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Pairs, groups and filaments of dwarf galaxies in the nearby Lynx-Cancer void as a reflection of void Dark Matter distribution
Tepliakova A.L.1 , Pustilnik S.A.
1

1

Special Astrophysical Observatory, SAO RAS;

Abstract
The web of the three-dimensional matter distribution in the Universe is well repro duced in the N-b o dy simulations of Dark Matter in voids, alb eit scaled-down (Gottlo eb er et al. 2003). However, observationally, the distribution of real galaxies in voids, exp ected to follow the DM halos distribution, is p o orly known due to lack of information on galaxies in voids in general. In the study the nearby Lynx-Cancer void, we find that dwarf galaxies p opulating this region form correlated stuctures - either pairs, or quasilinear filaments. The latter are suggested recently as "bridges" (Park & Lee 2009), along which the baryon matter can inflow into galaxies formed in a filament and feed their "activity". Voids are a suitable environment to check this mechanism. We present the list of Lynx-Cancer void pairs and probable filaments and some of their relevant parameters, and discuss the p otential of Lynx-Cancer void in studies prop erties of `low-mass' filaments.

Fig. 1: Illustration of DM halo distribution in a slice of 6 Mp c thickness of cub e with a side of 140 Mp c, from the simulation of 10 9 DM particles with Mpart =108 Mo and minimal b ound DM halo mass of 5в1010 Mo (Zhang et al. 2009, arXiv:0906.1654). Filaments are the most striking features.

Fig. 2: Illustration of DM halo distribution in a void with diameter of 30 Mpc, from the simulation of 109 DM particles with Mpart =6в107 Mo and minimal bound DM halo mass of 1.5в109 Mo (Gottloeber et al., 2003, MNRAS). About 400 DM halos with circular velocities Vrot > 20 km s-1 are expected to fill in the void.

The nearby void in Lynx-Cancer
The Lynx-Cancer void is one of the nearest known (Dcenter 14 Mp c, Pustilnik et al. 2003). Ab out 50 dwarf galaxies with absolute magnitudes MB down to ­12.5 are found to date within its b orders (Pustilnik & Tepliakova 2009). Apart the study of individual prop erties of void galaxies, we examine their spatial distribution, aiming to define the main elements. The filaments, exp ected in simulations, emerge clearly. However, the substantial fraction of void galaxies app ears to b e isolated. The total numb er of the void galaxies also app ears larger than exp ected in simulations.

Conclusions
The collected so far sample of low-mass galaxies in the nearby Lynx-Cancer void provides us with a unique opp ortunity to prob e the structure of the DM halo distribution in voids down to masses of 108 M . Thanks to relatively quite environment, the rotation velo cities of void dwarfs should b e go o d indicators of halo virial masses. The planned extension of the void galaxy sample in exp ense of the exp ected new void LSBDs should further increase the value of the sample, esp ecially for the quantitative confrontation of CDM simulations with the real sector of "low-mass" halos.

Fig. 3: The 3D view of the Lynx-Cancer void and the p ositions of luminous galaxies (M B <­19.0) delineating it. The sup ergalactic co ordinate grid (SGX, SGY, SGZ) is in units of km s -1 . Large filled green balls show p ositions of pairs and groups in which at least one `luminous' galaxy enters. Large black filled balls show p ositions of `isolated luminous' galaxies. Each luminous galaxy is joined with three the nearest neighb ours to help eye to feel the void b order. Dwarf galaxies p opulating inside the void are shown by small red squares. The large pink ball shows the conditional void center.

Fig. 4: The 3D view of the filament and pair memb ers (green balls) and isolated (blue) dwarf galaxies in the Lynx-Cancer void. The large red ball shows the p osition of the conditional void center.