Kinematic Distance Research Articles

East Asian VLBI Network astrometry toward the extreme outer Galaxy: Kinematic distance with the proper motion of G034.84−00.95

Abstract We aim to reveal the structure and kinematics of the Outer Scutum–Centaurus (OSC) arm located on the far side of the Milky Way through very long baseline interferometry (VLBI) astrometry using KaVA, which is composed of KVN (the Korean VLBI Network) and VERA (VLBI Exploration of Radio Astrometry). We report the proper motion of a 22 GHz H2O maser source, which is associated with the star-forming region G034.84−00.95, to be (μαcos δ, μδ) = (−1.61 ± 0.18, −4.29 ± 0.16) mas yr−1 in equatorial coordinates (J2000.0). We estimate the 2D kinematic distance to the source to be 18.6 ± 1.0 kpc, which is derived from the variance weighted average of kinematic distances with local standard of rest velocity and the galactic-longitude component of the measured proper motion. Our result places the source in the OSC arm and implies that G034.84−00.95 is moving away from the Galactic plane with a vertical velocity of −38 ± 16 km s−1. Since the H i supershell GS033+06−49 is located at a kinematic distance roughly equal to that of G034.84−00.95, it is expected that gas circulation occurs between the outer Galactic disk around G034.84−00.95 with a Galactocentric distance of $12.8^{+1.0}_{-0.9}\:$kpc and the halo. We evaluate possible origins of the fast vertical motion of G034.84−00.95, which are (1) supernova explosions and (2) cloud collisions with the Galactic disk. However, neither of these possibilities are matched with the results of VLBI astrometry or the spatial distributions of H ii regions and H i gas.

Mapping the Far Side of the Milky Way

AbstractGreat progress has been made using VLBI techniques to measure trigonometric parallaxes to masers associated with young, high-mass stars, in order to map the spiral structure of the Milky Way. However, large numbers of parallax distance have only been obtained over about half of the Galaxy. Here I discuss the use of 3-dimensional kinematic distances for completing the map with many sources well past the Galactic Center.

Peering into the Milky Way by FAST: IV. Identification of two new Galactic supernova remnants G203.1+6.6 and G206.7+5.9

A 5$^{\circ}$ $\times$ 7$^{\circ}$ sky area containing two large radio structures of G203.1+6.6 and G206.7+5.9 with a size of about 2.5$^{\circ}$ and 3.5$^{\circ}$ respectively is scanned by using the L-band 19-beam receiver of the Five-hundred-meter Aperture Spherical radio Telescope (FAST). The FAST L-band receiver covers a frequency range of 1.0-1.5 GHz. Commissioning of the receiving system, including the measurements of the half-power beam width, gain, and main-beam efficiency is made by observing the calibrators. The multi-channel spectroscopy backend mounted to the receiver allows an in-band spectral-index determination. The brightness-temperature spectral indices of both objects are measured to be $\beta$ $\sim$ $-$2.6 to $-$2.7. Polarized emission is detected from the archival Effelsberg $\lambda$11 cm data for all the shell structures of G203.1+6.6 and G206.7+5.9. These results clearly indicate a non-thermal synchrotron emitting nature, confirming that G203.1+6.6 and G206.7+5.9 are large shell-type supernova remnants (SNRs). Based on morphological correlation between the radio continuum emission of G206.7+5.9 and the HI structures, the kinematic distance to this new SNR is estimated to be about 440 pc, placing it in the Local Arm.

