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Context. The bulge represents the best compromise between old and massive Galactic components, and as such its study is a valuable opportunity to understand how the bulk of the Milky Way formed and evolved. In addition, being the only bulge in which we can individually resolve stars in all evolutionary sequences, the properties of its stellar content provide crucial insights into the formation of bulges. Aims. We are providing a detailed and comprehensive census of the Milky Way bulge stellar populations by producing deep and accurate photometric catalogs of the inner ∼300 deg2 of the Galaxy. Methods. We performed DAOPHOT/ALLFRAME point spread function (PSF) fitting photometry of multi-epochs J and Ks images provided by the VISTA Variables in the Vía Láctea (VVV) survey to obtain deep photometric catalogs. Artificial star experiments have been conducted on all images to properly assess the completeness and the accuracy of the photometric measurements. Results. We present a photometric database containing nearly 600 million stars across the bulge area surveyed by the VVV. Through the comparison of derived color-magnitude diagrams of selected fields representative of different levels of extinction and crowding, we show the quality, completeness and depth of the new catalogs. With the exception of the fields located along the plane, this new photometry samples stars down to ∼1–2 mag below the old main sequence turnoff with unprecedented accuracy. To demonstrate the tremendous potential inherent to this new dataset, we give a few examples of possible applications, including (i) star count studies through the dataset completeness map; (ii) surface brightness map; and (iii) cross-correlation with Gaia DR2. Conclusions. The database presented here represents an invaluable collection for the whole community, and we encourage its exploitation. The photometric catalogs including completeness information are publicly available through the ESO Science Archive as part of the MW-BULGE-PSPHOT release. [ABSTRACT FROM AUTHOR]

Context. Recent observational programs are providing a global view of the Milky Way bulge that serves as a template for detailed comparison with models and extragalactic bulges. A number of surveys (VVV, GIBS, GES, ARGOS, BRAVA, APOGEE) are producing comprehensive and detailed extinction, metallicity, kinematics, and stellar density maps of the Galactic bulge with unprecedented accuracy. However, the still missing key ingredient is the distribution of stellar ages across the bulge. Aims. To overcome this limitation, we aim to age-date the stellar population in several bulge fields with the ultimate goal of deriving an age map of the bulge. This paper presents the methodology and the first results obtained for a field along the bulge minor axis, at b = −6°. Methods. We use a new PSF-fitting photometry of the VISTA Variables in the Vía Láctea (VVV) survey data to construct deep color–magnitude diagrams of the bulge stellar population down to ∼2 mag below the main sequence turnoff. To address the contamination by foreground disk stars we adopt a statistical approach by using control-disk fields located at different latitudes (spanning approximately the bulge's range) and longitudes −30° and +20°. We generate synthetic photometric catalogs of complex stellar populations with different age and metallicity distributions, including the observational errors and completeness. The comparison between the color–magnitude diagrams of synthetic and observed disk-decontaminated bulge populations provides constraints on the stellar ages in the observed field. Results. We find the bulk of the bulge stellar population in the observed field along the minor axis to be older than ∼7.5 Gyr. In particular, when the metallicity distribution function spectroscopically derived by GIBS is used, the best fit to the data is obtained with a combination of synthetic populations with ages in between ∼7.5 Gyr and 11 Gyr. However, the fraction of stars younger than ∼10 Gyr strongly depends upon the number of blue straggler stars present in the bulge. Simulations show that the observed color–magnitude diagram of the bulge in the field along the minor axis is incompatible with the presence of a conspicuous population of intermediate-age and young (≲5 Gyr) stars. [ABSTRACT FROM AUTHOR]

