Testing core creation in hydrodynamical simulations using the HI kinematics of field dwarfs

The majority of recent hydrodynamical simulations indicate the creation of central cores in the mass profiles of low-mass halos, a process that is attributed to star formation-related baryonic feedback. Core creation is regarded as one of the most promising solutions to potential issues faced by the lambda cold dark matter (LambdaCDM) cosmology on small scales. For example, the reduced dynamical mass enclosed by cores can explain the low rotational velocities measured for nearby dwarf galaxies, thus possibly lifting the seeming contradiction with the LambdaCDM expectations (the so-called "too big to fail" problem). Here we test core creation as a solution of cosmological issues by using a sample of dwarfs with measurements of their atomic hydrogen (HI) kinematics extending to large radii. Using the NIHAO hydrodynamical simulation as an example, we show that core creation can successfully reproduce the kinematics of dwarfs with small kinematic radii, R <~ 1.5 kpc. However, the agreement with observations becomes poor once galaxies with kinematic measurements extending beyond the core region, R ~ 1.5 - 4 kpc, are considered. This result illustrates the importance of testing the predictions of hydrodynamical simulations that are relevant for cosmology against a broad range of observational samples. We would like to stress that our result is valid only under the following set of assumptions: i) that our sample of dwarfs with HI kinematics is representative of the overall population of field dwarfs, ii) that there are no severe measurement biases in the observational parameters of our HI dwarfs (e.g., related to inclination estimates), and iii) that the HI velocity fields of dwarfs are regular enough to allow the recovery of the true enclosed dynamical mass.Comment: v2 matches version accepted by A&A. About 5 pages, 1 figur

The Multi-Wavelength Tully-Fisher relation with spatially resolved HI kinematics

In this paper we investigate the statistical properties of the Tully-Fisher relation for a sample of 32 galaxies with measured distances from the Cepheid period-luminosity relation and/or TRGB stars. We take advantage of panchromatic photometry in 12 bands (from FUV to 4.5 $\mu$m) and of spatially resolved HI kinematics. We use these data together with three kinematic measures ($W^{i}_{50}$, $V_{max}$ and $V_{flat}$) extracted from the global HI profiles or HI rotation curves, so as to construct 36 correlations allowing us to select the one with the least scatter. We introduce a tightness parameter $\sigma_{\perp}$ of the TFr, in order to obtain a slope-independent measure of the goodness of fit. We find that the tightest correlation occurs when we select the 3.6 $\mu$m photometric band together with the $V_{flat}$ parameter extracted from the HI rotation curve.Comment: 16 pages, 16 figures, accepted for publication in MNRAS, minor changes due to proof correction

A new astrophysical solution to the Too Big To Fail problem - Insights from the MoRIA simulations

We test whether advanced galaxy models and analysis techniques of simulations can alleviate the Too Big To Fail problem (TBTF) for late-type galaxies, which states that isolated dwarf galaxy kinematics imply that dwarfs live in lower-mass halos than is expected in a {\Lambda}CDM universe. Furthermore, we want to explain this apparent tension between theory and observations. To do this, we use the MoRIA suite of dwarf galaxy simulations to investigate whether observational effects are involved in TBTF for late-type field dwarf galaxies. To this end, we create synthetic radio data cubes of the simulated MoRIA galaxies and analyse their HI kinematics as if they were real, observed galaxies. We find that for low-mass galaxies, the circular velocity profile inferred from the HI kinematics often underestimates the true circular velocity profile, as derived directly from the enclosed mass. Fitting the HI kinematics of MoRIA dwarfs with a theoretical halo profile results in a systematic underestimate of the mass of their host halos. We attribute this effect to the fact that the interstellar medium of a low-mass late-type dwarf is continuously stirred by supernova explosions into a vertically puffed-up, turbulent state to the extent that the rotation velocity of the gas is simply no longer a good tracer of the underlying gravitational force field. If this holds true for real dwarf galaxies as well, it implies that they inhabit more massive dark matter halos than would be inferred from their kinematics, solving TBTF for late-type field dwarf galaxies.Comment: 21 pages, 21 figures. Accepted for publication in A&A. Corrected certain values in Table

A new astrophysical solution to the Too Big To Fail problem: Insights from the MORIA simulations

