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21. Molecular cloud cores in the GC 50km/s cloud
ID:
ivo://CDS.VizieR/J/ApJ/872/121
Title:
Molecular cloud cores in the GC 50km/s cloud
Short Name:
J/ApJ/872/121
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Galactic center 50km/s molecular cloud (50MC) is the most remarkable molecular cloud in the Sagittarius A region. This cloud is a candidate for the massive star formation induced by cloud-cloud collision (CCC) with a collision velocity of ~30km/s that is estimated from the velocity dispersion. We observed the whole of the 50MC with a high angular resolution (~2.0"x1.4") in Atacama Large Millimeter/submillimeter Array cycle 1 in the H^13^CO^+^ J=1-0 and C^34^S J=2-1 emission lines. We identified 241 and 129 bound cores with a virial parameter of less than 2, which are thought to be gravitationally bound, in the H^13^CO^+^ and C^34^S maps using the clumpfind algorithm, respectively. In the CCC region, the bound H^13^CO^+^ and C^34^S cores are 119 and 82, whose masses are 68% and 76% of those in the whole 50MC, respectively. The distribution of the core number and column densities in the CCC are biased to larger densities than those in the non-CCC region. The distributions indicate that the CCC compresses the molecular gas and increases the number of the dense bound cores. Additionally, the massive bound cores with masses of >3000M_{sun}_ exist only in the CCC region, although the slope of the core mass function (CMF) in the CCC region is not different from that in the non-CCC region. We conclude that the compression by the CCC efficiently formed massive bound cores even if the slope of the CMF is not changed so much by the CCC.
22. New open clusters in Galactic anti-centre
ID:
ivo://CDS.VizieR/J/A+A/627/A35
Title:
New open clusters in Galactic anti-centre
Short Name:
J/A+A/627/A35
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Gaia Data Release 2 (DR2) provided an unprecedented volume of precise astrometric and excellent photometric data. In terms of data mining the Gaia catalogue, machine learning methods have shown to be a powerful tool, for instance in the search for unknown stellar structures. Particularly, supervised and unsupervised learning methods combined together significantly improves the detection rate of open clusters. We systematically scan Gaia DR2 in a region covering the Galactic anticentre and the Perseus arm (120{deg}<=l<=205{deg} and -10{deg}<=b<=10{deg}), with the goal of finding any open clusters that may exist in this region, and fine tuning a previously proposed methodology and successfully applied to TGAS data, adapting it to different density regions. Our methodology uses an unsupervised, density-based, clustering algorithm, DBSCAN, that identifies overdensities in the five-dimensional astrometric parameter space (l, b, {varpi}, pmRA*, pmDE) that may correspond to physical clusters. The overdensities are separated into physical clusters (open clusters) or random statistical clusters using an artificial neural network to recognise the isochrone pattern that open clusters show in a colour magnitude diagram. The method is able to recover more than 75% of the open clusters confirmed in the search area. Moreover, we detected 53 open clusters unknown previous to Gaia DR2, which represents an increase of more than 22% with respect to the already catalogued clusters in this region. We find that the census of nearby open clusters is not complete. Different machine learning methodologies for a blind search of open clusters are complementary to each other; no single method is able to detect 100% of the existing groups. Our methodology has shown to be a reliable tool for the automatic detection of open clusters, designed to be applied to the full Gaia DR2 catalogue.
23. NuSTAR hard X-ray survey of the Galactic Center. II.
ID:
ivo://CDS.VizieR/J/ApJ/825/132
Title:
NuSTAR hard X-ray survey of the Galactic Center. II.
