Search

We use low-amplitude long period variable (LA-LPV) candidates in Gaia DR3 to trace the kinematics and dynamics of the Milky Way bar. LA-LPVs, like other LPVs, are intrinsically bright and follow a tight period–luminosity relation, but unlike e.g. Mira variables, their radial velocity measurements are reliable due to their smaller pulsation amplitudes. We supplement the Gaia astrometric and radial velocity measurements with distance moduli assigned using a period–luminosity relation to acquire full 6D phase space information. The assigned distances are validated by comparing to geometric distances and StarHorse distances, which shows biases less than |$\sim 5~{{\rm per\ cent}}$|⁠. Our sample provides an unprecedented panoramic picture of the inner Galaxy with minimal selection effects. We map the kinematics of the inner Milky Way and find a significant kinematic signature corresponding to the Galactic bar. We measure the pattern speed of the Galactic bar using the continuity equation and find |$\Omega _{\rm b}=34.1\pm 2.4$|  km s |$^{-1}$|  kpc |$^{-1}$|⁠. We develop a simple robust and potential-independent method to measure the dynamical length of the bar using only kinematics and find |$R_{\rm b}\sim 4.0$|  kpc. We validate both measurements using N -body simulations. Assuming knowledge of the gravitational potential of the inner Milky Way, we analyse the orbital structure of the Galactic bar using orbital frequency ratios. The |$x_1$| orbits are the dominant bar-supporting orbital family in our sample. Amongst the selected bar stars, the |$x_1 v_1$| or 'banana' orbits constitute a larger fraction (⁠|$\sim 15~{{\rm per\ cent}}$|⁠) than other orbital families in the bar, implying that they are the dominant family contributing to the Galactic X-shape, although contributions from other orbital families are also present. [ABSTRACT FROM AUTHOR]

Context. The metallicity distribution function (MDF) of the Galactic bulge is characterized by a multi-peak shape, with a metal-poor peak centered at [Fe/H] ∼ −0.3 dex and a metal-rich peak centered at [Fe/H] ∼ +0.3 dex. The bimodality of the MDF is also reflected in the [α/Fe] versus [Fe/H] abundance ratios, suggesting the presence of different stellar populations in the bulge. Aims. In this work we aim to reproduce the observed MDF of the Galactic bulge by testing a scenario in which the metal-poor component of the bulge is formed by stars formed in situ, during a strong burst of star formation, while the metal-rich population is formed by stars created in situ during a second burst of star formation and/or stars accreted from the innermost part of the Galactic disk as an effect of a growing bar. Methods. We adopted a chemical evolution model that is able to follow the evolution of several chemical species with detailed nucleosynthesis prescriptions. In particular, because of the importance of the production of Fe in constraining the MDF, close attention is paid to the production of this element in both Type Ia supernovae and massive stars. In particular, we included yields from rotating massive stars with different rotational velocity prescriptions. Our model also takes the infall and outflow of gas into account, as well as the effect of stellar migration. Results are compared to ∼13 000 stars from the SDSS/APOGEE survey that belong to the region located at a Galactocentric distance RGC ≤ 3.5 kpc. Results. We successfully reproduce the observed double-peak shape of the bulge MDF as well as the abundance trends of the α elements relative to Fe by assuming both (i) a multi-burst star formation history with a quenching of the first burst of ∼102 Myr and (ii) migration of stars from the innermost part of the Milky Way disk, as an effect of a growing bar. According to our results, the fraction of the stellar mass of the bulge-bar that belongs to the inner disk is ∼40%. In terms of the nucleosynthesis, we conclude that models that assume either no rotation for massive stars or a distribution of rotational velocities that favors slow rotation at high metallicities best reproduce the observed MDF as well as the [α/Fe] and the [Ce/Fe] versus [Fe/H] abundance patterns. [ABSTRACT FROM AUTHOR]

Context. The abundances of the α-elements are key for understanding the early chemical enrichment of the Galactic bulge. The elements of interest present lines in different wavelength regions, and some of them show lines only in part of the spectra. In the present work, the CNO trio, the a-elements Mg, Si, Ca, and Ti, and odd-Z Na and Al are examined as measured from optical and H-band lines. Aims. The aim of this work is to carry out a detailed comparison of stellar parameters and abundances derived in the optical and near-infrared (H-band). We also inspect the best available lines for a list of bulge stars previously analyzed by the Apache Point Observatory Galactic Evolution Experiment (APOGEE) team in the H-band and by our group in the optical. This work is mainly of interest to spectroscopists. Methods. In the present work, we compared the stellar parameters and abundance results derived from APOGEE H-band spectra with optical analyses based on Ultraviolet and Visual Echelle Spectrograph at the Very Large Telescope (VLT/UVES) data for eight bulge stars. Results. We point out the most suitable wavelength region for each of the studied elements, and highlight difficulties in the derivation of stellar parameters both in the optical and H-band. The near-infrared will allow observations of a large number of stars in the near future given new instruments soon to be available. The identification of spectral lines in this spectral region and the investigation of their reliability are ongoing efforts worldwide. New instruments will also allow simultaneous observation of H-band and optical. [ABSTRACT FROM AUTHOR]

Context. A large number of globular clusters in the Milky Way have been studied in recent years, especially in hidden regions such as those of the Galactic bulge. Aims. The main goal of this work is to understand what we can learn if we include these new objects into the Milky Way globular cluster (GC) system that we know today. We compiled a catalog of 37 recently discovered globular clusters. Most of them are located in the Galactic bulge, but we also included some of the GCs for comparison. Methods. We used a range of distributions for investigating the Galactic GC system based on the metallicity, luminosity function, and age. We considered three samples. We first treated the new GC sample separately from the known and well characterized GCs. Consequently, we merged these two samples, thereby upgrading the Milky Way GC system. Furthermore, we performed a comparison between our clusters sample and the field star population. Results. We found a double-peaked distribution for the luminosity function, which shows an elongated faint end tail. Considering the "merged" sample, the luminosity function peaks at MVup = −7.00 ± 1.3 M V up = − 7.00 ± 1.3 $ M_{V}^{\mathrm{up}} = -7.00 \pm 1.3 $ mag and at MVup = −4.1 ± 0.48 M V up = − 4.1 ± 0.48 $ M_{V}^{\mathrm{up}} = -4.1 \pm 0.48 $ mag. The metallicity distributions also display a bimodality trend. In this case, we compare our new sample compilation with previously published ones, finding that the distributions are in good general agreement. We also constructed the metallicity distribution for the field star sample and, by comparing it with that of the GCs, we learned that a high percentage of field stars show [Fe/H] > 0; whereas we did not detect any GCs in the same metallicity range. To understand this inconsistency, we constructed the age–metallicity diagram for both samples, noting that the old and metal-poor population (age ≥ 8 Gyr and [Fe/H] ≤ −1.0) is represented by Gcs, while the young and metal-rich population (age < 8 Gyr and [Fe/H] > −1.0) corresponds to field stars. Conclusions. From the analysis of the GC luminosity function and metallicity distribution, we can conclude that many GCs, probably those that are very faint, have survived strong dynamical processes that are typical of the bulge regions. Moreover, we cannot exclude the possibility that some of them have been accreted during past merging events, especially the metal-poor component, whereas the metal-rich population may be related to the formation of the bulge and/or disk. Finally, the difference that we notice between the cluster and field star samples should be explored in the context of the evolutionary differences among these two stellar populations. [ABSTRACT FROM AUTHOR]

Context. The number of known globular clusters in the Galactic bulge has been increasing steadily thanks to different new surveys. Aims. The aim of this study is to provide a census of the newly revealed globular clusters in the Galactic bulge, and analyze their characteristics. Methods. In recent years, many globular clusters have been discovered or identified. The stellar populations to which they belong are indicated in their original studies: they are mostly bulge clusters, with some identified as disk or halo members. We collected 41 new globular clusters revealed in the last decade and compared them to the known bulge clusters. Results. The new clusters are intrinsically faint with MV of around −6.0 mag. The distance to the Sun of the ensemble of well-known and new bulge clusters is compatible with the Galactocentric distance measurements from the Galactic black hole location. The ensemble sample shows metallicity peaks at [Fe/H] ∼ −1.08 ± 0.35 and −0.51 ± 0.25 dex, confirming previous findings. The age–metallicity relation of the new clusters younger than 10 Gyr is compatible with that of the ex situ samples of the dwarf galaxies Sagittarius, Canis Majoris, and Gaia-Enceladus-Sausage. The clusters with ages between 11.5 and 13.5 Gyr show no age–metallicity relation, because they are all old. This is compatible with their formation in situ in the early Galaxy. [ABSTRACT FROM AUTHOR]