Supernova remnant W51C: optical and X-ray emission analysis

ABSTRACT We present observations of the optical and X-ray emission from the Galactic supernova remnant W51C. From [S ii] Fabry–Pérot interferometry and H α and [S ii] images we detect filaments that are part of the optical counterpart of the supernova remnant. We obtain the kinematic distance to W51C, showing that it is one of the shortest distances reported in the literature. We also estimate other physical properties such as the velocity of the shock induced in the cloudlets emitted at optical wavelengths and the electron density of those cloudlets. From XMM–Newton observatory archival data, we obtain images of the diffuse X-ray emission of this supernova remnant. The spectrum of the X-ray emission is explored to estimate X-ray parameters such as luminosity and temperature of the hot plasma in the supernova remnant. We fit a thermal model with a plasma temperature of 1.4 keV for an X-ray thermal luminosity of 2.0 × 1036 erg s−1. With the parameters described above we test the model proposed by White & Long to explain the mixed morphology observed in W51C. We obtain an initial energy of the supernova explosion of 8.4 × 1050 erg and an age of 13 000 yr. The derived initial energy is typical of supernova remnants, but in disagreement with respect to older estimations that found higher values and suggested that W51C was the result of the explosion of two supernovae.

CO(J = 1 – 0) Observations toward the Filamentary Cloud in the Galactic Region of 153.°60 ≤ l ≤ 156.°50 and 1.°85 ≤ b ≤ 3.°50

We present observations of the J = 1 – 0 transition lines of 12CO, 13CO, and C18O toward the Galactic region of 153.°60 ≤ l ≤ 156.°50 and 1.°85 ≤ b ≤ 3.°50, using the Purple Mountain Observatory 13.7 m millimeter telescope. Based on the 13CO data, one main filament and five subfilaments are found together as a network structure in the velocity interval of [−42.5, −30.0] km s−1. The kinematic distance of this molecular cloud is estimated to be ∼4.5 kpc. The median length, width, excitation temperature, and line mass of these filaments are ∼49 pc, ∼2.9 pc, ∼8.9 K, and ∼39 M ⊙ pc−1, respectively. The velocity structures along these filaments exhibit oscillatory patterns, which are likely caused by the fragmentation or accretion process along these filaments. The maximum accretion rate is estimated to be ∼700 M ⊙ pc−1. A total of ∼162 13CO clumps and ∼103 young stellar objects are identified in this region. Most of the clumps are in gravitationally bound states. Three H ii regions (G154.359+2.606, SH2-211, and SH2-212) are found to be located in the apexes of the filaments. Intense star-forming activity is found along the entire filamentary cloud. The observed results may help us to better understand the link between filaments and massive star formation.

On the Accuracy of Three-dimensional Kinematic Distances

Over the past decade, the BeSSeL Survey and the VERA project have measured trigonometric parallaxes to ≈250 massive, young stars using VLBI techniques. These sources trace spiral arms over nearly half of the Milky Way. What is now needed are accurate distances to such stars that are well past the Galactic center. Here we analyze the potential for addressing this need by combining line-of-sight velocities and proper motions to yield three-dimenensional (3D) kinematic distance estimates. For sources within about 10 kpc of the Sun, significant systematic uncertainties can occur, and trigonometric parallaxes are generally superior. However, for sources well past the Galactic center, 3D kinematic distances are robust and more accurate than can usually be achieved by trigonometic parallaxes.

Measurement of angular correlations of Compton-scattered gamma quanta from positron annihilation using GAGG:Ce scintillator matrices with single-side readout

We measured azimuthal correlations of the Compton-scattered gamma quanta from positron annihilation with two 8 × 8 matrices of Gadolinium Aluminum Gallium Garnet doped with Cerium. Each detector matrix contains 64 crystals of size 3 mm × 3 mm × 20 mm and it is read-out by a single Silicon Photo-multiplier (SiPM) array, with one SiPM matching one pixel. The studied single-side readout concept keeps the modules compact and cost-efficient on a large scale. Coincidence events were recorded using a Na-22 source placed between the modules. We clearly identify and reconstruct the Compton scattering events and we observe the excess of orthogonally scattered gammas over the ones with the parallel azimuthal angles. We present the measured azimuthal modulation factors for several kinematic selection criteria and different inter-pixel distances.

