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We present the results of an optical and near-IR spectroscopic study of giant nebular emission line halos associated with three z > 3 radio galaxies, 4C 41.17, 4C 60.07 and B2 0902+34. Previous deep narrow band Ly-alpha imaging had revealed complex morphologies with sizes up to 100 kpc), possibly connected to outflows and AGN feedback from the central regions. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km/s, and velocity shears that can mostly be interpreted as being due to rotation. The inner regions show shocked cocoons of gas closely associated with the radio lobes. These display disturbed kinematics and have expansion velocities and/or velocity dispersions >1000 km/s. The core region is chemically evolved, and we also find spectroscopic evidence for the ejection of enriched material in 4C 41.17 up to a distance of approximately 60 kpc along the radio-axis. The dynamical structures traced in the Ly-alpha line are, in most cases, closely echoed in the Carbon and Oxygen lines. This shows that the Ly-alpha line is produced in a highly clumped medium of small filling factor, and can therefore be used as a tracer of the dynamics of high-z radio galaxies (HzRGs). We conclude that these HzRGs are undergoing a final jet-induced phase of star formation with ejection of most of their interstellar medium before becoming "red and dead" Elliptical galaxies., Accepted for publication in AJ (June 2007 issue); 24 pages, 12 figures (reduced in size)

PKS 1138-262 is a massive radio galaxy at z = 2.16 surrounded by overdensities of Lya emitters, Ha emitters, EROs and X-ray emitters. Numerous lines of evidence exist that it is located in a forming cluster. We report on Keck spectroscopy of candidate members of this protocluster, including nine of the 18 X-ray sources detected by Pentericci et al. (2002) in this field. Two of these X-ray sources (not counting PKS 1138-262 itself) were previously confirmed to be members of the protocluster; we have discovered that an additional two (both AGN) are members of a filamentary structure, at least 3.5 Mpc in projection, aligned with the radio jet axis, the 150 kpc-sized emission-line halo, and the extended X-ray emission around the radio galaxy. Three of the nine X-ray sources observed are lower redshift AGN, and three are M-dwarf stars., 16 pages, 4 figures, To appear in AJ, September 2005

Accumulating observational evidence for a number of radio galaxies suggests an association between their jets and regions of active star formation. The standard picture is that shocks generated by the jet propagate through an inhomogeneous medium and trigger the collapse of overdense clouds, which then become active star-forming regions. In this contribution, we report on recent hydrodynamic simulations of radiative shock-cloud interactions using two different cooling models: an equilibrium cooling-curve model assuming solar metallicities and a non-equilibrium chemistry model appropriate for primordial gas clouds. We consider a range of initial cloud densities and shock speeds in order to quantify the role of cooling in the evolution. Our results indicate that for moderate cloud densities (>1 cm^{-3}) and shock Mach numbers (0.01 and total H_2 mass fractions of >10^{-5} for the cloud gas. Finally, we compare our results with the observations of jet-induced star formation in ``Minkowski's Object.'' We conclude that its morphology, star formation rate (~ 0.3M_solar/yr) and stellar mass (~ 1.2 x 10^7 M_solar) can be explained by the interaction of a 90,000 km/s jet with an ensemble of moderately dense (~ 10 cm^{-3}), warm (10^4 K) intergalactic clouds in the vicinity of its associated radio galaxy at the center of the galaxy cluster., 30 pages, 7 figures, submitted to Astrophysical Journal

Perhaps as many as 10% of high redshift radio galaxy (HzRG; z > 2) candidates that are selected using an Ultra Steep radio Spectrum (USS) criterion fail to show optical emission (continuum, lines) in deep Keck exposures. Their parent objects are only detected in the near-IR and are probably heavily obscured and/or at very high redshift. To search for signatures of dust and help constrain the nature and redshifts of these ``no-z'' radio galaxies, we have conducted a program of submillimeter and millimeter observations. Here we report the first results of a detailed study of one of these objects, WN J0305+3525. WN J0305+3525 appears associated with a small group of K ~ 21 - 22 objects and is strongly detected at both 850 micron and 1.25 mm. On the basis of its faint K-band magnitude, spectral energy distribution (SED) and other evidence we estimate that the radio galaxy is probably at a redshift z = 3 +/- 1. This would make WN J0305+3525 a radio-loud Hyper Luminous Infrared Galaxy (LFIR ~ 10^13 Lsun) similar to, but more obscured than, other dusty radio galaxies in this redshift range. This, together with the absence of Lya emission and compact (theta < 1.9") radio structure, suggests that WN J0305+3525 is embedded in a very dense, dusty medium and is probably at an early stage of its formation., 13 Pages LaTeX, including 3 Postscript figures

The 352 MHz Westerbork In the Southern Hemisphere (WISH) survey is the southern extension of the WENSS, covering 1.60 sr between -9 < DEC < -26 to a limiting flux density of ~18 mJy (5sigma). Due to the very low elevation of the observations, the survey has a much lower resolution in declination than in right ascension (54" x 54"cosec(DEC)). A correlation with the 1.4 GHz NVSS shows that the positional accuracy is less constrained in declination than in right ascension, but there is no significant systematic error. We present a source list containing 73570 sources. We correlate this WISH catalogue with the NVSS to construct a sample of faint Ultra Steep Spectrum (USS) sources, which is accessible for follow-up studies with large optical telescopes in the southern hemisphere. This sample is aimed at increasing the number of known high redshift radio galaxies to allow detailed follow-up studies of these massive galaxies and their environments in the early Universe., 12 Pages, including 5 PostScript figures. Accepted for publication in Astronomy & Astrophysics. The full WISH catalog with 73570 sources is available from http://www.strw.leidenuniv.nl/wenss/

