scholarly journals Cold H I in turbulent eddies and galactic spiral shocks

2006 ◽  
Vol 2 (S237) ◽  
pp. 363-367 ◽  
Author(s):  
Steven J. Gibson ◽  
A. Russell Taylor ◽  
Jeroen M. Stil ◽  
Christopher M. Brunt ◽  
Dain W. Kavars ◽  
...  
Keyword(s):  
Large Scale ◽  
Galactic Disk ◽  
Line Emission ◽  
Molecular State ◽  
Small Scale ◽  
Turbulent Eddies ◽  
Background Line ◽  
Galactic Spiral ◽  
Co Emission ◽  
Spiral Arm

AbstractH I 21cm-line self-absorption (HISA) reveals the shape and distribution of cold atomic clouds in the Galactic disk. Many of these clouds lack corresponding CO emission, despite being colder than purely atomic gas in equilibrium models. HISA requires background line emission at the same velocity, hence mechanisms that can produce such backgrounds. Weak, small-scale, and widespread absorption is likely to arise from turbulent eddies, while strong, large-scale absorption appears organized in cloud complexes along spiral arm shocks. In the latter, the gas may be evolving from an atomic to a molecular state prior to star formation, which would account for the incomplete HISA-CO agreement.

scholarly journals Linking the small-scale relativistic winds and the large-scale molecular outflows in the z = 1.51 lensed quasar HS 0810+2554

2020 ◽  
Vol 496 (1) ◽  
pp. 598-611
Author(s):  
G Chartas ◽  
E Davidson ◽  
M Brusa ◽  
C Vignali ◽  
M Cappi ◽  
...  
Keyword(s):  
Large Scale ◽  
Line Emission ◽  
Continuum Emission ◽  
Host Galaxy ◽  
Small Scale ◽  
Molecular Gas ◽  
Molecular Outflows ◽  
Peak Structure ◽  
Energy Conserving ◽  
Co Emission

ABSTRACT We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the quadruply lensed z =  1.51 quasar HS 0810+2554 which provide useful insight on the kinematics and morphology of the CO molecular gas and the ∼ 2 mm-continuum emission in the quasar host galaxy. Lens modelling of the mm-continuum and the spectrally integrated CO(J = 3→2) images indicates that the source of the mm-continuum has an eccentricity of e ∼ 0.9 with a size of ∼1.6 kpc and the source of line emission has an eccentricity of e ∼ 0.7 with a size of ∼1 kpc. The spatially integrated emission of the CO(J = 2→1) and CO(J = 3→2) lines shows a triple peak structure with the outer peaks separated by Δv21 = 220 ± 19 km s−1 and Δv32 = 245 ± 28 km s−1, respectively, suggesting the presence of rotating molecular CO line emitting gas. Lensing inversion of the high spatial resolution images confirms the presence of rotation of the line emitting gas. Assuming a conversion factor of αCO = 0.8 M⊙ (K km s−1 pc2)−1 we find the molecular gas mass of HS 0810+2554 to be MMol = (5.2 ± 1.5)/μ32 × 1010 M⊙, where μ32 is the magnification of the CO(J = 3→2) emission. We report the possible detection, at the 3.0–4.7σ confidence level, of shifted CO(J = 3→2) emission lines of high-velocity clumps of CO emission with velocities up to 1702 km s−1. We find that the momentum boost of the large-scale molecular wind is below the value predicted for an energy-conserving outflow given the momentum flux observed in the small-scale ultrafast outflow.

scholarly journals On Passing of Interstellar Clouds Through a Galactic Spiral Arm

2020 ◽  
pp. 41-56
Author(s):  
Alexander Zemlyakov ◽  
Mikhail Eremin ◽  
Ilya Kovalenko ◽  
Elena Zhukova
Keyword(s):  
Galactic Disk ◽  
Vertical Direction ◽  
Interstellar Gas ◽  
Hydrodynamic Simulation ◽  
Interstellar Clouds ◽  
Coriolis Forces ◽  
Adiabatic Flow ◽  
Low Mass ◽  
Galactic Spiral ◽  
Spiral Arm

It is believed that the taxonomy of interstellar clouds in their vicinity can serve as an indicator of the features of the geometry and intensity of galactic shock waves. In this paper, the authors present the results of a detailed two-dimensional hydrodynamic simulation of the passage of a cloud through the spiral arm of a galaxy and provide a brief analysis of the effects arising from this motion. The model of interstellar gas used assumes adiabatic flow in the spiral arm. The external gravitational field of the galactic disk and spiral arm is taken into account. The transverse dimensions of the arm in the calculations are taken as follows: the half-width of the arm is 1 kpc along the plane of the disk and 0.6 kpc in the vertical direction. A fragment of the flow is considered near and inside the spiral arm, the effects of the curvature of the arm and the influence of the Coriolis forces are neglected. It is shown that clouds passing through the arm are strongly deformed and lose a significant part of the mass or are completely destroyed in the case of low-mass clouds. The boundary value of the cloud mass at which complete destruction occurs lies in the interval between 3 000 and 6 000 M.

