124 research outputs found
A clumpy and anisotropic galaxy halo at z=1 from gravitational-arc tomography
Every star-forming galaxy has a halo of metal-enriched gas extending out to
at least 100 kpc, as revealed by the absorption lines this gas imprints on the
spectra of background quasars. However, quasars are sparse and typically probe
only one narrow pencil beam through the intervening galaxy. Close quasar pairs
and gravitationally lensed quasars have been used to circumvent this inherently
one-dimensional technique, but these objects are rare and the structure of the
circum-galactic medium remains poorly constrained. As a result, our
understanding of the physical processes that drive the re-cycling of baryons
across the lifetime of a galaxy is limited. Here we report integral-field
(tomographic) spectroscopy of an extended background source -a bright giant
gravitational arc. We can thus coherently map the spatial and kinematic
distribution of Mg II absorption -a standard tracer of enriched gas- in an
intervening galaxy system at redshift 0.98 (i.e., ~8 Gyr ago). Our
gravitational-arc tomography unveils a clumpy medium in which the
absorption-strength decreases with increasing impact parameter, in good
agreement with the statistics towards quasars; furthermore, we find strong
evidence that the gas is not distributed isotropically. Interestingly, we
detect little kinematic variation over a projected area of ~600 kpc squared,
with all line-of-sight velocities confined to within a few tens of km/s of each
other. These results suggest that the detected absorption originates from
entrained recycled material, rather than in a galactic outflow.Comment: Published online in Nature on 31 January 201
The polyamine “multiverse” and stress mitigation in crops: A case study with seed priming in quinoa
The importance of polyamines (PAs) in plant growth and development was recognised several decades ago and, since then, their role in cell proliferation, embryogenesis, organogenesis, flowering, fruit development and ripening, etc. has been investigated to a great extent. In more recent years, most of the attention on PAs has been focussed on their functions in biotic and, especially, abiotic stress responses. Exogenous application, transgenic plants over- or under-expressing PA biosynthetic genes, and mutants have been used to unveil their essential contribution to plant tolerance to salinity, drought, chilling, and heavy metal stresses, among others. In parallel, knowledge on their mechanisms of action has increased greatly and it is today evident that PA functions depend upon their ability to (a) bind electrostatically or covalently to numerous compounds thereby modulating membrane, cell wall, nucleic acid, and protein structure and functions, (b) produce hydrogen peroxide via their catabolic pathways, (c) interact with the biosynthetic and signaling pathways of practically all known phyto hormones,
and (d) interact with nitric oxide. In this review, a state-of-the-art overview of PA functions in plants
and their possible applications in mitigating stress in crop plants is provided. The potential of seed priming with PAs as an economically and environmentally valid approach for enhancing plant tolerance to adverse environmental conditions is discussed and some results from our study on quinoa and salt stress are presented
Spatially Resolved Outflows in a Seyfert Galaxy at z = 2.39
We present the first spatially resolved analysis of rest-frame optical and UV
imaging and spectroscopy for a lensed galaxy at z = 2.39 hosting a Seyfert
active galactic nucleus (AGN). Proximity to a natural guide star has enabled
high signal-to-noise VLT SINFONI + adaptive optics observations of rest-frame
optical diagnostic emission lines, which exhibit an underlying broad component
with FWHM ~ 700 km/s in both the Balmer and forbidden lines. Measured line
ratios place the outflow robustly in the region of the ionization diagnostic
diagrams associated with AGN. This unique opportunity - combining gravitational
lensing, AO guiding, redshift, and AGN activity - allows for a magnified view
of two main tracers of the physical conditions and structure of the
interstellar medium in a star-forming galaxy hosting a weak AGN at cosmic noon.
By analyzing the spatial extent and morphology of the Ly-alpha and
dust-corrected H-alpha emission, disentangling the effects of star formation
and AGN ionization on each tracer, and comparing the AGN induced mass outflow
rate to the host star formation rate, we find that the AGN does not
significantly impact the star formation within its host galaxy.Comment: 16 pages, 5 figures, accepted for publication in Ap
UVES/VLT high resolution absorption spectroscopy of the GRB080330 afterglow: a study of the GRB host galaxy and intervening absorbers
We study the Gamma Ray Burst (GRB) environment and intervening absorbers by
analyzing the optical absorption features produced by gas surrounding the GRB
or along its line of sight. We analyzed high resolution spectroscopic
observations (R=40000, S/N=3 - 6) of the optical afterglow of GRB080330, taken
with UVES at the VLT ~ 1.5 hours after the GRB trigger. The spectrum
illustrates the complexity of the ISM of the GRB host galaxy at z = 1.51 which
has at least four components in the main absorption system. We detect strong
FeII, SiII, and NiII excited absorption lines associated with the bluemost
component only. In addition to the host galaxy, at least two more absorbers
lying along the line of sight to the afterglow have been detected in the
redshift range 0.8 < z < 1.1, each exhibiting MgII absorption. For the bluemost
component in the host galaxy, we derive information about its distance from the
site of the GRB explosion. We do so by assuming that the excited absorption
lines are produced by indirect UV pumping, and compare the data with a time
dependent photo-excitation code. The distance of this component is found to be
280+40-50 pc, which is lower than found for other GRBs (1 - 6 kpc). We identify
two additional MgII absorbers, one of them with a rest frame equivalent width
