- ID:
- ivo://CDS.VizieR/J/A+A/656/A49
- Title:
- Decoding the morphological evolution of open clusters
- Short Name:
- J/A+A/656/A49
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The properties of open clusters such as metallicity, age, and morphology are useful tools in studies of the dynamic evolution of open clusters. The morphology of open clusters can help us better understand the evolution of such structures. We aim to analyze the morphological evolution of 1256 open clusters by combining the shapes of the sample clusters in the proper motion space with their morphology in the two-dimensional spherical Galactic coordinate system, providing their shape parameters based on a member catalog derived from Gaia Second Data Release as well as data from the literature. We applied a combination of a nonparametric bivariate density estimation with the least square ellipse fitting to derive the shape parameters of the sample clusters. We derived the shape parameters of the sample clusters in the two-dimensional spherical Galactic coordinate system and that of the proper motion space. By analyzing the dislocation of the sample clusters, we find that the dislocation, d; is related to the X-axis pointing toward the Galactic center, Y-axis pointing in the direction of Galactic rotation, and the Z-axis (log(|H|/pc)) that is positive toward the Galactic north pole. This finding underlines the important role of the dislocation of clusters in tracking the external environment of the Milky Way. The orientation (q_pm_) of the clusters, with e_pm_>=0.4, presents an aggregate distribution in the range of -45{deg} to 45{deg}, comprising about 74% of them. This probably suggests that these clusters tend to deform heavily in the direction of the Galactic plane. NGC 752 is in a slight stage of expansion in the two-dimensional space and will become deformed, in terms of its morphology, along the direction perpendicular to the original stretching direction in the future if no other events occur. The relative degree of deformation of the sample clusters in the short-axis direction decreases as their ages increase. On average, the severely distorted sample clusters in each group account for about 26%~9%. This possibly implies a uniform external environment in the range of |H|<=300pc if the sample completeness of each group is not taken into account.
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- ID:
- ivo://CDS.VizieR/J/A+A/650/A100
- Title:
- Decomposition of Galactic sky with autoencoders
- Short Name:
- J/A+A/650/A100
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- All-sky observations show both Galactic and non-Galactic diffuse emission, for example from interstellar matter or the cosmic microwave background (CMB). The decomposition of the emission into different underlying radiative components is an important signal reconstruction problem. We aim to reconstruct radiative all-sky components using spectral data, without incorporating knowledge about physical or spatial correlations. We built a self-instructing algorithm based on variational autoencoders following three steps: (1) We stated a forward model describing how the data set is generated from a smaller set of features, (2) we used Bayes' theorem to derive a posterior probability distribution, and (3) used variational inference and statistical independence of the features to approximate the posterior. From this, we derived a loss function and optimized it with neural networks. The resulting algorithm contains a quadratic error norm with a self-adaptive variance estimate to minimize the number of hyperparameters. We trained our algorithm on independent pixel vectors, each vector representing the spectral information of the same pixel in 35 Galactic all-sky maps ranging from the radio to the gamma-ray regime. The algorithm calculates a compressed representation of the input data. We find the feature maps derived in the algorithm's latent space show spatial structures that can be associated with all-sky representations of known astrophysical components. Our resulting feature maps encode (1) the dense interstellar medium (ISM), (2) the hot and dilute regions of the ISM, and (3) the CMB, without being informed about these components a priori. We conclude that Bayesian signal reconstruction with independent Gaussian latent space statistics is sufficient to reconstruct the dense and the dilute ISM, as well as the CMB, from spectral correlations only. The approximation of the posterior can be performed computationally efficient using variational inference and neural networks, making them a suitable approach to probabilistic data analysis.
- ID:
- ivo://CDS.VizieR/J/ApJ/783/6
- Title:
- Deconvolved Spitzer images of 89 protostars
- Short Name:
- J/ApJ/783/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To study the role of protosellar jets and outflows in the time evolution of the parent cores and the protostars, the astronomical community needs a large enough database of infrared images of protostars at the highest spatial resolution possible to reveal the details of their morphology. Spitzer provides unprecedented sensitivity in the infrared to study both the jet and outflow features, however, its spatial resolution is limited by its 0.85 m mirror. Here, we use a high-resolution deconvolution algorithm, "HiRes," to improve the visualization of spatial morphology by enhancing resolution (to subarcsecond levels in the IRAC bands) and removing the contaminating side lobes from bright sources in a sample of 89 protostellar objects. These reprocessed images are useful for detecting (1) wide-angle outflows seen in scattered light, (2) morphological details of H_2_ emission in jets and bow shocks, and (3) compact features in MIPS 24 {mu}m images as protostar/disk and atomic/ionic line emission associated with the jets. The HiRes FITS image data of such a large homogeneous sample presented here will be useful to the community in studying these protostellar objects. To illustrate the utility of this HiRes sample, we show how the opening angle of the wide-angle outflows in 31 sources, all observed in the HiRes-processed Spitzer images, correlates with age. Our data suggest a power-law fit to opening angle versus age with an exponent of ~0.32 and 0.02, respectively, for ages <= 8000 yr and >= 8000 yr.