scholarly journals The role of the sonic scale in the growth of magnetic field in compressible turbulence

2020 ◽  
Vol 493 (3) ◽  
pp. 4400-4408
Author(s):  
Itzhak Fouxon ◽  
Michael Mond
Keyword(s):  
Magnetic Field ◽  
Growth Rate ◽  
Large Scale ◽  
Compressible Turbulence ◽  
Small Scale ◽  
Integral Scale ◽  
Time Model ◽  
Turbulent Eddies ◽  
Field Amplification ◽  
The Magnetic Field

ABSTRACT We study the growth of small fluctuations of magnetic field in supersonic turbulence, the small-scale dynamo. The growth is due to the smallest and fastest turbulent eddies above the resistive scale. We observe that for supersonic turbulence these eddies are localized below the sonic scale ls, defined as the scale where the typical velocity of the turbulent eddies equals the speed of sound, and are therefore effectively incompressible. All previous studies have ignored the existence of the sonic scale and consequently treated the entire inertial range as made up of compressible eddies. However, at large Mach numbers ls is much smaller than the integral scale of the turbulence so the fastest growing mode of the magnetic field belongs to small-scale incompressible turbulence. We determine this mode and the associated growth rate numerically with the aid of a white noise in time model of turbulence whose approximate validity for the description of the Navier–Stokes turbulence is explained. For that purpose, we introduce a new non-dimensional number Rsm that we name the magnetosonic Reynolds number that describes the division of the magnetic field amplification range between small-scale incompressible eddies and large-scale supersonic ones. We show that indeed, as Rsm grows (which means that the incompressible eddies occupy a larger portion of the magnetic field amplification range) the growth rate of the fastest growing mode increases, while the spatial distribution of the growing magnetic field shifts to smaller scales. Our result implies the existence of small-scale dynamo for compressible homogeneous turbulence.

scholarly journals Understanding our Galaxy: from the center to outskirts

2007 ◽  
Vol 3 (S248) ◽  
pp. 470-473
Author(s):  
Z. Q. Shen ◽  
Y. Xu ◽  
J. L. Han ◽  
X. W. Zheng
Keyword(s):  
Magnetic Fields ◽  
Radio Source ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Disk ◽  
Spiral Arms ◽  
Compact Radio Source ◽  
Sgr A ◽  
Spiral Arm

AbstractWe describe the efforts to understand our Milky Way Galaxy, from its center to outskirts, including (1) the measurements of the intrinsic size of the galactic center compact radio source Sgr A*; (2) the determination of the distance from the Sun to the Perseus spiral arm; and (3) the revealing of large scale global magnetic fields of the Galaxy.With high-resolution millimeter-VLBI observations, Shen et al. (2005) have measured the intrinsic size of the radio-emitting region of the galactic center compact radio source Sgr A* to be only 1 AU in diameter at 3.5 mm. When combined with the lower limit on the mass of Sgr A*, this provides strong evidence for Sgr A* being a super-massive black hole. Comparison with the intrinsic size detection at 7 mm indicates a frequency-dependent source size, posing a tight constraint on various theoretical models.With VLBI phase referencing observations, Xu et al. (2006) have measured the trigonometric parallax of W3OH in the Perseus spiral arm with an accuracy of 10 μas and also its absolute velocity with an accuracy of 1 km s−1. This demonstrates the capability of probing the structure and kinematics of the Milky Way by determining distances to 12 GHz methanol (CH3OH) masers in star forming regions of distant spiral arms and Milky Way's outskirts.With pulsar dispersion measures and rotation measures, Han et al. (2006) can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the most inner Norma arm to the outer Perseus arm.

scholarly journals Vertical and slanted sound propagation in the near-ground atmosphere : amplitude and phase fluctuations

2021 ◽  
Author(s):  
Matthew Kamrath ◽  
Vladimir Ostashev ◽  
D. Wilson ◽  
Michael White ◽  
Carl Hart ◽  
...  
Keyword(s):  
Large Scale ◽  
Sound Propagation ◽  
Microphone Arrays ◽  
Small Scale ◽  
Sound Sources ◽  
Phase Fluctuations ◽  
Turbulent Eddies ◽  
Low Altitude ◽  
Detection And Localization ◽  
Large Eddies