We present the results of a high angular resolution (1.1 arcsec) and sensitivity (maximum of ∼0.1 mJy) radio survey at 1–2 GHz in the Galactic Bulge. This complements the X-ray Chandra Galactic Bulge Survey, and investigates the full radio source population in this dense Galactic region. Radio counterparts to sources at other wavelengths can aid in classification, as there are relatively few types of objects that are reasonably detectable in radio at kiloparsec distances, and even fewer that are detected in both X-rays and radio. This survey covers about 3 sq deg of the Galactic Bulge Survey area (spanning the Galactic coordinate range of −3° < l < +3° and +1.6° < b < +2.1°) as a first look into this region of the Galaxy with this combination of frequency, resolution, and sensitivity. Spectral indices within the observed band of 1–2 GHz were calculated for each source to assist in determining its emission mechanism. We find 1617 unique sources in the survey, 25 of which are radio counterparts to X-ray sources, and about 100 of which are steep-spectrum (α ≲ −1.4) point sources that are viable pulsar candidates. Four radio sources are of particular interest: a compact binary; an infrared transient with an inverted radio spectrum; a potential transitional millisecond pulsar candidate; and a very steep spectrum radio source with an X-ray and bright infrared counterpart. We discuss other notable sources, including possible radio transients, potential new planetary nebulae, and active galactic nuclei. [ABSTRACT FROM AUTHOR]

The gamma-ray Fermi -LAT Galactic Centre excess (GCE) has puzzled scientists for over 15 yr. Despite ongoing debates about its properties, and especially its spatial distribution, its nature remains elusive. We scrutinize how the estimated spatial morphology of this excess depends on models for the Galactic diffuse emission, focusing particularly on the extent to which the Galactic plane and point sources are masked. Our main aim is to compare a spherically symmetric morphology – potentially arising from the annihilation of dark matter (DM) particles – with a boxy morphology – expected if faint unresolved sources in the Galactic bulge dominate the excess emission. Recent claims favouring a DM-motivated template for the GCE are shown to rely on a specific Galactic bulge template, which performs worse than other templates for the Galactic bulge. We find that a non-parametric model of the Galactic bulge derived from the VISTA Variables in the Via Lactea survey results in a significantly better fit for the GCE than DM-motivated templates. This result is independent of whether a galprop -based model or a more non-parametric ring-based model is used to describe the diffuse Galactic emission. This conclusion remains true even when additional freedom is added in the background models, allowing for non-parametric modulation of the model components and substantially improving the fit quality. When adopted, optimized background models provide robust results in terms of preference for a boxy bulge morphology for the GCE, regardless of the mask applied to the Galactic plane. [ABSTRACT FROM AUTHOR]

Context. While orbital analysis studies were so far mainly focused on the Galactic halo, it is possible now to do these studies in the heavily obscured region close to the Galactic Centre. Aims. We aim to do a detailed orbital analysis of stars located in the nuclear stellar disc (NSD) of the Milky Way allowing us to trace the dynamical history of this structure. Methods. We integrated orbits of the observed stars in a non-axisymmetric potential. We used a Fourier transform to estimate the orbital frequencies. We compared two orbital classifications, one made by eye and the other with an algorithm, in order to identify the main orbital families. We also compared the Lyapunov and the frequency drift techniques to estimate the chaoticity of the orbits. Results. We identified several orbital families as chaotic, z-tube, x-tube, banana, fish, saucer, pretzel, 5:4, and 5:6 orbits. As expected for stars located in a NSD, the large majority of orbits are identified as z-tubes (or as a sub-family of z-tubes). Since the latter are parented by x2 orbits, this result supports the contribution of the bar (in which x2 orbits are dominant in the inner region) in the formation of the NSD. Moreover, most of the chaotic orbits are found to be contaminants from the bar or bulge which would confirm the predicted contamination from the most recent NSD models. Conclusions. Based on a detailed orbital analysis, we were able to classify orbits into various families, most of which are parented by x2-type orbits, which are dominant in the inner part of the bar. [ABSTRACT FROM AUTHOR]

We present a new set of tools to derive systemic velocities for single-mode RR Lyrae stars from visual and near-infrared spectra. We derived scaling relations and line-of-sight velocity templates using both APOGEE and Gaia spectroscopic products combined with photometric G-band amplitudes. We provide a means to estimate systemic velocities for the RR Lyrae subclasses, RRab and RRc. Our analysis indicates that the scaling relation between the photometric and line-of-sight velocity amplitudes is nonlinear, with a break in a linear relation occurring around ≈0.4 mag in both the V-band and G-band amplitudes. We did not observe such a break in the relation for the first-overtone pulsators. Using stellar pulsation models, we further confirm and examine the nonlinearity in scaling relation for the RRab subclass. We observed little to no variation with stellar parameters (mass, metallicity, and luminosity) in the scaling relation between the photometric and line-of-sight velocity amplitudes for fundamental-mode pulsators. We observed an offset in the scaling relation between the observations and stellar pulsation models, mainly in the low-amplitude RR Lyrae regime. This offset disappears when different sets of convective parameters are used. Thus, the Fourier amplitudes obtained from the photometry and line-of-sight velocity measurements can be utilized to constrain convective parameters of stellar pulsation models. The scaling relations and templates for APOGEE and Gaia data accurately predict systemic velocities compared to literature values. In addition, our tools derived from the Gaia spectra improve the precision of the derived systemic velocities by approximately 50 percent and provide a better description of the uncertainty distribution in comparison with previous studies. Our newly derived tools will be used for RR Lyrae variables observed toward the Galactic bulge. [ABSTRACT FROM AUTHOR]

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| < 10°, | b | < 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| < 5°) are on average shorter than the non-central (|ℓ| > 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. [ABSTRACT FROM AUTHOR]

Double-barred galaxies exhibit sub-kiloparsec secondary stellar bars that are crucial for channeling gases towards a central massive object (CMO) such as a supermassive black hole or a nuclear star cluster. Recent N -body simulations have uncovered a novel galaxy evolution scenario wherein the mass of the CMO increases owing to the secondary bar, resulting in the eventual destruction of the latter. Consequently, the CMO mass growth halts, thus suggesting a maximum CMO mass of ≈10−3 of the stellar mass of the galaxy. This study focuses on backbone orbit families, particularly double-frequency orbits, within double-barred galaxies. Consequently, the dynamic influence of a CMO on these orbits is investigated. The results of the study reveal the emergence of a new orbital resonance within the central region of the galaxy upon the introduction of a CMO. Orbits subjected to this resonance become chaotic and fail to support the secondary bar, ultimately resulting in the destruction of the entire structure. This is partly because of the inability of the secondary bar to obtain support from the newly generated orbit families following the appearance of resonance. Through the estimation of the condition of secondary bar destruction in realistic double-bar galaxies with varying pattern speeds, the results of the study establish that such destruction occurred when the CMO mass reached ≈10−3 of the galaxy mass. Furthermore, a physical explanation of the galaxy evolution scenario is provided, thereby elucidating the interaction between the CMO and the secondary bar. The understanding of the co-evolution of the secondary bar and the CMO, based on stellar orbital motion, is a crucial step towards future observational studies of stars within the bulge of the Milky Way. [ABSTRACT FROM AUTHOR]