We present optical and/or near-IR images of 128 ultra steep spectrum (USS) radio sources. Roughly half of the objects are identified in the optical images (R 94% are detected at K 5). The major axes of the identifications in K-band are preferentially oriented along the radio axes, with half of them having compact morphologies. The 22 sources with spectroscopic redshifts and K-band magnitudes follow the K-z relation found from previous radio samples, but with a larger scatter. We argue that this may be due to a dependence of K-magnitude on the radio power, with the highest radio power sources inhabiting the most massive host galaxies. We present a composite K-z diagram of radio-loud and radio-quiet galaxies, selected from the HDF-North and the Hawaii surveys. Out to z ~ 1, the radio-loud galaxies are >~ 2 magnitudes brighter. We argue that this is not due to a contribution from the AGN or emission lines. This difference strongly suggests that radio galaxies pinpoint the most massive systems out to the highest known redshifts, probably due to the mutual correlation of the mass of the galaxy and the radio power on the mass of the central black hole.

We present the results of UV spectropolarimetry (λrest 2000-3000 A) and far-UV spectroscopy (λrest 1500-2000 A) of two low-redshift narrow-line radio galaxies (NLRGs) taken with the Faint Object Spectrograph on board the Hubble Space Telescope (HST). Spectropolarimetry of several NLRGs has shown that, by the presence of broad permitted lines in polarized flux spectrum, they have hidden quasars seen through scattered light. Imaging polarimetry has shown that NLRGs including our targets often have large scattering regions of a few to 10 kpc scale. This has posed a problem concerning the nature of the scatterers in these radio galaxies. Their polarized continuum has the spectral index similar to or no bluer than that of quasars, which favors electrons as the dominant scattering particles. The large scattering region size, however, favors dust scattering because of its higher scattering efficiency compared to electrons. In this paper we investigate the polarized flux spectrum over a wide wavelength range, combining our UV data with previous optical/infrared polarimetry data. We infer that the scattering would be often caused by opaque dust clouds in the NLRGs and this would be part of the reason for the apparently gray scattering. In the high-redshift radio galaxies, these opaque clouds could be the protogalactic subunits inferred to be seen in the HST images. However, we still cannot rule out the possibility of electron scattering, which could imply the existence of a large gas mass surrounding these radio galaxies.

We present rest-frame UV and Lyα images of spatially resolved structures ("hosts") around five high-redshift radio-loud quasars obtained with the WFPC2 camera on the Hubble Space Telescope (HST). The quasars were imaged with the PC1 through the F555W ("V"-band) filter, which at the redshifts of the quasars (2.1 < z < 2.6) have central wavelengths of λrest ≈ 1500-1800 A, and at rest-frame Lyα using appropriately chosen narrowband filters with the WFC2. The objects were selected from ground-based imaging surveys. Those had shown that many radio-loud quasars at high redshift have prominent host galaxies that appeared to have properties similar to those of high-redshift radio galaxies. Our HST observations allow a more detailed investigation of quasar host morphologies and a comparison with similar HST studies of radio galaxies by others. Using several methods to measure and quantify the host properties we find that all five quasars are extended and that this "fuzz" contains ≈5%-40% of the total continuum flux and 15%-65% of the Lyα flux within a radius of about 15. The rest-frame UV luminosities of the hosts are log λPλ ≈ 11.9-12.5 L☉ (assuming no internal dust extinction), comparable to the luminous radio galaxies at similar redshifts and a factor 10 higher than both radio-quiet field galaxies at z ~ 2-3 and the most UV-luminous low-redshift starburst galaxies. The Lyα luminosities of the hosts are log LLyα ≈ 44.3-44.9 ergs s-1, which are also similar to the those of luminous high-redshift radio galaxies and considerably larger than the Lyα luminosities of high-redshift field galaxies. To generate the Lyα luminosities of the hosts would require roughly a few percent of the total observed ionizing luminosity of the quasar. The UV continuum morphologies of the hosts appear complex and knotty at the relatively high surface brightness levels of our exposures (about 24 V mag arcsec-2). In two quasars we find evidence for foreground galaxies that confuse the host galaxy morphologies and that are responsible for some of the perceived radio/optical misalignments observed in ground-based imaging data. We do find good alignment between the extended Lyα and the radio sources, strong evidence for jet-cloud interactions in two cases, again resembling radio galaxies, and what is possibly the most luminous radio-UV synchrotron jet in one of the hosts at z = 2.110. We discuss the significance of jet-cloud collisions in radio-loud quasars and their influence on radio morphologies in the framework of simple orientation-based quasar/radio galaxy unification schemes. Our observations suggest that the host galaxies of radio-loud steep-spectrum quasars are similar to those of radio galaxies and strengthen previous conclusions based on ground-based data that both types of objects are probably members of the same parent population.

We report the discovery of the most distant known active galactic nucleus, the radio galaxy TN J0924-2201 at z=5.19. The radio source was selected from a new sample of ultrasteep spectrum sources, has an extreme radio spectral index α=-1.63, and is identified at near-IR wavelengths with a very faint, K=21.3±0.3 object. Spectroscopic observations show a single emission line at λ~7530 A, which we identify as Lyα. The K-band image, sampling rest-frame U band, shows a multicomponent, radio-aligned morphology, which is typical of lower-redshift radio galaxies. TN J0924-2201 extends the near-IR Hubble, or K-z, relation for powerful radio galaxies to z>5 and is consistent with models of massive galaxies forming at even higher redshifts.

