Search

Start Over Subject milky way galaxy Validation Level 2
161. Far-UV spectra of Galactic corona sight lines
ID:
ivo://CDS.VizieR/J/ApJ/749/157
Title:
Far-UV spectra of Galactic corona sight lines
Short Name:
J/ApJ/749/157
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the properties of the transition temperature (T~10^5^K) gas in the Milky Way corona, based on the measurements of OVI, NV, CIV, SiIV, and FeIII absorption lines seen in the far-ultraviolet spectra of 58 sight lines to extragalactic targets, obtained with the Far-Ultraviolet Spectroscopic Explorer and the Space Telescope Imaging Spectrograph. In many sight lines the Galactic absorption profiles show multiple components, which are analyzed separately. We find that the highly ionized atoms are distributed irregularly in a layer with a scale height of about 3 kpc, which rotates along with the gas in the disk, without an obvious gradient in the rotation velocity away from the Galactic plane. Within this layer the gas has randomly oriented velocities with a dispersion of 40-60km/s. On average the integrated column densities are logN(OVI)=14.3, logN(NV)=13.5, logN(CIV)=14.2, logN(SiIV)=13.6, and logN(FeIII)=14.2, with a dispersion of just 0.2 dex in each case. In sight lines around the Galactic center and Galactic north pole, all column densities are enhanced by a factor ~2, while at intermediate latitudes in the southern sky there is a deficit in N(O VI) of about a factor of two, but no deficit for the other ions.
162. FEDReD. Extinction map with 2MASS and Gaia DR2
ID:
ivo://CDS.VizieR/J/A+A/641/A79
Title:
FEDReD. Extinction map with 2MASS and Gaia DR2
Short Name:
J/A+A/641/A79
Date:
21 Oct 2021
Publisher:
CDS
Description:
We aim to map the 3D distribution of the interstellar extinction of the Milky Way disk up to distances larger than those probed with the Gaia parallaxes alone. We apply the FEDReD algorithm to the 2MASS near-infrared photometry together with the Gaia DR2 astrometry and photometry. This algorithm uses a Bayesian deconvolution approach, based on an empirical HR-diagram representative of the local thin disk, in order to map the extinction as a function of distance for various fields of view. We analysed more than 5.6 million stars to obtain an extinction map of the entire Galactic disk within |b|<0.24{deg}. This map provides information up to 5kpc in the direction of the Galactic centre and at more than 7kpc in the direction of the anticentre. This map reveals the complete shape of structures known locally, such as the Vela complex or the split of the local arm. Furthermore our extinction map shows many large "clean bubbles" especially one in the Sagittarius-Carina complex, and four others which define a structure that we nickname the butterfly
163. [Fe/H] and kinematics of 26 Galactic bulge fields
ID:
ivo://CDS.VizieR/J/A+A/599/A12
Title:
[Fe/H] and kinematics of 26 Galactic bulge fields
Short Name:
J/A+A/599/A12
Date:
21 Oct 2021
Publisher:
CDS
Description:
Several recent studies have demonstrated that the Galactic bulge hosts two components with different mean metallicities, and possibly different spatial distribution and kinematics. As a consequence, both the metallicity distribution and the radial velocity of bulge stars vary across different line of sights. We present here the metallicity distribution function of red clump stars in 26 fields spread across a wide area of the bulge, with special emphasis on fields close to Galactic plane, at latitudes b=-2 and b=-1, that were not explored before. This work includes new metallicities from a sample of ~5000 K giant stars, observed at spectral resolution R~6500, in the Calcium II Triplet region. They are the main dataset of the GIRAFFE Inner Bulge Survey. As part of the same survey we have previously published results for a sample of ~600 K giant stars, at latitude b~-4 derived from higher resolution spectra (R=22500). The combined sample allows us to trace and characterize the metal poor and metal rich bulge populations down to the inner bulge. We present a density map for each of the two components. Contrary to the expectations from previous works, we found the metal poor population to be more centrally concentrated than the metal rich one, and with a more axisymmetric spatial distribution. The metal rich population, on the other hand, is arranged in a boxy distribution, consistent with an edge-on bar. By coupling metallicities and radial velocities we show that the metal poor population has a velocity dispersion that varies rather mildly with latitude. On the contrary, the metal rich population has a low velocity dispersion far from the plane (b=-8.5) but it has a steeper gradient with latitude, becoming higher than the metal poor one in the innermost field (b=-1). This work provides new observational constraints on the actual chemodynamical properties of the Galactic bulge, that will help discriminating among different formation models.
