Pseudo-bulge
A pseudo-bulge is a disc-shaped bulge in the center of a spiral galaxy that differs from normal bulges .
properties
The following properties diverge between classic bulges and pseudo-bulges:
- Pseudo-bulges are flatter.
- Pseudo-bulges can sometimes show a box-shaped structure , while the classic bulges are always disk-like.
- Pseudo-bulges can contain substructures such as rings, bars or spiral arms ; classic bulges, on the other hand, are always structureless.
- Pseudo-bulges contain more dust .
- Pseudo-bulges sometimes show signs of star formation over the past 100 million years.
- The color index of the pseudo-bulges is blue and supports the assumption that star formation took place in pseudo-bulges recently.
- The pseudo-bulges have a higher metallicity on average .
- The mean age of the stars in pseudo-bulges is slightly lower than that in classical bulges with 10 billion years in the vicinity of the local group .
- The brightness distribution differs through a Sersic index of n ≥ 2 for pseudo-bulges and n ≤ 2 for bulges without overlap.
- The kinematic properties of the two types of bulges differ: the higher speed of the stars in pseudo-bulges leads to greater flattening.
- The ratio of the mass of the central black hole to the luminosity of the bulge shows a different value than that of classical bulges and elliptical galaxies, while the latter are approximately the same.
Emergence
Classical bulges originally emerged as an isolated elliptical galaxy . This could have happened through a monolithic collapse or a merger of smaller galaxies.
In contrast, pseudo-bulges evolved through slow accretion processes in which gases migrated from the disc into the bulge. In galaxies with high redshifts , intense star formation has been observed near the center of galaxies, and gravitational instabilities may have resulted in the transport of matter towards the central black hole.
literature
- M. Fernandez Lorenzo et al .: Are (pseudo) bulges in isolated galaxies actually primordial relics? In: Astrophysics. Solar and Stellar Astrophysics . 2014, arxiv : 1405.3644v1 .
- Kaustubh Vaghmare et al .: A Spitzer Study of Pseudobulges in S0 Galaxies: Secular Evolution of Disks . In: Astrophysics. Solar and Stellar Astrophysics . 2013, arxiv : 1303.6144v2 .
- Ariel Keselman, Adi Nusser: Formation of Galactic Pseudo-bulges via Gas Rich Major Mergers . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1205.2716v1 .
- John C. Barentine, John Kormendy: Two Pseudobulges in the "Boxy Bulge" Galaxy NGC 5746 . In: Astrophysics. Solar and Stellar Astrophysics . 2012, arxiv : 1205.6876v1 .
- Yinghe Zhao: Stellar populations of classical and pseudo-bulges for a sample of isolated spiral galaxies . In: Astrophysics. Solar and Stellar Astrophysics . 2011, arxiv : 1109.4492v1 .