Bailing Out the Milky Way: Variation in the Properties of Massive Dwarfs Among Galaxy-Sized Systems

Recent kinematical constraints on the internal densities of the Milky Way's dwarf satellites have revealed a discrepancy with the subhalo populations of simulated Galaxy-scale halos in the standard CDM model of hierarchical structure formation. This has been dubbed the "too big to fail" problem, with reference to the improbability of large and invisible companions existing in the Galactic environment. In this paper, we argue that both the Milky Way observations and simulated subhalos are consistent with the predictions of the standard model for structure formation. Specifically, we show that there is significant variation in the properties of subhalos among distinct host halos of fixed mass and suggest that this can reasonably account for the deficit of dense satellites in the Milky Way. We exploit well-tested analytic techniques to predict the properties in a large sample of distinct host halos with a variety of masses spanning the range expected of the Galactic halo. The analytic model produces subhalo populations consistent with both Via Lactea II and Aquarius, and our results suggest that natural variation in subhalo properties suffices to explain the discrepancy between Milky Way satellite kinematics and these numerical simulations. At least ~10% of Milky Way-sized halos host subhalo populations for which there is no "too big to fail" problem, even when the host halo mass is as large as M_host = 10^12.2 h^-1 M_sun. Follow-up studies consisting of high-resolution simulations of a large number of Milky Way-sized hosts are necessary to confirm our predictions. In the absence of such efforts, the "too big to fail" problem does not appear to be a significant challenge to the standard model of hierarchical formation. [abridged]Comment: 12 pages, 3 figures; accepted by JCAP. Replaced with published versio

Light Nuclides Produced in the Proton-Induced Spallation of 238U at 1 GeV

The production of light and intermediate-mass nuclides formed in the reaction 1H+238U at 1 GeV was measured at the Fragment Separator (FRS) at GSI, Darmstadt. The experiment was performed in inverse kinematics, shooting a 1 A GeV 238U beam on a thin liquid-hydrogen target. 254 isotopes of all elements in the range from Z=7 to Z=37 were unambiguously identified, and the velocity distributions of the produced nuclides were determined with high precision. The results show that the nuclides are produced in a very asymmetric binary decay of heavy nuclei originating from the spallation of uranium. All the features of the produced nuclides merge with the characteristics of the fission products as their mass increases.Comment: 40 pages, 16 figures, 3 table

Understanding Dwarf Galaxies in order to Understand Dark Matter

Much progress has been made in recent years by the galaxy simulation community in making realistic galaxies, mostly by more accurately capturing the effects of baryons on the structural evolution of dark matter halos at high resolutions. This progress has altered theoretical expectations for galaxy evolution within a Cold Dark Matter (CDM) model, reconciling many earlier discrepancies between theory and observations. Despite this reconciliation, CDM may not be an accurate model for our Universe. Much more work must be done to understand the predictions for galaxy formation within alternative dark matter models.Comment: Refereed contribution to the Proceedings of the Simons Symposium on Illuminating Dark Matter, to be published by Springe