Short Name:
J/ApJ/825/132
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first survey results of hard X-ray point sources in the Galactic Center (GC) region by NuSTAR. We have discovered 70 hard (3-79 keV) X-ray point sources in a 0.6 deg^2^ region around Sgr A* with a total exposure of 1.7 Ms, and 7 sources in the Sgr B2 field with 300 ks. We identify clear Chandra counterparts for 58 NuSTAR sources and assign candidate counterparts for the remaining 19. The NuSTAR survey reaches X-ray luminosities of ~4x and ~8x10^32^ erg/s at the GC (8 kpc) in the 3-10 and 10-40 keV bands, respectively. The source list includes three persistent luminous X-ray binaries (XBs) and the likely run-away pulsar called the Cannonball. New source-detection significance maps reveal a cluster of hard (>10 keV) X-ray sources near the Sgr A diffuse complex with no clear soft X-ray counterparts. The severe extinction observed in the Chandra spectra indicates that all the NuSTAR sources are in the central bulge or are of extragalactic origin. Spectral analysis of relatively bright NuSTAR sources suggests that magnetic cataclysmic variables constitute a large fraction (>40%-60%). Both spectral analysis and logN-logS distributions of the NuSTAR sources indicate that the X-ray spectra of the NuSTAR sources should have kT>20 keV on average for a single temperature thermal plasma model or an average photon index of {Gamma}=1.5-2 for a power-law model. These findings suggest that the GC X-ray source population may contain a larger fraction of XBs with high plasma temperatures than the field population.
24. Point Sources from a Spitzer/IRAC Survey of the Galactic Center
ID:
ivo://irsa.ipac/Spitzer/Catalog/GALCENPSC
Title:
Point Sources from a Spitzer/IRAC Survey of the Galactic Center
Short Name:
GALCENPSC
Date:
01 Jun 2021 21:40:29
Publisher:
NASA/IPAC Infrared Science Archive
Description:
Spitzer/IRAC observations of the central 2.0 deg by 1.4 deg (~ 280 pc by 200 pc) of the Galaxy were obtained at 3.6-8.0 microns in Cycle 1 (GO 3677, PI: Stolovy). These data represent the highest spatial resolution (~2 arcsec) and sensitivity uniform large-scale map made to date of the Galactic Center at mid-infrared wavelengths. A point source catalog of 1,065,565 objects was obtained. The catalog includes magnitudes for the point sources at 3.6, 4.5, 5.8, and 8.0 microns, as well as JHK photometry from 2MASS. The point source catalog is confusion limited with average limits of 12.4, 12.1, 11.7, and 11.2 magnitudes for [3.6], [4.5], [5.8], and [8.0], respectively. The confusion limits are spatially variable because of stellar surface density, background surface brightness level, and extinction variations across the survey region. More details about the point source catalog can be found at Ramirez et al. 2008.
25. Proper motion catalogue of Galactic Centre
ID:
ivo://CDS.VizieR/J/A+A/632/A116
Title:
Proper motion catalogue of Galactic Centre
Short Name:
J/A+A/632/A116
Date:
21 Oct 2021
Publisher:
CDS
Description:
Proper motion studies of stars in the centre of the Milky Way have typically been limited to the Arches and Quintuplet clusters, and to the central parsec. Here we present the first results of a large-scale proper motion study of stars within several tens of parsecs of Sagittarius A* based on our 0.2" angular resolution GALACTICNUCLEUS survey (epoch 2015) combined with NICMOS/HST data from the Paschen-alpha survey (epoch 2008). This comprises the first extensive proper motion study of the central ~36'x16' of the Galaxy, which is not covered adequately by any of the existing astronomical surveys, such as Gaia, because of the extreme interstellar extinction(AV>~30mag). Proper motions can help us to disentangle the different stellar populations along the line-of-sight and interpret their properties in combination with multi-wavelength photometry from GALACTICNUCLEUS and other sources. It also allows us to infer the dynamics and interrelationships between different stellar components (Galactic bulge, nuclear stellar disk, nuclear stellar cluster) of the Galactic centre (GC). In particular, we use proper motions to detect co-moving groups of stars which are able to trace low-mass or partially-dissolved young clusters in the GC that can hardly be discovered by any other means. Our pilot study for this work is based on a field in the nuclear bulge associated with Hii regions that show the presence of young stars. We have detected the first group of co-moving stars coincident with an HII region. Using colour-magnitude diagrams, we have inferred that the co-moving stars are consistent with the post-main sequence stars with ages of few Myr. Simulations show that this group of stars is a real group that can indicate the existence of a dissolving or low-to-intermediate-mass young cluster. A census of these undiscovered clusters will ultimately help us to constrain star formation at the GC in the past few ten Myr.
