We perform a spectroscopic study to constrain the stellar initial mass function (IMF) by using a large sample of 24 781 early-type galaxies from the Sloan Digital Sky Survey-based Spheroids ...Panchromatic Investigation in Different Environmental Regions survey. Clear evidence is found of a trend between IMF and central velocity dispersion (σ0), evolving from a standard Kroupa/Chabrier IMF at σ0 ∼ 100 km s−1 towards a more bottom-heavy IMF with increasing σ0, becoming steeper than the Salpeter function at σ0 220 km s−1. We analyse a variety of spectral indices, combining gravity-sensitive features, with age- and metallicity-sensitive indices, and we also consider the effect of non-solar abundance variations. The indices, corrected to solar scale by means of semi-empirical correlations, are fitted simultaneously with the (nearly solar-scaled) extended MILES (MIUSCAT) stellar population models. Similar conclusions are reached when analysing the spectra with a hybrid approach, combining constraints from direct spectral fitting in the optical with those from IMF-sensitive indices. Our analysis suggests that σ0, rather than α/Fe, drives the variation of the IMF. Although our analysis cannot discriminate between a single power-law (unimodal) IMF and a low-mass ( 0.5 M) tapered (bimodal) IMF, robust constraints can be inferred for the fraction in low-mass stars at birth. This fraction (by mass) is found to increase from ∼20 per cent at σ0 ∼ 100 km s−1, up to ∼80 per cent at σ0 ∼ 300 km s−1. However, additional constraints can be provided with stellar mass-to-light (M/L) ratios: unimodal models predict M/L significantly larger than dynamical M/L, across the whole σ0 range, whereas a bimodal IMF is compatible. Our results are robust against individual abundance variations. No significant variation is found in Na and Ca in addition to the expected change from the correlation between α/Fe and σ0.
Recent results on the non-universality of the Initial Mass Function (IMF) have shown strong evidence of IMF variations with galaxy velocity dispersion, with a corresponding impact on other stellar ...population parameters, line indices and colours. Using a set of stellar population models with varying IMF slopes, we provide additional caveats on the assumption of a universal IMF. This study shows that the derived star formation histories of early-type galaxies vary significantly with the IMF slope. For instance, a steepening in the slope of a single power-law IMF decreases substantially, by a factor of up to 4, the contribution of the old stellar populations to the total light/mass. This trend is milder for a segmented-like IMF shape, where the contribution of the very low mass stars is decreased. It is also shown that, by tuning each IMF slope to its prescribed value according to each galaxy velocity dispersion, a sample of early-type galaxies covering a range of masses yield comparable star formation histories. On the one hand, a small contribution from relatively young stellar populations appears in the star formation histories of most massive elliptical galaxies when adopting a steep IMF. In addition, we find that low-mass early-type galaxies that look like genuinely young objects with a standard IMF (i.e. 'baby elliptical galaxies') turn out to be older when a slightly flatter IMF is employed. In summary, the use of a non-universal IMF, tuned according to the velocity dispersion of the galaxy, seems to provide more consistent results.
Breast background parenchymal enhancement (BPE) is correlated with the risk of breast cancer. BPE level is currently assessed by radiologists in contrast-enhanced mammography (CEM) using 4 classes: ...minimal, mild, moderate and marked, as described in
(BI-RADS). However, BPE classification remains subject to intra- and inter-reader variability. Fully automated methods to assess BPE level have already been developed in breast contrast-enhanced MRI (CE-MRI) and have been shown to provide accurate and repeatable BPE level classification. However, to our knowledge, no BPE level classification tool is available in the literature for CEM.
A BPE level classification tool based on deep learning has been trained and optimized on 7012 CEM image pairs (low-energy and recombined images) and evaluated on a dataset of 1013 image pairs. The impact of image resolution, backbone architecture and loss function were analyzed, as well as the influence of lesion presence and type on BPE assessment. The evaluation of the model performance was conducted using different metrics including 4-class balanced accuracy and mean absolute error. The results of the optimized model for a binary classification: minimal/mild versus moderate/marked, were also investigated.
