scholarly journals The Warm Gas in the Milky Way: The Kinematical Model of C iv and Its Connection to Si iv

2022 ◽  
Vol 924 (2) ◽  
pp. 86
Author(s):  
Zhijie Qu ◽  
Ryan Lindley ◽  
Joel N. Bregman
Keyword(s):  
Density Distribution ◽  
Milky Way ◽  
Galactic Center ◽  
Hubble Space Telescope ◽  
Density Ratio ◽  
Element Abundance ◽  
Spatial Density ◽  
Small Scale ◽  
Relative Extension ◽  
Kinematical Model

Abstract We compose a 265-sight-line Milky Way C iv line-shape sample using the Hubble Space Telescope/Cosmic Origins Spectrograph archive, which is complementary to the existing Si iv samples. C iv has a higher ionization potential (47–64 eV) than Si iv (33–45 eV), so it also traces warm gas, which is roughly cospatial with Si iv. The spatial density distribution and kinematics of C iv are identical to those Si iv within ≈2σ. C iv is more sensitive to the warm gas density distribution at large radii with a higher element abundance. Applying the kinematical model to the C iv sample, we find two possible solutions of the density distribution, which are distinguished by the relative extension along the disk midplane and the normal-line direction. Both solutions can reproduce the existing sample and suggest a warm gas disk mass of log M ( M ⊙ ) ≈ 8 and an upper limit of log M ( M ⊙ ) < 9.3 within 250 kpc, which is consistent with Si iv. There is a decrease in the C iv/Si iv column density ratio from the Galactic center to the outskirts by 0.2–0.3 dex, which may suggest a phase transition or different ionization mechanisms for C iv and Si iv. Also, we find that the difference between C iv and Si iv is an excellent tracer of small-scale features, and we find a typical size of 5°–10° for possible turbulence within individual clouds (≈1 kpc).

Detect the density profile with LAMOST K giants

2017 ◽  
Vol 13 (S334) ◽  
pp. 387-388
Author(s):  
Yan Xu ◽  
Chao Liu
Keyword(s):  
Density Distribution ◽  
Power Law ◽  
Density Profile ◽  
Milky Way ◽  
Galactic Center ◽  
Fitting Method ◽  
Stellar Halo ◽  
Model Independent ◽  
Power Law Index ◽  
K Giants

AbstractThe density distribution of the Milky Way halo is detected with 5351 LAMOST DR3 metal poor K giants using a nonparametric method. The nonparametric fitting method is a model independent way to estimate the halo density distribution while to a large extent avoiding the influence of the halo substucture. We show that the K giants density profile can be fitted well by single power law. We found no indication of a break in the power law index. The powerlaw index n = 5.0−0.64+0.64. The data show that the stellar halo is flattened at smaller radii, and becomes more spherical farther from the Galactic center. The flattening q(r=15Kpc)is about0.64, q(20Kpc) is about 0.8, q(30Kpc) is about 0.96.

scholarly journals A Statistical Estimation of the Occurrence of Extraterrestrial Intelligence in the Milky Way Galaxy

Galaxies ◽  
2021 ◽  
Vol 9 (1) ◽  
pp. 5
Author(s):  
Xiang Cai ◽  
Jonathan H. Jiang ◽  
Kristen A. Fahy ◽  
Yuk L. Yung
Keyword(s):  
Statistical Estimation ◽  
Milky Way ◽  
Galactic Center ◽  
Model Simulation ◽  
Temporal Variations ◽  
Extraterrestrial Intelligence ◽  
Milky Way Galaxy ◽  
The Galaxy ◽  
Peak Location ◽  
Intelligent Life

In the field of astrobiology, the precise location, prevalence, and age of potential extraterrestrial intelligence (ETI) have not been explicitly explored. Here, we address these inquiries using an empirical galactic simulation model to analyze the spatial–temporal variations and the prevalence of potential ETI within the Galaxy. This model estimates the occurrence of ETI, providing guidance on where to look for intelligent life in the Search for ETI (SETI) with a set of criteria, including well-established astrophysical properties of the Milky Way. Further, typically overlooked factors such as the process of abiogenesis, different evolutionary timescales, and potential self-annihilation are incorporated to explore the growth propensity of ETI. We examine three major parameters: (1) the likelihood rate of abiogenesis (λA); (2) evolutionary timescales (Tevo); and (3) probability of self-annihilation of complex life (Pann). We found Pann to be the most influential parameter determining the quantity and age of galactic intelligent life. Our model simulation also identified a peak location for ETI at an annular region approximately 4 kpc from the galactic center around 8 billion years (Gyrs), with complex life decreasing temporally and spatially from the peak point, asserting a high likelihood of intelligent life in the galactic inner disk. The simulated age distributions also suggest that most of the intelligent life in our galaxy are young, thus making observation or detection difficult.

