80 research outputs found
Fast outflow of neutral hydrogen in the radio galaxy 3C293
We report the detection of very broad HI absorption against the central
regions of the radio galaxy 3C293. The absorption profile, obtained with the
Westerbork Synthesis Radio Telescope, has a full width at zero intensity of
about 1400 km/s and most of this broad absorption (~1000 km/s) is blueshifted
relative to the systemic velocity. This absorption represents a fast outflow of
neutral gas from the central regions of this AGN. Possible causes for such an
outflow are discussed. We favour the idea that the interaction between the
radio jet and the rich ISM produces this outflow. Some of the implications of
this scenario are considered.Comment: 11 pages, 4 Figures To be published in: Astrophysical Journal Letter
A Radio Galaxy at z=5.19
We report the discovery of the most distant known AGN, the radio galaxy TN
J0924-2201 at z = 5.19. The radio source was selected from a new sample of
ultra-steep spectrum (USS) sources, has an extreme radio spectral index
alpha_365MHz^1.4GHz = -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 lambda ~ 7530A, which we identify as Ly-alpha. The K-band
image, sampling rest frame U-band, shows a multi-component, radio-aligned
morphology, 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.Comment: 11 Pages, including 3 PostScript figures. Accepted for publication in
the Astrophysical Journal Letter
Subaru Spectroscopy of the Giant Ly Nebula Associated with the High- Powerful Radio Galaxy 1243+036
We report results of our new spatially-resolved, optical spectroscopy of the
giant Ly nebula around a powerful radio galaxy 1243+036 (4C+03.24) at
. The nebula is extended over kpc from the nucleus, and forms
a pair of cones or elongated bubbles. The high-velocity ( km
s; blueshifted with respect to the systemic velocity)
Ly-emitting components are detected at both sides of the nucleus along
its major axis. The northwestern nebula is more spectacular in its velocity
shift (blueshifted by -1000 km s to -1400 km s) and in its width
( km s FWHM) over kpc scale. We discuss
possible origin of the nebula; 1) the shock-heated expanding bubble or
outflowing cone associated with the superwind activity of the host galaxy, 2)
halo gas photoionized by the anisotropic radiation from the active galactic
nuclei (AGN), and 3) the jet-induced star-formation or shock. The last
possibility may not be likely because Ly emission is distributed out of
the narrow channel of the radio jet. We show that the superwind model is most
plausible since it can explain both the characteristics of the morphology (size
and shape) and the kinematical structures (velocity shift and line width) of
the nebula although the photoionization by AGN may contribute to the excitation
to some extent.Comment: 12 pages, 2 figures, accepted for publication in A
The [OIII] Emission-line Nebula of the z=3.594 Radio Galaxy 4C +19.71
We have imaged the z=3.594 radio galaxy 4C +19.71 in the light of the
redshifted [OIII] 5007 angstrom emission line, using a narrow-band filter
centered at 2.3 microns with the Near Infrared Camera on the Keck Telescope.
The [OIII] nebula of 4C +19.71 has a size of 74 x 9 kpc, and a luminosity of 3
x 10^37 W. The rest frame equivalent width of the 5007 line, averaged over the
entire nebula, is 560 angstroms. The length of the major axis of the [OIII]
emission is nearly identical to the separation of the radio lobes seen at 1465
MHz (Rottgering, et al. 1994), and the position angle of the nebula is the same
as that of the two radio lobes. In addition, 4C +19.71 follows the optical
emission line vs. radio power correlation seen in other powerful radio
galaxies. The [OIII] and Lyman alpha emission line luminosities suggest that
the ionized gas mass lies in the range of 2 x 10^8 - 10^9 solar masses. The O/H
ratio in the nebula is at least a few tenths solar, and may be as high as a
factor of three above solar, indicating a previous phase of star formation in
4C +19.71. Thirty five percent of the total K-band flux is contributed by the
5007 angstrom emission line, and the continuum of 4C +19.71 has a K=19.6 mag.
This places 4C +19.71 along the K-z relation found for other radio galaxies and
radio loud quasars. If the continuum is dominated by starlight, the host galaxy
has a rest frame visual luminosity of about 40L*. There are no candidate
emission-line objects at the redshift of 4C +19.71 having [OIII] rest frame
equivalent widths of more than about 2% that of the radio galaxy itself within
a volume of 212 cubic Mpc.Comment: plain LaTex with 3 postscript figures. ApJ accepte
The D/H ratio at z = 3.57 toward Q 1937-1009
Deuterium abundance re-measurements by Burles and Tytler (1998; hereafter BT)
yielded D/H = (3.3 +/- 0.3) 10^{-5} and the robust upper limit D/H < 3.9
10^{-5} from the z_a = 3.572 system toward Q1937-1009. In this new analysis BT
adopted multicomponent microturbulent models together with the possibility to
vary freely the local continuum level around each HI line to improve the fit.
The procedure failed, however, to fit adequately D Ly-beta without recourse to
an additional H Ly-alpha contamination at the position of D Ly-beta. We show
that this obstacle may be successfully overcome within the framework of the
mesoturbulent model accounting (in contrast to the microturbulent
approximation) for a correlated structure of the large scale velocity field.
