- ID:
- ivo://CDS.VizieR/J/ApJ/773/67
- Title:
- Compact radio sources near the Galactic center
- Short Name:
- J/ApJ/773/67
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have observed the Galactic center (GC) region at 0.154 and 0.255GHz with the Giant Metrewave Radio Telescope. A total of 62 compact likely extragalactic (EG) sources are detected. Their scattering sizes decrease linearly with increasing angular distance from the GC up to about 1{deg}. The apparent scattering sizes of the sources are more than an order of magnitude less than predicted earlier by the NE2001 model of Galactic electron distribution within 359.5{deg}<l<0.5{deg} and -0.5{deg}<b<0.5{deg} (Hyperstrong Scattering Region) of the Galaxy. High free-free optical depths ({tau}) are observed toward most of the extended non-thermal sources within 0.6{deg} from the GC. Significant variation of {tau} indicates that the absorbing medium is patchy at an angular scale of ~10' and n_e_ is ~10/cm3, which matches the NE2001 model. This model predicts the EG sources to be resolved out from 1.4GHz interferometric surveys. However, out of 10 EG sources expected in the region, 8 likely EG are present in the 1.4GHz catalog. Ionized interfaces of dense molecular clouds to the ambient medium are most likely responsible for strong scattering and low radio frequency absorption. However, dense GC clouds traced by CS J=1-0 emission are found to have a narrow distribution of ~0.2{deg} across the Galactic plane. Angular distribution of most EG sources seen through the so-called Hyperstrong Scattering Region are random in b, and typically ~7 out of 10 sources will not be seen through the dense molecular clouds, which explains why most of them are not scatter broadened at 1.4GHz.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/80/211
- Title:
- Compact Radio Sources Near the Galactic Plane
- Short Name:
- J/ApJS/80/211
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The results of the extension of the 20-cm Galactic-plane survey reported by Zoonematkermani to Galactic latitudes of +/-1.8{deg} over the central region of the Milky Way are reported. A total of 1457 discrete radio sources down to flux densities of less than about 5mJy, and 95% completion is achieved at 20mJy. A detailed comparison of all radio sources from the survey in this longitude range with the IRAS Point Source Catalog provides classification for 13% of the objects, including 159 compact H II regions, and nearly 100 planetary nebulae, over 70 of which are identified. The identity of the remaining radio sources is discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/809/10
- Title:
- Compact radio sources within 30" of Sgr A*
- Short Name:
- J/ApJ/809/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Recent broadband 34 and 44GHz radio continuum observations of the Galactic center have revealed 41 massive stars identified with near-IR (NIR) counterparts, as well as 44 proplyd candidates within 30" of SgrA*. Radio observations obtained in 2011 and 2014 have been used to derive proper motions of eight young stars near Sgr A*. The accuracy of proper motion estimates based on NIR observations by Lu et al. (2009ApJ...690.1463L) and Paumard et al. (2006, J/ApJ/643/1011) have been investigated by using their proper motions to predict the 2014 epoch positions of NIR stars and comparing the predicted positions with those of radio counterparts in the 2014 radio observations. Predicted positions from Lu et al. show an rms scatter of 6mas relative to the radio positions, while those from Paumard et al. show rms residuals of 20mas. We also determine the mass-loss rates of 11 radio stars, finding rates that are on average ~2 times smaller than those determined from model atmosphere calculations and NIR data. Clumpiness of ionized winds would reduce the mass loss rate of WR and O stars by additional factors of 3 and 10, respectively. One important implication of this is a reduction in the expected mass accretion rate onto Sgr A* from stellar winds by nearly an order of magnitude to a value of a few x10^-7^m_{sun}_/yr. Finally, we present the positions of 318 compact radio sources within 30" of Sgr A*, 45 of which have stellar counterparts in the NIR K_s_ (2.18{mu}m) and L' (3.8{mu}m) bands.
- ID:
- ivo://CDS.VizieR/J/AJ/151/85
- Title:
- Companions to APOGEE stars. I.
- Short Name:
- J/AJ/151/85
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In its three years of operation, the Sloan Digital Sky Survey Apache Point Observatory Galactic Evolution Experiment (APOGEE-1) observed >14000 stars with enough epochs over a sufficient temporal baseline for the fitting of Keplerian orbits. We present the custom orbit-fitting pipeline used to create this catalog, which includes novel quality metrics that account for the phase and velocity coverage of a fitted Keplerian orbit. With a typical radial velocity precision of ~100-200 m/s, APOGEE can probe systems with small separation companions down to a few Jupiter masses. Here we present initial results from a catalog of 382 of the most compelling stellar and substellar companion candidates detected by APOGEE, which orbit a variety of host stars in diverse Galactic environments. Of these, 376 have no previously known small separation companion. The distribution of companion candidates in this catalog shows evidence for an extremely truncated brown dwarf (BD) desert with a paucity of BD companions only for systems with a<0.1-0.2 AU, with no indication of a desert at larger orbital separation. We propose a few potential explanations of this result, some which invoke this catalog's many small separation companion candidates found orbiting evolved stars. Furthermore, 16 BD and planet candidates have been identified around metal-poor ([Fe/H]<-0.5) stars in this catalog, which may challenge the core accretion model for companions >10 M_Jup_. Finally, we find all types of companions are ubiquitous throughout the Galactic disk with candidate planetary-mass and BD companions to distances of ~6 and ~16 kpc, respectively.