Thin disc, Thick Disc and Halo in a Simulated Galaxy

Within a cosmological hydrodynamical simulation, we form a disc galaxy with sub- components which can be assigned to a thin stellar disc, thick disk, and a low mass stellar halo via a chemical decomposition. The thin and thick disc populations so selected are distinct in their ages, kinematics, and metallicities. Thin disc stars are young (<6.6 Gyr), possess low velocity dispersion ({\sigma}U,V,W = 41, 31, 25 km/s), high [Fe/H], and low [O/Fe]. The thick disc stars are old (6.6<age<9.8 Gyrs), lag the thin disc by \sim21 km/s, possess higher velocity dispersion ({\sigma}U,V,W = 49, 44, 35 km/s), relatively low [Fe/H] and high [O/Fe]. The halo component comprises less than 4% of stars in the "solar annulus" of the simulation, has low metallicity, a velocity ellipsoid defined by ({\sigma}U,V,W = 62, 46, 45 km/s) and is formed primarily in-situ during an early merger epoch. Gas-rich mergers during this epoch play a major role in fuelling the formation of the old disc stars (the thick disc). This is consistent with studies which show that cold accretion is the main source of a disc galaxy's baryons. Our simulation initially forms a relatively short (scalelength \sim1.7 kpc at z=1) and kinematically hot disc, primarily from gas accreted during the galaxy's merger epoch. Far from being a competing formation scenario, migration is crucial for reconciling the short, hot, discs which form at high redshift in {\Lambda}CDM, with the properties of the thick disc at z=0. The thick disc, as defined by its abundances maintains its relatively short scale-length at z = 0 (2.31 kpc) compared with the total disc scale-length of 2.73 kpc. The inside-out nature of disc growth is imprinted the evolution of abundances such that the metal poor {\alpha}-young population has a larger scale-length (4.07 kpc) than the more chemically evolved metal rich {\alpha}-young population (2.74 kpc).Comment: Submitted to MNRAS. This version after helpful referee comments. Comments welcome to [email protected]

Beta Dips in the Gaia Era: Simulation Predictions of the Galactic Velocity Anisotropy Parameter (β) for Stellar Halos

The velocity anisotropy parameter, β, is a measure of the kinematic state of orbits in the stellar halo, which holds promise for constraining the merger history of the Milky Way (MW). We determine global trends for β as a function of radius from three suites of simulations, including accretion-only and cosmological hydrodynamic simulations. We find that the two types of simulations are consistent and predict strong radial anisotropy ($\langle \beta \rangle \sim 0.7$) for Galactocentric radii greater than 10 kpc. Previous observations of β for the MW's stellar halo claim a detection of an isotropic or tangential "dip" at r ~ 20 kpc. Using the N-body+SPH simulations, we investigate the temporal persistence, population origin, and severity of "dips" in β. We find that dips in the in situ stellar halo are long-lived, while dips in the accreted stellar halo are short-lived and tied to the recent accretion of satellite material. We also find that a major merger as early as z ~ 1 can result in a present-day low (isotropic to tangential) value of β over a broad range of radii and angles. While all of these mechanisms are plausible drivers for the β dip observed in the MW, each mechanism in the simulations has a unique metallicity signature associated with it, implying that future spectroscopic surveys could distinguish between them. Since an accurate knowledge of β(r) is required for measuring the mass of the MW halo, we note that significant transient dips in β could cause an overestimate of the halo's mass when using spherical Jeans equation modeling

Prospects in Analytical Atomic Spectrometry

Tendencies in five main branches of atomic spectrometry (absorption, emission, mass, fluorescence and ionization spectrometry) are considered. The first three techniques are the most widespread and universal, with the best sensitivity attributed to atomic mass spectrometry. In the direct elemental analysis of solid samples, the leading roles are now conquered by laser-induced breakdown and laser ablation mass spectrometry, and the related techniques with transfer of the laser ablation products into inductively-coupled plasma. Advances in design of diode lasers and optical parametric oscillators promote developments in fluorescence and ionization spectrometry and also in absorption techniques where uses of optical cavities for increased effective absorption pathlength are expected to expand. Prospects for analytical instrumentation are seen in higher productivity, portability, miniaturization, incorporation of advanced software, automated sample preparation and transition to the multifunctional modular architecture. Steady progress and growth in applications of plasma- and laser-based methods are observed. An interest towards the absolute (standardless) analysis has revived, particularly in the emission spectrometry.Comment: Proofread copy with an added full reference list of 279 citations. A pdf version of the final published review may be requested from Alexander Bol'shakov <[email protected]

О связи протонного облучения и термической обработки монокристаллического кремния с его структурой

