scholarly journals Synthetic line and continuum observations of simulated turbulent clouds: the apparent widths of filaments

2020 ◽  
Vol 499 (3) ◽  
pp. 3728-3737
Author(s):  
F D Priestley ◽  
A P Whitworth
Keyword(s):  
Radial Velocity ◽  
Surface Density ◽  
Line Emission ◽  
Continuum Emission ◽  
Full Time ◽  
Molecular Line ◽  
Line Intensities ◽  
Hydrodynamical Simulations ◽  
Proper Account ◽  
Synthetic Line

ABSTRACT Filamentary structures are ubiquitous in observations of real molecular clouds and also in simulations of turbulent, self-gravitating gas. However, making comparisons between observations and simulations is complicated by the difficulty of estimating volume densities observationally. Here, we have post-processed hydrodynamical simulations of a turbulent isothermal molecular cloud, using a full time-dependent chemical network. We have then run radiative transfer models to obtain synthetic line and continuum intensities that can be compared directly with those observed. We find that filaments have a characteristic width of ${\sim }0.1 \, {\rm pc}$, both on maps of their true surface density and on maps of their $850\, {\rm \mu m}$ dust continuum emission in agreement with previous work. On maps of line emission from CO isotopologues, the apparent widths of filaments are typically several times larger because the line intensities are poorly correlated with the surface density. On maps of line emission from dense gas tracers such as N2H+ and HCN, the apparent widths of filaments are ${\la}0.1\, {\rm pc}$. Thus, current observations of molecular-line emission are compatible with the universal $0.1 \, {\rm pc}$ filament width inferred from Herschel observations, provided proper account is taken of abundance, optical depth, and excitation considerations. We find evidence for ${\sim}0.4 \, {\rm km \, s^{-1}}$ radial velocity differences across filaments. These radial velocity differences might be a useful indicator of the mechanism by which a filament has formed or is forming, for example the turbulent cloud scenario modelled here, as against other mechanisms such as cloud–cloud collisions.

scholarly journals Inferring giant planets from ALMA millimeter continuum and line observations in (transition) disks

2018 ◽  
Vol 612 ◽  
pp. A104 ◽  
Author(s):  
S. Facchini ◽  
P. Pinilla ◽  
E. F. van Dishoeck ◽  
M. de Juan Ovelar
Keyword(s):  
Surface Density ◽  
Scattered Light ◽  
Temperature Drop ◽  
Line Emission ◽  
Continuum Emission ◽  
Rotational Line ◽  
Gas Temperature ◽  
Hydrodynamical Simulations ◽  
Dust Evolution ◽  
Transition Disks

Context. Radial gaps or cavities in the continuum emission in the IR-mm wavelength range are potential signatures of protoplanets embedded in their natal protoplanetary disk are. Hitherto, models have relied on the combination of mm continuum observations and near-infrared scattered light images to put constraints on the properties of embedded planets. Atacama Large Millimeter/submillimeter Array (ALMA) observations are now probing spatially resolved rotational line emission of CO and other chemical species. These observations can provide complementary information on the mechanism carving the gaps in dust and additional constraints on the purported planet mass. Aims. We investigate whether the combination of ALMA continuum and CO line observations can constrain the presence and mass of planets embedded in protoplanetary disks. Methods. We post-processed azimuthally averaged 2D hydrodynamical simulations of planet-disk models, in which the dust densities and grain size distributions are computed with a dust evolution code that considers radial drift, fragmentation, and growth. The simulations explored various planet masses (1 MJ ≤ Mp ≤ 15 MJ) and turbulent parameters (10−4 ≤ α ≤ 10−3). The outputs were then post-processed with the thermochemical code DALI, accounting for the radially and vertically varying dust properties. We obtained the gas and dust temperature structures, chemical abundances, and synthetic emission maps of both thermal continuum and CO rotational lines. This is the first study combining hydrodynamical simulations, dust evolution, full radiative transfer, and chemistry to predict gas emission of disks hosting massive planets. Results. All radial intensity profiles of 12CO, 13CO, and C18O show a gap at the planet location. The ratio between the location of the gap as seen in CO and the peak in the mm continuum at the pressure maximum outside the orbit of the planet shows a clear dependence on planet mass and is independent of disk viscosity for the parameters explored in this paper. Because of the low dust density in the gaps, the dust and gas components can become thermally decoupled and the gas becomes colder than the dust. The gaps seen in CO are due to a combination of gas temperature dropping at the location of the planet and of the underlying surface density profile. Both effects need to be taken into account and disentangled when inferring gas surface densities from observed CO intensity profiles; otherwise, the gas surface density drop at the planet location can easily be overestimated. CO line ratios across the gap are able to quantify the gas temperature drop in the gaps in observed systems. Finally, a CO cavity not observed in any of the models, only CO gaps, indicating that one single massive planet is not able to explain the CO cavities observed in transition disks, at least without additional physical or chemical mechanisms.

