Disk Major Axis Research Articles

The fountain of the luminous infrared galaxy Zw049.057 as traced by its OH megamaser

High-resolution ($0 $10-35$\,pc ) e-MERLIN ($ cm) and ($0 $6.5$\,pc ) ALMA ($ 1.1$ mm) observations have been used to image OH (hydroxyl) and H$_2$CO (formaldehyde) megamaser emission, and HCN $3 2$ emission toward the nuclear ($<100$ pc) region of the luminous infrared galaxy Zw049.057. Zw049.057 hosts a compact obscured nucleus (CON), and thus represents a class of galaxies that are often associated with inflow and outflow motions. Formaldehyde megamaser emission has been detected toward the nuclear region, $ 30$ pc ($0 and traces a structure along the disk major axis. OH megamaser (OHM) emission has been detected along the minor axis of the disk, $ 30$\,pc ($0 from the nucleus, where it exhibits a velocity gradient with extrema of $-20$ $ northwest (NW) of the disk. HCN $3 2$ emission reveals extended emission, along the disk minor axis out to $ 60$\,pc ($0 Analysis of the minor axis HCN emission reveals high-velocity features extending out to $) and collimated outflow that is enveloped by a wide-angle and slow ($ $) outflow that is traced by the OHM emission. Analysis of the outflow kinematics suggests that the slow wide-angle outflow will not reach escape velocity and will instead fall back to the galaxy disk, evolving as a so-called fountain flow, while the fast collimated outflow traced by HCN emission will likely escape the nuclear region. We suggest that the absence of OHM emission in the nuclear region is due to high densities there. Even though OHMs associated with outflows are an exception to conventional OHM emission, we expect them to be common in CON sources that host both OHM and H$_2$CO megamasers.

Dual-band, Multi-aperture Polarization Measurements of β Pictoris

We present high precision, dual-band aperture polarimetry of the β Pictoris debris disk. The polarization is aperture dependent, increasing from 5″ to 19″ and peaking, after interstellar subtraction at around 230–240 ppm in both g′ and r′ bands; the polarization vector is oriented perpendicular to the disk major-axis. By simple calculations, lower limits are placed on the polarization of scattered light interior to 200 au. The observations and calculations are consistent with prior spatially resolved polarimetric measurements of the disk that probe greater angular separations, and models for the interior developed from them.

The GRAVITY young stellar object survey

Aims. We aim to investigate the origin of the HI Brγ emission in young stars by using GRAVITY to image the innermost region of circumstellar disks, where important physical processes such as accretion and winds occur. With high spectral and angular resolution, we focus on studying the continuum and the HI Brγ-emitting area of the Herbig star HD 58647. Methods. Using VLTI-GRAVITY, we conducted observations of HD 58647 with both high spectral and high angular resolution. Thanks to the extensive uv coverage, we were able to obtain detailed images of the circumstellar environment at a sub-au scale, specifically capturing the continuum and the Brγ-emitting region. Through the analysis of velocity-dispersed images and photocentre shifts, we were able to investigate the kinematics of the HI Brγ-emitting region. Results. The recovered continuum images show extended emission where the disk major axis is oriented along a position angle of 14°. The size of the continuum emission at 5-σ levels is ~1.5 times more extended than the sizes reported from geometrical fitting (3.69 mas ± 0.02 mas). This result supports the existence of dust particles close to the stellar surface, screened from the stellar radiation by an optically thick gaseous disk. Moreover, for the first time with GRAVITY, the hot gas component of HD 58647 traced by the Brγ has been imaged. This allowed us to constrain the size of the Brγ-emitting region and study the kinematics of the hot gas; we find its velocity field to be roughly consistent with gas that obeys Keplerian motion. The velocity-dispersed images show that the size of the hot gas emission is from a more compact region than the continuum (2.3 mas ± 0.2 mas). Finally, the line phases show that the emission is not entirely consistent with Keplerian rotation, hinting at a more complex structure in the hot gaseous disk.

