Baryonic clues to the puzzling diversity of dwarf galaxy rotation curves. (arXiv:1911.09116v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Santos_Santos_I/0/1/0/all/0/1">Isabel M.E. Santos-Santos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Navarro_J/0/1/0/all/0/1">Julio F. Navarro</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robertson_A/0/1/0/all/0/1">Andrew Robertson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Benitez_Llambay_A/0/1/0/all/0/1">Alejandro Ben&#xed;tez-Llambay</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Oman_K/0/1/0/all/0/1">Kyle A. Oman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Lovell_M/0/1/0/all/0/1">Mark R. Lovell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Frenk_C/0/1/0/all/0/1">Carlos S. Frenk</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ludlow_A/0/1/0/all/0/1">Aaron D. Ludlow</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fattahi_A/0/1/0/all/0/1">Azadeh Fattahi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ritz_A/0/1/0/all/0/1">Adam Ritz</a>

We use a sample of galaxies with high-quality rotation curves to assess the
role of the luminous component (“baryons”) in the dwarf galaxy rotation curve
diversity problem. As in earlier work, we find that the shape of the rotation
curve correlates with baryonic surface density; high surface density galaxies
have rapidly-rising rotation curves consistent with cuspy cold dark matter
halos, slowly-rising rotation curves (characteristic of galaxies with inner
mass deficits or “cores”) occur only in low surface density galaxies. The
correlation, however, seems too weak in the dwarf galaxy regime to be the main
driver of the diversity. In particular, the observed dwarf galaxy sample
includes “cuspy” systems where baryons are unimportant in the inner regions and
“cored” galaxies where baryons actually dominate the inner mass budget. These
features are important diagnostics of the viability of various scenarios
proposed to explain the diversity, such as (i) baryonic inflows and outflows;
(ii) dark matter self-interactions (SIDM); (iii) variations in the baryonic
acceleration through the “mass discrepancy-acceleration relation” (MDAR); or
(iv) non-circular motions in gaseous discs. A reanalysis of existing data shows
that MDAR does not hold in the inner regions of dwarf galaxies and thus cannot
explain the diversity. Together with analytical modeling and cosmological
hydrodynamical simulations, our analysis shows that each of the remaining
scenarios has promising features, but none seems to fully account for the
observed diversity. The origin of the dwarf galaxy rotation curve diversity and
its relation to the small structure of cold dark matter remains an open issue.

We use a sample of galaxies with high-quality rotation curves to assess the
role of the luminous component (“baryons”) in the dwarf galaxy rotation curve
diversity problem. As in earlier work, we find that the shape of the rotation
curve correlates with baryonic surface density; high surface density galaxies
have rapidly-rising rotation curves consistent with cuspy cold dark matter
halos, slowly-rising rotation curves (characteristic of galaxies with inner
mass deficits or “cores”) occur only in low surface density galaxies. The
correlation, however, seems too weak in the dwarf galaxy regime to be the main
driver of the diversity. In particular, the observed dwarf galaxy sample
includes “cuspy” systems where baryons are unimportant in the inner regions and
“cored” galaxies where baryons actually dominate the inner mass budget. These
features are important diagnostics of the viability of various scenarios
proposed to explain the diversity, such as (i) baryonic inflows and outflows;
(ii) dark matter self-interactions (SIDM); (iii) variations in the baryonic
acceleration through the “mass discrepancy-acceleration relation” (MDAR); or
(iv) non-circular motions in gaseous discs. A reanalysis of existing data shows
that MDAR does not hold in the inner regions of dwarf galaxies and thus cannot
explain the diversity. Together with analytical modeling and cosmological
hydrodynamical simulations, our analysis shows that each of the remaining
scenarios has promising features, but none seems to fully account for the
observed diversity. The origin of the dwarf galaxy rotation curve diversity and
its relation to the small structure of cold dark matter remains an open issue.

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