312 research outputs found
The Morphology-Density-Relation: Impact on the Satellite Fraction
In the past years several authors studied the abundance of satellites around
galaxies in order to better estimate the halo masses of host galaxies. To
investigate this connection, we analyze galaxies with
from the hydrodynamical cosmological
simulation Magneticum. We find that the satellite fraction of centrals is
independent of their morphology. With the exception of very massive galaxies at
low redshift, our results do not support the assumption that the dark matter
(DM) haloes of spheroidal galaxies are significantly more massive than those of
disc galaxies at fixed . We show that the
density-morphology-relation starts to build up at and is independent
of the star-formation properties of central galaxies. We conclude that
environmental quenching is more important for satellites than for centrals. Our
simulations indicate that conformity is already in place at , where
formation redshift and current star-formation rate (SFR) of central and
satellite galaxies correlate. Centrals with low SFRs have formed earlier (at
fixed ) while centrals with high SFR formed later, with
typical formation redshifts well in agreement with observations. However, we
confirm the recent observations that the apparent number of satellites of
spheroidal galaxies is significantly larger than for disc galaxies. This
difference completely originates from the inclusion of companion galaxies, i.e.
galaxies that do not sit in the potential minimum of a DM halo. Thus, due to
the density-morphological-relation the number of satellites is not a good
tracer for the halo mass, unless samples are restricted to the central galaxies
of DM haloes.Comment: 17 pages, submitted to MNRAS, www.magneticum.or
Teachers’ Attitude towards Corporal Punishment: Elementary Schools of the Central Zone of Tigray Region in Ethiopia in Focus
Despite the plethora of policy and legal instruments banning corporal punishment (CP) in schools and the sea of knowledge about the negative consequences of CP in children, CP occupies a significant place in the scheme of affairs of schools across the globe. Ethiopia too is not an exception. Teachers’ attitude towards CP can predict their application of it. This investigation thus was designed to assess the magnitude and nature of teachers’ attitude towards CP and its association with various teacher variables. Data were collected through an individually administered instrument pack with three sections including a CorpAtt Scale from a sample of 199 first cycle government elementary school teachers of the Central Zone of Tigray Region in Ethiopia drawn using multistage cluster sampling procedure. The results revealed that teachers hold predominantly positive attitude towards CP. Teacher variables such as duration of service, perceived knowledge about problem behavior and its school based management, confidence in managing problem behavior with and without applying CP and the locale of schools are found to be associated with their attitude towards CP. Gender, age and status of training in special needs education were found not to be associated with their attitudes. Implications of the revelations are discussed against teacher education and training and policy management in the Ethiopian context.Keywords: attitude, behavior management, corporal punishment, elementary school, Ethiopi
Origin and properties of dual and offset active galactic nuclei in a cosmological simulation at z=2
In the last few years, it became possible to observationally resolve galaxies
with two distinct nuclei in their centre. For separations smaller than 10kpc,
dual and offset active galactic nuclei (AGN) are distinguished: in dual AGN,
both nuclei are active, whereas in offset AGN only one nucleus is active. To
study the origin of such AGN pairs, we employ a cosmological, hydrodynamic
simulation with a large volume of (182Mpc)^3 from the set of Magneticum
Pathfinder Simulations. The simulation self-consistently produces 35 resolved
black hole (BH) pairs at redshift z=2, with a comoving distance smaller than
10kpc. 14 of them are offset AGN and nine are dual AGN, resulting in a fraction
of (1.2 \pm 0.3)% AGN pairs with respect to the total number of AGN. In this
paper, we discuss fundamental differences between the BH and galaxy properties
of dual AGN, offset AGN and inactive BH pairs and investigate their different
triggering mechanisms. We find that in dual AGN the BHs have similar masses and
the corresponding BH from the less massive progenitor galaxy always accretes
with a higher Eddington ratio. In contrast, in offset AGN the active BH is
typically more massive than its non-active counterpart. Furthermore, dual AGN
in general accrete more gas from the intergalactic medium than offset AGN and
non-active BH pairs. This highlights that merger events, particularly minor
mergers, do not necessarily lead to strong gas inflows and thus, do not always
drive strong nuclear activity.Comment: 17 pages, 18 figures, accepted for publication in MNRAS, website:
http://www.magneticum.or
Declining rotation curves at in CDM galaxy formation simulations
Selecting disk galaxies from the cosmological, hydrodynamical simulation
Magneticum Pathfinder we show that almost half of our poster child disk
galaxies at show significantly declining rotation curves and low dark
matter fractions, very similar to recently reported observations. These
galaxies do not show any anomalous behavior, reside in standard dark matter
halos and typically grow significantly in mass until , where they span
all morphological classes, including disk galaxies matching present day
rotation curves and observed dark matter fractions. Our findings demonstrate
that declining rotation curves and low dark matter fractions in rotation
dominated galaxies at appear naturally within the CDM paradigm
and reflect the complex baryonic physics, which plays a role at the peak epoch
of star-formation. In addition, we find some dispersion dominated galaxies at
which host a significant gas disk and exhibit similar shaped rotation
curves as the disk galaxy population, rendering it difficult to differentiate
between these two populations with currently available observation techniques.Comment: 6 pages, 4 figures, ApJ Letters in press, www.magneticum.or
Connecting Angular Momentum and Galactic Dynamics: The complex Interplay between Spin, Mass, and Morphology
The evolution and distribution of the angular momentum of dark matter (DM)
halos have been discussed in several studies over the past decades. In
particular, the idea arose that angular momentum conservation should allow to
infer the total angular momentum of the entire DM halo from measuring the