Using the same observational data and the original continuum as determined by
Tytler et al. (1996), we obtained good fits. The one-component mesoturbulent
models provide D/H in the range (3.2 - 4.8) 10^{-5} and the total hydrogen
column density N(HI) = (5.6 - 7.0) 10^{17} cm^{-2}. This result is consistent
with that found by us from the z_a = 2.504 and z_a = 0.701 systems toward
Q1009+2956 and Q1718+4807, respectively. The range for D/H common to all three
analyses is D/H = (4.1 - 4.6) 10^{-5}. This value is consistent with standard
big bang nucleosynthesis [SBBN] if the baryon-to-photon ratio, \eta, is in the
range 4.2 10^{-10} <= \eta <= 4.6 10^{-10}, implying 0.0155 <= \Omega_b
h^2_{100} <= 0.0167.Comment: 8 pages, 2 Postscript figures, aaspp4.sty file, submit. ApJ Let
A Combined EIS-NVSS Survey Of Radio Sources (CENSORS) III: Spectroscopic observations
The Combined EIS-NVSS Survey Of Radio Sources (CENSORS) is a 1.4GHz radio
survey selected from the NRAO VLA Sky Survey (NVSS) and complete to a
flux-density of 7.2mJy. It targets the ESO Imaging Survey (EIS) Patch D, which
is a 3 by 2 square degree field centred on 09 51 36.0, -21 00 00 (J2000). This
paper presents the results of spectroscopic observations of 143 of the 150
CENSORS sources. The primary motivation for these observations is to achieve
sufficient spectroscopic completeness so that the sample may be used to
investigate the evolution of radio sources.
The observations result in secure spectroscopic redshifts for 63% of the
sample and likely redshifts (based on a single emission line, for example) for
a further 8%. Following the identification of the quasars and star-forming
galaxies in the CENSORS sample, estimated redshifts are calculated for the
remainder of the sample via the K-z relation for radio galaxies. Comparison of
the redshift distribution of the CENSORS radio sources to distributions
predicted by the various radio luminosity function evolution models of Dunlop &
Peacock 1990, results in no good match. This demonstrates that this sample can
be used to expand upon previous work in that field.Comment: Accepted for publication in MNRAS. This version has some reduced
resolution figures and 13 associated gif files. A version with all figures
incorporated (at full resolution) is available at
http://www.roe.ac.uk/~pnb/papers/censors_spectro.pd
Radio galaxies at z~2.5: results from Keck spectropolarimetry
In classifying the ensemble of powerful extragalactic radio sources,
considerable evidence has accumulated that radio galaxies and quasars are
orientation-dependent manifestations of the same parent population: massive
spheroidal galaxies containing correspondingly massive black holes. [...] In
this study, we exploit the opportunity to eliminate the quasar glare by
performing sensitive spectropolarimetry with the Keck II telescope of a sample
of radio galaxies with redshifts around 2.5. [...] We show that dust-reflected
quasar light generally dominates the restframe ultraviolet continuum of these
sources and that a highly clumped scattering medium results in almost grey
scattering of the active galactic nucleus photons. The observations, however,
do not exclude a substantial star formation rate averaged over a Gyr of
evolution. The sub-mm reradiation from the scattering dust is likely to
represent only a small fraction (~10%) of the total far infrared luminosity. An
analysis of the emission lines excited in the interstellar medium of the host
galaxy by the hard quasar radiation field reveals evidence of a dramatic
chemical evolution within the spheroid during this epoch. Secondary nitrogen
production in intermediate mass stars produces a characteristic signature in
the NV/CIV and NV/HeII line ratios which has been seen previously in the broad
line region of quasars at similar redshifts. We find intriguing correlations
between the strengths of the Ly alpha and NV emission lines and the degree of
ultraviolet continuum polarization which may represent the dispersal of dust
associated with the chemical enrichment of the spheroid.Comment: 24 pages, 12 figures, accepted for publication in Astronomy &
Astrophysics. Properly formatted for A4 and Letter paper formats ps files
available at http://www.eso.org/~jvernet/research.htm
Near-Infrared Spectroscopy of Powerful Radio Galaxies at z=2.2-2.4
Near-infrared spectroscopy (rest-frame 3700-6800 Angstroms) of eight high
redshift powerful radio galaxies (HzPRGs) at z = 2.2-2.6 is presented. Strong
forbidden lines and H-alpha emission were detected in all sources; the data
show evidence that the emission lines of the HzPRGs may contribute a
substantial fraction (approx. 25-98%) of their total observed H - and/or K
-band light. Diagnostic emission-line ratios for three of the eight HzPRGs are
consistent with the presence of a Seyfert 2 nucleus; the [O III] 5007 / H-beta
and [S II] 6716, 6731 / H-alpha ratios and/or limits of the remaining five
galaxies are inconclusive. Furthermore, all six of the galaxies for which both
H - and K -band spectra were obtained have observed [O III] 5007 / (H-alpha +[N
II] 6548, 6583) ratios consistent with Seyfert 2 ionization...Comment: LaTex, 39 pages with 9 postscript figures and 2 gif figures, ApJ
accepte
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