- ID:
- ivo://CDS.VizieR/J/A+A/612/L2
- Title:
- Compilation of stellar rotation data
- Short Name:
- J/A+A/612/L2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The distribution of the stellar rotation axes of 113 main sequence stars in the open cluster Praesepe are examined by using current photometric rotation periods, spectroscopic rotation velocities, and estimated stellar radii. Three different samples of stellar rotation data on spotted stars from the Galactic field and two independent samples of planetary hosts are used as control samples to support the consistency of the analysis. Considering the high completeness of the Praesepe sample and the behavior of the control samples, we find that the main sequence F-K stars in this cluster are susceptible to rotational axis alignment. Using a cone model, the most likely inclination angle is 76+/-14{deg} with a half opening angle of 47+/-24{deg}. Non-isotropic distribution of the inclination angles is preferred over the isotropic distribution, except if the rotation velocities used in this work are systematically overestimated. We found no indication of this being the case on the basis of the currently available data.
- ID:
- ivo://CDS.VizieR/J/MNRAS/473/1059
- Title:
- Complete sample of Galactic clump properties
- Short Name:
- J/MNRAS/473/1059
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The APEX Telescope Large Area Survey of the Galaxy (ATLASGAL) is an unbiased 870um submillimetre survey of the inner Galactic plane (|l|<60{deg} with |b|<1.5{deg}). It is the largest and most sensitive ground-based submillimetre wavelength Galactic survey to date and has provided a large and systematic inventory of all massive, dense clumps in the Galaxy (>=1000M_{sun}_ at a heliocentric distance of 20kpc) and includes representative samples of all of the earliest embedded stages of high-mass star formation. Here, we present the first detailed census of the properties (velocities, distances, luminosities and masses) and spatial distribution of a complete sample of ~8000 dense clumps located in the Galactic disc (5{deg}<|l|<60{deg}). We derive highly reliable velocities and distances to ~97 per cent of the sample and use mid- and far-infrared survey data to develop an evolutionary classification scheme that we apply to the whole sample. Comparing the evolutionary subsamples reveals trends for increasing dust temperatures, luminosities and linewidths as a function of evolution indicating that the feedback from the embedded protoclusters is having a significant impact on the structure and dynamics of their natal clumps. We find that the vast majority of the detected clumps are capable of forming a massive star and 88 per cent are already associated with star formation at some level. We find the clump mass to be independent of evolution suggesting that the clumps form with the majority of their mass in situ. We estimate the statistical lifetime of the quiescent stage to be ~5x10^4^yr for clump masses >1000M_{sun}_ decreasing to ~1x10^4^yr for clump masses >10000M_{sun}_. We find a strong correlation between the fraction of clumps associated with massive stars and peak column density. The fraction is initially small at low column densities, but reaching 100 per cent for column densities above 10^23^cm^x2^; there are no clumps with column densities above this value that are not already associated with massive star formation. All of the evidence is consistent with a dynamic view of star formation wherein the clumps form rapidly and are initially very unstable so that star formation quickly ensues.
- ID:
- ivo://CDS.VizieR/J/A+A/588/A97
- Title:
- Continuum sources from the THOR survey
- Short Name:
- J/A+A/588/A97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We carried out a large program with the Karl G. Jansky Very Large Array (VLA): "THOR: The HI, OH, Recombination line survey of the Milky Way". We observed a significant portion of the Galactic plane in the first quadrant of the Milky Way in the 21cm HI line, 4 OH transitions, 19 radio recombination lines, and continuum from 1 to 2GHz. In this paper we present a catalog of the continuum sources in the first half of the survey (l=14.0-37.9{deg} and l=47.1-51.2{deg}, |b|<1.1{deg}) at a spatial resolution of 10-25", depending on the frequency and sky position with a spatially varying noise level of ~0.3-1mJy/beam. The catalog contains ~4400 sources. Around 1200 of these are spatially resolved, and ~1000 are possible artifacts, given their low signal-to-noise ratios. Since the spatial distribution of the unresolved objects is evenly distributed and not confined to the Galactic plane, most of them are extragalactic. Thanks to the broad bandwidth of the observations from 1 to 2GHz, we are able to determine a reliable spectral index for ~1800 sources. The spectral index distribution reveals a double-peaked profile with maxima at spectral indices of alpha=-1 and alpha=0, corresponding to steep declining and flat spectra, respectively. This allows us to distinguish between thermal and non-thermal emission, which can be used to determine the nature of each source. We examine the spectral index of ~300 known HII regions, for which we find thermal emission with spectral indices around alpha=0. In contrast, supernova remnants (SNR) show non-thermal emission with alpha=-0.5 and extragalactic objects generally have a steeper spectral index of alpha=-1. Using the spectral index information of the THOR survey, we investigate potential SNR candidates. We classify the radiation of four SNR candidates as non-thermal, and for the first time, we provide strong evidence for the SNR origin of these candidates.
