309 research outputs found
On the [CII]-SFR relation in high redshift galaxies
After two ALMA observing cycles, only a handful of [CII]
emission line searches in z>6 galaxies have reported a positive detection,
questioning the applicability of the local [CII]-SFR relation to high-z
systems. To investigate this issue we use the Vallini et al. 2013 (V13) model,
based on high-resolution, radiative transfer cosmological simulations to
predict the [CII] emission from the interstellar medium of a z~7 (halo mass
) galaxy. We improve the V13 model by including
(a) a physically-motivated metallicity (Z) distribution of the gas, (b) the
contribution of Photo-Dissociation Regions (PDRs), (c) the effects of Cosmic
Microwave Background on the [CII] line luminosity. We study the relative
contribution of diffuse neutral gas to the total [CII] emission () for different SFR and Z values. We find that the [CII]
emission arises predominantly from PDRs: regardless of the galaxy properties,
% since, at these early epochs, the CMB temperature
approaches the spin temperature of the [CII] transition in the cold neutral
medium ( K). Our model predicts a high-z
[CII]-SFR relation consistent with observations of local dwarf galaxies
(). The [CII] deficit suggested by actual data
( in BDF3299 at z~7.1) if confirmed by deeper
ALMA observations, can be ascribed to negative stellar feedback disrupting
molecular clouds around star formation sites. The deviation from the local
[CII]-SFR would then imply a modified Kennicutt-Schmidt relation in z>6
galaxies. Alternatively/in addition, the deficit might be explained by low gas
metallicities ().Comment: 9 pages, 6 figures, replaced with the version accepted for
pubblication in Ap
CO line emission from galaxies in the Epoch of Reionization
We study the CO line luminosity (), the shape of the CO Spectral
Line Energy Distribution (SLED), and the value of the CO-to-
conversion factor in galaxies in the Epoch of Reionization (EoR). To this aim,
we construct a model that simultaneously takes into account the radiative
transfer and the clumpy structure of giant molecular clouds (GMCs) where the CO
lines are excited. We then use it to post-process state-of-the-art zoomed, high
resolution (), cosmological simulation of a main-sequence
(, ) galaxy, "Alth{\ae}a", at . We find that the CO emission
traces the inner molecular disk () of Alth{\ae}a with
the peak of the CO surface brightness co-located with that of the [CII] 158 emission. Its is comparable
to that observed in local galaxies with similar stellar mass. The high
() gas surface density in
Alth{\ae}a, its large Mach number (\mach), and the warm kinetic
temperature () of GMCs yield a CO SLED peaked at the
CO(7-6) transition, i.e. at relatively high-, and a CO-to-
conversion factor lower than that of the Milky Way. The ALMA observing time
required to detect (resolve) at 5 the CO(7-6) line from galaxies
similar to Alth{\ae}a is h ( h).Comment: 16 pages, 14 figures, accepted for publication in MNRA
Kinematics of galaxies from [CII] line emission
We study the kinematical properties of galaxies in the Epoch of Reionization
via the [CII] 158m line emission. The line profile provides information on
the kinematics as well as structural properties such as the presence of a disk
and satellites. To understand how these properties are encoded in the line
profile, first we develop analytical models from which we identify disk
inclination and gas turbulent motions as the key parameters affecting the line
profile. To gain further insights, we use "Althaea", a highly-resolved () simulated prototypical Lyman Break Galaxy, in the redshift range , when the galaxy is in a very active assembling phase. Based on
morphology, we select three main dynamical stages: I) Merger , II) Spiral Disk,
and III) Disturbed Disk. We identify spectral signatures of merger events,
spiral arms, and extra-planar flows in I), II), and III), respectively. We
derive a generalised dynamical mass vs. [CII]-line FWHM relation. If precise
information on the galaxy inclination is (not) available, the returned mass
estimate is accurate within a factor (). A Tully-Fisher relation is
found for the observed high- galaxies, i.e. for which we provide a simple, physically-based
interpretation. Finally, we perform mock ALMA simulations to check the
detectability of [CII]. When seen face-on, Althaea is always detected at ; in the edge-on case it remains undetected because the larger
intrinsic FWHM pushes the line peak flux below detection limit. This suggests
that some of the reported non-detections might be due to inclination effects.Comment: 14 pages, 12 figures, accepted for publication in MNRA
