Search

HL Tau is a Class I-II protostar embedded in an infalling and rotating envelope and possibly associated with a planet forming disk, and it is co-located in a 0.1 pc molecular cloud with two nearby young stellar objects. Our ALMA observations revealed two arc-like structures on a 1000 au scale connected to the disk, and their kinematics could not be explained with any conventional model of infalling and rotational motions. In this work, we investigate the nature of these arc-like structures connected to the HL Tau disk. We conducted new observations in the 13CO and C18O (3-2; 2-1) lines with JCMT and IRAM 30m, and obtained the ACA data with the 7-m array. With the single-dish, ACA, and ALMA data, we analyzed the gas motions on both 0.1 pc and 1000 au scales in the HL Tau region. We constructed new kinematical models of an infalling and rotating envelope with the consideration of relative motion between HL Tau and the envelope. By including the relative motion between HL Tau and its protostellar envelope, our kinematical model can explain the observed velocity features in the arc-like structures. The morphologies of the arc-like structures can also be explained with an asymmetric initial density distribution in our model envelope. In addition, our single-dish results support that HL Tau is located at the edge of a large-scale (0.1 pc) expanding shell driven by the wind or outflow from XZ Tau, as suggested in the literature. The estimated expanding velocity of the shell is comparable to the relative velocity between HL Tau and its envelope in our kinematical model. These results hints that the large-scale expanding motion likely impacts the protostellar envelope around HL Tau and affects its gas kinematics. We found that the mass infalling rate from the envelope onto the HL Tau disk can be decreased by a factor of two due to this impact by the large-scale expanding shell., Accepted by A&A

We observe the dust continuum at 225 GHz and CO isotopologue (12CO, 13CO, and C18O) J=2-1 emission lines toward the CR Cha protoplanetary disk using the Atacama Large Millimeter/Submillimeter Array (ALMA). The dust continuum image shows a dust gap-ring structure in the outer region of the dust disk. A faint dust ring is also detected around 120 au beyond the dust gap. The CO isotopologue lines indicate that the gas disk is more extended than the dust disk. The peak brightness temperature of the 13CO line shows a small bump around 130 au while 12CO and C18O lines do not show. We investigate two possible mechanisms for reproducing the observed dust gap-ring structure and a gas temperature bump. First, the observed gap structure can be opened by a Jupiter mass planet using the relation between the planet mass and the gap depth and width. Meanwhile, the radiative transfer calculations based on the observed dust surface density profile show that the observed dust ring could be formed by dust accumulation at the gas temperature bump, that is, the gas pressure bump produced beyond the outer edge of the dust disk., Comment: 21 pages, figures

Previous (sub)millimeter observations have found that the spectral indices of dust emission from some young stellar objects are lower than that of the black body emission in the Rayleigh-Jeans limit (i.e., 2.0). In particular, the recent Atacama Large Millimeter Array observations have spatially resolved that the innermost regions of the protoplanetary disks TW\,Hya and HD\,163296 present anomalously low (i.e., $, Comment: Accepted to ApJL

L1551 IRS 5 is a FUor-like object located in the Taurus star forming region. We present ALMA 1.3 mm continuum observations using a wide range of baselines. The observations recovered the two circumstellar disks composing the system and, for the first time, resolved the circumbinary ring. We determined the geometry and estimated lower mass limits for the circumstellar disks using simple models. We calculated lower limits for the total mass of both circumstellar disks. After subtracting the two circumstellar disk models from the image, the residuals show a clearly resolved circumbinary ring. Using a radiative transfer model, we show that geometrical effects can explain some of the brightness asymmetries found in the ring. The remaining features are interpreted as enhancements in the dust density., Comment: 8 pages, 3 figure, Accepted for publication in ApJL

We present new ALMA observations of the molecular gas and far-infrared continuum around the brightest cluster galaxy (BCG) in the cool-core cluster MACS 1931.8-2635. Our observations reveal $1.9 \pm 0.3 \times 10^{10}$ M$_{\odot}$ of molecular gas, on par with the largest known reservoirs of cold gas in a cluster core. We detect CO(1-0), CO(3-2), and CO(4-3) emission from both diffuse and compact molecular gas components that extend from the BCG center out to $\sim30$ kpc to the northwest, tracing the UV knots and H$\alpha$ filaments observed by HST. Due to the lack of morphological symmetry, we hypothesize that the $\sim300$ km s$^{-1}$ velocity of the CO in the tail is not due to concurrent uplift by AGN jets, rather we may be observing the aftermath of a recent AGN outburst. The CO spectral line energy distribution suggests that molecular gas excitation is influenced by processes related to both star formation and recent AGN feedback. Continuum emission in Bands 6 and 7 arises from dust and is spatially coincident with young stars and nebular emission observed in the UV and optical. We constrain the temperature of several dust clumps to be $\lesssim 10$ K, which is too cold to be directly interacting with the surrounding $\sim 4.8$ keV intracluster medium (ICM). The cold dust population extends beyond the observed CO emission and must either be protected from interacting with the ICM or be surrounded by local volumes of ICM that are several keV colder than observed by Chandra., Comment: Accepted for Publication in ApJ, 19 pages, 11 figures. Minor revisions to the discussion and accompanying figure

Filaments are ubiquitous structures in molecular clouds and play an important role in the mass assembly of stars. We present results of dynamical stability analyses for filaments in the infrared dark cloud G14.225$-$0.506, where a delayed onset of massive star formation was reported in the two hubs at the convergence of multiple filaments of parsec length. Full-synthesis imaging is performed with the Atacama Large Millimeter/submillimeter Array (ALMA) to map the $\mathrm{N_2H^+} \; (1-0)$ emission in two hub-filament systems with a spatial resolution of $\sim 0.034 \; \mathrm{pc}$. Kinematics are derived from sophisticated spectral fitting algorithm that accounts for line blending, large optical depth, and multiple velocity components. We identify five velocity coherent filaments and derive their velocity gradients with principal component analysis. The mass accretion rates along the filaments are up to $10^{-4} \; \mathrm{M_\odot \, \mathrm{yr^{-1}}}$ and are significant enough to affect the hub dynamics within one free-fall time ($\sim 10^5 \; \mathrm{yr}$). The $\mathrm{N_2H^+}$ filaments are in equilibrium with virial parameter $\alpha_\mathrm{vir} \sim 1.2$. We compare $\alpha_\mathrm{vir}$ measured in the $\mathrm{N_2H^+}$ filaments, $\mathrm{NH_3}$ filaments, $870 \; \mu\mathrm{m}$ dense clumps, and $3 \; \mathrm{mm}$ dense cores. The decreasing trend in $\alpha_\mathrm{vir}$ with decreasing spatial scales persists, suggesting an increasingly important role of gravity at small scales. Meanwhile, $\alpha_\mathrm{vir}$ also decreases with decreasing non-thermal motions. In combination with the absence of high-mass protostars and massive cores, our results are consistent with the global hierarchical collapse scenario., Comment: 31 pages, 21 figures, 2 movies (plus 2 more movies in the published version), accepted for publication in The Astrophysical Journal