The method of two-crystal X-ray diffractometry is used to control the quality and perfection of monocrystalline silicon obtained by implantation of hydrogen ions and subsequent thermal annealing, which is used in a number of semiconductor technologies. The principal feature of this approach is the ability to quickly obtain reliable experimental results, which was confirmed in this paper by the use of X-ray topography. The presented data provide information on the state of the disturbed layer of silicon crystals of n-type conductivity (ρ = 100 Om ⋅ cm) by orientation (111), 2 mm thick, implanted by protons with energy E = 200, 300, 100 + 200 + 300 keV, dose D = 2 ⋅ 1016cm-2 and subjected to subsequent thermal treatment in the temperature range T from 100 to 900 °С. We have established a non-monotonic dependence of the integral characteristics of the disturbed layer, namely the average effective thickness Leff and the average relative deformation ∆а/а, on annealing temperature, with the maximum level of distortion in the field of temperature ∼300 °С, using the method of integral characteristics. Obtained data allowed to assess the general condition of disturbed layer during thermal treatment.Метод двухкристальной рентгеновской дифрактометрии применен для контроля качества и совершенства монокристаллического кремния, получаемого с помощью имплантации ионов водорода и последующего термического отжига, который используется в ряде полупроводниковых технологий. Принципиальная особенность данного подхода состоит в возможности быстрого получения надежных экспериментальных результатов, что было подтверждено путем использования рентгеновской топографии. Представлены данные о состоянии нарушенного слоя кристаллов кремния n-типа проводимости (ρ = 100 Ом ⋅ см) ориентацией (111) толщиной 2 мм, имплантированных протонами с энергией Е = 200, 300 и 100 + 200 + 300 кэВ и дозой имплантации D = 2 ⋅ 1016 см-2 и подвергнутых последующей термической обработке в интервале температур Т от 100 до 900 °С. С использованием метода интегральных характеристик установлена немонотонная зависимость интегральных характеристик нарушенного слоя, а именно: средней эффективной толщины Lэфф и средней относительной деформации ∆а/а от температуры отжига, с максимальным уровнем искажений в области температуры ∼300 °С. Показано, что полученные данные позволили оценить общее состояние нарушенного слоя при термообработке

Нетозформирующая способность нейтрофилов у пациентов с ограниченным и распространенным туберкулезным процессом

The objective: to assess NETosis-forming ability of neutrophils in patients with limited and disseminated tuberculous lesions.Subjects and Methods. 44 new cases of respiratory tuberculosis were included in the study. Group 1 consisted of 22 patients with limited focal or infiltrative tuberculosis with no lung tissue destruction, Group 2 included 22 patients with disseminated tuberculosis with destruction of the lung tissue. Control Group (Group 0) included 22 healthy volunteers. NETosis-forming ability was assessed in vitro in the isolated fraction of neutrophils from peripheral venous blood. The ratio (%) of neutrophils of different degrees of activation and the ratio (%) of various forms of neutrophil extracellular traps (NET), the bacterial capture coefficient of NEL were calculated.Results. NETosis-forming ability of neutrophils in the patients from Groups 1 and 2 was more pronounced versus Group 0, and in Group 2 it was maximum. In Group 2, the bacterial capture rate by NET was statistically significantly lower versus Group 1 (p=0,0147), which may indicate some degree of «inferiority» of NET formed in Group 2.Цель исследования: оценить нетозобразующую способность нейтрофилов у пациентов с ограниченным и распространенным туберкулезным процессом.Материалы и методы. В исследование включено 44 пациента с впервые выявленным туберкулезом органов дыхания. Группу 1 составили 22 пациента с ограниченным очаговым или инфильтративным туберкулезным процессом без распада легочной ткани, группу 2 – 22 пациента с распространенным туберкулезным процессом в фазе распада. Контрольную группу (группа 0) составили 22 здоровых добровольца. Определяли нетозобразующую способность in vitro в изолированной фракции нейтрофилов периферической венозной крови. Рассчитывали: соотношение (%) нейтрофилов разной степени активации и соотношение (%) различных форм нейтрофильных внеклеточных ловушек (НВЛ), коэффициент захвата бактерий НВЛ. Результаты. Нетозобразующая способность нейтрофилов у пациентов групп 1 и 2 была более выраженной в сравнении с группой 0, причем в группе 2 она была максимальной. Коэффициент захвата бактерий НВЛ в группе 2 был статистически значимо ниже, чем в группе 1 (p=0,0147), что может указывать на некоторую степень «неполноценности» НВЛ, формируемых в группе 2