Supernova remnant G46.8–0.3: A new case of interaction with molecular material

Although the Galactic supernova remnant (SNR) G46.8–0.3 has been known for more than 50 yr, no specific studies of this source or its environment have been published to date. To make progress on this matter, we measured new flux densities from radio surveys and combined them with previous estimates carefully collected from the literature to create an improved and fully populated version of the integrated radio spectrum for G46.8–0.3. The resulting spectrum exhibits a featureless power-law form with an exponent α = −0.535 ± 0.012. The lack of a spectral turnover at the lowest radio frequencies, which is observable in many other SNRs, excludes the presence of abundant ionised gas either proximate to the SNR itself or along its line of sight. The analysis of local changes in the radio spectral index across G46.8–0.3 suggests a tendency to slightly steepen approximately at 1 GHz. Even if this steepening is real, it does not impact the integrated spectrum of the source. Deeper imaging of the radio structures of G46.8–0.3 and spectral maps constructed from matched raw data are needed to provide new insights into the local spectral properties of the remnant. On the basis of the spectral properties of the atomic gas, we placed the remnant at 8.7 ± 1.0 kpc and we revisited the distance to the nearby H ii region G046.495–00.241 to 7.3 ± 1.2 kpc. From evolutionary models and our distance estimate, we conclude that G46.8–0.3 is a middle-aged (~1 × 104 yr) SNR. Furthermore, we recognise several 12CO and 13CO molecular structures in the proximity of the remnant. We used combined CO-H i profiles to derive the kinematic distances to these features and characterise their physical properties. We provide compelling evidence for environmental molecular clouds physically linked to G46.8–0.3 at its centre, on its eastern edge, and towards the northern and southwestern rims on the far side of the SNR shell. Our study of the molecular matter does not confirm that the remnant is embedded in a molecular cavity as previously suggested. G46.8–0.3 shows a line-of-sight coincidence with the γ-ray source 4FGL J1918.1+1215c detected at GeV energies by the space telescope Fermi. A rough analysis based on the properties of the interstellar matter close to G46.8–0.3 indicates that the GeV γ-ray photons detected in the direction to the SNR can be plausibly attributed to hadronic collisions and/or bremsstrahlung radiation.

Our Galaxy’s youngest disc

ABSTRACT We investigate the structure of our Galaxy’s young stellar disc by fitting the distribution functions (DFs) of a new family to 5D Gaia data for a sample of $47\, 000$ OB stars. Tests of the fitting procedure show that the young disc’s DF would be strongly constrained by Gaia data if the distribution of Galactic dust were accurately known. The DF that best fits the real data accurately predicts the kinematics of stars at their observed locations, but it predicts the spatial distribution of stars poorly, almost certainly on account of errors in the best-available dust map. We argue that dust models could be greatly improved by modifying the dust model until the spatial distribution of stars predicted by a DF agreed with the data. The surface density of OB stars is predicted to peak at $R\simeq 5.5\, \mathrm{kpc}$, slightly outside the reported peak in the surface density of molecular gas; we suggest that the latter radius may have been underestimated through the use of poor kinematic distances. The velocity distributions predicted by the best-fitting DF for stars with measured line-of-sight velocities v∥ reveal that the outer disc is disturbed at the level of $10\, \mathrm{km\, s}^{-1}$ in agreement with earlier studies, and that the measured values of v∥ have significant contributions from the orbital velocities of binaries. Hence the outer disc is colder than it is sometimes reported to be.

The Long Filament of PSR J2030+4415

Abstract New X-ray and optical observations shed light on the remarkable X-ray filament of the gamma-ray pulsar PSR J2030+4415. Images of the associated Hα bow shock’s evolution over the past decade compared with its velocity structure provide an improved kinematic distance of ∼0.5 kpc. These velocities also imply that the pulsar spin axis lies ∼15° from the proper motion axis, which is close to the plane of the sky. The multi-bubble shock structure indicates that the bow shock standoff was compressed to a small value ∼20–30 yr ago when the pulsar broke through the bow shock to its present bubble. This compression allowed multi-TeV pulsar e ± to escape to the external interstellar medium (ISM), lighting up an external magnetic field structure as the filament. The narrow filament indicates excellent initial confinement and the full 15′ (2.2 pc = 7 lt-yr) projected length of the filament indicates rapid e ± propagation to its end. Spectral variation along the filament suggests that the injected particle energy evolved during the breakthrough event.

