Schleicher, Dominik R. G.

[["dc.bibliographiccitation.artnumber","A142"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","556"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Beck, Rainer"],["dc.date.accessioned","2018-11-07T09:21:42Z"],["dc.date.available","2018-11-07T09:21:42Z"],["dc.date.issued","2013"],["dc.description.abstract","Context. Observations of galaxies up to z similar to 2 show a tight correlation between far-infrared and radio continuum emission, suggesting a relation between star formation activity and magnetic fields in the presence of cosmic rays. Aims. We explain the far-infrared - radio continuum correlation by relating star formation and magnetic field strength in terms of turbulent magnetic field amplification, where turbulence is injected by supernova explosions from massive stars. We assess the potential evolution of this relation at high redshift, and explore the impact on the far-infrared - radio correlation. Methods. We calculate the expected amount of turbulence in galaxies based on their star formation rates, and infer the expected magnetic field strength due to turbulent dynamo amplification. We calculate the timescales for cosmic ray energy losses via synchrotron emission, inverse Compton scattering, ionization and bremsstrahlung emission, probing up to which redshift strong synchrotron emission can be maintained. Results. We find that the correlation between star formation rate and magnetic field strength in the local Universe can be understood as a result of turbulent magnetic field amplification. The ratio of radio to far-infrared surface brightness is expected to increase with total field strength. A continuation of the correlation is expected towards high redshifts. If the typical gas density in the interstellar medium increases at high z, we expect an increase of the magnetic field strength and the radio emission, as indicated by current observations. Such an increase would imply a modification, but not a breakdown of the far-infrared -radio correlation. We expect a breakdown at the redshift when inverse Compton losses start dominating over synchrotron emission. For a given star formation surface density, we calculate the redshift where the far-infrared -radio correlation will break down, yielding z similar to (Sigma(SFR)/0.0045 M-circle dot kpc(-2) yr(-1))(1/( 6-alpha/2)). In this relation, the parameter a describes the evolution of the characteristic ISM density in galaxies as (1 + z)(alpha). We note that observed frequencies of 1-10 GHz are particularly well-suited to explore this relation, as bremsstrahlung losses could potentially dominate at low frequencies. Conclusions. Both the possible raise of the radio emission at high redshift and the final breakdown of the far-infrared -radio correlation at a critical redshift will be probed by the Square Kilometre Array (SKA) and its pathfinders, while the typical ISM density in galaxies will be probed with ALMA. The combined measurements will thus allow a verification of the model proposed here."],["dc.identifier.doi","10.1051/0004-6361/201321707"],["dc.identifier.isi","000323893500142"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10870"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/29171"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","A new interpretation of the far-infrared - radio correlation and the expected breakdown at high redshift"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A22"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","572"],["dc.contributor.author","van Borm, C."],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Latif, A. H. M. Mahbub"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Spaans, M."],["dc.contributor.author","Grassi, T."],["dc.date.accessioned","2018-11-07T09:31:57Z"],["dc.date.available","2018-11-07T09:31:57Z"],["dc.date.issued","2014"],["dc.description.abstract","Context. The seeds of the first supermassive black holes may have resulted from the direct collapse of hot primordial gas in greater than or similar to 10(4) K haloes, forming a supermassive or quasi- star as an intermediate stage. Aims. We explore the formation of a protostar resulting from the collapse of primordial gas in the presence of a strong Lyman- Werner radiation background. Particularly, we investigate the impact of turbulence and rotation on the fragmentation behaviour of the gas cloud. We accomplish this goal by varying the initial turbulent and rotational velocities. Methods. We performed 3D adaptive mesh refinement simulations with a resolution of 64 cells per Jeans length using the ENZO code, simulating the formation of a protostar up to unprecedentedly high central densities of 10(21) cm(-3) and spatial scales of a few solar radii. To achieve this goal, we employed the KROME package to improve modelling of the chemical and thermal processes. Results. We find that the physical properties of the simulated gas clouds become similar on small scales, irrespective of the initial amount of turbulence and rotation. After the highest level of refinement was reached, the simulations have been evolved for an additional similar to 5 freefall times. A single bound clump with a radius of 2 x 10(-2) AU and a mass of similar to 7 x 10(-2) M fi is formed at the end of each simulation, marking the onset of protostar formation. No strong fragmentation is observed by the end of the simulations, regardless of the initial amount of turbulence or rotation, and high accretion rates of a few solar masses per year are