Secular Evolution of Galaxies

Abstract

Abstract. New observations in favour of a significant role of secular evolution are reviewed: central star formation boosted in pseudo-bulge barred galaxies, relations between bulge and disk, evidence for rejuvenated bulges. Numerical simulations have shown that secular evolution can occur through a cycle of bar formation and destruction, in which the gas plays a major role. Since bars are weakened or destroyed in gaseous disks, the high frequency of bars observed today requires external cold gas accretion, to replenish the disk and allow a new bar formation. The rate of gas accretion from external filaments is compatible with what is observed in cosmological simulations.Keywords. galaxies: general, galaxies: spiral, galaxies: bulges, galaxies: evolution, galaxies: formation, galaxies: starburst, galaxies: structure Role of secular evolutionSecular evolution is one of the three scenarios for galaxy formation and evolution. In a first one, monolithic collapse, gas clouds in free fall form stars so quickly that the resulting system is ellipsoidal. Disks then form afterward, through gas accretion around these bulges. In a second scenario, hierarchical formation, gas clouds have time to settle in rotating disks through dissipation, and form stars in thin spiral disks, which after several minor mergers, or a major merger, can also result in an ellipsoidal system. The secular evolution scenario also considers that spiral disks form first, then non-axisymmetric waves (bars and spirals) with their associated gravity torques and resonances, drive internal evolution, and in particular mass concentration towards the centre, and formation of bulges from the stellar disk. Spiral disks are continuously replenished through external gas accretion.

Comparison of physical characteristics of mass and luminosity function of disk systems in barred and unbarred spiral galaxies

“…Published Online First: March, 2024 https://doi.org/10.21123/bsj.2024.25401 P-ISSN: 2078-8665 -E-ISSN: 2411-7986 Baghdad Science Journal axial ratios of approximately 0.2, but only a smaller portion, typically less than one-third of the disk, participates in forming bars [1][2][3] . In a modern analysis involving H-band (1.65 μm) images of 186 bright galaxies, 56% were visually categorized as 'strongly barred,' 16% as 'weakly barred,' and 27% as 'unbarred in the near-infrared 4,5 .…”

The Relation between Globular Cluster Systems and Supermassive Black Holes in Spiral Galaxies. III. The Link to the M •–M * Correlation

“…We are in the process of studying the N GC versus M • correlation in all nine spirals with precise black hole measurements within 16 Mpc: NGC 1068, NGC 3368,NGC 4051,NGC 4151,NGC 4258,NGC 4395,NGC 4736,NGC 4826,and NGC 5055, although so far we only have full data sets for NGC 3368, NGC 4258, NGC 4395, NGC 4736, and NGC 4826. The bulge type was not considered when selecting the sample, but with one exception all of them seem to have a pseudobulge (Kormendy et al 2010;Kormendy & Ho 2013;Kormendy 2013), while NGC 4258, NGC 4826, and NGC 5055 may also have a classical bulge. The single exception, NGC 4395, is a pure disk, bulgeless, spiral (Filippenko & Ho 2003;Kormendy & Ho 2013).…”