We search for high-velocity stars in the inner region of the Galactic bulge using a selected sample of red clump stars. Some of those stars might be considered hypervelocity stars (HVSs). Even though the HVSs ejection relies on an interaction with the supermassive black hole (SMBH) at the centre of the Galaxy, there are no confirmed detections of HVSs in the inner region of our Galaxy. With the detection of HVSs, ejection mechanism models can be constrained by exploring the stellar dynamics in the Galactic centre through a recent stellar interaction with the SMBH. Based on a previously developed methodology by our group, we searched with a sample of preliminary data from version 2 of the Vista Variables in the Via Lactea (VVV) Infrared Astrometric Catalogue (VIRAC2) and Gaia DR3 data, including accurate optical and near-infrared proper motions. This search resulted in a sample of 46 stars with transverse velocities larger than the local escape velocity within the Galactic bulge, of which four are prime candidate HVSs with high-proper motions consistent with being ejections from the Galactic centre. Adding to that, we studied a sample of reddened stars without a Gaia DR3 counterpart and found 481 stars with transverse velocities larger than the local escape velocity, from which 65 stars have proper motions pointing out of the Galactic centre and are candidate HVSs. In total, we found 69 candidate HVSs pointing away from the Galactic centre with transverse velocities larger than the local escape velocity. [ABSTRACT FROM AUTHOR]

This study focuses on Pristine |$\_180956.78$| −294759.8 (hereafter P180956, [Fe/H] = −1.95 ± 0.02), a star selected from the Pristine Inner Galaxy Survey (PIGS), and followed-up with the recently commissioned Gemini High-resolution Optical SpecTrograph (GHOST) at the Gemini South telescope. The GHOST spectrograph's high efficiency in the blue spectral region (3700−4800 Å) enables the detection of elemental tracers of early supernovae (e.g. Al, Mn, Sr, and Eu). The star exhibits chemical signatures resembling those found in ultrafaint dwarf (UFD) systems, characterized by very low abundances of neutron-capture elements (Sr, Ba, and Eu), which are uncommon among stars in the Milky Way halo. Our analysis suggests that P180956 bears the chemical imprints of a small number (2 or 4) of low-mass hypernovae (⁠|$\sim 10{-}15{\rm \, M_\odot }$|⁠), which are needed to mostly reproduce the abundance pattern of the light-elements (e.g. [Si, Ti/Mg, Ca] ∼0.6), and one fast-rotating intermediate-mass supernova (⁠|$\sim 300{\rm \, km \ s^{-1}}$|⁠ , |$\sim 80{-}120{\rm \, M_\odot }$|⁠), which is the main channel contributing to the high [Sr/Ba] (∼+1.2). The small pericentric (⁠|$\sim 0.7{\rm \, kpc}$|⁠) and apocentric (⁠|$\sim 13{\rm \, kpc}$|⁠) distances and its orbit confined to the plane (⁠|$\lesssim 2{\rm \, kpc}$|⁠) indicate that this star was likely accreted during the early Galactic assembly phase. Its chemo-dynamical properties suggest that P180956 formed in a system similar to a UFD galaxy accreted either alone, as one of the low-mass building blocks of the proto-Galaxy, or as a satellite of Gaia–Sausage–Enceladus. The combination of Gemini's large aperture with GHOST's high efficiency and broad spectral coverage makes this new spectrograph one of the leading instruments for near-field cosmology investigations. [ABSTRACT FROM AUTHOR]

Studies of the dynamics of globular clusters assume different values of bar parameters (mass, velocity, and size) and analyse the results of orbit classifications over the range of the chosen values. It is also a usual thing that a spherical bulge component is converted into the bar to obtain a non-axisymmetric potential from an axisymmetric one. The choice of bar parameters and the way the bar is converted from the bulge introduce systematics into the orbit classifications that we explore in this study. We integrate orbits of 30 bulge globular clusters residing in the inner area of the Galaxy (R ≲ 5 kpc) backwards in time for three different potentials, two of which are obtained by fitting the rotation curve, and one is taken from the surrogate N -body model representing our Galaxy. We analyse each orbit in terms of dominant frequencies obtained from its coordinate spectra. We find that the bar pattern speed is a key factor in orbital classification. With an increase of the bar pattern speed, frequencies deviate more and more from the 'bar' frequency ratio 2:1. The bar-to-bulge mass ratio (assuming the total mass of the bar plus the bulge is fixed) and size of the bar play a smaller role. We also find that, in the N -body potential, the fraction of orbits that follow the bar is higher than in those obtained from fitting the rotation curve. [ABSTRACT FROM AUTHOR]

In this paper, the third of a series of papers, we present well-determined chemical abundances for 124 planetary nebulae (PNe) in the Galactic bulge from deep, long-slit FORS2 spectra from the 8.2 m ESO Very Large telescope (VLT). Prior to this work there were only ∼240 bulge PNe with chemical abundances previously determined over a ∼50 yr period and of highly variable quality. For 34 of these PNe we are presenting their abundances for the first time, which adds ∼14 per cent to the available sample of bulge PNe abundances. The interstellar reddening, physical conditions (electron densities, n e, temperatures, T e), and chemical compositions are derived as single values for each PN but also using different line diagnostics. Selected comparisons with the best literature fluxes for 75 PNe in common reveal that these significant new data are robust, reliable, and internally self-consistent forming the largest independent, high-quality, and well-understood derivation of PNe abundances currently available for study. [ABSTRACT FROM AUTHOR]

Context. The location of the Solar System complicates the detection extragalactic sources beyond the Milky Way plane. The optical observations are hampered in the so-called zone of avoidance (ZOA), where stellar crowding and Galactic absorption are severe. Observations at longer wavelengths are needed in order to discover new background galaxies and complete the census in the ZOA. Aims. The goal of this work is to identify galaxies behind the Milky Way bulge using near-infrared (NIR) data from the VISTA Variables in Vía Láctea (VVV) survey. Methods. To this end, we made use of different VISTA Science Archive (VSA) tools in order to extract relevant information from more than 32 billion catalogued sources in the VVV bulge region. We find that initial photometric restriction on sources from the VSA vvvSource table combined with restrictions on star–galaxy separation parameters obtained from Source Extractor is a successful strategy for achieving acceptable levels of contamination (60%) and high completeness (75%) in the construction of a galaxy target sample. To remove contaminating Galactic sources from the initial target sample, our methodology also incorporates a visual inspection of false-colour RGB images, a crucial quality control carried out following a specifically defined procedure. Results. Under this methodology, we find 14 480 galaxy candidates in the VVV bulge region, making this sample the largest catalogue to date in the ZOA. Moreover, these new sources provide a fresh picture of the Universe hidden behind the curtain of stars, dust, and gas in the unexplored Milky Way bulge region. Conclusions. The results from this work further demonstrate the potential of the VVV/VVVX survey to find and study a large number of galaxies and extragalactic structures obscured by the Milky Way, expanding our knowledge of the Universe in this challenging and impressive region of the sky. [ABSTRACT FROM AUTHOR]

Context. The inner Galaxy is a complex environment, and the relative contributions of different formation scenarios to its observed morphology and stellar properties are still debated. The different components are expected to have different spatial, kinematic, and metallicity distributions, and a combination of photometric, spectroscopic, and astrometric large-scale surveys is needed to study the formation and evolution of the Galactic bulge. Aims. The Blanco DECam Bulge Survey (BDBS) provides near-ultraviolet to near-infrared photometry for approximately 250 million unique stars over more than 200 square degrees of the southern Galactic bulge. By combining BDBS photometry with the latest Gaia astrometry, we aim to characterize the chemodynamics of red clump stars across the BDBS footprint using an unprecedented sample size and sky coverage. Methods. Our field of view of interest is |ℓ| ≤ 10°, −10° ≤b ≤ −3°. We constructed a sample of approximately 2.3 million red clump giants in the bulge with photometric metallicities, BDBS photometric distances, and proper motions. Photometric metallicities are derived from a (u − i)0 versus [Fe/H] relation; astrometry, including precise proper motions, is from the third data release (DR3) of the ESA satellite Gaia. We studied the kinematics of the red clump stars as a function of sky position and metallicity by investigating proper-motion rotation curves, velocity dispersions, and proper-motion correlations across the southern Galactic bulge. Results. By binning our sample into eight metallicity bins in the range of −1.5 dex < [Fe/H] < +1 dex, we find that metal-poor red clump stars exhibit lower rotation amplitudes, at ∼29 km s−1 kpc−1. The peak of the angular velocity is ∼39 km s−1 kpc−1 for [Fe/H] ∼ −0.2 dex, exhibiting declining rotation at higher [Fe/H]. The velocity dispersion is higher for metal-poor stars, while metal-rich stars show a steeper gradient with Galactic latitude, with a maximum dispersion at low latitudes along the bulge minor axis. Only metal-rich stars ([Fe/H] ≳ −0.5 dex) show clear signatures of the bar in their kinematics, while the metal-poor population exhibits isotropic motions with an axisymmetric pattern around Galactic longitude ℓ = 0. Conclusions. This work describes the largest sample of bulge stars with distance, metallicity, and astrometry reported to date, and shows clear kinematic differences with metallicity. The global kinematics over the bulge agrees with earlier studies. However, we see striking changes with increasing metallicity, and, for the first time, kinematic differences for stars with [Fe/H]>  − 0.5, suggesting that the bar itself may have kinematics that depends on metallicity. [ABSTRACT FROM AUTHOR]

