128 research outputs found
The FORS Deep Field Spectroscopic Survey
We present a catalogue and atlas of low-resolution spectra of a well defined
sample of 341 objects in the FORS Deep Field. All spectra were obtained with
the FORS instruments at the ESO VLT with essentially the same spectroscopic
set-up. The observed extragalactic objects cover the redshift range 0.1 to 5.0.
98 objects are starburst galaxies and QSOs at z > 2. Using this data set we
investigated the evolution of the characteristic spectral properties of bright
starburst galaxies and their mutual relations as a function of the redshift.
Significant evolutionary effects were found for redshifts 2 < z < 4. Most
conspicuous are the increase of the average C IV absorption strength, of the
dust reddening, and of the intrinsic UV luminosity, and the decrease of the
average Ly alpha emission strength with decreasing redshift. In part the
observed evolutionary effects can be attributed to an increase of the
metallicity of the galaxies with cosmic age. Moreover, the increase of the
total star-formation rates and the stronger obscuration of the starburst cores
by dusty gas clouds suggest the occurrence of more massive starbursts at later
cosmic epochs.Comment: 24 pages, 25 figures (35 PS files), 4 tables, accepted for
publication in A&A. v2: minor typos corrected and references update
On the dependence between UV luminosity and Lyman-alpha equivalent width in high redshift galaxies
We show that with the simple assumption of no correlation between the
Ly-alpha equivalent width and the UV luminosity of a galaxy, the observed
distribution of high redshift galaxies in an equivalent width - absolute UV
magnitude plane can be reproduced. We further show that there is no dependence
between Ly-alpha equivalent width and Ly-alpha luminosity in a sample of
Ly-alpha emitters. The test was expanded to Lyman-break galaxies and again no
dependence was found. Simultaneously, we show that a recently proposed lack of
large equivalent width, UV bright galaxies (Ando et al. 2006) can be explained
by a simple observational effect, based on too small survey volumes.Comment: 7 pages, 3 figures, 2 tables, accepted in MNRA
Lyman-alpha emission galaxies at a redshift of z = 5.7 in the FORS Deep Field
We present the results of a search for Lyman-alpha emission galaxies at z~
5.7 in the FORS Deep Field. The objective of this study is to improve the faint
end of the luminosity function of high-redshift Lyman-alpha emitting galaxies
and to derive properties of intrinsically faint Lyman-alpha emission galaxies
in the young universe. Using FORS2 at the ESO VLT and a set of special
interference filters, we identified candidates for high-redshift Lyman-alpha
galaxies. We then used FORS2 in spectroscopic mode to verify the
identifications and to study their spectral properties. The narrow-band
photometry resulted in the detection of 15 likely Lyman-alpha emission
galaxies. Spectra with an adequate exposure time could be obtained for eight
galaxies. In all these cases the presence of Lyman-alpha emission at z = 5.7
was confirmed spectroscopically. The line fluxes of the 15 candidates range
between 3 and 16 * 10^-21 Wm^-2, which corresponds to star-formation rates not
corrected for dust between 1 and 5 Msun/yr. The luminosity function derived for
our photometrically identified objects extends the published luminosity
functions of intrinsically brighter Lyman-alpha galaxies. With this technique
the study of high-redshift Lyman-alpha emission galaxies can be extended to low
intrinsic luminosities.Comment: 9 pages, 17 figures. Accepted by A&A. PDF version with higher
resolution figures here:
http://www.lsw.uni-heidelberg.de/users/jheidt/fdf/pubs/fdflae5_7_110406.pd
The nature of z ~ 2.3 Lyman-alpha emitters
We study the multi-wavelength properties of a set of 171 Ly-alpha emitting
candidates at redshift z = 2.25 found in the COSMOS field, with the aim of
understanding the underlying stellar populations in the galaxies. We especially
seek to understand what the dust contents, ages and stellar masses of the
galaxies are, and how they relate to similar properties of Ly-alpha emitters at
other redshifts. The candidates here are shown to have different properties
from those of Ly-alpha emitters found at higher redshift, by fitting the
spectral energy distributions (SEDs) using a Monte-Carlo Markov-Chain technique
and including nebular emission in the spectra. The stellar masses, and possibly
the dust contents, are higher, with stellar masses in the range log M_* = 8.5 -
11.0 M_sun and A_V = 0.0 - 2.5 mag. Young population ages are well constrained,
but the ages of older populations are typically unconstrained. In 15% of the
galaxies only a single, young population of stars is observed. We show that the
Ly-alpha fluxes of the best fit galaxies are correlated with their dust
properties, with higher dust extinction in Ly-alpha faint galaxies. Testing for
whether results derived from a light-weighted stack of objects correlate to
those found when fitting individual objects we see that stellar masses are
robust to stacking, but ages and especially dust extinctions are derived
incorrectly from stacks. We conclude that the stellar properties of Ly-alpha
emitters at z = 2.25 are different from those at higher redshift and that they
are diverse. Ly-alpha selection appears to be tracing systematically different
galaxies at different redshifts.Comment: 15 pages, 11 figures, 8 tables, accepted in A&A. Table 6 available in
full from the author
Galaxy Counterparts of metal-rich Damped Lyman-alpha Absorbers - I: The case of the z=2.35 DLA towards Q2222-0946
We have initiated a survey using the newly commissioned X-shooter
spectrograph to target candidate relatively metal-rich damped Lyman-alpha
absorbers (DLAs). The spectral coverage of X-shooter allows us to search for
not only Lyman-alpha emission, but also rest-frame optical emission lines. We
have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII],
Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first
paper resulting from the survey, we report on the discovery of the galaxy
counterpart of the z_abs = 2.354 DLA towards the z=2.926 quasar Q2222$-0946.
