We present the discovery of a z=4.13 galaxy TN J1338-1942, the most distant
radio galaxy in the southern hemisphere known to date. The source was selected
from a sample of Ultra Steep Spectrum (USS; ...alpha < -1.3) radio sources using
the Texas and NVSS catalogs. The discovery spectrum, obtained with the ESO 3.6m
telescope, shows bright extended Ly-alpha emission. The radio source has a very
asymmetric morphology, suggesting a strong interaction with an inhomogeneous
surrounding medium.
Radio sources have traditionally provided convenient beacons for probing the
early Universe. Hy Spinrad was among the first of the tenacious breed of
observers who would attempt to obtain optical ...identifications and spectra of
the faintest possible `radio galaxies' to investigate the formation and
evolution of galaxies at hy redshift. Modern telescopes and instruments have
made these tasks much simpler, although not easy, and here we summarize the
current status of our hunts for hy redshift radio galaxies (HyZRGs) using radio
spectral and near-IR selection.
PKS 1413+135 (z=0.24671) is one of very few radio-loud AGN with an apparent spiral host galaxy. Previous authors have attributed its nearly exponential infrared cutoff to heavy absorption but have ...been unable to place tight limits on the absorber or its location in the optical galaxy. In addition, doubts remain about the relationship of the AGN to the optical galaxy given the observed lack of re-emitted radiation. We present new HST, ASCA and VLBA observations which throw significant new light on these issues. The HST observations reveal an extrremely red color (V-H = 6.9 mag) for the active nucleus of PKS 1413+135, requiring both a spectral turnover at a few microns due to synchrotron aging and a GMC-sized absorber. We derive an intrinsic column N_H = 4.6^{+2.1}_{-1.6} times 10^{22}cm^{-2} and covering fraction f = 0.12^{+0.07}_{-0.05}. As the GMC is likely in the disk of the optical galaxy, our sightline is rather unlikely (P ~ 2 times 10^{-4}). The properties of the GMC typical of GMCs in our own galaxy. The HI absorber appears centered 25 milliarcseconds away from the nucleus, while the X-ray and nearly all of the molecular absorbers must cover the nucleus, implying a complicated geometry and cloud structure, with a molecular core along our line of sight to the nucleus. Interestingly, the HST/NICMOS data require the AGN to be decentered relative to the optical galaxy by 13 +/- 4 milliarcseconds. This could be interpreted as suggestive of an AGN location far in the background compared to the optical galaxy, but it can also be explained by obscuration and/or nuclear structure, which is more consistent with the observed lack of multiple images.
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 <S_{\rm 1.2mm}>=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.
Observations of the molecular gas phase in quasar host galaxies provide fundamental constraints on galaxy evolution at the highest redshifts. Molecular gas is the material out of which stars form; it ...can be traced by spectral line emission of carbon--monoxide (CO). To date, CO emission has been detected in more than a dozen quasar host galaxies with redshifts (z) larger 2, the record holder being at z=4.69. At these distances the CO lines are shifted to longer wavelengths, enabling their observation with sensitive radio and millimetre interferometers. Here we present the discovery of CO emission toward the quasar SDSS J114816.64+525150.3 (hereafter J1148+5251) at a redshift of z=6.42, when the universe was only 1/16 of its present age. This is the first detection of molecular gas at the end of cosmic reionization. The presence of large amounts of molecular gas (M(H_2)=2.2e10 M_sun) in an object at this time demonstrates that heavy element enriched molecular gas can be generated rapidly in the earliest galaxies.
We present the discovery of a z=4.13 galaxy TN J1338-1942, the most distant radio galaxy in the southern hemisphere known to date. The source was selected from a sample of Ultra Steep Spectrum (USS; ...alpha < -1.3) radio sources using the Texas and NVSS catalogs. The discovery spectrum, obtained with the ESO 3.6m telescope, shows bright extended Ly-alpha emission. The radio source has a very asymmetric morphology, suggesting a strong interaction with an inhomogeneous surrounding medium.
We report observations from the Hubble Space Telescope (HST) and the VLA on
the galactic environment, metallicity, and D/H in strong low-redshift Lya
absorption systems toward the bright BL Lac ...object PKS 2155-304. GHRS/G160M
spectra at 20 km/s resolution show 14 Lya absorbers, 6 clustered at cz =
16,100-18,500 km/s. ORFEUS claimed LyC absorption at z = 0.056 with N(HI) =
(2-5)x10^16 cm^-2, while our Lya data suggest N(HI) = (3-10)x10^14 cm^-2.
