309 research outputs found
A refined sub-grid model for black hole accretion and AGN feedback in large cosmological simulations
In large scale cosmological hydrodynamic simulations simplified sub-grid
models for gas accretion onto black holes and AGN feedback are commonly used.
Such models typically depend on various free parameters, which are not well
constrained. We present a new advanced model containing a more detailed
description of AGN feedback, where those parameters reflect the results of
recent observations. The model takes the dependency of these parameters on the
black hole properties into account and describes a continuous transition
between the feedback processes acting in the so-called radio-mode and
quasar-mode. In addition, we implement a more detailed description of the
accretion of gas onto black holes by distinguishing between hot and cold gas
accretion. Our new implementations prevent black holes from gaining too much
mass, particularly at low redshifts so that our simulations are now very
successful in reproducing the observed present-day black hole mass function.
Our new model also suppresses star formation in massive galaxies slightly more
efficiently than many state-of-the-art models. Therefore, the simulations that
include our new implementations produce a more realistic population of
quiescent and star-forming galaxies compared to recent observations, even if
some discrepancies remain. In addition, the baryon conversion efficiencies in
our simulation are - except for the high mass end - consistent with
observations presented in literature over the mass range resolved by our
simulations. Finally, we discuss the significant impact of the feedback model
on the low-luminous end of the AGN luminosity function.Comment: 25 pages, 19 figures. MNRAS accepted. Magneticum website:
http://www.magneticum.or
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
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
Cool Core Clusters from Cosmological Simulations
We present results obtained from a set of cosmological hydrodynamic
simulations of galaxy clusters, aimed at comparing predictions with
observational data on the diversity between cool-core (CC) and non-cool-core
(NCC) clusters. Our simulations include the effects of stellar and AGN feedback
and are based on an improved version of the smoothed particle hydrodynamics
code GADGET-3, which ameliorates gas mixing and better captures gas-dynamical
instabilities by including a suitable artificial thermal diffusion. In this
Letter, we focus our analysis on the entropy profiles, the primary diagnostic
we used to classify the degree of cool-coreness of clusters, and on the iron
profiles. In keeping with observations, our simulated clusters display a
variety of behaviors in entropy profiles: they range from steadily decreasing
profiles at small radii, characteristic of cool-core systems, to nearly flat
core isentropic profiles, characteristic of non-cool-core systems. Using
observational criteria to distinguish between the two classes of objects, we
find that they occur in similar proportions in both simulations and in
observations. Furthermore, we also find that simulated cool-core clusters have
profiles of iron abundance that are steeper than those of NCC clusters, which
is also in agreement with observational results. We show that the capability of
our simulations to generate a realistic cool-core structure in the cluster
population is due to AGN feedback and artificial thermal diffusion: their
combined action allows us to naturally distribute the energy extracted from
super-massive black holes and to compensate for the radiative losses of
low-entropy gas with short cooling time residing in the cluster core.Comment: 6 pages, 4 figures, accepted in ApJL, v2 contains some modifications
on the text (results unchanged
Cosmological hydrodynamical simulations of galaxy clusters: X-ray scaling relations and their evolution
We analyse cosmological hydrodynamical simulations of galaxy clusters to
study the X-ray scaling relations between total masses and observable
quantities such as X-ray luminosity, gas mass, X-ray temperature, and .
Three sets of simulations are performed with an improved version of the
smoothed particle hydrodynamics GADGET-3 code. These consider the following:
non-radiative gas, star formation and stellar feedback, and the addition of
feedback by active galactic nuclei (AGN). We select clusters with , mimicking the typical selection of
Sunyaev-Zeldovich samples. This permits to have a mass range large enough to
enable robust fitting of the relations even at . The results of the
analysis show a general agreement with observations. The values of the slope of
the mass-gas mass and mass-temperature relations at are 10 per cent lower
with respect to due to the applied mass selection, in the former case,
and to the effect of early merger in the latter. We investigate the impact of
the slope variation on the study of the evolution of the normalization. We
conclude that cosmological studies through scaling relations should be limited
to the redshift range , where we find that the slope, the scatter, and
the covariance matrix of the relations are stable. The scaling between mass and
is confirmed to be the most robust relation, being almost independent of
the gas physics. At higher redshifts, the scaling relations are sensitive to
the inclusion of AGNs which influences low-mass systems. The detailed study of
these objects will be crucial to evaluate the AGN effect on the ICM.Comment: 24 pages, 11 figures, 5 tables, replaced to match accepted versio
Element Mapping and Biomarker Analyses in an Early Byzantine City (CariÄin Grad, Serbia)