Context. Oxygen and zinc in the Galactic bulge are key elements for the understanding of the bulge chemical evolution. Oxygen-to-iron abundance ratios provide a most robust indicator of the star formation rate and chemical evolution of the bulge. Zinc is enhanced in metal-poor stars, behaving as an α-element, and its production may require nucleosynthesis in hypernovae. Most of the neutral gas at high redshift is in damped Lyman-alpha systems (DLAs), where Zn is also observed to behave as an α-element. Aims. The aim of this work is the derivation of the α-element oxygen, together with nitrogen, and the iron-peak element zinc abundances in 417 bulge giants, from moderate resolution (R ~ 22 000) FLAMES-GIRAFFE spectra. For stars in common with a set of UVES spectra with higher resolution (R ~ 45 000), the data are intercompared. The results are compared with literature data and chemodynamical models. Methods. We studied the spectra obtained for a large sample of red giant stars, chosen to be one magnitude above the horizontal branch, using FLAMES-GIRAFFE on the Very Large Telescope. We computed the O abundances using the forbidden [OI] 6300.3 Å and Zn abundances using the Zn I 6362.34 Å lines. Stellar parameters for these stars were established in a previous work from our group. Results. We present oxygen abundances for 358 stars, nitrogen abundances for 403 stars and zinc abundances were derived for 333 stars. Having oxygen abundances for this large sample adds information in particular at the moderate metallicities of −1.6 < [Fe/H] < −0.8. Zn behaves as an α-element, very similarly to O, Si, and Ca. It shows the same trend as a function of metallicity as the α-elements, i.e., a turnover around [Fe/H] ~ − 0.6, and then decreasing with increasing metallicity. The results are compared with chemodynamical evolution models of O and Zn enrichment for a classical bulge. DLAs also show an enhanced zinc-to-iron ratio, suggesting they may be enriched by hypernovae. [ABSTRACT FROM AUTHOR]

Context. Multiple stellar populations of different ages and metallicities reside in the Galactic bulge that trace its structure and provide clues to its formation and evolution. Aims. We present the near-infrared observations of population II Cepheids in the Galactic bulge from VISTA Variables in the Vía Láctea (VVV) survey. The JHKs photometry together with optical data from Optical Gravitational Lensing Experiment (OGLE) survey provide an independent estimate of the distance to the Galactic centre. The old, metal-poor and low-mass population II Cepheids are also investigated as useful tracers for the structure of the Galactic bulge. Methods. We identify 340 population II Cepheids in the VVV survey Galactic bulge catalogue based on their match with the OGLE-III Catalogue. The single-epoch JH and multi-epoch Ks observations complement the accurate periods and optical (VI) mean-magnitudes from OGLE. The sample consisting of BL Herculis and W Virginis subtypes is used to derive period-luminosity relations after correcting mean-magnitudes for the extinction. Our Ks-band period-luminosity relation, Ks = −2.189(0.056) [log (P)−1] + 11.187(0.032), is consistent with published work for BL Herculis and W Virginis variables in the Large Magellanic Cloud. Results. We present a combined OGLE-III and VVV catalogue with periods, classification, mean magnitudes, and extinction for 264 Galactic bulge population II Cepheids that have good-quality Ks-band light curves. The absolute magnitudes for population II Cepheids and RR Lyraes calibrated using Gaia and Hubble Space Telescope parallaxes, together with calibrated magnitudes for Large Magellanic Cloud population II Cepheids, are used to obtain a distance to the Galactic centre, R0 = 8.34 ± 0.03(stat.) ± 0.41(syst.), which changes by + 0.05-0.25 with different extinction laws. While noting the limitation of small number statistics, we find that the present sample of population II Cepheids in the Galactic bulge shows a nearly spheroidal spatial distribution, similar to metal-poor RR Lyrae variables. We do not find evidence of the inclined bar as traced by the metal-rich red-clump stars. Conclusions. Population II Cepheid and RR Lyrae variables follow similar period-luminosity relations and trace the same metal-poor old population in the Galactic bulge. The number density for population II Cepheids is more limited as compared to abundant RR Lyraes but they are bright and exhibit a wide range in period that provides a robust period-luminosity relation for an accurate estimate of the distance to the Galactic centre. [ABSTRACT FROM AUTHOR]