The optimized model achieved a 4-class balanced accuracy of 71.5% (95% CI: 71.2-71.9) with 98.8% of classification errors between adjacent classes. For binary classification, the accuracy reached 93.0%. A slight decrease in model accuracy is observed in the presence of lesions, but it is not statistically significant, suggesting that our model is robust to the presence of lesions in the image for a classification task. Visual assessment also confirms that the model is more affected by non-mass enhancements than by mass-like enhancements.
The proposed BPE classification tool for CEM achieves similar results than what is published in the literature for CE-MRI.
This is the first paper of a series presenting the Spheroids Panchromatic Investigation in Different Environmental Regions (SPIDER). The sample of spheroids consists of 5080 bright (Mr < −20) ...early-type galaxies (ETGs), in the redshift range of 0.05 to 0.095, with optical (griz) photometry and spectroscopy from the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) and near-infrared (YJHK) photometry from the UKIRT Infrared Deep Sky Survey-Large Area Survey (UKIDSS-LAS) (DR4). We describe how homogeneous photometric parameters (galaxy colours and structural parameters) are derived using grizYJHK wavebands. We find no systematic steepening of the colour–magnitude relation when probing the baseline from g−r to g−K, implying that internal colour gradients drive most of the mass–metallicity relation in ETGs. As far as structural parameters are concerned we find that the mean effective radius of ETGs smoothly decreases, by 30 per cent, from g through K, while no significant dependence on waveband is detected for the axial ratio, Sersic index and a4 parameters. Furthermore, velocity dispersions are remeasured for all the ETGs using starlight and compared to those obtained by SDSS. The velocity dispersions are rederived using a combination of simple stellar population models as templates, hence accounting for the kinematics of different galaxy stellar components. We compare our (2dphot) measurements of total magnitude, effective radius and mean surface brightness with those obtained as part of the SDSS pipeline (photo). Significant differences are found and reported, including comparisons with a third and independent part. A full characterization of the sample completeness in all wavebands is presented, establishing the limits of application of the characteristic parameters presented here for the analysis of the global scaling relations of ETGs.
ABSTRACT
We test cosmological hydrodynamical simulations of galaxy formation regarding the properties of the blue cloud (BC), green valley (GV), and red sequence (RS), as measured on the 4000Å break ...strength versus stellar mass plane at z = 0.1. We analyse the RefL0100N1504 run of EAGLE and the TNG100 run of IllustrisTNG project, by comparing them with the Sloan Digital Sky Survey (SDSS), while taking into account selection bias. Our analysis focuses on the GV, within stellar mass $\log \, \mathrm{{\it M}_\star /M_{\odot }} \simeq 10\!-\!11$, selected from the bimodal distribution of galaxies on the Dn(4000) versus stellar mass plane, following Angthopo et al. methodology. Both simulations match the fraction of AGN in the GV. However, they overproduce quiescent GV galaxies with respect to observations, with IllustrisTNG yielding a higher fraction of quiescent GV galaxies than EAGLE. In both, GV galaxies have older luminosity-weighted ages with respect to the SDSS, while a better match is found for mass-weighted ages. We find EAGLE GV galaxies quench their star formation early, but undergo later episodes of star formation, matching observations. In contrast, IllustrisTNG GV galaxies have a more extended star formation history, and quench more effectively at later cosmic times, producing the excess of quenched galaxies in GV compared with SDSS, based on the 4000Å break strength. These results suggest the AGN feedback subgrid physics, more specifically, the threshold halo mass for black hole input and the black hole seed mass, could be the primary cause of the overproduction of quiescent galaxies found with respect to the observational constraints.
