- ID:
- ivo://CDS.VizieR/J/MNRAS/464/194
- Title:
- Metallicity distribution in the GC
- Short Name:
- J/MNRAS/464/194
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowing the metallicity distribution of stars in the Galactic Centre has important implications for the formation history of the Milky Way nuclear star cluster. However, this distribution is not well known, and is currently based on a small sample of fewer than 100 stars. We obtained near-infrared K-band spectra of more than 700 late-type stars in the central 4pc^2^ of the Milky Way nuclear star cluster with the integral-field spectrograph KMOS (VLT). We analyse the medium-resolution spectra using a full-spectral fitting method employing the Gottingen spectral library of synthetic PHOENIX spectra. The derived stellar metallicities range from metal-rich [M/H]>+0.3dex to metal-poor [M/H]<-1.0dex, with a fraction of 5.2^+6.0^_-3.1_ per cent metal-poor ([M/H]<=-0.5dex) stars. The metal-poor stars are distributed over the entire observed field. The origin of metal-poor stars remains unclear. They could originate from infalling globular clusters. For the metal-rich stellar population ([M/H]>0dex), a globular cluster origin can be ruled out. As there is only a very low fraction of metal-poor stars in the central 4pc^2^ of the Galactic Centre, we believe that our data can discard a scenario in which the Milky Way nuclear star cluster is purely formed from infalling globular clusters.
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/534/A80
- Title:
- Metallicity of bulge clump giants in Baade's window
- Short Name:
- J/A+A/534/A80
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We seek to constrain the formation of the Galactic bulge by means of analysing the detailed chemical composition of a large sample of red clump stars in Baade's window. These stars were selected to minimise the contamination by other Galactic components, so they are good tracers of the bulge metallicity distribution in Baade's window, at least for stars more metal-rich than ~-1.5. We used an automatic procedure to measure [Fe/H] in a sample of 219 bulge red clump stars from R=20000 resolution spectra obtained with FLAMES/GIRAFFE at the VLT. The analysis was performed differentially with respect to the metal-rich local reference star MuLeo. For a subsample of 162 stars, we also derived [Mg/H] from spectral synthesis around the MgI triplet at 6319{AA}. The Fe and Mg metallicity distributions are both asymmetric with median values of +0.16 and +0.21, respectively. They show only a small proportion of stars at low metallicities, extending down to [Fe/H]=-1.1 or [Mg/H]=-0.7 The iron distribution is clearly bimodal, as revealed both by a deconvolution (from observational errors) and a Gaussian decomposition. The decomposition of the observed Fe and Mg metallicity distributions into Gaussian components yields two populations of equal sizes (50% each): a metal-poor component centred on [Fe/H]=-0.30 and [Mg/H]=-0.06 with a large dispersion and a narrow metal-rich component centred on [Fe/H]=+0.32 and [Mg/H]=+0.35. The metal-poor component shows high [Mg/Fe] ratios (around 0.3), while stars in the metal-rich component are found to have near solar ratios. Kinematical differences between the two components have also been found: the metal-poor component shows kinematics compatible with an old spheroid, while the metal-rich component is consistent with a population supporting a bar. In view of their chemical and kinematical properties, we suggest different formation scenarii for the two populations: a rapid formation time scale as an old spheroid for the metal-poor component (old bulge) and for the metal-rich component, a formation on a longer time scale driven by the evolution of the bar (pseudo-bulge).
- ID:
- ivo://CDS.VizieR/J/ApJ/798/77
- Title:
- Metallicity of RGB stars in 6 M31 dwarf galaxies
- Short Name:
- J/ApJ/798/77
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present global metallicity properties, metallicity distribution functions (MDFs), and radial metallicity profiles for the six most luminous M31 dwarf galaxy satellites: M32, NGC 205, NGC 185, NGC 147, Andromeda VII, and Andromeda II. The results presented are the first spectroscopic MDFs for dwarf systems surrounding a host galaxy other than the Milky Way (MW). Our sample consists of individual metallicity measurements for 1243 red giant branch member stars spread across these six systems. We determine metallicities based on the strength of the Ca II triplet lines using the empirical calibration of Carrera et al. (2013, J/MNRAS/434/1681), which is calibrated over the metallicity range -4<[Fe/H]<+0.5. We find that these M31 satellites lie on the same luminosity-metallicity relationship as the MW dwarf satellites. We do not find a trend between the internal metallicity spread and galaxy luminosity, contrary to previous studies. The MDF widths of And II and And VII are similar to the MW dwarf spheroidal (dSph) satellites of comparable luminosity; however, our four brightest M31 dwarf satellites are more luminous than any of the MW dSphs and have broader MDFs. The MDFs of our six M31 dwarf satellites are consistent with the leaky box model of chemical evolution, although our metallicity errors allow a wide range of evolution models. We find a significant radial gradient in metallicity in only two of our six systems, NGC 185 and Andromeda II, and flat radial metallicity gradients in the rest of our sample with no observed correlation between rotational support and radial metallicity gradients. Although the average properties and radial trends of the M31 dwarf galaxies agree with their MW counterparts at similar luminosity, the detailed MDFs are different, particularly at the metal-rich end.