Aims. We test whether or not realistic analysis techniques of advanced hydrodynamical simulations can alleviate the Too Big To Fail problem (TBTF) for late-type galaxies. TBTF states that isolated dwarf galaxy kinematics imply that dwarfs live in halos with lower mass than is expected in a A cold dark matter universe. Furthermore, we want to identify the physical mechanisms that are responsible for this observed tension between theory and observations. Methods. We use the MORIA suite of dwarf galaxy simulations to investigate whether observational effects are involved in TBTF for late-type field dwarf galaxies. To this end, we create synthetic radio data cubes of the simulated MORIA galaxies and analyse their HI kinematics as if they were real, observed galaxies. Results. We find that for low-mass galaxies, the circular velocity profile inferred from spatially resolved HI kinematics often underestimates the true circular velocity profile, as derived directly from the enclosed mass. Fitting the HI kinematics of MORIA dwarfs with a theoretical halo profile results in a systematic underestimate of the mass of their host halos. We attribute this effect to the fact that the interstellar medium of a low-mass late-type dwarf is continuously stirred by supernova explosions into a vertically puffed-up, turbulent state to the extent that the rotation velocity of the gas is simply no longer a good tracer of the underlying gravitational force field. If this holds true for real dwarf galaxies as well, it implies that they inhabit more massive dark matter halos than would be inferred from their kinematics, solving TBTF for late-type field dwarf galaxies

Activation Energy of Hydrogen–Methane Mixtures

In this work, the overall activation energy of the combustion of lean hydrogen–methane–air mixtures (equivalence ratio = 0.7−1.0 and hydrogen fraction in methane =0, 2, 4) is experimentally determined using thin-filament pyrometry of flames stabilised on a flat porous burner under normal conditions (=1 bar, T = 20 °C). The experimental data are compared with numerical calculations within the detailed reaction mechanism GRI3.0 and both approaches confirm the linear correlation between mass flow rate and inverse flame temperature predicted in the theory. An analysis of the numerical and experimental data shows that, in the limit of lean hydrogen–methane–air mixtures, the activation energy approaches a constant value, which is not sensitive to the addition of hydrogen to methane. The mass flow rate for a freely propagating flame and, thus, the laminar burning velocity, are measured for mixtures with different hydrogen contents. This mass flow rate, scaled over the characteristic temperature dependence of the laminar burning velocity for a one-step reaction mechanism, is found and it can also be used in order to estimate the parameters of the overall reaction mechanisms. Such reaction mechanisms will find implementation in the numerical simulation of practical combustion devices with complex flows and geometries

From light to baryonic mass: the effect of the stellar mass-to-light ratio on the Baryonic Tully-Fisher relation

In this paper, we investigate the statistical properties of the Baryonic Tully-Fisher relation (BTFr) for a sample of 32 galaxies with accurate distances based on n Cepheids and/or TRGB stars. We make use of homogeneously analysed photometry in 18 bands ranging from the far-ultraviolet to 160 μm, allowing us to investigate the effect of the inferred stellar mass-to-light ratio (ϒ⋆) on the statistical properties of the BTFr. Stellar masses of our sample galaxies are derived with four different methods based on full SED fitting, studies of stellar dynamics, near-infrared colours, and the assumption of the same Υ[3.6]⋆ for all galaxies. In addition, we use high-quality, resolved H I kinematics to study the BTFr based on three kinematic measures: Wi50 from the global H I profile, and Vmax and Vflat from the rotation curve. We find the intrinsic perpendicular scatter, or tightness, of our BTFr to be σ⊥ = 0.026 ± 0.013 dex, consistent with the intrinsic tightness of the 3.6 μm luminosity-based Tully-Fisher relation (TFr). However, we find the slope of the BTFr to be 2.99 ± 0.2 instead of 3.7 ± 0.1 for the luminosity-based TFr at 3.6 μm. We use our BTFr to place important observational constraints on theoretical models of galaxy formation and evolution by making comparisons with theoretical predictions based on either the Λ cold dark matter framework or modified Newtonian dynamics.AB acknowledges financial support from the CNES (Centre National d’Etudes Spatiales – France). EP is supported by a NOVA postdoctoral fellowship of the Netherlands Research School for Astronomy (NOVA). MV acknowledges the Netherlands Foundation for Scientific Research support through VICI grant 016.130.338. We acknowledge the Leids Kerkhoven–Bosscha Fonds (LKBF) for travel support. We acknowledge financial support from the DAGAL network from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7/2007-2013/ under REA grant agreement number PITNGA-2011-289313. We thank Elisabete da Cunha for making the MAGPHYS SED-fitting code publicly available

EDGE -- Dark matter or astrophysics? Clear prospects to break dark matter heating degeneracies with HI rotation in faint dwarf galaxies

