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11. GALACTICNUCLEUS IV. JHKs imaging survey
ID:
ivo://CDS.VizieR/J/A+A/653/A133
Title:
GALACTICNUCLEUS IV. JHKs imaging survey
Short Name:
J/A+A/653/A133
Date:
10 Mar 2022 11:26:04
Publisher:
CDS
Description:
The extreme extinction (A_V_~30mag) and its variation on arc-second scales towards the Galactic centre hamper the study of its stars. Their analysis is restricted to the near infrared (NIR) regime, where the extinction curve can be approximated by a broken power law for the JHKs bands. Therefore, correcting for extinction at these wavelengths is fundamental to analyse the structure and stellar population of the central regions of our Galaxy. We aim at: (1) Discussing different strategies to de-redden the photometry and checking the usefulness of extinction maps to deal with variable stars. (2) Building and making publicly available extinction maps for the NIR bands JHKs. (3) Creating a de-reddened catalogue of the GALACTICNUCLEUS (GNS) survey, identifying foreground stars. (4) Performing a preliminary analysis of the de-reddened $K_s$ luminosity functions (KLFs). We use photometry from the GNS survey to create extinction maps for the whole catalogue. We take red clump (RC) and red giant stars of similar brightness as a reference to build the maps, and de-redden the GNS photometry. We discuss the limitations of the process and analyse non-linear effects of the de-reddening. We create high resolution (~3'') extinction maps with low statistical and systematics uncertainties (<~5%), and compute average extinctions for each of the regions covered by the GNS. We check that our maps effectively correct the differential extinction reducing the spread of the RC features by a factor of ~2. We assess the validity of the broken power law approach computing two equivalent extinction maps A_H_ using either JH and HKs photometry for the same reference stars, and obtain compatible average extinctions within the uncertainties. Finally, we analyse de-reddened KLFs for different line-of-sights and find that the regions belonging to the NSD contain a homogeneous stellar population that is significantly different from the one in the innermost bulge regions.
12. GALACTICNUCLEUS: JHKs imaging survey
ID:
ivo://CDS.VizieR/J/A+A/610/A83
Title:
GALACTICNUCLEUS: JHKs imaging survey
Short Name:
J/A+A/610/A83
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Galactic Centre is of fundamental astrophysical interest, but existing near-infrared surveys fall short covering it adequately, either in terms of angular resolution, multi-wavelength coverage, or both. Here we introduce the GALACTICNUCLEUS survey, a JHKs imaging survey of the centre of the Milky Way with a 0.2" angular resolution. The purpose of this paper is to present the observations of Field 1 of our survey, centred approximately on SgrA* with an approximate size of 7.95'x3.43'. We describe the observational set-up and data reduction pipeline and discuss the quality of the data. Finally, we present the analysis of the data. The data were acquired with the near-infrared camera HAWK-I (High Acuity Wide field K-band Imager) at the ESO VLT (Very Large Telescope). Short readout times in combination with the speckle holography algorithm allowed us to produce final images with a stable, Gaussian PSF (point spread function) of 0.2" FWHM (full width at half maximum). Astrometric calibration is achieved via the VVV (VISTA Variables in the Via Lactea) survey and photometric calibration is based on the SIRIUS/IRSF (Infrared Survey Facility telescope) survey. The quality of the data is assessed by comparison between observations of the same field with different detectors of HAWK-I and at different times. We reach 5{sigma} uncertainties are less than 0.05" at J<=20, H<=17, and Ks<=16. We can distinguish five stellar populations in the colour-magnitude diagrams; three of them appear to belong to foreground spiral arms, and the other two correspond to high- and low-extinction star groups at the Galactic Centre. We use our data to analyse the near-infrared extinction curve and find some evidence for a possible difference between the extinction index between J-H and H-Ks. However, we conclude that it can be described very well by a power law with an index of JHKs=2.30+.-0.08. We do not find any evidence that this index depends on the position along the line of sight, or on the absolute value of the extinction. We produce extinction maps that show the clumpiness of the ISM (interstellar medium) at the Galactic Centre. Finally, we estimate that the majority of the stars have solar or super-solar metallicity by comparing our extinction-corrected colour-magnitude diagrams with isochrones with different metallicities and a synthetic stellar model with a constant star formation.
