Galaxies: Lighthouses in the Shoals of Dark Halos

TL;DR

This paper demonstrates that the radius of second turnaround in galaxy halos scales predictably across a wide mass range, providing a useful marker for understanding halo structure and galaxy distribution.

Contribution

It introduces observational evidence that the second turnaround radius scales as predicted over three orders of magnitude in halo mass, linking velocity zones to galaxy morphology.

Findings

Second turnaround radius scales with halo mass from 10^12 to 10^15 M_sun.

Inner zones are gas-poor, outer zones are gas-rich.

Dwarf galaxy numbers are roughly constant per unit halo mass.

Abstract

It is anticipated from hierarchical clustering theory that there are scaling relationships between halos over a wide range of mass. Observationally it can be difficult to identify the markers that characterize these relationships because of the small numbers of visible probes and confusion from contaminants in projection. Nonetheless, in favorable circumstances it is possible to identify a very useful marker: the radius of the caustic at second turnaround. In a few favorable circumstances it is possible to identify the radius of first turnaround, or zero velocity surface about a collapsed region. It will be shown that specifically the radius of second turnaround scales as anticipated over three orders of magnitude in mass from 10^12 to 10^15 M_sun. Halos are characterized by zones of dispersed velocities within the second turnaround caustic and zones of infall between the first and second turnaround radii. The inner zone is populated in the majority by gas poor morphologies and the outer zone is populated in the majority by gas rich morphologies. The numbers of dwarfs within the inner zone is roughly constant per unit halo mass.