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RE: The Local Volume
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Title: The Velocity Field of the Local Universe from Measurements of Type Ia Supernovae
Authors: Troels Haugboelle, Steen Hannestad, Bjarne Thomsen, Johan Fynbo, Jesper Sollerman, Saurabh Jha

We present a measurement of the velocity flow of the local universe relative to the CMB rest frame, based on the Jha, Riess & Kirshner (2007) sample of 133 low redshift type Ia supernovae. At a depth of 4500 km/s we find a dipole amplitude of 279 ±68 km/s in the direction (l,b) = (285±18,-10±15), consistent with earlier measurements and with the assumption that the local velocity field is dominated by the Great Attractor region. At a larger depth of 5900 km/s we find a shift in the dipole direction towards the Shapley concentration. We also present the first measurement of the quadrupole term in the local velocity flow at these depths. Finally, we have performed detailed studies based on N-body simulations of the expected precision with which the lowest multipoles in the velocity field can be measured out to redshifts of order 0.1. Our mock catalogues are in good agreement with current observations, and demonstrate that our results are robust with respect to assumptions about the influence of local environment on the type Ia supernova rate.

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Do Galaxies Follow Darwinian Evolution?
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VLT Survey Provides New Insight into Formation of Galaxies

Using VIMOS on ESO's Very Large Telescope, a team of French and Italian astronomers have shown the strong influence the environment exerts on the way galaxies form and evolve. The scientists have for the first time charted remote parts of the Universe, showing that the distribution of galaxies has considerably evolved with time, depending on the galaxies' immediate surroundings. This surprising discovery poses new challenges for theories of the formation and evolution of galaxies.
The 'nature versus nurture' debate is a hot topic in human psychology. But astronomers too face similar conundrums, in particular when trying to solve a problem that goes to the very heart of cosmological theories: are the galaxies we see today simply the product of the primordial conditions in which they formed, or did experiences in the past change the path of their evolution?
In a large, three-year long survey carried out with VIMOS, the Visible Imager and Multi-Object Spectrograph on ESO's VLT, astronomers studied more than 6,500 galaxies over a wide range of distances to investigate how their properties vary over different timescales, in different environments and for varying galaxy luminosities. They were able to build an atlas of the Universe in three dimensions, going back more than 9 billion years.
This new census reveals a surprising result. The colour-density relation, that describes the relationship between the properties of a galaxy and its environment, was markedly different 7 billion years ago. The astronomers thus found that the galaxies' luminosity, their initial genetic properties, and the environments they reside in have a profound impact on their evolution.

"Our results indicate that environment is a key player in galaxy evolution, but there's no simple answer to the 'nature versus nurture' problem in galaxy evolution. They suggest that galaxies as we see them today are the product of their inherent genetic information, evolved over time, as well as complex interactions with their environments, such as mergers" - Olivier Le Fèvre from the Laboratoire d'Astrophysique de Marseille, France, who coordinates the VIMOS VLT Deep Survey team that made the discovery.

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Credit ESA/VLT

Scientists have known for several decades that galaxies in the Universe's past look different to those in the present-day Universe, local to the Milky Way [3]. Today, galaxies can be roughly classified as red, when few or no new stars are being born, or blue, where star formation is still ongoing. Moreover, a strong correlation exists between a galaxy's colour and the environment it resides in: the more sociable types found in dense clusters are more likely to be red than the more isolated ones.
By looking back at a wide range of galaxies of a variety of ages, the astronomers were aiming to study how this peculiar correlation has evolved over time.

"Using VIMOS, we were able to use the largest sample of galaxies currently available for this type of study, and because of the instrument's ability to study many objects at a time we obtained many more measurements than previously possible" - Angela Iovino, from the Brera Astronomical Observatory, Italy, another member of the team.

The team's discovery of a marked variation in the 'colour-density' relationship, depending on whether a galaxy is found in a cluster or alone, and on its luminosity, has many potential implications. The findings suggest for example that being located in a cluster quenches a galaxy's ability to form stars more quickly compared with those in isolation. Luminous galaxies also run out of star-forming material at an earlier time than fainter ones.
They conclude that the connection between galaxies' colour, luminosity and their local environment is not merely a result of primordial conditions 'imprinted' during their formation - but just as for humans, galaxies' relationship and interactions can have a profound impact on their evolution.

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Posts: 131433
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Local Void
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Title: Our CMB Motion: The Role of the Local Void
Authors: R Brent Tully

A database with a high density of accurate distances is used to investigate the contributions to the motion of our Galaxy. It is found that the motion of the Local Group separates remarkably cleanly into 3 components: a large-scale attraction toward structure in the 'Great Attractor' sector, a mid-scale attraction toward the Virgo Cluster, and a local-scale 'repulsion' from the Local Void. These 3 components cause motions of comparable amplitudes and, conveniently, are directed almost orthogonal to one another.

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Nearby Spiral Galaxies
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Title: High Resolution Radio Maps of Four Nearby Spiral Galaxies
Authors: Chao-Wei Tsai (1), Jean L. Turner (1), Sara C. Beck (2), Lucian P. Crosthwaite (3), Paul T. P. Ho (4), David S. Meier (5); ((1) UCLA, (2) Tel Aviv Univ., (3) Northrop Grumman, (4) CfA & ASIAA, (5) NRAO)

Researchers report subarcsecond-resolution VLA imaging of the centres of four nearby spiral galaxies: IC 342, Maffei II, NGC 2903, and NGC 6946. In each galaxy, 7 - 12 compact radio continuum sources were identified within the central 15" x 15". Slightly over half of the compact sources appear to be HII regions with flat or positive spectral indices (alpha > -0.1). The HII regions with rising spectra are optically thick at centimetre wavelengths, and thus dense (n_i ~ 10^4 cm^(-3)) and young. The largest of these HII regions require the excitation of 500 - 800 O stars, within regions of only few parsecs extent. These clusters approach the sizes expected for globular clusters.

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Posts: 131433
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The Local Volume
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Title: Minivoids in the Local Volume
Authors: A. V. Tikhonov, I. D. Karachentsev

We consider a sphere of 7.5 Mpc radius, which contains 355 galaxies with accurately measured distances, to detect the nearest empty volumes. Using a simple void detection algorithm, we found six large (mini)voids in Aquila, Eridanus, Leo, Vela, Cepheus and Octans, each of more than 30 Mpc^3. Besides them, 24 middle-size "bubbles" of more than 5 Mpc^3 volume are detected, as well as 52 small "pores". The six largest minivoids occupy 58% of the considered volume. Addition of the bubbles and pores to them increases the total empty volume up to 75% and 81%, respectively. The detected local voids look like oblong potatoes with typical axial ratios b/a = 0.75 and c/a = 0.62 (in the triaxial ellipsoide approximation). Being arranged by the size of their volume, local voids follow power law of volumes-rankes dependence. A correlation Gamma-function of the Local Volume galaxies follows a power low with a formally calculated fractal dimension D = 1.5. We found that galaxies surrounding the local minivoids do not differ significantly from other nearby galaxies on their luminosity, but have appreciably higher hydrogen mass-to-luminosity ratio and also higher star formation rate. We recognise an effect of local expansion of typical minivoid to be Delta H/H_0~(25+-15)%.

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