Dust extinction map of the Galactic plane based on the VVV survey data

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.

Context. The census of the globular clusters (GCs) in the Milky Way is still a work in progress. The advent of new deep surveys has made it possible to discover many new star clusters both in the Galactic disk and bulge, but many of these new candidates have not yet been studied in detail, leaving a veil on their true physical nature. Aims. We explore the nature of 19 new GC candidates in the Galactic bulge by analysing their colour–magnitude diagrams (CMDs) in the near-infrared (NIR) using the VISTA Variables in the Via Láctea Survey (VVV) database. We estimate their main astrophysical parameters: reddening and extinction, distance, total luminosity, mean cluster proper motions (PMs), metallicity, and age. Methods. We obtain the cluster catalogues including the likely cluster members by applying a decontamination procedure on the observed CMDs based on the vector PM diagrams from VIRAC2. We adopt NIR reddening maps in order to calculate the reddening and extinction for each cluster, and then estimate the distance moduli and heliocentric distances. Metallicities and ages are evaluated by fitting theoretical stellar isochrones. We also calculate their luminosities in comparison with known Galactic GCs. Results. We estimate a wide reddening range of 0.25 ⩽ E(J − Ks)⩽2.0 mag and extinction 0.11 ⩽ AKs ⩽ 0.86 mag for the sample clusters, as expected in the bulge regions. The range of heliocentric distances is 6.8 ⩽ D ⩽ 11.4 kpc. This allows us to place these clusters between 0.56 and 3.25 kpc from the Galactic centre, assuming R⊙ = 8.2 kpc. Also, their PMs are kinematically similar to the typical motion of the Galactic bulge, apart from VVV-CL160, which shows different PMs. We also derive their metallicities and ages, finding −1.40⩽ [Fe/H] ⩽ 0.0 dex and t ≈ 8 − 13 Gyr respectively. The luminosities are calculated both in Ks- and V-bands, recovering −3.4 ⩽ MV ⩽ −7.5. We also examine the possible RR Lyrae members found in the cluster fields. Conclusions. Based on their positions, kinematics, metallicities, and ages, and comparing our results with the literature, we conclude that nine candidates are real GCs, seven need more observations to be fully confirmed as GCs, and three candidates are discarded as GCs and appear to be younger open clusters.

Dust plays a critical role in the study of the interstellar medium (ISM). Extinction maps derived from optical surveys often fail to capture regions with high column density due to the limited photometric depth in optical wavelengths. To address these limitations, we developed the XPNICER method based on near-infrared (NIR) photometric survey data. This method combines the previously established PNICER and Xpercentile techniques, enabling effective mitigation of foreground contamination and improved handling of complex dust structures in the Galactic plane, which thus can provide more accurate extinction estimates, particularly in highly obscured regions. By applying XPNICER to the Galactic Plane Survey from the UKIRT Infrared Deep Sky Survey, we have generated a series of two-dimensional (2D) dust extinction maps that span roughly ∼1800 deg2 of the Galactic plane (0○ ≲ l ≲ 110○ and 140○ ≲ l ≲ 232○, |b| ≲ 5○). These maps, with spatial resolutions between 30” and 300”, can trace extinction up to AV ∼ 30−40 mag. This new approach offers higher spatial resolution and better detection of high-extinction regions compared to previous large-scale dust-based maps of the Galactic plane, providing an independent and complementary measure of dust column densities.

Context. The discovery of brown dwarfs (BDs) in the solar neighborhood and young star clusters has helped to constraint the low-mass end of the stellar mass function and the initial mass function. We use data of the Vista Variables in the V\'ia L\'actea (VVV), a near-infrared (NIR) multiwavelength (Z Y J H Ks) multi-epoch (Ks) ESO Public Survey mapping the Milky Way bulge and southern Galactic plane to search for nearby BDs. Aims. The ultimate aim of the project is to improve the completeness of the census of nearby stellar and substellar objects towards the Galactic bulge and inner disk regions. Methods. Taking advantage of the homogeneous sample of VVV multi-epoch data, we identified stars with high proper motion (> 0.1"/yr), and then selected low-mass objects using NIR colors. We searched for a possible parallax signature using the all available Ks band epochs. We set some constraints on the month-to-year scale Ks band variability of our candidates, and even searched for possible transiting companions. We obtained NIR spectra to properly classify spectral type and then the physical properties of the final list of candidates. Results. We report the discovery of VVV BD001, a new member of the local volume-limited sample (within 20pc from the sun) with well defined proper motion, distance, and luminosity. The spectral type of this new object is an L5+-1, unusually blue dwarf. The proper motion for this BD is PM(\alpha)=-0.5455+-0.004 "/yr, PM(\delta)=-0.3255+-0.004 "/yr, and it has a parallax of 57+-4 mas which translates into a distance of 17.5 +- 1.1 pc. VVV BD001 shows no evidence of variability (\Delta Ks <0.05mag) over two years, especially constrained on a six month scale during the year 2012.

