Colloquium: Dark matter and angular momentum in nearby disc galaxies

© Pavel Mancera Pina

Dark matter and angular momentum are key parameters regulating the evolution of galaxies through cosmic time: they largely control their total mass, size, and morphology. In this thesis, we have exploited exquisite observations and state-of-the-art analysis tools to robustly measure the motions of the cold gas in disc galaxies, which in turn allows us to infer their dark matter and angular momentum.

In the first part of the thesis, we studied six gas-rich ultra-diffuse galaxies (UDGs). UDGs are very peculiar systems: they have similar effective radii as big spirals like the Milky Way but about 1000 times fewer stars, making them very diffuse. We found that our galaxies rotate much slower than other galaxies with similar baryonic mass, making them strong outliers of the baryonic Tully-Fisher relation. Moreover, our UDGs have baryon fractions as high as the cosmological average, and they appear to have dark matter distributions challenging to explain in the Cold Dark Matter model.

In the second part of the thesis, we obtained some of the most detailed measurements of the stellar, gas, and baryonic specific angular momentum of nearby disc galaxies to date. We discovered a new relationship between the baryonic mass, baryonic specific angular momentum, and gas content; this is one of the tightest known scaling relations of disc galaxies.

Finally, in the last part of the thesis, we accurately determined the dark matter content in a sample of nearby galaxies. For the first time, we systematically accounted for the fact that their gaseous discs are not razor-thin but thick and flared, which allowed us to obtain some of the most detailed estimations of the dark matter content in nearby galaxies. We also revisited baryonic and dark matter scaling relations, finding evidence of feedback processes imprinting signatures on them.