2MASS wide field extinction maps

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 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 present the results of a population synthesis of radio and γ-ray millisecond pulsars (MSPs) from the galactic disk (GD). Using 92 radio MSPs detected in 13 radio surveys and 54 Fermi MSPs detected as point sources in the first point source catalog, we establish six free parameters corresponding to the overall factor and the exponents of the period and period derivative dependence for each of the radio and γ-ray empirical luminosity models. We test three high-energy emission models described by the two-pole caustic slot-gap, outer-gap, and pair-starved polar-cap geometries. The simulated distributions of pulsar properties adequately describe the distributions of detected MSPs from the GD. We explore the γ-ray emission from groups of MSPs in globular clusters and in the galactic bulge. The simulation predicts reasonable numbers of Fermi MSPs detected in the other point source catalogs and anticipates a bright future for Fermi observations of MSPs, expecting a total of ≈170 MSP detections from the GD within 10 years. Our numbers of simulated MSPs in globular clusters are in agreement with those derived from Fermi detections. The simulation predicts that about 11,000 MSPs in the galactic bulge are required to explain the γ-ray galactic center excess.

\n Context. Infrared dark clouds (IRDCs) harbor progenitors of high-mass stars. Little is known of the parental molecular clouds of IRDCs.\n Aims. We demonstrate the feasibility of the near-infrared (NIR) dust extinction mapping in tracing the parental molecular clouds of IRDCs at the distances of D ≈ 2.5−8 kpc. \n Methods. We derive NIR extinction maps for 10 prominent IRDC complexes using a color-excess mapping technique and NIR data from the UKIDSS/Galactic Plane Survey. We compare the resulting maps to the 13CO emission line data, to the 8 μm dust opacity data, and to the millimeter dust emission data. We derive distances for the clouds by comparing the observed NIR source densities to the Besançon stellar distribution model and compare them to the kinematic distance estimates.\n Results. The NIR extinction maps provide a view of the IRDC complexes over the dynamical range of AV ≈ 2 − 40 mag, in spatial resolution of ~30″. The NIR extinction data correlate well with the 13CO data and probe a similar gas component, but also extend to higher column densities. The NIR data reveal a wealth of extended structures surrounding the dense gas traced by the 8 μm shadowing features and sub-mm dust emission, showing that the clouds contain typically ≳ 10 times more mass than traced by those tracers. The IRDC complexes of our sample contain a relatively high amount of high-column density material, and their cumulative column density distributions resemble active nearby star-forming clouds like Orion rather than less active clouds like California. \n Conclusions. The NIR dust extinction data provide a new powerful tool to probe the mass distribution of the parental molecular clouds of IRDCs up to the distances of D ~ 8 kpc. This encourages deeper NIR observations of IRDCs, because the sensitivity and resolution of the data can be directly enhanced with dedicated observations. In addition to mass distributions, the NIR data provide relatively reliable distance estimates.\n

We present an extinction map of a ~1700 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, A&A, 377, 1023) allow us to detect extinction as low as AK = 0.05 mag with a 2-σ 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.

Results from IRAS have shown that four compact sources exist within the central 0.°5 of the dark cloud Barnard 5 (B5) (Beichman et al .,1984, Ap. J. (Letters),278, L45). The source denoted IRS1 by those authors is the only IRAS source located within the core (~ 5’ × 10’). IRS1 appears pointlike in all bands except the 100 μm band. The NH3 maps of B5 (Benson, 1984, Ph.D thesis; Benson and Myers 1988, private communication) show two peaks of emission in the core of B5. The southernmost of the two peaks in NH3 emission corresponds to the location of the IRAS source while the northern peak, located approximately 2’ north of IRS1, has no IRAS counterpart. Boss (1985, ApJLett,288 L25) suggested that a second protostellar source could be present at the position of the northern NH3 peak based on his models of binary protostellar formation. We report observations of the B5 core at 160 and 360 μm which were made in order to test Boss’ hypothesis and to further study the environment of a known star forming region. The 360 μm observations were made at the NASA Infrared Telescope Facility and the 160 μm observations were made from the Kuiper Airborne Observatory using the University of Chicago submillimeter 32 detector array camera and Far-IR 32 detector array camera. Figures 1 and 2 are photometric maps of the B5 core at 360 and 160 μm, respectively, made using a 45“ beam. In figure 1, contour levels represent 1Jy/beam with the peak contour being 9 Jy/beam. In figure 2, contour levels represent 1.2 Jy/beam with the highest contour level at 10.8 Jy/beam. The (0,0) position corresponds to α(1950) = 03h44m28.s7 and δ(1950) = 32°44′30″. Both maps display a crescent shaped feature similar to that seen in the outer regions of B5 in the C18O observations (Goldsmith, Langer, and Wilson, 1986,Ap. J. (Letters) 303, L11) (GLW). The NH3 map (Benson and Myers, 1988) correlates much better with the 160 μm map than with the 360 pm map. Four regions of relatively high density are observed along the crescent ridge, which we have labelled A, B, C, and D. Region A corresponds to the position of the IRAS (IRS1) point. Regions B and C have not been previously identified, while D corresponds to the northernmost NH3 peak. The background flux from the ridge is r 4 JY/beam at 360 μm and r 3 JY/beam at 160 μm. After background subtraction and beam deconvolution, both A and B appeared approximately gaussian in shape with FWHM values of 44” and 32“, respectively, at 360 μm. The total flux densities for A and B at 360 μm are 12 Jy and 5 Jy, respectively, and total flux densities at 160 μm for A and B are 16 Jy and ≤1.5 Jy.