We present our observational results of the 1.1 mm continuum and the HCO+ (3-2) line in HL Tau at angular resolutions of 0.1" obtained with ALMA and our data analysis of the 2.9 mm and 1.1 mm continuum and the HCO+ (3-2) and (1-0) lines of the HL Tau disk. The Keplerian rotation of the HL Tau disk is well resolved in the HCO+ (3-2) emission, and the stellar mass is estimated to be 2.1+/-0.2 Msun with a disk inclination angle of 47 deg. The radial profiles of the HCO+ column density and excitation temperature are measured with the LTE analysis of the two transitions of the HCO+ emission. An HCO+ gas gap at a radius of 30 au, where the column density drops by a factor of 4-8, is found in the HCO+ column density profile, coincident with the dust gap traced by the continuum emission. No other clear HCO+ gas gap is seen. This HCO+ gas gap can be opened by a planet with mass of 0.5-0.8 Mj, which is comparable to the planet mass adopted in numerical simulations to form the dust gap at the same radius in the HL Tau disk. In addition to the disk component, a one-arm spiral with a length of ~3" (520 au) stretching out from the inner disk is observed in the HCO+ (3-2) emission. The observed velocity structures along the spiral suggest an infalling and rotating gas stream toward the inner disk., Comment: Accepted by ApJ

Aims. The response of a protoplanetary disk to luminosity bursts of various durations is studied with the purpose to determine the effect of the bursts on the strength and sustainability of gravitational instability in the disk. A special emphasis is paid to the spatial distribution of gas and grown dust (from 1 mm to a few centimetres) during and after the burst. Methods. Numerical hydrodynamics simulations were employed to study the dynamics of gas and dust in the thin-disk limit. Dust-to-gas friction, including back reaction and dust growth, were also considered. Bursts of various durations (from 100 yr to 500 yr) were initiated in accordance with a thermally ignited magnetorotational instability. Luminosity curves for constant- and declining-magnitude bursts were adopted to represent two typical limiting cases for FU Orionis-type eruptions. Results. The short-term effect of the burst is to reduce the strength of gravitational instability by heating and expanding the disk. The longest bursts with durations comparable to the revolution period of the spiral can completely dissolve the original two-armed spiral pattern in the gas disk by the end of the burst, while the shortest bursts only weaken the spiral pattern. The reaction of grown dust to the burst is somewhat different. The spiral-like initial distribution with deep cavities in the inter-armed regions transforms into a ring-like distribution with deep gaps. This transformation is mostly expressed for the longest-duration bursts. The long-term effect of the burst depends on the initial disk conditions at the onset of the burst. In some cases, vigorous disk fragmentation sets in several thousands of years after the burst, which was absent in the model without the burst. Several clumps with masses in the giant-planet mass range form in the outer disk regions. After the disk fragmentation phase, the spatial distribution of grown dust is characterized by multiple sharp rings located from tens to hundreds of astronomical units. The arrangement and sharpness of the rings depends on the strength of dust turbulent diffusion. The wide-orbit rings are likely formed as the result of dust-rich clump dispersal in the preceding gravitationally unstable phase. Conclusions. Luminosity bursts similar in magnitude to FU Orionis-type eruptions can have a profound effect on the dynamics of gas and dust in protoplanetary disks if the burst duration is comparable to, or longer than, the dynamical timescales. In this context, the spatial morphology of the gas-dust disk of V883 Ori, a FU Orionis-like object that is thought to be in the outburst phase for more than a century with an unknown onset date, may be used as test case for the burst models considered in this work. The potential relation of the obtained ring structures to a variety of gaps and rings observed in T Tauri disks remains to be established.

For the active T-Taur star RW Aur A we have performed long-term (~10 yr) monitoring observations of (1) jet imaging in the [Fe II] 1.644-micron emission line using Gemini-NIFS and VLT-SINFONI; (2) optical high-resolution spectroscopy using CFHT-ESPaDOnS; and (3) V-band photometry using the CrAO 1.25-m telescope and AAVSO. The latter two observations confirm the correlation of time variabilities between (A) the Ca II 8542 A and O I 7772 A line profiles associated with magnetospheric accretion, and (B) optical continuum fluxes. The jet images and their proper motions show that four knot ejections occurred at the star over the past ~15 years with an irregular interval of 2-6 years. The time scale and irregularity of these intervals are similar to those of the dimming events seen in the optical photometry data. Our observations show a possible link between remarkable (Delta_V < -1 mag.) photometric rises and jet knot ejections. Observations over another few years may confirm or reject this trend. If confirmed, this would imply that the location of the jet launching region is very close to the star (r <, 14 pages, 5 figures, Accepted by Astrophysical Journal

We present Atacama Large Millimeter/submillimeter Array (ALMA) and Karl G. Jansky Very Large Array (JVLA) observations of the massive infrared dark cloud NGC 6334S (also known as IRDC G350.56+0.44), located at the southwestern end of the NGC 6334 molecular cloud complex. The H$^{13}$CO$^{+}$ and the NH$_{2}$D lines covered by the ALMA observations at a $\sim$3$^{\prime\prime}$ angular resolution ($\sim$0.02 pc) reveal that the spatially unresolved non-thermal motions are predominantly subsonic and transonic, a condition analogous to that found in low-mass star-forming molecular clouds. The observed supersonic non-thermal velocity dispersions in massive star forming regions, often reported in the literature, might be significantly biased by poor spatial resolutions that broaden the observed line widths due to unresolved motions within the telescope beam. Our 3~mm continuum image resolves 49 dense cores, whose masses range from 0.17 to 14 $M_{\odot}$. The majority of them are resolved with multiple velocity components. Our analyses of these gas velocity components find an anti-correlation between the gas mass and the virial parameter. This implies that the more massive structures tend to be more gravitationally unstable. Finally, we find that the external pressure in the NGC 6334S cloud is important in confining these dense structures, and may play a role in the formation of dense cores, and subsequently, the embedded young stars., 30 pages, 10 figures, 2 tables, accepted for publication in The Astrophysical Journal

Aims. We aim to characterise certain physical properties of high-mass star-forming sites in the NGC 6334 molecular cloud, such as the core mass function (CMF), spatial distribution of cores, and mass segregation. Methods. We used the Atacama Large Millimeter/sub-millimeter Array (ALMA) to image the embedded clusters NGC 6334-I and NGC 6334-I(N) in the continuum emission at 87.6 GHz. We achieved a spatial resolution of 1300 au, enough to resolve different compact cores and fragments, and to study the properties of the clusters. Results. We detected 142 compact sources distributed over the whole surveyed area. The ALMA compact sources are clustered in different regions. We used different machine-learning algorithms to identify four main clusters: NGC 6334-I, NGC 6334-I(N), NGC 6334-I(NW), and NGC 6334-E. The typical separations between cluster members range from 4000 au to 12 000 au. These separations, together with the core masses (0.1–100 M⊙), are in agreement with the fragmentation being controlled by turbulence at scales of 0.1 pc. We find that the CMFs show an apparent excess of high-mass cores compared to the stellar initial mass function. We evaluated the effects of temperature and unresolved multiplicity on the derived slope of the CMF. Based on this, we conclude that the excess of high-mass cores might be spurious and due to inaccurate temperature determinations and/or resolution limitations. We searched for evidence of mass segregation in the clusters and we find that clusters NGC 6334-I and NGC 6334-I(N) show hints of segregation with the most massive cores located in the centre of the clusters. Conclusions. We searched for correlations between the physical properties of the four embedded clusters and their evolutionary stage (based on the presence of H II regions and infrared sources). NGC 6334-E appears as the most evolved cluster, already harbouring a well-developed H II region. NGC 6334-I is the second-most evolved cluster with an ultra-compact H II region. NGC 6334-I(N) contains the largest population of dust cores distributed in two filamentary structures and no dominant H II region. Finally, NGC 6334-I(NW) is a cluster of mainly low-mass dust cores with no clear signs of massive cores or H II regions. We find a larger separation between cluster members in the more evolved clusters favouring the role of gas expulsion and stellar ejection with evolution. The mass segregation, seen in the NGC 6334-I and NGC 6334-I(N) clusters, suggests a primordial origin for NGC 6334-I(N). In contrast, the segregation in NGC 6334-I might be due to dynamical effects. Finally, the lack of massive cores in the most evolved cluster suggests that the gas reservoir is already exhausted, while the less evolved clusters still have a large gas reservoir along with the presence of massive cores. In general, the fragmentation process of NGC 6334 at large scales (from filament to clump, i.e. at about 1 pc) is likely governed by turbulent pressure, while at smaller scales (scale of cores and sub-fragments, i.e. a few hundred au) thermal pressure starts to be more significant.

