ABSTRACT
Using new Very Large Telescope (VLT)/XShooter spectral observations we analyse the physical properties of five z ∼ 0.3–0.4 confirmed Lyman continuum (LyC) leakers. Strong resonant Mg ...ii λλ2796, 2803 Å emission lines (I(λλ2796, 2803)/I(Hβ) ≃ 10–38 per cent) and non-resonant Fe ii* λλ2612, 2626 Å emission lines are observed in spectra of five and three galaxies, respectively. We find high electron densities Ne ∼ 400 cm−3, significantly higher than in typical low-z, but comparable to those measured in z ∼ 2–3 star-forming galaxies (SFGs). The galaxies have a mean value of log N/O = –1.16, close to the maximum values found for SFGs in the metallicity range of 12 + log O/H ≃ 7.7–8.1. All 11 low-z LyC emitting galaxies found by Izotov et al., including the ones considered in this study, are characterized by high equivalent width (EW) (Hβ) ∼ 200–400 Å, high ionization parameter (log(U) = –2.5 to –1.7), high average ionizing photon production efficiency ξ = 1025.54 Hz erg−1, and hard ionizing radiation. On the Baldwin–Phillips–Terlevich (BPT) diagram we find the same offset of our leakers from low-z main-sequence SFGs as that for local analogues of Lyman-break galaxies (LBGs) and extreme SFGs at z ∼ 2–3. We confirm the effectiveness of the He i emission lines diagnostics proposed by Izotov et al. in searching for LyC leaker candidates and find that their intensity ratios correspond to those in a median with low neutral hydrogen column density N(H i) = 1017–5 × 1017 cm−2 that permit leakage of LyC radiation, likely due to their density-bounded H ii regions.
We present a detailed 2D study of the ionized ionized interstellar medium (ISM) of IZw18 using new Potsdam Multi-Aperture Spectrophotometer-integral field unit (PMAS-IFU) optical observations. IZw18 ...is a high-ionization galaxy which is among the most metal-poor starbursts in the local Universe. This makes IZw18 a local benchmark for understanding the properties most closely resembling those prevailing at distant starbursts. Our IFU aperture (∼1.4 × 1.4 kpc2) samples the entire IZw18 main body and an extended region of its ionized gas. Maps of relevant emission lines and emission line ratios show that higher-excitation gas is preferentially located close to the north-west knot and thereabouts. We detect a Wolf–Rayet feature near the north-west knot. We derive spatially resolved and integrated physical–chemical properties for the ionized gas in IZw18. We find no dependence between the metallicity indicator R23 and the ionization parameter (as traced by O iii/O ii) across IZw18. Over ∼0.30 kpc2, using the O iii λ4363 line, we compute T
eO iii values (∼15 000–25 000 K), and oxygen abundances are derived from the direct determinations of T
eO iii. More than 70 per cent of the higher-T
eO iii (≳22 000 K) spaxels are He iiλ4686-emitting spaxels too. From a statistical analysis, we study the presence of variations in the ISM physical–chemical properties. A galaxy-wide homogeneity, across hundreds of parsecs, is seen in O/H. Based on spaxel-by-spaxel measurements, the error-weighted mean of 12 + log(O/H) = 7.11 ± 0.01 is taken as the representative O/H for IZw18. Aperture effects on the derivation of O/H are discussed. Using our IFU data we obtain, for the first time, the IZw18 integrated spectrum.
We studied the global and local M-Z relation based on the first data available from the CALIFA survey (150 galaxies). This survey provides integral field spectroscopy of the complete optical extent ...of each galaxy, with a resolution high enough to separate individual HIT regions and/or aggregations. About 3000 individual HIT regions have been detected. The spectra cover the wavelength range between 0113727 and SIT 6731, with a sufficient signal-to-noise ratio to derive the oxygen abundance and star-formation rate associated with each region. In addition, we computed the integrated and spatially resolved stellar masses based on SDSS photometric data. We explore the relations between the stellar mass, oxygen abundance and star-formation rate using this dataset. Our results agree with the scenario in which gas recycling in galaxies, both locally and globally, is much faster than other typical timescales, such like that of gas accretion by inflow and/or metal loss due to outflows. In essence, late-type/disk-dominated galaxies seem to be in a quasi-steady situation, with a behavior similar to the one expected from an instantaneous recycling/closed-box model.
