A Strong Dichotomy in S0 Disk Profiles Between the Virgo Cluster and the Field

We report evidence for a striking difference between S0 galaxies in the local field and in the Virgo Cluster. While field S0 galaxies have disks whose surface-brightness profiles are roughly equally divided between the three main types (Types I, II, and III: single-exponential, truncated, and antitruncated), Virgo S0s appear to be entirely lacking in disk truncations. More specifically, the fraction of truncations in S0 galaxies with M_B < -17 is 28% +7/-6% for the field, versus 0% +4/-0% for the Virgo Cluster galaxies; the difference is significant at the 99.7% level. The discrepancy is made up almost entirely by Type I profiles, which are almost twice as frequent in the Virgo Cluster as they are in the field. This suggests that S0 formation may be driven by different processes in cluster and field environments, and that outer-disk effects can be useful tests of S0 formation models.Comment: pdflatex, 6 pages, 3 PDF figures (emulateapj format). To appear in The Astrophysical Journal Letter

Surface photometry and structure of high redshift disk galaxies in the HDF-S NICMOS field

A photometric study of 22 disk galaxies at redshifs z=0.5-2.6 is conducted, using deep NICMOS J and H band and STIS open mode observations of the HDF-S NICMOS parallel field. Rest-frame B-profiles and (U-V) color profiles are constructed. A number of disks show steeper decrease of luminosity than exponential, referring to disk truncation. Shape of the luminosity profiles does not vary with redshift, but galactic sizes decrease significantly. (U-V) colors and color gradients suggest more intense and centrally concentrated star formation at earlier epochs. On the basis of (U-V) color and chemical evolution models, the disks at z~2.5 have formed between z=3.5-7. The studied parameters are idependent of absolute B luminosity within the sample.Comment: 13 pages, 8 figures, Astron. Astrophys. accepte

HST observations of nuclear stellar disks

We present observations of four nearby early-type galaxies with previously known nuclear stellar disks using two instruments on-board the Hubble Space Telescope. We observed NGC4128, NGC4612, and NGC5308 with the Wide Field Planetary Camera 2, and the same three galaxies, plus NGC4570, with the Space Telescope Imaging Spectrograph. We have detected a red nucleus in NGC4128, a blue nucleus in NGC4621, and a blue disk in NGC5308. Additionally, we have discovered a blue disk-like feature with position angle ~15 degrees from the major axis in NGC4621. In NGC5308 there is evidence for a blue region along the minor axis. We discovered a blue transient on the images of NGC4128 at position 0.14" west and 0.32" north from the nucleus. The extracted kinematic profiles belong to two groups: fast (NGC4570 and NGC5308) and kinematically disturbed rotators (NGC4128 and NGC4621). We report the discovery of a kinematically decoupled core in NGC4128. Galaxies have mostly old (10-14 Gyr) stellar populations with large spread in metallicities (sub- to super-solar). We discuss the possible formation scenarios, including bar-driven secular evolution and the influence of mergers, which can explain the observed color and kinematic features.Comment: 22 pages, 14 figures, A&A in pres

Frequency and properties of bars in cluster and field galaxies at intermediate redshifts

We present a study of large-scale bars in field and cluster environments out to redshifts of ~0.8 using a final sample of 945 moderately inclined disk galaxies drawn from the EDisCS project. We characterize bars and their host galaxies and look for relations between the presence of a bar and the properties of the underlying disk. We investigate whether the fraction and properties of bars in clusters are different from their counterparts in the field. The total optical bar fraction in the redshift range z=0.4-0.8 (median z=0.60), averaged over the entire sample, is 25% (20% for strong bars). For the cluster and field subsamples, we measure bar fractions of 24% and 29%, respectively. We find that bars in clusters are on average longer than in the field and preferentially found close to the cluster center, where the bar fraction is somewhat higher (~31%) than at larger distances (~18%). These findings however rely on a relatively small subsample and might be affected by small number statistics. In agreement with local studies, we find that disk-dominated galaxies have a higher optical bar fraction (~45%) than bulge-dominated galaxies (~15%). This result is based on Hubble types and effective radii and does not change with redshift. The latter finding implies that bar formation or dissolution is strongly connected to the emergence of the morphological structure of a disk and is typically accompanied by a transition in the Hubble type. (abridged)Comment: 17 pages, accepted for publication in A&