Mapping metals at high redshift with far-infrared lines
Cosmic metal enrichment is one of the key physical processes regulating
galaxy formation and the evolution of the intergalactic medium (IGM). However,
determining the metal content of the most distant galaxies has proven so far
almost impossible; also, absorption line experiments at become
increasingly difficult because of instrumental limitations and the paucity of
background quasars. With the advent of ALMA, far-infrared emission lines
provide a novel tool to study early metal enrichment. Among these, the [CII]
line at 157.74 m is the most luminous line emitted by the interstellar
medium of galaxies. It can also resonant scatter CMB photons inducing
characteristic intensity fluctuations () near the peak of the
CMB spectrum, thus allowing to probe the low-density IGM. We compute both [CII]
galaxy emission and metal-induced CMB fluctuations at by using
Adaptive Mesh Refinement cosmological hydrodynamical simulations and produce
mock observations to be directly compared with ALMA BAND6 data ( GHz). The [CII] line flux is correlated with as
. Such
relation is in very good agreement with recent ALMA observations (e.g. Maiolino
et al. 2015; Capak et al. 2015) of galaxies. We predict that a
() galaxy can be detected at in
(2000) hours, respectively. CMB resonant scattering can produce Jy/beam emission/absorptions features that are very challenging to be
detected with current facilities. The best strategy to detect these signals
consists in the stacking of deep ALMA observations pointing fields with known
galaxies. This would allow to simultaneously detect both
[CII] emission from galactic reionization sources and CMB fluctuations produced
by metals.Comment: 13 pages, 6 figure
Ochrobactrum sp. MPV1 from a dump of roasted pyrites can be exploited as bacterial catalyst for the biogenesis of selenium and tellurium nanoparticles
Background: Bacteria have developed different mechanisms for the transformation of metalloid oxyanions to non-toxic chemical forms. A number of bacterial isolates so far obtained in axenic culture has shown the ability to bioreduce selenite and tellurite to the elemental state in different conditions along with the formation of nanoparticles-both inside and outside the cells-characterized by a variety of morphological features. This reductive process can be considered of major importance for two reasons: firstly, toxic and soluble (i.e. bioavailable) compounds such as selenite and tellurite are converted to a less toxic chemical forms (i.e. zero valent state); secondly, chalcogen nanoparticles have attracted great interest due to their photoelectric and semiconducting properties. In addition, their exploitation as antimicrobial agents is currently becoming an area of intensive research in medical sciences. Results: In the present study, the bacterial strain Ochrobactrum sp. MPV1, isolated from a dump of roasted arsenopyrites as residues of a formerly sulfuric acid production near Scarlino (Tuscany, Italy) was analyzed for its capability of efficaciously bioreducing the chalcogen oxyanions selenite (SeO32-) and tellurite (TeO32-) to their respective elemental forms (Se0 and Te0) in aerobic conditions, with generation of Se- and Te-nanoparticles (Se- and TeNPs). The isolate could bioconvert 2 mM SeO32- and 0.5 mM TeO32- to the corresponding Se0 and Te0 in 48 and 120 h, respectively. The intracellular accumulation of nanomaterials was demonstrated through electron microscopy. Moreover, several analyses were performed to shed light on the mechanisms involved in SeO32- and TeO32- bioreduction to their elemental states. Results obtained suggested that these oxyanions are bioconverted through two different mechanisms in Ochrobactrum sp. MPV1. Glutathione (GSH) seemed to play a key role in SeO32- bioreduction, while TeO32- bioconversion could be ascribed to the catalytic activity of intracellular NADH-dependent oxidoreductases. The organic coating surrounding biogenic Se- and TeNPs was also characterized through Fourier-transform infrared spectroscopy. This analysis revealed interesting differences among the NPs produced by Ochrobactrum sp. MPV1 and suggested a possible different role of phospholipids and proteins in both biosynthesis and stabilization of such chalcogen-NPs. Conclusions: In conclusion, Ochrobactrum sp. MPV1 has demonstrated to be an ideal candidate for the bioconversion of toxic oxyanions such as selenite and tellurite to their respective elemental forms, producing intracellular Se- and TeNPs possibly exploitable in biomedical and industrial applications.[Figure not available: see fulltext.
