Journal Article

Kinematically quiet haloes around <i>z</i> ∼ 2.5 radio galaxies. Keck spectroscopy

M. Villar-Martín, J. Vernet, S. di Serego Alighieri, R. Fosbury, A. Humphrey and L. Pentericci

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 346, issue 1, pages 273-294
Published in print November 2003 | ISSN: 0035-8711
Published online November 2003 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1046/j.1365-2966.2003.07090.x
Kinematically quiet haloes around z ∼ 2.5 radio galaxies. Keck spectroscopy

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Abstract

We present the results of the kinematic study of the extended gas in a sample of 10 high-redshift radio galaxies (z∼ 2.5) based on high signal-to-noise ratio Keck II and Very Large Telescope (VLT) long-slit spectroscopy. In addition to the typical high surface brightness kinematically perturbed regions (FWHM and velocity shifts >1000 km s−1), we find in all objects giant low surface brightness haloes that show quieter kinematics with typical emission-line FWHM and velocity shifts of ∼several hundred km s−1.

The giant haloes often extend for more than 100 kpc and sometimes beyond the radio structures. They emit lines other than Lyα (C iv, He ii and N v in some cases), typically found in the spectra of high-redshift active galaxies. Continuum is also often detected. The haloes are enriched with heavy elements at tens of kpc from the active nucleus. Typical Lyα luminosities and surface brightness (within the slit) are in the range 1043−44 erg s−1 and several × 10−17 to −16 erg cm−2 s−1 arcsec−2, respectively. Estimated densities are in the range ∼17–150 cm−3. The quasar continuum is the dominant source of ionization of the quiescent haloes along the radio axis. The implied total quasar ionizing luminosities are in the range ∼several × 1045–1047 erg s−1, in the same range as radio-loud quasars at comparable redshift.

The detection of giant quiescent haloes in all objects suggests that they could be a common ingredient of high-redshift radio galaxies. The radio galaxies seem to be embedded within the haloes. The nature and the origin of the haloes, together with the cosmological implications, are also discussed.

Keywords: galaxies: active; galaxies: formation; galaxies: high-redshift; early Universe

Journal Article.  12758 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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