scholarly journals Interpretation of velocity distribution of the inner regions of the Galaxy

1964 ◽  
Vol 20 ◽  
pp. 195-199 ◽  
Author(s):  
G. de Vaucouleurs
Keyword(s):  
Velocity Distribution ◽  
Spiral Structure ◽  
The Other ◽  
Galactic Centre ◽  
Line Profiles ◽  
Spiral Pattern ◽  
Other Hand ◽  
The Galaxy

I. The large positive and negative velocities in the 21-cm line profiles near the galactic centre have indicated the presence of substantial departures from circular motions in the central parts of the Galaxy. The Leiden astronomers (Oort and Rougoor 1958; Rougoor and Oort 1960) have interpreted these observations in terms of an “expanding arm” at a mean distance of about 3 kpc from the centre. It is not clear how these arms or arcs are related to the regular spiral structure, if the Galaxy is an ordinary spiral similar to M31 as commonly assumed. If, on the other hand, the Galaxy is similar to the SAB(r) or SAB(rs) systems, as suggested by the multiplicity of the spiral pattern discussed in another communication, a different interpretation of the velocity distribution is possible.

Density waves in disk galaxies

1967 ◽  
Vol 31 ◽  
pp. 313-317 ◽  
Author(s):  
C. C. Lin ◽  
F. H. Shu
Keyword(s):  
Mathematical Analysis ◽  
Spiral Structure ◽  
Stellar System ◽  
Collective Modes ◽  
Disk Galaxies ◽  
Spiral Pattern ◽  
Density Waves ◽  
The Galaxy ◽  
Detailed Mathematical Analysis

Density waves in the nature of those proposed by B. Lindblad are described by detailed mathematical analysis of collective modes in a disk-like stellar system. The treatment is centered around a hypothesis of quasi-stationary spiral structure. We examine (a) the mechanism for the maintenance of this spiral pattern, and (b) its consequences on the observable features of the galaxy.

USE OF THE GALAXY AS A TOOL FOR SPATIAL AND TEMPORAL ORIENTATION DURING THE EARLY ISLAMIC PERIOD AND UP TO THE 15TH CENTURY

2021 ◽  
Vol 31 (1) ◽  
pp. 1-44
Author(s):  
Andreas Eckart
Keyword(s):  
Milky Way ◽  
The Other ◽  
Temporal Orientation ◽  
Islamic Period ◽  
Space And Time ◽  
15Th Century ◽  
Other Hand ◽  
The Galaxy ◽  
Early Islamic Period ◽  
Early Islamic

AbstractWe study to what extent the Milky Way was used as an orientation tool at the beginning of the Islamic period covering the 8th to the 15th century, with a focus on the first half of that era. We compare the texts of three authors from three different periods and give detailed comments on their astronomical and traditional content. The text of al-Marzūqī summarises the information on the Milky Way put forward by the astronomer and geographer ʾAbū Ḥanīfa al-Dīnawarī. The text makes it clear that in some areas the Milky Way could be used as a geographical guide to determine the approximate direction toward a region on Earth or the direction of prayer. In the 15th century, the famous navigator Aḥmad b. Māǧid describes the Milky Way in his nautical instructions. He frequently demonstrates that the Milky Way serves as a guidance aid to find constellations and stars that are useful for precise navigation on land and at sea. On the other hand, Ibn Qutayba quotes in his description of the Milky Way a saying from the famous Bedouin poet Ḏū al-Rumma, which is also mentioned by al-Marzūqī. In this saying the Milky Way is used to indicate the hot summer times in which travelling the desert was particularly difficult. Hence, the Milky Way was useful for orientation in space and time and was used for agricultural and navigational purposes.

scholarly journals Distribution of velocity and temperature between concentric rotating cylinders

1935 ◽  
Vol 151 (874) ◽  
pp. 494-512 ◽  
Keyword(s):  
Turbulent Flow ◽  
Velocity Distribution ◽  
The Other ◽  
Momentum Transport ◽  
Rotating Cylinders ◽  
Simultaneous Measurements ◽  
Other Hand ◽  
Vorticity Transport