13. GALACTICNUCLEUS JHKs imaging survey. II.
ID:
ivo://CDS.VizieR/J/A+A/631/A20
Title:
GALACTICNUCLEUS JHKs imaging survey. II.
Short Name:
J/A+A/631/A20
Date:
21 Oct 2021
Publisher:
CDS
Description:
The high extinction and extreme source crowding of the central regions of the Milky Way are serious obstacles to the study of the structure and stellar population of the Galactic centre (GC). Surveys that cover the GC region (2MASS, UKIDSS, VVV, SIRIUS) do not have the necessary high angular resolution. Therefore, a high angular resolution survey in the near infrared is crucial to improve the state of the art. Here, we present the GALACTICNUCLEUS catalogue, a near infrared JHKs high angular resolution (0.2") survey of the nuclear bulge of the Milky Way. We explain in detail the data reduction, data analysis, calibration, and uncertainty estimation of the GALACTICNUCLEUS survey. We assess the data quality comparing our results with previous surveys. We obtained accurate JHKs photometry ~3.3x10^6^ stars in the GC detecting around 20% in J, 65% in H and 90% in Ks. The survey covers a total area of ~0.3 square degrees, which corresponds to ~6000pc^2^. The GALACTICNUCLEUS survey reaches 5 sigma detections for J~22mag, H~21mag and Ks~21mag. The uncertainties are below 0.05mag at J~21mag, H~19mag and Ks~18mag. The zero point systematic uncertainty is <~0.04mag in all three bands. We present colour-magnitude diagrams for the different regions covered by the survey.
14. Galactic Plane Infrared Polarization Survey, DR4
ID:
ivo://CDS.VizieR/J/ApJS/249/23
Title:
Galactic Plane Infrared Polarization Survey, DR4
Short Name:
J/ApJS/249/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Galactic Plane Infrared Polarization Survey (GPIPS) seeks to characterize the magnetic field in the dusty Galactic disk using near-infrared stellar polarimetry. All GPIPS observations were completed using the 1.83m Perkins telescope and Mimir instrument. GPIPS observations surveyed 76 deg^2^ of the northern Galactic plane, from Galactic longitudes 18{deg}-56{deg} and latitudes -1{deg} to +1{deg}, in the H band (1.6 {mu}m). Surveyed stars span 7th-16th mag, resulting in nearly 10 million stars with measured linear polarizations. Of these stars, ones with m_H_<12.5mag and polarization percentage uncertainties under 2% were judged to be high quality and number over one million. GPIPS data reveal plane-of-sky magnetic field orientations for numerous interstellar clouds for A_V_ values to ~30mag. The average sky separation of stars with m_H_<12.5mag is about 30'', or about 60 per Planck polarization resolution element. Matching to Gaia DR2 showed the brightest GPIPS stars are red giants with distances in the 0.6-7.5kpc range. Polarization orientations are mostly parallel to the Galactic disk, with some zones showing significant orientation departures. Changes in orientations are stronger as a function of Galactic longitude than of latitude. Considered at 10' angular scales, directions that show the greatest polarization fractions and narrowest polarization position angle distributions are confined to about 10 large, coherent structures that are not correlated with star-forming clouds. The GPIPS polarimetric and photometric data products (Data Release 4 catalogs and images) are publicly available for over 13 million stars.
