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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

We report the serendipitous detection in high-resolution optical spectroscopy of a strong, asymmetric Ly-alpha emission line at z = 5.190. The detection was made in a 2.25 hour exposure with the Echelle Spectrograph and Imager on the Keck II telescope through a spectroscopic slit of dimensions 1" x 20". The progenitor of the emission line, J123649.2+621539 (hereafter ES1), lies in the Hubble Deep Field North West Flanking Field where it appears faint and compact, subtending just 0.3" (FWHM) with I(AB) = 25.4. The ES1 Ly-alpha line flux of 3.0 x 10^(-17) ergs/cm^2/s corresponds to a luminosity of 9.0 x 10^(42) ergs/s, and the line profile shows the sharp blue cut-off and broad red wing commonly observed in star-forming systems and expected for radiative transfer in an expanding envelope. We find that the Ly-alpha profile is consistent with a galaxy-scale outflow with a velocity of v > 300 km/s. This value is consistent with wind speeds observed in powerful local starbursts (typically 10^2 to 10^3 km/s), and compares favorably to simulations of the late-stage evolution of Ly-alpha emission in star-forming systems. We discuss the implications of this high-redshift galactic wind for the early history of the evolution of galaxies and the intergalactic medium, and for the origin of the UV background at z > 3.

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 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.

We have carried out a spectropolarimetric search for hidden broad-line quasars in three ultraluminous infrared galaxies (ULIRGs) discovered in the positional correlations between sources detected in deep radio surveys and the IRAS Faint Source Catalog. Only the high-ionization Seyfert 2 galaxy TF J1736+1122 is highly polarized, displaying a broad-line spectrum visible in polarized light. The other two objects, TF J1020+6436 and FF J1614+3234, display spectra dominated by a population of young (A-type) stars similar to those of ``E + A'' galaxies. They are unpolarized, showing no sign of hidden broad-line regions. The presence of young starburst components in all three galaxies indicates that the ULIRG phenomenon encompasses both AGN and starburst activity, but the most energetic ULIRGs do not necessarily harbor ``buried quasars''. We find that a luminous infrared galaxy is most likely to host an obscured quasar if it exhibits a high-ionization ([O III] 5007/Hb >~ 5) spectrum typical of a ``classic'' Seyfert 2 galaxy with little or no Balmer absorption lines, is ``ultraluminous'' (L_IR >~ 10^12 L_sun), and has a ``warm'' IR color (f_25/f_60 >~ 0.25). The detection of hidden quasars in this group but not in the low-ionization, starburst-dominated ULIRGs (classified as LINERs or H II galaxies) may indicate an evolutionary connection, with the latter being found in younger systems., 30 pages, including 3 tables and 8 figs, to be published in the Astrophysical Journal

We report the discovery of five broad-absorption-line (BAL) QSOs in a complete sample of 111 ultraviolet excess (UVX) QSO candidates also detected in the NRAO VLA Sky Survey. All five BAL QSOs, which include two high-ionization BAL QSOs and three low-ionization BAL QSOs, are formally radio-loud. Of QSOs with z > 0.4, 3+/-2% show low-ionization BALs, and of QSOs with z > 1.5, all radio-loud, 9+/-5% show BALs; these frequencies are consistent with those of optical surveys. While the first reported radio-loud BAL QSO, FIRST J155633.8+351758, is likely to be heavily dust reddened and thus less radio-loud than indicated by its observed radio-to-optical luminosity, these QSOs are UVX selected and probably free of significant dust along the line of sight. We point out unusual features in two of the BAL QSOs and discuss the significance finding these heretofore rare objects., 9 pages, 1 figure, accepted by ApJ Letters. Table 1 has been revised with a 0.24 mag zero point correction to the BAL QSO U-Bj colors

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 Keck spectropolarimetry of the highly polarized radio-loud quasar 3CR 68.1 (z=1.228, V=19). The polarization increases from 5 in the red (4000 A rest-frame) to >10% in the blue (1900 A rest-frame). The broad emission lines are polarized the same as the continuum, which shows that 3CR 68.1 is not a blazar as it has sometimes been regarded in the past. We also present measurements of the emission lines and a strong, blueshifted, associated absorption line system, as well as a detection at the emission-line redshift of Ca II K absorption, presumably from stars in the host galaxy. 3CR 68.1 belongs to an observationally rare class of highly polarized quasars that are neither blazars nor partially obscured radio-quiet QSOs. Taking into account 3CR 68.1's other unusual properties, such as its extremely red spectral energy distribution and its extreme lobe dominance, we explain our spectropolarimetric results in terms of unified models. We argue that we have a dusty, highly inclined view of 3CR 68.1, with reddened scattered (polarized) quasar light diluted by even more dust-reddened quasar light reaching us directly from the nucleus., 20 pages, includes 3 tables, 6 figures. Accepted by ApJ

We present Keck spectropolarimetry of two rare low-ionization broad absorption line (BAL) quasars (QSOs), FIRST J084044.5+363328 and FIRST J155633.8+351758, that also exhibit narrow absorption lines from metastable excited levels of Fe II (iron Lo-BALs). These QSOs were discovered in optical follow-ups to a deep radio survey; FIRST J155633.8+351758 is radio-loud, the first BAL QSO so identified. FIRST J084044.5+363328 is highly polarized and exhibits many features found in other BAL QSOs. The continuum is ? 4% polarized near the 2000 ? rest frame, falling to ? 2% at longer wavelengths, at a position angle of ? 50?. The emission lines are unpolarized. The polarization rises to ? 8% in the low-ionization troughs of Mg II ?2800 and Al III ?1860. The polarization and its position angle vary in a complicated manner across the metastable Fe II absorption lines, which suggests that more than one mechanism is at work or that the system geometry is complex. FIRST J155633.8+351758 may be the most highly polarized BAL QSO known, and it exhibits other unusual polarization properties compared with those of other highly polarized BAL QSOs. The continuum is ? 13% polarized near the 2000 ? rest frame, falling to ? 7% at longer wavelengths, at a position angle of 153?. The emission lines are polarized like the continuum, but in the absorption troughs the polarization drops to zero. Currently available data cannot yet discriminate among the possible lines of sight to BAL QSOs (edge-on, pole-on, or random).

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 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

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.

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.

We report the discovery of a strong correlation between the radio and optical morphologies of distant (z ≥ 0.6), powerful radio galaxies. The isophotal axes of highly elongated distant 3CR galaxies, measured both in the light of stellar continua and extranuclear emission lines, tend to align with the radio source axes. This correlation suggests that there is a profound relation between these extremely powerful radio sources and their host galaxies. We propose that the most natural explanation of the effect is that the radio jets and/or backflows from the radio lobes interact with the interstellar media of the gas-rich galaxies associated with 3CR sources and stimulate large-scale star formation. This proposed mechanism can provide a physical explanation for the high star formation and evolution rates of 3CR galaxies at large look-back times found in earlier photometric studies. Thus, the formation and evolution of powerful radio galaxies and radio-quiet giant ellipticals may differ substantially.