scholarly journals Extragalactic science with ALMA

2011 ◽  
Vol 7 (S284) ◽  
pp. 494-495
Author(s):  
George J. Bendo ◽  
Keyword(s):  
Molecular Clouds ◽  
High Redshift ◽  
Atacama Desert ◽  
Line Emission ◽  
Continuum Emission ◽  
Synchrotron Emission ◽  
Molecular Line ◽  
Molecular Lines ◽  
Nearby Galaxies ◽  
Detailed Imaging

AbstractThe Atacama Large Millimeter/submillimeter Array (ALMA) is a telescope comprising 66 antennas that is located in the Atacama Desert in Chile, one of the driest locations on Earth. When the telescope is fully operational, it will perform observations over ten receiver bands at wavelengths from 9.5-0.32 mm (31-950 GHz) with unprecedented sensitivities to continuum emission from cold (<20 K) dust, Bremsstrahlung, and synchrotron emission as well as submillimetre and millimetre molecular lines. With baselines out to 16km and dynamic reconfiguration, ALMA will achieve spatial resolutions ranging from 3″ to 0.010″, allowing for detailed imaging of continuum or molecular line emission from 0.1-1 kpc scale gas and dust discs in high-redshift sources or 10-100 pc scale molecular clouds and substructures within nearby galaxies. Science observations started on 30 September 2011 with 16 antennas and four receiver bands on baselines up to 400 m. The telescope's capabilities will steadily improve until full operations begin in 2013.

scholarly journals Searching for chemical signatures of planet formation

2018 ◽  
Vol 14 (S345) ◽  
pp. 362-364
Author(s):  
Ch. Rab ◽  
G.A. Muro-Arena ◽  
I. Kamp ◽  
C. Dominik ◽  
L.B.F.M. Waters ◽  
...  
Keyword(s):  
Planet Formation ◽  
Line Emission ◽  
Continuum Emission ◽  
Gap Formation ◽  
Molecular Line ◽  
Chemical Models ◽  
Chemical Signatures ◽  
Dust Distribution ◽  
The Impact ◽  
Multiple Molecules

AbstractHigh spatial resolution observations with ALMA and VLT/SPHERE show gaps and rings in continuum emission of protoplanetary disks, possibly indicating ongoing planet formation. However, it is still unclear if the gas follows the dust distribution. We present radiation thermo-chemical models for the disk of HD 163296 to study the impact of dust and gas gaps on the chemistry and molecular line emission. We compare a model with only dust gaps to a model that also has gas gaps. In both models, rings and gaps are visible in (sub)mm molecular line emission. Due to chemistry, certain molecules are sensitive to dust gaps where others are more sensitive to gas depletion. Observations of multiple molecules might allow to accurately determine the degree of gas depletion within the dust gaps, information crucial to discriminate between gap formation theories (e.g. planets, ice lines).

scholarly journals Discovery of Molecular-line Polarization in the Disk of TW Hya

