107 research outputs found
Equivalent widths of Lyman emitters in MUSE-Wide and MUSE-Deep
The aim of this study is to better understand the connection between the
Lyman rest-frame equivalent width (EW) and spectral properties as
well as ultraviolet (UV) continuum morphology by obtaining reliable EW
histograms for a statistical sample of galaxies and by assessing the fraction
of objects with large equivalent widths. We used integral field spectroscopy
from MUSE combined with broad-band data from the Hubble Space Telescope (HST)
to measure EW. We analysed the emission lines of Lyman
emitters (LAEs) detected in the full MUSE-Wide (one hour exposure time) and
MUSE-Deep (ten hour exposure time) surveys and found UV continuum counterparts
in archival HST data. We fitted the UV continuum photometric images using the
Galfit software to gain morphological information on the rest-UV emission and
fitted the spectra obtained from MUSE to determine the double peak fraction,
asymmetry, full-width at half maximum, and flux of the Lyman line. The
two surveys show different histograms of Lyman EW. In MUSE-Wide,
of objects have EW \r{A}, while this fraction is only
in MUSE-Deep and for the full sample. This includes objects
without HST continuum counterparts (one-third of our sample), for which we give
lower limits for EW. The object with the highest securely measured EW
has EW \r{A} (the highest lower limit being EW \r{A}).
We investigate the connection between EW and Lyman spectral or UV
continuum morphological properties. The survey depth has to be taken into
account when studying EW distributions. We find that in general, high
EW objects can have a wide range of spectral and UV morphological
properties, which might reflect that the underlying causes for high EW
values are equally varied. (abridged)Comment: 28 pages, 21 + 1 figures, 7 + 1 tables, accepted for publication in
A&
Recovery and analysis of rest-frame UV emission lines in 2052 galaxies observed with MUSE at 1.5 < z < 6.4
Rest-frame ultraviolet (UV) emission lines probe electron densities, gas-phase abundances, metallicities, and ionization parameters of the emitting star-forming galaxies and their environments. The strongest main UV emission line, Lyα, has been instrumental in advancing the general knowledge of galaxy formation in the early universe. However, observing Lyα emission becomes increasingly challenging at zââłâ6 when the neutral hydrogen fraction of the circumgalactic and intergalactic media increases. Secondary weaker UV emission lines provide important alternative methods for studying galaxy properties at high redshift. We present a large sample of rest-frame UV emission line sources at intermediate redshift for calibrating and exploring the connection between secondary UV lines and the emitting galaxiesâ physical properties and their Lyα emission. The sample of 2052 emission line sources with 1.5â<âzâ<â6.4 was collected from integral field data from the MUSE-Wide and MUSE-Deep surveys taken as part of Guaranteed Time Observations. The objects were selected through untargeted source detection (i.e., no preselection of sources as in dedicated spectroscopic campaigns) in the three-dimensional MUSE data cubes. We searched optimally extracted one-dimensional spectra of the full sample for UV emission features via emission line template matching, resulting in a sample of more than 100 rest-frame UV emission line detections. We show that the detection efficiency of (non-Lyα) UV emission lines increases with survey depth, and that the emission line strength of HeâŻIIλ1640 Ă
, [OâŻIII] λ1661 + OâŻIII] λ1666, and [SiâŻIII] λ1883 + SiâŻIII] λ1892 correlate with the strength of [CâŻIII] λ1907 + CâŻIII] λ1909. The rest-frame equivalent width (EW0) of [CâŻIII] λ1907 + CâŻIII] λ1909 is found to be roughly 0.22 ± 0.18 of EW0(Lyα). We measured the velocity offsets of resonant emission lines with respect to systemic tracers. For CâŻIVλ1548 + CâŻIVλ1551 we find that ÎvCâŻIV âČ 250 km sâ1, whereas ÎvLyα falls in the range of 250â500 km sâ1 which is in agreement with previous results from the literature. The electron density ne measured from [SiâŻIII] λ1883 + SiâŻIII] λ1892 and [CâŻIII] λ1907 + CâŻIII] λ1909 line flux ratios is generally < 105 cmâ3 and the gas-phase abundance is below solar at 12â
+â
log10(O/H)â8. Lastly, we used âPhotoIonization Model Probability Density Functionsâ to infer physical parameters of the full sample and individual systems based on photoionization model parameter grids and observational constraints from our UV emission line searches. This reveals that the UV line emitters generally have ionization parameter log10(U)ââââ2.5 and metal mass fractions that scatter around Zâââ10â2, that is Zâââ0.66âZâ. Value-added catalogs of the full sample of MUSE objects studied in this work and a collection of UV line emitters from the literature are provided with this paper
The ALMA REBELS survey: obscured star formation in massive Lyman-break galaxies at z = 4-8 revealed by the IRX- and relations
We investigate the degree of dust obscured star formation in 49 massive
() Lyman-break galaxies (LBGs) at
- observed as part of the ALMA Reionization Era Bright Emission
Line Survey (REBELS) large program. By creating deep stacks of the photometric
data and the REBELS ALMA measurements we determine the average rest-frame UV,
optical and far-infrared (FIR) properties which reveal a significant fraction
(-) of obscured star formation, consistent with
previous studies. From measurements of the rest-frame UV slope, we find that
the brightest LBGs at these redshifts show bluer () colours
than expected from an extrapolation of the colour-magnitude relation found at
fainter magnitudes. Assuming a modified blackbody spectral-energy distribution
(SED) in the FIR (with dust temperature of and
), we find that the REBELS sources are in agreement with
the local ''Calzetti-like'' starburst Infrared-excess (IRX)- relation.