This is the second in a series of papers discussing the radio, optical, and near-IR properties of a large and complete sample of radio sources selected from the Molonglo Reference Catalog (MRC) at 408 MHz. The sample consists of 557 radio sources from the MRC that have S0.408 ≥ 0.95 Jy, -30° 4.860.408>0.5 and linear size l 20 kpc (for H0 = 50 km s-1 Mpc-1; q0 = 0.5).

We present deep near-IR images of high redshift radio galaxies obtained with NIRC on the Keck I telescope. In most cases, the near-IR data sample rest wavelengths at ~4000 Angstroms, free of strong emission lines. At z > 3, the rest frame optical morphologies generally have faint, large-scale emission surrounding multiple components of ~10 kpc size. The brightest of the small knots are often aligned with the radio structures. At z < 3, the morphologies change dramatically, showing single, compact structures without radio-aligned features. The sizes and luminosities of the individual components in the z > 3 radio galaxies are similar to those of the radio-quiet star-forming galaxies discovered at z ~ 3 by the Lyman dropout technique. The rest frame optical colors of the z > 3 radio galaxies are consistent with models in which recent star formation dominates the observed IR light, and in one case (4C 41.17) we have direct spectroscopic evidence for massive star formation (Dey et al. 1997a). Our results suggest that the z > 3 radio galaxies evolve into very massive elliptical galaxies at 2 < z < 3, in qualitative agreement with the hierarchical model of galaxy formation. We also discuss the Hubble diagram of radio galaxies, the possibility of a radio power dependence in the K-z relation, and the implications for radio galaxy formation., Accepted for publication in The Astrophysical Journal; 34 pages including 8 postscript figures; plates 1-4 may be obtained from ftp://bigz.berkeley.edu/pub/nirc/

We present the first results of optical spectropolarimetry of high z radio galaxies performed at the W.M. Keck 10m telescope, and discuss the main implications about the components of the UV continuum and the relation to the Unified Model of radio—loud AGN.

We used the Near Infrared Camera on Keck I to obtain Ks-band images of four candidate high-redshift radio galaxies selected using optical and radio data in the NOAO Deep Wide-Field Survey in Bootes. Our targets have 1.4 GHz radio flux densities greater than 1 mJy, but are undetected in the optical to fainter than 24 Vega mag. Spectral energy distribution fitting suggests that three of these objects are at z > 3, with radio luminosities near the FR-I / FR-II break. The other has photometric redshift 1.2, but may in fact be at higher redshift. Two of the four objects exhibit diffuse morphologies in Ks -band, suggesting that they are still in the process of forming., 25 pages, 8 figures, accepted for publication in AJ; minor changes to match published version

We present the first results of a multiwavelength study of IRAS galaxies with excess radio emission. The sample was selected by cross-correlating the IRAS Faint Source Survey (for |b| ≥ 50°) and the Point Source Catalogue (for 10° < |b| < 50°) with the Texas radio survey. Recent optical (imaging and spectroscopic) and radio (VLA) observations are discussed. These observations will be used to investigate possible connections between radio galaxy activity, star formation and galaxy interactions.

We present results from a Keck optical and near IR spectroscopic study of the giant emission line halos of the z>3 High Redshift Radio Galaxies (HiZRGs) 4C 41.17, 4C 60.07 and B2 0902+34. The outer regions of these halos show quiet kinematics with typical velocity dispersions of a few hundred km∈s-1 and velocity shears consistent with rotation. The inner regions contain shocked, clumpy cocoons of gas closely associated with the radio lobes with disturbed kinematics and expansion velocities and/or velocity dispersions >1000 km∈s-1. We also find evidence for the ejection of chemically enriched material in 4C 41.17 up to a distance of 60 kpc along the radio-axis. We infer that these HiZRGs are undergoing a final jet-induced phase of star formation with the ejection of most of their interstellar medium before evolving to become "red and dead" Elliptical galaxies. © 2007 Springer Science+Business Media B.V.

We present the results of a comprehensive Spitzer survey of 69 radio galaxies across 160% for ~75% the high redshift radio galaxies. As expected from unified models of AGN, the stellar fraction of the rest-frame H-band luminosity has no correlation with redshift, radio luminosity, or rest-frame mid-IR (5um) luminosity. Additionally, while the stellar H-band luminosity does not vary with stellar fraction, the total H-band luminosity anti-correlates with the stellar fraction as would be expected if the underlying hosts of these radio galaxies comprise a homogeneous population. The resultant stellar luminosities imply stellar masses of 10^{11-11.5}Msun even at the highest redshifts. Powerful radio galaxies tend to lie in a similar region of mid-IR color-color space as unobscured AGN, despite the stellar contribution to their mid-IR SEDs at shorter-wavelengths. The mid-IR luminosities alone classify most HzRGs as LIRGs or ULIRGs with even higher total-IR luminosities. As expected, these exceptionally high mid-IR luminosities are consistent with an obscured, highly-accreting AGN. We find a weak correlation of stellar mass with radio luminosity., Comment: 63 pages, 14 figures, accepted for publication in ApJS