We identified a sample of 58 candidate stars with metallicity [Fe/H] ≲ −0.8 that likely belong to the old bulge spheroid stellar population, and analyse their Na and Al abundances from Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra. In a previous work, we inspected APOGEE-Stellar Parameter and Chemical Abundance Pipeline abundances of C, N, O, Mg, Al, Ca, Si, and Ce in this sample. Regarding Na lines, one of them appears very strong in about 20 per cent of the sample stars, but it is not confirmed by other Na lines, and can be explained by sky lines, which affect the reduced spectra of stars in a certain radial velocity range. The Na abundances for 15 more reliable cases were taken into account. Al lines in the H band instead appear to be very reliable. Na and Al exhibit a spread in abundances, whereas no spread in N abundances is found, and we found no correlation between them, indicating that these stars could not be identified as second-generation stars that originated in globular clusters. We carry out the study of the behaviour of Na and Al in our sample of bulge stars and literature data by comparing them with chemodynamical evolution model suitable for the Galactic bulge. The Na abundances show a large spread, and the chemodynamical models follow the main data, whereas for aluminum instead, the models reproduce very satisfactorily the nearly secondary-element behaviour of aluminum in the metallicity range below [Fe/H] ≲ −1.0. For the lower-metallicity end ([Fe/H < −2.5), hypernovae are assumed to be the main contributor to yields. [ABSTRACT FROM AUTHOR]

The presence of dust in spiral galaxies affects the ability of photometric decompositions to retrieve the parameters of their main structural components. For galaxies in an edge-on orientation, the optical depth integrated over the line of sight is significantly higher than for those with intermediate or face-on inclinations, so it is only natural to expect that for edge-on galaxies, dust attenuation should severely influence measured structural parameters. In this paper, we use radiative transfer simulations to generate a set of synthetic images of edge-on galaxies that are then analysed via decomposition. Our results demonstrate that for edge-on galaxies, the observed systematic errors of the fit parameters are significantly higher than for moderately inclined galaxies. Even for models with a relatively low dust content, all structural parameters suffer offsets that are far from negligible. In our search for ways to reduce the impact of dust on retrieved structural parameters, we test several approaches, including various masking methods and an analytical model that incorporates dust absorption. We show that using such techniques greatly improves the reliability of decompositions for edge-on galaxies. [ABSTRACT FROM AUTHOR]

This is the third paper in a series that attempts to observe a clear signature of the Galactic bar/bulge using kinematic observations of the bulge stellar populations in low foreground extinction windows. We report on the detection of ∼100 000 new proper motions in four fields covering the far side of the Galactic bar/bulge, at negative longitudes. Our proper motions have been obtained using observations from the Advance Camera for Surveys (ACS), on board of the Hubble Space Telescope (HST), with a time-baseline of 8–9 years, which has produced accuracies better than 0.5 mas yr−1 for a significant fraction of the stellar populations with F 814 W < 23 mag. Interestingly, as shown in previous works, the Hess diagrams show a strikingly similar proper motion distribution to fields closer to the Galactic center and consistent with an old stellar population. The observed kinematics point to a significant bulge rotation, which seems to predominate even in fields as far as l ≃ −8°, and is also reflected in the changes of the velocity ellipsoid in the l, b plane as a function of distance. [ABSTRACT FROM AUTHOR]

The chemical fingerprints of the first stars are retained within the photospheres of ancient unevolved metal-poor stars. A significant fraction of these stellar fossils is represented by stars known as Carbon-Enhanced Metal-Poor (CEMP), |$\mathrm{[C/Fe]} \gt +0.7$| and |$\mathrm{[Fe/H]} \lt -2$|⁠ , which are likely imprinted by low-energy primordial supernovae. These CEMP stars are largely observed in the Galactic halo and ultrafaint dwarf galaxies, with values reaching |$\rm [C/Fe]=+4.5$|⁠. The Galactic bulge is predicted to host the oldest stars, but it shows a striking dearth of CEMP stars with |$\rm [C/Fe]\gtrsim +2.0$|⁠. Here, we explore the possible reasons for this anomaly by performing a statistical analysis of the observations of metal-poor stars in combination with the predictions of Lambda cold dark matter models. We suggest that the dearth of CEMP stars with high |$\mathrm{[C/Fe]}$| is not due to the low statistics of observed metal-poor stars but is the result of the different formation process of the bulge. N -body simulations show that the first star-forming haloes which end up in the bulge are characterized by the highest star formation rates. These rates enable the formation of rare massive first stars exploding as pair-instability supernovae (PISNe), which wash out the signature of primordial faint supernovae. We demonstrate that the mean |$\mathrm{[C/Fe]}$| of first stars polluted environments decreases with the increasing contribution of PISNe. We conclude that the dearth of CEMP stars in the Galactic bulge indirectly probes the existence of elusive PISNe, and propose a novel method which exploits this lack to constrain the mass distribution of the first stars. [ABSTRACT FROM AUTHOR]

The separation of oxygen- and carbon-rich asymptotic giant branch sources is crucial for their accurate use as local and cosmological distance and age/metallicity indicators. We investigate the use of unsupervised learning algorithms for classifying the chemistry of long-period variables from Gaia DR3's BP/RP spectra. Even in the presence of significant interstellar dust, the spectra separate into two groups attributable to O-rich and C-rich sources. Given these classifications, we utilize a supervised approach to separate O-rich and C-rich sources without blue and red photometers (BP/RP) spectra but instead given broadband optical and infrared photometry finding a purity of our C-rich classifications of around 95 per cent. We test and validate the classifications against other advocated colour–colour separations based on photometry. Furthermore, we demonstrate the potential of BP/RP spectra for finding S-type stars or those possibly symbiotic sources with strong emission lines. Although our classification suggests the Galactic bar-bulge is host to very few C-rich long-period variable stars, we do find a small fraction of C-rich stars with periods |$\gt 250\, \mathrm{day}$| that are spatially and kinematically consistent with bar-bulge membership. We argue the combination of the observed number, the spatial alignment, the kinematics, and the period distribution disfavour young metal-poor star formation scenarios either in situ or in an accreted host, and instead, these stars are highly likely to be the result of binary evolution and the evolved versions of blue straggler stars already observed in the bar-bulge. [ABSTRACT FROM AUTHOR]

We present a novel method for constraining the length of the Galactic bar using 6D phase-space information to directly integrate orbits. We define a pseudo-length for the Galactic bar, named R Freq, based on the maximal extent of trapped bar orbits. We find the R Freq measured from orbits is consistent with the R Freq of the assumed potential only when the length of the bar and pattern speed of said potential is similar to the model from which the initial phase-space coordinates of the orbits are derived. Therefore, one can measure the model's or the Milky Way's bar length from 6D phase-space coordinates by determining which assumed potential leads to a self-consistent measured R Freq. When we apply this method to ≈210 000 stars in APOGEE DR17 and Gaia eDR3 data, we find a consistent result only for potential models with a dynamical bar length of ≈3.5 kpc. We find the Milky Way's trapped bar orbits extend out to only ≈3.5 kpc, but there is also an overdensity of stars at the end of the bar out to 4.8 kpc which could be related to an attached spiral arm. We also find that the measured orbital structure of the bar is strongly dependent on the properties of the assumed potential. [ABSTRACT FROM AUTHOR]

