380 research outputs found
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
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
Systematic variation of central mass density slope in early-type galaxies
We study the total density distribution in the central regions (
effective radius, ) of early-type galaxies (ETGs), using data from
the SPIDER survey. We model each galaxy with two components (dark matter halo +
stars), exploring different assumptions for the dark matter (DM) halo profile,
and leaving stellar mass-to-light () ratios as free fitting
parameters to the data. For a Navarro et al. (1996) profile, the slope of the
total mass profile is non-universal. For the most massive and largest ETGs, the
profile is isothermal in the central regions (), while for
the low-mass and smallest systems, the profile is steeper than isothermal, with
slopes similar to those for a constant-M/L profile. For a concentration-mass
relation steeper than that expected from simulations, the correlation of
density slope with mass tends to flatten. Our results clearly point to a
"non-homology" in the total mass distribution of ETGs, which simulations of
galaxy formation suggest may be related to a varying role of dissipation with
galaxy mass.Comment: 3 pages, 1 figure, to appear on the refereed Proceeding of the "The
Universe of Digital Sky Surveys" conference held at the INAF--OAC, Naples, on
25th-28th november 2014, to be published on Astrophysics and Space Science
Proceedings, edited by Longo, Napolitano, Marconi, Paolillo, Iodic
In the absence of ATPase activity, pre-RC formation is blocked prior to MCM2-7 hexamer dimerization
The origin recognition complex (ORC) of Saccharomyces cerevisiae binds origin DNA and cooperates with Cdc6 and Cdt1 to load the replicative helicase MCM2–7 onto DNA. Helicase loading involves two MCM2–7 hexamers that assemble into a double hexamer around double-stranded DNA. This reaction requires ORC and Cdc6 ATPase activity, but it is unknown how these proteins control MCM2–7 double hexamer formation. We demonstrate that mutations in Cdc6 sensor-2 and Walker A motifs, which are predicted to affect ATP binding, influence the ORC–Cdc6 interaction and MCM2–7 recruitment. In contrast, a Cdc6 sensor-1 mutant affects MCM2–7 loading and Cdt1 release, similar as a Cdc6 Walker B ATPase mutant. Moreover, we show that Orc1 ATP hydrolysis is not involved in helicase loading or in releasing ORC from loaded MCM2–7. To determine whether Cdc6 regulates MCM2–7 double hexamer formation, we analysed complex assembly. We discovered that inhibition of Cdc6 ATPase restricts MCM2–7 association with origin DNA to a single hexamer, while active Cdc6 ATPase promotes recruitment of two MCM2–7 hexamer to origin DNA. Our findings illustrate how conserved Cdc6 AAA+ motifs modulate MCM2–7 recruitment, show that ATPase activity is required for MCM2–7 hexamer dimerization and demonstrate that MCM2–7 hexamers are recruited to origins in a consecutive process
Characterising Tidal Features Around Galaxies in Cosmological Simulations
Tidal features provide signatures of recent mergers and offer a unique insight into the assembly history of galaxies. The Vera C. Rubin Observatory’s Legacy Survey of Space and Time (LSST) will enable an unprecedentedly large survey of tidal features around millions of galaxies. To decipher the contributions of mergers to galaxy evolution it will be necessary to compare the observed tidal features with theoretical predictions. Therefore, we use cosmological hydrodynamical simulations NewHorizon, eagle, IllustrisTNG, and Magneticum to produce LSST-like mock images of z ∼ 0 galaxies (z ∼ 0.2 for NewHorizon) with M. We perform a visual classification to identify tidal features and classify their morphology. We find broadly good agreement between the simulations regarding their overall tidal feature fractions: , , and , and their specific tidal feature fractions. Furthermore, we find excellent agreement regarding the trends of tidal feature fraction with stellar and halo mass. All simulations agree in predicting that the majority of central galaxies of groups and clusters exhibit at least one tidal feature, while the satellite members rarely show such features. This agreement suggests that gravity is the primary driver of the occurrence of visually-identifiable tidal features in cosmological simulations, rather than subgrid physics or hydrodynamics. All predictions can be verified directly with LSST observations
Cryo-EM structure of a helicase loading intermediate containing ORC-Cdc6-Cdt1-MCM2-7 bound to DNA