Влияние гимантана на уровень продуктов перекисного окисления липидов в головном мозге при экспериментальном паркинсоническом синдроме

In two animaL modeLs of parkinsonian syndrome - induced by 1-methyL-4-phenyL-1,2,3,6-tetrahydropiridine (MPTP) in C57BL/6 mice and 6-hydroxidopamine (6-OHDA) in rats noveL antiparkinsonian drug hemantane was shown to reduce the increase of brain LeveL of Lipid peroxidation caused by both neurotoxines. In prefrontaL cortex and striatum of mice which were treated with hemantane 10 mg/kg 5 days before MPTP and 5 days together with MPTP and in rats which received hemantane during 21 days after 6-OHDA injection in mediaL forebrain bundLe the LeveLs of maLondiaLdehyde and conjugated dienes were significantLy Lower than in untreated animaLs. The data obtained is consistent with antioxidant properties of hemantane.На двух моделях паркинсонического синдрома (ПС), индуцированного 1-метил-4-фенил-1,2,3,6-тетрагидропиридином (МФТП) у мышей C57BL/6 и 6-гидроксидофамином (6-ГОДА) у крыс, показана способность нового противопаркинсонического препарата гимантана в эффективной дозе 10 мг/кг при двух режимах введения (5 дней до нейротоксина МФТП и совместно с ним в течение 5 дней, а также при введении в течение 21 дня на фоне развивающегося 6-ГОДА индуцированного ПС) ослаблять вызываемую нейротоксинами активацию перекисного окисления липидов. Введение гимантана приводило к снижению уровней малонового альдегида и диеновых конъюгатов во фронтальной коре и стриатуме. Полученные данные согласуются с ранее установленными антиоксидантными свойствами гимантана

Стресс-индуцированная дисфункция тромбоцитов у крыс с фолат-зависимой гипергомоцистеинемией

A rat model of experimental hyperhomocysteinemia (HHC) caused by chronic folic acid deficiency was used to study the impact of swimming stress on the values of agonist-induced platelet aggregation and ATP release. At week 8 of HHC development, platelet aggregability and ATP levels in response to test inductors (ADP, thrombin, and collagen) moderately increased. After stress, the rate of platelet aggregation showed a more increase in rats with HHC; however, the increment was less pronounced than in the control group. The similar changes was observed in ATP, the release of which from dense platelet granules decreased in the experimental animals exposed to stress changes as compared to the controls. The experimental findings suggest that the stress potentiates platelet dysfunction in HHC. На модели экспериментальной гипергомоцистеинемии (ГГЦ) у крыс, вызванной хроническим дефицитом в организме фолиевой кислоты, изучалось влияние плавательного стресса на показатели агонист-индуцированной агрегации тромбоцитов и реакцию высвобождения из них АТФ. Показано, что на восьмой неделе развития ГГЦ агре-гационная способность тромбоцитов, как и уровень АТФ на все исследованные индукторы (АДФ, тромбин, коллаген), умеренно повышались. После стрессовой нагрузки интенсивность агрегации тромбоцитов у крыс с ГГЦ еще более возрастала, однако прирост ее был менее выраженным, чем в контрольной группе. Аналогичная динамика зарегистрирована со стороны АТФ, выброс которого из плотных тромбоцитарных гранул опытных животных, подвергнутых стрессу, уменьшался по сравнению с контролем. Результаты экспериментов свидетельствуют о потенцирующем влиянии стресса на дисфункцию тромбоцитов при ГГЦ.