A detailed analysis of how environment affects the star formation history of early-type galaxies (ETGs) is undertaken via high signal-to-noise ratio stacked spectra obtained from a sample of 20 977 ...ETGs (morphologically selected) from the Sloan Digital Sky Survey-based SPIDER survey. Two major parameters are considered for the study: the central velocity dispersion (...), which relates to local drivers of star formation, and the mass of the host halo, which relates to environment-related effects. In addition, we separate the sample between centrals (the most massive galaxy in a halo) and satellites. We derive trends of age, metallicity, and alpha /Fe enhancement, with ... We confirm that the major driver of stellar population properties in ETGs is velocity dispersion, with a second-order effect associated with the central/satellite nature of the galaxy. No environmental dependence is detected for satellite ETGs, except at low ... - where satellites in groups or in the outskirts of clusters tend to be younger than those in the central regions of clusters. In contrast, the trends for centrals show a significant dependence on halo mass. Central ETGs in groups (i.e. with a halo mass >10... M...) have younger ages, lower alpha /Fe, and higher internal reddening, than 'isolated' systems (i.e. centrals residing in low-mass, <10... M..., haloes). Our findings imply that central ETGs in groups formed their stellar component over longer time scales than 'isolated' centrals, mainly because of gas-rich interactions with their companion galaxies. (ProQuest: ... denotes formulae/symbols omitted.)
We present a complete analysis of the Fundamental Plane (FP) of early-type galaxies (ETGs) in the nearby Universe (z < 0.1). The sample, as defined in Paper I, comprises 39 993 ETGs located in ...environments covering the entire domain in local density (from field to cluster). We derive the FP in the grizYJHK wavebands with a detailed discussion on fitting procedure, bias due to selection effects and bias due to correlated errors on the effective parameters, re and 〈μ〉e, as key factors in obtaining meaningful FP coefficients. Studying the Kormendy relation (KR) we find that its slope varies from g (3.44 ± 0.04) through K (3.80 ± 0.02) implying that smaller size ETGs have a larger ratio of optical to near-infrared (NIR) radii than galaxies with larger re. We also examine the Faber–Jackson (FJ) relation and find that its slope is similar for all wavebands, within the uncertainties, with a mean value of 0.198 ± 0.007. Writing the FP equation as log re=a log σ0+b〈μ〉e+c, we find that the ‘a’ varies from 1.38 ± 0.02 in g to 1.55 ± 0.02 in K, implying a 12 per cent variation across the grizYJHK wavelength baseline. The corresponding variation of ‘b’ is negligible (b∼ 0.316), while ‘c’ varies by ∼10 per cent. We show that the waveband dependence of the FJ and KR results from the complex variation of the distribution of galaxies in the face-on projection of the FP as well as by the change of FP coefficients with waveband. We find that ‘a’ and ‘b’ become smaller for higher Sersic index and larger axial ratios, independent of the waveband. This suggests that these variations are likely to be related to differences in structural and dynamical (rather than stellar population) properties of ETGs. It is noticeable that galaxies with bluer colours and disc-like isophotes have smaller ‘b’, with the effect decreasing smoothly from g through K. Considering a power-law relation between mass-to-light ratio and (dynamical) mass, M/L∝Mγ, we estimate γ from the FP coefficients in grizYJHK. The γ decreases from 0.224 ± 0.008 in g to 0.186 ± 0.009 in K band. Using the γ values, we estimate the variation of age and metallicity of the stellar populations present in massive galaxies per decade in stellar mass. This analysis shows that in the NIR the tilt of the FP is not due to stellar population variation, and that ETGs have coeval stellar populations with an age variation of a few per cent per decade in mass, and a corresponding metallicity increase of ∼23 per cent. We also show that current semi-analytical models of galaxy formation reproduce very well these amounts of variation of age and metallicity with respect to stellar mass.