Acoustic and Articulatory Characteristics of English Semivowels /ɹ, l, w/ Produced by Adult Second-Language Speakers.

This study presents the results of acoustic and kinematic analyses of word-initial semivowels (/ɹ, l, w/) produced by second-language (L2) speakers of English whose native language is Korean. In addition, the relationship of acoustic and kinematic measures to the ratings of foreign accent was examined by correlation analyses. Eleven L2 speakers and 10 native speakers (first language [L1]) of English read The Caterpillar passage. Acoustic and kinematic data were simultaneously recorded using an electromagnetic articulography system. In addition to speaking rate, two acoustic measures (ratio of third-formant [F3] frequency to second-formant [F2] frequency and duration of steady states of F2) and two kinematic measures (lip aperture and duration of lingual maximum hold) were obtained from individual target sounds. To examine the degree of contrast among the three sounds, acoustic and kinematic Euclidean distances were computed on the F2-F3 and x-y planes, respectively. Compared with L1 speakers, L2 speakers exhibited a significantly slower speaking rate. For the three semivowels, L2 speakers showed a reduced F3/F2 ratio during constriction, increased lip aperture, and reduced acoustic Euclidean distances among semivowels. Additionally, perceptual ratings of foreign accent were significantly correlated with three measures: duration of steady F2, acoustic Euclidean distance, and kinematic Euclidean distance. The findings provide acoustic and kinematic evidence for challenges that L2 speakers experience in the production of English semivowels, especially /ɹ/ and /w/. The robust and consistent finding of reduced contrasts among semivowels and their correlations with perceptual accent ratings suggests using sound contrasts as a potentially effective approach to accent modification paradigms.

VERA astrometry toward the Perseus arm gap

Abstract The Perseus arm has a gap in Galactic longitudes (l) between 50° and 80° (hereafter the Perseus arm gap) where the arm has little star formation activity. To better understand the gap, we conducted astrometric observations with VERA (VLBI Exploration of Radio Astrometry) and analyzed archival H i data. We report on parallax and proper motion results from four star-forming regions, of which G050.28−00.39 and G070.33+01.59 are likely associated with the gap. The measured parallaxes are 0.140 ± 0.018 (mas), 0.726 ± 0.038 (mas), 0.074 ± 0.037 (mas), and 0.118 ± 0.035 (mas) for G050.28−00.39, G053.14+00.07, G070.33+01.59, and G079.08+01.33, respectively. Since the fractional parallax error of G070.33+01.59 is large (0.5), we estimated a 3D kinematic distance of the source of 7.7 ± 1.0 kpc using both the LSR velocity (VLSR) and the measured proper motion. Perseus-arm sources G049.41+00.32 and G050.28−00.39 lag relative to a Galactic rotation by 77 ± 17 km s−1 and 31 ± 10 km s−1, respectively. The noncircular motion of G049.41+00.32 cannot be explained by the gravitational potential of the Perseus arm. We discovered rectangular holes with integrated brightness temperatures of <30 K arcdeg in l vs. VLSR of the H i data. One of the holes is centered near (l, VLSR) = (47°, −15 km s−1), and G049.41+00.32 is associated with the rim of the hole. However, G050.28−00.39 is not associated with the hole. We found extended H i emission on one side of the Galactic plane when integrating the H i data over the velocity range covering the hole (i.e., VLSR = [−25, −5] km s−1). G049.41+00.32 and G050.28−00.39 are moving toward the emission. The Galactic H i disk at the same velocity range showed an arc structure, indicating that the disk was pushed from the lower side of the disk. All the observational results might be explained by a cloud collision with the Galactic disk.

