Interconnection of Cosmic Voids. Daeseong Park & Jounghun Lee! (Seoul National University)

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1 Interconnection of Cosmic Voids Daeseong Park & Jounghun Lee! (Seoul National University)

2 Formation and evolution of cosmic voids Rarefaction due to the self under density Tidal effect from the surrounding matter

3 I. Void Spin Statistics: Is it possible to analytically model the tidal effect on the cosmic voids by using the first principles?

4 Identification of Cosmic Voids Applying the HV02 void-finder algorithm (Hoyle & Vogeley 2002) to the Millennium galaxy catalog (Springel et al. 2005).! a total of voids are identified at z=0.!! Selecting only those voids which contain more than 30 galaxies to measure their spins:! a total of voids are selected

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6 image credit: by Matthias & White

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9 Void Spin-Spin Correlations The spin-spin correlation function is defined as!!! The prediction of the linear tidal torque theory (LTTT)

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11 Discussion and Conclusion I The tidal effect from the surrounding matter distribution on the voids can be quantitatively described by measuring the void spin-spin correlations.! The linear tidal torque theory provides an accurate model for the void spin-spin correlation without any fitting parameter.! It still remains a challenging issue to measure the peculiar velocities of the void galaxies from observations.

12 II. Void-Supercluster Alignments: Is it possible to analytically describe the cross-correlations between the voids and the large scale structures?

13 Void-Supercluster Alignments image credit: Cunnama, Power, Newton and Cui (ICRAR). where y α,y β,y γ are the major,! intermediate and minor! principal axes of the inertia! tensor of the superclusters,! respectively.

14 Prediction of the LTTT The smoothing scale, R, is the minimum Lagrangian radius enclosing the void-! supercluster pair.

15 Identification of Superclusters Applying the friends-of-friends (FoF) algorithm with linking length L=6 h -1 Mpc to the catalog of the clustersized halos with M 1.75x10 13 h -1 M from the Millennium simulations (Springel et al. 2005)! a total of 4014 superclusters are identified! 345 superclusters are found to contain more 5 or more halos! Determining the principal axes of the inertia tensors of the selected superclusters

16 where N po (L) and N sc (L)! are the number of superclusters! found in the random sample! and the Millennium run sample! with the linking length of L,! respectively

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20 Discussion & Conclusion II There are strong cross-correlations between the void spin axes and the minor principal axes of the neighbor superclusters! This result reflects the effect of the large-scale tidal field on the cosmic voids as well as the filamentary cosmic web.! It will be interesting to detect this void-supercluster alignments from observations.! It may provide a new powerful way to constrain the neutrino mass.

21 III. The Bridge Effect of Void Filaments: Can the physical properties of the void galaxies be explained by the bridge effect of void filaments?

22 Identification of Void Filaments Applying the minimal spanning tree (MST) algorithm (Barrow et al. 1985; Colberg 1997) to the galaxies in the voids identified from the Millennium run galaxy catalog: Park & Lee 2007, MNRAS, 400,1105

23 Linearity of a Void Filament The linearity is defined as the end to end distance to the total length:! node!! R L =S/ΣL edge It measures the straightness of a filamentary structure. edge

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26 Cross Correlations between R L and P G Cross-correlations between the linearity of the void filaments and the physical quantity of the void galaxies located in the void filaments considered:! central blackhole mass, stellar mass, star formation rate, total mass, halo mass difference! The linear cross correlation coefficient is calculated as

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28 Interpretation The galaxies contained in more straight void filaments tend to have more massive central blackholes, more stellar masses, and higher star formation rate.!! The more straight filaments in voids supply baryonic gases more efficiently.! Only the void filaments are considered since they are pristine.! It has to be examined whether or not the bridge effect may due to the difference in the formation epochs.! The galaxies in more straight filaments in voids may form more recently.

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30 Future Works It will be necessary to confirm the presence of the bridge effect of void filaments by using hydrodynamic simulations.! It should be also necessary to test the robustness of this result against the void-finding algorithm and the filament-identification scheme.! It will be desirable to have an analytic model for the bridge effect of void filaments! galaxy three point function (?)