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arXiv · 1404.5636

The abundance of Bullet-groups in LCDM

J. G. Fernandez-Trincado·J. E. Forero-Romero·G. Foex·T. Verdugo·V. Motta
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Abstract

We estimate the expected distribution of displacements between the two dominant dark matter (DM) peaks (DM-DM displacements) and between DM and gaseous baryon peak (DM-gas displacements) in dark matter halos with masses larger than $10^{13}$ Msun/h. We use as a benchmark the observation of SL2S J08544-0121, which is the lowest mass system ($1.0\times 10^{14}$ Msun/h) observed so far featuring a bi-modal dark matter distribution with a dislocated gas component. We find that $(50 \pm 10)$% of the dark matter halos with circular velocities in the range 300 km/s to 700 km/s (groups) show DM-DM displacements equal or larger than $186 \pm 30$ kpc/h as observed in SL2S J08544-0121. For dark matter halos with circular velocities larger than 700 km/s (clusters) this fraction rises to 70 $\pm$ 10%. Using the same simulation we estimate the DM-gas displacements and find that 0.1 to 1.0% of the groups should present separations equal or larger than $87\pm 14$kpc/h corresponding to our observational benchmark; for clusters this fraction rises to (7 $\pm$ 3)%, consistent with previous studies of dark matter to baryon separations. Considering both constraints on the DM-DM and DM-gas displacements we find that the number density of groups similar to SL2S J08544-0121 is $\sim 6.0\times 10^{-7}$ Mpc$^{-3}$, three times larger than the estimated value for clusters. These results open up the possibility for a new statistical test of LCDM by looking for DM-gas displacements in low mass clusters and groups.

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J. G. Fernandez-Trincado, J. E. Forero-Romero, G. Foex, T. Verdugo, V. Motta. 2014-06-02. The abundance of Bullet-groups in LCDM. https://doi.org/10.1088/2041-8205%2F787%2F2%2Fl34

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