15. Gal. Center MAGIC diffuse gamma-ray emission
ID:
ivo://CDS.VizieR/J/A+A/642/A190
Title:
Gal. Center MAGIC diffuse gamma-ray emission
Short Name:
J/A+A/642/A190
Date:
21 Oct 2021
Publisher:
CDS
Description:
In the presence of a sufficient amount of target material, gamma rays can be used as a tracer in the search for sources of Galactic cosmic rays (CRs). Here we present deep observations of the Galactic Center (GC) region with the MAGIC telescopes and use them to infer the underlying CR distribution and to study the alleged PeV proton accelerator (PeVatron) at the center of our Galaxy. We used data from 100hr observations of the GC region conducted with the MAGIC telescopes over five years (from 2012 to 2017). Those were collected at high zenith angles (58-70deg), leading to a larger energy threshold, but also an increased effective collection area compared to low zenith observations. Using recently developed software tools, we derived the instrument response and background models required for extracting the diffuse emission in the region. We used existing measurements of the gas distribution in the GC region to derive the underlying distribution of CRs. We present a discussion of the associated biases and limitations of such an approach. We obtain a significant detection for all four model components used to fit our data (Sgr A*, "Arc", G0.9+0.1, and an extended component for the Galactic Ridge). We observe no significant difference between the gamma-ray spectra of the immediate GC surroundings, which we model as a point source (Sgr A*) and the Galactic Ridge. The latter can be described as a power-law with index 2 and an exponential cut-off at around 20TeV with the significance of the cut-off being only 2{sigma}. The derived cosmic-ray profile hints to a peak at the GC position and with a measured profile index of 1.2+/-0.3 is consistent with the 1/r radial distance scaling law, which supports the hypothesis of a CR accelerator at the GC. We argue that the measurements of this profile are presently limited by our knowledge of the gas distribution in the GC vicinity.
16. Gas structure comparison; NGC 253 and Milky Way
ID:
ivo://CDS.VizieR/J/ApJ/899/158
Title:
Gas structure comparison; NGC 253 and Milky Way
Short Name:
J/ApJ/899/158
Date:
14 Mar 2022 07:10:20
Publisher:
CDS
Description:
We compare molecular gas properties in the starbursting center of NGC253 and the Milky Way Galactic center (GC) on scales of ~1-100pc using dendrograms and resolution-, area-, and noise-matched data sets in CO(1-0) and CO(3-2). We find that the size-line width relations in NGC253 and the GC have similar slope, but NGC253 has larger line widths by factors of ~2-3. The {sigma}2/R dependency on column density shows that, in the GC, on scales of 10-100pc the kinematics of gas over N>3x1021/cm^2^ are compatible with gravitationally bound structures. In NGC253 this is only the case for column densities N>3x1022/cm^2^. The increased line widths in NGC253 originate in the lower column density gas. This high velocity dispersion, not gravitationally self-bound gas, is likely in transient structures created by the combination of high average densities and feedback in the starburst. The high densities turn the gas molecular throughout the volume of the starburst, and the injection of energy and momentum by feedback significantly increases the velocity dispersion at a given spatial scale over what is observed in the GC.
17. 1482 Gaussian clumps in the Central Molecular Zone
ID:
ivo://CDS.VizieR/J/ApJ/897/89
Title:
1482 Gaussian clumps in the Central Molecular Zone
Short Name:
J/ApJ/897/89
Date:
11 Mar 2022
Publisher:
CDS
Description:
We carry out a systematic study of the density structure of gas in the Central Molecular Zone (CMZ) in the Galactic center by extracting clumps from the APEX Telescope Large Area Survey of the Galaxy survey at 870{mu}m. We find that the clumps follow a scaling of m={rho}_0_r^3^, which corresponds to a characteristic density of n_H_2__=1.6x10^3^/cm^3^ ({rho}_0_=112M{sun}/pc^3^) with a variation of ~0.5dex, where we assumed a gas-to-dust mass ratio of 100. This characteristic density can be interpreted as the result of thermal pressure equilibrium between the molecular gas and the warm ambient interstellar medium. Such an equilibrium can plausibly be established since shear has approximately the same strength as self-gravity. Our findings may explain the fact that star formation in the CMZ is highly inefficient compared to the rest of the Milky Way disk. We also identify a population of clumps whose densities are two orders of magnitudes higher in the vicinity of the Sgr B2 region, which we propose are produced by collisions between the clumps of lower densities. For these collisions to occur, processes such as compressive tides probably have created the appropriate condition by assembling the clumps together.
18. HCN, HNC, H13CN & HC3N of Galactic Center map. II.
ID:
ivo://CDS.VizieR/J/ApJ/903/111
Title:
HCN, HNC, H13CN & HC3N of Galactic Center map. II.
