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Start Over Subject galactic center Content Level Research
1. Abundances and ages of stars in the Milky Way bulge
ID:
ivo://CDS.VizieR/J/ApJ/900/4
Title:
Abundances and ages of stars in the Milky Way bulge
Short Name:
J/ApJ/900/4
Date:
14 Mar 2022 07:37:10
Publisher:
CDS
Description:
The age and chemical characteristics of the Galactic bulge link to the formation and evolutionary history of the Galaxy. Data-driven methods and large surveys enable stellar ages and precision chemical abundances to be determined for vast regions of the Milky Way, including the bulge. Here, we use the data-driven approach of The Cannon, to infer the ages and abundances for 125367 stars in the Milky Way, using spectra from Apache Point Observatory Galaxy Evolution Experiment (apogee) DR14. We examine the ages and metallicities of 1654 bulge stars within R_GAL_<3.5kpc. We focus on fields with b<12{deg}, and out to longitudes of l<15{deg}. We see that stars in the bulge are about twice as old ({tau}=8Gyr), on average, compared to those in the solar neighborhood ({tau}=4Gyr), with a larger dispersion in [Fe/H] (~0.38 compared to 0.23dex). This age gradient comes primarily from the low-{alpha} stars. Looking along the Galactic plane, the very central field in the bulge shows by far the largest dispersion in [Fe/H] ({sigma}[Fe/H]~0.4dex) and line-of- sight velocity ({sigma}vr~90km/s), and simultaneously the smallest dispersion in age. Moving out in longitude, the stars become kinematically colder and less dispersed in [Fe/H], but show a much broader range of ages. We see a signature of the X-shape within the bulge at a latitude of b=8{deg}, but not at b=12{deg}. Future apogee and other survey data, with larger sampling, affords the opportunity to extend our approach and study in more detail, to place stronger constraints on models of the Milky Way.
2. Accurate OH maser positions. II. The GC.
ID:
ivo://CDS.VizieR/J/ApJS/239/15
Title:
Accurate OH maser positions. II. The GC.
Short Name:
J/ApJS/239/15
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high spatial resolution observations of ground-state OH masers achieved using the Australia Telescope Compact Array (ATCA). These observations were conducted toward 171 pointing centers where OH maser candidates were identified previously in the Southern Parkes Large-Area Survey in Hydroxyl (SPLASH) toward the Galactic center region between Galactic longitudes of 355* and 5* and Galactic latitudes of -2{deg} and +2{deg}. We detect maser emission toward 162 target fields and suggest that six out of nine nondetections are due to intrinsic variability. Due to the superior spatial resolution of the follow-up ATCA observations, we have identified 356 OH maser sites in the 162 target fields with maser detections. Almost half (161 of 356) of these maser sites have been detected for the first time in these observations. After comparing the positions of these 356 maser sites to the literature, we find that 269 (76%) sites are associated with evolved stars (two of which are PNe), 31 (9%) are associated with star formation, and four are associated with supernova remnants; we were unable to determine the origin of the remaining 52 (15%) sites. Unlike the pilot region, the infrared colors of evolved star sites with symmetric maser profiles in the 1612MHz transition do not show obvious differences compared with those of evolved star sites with asymmetric maser profiles.
3. ALMA obs. of massive clouds in the CMZ
ID:
ivo://CDS.VizieR/J/ApJ/894/L14
Title:
ALMA obs. of massive clouds in the CMZ
Short Name:
J/ApJ/894/L14
Date:
19 Jan 2022 13:10:58
Publisher:
CDS
Description:
We report Atacama Large Millimeter/submillimeter Array (ALMA) Band 6 continuum observations of 2000au resolution toward four massive molecular clouds in the Central Molecular Zone of the Galaxy. To study gas fragmentation, we use the dendrogram method to identify cores as traced by the dust continuum emission. The four clouds exhibit different fragmentation states at the observed resolution despite having similar masses at the cloud scale (~1-5pc). Assuming a constant dust temperature of 20K, we construct core mass functions of the clouds and find a slightly top-heavy shape as compared to the canonical initial mass function, but we note several significant uncertainties that may affect this result. The characteristic spatial separation between the cores as identified by the minimum spanning tree method, ~10^4^au, and the characteristic core mass, 1-7M_{sun}_, are consistent with predictions of thermal Jeans fragmentation. The three clouds showing fragmentation may be forming OB associations (stellar mass ~10^3^M_{sun}_). None of the four clouds under investigation seem to be currently able to form massive star clusters like the Arches and the Quintuplet (>~10^4^M_{sun}_), but they may form such clusters by further gas accretion onto the cores.