found. Conclusions. Given such high accretion rates, a quasi- star of 105 M fi is expected to form within 105 years."],["dc.description.sponsorship","Deutsche Forschungsgemeinschaft (DFG) [SFB 963 / 1]"],["dc.identifier.doi","10.1051/0004-6361/201424658"],["dc.identifier.fs","609689"],["dc.identifier.isi","000346101700037"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/11406"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/31640"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Effects of turbulence and rotation on protostar formation as a precursor of massive black holes"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A46"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","545"],["dc.contributor.author","Hocuk, S."],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Spaans, M."],["dc.contributor.author","Cazaux, S."],["dc.date.accessioned","2018-11-07T09:06:06Z"],["dc.date.available","2018-11-07T09:06:06Z"],["dc.date.issued","2012"],["dc.description.abstract","Star formation in the centers of galaxies is thought to yield massive stars with a possibly top-heavy stellar mass distribution. It is likely that magnetic fields play a crucial role in the distribution of stellar masses inside star-forming molecular clouds. In this context, we explore the effects of magnetic fields, with a typical field strength of 38 mu G, such as in RCW 38, and a field strength of 135 mu G, similar to NGC 2024 and the infrared dark cloud G28.34+0.06, on the initial mass function (IMF) near (<= 10 pc) a 10(7) solar mass black hole. Using these conditions, we perform a series of numerical simulations with the hydrodynamical code FLASH to elucidate the impact of magnetic fields on the IMF and the star-formation efficiency (SFE) emerging from an 800 solar mass cloud. We find that the collapse of a gravitationally unstable molecular cloud is slowed down with increasing magnetic field strength and that stars form along the field lines. The total number of stars formed during the simulations increases by a factor of 1.5-2 with magnetic fields. The main component of the IMF has a lognormal shape, with its peak shifted to sub-solar (<= 0.3 M-circle dot) masses in the presence of magnetic fields, due to a decrease in the accretion rates from the gas reservoir. In addition, we see a top-heavy, nearly flat IMF above similar to 2 solar masses, from regions that were supported by magnetic pressure until high masses are reached. We also consider the effects of X-ray irradiation if the central black hole is active. X-ray feedback inhibits the formation of sub-solar masses and decreases the SFEs even further. Thus, the second contribution is no longer visible. We conclude that magnetic fields potentially change the SFE and the IMF both in active and inactive galaxies, and need to be taken into account in such calculations. The presence of a flat component of the IMF would be a particularly relevant signature for the importance of magnetic fields, as it is usually not found in hydrodynamical simulations."],["dc.identifier.doi","10.1051/0004-6361/201219628"],["dc.identifier.fs","596754"],["dc.identifier.isi","000309254900046"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9614"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/25480"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","The impact of magnetic fields on the IMF in star-forming clouds near a supermassive black hole"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.firstpage","A84"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","602"],["dc.contributor.author","Chamani, Wara"],["dc.contributor.author","Dörschner, Stephanie"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.date.accessioned","2020-12-10T18:11:34Z"],["dc.date.available","2020-12-10T18:11:34Z"],["dc.date.issued","2017"],["dc.identifier.doi","10.1051/0004-6361/201730440"],["dc.identifier.eissn","1432-0746"],["dc.identifier.issn","0004-6361"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/16808"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/74064"],["dc.notes.intern","DOI Import GROB-354"],["dc.notes.intern","Merged from goescholar"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Turbulent gas accretion between supermassive black-holes and star-forming rings in the circumnuclear disk"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A101"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","540"],["dc.contributor.author","Latif, A. H. M. Mahbub"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Spaans, M."],["dc.date.accessioned","2018-11-07T09:11:27Z"],["dc.date.available","2018-11-07T09:11:27Z"],["dc.date.issued","2012"],["dc.description.abstract","Numerical simulations suggest that the first galaxies are formed in protogalactic halos with virial temperatures >= 10(4) K. It is likely that such halos are polluted with trace amounts of metals produced by the first generation of stars. The presence of dust can significantly change the chemistry and dynamics of early galaxies. In this article, we aim to assess the role of dust on the thermal and dynamical evolution of the first galaxies in the presence of a background UV flux, and its implications for the observability of Lyman-alpha emitters and sub-mm sources. We have performed high resolution cosmological simulations using the adaptive mesh refinement code FLASH to accomplish this goal. We have developed a chemical network appropriate for these conditions and coupled it with the FLASH code. The main ingredients of our chemical model include the