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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.
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The radio galaxy K-z relation to z ~ 4.5

ArXiv astro-ph/0103364 (2001)

Authors:

Matt J Jarvis, Steve Rawlings, Steve Eales, Katherine M Blundell, Chris J Willott

Abstract:

Using a new radio sample, 6C* designed to find radio galaxies at z > 4 along with the complete 3CRR and 6CE sample we extend the radio galaxy K-z relation to z~4.5. The 6C* K-z data significantly improve delineation of the K-z relation for radio galaxies at high redshift (z > 2). Accounting for non-stellar contamination, and for correlations between radio luminosity and estimates of stellar mass, we find little support for previous claims that the underlying scatter in the stellar luminosity of radio galaxies increases significantly at z > 2. This indicates that we are not probing into the formation epoch until at least z > 3.
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First Results from the 2dF QSO redshift survey

ArXiv astro-ph/0103064 (2001)

Authors:

BJ Boyle, SM Croom, RJ Smith, T Shanks, PJ Outram, F Hoyle, L Miller, NS Loaring

Abstract:

We present some initial results from the 2dF QSO redshift survey. The aim of the survey is to produce an optically-selected catalogue of 25000 QSOs over the redshift range 0
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The 2dF QSO Redshift Survey - 10K@2K!

ArXiv astro-ph/0103056 (2001)

Authors:

T Shanks, BJ Boyle, SM Croom, F Hoyle, N Loaring, L Miller, PJ Outram, RJ Smith

Abstract:

With ~10000 QSO redshifts, the 2dF QSO Redshift Survey (2QZ) is already the biggest individual QSO survey. The aim for the survey is to have ~25000 QSO redshifts, providing an order of magnitude increase in QSO clustering statistics. We first describe the observational parameters of the 2dF QSO survey. We then describe several highlights of the survey so far; we present new estimates of the QSO luminosity function and the QSO correlation function. We also present the first estimate of the QSO power spectrum from the 2QZ catalogue, probing the form of the fluctuation power-spectrum out to the \~1000h-1Mpc scales only previously probed by COBE. We find a power spectrum which is steeper than the prediction of standard CDM and more consistent with the prediction of Lambda-CDM. The best-fit value for the power spectrum shape parameter for a range of cosmologies is Gamma=0.1+-0.1. Finally, we discuss how the complete QSO survey will be able to constrain the value of Omega_Lambda by combining results from the evolution of QSO clustering and from a geometric test of clustering isotropy.
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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.
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