We report high angular resolution observations of linearly polarized dust emission towards the Class 0 young stellar object (YSO) NGC1333 IRAS4A (hereafter, IRAS4A) using the Karl G. Jansky Very Large Array (JVLA) at K (11.5-16.7 mm), Ka (8.1-10.3 mm), and Q bands (6.3-7.9 mm), and using the Atacama Large Millimeter Array (ALMA) at Band 6 (1.2 mm) and Band 7 (0.85-0.89 mm). On 100-1000 AU scales, all of these observations consistently trace the hourglass shaped magnetic field topology as shown in the previous studies. In the innermost 100 AU region of IRAS4A1, the polarization position angles (E-field) detected at 6.3-16.7 mm are consistent, however, are nearly 90 degrees offset from those detected at 1.2 mm and 0.85-0.89 mm. Such a 90 degree offset may be explained by that the inner $\sim$100 AU area is optically thick at wavelengths shorter than $\sim$1.5 mm, whereby the observations probe the absorption of aligned dust against the weakly or unpolarized warm dust emission from the innermost region. This can also consistently explain why the highest angular resolution ALMA images at Band 7 show that the polarization percentage increases with dust brightness temperature in the inner $\sim$100 AU region of IRAS4A1. Following this interpretation and assuming that the dust grains are aligned with the magnetic fields, the inferred magnetic field position angle based on the 90$^{\circ}$ rotated at 6.3-7.9 mm in the central peak of IRAS4A1 is $\sim-22^{\circ}$, which is approximately consistent with the outflow direction $\sim-9^{\circ}$., Comment: 11 pages, 4 figures; submitted to ApJ

FU Orionis objects are low-mass pre-main sequence stars characterized by dramatic outbursts of several magnitudes in brightness. These outbursts are linked to episodic accretion events in which stars gain a significant portion of their mass. The physical processes behind these accretion events are not yet well understood. The archetypical FU Ori system, FU Orionis, is composed of two young stars with detected gas and dust emission. The continuum emitting regions have not been resolved until now. Here, we present 1.3 mm observations of the FU Ori binary system with ALMA. The disks are resolved at 40 mas resolution. Radiative transfer modeling shows that the emission from FU Ori north (primary) is consistent with a dust disk with a characteristic radius of $\sim$11 au. The ratio between major and minor axes shows that the inclination of the disk is $\sim$37 deg. FU Ori south is consistent with a dust disk of similar inclination and size. Assuming the binary orbit shares the same inclination angle as the disks, the deprojected distance between north and south components is 0.6'', i.e. $\sim$250 au. Maps of $^{12}$CO emission show a complex kinematic environment with signatures disk rotation at the location of the northern component, and also (to a lesser extent) for FU Ori south. The revised disk geometry allows us to update FU Ori accretion models (Zhu et al.), yielding a stellar mass and mass accretion rate of FU Ori north of 0.6 M$_{\odot}$ and 3.8$\times10^{-5}$ M$_{\odot}$ yr$^{-1}$, respectively., 9 pages, 4 figures, accepted for publication in ApJ

We report new, $\sim$1000 AU spatial resolution observations of 225 GHz dust continuum emission towards the OB cluster-forming molecular clump G33.92+0.11. On parsec scales, this molecular clump presents a morphology with several arm-like dense gas structures surrounding the two central massive ($\gtrsim$100 $M_{\odot}$) cores. From the new, higher resolution observations, we identified 28 localized, spatially compact dust continuum emission sources, which may be candidates of young stellar objects. Only one of them is not embedded within known arm-like (or elongated) dense gas structures. The spatial separations of these compact sources can be very well explained by Jeans lengths. We found that G33.92+0.11 may be consistently described by a marginally centrifugally supported, Toomre unstable accretion flow which is approximately in a face-on projection. The arm-like overdensities are natural consequence of the Toomre instability, which can fragment to form young stellar objects in shorter time scales than the timescale of the global clump contraction. On our resolved spatial scales, there is not yet evidence that the fragmentation is halted by turbulence, magnetic field, or stellar feedback., 24 pages, 18 figures. Accepted to publish on December 04, 2018; updated to arXiv on December 05, 2018

We performed the new JVLA full polarization observations at 40-48 GHz (6.3-7.5 mm) towards the nearby ($d$ $=$147$\pm$3.4 pc) Class 0 YSO IRAS 16293-2422, and compare with the previous SMA observations reported by Rao et al. (2009; 2014). We observed the quasar J1407+2827 which is weakly polarized and can be used as a leakage term calibrator for $$100 au scales, and becomes toroidal on smaller scales. However, this interpretation remains uncertain due to the high dust optical depths at the central region of IRAS\,16293-2422\,B and the uncertain temperature profile. We suggest that dust polarization at wavelengths comparable or longer than 7\,mm may still trace interstellar magnetic field. Future sensitive observations of dust polarization in the fully optically thin regime will have paramount importance for unambiguously resolving the magnetic field configuration., Comment: 14 pages, 7 figures, accepted to A&A. Comments are welcome

We present near-IR imaging polarimetry of five classical FU Ori-type objects (FU Ori, V1057 Cyg, V1515 Cyg, V1735 Cyg, Z CMa) with a $\sim$0\farcs1 resolution observed using HiCIAO+AO188 at Subaru Telescope. We observed scattered light associated with circumstellar dust around four of them (i.e., all but V1515 Cyg). Their polarized intensity distribution shows a variety of morphologies with arms, tails or streams, spikes and fragmented distributions, many of which were reported in our previous paper. The morphologies of these reflection nebulae significantly differ from many other normal young stellar objects (Class I-II objects). These structures are attributed to gravitationally unstable disks, trails of clump ejections, dust blown by a wind or a jet, and a stellar companion. We can consistently explain our results with the scenario that their accretion outbursts (FUor outbursts) are triggered by gravitationally fragmenting disks, and with the hypothesis that many low-mass young stellar objects experience such outbursts., 21 pages, 10 figures, accepted by ApJ; resubmitted to astro-ph on August 22, 2018