164. Fe, Mg, Ti in Galactic clusters
ID:
ivo://CDS.VizieR/J/A+A/628/A54
Title:
Fe, Mg, Ti in Galactic clusters
Short Name:
J/A+A/628/A54
Date:
02 Nov 2021 11:16:10
Publisher:
CDS
Description:
We test the effects of non-local thermodynamic equilibrium (NLTE) on the spectra of FGK-type stars across a wide range of metallicity and to derive abundance of Fe, Mg, and Ti for a sample of Galactic star clusters. We extend the Payne fitting approach to draw on NLTE and LTE spectral models in order to determine stellar parameters and chemical abundances for the Gaia-ESO benchmark stars. We also analyse the medium-resolution Giraffe spectra of 742 stars in 13 open and globular clusters in the Milky Way galaxy. We show that this approach accurately recovers effective temperatures, surface gravities, and abundances of the benchmark stars and clusters members. The differences between NLTE and LTE stellar parameters are small for the metal-rich stars. However, for metal-poor stars [Fe/H]<-1, the NLTE estimates of Teff, log(g) and [Fe/H] are higher than LTE estimates, and the systematic offset increases with decreasing metallicity. Our LTE measurements of metallicities and abundances in the Galactic clusters are in a good agreement with the earlier literature studies. For the majority of these clusters, our study yields the first estimates of NLTE abundances of Fe, Mg and Ti. The NLTE [Fe/H] are systematically higher, whereas the average NLTE [Mg/Fe] abundance ratios are ~0.15dex lower, compared to LTE. All clusters investigated in this work appear homogeneous in Fe and Ti, with the intra-cluster abundance variations of less then 0.1dex. We confirm large dispersions of [Mg/Fe] ratios for NGC 2808, NGC 4833 and M 15. Our results shows that NLTE analysis change the mean abundance ratios in the clusters, but does not influence the intra-cluster abundance dispersions. Combining the Payne fitting approach with NLTE spectral models as input is a powerful tool for a detailed exploration of the large-scale spectroscopic stellar surveys.
165. First quadrant IRDCs in CS(2-1) with Mopra
ID:
ivo://CDS.VizieR/J/ApJ/764/102
Title:
First quadrant IRDCs in CS(2-1) with Mopra
Short Name:
J/ApJ/764/102
Date:
21 Oct 2021
Publisher:
CDS
Description:
Infrared dark clouds (IRDCs) are believed to host the earliest stages of high-mass star and cluster formation. Because O stars typically travel short distances over their lifetimes, if IRDCs host the earliest stages of high-mass star formation then these cold, dense molecular clouds should be located in or near the spiral arms in the Galaxy. The Galactic distribution of a large sample of IRDCs should therefore provide information on Galactic structure. Moreover, determination of distances enables mass and luminosity calculations. We have observed a large sample of IRDC candidates in the first Galactic quadrant in the dense gas tracer CS(2-1) using the Mopra telescope in order to determine kinematic distances from the molecular line velocities. We find that the IRDCs are concentrated around a Galactocentric distance of ~4.5kpc, agreeing with the results of Simon et al. (2006, J/ApJ/653/1325). This distribution is consistent with the location of the Scutum-Centaurus spiral arm. The group of IRDCs near the Sun in the first quadrant detected in ^13^CO(1-0) in Simon et al. is not detected in the CS data. This discrepancy arises from the differences in the critical densities between the ^13^CO(1-0) and CS(2-1) lines. We determine that the Midcourse Space Experiment selected IRDCs are not a homogeneous population, and ^13^CO(1-0) traces a population of IRDCs with lower column densities and lower 1.1 mm flux densities in addition to more dense IRDCs detected in CS. Masses of the first quadrant IRDCs are calculated from ^13^CO(1-0) maps. We find a strong peak in the Galactocentric IRDC mass surface density distribution at R_Gal_~4.5kpc.