We present neutral hydrogen, ultraviolet, optical and near-infrared imaging, and optical spectroscopy, of Minkowski's Object (MO), a star forming peculiar galaxy near NGC 541. The observations strengthen evidence that star formation in MO was triggered by the radio jet from NGC 541. Key new results are the discovery of a 4.9E8 solar mass double HI cloud straddling the radio jet downstream from MO, where the jet changes direction and decollimates; strong detections of MO, also showing double structure, in UV and H-alpha; and numerous HII regions and associated clusters in MO. In UV, MO resembles the radio-aligned, rest-frame UV morphologies in many high redshift radio galaxies (HzRGs), also thought to be caused by jet-induced star formation. MO's stellar population is dominated by a 7.5 Myr-old, 1.9E7 solar mass instantaneous burst, with current star formation rate 0.52 solar masses per year (concentrated upstream from where the HI column density is high). This is unlike the jet-induced star formation in Centaurus A, where the jet interacts with pre-existing cold gas; in MO the HI may have cooled out of a warmer, clumpy intergalactic or interstellar medium as a result of jet interaction, followed by collapse of the cooling clouds and subsequent star formation (consistent with numerical simulations). Since the radio source that triggered star formation in MO is much less luminous, and therefore more common, than powerful HzRGs, and because the environment around MO is not particularly special in terms of abundant dense, cold gas, jet-induced star formation in the early universe might be even more prevalent than previously thought., 52 pages, 15 figures, accepted for publication in ApJ

We have detected CO(4-3) in the z=3.8 radio galaxy 4C 41.17 with the IRAM Interferometer. The CO is in two massive (M_dyn ~ 6 x 10^10 M_Sun) systems separated by 1.8" (13 kpc), and by 400 km/s in velocity, which coincide with two different dark lanes in a deep Ly-alpha image. One CO component coincides with the cm-radio core of the radio galaxy, and its redshift is close to that of the HeII AGN line. The second CO component is near the base of a cone-shaped region southwest of the nucleus, which resembles the emission-line cones seen in nearby AGN and starburst galaxies. The characteristics of the CO sources and their mm/submm dust continuum are similar to those found in ultraluminous IR galaxies and in some high-z radio galaxies and quasars. The fact that 4C 41.17 contains two CO systems is further evidence for the role of mergers in the evolution of galaxies at high redshift., Comment: 5 Pages, including 4 PostScript figures. Accepted for publication in Astronomy & Astrophysics Letters

We present a 1.2 mm (250 GHz) map obtained with MAMBO on the IRAM 30m telescope of the central 25 arcmin^2 of the proto-cluster surrounding the z=4.1 radio galaxy TN J1338-1942. The map reaches a 1sigma sensitivity of 0.6 mJy in the central area, increasing to 1.2 mJy at the edges. We detect 10 candidate mm sources, of which 8 are also detected in a deep VLA 1.4 GHz map and/or a VLT R-band image. Three sources have a flux density S_{1.2 mm}>4.0 mJy, representing a 7sigma overdensity compared to random field surveys, which predict only 1 such source in our map area. We obtained SCUBA/JCMT 850 um and 450 um photometry of six radio/optically identified MAMBO sources, confirming 5 of them with S/N>4. Radio-to-mm and mm-to-submm redshift estimators cannot put strong constraints on the redshifts of these MAMBO sources, but 9 of them are consistent within the uncertainties (mean Delta z=+2.6) with z=4.1. One faint MAMBO source is possibly identified with an extremely red object (R-K=6.1) at a likely spectroscopic redshift z=1.18. The four brightest MAMBO sources are all located north of the radio galaxy, while the densest area of companion Ly-alpha excess and Lyman break galaxies is to the southeast. None of the 14 spectroscopically confirmed Ly-alpha emitters in the MAMBO field are detected at 1.2 mm; their average 1.2 mm flux density is =0.25+-0.24 mJy. If the mm sources lie at z=4.1, none of them show excess Ly-alpha emission in our narrow-band images. Both populations thus show no apparent overlap, possibly due to dust quenching the Ly-alpha emission. If the mm sources are part of the proto-cluster, our results suggest that galaxies with star formation rates of a few 1000 M_{Sun} yr^{-1} could be spread throughout the proto-cluster over projected scales of at least 2 Mpc., Comment: 13 Pages, including 9 PostScript figures. Accepted for publication in Astronomy & Astrophysics

High redshift radio galaxies (HzRGs) are key targets for studies of the formation and evolution of massive galaxies. The role of dust in these processes is uncertain. We have therefore observed the dust continuum emission from a sample of z > 3 radio galaxies with the SCUBA bolometer array. We confirm and strengthen earlier results, that HzRGs are massive starforming systems and that submillimeter detection rate appears to be primarily a strong function of redshift. We also observed HzRG-candidates which have sofar eluded spectroscopic redshift determination. Four of these have been detected, and provide evidence that they may be extremely obscured radio galaxies, possibly in an early stage of their evolution., 6 Pages, including 7 PostScript figures. To appear in the proceedings of the conference "Radio Galaxies: Past, present and future", Leiden, 11-15 Nov 2002, eds. M. Jarvis, et al

