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Register a new user2MASS wide field extinction maps: II. The Ophiuchus and the Lupus cloud complexe
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We present an extinction map of a ~1,700 deg sq region that encloses the Ophiuchus, the Lupus, and the Pipe dark complexes using 42 million stars from the Two Micron All Sky Survey (2MASS) point source catalog. The use of a robust and optimal near-infrared method to map dust column density (Nicer, described in Lombardi & Alves 2001) allow us to detect extinction as low as A_K = 0.05 mag with a 2-sigma significance, and still to have a resolution of 3 arcmin on our map. We also present a novel, statistically sound method to characterize the small-scale inhomogeneities in molecular clouds. Finally, we investigate the cloud structure function, and show that significant deviations from the results predicted by turbulent models are observed.
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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.
We combine extinction maps from the Two Micron All Sky Survey (2MASS) with Hipparcos and Tycho parallaxes to obtain reliable and high-precision estimates of the distance to the Ophiuchus and Lupus dark complexes. Our analysis, based on a rigorous maximum-likelihood approach, shows that the rho-Ophiuchi cloud is located at (119 +/- 6) pc and the Lupus complex is located at (155 +/- 8) pc; in addition, we are able to put constraints on the thickness of the clouds and on their orientation on the sky (both these effects are not included in the error estimate quoted above). For Ophiuchus, we find some evidence that the streamers are closer to us than the core. The method applied in this paper is currently limited to nearby molecular clouds, but it will find many natural applications in the GAIA-era, when it will be possible to pin down the distance and three-dimensional structure of virtually every molecular cloud in the Galaxy.
Fully sampled degree-scale maps of the 13CO 2-1 and CO 4-3 transitions toward three members of the Lupus Molecular Cloud Complex - Lupus I, III, and IV - trace the column density and temperature of the molecular gas. Comparison with IR extinction maps from the c2d project requires most of the gas to have a temperature of 8-10 K. Estimates of the cloud mass from 13CO emission are roughly consistent with most previous estimates, while the line widths are higher, around 2 km/s. CO 4-3 emission is found throughout Lupus I, indicating widespread dense gas, and toward Lupus III and IV. Enhanced line widths at the NW end and along the edge of the B228 ridge in Lupus I, and a coherent velocity gradient across the ridge, are consistent with interaction between the molecular cloud and an expanding HI shell from the Upper-Scorpius subgroup of the Sco-Cen OB Association. Lupus III is dominated by the effects of two HAe/Be stars, and shows no sign of external influence. Slightly warmer gas around the core of Lupus IV and a low line width suggest heating by the Upper-Centaurus-Lupus subgroup of Sco-Cen, without the effects of an HI shell.
Extinction remains one of the most reliable methods of measuring column density of nearby Galactic interstellar clouds. The current and ongoing near-infrared surveys enable the mapping of extinction over large sky areas. We produce allsky extinction maps using the 2MASS near-infrared survey. We use the NICER and NICEST methods to convert the near-infrared colour excesses to extinction estimates. The results are presented in Healpix format at the resolutions of 3.0, 4.5, and 12.0 arcmin. The main results of this study are the calculated J-band extinction maps. The comparison with earlier large-scale extinction mappings shows good correspondence but also demonstrates the presence of resolution-dependent bias. A large fraction of the bias can be corrected by using the NICEST method. For individual regions, best extinction estimates are obtained by careful analysis of the local stellar population and the use of the highest resolution afforded by the stellar density. However, the uniform allsky maps should still be useful for many global studies and as the first step into the investigation of individual clouds.
Deep R-band CCD linear polarimetry collected for fields with lines-of-sight toward the Lupus I molecular cloud is used to investigate the properties of the magnetic field within this molecular cloud. The observed sample contains about 7000 stars, almost 2000 of them with polarization signal-to-noise ratio larger than 5. These data cover almost the entire main molecular cloud and also sample two diffuse infrared patches in the neighborhood of Lupus I. The large scale pattern of the plane-of-sky projection of the magnetic field is perpendicular to the main axis of Lupus I, but parallel to the two diffuse infrared patches. A detailed analysis of our polarization data combined with the Herschel/SPIRE 350 um dust emission map shows that the principal filament of Lupus I is constituted by three main clumps acted by magnetic fields having different large-scale structure properties. These differences may be the reason for the observed distribution of pre- and protostellar objects along the molecular cloud and its apparent evolutive stage. On the other hand, assuming that the magnetic field is composed by a large-scale and a turbulent components, we find that the latter is rather similar in all three clumps. The estimated plane-of-sky component of the large-scale magnetic field ranges from about 70 uG to 200 uG in these clumps. The intensity increases towards the Galactic plane. The mass-to-magnetic flux ratio is much smaller than unity, implying that Lupus I is magnetically supported on large scales.
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