4. Arches cluster JVLA 6 and 10GHz images
ID:
ivo://CDS.VizieR/J/A+A/647/A110
Title:
Arches cluster JVLA 6 and 10GHz images
Short Name:
J/A+A/647/A110
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present high angular resolution radio observations of the Arches cluster in the Galactic centre, one of the most massive young clusters in the Milky Way. The data were acquired in two epochs and at 6 and 10 GHz with the Karl G. Jansky Very Large Array (JVLA). The rms noise reached is 3-4 times better than previous observations and we have almost doubled the number of known radio stars in the cluster. Nine of them have spectral indices consistent with thermal emission from ionised stellar winds. One is a confirmed wind colliding binary and two sources are ambiguous cases. Regarding variability, the radio emission appears to be stable on time scales of a few to ten years. Finally, we have showed that the number of radio stars can be used as a tool for constraining the age or mass of a cluster and also its mass function.
5. Bulge RR Lyrae VVVDR4 photometry
ID:
ivo://CDS.VizieR/J/other/ApSS/363.127
Title:
Bulge RR Lyrae VVVDR4 photometry
Short Name:
J/other/ApSS/363
Date:
21 Oct 2021
Publisher:
CDS
Description:
This study's objective was to exploit infrared VVV (VISTA Variables in the Via Lactea) photometry for high latitude RRab stars to establish an accurate Galactic Centre distance. RRab candidates were discovered and reaffirmed (n=4194) by matching Ks photometry with templates via chisq minimization, and contaminants were reduced by ensuring targets adhered to a strict period-amplitude (Ks) trend and passed the Elorietta et al. (2016A&A...595A..82E) classifier. The distance to the Galactic Centre was determined from a high latitude Bulge subsample (|b|>4, RGC=8.30+/-0.36kpc, random uncertainty is relatively negligible), and importantly, the comparatively low color-excess and uncrowded location mitigated uncertainties tied to the extinction law, the magnitude-limited nature of the analysis, and photometric contamination. Circumventing those problems resulted in a key uncertainty being the MKs relation, which was derived using LMC RRab stars (MKs=-(2.66+/-0.06)logP-(1.03+/-0.06), (J-Ks)0=(0.31+/-0.04)logP +(0.35+/-0.02), assuming mu0LMC=18.43). The Galactic Centre distance was not corrected for the cone-effect. Lastly, a new distance indicator emerged as brighter overdensities in the period-magnitude-amplitude diagrams analyzed, which arise from blended RRab and red clump stars. Blending may thrust faint extragalactic variables into the range of detectability.
6. Compact clouds in a sensitive GBT HI survey
ID:
ivo://CDS.VizieR/J/ApJ/855/33
Title:
Compact clouds in a sensitive GBT HI survey
Short Name:
J/ApJ/855/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a new sensitive survey of neutral hydrogen above and below the Galactic Center with the Green Bank Telescope. The observations extend up to Galactic latitude |b|<10{deg} with an effective angular resolution of 9.5' and an average rms brightness temperature noise of 40mK in a 1km/s channel. The survey reveals the existence of a population of anomalous high-velocity clouds extending up to heights of about 1.5kpc from the Galactic plane and showing no signature of Galactic rotation. These clouds have local standard of rest velocities |V_LSR_|<~360km/s, and assuming a Galactic Center origin, they have sizes of a few tens of parsec and neutral hydrogen masses spanning 10-10^5^M_{sun}_. Accounting for selection effects, the cloud population is symmetric in longitude, latitude, and VLSR. We model the cloud kinematics in terms of an outflow expanding from the Galactic Center and find the population consistent with being material moving with radial velocity V_w_~330km/s distributed throughout a bicone with opening angle {alpha}>140{deg}. This simple model implies an outflow luminosity L_w_>3x10^40^erg/s over the past 10Myr, consistent with star formation feedback in the inner region of the Milky Way, with a cold gas mass-loss rate <~0.1M_{sun}_/yr. These clouds may represent the cold gas component accelerated in the nuclear wind driven by our Galaxy, although some of the derived properties challenge current theoretical models of the entrainment process.