The “Maggie” filament: Physical properties of a giant atomic cloud

Context. The atomic phase of the interstellar medium plays a key role in the formation process of molecular clouds. Due to the line-of-sight confusion in the Galactic plane that is associated with its ubiquity, atomic hydrogen emission has been challenging to study. Aims. We investigate the physical properties of the “Maggie” filament, a large-scale filament identified in H I emission at line-of-sight velocities, vLSR ~−54 km s−1. Methods. Employing the high-angular resolution data from The H I/OH Recombination line survey of the inner Milky Way (THOR), we have been able to study H I emission features at negative vLSR velocities without any line-of-sight confusion due to the kinematic distance ambiguity in the first Galactic quadrant. In order to investigate the kinematic structure, we decomposed the emission spectra using the automated Gaussian fitting algorithm GAUSSPY+. Results. We identify one of the largest, coherent, mostly atomic H I filaments in the Milky Way. The giant atomic filament Maggie, with a total length of 1.2 ± 0.1 kpc, is not detected in most other tracers, and it does not show signs of active star formation. At a kinematic distance of 17 kpc, Maggie is situated below (by ≈500 pc), but parallel to, the Galactic H I disk and is trailing the predicted location of the Outer Arm by 5−10 km s−1 in longitude-velocity space. The centroid velocity exhibits a smooth gradient of less than ±3 km s−1 (10 pc)−1 and a coherent structure to within ±6 km s−1. The line widths of ~10 km s−1 along the spine of the filament are dominated by nonthermal effects. After correcting for optical depth effects, the mass of Maggie’s dense spine is estimated to be 7.2−1.9+2.5 × 105 M⊙. The mean number density of the filament is ~4 cm−3, which is best explained by the filament being a mix of cold and warm neutral gas. In contrast to molecular filaments, the turbulent Mach number and velocity structure function suggest that Maggie is driven by transonic to moderately supersonic velocities that are likely associated with the Galactic potential rather than being subject to the effects of self-gravity or stellar feedback. The probability density function of the column density displays a log-normal shape around a mean of ⟨NH I⟩ = 4.8 × 1020 cm−2, thus reflecting the absence of dominating effects of gravitational contraction. Conclusions. While Maggie’s origin remains unclear, we hypothesize that Maggie could be the first in a class of atomic clouds that are the precursors of giant molecular filaments.

Discovery of a Wind-blown Bubble Associated with the Supernova Remnant G346.6-0.2: A Hint for the Origin of Recombining Plasma

Abstract We report on CO and H i studies of the mixed-morphology supernova remnant (SNR) G346.6−0.2. We find a wind-blown bubble along the radio continuum shell with an expansion velocity of ∼10 km s−1, which was likely formed by strong stellar winds from the high-mass progenitor of the SNR. The radial velocities of the CO/H i bubbles at V LSR = −82 to −59 km s−1 are also consistent with those of shock-excited 1720 MHz OH masers. The molecular cloud in the northeastern shell shows a high kinetic temperature of ∼60 K, suggesting that shock heating occurred. The H i absorption studies imply that G346.6−0.2 is located on the farside of the Galactic center from us, and the kinematic distance of the SNR is derived to be 11.1 − 0.3 + 0.5 kpc. We find that the CO line intensity has no specific correlation with the electron temperature of recombining plasma, implying that the recombining plasma in G346.6−0.2 was likely produced by adiabatic cooling. With our estimates of the interstellar proton density of 280 cm−3 and gamma-ray luminosity <5.8 × 1034 erg s−1, the total energy of accelerated cosmic rays of W p < 9.3 × 1047 erg is obtained. A comparison of the age–W p relation to other SNRs suggests that most of the accelerated cosmic rays in G346.6−0.2 have escaped from the SNR shell.

A Kiloparsec-scale Molecular Wave in the Inner Galaxy: Feather of the Milky Way?

