Evolution of dwarf galaxies: a dynamical perspective

Abstract

For a rotating galaxy, the inner circular-velocity gradient d R V(0) provides a direct estimate of the central dynamical mass density, including gas, stars, and dark matter. We consider 60 low-mass galaxies with high-quality H I and/or stellar rotation curves (including starbursting dwarfs, irregulars, and spheroidals), and estimatewhere R d is the galaxy scale length. For gas-rich dwarfs, we find that V R d /R d correlates with the central surface brightness μ 0 , the mean atomic gas surface density Σ gas , and the star formation rate surface density Σ SFR . Starbursting galaxies, such as blue compact dwarfs (BCDs), generally have higher values of V R d /R d than dwarf irregulars, suggesting that the starburst is closely related to the inner shape of the potential well. There are, however, some "compact" irregulars with values of V R d /R d similar to BCDs. Unless a redistribution of mass takes place, BCDs must evolve into compact irregulars. Rotating spheroidals in the Virgo cluster follow the same correlation between V R d /R d and μ 0 as gasrich dwarfs. They have values of V R d /R d comparable to those of BCDs and compact irregulars, pointing to evolutionary links between these types of dwarfs. Finally, we find that, as for spiral galaxies and massive starbursts, the star-formation activity in dwarfs can be parametrized as Σ SFR = Σ gas /τ orb , where τ orb is the orbital time and 0.02.

The Baryonic Self Similarity of Dark Matter

“…A correlation between the gas content and the structure of the gravitational potential is observed (Alard 2011). This analysis is reinforced by the results of Lelli et al (2013Lelli et al ( , 2014, who find similar results with the additional finding that the structure of the potential is also related to the star formation activity. These observational results show that baryonic process related to stellar formation are responsible for the modification of the gravitational potential.…”

Dynamics of starbursting dwarf galaxies

“…We also derived mean H I surface density profiles binned by the value of the birthrate parameter b (see Table 1), but found no strong relation between b and the shape of the H I surface density profile. The relation between star formation, gas surface density, and internal dynamics is further investigated and discussed in Lelli et al (2014).…”

“…A detailed comparison between the rotation curves of BCDs and Irrs is presented in Lelli et al (2014). Irrs generally have regularly rotating H I disks.…”

“…We also found that complex H I kinematics are much more common in BCDs (∼50%) than in typical Irrs (∼10%), likely due to the effects of stellar feedback and/or of the triggering mechanism (interactions/mergers or disk instabilities). In Lelli et al (2014), we present a comparison between the rotation curves of BCDs and those of Irrs, and discuss the link between the starburst, the gas concentration, and the gravitational potential (see also Lelli et al 2012a,b). Here we compare the baryonic fractions of BCDs with those of gas-rich Irrs and gas-poor spheroidals (Sphs).…”

Dark influences

“…In general many dwarf systems with increased star formation rates (SFR) have been found to be irregular or to show signs of disturbances (Taylor et al 1995;Ekta & Chengalur 2010;López-Sánchez 2010;Holwerda et al 2013;Lelli et al 2014b;Knapen & Cisternas 2015), but in a number of cases no visible companion has been found (Brosch et al 2004;Ekta & Chengalur 2010;López-Sánchez 2010;Lelli et al 2014b). Other possible origins of the increase in star formation and the irregular morphology are cosmological gas inflows (see for example Verbeke et al 2014) or re-accretion of material blown out by previous starbursts, and varying internal instabilities (e.g., Meurer et al 1998;van Zee et al 2001;Lelli et al 2014a;Elmegreen et al 2012;Bekki & Freeman 2002).…”