Asymmetries in random motions of neutral hydrogen gas in spiral galaxies

Context. The velocity dispersion ellipsoid of gas in galactic discs is usually assumed to be isotropic. Under this approximation, no projection effect occurs in the random motions of gas, as traced by the line-of-sight velocity dispersion. However, it has been recently shown that random motions of the neutral hydrogen gas of the Triangulum galaxy (M 33) exhibit a bisymmetric perturbation which is aligned with the minor axis of the galaxy, suggesting a projection effect. Aims. To investigate if perturbations in the velocity dispersion of nearby discs are comparable to those of M 33, the sample is extended to 32 galaxies from The H I Nearby Galaxy Survey (THINGS) and the Westerbork H I Survey of Spiral and Irregular Galaxies (WHISP). Methods. We studied velocity asymmetries in the disc planes by performing Fourier transforms of high-resolution H I velocity dispersion maps corrected for beam-smearing effects, and we measured the amplitudes and phase angles of the Fourier harmonics. Results. In all velocity dispersion maps, we find strong perturbations of first, second, and fourth orders. The strongest asymmetry is the bisymmetry, which is predominantly associated with the presence of spiral arms. The first order asymmetry is generally orientated close to the disc major axis, and the second and fourth order asymmetries are preferentially orientated along intermediate directions between the major and minor axes of the discs. These results are evidence that strong projection effects shape the H I velocity dispersion maps. The most likely source of systematic orientations is the anisotropy of velocities, through the projection of streaming motions that are stronger along one of the planar directions in the discs. Moreover, systematic phase angles of asymmetries in the H I velocity dispersion could arise from tilted velocity ellipsoids, that is when the velocities are correlated. We expect a larger incidence of correlation between the radial and tangential velocities of H I gas with |ρRθ|∼0.6, which could be tested against the kinematics of the youngest stellar populations of the Milky Way. Conclusions. H I velocity dispersions cannot be considered devoid of projection effects. The systematic orientations of asymmetries can be explained by the projection of unresolved streaming motions mainly arising from spiral arms. Our methodology is a powerful tool to constrain the dominant direction of streaming motions and thus the shape of the velocity ellipsoid of H I gas, which is de facto anisotropic at the angular scales probed by the observations. The next step is to study the shape of the velocity ellipsoids of molecular and ionised gas and their link with galaxy mass and/or morphology, in addition to extending the sample size.

The Chemodynamics of the Stellar Populations in M31 from APOGEE Integrated-light Spectroscopy

We present an analysis of nearly 1000 near-infrared, integrated-light spectra from APOGEE in the inner ∼7 kpc of M31. We utilize full-spectrum fitting with A-LIST simple stellar population spectral templates that represent a population of stars with the same age, [M/H], and [α/M]. With this, we determine the mean kinematics, metallicities, α abundances, and ages of the stellar populations of M31's bar, bulge, and inner disk (∼4–7 kpc). We find a nonaxisymmetric velocity field in M31 resulting from the presence of a bar. The bulge of M31 is less metal-rich (mean [M/H] = dex) than the disk, features minima in metallicity on either side of the bar ([M/H] ∼ −0.2), and is enhanced in α abundance (mean [α/M] = ). The disk of M31 within ∼7 kpc is enhanced in both metallicity ([M/H] = ) and α abundance ([α/M] = ). Both of these structural components are uniformly old at ≃12 Gyr. We find the mean metallicity increases with distance from the center of M31, with the steepest gradient along the disk major axis (0.043 ± 0.021 dex kpc−1). This gradient is the result of changing light contributions from the bulge and disk. The chemodynamics of stellar populations encodes information about a galaxy’s chemical enrichment, star formation history, and merger history, allowing us to discuss new constraints on M31's formation. Our results provide a stepping stone between our understanding of the Milky Way and other external galaxies.

