on $IRAS$\nPoint Source Catalog and 2MASS near-infrared database, 12 protostellar objects\nand 1666 young stellar objects (YSOs) candidates (including 154 CTTSs and 419\nHAeBe stars) are selected. In the interacting regions, the significant\nenhancement of the number of protostellar objects and YSOs indicates the\npresence of some recently formed stars. After comparing the characteristic\ntimescales of star formation with the age of IC443, we conclude that the\nprotostellar objects and YSOs candidates are not triggered by IC443. For the\nage of stellar winds shell, we have performed calculation on the basis of\nstellar winds shell expansion model. The results and analysis suggest that the\nformation of these stars may be triggered by the stellar winds of IC443\nprogenitor.\n

view Abstract Citations (4) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Optical Survey of IRAS Fields in the Draco Cloud Region Johnson, H. M. ; Klemola, A. R. Abstract This paper reports the results of examining POSS plates in 5arcmin×5arcmin regions that surround the 56 unidentified IRAS Point Source Catalog (PSC) objects within a 36 square degree area around the inbound Draco molecular cloud at l = 90°, b = +38°. Both stellar and nonstellar POSS images are cataloged with accurate coordinates and estimated blue magnitudes. Coordinated finder charts are provided for all objects, and are illustrated with the PSC error ellipses of 95% confidence. Several galaxies and stars found inside the error-ellipse fields are probable counterparts of PSC objects that are not projected in cloud clumps. Other stellar and nonstellar POSS images are projected in or near 100 μm - only sources that may be cloud globules. Some of the 23 empty error-ellipse fields may be centered on opaque dust. Publication: The Astrophysical Journal Supplement Series Pub Date: March 1987 DOI: 10.1086/191179 Bibcode: 1987ApJS...63..701J Keywords: Infrared Astronomy Satellite; Infrared Sources (Astronomy); Molecular Clouds; Astronomical Coordinates; Infrared Stars; Tables (Data); Astronomy; INFRARED: SOURCES; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (57)

While plane-of-sky magnetic field observations in molecular clouds are now common, observations of their line-of-sight magnetic field remain limited. To address this issue, M. Tahani et al. developed a technique based on Faraday rotation. The technique incorporates an ON–OFF approach to identify the rotation measure induced by the magnetic fields associated with the cloud. The upcoming abundance of observations of Faraday rotation from the Square Kilometre Array and its pathfinders necessitates robustly tested software to automatically obtain line-of-sight magnetic fields of molecular clouds. We developed software, called MC-BLOS (for molecular cloud line-of-sight magnetic field; DOI:10.5281/zenodo.15338512), to carry out the technique in an automated manner. The software’s inputs are Faraday rotation of point sources, maps of extinction or column density, results from chemical evolution code, and a parameter file that allows the user to specify the cloud name or other parameters pertaining to the technique. For each cloud, the software invokes a set of predefined initial parameters such as density, temperature, and surrounding boundary, which the user can modify. The software then runs the technique automatically, outputting line-of-sight magnetic field maps and tables (including uncertainties) at the end of the process. MC-BLOS generates diagnostic files for result evaluation and input parameter refinement, allowing for expert judgment in parameter selection. We have tested the software on previously published clouds, and the results are consistent within the reported uncertainty range. This software will facilitate the analysis of forthcoming observations of Faraday rotation, enabling a better understanding of the role of magnetic fields in molecular cloud dynamics and star formation.

In the last years substantial progress has been made in modelling turbulent clouds and describing their structure by characteristic parameters. The missing link for a systematic comparison between models and observations is the lack of ecient radiative transfer algorithms to generate molecular line maps from the models comparable to the observed maps. A fully self- consistent solution of the radiative transfer problem is computationally very demanding and hardly suited to evaluate a large set of cloud models with regard to their agreement with observed molecular cloud structures. We introduce a new, computationally ecient code to calculate the line profiles based on two reasonable approximations. It is able to compute the molecular line maps in turbulent cloud models with an accuracy of about 20% fast enough to be run on large sets of model clouds. Applying the code to hydrodynamic, and magnetohydrodynamic cloud models we study how their structure would appear in molecular line observations. We show that no single molecular line provides a good measure for the density structure in the models. The X factor, translating the integrated line intensities into column densities, can be approximately constant within a density range covering up to a factor 100 in few transitions but for each line this behaviour breaks down outside of a limited range of densities. Optical depth eects and subthermal excitation result in a significant modification of the distribution of line intensities relative to the column density distribution. All lower transitions of CO isotopes only trace gas at low and intermediate densities which is distributed over all scales in molecular clouds. Turbulence models driven on the largest scales reproduce the observed scaling behaviour. Higher CO tran- sitions are only excited in dense cores resulting from shocks or gravitational collapse. The existence of massive dense cores resulting from collapse can only be inferred when comparing observations in dierent transitions taken with an excellent signal-to-noise ratio or from dedicated high-density tracers. The line profiles obtained from turbulence models driven on large scales break up into several fragments in contrast to obser- vations of molecular clouds without heavy star-formation which show typically smooth profiles with close-to-Gaussian shape. None of the turbulence simulations provides a good match of all observed properties for this type of clouds. The velocity scaling behaviour of all observations and turbulence models is consistent with the interpretation of a molecular cloud as shock- dominated medium. More observational data are needed to provide a reliable conclusion on the degree of intermittency. As molecular lines fail to reflect the density structure of an interstellar cloud line observations should be combined with dust continuum observations to deduce column densities. On the other hand we need the velocity information contained in line observations to discriminate between dierent turbulence models.

