scholarly journals Dynamics of galaxy structures in the Local Volume

2014 ◽  
Vol 11 (S308) ◽  
pp. 173-180
Author(s):  
I. D. Karachentsev
Keyword(s):  
Milky Way ◽  
Local Density ◽  
Stellar Mass ◽  
Nearby Galaxy ◽  
Mass Ratio ◽  
Local Volume ◽  
Orbital Masses ◽  
The Galaxy ◽  
The Mean

AbstractI consider a sample of ‘Updated Nearby Galaxy Catalog’ that contains eight hundred objects within 11 Mpc. Environment of each galaxy is characterized by a tidal index Θ1 depending on separation and mass of the galaxy Main Disturber (=MD). The UNGC galaxies with a common MD are ascribed to its ‘suite’ and ranked according to their Θ1. Fifteen the most populated suites contain more than half of the UNGC sample. The fraction of MDs among the brightest galaxies is almost 100% and drops to 50% at M_B = -18 mag. The observational properties of galaxies accumulated in UNGC are used to derive orbital masses of giant galaxies via motions of their satellites. The average orbital-to-stellar mass ratio for them is MorbM* ≃ 30, corresponding to the mean local density of matter Ωm ≃ 0.09, i.e 1/3 of the global cosmic one. The dark-to-stellar mass ratio for the Milky Way and M31 is typical for other neighboring giant galaxies.

scholarly journals The Sheet of Giants: Unusual properties of the Milky Way’s immediate neighbourhood

2020 ◽  
Vol 494 (2) ◽  
pp. 2600-2617 ◽  
Author(s):  
Maria K Neuzil ◽  
Philip Mansfield ◽  
Andrey V Kravtsov
Keyword(s):  
Milky Way ◽  
Number Density ◽  
Local Volume ◽  
Oblate Ellipsoid ◽  
Galaxy Distribution ◽  
Λcdm Model ◽  
The Galaxy ◽  
Nearby Galaxies ◽  
The Mean ◽  
The Impact

ABSTRACT We quantify the shape and overdensity of the galaxy distribution in the ‘Local Sheet’ within a sphere of R = 8 Mpc and compare these properties with the expectations of the ΛCDM model. We measure ellipsoidal axis ratios of c/a ≈ 0.16 and b/a ≈ 0.79, indicating that the distribution of galaxies in the Local Volume can be approximated by a flattened oblate ellipsoid, consistent with the ‘sheet’-like configuration noted in previous studies. In contrast with previous estimates that the Local Sheet has a density close to average, we find that the number density of faint and bright galaxies in the Local Volume is ≈1.7 and ≈5.2 times denser, respectively, than the mean number density of galaxies of the same luminosity. Comparison with simulations shows that the number density contrasts of bright and faint galaxies within 8 Mpc alone make the Local Volume a ≈2.5 σ outlier in the ΛCDM cosmology. Our results indicate that the cosmic neighbourhood of the Milky Way may be unusual for galaxies of similar luminosity. The impact of the peculiar properties of our neighbourhood on the properties of the Milky Way and other nearby galaxies is not yet understood and warrants further study.

scholarly journals Exploring galaxy colour in different environments of the cosmic web with SDSS

2020 ◽  
Vol 498 (4) ◽  
pp. 6069-6082
Author(s):  
Biswajit Pandey ◽  
Suman Sarkar
Keyword(s):  
Local Density ◽  
Stellar Mass ◽  
Sloan Digital Sky Survey ◽  
Local Dimension ◽  
Sky Survey ◽  
The Galaxy ◽  
Colour Distribution ◽  
The Mean ◽  
Red Galaxies