Abstract We report the discovery of a velocity coherent, kiloparsec-scale molecular structure toward the Galactic center region with an angular extent of 30° and an aspect ratio of 60:1. The kinematic distance of the CO structure ranges between 4.4 and 6.5 kpc. Analysis of the velocity data and comparison with the existing spiral arm models support that a major portion of this structure is either a subbranch of the Norma arm or an interarm giant molecular filament, likely to be a kiloparsec-scale feather (or spur) of the Milky Way, similar to those observed in nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent, considering the uncertainties in the kinematic distances, and it could be as long as 4 kpc. The vertical distribution of this highly elongated structure reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms responsible for the origin of such a kiloparsec-scale filament and its wavy morphology remains unclear. The distinct wave-like shape and its peculiar orientation makes this cloud, named as the Gangotri wave, one of the largest and most intriguing structures identified in the Milky Way.

The diffuse interstellar band around 8620 Å

Context.Diffuse interstellar bands (DIBs) are important interstellar absorption features of which the origin is still debated. With the large data sets from modern spectroscopic surveys, background stars are widely used to show how the integrated columns of DIB carriers accumulate from the Sun to great distances. To date, studies on the kinematics of the DIB carriers are still rare.Aims.We aim to make use of the measurements from the Giraffe Inner Bulge Survey (GIBS) and theGaia–ESO survey (GES) to study the kinematics and distance of the carrier of DIBλ8620, as well as other properties.Methods.The DIBs were detected and measured following the same procedures as in Zhao et al. (2021, A&A, 645, A14; hereafter Paper I), assuming a Gaussian profile. The median radial velocities of the DIB carriers in 38 GIBS and GES fields were used to trace their kinematics, and the median distances of the carriers in each field were estimated by the median radial velocities and two applied Galactic rotation models.Results.We successfully detected and measured DIBλ8620 in 760 of 4117 GES spectra with |b| ≤ 10° and signal-to-noise ratio (S∕N) > 50. Combined with the DIBs measured in GIBS spectra (Paper I), we confirmed a tight relation between EW andE(J−KS) as well asAV, with similar fitting coefficients to those found by previous works. With a more accurate sample and the consideration of the solar motion, the rest-frame wavelength of DIBλ8620 was redetermined as 8620.83 Å, with a mean fit error of 0.36 Å. We studied the kinematics of the DIB carriers by tracing their median radial velocities in each field in the local standard of rest (VLSR) and into the galactocentric frame (VGC), respectively, as a function of the Galactic longitudes. Based on the medianVLSRand two Galactic rotation models, we obtained valid kinematic distances of the DIB carriers for nine GIBS and ten GES fields. We also found a linear relation between the DIBλ8620 measured in this work and the near-infrared DIB in APOGEE spectra at 1.5273 μm, and we estimated the carrier abundance to be slightly lower compared to the DIBλ15273.Conclusions.We demonstrate that the DIB carriers can be located much closer to the observer than the background stars based on the following arguments: (i) qualitatively, the carriers occupy in the Galactic longitude–velocity diagram typical rotation velocities of stars in the local Galactic disk, while the background stars in the GIBS survey are mainly located in the Galactic bulge; (ii) quantitatively, all the derived kinematic distances of the DIB carriers are smaller than the median distances to background stars in each field. A linear correlation between DIBλ8620 and DIBλ15273 has been established, showing similar carrier abundances and making them both attractive for future studies of the interstellar environments.

Kinematics of the western filament of W50

ABSTRACT We study the kinematics of the western optical filament of the radio shell W50 with imaging Fabry–Perot spectroscopy using the [S ii] (λ6717 Å and λ6731 Å) line doublet. The high [S ii]/H α line ratio of this filament, as well as the complexity of the radial velocity profiles obtained in this work ensure that this filament and diffuse regions are the optical counterpart of W50 hosting the peculiar object SS 433. We derive a kinematical distance of 4.7 ± 0.5 kpc, validating a previously derived distance based on the assumption that H i or CO gas is associated with W50. Our distance estimate is in agreement with the distance to SS 433 derived from proper motions. Shock velocities of up to 120 km s−1 are estimated for the [S ii] emitting regions. We derive an age between 1.0 and 1.9 × 105 yr considering that W50 is a remnant of a supernova explosion or a bubble blown by the action of the jets of the central SS 433 source, respectively. Age values are compatible with the age of SS 433. We also estimate the energy deposited by the supernova in the interstellar medium and alternatively, the luminosity of a wind-blown bubble fed by the relativistic jets of SS 433, obtaining reasonable values. We examine the different scenarios for the formation of W50. We conclude that a supernova remnant scenario rejuvenated by the interaction of SS 433 jets, acting as a piston, evolving in a three-phase medium with photo-evaporation, describes better the different observations and theoretical models of this system.

