Group Galaxies (group + galaxy)

Distribution by Scientific Domains


Selected Abstracts


Unsolved problems in observational astronomy.

ASTRONOMISCHE NACHRICHTEN, Issue 6-8 2004

Abstract We present the highlights of current observational programs in stellar optical spectroscopy carried out with 8-10 m class telescopes as well as with smaller telescopes. Topics discussed include: 1. light elements abundances and their cosmological implications; 2. search for Population III stars and spectroscopy of extremely metal deficient stars; 3. abundances of different stellar populations in the Galaxy; 4. spectroscopy of resolved stars in Local Group galaxies; 5. Li and Be abundances and internal mixing in stars; 6. spectroscopy of very-low mass stars and brown dwarfs; 7. radial velocity search of extrasolar planets; 8. stellar oscillations and asteroseismology; 9. stellar magnetic activity and Doppler imaging of stellar surface features. We also highlight the role that dedicated 1-2 m automatic telescopes with spectroscopic capabilities can play in several fields of stellar optical spectroscopy. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Evolution in the discs and bulges of group galaxies since z= 0.4

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 4 2008
Sean L. McGee
ABSTRACT We present quantitative morphology measurements of a sample of optically selected group galaxies at 0.3 < z < 0.55 using the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) and the gim2d surface brightness fitting software package. The group sample is derived from the Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2) and follow-up Magellan spectroscopy. We compare these measurements to a similarly selected group sample from the Millennium Galaxy Catalogue (MGC) at 0.05 < z < 0.12. We find that, at both epochs, the group and field fractional bulge luminosity (B/T) distributions differ significantly, with the dominant difference being a deficit of disc-dominated (B/T < 0.2) galaxies in the group samples. At fixed luminosity, z= 0.4 groups have ,5.5 ± 2 per cent fewer disc-dominated galaxies than the field, while by z= 0.1 this difference has increased to ,19 ± 6 per cent. Despite the morphological evolution we see no evidence that the group environment is actively perturbing or otherwise affecting the entire existing disc population. At both redshifts, the discs of group galaxies have similar scaling relations and show similar median asymmetries as the discs of field galaxies. We do find evidence that the fraction of highly asymmetric, bulge-dominated galaxies is 6 ± 3 per cent higher in groups than in the field, suggesting there may be enhanced merging in group environments. We replicate our group samples at z= 0.4 and 0 using the semi-analytic galaxy catalogues of Bower et al. This model accurately reproduces the B/T distributions of the group and field at z= 0.1. However, the model does not reproduce our finding that the deficit of discs in groups has increased significantly since z= 0.4. [source]