2021 ◽  
Vol 922 (2) ◽  
pp. 139
Author(s):  
Richard Teague ◽  
Charles L. H. Hull ◽  
Stéphane Guilloteau ◽  
Edwin A. Bergin ◽  
Anne Dutrey ◽  
...  
Keyword(s):  
Linear Polarization ◽  
Line Emission ◽  
Emission Lines ◽  
Continuum Emission ◽  
Azimuthal Dependence ◽  
Molecular Line ◽  
Polarization Fraction ◽  
Co Emission ◽  
Higher Sensitivity ◽  
The Continuum

Abstract We report observations of polarized line and continuum emission from the disk of TW Hya using the Atacama Large Millimeter/submillimeter Array. We target three emission lines, 12CO (3–2), 13CO (3–2), and CS (7–6), to search for linear polarization due to the Goldreich–Kylafis effect, while simultaneously tracing the continuum polarization morphology at 332 GHz (900 μm), achieving a spatial resolution of 0.″5 (30 au). We detect linear polarization in the dust continuum emission; the polarization position angles show an azimuthal morphology, and the median polarization fraction is ∼0.2%, comparable to previous, lower frequency observations. Adopting a “shift-and-stack” technique to boost the sensitivity of the data, combined with a linear combination of the Q and U components to account for their azimuthal dependence, we detect weak linear polarization of 12CO and 13CO line emission at a ∼10σ and ∼5σ significance, respectively. The polarization was detected in the line wings, reaching a peak polarization fraction of ∼5% and ∼3% for the two molecules between disk radii of 0.″5 and 1″. The sign of the polarization was found to flip from the blueshifted side of the emission to the redshifted side, suggesting a complex, asymmetric polarization morphology. Polarization is not robustly detected for the CS emission; however, a tentative signal, comparable in morphology to that found for the 12CO and 13CO emission, is found at a ≲3σ significance. We are able to reconstruct a polarization morphology, consistent with the azimuthally averaged profiles, under the assumption that this is also azimuthally symmetric, which can be compared with future higher-sensitivity observations.

scholarly journals ALMA continuum observations of the protoplanetary disk AS 209

2018 ◽  
Vol 610 ◽  
pp. A24 ◽  
Author(s):  
D. Fedele ◽  
M. Tazzari ◽  
R. Booth ◽  
L. Testi ◽  
C. J. Clarke ◽  
...  
Keyword(s):  
Surface Density ◽  
Giant Planet ◽  
Outer Edge ◽  
Continuum Emission ◽  
High Angular Resolution ◽  
Strong Constraint ◽  
Star Forming ◽  
Pile Up ◽  
Gap Opening ◽  
Hydrodynamical Simulations

This paper presents new high angular resolution ALMA 1.3 mm dust continuum observations of the protoplanetary system AS 209 in the Ophiuchus star forming region. The dust continuum emission is characterized by a main central core and two prominent rings at r = 75 au and r = 130 au intervaled by two gaps at r = 62 au and r = 103 au. The two gaps have different widths and depths, with the inner one being narrower and shallower. We determined the surface density of the millimeter dust grains using the 3D radiative transfer disk code DALI. According to our fiducial model the inner gap is partially filled with millimeter grains while the outer gap is largely devoid of dust. The inferred surface density is compared to 3D hydrodynamical simulations (FARGO-3D) of planet-disk interaction. The outer dust gap is consistent with the presence of a giant planet (Mplanet ~ 0.7 MSaturn); the planet is responsible for the gap opening and for the pile-up of dust at the outer edge of the planet orbit. The simulations also show that the same planet could be the origin of the inner gap at r = 62 au. The relative position of the two dust gaps is close to the 2:1 resonance and we have investigated the possibility of a second planet inside the inner gap. The resulting surface density (including location, width and depth of the two dust gaps) are in agreement with the observations. The properties of the inner gap pose a strong constraint to the mass of the inner planet (Mplanet < 0.1 MJ). In both scenarios (single or pair of planets), the hydrodynamical simulations suggest a very low disk viscosity (α < 10−4). Given the young age of the system (0.5–1 Myr), this result implies that the formation of giant planets occurs on a timescale of ≲1 Myr.