Millimeter gap contrast as a probe for turbulence level in protoplanetary disks

Turbulent motions are believed to regulate angular momentum transport and influence dust evolution in protoplanetary disks. Measuring the strength of turbulence is challenging through gas line observations because of the requirement for high spatial and spectral resolution data, and an exquisite determination of the temperature. In this work, taking the well-known HD 163296 disk as an example, we investigated the contrast of gaps identified in high angular resolution continuum images as a probe for the level of turbulence. With self-consistent radiative transfer models, we simultaneously analyzed the radial brightness profiles along the disk major and minor axes, and the azimuthal brightness profiles of the B67 and B100 rings. By fitting all the gap contrasts measured from these profiles, we constrained the gas-to-dust scale height ratio $\Lambda$ to be $3.0_{-0.8}^{+0.3}$, $1.2_{-0.1}^{+0.1}$ and ${\ge}\,6.5$ for the D48, B67 and B100 regions, respectively. The varying gas-to-dust scale height ratios indicate that the degree of dust settling changes with radius. The inferred values for $\Lambda$ translate into a turbulence level of $\alpha_{\rm turb}\,{<}\,3\times10^{-3}$ in the D48 and B100 regions, which is consistent with previous upper limits set by gas line observations. However, turbulent motions in the B67 ring are strong with $\alpha_{\rm turb}\,{\sim}1.2\,{\times}\,10^{-2}$. Due to the degeneracy between $\Lambda$ and the depth of dust surface density drops, the turbulence strength in the D86 gap region is not constrained.

Disks and Outflows in the Intermediate-mass Star-forming Region NGC 2071 IR

We present Atacama Large Millimeter Array band 6/7 (1.3 mm/0.87 mm) and Very Large Array Ka-band (9 mm) observations toward NGC 2071 IR, an intermediate-mass star-forming region. We characterize the continuum and associated molecular line emission toward the most luminous protostars, i.e., IRS1 and IRS3, on ∼100 au (0.″2) scales. IRS1 is partly resolved in the millimeter and centimeter continuum, which shows a potential disk. IRS3 has a well-resolved disk appearance in the millimeter continuum and is further resolved into a close binary system separated by ∼40 au at 9 mm. Both sources exhibit clear velocity gradients across their disk major axes in multiple spectral lines including C18O, H2CO, SO, SO2, and complex organic molecules like CH3OH, 13CH3OH, and CH3OCHO. We use an analytic method to fit the Keplerian rotation of the disks and give constraints on physical parameters with a Markov Chain Monte Carlo routine. The IRS3 binary system is estimated to have a total mass of 1.4–1.5 M ⊙. IRS1 has a central mass of 3–5 M ⊙ based on both kinematic modeling and its spectral energy distribution, assuming that it is dominated by a single protostar. For both IRS1 and IRS3, the inferred ejection directions from different tracers, including radio jet, water maser, molecular outflow, and H2 emission, are not always consistent, and for IRS1 these can be misaligned by ∼50°. IRS3 is better explained by a single precessing jet. A similar mechanism may be present in IRS1 as well but an unresolved multiple system in IRS1 is also possible.

CO Line Emission Surfaces and Vertical Structure in Midinclination Protoplanetary Disks

High spatial resolution CO observations of midinclination (≈30°–75°) protoplanetary disks offer an opportunity to study the vertical distribution of CO emission and temperature. The asymmetry of line emission relative to the disk major axis allows for a direct mapping of the emission height above the midplane, and for optically thick, spatially resolved emission in LTE, the intensity is a measure of the local gas temperature. Our analysis of Atacama Large Millimeter/submillimeter Array archival data yields CO emission surfaces, dynamically constrained stellar host masses, and disk atmosphere gas temperatures for the disks around the following: HD 142666, MY Lup, V4046 Sgr, HD 100546, GW Lup, WaOph 6, DoAr 25, Sz 91, CI Tau, and DM Tau. These sources span a wide range in stellar masses (0.50–2.10 M ⊙), ages (∼0.3–23 Myr), and CO gas radial emission extents (≈200–1000 au). This sample nearly triples the number of disks with mapped emission surfaces and confirms the wide diversity in line emitting heights (z/r ≈ 0.1 to ≳0.5) hinted at in previous studies. We compute the radial and vertical CO gas temperature distributions for each disk. A few disks show local temperature dips or enhancements, some of which correspond to dust substructures or the proposed locations of embedded planets. Several emission surfaces also show vertical substructures, which all align with rings and gaps in the millimeter dust. Combining our sample with literature sources, we find that CO line emitting heights weakly decline with stellar mass and gas temperature, which, despite large scatter, is consistent with simple scaling relations. We also observe a correlation between CO emission height and disk size, which is due to the flared structure of disks. Overall, CO emission surfaces trace ≈2–5× gas pressure scale heights (Hg) and could potentially be calibrated as empirical tracers of Hg.