ABSTRACT We analyse a set of volume-limited samples from the Sloan Digital Sky Survey (SDSS) to study the dependence of galaxy colour on different environments of the cosmic web. We measure the local dimension of galaxies to determine the geometry of their embedding environments and find that filaments host a higher fraction of red galaxies than sheets at each luminosity. We repeat the analysis at a fixed density and recover the same trend, which shows that galaxy colours depend on geometry of environments besides local density. At a fixed luminosity, the fraction of red galaxies in filaments and sheets increases with the extent of these environments. This suggests that the bigger structures have a larger baryon reservoir favouring higher accretion and larger stellar mass. We find that the mean colour of the red and blue populations are systematically higher in the environments with smaller local dimension and increases monotonically in all the environments with luminosity. We observe that the bimodal nature of the galaxy colour distribution persists in all environments and all luminosities, which suggests that the transformation from blue to red galaxy can occur in all environments.

scholarly journals ‘Scraggy’ dark haloes around bulge-less spiral

2019 ◽  
Vol 486 (3) ◽  
pp. 3697-3701 ◽  
Author(s):  
I D Karachentsev ◽  
V E Karachentseva
Keyword(s):  
Total Mass ◽  
Spiral Galaxies ◽  
Stellar Mass ◽  
Low Density ◽  
Mean Square ◽  
Velocity Difference ◽  
Orbital Mass ◽  
Local Volume ◽  
The Mean ◽  
K Band

ABSTRACT We use a sample of 220 face-on bulge-less galaxies situated in the low-density environment to estimate their total mass via orbital motions of supposed rare satellites. Our inspection reveals 43 dwarf companions having the mean projected separation of 130 kpc and the mean-square velocity difference of 96 km s−1. For them, we obtain the mean orbital-mass-to-K-band luminosity ratio of 20 ± 3. Seven bulge-less spirals in the Local Volume are also characterized by the low mean ratio, Morb/LK = 22 ± 5. We conclude that bulge-less Sc–Scd–Sd galaxies have poor dark haloes, about two times lower than that of bulgy spiral galaxies of the same stellar mass.

scholarly journals The last breath of the Sagittarius dSph

2020 ◽  
Vol 497 (4) ◽  
pp. 4162-4182 ◽  
Author(s):  
Eugene Vasiliev ◽  
Vasily Belokurov
Keyword(s):  
Milky Way ◽  
Dwarf Galaxy ◽  
3D Structure ◽  
Major Axis ◽  
Final State ◽  
Tidal Forces ◽  
The Galaxy ◽  
The Mean ◽  
Red Clump ◽  
Astrometric Data

ABSTRACT We use the astrometric and photometric data from Gaia Data Release 2 and line-of-sight velocities from various other surveys to study the 3D structure and kinematics of the Sagittarius dwarf galaxy. The combination of photometric and astrometric data makes it possible to obtain a very clean separation of Sgr member stars from the Milky Way foreground; our final catalogue contains 2.6 × 105 candidate members with magnitudes G < 18, more than half of them being red clump stars. We construct and analyse maps of the mean proper motion and its dispersion over the region ∼30 × 12 deg, which show a number of interesting features. The intrinsic 3D density distribution (orientation, thickness) is strongly constrained by kinematics; we find that the remnant is a prolate structure with the major axis pointing at ∼45° from the orbital velocity and extending up to ∼5 kpc, where it transitions into the stream. We perform a large suite of N-body simulations of a disrupting Sgr galaxy as it orbits the Milky Way over the past 2.5 Gyr, which are tailored to reproduce the observed properties of the remnant (not the stream). The richness of available constraints means that only a narrow range of parameters produce a final state consistent with observations. The total mass of the remnant is $\sim \!4\times 10^8\, \mathrm{M}_\odot$, of which roughly a quarter resides in stars. The galaxy is significantly out of equilibrium, and even its central density is below the limit required to withstand tidal forces. We conclude that the Sgr galaxy will likely be disrupted over the next Gyr.