In this paper we explore the effects of self-obscuration in protostellar disks with a radially decreasing temperature gradient and a colder midplane. We are motivated by recent reports of resolved dark lanes (`hamburgers') and (sub)mm spectral indices systematically below the ISM value for optically thin dust $\alpha_{\rm ISM} =3.7$. We explore several model grids, scaling disk mass and varying inclination angle $i$ and observing frequency $\nu$ from the VLA Ka band ($\sim 37$ GHz) to ALMA Band 8 ($\sim 405$ GHz). We also consider the effects of decreasing the index of the (sub-)mm dust opacity power law $\beta$ from 1.7 to 1. We find that a distribution of disk masses in the range $M_{\rm disk} = 0.01-2~M_\odot$ is needed to reproduce the observed distribution of spectral indices, and that assuming a fixed $\beta =1.7$ gives better results than $\beta=1$. A wide distribution of disk masses is also needed to produce some cases with $\alpha \times10$, and are consistent with recent hydrodynamical simulations. Although we do not rule out the possibility of some grain growth occurring within the short protostellar timescales, we conclude that self-obscuration needs to be taken into account., Comment: Accepted to The Astrophysical Journal Supplement

We present combined observations of the NH3 (J,K) = (1,1) and (2,2) inversion transitions towards OMC1 in Orion A obtained by the Karl G. Jansky Very Large Array (VLA) and the 100 m Robert C. Byrd Green Bank Telescope (GBT). With an angular resolution of 6" (0.01 pc), these observations reveal with unprecedented detail the complex filamentary structure extending north of the active Orion BN/KL region in a field covering 6' x 7'. We find a 0.012 pc wide filament within OMC1, with an aspect ratio of ~37:1, that was missed in previous studies. Its orientation is directly compared to the relative orientation of the magnetic field from the James Clerk Maxwell Telescope BISTRO survey in Orion A. We find a small deviation of ~11 deg between the mean orientation of the filament and the magnetic field, suggesting that they are almost parallel to one another. The filament's column density is estimated to be 2-3 orders of magnitude larger than the filaments studied with Herschel and is possibly self-gravitating given the low values of turbulence found. We further produce maps of the gas kinematics by forward modeling the hyperfine structure of the NH3 (J,K) = (1,1) and (2,2) lines. The resulting distribution of velocity dispersions peaks at ~0.5 km/s, close to the subsonic regime of the gas. This value is about 0.2 km/s smaller than previously measured in single-dish observations of the same region, suggesting that higher angular and spectral resolution observations will identify even lower velocity dispersions that might reach the subsonic turbulence regime in dense gas filaments., Comment: Accepted for publication in ApJ. The combined data cubes of the NH3 (1,1) and (2,2) transitions as well as the resulting parameter maps are provided as FITS-files on Harvard Dataverse (https://doi.org/10.7910/DVN/QLD7TC); updated references

Spatially resolved structures in protoplanetary disks hint at unseen planets. Previous imaging observations of the transitional disk around MWC 758 revealed an inner cavity, a ring-like outer disk, emission clumps, and spiral arms, all possibly generated by companions. We present ALMA dust continuum observations of MWC 758 at 0.87 millimeter (mm) wavelength with 43$\times$39 mas angular resolution (6.9$\times$6.2 AU) and 20 $\mu$Jy beam$^{-1}$ rms. The central sub-mm emission cavity is revealed to be eccentric; once deprojected, its outer edge can be well-fitted by an ellipse with an eccentricity of 0.1 and one focus on the star. The broad ring-like outer disk is resolved into three narrow rings with two gaps in between. The outer two rings tentatively show the same eccentricity and orientation as the innermost ring bounding the inner cavity. The two previously known dust emission clumps are resolved in both the radial and azimuthal directions, with radial widths equal to $\sim$4$\times$ the local scale height. Only one of the two spiral arms previously imaged in near-infrared (NIR) scattered light is revealed in ALMA dust emission, at a slightly larger stellocentric distance owing to projection effects. We also submit evidence of disk truncation at $\sim$100 AU based on comparing NIR imaging observations with models. The spirals, the north clump, and the truncated disk edge are all broadly consistent with the presence of one companion exterior to the spirals at roughly 100 AU., Comment: accepted by ApJ; the fits file of the ALMA image will be made available by ApJ

The Galactic center uniquely provides opportunities to resolve how star clusters form in neutral gas overdensities engulfed in a large-scale accretion flow. We have performed sensitive Green Bank 100m Telescope (GBT), Karl G. Jansky Very Large Array (JVLA), and Submillimeter Array (SMA) mapping observations of molecular gas and thermal dust emission surrounding the Galaxy"s supermassive black hole (SMBH) Sgr A*. We resolved several molecular gas streams orbiting the center on ≳10 pc scales. Some of these gas streams appear connected to the well-known 2{4 pc scale molecular circumnuclear disk (CND). The CND may be the tidally trapped inner part of the large-scale accretion flow, which incorporates in flow via exterior gas laments/arms, and ultimately feeds gas toward Sgr A * . Our high resolution GBT+JVLA NH3 images and SMA+JCMT 0.86 mm dust continuum image consistently reveal abundant dense molecular clumps in this region. These gas clumps are characterized by ≳100 times higher virial masses than the derived molecular gas masses based on 0.86 mm dust continuum emission. In addition, Class I CH₃OH masers and some H₂O masers are observed to be well associated with the dense clumps. We propose that the resolved gas clumps may be pressurized gas reservoirs for feeding the formation of 1-10 solar-mass stars. These sources may be the most promising candidates for ALMA to probe the process of high-mass star-formation in the Galactic center.

We have modified the iterative procedure introduced by Lin et al. (2016), to systematically combine the submm images taken from ground based (e.g., CSO, JCMT, APEX) and space (e.g., Herschel, Planck) telescopes. We applied the updated procedure to observations of three well studied Infrared Dark Clouds (IRDCs): G11.11-0.12, G14.225-0.506 and G28.34+0.06, and then performed single-component, modified black-body fits to derive $\sim$10$"$ resolution dust temperature and column density maps. The derived column density maps show that these three IRDCs exhibit complex filamentary structures embedding with rich clumps/cores. We compared the column density probability distribution functions (N-PDFs) and two-point correlation (2PT) functions of the column density field between these IRDCs with several OB cluster-forming regions. Based on the observed correlation and measurements, and complementary hydrodynamical simulations for a 10$^{4}$ $\rm M_{\odot}$ molecular cloud, we hypothesize that cloud evolution can be better characterized by the evolution of the (column) density distribution function and the relative power of dense structures as a function of spatial scales, rather than merely based on the presence of star-forming activity. Based on the small analyzed sample, we propose four evolutionary stages, namely: {\it cloud integration, stellar assembly, cloud pre-dispersal and dispersed-cloud.} The initial {\it cloud integration} stage and the final {\it dispersed cloud} stage may be distinguished from the two intermediate stages by a steeper than $-$4 power-law index of the N-PDF. The {\it cloud integration} stage and the subsequent {\it stellar assembly} stage are further distinguished from each other by the larger luminosity-to-mass ratio ($>$40 $\rm L_{\odot}/M_{\odot}$) of the latter., 14 pages, 13 figures; accepted for publication in ApJ