The relation between the mass of the supermassive black hole (SMBH) in the center of galaxies and their bulge mass or central velocity dispersion is well known. This suggests a coevolution between the SMBHs and their galaxy hosts. Our aim is to study this relation, specifically, for radio loud galaxies, and as a function of redshift z. We selected a sample of 42 radio galaxies and active galactic nuclei (AGN) with broad emission lines and spectroscopic redshifts between z = 0:34 by cross-matching the low radio frequency sources from Very Large Array (VLA) FIRST with spectroscopically confirmed galaxies from wide-field surveys, including Sloan Digital Sky Survey (SDSS) DR14 ugriz and Dark Energy Survey (DES) DR2 grzY in the optical, Wield Infrared Survey Explorer (WISE), and the Galaxy And Mass Assembly (GAMA) spectroscopic survey. We characterized the stellar mass (M), star formation, and black hole properties (mass of the central SMBH, Eddington ratio, and jet power, Qjet). The relation between SMBH mass, M, and z is placed into context by comparing them with scaling relations (MBH-M, MBH=M-z, MBH-Qjet, and Qjet-) from the literature. On the basis of a multiwavelength spectral energy distribution modeling, our radio sources are broadly consistent with being on the star-forming main sequence. They have sub-Eddington accretion rates,' 1% on average, as typically found in type I AGN, while higher accretion rates favor more powerful jets to be launched by the central engine. We find overmassive SMBHs in (17±5)% of our radio sources, similarly to previous studies on nearby early-type galaxies. Altogether, an evolutionary scenario in which radio-mode AGN feedback regulates the accretion onto the SMBHs and the stellar mass assembly of the radio sources is discussed, which may explain the observed phenomenology. This pilot study represents a benchmark for future studies using wide-field surveys such as those with Euclid and the Vera Rubin Observatory. [ABSTRACT FROM AUTHOR]

The information on Galactic assembly time is imprinted on the chemodynamics of globular clusters. This makes them important probes that help us to understand the formation and evolution of the Milky Way. Discerning between in-situ and ex-situ origin of these objects is difficult when we study the Galactic bulge, which is the most complex and mixed component of the Milky Way. To investigate the early evolution of the Galactic bulge, we analysed the globular cluster NGC 6355. We derived chemical abundances and kinematic and dynamic properties by gathering information from high-resolution spectroscopy with FLAMES-UVES, photometry with the Hubble Space Telescope, and Galactic dynamic calculations applied to the globular cluster NGC 6355. We derive an age of 13.2 ± 1.1 Gyr and a metallicity of [Fe/H]  =   − 1.39 ± 0.08 for NGC 6355, with α-enhancement of [α/Fe]  =   + 0.37 ± 0.11. The abundance pattern of the globular cluster is compatible with bulge field RR Lyrae stars and in-situ well-studied globular clusters. The orbital parameters suggest that the cluster is currently confined within the bulge volume when we consider a heliocentric distance of 8.54 ± 0.19 kpc and an extinction coefficient of RV = 2.84 ± 0.02. NGC 6355 is highly likely to come from the main bulge progenitor. Nevertheless, it still has a low probability of being formed from an accreted event because its age is uncertain and because of the combined [Mg/Mn] [Al/Fe] abundance. Its relatively low metallicity with respect to old and moderately metal-poor inner Galaxy clusters may suggest a low-metallicity floor for globular clusters that formed in-situ in the early Galactic bulge. [ABSTRACT FROM AUTHOR]

Context. Until now, heavy interstellar extinction has meant that only a few studies of chemical abundances have been possible in the inner Galactic bulge. However, it is crucial to learn more about this structure in order to better understand the formation and evolution of the centre of the Galaxy and galaxies in general. Aims. In this paper, we aim to derive high-precision α-element abundances using CRIRES high-resolution IR spectra of 72 cool M giants of the inner Galactic bulge. Methods. Silicon, magnesium, and calcium abundances were determined by fitting a synthetic spectrum for each star. We also incorporated recent theoretical data into our spectroscopic analysis (i.e. updated K-band line list, better broadening parameter estimation, non-local thermodynamic equilibrium (NLTE) corrections). We compare these inner bulge α abundance trends with those of solar neighbourhood stars observed with IGRINS using the same line list and analysis technique; we also compare our sample to APOGEE DR17 abundances for inner bulge stars. We investigate bulge membership using spectro-photometric distances and orbital simulations. We construct a chemical-evolution model that fits our metallicity distribution function (MDF) and our α-element trends. Results. Among our 72 stars, we find four that are not bulge members. [Si/Fe] and [Mg/Fe] versus [Fe/H] trends show a typical thick disc α-element behaviour, except that we do not see any plateau at supersolar metallicities as seen in other works. The NLTE analysis lowers [Mg/Fe] typically by ∼0.1 dex, resulting in a noticeably lower trend of [Mg/Fe] versus [Fe/H]. The derived [Ca/Fe] versus [Fe/H] trend has a larger scatter than those for Si and Mg, but is in excellent agreement with local thin and thick disc trends. With our updated analysis, we constructed one of the most detailed studies of the α abundance trends of cool M giants in the inner Galactic bulge. We modelled these abundances by adopting a two-infall chemical-evolution model with two distinct gas-infall episodes with timescales of 0.4 Gyr and 2 Gyr, respectively. Conclusions. Based on a very meticulous spectral analysis, we have constructed detailed and precise chemical abundances of Mg, Si, and Ca for cool M giants. The present study can be used as a benchmark for future spectroscopic surveys. [ABSTRACT FROM AUTHOR]

The diffuse Fe XXV (6.7 keV) line emission observed in the Galactic ridge is widely accepted to be produced by a superposition of a large number of unresolved X-ray point sources. In the very central degrees of our Galaxy, however, the existence of an extremely hot (~7 keV) diffuse plasma is still under debate. In this work we measure the Fe XXV line emission using all available XMM-Newton observations of the Galactic centre (GC) and inner disc (−10° < ℓ < 10°, −2° < b < 2°). We use recent stellar mass distribution models to estimate the amount of X-ray emission originating from unresolved point sources, and find that within a region of ℓ = ±1° and b = ±0.25° the 6.7keV emission is 1.3–1.5 times in excess of what is expected from unresolved point sources. The excess emission is enhanced towards regions where known supernova remnants are located, suggesting that at least a part of this emission is due to genuine diffuse very hot plasma. If the entire excess is due to very hot plasma, an energy injection rate of at least ~6 × 1040 erg s−1 is required, which cannot be provided by the measured supernova explosion rate or past Sgr A* activity alone. However, we find that almost the entire excess we observe can be explained by assuming GC stellar populations with iron abundances ~1.9 times higher than those in the bar/bulge, a value that can be reproduced by fitting diffuse X-ray spectra from the corresponding regions. Even in this case, a leftover X-ray excess is concentrated within ℓ = ±0.3° and b = ±0.15°, corresponding to a thermal energy of ~2 × 1052 erg, which can be reproduced by the estimated supernova explosion rate in the GC. Finally we discuss a possible connection to the observed GC Fermi-LAT excess. [ABSTRACT FROM AUTHOR]

Due to its proximity, the stellar populations of the Galactic bulge (GB) can be resolved and can be studied in detail. This allows tracing the bulge metallicity distribution function (MDF) for different spatial regions within the bulge, which may give us clues about the bulge formation and evolution scenarios. In this work, we developed a chemical evolution model (CEM), taking into account the mass distribution in the bulge and disc, to derive the radial dependence of this time-scale in the Galaxy. Since the infall rate depends on that time-scale in the CEM, the results of the model were used to test a scenario where the bulge is formed inside-out. The obtained results for the [α/Fe] versus [Fe/H] relationship, the MDF and the [Fe/H] radial gradient in the bulge have been compared to available data in the literature. The model is able to reproduce most of the observational data: the spread in the relation [α/Fe] versus [Fe/H], the MDF shape in different regions of the bulge, the [Fe/H] radial gradient inside it, and the age–metallicity relation, as well as the [α/Fe] evolution with age. The results of the model point to a scenario where the bulk of the bulge stars pre-existed the boxy/peanut X-shape bar formation. As a result, the classical origin of the GB is not ruled out, and this scenario may be invoked to explain the chemical properties of the GB. [ABSTRACT FROM AUTHOR]