Studies of the properties of the inner Galactic Bulge depend strongly on the assumptions about the interstellar extinction. Most of the extinction maps available in the literature lack the information about the distance. We combine the observations with the Besancon model of the Galaxy to investigate the variations of extinction along different lines of sight towards the inner Galactic bulge as a function of distance. In addition we study the variations in the extinction law in the Bulge. We construct color-magnitude diagrams with the following sets of colors: H-Ks and J-Ks from the VVV catalogue as well as Ks-[3.6], Ks-[4.5], Ks-[5.8] and Ks-[8.0] from GLIMPSE-II catalogue matched with 2MASS. Using the newly derived temperature-color relation for M giants that match better the observed color-magnitude diagrams we then use the distance-color relations to derive the extinction as a function of distance. The observed colors are shifted to match the intrinsic colors in the Besan\c{c}on model, as a function of distance, iteratively thereby creating an extinction map with three dimensions: two spatial and one distance dimension along each line of sight towards the bulge. Colour excess maps are presented at a resolution of 15' x 15' for 6 different combinations of colors, in distance bins of 1 kpc. The high resolution and depth of the photometry allows to derive extinction maps to 10 kpc distance and up to 35 magnitudes of extinction in Av (3.5 mag in Aks). Integrated maps show the same dust features and consistent values with the other 2D maps. Starting from the color excess between the observations and the model we investigate the extinction law in near-infrared and its variation along different lines of sight.

Three dimensional interstellar extinction maps provide a powerful tool for stellar population analysis. We use data from the VISTA Variables in the Via Lactea survey together with the Besan\c{c}on stellar population synthesis model of the Galaxy to determine interstellar extinction as a function of distance in the Galactic bulge covering $ -10 < l < 10$ and $-10 < b <5$. We adopted a recently developed method to calculate the colour excess. First we constructed the H-Ks vs. Ks and J-Ks vs. Ks colour-magnitude diagrams based on the VVV catalogues that matched 2MASS. Then, based on the temperature-colour relation for M giants and the distance-colour relations, we derived the extinction as a function of distance. The observed colours were shifted to match the intrinsic colours in the Besan\c{c}on model as a function of distance iteratively. This created an extinction map with three dimensions: two spatial and one distance dimension along each line of sight towards the bulge. We present a 3D extinction map that covers the whole VVV area with a resolution of 6' x 6', using distance bins of 0.5 kpc. The high resolution and depth of the photometry allows us to derive extinction maps for a range of distances up to 10 kpc and up to 30 magnitudes of extinction in $A_{V}$. Integrated maps show the same dust features and consistent values as other 2D maps. We discuss the spatial distribution of dust features in the line of sight, which suggests that there is much material in front of the Galactic bar, specifically between 5-7 kpc. We compare our dust extinction map with high-resolution $\rm ^{12}CO$ maps towards the Galactic bulge, where we find a good correlation between $\rm ^{12}CO$ and $\rm A_{V}$. We determine the X factor by combining the CO map and our dust extinction map. Our derived average value is consistent with the canonical value of the Milky Way.

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.

Aims: We derive the probability density functions (PDFs) of column density for a complete sample of prominent molecular cloud complexes closer than 200 pc. Methods: We derive near-infrared dust extinction maps for 23 molecular cloud complexes, using the "nicest" colour excess mapping technique and data from the 2MASS archive. The extinction maps are then used to examine the column density PDFs in the clouds. Results: The column density PDFs of most molecular clouds are well-fitted by log-normal functions at low column densities (0.5 mag < A_v < 3-5 mag). However, at higher column densities prominent, power-law-like wings are common. In particular, we identify a trend among the PDFs: active star-forming clouds always have prominent non-log-normal wings. In contrast, clouds without active star formation resemble log-normals over the whole observed column density range, or show only low excess of higher column densities. This trend is also reflected in the cumulative PDFs, showing that the fraction of high column density material is significantly larger in star-forming clouds. These observations are in agreement with an evolutionary trend where turbulent motions are the main cloud-shaping mechanism for quiescent clouds, but the density enhancements induced by them quickly become dominated by gravity (and other mechanisms) which is strongly reflected by the shape of the column density PDFs. The dominant role of the turbulence is restricted to the very early stages of molecular cloud evolution, comparable to the onset of active star formation in the clouds.