Which Part of Dense Cores Feeds Material to Protostars? The Case of L1489 IRS

Abstract We have conducted mapping observations (∼2′ × 2′) of the Class I protostar L1489 IRS using the 7 m array of the Atacama Compact Array and the IRAM 30 m telescope in C18O 2–1 emission to investigate the gas kinematics on 1000–10,000 au scales. The C18O emission shows a velocity gradient across the protostar in a direction almost perpendicular to the outflow. The radial profile of the peak velocity was measured from a C18O position–velocity diagram cut along the disk major axis. The measured peak velocity decreases with radius at radii of ∼1400–2900 au, but increases slightly or is almost constant at radii of r ≳ 2900 au. Disk-and-envelope models were compared with the observations to understand the nature of the radial profile of the peak velocity. The measured peak velocities are best explained by a model where the specific angular momentum is constant within a radius of 2900 au but increases with radius outside 2900 au. We calculated the radial profile of the specific angular momentum from the measured peak velocities and compared it to analytic models of core collapse. The analytic models reproduce well the observed radial profile of the specific angular momentum and suggest that material within a radius of ∼4000–6000 au in the initial dense core has accreted to the central protostar. Because dense cores are typically ∼10,000–20,000 au in radius, and as L1489 IRS is close to the end of its mass accretion phase, our result suggests that only a fraction of a dense core eventually forms a star.

Molecules with ALMA at Planet-forming Scales (MAPS). IV. Emission Surfaces and Vertical Distribution of Molecules

Abstract The Molecules with ALMA at Planet-forming Scales (MAPS) Large Program provides a unique opportunity to study the vertical distribution of gas, chemistry, and temperature in the protoplanetary disks around IM Lup, GM Aur, AS 209, HD 163296, and MWC 480. By using the asymmetry of molecular line emission relative to the disk major axis, we infer the emission height (z) above the midplane as a function of radius (r). Using this method, we measure emitting surfaces for a suite of CO isotopologues, HCN, and C2H. We find that 12CO emission traces the most elevated regions with z / r &gt; 0.3 , while emission from the less abundant 13CO and C18O probes deeper into the disk at altitudes of z / r ≲ 0.2 . C2H and HCN have lower opacities and signal-to-noise ratios, making surface fitting more difficult, and could only be reliably constrained in AS 209, HD 163296, and MWC 480, with z / r ≲ 0.1 , i.e., relatively close to the planet-forming midplanes. We determine peak brightness temperatures of the optically thick CO isotopologues and use these to trace 2D disk temperature structures. Several CO temperature profiles and emission surfaces show dips in temperature or vertical height, some of which are associated with gaps and rings in line and/or continuum emission. These substructures may be due to local changes in CO column density, gas surface density, or gas temperatures, and detailed thermochemical models are necessary to better constrain their origins and relate the chemical compositions of elevated disk layers with those of planet-forming material in disk midplanes. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

A Case of Simultaneous Star and Planet Formation

Abstract While it is widely accepted that planets are formed in protoplanetary disks, there is still much debate on when this process happens. In a few cases protoplanets have been directly imaged, but for the vast majority of systems, disk gaps and cavities—seen especially in dust continuum observations—have been the strongest evidence of recent or ongoing planet formation. We present Atacama Large Millimeter/submillimeter Array observations of a nearly edge-on (i = 75°) disk containing a giant gap seen in dust but not in 12CO gas. Inside the gap, the molecular gas has a warm (100 K) component coinciding in position with a tentative free–free emission excess observed with the Karl G. Jansky Very Large Array. Using 1D hydrodynamic models, we find the structure of the gap is consistent with being carved by a planet with 4–70 M Jup. The coincidence of free–free emission inside the planet-carved gap points to the planet being very young and/or still accreting. In addition, the 12CO observations reveal low-velocity large-scale filaments aligned with the disk major axis and velocity coherent with the disk gas that we interpret as ongoing gas infall from the local interstellar medium. This system appears to be an interesting case where both a star (from the environment and the disk) and a planet (from the disk) are growing in tandem.

