228 research outputs found
On the Origin of Lyman Blobs at High Redshift: Submillimetric Evidence for a Hyperwind Galaxy at z=3.1
The most remarkable class of high-redshift objects observed so far is
extended Ly emission-line blobs found in an over-density region at
redshift 3.1. They may be either a dust-enshrouded, extreme starburst galaxy
with a large-scale galactic outflow (superwind) or cooling radiation from dark
matter halos. Recently one of these Ly blobs has been detected at
submillimeter wavelengths (450 and 850 m). Here we show that its
rest-frame spectral energy distribution between optical and far-infrared is
quite similar to that of Arp 220, which is a typical ultraluminous
starburst/superwind galaxy in the local universe. This suggests strongly that
the superwind model proposed by Taniguchi & Shioya is applicable to this
Ly blob. Since the blob is more luminous in the infrared by a factor of
30 than Arp 220, it comprises a new population of hyperwind galaxies at high
redshift.Comment: 4 pages, 1 figure. ApJ (Letters), in pres
Absorbers and Globular Cluster Formation in Powerful High Redshift Radio Galaxies
A radiative hydrodynamic simulation for a typical, powerful high redshift
radio galaxy is presented. The jet is injected at one third the speed of light
into a 10000 times denser, homogeneous medium. In the beginning of the
simulation, the bow shock consists of a spherical shell that is similar to a
spherical blast wave. This shell cools radiatively down to approximately 10,000
K, providing after 6 Mio yrs a neutral column of 3.8 x 10^21 cm^-2 around the
whole system. The shell starts to fragment and forms condensations. This
absorbing screen will cover a smaller and smaller fraction of the radio source,
and therefore the emission line region, and eventually form stars in typically
10,000 globular clusters of one million solar masses. Approximately 10^9 solar
masses are entrained into the radio cocoon. This gas, cooling and illuminated
from the radio source, could be the emission line gas observed in high
redshifted radio galaxies and radio loud quasars. The neutral column behind the
bow shock can account for the absorption found in almost all of the small
sources. The globular cluster excess of approximately 10^4 systems found in
present day brightest cluster galaxies (BCGs), which are believed to be the
vestiges of these objects, is consistent with the presented scenario.Comment: A&A, accepted for publication. 4 pages, 2 figure
Radiative Transfer with Finite Elements II. Ly-alpha Line Transfer in Moving Media
A finite element method for solving the resonance line transfer problem in
moving media is presented. The algorithm works in three spatial dimensions on
unstructured grids which are adaptively refined by means of an a posteriori
error indicator. Frequency discretization is implemented via a first-order
Euler scheme. We discuss the resulting matrix structure for coherent isotropic
scattering and complete redistribution. The solution is performed using an
iterative procedure, where monochromatic radiative transfer problems are
successively solved. The present implementation is applicable for arbitrary
model configurations with an optical depth up to 10^(3-4). Results of Ly-alpha
line transfer calculations for a spherically symmetric model, a disk-like
configuration, and a halo containing three source regions are discussed. We
find the characteristic double-peaked Ly-alpha line profile for all models with
an optical depth > 1. In general, the blue peak of the profile is enhanced for
models with infall motion and the red peak for models with outflow motion. Both
velocity fields produce a triangular shape in the two-dimensional Ly-alpha
spectra, whereas rotation creates a shear pattern. Frequency-resolved Ly-alpha
images may help to find the number and position of multiple Ly-alpha sources
located in a single halo. A qualitative comparison with observations of
extended Ly-alpha halos associated with high redshift galaxies shows that even
models with lower hydrogen column densities than required from profile fitting
yield results which reproduce many features in the observed line profiles and
two-dimensional spectra.Comment: 13 pages, accepted for publication in A&
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
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
Lyman Alpha Imaging of a Proto-Cluster Region at <z>=3.09
We present very deep imaging observations, through a narrow-band filter tuned
to Lyman alpha at , of a volume containing a significant over-density
of galaxies at this redshift previously discovered in our survey for
continuum-selected Lyman break galaxies (LBGs). The new observations are used
in conjunction with our spectroscopic results on LBGs to compare the
effectiveness of continuum and emission line searches for star forming galaxies
at high redshift, and to extend the search for members of the structure at =
3.09 to much fainter continuum luminosities. We find that only 20-25 percent of
all galaxies at a given UV continuum luminosity would be flagged as narrow-band
excess objects subject to the typical limits W_Lya > 80 Angstroms in the
observed frame. The density enhancement of strong Lyman alpha emitters in this
field is consistent with that inferred from the analysis of the spectroscopic
Lyman break galaxy sample in the same region (6+/-1), but extends to continuum
luminosities up to 2 magnitudes fainter. There is no evidence for a
significantly higher fraction of large Lyman alpha line equivalent widths at
faint continuum luminosities. By combining the 24 spectroscopic members of the
z=3.09 ``spike'' with the narrow-band candidates, we are able to produce a
sample of 162 objects which are either known or likely members of this large
structure. We have also discovered two extremely large and diffuse Lyman alpha
emitting ``blobs'', which have physical extents >100/h kpc and Lyman alpha line
fluxes 20-40 times larger than the typical line emitters at the same redshifts
in the field. The possible nature of the ``blobs'' is discussed. (abstract
abridged)Comment: To appear in the ApJ, 31 pages, aaste
Giant Lya nebulae associated with high redshift radio galaxies
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.Comment: 36 Pages, including 8 Postscript figures. Accepted for publication in
the Astrophysical Journa
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
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