\n \nWe present an extinction map of the Polaris molecular cirrus cloud derived\nfrom star counts and compare it with the Schlegel et al. ([CITE]) extinction map\nderived from the far-infrared dust opacity.\nWe find that, within the Polaris cloud, the Schlegel et al. ([CITE])\nAV values are a factor 2 to 3 higher than the star count values. \nWe propose that this discrepancy results from a difference in \n$\\tau_{\\rm FIR}/ A_V$ between the diffuse atomic medium and the Polaris \ncloud. We use the difference in spectral energy distribution, warm for \nthe diffuse atomic medium, cold for the Polaris cloud, to separate\ntheir respective contribution to the line of sight integrated infrared\nemission and find that the $\\tau_{\\rm FIR}/ A_V$ of cold dust in\nPolaris is on average 4 times higher than the Schlegel et al. ([CITE]) value for dust\nin atomic cirrus. This change in dust property could be interpreted by a\ngrowth of fluffy particles within low opacity molecular cirrus clouds such\nas Polaris. \nOur work suggests that variations in dust emissivity must be taken \ninto account to estimate AV from dust emission wherever cold\ninfrared emission is present (i.e. molecular clouds). \n \n\n

We present an extinction map of the Polaris molecular cirrus cloud derived from star counts and compare it with the Schlegel et al. [13] extinction map derived from the far-infrared dust opacity. We find that, within the Polaris cloud, the Schlegel et al. [13] AV values are, on average, a factor 2 higher than the star count values. We propose that this discrepancy results from a difference in τFIR/AV between the diffuse atomic medium and the Polaris cloud. We use the difference in spectral energy distribution, warm for the diffuse atomic medium, cold for the Polaris cloud, to separate their respective contribution to the line of sight integrated infrared emission and find that the τFIR/AV of cold dust in Polaris is on average 4 times higher than the Schlegel et al. [13] value for dust in atomic cirrus. This change in dust property could be interpreted by a growth of fluffy particles within low opacity molecular cirrus clouds such as Polaris. Our work suggests that variations in dust emissivity must be taken into account to estimate AV from dust emission wherever cold infrared emission is present (i.e. molecular clouds).

We search for evidence of a relation between properties of young stellar objects (YSOs) and their parent molecular clouds to understand the initial conditions of high-mass star formation. A sample of 135 sources was selected from the Infrared Astronomical Satellite (IRAS) Point Source Catalog, on the basis of their red color to enhance the possibility of discovering young sources. Using the Kolner Observatorium fur SubMillimeter Astronomie (KOSMA) 3-m telescope, a single-point survey in 13CO(2-1) was carried out for the entire sample, and 14 sources were mapped further. Archival mid-infrared (MIR) data were compared with the 13CO emissions to identify evolutionary stages of the sources. A 13CO observed sample was assembled to investigate the correlation between 13CO line width of the clouds and the luminosity of the associated YSOs. We identified 98 sources suitable for star formation analyses for which relevant parameters were calculated. We detected 18 cores from 14 mapped sources, which were identified with eight pre-UC HII regions and one UC HII region, two high-mass cores earlier than pre-UC HII phase, four possible star forming clusters, and three sourceless cores. By compiling a large (360 sources) 13CO observed sample, a good correlation was found between the 13CO line width of the clouds and the bolometric luminosity of the associated YSOs, which can be fitted as a power law: lg(dV13/km/s)=-0.023+0.135lg(Lbol/Lsolar). Results show that luminous (>10^3Lsolar) YSOs tend to be associated with both more massive and more turbulent (dV13>2km/s) molecular cloud structures.