Context: As observational evidence steadily accumulates, the nature of the Galactic bulge has proven to be rather complex: the structural, kinematic, and chemical analyses often lead to contradictory conclusions. The nature of the metal-rich bulge - and especially of the metal-poor bulge - and their relation with other Galactic components, still need to be firmly defined on the basis of statistically significant high-quality data samples. Aims: We used the fourth internal data release of the Gaia-ESO survey to characterize the bulge metallicity distribution function (MDF), magnesium abundance, spatial distribution, and correlation of these properties with kinematics. Moreover, the homogeneous sampling of the different Galactic populations provided by the Gaia-ESO survey allowed us to perform a comparison between the bulge, thin disk, and thick disk sequences in the [Mg/Fe] vs. [Fe/H] plane in order to constrain the extent of their eventual chemical similarities. Methods: We obtained spectroscopic data for ~2500 red clump stars in 11 bulge fields, sampling the area -10° ≤ l ≤ + 8° and -10° ≤ b ≤ -4° from the fourth internal data release of the Gaia-ESO survey. A sample of ~6300 disk stars was also selected for comparison. Spectrophotometric distances computed via isochrone fitting allowed us to define a sample of stars likely located in the bulge region. Results: From a Gaussian mixture models (GMM) analysis, the bulge MDF is confirmed to be bimodal across the whole sampled area. The relative ratio between the two modes of the MDF changes as a function of b, with metal-poor stars dominating at high latitudes. The metal-rich stars exhibit bar-like kinematics and display a bimodality in their magnitude distribution, a feature which is tightly associated with the X-shape bulge. They overlap with the metal-rich end of the thin disk sequence in the [Mg/Fe] vs. [Fe/H] plane. On the other hand, metal-poor bulge stars have a more isotropic hot kinematics and do not participate in the X-shape bulge. Their Mg enhancement level and general shape in the [Mg/Fe] vs. [Fe/H] plane is comparable to that of the thick disk sequence. The position at which [Mg/Fe] starts to decrease with [Fe/H], called the "knee", is observed in the metal-poor bulge at [Fe/H] knee = -0.37 ± 0.09, being 0.06 dex higher than that of the thick disk. Although this difference is inside the error bars, it suggest a higher star formation rate (SFR) for the bulge than for the thick disk. We estimate an upper limit for this difference of Δ [Fe/H] knee = 0.24 dex. Finally, we present a chemical evolution model that suitably fits the whole bulge sequence by assuming a fast (<1 Gyr) intense burst of stellar formation that takes place at early epochs. Conclusions: We associate metal-rich stars with the bar boxy/peanut bulge formed as the product of secular evolution of the early thin disk. On the other hand, the metal-poor subpopulation might be the product of an early prompt dissipative collapse dominated by massive stars. Nevertheless, our results do not allow us to firmly rule out the possibility that these stars come from the secular evolution of the early thick disk. This is the first time that an analysis of the bulge MDF and α-abundances has been performed in a large area on the basis of a homogeneous, fully spectroscopic analysis of high-resolution, high S/N data. [ABSTRACT FROM AUTHOR]

Context. Our view of the structure of the Milky Way and, in particular, its bulge is obscured by the intervening stars, dust, and gas in the disc. While great progress in understanding the bulge has been achieved with past and ongoing observations, the comparison of its global chemodynamical properties with respect to those of bulges seen in external galaxies has yet to be accomplished. Aims. We used the Multi Unit Spectroscopic Explorer (MUSE) instrument installed on the Very Large Telescope (VLT) to obtain spectral and imaging coverage of NGC 4710. The wide area and excellent sampling of the MUSE integral field spectrograph allows us to investigate the dynamical properties of the X-shaped bulge of NGC 4710 and compare it with the properties of the X-shaped bulge of the Milky Way. Methods. We measured the radial velocities, velocity dispersion, and stellar populations using a penalised pixel full spectral fitting technique adopting simple stellar populations models, on a 1' ? 1' area centred on the bulge of NGC 4710.We constructed the velocity maps of the bulge of NGC 4710 and investigated the presence of vertical metallicity gradients. These properties were compared to those of the Milky Way bulge and to a simulated galaxy with a box y-peanut bulge. Results. We find the line-of-sight velocity maps and 1D rotation curves of the bulge of NGC 4710 to be remarkably similar to those of the MilkyWay bulge. Some specific differences that were identified are in good agreement with the expectations from variations in the bar orientation angle. The bulge of NGC 4710 has a boxy-peanut morphology with a pronounced X-shape, showing no indication of any additional spheroidally distributed bulge population, in which we measure a vertical metallicity gradient of 0.35 dex/kpc. Conclusions. The general properties of NGC 4710 are very similar to those observed in the Milky Way bulge. However, it has been suggested that the Milky Way bulge has an additional component that is comprised of the oldest, most metal-poor stars, which is not part of the boxy-peanut bulge structure. Such a population is not observed in NGC 4710, but could be hidden in the integrated light we observed. [ABSTRACT FROM AUTHOR]