The new generation of IR surveys are revealing and quantifying Galactic features, providing an improved 3-D interpretation of our own Galaxy. We present an analysis of the global distribution of dust clouds in the bulge using the near-IR photometry of 157 million stars from the VVV Survey. We investigate the color magnitude diagram of the Milky Way bulge which shows a red giant clump of core He burning stars that is split in two color components, with a mean color difference of (Z-Ks)=0.55 magnitudes equivalent to A_V=2.0 magnitudes. We conclude that there is an optically thick dust lane at intermediate latitudes above and below the plane, that runs across several square degrees from l=-10 deg to l=+10 deg. We call this feature the "Great Dark Lane". Although its exact distance is uncertain, it is located in front of the bulge. The evidence for a large-scale great dark lane within the Galactic bulge is important in order to constrain models of the barred Milky Way bulge and to compare our galaxy with external barred galaxies, where these kinds of features are prominent. We discuss two other potential implications of the presence of the Great Dark Lane for microlensing and bulge stellar populations studies.

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.

Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily-reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both 2D and 3D extinction maps, using independent extinction measures based on a large spectroscopic sample of stars towards the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution $H$-band APOGEE spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants towards the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, 2D bulge extinction maps and 3D extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the 2D and 3D extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats.

Recent data from the VVV survey have strengthened evidence for a structural change in the Galactic bulge inwards of |l|<=4 deg. Here we show with an N-body barred galaxy simulation that a boxy bulge formed through the bar and buckling instabilities effortlessly matches measured bulge longitude profiles for red clump stars. The same simulation snapshot was earlier used to clarify the apparent boxy bulge - long bar dichotomy, for the same orientation and scaling. The change in the slope of the model longitude profiles in the inner few degrees is caused by a transition from highly elongated to more nearly axisymmetric isodensity contours in the inner boxy bulge. This transition is confined to a few degrees from the Galactic plane, thus the change of slope is predicted to disappear at higher Galactic latitudes. We also show that the nuclear star count map derived from this simulation snapshot displays a longitudinal asymmetry similar to that observed in the 2MASS data, but is less flattened to the Galactic plane than the 2MASS map. These results support the interpretation that the Galactic bulge originated from disk evolution, and question the evidence advanced from star count data for the existence of a secondary nuclear bar in the Milky Way.

In this study, we derived a galactic extinction map in high ecliptic latitudes for $ \mid{\beta}\mid$$ &amp;gt;$ 30$ ^\circ$ . The dust temperature distribution was derived from the intensities at 100 and 140 $ \mu$ m with a spatial resolution of 5$ '$ . The intensity at 140 $ \mu$ m was derived from the intensities at 60 and 100 $ \mu$ m of the IRAS data, assuming two tight correlations between the intensities at 60, 100, and 140 $ \mu$ m of the COBE/DIRBE data. We found that these correlations can be separated into two correlations by the antenna temperature of the radio continuum at 41 GHz. Because the present study can trace the 5$ '$-scale spatial variation in the dust temperature distribution, it has an advantage over the extinction map derived by Schlegel, Finkbeiner, and Davis (1998, ApJ, 500, 525), who used the DIRBE maps to derive the dust temperature distribution with a spatial resolution of 1$ ^\circ$ . We estimated the accuracy of our method by comparing it with that of Schlegel, Finkbeiner, and Davis (1998, ApJ, 500, 525). The spatial-resolution difference was found to be significant. The area in which the significant difference is confirmed occupies 28% of the region for $ \mid{\beta}\mid$$ &amp;gt;$ 30$ ^\circ$ . With respect to the estimated extragalactic reddening, the present study has an advantage over the extinction map derived by Dobashi (2011, PASJ, 63, 1), which was based on the 2MASS Point Source Catalog, because our extinction map was derived based on far-infrared emission. Dobashi's extinction map exhibits a maximum value that is lower than that of our map in the galactic plane, and a signal-to-noise ratio that is lower than that of our map in high galactic latitudes. This significant difference is confirmed in 81% of the region for $ \mid{\beta}\mid$$ &amp;gt;$ 30$ ^\circ$ . In the areas where the significant differences are confirmed, the extinction should be estimated using our method, rather than the previous methods.