26. Radio continuum param. of Galactic HII regions
ID:
ivo://CDS.VizieR/J/ApJ/901/51
Title:
Radio continuum param. of Galactic HII regions
Short Name:
J/ApJ/901/51
Date:
15 Feb 2022 14:31:45
Publisher:
CDS
Description:
Sgr E is a massive star formation complex found toward the Galactic center that consists of numerous discrete, compact HII regions. It is located at the intersection between the central molecular zone (CMZ) and the far dust lane of the Galactic bar, similar to "hot spots" seen in external galaxies. Compared with other Galactic star formation complexes, the Sgr E complex is unusual because its HII regions all have similar radio luminosities and angular extents, and they are deficient in ~10{mu}m emission from their photodissociation regions (PDRs). Our Green Bank Telescope radio recombination line observations increase the known membership of Sgr E to 19 HII regions. There are 43 additional HII region candidates in the direction of Sgr E, 26 of which are detected for the first time here using MeerKAT 1.28GHz data. Therefore, the true HII region population of Sgr E may number >60. Using APEX SEDIGISM ^13^CO 2->1 data we discover a 3.0x10^5^M_{sun}_ molecular cloud associated with Sgr E, but find few molecular or far-infrared concentrations at the locations of the Sgr E HII regions. Comparison with simulations and an analysis of its radio continuum properties indicate that Sgr E formed upstream in the far dust lane of the Galactic bar a few million years ago and will overshoot the CMZ, crashing into the near dust lane. We propose that the unusual infrared properties of the Sgr E HII regions are caused by their orbits about the Galactic center, which have possibly stripped their PDRs.
27. RR Lyrae cand. in the Galactic Center
ID:
ivo://CDS.VizieR/J/ApJ/863/79
Title:
RR Lyrae cand. in the Galactic Center
Short Name:
J/ApJ/863/79
Date:
21 Oct 2021
Publisher:
CDS
Description:
Deep near-IR images from the VISTA Variables in the Via Lactea (VVV) Survey were used to search for RR Lyrae stars within 100 arcmin from the Galactic Center. A large sample of 960 RR Lyrae of type ab (RRab) stars were discovered. A catalog is presented featuring the positions, magnitudes, colors, periods, and amplitudes for the sample, in addition to estimated reddenings, distances, and metallicities, and measured individual relative proper motions. We use the reddening-corrected Wesenheit magnitudes, defined as W_Ks_=Ks-0.428x(J-Ks), in order to isolate bona fide RRL belonging to the Galaxy Center, finding that 30 RRab are foreground/background objects. We measure a range of extinctions from A_Ks_=0.19 to 1.75mag for the RRab in this region, finding that large extinction is the main cause of the sample incompleteness. The mean period is P=0.5446+/-0.0025d, yielding a mean metallicity of [Fe/H]=-1.30+/-0.01 ({sigma}=0.33)dex for the RRab sample in the Galactic Center region. The median distance for the sample is D=8.05+/-0.02kpc. We measure the RRab surface density using the less reddened region sampled here, finding a density of 1000 RRab/sq deg at a projected Galactocentric distance R_G_=1.6deg. Under simple assumptions, this implies a large total mass (M>10^9^M_{sun}_) for the old and metal-poor population contained inside RG. We also measure accurate relative proper motions, from which we derive tangential velocity dispersions of {sigma}V_l_=125.0 and {sigma}V_b_=124.1km/s along the Galactic longitude and latitude coordinates, respectively. The fact that these quantities are similar indicate that the bulk rotation of the RRab population is negligible, and implies that this population is supported by velocity dispersion. In summary, there are two main conclusions of this study. First, the population as a whole is no different from the outer bulge RRab, predominantly a metal-poor component that is shifted with respect to the Oosterhoff type I population defined by the globular clusters in the halo. Second, the RRab sample, as representative of the old and metal-poor stellar population in the region, has high velocity dispersions and zero rotation, suggesting a formation via dissipational collapse.
