Approximately 10% of active galactic nuclei exhibit relativistic jets, which are powered by the accretion of matter onto supermassive black holes. Although the measured width profiles of such jets on ...large scales agree with theories of magnetic collimation, the predicted structure on accretion disk scales at the jet launch point has not been detected. We report radio interferometry observations, at a wavelength of 1.3 millimeters, of the elliptical galaxy M87 that spatially resolve the base of the jet in this source. The derived size of 5.5 ± 0.4 Schwarzschild radii is significantly smaller than the innermost edge of a retrograde accretion disk, suggesting that the M87 jet is powered by an accretion disk in a prograde orbit around a spinning black hole.
Aims. The circumstellar disk of AB Aurigae has garnered strong attention owing to the apparent existence of spirals at a relatively young stage and also the asymmetric disk traced in thermal dust ...emission. However, the physical conditions of the spirals are still not well understood. The origin of the asymmetric thermal emission is unclear. Methods. We observed the disk at 230 GHz (1.3 mm) in both the continuum and the spectral line 12CO J = 2 → 1 with IRAM 30-m, the Plateau de Bure interferometer, and the SubMillimeter Array to sample all spatial scales from 0\hbox{$\farcs$} . ″ 37 to about 50′′. To combine the data obtained from these telescopes, several methods and calibration issues were checked and discussed. Results. The 1.3 mm continuum (dust) emission is resolved into inner disk and outer ring. The emission from the dust ring is highly asymmetric in azimuth, with intensity variations by a factor 3. Molecular gas at high velocities traced by the CO line is detected next to the stellar location. The inclination angle of the disk is found to decrease toward the center. On a larger scale, based on the intensity weighted dispersion and the integrated intensity map of 12CO J = 2 → 1, four spirals are identified, where two of them are also detected in the near infrared. The total gas mass of the 4 spirals (Mspiral) is 10-7 < Mspiral < 10-5M⊙, which is 3 orders of magnitude smaller than the mass of the gas ring. Surprisingly, the CO gas inside the spiral is apparently counter-rotating with respect to the CO disk, and it only exhibits small radial motion. Conclusions. The wide gap, the warped disk, and the asymmetric dust ring suggest that there is an undetected companion with a mass of 0.03 M⊙ at a radius of 45 AU. The different spirals would, however, require multiple perturbing bodies. While viable from an energetic point of view, this mechanism cannot explain the apparent counter-rotation of the gas in the spirals. Although an hypothetical fly-by cannot be ruled out, the most likely explanation of the AB Aurigae system may be inhomogeneous accretion well above or below the main disk plane from the remnant envelope, which can explain both the rotation and large-scale motions detected with the 30-m image.
Abstract
This paper presents the second data release of the Hyper Suprime-Cam Subaru Strategic Program, a wide-field optical imaging survey using the 8.2 m Subaru Telescope. The release includes data ...from 174 nights of observation through 2018 January. The Wide layer data cover about 300 deg$^2$ in all five broad-band filters ($grizy$) to the nominal survey exposure (10 min in $gr$ and 20 min in $izy$). Partially observed areas are also included in the release; about 1100 deg$^2$ is observed in at least one filter and one exposure. The median seeing in the i-band is ${0_{.}^{\prime \prime }6}$, demonstrating the superb image quality of the survey. The Deep (26 deg$^2$) and UltraDeep (4 deg$^2$) data are jointly processed and the UltraDeep-COSMOS field reaches an unprecedented depth of $i\sim 28$ at $5 \, \sigma$ for point sources. In addition to the broad-band data, narrow-band data are also available in the Deep and UltraDeep fields. This release includes a major update to the processing pipeline, including improved sky subtraction, PSF modeling, object detection, and artifact rejection. The overall data quality has been improved, but this release is not without problems; there is a persistent deblender problem as well as new issues with masks around bright stars. The user is encouraged to review the issue list before utilizing the data for scientific explorations. All the image products as well as catalog products are available for download. The catalogs are also loaded into a database, which provides an easy interface for users to retrieve data for objects of interest. In addition to these main data products, detailed galaxy shape measurements withheld from Public Data Release 1 (PDR1) are now available to the community. The shape catalog is drawn from the S16A internal release, which has a larger area than PDR1 (160 deg$^2$). All products are available at the data release site, https://hsc-release.mtk.nao.ac.jp/.
HH 212 is a nearby (400 pc) Class 0 protostellar system recently found to host a "hamburger"-shaped dusty disk with a radius of ∼60 au, deeply embedded in an infalling-rotating flattened envelope. We ...have spatially resolved this envelope-disk system with the Atacama Large Millimeter/submillimeter Array at up to ∼16 au (0 04) resolution. The envelope is detected in HCO+ J = 4-3 down to the dusty disk. Complex organic molecules (COMs) and doubly deuterated formaldehyde (D2CO) are detected above and below the dusty disk within ∼40 au of the central protostar. The COMs are methanol (CH3OH), deuterated methanol (CH2DOH), methyl mercaptan (CH3SH), and formamide (NH2CHO, a prebiotic precursor). We have modeled the gas kinematics in HCO+ and COMs and found a centrifugal barrier (CB) at a radius of ∼44 au, within which a Keplerian rotating disk is formed. This indicates that HCO+ traces the infalling-rotating envelope down to the CB and COMs trace the atmosphere of a Keplerian rotating disk within the CB. The COMs are spatially resolved for the first time, both radially and vertically, in the atmosphere of a disk in the earliest, Class 0 phase of star formation. Our spatially resolved observations of COMs favor their formation in the disk rather than a rapidly infalling (warm) inner envelope. The abundances and spatial distributions of the COMs provide strong constraints on models of their formation and transport in low-mass star formation.
