Rodriguez Moncada Silvio
Argentina – IATE
On the origin of bulgeless galaxies
Bulgeless galaxies can be difficult to accommodate in a hierarchical formation scenario, like $\Lambda$CDM, where mergers are an important growth mechanism. However, the large amount of observational evidence indicates that these galaxies are common in our universe. We analyse these objects by selecting a sample of galaxies with a negligible spheroidal component from Illustris TNG100, showing that those galaxies also exist in $\Lambda$CDM simulations. Bulgeless galaxies seem to be the tail of a bulge-to-total ratio distribution instead of a different population. We find that the stars of our bulgeless galaxies tend to be younger, and also with higher specific star formation rates, compared to our average disc-like control sample. Also bulgeless galaxies tend to have their major mergers earlier than average disc-like galaxies. Our results seem to indicate that the most important factor that differentiate bulgeless from the average galaxies is in the gas that forms the disc. We notice that bulgeless galaxies have been forming stars aligned with the disc for longer times than for other galaxies. We measure the shape of the group gas at the redshift at which the stars start to form aligned with the disc, and find that the major axis of gas tends to be closer to be perpendicular to the disc angular momentum for bulgeless galaxies than for normal spirals. We also notice that the velocity dispersion perpendicular to the disc is lower for bulgeless galaxies than to their counterpart, and has been low for a longer period of time.