- ID:
- ivo://CDS.VizieR/J/ApJS/230/17
- Title:
- CO obs. of MCs in the Extreme Outer Galaxy region
- Short Name:
- J/ApJS/230/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of an unbiased CO survey in the Galactic range of 34.75{deg}<=l<=45.25{deg} and -5.25{deg}<=b<=5.25{deg}, and the velocity range beyond the Outer arm. A total of 168 molecular clouds (MCs) are identified within the Extreme Outer Galaxy (EOG) region, and 31 of these MCs are associated with ^13^CO emission. However, none of them show significant C^18^O emission under the current detection limit. The typical size and mass of these MCs are 5pc and 3x10^3^M_{sun}_, implying a lack of large and massive MCs in the EOG region. Similar to MCs in the outer Galaxy, the velocity dispersions of EOG clouds are also correlated with their sizes; however, they are well displaced below the scaling relationship defined by the inner Galaxy MCs. These MCs with a median Galactocentric radius of 12.6kpc show very different distributions from those of the MCs in the Outer arm published in our previous paper, while roughly following the Outer Scutum-Centaurus arm defined by Dame & Thaddeus (2011ApJ...734L..24D). This result may provide robust evidence for the existence of the Outer Scutum-Centaurus arm. The lower limit of the total mass of this segment is about 2.7x10^5^M_{sun}_, which is about one magnitude lower than that of the Outer arm. The mean thickness of the gaseous disk is about 1.45{deg} or 450pc, and the scale height is about 1.27{deg}, or 400pc above the b=0{deg} plane. The warp traced by CO emission is very obvious in the EOG region and its amplitude is consistent with the predictions by other warp models using different tracers, such as dust, HI, and stellar components of our Galaxy.
- ID:
- ivo://CDS.VizieR/J/ApJS/254/3
- Title:
- CO obs. of molecular clouds in the MW midplane
- Short Name:
- J/ApJS/254/3
- Date:
- 17 Jan 2022 11:34:49
- Publisher:
- CDS
- Description:
- In this work, we study the properties of molecular clouds in the second quadrant of the Milky Way Midplane, from l=104.75{deg} to l=119.75{deg}, and b=-5.25{deg} to b=5.25{deg}, using the ^12^CO, ^13^CO, and C^18^O J=1-0 emission line data from the Milky Way Imaging Scroll Painting project. We identify 857 and 300 clouds in the ^12^CO and ^13^CO spectral cubes, respectively, using the DENDROGRAM + SCIMES algorithms. The distances of the molecular clouds are estimated, and physical properties such as the mass, size, and surface densities of the clouds are tabulated. The molecular clouds in the Perseus Arm are about 30-50 times more massive, and 4-6 times larger than the clouds in the Local Arm. This result, however, is likely to be biased by distance selection effects. The surface densities of the clouds are enhanced in the Perseus Arm, with an average value of ~100M_{sun}_/pc^2^. Here. we select the 40 most extended (>0.35arcdeg^2^) molecular clouds from the ^12^CO catalog to build the H_2_ column density probability distribution function (N-PDF). Some 78% of the N-PDFs of the selected molecular clouds are well fitted with log-normal functions with only small deviations at high densities, corresponding to star-forming regions with scales of ~1-5pc in the Local Arm, and ~5-10pc in the Perseus Arm. About 18% of the selected molecular clouds have power-law N-PDFs at high densities. In these molecular clouds, the majority of the regions fitted with the power law correspond to molecular clumps at sizes of ~1pc, or filaments at widths of ~1pc.
- ID:
- ivo://CDS.VizieR/J/ApJ/798/L27
- Title:
- CO obs. of molecular clouds in the 2nd quadrant
- Short Name:
- J/ApJ/798/L27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Combining H I data from the Canadian Galactic Plane Survey and CO data from the Milky Way Imaging Scroll Painting project (MWISP), we have identified a new segment of a spiral arm between Galactocentric radii of 15 and 19kpc that apparently lies beyond the Outer Arm in the second Galactic quadrant. Over most of its length, the arm is 400-600pc thick in z. The new arm appears to be the extension of the distant arm recently discovered by Dame & Thaddeus (2011ApJ...734L..24D) as well as the Scutum-Centaurus Arm into the outer second quadrant. Our current survey identified a total of 72 molecular clouds with masses on the order of 10^2^-10^4^M_{sun}_ that probably lie in the new arm. When all of the available data from the CO molecular clouds are fit, the best-fitting spiral model gives a pitch angle of 9.3{deg}+/-0.7{deg}.