Aims. Our aim is to characterize the polarized continuum emission properties including intensity, polarization position angle, and polarization percentage of Sgr A* at ~100 (3.0 mm), ~230 (1.3 mm), ...~345 (0.87 mm), ~500 (0.6 mm), and ~700 GHz (0.43 mm). Methods. We report continuum emission properties of Sgr A* at the above frequency bands, based on the Atacama Large Millimeter Array (ALMA) observations. We measured flux densities of Sgr A* from ALMA single pointing and mosaic observations. We performed sinusoidal fittings to the observed (XX-YY)/I intensity ratios, to derive the polarization position angles and polarization percentages. Results. We successfully detect polarized continuum emission from all observed frequency bands. We observed lower Stokes I intensity at ~700 GHz than that at ~500 GHz, which suggests that emission at ≳500 GHz is from the optically thin part of a synchrotron emission spectrum. Both the Stokes I intensity and the polarization position angle at our highest observing frequency of ~700 GHz, may vary with time. However, as yet we do not detect variation in the polarization percentage at >500 GHz. The polarization percentage at ~700 GHz is likely lower than that at ~500 GHz. By comparing the ~500 GHz and ~700 GHz observations with the observations at lower frequency bands, we suggest that the intrinsic polarization position angle of Sgr A* varies with time. This paper also reports the measurable polarization properties from the observed calibration quasars. Conclusions. Future simultaneous multi-frequency polarization observations are required to clarify the time and frequency variation of the polarization position angle and polarization percentage.
We report the ALMA Cycle 2 observations of the Class I binary protostellar system L1551 NE in the 0.9 mm continuum, C18O (3-2), 13CO (3-2), SO (78-67), and CS (7-6) emission. At 0 18 (=25 au) ...resolution, ∼4 times higher than that of our Cycle 0 observations, the circumbinary disk (CBD) as seen in the 0.9 mm emission is shown to be composed of a northern and a southern spiral arm, with the southern arm connecting to the circumstellar disk (CSD) around Source B. The western parts of the spiral arms are brighter than the eastern parts, suggesting the presence of an m = 1 spiral mode. In the C18O emission, the infall gas motions in the interarm regions and the outward gas motions in the arms are identified. These observed features are well reproduced with our numerical simulations, where gravitational torques from the binary system impart angular momenta to the spiral-arm regions and extract angular momenta from the interarm regions. Chemical differentiation of the CBD is seen in the four molecular species. Our Cycle 2 observations have also resolved the CSDs around the individual protostars, and the beam-deconvolved sizes are 0 29 × 0 19 (=40 × 26 au) (P.A. = 144°) and 0 26 × 0 20 (=36 × 27 au) (P.A. = 147°) for Sources A and B, respectively. The position and inclination angles of these CSDs are misaligned with those of the CBD. The C18O emission traces the Keplerian rotation of the misaligned disk around Source A.
Protostellar jets are one of the most intriguing signposts in star formation. Recent detection of a jet rotation indicates that they can carry away angular momenta from the innermost edges of the ...disks, allowing the disks to feed the central protostars. In current jet-launching models, magnetic fields are required to launch and collimate the jets, however, observationally, it is still uncertain if magnetic fields are really present in the jets. Here we report a clear detection of SiO line polarization in the HH 211 protostellar jet. Since this line polarization has been attributed to the Goldreich-Kylafis effect in the presence of magnetic field, our observations show convincingly the presence of magnetic field in a jet from a low-mass protostar. The implied magnetic field could be mainly toroidal, as suggested in current jet-launching models, in order to collimate the jet at large distances.
We report the results of ALMA observations of a protoplanetary disk surrounding the Herbig Ae star AB Aurigae. We obtained high-resolution (0 1; 14 au) images in 12CO J = 2 − 1 emission and in the ...dust continuum at the wavelength of 1.3 mm. The continuum emission is detected at the center and at the ring with a radius (r) of ∼120 au. The CO emission is dominated by two prominent spirals within the dust ring. These spirals are trailing and appear to be about 4 times brighter than their surrounding medium. Their kinematics is consistent with Keplerian rotation at an inclination of 23°. The apparent two-arm-spiral pattern is best explained by tidal disturbances created by an unseen companion located at r of 60-80 au, with dust confined in the pressure bumps created outside this companion orbit. An additional companion at r of 30 au, coinciding with the peak CO brightness and a large pitch angle of the spiral, would help to explain the overall emptiness of the cavity. Alternative mechanisms to excite the spirals are discussed. The origin of the large pitch angle detected here remains puzzling.
We present observations of CO(3-2) and 13CO(3-2) emission near the supernebula in the dwarf galaxy NGC 5253, which contains one of the best examples of a potential globular cluster in formation. The ...0 3 resolution images reveal an unusual molecular cloud, "Cloud D1," that is coincident with the radio-infrared supernebula. The ∼6 pc diameter cloud has a linewidth, Δ v = 21.7 , that reflects only the gravitational potential of the star cluster residing within it. The corresponding virial mass is 2.5 × 105 . The cluster appears to have a top-heavy initial mass function, with M* 1-2 . Cloud D1 is optically thin in CO(3-2), probably because the gas is hot. Molecular gas mass is very uncertain but constitutes <35% of the dynamical mass within the cloud boundaries. In spite of the presence of an estimated ∼1500-2000 O stars within the small cloud, the CO appears relatively undisturbed. We propose that Cloud D1 consists of molecular clumps or cores, possibly star-forming, orbiting with more evolved stars in the core of the giant cluster.
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