We analyse the Fundamental Plane (FP) relation of 39 993 early-type galaxies (ETGs) in the optical (griz) and 5080 ETGs in the near-infrared (NIR; YJHK) wavebands, forming an optical+NIR sample of ...4589 galaxies. We focus on the analysis of the FP as a function of the environment where galaxies reside. We characterize the environment using the largest group catalogue, based on 3D data, generated from the Sloan Digital Sky Survey at low redshift (z < 0.1). We find that the intercept ‘c’ of the FP decreases smoothly from high- to low-density regions, implying that galaxies at low density have on average lower mass-to-light ratios than their high-density counterparts. The ‘c’ also decreases as a function of the mean characteristic mass of the parent galaxy group. However, this trend is weak and completely accounted for by the variation of ‘c’ with local density. The variation of the FP offset is the same in all wavebands, implying that ETGs at low density have younger luminosity-weighted ages than cluster galaxies, consistent with the expectations of semi-analytical models of galaxy formation. We measure an age variation of ∼0.048 dex (∼11 per cent) per decade of local galaxy density. This implies an age difference of about 32 per cent (∼3 Gyr) between galaxies in the regions of highest density and the field. We find the metallicity decreasing, at ∼2σ, from low to high density. We also find 2.5σ evidence that the variation in age per decade of local density augments, up to a factor of 2, for galaxies residing in massive relative to poor groups. The velocity dispersion slope of the FP, a, tends to decrease with local galaxy density, with galaxies in groups having smaller a than those in the field, independent of the waveband used to measure the structural parameters. Environmental effects (such as tidal stripping) may elucidate this result, producing a steeper variation of dark-matter fraction and/or non-homology along the ETG’s sequence at higher density. In the optical, the surface brightness slope, b, of the FP increases with local galaxy density, being larger for group relative to field galaxies. The difference vanishes in the NIR, as field galaxies show a small (∼2.5 per cent) but significant increase of b from g through K, while group galaxies (particularly those in rich clusters) do not. The trend of b with the environment results from galaxies residing in more massive clusters, since for groups no variation of b with local density is detected. A possible explanation for these findings is that the variation of stellar population properties with mass in ETGs is shallower for galaxies at high density, resulting from tidal stripping and quenching of star formation in galaxies falling into the group’s potential well. We do not detect any dependence of the FP coefficients on the presence of substructures in parent galaxy groups.
Identifying effective drugs for Coronavirus disease 2019 (COVID-19) is urgently needed. An efficient approach is to evaluate whether existing approved drugs have anti-SARS-CoV-2 effects. The ...antiviral properties of lithium salts have been studied for many years. Their anti-inflammatory and immune-potentiating effects result from the inhibition of glycogen synthase kinase-3.
To obtain pre-clinical evidence on the safety and therapeutic effects of lithium salts in the treatment of COVID-19.
Six different concentrations of lithium, ranging 2–12 mmol/L, were evaluated. Lithium inhibited the replication of SARS-CoV-2 virus in a dose-dependent manner with an IC50 value of 4 mmol/L. Lithium-treated wells showed a significantly higher percentage of monolayer conservation than viral control, particularly at concentrations higher than 6 mmol/L, verified through microscopic observation, the neutral red assay, and the determination of N protein in the supernatants of treated wells. Hamsters treated with lithium showed less intense disease with fewer signs. No lithium-related mortality or overt signs of toxicity were observed during the experiment. A trend of decreasing viral load in nasopharyngeal swabs and lungs was observed in treated hamsters compared to controls.
These results provide pre-clinical evidence of the antiviral and immunotherapeutic effects of lithium against SARS-CoV-2, which supports an advance to clinical trials on COVID-19′s patients.
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•Antiviral, anti-inflammatory and immune-potentiating effects of lithium salts have been described.•Lithium directly inhibits the replication of SARS-CoV-2 in Vero E6 cells in a concentration-dependent manner with an IC50 of 4 mmol/L.•Syrian hamsters treated with human therapeutic doses of lithium showed a less intense disease.
We characterize the kinematics, morphology, stellar populations and star formation histories of a sample of massive compact galaxies in the nearby Universe, which might provide a closer look at the ...nature of their high-redshift (z >rsim 1.0) massive counterparts. We find that nearby compact massive objects show elongated morphologies and are fast rotators. New high-quality long-slit spectra show that they have young mean luminosity-weighted ages (
2 Gyr) and metallicities solar or above (Z/H >rsim 0.0). No significant stellar population gradients are found. The analysis of their star formation histories suggests that these objects have experienced recently enormous bursts which, in some cases, represent unprecedented large fractions of their total stellar mass. These galaxies seem to be truly unique, as they do not follow the characteristic kinematical and stellar population patterns of present-day massive ellipticals, spirals or even dwarfs.
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