formation of molecules (both in the gas phase and on dust grains), a multi-level treatment of atomic hydrogen, line trapping of Ly-alpha photons and, photoionization and photodissociation processes in a UV background. We found that the formation of molecules (H-2 and HD) is significantly enhanced in the presence of dust grains as compared to only gas phase reactions by up to two orders of magnitude. The presence of dust may thus establish a molecular ISM in high-redshift galaxies. The presence of a background UV flux strongly influences the formation of molecules by photodissociating them. We explore the evolution after a major merger, leading to the formation of a binary disk. These disks have gas masses of similar to 10(7) M-circle dot at a redshift of 5.4. Each disk lies in a separate subhalo as a result of the merger event. The disks are supported by turbulent pressure due to the highly supersonic turbulence present in the halo. For values of J(21) = 1000 (internal flux), we find that fragmentation may be enhanced due to thermal instabilities in the hot gas. The presence of dust does not significantly reduce the Ly-alpha emission. The emission of Ly-alpha is extended and originates from the envelope of the halo due to line trapping effects. We also find that dust masses of a few x10(8) M-circle dot are required to observe the dust continuum emission from z similar to 5 galaxies with ALMA."],["dc.identifier.doi","10.1051/0004-6361/201118295"],["dc.identifier.fs","596713"],["dc.identifier.isi","000303315400115"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/9598"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/26725"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","The implications of dust for high-redshift protogalaxies and the formation of binary disks"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A13"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","561"],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Grassi, T."],["dc.date.accessioned","2018-11-07T09:46:39Z"],["dc.date.available","2018-11-07T09:46:39Z"],["dc.date.issued","2014"],["dc.description.abstract","Context. Population III stars are the first stars in the Universe to form at z = 20-30 out of a pure hydrogen and helium gas in minihalos of 10(5)-10(6) M-circle dot. Cooling and fragmentation is thus regulated via molecular hydrogen. At densities above 10(8) cm(-3), the three-body H-2 formation rates are particularly important for making the gas fully molecular. These rates were considered to be uncertain by at least a few orders of magnitude. Aims. We explore the impact of recently derived accurate three-body H-2 formation for three different minihalos, and compare them with the results obtained with three-body rates employed in previous other studies. Methods. The calculations were performed with the cosmological hydrodynamics code ENZO (release 2.2) coupled with the chemistry package KROME (including a network for primordial chemistry), which was previously shown to be accurate in high-resolution simulations. Results. While the new rates can shift the point where the gas becomes fully molecular, leading to a different thermal evolution, there is no trivial trend in the way this occurs. While one might naively expect the results to follow the rate coefficients trend, the behavior can vary depending on the dark-matter halo that is explored. Conclusions. We conclude that employing the correct three-body rates is about equally important as the use of appropriate initial conditions, and that the resulting thermal evolution needs to be calculated for every halo individually."],["dc.description.sponsorship","DFG [SCHL 1964/1-1]; CINECA consortium; [SFB 963/1]"],["dc.identifier.doi","10.1051/0004-6361/201322387"],["dc.identifier.fs","609680"],["dc.identifier.isi","000330584000013"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10884"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/34928"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Primordial star formation: relative impact of H-2 three-body rates and initial conditions"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A87"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","560"],["dc.contributor.author","Schober, Jennifer"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Klessen, Ralf S."],["dc.date.accessioned","2018-11-07T09:16:53Z"],["dc.date.available","2018-11-07T09:16:53Z"],["dc.date.issued","2013"],["dc.description.abstract","The Universe at present is highly magnetized, with fields of a few 10 5 G and coherence lengths greater than 10 kpc in typical galaxies like the Milky Way. We propose that the magnetic field was already amplified to these values during the formation and the early evolution of galaxies. Turbulence in young galaxies is driven by accretion, as well as by supernova (SN) explosions of the first generation of stars. The small-scale dynamo can convert the turbulent kinetic energy into magnetic energy and amplify very weak primordial seed fields on short timescales. Amplification takes place in two phases: in the kinematic phase the magnetic field grows exponentially, with the largest growth rate on the smallest nonresistive scale. In the following nonlinear phase the magnetic energy is shifted toward larger scales until the dynamo saturates on the turbulent forcing scale. To describe the amplification of the magnetic field quantitatively, we modeled the microphysics in the interstellar medium (ISM) of young galaxies and determined the growth rate of the small-scale