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On the origin of the color-magnitude relation in the Virgo Cluster

Astrophysical Journal 551:2 PART 2 (2001)

Authors:

A Vazdekis, H Kuntschner, RL Davies, N Arimoto, O Nakamura, R Peletier

Abstract:

We explore the origin of the color-magnitude relation (CMR) of early-type galaxies in the Virgo Cluster using spectra of very high signal-to-noise ratio for six elliptical galaxies selected along the CMR. The data are analyzed using a new evolutionary stellar population synthesis model to generate galaxy spectra at the resolution given by their velocity dispersions. In particular, we use a new age indicator that is virtually free of the effects of metallicity. We find that the luminosity-weighted mean ages of Virgo ellipticals are greater than ∼8 Gyr and show no clear trend with galaxy luminosity. We also find a positive correlation of metallicity with luminosity, color, and velocity dispersion. We conclude that the CMR is driven primarily by a luminosity-metallicity correlation. However, not all elements increase equally with the total metallicity, and we speculate that the CMR may be driven by both a total metallicity increase and a systematic departure from solar abundance ratios of some elements along the CMR. A full understanding of the role played by the total metallicity, abundance ratios, and age in generating the CMR requires the analysis of spectra of very high quality, such as those reported here, for a larger number of galaxies in Virgo and other clusters.

The 2dF QSO Redshift Survey - V. The 10k catalogue

ArXiv astro-ph/0104095 (2001)

Authors:

SM Croom, RJ Smith, BJ Boyle, T Shanks, NS Loaring, L Miller, IJ Lewis

Abstract:

We present a catalogue comprising over 10000 QSOs covering an effective area of 289.6 sq. degrees, based on spectroscopic observations with the 2-degree Field instrument at the Anglo-Australian Telescope. This catalogue forms the first release of the 2-degree Field QSO Redshift Survey. QSO candidates with 18.25

A measurement of the cosmological mass density from clustering in the 2dF galaxy redshift survey

Nature 410:6825 (2001) 169-173

Authors:

JA Peacock, S Cole, P Norberg, CM Baugh, J Bland-Hawthorn, T Bridges, RD Cannon, M Colless, C Collins, W Couch, G Dalton, K Deeley, R De Propris, SP Driver, G Efstathiou, RS Ellis, CS Frenk, K Glazebrook, C Jackson, O Lahav, I Lewis, S Lumsden, S Maddox, WJ Percival, BA Peterson, I Price, W Sutherland, K Taylor

Abstract:

The large-scale structure in the distribution of galaxies is thought to arise from the gravitational instability of small fluctuations in the initial density field of the Universe. A key test of this hypothesis is that forming superclusters of galaxies should generate a systematic infall of other galaxies. This would be evident in the pattern of recessional velocities, causing an anisotropy in the inferred spatial clustering of galaxies. Here we report a precise measurement of this clustering, using the redshifts of more than 141,000 galaxies from the two-degree-field (2dF) galaxy redshift survey. We determine the parameter β = Ω0.6/b = 0.43 ± 0.07, where Ω is the total mass-density parameter of the Universe and b is a measure of the 'bias' of the luminous galaxies in the survey. (Bias is the difference between the clustering of visible galaxies and of the total mass, most of which is dark.) Combined with the anisotropy of the cosmic microwave background, our results favor a low-density Universe with Ω ≈ 0.3.

A measurement of the cosmological mass density from clustering in the 2dF Galaxy Redshift Survey

Nature 410 (2001) 169-173

Authors:

GB Dalton, J.A. Peacock, S.M. Cole, P. Norberg

Galaxy mapping with the sauron integral-field spectrograph: The star formation history of NGC 4365

Astrophysical Journal 548:1 PART 2 (2001)

Authors:

RL Davies, H Kuntschner, E Emsellem, R Bacon, M Bureau, CM Carollo, Y Copin, BW Miller, G Monnet, RF Peletier, EK Verolme, PT De Zeeuw

Abstract:

We report the first wide-field mapping of the kinematics and stellar populations in the E3 galaxy NGC 4365. The velocity maps extend previous long-slit work. They show two independent kinematic subsystems: the central 300 pc × 700 pc rotates about the projected minor axis, and the main body of the galaxy, 3 kpc × 4 kpc, rotates almost at right angles to this. The line strength maps show that the metallicity of the stellar population decreases from a central value greater than solar to one-half solar at a radius of 2 kpc. The decoupled core and main body of the galaxy have the same luminosity-weighted age, ≈14 Gyr, and the same elevated magnesium-to-iron ratio. The two kinematically distinct components have thus shared a common star formation history. We infer that the galaxy underwent a sequence of mergers associated with dissipative star formation that ended ≳ 12 Gyr ago. The misalignment between the photometric and kinematic axes of the main body is unambiguous evidence of triaxiality. The similarity of the stellar populations in the two components suggests that the observed kinematic structure has not changed substantially in 12 Gyr.