Minivoids in the Local Volume

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Mini-voids in the Local Volume

• A.Tikhonov, St. Petersburg Univ.
  I.Karachentsev, SAO RAS RUSSIA

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Abstract

• 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
  Mpc3. Besides them, 24 middle-size "bubbles" of
  more than 5 Mpc3 volume are detected, as well as
  52 small "pores".
• The six largest mini-voids 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.

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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). 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 recognize an effect of local
expansion of typical minivoid to be ?H/H0 (25
15).
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Distribution of 355 nearby galaxies within 7.5 Mpc
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Illustration of action of the void-finding
algorithm in a case of 2D point-like
distribution. Seed spheres and voids growing from
them are shown. The numerals indicate the order
of detection of voids from large seed spheres to
smaller ones.
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Distribution of six large mini-voids within the
sphere of radius 7.5 Mpc
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Distribution of two nearest bubbles (N 20 and
18) and four pores within 3 Mpc
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Directions of major axes of 30 voids
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The void volumes vs. their ranks (left), and the
correlation Gamma-function for 355 galaxies in
the Local Volume
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Distribution of nearby galaxies (dots) and voids
(circles) within 25 Mpc
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The same distribution, but in the Galactic
coordinates
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3D distribution of galaxies (dots) and large
voids within 25 Mpc
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The Local (Tully) void
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Galaxies surrounding the Local (Tully) void