It is not possible to distinguish between the Momentum Transport and the Vorticity Transport theories of turbulent flow by measurements of the distribution of velocity in a fluid flowing under pressure through pipes or between parallel planes. Only simultaneous measurements of temperature and velocity distribution are capable of distinguishing between the two theories in these cases. On the other hand, it will be seen later that measurements of the distribution of velocity between concentric rotating cylinders are capable of distinguishing between the two theories; in fact the predictions of the two theories in this case are sharply contrasted and mutually exclusive.

scholarly journals The strange case of the peculiar spiral galaxy NGC 5474

2020 ◽  
Vol 634 ◽  
pp. A124 ◽  
Author(s):  
M. Bellazzini ◽  
F. Annibali ◽  
M. Tosi ◽  
A. Mucciarelli ◽  
M. Cignoni ◽  
...  
Keyword(s):  
Old Age ◽  
Spiral Galaxy ◽  
The Other ◽  
Spiral Pattern ◽  
Stellar Content ◽  
Peculiar Star ◽  
Space Telescope ◽  
Stellar Disc ◽  
Star Forming ◽  
The Galaxy

We present the first analysis of the stellar content of the structures and substructures identified in the peculiar star-forming galaxy NGC 5474, based on Hubble Space Telescope resolved photometry from the LEGUS survey. NGC 5474 is a satellite of the giant spiral M 101, and it is known to have a prominent bulge that is significantly off-set from the kinematic centre of the underlying H I and stellar disc. The youngest stars (age ≲ 100 Myr) trace a flocculent spiral pattern extending out to ≳8 kpc from the centre of the galaxy. On the other hand, intermediate-age (age ≳ 500 Myr) and old (age ≳ 2 Gyr) stars dominate the off-centred bulge and a large substructure residing in the south-western part of the disc (SW over-density) and they are not correlated with the spiral arms. The old age of the stars in the SW over-density suggests that this may be another signature of any dynamical interactions that have shaped this anomalous galaxy. We suggest that a fly by with M 101, generally invoked as the origin of the anomalies, may not be sufficient to explain all the observations. A more local and more recent interaction may help to put all the pieces of this galactic puzzle together.

scholarly journals The Milky Way: summary and outlook

1985 ◽  
Vol 106 ◽  
pp. 635-639
Author(s):  
Jeremiah P. Ostriker
Keyword(s):  
Empirical Evidence ◽  
Milky Way ◽  
Oblate Spheroid ◽  
The Other ◽  
Human Thought ◽  
Conspicuous Feature ◽  
Other Hand ◽  
Absorption Of Light ◽  
The Galaxy ◽  
The One

First let me review the historical discussions presented during our symposium: the papers by Paul, Gingerich, Hoskin and Smith. I was greatly impressed by the power of abstract human thought in its confrontation with resistant reality. On the one hand we see again and again extraordinary prescience, where abstract beliefs based on little or no empirical evidence–like the island-universe hypothesis–turn out to be, in their essentials, true. Clearly, we often know more than we know that we know. On the other hand, there are repeated instances of resistance to the most obvious truth due to ingrained beliefs. These may be termed conspiracies of silence. Van Rhijn and Shapley agreed about few things. But one of them was that there was no significant absorption of light in the Galaxy. Yet the most conspicuous feature of the night sky is the Milky Way, and the second most conspicuous feature is the dark rift through its middle. What looks to the most untutored eye like a “sandwich” was modeled as an oblate spheroid. These eminent scientists must have known about the rift, but somehow wished it away in their analyses. I find that very curious. Other examples from earlier times abound. We all know that the Crab supernova was seen from many parts of the globe but, though it was bright enough to be detected by the unaided eye in daylight, its existence was never–so far as we know–recorded in Europe. It did not fit in with the scheme of things, so it was not seen.