We analyse column density and temperature maps derived from Herschel dust continuum observations of a sample of massive infrared dark clouds (G11.11-0.12, G18.82-0.28, G28.37+0.07, G28.53-0.25). We disentangle the velocity structure of the clouds using 13CO 1-0 and 12CO 3-2 data, showing that these IRDCs are the densest regions in massive giant molecular clouds and not isolated features. The probability distribution function (PDF) of column densities for all clouds have a power-law distribution over all (high) column densities, regardless of the evolutionary stage of the cloud: G11.11-0.12, G18.82-0.28, and G28.37+0.07 contain (proto)-stars, while G28.53-0.25 shows no signs of star formation. This is in contrast to the purely log-normal PDFs reported for near/mid-IR extinction maps. We only find a log-normal distribution for lower column densities, if we perform PDFs of the column density maps of the whole GMC in which the IRDCs are embedded. By comparing the PDF slope and the radial column density profile, we attribute the power law to the effect of large-scale gravitational collapse and to local free-fall collapse of pre- and protostellar cores. Independent from the PDF analysis, we find infall signatures in the spectral profiles of 12CO for G28.37+0.07 and G11.11-0.12, supporting the scenario of gravitational collapse. IRDCs are the densest regions within GMCs, which may be the progenitors of massive stars or clusters. At least some of the IRDCs are probably the same features as ridges (high column density regions with N>1e23 cm-2 over small areas), which were defined for nearby IR-bright GMCs. Because IRDCs are only confined to the densest (gravity dominated) cloud regions, the PDF constructed from this kind of a clipped image does not represent the (turbulence dominated) low column density regime of the cloud.

We use the COMPLETE Survey's observations of the Perseus star-forming region to assess and intercompare three methods for measuring column density in molecular clouds: extinction mapping (NIR); thermal emission mapping (FIR); and mapping the intensity of CO isotopologues. The structures shown by all three tracers are morphologically similar, but important differences exist. Dust-based measures give similar, log-normal, distributions for the full Perseus region, once careful calibration corrections are made. We also compare dust- and gas-based column density distributions for physically-meaningful sub-regions of Perseus, and we find significant variations in the distributions for those regions. Even though we have used 12CO data to estimate excitation temperatures, and we have corrected for opacity, the 13CO maps seem unable to give column distributions that consistently resemble those from dust measures. We have edited out the effects of the shell around the B-star HD 278942. In that shell's interior and in the parts where it overlaps the molecular cloud, there appears to be a dearth of 13CO, likely due either to 13CO not yet having had time to form in this young structure, and/or destruction of 13CO in the molecular cloud. We conclude that the use of either dust or gas measures of column density without extreme attention to calibration and artifacts is more perilous than even experts might normally admit. And, the use of 13CO to trace total column density in detail, even after proper calibration, is unavoidably limited in utility due to threshold, depletion, and opacity effects. If one's main aim is to map column density, then dust extinction seems the best probe. Linear fits amongst column density tracers are given, quantifying the inherent uncertainties in using one tracer (when compared with others). [abridged]

