Kinematically quiet haloes around z   2.5 radio galaxies. Keck spectroscopy

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.

Spectroscopy of 7 radio-loud QSOs at 2 < z < 6: giant Lyman α emission nebulae accreting on to host galaxies

“…Also, detection of extended HeII emission tracing the same velocity as Lyman-α, from the Q2222+051 nebula here, and many others (e.g. Villar-Martín et al 2003;Sánchez and Humphrey 2009), suggests the photoionized gas is in HzLAN observed directly, as HI could not backscatter the HeII line in the same way as Lyman-α. And the correlation of Humphrey et al (2007), followed by at least Q0805+046 in this sample, implies that redshifted Lyman-α usually comes (directly) from the near side of the nebulae.…”

“…However, whereas almost all of the radio galaxy nebulae in Villar-Martín et al (2003 and Humphrey et al (2007) show substantial velocity gradients (shears), amounting to ∆(v) = 200-770 km s −1 across the nebular diameter, our 5 RL-QSO nebulae have much flatter velocity profiles (Fig 14). Neither do we find examples of nebulae with more redshifted centres (like Q1425+606 and MRC 1558-003), although such an effect (if limited to a small central area) might have been hidden within the much stronger broad-line emission from the QSOs.…”

“…From their findings the Q2338+042 nebula fits the same pattern as the rest of our sample with a broad FWHM of up to 1300 km s −1 , a small redshift relative to the AGN (∆(v) ∼ 100-200 km s −1 ) and little or no internal velocity gradient. Previously, Villar-Martín et al (2003), performed longslit Keck and VLT spectroscopy of 10 radio galaxies with extensive nebulae (∼ 10-14 arcsec) at 2 < z < 3. The HeII1640 and Lyman-α emission lines gave similar ∆(v) curves, showing velocity shifts across the nebula diameters ranging from near-zero to ≃ 600 km s −1 .…”

“…Ojik et al 1997;Villar-Martín et al 2003;Sánchez and Humphrey 2009) or radio-loud QSOs (e.g. Heckman et al 1991a,b).…”

“…Humphrey et al (2008), with integral-field and long-slit spectroscopy of another HzRG at z = 2.63, found a double set of absorption lines at large blueshifts ≃ 600 and 2000 km s −1 , in Lyman-α and several other lines such as SiIV(1393SiIV( ,1402, again covering the whole emission nebula. Villar-Martín et al (2003), using long-slit spectroscopy (Keck-Low Resolution Imaging Spectrometer, R ≃ 2000) of 10 radio galaxies at 2.2 < z < 3, found the spectra of the giant nebulae to show, in addition to the strong Lyman-α, HeII1640 and in some cases CIV1550 and/or NV1240 emission lines. These nebula lines showed relatively moderate velocity dispersions (FWHM ≃ 250-800 km s −1 ), and in most cases significant velocity shifts of a few hundred km s −1 across the ∼ 100 kpc nebula diameter.…”