Linienprofilanalyse von Röntgen-Weitwinkelreflexen mittels Fourier-Transformation zur Bestimmung von Mikrospannungen und parakristallinen Störungen / Analysis of X-Ray Line Profiles for Microstrains and Paracrystalline Distortions by Fourier Transformation

1974 ◽  
Vol 29 (8) ◽  
pp. 1152-1158 ◽  
Keyword(s):  
Gaussian Distribution ◽  
Fourier Transformation ◽  
The Other ◽  
Line Profiles ◽  
Linear Polyethylene ◽  
X Ray ◽  
Other Hand ◽  
Distortion Analysis ◽  
Diffraction Patterns

Many synthetic and biopolymers are paracrystalline. The same holds for some catalysts, graphites and semiconductors. This can be proved directly by diffraction patterns, the integral widths being proportional to (sin ϑ)2 for the higher orders of reflection of the same net plane. To test this, three orders of reflections must be observable. Warren, on the other hand, has shown that microstrains with a Gaussian distribution can directly be calculated from the line profiles of only two reflections by Fourier-Transformation. His method is expanded here to other types of microstrains and to paracrystalline distortions by carefully taking into account a termination effect. Examples are given for turbostratic graphite, linear polyethylene and annealed polybutene I. They demonstrate how useful this method is for distortion analysis.

scholarly journals CO observations of spiral structure and the lifetime of giant molecular clouds

1979 ◽  
Vol 84 ◽  
pp. 277-283
Author(s):  
N. Z. Scoville ◽  
P. M. Solomon ◽  
D. B. Sanders
Keyword(s):  
Molecular Cloud ◽  
Mass Fraction ◽  
Molecular Clouds ◽  
Spiral Structure ◽  
Large Mass ◽  
Giant Molecular Clouds ◽  
Spiral Pattern ◽  
The Galaxy ◽  
Co Emission ◽  
Co Observations

Observations of CO emission at ℓ=0 to 70°, |b| ≤ 1° are analyzed to give a map of the molecular cloud distribution in the galaxy as viewed from the galactic pole. From the fact that this distribution shows no obvious spiral pattern we conclude that the giant molecular clouds sampled in the CO line are situated in both arm and interarm regions and they must last more than 108 years. A similar age estimate is deduced from the large mass fraction of H2 in the interstellar medium in the interior of the galaxy. An implication of this longevity is that the great masses of these clouds may be accumulated through cloud-cloud collisions of originally smaller clouds.

scholarly journals Theoretical 21-cm line profiles: Comparison with observations

1970 ◽  
Vol 38 ◽  
pp. 391-396 ◽  
Author(s):  
C. Yuan
Keyword(s):  
Galactic Plane ◽  
Density Wave ◽  
Neutral Hydrogen ◽  
Wave Theory ◽  
Line Profiles ◽  
Spiral Pattern ◽  
The Galaxy ◽  
Density Wave Theory ◽  
Good Agreement

In order to make a direct comparison with observations of the 21-cm line of neutral hydrogen, theoretical profiles based on the ideas of the density-wave theory are constructed for a modified Schmidt model of the Galaxy and its theoretical spiral pattern. The comparison has covered galactic longitudes lII = 30° −330° with 10° intervals in the galactic plane. Good agreement is found in most of the above directions.

Investigating the early phase of the galaxy evolution through high-z damped Lyα absorption systems

2019 ◽  
Vol 15 (S341) ◽  
pp. 294-296
Author(s):  
Kazuyuki Ogura ◽  
Tohru Nagao ◽  
Masatoshi Imanishi ◽  
Nobunari Kashikawa ◽  
Yoshiaki Taniguchi ◽  
...  
Keyword(s):  
Physical Properties ◽  
Galaxy Evolution ◽  
Early Phase ◽  
Luminosity Function ◽  
The Other ◽  
Other Hand ◽  
The Galaxy

AbstractWe present the physical properties of Lyα emitters (LAEs) in a “DLA-concentrated regions” where there are 3 or more DLA within (50 Mpc)3 cubic box. We observed LAEs in a DLA-concentrated region at z = 2.3, the J1230+34 field, with Subaru/Suprime-Cam. In the 50 Mpc scale, we found no deferences in properties of LAEs such as Lyα luminosity function in the DLA-concentrated region compared to other fields at similar redshift. On the other hand, we found a ∼10 Mpc scale LAE overdensity around a strong DLA with NHI = 1021.08 cm−2.

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