Aims. We present a new calibration of the calcium II triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and is in general especially well suited for solar and supersolar metallicity giants, which are typical of external massive galaxies. Methods. About 150 bulge K giants were observed with the GIRAFFE spectrograph at the VLT with a resolution of R - 20 000 and at R ∼ 6000. In the first case, the spectra allowed us to directly determine the Fe abundances from several unblended Fe lines, deriving what we call here high-resolution [Fe/H] measurements. The low-resolution spectra allowed us to measure equivalent widths of the two strongest lines of the near-infrared calcium II triplet at 8542 and 8662 Å. Results. By comparing the two measurements, we derived a relation between calcium equivalent widths and [Fe/H] that is linear over the metallicity range probed here, -1<[Fe/H]<+0.7. By adding a small second-order correction based on literature globular cluster data, we derived the unique calibration equation [Fe/H]CaT = -3.150 + 0.432W' + 0.006W'2, with an rms dispersion of 0.197 dex, valid across the whole metallicity range -2.3 < [Fe/H] < +0.7. [ABSTRACT FROM AUTHOR]

The new generation of IR surveys are revealing and quantifying Galactic features that provide an improved 3D 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 into two color components, with a mean color difference of (Z - Ks) = 0.55 mag that is equivalent to AV = 2.0 mag. We conclude that there is an optically thick dust lane at intermediate latitudes above and below the plane that stretches across several square degrees from l = -10° to l = +10°.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 for constraining models of the barred Milky Way bulge and for comparing our galaxy with external barred galaxies in which these types of features are prominent. We discuss two other potential implications of the great dark lane for microlensing and bulge stellar populations studies. [ABSTRACT FROM AUTHOR]

Aims. Observational studies of the MilkyWay bulge are providing increasing evidence of its complex chemo-dynamical patterns and morphology. Our intent is to use the iDR1 Gaia-ESO Survey (GES) data set to provide new constraints on the metallicity and kinematic trends of the Galactic bulge, exploring the viability of the currently proposed formation scenarios. Methods. We analyzed the stellar parameters and radial velocities of ~1200 stars in five bulge fields wich are located in the region -10° < l < 7° and -10° < b < -4°.We use VISTA Variables in the Via Lactea (VVV) photometry to verify the internal consistency of the atmospheric parameters recommended by the consortium. As a by-product, we obtained reddening values using a semi-empirical Teff -color calibration.We constructed the metallicity distribution functions and combined them with photometric and radial velocity data to analyze the properties of the stellar populations in the observed fields. Results. From a Gaussian decomposition of the metallicity distribution functions, we unveil a clear bimodality in all fields, with the relative size of components depending of the specific position on the sky. In agreement with some previous studies, we find a mild gradient along the minor axis (-0.05 dex/deg between b = -6° and b = -10°) that arises from the varying proportion of metal-rich and metal-poor components. The number of metal-rich stars fades in favor of the metal-poor stars with increasing b. The K-magnitude distribution of the metal-rich population splits into two peaks for two of the analyzed fields that intersects the near and far branches of the X-shaped bulge structure. In addition, two lateral fields at (l; b) = (7; -9) and (l; b) = (-10; -8) present contrasting characteristics. In the former, the metallicity distribution is dominated by metal-rich stars, while in the latter it presents a mix of a metal-poor population and and a metal-intermediate one, of nearly equal sizes. Finally, we find systematic di erences in the velocity dispersion between the metal-rich and the metal-poor components of each field. Conclusions. The iDR1 bulge data show chemo-dynamical distributions that are consistent with varying proportions of stars belonging to (i) a metal-rich boxy/peanut X-shaped component, with bar-like kinematics; and (ii) a metal-poor more extended rotating structure with a higher velocity dispersion that dominates far from the Galactic plane. These first GES data already allow studying the detailed spatial dependence of the Galactic bulge populations, thanks to the analysis of individual fields with relatively high statistics. [ABSTRACT FROM AUTHOR]