Tiny-scale Structure Discovered toward PSR B1557–50

Abstract Optical depth variations in the Galactic neutral interstellar medium (ISM) with spatial scales from hundreds to thousands of astronomical units have been observed through H i absorption against pulsars and continuum sources, while extremely small structures with spatial scales of tens of astronomical units remain largely unexplored. The nature and formation of such tiny-scale atomic structures (TSAS) need to be better understood. We report a tentative detection of TSAS with a signal-to-noise ratio of 3.2 toward PSR B1557−50 in the second epoch of two Parkes sessions just 0.36 yr apart, which are the closest-spaced spectral observations toward this pulsar. One absorption component showing marginal variations has been identified. Based on the pulsar’s proper motion of 14 mas yr−1 and the component’s kinematic distance of 3.3 kpc, the corresponding characteristic spatial scale is 17 au, which is among the smallest sizes of known TSAS. Assuming a similar line-of-sight (LOS) depth, the tentative TSAS cloud detected here is overdense and overpressured relative to the cold neutral medium (CNM), and can radiatively cool fast enough to be in thermal equilibrium with the ambient environment. We find that turbulence is not sufficient to confine the overpressured TSAS. We explore the LOS elongation that would be required for the tentative TSAS to be at the canonical CNM pressure, and find that it is ∼5000—much larger than filaments observed in the ISM. We see some evidence of line width and temperature variations in the CNM components observed at the two epochs, as predicted by models of TSAS-like cloud formation colliding warm neutral medium flows.

Sustaining Star Formation in the Galactic Star Cluster M 36?

Abstract We present comprehensive characterization of the Galactic open cluster M 36. Some 200 member candidates, with an estimated contamination rate of ∼8%, have been identified on the basis of proper motion and parallax measured by the Gaia DR2. The cluster has a proper motion grouping around ( mas yr−1, and μ δ = − 3.35 ± 0.02 mas yr−1), distinctly separated from the field population. Most member candidates have parallax values 0.7–0.9 mas, with a median value of 0.82 ± 0.07 mas (distance ∼1.20 ± 0.13 kpc). The angular diameter of determined from the radial density profile then corresponds to a linear extent of 9.42 ± 0.14 pc. With an estimated age of ∼15 Myr, M 36 is free of nebulosity. To the southwest of the cluster, we discover a highly obscured (A V up to ∼23 mag), compact (∼ ) dense cloud, within which three young stellar objects in their infancy (ages ≲0.2 Myr) are identified. The molecular gas, 3.6 pc in extent, contains a total mass of (2–3) × 102 M ⊙, and has a uniform velocity continuity across the cloud, with a velocity range of −20 to −22 km s−1, consistent with the radial velocities of known star members. In addition, the cloud has a derived kinematic distance marginally in agreement with that of the star cluster. If physical association between M 36 and the young stellar population can be unambiguously established, this manifests a convincing example of prolonged star formation activity spanning up to tens of Myr in molecular clouds.

Atlas of CO-line Shells and Cavities around Galactic Supernova Remnants with FUGIN*

Abstract A morphological search for molecular shells and cavities was performed around 63 Galactic supernova remnants (SNRs) at 10° ≤ l ≤ 50°, ∣b∣ ≤ 1° using the FOREST Unbiased Galactic Imaging survey with the Nobeyama 45 m telescope CO-line data at high-angular (20″) and high-velocity (1.3 km s−1) resolutions. The results are presented as supplementary data for general purpose investigations of the interaction between SNRs and interstellar matter in the form of an atlas of CO-line maps superposed on radio continuum maps at 20 cm along with a list of their kinematic distances determined from CO-line radial velocities.