Higher columns are possible if the Lya line core at 17,000 +/- 50 km/s contains
narrow HI components. We identify the Lya cluster with a group of five HI
galaxies offset by 400-800 kpc from the sightline. The two strongest absorption
features cover the same velocity range as the HI emission in the two galaxies
closest to the line of sight. If the Lya is associated with these galaxies,
they must have huge halos of highly turbulent, mostly ionized gas. The Lya
absorption could also arise from an extended sheet of intragroup gas, or from
smaller primordial clouds and halos of dwarf galaxies. We see no absorption
from SiIII 1206, CIV 1548, or DI Lya. Photoionization models yield limits of
(Si/H) < 0.003 solar, (C/H) < 0.005 solar, (D/H) < 2.8x10^-4 (4 sigma) if N(HI)
= 2x10^16 cm^-2. The limits increase to 0.023 solar and D/H < 2.8x10^-3 if
N(HI) = 2x10^15 cm^-2. The data suggest that the IGM in this group has not been
enriched to the levels suggested by X-ray studies of intracluster gas and that
these absorbers could be primordial gas clouds.
We present Spitzer observations of thirteen z~6 quasars using the Infrared Array Camera (IRAC) and Multiband Imaging Photometer for Spitzer (MIPS). All the quasars except SDSS J000552.34-000655.8 ...(SDSS J0005-0006) were detected with high S/N in the four IRAC channels and the MIPS 24um band, while SDSS J0005-0006 was marginally detected in the IRAC 8.0um band, and not detected in the MIPS 24um band. We find that most of these quasars have prominent emission from hot dust as evidenced by the observed 24um fluxes. Their spectral energy distributions (SEDs) are similar to those of low-redshift quasars at rest-frame 0.15-3.5 um, suggesting that accretion disks and hot-dust structures for these sources already have reached maturity. However, SDSS J0005-0006 has an unusual SED that lies significantly below low-redshift SED templates at rest-frame 1 and 3.5 um, and thus shows a strong near-IR (NIR) deficit and no hot-dust emission. Type I quasars with extremely small NIR-to-optical flux ratios like SDSS J0005-0006 are not found in low-redshift quasar samples, indicating that SDSS J0005-0006 has different dust properties at high redshift. We combine the Spitzer observations with X-ray, UV/optical, mm/submm and radio observations to determine bolometric luminosities for all the quasars. We find that the four quasars with central black-hole mass measurements have Eddington ratios of order unity.
Radio sources have traditionally provided convenient beacons for probing the early Universe. Hy Spinrad was among the first of the tenacious breed of observers who would attempt to obtain optical ...identifications and spectra of the faintest possible `radio galaxies' to investigate the formation and evolution of galaxies at hy redshift. Modern telescopes and instruments have made these tasks much simpler, although not easy, and here we summarize the current status of our hunts for hy redshift radio galaxies (HyZRGs) using radio spectral and near-IR selection.
We report observations from the Hubble Space Telescope (HST) and the VLA on the galactic environment, metallicity, and D/H in strong low-redshift Lya absorption systems toward the bright BL Lac ...object PKS 2155-304. GHRS/G160M spectra at 20 km/s resolution show 14 Lya absorbers, 6 clustered at cz = 16,100-18,500 km/s. ORFEUS claimed LyC absorption at z = 0.056 with N(HI) = (2-5)x10^16 cm^-2, while our Lya data suggest N(HI) = (3-10)x10^14 cm^-2. Higher columns are possible if the Lya line core at 17,000 +/- 50 km/s contains narrow HI components. We identify the Lya cluster with a group of five HI galaxies offset by 400-800 kpc from the sightline. The two strongest absorption features cover the same velocity range as the HI emission in the two galaxies closest to the line of sight. If the Lya is associated with these galaxies, they must have huge halos of highly turbulent, mostly ionized gas. The Lya absorption could also arise from an extended sheet of intragroup gas, or from smaller primordial clouds and halos of dwarf galaxies. We see no absorption from SiIII 1206, CIV 1548, or DI Lya. Photoionization models yield limits of (Si/H) < 0.003 solar, (C/H) < 0.005 solar, (D/H) < 2.8x10^-4 (4 sigma) if N(HI) = 2x10^16 cm^-2. The limits increase to 0.023 solar and D/H < 2.8x10^-3 if N(HI) = 2x10^15 cm^-2. The data suggest that the IGM in this group has not been enriched to the levels suggested by X-ray studies of intracluster gas and that these absorbers could be primordial gas clouds.