Short Name:
J/ApJ/903/111
Date:
15 Mar 2022
Publisher:
CDS
Description:
We report a statistical analysis exploring the origin of the overall low star formation efficiency (SFE) of the Galactic central molecular zone (CMZ) and the SFE diversity among the CMZ clouds using a wide-field HCN J=4-3 map, whose optically thin critical density (~10^7^/cm^3^) is the highest among the tracers ever used in CMZ surveys. Logistic regression is performed to empirically formulate star formation probability of 195 HCN clumps, 13 of which contain star formation signatures. The explanatory parameters in the best-fit model are reduced into the virial parameter {alpha}_vir_ without significant contribution from other parameters, whereas the performance of the model without {alpha}_vir_ is no better than that using randomly generated data. The threshold {alpha}_vir_ is 6, which translates into a volume density (n_H_2__) of 10^4.6^/cm^3^ with the n_H_2__-{alpha}_vir_ correlation. The scarcity of the low-{alpha}_vir_ clumps, whose fraction to all HCN clumps is 0.1, can be considered as one of the immediate causes of the suppressed SFE. No correlation between the clump size or mass and star formation probability is found, implying that HCN J= 4-3 does not immediately trace the mass of star-forming gas above a threshold density. Meanwhile, star-forming and non-star-forming clouds are degenerate in the physical parameters of the CS J=1-0 clouds, highlighting the efficacy of the HCN J=4-3 line to probe star-forming regions in the CMZ. The timescale of the high-{alpha}_vir_ to low-{alpha}_vir_ transition is <~2Myr, which is consistent with the tidal compression and X1/X2 orbit transition models but possibly does not fit the cloud-cloud collision picture.
19. Keck/NIRC2 obs. of the Galactic Center
ID:
ivo://CDS.VizieR/J/ApJ/873/65
Title:
Keck/NIRC2 obs. of the Galactic Center
Short Name:
J/ApJ/873/65
Date:
21 Oct 2021
Publisher:
CDS
Description:
Precision measurements of the stars in short-period orbits around the supermassive black hole at the Galactic Center are now being used to constrain general relativistic effects, such as the gravitational redshift and periapse precession. One of the largest systematic uncertainties in the measured orbits has been errors in the astrometric reference frame, which is derived from seven infrared-bright stars associated with SiO masers that have extremely accurate radio positions, measured in the Sgr A*-rest frame. We have improved the astrometric reference frame within 14" of the Galactic Center by a factor of 2.5 in position and a factor of 5 in proper motion. In the new reference frame, Sgr A* is localized to within a position of 0.645mas and proper motion of 0.03mas/yr. We have removed a substantial rotation (2.25{deg} per decade), that was present in the previous less-accurate reference frame used to measure stellar orbits in the field. With our improved methods and continued monitoring of the masers, we predict that orbital precession predicted by general relativity will become detectable in the next ~5yr.
20. Kinematic structure of the Galactic Center S cluster
ID:
ivo://CDS.VizieR/J/ApJ/896/100
Title:
Kinematic structure of the Galactic Center S cluster
Short Name:
J/ApJ/896/100
Date:
11 Mar 2022
Publisher:
CDS
Description:
We present a detailed analysis of the kinematics of 112 stars that mostly comprise the high-velocity S cluster and orbit the supermassive black hole Sgr A* at the center of the Milky Way. For 39 of them, orbital elements are known; for the remainder, we know proper motions. The distribution of the inclinations and the proper motion flight directions deviate significantly from a uniform distribution, which one expects if the orientation of the orbits are random. Across the central arcseconds, the S-cluster stars are arranged in two almost edge-on disks that are located at a position angle approximately +/-45{deg} with respect to the Galactic plane. The angular momentum vectors for stars in each disk point in both directions, i.e., the stars in a given disk rotate in opposite ways. The poles of this structure are located only about 25{deg} from the line of sight. This structure may be the result of a resonance process that started with the formation of the young B-dwarf stars in the cluster about 6Myr ago. Alternatively, it indicated the presence of a disturber at a distance from the center comparable to the distance of the compact stellar association IRS 13.