1711.07985
Declining rotation curves at $z=2$: a natural phenomenon in $\Lambda$CDM cosmology
Teklu, et al
Selecting disk galaxies from the cosmological, hydrodynamical sim Magneticum Pathfinder, show that almost half of the poster child disk galaxies at z=2 show significantly declining rotation curves and low DM fractions, very similar to recently reported observations. These galaxies do not show any anomalous behavior, reside in standard DM haloes and typically grow significantly in mass until z=0, where they span all morphological classes, including disk galaxies matching present day rotation curves and observed DM fractions. The findings demonstrate that declining rotation curves and low DM fractions in rotation dominated galaxies at z=2 appear naturally within the LCDM paradigm and reflect the complex baryonic physics, which plays a role at the peak epoch of SF. In addition, find that dispersion dominated galaxies at z=2, which host a significant gas disk, exhibit similar shaped rotation curves as the disk galaxy population, rendering it difficult to differentiate between these two populations with currently available observation techniques.
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