By reanalysing the data available for 108 galaxies at - from the
ALPINE ALMA large program using a consistent methodology and assumed FIR SED,
we show that from -, massive galaxies selected in the rest-frame
UV have no appreciable evolution in their derived IRX- relation. When
comparing the IRX- relation derived from the combined ALPINE and
REBELS sample to relations established at , we find a deficit in the
IRX, indicating that at the proportion of obscured star formation is
lower by a factor of at a given a . Our IRX-
results are in good agreement with the high-redshift predictions of simulations
and semi-analytic models for galaxies with similar stellar masses
and SFRs.Comment: 18 pages, 10 figures, 2 tables (plus 1 figure and 2 tables in the
appendix). Updated to match MNRAS accepted version after minor correction
Interpreting the Si II and C II line spectra from the COS Legacy Spectroscopic SurveY using a virtual galaxy from a high-resolution radiation-hydrodynamic simulation
Observations of low-ionization state (LIS) metal lines provide crucial
insights into the interstellar medium of galaxies, yet, disentangling the
physical processes responsible for the emerging line profiles is difficult.
This work investigates how mock spectra generated using a single galaxy in a
radiation-hydrodynamical simulation can help us interpret observations of a
real galaxy. We create 22,500 C II and Si II spectra from the virtual galaxy at
different times and through multiple lines of sight and compare them with the
45 observations of low-redshift star-forming galaxies from the COS Legacy
Spectroscopic SurveY (CLASSY). We find that the mock profiles provide accurate
replicates to the observations of 38 galaxies with a broad range of stellar
masses ( to ) and metallicities (0.02 to 0.55 ).
Additionally, we highlight that aperture losses explain the weakness of the
fluorescent emission in several CLASSY spectra and must be accounted for when
comparing simulations to observations. Overall, we show that the evolution of a
single simulated galaxy can produce a large diversity of spectra whose
properties are representative of galaxies of comparable or smaller masses.
Building upon these results, we explore the origin of the continuum, residual
flux, and fluorescent emission in the simulation. We find that these different
spectral features all emerge from distinct regions in the galaxy's ISM, and
their characteristics can vary as a function of the viewing angle. While these
outcomes challenge simplified interpretations of down-the-barrel spectra, our
results indicate that high-resolution simulations provide an optimal framework
to interpret these observations.Comment: Accepted for publication in Ap
Steam gasification of sewage sludge for synthesis processes
The paper presents measurement results of a gasification test run. Municipal sewage sludge from a digestion tower is gasified in an advanced dual fluidized bed reactor system. Steam is used as gasification agent and an olivine-limestone mixture as bed material. The fuel analysis shows a very high ash content and a low heating value of the dried sewage sludge. In addition, a significant amount of nitrogen in the fuel is present, leading to a high ammonia content in the product gas.Sintering effects caused by the high ash content do not occur. Thus, a gasification process without limitation is achieved. The fuel input is located in the lower gasification reactor operating as bubbling fluidized bed, whereas the upper gasification reactor is designed as a column of turbulent fluidized zones for tar cracking. The results show an efficient in-situ tar reduction. With a look on the product gas composition a comparatively high carbon dioxide and a low carbon monoxide content is surprising. It is obvious that an iron oxide reduction of the initial fuel ash occur in the gasification reactor. In addition, it is assumed that the significant iron content in the fuel ash also leads to a transport of oxygen from the combustion reactor to the gasification reactor. Thus, carbon monoxide and hydrogen are oxidized in the gasification reactor by the circulating iron-rich ash particles (chemical looping effect).FFG - Ăsterr. Forschungsförderungs- gesellschaft mbH4351
How to make complexity look simple? Conveying ecosystems restoration complexity for socio-economic research and public engagement
