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 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.

scholarly journals High-Redshift Molecular Clouds and Absorption-Line Spectra of Quasars

1983 ◽  
Vol 104 ◽  
pp. 365-366
Author(s):  
D. A. Varshalovich ◽  
S. A. Levshakov
Keyword(s):  
Absorption Line ◽  
Molecular Clouds ◽  
High Redshift ◽  
Optical Spectra ◽  
Molecular Lines

The optical spectra of distant quasars (OQ 172, PHL 957, PKS 0237–233 and 11 others) were reanalysed with the purpose of searching molecular lines /2, 4/.

scholarly journals Velocity profiles of [CII], [CI], CO, and [OI] and physical conditions in four star-forming regions in the Large Magellanic Cloud

2019 ◽  
Vol 621 ◽  
pp. A62 ◽  
Author(s):  
Yoko Okada ◽  
Rolf Güsten ◽  
Miguel Angel Requena-Torres ◽  
Markus Röllig ◽  
Jürgen Stutzki ◽  
...  
Keyword(s):  
Physical Properties ◽  
High Redshift ◽  
Line Emission ◽  
Chemical Species ◽  
Large Magellanic Cloud ◽  
Magellanic Cloud ◽  
Continuum Emission ◽  
Line Profiles ◽  
Star Forming ◽  
Star Forming Regions

Aims. The aim of our study is to investigate the physical properties of the star-forming interstellar medium (ISM) in the Large Magellanic Cloud (LMC) by separating the origin of the emission lines spatially and spectrally. The LMC provides a unique local template to bridge studies in the Galaxy and high redshift galaxies because of its low metallicity and proximity, enabling us to study the detailed physics of the ISM in spatially resolved individual star-forming regions. Following Okada et al. (Okada, Y., Requena-Torres, M. A., Güsten, R., et al. 2015, A&A, 580, A54), we investigate different phases of the ISM traced by carbon-bearing species in four star-forming regions in the LMC, and model the physical properties using the KOSMA-τ PDR model. Methods. We mapped 3–13 arcmin2 areas in 30 Dor, N158, N160, and N159 along the molecular ridge of the LMC in [C II] 158 μm with GREAT on board SOFIA. We also observed the same area with CO(2-1) to (6-5), 13CO(2-1) and (3-2), [C I] 3P1–3P0 and 3P2–3P1 with APEX. For selected positions in N159 and 30 Dor, we observed [O I] 145 μm and [O I] 63 μm with upGREAT. All spectra are velocity resolved. Results. In all four star-forming regions, the line profiles of CO, 13CO, and [C I] emission are similar, being reproduced by a combination of Gaussian profiles defined by CO(3-2), whereas [C II] typically shows wider line profiles or an additional velocity component. At several positions in N159 and 30 Dor, we observed the velocity-resolved [O I] 145 and 63 μm lines for the first time. At some positions, the [O I] line profiles match those of CO, at other positions they are more similar to the [C II] profiles. We interpret the different line profiles of CO, [C II] and [O I] as contributions from spatially separated clouds and/or clouds in different physical phases, which give different line ratios depending on their physical properties. We modeled the emission from the CO, [C I], [C II], and [O I] lines and the far-infrared continuum emission using the latest KOSMA-τ PDR model, which treats the dust-related physics consistently and computes the dust continuum SED together with the line emission of the chemical species. We find that the line and continuum emissions are not well-reproduced by a single clump ensemble. Toward the CO peak at N159 W, we propose a scenario that the CO, [C II], and [O I] 63 μm emission are weaker than expected because of mutual shielding among clumps.

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 The resolved radio–FIR correlation in nearby galaxies with Herschel and Spitzer

2011 ◽  
Vol 7 (S284) ◽  
pp. 400-403
Author(s):  
Fatemeh S. Tabatabaei ◽  
Eva Schinnerer ◽  
Eric Murphy ◽  
Rainer Beck ◽  
Annie Hughes ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Diffusion Length ◽  
Spatial Scales ◽  
Cosmic Ray ◽  
Far Infrared ◽  
Scale Dependence ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Synchrotron Emission ◽  
Nearby Galaxies

AbstractWe investigate the correlation between the far-infrared (FIR) and radio continuum emission from NGC6946 on spatial scales between 0.9 and 17 kpc. We use the Herschel PACS (70, 100, 160μm) and SPIRE (250μm) data from the KINGFISH project. Separating the free-free and synchrotron components of the radio continuum emission, we find that FIR is better correlated with the free-free than the synchrotron emission. Compared to a similar study in M33 and M31, we find that the scale dependence of the synchrotron–FIR correlation in NGC6946 is more similar to M31 than M33. The scale dependence of the synchrotron–FIR correlation can be explained by the turbulent-to-ordered magnetic field ratio or, equivalently, the diffusion length of the cosmic ray electrons in these galaxies.