Soil analyses have a high potential to contribute to the investigation of daily life in ancient settlements. They can help to locate areas of food production, areas of waste disposal, latrines, stables and further functional areas. However, the applicability of these analyses is still restricted by a limited number of studies and a limited knowledge of their validity. In a multi-disciplinary project investigating the daily life in an early byzantine city (CariÄin Grad), a multi-element-mapping and biomarker analyses were performed. The study focused on a comparison of the soil data with the data from other disciplines. The CariÄin Grad CariÄin Grad site in southern Serbia offered excellent conditions for this methodological study. It is supposed to be identical to Iustiniana Prima, an administrative center founded by the emperor Justinian. The period of occupation covered less than 90 years from circa 530 to 615 AD. The site remained undisturbed from later settlement encroachments. Therefore, it allows a rare archaeological âsnapshotâ of a short period of very intensive use. By analyses of the amounts of total organic carbon, total phosphorus and further elements (aqua-regia extraction), it was possible to divide different functional areas within the city. Element ratios and biomarkers including faecal steroids were used to get information on the specific use of the functional areas as well as on animal husbandry within the settlement. Data of soil analyses were compared and correlated with data that were obtained by consequent single point measurement and examination of the archaeological remains, 3D photography of the structures as well as archaeobotanical and archaeozoological analyses
Antitumor activity of an Artemisia annua herbal preparation and identification of active ingredients
Neutral hydrogen in galaxy clusters: impact of AGN feedback and implications for intensity mapping
By means of zoom-in hydrodynamic simulations, we quantify the amount of neutral hydrogen (H i) hosted by groups and clusters of galaxies. Our simulations, which are based on an improved formulation of smoothed particle hydrodynamics, include radiative cooling, star formation, metal enrichment and supernova feedback, and can be split into two different groups, depending on whether feedback from active galactic nuclei (AGN) is turned on or off. Simulations are analysed to account for H I self-shielding and the presence of molecular hydrogen. We find that the mass in neutral hydrogen of dark matter haloes monotonically increases with the halo mass and can be well described by a power law of the form MH I(M, Z) 1d M3/4. Our results point out that AGN feedback reduces both the total halo mass and its H i mass, although it is more efficient in removing H i. We conclude that AGN feedback reduces the neutral hydrogen mass of a given halo by ~50 per cent, with a weak dependence on halo mass and redshift. The spatial distribution of neutral hydrogen within haloes is also affected by AGN feedback, whose effect is to decrease the fraction of H i that resides in the halo inner regions. By extrapolating our results to haloes not resolved in our simulations, we derive astrophysical implications from the measurements of \u3a9H I(Z): haloes with circular velocities larger than ~25 km s-1 are needed to host H i in order to reproduce observations. We find that only the model with AGN feedback is capable of reproducing the value of \u3a9HIbHI derived from available 21 cm intensity mapping observations. \ua9 2016 The Authors
Pressure of the hot gas in simulations of galaxy clusters
14siWe analyse the radial pressure profiles, the intracluster medium (ICM) clumping factor and the Sunyaev-Zel'dovich (SZ) scaling relations of a sample of simulated galaxy clusters and groups identified in a set of hydrodynamical simulations based on an updated version of the treepm-SPH GADGET-3 code. Three different sets of simulations are performed: the first assumes non-radiative physics, the others include, among other processes, active galactic nucleus (AGN) and/or stellar feedback. Our results are analysed as a function of redshift, ICM physics, cluster mass and cluster cool-coreness or dynamical state. In general, the mean pressure profiles obtained for our sample of groups and clusters show a good agreement with X-ray and SZ observations. Simulated cool-core (CC) and non-cool-core (NCC) clusters also show a good match with real data. We obtain in all cases a small (if any) redshift evolution of the pressure profiles of massive clusters, at least back to z = 1. We find that the clumpiness of gas density and pressure increases with the distance from the cluster centre and with the dynamical activity. The inclusion of AGN feedback in our simulations generates values for the gas clumping (â{C}_{Ï }Ë 1.2 at R200) in good agreement with recent observational estimates. The simulated YSZ-M scaling relations are in good accordance with several observed samples, especially for massive clusters. As for the scatter of these relations, we obtain a clear dependence on the cluster dynamical state, whereas this distinction is not so evident when looking at the subsamples of CC and NCC clusters.openopenPlanelles, S.; Fabjan, D.; Borgani, S.; Murante, G.; Rasia, E.; Biffi, V.; Truong, N.; Ragone-Figueroa, C.; Granato, G. L.; Dolag, K.; Pierpaoli, E.; Beck, A. M.; Steinborn, Lisa K.; Gaspari, M.Planelles, S.; Fabjan, D.; Borgani, Stefano; Murante, G.; Rasia, E.; Biffi, Veronica; Truong, N.; Ragone Figueroa, C.; Granato, G. L.; Dolag, K.; Pierpaoli, E.; Beck, A. M.; Steinborn, Lisa K.; Gaspari, M
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