166. First results from Mopra HCO^+^ maps
ID:
ivo://CDS.VizieR/J/ApJS/196/12
Title:
First results from Mopra HCO^+^ maps
Short Name:
J/ApJS/196/12
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Census of High- and Medium-mass Protostars (CHaMP) is the first large-scale, unbiased, uniform mapping survey at sub-parsec-scale resolution of 90GHz line emission from massive molecular clumps in the Milky Way. We present the first Mopra (ATNF) maps of the CHaMP survey region (300{deg}>l>280{deg}) in the HCO^+^J=1->0 line, which is usually thought to trace gas at densities up to 10^11^m^-3^. In this paper, we introduce the survey and its strategy, describe the observational and data reduction procedures, and give a complete catalog of moment maps of the HCO^+^J=1->0 emission from the ensemble of 303 massive molecular clumps. From these maps we also derive the physical parameters of the clumps, using standard molecular spectral-line analysis techniques.
167. Fluxes & physical param. of blended YSOs
ID:
ivo://CDS.VizieR/J/ApJ/864/71
Title:
Fluxes & physical param. of blended YSOs
Short Name:
J/ApJ/864/71
Date:
21 Oct 2021
Publisher:
CDS
Description:
Despite significant evidence suggesting that intermediate- and high-mass stars form in clustered environments, how stars form when the available resources are shared is still not well understood. A related question is whether the initial mass function (IMF) is in fact universal across galactic environments, or whether it is an average of IMFs that differ, for example, in massive versus low-mass molecular clouds. One of the long-standing problems in resolving these questions and in the study of young clusters is observational: how to accurately combine multiwavelength data sets obtained using telescopes with different spatial resolutions. The resulting confusion hinders our ability to fully characterize clustered star formation. Here we present a new method that uses Bayesian inference to fit the blended spectral energy distributions and images of individual young stellar objects (YSOs) in confused clusters. We apply this method to the infrared photometry of a sample comprising 70 Spitzer-selected, low-mass (M_cl_<100M_{sun}_) young clusters in the galactic plane, and we use the derived physical parameters to investigate how the distribution of YSO masses within each cluster relates to the total mass of the cluster. We find that for low-mass clusters this distribution is indistinguishable from a randomly sampled Kroupa IMF for this range of cluster masses. Therefore, any effects of self-regulated star formation that affect the IMF sampling are likely to play a role only at larger cluster masses. Our results are also compatible with smoothed particle hydrodynamics models that predict a dynamical termination of the accretion in protostars, with massive stars undergoing this stopping at later times in their evolution.
168. Foreground Galactic stars properties
ID:
ivo://CDS.VizieR/J/A+A/555/A12
Title:
Foreground Galactic stars properties
Short Name:
J/A+A/555/A12
Date:
21 Oct 2021
Publisher:
CDS
Description:
We study the chemical and kinematic properties of roughly a thousand FLAMES-GIRAFFE LR8 spectra of faint magnitude foreground Galactic stars observed serendipitously during extra-galactic surveys in four lines-of-sight: three in the southern Galactic hemisphere (surveys of the Carina, Fornax and Sculptor dwarf spheroidal galaxies) and one in the northern Galactic hemisphere (a survey of the Sextans dwarf spheroidal galaxy). The foreground stars span distances up to ~3kpc from the Galactic plane and Galactocentric radii up to 11kpc. The stellar atmospheric parameters (effective temperature, surface gravity, metallicity) are obtained by an automated parameterisation pipeline and the distances of the stars are then derived by a projection of the atmospheric parameters on a set of theoretical isochrones using a Bayesian approach. The metallicity gradients are estimated for each line-of-sight and compared with predictions from the Besancon model of the Galaxy, in order to test the chemical structure of the thick disc. Finally, we use the radial velocities in each line-of-sight to derive a proxy for either the azimuthal or the vertical component of the orbital velocity of the stars. Only three lines-of-sight have a sufficient number of foreground stars for a robust analysis. Towards Sextans in the Northern Galactic hemisphere and Sculptor in the South, we measure a consistent decrease in mean metallicity with height from the Galactic plane, suggesting a chemically symmetric thick disc. This decrease can either be due to an intrinsic thick disc metallicity gradient, or simply due to a change in the thin disc/thick disc population ratio and no intrinsic metallicity gradients for the thick disc. We favour the latter explanation. In contrast, we find evidence of an unpredicted metal-poor population in the direction of Carina. This population was earlier detected by Wyse et al. (2006ApJ...639L..13W), but our more detailed analysis provides robust estimates of its location (|Z|<1kpc), metallicity (-2<[M/H]<-1dex) and azimuthal orbital velocity (V_phi_~120km/s).