We report deep Keck narrow-band Lya images of the luminous z > 3 radio galaxies 4C 41.17, 4C 60.07, and B2 0902+34. The images show giant, 100-200 kpc scale emission line nebulae, centered on these galaxies, which exhibit a wealth of morphological structure, including extended low surface brightness emission in the outer regions, radially directed filaments, cone-shaped structures and (indirect) evidence for extended Lya absorption. We discuss these features within a general scenario where the nebular gas cools gravitationally in large Cold Dark Matter (CDM) halos, forming stars and multiple stellar systems. Merging of these ``building'' blocks triggers large scale starbursts, forming the stellar bulges of massive radio galaxy hosts, and feeds super-massive black holes which produce the powerful radio jets and lobes. The radio sources, starburst superwinds and AGN radiation then disrupt the accretion process limiting galaxy and black hole growth, and imprint the observed filamentary and cone-shaped structures of the Lya nebulae., 36 Pages, including 8 Postscript figures. Accepted for publication in the Astrophysical Journal

We present results of a comprehensive multi-frequency study of the radio galaxy B3 J2330+3927. The 1.9" wide radio source, consisting of 3 components, is bracketed by 2 objects in our Keck K-band image. Optical and near-IR Keck spectroscopy of these two objects yield z=3.087+-0.004. The brightest (K=18.8) object has a standard type II AGN spectrum, and is the most likely location of the AGN, which implies a one-sided jet radio morphology. Deep 113 GHz observations with the IRAM Plateau de Bure Interferometer reveal CO J=4-3 emission, which peaks at the position of the AGN. The CO line is offset by 500 km/s from the systemic redshift of the AGN, but corresponds very closely to the velocity shift of an associated HI absorber seen in Lya. This strongly suggests that both originate from the same gas reservoir surrounding the AGN host galaxy. Simultaneous 230 GHz interferometer observations find a ~3x lower integrated flux density when compared to single dish 250 GHz observations with MAMBO at the IRAM 30m telescope. This can be interpreted as spatially resolved thermal dust emission at scales of 0.5" to 6". Finally, we present a tau 2 radio galaxies observed to date with the WSRT. We present mass estimates for the atomic, neutral, and ionized hydrogen, and for the dust, ranging from M(HI)=2x10^7 M_Sun derived from the associated HI absorber in Lya up to M(H_2)=7x10^{10} M_Sun derived from the CO emission. This indicates that the host galaxy is surrounded by a massive reservoir of gas and dust. The K-band companion objects may be concentrations within this reservoir, which will eventually merge with the central galaxy hosting the AGN., 16 Pages, including 11 PostScript figures. Accepted for publication in Astronomy & Astrophysics

We present a short overview of radio surveys for AGN, including the `complete' flux limited surveys and `filtered' surveys. We also describe our ultra-steep spectrum search for the highest redshift radio galaxies, and our follow-up VLA and ATCA observations of the most distant (z=5.19) and the most luminous z, 6 Pages, including 4 PostScript figures. To appear in IAU Colloq. 184, AGN Surveys, ed. R. F. Green, E. Ye. Khachikian, & D. B. Sanders (San Francisco: ASP), in press

The BIGGEST starbursts at the HIGHEST redshifts are associated with high redshift radio galaxies (HzRGs). They may well mark the beginnings of the most massive galaxies seen today. We review current evidence in support of large scale starbursts in HzRGs, and will discuss recent results of sub-mm observations.

We present optical spectroscopy of 62 objects selected from several samples of ultra steep spectrum (USS) radio sources. 46 of these are from our primary catalog, consisting of 669 sources with radio spectral indices alpha < -1.30 (S_nu ~ nu^alpha); this first spectroscopic sub-sample was selected on the basis of their faint optical and near-IR identifications. Most are identified 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 identified with quasars, of which at least three have very red spectral energy distributions. The source TN J0936-2242 is identified 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~1.5. Five sources show continuum emission, but fail to show any clear emission or absorption features, despite integrations of ~1 h with the Keck telescope. We suggest that these objects could be (i) radio galaxies with faint emission lines in the ``redshift desert'' at 1.5 7 candidates., Comment: 59 Pages, including 59 PostScript figures. Accepted for publication in the Astronomical Journal (March 2001 issue). Tables 5 and 6 will be available in electronic format on the AJ website or upon request

At low redshifts powerful radio sources are uniquely associated with massive galaxies, and are thought to be powered by supermassive black holes. Modern 8m -- 10m telescopes may be used used to find their likely progenitors at very high redshifts to study their formation and evolution.

Since radio sources with Ultra Steep Spectra (USS; alpha 10 mJy and covers virtually the entire sky outside the Galactic plane (|b|>15). For our 2 largest samples, covering declination > -35, we selected only sources with angular sizes Theta < 1'. For 410 sources, we present radio-maps with 0.3" to ~5" resolution from VLA and ATCA observations or from the FIRST survey, which allows the optical identification of these radio sources. We find that the spectral index distribution of 143,000 sources from the WENSS and NVSS consists of a steep spectrum galaxy and a flat spectrum quasar population, with the relative contribution of flat spectrum sources doubling from S_1400 >0.1 Jy to S_1400 >2.5 Jy. The identification fraction of our USS sources on the POSS (R 3) that is selected in a way that does not suffer from dust extinction or any other optical bias [abridged]., Comment: 28 Pages, 12 PostScript figures. Accepted for publication in Astronomy & Astrophysics Supplements. Appendices B, C & D available on http://www.strw.LeidenUniv.nl/~debreuck/papers

High redshift radio galaxies (HzRGs) provide unique targets for the study of the formation and evolution of massive galaxies and galaxy clusters at very high redshifts. We discuss how efficient HzRG samples are selected, the evidence for strong morphological evolution at near-infrared wavelengths, and for jet-induced star formation in the z = 3.800 HzRG 4C41.17.