scholarly journals Remarkable Symmetries in the Milky Way Disc's Magnetic Field

2011 ◽  
Vol 28 (2) ◽  
pp. 171-176 ◽  
Author(s):  
P. P. Kronberg ◽  
K. J. Newton-McGee
Keyword(s):  
Magnetic Structure ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Field Structure ◽  
Field Pattern ◽  
Close Coupling ◽  
Sign Change

AbstractWe apply a new, expanded compilation of extragalactic source Faraday rotation measures (RM) to investigate the broad underlying magnetic structure of the Galactic disk at latitudes ∣b∣ ≲15° over all longitudes l, where our total number of RMs is comparable to those in the combined Canadian Galactic Plane Survey (CGPS) at ∣b∣ < 4° and the Southern Galactic Plane (SGPS) ∣b∣<1.5°. We report newly revealed, remarkably coherent patterns of RM at ∣b∣≲15° from l∼270° to ∼90° and RM(l) features of unprecedented clarity that replicate in l with opposite sign on opposite sides of the Galactic center. They confirm a highly patterned bisymmetric field structure toward the inner disc, an axisymmetic pattern toward the outer disc, and a very close coupling between the CGPS/SGPS RMs at ∣b∣≲3° (‘mid-plane’) and our new RMs up to ∣b∣∼15° (‘near-plane’). Our analysis also shows the vertical height of the coherent component of the disc field above the Galactic disc's mid-plane—to be ∼1.5 kpc out to ∼6 kpc from the Sun. This identifies the approximate height of a transition layer to the halo field structure. We find no RM sign change across the plane within ∣b∣∼15° in any longitude range. The prevailing disc field pattern and its striking degree of large-scale ordering confirm that our side of the Milky Way has a very organized underlying magnetic structure, for which the inward spiral pitch angle is 5.5°±1° at all ∣b∣ up to ∼12° in the inner semicircle of Galactic longitudes. It decreases to ∼0° toward the anticentre.

scholarly journals LIGHT SUPERCONDUCTING STRINGS IN THE GALAXY

2007 ◽  
Vol 16 (12b) ◽  
pp. 2399-2405 ◽  
Author(s):  
FRANCESC FERRER ◽  
TANMAY VACHASPATI
Keyword(s):  
Magnetic Field ◽  
Spatial Distribution ◽  
Particle Physics ◽  
Milky Way ◽  
Gamma Ray ◽  
Galactic Center ◽  
Line Emission ◽  
Galactic Magnetic Field ◽  
The Galaxy ◽  
Intense Source

Observations of the Milky Way by the SPI/INTEGRAL satellite have confirmed the presence of a strong 511 keV gamma ray line emission from the bulge, which requires an intense source of positrons in the galactic center. These observations are hard to account for by conventional astrophysical scenarios, whereas other proposals, such as light DM, face stringent constraints from the diffuse gamma ray background. Here we suggest that light superconducting strings could be the source of the observed 511 keV emission. The associated particle physics, at the ~ 1 TeV scale, is within the reach of planned accelerator experiments, while the distinguishing spatial distribution, proportional to the galactic magnetic field, could be mapped by SPI or by future, more sensitive satellite missions.

scholarly journals A Kiloparsec-scale Molecular Wave in the Inner Galaxy: Feather of the Milky Way?

2021 ◽  
Vol 921 (2) ◽  
pp. L42
Author(s):  
V. S. Veena ◽  
P. Schilke ◽  
Á. Sánchez-Monge ◽  
M. C. Sormani ◽  
R. S. Klessen ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Aspect Ratio ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Galactic Center ◽  
Velocity Data ◽  
Sinusoidal Wave ◽  
Angular Extent ◽  
The Vertical Distribution ◽  
Spiral Arm

Abstract We report the discovery of a velocity coherent, kiloparsec-scale molecular structure toward the Galactic center region with an angular extent of 30° and an aspect ratio of 60:1. The kinematic distance of the CO structure ranges between 4.4 and 6.5 kpc. Analysis of the velocity data and comparison with the existing spiral arm models support that a major portion of this structure is either a subbranch of the Norma arm or an interarm giant molecular filament, likely to be a kiloparsec-scale feather (or spur) of the Milky Way, similar to those observed in nearby spiral galaxies. The filamentary cloud is at least 2.0 kpc in extent, considering the uncertainties in the kinematic distances, and it could be as long as 4 kpc. The vertical distribution of this highly elongated structure reveals a pattern similar to that of a sinusoidal wave. The exact mechanisms responsible for the origin of such a kiloparsec-scale filament and its wavy morphology remains unclear. The distinct wave-like shape and its peculiar orientation makes this cloud, named as the Gangotri wave, one of the largest and most intriguing structures identified in the Milky Way.

