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We present an analytic model of the stellar mass distribution of the Milky Way bar. The model is obtained by fitting a multicomponent parametric density distribution to a made-to-measure N -body model of Portail et al. constructed to match a variety of density and kinematics observational data. The analytic model reproduces in detail the 3D density distribution of the N -body bar including the X-shape. The model and the gravitational potential it generates are available as part of the software package agama for galactic dynamics, and can be readily used for orbit integrations, hydrodynamical simulations, or other applications. [ABSTRACT FROM AUTHOR]

Windows of low extinction in the Milky Way (MW) have been used along the past decades for the study of the Galactic structure and the stellar population across the inner bulge and disc. Here, we report the analysis of another low extinction near-IR window discovered by the VISTA Variables in the Vía Láctea Survey (VVV). VVV WIN 1733−3349 is about half a degree in size and is conveniently located right in the MW plane, at Galactic coordinates (l , b) = (−5.2, −0.3). The mean extinction of VVV WIN 1733−3349 is |$A_{K_{\mathrm{ s}}}$|  = 0.61 ± 0.08 mag, which is much smaller than the extinction in the surrounding area. The excess in the star counts is consistent with the reduced extinction and complemented by studying the distribution of red clump (RC) stars. Thanks to the strategic low-latitude location of VVV WIN 1733−3349, we are able to interpret their RC density fluctuations with the expected overdensities due to the presence of the spiral arms beyond the bulge. In addition, we find a clear excess in the number of microlensing events within the window, which corroborates our interpretation that VVV WIN 1733−3349 is revealing the far side of the MW bulge. [ABSTRACT FROM AUTHOR]

Our Galaxy is known to contain a central boxy/peanut-shaped bulge, yet the importance of a classical, pressure-supported component within the central part of the Milky Way is still being debated. It should be most visible at low metallicity, a regime that has not yet been studied in detail. Using metallicity-sensitive narrow-band photometry, the Pristine Inner Galaxy Survey (PIGS) has collected a large sample of metal-poor (⁠|$\rm {[Fe/H]}\, \lt -1.0$|⁠) stars in the inner Galaxy to address this open question. We use PIGS to trace the metal-poor inner Galaxy kinematics as function of metallicity for the first time. We find that the rotational signal decreases with decreasing [Fe/H] , until it becomes negligible for the most metal-poor stars. Additionally, the velocity dispersion increases with decreasing metallicity for |$-3.0 \lt \rm {[Fe/H]}\, \lt -0.5$|⁠ , with a gradient of −44 ± 4 km s−1 dex−1. These observations may signal a transition between Galactic components of different metallicities and kinematics, a different mapping on to the boxy/peanut-shaped bulge for former disc stars of different metallicities and/or the secular dynamical and gravitational influence of the bar on the pressure-supported component. Our results provide strong constraints on models that attempt to explain the properties of the inner Galaxy. [ABSTRACT FROM AUTHOR]

Red clump stars are commonly used to map the reddening and morphology of the inner regions of the Milky Way. We use the new photometric catalogues of the VISTA Variables in the Vía Láctea survey to achieve twice the spatial resolution of previous reddening maps for Galactic longitudes |$\rm -10^{\circ }\lt l\lt 10^{\circ }$| and latitudes |$\rm -1.5^{\circ }\lt b\lt 1.5^{\circ }$|⁠. We use these de-reddened catalogues to construct the |$\rm K_{s}$| luminosity function around the red clump in the Galactic plane. We show that the secondary peak (fainter than the red clump) detected in these regions does not correspond to the bulge red-giant branch bump alone, as previously interpreted. Instead, this fainter clump corresponds largely to the over-density of red clump stars tracing the spiral arm structure behind the Galactic bar. This result suggests that studies aiming to characterize the bulge red-giant branch bump should avoid low galactic latitudes (⁠|$\rm |b|\lt 2^{\circ }$|⁠), where the background red clump population contributes significant contamination. It furthermore highlights the need to include this structural component in future modelling of the Galactic bar. [ABSTRACT FROM AUTHOR]

We use N-body chemo-dynamic simulations to study the coupling between morphology, kinematics and metallicity of the bar/bulge region of our Galaxy. We make qualitative comparisons of our results with available observations and find very good agreement. We conclude that this region is complex, since it comprises several stellar components with different properties - i.e. a boxy/peanut bulge, thin and thick disc components, and, to lesser extents, a disky pseudobulge, a stellar halo and a small classical bulge - all cohabiting in dynamical equilibrium. Our models show strong links between kinematics and metallicity, or morphology and metallicity, as already suggested by a number of recent observations. We discuss and explain these links. [ABSTRACT FROM AUTHOR]

We have used N-body simulations for the Milky Way to investigate the kinematic and structural properties of the old metal-poor stellar halo in the barred inner region of the Galaxy. We find that the extrapolation of the density distribution for bulge RR Lyrae stars, ρ ~ r-3, approximately matches the number density of RR Lyrae in the nearby stellar halo. We follow the evolution of such a tracer population through the formation and evolution of the bar and box/peanut bulge in the N-body model. We find that its density distribution changes from oblate to triaxial, and that it acquires slow rotation in agreement with recent measurements. The maximum radial velocity is ~15-25 km s-1 at |l| = 10°-30°, and the velocity dispersion is ~120 kms-1. Even though the simulated metal-poor halo in the bulge has a barred shape, just 12 per cent of the orbits follow the bar, and it does not trace the peanut/X structure. With these properties, the RR Lyrae population in the Galactic bulge is consistent with being the inward extension of the Galactic metal-poor stellar halo. [ABSTRACT FROM AUTHOR]

Discovered in 1996 by BeppoSAX during a single type-I burst event, SAX J 2349 was classified as ‘burst-only’ source. Its persistent emission, either in outburst or in quiescence, had never been observed before 2008 October, when SAX J 2349 was observed for the first time in outburst. Based on INTEGRAL observations, we present here the first high-energy emission study (above 10 keV) of a so-called ‘burst-only’. During the outburst, the SAX J 2349 flux decreased from 10 to 4 mCrab in 18–40 keV, while it was found being in a constant low/hard spectral state. The broad-band (0.3–100 keV) averaged spectrum obtained by combining INTEGRAL/IBIS and Swift/XRT data has been fitted with a thermal Comptonization model and an electron temperature ≳24 keV inferred. However, the observed high column density does not allow the detection of the emission from the neutron star surface. Based on the whole set of observations of SAX J 2349, we are able to provide a rough estimate of the duty cycle of the system and the time-averaged mass-accretion rate. We conclude that the low to very low luminosity of SAX J 2349 during outburst may make it a good candidate to harbour a very compact binary system. [ABSTRACT FROM AUTHOR]

We study the two-dimensional surface brightness distribution of the Galactic X-ray background emission outside the central degree around Sgr A* in the 6.7-keV line as measured by the Proportional Counter Array spectrometer of the Rossi X-ray Timing Explorer observatory. The use of the emission line instead of continuum (3–20 keV) radiation and application of time-variability filtering to the long data set allows us to strongly suppress the contamination of the Galactic ridge X-ray emission (GRXE) map by bright point-sources. The surface brightness in the 6.7-keV line demonstrates very good correspondence with the near-infrared surface brightness over the whole Galaxy, supporting the notion that the GRXE consists mostly of integrated emission from weak Galactic X-ray sources. We find compatible linear correlations between near-infrared and 6.7-keV surface brightness for the bulge and disc of the Galaxy. This indicates that the populations of weak X-ray sources making up the GRXE in the disc and in the bulge are not significantly different. [ABSTRACT FROM AUTHOR]