The neonicotinoid insecticide imidacloprid (IMI) affects the insect central nervous system and is successfully applied to control pests for a variety of agricultural crops. In the current study, ...acute toxicity and genotoxicity of the IMI-containing commercial formulation insecticide Glacoxan Imida (35 percent IMI) was evaluated on Hypsiboas pulchellus (Anura: Hylidae) tadpoles exposed under laboratory conditions. A lethal effect was evaluated as the end point for lethality, whereas micronucleus (MN) frequency and DNA single-strand breaks evaluated by the single cell gel electrophoresis (SCGE) assay were employed as end points for genotoxicity. Sublethal end points were assayed within the 12.5–37.5mg/L IMI concentration range. Experiments were performed on tadpoles at stage 36 (range, 35–37) according to the classification proposed by Gosner. Lethality studies revealed an LC50 96h value of 52.622mg/L IMI. Increased frequency of MNs was only observed when 25.0mg/L was assayed for 96h, whereas no other nuclear abnormalities were induced. Increase of the genetic damage index was observed at 48h of treatment within the 12.5–37.5mg/L concentration range, whereas an increased frequency of DNA damage was observed only in tadpoles treated with 37.5mg/L IMI for 96h. This study represents the first evidence of the acute lethal and genotoxic effects exerted by IMI on tadpoles of an amphibian species native to Argentina under laboratory conditions.
•IMI lethal and genotoxic properties were evaluated on Hypsiboas pulchellus.•Determination of LC50 96h was employed as lethal end point.•IMI induced micronuclei and DNA single-strand breaks in circulating blood cells.•First evidence of genotoxicity exerted by IMI on an Argentinean amphibian species.
Aims.
Star-forming galaxies with nebular He
II
emission contain very energetic ionizing sources of radiation, which can be considered as analogs to the major contributors of the reionization of the ...Universe in early epochs. It is therefore of great importance to provide a reliable absolute scale for the equivalent effective temperature (
T
*
) for these sources.
Methods.
We study a sample of local (
z
< 0.2) star-forming galaxies showing optical nebular He
II
emission using the so-called softness diagrams, involving emission lines of two elements in two consecutive stages of ionization (e.g., S
II
/S
III
vs. O
II
/O
III
). We use for the first time the He
I
/He
II
ratio in these diagrams in order to explore the higher range of
T
*
expected in these objects, and to investigate the role of possible mechanisms driving the distribution of galaxy points in these diagrams. We build grids of photoionization models covering different black-body temperatures, model cluster atmospheres, and density-bounded geometries to explain the conditions observed in the sample.
Results.
We verified that the use of the softness diagrams including the emission-line ratio He
I
/He
II
combined with black-body photoionization models can provide an absolute scale of
T
*
for these objects. The application of a Bayesian-like code indicates
T
*
in the range 50−80 kK for the sample of galaxies, with a mean value higher than 60 kK. The average of these high temperature values can only be reproduced using cluster model populations with nearly metal-free stars, although such ionizing sources cannot explain either the highest
T
*
values, beyond 1
σ
, or the dispersion observed in the softness diagrams. According to our photoionization models, most sample galaxies could be affected to some extent by ionizing photon leaking, presenting a mean photon absorption fraction of 26% or higher depending on the metallicity assumed for the ionizing cluster. The entire range of He
I
/He
II
, S
II
/S
III
, and O
II
/O
III
ratios for these HeII-emitting galaxies is reproduced with our models, combining nearly metal-free ionizing clusters and photon leaking under different density-bounded conditions.
The star formation rate (SFR) is one of the main parameters used to analyze the evolution of galaxies through time. Integral field spectroscopy (IFS) is clearly the way to overcome this kind of ...limitation. We obtain integrated Halpha, ultraviolet (UV) and infrared (IR)-based SFR measurements for 272 galaxies from the C ALIFA survey at 0.005 < z < 0.03 using single-band and hybrid tracers. We aim to determine whether the extinction-corrected Halpha luminosities provide a good measure of the SFR and to shed light on the origin of the discrepancies between tracers. In the local Universe, the Halpha luminosity derived from IFS observations can be used to measure SFR, at least in statistically-significant, optically-selected galaxy samples, once stellar continuum absorption and dust attenuation effects are accounted for. The analysis of the SFR calibrations by galaxies properties could potentially be used by other works to study the impact of different selection criteria in the SFR values derived, and to disentangle selection effects from other physically motivated differences, such as environmental or evolutionary effects.
