scholarly journals The Effect of Drag from the Galactic Hot Halo on the Magellanic Stream and Leading Arm

2011 ◽  
Vol 28 (2) ◽  
pp. 117-127 ◽  
Author(s):  
Jonathan Diaz ◽  
Kenji Bekki
Keyword(s):  
Density Gradient ◽  
Column Density ◽  
Numerical Models ◽  
Neutral Hydrogen ◽  
Magellanic Clouds ◽  
Negative Effects ◽  
Global Properties ◽  
Ram Pressure ◽  
Magellanic Stream ◽  
Drag Term

AbstractWe study the effect of drag induced by the Galactic hot halo on the two neutral hydrogen (HI) cloud complexes associated with the Large and Small Magellanic Clouds: the Magellanic Stream (MS) and the Leading Arm (LA). In particular, we adopt the numerical models of previous studies and re-simulate the tidal formation of the MS and LA with the inclusion of a drag term. We find that the drag has three effects which, although model-dependent, may bring the tidal formation scenario into better agreement with observations: correcting the LA kinematics, reproducing the MS column density gradient, and enhancing the formation of MS bifurcation. We furthermore propose a two-stage mechanism by which the bifurcation forms. In general, the inclusion of drag has a variety of both positive and negative effects on the global properties of the MS and LA, including their on-sky positions, kinematics, radial distances, and column densities. We also provide an argument which suggests that ram-pressure stripping and tidal stripping are mutually exclusive candidates for the formation of the MS and LA.

scholarly journals The Kinematics of the Magellanic Clouds

1995 ◽  
Vol 166 ◽  
pp. 273-282
Author(s):  
B.E. Westerlund
Keyword(s):  
Galactic Halo ◽  
Neutral Hydrogen ◽  
Magellanic Clouds ◽  
Great Promise ◽  
Common Envelope ◽  
The Past ◽  
Ram Pressure ◽  
Long Time ◽  
Magellanic Stream ◽  
Magellanic System

It is essential for our understanding of the evolution of the Magellanic System, comprising the Large and the Small Magellanic Cloud, the Intercloud or Bridge region and the Magellanic Stream, to know its motions in the past. The Clouds have a common envelope of neutral hydrogen; this indicates that they have been bound to each others for a long time. The Magellanic System moves in the gravitational potential of our Galaxy; it is exposed to ram pressure through its movement in the galactic halo. Both effects ought to be noticeable in their present structure and kinematics. It is generally assumed, but not definitely proven, that the Clouds have been bound to our Galaxy for at least the last 7 Gyr. Most models assume that the Clouds lead the Magellanic Stream. The interaction between the Clouds has influenced their structure and kinematics severely. The effects should be possible to trace in the motions of their stellar and gaseous components as pronounced disturbances. Recent astrometric contributions in this field show a great promise for the future if still higher accuracy can be achieved.

scholarly journals THE MAGELLANIC STREAM SYSTEM. I. RAM-PRESSURE TAILS AND THE RELICS OF THE COLLISION BETWEEN THE MAGELLANIC CLOUDS

2015 ◽  
Vol 813 (2) ◽  
pp. 110 ◽  
Author(s):  
F. Hammer ◽  
Y. B. Yang ◽  
H. Flores ◽  
M. Puech ◽  
S. Fouquet
Keyword(s):  
Magellanic Clouds ◽  
Ram Pressure ◽  
Stream System ◽  
Magellanic Stream

scholarly journals The Magellanic Stream: Observational Considerations

1979 ◽  
Vol 84 ◽  
pp. 547-556 ◽  
Author(s):  
D. S. Mathewson ◽  
V. L. Ford ◽  
M. P. Schwarz ◽  
J. D. Murray
Keyword(s):  
Local Group ◽  
Galactic Center ◽  
Neutral Hydrogen ◽  
Great Circle ◽  
Magellanic Clouds ◽  
Systematic Variation ◽  
The Sun ◽  
The South ◽  
The Galaxy ◽  
Magellanic Stream

The Magellanic Stream is an arc of neutral hydrogen which nearly follows a great circle and which contains the Magellanic Clouds - hence its name (Mathewson, Cleary and Murray 1974). This great circle passes within a few degrees of the south galactic pole and lies close to the supergalactic plane. Mathewson and Schwarz (1976) argued that this indicates that the Magellanic Stream and Magellanic Clouds are not bound to the Galaxy. To reinforce this argument, they pointed out that around the supergalactic plane there is a similar systematic variation in the velocities of the Local Group and those of the Stream which may be due to the reflection of the motion of the galactic center if the velocity of rotatior of the Sun is 225 km s−1; if it is 290 km s−1 then the grounds for this argument would disappear.