Context. The presence of a bar affects the distribution and dynamics of a stellar disk at all scales, from a fraction of a kpc in the inner central region to tens of kpc at the disk's edge. The quantitative study of the disk response to a bar can be hampered by the presence of dust, which is common in late type spirals. Aims. We want to quantify the structures in the stellar disk of the barred Sc galaxy NGC 253 located in the Sculptor group, at 3.47 Mpc distance. Methods. We use J and Ks band images acquired with the VISTA telescope as part of the Science Verification. The wide field of view and the high angular resolution of this survey facility allow the mapping of the large and small scale structure of the stellar disk in NGC 253. We use unsharp masking and two dimensional modelling of the smooth light distribution in the disk to identify and measure the sub-structures induced by the bar in the stellar disk of NGC 253. We build azimuthally-averaged profiles in the J and Ks bands to measure the radial surface brightness profile of the central bulge, bar and disk. Results. Moving outward from the galaxy center, we find a nuclear ring within the bright 1 kpc diameter nucleus, then a bar, a ring with 2.9 kpc radius, and spiral arms in the outer disk. From the Ks image we obtain a new measure of the de-projected length of the bar of 2.5 kpc. The bar's strength, as derived from the curvature of the dust lanes in the J-Ks image, is typical of weak bars with Δα = 25 degree/kpc. From the de-projected length of the bar, we establish the co-rotation radius (RCR = 3 kpc) and bar pattern speed (Ωb = 61.3 kms-1 kpc-1), which provides the connection between the high frequency structures in the disk and the orbital resonances induced by the bar. The nuclear ring is located at the Inner Lindblad resonance. The second ring (at 2.9 kpc) does not have a resonant origin, but it could be a merger remnant or a transient structure formed during an intermediate stage of the bar formation. The inferred bar pattern speed places the Outer Lindblad resonance within the optical disk at 4.9 kpc, in the same radial range as the peak in the HI surface density. The disk of NGC 253 has a down-bending profile with a break at R ~ 9.3 kpc, which corresponds to about 3 times the scale length of the inner disk. We discuss the evidence for a threshold in star formation efficiency as a possible explanation for the steep gradient in the surface brightness profile at large radii. Conclusions. The near-infrared photometry unveils the dynamical response of the NGC 253 stellar disk to its central bar. The formation of the bar may be related to the merger event that determined the truncation of stars and gas at large radii and the perturbation of the disk's outer edge. [ABSTRACT FROM AUTHOR]

Context. Three dimensional interstellar extinction maps provide a powerful tool for stellar population analysis. However, until now, these 3D maps were rather limited by sensitivity and spatial resolution. Aims. We use data from the VISTA Variables in the Via Lactea survey together with the Besançon stellar population synthesis model of the Galaxy to determine interstellar extinction as a function of distance in the Galactic bulge covering −10°

Context. The Galactic bulge is a massive, old component of the Milky Way. It is known to host a bar, and it has recently been demonstrated to have a pronounced boxy/peanut structure in its outer region. Several independent studies suggest the presence of more than one stellar populations in the bulge, with different origins and a relative fraction changing across the bulge area. Aims. This is the first of a series of papers presenting the results of the Giraffe Inner Bulge Survey, carried out at the ESO-VLT with the multifibre spectrograph FLAMES. Spectra of ~5000 red clump giants in 24 bulge fields have been obtained at resolution R = 6500, in the infrared Calcium triplet wavelength region at ~8500 Å. They are used to derive radial velocities and metallicities, based on new calibration specifically devised for this project. Radial velocities for another ~1200 bulge red clump giants, obtained from similar archive data, have been added to the sample. Higher resolution spectra have been obtained for ~450 additional stars at latitude b = -3.5, with the aim of investigating chemical abundance patterns variations with longitude, across the inner bulge. In total we present here radial velocities for 6392 red clump stars. Methods. We present here the target selection criteria, observing strategy and the catalog with radial velocity measurements for all the target stars. Results. We derive a radial velocity, and velocity dispersion map of the Milky Way bulge, useful to be compared with similar maps of external bulges, and to infer the expected velocities and dispersion at any line of sight. The K-type giants kinematics is consistent with the cylindrical rotation pattern of M-giants from the BRAVA survey. Our sample enables to extend this result to latitude b = -2, closer to the Galactic plane than probed by previous surveys. Finally, we find strong evidence for a velocity dispersion peak at (0, -1) and (0, -2), possibily indicative of a high density peak in the central ~250 pc of the bulge. [ABSTRACT FROM AUTHOR]

