1,325 research outputs found
The Stellar Mass Fundamental Plane: The virial relation and a very thin plane for slow-rotators
Early-type galaxies -- slow and fast rotating ellipticals (E-SRs and E-FRs)
and S0s/lenticulars -- define a Fundamental Plane (FP) in the space of
half-light radius , enclosed surface brightness and velocity
dispersion . Since and are distance-independent
measurements, the thickness of the FP is often expressed in terms of the
accuracy with which and can be used to estimate sizes .
We show that: 1) The thickness of the FP depends strongly on morphology. If the
sample only includes E-SRs, then the observed scatter in is ,
of which only is intrinsic. Removing galaxies with
further reduces the observed scatter to ( intrinsic). The observed scatter increases to the usually
quoted in the literature if E-FRs and S0s are added. If the FP is defined using
the eigenvectors of the covariance matrix of the observables, then the E-SRs
again define an exceptionally thin FP, with intrinsic scatter of only
orthogonal to the plane. 2) The structure within the FP is most easily
understood as arising from the fact that and are nearly
independent, whereas the and correlations are nearly
equal and opposite. 3) If the coefficients of the FP differ from those
associated with the virial theorem the plane is said to be `tilted'. If we
multiply by the global stellar mass-to-light ratio and we account
for non-homology across the population by using S\'ersic photometry, then the
resulting stellar mass FP is less tilted. Accounting self-consistently for
gradients will change the tilt. The tilt we currently see suggests that
the efficiency of turning baryons into stars increases and/or the dark matter
fraction decreases as stellar surface brightness increases.Comment: 13 pages, 9 figures, 3 tables, accepted for publication in MNRA
The maximum entropy formalism and the idiosyncratic theory of biodiversity
Why does the neutral theory, which is based on unrealistic assumptions, predict diversity patterns so accurately? Answering questions like this requires a radical change in the way we tackle them. The large number of degrees of freedom of ecosystems pose a fundamental obstacle to mechanistic modelling. However, there are tools of statistical physics, such as the maximum entropy formalism (MaxEnt), that allow transcending particular models to simultaneously work with immense families of models with different rules and parameters, sharing only well-established features. We applied MaxEnt allowing species to be ecologically idiosyncratic, instead of constraining them to be equivalent as the neutral theory does. The answer we found is that neutral models are just a subset of the majority of plausible models that lead to the same patterns. Small variations in these patterns naturally lead to the main classical species abundance distributions, which are thus unified in a single framework
Feasibility of using rural waste products to increase the denitrification efficiency in a surface flow constructed wetland
A surface flow constructed wetland (CW) was set in the Lerma gully to decrease nitrate (NO3 -) pollution from agricultural runoff water. The water flow rate and NO3 - concentration were monitored at the inlet and the outlet, and sampling campaigns were performed which consisted of collecting six water samples along the CW flow line. After two years of operation, the NO3 - attenuation was limited at a flow rate of ~2.5 L/s and became negligible at ~5.5 L/s. The present work aimed to assess the feasibility of using rural waste products (wheat hay, corn stubble, and animal compost) to induce denitrification in the CW, to assess the effect of temperature on this process, and to trace the efficiency of the treatment by using isotopic tools. In the first stage, microcosm experiments were performed. Afterwards, the selected waste material was applied in the CW, and the treatment efficiency was evaluated by means of a chemical and isotopic characterization and using the isotopic fractionation (e) values calculated from laboratory experiments to avoid field-scale interference. The microcosms results showed that the stubble was the most appropriate material for application in the CW, but the denitrification rate was found to decrease with temperature. In the CW, biostimulation in autumn-winter promoted NO3 - attenuation between two weeks and one month (a reduction in NO3 - between 1.2 and 1.5 mM was achieved). After the biostimulation in spring-summer, the attenuation was maintained for approximately three months (NO3 - reduction between 0.1 and 1.5 mM). The e15NNO3/N2 and e18ONO3/N2 values obtained from the laboratory experiments allowed to estimate the induced denitrification percentage. At an approximate average flow rate of 16 L/s, at least 60% of NO3 - attenuation was achieved in the CW. The field samples exhibited a slope of 1.0 for d18O-NO3 - versus d15N-NO3 -, similar to those of the laboratory experiments (0.9–1.2). Plant uptake seemed to play a minor role in NO3 - attenuation in the CW. Hence, the application of stubble in the CW allowed the removal of large amounts of NO3 - from the Lerma gully, especially when applied during the warm months, but its efficacy was limited to a short time period (up to three months). © 2019 Elsevier B.V
The half mass radius of MaNGA galaxies: Effect of IMF gradients
Gradients in the stellar populations (SP) of galaxies -- e.g., in age,
metallicity, stellar Initial Mass Function (IMF) -- can result in gradients in
the stellar mass to light ratio, . Such gradients imply that the
distribution of the stellar mass and light are different. For old SPs, e.g., in
early-type galaxies at , the gradients are weak if driven by
variations in age and metallicity, but significantly larger if driven by the
IMF. A gradient which has larger in the center increases the estimated
total stellar mass () and reduces the scale which contains half this mass
(), compared to when the gradient is ignored. For the IMF gradients
inferred from fitting MILES simple SP models to the H,