The Magellanic System

1985 ◽  
Vol 6 (1) ◽  
pp. 104-109 ◽  
Author(s):  
D. S. Mathewson
Keyword(s):  
Globular Clusters ◽  
Neutral Hydrogen ◽  
Close Encounter ◽  
Polar Ring ◽  
Ram Pressure ◽  
Cepheid Variables ◽  
Ultimate Fate ◽  
Magellanic Stream ◽  
Gaseous Halo ◽  
Magellanic System

AbstractThis review concentrates on observations of neutral hydrogen in the Magellanic System, and what they reveal about the structure, dynamics, evolution and ultimate fate of the LMC and SMC. Some recent observations of 161 Cepheid variables in the SMC are used together with the HI observations to determine the geometry of the SMC. These show that it has an amazing depth of at least 30 kpc. To explain the results it is proposed that the SMC had a close encounter with the LMC which has warped the disk of the LMC, produced the bridge between the two galaxies and tidally fissioned the SMC. The SMC is in the process of irreversible disintegration. It is believed that the Magellanic Clouds are not bound to our Galaxy and approached us from the direction of Andromeda. They may have had a close encounter with Andromeda 3 x 109 years ago, which may explain the massive starburst which occurred in the LMC and SMC at that time. It is believed that the Magellanic Stream has been swept out of the inter-Cloud region by the ram pressure of the gaseous halo of our Galaxy. If dynamic friction is sufficient for the Clouds to be captured and to eventually collide with our Galaxy, a polar ring will be formed similar to that observed in some other galaxies. The polar ring of dwarf spheroidals and outlying globular clusters at present encircling our Galaxy may be the remnants of a previous collision with some other galaxy 6 x 109 years ago.

scholarly journals Influence of Gravitational Lensing on Estimates of Ω in Neutral Hydrogen

1996 ◽  
Vol 173 ◽  
pp. 97-98
Author(s):  
Matthias Bartelmann ◽  
Abraham Loeb
Keyword(s):  
Observational Data ◽  
Gravitational Lensing ◽  
Column Density ◽  
Spiral Galaxies ◽  
Neutral Hydrogen ◽  
Absorption Lines ◽  
Gravitational Lenses ◽  
High Column

A wealth of observational data supports the commonly held view that damped Lyman-α (Lyα) absorption in QSO spectra is associated with neutral-hydrogen (HI) disks in spiral galaxies. Most of the HI probed by QSO absorption lines is traced by damped Lyα lines because of their high column densities, N > 1020 cm–2. The spiral galaxies hosting the HI disks can act as gravitational lenses on the QSOs. If the HI column density increases towards the center of the disks, as suggested by observations of local galaxies, the magnification bias preferentially selects for high column-density systems. The estimates of HI in damped Lyα systems can then systematically be distorted by gravitational lensing.

The HRS GTO program to study the neutral hydrogen column density and D/H ratio in the local interstellar medium

1986 ◽  
Vol 6 (2) ◽  
pp. 91-94
Author(s):  
J.L. Linsky, ◽  
W.B. Landsman ◽  
B.D. Savage ◽  
S.R. Heap ◽  
A.M. Smith ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Column Density ◽  
Neutral Hydrogen ◽  
Local Interstellar Medium ◽  
Hydrogen Column Density

scholarly journals How to Model the Chemical Evolution of Galaxies

1993 ◽  
Vol 155 ◽  
pp. 557-566
Author(s):  
Joachim Köppen
Keyword(s):  
Star Formation ◽  
Chemical Evolution ◽  
Time Scale ◽  
Life Time ◽  
Magellanic Clouds ◽  
Formation Time ◽  
List Type ◽  
The Galaxy ◽  
H Ii Region ◽  
Magellanic Stream

For a first interpretation of the comparison of observational data, the crude “Simple Model” of chemical evolution is quite useful. Since it has well been described in the literature (e.g. Pagel and Patchett 1975, Tinsley 1980), let us here just review the assumptions and whether they are satisfied: 1.The galaxy is a closed system, with no exchange of matter with its surroundings: For the solar neighbourhood this probably is not true (the infamous Gdwarf-“problem”, Pagel 1989b). For the Magellanic Clouds this is most certainly wrong, because of the presence of the Inter-Cloud Region and the Magellanic Stream, and evidence for interaction with each other and the Galaxy as well (cf. e.g. Westerlund 1990).2.It initially consists entirely of gas (without loss of generality of primordial composition): This is good approximation also for models with gas infall, as long as the infall occurs with a time scale shorter than the star formation time scale.3.The metal production of the average stellar generation (the yield y) is constant with time: Initially, it is reasonable to make this assumption. For tables of the oxygen yield see Koppen and Arimoto (1991).4.The metal rich gas ejected by the stars is completely mixed with the ambient gas. To neglect the finite stellar life times (“instantaneous recycling approximation”) is appropriate for elements synthesized in stars whose life time is much shorter than the star formation time scale, such as oxygen, neon, sulphur, and argon.5.The gas is well mixed at all times: We don't know. The dispersion of H II region abundances may give an indication. In the Magellanic Clouds Dufour (1984) finds quite a low value (±0.08 dex for oyxgen).

