Spectroscopy of Ultra–steep-Spectrum Radio Sources

Abstract

We present optical spectroscopy of 62 objects selected from several samples of ultraÈsteep-spectrum radio sources. Forty-six of these are from our primary catalog, consisting of 669 sources with radio spectral indices a \ [1.30 this Ðrst spectroscopic subsample was selected on the basis of their faint (S l P la) ; optical and near-IR identiÐcations. Most are identiÐed as narrow-lined radio galaxies with redshifts ranging from z \ 0.25 to z \ 5.19. Ten objects are at z [ 3, nearly doubling the number of such sources known to date. Four of the USS radio sources are identiÐed with quasars, of which at least three have very red spectral energy distributions. The source TN J0936[2242 is identiÐed with an extremely red object (ERO, R[K [ 5) ; both it and a close companion are at z \ 1.479. The spectrum of the ERO closely resembles that of previously discovered radio galaxies at z D 1.5. Five sources show continuum emission, but fail to show any clear emission or absorption features, despite integrations of D1 hr with the Keck telescope. We suggest that these objects could be (1) radio galaxies with faint emission lines in the "" redshift desert ÏÏ at (2) radio galaxies with an obscured active galactic nucleus, which 1.5 [ z [ 2.3, are dominated by a stellar continuum observed with an insufficient signal-to-noise ratio, or (3) pulsars. Three radio sources identiÐed with faint objects in the K-band images remain undetected in 50È90 minute spectroscopic integrations with the Keck telescope, and are possible z [ 7 candidates.

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

“…The SINFONI maps of NVSS J210626-314003 and TXS 2353-003 are shown in Figs (De Breuck et al 2001), but was in hindsight probably affected by a Cosmic ray. We did not identify any possible emission line consistent with the previous redshift z = 2.59, although [OIII]λλ4959, 5007 and Hβ should fall into the H band, and [NII]λλ6548, 6583, and Hα should fall into the K band at that redshift.…”

The environments of Ly α blobs – I. Wide-field Ly α imaging of TN J1338−1942, a powerful radio galaxy at z ≃ 4.1 associated with a giant Ly α nebula★

“…This value roughly corresponds to Ly α luminosities corresponding to the brightest high-redshift radio galaxies (e.g. De Breuck et al 2001;Reuland et al 2003). Equation (2) selects those sources with Ly α excess in the intermediate-band filter, corresponding to an EW of 200 Å ( 40 Å in the rest frame).…”

Witnessing the transformation of a quasar host galaxy at z = 1.6

“…Naturally, this final stage introduces a bias such that radio galaxies which do not have bright emission lines are missing from catalogues of spectroscopically confirmed high-z radio galaxies (e.g. Lacy et al 1999;De Breuck et al 2001;Willott, Rawlings & Blundell 2001 (W01); De Breuck et al 2006;Bryant et al 2009;Filho et al 2011). Radio galaxies which do not show emission lines, even after long spectroscopic integrations at 4-10 m class telescopes, may account for up to 30 per cent of all steep-spectrum high-z radio galaxy candidates (see e.g.…”