Sound propagation along vertical and slanted paths through the near-ground atmosphere impacts detection and localization of low-altitude sound sources, such as small unmanned aerial vehicles, from ground-based microphone arrays. This article experimentally investigates the amplitude and phase fluctuations of acoustic signals propagating along such paths. The experiment involved nine microphones on three horizontal booms mounted at different heights to a 135-m meteorological tower at the National Wind Technology Center (Boulder, CO). A ground-based loudspeaker was placed at the base of the tower for vertical propagation or 56m from the base of the tower for slanted propagation. Phasor scatterplots qualitatively characterize the amplitude and phase fluctuations of the received signals during different meteorological regimes. The measurements are also compared to a theory describing the log-amplitude and phase variances based on the spectrum of shear and buoyancy driven turbulence near the ground. Generally, the theory correctly predicts the measured log-amplitude variances, which are affected primarily by small-scale, isotropic turbulent eddies. However, the theory overpredicts the measured phase variances, which are affected primarily by large-scale, anisotropic, buoyantly driven eddies. Ground blocking of these large eddies likely explains the overprediction.

scholarly journals Disk-halo interactions: molecular clouds in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 177-181
Author(s):  
D. Riquelme ◽  
J. Martín-Pintado ◽  
R. Mauersberger ◽  
S. Martín ◽  
L. Bronfman
Keyword(s):  
Molecular Cloud ◽  
Molecular Clouds ◽  
Large Scale ◽  
Galactic Center ◽  
Galactic Disk ◽  
Isotopic Ratio ◽  
Small Scale ◽  
Kinetic Temperature ◽  
Temperature Regimes ◽  
Gas Accretion

AbstractWe study the disk-halo interaction, in the context of orbits and Giant Molecular loops (GMLs) in the Galactic center (GC) region. From a large scale survey of the central kpc of the Galaxy, in SiO J = (2 − 1), HCO+J = (1 − 0) and H13CO+J = (1 − 0) molecular emission, we identify shock regions traced by the enhancement of the SiO. These positions were studied using the 12C/13C isotopic ratio to trace gas accretion/ejection. We found a systematically higher 12C/13C isotopic ratio (> 40) toward the GMLs and the x1 orbits than for the GC standard molecular clouds (20–25). The high isotopic ratios are consistent with the accretion of the gas from the halo and from the outskirts of the Galactic disk. From multi-transitional observations of NH3, we derive two kinetic temperature regimes (one warm at ∼150 K and one cold at ∼40 K) for all the positions, except for the GMLs positions where only the warm component is present. The fractional abundances derived from the different molecules support the shock origin for the heating mechanism in the GC. We also present a detailed study of one molecular cloud placed in the foot points of two giant molecular loops, where two of the previously selected positions are placed. Using the 22m Mopra telescope we mapped the molecular cloud M − 3.8 + 0.9 in 3-mm molecular lines. The data show structures at small scale in SiO emission, with narrower line profiles than those of, e.g, HCO+ or HCN, which indicate that the shocks are dynamically confined. The data also show clear differences between different molecular tracers, e.g., between the SiO and HCO+ emission, which would indicate differences in the physical properties and chemistry within the cloud.

scholarly journals Magnetic fields in our Galaxy on large and small scales

2007 ◽  
Vol 3 (S242) ◽  
pp. 55-63 ◽  
Author(s):  
J. L. Han
Keyword(s):  
Magnetic Fields ◽  
Large Scale ◽  
Galactic Disk ◽  
Zeeman Splitting ◽  
Hii Regions ◽  
Small Scale ◽  
Small Scales ◽  
Dispersion Measures ◽  
Star Formation Regions ◽  
Galactic Distribution

AbstractMagnetic fields have been observed on all scales in our Galaxy, from AU to kpc. With pulsar dispersion measures and rotation measures, we can directly measure the magnetic fields in a very large region of the Galactic disk. The results show that the large-scale magnetic fields are aligned with the spiral arms but reverse their directions many times from the innermost arm (Norma) to the outer arm (Perseus). The Zeeman splitting measurements of masers in HII regions or star-formation regions not only show the structured fields inside clouds, but also have a clear pattern in the global Galactic distribution of all measured clouds which indicates the possible connection of the large-scale and small-scale magnetic fields.

scholarly journals Star Formation in the Southern Spiral Arm of M31

1987 ◽  
Vol 115 ◽  
pp. 622-624 ◽  
Author(s):  
T. Ichikawa ◽  
M. Nakano ◽  
Y. D. Tanaka
Keyword(s):  
Star Formation ◽  
Thermal Emission ◽  
Line Emission ◽  
Published Data ◽  
Large Hole ◽  
Hii Region ◽  
Dark Clouds ◽  
Ob Associations ◽  
Co Emission ◽  
Spiral Arm