scholarly journals Non-Local Origin of a Substantial Portion of the Soft X-Ray Background

1984 ◽  
Vol 81 ◽  
pp. 204-210
Author(s):  
George W. Clark
Keyword(s):  
Column Density ◽  
Angular Resolution ◽  
General Trend ◽  
Neutral Hydrogen ◽  
Substantial Portion ◽  
X Ray ◽  
Local Origin ◽  
Sky Survey ◽  
Non Local ◽  
X Ray Background

Comparison of the SAS-3 soft X-ray sky survey (F. Marshall and G. Clark 1984) with the 21-cm neutral hydrogen survey of Stark et al. (1984) confirms the well-known anticorrelation between the counting rates in the C-band (0.10-0.28 keV) and the column density of neutral hydrogen, and demonstrates that this anticorrelation is significant on all angular scales ranging from that of the general trend from the galactic equator to the poles down to the angular resolution of the detector (2°.7 FWHM). Included in this general anticorrelation are numerous instances of what appear to be soft X-ray “shadows” of nearby (100-300 pc) 21-cm features, and several bright X-ray regions coincident with “holes” in the ISM.

scholarly journals The Cold Gas Content of Elliptical Galaxies

1996 ◽  
Vol 171 ◽  
pp. 393-393
Author(s):  
W.K. Huchtmeier ◽  
L.J. Sage ◽  
C. Henkel
Keyword(s):  
Molecular Hydrogen ◽  
Neutral Hydrogen ◽  
Elliptical Galaxies ◽  
Radial Velocities ◽  
The Other ◽  
Gas Content ◽  
Global Properties ◽  
Two Samples ◽  
Nearby Galaxies ◽  
Cold Gas

The 100m radiotelescope at Effelsberg has been used to observe two samples of elliptical galaxies in the 21cm line of neutral hydrogen. One sample is defined by the elliptical galaxies in the Revised-Shapely-Ames catalog (RSA) (Huchtmeier 1994, Astron.Astrophys 286, p.389); the other sample is defined by all elliptical galaxies with IRAS 100 μ fluxes ≥ 500mJy north of declination –310 (Huchtmeier, Sage, Henkel 1995 Astron.Astrophys. in press). Among the detected galaxies there are 23 (RSA) and 24 (IRAS) isolated elliptical galaxies free of confusion by nearby galaxies with similar radial velocities. Global properties of these two samples of elliptical galaxies are discussed: their HI-properties, optical and IR luminosities, their optical colors, their masses of dust and of molecular hydrogen.

scholarly journals The response of the H geocorona between 3 and 8 <i>R</i><sub>e</sub> to geomagnetic disturbances studied using TWINS stereo Lyman-<i>α</i> data

2017 ◽  
Vol 35 (1) ◽  
pp. 171-179 ◽  
Author(s):  
Jochen H. Zoennchen ◽  
Uwe Nass ◽  
Hans J. Fahr ◽  
Jerry Goldstein
Keyword(s):  
Solar Minimum ◽  
Column Density ◽  
Geomagnetic Storms ◽  
Neutral Hydrogen ◽  
Wind Pressure ◽  
Time Shift ◽  
Line Center ◽  
Storm Event ◽  
Geomagnetic Disturbances ◽  
Pressure Peak

Abstract. Circumterrestrial Lyman-α column brightness observations from 3–8 Earth radii (Re) have been used to study temporal density variations in the exospheric neutral hydrogen as response to geomagnetic disturbances of different strength, i.e., Dst peak values between −26 and −147 nT. The data used were measured by the two Lyman-α detectors (LAD1/2) onboard both TWINS satellites between the solar minimum of 2008 and near the solar maximum of 2013. The solar Lyman-α flux at 121.6 nm is resonantly scattered near line center by exospheric H atoms and measured by the TWINS LADs. Along a line of sight (LOS), the scattered LOS-column intensity is proportional to the LOS H column density, assuming optically thin conditions above 3 Re. In the case of the eight analyzed geomagnetic storms we found a significant increase in the exospheric Lyman-α flux between 9 and 23 % (equal to the same increase in H column density ΔnH) compared to the undisturbed case short before the storm event. Even weak geomagnetic storms (e.g., Dst peak values  ≥  −41 nT) under solar minimum conditions show increases up to 23 % of the exospheric H densities. The strong H density increase in the observed outer exosphere is also a sign of an enhanced H escape flux during storms. For the majority of the storms we found an average time shift of about 11 h between the time when the first significant dynamic solar wind pressure peak (pSW) hits the Earth and the time when the exospheric Lyman-α flux variation reaches its maximum. The results show that the (relative) exospheric density reaction of ΔnH have a tendency to decrease with increasing peak values of Dst index or the Kp index daily sum. Nevertheless, a simple linear correlation between ΔnH and these two geomagnetic indices does not seem to exist. In contrast, when recovering from the peak back to the undisturbed case, the Kp index daily sum and the ΔnH essentially show the same temporal recovery.

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