This is the first in a series of papers that present sets of different results for 136 compact, known planetary nebulae within a 10 × 10 degree region of the Galactic bulge. We use a large, previously unpublished sample of our own extensive ESO 8-m VLT deep imaging and spectroscopic data. This is combined with archival deep Hubble Space Telescope imaging where available to provide a detailed morphological classification and study. The influence of angular resolution and sensitivity when assigning a morphology is discussed. A large fraction (68 per cent) of the sample are shown to be bipolars and the implications for this in the context of planetary nebulae progenitors are explored. Four new planetary nebula central stars are also identified which are not in Gaia. This is based on both Very Large Telescope (VLT) and deep archival Pan-STARRS broad-band imagery. Some 11 putative central stars previously reported, based on Gaia positions, are also not the true central star. In other cases, the Gaia central stars reported in the literature are actually based on the overall centroid position of a very compact planetary nebula rather than the actual central star within it. Gaia parallax distances and kinematic ages for PNe in this sample are provided where possible based on fresh angular size measures from the new VLT imagery and Gaia distances and literature expansion velocities when available. All these results are discussed within the context of the overall characteristics of the Galactic bulge and its planetary nebula population. [ABSTRACT FROM AUTHOR]

We present the late-time evolution of m12m, a cosmological simulation of a Milky Way-like galaxy from the FIRE project. The simulation forms a bar after redshift z = 0.2. We show that the evolution of the model exhibits behaviours typical of kinematic fractionation, with a bar weaker in older populations, an X-shape traced by the younger, metal-rich populations, and a prominent X-shape in the edge-on mean metallicity map. Because of the late formation of the bar in m12m, stars forming after 10 Gyr (z = 0.34) significantly contaminate the bulge, at a level higher than is observed at high latitudes in the Milky Way, implying that its bar cannot have formed as late as in m12m. We also study the model's vertex deviation of the velocity ellipsoid as a function of stellar metallicity and age in the equivalent of Baade's Window. The formation of the bar leads to a non-zero vertex deviation. We find that metal-rich stars have a large vertex deviation (∼40◦), which becomes negligible for metal-poor stars, a trend also found in the Milky Way, despite not matching in detail. We demonstrate that the vertex deviation also varies with stellar age and is large for stars as old as 9 Gyr, while 13 Gyr old stars have negligible vertex deviation. When we exclude stars that have been accreted, the vertex deviation is not significantly changed, demonstrating that the observed variation of vertex deviation with metallicity is not necessarily due to an accreted population.

Massive (≥8 M⊙) stars perish via one of two fates: core-collapse supernovae (CCSNe), which release synthesized heavy elements, or failed supernovae, thereby forming black holes. In the conventional Galactic chemical evolution (GCE) scheme, a substantial portion of massive stars, e.g. all stars in the mass range of 8–100 M⊙, are assumed to enrich the Galaxy with their nucleosynthetic products. However, this hypothesis conflicts with the observations, namely, few CCSNe whose progenitor stars are more massive than ∼18 M⊙. Here, we show that the chemical characteristics shaped by local thin disc stars are compatible with the predictions by enrichment via CCSNe limited to less massive progenitors in the new paradigm of Galactic dynamics that allows stars to migrate from the inner disc. This renewed GCE model predicts that the bursting star formation events − which are considered to take place in the Galactic bulge and in the thick disc − generate more numerous low-mass CCSNe than those expected from the locally determined canonical initial mass function. This finding suggests a high rate of CCSNe in early-type galaxies, which reflects a unique cosmic history of the CCSN rate. With considerable contributions from these galaxies to the cosmic star formation rates in the early Universe, we predict a more steeply increasing slope of the CCSN rate with increasing redshift than that in proportion to cosmic star formation. This predicted redshift evolution agrees well with the measured rates for |$0 \lesssim z \lesssim 0.8$|⁠ ; however, its predicted CCSN rate for higher z calls for more precise data from future surveys. [ABSTRACT FROM AUTHOR]

The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H]<−2.0) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457 and P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H]<−3.0) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]∼−2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way. [ABSTRACT FROM AUTHOR]

We analyse the distribution of Mira variable stars in the central region of the Milky Way. We find that with increasing period, i.e. decreasing age, the Miras shift towards negative Galactic longitudes ℓ. Comparing to a cosmological zoom simulation of a barred galaxy, we find that this shift with age can be explained by an age-morphology dependence of the boxy peanut/bulge. Owing to a combination of projection effects and the limitation of the range of Galactic longitudes, the near hump at ℓ > 0 is more truncated for younger populations, and the far hump at ℓ < 0 dominates the observed distributions. [ABSTRACT FROM AUTHOR]

The chemo-dynamics of the stellar populations in the Galactic Bulge inform and constrain the Milky Way's formation and evolution. The metal-poor population is particularly important in light of cosmological simulations, which predict that some of the oldest stars in the Galaxy now reside in its center. The metal-poor bulge appears to consist of multiple stellar populations that require chemo-dynamical analyses to disentangle. In this paper, I describe the detailed chemo-dynamical study of the metal-poor stars in the inner Galaxy, named The COMBS Survey which uses VLT/FLAMES spectra of 350 metal-poor stars. I discuss the results and the implications for early Milky Way formation and chemical evolution. In addition, I preview results from an ongoing survey of carbon-enhanced metal-poor stars, which are thought to be solely enriched by the first generation of stars. [ABSTRACT FROM AUTHOR]

The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H < – 2.0]) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457, P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H < – 3.0]) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]∼ – 2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way. [ABSTRACT FROM AUTHOR]

We present theoretical mass estimates of 26Al and 60Fe throughout the Galaxy, performed with a numerical chemical evolution model including detailed nucleosynthesis prescriptions for stable and radioactive nuclides. We compared the results for several sets of stellar yields taken from the literature, for massive, low and intermediate mass stars, nova systems (only for 26Al) and supernovae Type Ia. We then computed the total masses of 26Al and 60Fe in the Galaxy. We studied the bulge and the disc of the Galaxy in a Galactocentric radius range of 0–22 kpc. We assumed that the bulge region (within 2 kpc) evolved quickly suffering a strong star formation burst, while the disc formed more slowly and inside–out. We compared our results with the 26Al mass observed by the gamma-ray surveys COMPTEL and INTEGRAL to select the best model. Concerning 60Fe, we do not have any observed mass value so we just performed a theoretical prediction for future observations. In conclusion, low, intermediate mass stars, and Type Ia supernovae contribute negligibly to the two isotopes, while massive stars are the dominant source. The nova contribution is, however, necessary to reproduce the observations of 26Al. Our best model predicts 2.12 M⊙ of 26Al, in agreement with observations, while for 60Fe our best mass estimate is ∼1.05 M⊙. We also predicted the present injection rate of 26Al and 60Fe in the Galaxy and compared it with previous results, and we found a larger present time injection rate along the disc. [ABSTRACT FROM AUTHOR]

The central part of the Galaxy hosts a multitude of stellar populations, including the spheroidal bulge stars, stars moved to the bulge through secular evolution of the bar, inner halo, inner thick disc, inner thin disc, as well as debris from past accretion events. We identified a sample of 58 candidate stars belonging to the stellar population of the spheroidal bulge, and analyse their abundances. The present calculations of Mg, Ca, and Si lines are in agreement with the ASPCAP abundances, whereas abundances of C, N, O, and Ce are re-examined. We find normal α-element enhancements in oxygen, similar to magnesium, Si, and Ca abundances, which are typical of other bulge stars surveyed in the optical in Baade's Window. The enhancement of [O/Fe] in these stars suggests that they do not belong to accreted debris. No spread in N abundances is found, and none of the sample stars is N-rich, indicating that these stars are not second generation stars originated in globular clusters. Ce instead is enhanced in the sample stars, which points to an s-process origin such as due to enrichment from early generations of massive fast rotating stars, the so-called spinstars. [ABSTRACT FROM AUTHOR]