- ID:
- ivo://CDS.VizieR/J/A+A/531/A92
- Title:
- Deep all-sky census of the Hyades
- Short Name:
- J/A+A/531/A92
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- On the basis of the PPMXL catalogue we perform an all-sky census of the Hyades down to masses of about 0.2M_{sun}_ in a region up to 30pc from the cluster centre. We use the proper motions from PPMXL in the convergent point method to determine probable kinematic members. From 2MASS photometry and CMC14 r'-band photometry, we derive empirical colour-absolute magnitude diagrams and, finally, determine photometric membership for all kinematic candidates. This is the first deep (r'<17) all-sky survey of the Hyades allowing a full three-dimensional analysis of the cluster. The survey is complete down to at least M_{K_s_}_=7.3 or 0.25M_{sun}_. We find 724 stellar systems co-moving with the bulk Hyades space velocity, which represent a total mass of 435M_{sun}_. The tidal radius is about 9pc, and 275M_{sun}_ (364 systems) are gravitationally bound. This is the cluster proper. Its mass density profile is perfectly fitted by a Plummer model with a central density of 2.21M_{sun}_/pc^3^ and a core radius of r_co_=3.10pc, while the half-mass radius is r_h_=4.1pc. There are another 100M_{sun}_ in a volume between one and two tidal radii (halo), and another 60M_{sun}_ up to a distance of 30pc from the centre. Strong mass segregation is inherent in the cluster. The present-day luminosity and mass functions are noticeably different in various parts of the cluster (core, corona, halo, and co-movers). They are strongly evolved compared to presently favoured initial mass functions. The analysis of the velocity dispersion of the cluster shows that about 20% of its members must be binaries. As a by-product, we find that presently available theoretical isochrones are not able to adequately describe the near-infrared colour-absolute magnitude relation for those cluster stars that are less massive than about 0.6M_{sun}_.
- ID:
- ivo://CDS.VizieR/J/MNRAS/478/3721
- Title:
- Deep ALMA photometry of distant X-ray AGN
- Short Name:
- J/MNRAS/478/3721
- Date:
- 10 Dec 2021 00:23:44
- Publisher:
- CDS
- Description:
- We present the star formation rates (SFRs) of a sample of 109 galaxies with X-ray-selected active galactic nuclei (AGNs) with moderate to high X-ray luminosities (L_2-8keV_=10^42^-10^45^erg/s), at redshifts 1<z<4.7, that were selected to be faint or undetected in the Herschel bands. We combine our deep Atacama large (sub-)millimetre array (ALMA) continuum observations with deblended 8-500um photometry from Spitzer and Herschel, and use infrared (IR) spectral energy distribution (SED) fitting and AGN - star formation decomposition methods. The addition of the ALMA photometry results in an order of magnitude more X-ray AGN in our sample with a measured SFR (now 37%). The remaining 63 % of the sources have SFR upper limits that are typically a factor of 2-10 times lower than the pre-ALMA constraints. With the improved constraints on the IR SEDs, we can now identify a mid-IR (MIR) AGN component in 50% of our sample, compared to only ~1% previously. We further explore the F_870um_/F_24um_ -redshift plane as a tool for the identification of MIR-emitting AGN, for three different samples representing AGN-dominated, star formation-dominated, and composite sources. We demonstrate that the F_870um_/F_24um_ -redshift plane can successfully split between AGN and star formation-dominated sources, and can be used as an AGN identification method.
- ID:
- ivo://CDS.VizieR/J/AJ/132/2409
- Title:
- Deep ATLAS radio observations of CDFS
- Short Name:
- J/AJ/132/2409
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from the Australia Telescope Large Area Survey, which consists of deep radio observations of a 3.7deg^2^ field surrounding the Chandra Deep Field-South, largely coincident with the infrared Spitzer Wide-Area Infrared Extragalactic (SWIRE) Survey. We also list cross-identifications to infrared and optical photometry data from SWIRE, and ground-based optical spectroscopy. A total of 784 radio components are identified, corresponding to 726 distinct radio sources, nearly all of which are identified with SWIRE sources. Of the radio sources with measured redshifts, most lie in the redshift range 0.5-2 and include both star-forming galaxies and active galactic nuclei. We identify a rare population of infrared-faint radio sources that are bright at radio wavelengths but are not seen in the available optical, infrared, or X-ray data. Such rare classes of sources can only be discovered in wide, deep surveys such as this.
