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 Galactic spiral structure

2009 ◽  
Vol 465 (2111) ◽  
pp. 3425-3446 ◽  
Author(s):  
Charles Francis ◽  
Erik Anderson
Keyword(s):  
Pitch Angle ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Stellar Orbits ◽  
Grand Design ◽  
Galactic Spiral Structure ◽  
Pattern Speed ◽  
Galactic Spiral ◽  
Almost All ◽  
Spiral Arm

We describe the structure and composition of six major stellar streams in a population of 20 574 local stars in the New Hipparcos Reduction with known radial velocities. We find that, once fast moving stars are excluded, almost all stars belong to one of these streams. The results of our investigation have led us to re-examine the hydrogen maps of the Milky Way, from which we identify the possibility of a symmetric two-armed spiral with half the conventionally accepted pitch angle. We describe a model of spiral arm motions that matches the observed velocities and compositions of the six major streams, as well as the observed velocities of the Hyades and Praesepe clusters at the extreme of the Hyades stream. We model stellar orbits as perturbed ellipses aligned at a focus in coordinates rotating at the rate of precession of apocentre. Stars join a spiral arm just before apocentre, follow the arm for more than half an orbit, and leave the arm soon after pericentre. Spiral pattern speed equals the mean rate of precession of apocentre. Spiral arms are shown to be stable configurations of stellar orbits, up to the formation of a bar and/or ring. Pitch angle is directly related to the distribution of orbital eccentricities in a given spiral galaxy. We show how spiral galaxies can evolve to form bars and rings. We show that orbits of gas clouds are stable only in bisymmetric spirals. We conclude that spiral galaxies evolve toward grand design two-armed spirals. We infer from the velocity distributions that the Milky Way evolved into this form about 9 billion years ago (Ga).

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 A Circulation Hypothesis of Spiral Galaxies

1998 ◽  
Vol 188 ◽  
pp. 293-294
Author(s):  
Chen Linfei
Keyword(s):  
Spiral Galaxies ◽  
Spiral Structure ◽  
Galactic Center ◽  
Circulatory System ◽  
Spiral Arms ◽  
The Galaxy ◽  
Spiral Arm

A circulation hypothesis of spiral galaxies is proposed here to explain their spiral structure: the spiral arm material is going to the galactic center along a spiral orbit and then ejects from the galactic center in the form of two-way jets in opposite directions and finally, the ejected jets return to the galaxy in the form of spiral arms again, thereby forming a closed circulatory system.

scholarly journals A Comparison of the Simulations and Observations for a Nearby Spiral Arm

2021 ◽  
Vol 8 ◽  
Author(s):  
Martin Piecka ◽  
Ernst Paunzen
Keyword(s):  
Milky Way ◽  
Spiral Galaxies ◽  
Spiral Structure ◽  
Kinematic Model ◽  
Current Data ◽  
Observational Evidence ◽  
Open Clusters ◽  
Spiral Arms ◽  
Diffuse Interstellar Bands ◽  
Spiral Arm

The analysis is focused on the ability of galactic open clusters to trace the spiral arms, based on the recent data releases from Gaia. For this, a simple 1D description of the motion of spiral arms and clusters is introduced. As next step, results are verified using a widely accepted kinematic model of the motion in spiral galaxies. As expected, both approaches show that open clusters older than about 100 Myr are bad tracers of spiral arms. The younger clusters (ideally < 30 Myr) should be used instead. This agrees with the most recent observational evidence. The latest maps of the diffuse interstellar bands are compared with the spiral structure of the Milky Way and the Antennae Galaxies. The idea of these bands being useful for studying a galactic structure cannot be supported based on the current data.

scholarly journals Scientific Background to the UKST Hα Survey

1998 ◽  
Vol 15 (1) ◽  
pp. 5-8 ◽  
Author(s):  
M. R. W. Masheder ◽  
S. Phillipps ◽  
Q. A. Parker
Keyword(s):  
Milky Way ◽  
Spiral Galaxies ◽  
Virgo Cluster ◽  
Magellanic Clouds ◽  
Special Issue ◽  
Successful Development ◽  
Angular Extent ◽  
Tremendous Importance ◽  
Dominant Process ◽  
Optical Indicator