Context. Outskirts of large galaxies contain important information about galaxy formation and assembly. Resolved star count studies can probe the extremely low surface brightness of the outer halos. Aims. NGC 253 is a nearly edge-on disk galaxy in the Sculptor group, of which we resolved the halo stars from ground-based images, with the aim of studying its stellar population content, the structure and the overall extent of the halo. Methods. We use Z and J-band images from the VIRCAM camera mounted on the VISTA telescope to construct the spatially resolved J vs. Z-J color-magnitude diagrams (CMDs). The very deep photometry and the wide area covered allow us to trace the red giant branch (RGB) and asymptotic giant branch (AGB) stars that belong to the halo of NGC 253 out to 50 kpc along the galaxy's minor axis. Results. We confirm the existence of an extra-planar stellar component of the disk, with a very prominent southern shelf and a symmetrical feature on the north side. The only additional visible substructure is an overdensity in the north-west part of the halo ~28 kpc distant from the plane and extending over 20 kpc parallel with the disk of the galaxy. Our data are not deep enough to distinguish its stellar population from that of the surrounding halo, but the excess of stars above the smooth halo traces the mass of the parent population of ~7.5×106 M☉. From stellar counts, we measure the transition from the disk to the halo at a radial distance of about 25 kpc with a clear break in the number density profile. The isodensity contours show that the inner halo is a flattened structure that blends with a more extended, diffuse, rounder outer halo. Such external structure can be traced to the very edge of our image out to 50 kpc from the disk plane. The number density profile of the stars in the stellar halo follows a power law with index -1.6, as a function of radius. The CMD shows a very homogeneous stellar population across the field. By comparing isochrones with the CMD, we conclude that the RGB stars are ~8 Gyr old or more, while the AGB stars trace a population of about 2 × 108 M☉ formed from ~0.5 to a few Gyr ago. Surprisingly, part of the latter population appears scattered over a wide area. We explore several ideas to explain the origin of this relatively young component in the inner halo of NGC 253. [ABSTRACT FROM AUTHOR]

Aims. In some scenarios for the formation of the Milky Way bulge, the stellar population at the edges of the boxy bulge may be younger than those on the minor axis or close to the Galactic center. So far the only bulge region where deep color-magnitude diagrams have been obtained is indeed along the minor axis. To overcome this limitation, we aim to age-date the bulge stellar populations far away from the bulge minor axis. Methods. Color-magnitude diagrams and luminosity functions have been obtained from deep near-IR VLT/HAWK-I images taken at the two Southern corners of the boxy bulge, i.e., near the opposite edges of the Galactic bar. The foreground disk contamination has been statistically removed using a pure disk field observed with the same instrument and located approximately at similar Galactic latitudes of the two bulge fields and ~30° in longitude away from the Galactic center. For each bulge field, mean reddening and distance are determined using the position of red clump stars, and the metallicity distribution is derived photometrically using the color distribution of stars in the upper red giant branch. Results. The resulting metallicity distribution function of both fields peaks around [Fe/H] ∼ -0.1 dex, with the bulk of the stellar population having a metallicity within the range: -1 dex ≲ [Fe/H] ≲ +0.4 dex, quite similar to that of other inner bulge fields. As for the previously explored inner fields, the color-magnitude diagrams of the two bar fields are consistent with their stellar population being older than ~10 Gyr, with no obvious evidence of younger population. Conclusions. The stellar population of the corners of the boxy bulge appears to be coeval with those within the innermost ~4° from the Galactic center. [ABSTRACT FROM AUTHOR]

Aims. We investigate the large-scale metallicity distribution in the Galactic bulge using large spatial coverage to constrain the bulge formation scenario. Methods. We use the VISTA variables in the Via Lactea (VVV) survey data and 2MASS photometry, which cover 320 sqdeg of the Galactic bulge, to derive photometric metallicities by interpolating the (J − Ks)0 colors of individual red giant branch stars based on a set of globular cluster ridge lines. We then use this information to construct the first global metallicity map of the bulge with a resolution of 30′ × 45′. Results. The metallicity map of the bulge revealed a clear vertical metallicity gradient of ~0.04 dex/deg (~0.28 dex/kpc), with metal-rich stars ([Fe/H] ~ 0) dominating the inner bulge in regions closer to the Galactic plane (∣b∣ < 5). At larger scale heights, the mean metallicity of the bulge population becomes significantly more metal poor. Conclusions. This fits in the scenario of a boxy bulge originating from the vertical instability of the Galactic bar, formed early via secular evolution of a two-component stellar disk. Older metal-poor stars dominate at higher scale heights due to the non-mixed orbits of originally hotter thick disk stars. [ABSTRACT FROM AUTHOR]

