mini voids in the local volume
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Mini-voids in the Local Volume. A.Tikhonov , St. Petersburg Univ. I.Karachentsev, SAO RAS RUSSIA. Abstract.

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mini voids in the local volume

Mini-voids in the Local Volume

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

abstract
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.

slide3

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 ΔH/H0 ≈ (25 ± 15)%.

slide5

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.

slide12
The void volumes vs. their ranks (left), and the correlation Gamma-function for 355 galaxies in the Local Volume
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