We present the largest and most homogeneous catalog of H ii regions and associations compiled so far. The catalog comprises more than 7000 ionized regions, extracted from 306 galaxies observed by the ...CALIFA survey. We describe the procedures used to detect, select, and analyze the spectroscopic properties of these ionized regions. In the current study we focus on characterizing of the radial gradient of the oxygen abundance in the ionized gas, based on the study of the deprojecteddistribution of H ii regions. We found that all galaxies without clear evidence of an interaction present a common gradient in the oxygen abundance, with a characteristic slope of αO/H = −0.1 dex/re between 0.3 and 2 disk effective radii (re), and a scatter compatible with random fluctuations around this value, when the gradient is normalized to the disk effective radius. The slope is independent of morphology, the incidence of bars, absolute magnitude, or mass. Only those galaxies with evidence of interactions and/or clear merging systems present a significantly shallower gradient, consistent with previous results. The majority of the 94 galaxies with H ii regions detected beyond two disk effective radii present a flattening in the oxygen abundance. The flattening is statistically significant. We cannot provide a conclusive answer regarding the origin of this flattening. However, our results indicate that its origin is most probably related to the secular evolution of galaxies. Finally, we find a drop/truncation of the oxygen abundance in the inner regions for 26 of the galaxies. All of them are non-interacting, mostly unbarred Sb/Sbc galaxies. This feature is associated with a central star-forming ring, which suggests that both features are produced by radial gas flows induced by resonance processes. Our result suggests that galaxy disks grow inside-out, with metal enrichment driven by the local star formation history and with a small variation galaxy-by-galaxy. At a certain galactocentric distance, the oxygen abundance seems to be correlated well with the stellar mass density and total stellar mass of the galaxies, independently of other properties of the galaxies. Other processes, such as radial mixing and inflows/outflows seem to have a limited effect on shaping of the radial distribution of oxygen abundances, although they are not ruled out.
Imazethapyr, a post-emergent herbicide used in worldwide soybean and corn crops, induces genetic and biochemical alterations in aquatic vertebrates. This study examined the relationship between ...biomarkers at different organization levels and imazethapyr real-life route exposure in
Boana pulchella
adults. Frogs were exposed to imazethapyr-based formulation Pivot
®
H (10.59%) at concentrations representing possible acute routes: field runoff (S1:10 mg.L
−1
), exposure after direct foliar application (S2:100 mg.L
−1
) and during direct foliar application (S3:1000 mg.L
−1
). Post-exposure, endpoints levels were evaluated: organism alterations, biochemical activities and cytogenetic assays. Forty-eight hours post-exposure, antioxidant enzymes decrease, micronuclei induction and DNA damage were observed in all scenarios, while cholinesterase activity increase and body condition reduction were observed in frog-exposed to S3. Ninety-six hours post-exposure, frogs showed glutathione-S-transferase inhibition in S1, micronuclei induction in S2 and S3, and DNA-damage increase in S3. Herbicides routes of exposures in real-life could indicate that authorized applications have a risk to amphibian populations.
•Effects of imidacloprid (IMI) were evaluated on Hypsiboas pulchellus tadpoles.•Mortality studies revealed a LC5096h value of 84.91mg/L of IMI.•IMI induced both micronuclei and DNA strand breaks in ...circulating blood cells.•Binucleated, blebbed, and notched cells were induced after 48 and 96h of treatment.•First evidence of deleterious effects of IMI on an Argentinean amphibian species.
Acute toxicity and genotoxicity of imidacloprid (IMI) was evaluated on Hypsiboas pulchellus (Anura: Hylidae) tadpoles exposed under laboratory conditions. A lethal effect was used as the end point for lethality, whereas the frequency of micronuclei (MNs) and DNA single-strand breaks evaluated by the single cell gel electrophoresis assay were employed as end points for genotoxicity. Experiments were performed on tadpoles at stage 36 (range, 35–37) according to the classification proposed by Gosner. Mortality studies revealed an LC50 (96h) value of 84.91mg/L IMI (95% confidence limits, 77.20–93.04). While increased frequency of MNs was observed when 15 and 30mg/L were assayed for 48h, only 15mg/L increased the frequency of MNs in tadpoles exposed for 96h. Furthermore, other nuclear abnormalities, i.e., binucleated cells and blebbed and notched nuclei, were induced in tadpoles exposed for both 48h when treated with 15mg/L and 96h when treated with 15 and 30mg/L. An increase in the genetic damage index was observed in tadpoles treated with 30mg/L for 48 and 96h. This study represents the first evidence of acute lethal and sublethal effects exerted by IMI on tadpoles of an amphibian species native to Argentina. Finally, our findings highlight the hazardous properties of this insecticide for nontarget living species exposed to this agrochemical.
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