Context. A detailed study of the Galactic bulge stellar population necessarily requires an accurate representation of the interstellar extinction, particularly toward the Galactic plane and center, where severe and differential reddening is expected to vary on sub-arcmin scales. Although recent infrared surveys have addressed this problem by providing extinction maps across the whole Galactic bulge area, dereddened color-magnitude diagrams near the plane and center appear systematically undercorrected, prompting the need for higher resolution. These undercorrections affect any stellar study sensitive to color (e.g., star formation history analyses via color-magnitude diagram fitting), either making them inaccurate or limiting them to small and relatively stable extinction windows where this value is low and better constrained. Aims. This study is aimed at providing a high-resolution (2 arcmin to ∼10 arcsec) color excess map for the VVV bulge area in J − Ks color. Methods. We used the MW-BULGE-PSFPHOT catalogs, sampling ∼300 deg2 across the Galactic bulge (|l| &lt; 10° and −10° &lt; b &lt; 5°) to isolate a sample of red clump and red giant branch stars, for which we calculated the average J − Ks color in a fine spatial grid in (l, b) space. Results. We obtained an E(J − Ks) map spanning the VVV bulge area of roughly 300 deg2, with the equivalent of a resolution between ∼1 arcmin for bulge outskirts (l &lt; 6°) to below 20 arcsec within the central |l| &lt; 1°, and below 10 arcsec for the innermost area (|l| &lt; 1° and |b| &lt; 3°).

We use the Vista Variables in the Via Lactea (VVV) ESO public survey data to measure extinction values in the complete area of the Galactic bulge covered by the survey at high resolution. We derive reddening values using the method described in Paper I. This is based on measuring the mean (J-Ks) color of red clump giants in small subfields of 2' to 6' in the following bulge area: -10.3<b<+5.1 and -10<l<+10.4. To determine the reddening values E(J-Ks) for each region, we measure the RC color and compare it to the (J-Ks) color of RC stars measured in Baade's window, for which we adopt E(B-V)=0.55. This allows us to construct a reddening map sensitive to small scale variations minimizing the problems arising from differential extinction. The significant reddening variations are clearly observed on spatial scales as small as 2'. We find a good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are not reliable for regions within |b| < 6. In the inner regions we compare our results with maps derived from DENIS and Spitzer surveys. While we find good agreement with other studies in the corresponding overlapping regions, our extinction map has better quality due to both higher resolution and a more complete spatial coverage in the Bulge. We investigate the importance of differential reddening and demonstrate the need for high resolution extinction maps for detailed studies of Bulge stellar populations and structure. The extinction variations on scales of up to 2'-6', must be taken into account when analysing the stellar populations of the Bulge.

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.

The spatial variations in PAH band intensities are normally attributed to the physical conditions of the emitting PAHs, 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 H ii region IRAS 12063-6259. We use these data to construct multiple independent extinction maps and also to measure the main PAH features (6.2, 7.7, 8.6 and 11.2 {\mu}m) in the MIR. Three extinction maps are derived: the first using the NIR hydrogen lines and case B recombination theory; the second combining the NIR data with radio data; and the third making use of the Spitzer/IRS MIR observations to measure the 9.8 {\mu}m silicate absorption feature using the Spoon method and PAHFIT (as the depth of this feature can be related to overall extinction). The silicate absorption over the bright, southern component of IRAS 12063-6259 is almost absent while the other methods find significant extinction. While such breakdowns of the relationship between the NIR extinction and the 9.8 {\mu}m absorption 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. It was found that in most cases, the PAH band intensity variations persist even after dereddening, implying that extinction is not the main cause of the PAH band intensity variations.