169. Fraction of bulge metal poor & metal rich stars
ID:
ivo://CDS.VizieR/J/A+A/618/A147
Title:
Fraction of bulge metal poor & metal rich stars
Short Name:
J/A+A/618/A147
Date:
21 Oct 2021
Publisher:
CDS
Description:
Recent spectroscopic surveys of the Galactic bulge have unambiguously shown that the bulge contains two main components, which are best separated by their iron content, but also differ in spatial distribution, kinematics, and abundance ratios. The so-called metal poor component peaks at [Fe/H]~-0.4, while the metal rich component peaks at [Fe/H]~+0.3. The total metallicity distribution function is therefore bimodal with a dip at [Fe/H]~0. The relative fraction of the two components changes significantly across the bulge area. We provide, for the first time, the fractional contribution of the metal poor and metal rich stars to the stellar mass budget of the Galactic bulge and its variation across the bulge area. This result follows from the combination of the stellar mass profile obtained empirically, by our group, from VISTA Variables in the Via Lactea data, with the relative fraction of metal poor and metal rich stars, across the bulge area, derived from the GIRAFFE Inner Bulge spectroscopic Survey. We find that metal poor stars make up 48% of the total stellar mass of the bulge, within the region |l|<10, |b|<9.5 and that the remaining 52% are made up of metal rich stars. The latter dominate the mass budget at intermediate latitudes |b|~4, but become marginal in the outer bulge (|b|>8). The metal poor component is more axisymmetric than the metal rich component, and it is at least comparable and possibly slightly dominant in the inner few degrees. As a result, the metal poor component, which does not follow the main bar, is not marginal in terms of the total mass budget as previously thought, and this new observational evidence must be included in bulge models. While the trend of the total radial velocity dispersion follows the total stellar mass, when we examine the velocity dispersion of each component individually, we find that metal poor stars have higher velocity dispersion where they make up a smaller fraction of the stellar mass, and vice versa. This is due to the kinematical and spatial distribution of the two metallicity components being significantly different, as already discussed in the literature.
170. FUGIN. VII. Galactic plane HI clouds
ID:
ivo://CDS.VizieR/J/PASJ/72/43
Title:
FUGIN. VII. Galactic plane HI clouds
Short Name:
J/PASJ/72/43
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze molecular-gas formation in neutral atomic hydrogen (HI) clouds using the latest CO data, obtained from the FOREST (four-beam receiver system on the 45m telescope) unbiased Galactic plane imaging survey with the Nobeyama 45m telescope, and using HI data taken from the Very Large Array Galactic plane survey. We applied a dendrogram algorithm to the HI data cube to identify HI clouds, and we calculated the HI mass and molecular-gas mass by summing the CO line intensity within each HI cloud. On the basis of the results, we created a catalog of 5737 identified HI clouds with local standard of rest (LSR) velocity of VLSR<=-20km/s in galactic longitude and latitude ranges of 20{deg}<=l<=50{deg} and -1{deg}<=b<=1{deg}, respectively. We found that most of the HI clouds are distributed within a Galactocentric distance of 16kpc, and most of them are in the cold neutral medium phase. In addition, we determined that the high-mass end of the HI mass function is fitted well with a power-law function with an index of 2.3. Although two sequences of self-gravitating and diffuse clouds are expected to appear in the M_tot_-M_H2_ diagram according to previous works based on a plane-parallel model, the observational data show only a single sequence with large scattering within these two sequences. This implies that most of the clouds are mixtures of these two types of clouds. Moreover, we suggest the following scenario of molecular-gas formation: an HI-dominant cloud evolved with increasing H2 mass along a path of M_H2_{prop.to}M^2^_tot_ by collecting diffuse gas before reaching and moving along the curves of the two sequences.