angular momentum of the baryonic component, which is populating the center of
the halo, especially for disk galaxies. To test this idea and to understand the
connection between the angular momentum of the DM halo and its galaxy, we use
the Magneticum simulations. We successfully produce populations of spheroidal
and disk galaxies self-consistently. Thus, we are able to study the dependence
of galactic properties on their morphology. We find that (1) the specific
angular momentum of stars in disk and spheroidal galaxies as a function of
their stellar mass compares well with observational results; (2) the specific
angular momentum of the stars in disk galaxies is slightly smaller compared to
the specific angular momentum of the cold gas, in good agreement with
observations; (3) simulations including the baryonic component show a dichotomy
in the specific stellar angular momentum distribution when splitting the
galaxies according to their morphological type (this dichotomy can also be seen
in the spin parameter, where disk galaxies populate halos with slightly larger
spin compared to spheroidal galaxies); (4) disk galaxies preferentially
populate halos in which the angular momentum vector of the DM component in the
central part shows a better alignment to the angular momentum vector of the
entire halo; and (5) the specific angular momentum of the cold gas in disk
galaxies is approximately 40 percent smaller than the specific angular momentum
of the total DM halo and shows a significant scatter.Comment: 25 pages, accepted by ApJ, www.magneticum.or
{\Lambda}CDM with baryons vs. MOND: the time evolution of the universal acceleration scale in the Magneticum simulations
MOdified Newtonian Dynamics (MOND) is an alternative to the standard Cold
Dark Matter (CDM) paradigm which proposes an alteration of Newton's laws of
motion at low accelerations, characterized by a universal acceleration scale
a_0. It attempts to explain observations of galactic rotation curves and
predicts a specific scaling relation of the baryonic and total acceleration in
galaxies, referred to as the Rotational Acceleration Relation (RAR), which can
be equivalently formulated as a Mass Discrepancy Acceleration Relation (MDAR).
The appearance of these relations in observational data such as SPARC has lead
to investigations into the existence of similar relations in cosmological
simulations using the standard {\Lambda}CDM model. Here, we report the
existence of an RAR and MDAR similar to that predicted by MOND in {\Lambda}CDM
using a large sample of galaxies extracted from a cosmological, hydrodynamical
simulation (Magneticum). Furthermore, by using galaxies in Magneticum at
different redshifts, a prediction for the evolution of the inferred
acceleration parameter a_0 with cosmic time is derived by fitting a MOND force
law to these galaxies. In Magneticum, the best fit for a_0 is found to increase
by a factor of approximately 3 from redshift z = 0 to z = 2. This offers a
powerful test from cosmological simulations to distinguish between MOND and
{\Lambda}CDM observationally.Comment: 13 pages, 13 figures; accepted by MNRA
Invitro Antibacterial Screening of Extracts from Selected Ethiopian Medicinal Plants
Indigenous knowledge, literature reports and ethnobotanical records suggest that plants are the basis for medicines. They constitute natural source of antimicrobial drugs that will provide novel or lead compounds for the fight against disease. In this study, the antimicrobial activity of three selected Ethiopian medicinal plants was studied with the objective of screening their antibacterial activity. The fruits of Measalanceolata, aerial part of Cissus quadrangularis and leaf of Dodonae angustifolia were collected, air dried under shed, powdered and soaked in 80% methanol and extracted. In vitro antibacterial activity of the extracts was tested at different concentrations by using agar disc diffusion method and measuring the zone of inhibition. The plant extracts showed broad spectrum activity against gram positive (S. aureus) as well as gram negative (E. coli) bacteria, except Cissus quadrangularis which did not show any activity against E. coli. Furthermore, the plant extracts had also concentration dependant zone of inhibition against the tested bacteria. In fact, the highest activity was obtained for Dodonae angustifolia at 1000mg/ml against S. aureus. The activities are attributed to the presence of some secondary metabolites present in the tested plants which have been associated with antibacterial activities. This finding suggests that these medicinal plants can be potential source to isolate antibacterial drugs.Keywords: Antibacterial activity, Disc diffusion, E. coli, Plant extract and S. aureus
An improved SPH scheme for cosmological simulations
We present an implementation of smoothed particle hydrodynamics (SPH) with
improved accuracy for simulations of galaxies and the large-scale structure. In
particular, we combine, implement, modify and test a vast majority of SPH
improvement techniques in the latest instalment of the GADGET code. We use the
Wendland kernel functions, a particle wake-up time-step limiting mechanism and
a time-dependent scheme for artificial viscosity, which includes a high-order
gradient computation and shear flow limiter. Additionally, we include a novel
prescription for time-dependent artificial conduction, which corrects for
gravitationally induced pressure gradients and largely improves the SPH
performance in capturing the development of gas-dynamical instabilities. We
extensively test our new implementation in a wide range of hydrodynamical
standard tests including weak and strong shocks as well as shear flows,
turbulent spectra, gas mixing, hydrostatic equilibria and self-gravitating gas
clouds. We jointly employ all modifications; however, when necessary we study
the performance of individual code modules. We approximate hydrodynamical
states more accurately and with significantly less noise than standard SPH.
Furthermore, the new implementation promotes the mixing of entropy between
different fluid phases, also within cosmological simulations. Finally, we study
the performance of the hydrodynamical solver in the context of radiative galaxy
formation and non-radiative galaxy cluster formation. We find galactic disks to
be colder, thinner and more extended and our results on galaxy clusters show
entropy cores instead of steadily declining entropy profiles. In summary, we
demonstrate that our improved SPH implementation overcomes most of the
undesirable limitations of standard SPH, thus becoming the core of an efficient
code for large cosmological simulations.Comment: 21 figures, 2 tables, accepted to MNRA
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