AbstractThe dominant process in the evolution of spiral galaxies like our own is clearly the formation of new stars, and the leading optical indicator of this is Hα emission. Considering the tremendous importance of star formation and its variation within and between galaxies, it is surprising just how little survey work has been carried out at Hα. After the successful development of Tech Pan films for deep photographic imaging with the UKST, and given the particular sensitivity of Tech Pan at wavelengths near Hα, it was natural to consider the possibilities for a narrowband Hα imaging survey of large angular extent. This idea quickly developed into a full-blown survey of the whole of the Southern Milky Way, of the Magellanic Clouds, and of selected extragalactic regions of interest such as that around the Virgo Cluster. This special issue is devoted to the discussion of the details of making and using this survey.

scholarly journals PG 1610+062: a runaway B star challenging classical ejection mechanisms

2019 ◽  
Vol 628 ◽  
pp. L5 ◽  
Author(s):  
A. Irrgang ◽  
S. Geier ◽  
U. Heber ◽  
T. Kupfer ◽  
F. Fürst
Keyword(s):  
Main Sequence ◽  
Milky Way ◽  
Galactic Center ◽  
Rotational Velocity ◽  
Proper Motions ◽  
B Stars ◽  
Supermassive Black Hole ◽  
Ejection Mechanism ◽  
Runaway Stars ◽  
Spiral Arm

Hypervelocity stars are rare objects, mostly main-sequence (MS) B stars, traveling so fast that they will eventually escape from the Milky Way. Recently, it has been shown that the popular Hills mechanism, in which a binary system is disrupted via a close encounter with the supermassive black hole at the Galactic center, may not be their only ejection mechanism. The analyses of Gaia data ruled out a Galactic center origin for some of them, and instead indicated that they are extreme disk runaway stars ejected at velocities exceeding the predicted limits of classical scenarios (dynamical ejection from star clusters or binary supernova ejection). We present the discovery of a new extreme disk runaway star, PG 1610+062, which is a slowly pulsating B star bright enough to be studied in detail. A quantitative analysis of spectra taken with ESI at the Keck Observatory revealed that PG 1610+062 is a late B-type MS star of 4–5 M⊙ with low projected rotational velocity. Abundances (C, N, O, Ne, Mg, Al, Si, S, Ar, and Fe) were derived differentially with respect to the normal B star HD 137366 and indicate that PG 1610+062 is somewhat metal rich. A kinematic analysis, based on our spectrophotometric distance (17.3 kpc) and on proper motions from Gaia’s second data release, shows that PG 1610+062 was probably ejected from the Carina-Sagittarius spiral arm at a velocity of 550 ± 40 km s−1, which is beyond the classical limits. Accordingly, the star is in the top five of the most extreme MS disk runaway stars and is only the second among the five for which the chemical composition is known.

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 Globular Cluster and Galaxy Formation: M31, the Milky Way, and Implications for Globular Cluster Systems of Spiral Galaxies

2004 ◽  
Vol 614 (1) ◽  
pp. 158-166 ◽  
Author(s):  
David Burstein ◽  
Yong Li ◽  
Kenneth C. Freeman ◽  
John E. Norris ◽  
Michael S. Bessell ◽  
...  
Keyword(s):  
Galaxy Formation ◽  
Globular Cluster ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Cluster Systems

scholarly journals Several evolutionary channels for bright planetary nebulae

2015 ◽  
Vol 11 (S317) ◽  
pp. 344-345 ◽  
Author(s):  
Michael G. Richer ◽  
Marshall L. McCall
Keyword(s):  
Spectral Properties ◽  
Milky Way ◽  
Spiral Galaxies ◽  
Planetary Nebulae

AbstractThe populations of bright planetary nebulae in the discs of spirals appear to differ in their spectral properties from those in ellipticals and the bulges of spirals. The bright planetary nebulae from the bulge of the Milky Way are entirely compatible with those observed in the discs of spiral galaxies. The similarity might be explained if the bulge of the Milky Way evolved secularly from the disc, in which case the bulge should be regarded as a pseudo-bulge.

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