Bar pattern speed evolution over the last 7 Gyr^⋆,⋆⋆

¹ Dpto. de Física Teórica y del Cosmos, University of Granada, Facultad de Ciencias (Edificio Mecenas), 18071 Granada, Spain
e-mail: isa@ugr.es
² Instituto Carlos I de Física Teórica y Computación  
³ Instituto de Astrofísica de Canarias, C/ Vía Láctea s/n, 38200 La Laguna, Spain
e-mail: [jalfonso;jairo]@iac.es
⁴ Departamento de Astrofísica, Universidad de La Laguna, C/ Astrofísico Francisco Sánchez, 38205 La Laguna, Spain

Received: 3 November 2011
Accepted: 3 February 2012

Abstract

Context. The tumbling pattern of a bar is the main parameter characterising its dynamics. From numerical simulations, its evolution since bar formation is tightly linked to the dark halo in which the bar is formed through dynamical friction and angular momentum exchange. Observational measurements of the bar pattern speed with redshift can restrict models of galaxy formation and bar evolution.

Aims. We aim to determine for the first time the bar pattern speed evolution with redshift based on morphological measurements.

Methods. We have selected a sample of 44 low-inclination ringed galaxies from the SDSS and COSMOS surveys covering the redshift range 0 < z < 0.8 to investigate the evolution of the bar pattern speed. We derived morphological ratios between the deprojected outer ring radius (R_ring) and the bar size (R_bar). This quantity is related to the parameter ℛ = R_CR/R_bar used for classifiying bars in slow and fast rotators, and allows us to investigate possible differences with redshift.

Results. We obtain a similar distribution of R at all redshifts. We do not find any systematic effect that could be forcing this result.

Conclusions. The results obtained here are compatible with the main bulk of the bar population (~70%) being fast-rotators and with no evolution of the pattern speed with redshift. We argue that if bars are long-lasting structures, the results presented here imply that there has not been a substantial angular momentum exchange between the bar and halo, as predicted by numerical simulations. In consequence, this might imply that the discs of these high surface-brightness galaxies are maximal.