dynamo. We estimated the resulting saturation field strengths and dynamo timescales for two turbulent forcing mechanisms: accretion-driven turbulence and SN-driven turbulence. We compare them to the field strength that is reached when only stellar magnetic fields are distributed by SN explosions. We find that the small-scale dynamo is much more efficient in magnetizing the ISM of young galaxies. In the case of accretion-driven turbulence, a magnetic field strength on the order of 10 6 G is reached after a time of 24 270 Myr, while in SN-driven turbulence the dynamo saturates at field strengths of typically 10 5 G after only 4 15 Myr. This is considerably shorter than the Hubble time. Our work can help for understanding why present-day galaxies are highly magnetized."],["dc.identifier.doi","10.1051/0004-6361/201322185"],["dc.identifier.isi","000328754500087"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10883"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/28038"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Magnetic field amplification in young galaxies"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","013055"],["dc.bibliographiccitation.issue","1"],["dc.bibliographiccitation.journal","New Journal of Physics"],["dc.bibliographiccitation.volume","15"],["dc.contributor.affiliation","Bovino, S;"],["dc.contributor.affiliation","Schleicher, D R G;"],["dc.contributor.affiliation","Schober, J;"],["dc.contributor.author","Bovino, Stefano"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Schober, Jennifer"],["dc.date.accessioned","2018-11-07T09:29:02Z"],["dc.date.available","2018-11-07T09:29:02Z"],["dc.date.issued","2013"],["dc.date.updated","2022-02-10T06:47:23Z"],["dc.description.abstract","The small-scale dynamo provides a highly efficient mechanism for the conversion of turbulent into magnetic energy. In astrophysical environments, such turbulence often occurs at high Mach numbers, implying steep slopes in the turbulent spectra. It is thus a central question whether the small-scale dynamo can amplify magnetic fields in the interstellar or intergalactic media, where such Mach numbers occur. To address this long-standing issue, we employ the Kazantsev model for turbulent magnetic field amplification, systematically exploring the effect of different turbulent slopes, as expected for Kolmogorov, Burgers, the Larson laws and results derived from numerical simulations. With the framework employed here, we give the first solution encompassing the complete range of magnetic Prandtl numbers, including Pm << 1, Pm similar to 1 and Pm >> 1. We derive scaling laws of the growth rate as a function of hydrodynamic and magnetic Reynolds number for Pm similar to 1 and Pm >> 1 for all types of turbulence. A central result concerns the regime of Pm similar to 1, where the magnetic field amplification rate increases rapidly as a function of Pm. This phenomenon occurs for all types of turbulence we have explored. We further find that the dynamo growth rate can be decreased by a few orders of magnitude for turbulence spectra steeper than Kolmogorov. We calculate the critical magnetic Reynolds number Rm(c) for magnetic field amplification, which is highest for the Burgers case. As expected, our calculation shows a linear behaviour of the amplification rate close to the threshold proportional to (Rm - Rm(c)). On the basis of the Kazantsev model, we therefore expect the existence of the small-scale dynamo for a given value of Pm as long as the magnetic Reynolds number is above the critical threshold."],["dc.description.sponsorship","Open-Access-Publikationsfonds 2013"],["dc.identifier.doi","10.1088/1367-2630/15/1/013055"],["dc.identifier.eissn","1367-2630"],["dc.identifier.fs","602614"],["dc.identifier.isi","000314341600002"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/8703"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/30926"],["dc.language.iso","en"],["dc.notes","PACS: 98.62.En Electric and magnetic fields\r\n\r\n95.30.Lz Hydrodynamics\r\n\r\n98.58.Ay Physical properties (abundances, electron density, magnetic fields, scintillation, scattering, kinematics, dynamics, turbulence, etc.)"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","IOP Publishing"],["dc.relation.issn","1367-2630"],["dc.relation.orgunit","Fakultät für Physik"],["dc.rights.uri","http://creativecommons.org/licenses/by/3.0/"],["dc.title","Turbulent magnetic field amplification from the smallest to the largest magnetic Prandtl numbers"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A34"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","560"],["dc.contributor.author","Wutschik, Stephanie"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.contributor.author","Palmer, Thomas S."],["dc.date.accessioned","2018-11-07T09:16:54Z"],["dc.date.available","2018-11-07T09:16:54Z"],["dc.date.issued","2013"],["dc.description.abstract","Aims. We explore the evolution of supermassive black holes (SMBH) centered in a circumnuclear disk (CND) as a function of the mass supply from the host galaxy and considering different star formation laws, which may give rise to a self-regulation via the injection of supernova-driven turbulence. Methods. A system of equations describing star formation, black hole accretion and angular momentum transport in the disk was solved self-consistently for an axisymmetric disk in which the gravitational potential includes contributions from the black hole, the disk and the hosting galaxy. Our model extends the framework provided by Kawakatu & Wada (2008, ApJ, 681, 73), by separately considering the inner and outer part of the disk, and by introducing a potentially non-linear dependence of the star formation rate on the gas surface density and the turbulent velocity. The star formation recipes are calibrated using observational data for NGC 1097, while the accretion model is based on turbulent viscosity as a source of angular momentum transport in a thin viscous accretion disk. Results. We find that current data provide no strong constraint on the star formation recipe, and can in particular not distinguish between models entirely regulated by the surface density, and models including a dependence on the turbulent velocity. The evolution of the black hole mass, on the other hand, strongly depends on the applied star formation law, as well as the mass supply from the host galaxy. We suggest to explore the star formation process in local AGN with high-resolution ALMA observations to break the degeneracy between different star formation models."],["dc.identifier.doi","10.1051/0004-6361/201321895"],["dc.identifier.isi","000328754500034"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/10882"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/28039"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Star formation and accretion in the circumnuclear disks of active galaxies"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]

[["dc.bibliographiccitation.artnumber","A32"],["dc.bibliographiccitation.journal","Astronomy and Astrophysics"],["dc.bibliographiccitation.volume","579"],["dc.contributor.author","Lichtenberg, Tim"],["dc.contributor.author","Schleicher, Dominik R. G."],["dc.date.accessioned","2018-11-07T09:54:59Z"],["dc.date.available","2018-11-07T09:54:59Z"],["dc.date.issued","2015"],["dc.description.abstract","The astonishing diversity in the observed planetary population requires theoretical efforts and advances in planet formation theories. The use of numerical approaches provides a method to tackle the weaknesses of current models and is an important tool to close gaps in poorly constrained areas such as the rapid formation of giant planets in highly evolved systems. So far, most numerical approaches make use of Lagrangian-based smoothed-particle hydrodynamics techniques or grid-based 2D axisymmetric simulations. We present a new global disk setup to model the first stages of giant planet formation via gravitational instabilities (GI) in 3D with the block-structured adaptive mesh refinement (AMR) hydrodynamics code ENZO. With this setup, we explore the potential impact of AMR techniques on the fragmentation and clumping due to large-scale instabilities using different AMR configurations. Additionally, we seek to derive general resolution criteria for global simulations of self-gravitating disks of variable extent. We run a grid of simulations with varying AMR settings, including runs with a static grid for comparison. Additionally, we study the effects of varying the disk radius. The physical settings involve disks with R-disk = 10, 100 and 300 AU, with a mass of M-disk approximate to 0 : 05 M-circle dot and a central object of subsolar mass (M-star = 0.646 M-circle dot). To validate our thermodynamical approach we include a set of simulations with a dynamically stable profile (Q(init) = 3) and similar grid parameters. The development of fragmentation and the buildup of distinct clumps in the disk is strongly dependent on the chosen AMR grid settings. By combining our findings from the resolution and parameter studies we find a general lower limit criterion to be able to resolve GI induced fragmentation features and distinct clumps, which induce turbulence in the disk and seed giant planet formation. Irrespective of the physical extension of the disk, topologically disconnected clump features are only resolved if the fragmentation-active zone of the disk is resolved with at least 100 cells. The latter corresponds to a minimum requirement for all global disk setups. Our simulations illustrate the capabilities of AMR-based modeling techniques for planet formation simulations and underline the importance of balanced refinement settings to reproduce fragmenting structures. The clumps in our models are migrating inward and are eventually destroyed because of tidal disruptions, reflecting the absence of radiative feedback from the central star, which may stabilize the clumps on larger scales. We expect that the inclusion of additional physics, like a radiation transport mechanism and the formation of sink particles, will provide a detailed framework to study the formation of planets via gravitational instabilities in a global disk view."],["dc.identifier.doi","10.1051/0004-6361/201424528"],["dc.identifier.isi","000358877100044"],["dc.identifier.purl","https://resolver.sub.uni-goettingen.de/purl?gs-1/12443"],["dc.identifier.uri","https://resolver.sub.uni-goettingen.de/purl?gro-2/36656"],["dc.notes.intern","Merged from goescholar"],["dc.notes.status","zu prüfen"],["dc.notes.submitter","Najko"],["dc.publisher","Edp Sciences S A"],["dc.relation.issn","1432-0746"],["dc.relation.issn","0004-6361"],["dc.relation.orgunit","Fakultät für Physik"],["dc.title","Modeling gravitational instabilities in self-gravitating protoplanetary disks with adaptive mesh refinement techniques"],["dc.type","journal_article"],["dc.type.internalPublication","yes"],["dc.type.peerReviewed","yes"],["dc.type.status","published"],["dc.type.version","published_version"],["dspace.entity.type","Publication"]]