In this paper, we report on the detection of RRab stars with quasi-identical-shape light curves but period differences as large as 0.05–0.21 d using the Galactic bulge data of the OGLE-IV survey. We have examined stars with shorter periods than the Oosterhoff I ridge of the bulge. These stars generally have smaller amplitudes and larger Fourier phase-differences than the typical bulge RRab stars have at the same period. Many of these 'anomalous' stars have good-quality light curves without any sign of the Blazhko modulation. Examining their Fourier parameters revealed that several of these stars show very similar light curve to the typical bulge RR Lyrae. We found hundreds of quasi-identical-shape light-curve pairs with different periods between the 'anomalous'- and the 'normal'-position RRab stars based on the OGLE I -band data. The OGLE V -band, and the archive VVV and MACHO surveys Ks -, b - and r -band data of these stars were also checked for light-curve-shape similarity. Finally, 149 pairs with identical-shape light curves in each available photometric band were identified. Calculating the physical properties of the variables using empirical formulae, on average, −0.5 dex, −0.13 mag, 0.67, and 165 K differences between the [Fe/H], MV , R/R⊙, and T eff values of the members of the pairs are derived, being the short-period stars less metal-poor, fainter, smaller, and hotter than the long-period variables. To explain the existence of variables with different physical properties and pulsation periods but with identical-shape light curves is a challenging task for modelling. [ABSTRACT FROM AUTHOR]

We present an analysis on the behaviour of the Galactic bulge and the Large Magellanic Cloud (LMC) δ Scuti stars in terms of period–colour and amplitude–colour (PCAC) relations at maximum, mean, and minimum light. The publicly available Optical Gravitational Lensing Experiment-IV (OGLE-IV) light curves for Galactic bulge and OGLE-III light curves for LMC δ Scuti stars are exploited for the analysis. It has been found that the Galactic bulge δ Scuti stars obey flat PC relations at maximum/mean/minimum light, while the LMC δ Scutis have sloped, sloped , and flat PC relations at maximum, mean , and minimum light, respectively. Both the Galactic bulge and the LMC δ Scutis have sloped, flat , and sloped AC relations at maximum, mean , and minimum light, respectively. These relations also show that Galactic δ Scutis are hotter as compared to their LMC counterparts. The period–amplitude (PA) relations for δ Scutis exhibit different behaviour in the Galactic bulge and the LMC. The LMC variables are found to have higher amplitudes at a given period. The amplitude of the Galactic bulge δ Scuti shows a bimodal distribution which can be modelled using a two-component Gaussian Mixture Model: one component with a lower amplitude and another with a higher amplitude. The observed behaviour of the δ Scuti PCAC relations can be explained using the theory of the interaction of hydrogen ionization front (HIF) and stellar photosphere as well as the PA diagram. We use mesa-rsp to calculate theoretical non-linear hydrodynamical pulsation models for δ Scuti stars with input metallicities of Z  = 0.02 and Z  = 0.008 appropriate for the Galactic bulge and LMC, respectively. The observed PCAC relations and theoretical calculations support the HIF–photosphere interaction theory. [ABSTRACT FROM AUTHOR]

The properties of the Milky Way's nuclear stellar disc give crucial information on the epoch of bar formation. Mira variables are promising bright candidates to study the nuclear stellar disc, and through their period–age relation dissect its star formation history. We report on a sample of 1782 Mira variable candidates across the central |$3\times 3\, \mathrm{deg}^2$| of the Galaxy using the multi-epoch infrared VISTA Variables in Via Lactea (VVV) survey. We describe the algorithms employed to select candidate variable stars and then model their light curves using periodogram and Gaussian process methods. By combining with WISE, 2MASS, and other archival photometry, we model the multiband light curves to refine the periods and inspect the amplitude variation between different photometric bands. The infrared brightness of the Mira variables means many are too bright and missed by VVV. However, our sample follows a well-defined selection function as expected from artificial star tests. The multiband photometry is modelled using stellar models with circumstellar dust that characterize the mass-loss rates. We demonstrate how ≳90 per cent of our sample is consistent with O-rich chemistry. Comparison to period–luminosity relations demonstrates that the bulk of the short period stars are situated at the Galactic Centre distance. Many of the longer period variables are very dusty, falling significantly under the O-rich Magellanic Cloud and solar neighbourhood period–luminosity relations and exhibit high mass-loss rates of |$\sim 2.5\times 10^{-5}M_\odot \, \mathrm{yr}^{-1}$|⁠. The period distribution appears consistent with the nuclear stellar disc forming |$\gtrsim 8\, \mathrm{Gyr}$| ago, although it is not possible to disentangle the relative contributions of the nuclear stellar disc and the contaminating bulge. [ABSTRACT FROM AUTHOR]

Despite the advances provided by large-scale photometric surveys, stellar features – such as metallicity – generally remain limited to spectroscopic observations often of bright, nearby low-extinction stars. To rectify this, we present a neural network approach for estimating the metallicities and distances of red giant stars with 8-band photometry and parallaxes from Gaia EDR3 and the 2MASS and WISE surveys. The algorithm accounts for uncertainties in the predictions arising from the range of possible outputs at each input and from the range of models compatible with the training set (through drop-out). A two-stage procedure is adopted where an initial network to estimate photoastrometric parallaxes is trained using a large sample of noisy parallax data from Gaia EDR3 and then a secondary network is trained using spectroscopic metallicities from the APOGEE and LAMOST surveys and an augmented feature space utilizing the first-stage parallax estimates. The algorithm produces metallicity predictions with an average uncertainty of |$\pm 0.19\, \mathrm{dex}$|⁠. The methodology is applied to stars within the Galactic bar/bulge with particular focus on a sample of 1.69 million objects with Gaia radial velocities. We demonstrate the use and validity of our approach by inspecting both spatial and kinematic gradients with metallicity in the Galactic bar/bulge recovering previous results on the vertical metallicity gradient (−0.528 ± 0.002 dex kpc−1) and the vertex deviation of the bar (⁠|$-21.29\pm 2.74\, \mathrm{deg}$|⁠). [ABSTRACT FROM AUTHOR]

We report the discovery of a giant planet in event UKIRT-2017-BLG-001, detected by the United Kingdom Infrared Telescope (UKIRT) microlensing survey. The mass ratio between the planet and its host is =-q 1.50+0.170-0.14 0.17 3, about 1.5 times the Jupiter/Sun mass ratio. The event lies 0 .35 from the Galactic center and suffers from high extinction of AK=1.68. Therefore, it could be detected only by a near-infrared (NIR) survey. The field also suffers from large spatial differential extinction, which makes it difficult to estimate the source properties required to derive the angular Einstein radius. Nevertheless, we find evidence suggesting that the source is located in the far disk. If correct, this would be the first source star of a microlensing event to be identified as belonging to the far disk. We estimate the lens mass and distance using a Bayesian analysis to find that the planet's mass is 1.28+ M0.44 J 0.37 , and it orbits a-+ 0.81 +0.21-0.27 Ṁ 0.21 star at an instantaneous projected separation of 4.18+0.96-0.88au. The system is at a distance of-6.3+16-2.1kpc, and so likely resides in the Galactic bulge. In addition, we find a non-standard extinction curve in this field, in agreement with previous results toward high-extinction fields near the Galactic center.

