THEHST/ACS COMA CLUSTER SURVEY. VIII. BARRED DISK GALAXIES IN THE CORE OF THE COMA CLUSTER

Abstract

We use high-resolution (∼0. 1) F814W Advanced Camera for Surveys (ACS) images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z ∼ 0.02 to study bars in massive disk galaxies (S0s), as well as low-mass dwarf galaxies in the core of the Coma cluster, the densest environment in the nearby universe. Our study helps to constrain the evolution of bars and disks in dense environments and provides a comparison point for studies in lower density environments and at higher redshifts. Our results are: (1) we characterize the fraction and properties of bars in a sample of 32 bright (M V −18, M * > 10 9.5 M ) S0 galaxies, which dominate the population of massive disk galaxies in the Coma core. We find that the measurement of a bar fraction among S0 galaxies must be handled with special care due to the difficulty in separating unbarred S0s from ellipticals, and the potential dilution of the bar signature by light from a relatively large, bright bulge. The results depend sensitively on the method used: the bar fraction for bright S0s in the Coma core is 50% ± 11%, 65% ± 11%, and 60% ± 11% based on three methods of bar detection, namely, strict ellipse fit criteria, relaxed ellipse fit criteria, and visual classification. (2) We compare the S0 bar fraction across different environments (the Coma core, A901/902, and Virgo) adopting the critical step of using matched samples and matched methods in order to ensure robust comparisons. We find that the bar fraction among bright S0 galaxies does not show a statistically significant variation (within the error bars of ±11%) across environments which span two orders of magnitude in galaxy number density (n ∼ 300-10,000 galaxies Mpc −3 ) and include rich and poor clusters, such as the core of Coma, the A901/902 cluster, and Virgo. We speculate that the bar fraction among S0s is not significantly enhanced in rich clusters compared to low-density environments for two reasons. First, S0s in rich clusters are less prone to bar instabilities as they are dynamically heated by harassment and are gas poor as a result of ram pressure stripping and accelerated star formation. Second, high-speed encounters in rich clusters may be less effective than slow, strong encounters in inducing bars. (3) We also take advantage of the high resolution of the ACS (∼50 pc) to analyze a sample of 333 faint (M V > −18) dwarf galaxies in the Coma core. Using visual inspection of unsharp-masked images, we find only 13 galaxies with bar and/or spiral structure. An additional eight galaxies show evidence for an inclined disk. The paucity of disk structures in Coma dwarfs suggests that either disks are not common in these galaxies or that any disks present are too hot to develop instabilities.

AGN spiral galaxies in groups: effects of bars

“…Andersen (1996) found that the radial distribution of the barred spirals in the Virgo cluster is clearly different than that of the spirals without bars, showing that barred galaxies are more centrally condensed than the unbarred ones. Moreover, observational studies in several galaxy clusters also found an increase in the bar fraction in the dense core of the clusters (Andersen 1996;Barazza et al 2009;Marinova et al 2012). From numerical studies, Byrd & Valtonen (1990) argued that the observed tendency for disk galaxies in the center of rich clusters to be barred is due to the strong tidal field.…”

“…More recently, Marinova et al (2012), using high resolution images from the Hubble Space Telescope ACS Treasury survey of the Coma cluster at z ≈ 0.02, studied bars in the dense core of this cluster. They found a hint of an increase in the mean bar fraction toward the core of the Coma.…”

Secular evolution in disk galaxies

“…It is difficult to test this (for example) by looking for an excess of barred galaxies in dense environments such as the Coma cluster. The reason is that any extra tendency to form bars where there are many galaxy encounters must compete with and may lose out to the stabilizing effects of disk heating (Marinova et al 2012;see Kormendy & Bender 2012 for evidence that disk heating happens even in the Virgo cluster). (d) Occam's razor is a dangerous weapon.…”

Automated bar detection in local disk galaxies from the SDSS

“…If and how the bar fraction evolves across the cosmic time is still under debate (Jogee et al, 2004;Sheth et al, 2008) as well as the exact determination of the dependence of the bar frequency on stellar mass (especially at the faint end of the mass function) and on galaxy environment (Thompson, 1981;Marinova et al, 2012;Skibba et al, 2012;Lansbury et al, 2014;Alonso et al, 2014). For example, Masters et al (2012), Skibba et al (2012), Méndez-Abreu et al (2012), Gavazzi et al (2015) all consistently report a bar fraction that increases with increasing mass.…”