Fe, [MgFe] and TiO absorption lines measured in
spatially resolved spectra of early-type galaxies in the MaNGA survey, the
fractional change in can be significantly larger than that in ,
especially when the light is more centrally concentrated. The
correlation which results is offset by 0.3 dex to smaller sizes compared to
when these gradients are ignored. Comparisons with `quiescent' galaxies at
higher- must account for evolution in SP gradients (especially age and IMF)
and the light profile before drawing conclusions about how and
evolve. The implied merging between higher- and the present is less
contrived if at is closer to our IMF-driven gradient
calibration than to unity.Comment: 16 pages, 15 figures, accepted for publication in MNRA
Classical Singularities In Chaotic Atom-Surface Scattering
In this paper we show that the diffraction condition for the scattering of atoms from surfaces leads to the appearance of a distinct type of classical singularity. Moreover, it is also shown that the onset of classical trapping or classical chaos is closely related to the bifurcation set of the diffraction-order function around the surface points presenting the rainbow effect. As an illustration of this dynamic, application to the scattering of He atoms by the stepped Cu(115) surface is presented using both a hard corrugated one-dimensional wall and a soft corrugated Morse potential
Galaxy properties as revealed by MaNGA. III. Kinematic profiles and stellar population gradients in S0s
This is the third paper of a series where we study the stellar population
gradients (SP; ages, metallicities, -element abundance ratios and
stellar initial mass functions) of early type galaxies (ETGs) at
from the MaNGA-DR15 survey. In this work we focus on the S0 population and
quantify how the SP varies across the population as well as with galactocentric
distance. We do this by measuring Lick indices and comparing them to stellar
population synthesis models. This requires spectra with high signal-to-noise
which we achieve by stacking in bins of luminosity (L) and central velocity
dispersion (). We find that: 1) There is a bimodality in the S0
population: S0s more massive than show stronger
velocity dispersion and age gradients (age and decrease outwards)
but little or no metallicity gradient, while the less massive ones present
relatively flat age and velocity dispersion profiles, but a significant
metallicity gradient (i.e. [M/H] decreases outwards). Above
the number of S0s drops sharply. These two mass scales
are also where global scaling relations of ETGs change slope. 2) S0s have
steeper velocity dispersion profiles than fast rotating elliptical galaxies
(E-FRs) of the same luminosity and velocity dispersion. The kinematic profiles
and stellar population gradients of E-FRs are both more similar to those of
slow rotating ellipticals (E-SRs) than to S0s, suggesting that E-FRs are not
simply S0s viewed face-on. 3) At fixed , more luminous S0s and E-FRs
are younger, more metal rich and less -enhanced. Evidently for these
galaxies, the usual statement that 'massive galaxies are older' is not true if
is held fixed.Comment: Accepted for publication in MNRAS. 15 pages, 20 figure
Evaluating the potential use of a dairy industry residue to induce denitrification in polluted water bodies: a flow-through experiment
Improving the effectiveness and economics of strategies to remediate groundwater nitrate pollution is a matter of concern. In this context, the addition of whey into aquifers could provide a feasible solution to attenuate nitrate contamination by inducing heterotrophic denitrification, while recycling an industry residue. Before its application, the efficacy of the treatment must be studied at laboratory-scale to optimize the application strategy in order to avoid the generation of harmful intermediate compounds. To do this, a flow-through denitrification experiment using whey as organic C source was performed, and different C/N ratios and injection periodicities were tested. The collected samples were analyzed to determine the chemical and isotopic composition of N and C compounds. The results proved that whey could promote denitrification. Nitrate was completely removed when using either a 3.0 or 2.0 C/N ratio. However, daily injection with C/N ratios from 1.25 to 1.5 seemed advantageous, since this strategy decreased nitrate concentration to values below the threshold for water consumption while avoiding nitrite accumulation and whey release with the outflow. The isotopic results confirmed that nitrate attenuation was due to denitrification and that the production of DIC was related to bacterial whey oxidation. Furthermore, the isotopic data suggested that when denitrification was not complete, the outflow could present a mix of denitrified and nondenitrified water. The calculated isotopic fractionation values (ε15NNO3/N2 and ε18ONO3/N2) might be applied in the future to quantify the efficiency of the bioremediation treatments by whey application at field-scale
Numerical modeling of enhanced biodenitrification in a laboratory flow-through experiment
High concentration of nitrate (NO3) in water resources has become a widespread and important environmental contaminant, being anthropogenic nitrogen input the principal source of NO3− pollution (Arauzo, 2017). Underanaerobic conditions, microbial reduction of NO3 to N2(g) to oxidize dissolved organic carbon (DOC) is the principal NO3 attenuation process in groundwater aquifers (Matchett et al., 2019)
Nitrate and Nitrite Attenuation by Fe(II) Minerals: Biotic and Abiotic Reactions
Nitrate (NO3-) pollution of groundwaterhas become a relevant issue and anenvironmental priority as it is related toecological and human health problems(Rivett et al. 2008) and its concentration is still above the threshold limit of 50mg/L in many areas (Nitrate Directive, 91/676/EEC). Contamination sources of NO3 - are linked to extensive use of fertilizers, inappropriate placement of animal waste and spills from septic system effluents
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