scholarly journals 4.5. Sub-mm [C I] and CO observations of molecular clouds presumably interacting by the G359.54+0.18 nonthermal filaments

1998 ◽  
Vol 184 ◽  
pp. 175-176
Author(s):  
J. Staguhn ◽  
J. Stutzki ◽  
S. P. Balm ◽  
A. A. Stark ◽  
A. P. Lane
Keyword(s):  
Molecular Clouds ◽  
Line Emission ◽  
Recombination Line ◽  
Molecular Line ◽  
Line Intensities ◽  
Angular Extent ◽  
H Ii Region ◽  
Morphological Differences ◽  
5 Ghz ◽  
Co Observations

We have investigated the physical properties of molecular clouds which are presumably interacting with the G359.54+0.18 Nonthermal Filaments and an associated H ii region east of the filaments (Staguhn et al., 1996). The sub-mm spectra of 12CO(3-2) were observed with the KOSMA 3 m telescope, while the 490 GHz [C i] 3P1 →3P0 observations were made with the AST/RO 1.7 m sub-mm telescope. Fig. 1 shows channel maps of the integrated CO and [C i] line intensities in the velocity range of the recombination line observed towards the nearby H ii region. This H ii region is traced by the VLA 5 GHz continuum observations which are shown as contours in the central parts of the maps. The G359.54+0.18 Nonthermal Filaments, situated further to the west, appear to be morphologically associated with the H ii region. The [C i] emission of the molecular cloud east of the filaments which is kinematically linked to the H ii region is anti-correlated with the molecular line emission over a large angular extent. It is unlikely that the large morphological differences between [C i] and CO in this region can be explained exclusively by a high abundance of neutral carbon in the surface regions of dense molecular clumps, as is usually the case in PDR regions near the Sun.

scholarly journals Missing [C ii] emission from early galaxies

2020 ◽  
Vol 499 (4) ◽  
pp. 5136-5150 ◽  
Author(s):  
S Carniani ◽  
A Ferrara ◽  
R Maiolino ◽  
M Castellano ◽  
S Gallerani ◽  
...  
Keyword(s):  
Surface Brightness ◽  
Angular Resolution ◽  
Signal To Noise Ratio ◽  
Line Emission ◽  
Continuum Emission ◽  
Signal To Noise ◽  
Noise Ratio ◽  
Hydrodynamical Simulations ◽  
Early Galaxies

ABSTRACT ALMA observations have revealed that [C ii] 158 μm line emission in high-z galaxies is ≈2–3 × more extended than the UV continuum emission. Here we explore whether surface brightness dimming (SBD) of the [C ii] line is responsible for the reported [C ii] deficit, and the large $L_{\rm [O\, \small {III}]}/L_{\rm [C\, \small {II}]}$ luminosity ratio measured in early galaxies. We first analyse archival ALMA images of nine z &gt; 6 galaxies observed in both [C ii] and [O iii]. After performing several uv-tapering experiments to optimize the identification of extended line emission, we detect [C ii] emission in the whole sample, with an extent systematically larger than the [O iii] emission. Next, we use interferometric simulations to study the effect of SBD on the line luminosity estimate. About 40 per cent of the extended [C ii] component might be missed at an angular resolution of 0.8 arcsec, implying that $L_{\rm [C\, \small {II}]}$ is underestimated by a factor ≈2 in data at low (&lt;7) signal-to-noise ratio. By combining these results, we conclude that $L_{\rm [C\, \small {II}]}$ of z &gt; 6 galaxies lies, on average, slightly below the local $L_{\rm [C\, \small {II}]}-\mathrm{ SFR}$ relation (Δz =  6–9 = −0.07 ± 0.3), but within the intrinsic dispersion of the relation. SBD correction also yields $L_{\rm [O\, \small {III}]}/L_{\rm [C\, \small {II}]}\lt 10$, i.e. more in line with current hydrodynamical simulations.