We present Submillimeter Array 880 $\mu$m dust polarization observations of six massive dense cores in the DR21 filament. The dust polarization shows complex magnetic field structures in the massive dense cores with sizes of 0.1 pc, in contrast to the ordered magnetic fields of the parsec-scale filament. The major axes of the massive dense cores appear to be aligned either parallel or perpendicular to the magnetic fields of the filament, indicating that the parsec-scale magnetic fields play an important role in the formation of the massive dense cores. However, the correlation between the major axes of the cores and the magnetic fields of the cores is less significant, suggesting that during the core formation, the magnetic fields below 0.1 pc scales become less important than the magnetic fields above 0.1 pc scales in supporting a core against gravity. Our analysis of the angular dispersion functions of the observed polarization segments yields the plane-of-sky magnetic field strengths of 0.4--1.7 mG of the massive dense cores. We estimate the kinematic, magnetic, and gravitational virial parameters of the filament and the cores. The virial parameters show that in the filament, the gravitational energy is dominant over magnetic and kinematic energies, while in the cores, the kinematic energy is dominant. Our work suggests that although magnetic fields may play an important role in a collapsing filament, the kinematics arising from gravitational collapse must become more important than magnetic fields during the evolution from filaments to massive dense cores., Comment: 10 Figures, 5 Tables, ApJ accepted

The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and it is still embedded in a protostellar envelope with a size of thousands of au. In this work, we study the gas kinematics in the envelope and its possible influence on the embedded disk. We present our new ALMA cycle 3 observational results of HL Tau in the 13CO (2-1) and C18O (2-1) emission at resolutions of 0.8" (110 au), and we compare the observed velocity pattern with models of different kinds of gas motions. Both the 13CO and C18O emission lines show a central compact component with a size of 2" (280 au), which traces the protoplanetary disk. The disk is clearly resolved and shows a Keplerian motion, from which the protostellar mass of HL Tau is estimated to be 1.8+/-0.3 M$_\odot$, assuming the inclination angle of the disk to be 47 deg from the plane of the sky. The 13CO emission shows two arc structures with sizes of 1000-2000 au and masses of 3E-3 M$_\odot$ connected to the central disk. One is blueshifted and stretches from the northeast to the northwest, and the other is redshifted and stretches from the southwest to the southeast. We find that simple kinematical models of infalling and (counter-)rotating flattened envelopes cannot fully explain the observed velocity patterns in the arc structures. The gas kinematics of the arc structures can be better explained with three-dimensional infalling or outflowing motions. Nevertheless, the observed velocity in the northwestern part of the blueshifted arc structure is ~60-70% higher than the expected free-fall velocity. We discuss two possible origins of the arc structures: (1) infalling flows externally compressed by an expanding shell driven by XZ Tau and (2) outflowing gas clumps caused by gravitational instabilities in the protoplanetary disk around HL Tau., Comment: Accepted by A&A

Young stellar objects (YSOs) may undergo periods of active accretion (outbursts), during which the protostellar accretion rate is temporarily enhanced by a few orders of magnitude. Whether or not these accretion outburst YSOs possess similar dust/gas reservoirs to each other, and whether or not their dust/gas reservoirs are similar as quiescent YSOs, are issues not yet clarified. The aim of this work is to characterize the millimeter thermal dust emission properties of a statistically significant sample of long and short duration accretion outburst YSOs (i.e., FUors and EXors) and the spectroscopically identified candidates of accretion outbursting YSOs (i.e., FUor-like objects). We have carried out extensive Submillimeter Array (SMA) observations mostly at $\sim$225 GHz (1.33 mm) and $\sim$272 GHz (1.10 mm), from 2008 to 2017. We covered accretion outburst YSOs located at $$3-$\sigma$ significance. Detected sources except for the two cases of V883 Ori and NGC 2071 MM3 were observed with $\sim$1$"$ angular resolution. Overall our observed targets show a systematically higher millimeter luminosity distribution than those of the $M_{*}>$0.3 $M_{\odot}$ Class II YSOs in the nearby ($\lesssim$400 pc) low-mass star-forming molecular clouds (e.g., Taurus, Lupus, Upp Scorpio, and Chameleon I). In addition, at 1 mm our observed confirmed binaries or triple-system sources are systematically fainter than the rest of the sources even though their 1 mm fluxes are broadly distributed. We may have detected $\sim$30-60\% millimeter flux variability from V2494 Cyg and V2495 Cyg, from the observations separated by $\sim$1 year., Comment: 23 pages, 17 figures, accepted to A&A

We are motivated by the recent measurements of dust opacity indices beta around young stellar objects (YSOs), which suggest that efficient grain growth may have occurred earlier than the Class I stage. The present work makes use of abundant archival interferometric observations at submillimeter,millimeter, and centimeter wavelength bands to examine grain growth signatures in the dense inner regions (, 13 pages, 5 figures, 5 tables, accepted for publication in ApJ

We present observations towards a high-mass ($\rm >40\,M_{\odot}$), low luminosity ($\rm, Comment: 8 pages, 3 figures, submitted to ApJ on Jan. 18th, 2016, accepted on May. 5th, 2016

Young stellar objects (YSOs) may not accumulate their mass steadily, as was previously thought, but in a series of violent events manifesting themselves as sharp stellar brightening. These events can be caused by fragmentation due to gravitational instabilities in massive gaseous disks surrounding young stars, followed by migration of dense gaseous clumps onto the star. We report our high angular resolution, coronagraphic near-infrared polarization imaging observations using the High Contrast Instrument for the Subaru Next Generation Adaptive Optics (HiCIAO) of the Subaru 8.2 m Telescope, towards four YSOs which are undergoing luminous accretion outbursts. The obtained infrared images have verified the presence of several hundred AUs scale arms and arcs surrounding these YSOs. In addition, our hydrodynamics simulations and radiative transfer models further demonstrate that these observed structures can indeed be explained by strong gravitational instabilities occurring at the beginning of the disk formation phase. The effect of those tempestuous episodes of disk evolution on star and planet formation remains to be understood., 10 pages, 8 figures; revised version published by Science Advances

We present monitoring observations of the active T Tauri star RW Aur, from 2010 October to 2015 January, using optical high-resolution (R>10000) spectroscopy with CFHT-ESPaDOnS. Optical photometry in the literature shows bright, stable fluxes over most of this period, with lower fluxes (by 2-3 mag.) in 2010 and 2014. In the bright period our spectra show clear photospheric absorption, complicated variation in the Ca II 8542 A emission}profile shapes, and a large variation in redshifted absorption in the O I 7772 and 8446 A and He I 5876 A lines, suggesting unstable mass accretion during this period. In contrast, these line profiles are relatively uniform during the faint periods, suggesting stable mass accretion. During the faint periods the photospheric absorption lines are absent or marginal, and the averaged Li I profile shows redshifted absorption due to an inflow. We discuss (1) occultation by circumstellar material or a companion and (2) changes in the activity of mass accretion to explain the above results, together with near-infrared and X-ray observations from 2011-2015. Neither scenario can simply explain all the observed trends, and more theoretical work is needed to further investigate their feasibilities., 23 pages, 11 figures, 4 tables, accepted by Astrophysical Journal; some typos corrected on 4/18/2016