The high redshift radio galaxy 4C41.17 consists of a powerful radio source in which previous work has shown that there is strong evidence for jet-induced star formation along the radio axis. We argue that nuclear photoionization is not responsible for the excitation of the emission line clouds and we construct a jet-cloud interaction model to explain the major features revealed by the data. The interaction of a high-powered jet with a dense cloud in the halo of 4C41.17 produces shock-excited emission-line nebulosity through ~1000 km/s shocks and induces star formation. The CIII to CIV line ratio and the CIV luminosity emanating from the shock, imply that the pre-shock density in the line-emitting cloud is high enough (~1-10 cm^-3) that shock initiated star formation could proceed on a timescale of order a few x 10^6 yrs, well within the estimated dynamical age of the radio source. Broad (FWHM ~ 100 - 1400 km/s) emission lines are attributed to the disturbance of the gas cloud by a partial bow--shock and narrow emission lines (FWHM ~ 500 - 650 km/s) (in particular CIV) arise in precursor emission in relatively low metallicity gas. The implied baryonic mass ~ 8 \times 10^{10} solar masses of the cloud is high and implies that Milky Way size condensations existed in the environments of forming radio galaxies at a redshift of 3.8. Our interpretation of the data provides a physical basis for the alignment of the radio, emission-line and UV continuum images in some of the highest redshift radio galaxies and the analysis presented here may form a basis for the calculation of densities and cloud masses in other high redshift radio galaxies., Comment: 18 pages, 5 figures; uses astrobib.sty and aaspp4.sty. Better versions of figures available via anonymous from ftp://mso.anu.edu.au:pub/pub/geoff/4C41.17

We have started a search for High Redshift Radio Galaxies (HZRGs) in an area covering 7 sr by selecting a sample of Ultra Steep Spectrum (USS) sources with a low flux density cut-off S(1400 MHz) > 10 mJy and a steep spectral index cut-off of alpha < -1.3 (S ~ nu**alpha) from the WENSS, NVSS and TEXAS surveys. Our first results for 27 sources show that we are almost twice as effective in finding HZRGs than than surveys of relatively bright radio sources with a spectral index cut-off of alpha < -1.0. The redshift distribution is consistent with an extension of the z - alpha relation to alpha < -1.3, but a large fraction of our sample (40%) consists of objects which are too faint to observe with 3-4m class telescopes. Our search is aimed at increasing the number of very high redshift radio galaxies for further detailed studies of the formation and evolution of massive galaxies and their environment.

Spectropolarimetric observations obtained with the W. M. Keck Telescope of the z=3.8 radio galaxy 4C41.17 show that the UV continuum emission from this galaxy, which is aligned with the radio axis, is unpolarized (P[2sigma] < 2.4%). This implies that scattered AGN light, which is generally the dominant contributor to the rest-frame UV emission in z~1 radio galaxies, is unlikely to be a major component of the UV flux from 4C41.17. The spectrum shows absorption lines that are similar to those detected in the spectra of the recently discovered population of star forming galaxies at z~2-3. A galaxian outflow may contribute partially to the low ionization absorption lines; however, the high velocity wings of the high ionization lines are unlikely to be dominated by a galaxian wind since the implied outflow mass is very large. The detection of stellar absorption lines, the shape of the SiIV profile, the unpolarized continuum, the inability of any AGN-related processes to account for the UV flux, and the similarity of the UV continuum spectra of 4C41.17 and the nearby starburst region NGC 1741B1 suggest that the UV light in 4C41.17 is dominated by young stars. If so, the implied star-formation rate is roughly 140-1100Msun/yr. We discuss the possibility that star formation in 4C41.17 was triggered by the radio source. Our data are consistent with the hypothesis that 4C41.17 is undergoing its major epoch of star formation at z~4, and that by z~1 it will have evolved to have spectral and morphological properties similar to those observed in known z~1 powerful radio galaxies., 28 pages (Latex text + figures); Accepted for publication in The Astrophysical Journal (Dec 1, 1997 issue)

We report spectropolarimetric observations obtained with the W.M. Keck Telescope of the high redshift z=1.824 aligned radio galaxy 3C256. Our observations confirm that the spatially extended UV continuum emission from this galaxy is polarized (P_V = 10.9% +/- 0.9%) with the electric vector perpendicular to the aligned radio and optical major axes (PA = 48.0 +/- 2.4 degrees). This strongly suggests that a significant fraction of the rest frame UV continuum emission from the galaxy is not starlight, but is instead scattered light from a powerful AGN which is hidden from our direct view. The narrow emission lines, including MgII, are unpolarized. The percentage polarization of the continuum emission and the polarization position angle are roughly constant as a function of wavelength. The present data do not permit us to discriminate between cool electrons and dust as the origin of the scattering. But scattering by hot (T > 10^7 K) electrons cannot be the dominant process, since such a population would overproduce X-ray emission. A large population of cooler T ~ 10^4 K electrons could be responsible for both the line emission and the scattered light, but would require that the dust to gas ratio in the scattering cones is 0.001 times smaller than that in our Galaxy and would imply that a large fraction of the baryonic mass in the galaxy is in the ionized component of its ISM. Dust scattering is more efficient, but would result in detectable extinction of the emission line spectrum unless the dust distribution is more highly clumped than the line emitting gas. Finally, we detect a strong (EW = 12A) broad (FWHM=6500 km/s) absorption line centered at 1477A. We conclude that the most likely explanation is that the absorption is due to a high velocity BAL cloud near the nucleus of 3C256., Uu-encoded compressed gzip tarfile containing 41 page LaTex file, 10 postscript figs, and AASTex style files. To appear in July 1, 1996 ApJ vol. 465