The Inner Disk of RY Tau: Evidence of Stellar Occultation by the Disk Atmosphere at the Sublimation Rim from K-band Continuum Interferometry

Abstract We present models of the inner region of the circumstellar disk of RY Tau that aim to explain our near-infrared (K-band: 2.1 μm) interferometric observations, while remaining consistent with the optical to near-infrared portions of the spectral energy distribution. Our submilliarcsecond-resolution CHARA Array observations are supplemented with shorter baseline, archival data from PTI, KI, and VLTI/GRAVITY and modeled using an axisymmetric Monte Carlo radiative transfer code. The K-band visibilities are well fit by models incorporating a central star illuminating a disk with an inner edge shaped by dust sublimation at 0.210 ± 0.005 au, assuming a viewing geometry adopted from millimeter interferometry (65° inclined with a disk major axis position angle of 23°). This sublimation radius is consistent with that expected of silicate grains with a maximum size of 0.36–0.40 μm contributing to the opacity, and is an order of magnitude further from the star than the theoretical magnetospheric truncation radius. The visibilities on the longest baselines probed by CHARA indicate that we lack a clear line of sight to the stellar photosphere. Instead, our analysis shows that the central star is occulted by the disk surface layers close to the sublimation rim. While we do not see direct evidence of temporal variability in our multiepoch CHARA observations, we suggest the aperiodic photometric variability of RY Tau is likely related temporal and/or azimuthal variations in the structure of the disk surface layers.

Lyman α absorption beyond the disc of simulated spiral galaxies

ABSTRACT We present an analysis of the origin and properties of the circumgalactic medium (CGM) in a suite of 11 cosmological zoom simulations resembling present-day spiral galaxies. On average the galaxies retain about 50 per cent of the cosmic fraction in baryons, almost equally divided into disc (interstellar medium) gas, cool CGM gas and warm-hot CGM gas. At radii smaller than 50 kpc the CGM is dominated by recycled warm-hot gas injected from the central galaxy, while at larger radii it is dominated by cool gas accreted on to the halo. The recycled gas typically accounts for one-third of the CGM mass. We introduce the novel publicly available analysis tool pygad to compute ion abundances and mock absorption spectra. For Lyman α absorption, we find good agreement of the simulated equivalent width (EW) distribution and observations out to large radii. Disc galaxies with quiescent assembly histories show significantly more absorption along the disc major axis. By comparing the EW and H i column densities, we find that CGM Lyman α absorbers are best represented by an effective line width b ≈ 50–70 km s−1 that increases mildly with halo mass, larger than typically assumed.

Is the gap in the DS Tau disc hiding a planet?

ABSTRACT Recent millimetre-wavelength surveys performed with the Atacama Large Millimeter Array (ALMA) have revealed protoplanetary discs characterized by rings and gaps. A possible explanation for the origin of such rings is the tidal interaction with an unseen planetary companion. The protoplanetary disc around DS Tau shows a wide gap in the ALMA observation at 1.3 mm. We construct a hydrodynamical model for the dust continuum observed by ALMA assuming the observed gap is carved by a planet between one and five Jupiter masses. We fit the shape of the radial intensity profile along the disc major axis varying the planet mass, the dust disc mass, and the evolution time of the system. The best-fitting model is obtained for a planet with $M_{\rm p}=3.5\, \mathrm{ M}_{\rm Jup}$ and a disc with $M_{\rm dust}= 9.6\,\times \,10^{-5}\, \mathrm{ M}_{\odot }$. Starting from this result, we also compute the expected signature of the planet in the gas kinematics, as traced by CO emission. We find that such a signature (in the form of a ‘kink’ in the channel maps) could be observed by ALMA with a velocity resolution between $0.2-0.5\, \rm {kms}^{-1}$ and a beam size between 30 and 50 mas.