We present observations of the 1.3 mm continuum emission toward hub-N and hub-S of the infrared dark cloud G14.225-0.506 carried out with the Submillimeter Array, together with observations of the dust emission at 870 and 350 microns obtained with APEX and CSO telescopes. The large scale dust emission of both hubs consists of a single peaked clump elongated in the direction of the associated filament. At small scales, the SMA images reveal that both hubs fragment into several dust condensations. The fragmentation level was assessed under the same conditions and we found that hub-N presents 4 fragments while hub-S is more fragmented, with 13 fragments identified. We studied the density structure by means of a simultaneous fit of the radial intensity profile at 870 and 350 microns and the spectral energy distribution adopting a Plummer-like function to describe the density structure. The parameters inferred from the model are remarkably similar in both hubs, suggesting that density structure could not be responsible in determining the fragmentation level. We estimated several physical parameters such as the level of turbulence and the magnetic field strength, and we found no significant differences between these hubs. The Jeans analysis indicates that the observed fragmentation is more consistent with thermal Jeans fragmentation compared with a scenario that turbulent support is included. The lower fragmentation level observed in hub-N could be explained in terms of stronger UV radiation effects from a nearby HII region, evolutionary effects, and/or stronger magnetic fields at small scales, a scenario that should be further investigated., Comment: 14 pages, 5 figures. Accepted for publication in ApJ

Our aim is to characterize the polarized continuum emission properties including intensity, polarization position angle, and polarization percentage of Sgr A* at $\sim$100 (3.0 mm), $\sim$230 (1.3 mm), $\sim$345 (0.87 mm), $\sim$500 (0.6 mm), and $\sim$700 GHz (0.43 mm). 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. We successfully detect polarized continuum emission from all observed frequency bands. We observed lower Stokes I intensity at $\sim$700 GHz than that at $\sim$500 GHz, which suggests that emission at $\gtrsim$500 GHz is from optically thin part of a synchrotron emission spectrum. Both the Stokes I intensity and the polarization position angle at our highest observing frequency of $\sim$700 GHz, may be varying with time. However, we do not yet detect variation in the polarization percentage at $>$500 GHz. The polarization percentage at $\sim$700 GHz is likely lower than that at $\sim$500 GHz. By comparing the $\sim$500 GHz and $\sim$700 GHz observations with the observations at lower frequency bands, we suggest that the intrinsic polarization position angle of Sgr A* is varying with time. This paper also reports the measurable polarization properties from the observed calibration quasars. The future simultaneous multi-frequency polarization observations are required for clarifying the time and frequency variation of polarization position angle and polarization percentage., 11 pages, 10 figures, submitted to A&A; first referee report received. arXiv admin note: text overlap with arXiv:1604.00599

Protostellar (class 0/I) disks, having masses comparable to those of their nascent host stars, and fed continuously from their natal infalling envelopes, are prone to gravitational instability (GI). Motivated by advances in near-infrared (NIR) adaptive optics imaging and mm-wave interferometry, we explore the observational signatures of GI in disks, using hydrodynamical and Monte Carlo radiative transfer simulations to synthesize NIR scattered light images and mm dust continuum maps. Spiral arms induced by GI, located at disk radii of hundreds of AUs, are local overdensities and have their photospheres displaced to higher altitudes above the disk midplane, arms therefore scatter more NIR light from their central stars than inter-arm regions, and are detectable at distances up to 1 kpc by Gemini/GPI, VLT/SPHERE, and Subaru/HiCIAO/SCExAO. By contrast, collapsed clumps formed by disk fragmentation have such strong local gravitational fields that their scattering photospheres are at lower altitudes, such fragments appear fainter than their surroundings in NIR scattered light. Spiral arms and streamers recently imaged in four FU Ori systems at NIR wavelengths resemble GI-induced structures and support the interpretation that FUors are gravitationally unstable protostellar disks. At mm wavelengths, both spirals and clumps appear brighter in thermal emission than the ambient disk and can be detected by ALMA at distances up to 0.4 kpc with one-hour integration times at ~0.1 arcsec resolution. Collapsed fragments having masses >=1 MJ can be detected by ALMA within ~10 minutes., ApJ accepted

We report the arcsecond resolution SMA observations of the $^{12}$CO (2-1) transition in the massive cluster forming region G10.6-0.4. In these observations, the high velocity $^{12}$CO emission is resolved into individual outflow systems, which have a typical size scale of a few arcseconds. These molecular outflows are energetic, and are interacting with the ambient molecular gas. By inspecting the shock signatures traced by CH$_{3}$OH, SiO, and HCN emissions, we suggest that abundant star formation activities are distributed over the entire 0.5 pc scale dense molecular envelope. The star formation efficiency over one global free-fall timescale (of the 0.5 pc molecular envelope, $\sim10^{5}$ years) is about a few percent. The total energy feedback of these high velocity outflows is higher than 10$^{47}$ erg, which is comparable to the total kinetic energy in the rotational motion of the dense molecular envelope. From order-of-magnitude estimations, we suggest that the energy injected from the protostellar outflows is capable of balancing the turbulent energy dissipation. No high velocity bipolar molecular outflow associated with the central OB cluster is directly detected, which can be due to the photo-ionization., Comment: 42 pages, 14 figures, accepted by ApJ

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the dust continuum emission at 1.3 mm and 12CO J=2-1 line emission of the transitional disk around DM Tau. DM Tau's disk is thought to possess a dust-free inner cavity inside a few au, from the absence of near-infrared excess on its spectral energy distribution (SED). Previous submillimeter observations were, however, unable to detect the cavity; instead, a dust ring ~20 au in radius was seen. The excellent angular resolution achieved in the new ALMA observations, 43 x 31 mas, allows discovery of a 4 au radius inner dust ring, confirming previous SED modeling results. This inner ring is symmetric in continuum emission, but asymmetric in 12CO emission. The known (outer) dust ring at ~20 au is recovered and shows azimuthal asymmetry with a strong-weak side contrast of ~1.3. The gap between these two rings is depleted by a factor of ~40 in dust emission relative to the outer ring. An extended outer dust disk is revealed, separated from the outer ring by another gap. The location of the inner ring is comparable to that of the main asteroid belt in the solar system. As a disk with a "proto-asteroid belt," the DM Tau system offers valuable clues to disk evolution and planet formation in the terrestrial planet forming region., 14 pages, 5 figures, 2 tables. Accepted for publication in ApJ Letter

We report Submillimeter Array molecular line observations in the 345 GHz band of five massive dense cores, Cyg-N38, Cyg-N43, Cyg-N48, Cyg-N51, and Cyg-N53 in the DR21 filament. The molecular line data reveal several dynamical features of the cores: (1) prominent outflows in all cores seen in the CO and SiO lines, (2) significant velocity gradients in Cyg-N43 and Cyg-N48 seen in the H13CN and H13CO+ lines suggesting 0.1-pc-scale rotational motions, and (3) possible infalls in Cyg-N48 found in the SiO and SO lines. Comparing the molecular line data and our dust polarization data in Ching et al. (2017), we find that the gradients of line-of-sight velocities appear to be randomly oriented relative to the plane-of-sky magnetic fields. Our simulations suggest that this random alignment implies parallel or random alignment between the velocity gradients and magnetic fields in the three dimensional space. The linewidths of H13CN emission are consistently wider than those of H13CO+ emission in the 3''-10'' detectable scales, which can be explained by the existence of ambipolar diffusion with maximum plane-of-the-sky magnetic field strengths of 1.9 mG and 5.1 mG in Cyg-N38 and Cyg-N48, respectively. Our results suggest that the gas dynamics may distort the magnetic fields of the cores of into complex structures and ambipolar diffusion could be important in dissipating the magnetic energies of the cores., Comment: 28 pages, 22 figures, ApJ accepted