Ecosystems degradation represents one of the major global challenges at the present time, threating peopleâs livelihoods and well-being worldwide. Ecosystem restoration therefore seems no longer an option, but an imperative. Restoration challenges are such that a dialogue has begun on the need to re-shape restoration as a science. A critical aspect of that reshaping process is the acceptance that restoration science and practice needs to be coupled with socio-economic research and public engagement. This inescapably means conveying complex ecosystemâs information in a way that is accessible to the wider public. In this paper we take up this challenge with the ultimate aim of contributing to making a step change in scienceâs contribution to ecosystems restoration practice. Using peatlands as a paradigmatically complex ecosystem, we put in place a transdisciplinary process to articulate a description of the processes and outcomes of restoration that can be understood widely by the public. We provide evidence of the usefulness of the process and tools in addressing four key challenges relevant to restoration of any complex ecosystem: (1) how to represent restoration outcomes; (2) how to establish a restoration reference; (3) how to cope with varying restoration time-lags and (4) how to define spatial units for restoration. This evidence includes the way the process resulted in the creation of materials that are now being used by restoration practitioners for communication with the public and in other research contexts. Our main contribution is of an epistemological nature: while ecosystem services-based approaches have enhanced the integration of academic disciplines and non-specialist knowledge, this has so far only followed one direction (from the biophysical underpinning to the description of ecosystem services and their appreciation by the public). We propose that it is the mix of approaches and epistemological directions (including from the public to the biophysical parameters) what will make a definitive contribution to restoration practice
Lipid (per) oxidation in mitochondria:an emerging target in the ageing process?
Lipids are essential for physiological processes such as maintaining membrane integrity, providing a source of energy and acting as signalling molecules to control processes including cell proliferation, metabolism, inflammation and apoptosis. Disruption of lipid homeostasis can promote pathological changes that contribute towards biological ageing and age-related diseases. Several age-related diseases have been associated with altered lipid metabolism and an elevation in highly damaging lipid peroxidation products; the latter has been ascribed, at least in part, to mitochondrial dysfunction and elevated ROS formation. In addition, senescent cells, which are known to contribute significantly to age-related pathologies, are also associated with impaired mitochondrial function and changes in lipid metabolism. Therapeutic targeting of dysfunctional mitochondrial and pathological lipid metabolism is an emerging strategy for alleviating their negative impact during ageing and the progression to age-related diseases. Such therapies could include the use of drugs that prevent mitochondrial uncoupling, inhibit inflammatory lipid synthesis, modulate lipid transport or storage, reduce mitochondrial oxidative stress and eliminate senescent cells from tissues. In this review, we provide an overview of lipid structure and function, with emphasis on mitochondrial lipids and their potential for therapeutic targeting during ageing and age-related disease
The ALMA REBELS survey: obscured star formation in massive Lyman-break galaxies at z = 4-8 revealed by the IRX-ÎČ and M*relations
We investigate the degree of dust obscured star formation in 49 massive (log 10 ( M*/M â) > 9) Lyman-break galaxies (LBGs) at z = 6.5-8 observed as part of the Atacama Large Millimeter/submillimeter Array (ALMA) Reionization Era Bright Emission Line Surv e y (REBELS) large program. By creating deep stacks of the photometric data and the REBELS ALMA measurements we determine the average rest-frame ultraviolet (UV), optical, and far-infrared (FIR) properties which reveal a significant fraction ( f obs = 0.4-0.7) of obscured star formation, consistent with previous studies. From measurements of the rest-frame UV slope, we find that the brightest LBGs at these redshifts show bluer ( ÎČâ -2.2) colours than expected from an extrapolation of the colour-magnitude relation found at fainter magnitudes. Assuming a modified blackbody spectral energy distribution (SED) in the FIR (with dust temperature of T d = 46 K and ÎČd = 2.0), we find that the REBELS sources are in agreement with the local 'Calzetti-like' starburst Infrared-excess (IRX)-ÎČrelation. By re-analysing the data available for 108 galaxies at z â 4-6 from the ALMA Large Program to Investigate C + at Early Times (ALPINE) using a consistent methodology and assumed FIR SED, we show that from z â 4-8, massive galaxies selected in the rest-frame UV have no appreciable evolution in their derived IRX-ÎČrelation. When comparing the IRX-M*relation derived from the combined ALPINE and REBELS sample to relations established at z 4 the proportion of obscured star formation is lower by a factor of âł3 at a given a M*. Our IRX-ÎČresults are in good agreement with the high-redshift predictions of simulations and semi-analytic models for z â 7 galaxies with similar stellar masses and star formation rates
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