The GRAVITY young stellar object survey

Context. The inner regions of the discs of high-mass young stellar objects (HMYSOs) are still poorly known due to the small angular scales and the high visual extinction involved. Aims. We deploy near-infrared spectro-interferometry to probe the inner gaseous disc in HMYSOs and investigate the origin and physical characteristics of the CO bandhead emission (2.3–2.4 μm). Methods. We present the first GRAVITY/VLTI observations at high spectral (ℛ = 4000) and spatial (mas) resolution of the CO overtone transitions in NGC 2024 IRS 2. Results. The continuum emission is resolved in all baselines and is slightly asymmetric, displaying small closure phases (≤8°). Our best ellipsoid model provides a disc inclination of 34° ±1°, a disc major axis position angle (PA) of 166° ± 1°, and a disc diameter of 3.99 ± 0.09 mas (or 1.69 ± 0.04 au, at a distance of 423 pc). The small closure phase signals in the continuum are modelled with a skewed rim, originating from a pure inclination effect. For the first time, our observations spatially and spectrally resolve the first four CO bandheads. Changes in visibility, as well as differential and closure phases across the bandheads are detected. Both the size and geometry of the CO-emitting region are determined by fitting a bidimensional Gaussian to the continuum-compensated CO bandhead visibilities. The CO-emitting region has a diameter of 2.74±0.070.08 mas (1.16 ± 0.03 au), and is located in the inner gaseous disc, well within the dusty rim, with inclination and PA matching the dusty disc geometry, which indicates that both dusty and gaseous discs are coplanar. Physical and dynamical gas conditions are inferred by modelling the CO spectrum. Finally, we derive a direct measurement of the stellar mass of M* ∼ 14.7−3.6+2 M⊙ by combining our interferometric and spectral modelling results.

Testing the Tremaine–Weinberg Method Applied to Integral-field Spectroscopic Data Using a Simulated Barred Galaxy

Abstract Tremaine and Weinberg (TW) proposed a conceptually simple procedure relying on long-slit spectroscopy to measure the pattern speeds of bars (Ωp) in disk galaxies. Using a simulated galaxy, we investigate the potential biases and uncertainties of TW measurements using increasingly popular integral-field spectrographs (IFSs), for which multiple pseudo-slits (and thus independent measurements) can be constructed with a single observation. Most importantly, to establish the spatial coverage required and ensure the validity of the measurements, the inferred Ωp must asymptotically converge as the (half-)length of each pseudo-slit used is increased. The requirement for our simulation is to reach ≈1.3 times the half-light radius, but this may vary from galaxy to galaxy. Only those slits located within the bar region yield accurate measurements. We confirm that the position angle of the disk is the dominant source of systematic error in TW Ωp measurements, leading to under/overestimates of tens of percent for inaccuracies of even a few degrees. Recasting the data so that the data grid aligns with the disk major axis leads to slightly reduced uncertainties. Accurate measurements are obtained only for well-defined ranges of the bar angle (relative to the galaxy major axis) ϕ bar and the inclination angle i, here 10° ≲ ϕ bar ≲ 75° and 105° ≲ ϕ bar ≲ 170° and 15° ≲ i ≲ 70°. The adopted (pseudo-)slit widths, spatial resolution, and (unless extremely aggressive) spatial binning of IFS data have no significant impact on the measurements. Our results thus provide useful guidelines for reliable and accurate direct Ωp measurements with IFS observations.

The Nuclear Source of the Galactic Wind in NGC 253

Abstract We present Brγ emission line kinematics of the nuclear region of NGC 253, recently known to host a strong galactic wind that limits the global star formation of the galaxy. We obtained high-resolution long-slit spectroscopic data with PHOENIX at Gemini South, positioning the slit on the nucleus infrared core (IRC), close to the nuclear disk major axis. The spatial resolution was 0.″35 (∼6 pc) and the slit length was 14″ (∼240 pc). The spectral resolution was ∼74,000, unprecedentedly high for galactic nuclei observations at ∼2.1 μm. The line profiles appear highly complex, with blue asymmetry up to 3.″5 away of the IRC, and red asymmetries further away to northeast. Several Gaussian components are necessary to fit the profile, nevertheless a narrow and a wide one predominate. The IRC presents kinematic widths above 700 km s−1 (FWZI), and broad component FWHM ∼ 400 km s−1, the highest detected in a nearby galaxy. At the IRC, the blueshifted broad component displays a 90 km s−1 bump in radial velocity distribution, a feature we previously detected in molecular gas kinematics. The narrow component velocity dispersion (∼32 km s−1) is within the expected for normal galaxies and luminous infrared galaxies (LIRGs). Intermediate components (FWHM ∼ 150 km s−1, redshifted to the northeast, blueshifted to the southwest) appear at some positions, as well as weaker blue (−215 km s−1) and red line wings (+300 km s−1). The IRC depicts a large broad-versus-narrow line flux ratio (F(B)/F(N) ∼ 1.35), and the broad component seems only comparable with those observed at very high star-forming rate galaxies. The results indicate that the IRC would be the main source of the galactic winds originated in the central region of NGC 253.