The central region of the massive star-forming cloud G33.92+0.11 was investigated with the emission from the deuterated species HDCS and DCN observed at sub-arcsecond angular resolution (~07) using ALMA. HDCS shows a distributed emission throughout the region, and its large relative abundance in the most recent star-forming region suggests that there still exists a significant amount of cold gas associated with the hot core region. A high degree of HDCS fractionation (HDCS/H2CS > 0.1) was found in the north region between star-forming clumps where the cold dense pre-collapse gas may still exist. DCN appears to have a good correlation with the continuum emission. This species traces both cold and warm dense gas probably by typical cold deuterium fractionation reactions and also by the lukewarm fractionation reactions. Near the densest cores where massive stars have already formed and dust mantles are evaporating, the DCN/HDCS abundance ratio was found to be larger by a factor of a few than other positions. This may suggest that the DCN abundance has been increased through the lukewarm fractionation processes in the gas phase.

This is the first paper of our series of high resolution (1") studies of the massive star forming region G10.6--0.4. We present the emission line observations of the hot core type tracers (O$^{13}$CS, OCS, SO$_{2}$) with $\sim$0$"$.5 resolution. By comparing the results to the high--resolution NH$_{3}$ absorption line observation, we confirm for the first time the rotationally flattened hot toroid in the central $, Comment: 26 pages, 5 figures, Accepted by ApJ

The long-term evolution of a circumstellar disk starting from its formation and ending in the T Tauri phase was simulated numerically with the purpose of studying the evolution of dust in the disk with distinct values of viscous \alpha-parameter and dust fragmentation velocity v_frag. We solved numerical hydrodynamics equations in the thin-disk limit, which are modified to include a dust component consisting of two parts: sub-micron-sized dust and grown dust with a maximum radius a_r. The former is strictly coupled to the gas, while the latter interacts with the gas via friction. The conversion of small to grown dust, dust growth, and dust self-gravity are also considered. We found that the process of dust growth known for the older protoplanetary phase also holds for the embedded phase of disk evolution. The dust growth efficiency depends on the radial distance from the star - a_r is largest in the inner disk and gradually declines with radial distance. In the inner disk, a_r is limited by the dust fragmentation barrier. The process of small-to-grown dust conversion is very fast once the disk is formed. The total mass of grown dust in the disk (beyond 1 AU) reaches tens or even hundreds of Earth masses already in the embedded phase of star formation and even a greater amount of grown dust drifts in the inner, unresolved 1 AU of the disk. Dust does not usually grow to radii greater than a few cm. A notable exception are models with \alpha, Comment: accepted by Astronomy & Astrophysics

Filamentary structures are ubiquitous in high-mass star-forming molecular clouds. Their relation with high-mass star formation is still to be understood. Here we report interferometric observations toward 8 filamentary high-mass star-forming clouds. A total of 50 dense cores are identified in these clouds, most of which present signatures of high-mass star formation. Five of them are not associated with any star formation indicators, hence are prestellar core candidates. Evolutionary phases of these cores and their linewidths, temperatures, NH$_3$ abundances, and virial parameters are found to be correlated. In a sub-sample of 4 morphologically well-defined filaments, we find that their fragmentation can not be solely explained by thermal or turbulence pressure support. We also investigate distributions of gas temperatures and non-thermal motions along the filaments, and find a spatial correlation between non-thermal linewidths and star formation activities. We find evidence of gas flows along these filaments, and derive an accretion rate along filaments of $\sim$10$^{-4}$ M$_\odot$ yr$^{-1}$. These results suggest a strong relationship between massive filaments and high-mass star formation, through i) filamentary fragmentation in very early evolutionary phases to form dense cores, ii) accretion flows along filaments that are important for the growth of dense cores and protostars, and iii) enhancement of non-thermal motion in the filaments by the feedback or accretion during star formation., Comment: 31 pages, 11 figures, 8 tables, ApJ Accepted. 3-D interactive figures to visualize outflows (see Figure 7) will be published online, and are available at https://xinglunju.github.io/outflows.html

Ground-based observations at terahertz (THz) frequencies are a newly explorable area of astronomy for the next ten years. We discuss science cases for a first-generation 10-m class THz telescope, focusing on the Greenland Telescope as an example of such a facility. We propose science cases and provide quantitative estimates for each case. The largest advantage of ground-based THz telescopes is their higher angular resolution (~ 4 arcsec for a 10-m dish), as compared to space or airborne THz telescopes. Thus, high-resolution mapping is an important scientific argument. In particular, we can isolate zones of interest for Galactic and extragalactic star-forming regions. The THz windows are suitable for observations of high-excitation CO lines and [N II] 205 um lines, which are scientifically relevant tracers of star formation and stellar feedback. Those lines are the brightest lines in the THz windows, so that they are suitable for the initiation of ground-based THz observations. THz polarization of star-forming regions can also be explored since it traces the dust population contributing to the THz spectral peak. For survey-type observations, we focus on ``sub-THz'' extragalactic surveys, whose uniqueness is to detect galaxies at redshifts z ~ 1--2, where the dust emission per comoving volume is the largest in the history of the Universe. Finally we explore possibilities of flexible time scheduling, which enables us to monitor active galactic nuclei, and to target gamma-ray burst afterglows. For these objects, THz and submillimeter wavelength ranges have not yet been explored., 39 pages, 17 figures, accepted for publication in PASJ (as a review paper)

C$_2$H is a representative hydrocarbon that is abundant and ubiquitous in the interstellar medium (ISM). To study its chemical properties, we present Submillimeter Array (SMA) observations of the C$_2$H $N=3-2$ and HC$_3$N $J=30-29$ transitions and the 1.1 mm continuum emission toward four OB cluster-forming regions, AFGL 490, ON 1, W33 Main, and G10.6-0.4, which cover a bolometric luminosity range of $\sim$10$^3$--10$^6$ $L_{\odot}$. We found that on large scales, the C$_2$H emission traces the dense molecular envelope. However, for all observed sources, the peaks of C$_2$H emission are offset by several times times 10$^4$ AU from the peaks of 1.1 mm continuum emission, where the most luminous stars are located. By comparing the distribution and profiles of C$_2$H hyperfine lines and the 1.1 mm continuum emission, we find that the C$_2$H column density (and abundance) around the 1.1 mm continuum peaks is lower than those in the ambient gas envelope. Chemical models suggest that C$_2$H might be transformed to other species owing to increased temperature and density; thus, its reduced abundance could be the signpost of the heated molecular gas in the $\sim$10$^4$ AU vicinity around the embedded high-mass stars. Our results support such theoretical prediction for centrally embedded $\sim10^3$--$10^6L_{\odot}$ OB star-forming cores, while future higher-resolution observations are required to examine the C$_2$H transformation around the localized sites of high-mass star formation., Comment: 10 pages, 6 figures. ApJ accepted. Comments welcome

