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 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 DENIS Observations of Multibeam Galaxies in the Zone of Avoidance

1999 ◽  
Vol 16 (1) ◽  
pp. 42-47 ◽  
Author(s):  
A. Schröder ◽  
R. C. Kraan-Korteweg ◽  
G. A. Mamon
Keyword(s):  
Velocity Field ◽  
Large Scale ◽  
Near Infrared ◽  
Milky Way ◽  
Selection Effects ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
Multi Wavelength ◽  
Zone Of Avoidance ◽  
Fisher Relation

AbstractRoughly 25% of the optical extragalactic sky is obscured by the dust and stars of our Milky Way. Dynamically important structures might still lie hidden in this zone. Various surveys are presently being employed to uncover the galaxy distribution in the Zone of Avoidance (ZOA), but all suffer from (different) limitations and selection effects. We illustrate the promise of using a multi-wavelength approach for extragalactic large-scale studies behind the ZOA, i.e. a combination of three surveys, optical, systematic blind HI and near-infrared (NIR), which will allow the mapping of the peculiar velocity field in the ZOA through the NIR Tully–Fisher relation. In particular, we present here the results of cross-identifying HI-detected galaxies with the DENIS NIR survey, and the use of NIR colours to determine foreground extinctions.

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 Dipole Anisotropy in the Lick galaxy catalogue

1988 ◽  
Vol 130 ◽  
pp. 510-511
Author(s):  
Manolis Plionis
Keyword(s):  
Large Scale ◽  
The South ◽  
Microwave Background ◽  
Cluster Sample ◽  
Cosmological Principle ◽  
The North ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
Apparent Reason

The Shane & Wirtanen (SW) galaxy catalog, as reduced by Seldner et al (SSGP), is used to calculate the dipole vector of the galaxy distribution. The catalogue covers 86% of the North and 53% of the South Galactic cap (totally 8.8 steradians) and contains about 810,000 galaxies binned in 10′ × 10′ cells with magnitude limit mB ∼ 18.8. Dipoles have been found in the IRAS and in an optical catalogue based on the ESO, UGC and MCG catalogues, with average depths of ∼ 100 h−1 and ∼ 50 h−1 Mpc respectively. The direction of these dipoles is consistent with that of the microwave background dipole which means that the structures responsible for the dipole are present within the limits of the shallower catalogue and dominate the large-scale morpology of the galaxy distribution in both catalogues. It can therefore be expected that these structures will be ‘washed out’ by more distant structures dominating the deeper SW catalogue. The characteristic depth of the SW catalogue is 360 h−1 and the median depth of a cluster sample, identified from the SW catalogue by an objective proccedure, is ∼ 180 h−1 Mpc. Even if a dipole is found there is no apparent reason for it to point towards the MWB dipole direction since other galaxy fluctuations, comparable in size with those responsible for the MWB dipole, should be present in the SW catalogue if the Cosmological Principle is relevant on scales traced by the catalogue.

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.

scholarly journals A kinematic confirmation of the hidden Vela supercluster

2019 ◽  
Vol 490 (1) ◽  
pp. L57-L61 ◽  
Author(s):  
Hélène M Courtois ◽  
Renée C Kraan-Korteweg ◽  
Alexandra Dupuy ◽  
Romain Graziani ◽  
Noam I Libeskind
Keyword(s):  
Excellent Agreement ◽  
Mass Concentration ◽  
Large Scale ◽  
Milky Way ◽  
Large Scale Structure ◽  
Peculiar Velocity ◽  
The Galaxy ◽  
Zone Of Avoidance ◽  
First Time ◽  
The Universe

ABSTRACT The Universe region obscured by the Milky Way is very large and only future blind large H i redshift, and targeted peculiar surveys on the outer borders will determine how much mass is hidden there. Meanwhile, we apply for the first time two independent techniques to the galaxy peculiar velocity catalogue CosmicFlows−3 in order to explore for the kinematic signature of a specific large-scale structure hidden behind this zone: the Vela supercluster at cz ∼18 000 km s−1. Using the gravitational velocity and density contrast fields, we find excellent agreement when comparing our results to the Vela object as traced in redshift space. The article provides the first kinematic evidence of a major mass concentration (knot of the Cosmic Web) located in the direction behind Vela constellation, pin pointing that the Zone of Avoidance should be surveyed in detail in the future.

scholarly journals Is the Universe homogeneous?

2011 ◽  
Vol 369 (1957) ◽  
pp. 5115-5137 ◽  
Author(s):  
Roy Maartens
Keyword(s):  
Cosmic Microwave Background ◽  
Light Cone ◽  
Space Time ◽  
Gravity Models ◽  
Microwave Background ◽  
The Past ◽  
Galaxy Distribution ◽  
The Galaxy ◽  
The Universe ◽  
Past Light Cone

The standard model of cosmology is based on the existence of homogeneous surfaces as the background arena for structure formation. Homogeneity underpins both general relativistic and modified gravity models and is central to the way in which we interpret observations of the cosmic microwave background (CMB) and the galaxy distribution. However, homogeneity cannot be directly observed in the galaxy distribution or CMB, even with perfect observations, since we observe on the past light cone and not on spatial surfaces. We can directly observe and test for isotropy, but to link this to homogeneity we need to assume the Copernican principle (CP). First, we discuss the link between isotropic observations on the past light cone and isotropic space–time geometry: what observations do we need to be isotropic in order to deduce space–time isotropy? Second, we discuss what we can say with the Copernican assumption. The most powerful result is based on the CMB: the vanishing of the dipole, quadrupole and octupole of the CMB is sufficient to impose homogeneity. Real observations lead to near-isotropy on large scales—does this lead to near-homogeneity? There are important partial results, and we discuss why this remains a difficult open question. Thus, we are currently unable to prove homogeneity of the Universe on large scales, even with the CP. However, we can use observations of the cosmic microwave background, galaxies and clusters to test homogeneity itself.

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