We analyse 1602 microlensing events found in the VISTA Variables in the Via Lactea (VVV) near-infrared (NIR) survey data. We obtain spatially resolved, efficiency-corrected time-scale distributions across the Galactic bulge (|ℓ| &amp;lt; 10°, |b| &amp;lt; 5°), using a Bayesian hierarchical model. Spatially resolved peaks and means of the time-scale distributions, along with their marginal distributions in strips of longitude and latitude, are in agreement at a 1σ level with predictions based on the Besançon model of the Galaxy. We find that the event time-scales in the central bulge fields (|ℓ| &amp;lt; 5°) are on average shorter than the non-central (|ℓ| &amp;gt; 5°) fields, with the average peak of the lognormal time-scale distribution at 23.6 ± 1.9 d for the central fields and 29.0 ± 3.0 d for the non-central fields. Our ability to probe the structure of the bulge with this sample of NIR microlensing events is limited by the VVV survey’s sparse cadence and relatively small number of detected microlensing events compared to dedicated optical surveys. Looking forward to future surveys, we investigate the capability of the Roman telescope to detect spatially resolved asymmetries in the time-scale distributions. We propose two pairs of Roman fields, centred on (ℓ = ±9, 5°, b = −0.125°) and (ℓ = −5°, b = ±1.375°) as good targets to measure the asymmetry in longitude and latitude, respectively.

We present a deep multicolor NIR survey that we are currently undertaking at the Instituto de Astrofisica de Canarias (Spain). The aim of the survey is obtain deep star counts in selected areas distributed along the Galactic plane to analyze the large scale structure of the Milky Way and the galactic components, in particular the Galactic bar. We are at least one magnitude deeper than in 2MASS and DENIS Galactic surveys, and even more in the inner Galaxy, as we are less limited by source confusion. This provides a better analysis of those regions where the extinction is higher. 1. Near Infrared Galactic surveys Star counts have long been used to examine the stellar contents in the Galaxy (see Paul 1993), where the structural parameters of the various geometric components are still far from being completely known. In the last two decades there has been large advances in this topic with the use of detailed models of stellar galactic distribution along with large area, high sensitivity and multicolor star counts surveys. The near infrared (NIR) surveys (Garzon et al. 1993, Skrutskie et al. 1997, Epchtein et al. 1999) are extremely valuables for the analysis of the Galactic structure because of smaller interstellar extinction compared with the optical bands, in particular in the hidden in plane areas of the inner Galaxy. It is in this zone where we have concentrated our observational effort with the multicolor survey we are now presenting here. 2. Observation Technique Observations are made using CAIN, the facility NIR camera on the 1.5m Telescopio Carlos Sanchez (TCS) (Observatorio del Teide, Tenerife). The sky is being surveyed in series of 20x12 arcmin, divided in a grid of 3x5 frames around the selected central position. The field of view of the CAIN camera is 4.25x4.25 with a plate scale of 1pix, and with overlaps of 20 between consecutive frames. Telescope pointings are mainly distributed along the Galactic plane or not very far from it (|b|≤5), as one of the purposes of the survey is characterizing the stellar content of the Galactic disc. Typical exposure times are 15 sec both in the J and H bands, and 16 sec in the K band. With those integration times, the limiting magnitudes are 17, 16.5 and 15.2 in J,H, and Ks respectively. There is also a serie of observations where the exposure times were increased by a factor 5 with the aim of obtainig deeper photometry in some specific areas of the sky. With this procedure we are more than 1.2 magnitudes deeper than the nominal survey in the outer Galactic disc (l>45). 275 276 Cabrera-Lavers et al. Data have been collected and reduced at the IAC for approximately 600 fields to date, with more than 10 millon of point sources detected. Photometry have been done using standard IRAF DAOPHOT package, with correction from analytic PSFs before extracting final magnitudes. Calibration has been done by using Faint Star standards (FS) from the UKIRT catalog. Table 1. Mean transformation coefficients for the TCS-CAIN survey. Filter zero-point (mag) kλ (mag airmass ) J 21.184±0.035 0.188±0.012 H 21.041±0.033 0.156±0.014 Ks 20.272±0.033 0.168±0.015 Astrometry reduction is done using USNO-A2.0 catalog as reference. From the residuals a general distortion pattern is derived. This vector field of residuals produces a correction function which is then applied to the measured coordinates to improve the position accuracy. Comparison of objects lying in overlapped frames indicates an internal accuracy of 0.03 mag for the photometric zeropoints and 0. 2 for the astrometry. 8 10 12 14 16 18 10 2 10 3 10 4 10 5 10 6