This is a white paper for project ngVLA This paper discusses compelling science cases for a future long-baseline interferometer operating at millimeter and centimeter wavelengths, like the proposed Next Generation Vary Large Array (ngVLA). We report on the activities of the Cradle of Life science working group, which focused on the formation of low- and high-mass stars, the formation of planets and evolution of protoplanetary disks, the physical and compositional study of Solar System bodies, and the possible detection of radio signals from extraterrestrial civilizations. We propose 19 scientific projects based on the current specification of the ngVLA. Five of them are highlighted as possible Key Science Projects: (1) Resolving the density structure and dynamics of the youngest HII regions and high-mass protostellar jets, (2) Unveiling binary/multiple protostars at higher resolution, (3) Mapping planet formation regions in nearby disks on scales down to 1 AU, (4) Studying the formation of complex molecules, and (5) Deep atmospheric mapping of giant planets in the Solar System. For each of these projects, we discuss the scientific importance and feasibility. The results presented here should be considered as the beginning of a more in-depth analysis of the science enabled by such a facility, and are by no means complete or exhaustive.

We present new high-resolution ($\sim$0\farcs09) $H$-band imaging observations of the circumstellar disk around the T Tauri star SU Aur. Our observations with Subaru-HiCIAO have revealed the presence of scattered light as close as 0\farcs15 ($\sim$20 AU) to the star. Within our image, we identify bright emission associated with a disk with a minimum radius of $\sim$90 AU, an inclination of $\sim$35\degr from the plane of the sky, and an approximate P.A. of 15\degr for the major axis. We find a brightness asymmetry between the northern and southern sides of the disk due to a non-axisymmetric disk structure. We also identify a pair of asymmetric tail structures extending east and west from the disk. The western tail extends at least 2\farcs5 (350 AU) from the star, and is probably associated with a reflection nebula previously observed at optical and near-IR wavelengths. The eastern tail extends at least 1\arcsec (140 AU) at the present signal-to-noise. These tails are likely due to an encounter with an unseen brown dwarf, but our results do not exclude the explanation that these tails are outflow cavities or jets., Comment: 12 pages, 3 figures, accepted by ApJ

How rapidly collapsing parsec-scale massive molecular clumps feed high-mass stars, and how they fragment to form OB clusters, have been outstanding questions in the field of star-formation. In this work, we report the resolved structures and kinematics of the approximately face-on, rotating massive molecular clump, G33.92+0.11. Our high resolution Atacama Large Millimeter/submillimeter Array (ALMA) images show that the spiral arm-like gas overdensities form in the eccentric gas accretion streams. First, we resolved that the dominant part of the $\sim$0.6 pc scale massive molecular clump (3.0$^{+2.8}_{-1.4}$$\cdot$10$^{3}$ $M_{\odot}$) G33.92+0.11 A is tangled with several 0.5-1 pc size molecular arms spiraling around it, which may be connected further to exterior gas accretion streams. Within G33.92+0.11 A, we resolved the $\sim$0.1 pc width gas mini-arms connecting with the two central massive (100-300 $M_{\odot}$) molecular cores. The kinematics of arms and cores elucidate a coherent accretion flow continuing from large to small scales. We demonstrate that the large molecular arms are indeed the cradles of dense cores, which are likely current or future sites of high-mass star formation. Since these deeply embedded massive molecular clumps preferentially form the highest mass stars in the clusters, we argue that dense cores fed by or formed within molecular arms play a key role in making the upper end of the stellar and core mass functions., Comment: 20 pages, formally published by ApJ

We report Submillimeter Array (SMA) 1.3 mm high angular resolution observations towards the four EXor type outbursting young stellar objects (YSOs) VY Tau, V1118 Ori, V1143 Ori, and NY Ori. The data mostly show low dust masses $M_{dust}$ in the associated circumstellar disks. Among the sources, NY Ori possesses a relatively massive disk with $M_{dust} \sim 9 \times 10^{-4}$ $M_{\odot}$. V1118 Ori has a marginal detection equivalent to $M_{dust} \sim 6 \times 10^{-5}$ $M_{\odot}$. V1143 Ori has a non-detection also equivalent to $M_{dust} < 6 \times 10^{-5}$ $M_{\odot}$. For the nearest source VY Tau, we get a surprising non-detection which provides a stringent upper limit $M_{dust} < 6 \times 10^{-6}$ $M_{\odot}$. We interpret our findings as suggesting that the gas and dust reservoirs that feed the short duration, repetitive optical outbursts seen in some EXors may be limited to the small scale, innermost region of their circumstellar disks. This hot dust may have escaped our detection limits. Follow-up, more sensitive millimeter observations are needed to improve our understanding of the triggering mechanisms of EXor type outbursts., 6 pages, 1 figure, accepted to ApJL

There is increasing evidence that episodic accretion is a common phenomenon in Young Stellar Objects (YSOs). Recently, the source HOPS 383 in Orion was reported to have a mid-infrared?and bolometric?luminosity increase between 2004 and 2008, constituting the first clear example of a class 0 YSO (a protostar) with a large accretion burst. The usual assumption that in YSOs accretion and ejection follow each other in time needs to be tested. Radio jets at centimeter wavelengths are often the only way of tracing the jets from embedded protostars. We searched the Very Large Array archive for the available observations of the radio counterpart of HOPS 383. The data show that the radio flux of HOPS 383 varies only mildly from 1998 January to 2014 December, staying at the level of ?200?300 ?Jy in the X band (?9 GHz), with a typical uncertainty of 10?20 ?Jy in each measurement. We interpret the absence of a radio burst as suggesting that accretion and ejection enhancements do not follow each other in time, at least not within timescales shorter than a few years. Time monitoring of more objects and specific predictions from simulations are needed to clarify the details of the connection betwen accretion and jets/winds in YSOs.

We highlight distinct and systematic observational features of magnetic field morphologies in polarized submm dust continuum. We illustrate this with specific examples and show statistical trends from a sample of 50 star-forming regions., Comment: 4 pages, 3 figures; to appear in the EAS Proceedings of the 6th Zermatt ISM Symposium "Conditions and Impact of Star Formation from Lab to Space", September 2015

We present Submillimeter Array (SMA) observations at 345 GHz towards the intermediate/high-mass cluster-forming region NGC 6334 V. From the dust emission we spatially resolve three dense condensations, the brightest one presenting the typical chemistry of a hot core. The magnetic field (derived from the dust polarized emission) shows a bimodal converging pattern towards the hot core. The molecular emission traces two filamentary structures at two different velocities, separated by 2 km/s, converging to the hot core and following the magnetic field distribution. We compare the velocity field and the magnetic field derived from the SMA observations with MHD simulations of star-forming regions dominated by gravity. This comparison allows us to show how the gas falls in from the larger-scale extended dense core (~0.1 pc) of NGC 6334 V towards the higher-density hot core region (~0.02 pc) through two distinctive converging flows dragging the magnetic field, whose strength seems to have been overcome by gravity., 13 pages, 11 figures, accepted for publication in ApJ