We have analyzed the IRAS data for 182 galaxies in order to determine accurate measures of their total flux densities, especially for galaxies that are partially resolved by IRAS. These galaxies are a subset of a complete, magnitude-limited sample whose molecular contents are being measured using the Five College Radio Astronomy Observatory (FCRAO) 14 m millimeter telescope as part of the FCRAO Extragalactic CO Survey. Here, we present IR flux densities at 12, 25, 60, and 100 microns from co-added IRAS data, including results for 50 galaxies in the Virgo cluster. For galaxies with optical diameters between 5' and 8', we find that the Point Source Catalog (PSC) typically underestimates the flux density by a factor of 2 at 60 microns and by a factor of 1.5 at 100 microns. Furthermore, flux densities at 12 and 25 microns are reported for 63 galaxies for which only upper limits are reported in the PSC. IR luminosities, colors, and warm dust masses are derived for the 182 galaxies, and these quantities are compared with the interstellar gas masses and optical luminosities of the galaxies. The H_2_ masses reported here have been derived from models for the source distributions and are corrected for source-beam coupling for our previously published CO observations of 124 galaxies. The IR luminosity is found to correlate better with the molecular mass than with the total H I mass or the total H I+ H_2_ mass for galaxies with L_IR_ above 10^10^ L_sun_. This is consistent with the IR emission arising primarily from dust in molecular clouds for galaxies with L_IR_ &gt; 10^10^ L-sun_ since the interstellar medium (ISM) with the inner disk for these galaxies is primarily molecular. The best correlation we find is that between the warm dust masses inferred from IRAS data and the molecular masses derived from CO observations, such that M(H_2_) is proportional to M^1.0^_dust_. The mean value of M(H_2_)/M_dust_ in this sample is 570+/-50; that this value is higher than 100 probably reflects the fact that IRAS is not sensitive to the cold dust emitting beyond 120 microns. From fits to the comparisons of L_IR_ and L_B_ with M(H_2_) and M(H I), we find that L_IR_ is proportional to M(H_2_)^1.0^ and L_B_ is proportional to M(H_2_)^0.72^, with similar exponents for the comparison of L_IR_ and L_B_ with M(H I). We suggest that extinction may lower the blue luminosities in the most luminous galaxies relative to the IR luminosity, since the luminous galaxies have higher H_2_ surface densities and therefore larger dust column densities in their central regions. We demonstrate that the IR luminosity is a measure of the star formation rate for this sample from the correlation of Hα and IR luminosities. If L_IR_ measures the star formation rate, then the ratio L_IR_/M(H_2_) measures the stellar luminosity per unit H_2_ mass, which we call the star formation efficiency. Furthermore, we find a good correlation between L_IR_/M(H_2_) and the global Hα equivalent widths for 26 late-type spiral galaxies, from which we suggest that galaxies that are forming large numbers of high-mass stars are doing so through efficient conversion of gas into stars.

We present results of a study on the Circinus cloud based on {sup 13}CO (J = 1 - 0) data as well as visual to near-infrared (JHK{sub S}) extinction maps, to investigate the distributions of gas and dust around the cloud. The global {sup 13}CO distribution of the Circinus cloud is revealed for the first time, and the total molecular mass of the cloud is estimated to be 2.5 x 10{sup 4} M{sub sun} for the assumed distance 700 pc. Two massive clumps in the cloud, called Circinus-W and Circinus-E, have a mass of {approx}5 x 10{sup 3} M{sub sun}. These clumps are associated with a number of young stellar objects (YSOs) searched for in the literature, indicating that they are the most active star-forming sites in Circinus. All of the extinction maps show good agreement with the {sup 13}CO distribution. We derived the average N({sup 13}CO)/A{sub V} ratio in the Circinus cloud to be 1.25 x 10{sup 15} cm{sup -2} mag{sup -1} by comparing the extinction maps with the {sup 13}CO data. The extinction maps also allowed us to probe into the reddening law over the Circinus cloud. We found that there is a clear change in dust propertiesmore » in the densest regions of Circinus-W and Circinus-E, possibly due to grain growth in the dense cloud interior. Among the YSOs found in the literature, we attempted to infer the ages and masses of the H{alpha} emission-line stars forming in the two clumps, and found that they are likely to be younger than 1 Myr, having a relatively small mass of {approx}<2 M{sub sun} at the zero-age main sequence.« less

The spatial variations in polycyclic aromatic hydrocarbon (PAH) band intensities are generally attributed to variations of the physical conditions in the environment hosting the emitting PAH molecules. However, in recent years, it has been suggested that such variations are caused mainly by extinction. To resolve this question, we have obtained near-infrared (NIR), mid-infrared (MIR) and radio observations of the compact HII region IRAS 12063-6259. We use these data to construct multiple independent extinction maps and to measure the main PAH feature intensities (6.2, 7.7, 8.6 and 11.2 µm). Three extinction maps are derived: the first using the NIR hydrogen lines and case B recombination theory; the second combining the NIR data, radio data and case B recombination; and the third making use of the Spitzer/IRS MIR observations to measure the 9.8 µm silicate absorption feature intensity using the Spoon method and PAHFIT. We conclude that different areas of IRAS 12063-6259 possess markedly different extinction properties, with some regions displaying both silicate absorption and corresponding NIR extinction, and other regions displaying NIR extinction and no corresponding silicate absorption. While such breakdowns of the relationship between the NIR extinction and the silicate absorption strength have been observed in molecular clouds, they have never been observed for HII regions. We then compare the PAH intensity variations in the Spitzer/IRS data after dereddening to those found in the original data. Generally it was found that the PAH band intensity variations persist even after dereddening, implying that extinction is not the main cause of the PAH band intensity variations.