We present photometric metallicity measurements for a sample of 2.6 million bulge red clump stars extracted from the Blanco DECam Bulge Survey (BDBS). Similar to previous studies, we find that the bulge exhibits a strong vertical metallicity gradient, and that at least two peaks in the metallicity distribution functions appear at b < −5°. We can discern a metal-poor ([Fe/H] ∼ −0.3) and metal-rich ([Fe/H] ∼ +0.2) abundance distribution that each show clear systematic trends with latitude, and may be best understood by changes in the bulge's star formation/enrichment processes. Both groups exhibit asymmetric tails, and as a result we argue that the proximity of a star to either peak in [Fe/H] space is not necessarily an affirmation of group membership. The metal-poor peak shifts to lower [Fe/H] values at larger distances from the plane while the metal-rich tail truncates. Close to the plane, the metal-rich tail appears broader along the minor axis than in off-axis fields. We also posit that the bulge has two metal-poor populations – one that belongs to the metal-poor tail of the low latitude and predominantly metal-rich group, and another belonging to the metal-poor group that dominates in the outer bulge. We detect the X-shape structure in fields with |Z| > 0.7 kpc and for stars with [Fe/H] > −0.5. Stars with [Fe/H] < −0.5 may form a spheroidal or 'thick bar' distribution while those with [Fe/H] |$\gtrsim$| −0.1 are strongly concentrated near the plane. [ABSTRACT FROM AUTHOR]

We use near-infrared photometry and astrometry from the VISTA Variables in the Via Lactea (VVV) survey to analyse microlensing events containing annual microlensing parallax information. These events are located in highly extincted and low-latitude regions of the Galactic bulge typically off-limits to optical microlensing surveys. We fit a catalogue of 1959 events previously found in the VVV and extract 21 microlensing parallax candidates. The fitting is done using nested sampling to automatically characterize the multimodal and degenerate posterior distributions of the annual microlensing parallax signal. We compute the probability density in lens mass-distance using the source proper motion and a Galactic model of disc and bulge deflectors. By comparing the expected flux from a main sequence lens to the baseline magnitude and blending parameter, we identify four candidates which have probability >50 per cent that the lens is dark. The strongest candidate corresponds to a nearby (≈0.78 kpc), medium-mass (⁠|$1.46^{+1.13}_{-0.71} \ M_{\odot }$|⁠) dark remnant as lens. In the next strongest, the lens is located at heliocentric distance ≈5.3 kpc. It is a dark remnant with a mass of |$1.63^{+1.15}_{-0.70} \ M_{\odot }$|⁠. Both of those candidates are most likely neutron stars, though possibly high-mass white dwarfs. The last two events may also be caused by dark remnants, though we are unable to rule out other possibilities because of limitations in the data. We are also demonstrating future possibilities of studying similar events with the Roman Space Telescope by modelling a mock dataset of Roman photometry and astrometry for an event resembling our strongest candidate. [ABSTRACT FROM AUTHOR]

We present an analysis of high-latitude δ Scuti stars (| b | > 1°) in the Galactic bulge region (−8 |${_{.}^{\circ}}$| 3 < l < 9 |${_{.}^{\circ}}$| 4) using a clean sample of the photometric data of 7440 stars recently released by the OGLE-IV project. The geometrical parameters of the bulge are determined based on Maximum Likelihood (ML) analysis in five-dimensional parameter space. More refined values of these parameters as well as their uncertainties are obtained from a fully Bayesian Markov chain Monte Carlo (MCMC) analysis. Approximating the bulge as an ellipsoid, the distribution of the number density of stars as a function of Galacto-centric distance has been modelled using three distribution functions: two Exponential (⁠|$\rm E_{1},\rm E_{2}$|⁠) types and one Gaussian (⁠|$\rm G$|⁠) type. Based on the AIC and BIC values, the exponential model |$\rm E_{1}$| is chosen as the best statistical model for the parameter values obtained from the MCMC analysis. The MCMC analysis yields the following results: the mean distance to the Galactic Centre (GC) is found to be R 0 = 8.034 ± 0.012stat ± 0.586sys kpc; the bulge δ Scuti distribution has a triaxial shape with normalized (a ≡ 1) axes ratios (a : b : c) as 1.000 ± 0.005: 0.348 ± 0.002: 0.421 ± 0.002. Here a is the semi-major axis lying in the Galactic plane and pointing towards us; b and c are the two semi-minor axes, the former lying in the Galactic plane and the later perpendicular to it. Smaller values of b as compared to a obtained for Galacto-centric distances R ≥ 2.0 kpc indicate the presence of a bar-like structure of the bulge with a bar angle of 22 |${_{.}^{\circ}}$| 006 ± 2 |${_{.}^{\circ}}$| 078. [ABSTRACT FROM AUTHOR]

The extinction law from 0.9 to 8 microns in the inner |$3\times 3\deg ^2$| of the Milky Way is measured using data from VISTA Variables in the Via Lactea, GLIMPSE, and WISE. Absolute extinction ratios are found by requiring that the observed red clump density peaks at the GRAVITY collaboration distance to the Galactic centre. When combined with selective extinction ratios measured from the bulge giant colour–colour diagrams, we find an extinction law of |$A_Z:A_Y:A_J:A_H:A_{K_s}:A_{W1}:A_{[3.6]}:A_{[4.5]}:A_{W2}:A_{[5.8]}:A_{[8.0]} =7.19(0.30):5.11(0.20):3.23(0.11):1.77(0.04):1:0.54(0.02):0.46(0.03):0.34(0.03):0.32(0.03):0.24(0.04):0.28(0.03)$| valid for low extinctions where non-linearities are unimportant. These results imply an extinction law from the Rayleigh Jeans colour excess method of |$A_{K_s}=0.677(H-[4.5]-0.188)$|⁠. We find little evidence for significant selective extinction ratio variation over the inspected region (around |$5\, \mathrm{per\, cent}$|⁠). Assuming the absolute extinction ratios do not vary across the inspected region gives an independent measurement of the absolute Ks magnitude of the red clump at the Galactic Centre of |$(-1.61\pm 0.07)\, \mathrm{mag}$|⁠. This is very similar to the value measured for solar neighbourhood red clump stars giving confidence in the use of red clump stars as standard candles across the Galaxy. As part of our analysis, we inspect the completeness of PSF photometry from the VVV survey using artificial star tests, finding |$90\, \mathrm{per\, cent}$| completeness at |$K_s\approx 16 \, (17)$| in high (low) density regions and good agreement with the number counts with respect to the GALACTICNUCLEUS and DECAPS catalogues over small regions of the survey. [ABSTRACT FROM AUTHOR]

It has been proposed that the globular cluster-like system Terzan 5 is the surviving remnant of a primordial building block of the Milky Way bulge, mainly due to the age/metallicity spread and the distribution of its stars in the α–Fe plane. We employ Sloan Digital Sky Survey data from the Apache Point Observatory Galactic Evolution Experiment to test this hypothesis. Adopting a random sampling technique, we contrast the abundances of 10 elements in Terzan 5 stars with those of their bulge field counterparts with comparable atmospheric parameters, finding that they differ at statistically significant levels. Abundances between the two groups differ by more than 1σ in Ca, Mn, C, O, and Al, and more than 2σ in Si and Mg. Terzan 5 stars have lower [α/Fe] and higher [Mn/Fe] than their bulge counterparts. Given those differences, we conclude that Terzan 5 is not the remnant of a major building block of the bulge. We also estimate the stellar mass of the Terzan 5 progenitor based on predictions by the Evolution and Assembly of GaLaxies and their Environments suite of cosmological numerical simulations, concluding that it may have been as low as ∼3 × 108 M⊙ so that it was likely unable to significantly influence the mean chemistry of the bulge/inner disc, which is significantly more massive (∼1010 M⊙). We briefly discuss existing scenarios for the nature of Terzan 5 and propose an observational test that may help elucidate its origin. [ABSTRACT FROM AUTHOR]

Like most spiral galaxies, the Milky Way contains a population of blue, metal-poor globular clusters and another of red, metal-rich ones. Most of the latter belong to the bulge, and therefore they are poorly studied compared to the blue (halo) ones because they suffer higher extinction and larger contamination from field stars. These intrinsic difficulties, together with a lack of low-mass bulge globular clusters, are reasons to believe that their census is not complete yet. Indeed, a few new clusters have been confirmed in the last few years. One of them is VVV CL001, the subject of the present study. We present a new spectroscopic analysis of the recently confirmed globular cluster VVV CL001, made by means of MUSE@VLT integral field data. Individual spectra were extracted for stars in the VVV CL001 field. Radial velocities were derived by cross-correlation with synthetic templates. Coupled with proper motions from the VVV (VISTA Variables in the Vía Láctea) survey, these data allow us to select 55 potential cluster members, for which we derive metallicities using the public code The Cannon. The mean radial velocity of the cluster is V helio = −324.9 ± 0.8 km s−1, as estimated from 55 cluster members. This high velocity, together with a low metallicity [Fe/H] = −2.04 ± 0.02 dex, suggests that VVV CL001 could be a very old cluster. The estimated distance is d  = 8.23 ± 0.46 kpc, placing the cluster in the Galactic bulge. Furthermore, both its current position and the orbital parameters suggest that VVV CL001 is most probably a bulge globular cluster. [ABSTRACT FROM AUTHOR]

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]