scholarly journals Nonlinear Dynamo in a Disk Galaxy

1993 ◽  
Vol 157 ◽  
pp. 349-353
Author(s):  
A. Poezd ◽  
A. Shukurov ◽  
D.D. Sokoloff
Keyword(s):  
Magnetic Field ◽  
Milky Way ◽  
Dynamo Model ◽  
The Galaxy ◽  
Seed Field ◽  
Andromeda Nebula ◽  
The Mean ◽  
Dynamo Equation ◽  
The Magnetic Field

A nonlinear thin-disk galactic dynamo model based on α-quenching is proposed. Assuming that the mean helicity depends on the magnetic field strength averaged across the disk, we derive a universal form of nonlinearity in the radial dynamo equation. We discuss the evolution of the regular magnetic field in the Milky Way and the Andromeda Nebula. It is argued that the reversals of the regular magnetic field in the Galaxy are a relic inherited from the structure of the seed field. We also briefly discuss the role of the turbulent diamagnetism and the effects of galactic evolution on the dynamo.

scholarly journals Mapping the Hidden Universe: The Galaxy Distribution in the Zone of Avoidance

2000 ◽  
Vol 17 (1) ◽  
pp. 6-12 ◽  
Author(s):  
Renée C. Kraan-Korteweg ◽  
Sebastian Juraszek
Keyword(s):  
Milky Way ◽  
Current Status ◽  
Microwave Background ◽  
Galaxy Distribution ◽  
Velocity Flow ◽  
The Galaxy ◽  
The Mean ◽  
Zone Of Avoidance ◽  
Mean Time ◽  
Great Attractor

AbstractDue to the foreground extinction of the Milky Way, galaxies become increasingly faint as they approach the Galactic Equator creating a ‘zone of avoidance’ (ZOA) in the distribution of optically visible galaxies of about 25%. A ‘whole-sky’ map of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor (GA) region. The current status of deep optical galaxy searches behind the Milky Way and their completeness as a function of foreground extinction will be reviewed. It has been shown that these surveys—which in the mean time cover the whole ZOA (Figure 2)—result in a considerable reduction of the ZOA from extinction levels of AB =1m.0 (Figure 1) to AB =3m.0 (Figure 3). In the remaining, optically opaque ZOA, systematic HI surveys are powerful in uncovering galaxies, as is demonstrated for the GA region with data from the full sensitivity Parkes Multibeam HI survey (300°≤l≤332°, ∣b∣≤5°.5, Figure 4).

scholarly journals A contribution of star-forming clumps and accreting satellites to the mass assembly of z ∼ 2 galaxies

2019 ◽  
Vol 489 (2) ◽  
pp. 2792-2818 ◽  
Author(s):  
A Zanella ◽  
E Le Floc’h ◽  
C M Harrison ◽  
E Daddi ◽  
E Bernhard ◽  
...  
Keyword(s):  
Star Formation ◽  
Star Formation Rate ◽  
Formation Rate ◽  
Stellar Mass ◽  
Mass Ratio ◽  
Star Forming ◽  
Spatially Resolved ◽  
The Galaxy ◽  
Mass Assembly

ABSTRACT We investigate the contribution of clumps and satellites to the galaxy mass assembly. We analysed spatially resolved HubbleSpace Telescope observations (imaging and slitless spectroscopy) of 53 star-forming galaxies at z ∼ 1–3. We created continuum and emission line maps and pinpointed residual ‘blobs’ detected after subtracting the galaxy disc. Those were separated into compact (unresolved) and extended (resolved) components. Extended components have sizes ∼2 kpc and comparable stellar mass and age as the galaxy discs, whereas the compact components are 1.5 dex less massive and 0.4 dex younger than the discs. Furthermore, the extended blobs are typically found at larger distances from the galaxy barycentre than the compact ones. Prompted by these observations and by the comparison with simulations, we suggest that compact blobs are in situ formed clumps, whereas the extended ones are accreting satellites. Clumps and satellites enclose, respectively, ∼20 per cent and ≲80 per cent of the galaxy stellar mass, ∼30 per cent and ∼20 per cent of its star formation rate. Considering the compact blobs, we statistically estimated that massive clumps (M⋆ ≳ 109 M⊙) have lifetimes of ∼650 Myr, and the less massive ones (108 < M⋆ < 109 M⊙) of ∼145 Myr. This supports simulations predicting long-lived clumps (lifetime ≳ 100 Myr). Finally, ≲30 per cent (13 per cent) of our sample galaxies are undergoing single (multiple) merger(s), they have a projected separation ≲10 kpc, and the typical mass ratio of our satellites is 1:5 (but ranges between 1:10 and 1:1), in agreement with literature results for close pair galaxies.