scholarly journals Milky Way Rotation Models from Neutral Hydrogen and Molecular Clouds: Galactic Constants, Common Details and Differences

2000 ◽  
Vol 174 ◽  
pp. 403-407
Author(s):  
Igor’ I. Nikiforov
Keyword(s):  
Milky Way ◽  
Galactic Center ◽  
Kinematic Model ◽  
Neutral Hydrogen ◽  
Galactic Rotation ◽  
Kinematic Data ◽  
Galactic Rotation Curve ◽  
The Common ◽  
Center Distance

Kinematic data from neutral hydrogen observations provide information to solve the interdependent problems of the determination of the main Galactic constants (the Solar-Galactic center distance R0, the Oort constant A and others) and the Galactic rotation curve (Nikiforov & Petrovskaya 1994, hereafter NP94, and references therein). However, in the standard method for finding R0 by comparing the rotations of HI clouds and some other objects (typically HII regions/CO clouds), the kinematic model, constructed typically solely from HI data, is considered to be the same for both galactic subsystems (e.g. Merrifield 1992). In practice a discrepancy between their rotation curves can produce strongly erroneous results (Merrifield 1992, NP94). Establishing the common rotation law from HI plus HII/CO data in NP94 is only a part of attacking the problem.

scholarly journals Heating of Milky Way disc stars by dark matter fluctuations in cold dark matter and fuzzy dark matter paradigms

2019 ◽  
Vol 485 (2) ◽  
pp. 2861-2876 ◽  
Author(s):  
Benjamin V Church ◽  
Philip Mocz ◽  
Jeremiah P Ostriker
Keyword(s):  
Dark Matter ◽  
Galaxy Formation ◽  
Quantum Interference ◽  
Cold Dark Matter ◽  
Milky Way ◽  
Velocity Dispersion ◽  
Formation Rate ◽  
Density Fluctuations ◽  
Particle Mass ◽  
Small Scale

ABSTRACT Although highly successful on cosmological scales, cold dark matter (CDM) models predict unobserved overdense ‘cusps’ in dwarf galaxies and overestimate their formation rate. We consider an ultralight axion-like scalar boson which promises to reduce these observational discrepancies at galactic scales. The model, known as fuzzy dark matter (FDM), avoids cusps, suppresses small-scale power, and delays galaxy formation via macroscopic quantum pressure. We compare the substructure and density fluctuations of galactic dark matter haloes comprised of ultralight axions to conventional CDM results. Besides self-gravitating subhaloes, FDM includes non-virialized overdense wavelets formed by quantum interference patterns, which are an efficient source of heating to galactic discs. We find that, in the solar neighbourhood, wavelet heating is sufficient to give the oldest disc stars a velocity dispersion of ${\sim } {30}{\, \mathrm{km\, s}^{-1}}$ within a Hubble time if energy is not lost from the disc, the velocity dispersion increasing with stellar age as σD ∝ t0.4 in agreement with observations. Furthermore, we calculate the radius-dependent velocity dispersion and corresponding scaleheight caused by the heating of this dynamical substructure in both CDM and FDM with the determination that these effects will produce a flaring that terminates the Milky Way disc at $15\!-\!20{\, \mathrm{kpc}}$. Although the source of thickened discs is not known, the heating due to perturbations caused by dark substructure cannot exceed the total disc velocity dispersion. Therefore, this work provides a lower bound on the FDM particle mass of ma &gt; 0.6 × 10−22 eV. Furthermore, FDM wavelets with this particle mass should be considered a viable mechanism for producing the observed disc thickening with time.

scholarly journals Integrated spectroscopy of extragalactic Globular Clusters

2019 ◽  
Vol 14 (S351) ◽  
pp. 155-160
Author(s):  
Charli M. Sakari
Keyword(s):  
Globular Clusters ◽  
Milky Way ◽  
Light Element ◽  
Element Abundance ◽  
Future Perspectives ◽  
Host Galaxies ◽  
Chemical Abundances ◽  
Essential Information ◽  
Light Element Abundance ◽  
Detailed Chemical

AbstractIntegrated light (IL) spectroscopy enables studies of stellar populations beyond the Milky Way and its nearest satellites. In this paper, I will review how IL spectroscopy reveals essential information about globular clusters and the assembly histories of their host galaxies, concentrating particularly on the metallicities and detailed chemical abundances of the GCs in M31. I will also briefly mention the effects of multiple populations on IL spectra, and how observations of distant globular clusters help constrain the source(s) of light-element abundance variations. I will end with future perspectives, emphasizing how IL spectroscopy can bridge the gap between Galactic and extragalactic astronomy.

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