Conspicuous dust lanes define the spiral arm in the south of M31. The integrated HI line emission map shows several large cloudlike structures with sizes ranging from hundreds to thousands of parsecs, forming a spiral arm along the dust lanes (Figure 1). To investigate how such super clouds correlate with star formation phenomena, we present in Figure 2 a compilation of published data on: CO emission, dark clouds, HII regions, OB associations, and thermal infrared radiation from IRAS. The CO emission distribution is similar to that of HI and also forms large cloudlike structures. The large CO clouds P, Q, and R, which are located in the high density HI areas, have bright HII region complexes of several hundred parsecs at their outer edges. Further out large OB associations are found. In contrast, cloud B, which shows weaker CO emission, has a large and diffuse HII region which may be relatively old. This giant HII region is located in a large hole of HI and dark clouds (Brinks 1981). The IRAS maps show strong correlated thermal emission from the dust lanes. The luminosity from the star formation activity heats the dust in the molecular clouds. The local peaks at A, P, and Q in the 25 μm band, extending 200-300 pc, have revealed the existence of massive young stars embedded in the clouds.

scholarly journals Conference summary: triggered star formation in a turbulent ISM

2006 ◽  
Vol 2 (S237) ◽  
pp. 384-389 ◽  
Author(s):  
Bruce G. Elmegreen
Keyword(s):  
Star Formation ◽  
Large Scale ◽  
Formation Rate ◽  
Small Scale ◽  
Space And Time ◽  
Gravitational Instabilities ◽  
Rate Limiting Step ◽  
Dynamical Time ◽  
Galactic Spiral ◽  
Rate Limiting

AbstractWhile the overall star formation rate in a galaxy appears to depend primarily on the gas mass and density, with the timescale for conversion of gas into stars given by the dynamical time, turbulence and explosions are still important for the process of star formation because they control the birth correlations in space and time. Most star formation appears triggered by some specific process, whether it is a galactic spiral shock, the expansion of a superbubble, the compression of a bright-rimmed globule, or some seemingly random compressive event in a supersonically turbulent flow. These processes give space and time sequences for star birth that are well observed. Many examples were given at this conference. Shocks are the link between large-scale but weak galactic processes and small-scale but strong final collapses. The rate limiting step is on the largest scale, where the dynamical time is slowest. Both gravitational instabilities and pressurized triggering seem to work on the same local dynamical time, making it difficult to tell that star formation is highly triggered when observing only galactic scales.

scholarly journals Detectability of 21-cm signal during the epoch of reionization with 21-cm-Lyman-α emitter cross-correlation – III. Model dependence

2020 ◽  
Vol 494 (3) ◽  
pp. 3131-3140 ◽  
Author(s):  
Kenji Kubota ◽  
Akio K Inoue ◽  
Kenji Hasegawa ◽  
Keitaro Takahashi
Keyword(s):  
Power Spectrum ◽  
Luminosity Function ◽  
Large Scale ◽  
Cross Correlation ◽  
Line Emission ◽  
Observation Time ◽  
Dark Matter Halo ◽  
Small Scale ◽  
Cross Power Spectrum ◽  
The Continuum

ABSTRACT Detecting H i 21-cm line in the intergalactic medium during the epoch of reionization suffers from foreground contamination such as Galactic synchrotron and extragalactic radio sources. Cross-correlation between the 21-cm line and Lyman-α emitter (LAE) galaxies is a powerful tool to identify the 21-cm signal since the 21-cm line emission has correlation with LAEs, while the LAEs are statistically independent of the foregrounds. So far, the detectability of 21-cm-LAE cross-power spectrum has been investigated with simple LAE models where the observed Lyα luminosity is proportional to the dark matter halo mass. However, the previous models were inconsistent with the latest observational data of LAEs obtained with Subaru/Hyper Suprime-Cam (HSC). Here, we revisit the detectability of 21-cm-LAE cross-power spectrum adopting a state-of-the-art LAE model consistent with all Subaru/HSC observations such as the Lyα luminosity function, LAE angular autocorrelation, and the LAE fractions in the continuum selected galaxies. We find that resultant cross-power spectrum with the updated LAE model is reduced at small scales ($k\sim 1\ \rm Mpc^{-1}$) compared to the simple models, while the amplitudes at large scales ($k \lesssim 0.2 \ \rm Mpc^{-1}$) are not affected so much. We conclude that the large-scale signal would be detectable with Square Kilometre Array (SKA) and HSC LAE cross-correlation but detecting the small-scale signal would require an extended HSC LAE survey with an area of $\sim 75\ \rm deg^2$ or 3000 h observation time of 21-cm line with SKA.

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