Low-mass dwarf galaxies are expected to showcase pristine `cuspy' inner dark matter density profiles compared to their stellar sizes, as they form too few stars to significantly drive dark matter heating through supernovae-driven outflows. Here, we study such simulated faint systems ($10^4 \leq M_{\star} \leq 2\times 10^6 \, M_\mathrm{\odot}$) drawn from high-resolution (3 pc) cosmological simulations from the `Engineering Dwarf Galaxies at the Edge of galaxy formation' (EDGE) project. We confirm that these objects have steep and rising inner dark matter density profiles at $z=0$, little affected by galaxy formation effects. But five dwarf galaxies from the suite showcase a detectable HI reservoir ($M_{\mathrm{HI}}\approx 10^{5}-10^{6} \, M_\mathrm{\odot}$), analogous to the observed population of faint, HI-bearing dwarf galaxies. These reservoirs exhibit episodes of ordered rotation, opening windows for rotation curve analysis. Within actively star-forming dwarfs, stellar feedback easily disrupts the tenuous HI discs ($v_{\phi} \approx 10\, \mathrm{km} \, \mathrm{s}^{-1}$), making rotation short-lived ($\ll 150 \, \mathrm{Myr}$) and more challenging to interpret for dark matter inferences. Contrastingly, we highlight a long-lived ($\geq 500 \, \mathrm{Myr}$) and easy-to-interpret HI rotation curve extending to $\approx 2\, r_{1/2, \text{3D}}$ in a quiescent dwarf, that has not formed new stars since $z=4$. This stable gas disc is supported by an oblate dark matter halo shape that drives high angular momentum gas flows. Our results strongly motivate further searches for HI rotation curves in the observed population of HI-bearing low-mass dwarfs, that provide a key regime to disentangle the respective roles of dark matter microphysics and galaxy formation effects in driving dark matter heating.Comment: Main text 10 pages, submitted to MNRAS. Comments welcome

Исследование методов сплочения коллектива для повышения производительности персонала в организации

В статье представлено исследование методов сплочения коллектива с целью повышения производительности сотрудников в организации. Управление сплоченностью персонала играет важную роль в формировании рабочего потенциала и создании благоприятной среды для повышения результативности работников. В исследовании содержится анализ теоретических подходов к управлению сплоченностью, основные признаки сплоченного коллектива и проблемы, которые могут возникнуть из-за его отсутствия. В статье представлены результаты проведенного авторами исследования методов сплочения коллектива.The article presents a research devoted to the study of team building methods in order to improve employee performance in the organization. Managing staff cohesion plays an important role in building work potential and creating a favorable environment for improving employee performance. The article presents the analysis of conceptual approaches to staff cohesion management, the main attributes of a cohesive team and the problems that can arise due to its absence. This article reveals the results of the authors' research into the methods of team building

Regulation der Genexpression von MYCN in humanen Neuoblastomzellen durch Transkriptionsfaktoren der E2F-Familie

Seit fast 30 Jahren ist bekannt, dass die Amplifikation und Expression des Onkogens MYCN in Neuroblastomen mit einer sehr ungünstigen Prognose für die Patienten einhergeht. Dennoch liegen die Mechanismen der Genregulation von MYCN weiterhin größtenteils im Dunkeln. Die Präsenz potentieller Bindungsstellen für E2F-Proteine im Promotor des MYCN-Gens sowie Zellkulturexperimente lieferten Hinweise auf eine Rolle der Transkriptionsfaktoren der E2F-Familie in der Regulation der N-myc-Expression. Ziel dieser Arbeit war die Beantwortung der Frage, ob E2F-Proteine notwendig sind, um eine primär hohe Expression von N-myc in Neuroblastomzellen mit Amplifikation des Onkogens aufrechtzuerhalten, und ob sie hinreichend sind, um die Transkription von MYCN in Zellen ohne endogene Expression von N-myc einzuleiten. Durch Überexpression des Tumorsuppressorproteins p16, welches zu einer Inaktivierung endogener E2F-Proteine führt, konnte die MYCN-mRNA-Menge in Neuroblastomzellen deutlich gesenkt werden. Vergleichbare Resultate wurden durch Expression von dominant negativem E2F-1 erzielt. Da in einigen Studien gezeigt werden konnte, dass Myc-Proteine ihrerseits E2F-Gene aktivieren können, nehmen wir an, in aggressiven Neuroblastomen könnte eine positive Rückkopplungsschleife zwischen E2F-Transkriptionsfaktoren auf der einen und N-myc auf der anderen Seite existieren, die die gesteigerte Aktivität des MYCN-Onkogens aufrechterhält. Stabil transfizierte E2F-ER-Fusionsproteine waren jedoch nicht in der Lage, das endogene MYCN-Gen in Neuroblastomzellen ohne Expression von N-myc anzuschalten. E2F-Proteine werden folglich für das volle Ausmaß der starken Expression von N-myc in Neuroblastomen benötigt, sind aber nicht ausreichend, um das Onkogen MYCN in Zellen ohne endogenes N-myc zu aktivieren. In der Zukunft könnte durch Verhinderung der Bindung von E2F-Proteinen an den MYCN-Promotor oder durch gentherapeutische Ansätze, die z.B. mittels viraler Infektion den Signalweg zwischen p16 und E2F rekonstruieren, die Expression von N-myc in Neuroblastomen gesenkt werden, so dass die Aggressivität der Tumore reduziert und die individuelle Prognose der Patienten verbessert werden könnte