This is the first in a series of papers discussing the properties of a complete set of radio sources selected near {ital S}{sub 408}=1 Jy. We present optical or infrared identifications for a sample of 452 radio galaxies. The sources were selected from the 408 MHz Molonglo Reference Catalog, restricted only by flux density and position on the sky, as follows: {ital S}{sub 408}{ge}0.95 Jy and {minus}30{degree}{lt}decl. (1950){lt}{minus}20{degree}, and 9{sup h}20{sup m}{lt}R.A.(1950){lt}14{sup h}4{sup m} or 20{sup h}20{sup m}{lt}R.A.(1950){lt}6{sup h}14{sup m}. This complete sample, the MRC/1 Jy survey, contains 558 radio galaxies or quasars, of which six are occulted by bright stars or galaxies and two are multiple confused sources. Of the remaining 550 sources, 527, or 96{percent}, are identified to an {ital r} magnitude of 25, and eight additional sources are identified to {ital K}=19. Of the 17 unocculted objects that remain unidentified, 15 are sources for which we have either poor radio maps or inadequate optical/IR images. This paper presents finding charts and astrometric positions for the 452 sources that are not identified as either quasars or BL Lacertae objects. Magnitudes in the {ital r} passband accurate to typically 0.1 mag are given for 353 of the radio galaxymore » identifications. Redshifts for 268 of the galaxies are also listed; these have been derived from 450 spectroscopic observations. The radio observations, quasar and BL Lac identifications, spectroscopy, and near-IR images will be presented in subsequent papers in this series. {copyright} {ital 1996 The American Astronomical Society.}« less

We report the discovery of a blue, star-forming region in the eastern lobe of the nearby (z=0.0794), classical double-lobed radio galaxy 3C 285. This region is elongated along the radio source axis, and its optical line emission, and possibly its optical continuum emission, appear to be edge-brightened on the side facing the nucleus of 3C 285. We propose that the star formation in this region was triggered by the passage of the radio lobe through a region of dense gas in the intergalactic medium. Our observations add support to models in which powerful radio sources induce star formation through the compression of dense ambient material and are also in agreement with such an interpretation for the alignment effect observed in high-redshift radio galaxies

3C 364 has many of the credentials of a luminous radio galaxy at very high redshift: faint optical magnitude (m R =22), ultrasteep radio spectrum (α=1.29), and apparent multimodal galaxy morphology associated with (but nearly perpendicular to) a small (2″) double radio source. However, our spectroscopy shows it to be at a relatively modest redshift of z=0.917. Its spectrum is dominated by a red stellar continuum and strong [O II] emission. The infrared magnitude of 3C 364 is K=17.27, typical for 3CR and 1 Jy-class radio galaxies at z∼0.9.

VLA radio observations and optical imaging and spectroscopy of the Einstein radio ring 0218+357 are presented. The ring is detected at 22.4 GHz and shows a basically similar structure at 5, 15, and 22.4 GHz. The B component has varied and was about 15 percent brighter in the 8.4 GHz data than in the data of Patnaik et al. (1992). The ring is highly polarized. A weak jetlike feature extending out roughly 2 arcsec to the southeast of component A is detected at 6 cm. The source has amorphous radio structure extending out to about 11 arcsec from the core. For an adopted redshift of 0.68, the extended radio emission is very powerful. The optical spectrum is rather red and shows no strong features. A redshift of about 0.68 is obtained. The identification is a faint compact m(r) about 20 galaxy which extends to about 4.5 arcsec (about 27 kpc). As much as 50 percent of the total light may be due to a central AGN. The observed double core and ring may be produced by an off-center radio core with extended radio structure.

The spatial distributions of thermal emission-line gas and nonthermal radio-emitting plasma in powerful radio galaxies are examined. At high redshifts and luminosities, the thermal gas is distributed very asymmetrically with respect to the galaxy nucleus. The one-sidedness of the emission line regions is clear evidence of an intrinsically asymmetric property of powerful radio sources. The radio sources are more asymmetric in their lobe spacings at high redshifts, but not at a highly significant level

U and B continuum and Ly-alpha images obtained with the UV-flooded TI2 CCD at the prime focus of the 4-m telescope at KPNO during May and November 1988 are reported for 19 radio-loud high-redshift QSOs. The data are presented in extensive contour maps, radial surface-brightness profiles, and tables and discussed in detail. Ly-alpha emission with typical luminosity about 10 to the 44th erg/sec and spatial extent about 100 kpc is spatially resolved in 15 QSOs, and these nebulae are attributed to the photoionization of the interstellar or intergalactic medium of young or proto galaxies by radiation escaping anisotropically along the radio axis of the QSO. The mechanisms possibly responsible for the Ly-alpha emission and for the UV fuzz seen around some of the QSOs are explored. 84 refs.

Using the Video Camera (e.g. Butcher et al. 1980) and the High Gain Video Spectrometer (e.g. Heckman et al. 1981) we are carrying out a program at Kitt Peak to search for optical line emission associated with the jets and lobes of radio galaxies. Several sources have been found in which extended optical line emission is clearly related to the nonthermal radio emission. Some general information on these and a few other sources is summarized in Table 1.