Context. Studies of the properties of the inner Galactic bulge strongly depend on the assumptions made about interstellar extinction. Most of the extinction maps available in the literature lack the information about the distance. Aims. We combine observations with the Besançon model of the Galaxy to investigate the variations of extinction along different lines of sight toward the inner Galactic bulge as a function of distance. In addition we study the variations in the extinction law in the bulge. Methods. We constructed color-magnitude diagrams with the following sets of colors: H-Ks and J-Ks from the VVV catalog and Ks-[3.6], Ks-[4.5], Ks-[5.8] and Ks-[8.0] from GLIMPSE-II catalog matched with 2MASS. Using the newly derived temperature-color relation for M giants that match the observed color-magnitude diagrams better we then used the distance-color relations to derive the extinction as a function of distance. The observed colors were shifted to match the intrinsic colors in the Besançon model as a function of distance, thereby iteratively creating an extinction map with three dimensions: two spatial and one distance dimension along each line of sight toward the bulge. Results. Color excess maps are presented at a resolution of 15' × 15' for six different combinations of colors in distance bins of 1 kpc. The high resolution and depth of the photometry allows us to derive extinction maps to 10 kpc distance and up to 35 mag 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. [ABSTRACT FROM AUTHOR]

Context. The Milky Way (MW) bulge is a fundamental Galactic component for understanding the formation and evolution of galaxies, in particular our own. The ESO Public Survey VISTA Variables in the Via Láctea is a deep near-JR survey mapping the Galactic bulge and southern plane. Particularly for the bulge area, VVV is covering ∼315 deg2. Data taken during 2010 and 2011 covered the entire bulge area in the JHKs bands. Aims. We used VVV data for the whole bulge area as a single and homogeneous data set to build for the first time a single colour-magnitude diagram (CMD) for the entire Galactic bulge. Methods. Photometric data in the JHKs bands were combined to produce a single and huge data set containing 173 150 467 sources in the three bands, for the ∼315 deg2 covered by VVV in the bulge. Selecting only the data points flagged as stellar, the total number of sources is 84095 284. Results. We built the largest colour-magnitude diagrams published up to date, containing 173.1+ million sources for all data points, and more than 84.0 million sources accounting for the stellar sources only. The CMD has a complex shape, mostly owing to the complexity of the stellar population and the effects of extinction and reddening towards the Galactic centre. The red clump (RC) giants are seen double in magnitude at b ∼ -8°-10°, while in the inner part (b ∼ -3°) they appear to be spreading in colour, or even splitting into a secondary peak. Stellar population models show the predominance of main-sequence and giant stars. The analysis of the outermost bulge area reveals a well-defined sequence of late K and M dwarfs, seen at (J - Ks) ∼ 0.7-0.9 mag and Ks ≳ 14 mag. Conclusions. The interpretation of the CMD yields important information about the MW bulge, showing the fingerprint of its structure and content. We report a well-defined red dwarf sequence in the outermost bulge, which is important for the planetary transit searches of VVV. The double RC in magnitude seen in the outer bulge is the signature of the X-shaped MW bulge, while the spreading of the RC in colour, and even its splitting into a secondary peak, are caused by reddening effects. The region around the Galactic centre is harder to interpret because it is strongly affected by reddening and extinction. [ABSTRACT FROM AUTHOR]