Deep into the structure of the first galaxies: SERRA views
We study the formation and evolution of a sample of Lyman Break Galaxies in
the Epoch of Reionization by using high-resolution (),
cosmological zoom-in simulations part of the SERRA suite. In SERRA, we follow
the interstellar medium (ISM) thermo-chemical non-equilibrium evolution, and
perform on-the-fly radiative transfer of the interstellar radiation field
(ISRF). The simulation outputs are post-processed to compute the emission of
far infrared lines ([CII], [NII], and [OIII]). At , the most massive
galaxy, `Freesia', has an age , stellar mass
, and a star formation rate
, due to a recent burst.
Freesia has two stellar components (A and B) separated by ; other 11 galaxies are found within . The
mean ISRF in the Habing band is and is spatially uniform; in
contrast, the ionisation parameter is , and
has a patchy distribution peaked at the location of star-forming sites. The
resulting ionising escape fraction from Freesia is .
While [CII] emission is extended (radius 1.54 kpc), [OIII] is concentrated in
Freesia-A (0.85 kpc), where the ratio . As many high- galaxies, Freesia lies below the local [CII]-SFR
relation. We show that this is the general consequence of a starburst phase
(pushing the galaxy above the Kennicutt-Schmidt relation) which
disrupts/photodissociates the emitting molecular clouds around star-forming
sites. Metallicity has a sub-dominant impact on the amplitude of [CII]-SFR
deviations.Comment: 22 pages, 14 figures, accepted by MNRA
Mesocosm‐based simulations to optimize a bioremediation strategy for the effective restoration of wildfire‐impacted soils contaminated with high‐molecular‐weight hydrocarbons
Aims: We obtained four microbial isolates from soil exposed to forest fire and evaluated their potential bioremediation activity when combined with a biosurfactant-producing bacterial strain for the decontamination of wildfire-impacted soil polluted with high-molecular-weight (HMW) hydrocarbons. Methods and Results: We established mesocosm trials to compare three bioremediation strategies: natural attenuation, bioaugmentation and biostimulation. Chemical analysis, culture-dependent and culture-independent methods were used to evaluate the bioremediation efficiency and speciation of the microbial cenoses based on these approaches. After treatment for 90 days, bioaugmentation removed 75·2–75·9% of the HMW hydrocarbons, biostimulation removed 63·2–69·5% and natural attenuation removed ~22·5%. Hydrocarbon degradation was significantly enhanced in the mesocosm supplemented with the biosurfactant-producing bacterial strain after 20 and 50 days of treatment compared to the other bioremediation strategies. Conclusions: We found that the bioaugmentation approach was more effective than biostimulation and natural attenuation for the removal of HMW hydrocarbons from fire-impacted soil. Significance and Impact of the Study: Our study showed that micro-organisms from wildfire-impacted soil show significant potential for bioremediation, and that biosurfactant-producing bacterial strains can be combined with them as part of an effective bioremediation strategy
Antimicrobial activity of biogenically produced spherical Se-nanomaterials embedded in organic material against Pseudomonas aeruginosa and Staphylococcus aureus strains on hydroxyapatite-coated surfaces
In an effort to prevent the formation of pathogenic biofilms on hydroxyapatite (HA)-based clinical devices and surfaces, we present a study evaluating the antimicrobial efficacy of Spherical biogenic Se-Nanostructures Embedded in Organic material (Bio Se-NEMO-S) produced by Bacillus mycoides SelTE01 in comparison with two different chemical selenium nanoparticle (SeNP) classes. These nanomaterials have been studied as potential antimicrobials for eradication of established HA-grown biofilms, for preventing biofilm formation on HA-coated surfaces and for inhibition of planktonic cell growth of Pseudomonas aeruginosa NCTC 12934 and Staphylococcus aureus ATCC 25923. Bio Se-NEMO resulted more efficacious than those chemically produced in all tested scenarios. Bio Se-NEMO produced by B. mycoides SelTE01 after 6 or 24 h of Na 2 SeO 3 exposure show the same effective antibiofilm activity towards both P. aeruginosa and S. aureus strains at 0.078 mg ml −1 (Bio Se-NEMO 6 ) and 0.3125 mg ml −1 (Bio Se-NEMO 24 ). Meanwhile, chemically synthesized SeNPs at the highest tested concentration (2.5 mg ml −1 ) have moderate antimicrobial activity. The confocal laser scanning micrographs demonstrate that the majority of the P. aeruginosa and S. aureus cells exposed to biogenic SeNPs within the biofilm are killed or eradicated. Bio Se-NEMO therefore displayed good antimicrobial activity towards HA-grown biofilms and planktonic cells, becoming possible candidates as new antimicrobials
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