- ID:
- ivo://CDS.VizieR/J/ApJ/808/108
- Title:
- M2FS stellar spectroscopy of Reticulum 2
- Short Name:
- J/ApJ/808/108
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from spectroscopic observations with the Michigan/Magellan Fiber System (M2FS) of 182 stellar targets along the line of sight (LOS) to the newly discovered "ultrafaint" object Reticulum 2 (Ret 2). For 37 of these targets, the spectra are sufficient to provide simultaneous estimates of LOS velocity ({nu}i_los_, median random error {delta}_{nu}los_=1.4km/s), effective temperature (T_eff_, {delta}_Tef_=478K), surface gravity (logg, {delta}_logg_=0.63dex), and iron abundance ([Fe/H], {delta}_[Fe/H]_=0.47dex). We use these results to confirm 17 stars as members of Ret 2. From the member sample we estimate a velocity dispersion of {sigma}_{nu}los_=3.6_-0.7_^+1.0^km/s about a mean of <{nu}_los_>=64.3_1.2_^+1.2^km/s in the solar rest frame (~-90.9km/s in the Galactic rest frame), and a metallicity dispersion of {sigma}_[Fe/H]_=0.49_-0.14_^+0.19^dex about a mean of <[Fe/H]_>=-2.58_-0.33_^+0.34^. These estimates marginalize over possible velocity and metallicity gradients, which are consistent with zero. Our results place Ret 2 on chemodynamical scaling relations followed by the Milky Way's dwarf-galactic satellites. Under assumptions of dynamic equilibrium and negligible contamination from binary stars --both of which must be checked with deeper imaging and repeat spectroscopic observations-- the estimated velocity dispersion suggests a dynamical mass of M(R_h_)~5R_h_{sigma}_{nu}los_^2^/(2G)=2.4_-0.8_^+1.4^x10^5^M_{sun}_ enclosed within projected halflight radius R_h_~32pc, with mass-to-light ratio ~2M(R_h_)/L_V_=467_-168_^+286^ in solar units.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/3811
- Title:
- M33 GALEX catalogue of UV point sources
- Short Name:
- J/MNRAS/450/3811
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The hottest stars (>10000K), and by extension typically the most massive ones, are those that will be prevalent in the ultraviolet (UV) portion of the electromagnetic spectrum, and we expect to numerous B, O and WR (WR) stars to be bright in UV data. In this paper, we update the previous point source UV catalogue of M33, created using the Ultraviolet Imaging Telescope (UIT), using data from the Galaxy Evolution Explorer (GALEX). We utilize point spread function photometry to optimally photometer sources in the crowded regions of the galaxy, and benefit from GALEX's increased sensitivity compared to UIT. We match our detections with data from the Local Group Galaxies Survey to create a catalogue with photometry spanning from the far-UV through the optical for a final list of 24738 sources. All of these sources have far-UV (FUV; 1516{AA}), near-UV (NUV; 2267{AA}) and V data, and a significant fraction also have U, B, R and I data as well. We also present an additional 3000 sources that have no matching optical counterpart. We compare all of our sources to a catalogue of known WR stars in M33 and find that we recover 114 of 206 stars with spatially-coincident UV point sources. Additionally, we highlight and investigate those sources with unique colours as well as a selection of other well-studied sources in M33.
- ID:
- ivo://CDS.VizieR/J/AJ/128/245
- Title:
- M giant stars in the Sagittarius dwarf galaxy
- Short Name:
- J/AJ/128/245
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained moderate resolution (~6km/s) spectroscopy of several hundred M giant candidates selected from Two Micron All Sky Survey photometry (Cat. <II/246>). Radial velocities are presented for stars mainly in the southern Galactic hemisphere, and the primary targets have Galactic positions consistent with association to the tidal tail system of the Sagittarius (Sgr) dwarf galaxy.