Context. The Milky Way bulge is the nearest galactic bulge and the most readily accessible laboratory for studies of stellar populations in spheroids based on individual stellar abundances and kinematics. These studies are challenged by the strongly variable and often large extinction on a small spatial scale. Aims. 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. Methods. 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' × 2' to 6' × 6' in the following bulge area: -10.3° ≤ b ≤ +5.1° and -10.0° ≤ 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. Results. The significant reddening variations are clearly observed on spatial scales as small as 2'. We find good agreement between our extinction measurements and Schlegel maps in the outer bulge, but, as already stated in the literature the Schlegel maps are unreliable 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 is of higher quality owing to both its higher resolution and a more complete spatial coverage of the bulge. We investigate the importance of differential reddening and demonstrate the need for high spatial resolution extinction maps for detailed studies of bulge stellar populations and structure. Conclusions. We present the first extinction map covering uniformly ∼ 315 sq. deg. of the Milky Way bulge at high spatial resolution. We consider a 30 arcmin window at a latitude of b = -4°, which corresponds to a frequently studied low extinction window, the so-called Baade's Window, and find that its AKs values can vary by up to 0.1 mag. Larger extinction variations are observed at lower Galactic latitudes. The extinction variations on scales of up to 2'-6' must be taken into account when analyzing the stellar populations of the Galactic bulge. [ABSTRACT FROM AUTHOR]

We present the first chemical analysis of stars on the double subgiant branch (SGB) of the globular cluster NGC 1851. We obtained 48 Magellan IMACS spectra of subgiants and fainter stars covering the spectral region between 3650-6750 Å to derive C and N abundances from the spectral features at 4300 Å (G-band) and at ∼3883 Å (CN).We added to our sample ∼45 unvevolved stars previously observed with FORS2 at the VLT. These two datasets were homogeneously reduced and analyzed. We derived abundances of C and N for a total of 64 stars and found considerable star-to-star variations in both [C/H] and [N/H] at all luminosities extending to the red giant branch (RGB) base (V ∼ 18.9). These abundances appear to be strongly anticorrelated, as would be expected from the CN-cycle enrichment, but we did not detect any bimodality in the C or N content. We used Hubble space telescope (HST) and ground-based photometry to select two groups of faint- and bright-SGB stars from the visual and Strömgren color-magnitude diagrams. Significant variations in the carbon and nitrogen abundances are present among stars of each group, which indicates that each SGB hosts multiple subgenerations of stars. Bright- and faint-SGB stars differ in the total C+N content, where the fainter SGB have about 2.5 times the C+N content of the brighter ones. Coupling our results with literature photometric data and abundance determinations from highresolution studies, we identify the fainter SGB with the red-RGB population, which also should be richer on average in Ba and other s-process elements, as well as in Na and N, when compared to brighter SGB and the blue-RGB population. [ABSTRACT FROM AUTHOR]

Context. The ESO public survey VISTA variables in the Vía Láctea (VVV) started in 2010. VVV targets 562 sq. deg in the Galactic bulge and an adjacent plane region and is expected to run for about five years. Aims. We describe the progress of the survey observations in the first observing season, the observing strategy, and quality of the data obtained. Methods. The observations are carried out on the 4-m VISTA telescope in the ZYJHKs filters. In addition to the multi-band imaging the variability monitoring campaign in the Ks filter has started. Data reduction is carried out using the pipeline at the Cambridge Astronomical Survey Unit. The photometric and astrometric calibration is performed via the numerous 2MASS sources observed in each pointing. Results. The first data release contains the aperture photometry and astrometric catalogues for 348 individual pointings in the ZYJHKs filters taken in the 2010 observing season. The typical image quality is ∼0.''9-1.''0. The stringent photometric and image quality requirements of the survey are satisfied in 100% of the JHKs images in the disk area and 90% of the JHKs images in the bulge area. The completeness in the Z and Y images is 84% in the disk, and 40% in the bulge. The first season catalogues contain 1.28 ×108 stellar sources in the bulge and 1.68 ×108 in the disk area detected in at least one of the photometric bands. The combined, multi-band catalogues contain more than 1.63 ×108 stellar sources. About 10% of these are double detections because of overlapping adjacent pointings. These overlapping multiple detections are used to characterise the quality of the data. The images in the JHKs bands extend typically ∼4 mag deeper than 2MASS. The magnitude limit and photometric quality depend strongly on crowding in the inner Galactic regions. The astrometry for Ks = 15-18 mag has rms ∼ 35-175 mas. Conclusions. The VVV Survey data products offer a unique dataset to map the stellar populations in the Galactic bulge and the adjacent plane and provide an exciting new tool for the study of the structure, content, and star-formation history of our Galaxy, as well as for investigations of the newly discovered star clusters, star-forming regions in the disk, high proper motion stars, asteroids, planetary nebulae, and other interesting objects [ABSTRACT FROM AUTHOR]