We are studying the column density distribution of all nearby giant molecular clouds. As part of this project we generated several all sky extinction maps. They are calculated using the median near infrared colour excess technique applied to data from the Two Micron All-Sky Survey (2MASS). Our large scale approach allows us to fit spline functions to extinction free regions in order to accurately determine the colour excess values. Two types of maps are presented: i) Maps with a constant noise and variable spatial resolution; ii) Maps with a constant spatial resolution and variable noise. Our standard Av map uses the nearest 49 stars to the centre of each pixel for the determination of the extinction. The one sigma variance is constant at 0.28mag Av in the entire map. The distance to the 49th nearest star varies from below 1arcmin near the Galactic Plane to about 10arcmin at the poles, but is below 5arcmin for all giant molecular clouds (|b|< 30degr). A comparison with existing large scale maps shows that our extinction values are systematically larger by 20% compared to Dobashi et al. and 40% smaller compared to Schlegel et al.. This is most likely caused by the applied star counting technique in Dobashi et al. and systematic uncertainties in the dust temperature and emissivity in Schlegel et al.. Our superior resolution allows us to detect more small scale high extinction cores compared to the other two maps.

We aim to better understand how the spatial structure of molecular clouds is governed by turbulence. For that, we study the large-scale spatial distribution of low density molecular gas and search for characteristic length scales. We employ a 35 square degrees 13CO 1-0 molecular line survey of Cygnus X and visual extinction (A_V) maps of 17 Galactic clouds to analyse the spatial structure using the Delta-variance method. This sample contains a large variety of different molecular cloud types with different star forming activity. The Delta-variance spectra obtained from the A_V maps show differences between low-mass star-forming (SF) clouds and massive giant molecular clouds (GMC) in terms of shape of the spectrum and its power-law exponent beta. Low-mass SF clouds have a double-peak structure with characteristic size scales around 1 pc (though with a large scatter around this value) and 4 pc. GMCs show no characteristic scale in the A_V-maps, which can partly be ascribed to a distance effect due to a larger line-of-sight (LOS) confusion. The Delta-variance for Cygnus, determined from the 13CO survey, shows characteristic scales at 4 pc and 40 pc, either reflecting the filament structure and large-scale turbulence forcing or - for the 4 pc scale - the scale below which the 13CO 1-0 line becomes optically thick. Though there are different processes that can introduce characteristic scales, i.e. geometry, decaying turbulence the transition scale from supersonic to subsonic turbulence (the sonic scale), line-of-sight effects and energy injection due to expanding supernova shells, outflows, HII-regions, and the relative contribution of these effects strongly varies from cloud to cloud, it is remarkable that the resulting turbulent structure of molecular clouds shows similar characteristics.

We present an extinction map of the Large Magellanic Cloud (LMC), using 204,502 stars from the Two Micron All Sky Survey point source catalog. We first use the NICE method to determine the reddening distribution, \ehk and \ejh, which we compare to the HI distribution to find a near-infrared reddening law of $\ejh/\ehk=1.20\pm 0.04$. A visual extinction map ($\sim 6^\circ\times 6^\circ$) of the LMC is created using the NICER method; at 4 arcmin resolution, a mean value of $\av=0.38$ mag is found. We derive the LMC CO-to-H$_2$ conversion factor, $\x{LMC}$, independent of assumptions about the virialization of giant molecular clouds, by comparing the NICER extinction map with NANTEN $^{12}$CO observations. In regions where $\av>1$ mag and $^{12}$CO emission is $\ge$ 2 \counits, we measure $\x{LMC}=9.3\pm 0.4\times 10^{20} \xunits$. In the same regions, the LMC contains a total molecular mass of $(4.5\pm 0.2)\times 10^7 \msun$.

We present (1) new fully sampled maps of CO and J = 2–1 emission and CO J = 3–2 emission toward the molecular clouds Cep B and C, associated with the Cep OB3 association; (2) a map of extinction, A V , derived from IR colors of background stars; and (3) the distribution of young stellar objects (YSOs) over the same field as the molecular maps. An LTE analysis of the CO and maps yields the distribution of molecular column densities and temperatures. Substantial variations are evident across the clouds; smaller subregions show correlations between molecular properties and dust extinction, consistent with a picture of outer photodissociation regions with a layer of CO-dark molecular gas, a CO self-shielded interior, and an inner cold dense region where CO is largely depleted onto grains. Comparing the distribution of YSOs with molecular gas surface density shows a power-law relation very similar in slope to that for the giant molecular cloud associated with the H ii region Sh2-235 from a previous paper in this series that employed the same methodology. We note the presence of several compact, isolated CO emission sources in the J = 3–2 maps. The gas temperature and velocity dispersion yield a map of the sonic Mach number, which varies across the cloud but always exceeds unity, confirming the pervasiveness of supersonic turbulence over length scales ≳0.1 pc (the map resolution). We also compute a J = 2–1 CO X-factor that varies with position but is, on average, within 20% of the Galactic average derived from CO J = 1–0 observations.