- ID:
- ivo://CDS.VizieR/J/MNRAS/455/820
- Title:
- M87 globular cluster candidates catalog
- Short Name:
- J/MNRAS/455/820
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new photometric catalogue of the rich globular cluster (GC) system around M87, the brightest cluster galaxy in Virgo. Using archival Next Generation Virgo Cluster Survey images in the ugriz bands, observed with Canada-France-Hawaii Telescope/MegaPrime, we perform a careful subtraction of the galaxy's halo light in order to detect objects at small galactocentric radii as well as in the wider field, and find 17620 GC candidates over a radius range from 1.3 to 445kpc with g<24mag. By inferring their colour, radial and magnitude distributions in a Bayesian way, we find that they are well described as a mixture of two GC populations and two distinct contaminant populations, but confirm earlier findings of radius-dependent colour gradients in both GC populations. This is consistent with a picture in which the more enriched GCs reside deeper in the galaxy's potential well, indicating a role for dissipative collapse in the formation of both the red and the blue GCs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/462/1444
- Title:
- MHO catalogue for Cassiopeia and Auriga
- Short Name:
- J/MNRAS/462/1444
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the analysis of 35.5deg^2^ of images in the 1-0 S(1) line of H_2_ from the UK Widefield Infrared Survey for H_2_ (UWISH2) towards Cassiopeia and Auriga. We have identified 98 Molecular Hydrogen emission-line Objects (MHOs) driven by Young Stellar Objects, 60 per cent of which are bipolar outflows and all are new discoveries. We estimate that the UWISH2-extended emission object catalogue contains fewer than 2 per cent false positives and is complete at the 95 per cent level for jets and outflows brighter than the UWISH2 detection limit. We identified reliable driving source candidates for three quarters of the detected outflows, 40 per cent of which are associated with groups and clusters of stars. The driving source candidates are 20 per cent protostars, the remainder are Classical T-Tauri Stars. We also identified 15 new star cluster candidates near MHOs in the survey area. We find that the typical outflow identified in the sample has the following characteristics: the position angles are randomly orientated; bipolar outflows are straight within a few degrees; the two lobes are slightly asymmetrical in length and brightness; the length and brightness of the lobes are not correlated; typical time gaps between major ejections of material are 1-3 kyr, hence FU-Ori or EX-Ori eruptions are most likely not the cause of these, but we suggest MNors as a possible source. Furthermore, we find that outflow lobe length distributions are statistically different from the widely used total length distributions. There are a larger than expected number of bright outflows indicating that the flux distribution does not follow a power law.
- ID:
- ivo://CDS.VizieR/J/MNRAS/421/3257
- Title:
- MHO catalogue for Serpens and Aquila
- Short Name:
- J/MNRAS/421/3257
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Jets and outflows from young stellar objects (YSOs) are important signposts of currently ongoing star formation. In order to study these objects, we are conducting an unbiased survey along the Galactic plane in the 1-0 S(1) emission line of molecular hydrogen at 2.122 um using the United Kingdom Infrared Telescope. In this paper, we are focusing on a 33-deg^2^-sized region in Serpens and Aquila (18{deg}<l<30{deg}; -1.5{deg}<b<+1.5{deg}). We trace 131 jets and outflows from YSOs, which results in a 15-fold increase in the total number of known molecular hydrogen outflows. Compared to this, the total integrated 1-0 S(1) flux of all objects just about doubles, since the known objects occupy the bright end of the flux distribution. Our completeness limit is 3x10^-18^W/m^2^ with 70 per cent of the objects having fluxes of less than 10^-17^W/m^2^.
- ID:
- ivo://CDS.VizieR/J/ApJ/844/38
- Title:
- MHOs toward 22 regions with H2 fluxes
- Short Name:
- J/ApJ/844/38
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a narrow-band near-infrared imaging survey for Molecular Hydrogen emission-line Objects (MHOs) toward 26 regions containing high-mass protostellar candidates and massive molecular outflows. We have detected a total of 236 MHOs, 156 of which are new detections, in 22 out of the 26 regions. We use H_2_2.12{mu}m/H_2_2.25{mu}m flux ratios, together with morphology, to separate the signatures of fluorescence associated with photo- dissociation regions (PDRs) from shocks associated with outflows in order to identify the MHOs. PDRs have typical low flux ratios of ~1.5-3, while the vast majority of MHOs display flux ratios typical of C-type shocks (~6-20). A few MHOs exhibit flux ratios consistent with expected values for J-type shocks (~3-4), but these are located in regions that may be contaminated with fluorescent emission. Some previously reported MHOs have low flux ratios, and are likely parts of PDRs rather than shocks indicative of outflows. We identify a total of 36 outflows across the 22 target regions where MHOs were detected. In over half these regions, MHO arrangements and fluorescent structures trace features present in CO outflow maps, suggesting that the CO emission traces a combination of dynamical effects, which may include gas entrained in expanding PDRs as well as bipolar outflows. Where possible, we link MHO complexes to distinct outflows and identify candidate driving sources.