Physical and Chemical Conditions of the Protostellar Envelope and the Protoplanetary Disk in HL Tau

Abstract We report our Submillimeter Array (SMA) observations of the Class I–II protostar HL Tau in 13CO (2–1), C18O (2–1), SO(56–45), and 1.3 mm dust-continuum emission and our analyses of the ALMA long baseline data of HCO+ (1–0) emission. The 1.3 mm continuum emission observed with the SMA shows compact (∼0.″8 × 0.″5) and extended (∼6.″5 × 4.″3) components, tracing the protoplanetary disk and the protostellar envelope, respectively. The 13CO, C18O, and HCO+ show a compact (∼200 au) component at velocities higher than 3 km s−1 from the systemic velocity and an extended (∼1000 au) component at lower velocities. The high-velocity component traces the Keplerian rotating disk, and the low-velocity component traces the infalling envelope. The HCO+ high-velocity component is fitted with a Keplerian disk model with a central stellar mass of 1.4 M ⊙. The radial intensity profiles of 13CO and C18O along the disk major axis are fitted with a disk+envelope model, and the gas masses of the disk and envelope are estimated to be (2–40) × 10–4 M ⊙ and M ⊙, respectively. The disk dust mass has been estimated to be (1–3) × 10−3 M ⊙ in the literature. Thus, our estimated disk gas mass suggests that the gas-to-dust mass ratio in the disk is &lt;10, a factor of 10 lower than the estimated ratio in the envelope. We discuss possible gas depletion or CO depletion in the planet-forming candidate HL Tau in the context of disk and envelope evolution.

Submillimetre dust polarization and opacity in the HD163296 protoplanetary ring system

ABSTRACT We present ALMA images of the sub-mm continuum polarization and spectral index of the protoplanetary ringed disc HD163296. The polarization fraction at 870 µm is measured to be ∼0.9 per cent in the central core and generally increases with radius along the disc major axis. It peaks in the gaps between the dust rings, and the largest value (∼4 per cent) is found between rings 1 and 2. The polarization vectors are aligned with the disc minor axis in the central core, but become more azimuthal in the gaps, twisting by up to ±9° in the gap between rings 1 and 2. These general characteristics are consistent with a model of self-scattered radiation in the ringed structure, without requiring an additional dust alignment mechanism. The 870/1300 µm dust spectral index exhibits minima in the centre and the inner rings, suggesting these regions have high optical depths. However, further refinement of the dust or the disc model at higher resolution is needed to reproduce simultaneously the observed degree of polarization and the low spectral index.

ALMA Dust Polarization Observations of Two Young Edge-on Protostellar Disks

Abstract Polarized emission is detected in two young nearly edge-on protostellar disks in 343 GHz continuum at ∼50 au (∼0.″12) resolution with Atacama Large Millimeter/submillimeter Array. One disk is in HH 212 (Class 0) and the other in the HH 111 (early Class I) protostellar system. The polarization fraction is ∼1%. The disk in HH 212 has a radius of ∼60 au. The emission is mainly detected from the nearside of the disk. The polarization orientations are almost perpendicular to the disk major axis, consistent with either self-scattering or emission by grains aligned with a poloidal field around the outer edge of the disk because of the optical depth effect and temperature gradient; the presence of a poloidal field would facilitate the launching of a disk wind, for which there is already tentative evidence in the same source. The disk of HH 111 VLA 1 has a larger radius of ∼220 au and is thus more resolved. The polarization orientations are almost perpendicular to the disk major axis in the nearside, but more along the major axis in the farside, forming roughly half of an elliptical pattern there. It appears that toroidal and poloidal magnetic field may explain the polarization on the near and far sides of the disk, respectively. However, it is also possible that the polarization is due to self-scattering. In addition, alignment of dust grains by radiation flux may play a role in the farside. Our observations reveal a diversity of disk polarization patterns that should be taken into account in future modeling efforts.