This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable
redshifts and there is evidence for substantial depletion of refractory
elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII
and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and
-0.99+/-0.06, respectively. The galaxy is detected in the Lyman-alpha, [OIII]
lambda4959,5007 Halpha emission lines at an impact parameter of about 0.8
arcsec (6 kpc at z_abs = 2.354). We infer a star-formation rate of 10 M_sun
yr^-1, which is a lower limit due to the possibility of slit-loss. Compared to
the recently determined Halpha luminosity function for z=2.2 galaxies the
DLA-galaxy counterpart has a luminosity of L~0.1L^*_Halpha. The emission-line
ratios are 4.0 (Lyalpha/Halpha) and 1.2 ([OIII]/Halpha). The Lyalpha line shows
clear evidence for resonant scattering effects, namely an asymmetric,
redshifted (relative to the systemic redshift) component and a much weaker
blueshifted component. The fact that the blueshifted component is relatively
weak indicates the presence of a galactic wind. The properties of the galaxy
counterpart of this DLA is consistent with the prediction that metal-rich DLAs
are associated with the most luminous of the DLA-galaxy counterparts.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a starburst-driven outflow
We present the detection of Ly-alpha, [OIII] and H-alpha emission associated
with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards
the quasar SDSS J113520-001053. This is the largest HI column density ever
measured along a QSO line of sight, though typical of what is seen in GRB-DLAs.
This absorption system also classifies as ultrastrong MgII system with
W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion
factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally
larger than) the mean values found in the general QSO-DLA population. The
[OIII]-Ha emitting region has a very small impact parameter with respect to the
QSO line of sight, b=0.1", and is unresolved. From the Ha line, we measure
SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More
strikingly, the blue and red Ly-a peaks arise from distinct regions extended
over a few kpc on either side of the star-forming region. We propose that this
is the consequence of Ly-a transfer in outflowing gas. The presence of
starburst-driven outflows is also in agreement with the large SFR together with
a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV
continuum luminosity of the galaxy, we estimate an age of at most a few 10^7
yr, again consistent with a recent starburst scenario. We interpret the data as
the observation of a young, gas rich, compact starburst galaxy, from which
material is expelled through collimated winds powered by the vigorous star
formation activity. We substantiate this picture by modelling the radiative
transfer of Ly-a photons in the galactic counterpart. Though our model (a
spherical galaxy with bipolar outflowing jets) is a simplistic representation
of the true gas distribution and velocity field, the agreement between the
observed and simulated properties is particularly good. [abridged]Comment: 15 pages, 18 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
Testing the inverse-Compton catastrophe scenario in the intra-day variable blazar S5 0716+71. I. Simultaneous broadband observations during November 2003
Some intra-day variable, compact extra-galactic radio sources show brightness
temperatures severely exceeding 10^{12} K, the limit set by catastrophic
inverse-Compton (IC) cooling in sources of incoherent synchrotron radiation.
The violation of the IC limit, possible under non-stationary conditions, would
lead to IC avalanches in the soft-gamma-ray energy band during transient
periods. For the first time, broadband signatures of possible IC catastrophes
were searched for in S5 0716+71. A multifrequency observing campaign targetting
S5 0716+71 was carried out in November 2003 under the framework of the European
Network for the Investigation of Galactic nuclei through Multifrequency
Analysis (ENIGMA) together with a campaign by the Whole Earth Blazar Telescope
(WEBT), involving a pointing by the soft-gamma-ray satellite INTEGRAL, optical,
near-infrared, sub-millimeter, millimeter, radio, and Very Long Baseline Array
(VLBA) monitoring. S5 0716+71 was very bright at radio frequencies and in a
rather faint optical state during the INTEGRAL pointing; significant inter-day
and low intra-day variability was recorded in the radio regime, while typical
fast variability features were observed in the optical band. No correlation was
found between the radio and optical emission. The source was not detected by
INTEGRAL, neither by the X-ray monitor JEM-X nor by the gamma-ray imager ISGRI,
but upper limits to the source emission in the 3-200 keV energy band were
estimated. A brightness temperature Tb>2.1x10^{14} K was inferred from the
radio variability, but no corresponding signatures of IC avalanches were
recorded at higher energies. The absence of IC-catastrophe signatures provides
either a lower limit delta>8 to the Doppler factor affecting the radio emission
or strong constraints for modelling of the Compton catastrophes in S5 0716+71.Comment: 15 pages, 3 EPS figures, 3 tables, to appear in A&
Ion homeostasis in the Chloroplast
peer reviewedThe chloroplast is an organelle of high demand for macro- and micro-nutrient ions, which are required for the maintenance of the photosynthetic process. To avoid deficiency while preventing excess, homeostasis mechanisms must be tightly regulated. Here, we describe the needs for nutrient ions in the chloroplast and briefly highlight their functions in the chloroplastidial metabolism. We further discuss the impact of nutrient deficiency on chloroplasts and the acclimation mechanisms that evolved to preserve the photosynthetic apparatus. We finally present what is known about import and export mechanisms for these ions. Whenever possible, a comparison between cyanobacteria, algae and plants is provided to add an evolutionary perspective to the description of ion homeostasis mechanisms in photosynthesis
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