- ID:
- ivo://CDS.VizieR/J/MNRAS/427/679
- Title:
- Deep blank field catalogue
- Short Name:
- J/MNRAS/427/679
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The observation of blank fields, defined as regions of the sky that are devoid of stars down to a given threshold magnitude, constitutes one of the most relevant calibration procedures required for the proper reduction of astronomical data obtained following typical observing strategies. In this work, we have used the Delaunay triangulation to search for deep blank fields throughout the whole sky, with a minimum size of 10-arcmin in diameter and an increasing threshold magnitude from 15 to 18 in the R band of the USNO-B Catalog of the United States Naval Observatory. The result is a catalogue with the deepest blank fields known so far. A short sample of these regions has been tested with the 10.4m Gran Telescopio Canarias, and it has been shown to be extremely useful for medium and large size telescopes. Because some of the regions found could also be suitable for new extragalactic studies, we have estimated the galactic extinction in the direction of each deep blank field. This catalogue is accessible through the Virtual Observatory tool TESELA, and the user can retrieve - and visualise using Aladin - the deep blank fields available near a given position in the sky.
- ID:
- ivo://CDS.VizieR/J/MNRAS/261/657
- Title:
- Deep CCD photometry of Leo II
- Short Name:
- J/MNRAS/261/657
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep colour-magnitude diagram of the central 7 x 7 arcmin2 region of Leo II. The diagram shows a well-defined giant branch and a red horizontal branch, heavily populated on the red side but extending far into the blue. Having a low metallicity ([Fe/H]=-1.9), the Leo II diagram is similar to those of outer halo clusters suffering from the second-parameter syndrome. From the mean apparent magnitude of candidate RR Lyrae stars, (VHB) = 22.10, we estimate the distance of Leo II to be 215 kpc, a value similar to previous estimates. A number of variable-star candidates are identified and two new very red giants have been found. Comparison with the other dwarf spheroidals of the Local Group reveals that Leo II belongs to the group of four small and faint dwarf spheroidal galaxies.
- ID:
- ivo://CDS.VizieR/J/AJ/155/110
- Title:
- Deep CFHT imaging of VVDS-F22 field. II. Quasars
- Short Name:
- J/AJ/155/110
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of a faint quasar survey in a one-square-degree field. The aim is to test the Y-K/g-z and J-K/i-Y color selection criteria for quasars at faint magnitudes to obtain a complete sample of quasars based on deep optical and near-infrared color-color selection and to measure the faint end of the quasar luminosity function (QLF) over a wide redshift range. We carried out a quasar survey based on the Y-K/g-z and J-K/i-Y quasar selection criteria, using the deep Y-band data obtained from our CFHT/WIRCam Y-band images in a two-degree field within the F22 field of the VIMOS VLT deep survey, optical co-added data from Sloan Digital Sky Survey Stripe 82 and deep near-infrared data from the UKIDSS Deep Extragalactic Survey in the same field. We discovered 25 new quasars at 0.5<z<4.5 and i<22.5 mag within one-square-degree field. The survey significantly increases the number of faint quasars in this field, especially at z~2-3. It confirms that our color selections are highly complete in a wide redshift range (z<4.5), especially over the quasar number density peak at z~2-3, even for faint quasars. Combining all previous known quasars and new discoveries, we construct a sample with 109 quasars and measure the binned QLF and parametric QLF. Although the sample is small, our results agree with a pure luminosity evolution at lower redshift and luminosity evolution and density evolution model at redshift z>2.5.
- ID:
- ivo://CDS.VizieR/J/ApJ/766/14
- Title:
- Deep Chandra bulge field X-ray point sources
- Short Name:
- J/ApJ/766/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Apparently diffuse X-ray emission has been known to exist along the central quarter of the Galactic Plane since the beginning of X-ray astronomy; this is referred to as the Galactic Ridge X-ray emission (GRXE). Recent deep X-ray observations have shown that numerous X-ray point sources account for a large fraction of the GRXE in the hard band (2-8keV). However, the nature of these sources is poorly understood. Using the deepest X-ray observations made in the Chandra bulge field, we present the result of a coherent photometric and spectroscopic analysis of individual X-ray point sources for the purpose of constraining their nature and deriving their fractional contributions to the hard-band continuum and Fe K line emission of the GRXE. Based on the X-ray color-color diagram, we divided the point sources into three groups: A (hard), B (soft and broad spectrum), and C (soft and peaked spectrum). The group A sources are further decomposed spectrally into thermal and non-thermal sources with different fractions in different flux ranges. From their X-ray properties, we speculate that the group A non-thermal sources are mostly active galactic nuclei and the thermal sources are mostly white dwarf (WD) binaries such as magnetic and non-magnetic cataclysmic variables (CVs), pre-CVs, and symbiotic stars, whereas the group B and C sources are X-ray active stars in flares and quiescence, respectively. In the log N-log S curve of the 2-8 keV band, the group A non-thermal sources are dominant above {approx}10^-14^erg/cm2/s, which is gradually taken over by Galactic sources in the fainter flux ranges. The Fe K{alpha} emission is mostly from the group A thermal (WD binaries) and the group B (X-ray active stars) sources.