Powerful radio galaxies are unique at the present time in that they have optically resolvable structures that can observed over a range of look-back times comparable to the Hubble time. This allows us to examine how their morphologies evolve with cosmic time in their stellar continuum, thermal line-emitting gas, and non-thermal synchrotron emitting plasmas. The continuum shapes of high redshift radio galaxies become more elongated at high redshift and are closely aligned with their radio source axes. The extended emission line regions were larger and more luminous in the past and they too are well aligned with their radio source axes. Finally, the radio sources themselves were more asymmetric in the past both in terms of their structures and in the flux densities, spectral indices and polarization of the diffuse lobes.

Optical and radio observations of nearby and distant powerful radio galaxies with extended optical emission-line regions are discussed. Comparisons of optical emission-line images with radio continuum maps, supplemented with detailed optical spectroscopy, show that the interaction of radio jets and lobes with ambient gas can have dramatic consequences for both the radio source and its surrounding medium. We will discuss evidence for the occurence of large scale star formation and collimated ionizing radiation along the axes of radio galaxies. We also present preliminary results indicative of large rotation measures in two distant radio galaxies.

Optical and radio observations of nearby and distant powerful radio galaxies with extended optical emission-line regions are reviewed. Comparisons of optical emission-line images with radio continuum maps, supplemented with detailed optical spectroscopy, show that the interaction of radio jets and hot spots with ambient gas can have dramatic consequences for both the radio source and its surrounding medium. I will discuss evidence for the deflection and decollimation of (low power) jets, gas entrainment by jets and hot spots, Faraday depolarization/rotation near regions of dense ionized gas, enhanced star formation along radio source trajectories, and collimated ionizing radiation from radio galaxy nuclei.

We report on the results of long-slit spectroscopy and interference filter imaging of powerful 3CR radio galaxies. Narrow-band [OII]A3727 imaging often reveals extensive regions of extranuclear emission associated with these objects. The extended [OII] emission is distributed on scales of several tens of kpc, it is often more luminous than the nuclear emission, and shows large velocity gradients. We discuss the physical conditions in these nebulae and their relation to the radio source structure. In particular, we examine the ionization mechanism for the gas, and find that photoionization models reproduce the observed emission line strengths reasonably well. The source of the ionizing photons, however, is not clear; the large luminosities of the extended gas suggesting that some form of in situ ionization may be occurring. Compared to the low-z cooling flow filaments, the 3CR emission regions are larger, more luminous, and generally show higher excitation. Futhermore, the distant radio galaxies show evidence for much stronger interactions with their radio sources than is seen in nearby cooling flow filaments.

The occurence of extended optical emission-line regions in many, relatively nearby radio galaxies is now well documented (Danziger, Fosbury, these Proc.; Heckman et al., these Proc.; Baum 1986; van Breugel 1986). In most cases the emission-line gas is found along the radio source axes and detailed studies of several sources have shown that many radio and optical properties are intimately related. Often emission-line regions are found adjacent to bright radio knots, and the radio morphologies appear distorted, indicating that jet/gas collisions occur. The low percentages polarization of the radio continuum, and large velocity gradients and line widths of the emission-line gas at these locations furthermore suggest that entrainment of surrounding gas occurs. Recent optical observations of more distant, very powerful (Cygnus A type) radio galaxies show that similar correlations may exist as in the nearby, lower power sources, but that the conditions appear much more extreme (McCarthy et al., these Proc).

We report the discovery of a large cloud of ionized gas associated with the high-redshift radio source 3C 326.1 New radio-frequency images made at 4.9 GHz and 15 GHz with the Very Large Array show the radio source to be a small double (~ 7") without a detectable core at the level of ~ 0.5 mJy. Long-slit spectrograms and Lγa imaging reveal a ~ 100 kpc diameter cloud of ionized gas with a redshift of 1.825 encompassing the radio source. Deep broad-band images show two faint (V = 23.5-24.5) blue objects located on the periphery of the cloud, as well as some very faint (V = 25-26) extremely blue diffuse objects roughly coincident with the brightest regions of the cloud. Long-slit CCD spectra suggest that the Lγa emission from the cloud has a large intrinsic width (FWHM ≈ 1000 km s^(-1)). Spectra taken in the red show weak extended emission from C II] and C III], but C IV emission has not been detected. The large equivalent width of Lγa and the relative strengths of the carbon lines are consistent with H n region-type photoionization. We tentatively propose that 3C 326.1 is a young and/or forming galaxy.

The discovery of an unusual stellar object apparently associated with the powerful radio source 3C 435B is reported. Radiofrequency observations show that radio source to be composed of two extended sources with centroids separated by 10 arcsec and roughly equal flux densities. The smaller of the two sources is coincident with Smith and Spinrad's (1980) identification of an R = 19 galaxy at z = 0.461. The larger of the two sources consists of a strong core at 20 cm and two lobes. The core is coincident with a faint blue stellar object which has strong Balmer-series absorption lines of hydrogen at zero redshift. The spectrum also shows four strong, narrow emission lines identified as forbidden O II, forbidden Ne III, forbidden Ne IV, and forbidden Ne V at a redshift of 0.865. They have relative strengths typical of radio galaxies at z of about one. It is proposed that this is a rare case of an early-type high-latitude galactic star superposed along the line of sight to a distant radio galaxy. 26 references.