larger than 1A. The distance between the GRB and the absorber measured in this
paper confirms that the power of the GRB radiation can influence the conditions
of the interstellar medium up to a distance of at least several hundred pc. For
the intervening absorbers, we confirm the trend that on average one strong
intervening system is found per afterglow, as has been noted in studies
exhibiting an excess of strong MgII absorbers along GRB sightlines compared to
quasars.Comment: 8 Pages, 7 ps figures, A&A in pres
On the connection between the intergalactic medium and galaxies: the H I–galaxy cross-correlation at z ≲ 1
We present a new optical spectroscopic survey of 1777 ‘star-forming’ (‘SF’) and 366 ‘non-star-forming’ (‘non-SF’) galaxies at redshifts z ∼ 0-1 (2143 in total), 22 AGN and 423 stars, observed by instruments such as the Deep Imaging Multi-Object Spectrograph, the Visible Multi-Object Spectrograph and the Gemini Multi-Object Spectrograph, in three fields containing five quasi-stellar objects (QSOs) with Hubble Space Telescope (HST) ultraviolet spectroscopy. We also present a new spectroscopic survey of 173 ‘strong’ (1014 ≤ NHI≲ 1017 cm−2) and 496 ‘weak’ (1013 ≲ NHI 50 per cent of ‘weak’ H i systems reside within galaxy voids (hence not correlated with galaxies), and are confined in dark matter haloes of masses smaller than those hosting ‘strong’ systems and/or galaxies. We speculate that H i systems within galaxy voids might still be evolving in the linear regime even at scales ≲2 Mpc
GRB 021004: Tomography of a gamma-ray burst progenitor and its host galaxy
We analyse the distribution of matter around the progenitor star of gamma-ray
burst GRB 021004 as well as the properties of its host galaxy with
high-resolution echelle as well as near-infrared spectroscopy. Observations
were taken by the 8.2m Very Large Telescope with the Ultraviolet and Visual
Echelle spectrograph (UVES) and the Infrared Spectrometer And Array Camera
(ISAAC) between 10 and 14 hours after the onset of the event. We report the
first detection of emission lines from a GRB host galaxy in the near-infrared,
detecting H-alpha and the [O III] doublet. These allow an independent
measurement of the systemic redshift (z = 2.3304 +/- 0.0005) which is not
contaminated by absorption as the Ly-alpha line is, and the deduction of
properties of the host galaxy. From the visual echelle spectroscopy, we find
several absorption line groups spanning a range of about 3,000 km/s in velocity
relative to the redshift of the host galaxy. The absorption profiles are very
complex with both velocity-broadened components extending over several 100 km/s
and narrow lines with velocity widths of only 20 km/s. By analogy with QSO
absorption line studies, the relative velocities,widths, and degrees of
ionization of the lines ("line-locking", "ionization--velocity correlation")
show that the progenitor had both an extremely strong radiation field and
several distinct mass loss phases (winds). These results are consistent with
GRB progenitors being massive stars, such as Luminous Blue Variables (LBVs) or
Wolf--Rayet stars, providing a detailed picture of the spatial and velocity
structure of the GRB progenitor star at the time of explosion. The host galaxy
is a prolific star-forming galaxy with a SFR of about 40 solar masses per year.Comment: 11 pages, 5 figures. Accepted for publication in Astronomy and
Astrophysics
Dissecting a 30 kpc galactic outflow at 1.7
We present the spatially resolved measurements of a cool galactic outflow in
the gravitationally lensed galaxy RCS0327 at using VLT/MUSE
IFU observations. We probe the cool outflowing gas, traced by blueshifted Mg II
and Fe II absorption lines, in 15 distinct regions of the same galaxy in its
image-plane. Different physical regions, 5 to 7 kpc apart within the galaxy,
drive the outflows at different velocities ( to km
s), and mass outflow rates ( 183 to 527 $M_{\odot}\
yr^{-1}^{-1}^2^2
\sim -120-242^{-1}\simM_{\odot}\ yr^{-1}\geq\approx$ 10% of the total energy flux
provided by star-formation. These estimates suggest that the outflow in RCS0327
is energy driven. This work shows the importance of small scale variations of
outflow properties due to the variations of local stellar properties of the
host galaxy in the context of galaxy evolution.Comment: 24 pages, 15 figures, 6 tables, submitted to MNRA
A 30 kpc Spatially Extended Clumpy and Asymmetric Galactic Outflow at z 1.7
We image the spatial extent of a cool galactic outflow with fine structure Fe
II emission and resonant Mg II emission in a gravitationally lensed
star-forming galaxy at . The Fe II and Mg II
(continuum-subtracted) emissions span out to radial distances of 14.33
kpc and 26.5 kpc, respectively, with maximum spatial extents of 21 kpc
for Fe II emission and 30 kpc for Mg II emission. Mg II residual
emission is patchy and covers a total area of 184 kpc, constraining
the minimum area covered by the outflowing gas to be 13% of the total
area. Mg II emission is asymmetric and shows 21% more extended emission
along the declination direction. We constrain the covering fractions of the Fe
II and Mg II emission as a function of radial distance and characterize
them with a power law model. The Mg II 2803 emission line shows two
kinematically distinct emission components, and may correspond to two distinct
shells of outflowing gas with a velocity separation of 400
km/s. By using multiple images with different magnifications of the galaxy in
the image plane, we trace the Fe II, Mg II emissions around three
individual star-forming regions. In all cases, both the Fe II and Mg II
emissions are more spatially extended compared to the star forming regions
traced by the [O II] emission. These findings provide robust constraints on the
spatial extent of the outflowing gas, and combined with outflow velocity and
column density measurements will give stringent constraints on mass outflow
rates of the galaxy.Comment: 22 pages, 14 figures, 4 tables, accepted to ApJ, the referee comments
are incorporated in this versio
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