7. CS isotopes towards Galactic centre clouds
ID:
ivo://CDS.VizieR/J/A+A/642/A222
Title:
CS isotopes towards Galactic centre clouds
Short Name:
J/A+A/642/A222
Date:
21 Oct 2021
Publisher:
CDS
Description:
Measuring isotopic ratios is a sensitive technique to obtain information on stellar nucleosynthesis and chemical evolution. We present measurements of the carbon and sulphur abundances in the interstellar medium of the central region of our Galaxy. The selected targets are the +50km/s Cloud and several line-of-sight clouds towards Sgr B2(N). Towards the +50km/s Cloud, we observed the J=2-1 rotational transitions of ^12^C^32^S, ^12^C^34^S, ^13^C^32^S, ^12^C^33^S, and ^13^C^34^S, and the J=3-2 transitions of ^12^C^32^S and ^12^C^34^S with the IRAM-30m telescope, as well as the J=6-5 transitions of ^12^C^34^S and ^13^C^32^S with the APEX 12m telescope, all in emission. The J=2-1 rotational transitions of ^12^C^32^S, ^12^C^34^S, ^13^C^32^S, and ^13^C^34^S were observed with ALMA in Sgr B2(N)'s envelope, with those of ^12^C^32^S and ^12^C^34^S also observed in the line-of-sight clouds towards Sgr B2(N), all in absorption. In the +50km/s Cloud, we derive a ^12^C/^13^C isotopic ratio of 22.1^+3.3^_-2.4_, that leads, with the measured ^13^C^32^S/^12^C^34^S line intensity ratio, to a ^32^S/^34^S ratio of 16.3^+3.0^_-2.4_. We have also derived the ^32^S/^34^S isotopic ratio more directly from the two isotopologues ^13^C^32^S and ^13^C^34^S, which leads to an independent ^32^S/^34^S estimation of 16.3^+2.1^_-1.7_ and 17.9+/-5.0 for the +50km/s Cloud and Sgr B2(N), respectively. We also obtain a ^34^S/^33^S ratio of 4.3+/-0.2 in the +50km/s Cloud. Previous studies observed a decreasing trend in the ^32^S/^34^S isotopic ratios when approaching the Galactic centre. Our result indicates a termination of this tendency at least at a galactocentric distance of 130^+60^_-30_pc. This is at variance with findings based on ^12^C/^13^C, ^14^N/^15^N and ^18^O/^17^O isotope ratios, where the above-mentioned trend is observed to continue right to the central molecular zone. This can indicate a drop in the production of massive stars at the Galactic centre, in the same line as recent metallicity gradient ([Fe/H]) studies, and opens the work towards a comparison with Galactic and stellar evolution models.