In eukaryotes, the Cdt1-bound replicative helicase core MCM2-7 is loaded onto DNA by the ORC-Cdc6 ATPase to form a prereplicative complex (pre-RC) with an MCM2-7 double hexamer encircling DNA. Using purified components in the presence of ATP-γS, we have captured in vitro an intermediate in pre-RC assembly that contains a complex between the ORC-Cdc6 and Cdt1-MCM2-7 heteroheptamers called the OCCM. Cryo-EM studies of this 14-subunit complex reveal that the two separate heptameric complexes are engaged extensively, with the ORC-Cdc6 N-terminal AAA+ domains latching onto the C-terminal AAA+ motor domains of the MCM2-7 hexamer. The conformation of ORC-Cdc6 undergoes a concerted change into a right-handed spiral with helical symmetry that is identical to that of the DNA double helix. The resulting ORC-Cdc6 helicase loader shows a notable structural similarity to the replication factor C clamp loader, suggesting a conserved mechanism of action
The MAGPI Survey: Drivers of kinematic asymmetries in the ionised gas of star-forming galaxies
Galaxy gas kinematics are sensitive to the physical processes that contribute
to a galaxy's evolution. It is expected that external processes will cause more
significant kinematic disturbances in the outer regions, while internal
processes will cause more disturbances for the inner regions. Using a subsample
of 47 galaxies () from the Middle Ages Galaxy Properties with
Integral Field Spectroscopy (MAGPI) survey, we conduct a study into the source
of kinematic disturbances by measuring the asymmetry present in the ionised gas
line-of-sight velocity maps at the (inner regions) and (outer
regions) elliptical annuli. By comparing the inner and outer kinematic
asymmetries, we aim to better understand what physical processes are driving
the asymmetries in galaxies. We find the local environment plays a role in
kinematic disturbance, in agreement with other integral field spectroscopy
studies of the local universe, with most asymmetric systems being in close
proximity to a more massive neighbour. We do not find evidence suggesting that
hosting an Active Galactic Nucleus (AGN) contributes to asymmetry within the
inner regions, with some caveats due to emission line modelling. In contrast to
previous studies, we do not find evidence that processes leading to asymmetry
also enhance star formation in MAGPI galaxies. Finally, we find a weak
anti-correlation between stellar mass and asymmetry (ie. high stellar mass
galaxies are less asymmetric). We conclude by discussing possible sources
driving the asymmetry in the ionised gas, such as disturbances being present in
the colder gas phase (either molecular or atomic) prior to the gas being
ionised, and non-axisymmetric features (e.g., a bar) being present in the
galactic disk. Our results highlight the complex interplay between ionised gas
kinematic disturbances and physical processes involved in galaxy evolution.Comment: e.g., 20 pages, 19 figure
Biomarker of food intake for assessing the consumption of dairy and egg products
Foods of animal origin constitute one of the predominant food groups consumed in Western diets. They play an essential role in human nutrition as they represent an excellent source of high quality proteins, vitamins, minerals and fats. Foods of animal origin are highly diverse (e.g. meat, fish, dairy products and eggs) and their associations with a range of nutritional and health outcomes are therefore heterogeneous. Such associations are also often weak or debated due to the difficulty in establishing correct assessments of dietary intake. Therefore, in order to better characterize associations between the consumption of specific foods of animal origin and health outcomes, it is important to identify reliable biomarkers of food intake (BFIs). BFIs provide a more accurate measure of intake and are independent of the memory and sincerity of the subjects as well as of their knowledge about the consumed foods. To date, only a very limited number of compounds have been proposed as biomarkers of the intake of foods of animal origin and further studies are necessary to validate them and to discover new candidate BFIs. We have, therefore, conducted a systematic search of the scientific literature to evaluate the current status of potential BFIs for each category of foods of animal origin commonly consumed in Europe. This review reports on candidate biomarkers for dairy products and eggs intake, while biomarkers for fish and meat intake will be published separately. Remarkably, validated BFIs for dairy products and eggs are not available. A series of challenges hinders their identification and validation, in particular the heterogeneous composition of each food within a product category and the lack of specificity of the markers identified so far. Untargeted metabolomic strategies may allow the identification of novel food biomarkers, that, when taken separately or in combination, could be used to assess the intake of dairy products and eggs
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