28. SCUBA-2 Galactic Center compact source catalog
ID:
ivo://CDS.VizieR/J/ApJS/234/22
Title:
SCUBA-2 Galactic Center compact source catalog
Short Name:
J/ApJS/234/22
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new JCMT SCUBA-2 observations of the Galactic Center region from 355{deg}<l<5{deg} and b<+/-1{deg}, covering 10x2 square degrees along the Galactic Plane to a depth of 43mJy/beam at 850{mu}m and 360mJy/beam at 450{mu}m. We describe the mapping strategy and reduction method used. We present ^12^CO(3-2) observations of selected regions in the field. We derive the molecular-line conversion factors (mJy/beam per K.km/s) at 850 and 450{mu}m, which are then used to obtain the amount of contamination in the continuum maps due to ^12^CO(3-2) emission in the 850{mu}m band. Toward the fields where the CO contamination has been accounted for, we present an 850{mu}m CO-corrected compact source catalog. Finally, we look for possible physical trends in the CO contamination with respect to column density, mass, and concentration. No trends were seen in the data despite the recognition of three contributors to CO contamination: opacity, shocks, and temperature, which would be expected to relate to physical conditions. These SCUBA-2 Galactic Center data are available via http://doi.org/10.11570/17.0009.
29. Spitzer/IRS observations of the Galactic Center
ID:
ivo://CDS.VizieR/J/ApJ/857/59
Title:
Spitzer/IRS observations of the Galactic Center
Short Name:
J/ApJ/857/59
Date:
21 Oct 2021
Publisher:
CDS
Description:
It has long been shown that the extreme ultraviolet spectrum of the ionizing stars of HII regions can be estimated by comparing the observed line emission to detailed models. In the Galactic Center (GC), however, previous observations have shown that the ionizing spectral energy distribution (SED) of the local photon field is strange, producing both very low excitation ionized gas (indicative of ionization by late O stars) and also widespread diffuse emission from atoms too highly ionized to be found in normal HII regions. This paper describes the analysis of all GC spectra taken by Spitzer's Infrared Spectrograph and downloaded from the Spitzer Heritage Archive. In it, HII region densities and abundances are described, and serendipitously discovered candidate planetary nebulae, compact shocks, and candidate young stellar objects are tabulated. Models were computed with Cloudy, using SEDs from Starburst99 plus additional X-rays, and compared to the observed mid-infrared forbidden and recombination lines. The ages inferred from the model fits do not agree with recent proposed star formation sequences (star formation in the GC occurring along streams of gas with density enhancements caused by close encounters with the black hole, Sgr A*), with Sgr B1, Sgr C, and the Arches Cluster being all about the same age, around 4.5Myr old, with similar X-ray requirements. The fits for the Quintuplet Cluster appear to give a younger age, but that could be caused by higher-energy photons from shocks from stellar winds or from a supernova.
30. Ultradeep catalog of X-ray point sources in the GC
ID:
ivo://CDS.VizieR/J/ApJS/235/26
Title:
Ultradeep catalog of X-ray point sources in the GC
Short Name:
J/ApJS/235/26
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an updated catalog of X-ray point sources in the inner 500" (~20pc) of the Galactic center (GC), where the nuclear star cluster (NSC) stands, based on a total of ~4.5Ms of Chandra observations taken from 1999 September to 2013 April. This ultradeep data set offers unprecedented sensitivity for detecting X-ray sources in the GC, down to an intrinsic 2-10keV luminosity of 1.0x10^31^erg/s. A total of 3619 sources are detected in the 2-8keV band, among which ~3500 are probable GC sources and ~1300 are new identifications. The GC sources collectively account for ~20% of the total 2-8keV flux from the inner 250" region where detection sensitivity is the greatest. Taking advantage of this unprecedented sample of faint X-ray sources that primarily traces the old stellar populations in the NSC, we revisit global source properties, including long-term variability, cumulative spectra, luminosity function, and spatial distribution. Based on the equivalent width and relative strength of the iron lines, we suggest that in addition to the arguably predominant population of magnetic cataclysmic variables (CVs), nonmagnetic CVs contribute substantially to the detected sources, especially in the lower-luminosity group. On the other hand, the X-ray sources have a radial distribution closely following the stellar mass distribution in the NSC, but much flatter than that of the known X-ray transients, which are presumably low-mass X-ray binaries (LMXBs) caught in outburst. This, together with the very modest long-term variability of the detected sources, strongly suggests that quiescent LMXBs are a minor (less than a few percent) population.

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