8. First Fermi-LAT Inner Galaxy point source catalog
ID:
ivo://CDS.VizieR/J/ApJ/819/44
Title:
First Fermi-LAT Inner Galaxy point source catalog
Short Name:
J/ApJ/819/44
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Fermi Large Area Telescope (LAT) has provided the most detailed view to date of the emission toward the Galactic center (GC) in high-energy {gamma}-rays. This paper describes the analysis of data taken during the first 62 months of the mission in the energy range 1-100GeV from a 15{deg}x15{deg} region about the direction of the GC. Specialized interstellar emission models (IEMs) are constructed to enable the separation of the {gamma}-ray emissions produced by cosmic ray particles interacting with the interstellar gas and radiation fields in the Milky Way into that from the inner ~1kpc surrounding the GC, and that from the rest of the Galaxy. A catalog of point sources for the 15{deg}x15{deg} region is self-consistently constructed using these IEMs: the First Fermi-LAT Inner Galaxy Point Source Catalog (1FIG). The spatial locations, fluxes, and spectral properties of the 1FIG sources are presented, and compared with {gamma}-ray point sources over the same region taken from existing catalogs. After subtracting the interstellar emission and point-source contributions a residual is found. If templates that peak toward the GC are used to model the positive residual the agreement with the data improves, but none of the additional templates tried account for all of its spatial structure. The spectrum of the positive residual modeled with these templates has a strong dependence on the choice of IEM.
9. Gaia DR2 confirmed new nearby open clusters
ID:
ivo://CDS.VizieR/J/A+A/618/A59
Title:
Gaia DR2 confirmed new nearby open clusters
Short Name:
J/A+A/618/A59
Date:
21 Oct 2021
Publisher:
CDS
Description:
The publication of the Gaia Data Release 2 (Gaia DR2) opens a new era in astronomy. It includes precise astrometric data (positions, proper motions, and parallaxes) for more than 1.3 billion sources, mostly stars. To analyse such a vast amount of new data, the use of data-mining techniques and machine-learning algorithms is mandatory. A great example of the application of such techniques and algorithms is the search for open clusters (OCs), groups of stars that were born and move together, located in the disc. Our aim is to develop a method to automatically explore the data space, requiring minimal manual intervention. We explore the performance of a density-based clustering algorithm, DBSCAN, to find clusters in the data together with a supervised learning method such as an artificial neural network (ANN) to automatically distinguish between real OCs and statistical clusters. The development and implementation of this method in a five-dimensional space (l, b, p, {mu}_{alpha}_^*^, {mu}_{delta}_) with the Tycho-Gaia Astrometric Solution (TGAS) data, and a posterior validation using Gaia DR2 data, lead to the proposal of a set of new nearby OCs. We have developed a method to find OCs in astrometric data, designed to be applied to the full Gaia DR2 archive.
10. Galactic center CO rot-vib absorption lines
ID:
ivo://CDS.VizieR/J/A+A/626/A44
Title:
Galactic center CO rot-vib absorption lines
Short Name:
J/A+A/626/A44
Date:
21 Oct 2021
Publisher:
CDS
Description:
In the near- to mid-infrared wavelength domain, bright continuum sources in the central parsec of the Galactic center (GC) are subject to foreground absorption. These sources therefore represent ideal probes of the intervening material that is responsible for the absorption along the line of sight. Our aim is to shed light on the location and physics of the absorbing clouds. We try to find out which of the gaseous absorbing materials is intimately associated with the GC and which one is associated with clouds at a much larger distance. We used the capabilities of CRIRES spectrograph located at ESO Very Large Telescope in Chile to obtain absorption spectra of individual lines at a high spectral resolution of R=65000, that is, 5km/s. We observed the 12CO R(0), P(1), P(2), P(3), P(4), P(5), P(6), P(7) and P(9) transition lines, applied standard data reduction, and compared the results with literature data. Results. We present the results of CRIRES observations of 13 infrared sources located in the central parsec of the Galaxy. The data provide direct evidence for a complex structure of the interstellar medium along the line of sight and in the close environment of the central sources. In particular we find four cold foreground clouds at radial velocities vLS R of the order of -145, -85, -60, and -40+\/-15km/s that show absorption in the lower transition lines from R(0) to P(2) and in all the observed spectra.We also find in all sources an absorption in velocity range of 50-60km/s, possibly associated with the so-called 50km/s cloud and suggesting an extension of this cloud in front of the GC. Finally, we detect individual absorption lines that are probably associated with material much closer to the center and with the sources themselves, suggesting the presence of cold gas in the local region.