scholarly journals Water maser and radio continuum emission towards IRAS 23139+5939

2007 ◽  
Vol 3 (S242) ◽  
pp. 180-181
Author(s):  
M. A. Trinidad ◽  
S. Curiel ◽  
J. M. Torrelles ◽  
L. F. Rodríguez ◽  
V. Migenes ◽  
...  
Keyword(s):  
Flux Density ◽  
Line Emission ◽  
The Other ◽  
Radio Continuum ◽  
High Mass ◽  
Continuum Emission ◽  
Maser Line ◽  
Water Masers ◽  
Water Maser ◽  
The Continuum

AbstractWe present simultaneous observations of continuum (3.5 and 1.3cm) and water maser line emission (1.3cm) carried out with the VLA-A toward the high-mass object IRAS 23139+5939. We detected two radio continuum sources at 3.5cm separated by 0”5 (~2400 AU), I23139 and I23139S. Based on the observed continuum flux density and the spectral index, we suggest that I23139 is a thermal radio jet associated with a high-mass YSO. On the other hand, based on the spatio-kinematical distribution of the water masers, together with the continuum emission information, we speculate that I23139S is also a jet source powering some of the masers detected in the region.

scholarly journals Molecular line emission in NGC 1068 imaged with ALMA

2014 ◽  
Vol 570 ◽  
pp. A28 ◽  
Author(s):  
S. Viti ◽  
S. García-Burillo ◽  
A. Fuente ◽  
L. K. Hunt ◽  
A. Usero ◽  
...  
Keyword(s):  
Line Emission ◽  
Molecular Line ◽  
Ngc 1068

scholarly journals Understanding biases in measurements of molecular cloud kinematics using line emission

2020 ◽  
Vol 498 (2) ◽  
pp. 2440-2455
Author(s):  
Yuxuan (宇轩) Yuan (原) ◽  
Mark R Krumholz ◽  
Blakesley Burkhart
Keyword(s):  
Magnetic Field ◽  
Molecular Cloud ◽  
Molecular Clouds ◽  
Velocity Dispersion ◽  
Signal To Noise Ratio ◽  
Line Emission ◽  
Molecular Line ◽  
Velocity Dispersions ◽  
Cloud Kinematics ◽  
Measurement Biases

ABSTRACT Molecular line observations using a variety of tracers are often used to investigate the kinematic structure of molecular clouds. However, measurements of cloud velocity dispersions with different lines, even in the same region, often yield inconsistent results. The reasons for this disagreement are not entirely clear, since molecular line observations are subject to a number of biases. In this paper, we untangle and investigate various factors that drive linewidth measurement biases by constructing synthetic position–position–velocity cubes for a variety of tracers from a suite of self-gravitating magnetohydrodynamic simulations of molecular clouds. We compare linewidths derived from synthetic observations of these data cubes to the true values in the simulations. We find that differences in linewidth as measured by different tracers are driven by a combination of density-dependent excitation, whereby tracers that are sensitive to higher densities sample smaller regions with smaller velocity dispersions, opacity broadening, especially for highly optically thick tracers such as CO, and finite resolution and sensitivity, which suppress the wings of emission lines. We find that, at fixed signal-to-noise ratio, three commonly used tracers, the J = 4 → 3 line of CO, the J = 1 → 0 line of C18O, and the (1,1) inversion transition of NH3, generally offer the best compromise between these competing biases, and produce estimates of the velocity dispersion that reflect the true kinematics of a molecular cloud to an accuracy of $\approx 10{{\ \rm per\ cent}}$ regardless of the cloud magnetic field strengths, evolutionary state, or orientations of the line of sight relative to the magnetic field. Tracers excited primarily in gas denser than that traced by NH3 tend to underestimate the true velocity dispersion by $\approx 20{{\ \rm per\ cent}}$ on average, while low-density tracers that are highly optically thick tend to have biases of comparable size in the opposite direction.

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