Fingerprints of the hierarchical building-up of the structure on the gas kinematics of galaxies

Abstract

Context. Recent observational and theoretical works have suggested that the Tully-Fisher relation might be generalised to include dispersion-dominated systems by combining the rotation and dispersion velocity in the definition of the kinematical indicator. Mergers and interactions have been pointed out as responsible of driving turbulent and disordered gas kinematics, which could generate TullyFisher relation outliers. Aims. We investigated the gas kinematics of galaxies by using a simulated sample that includes gas-disc-dominated as well as spheroid-dominated systems. We paid particular attention to the scatter evolution of the Tully-Fisher relation. We also determined the gas-phase velocity indicator, which traces the potential well of the galaxy better. Methods. Cosmological hydrodynamical simulations that include a multiphase model and physically motivated supernova feedback were performed to follow the evolution of galaxies as they are assembled. We analysed the gas kinematics of the surviving gas discs to estimate all velocity indicators. Results. Both the baryonic and stellar Tully-Fisher relations for gas-disc-dominated systems are tight while, as more dispersiondominated systems are included, the scatter increases. We found a clear correlation between σ/V rot and morphology, with dispersiondominated systems exhibiting higher values (>0.7). Mergers and interactions can affect the rotation curves directly or indirectly, inducing a scatter in the Tully-Fisher relation larger than the simulated evolution since z ∼ 3. Kinematical indicators, which combine rotation velocity and dispersion velocity, can reduce the scatter in the baryonic and the stellar mass-velocity relations. In particular, s 1.0 = (V 2 rot + σ 2 ) 0.5 seems to be the best tracer of the circular velocity at larger radii. Our findings also show that the lowest scatter in both relations is obtained if the velocity indicators are measured at the maximum of the rotation curve. Conclusions. In agreement with previous works, we found that the gas kinematics of galaxies is significantly regulated by mergers and interactions, which play a key role in inducing gas accretion, outflows and starbursts. The joint action of these processes within a hierarchical ΛCDM Universe generates a mean simulated Tully-Fisher relation in good agreement with observations since z ∼ 3 but with a scatter depending on morphology. The rotation velocity estimated at the maximum of the gas rotation curve is found to be the best proxy for the potential well regardless of morphology.

Extremely metal-poor galaxies: The H i content

“…As pointed out in Kannappan et al (2002), the dispersion in the TF relation, particularly regarding the dwarf galaxy population, is mainly related to recent perturbations in their evolution, which is consistent with Kassin et al (2007) and de Rossi et al (2012), who argue that the dispersion and residuals correlate with the morphology and kinematical indicators. (2007) to w 50 , assuming a Gaussian shape for the line profile, such that v circ = 1.52 × w 50 /2 (e.g., Gurovich et al 2010).…”

The Sami Galaxy Survey: Galaxy Interactions and Kinematic Anomalies in Abell 119

“…Recently, Cortese et al (2014 found that early-type galaxies exhibit a T-F relation similar to spirals, although with markedly larger scatter. These findings imply that the T-F relation is a general trend in "regular" rotating systems regardless of galaxy morphology, and if dynamical interactions change the angular momentum of galaxies, they introduce scatter in the T-F relation (Kassin et al 2007;Covington et al 2010;De Rossi et al 2012).…”

Formation of S0 galaxies through mergers

“…There are other mechanisms that can lead to the formation of an S0 galaxy, for instance internal secular processes such as bars or strong gas outflows and inflows induced by torques and nuclear activity (Laurikainen et al 2009(Laurikainen et al , 2013De Rossi et al 2012). Furthermore, some studies argue that the mechanisms producing S0 galaxies do not mainly depend on the environment, but on the mass of the galaxy (e.g.…”

“…Conversely, major mergers can transform spiral galaxies initially obeying the TFR into a remnant typically in an outlier location (e.g. Kauffmann et al 1999;Kronberger et al 2007;Covington et al 2010;De Rossi et al 2012). Covington et al (2010) analysed the location of intermediate and advanced stages of major and minor mergers in the stellar TFR, an analogue of the traditional TFR in which the luminosity is replaced by the stellar mass of the galaxy (log(V rot,max ) -M ⋆ ).…”