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.

Recent Results on Associations: Anatomy of CMa OB1 and Mon OB1

1980 ◽  
Vol 85 ◽  
pp. 33-49 ◽  
Author(s):  
William Herbst
Keyword(s):  
Molecular Clouds ◽  
Line Emission ◽  
T Tauri Stars ◽  
Molecular Line ◽  
Dark Clouds ◽  
T Tauri ◽  
Sky Survey ◽  
Objective Prism ◽  
Cloud Complex ◽  
Reflection Nebulae

Three types of associations are presently recognized. These are OB, R, and T, and represent, respectively, concentrations of O and B type stars, reflection nebulae, and T Tauri stars, in certain regions of the sky. OB and T associations are identified on objective prism plates; R associations may be found using direct plates such as those of the Palomar Sky Survey. All associations are intimately connected with what appear optically as dark clouds and are now detected as sources of molecular line emission and known as molecular clouds. Often, all three types of associations are found within the same cloud complex (eg, Mon OB1). However, there are also examples of T associations (Taurus) and R associations (Mon R2) which are not connected with recognized OB associations.

scholarly journals Molecular Studies of Herbig-Haro Objects

1992 ◽  
Vol 150 ◽  
pp. 373-378
Author(s):  
Salvador Curiel
Keyword(s):  
Angular Resolution ◽  
Line Emission ◽  
High Angular Resolution ◽  
Molecular Line ◽  
Infrared Observations ◽  
Molecular Studies ◽  
Complex Variety ◽  
Molecular Lines ◽  
Hh Objects ◽  
Optical Wavelengths

Recent ultraviolet, infrared, millimeter and centimeter-wavelength observations have revealed that HH objects are also sources of molecular line emission. Infrared observations have shown that H2 line emission in HH objects presents a wide and complex variety of morphologies, being in most of the cases similar to that observed at optical wavelengths. New high-angular resolution radio observations of molecular lines have revealed that small high-density condensations are frequently found in association with HH objects. Below, a brief review of molecular emission in HH objects is presented.

scholarly journals LEGO – II. A 3 mm molecular line study covering 100 pc of one of the most actively star-forming portions within the Milky Way disc

2020 ◽  
Vol 497 (2) ◽  
pp. 1972-2001
Author(s):  
A T Barnes ◽  
J Kauffmann ◽  
F Bigiel ◽  
N Brinkmann ◽  
D Colombo ◽  
...  
Keyword(s):  
Column Density ◽  
Milky Way ◽  
Line Emission ◽  
Chemical Properties ◽  
Molecular Line ◽  
Star Forming ◽  
Emission Efficiency ◽  
Single Region ◽  
High Emission ◽  
Molecular Lines

ABSTRACT The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60 arcsec (∼3 pc) resolution observations of many 3 mm band molecular lines across a large map of the W49 massive star-forming region (∼100 pc × 100 pc at 11 kpc), which were taken as part of the ‘LEGO’ IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H2 column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density (1022 cm−2) and moderate temperatures (35 K), whilst e.g. N2H+ emits most efficiently towards lower temperatures (1022 cm−2; &lt;20 K). We determine $X_{\mathrm{CO} (1-0)} \sim 0.3 \times 10^{20} \, \mathrm{cm^{-2}\, (K\, km\, s^{-1})^{-1}}$, and $\alpha _{\mathrm{HCN} (1-0)} \sim 30\, \mathrm{M_\odot \, (K\, km\, s^{-1}\, pc^2)^{-1}}$, which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.

scholarly journals The Evolution of QSO Spectra: Evidence for Microlensing?

1996 ◽  
Vol 173 ◽  
pp. 289-290
Author(s):  
Paul J. Francis ◽  
Anuradha Koratkar
Keyword(s):  
Equivalent Width ◽  
High Redshift ◽  
Line Emission ◽  
Compact Objects ◽  
Emission Lines ◽  
Continuum Emission ◽  
The Continuum

We find that the spectra of QSOs evolve: high redshift QSOs (z > 1.5) have lower equivalent width emission lines than low redshift QSOs (z < 0.5) with the same luminosities and radio properties.We propose that microlensing by compact objects may account for the apparent evolution. If Ω ∼ 0.05 in compact objects, the continuum emission from many high redshift QSOs will be amplified, but not the line emission, leading to the observed decrease in the apparent equivalent widths.

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