scholarly journals Fluctuations of the Diffuse Galactic Background

1990 ◽  
Vol 139 ◽  
pp. 99-99
Author(s):  
K. Mattila
Keyword(s):  
Milky Way ◽  
Interstellar Matter ◽  
Observational Material ◽  
The Galaxy ◽  
The Mean ◽  
Dust Distribution ◽  
Galactic Background

An analysis of fluctuations in the brightness of the Milky Way using the concept that interstellar matter occurs in the form of discrete clouds was first applied by Ambarzumian (1940, 1944). This theory was formulated in a general way and discussed in great detail in a series of papers by Chandrasekhar and Münch (1950a, 1950b, 1951, 1952), by Münch and Chandrasekhar (1952), and by Limber (1953). More recently Peters (1970) presented an analysis of this kind based on extensive photographic observational material. Although the influence of clumpiness of the dust distribution on the mean integrated starlight was thoroughly discussed in these papers, it has not been properly included in most of the photometric models of the Galaxy. Only the models of Caplan and Grec (1979) and Mattila (1980a, 1980b) incorporate these effects.

scholarly journals A numerical testbed for hypotheses of extraterrestrial life and intelligence

2009 ◽  
Vol 8 (2) ◽  
pp. 121-131 ◽  
Author(s):  
D.H. Forgan
Keyword(s):  
Monte Carlo ◽  
Milky Way ◽  
Extraterrestrial Life ◽  
Extraterrestrial Intelligence ◽  
Stochastic Nature ◽  
The Galaxy ◽  
The Mean ◽  
Biological Attributes ◽  
As If

AbstractThe search for extraterrestrial intelligence (SETI) has been heavily influenced by solutions to the Drake Equation, which returns an integer value for the number of communicating civilizations resident in the Milky Way, and by the Fermi Paradox, glibly stated as: ‘If they are there, where are they?’. Both rely on using average values of key parameters, such as the mean signal lifetime of a communicating civilization. A more accurate answer must take into account the distribution of stellar, planetary and biological attributes in the galaxy, as well as the stochastic nature of evolution itself. This paper outlines a method of Monte Carlo realization that does this, and hence allows an estimation of the distribution of key parameters in SETI, as well as allowing a quantification of their errors (and the level of ignorance therein). Furthermore, it provides a means for competing theories of life and intelligence to be compared quantitatively.

scholarly journals Searching for observational evidence of radial mixing in the Milky Way disk

2012 ◽  
Vol 10 (H16) ◽  
pp. 356-356
Author(s):  
Misha Haywood
Keyword(s):  
Large Scale ◽  
Milky Way ◽  
Theoretical Studies ◽  
Secular Evolution ◽  
Chemical Gradients ◽  
Current State ◽  
The Galaxy ◽  
The Subject ◽  
The Mean ◽  
State Of Affairs

AbstractSecular evolution in disks through angular momentum redistribution of stars induce radial mixing of their orbits. While theoretical studies and simulations now abound on the subject - with various predicted effects: disks growth, flattening of metallicity gradients, possible reversing of the mean age as a function of radius in disk, etc, observational evidences remain sparse. In the Galaxy, possible signatures are searched for in the local distributions of velocities, abundances and ages, or in the variation of large scale chemical gradients with time. I will present the current state of affairs and discuss what kind of evidences is available from data in the Milky Way.

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