On the origin of the neutral hydrogen supershells: the ionized progenitors and the limitations of the multiple supernovae hypothesis

Here we address the question whether the ionized shells associated with giant HII regions can be progenitors of the larger HI shell-like objects found in the Milky Way and other spiral and dwarf irregular galaxies. We use for our analysis a sample of 12 HII shells presented recently by Rela\~no et al. (2005, 2007). We calculate the evolutionary tracks that these shells would have if their expansion is driven by multiple supernovae explosions from the parental stellar clusters. We find, contrary to Rela\~no et al. (2007), that the evolutionary tracks of their sample HII shells are inconsistent with the observed parameters of the largest and most massive neutral hydrogen supershells. We conclude that HII shells found inside giant HII regions may represent the progenitors of small or intermediate HI shells, however they cannot evolve into the largest HI objects unless, aside from the multiple supernovae explosions, an additional energy source contributes to their expansion.Comment: Accepted for publication in ApJ, tentatively scheduled for the ApJ July 1, 2008, v681n1 issue. 19 pages, 4 figure

Reasons of pathologies of yakutian mammoths’ tusks in late pleistocene by data of isotopic and geochemical investigations

Among the remnants of Late Pleistocene mammals collected on the coast of the Laptev Sea, there are the tusks of woolly mammoth (Mammuthus primigenius) with abnormalities. An analysis of the isotopic composition of carbon from their bone carbonate hydroxylapatite, as well as geochemical studies of the substance of such tusks (35 items, a total of 38 samples) by x-ray fluorescence method was conducted. Significant differences in the chemical composition of the tusks with abnormalities and “normal” tusks in such the elements as Sr, Mg, Si, Al, Mn, Fe, Zn, etc. were revealed. An attempt to express the obtained anomalies of the chemical composition in the terms adopted in the description of microelementoses was made. It was determined that most studied mammoths lived in the cold epochs, however, the pathology of the tusks were observed for animals living both in the cold and warm epochs of the Late Pleistocene. The causes of occurrence of pathologies probably were linked to different types of physiological disorders affecting the growth and development of the tusks and, possibly, with changes in the geochemical background influencing the population of woolly mammoth in the North of Yakutia

Environment, Ram Pressure, and Shell Formation in HoII

Neutral hydrogen VLA D-array observations of the dwarf irregular galaxy HoII, a prototype galaxy for studies of shell formation, are presented. HI is detected to radii over 16' or 4 R_25, and M_HI=6.44x10^8 M_sun. The total HI map has a comet-like appearance suggesting that HoII is affected by ram pressure from an intragroup medium (IGM). A rotation curve corrected for asymmetric drift was derived and an analysis of the mass distribution yields a total mass 6.3x10^9 M_sun, of which about 80% is dark. HoII lies northeast of the M81 group's core, along with Kar52 (M81dwA) and UGC4483. No signs of interaction are observed and it is argued that HoII is part of the NGC2403 subgroup, infalling towards M81. A case is made for ram pressure stripping and an IGM in the M81 group. Stripping of the disk outer parts would require an IGM density n_IGM>=4.0x10^-6 atoms/cm^3 at the location of HoII. This corresponds to 1% of the virial mass of the group uniformly distributed over a volume just enclosing HoII and is consistent with the X-ray properties of small groups. It is argued that existing observations of HoII do not support self-propagating star formation scenarios, whereby the HI holes and shells are created by supernova explosions and stellar winds. Many HI holes are located in low surface density regions of the disk, where no star formation is expected or observed. Ram pressure has the capacity to enlarge preexisting holes and lower their creation energies, helping to bridge the gap between the observed star formation rate and that required to create the holes. (abridged)Comment: 43 pages, including 7 figures. 4 figures available as JPEG only. Complete manuscript including full resolution figures available at http://www.strw.leidenuniv.nl/~bureau/pub_list.html . Accepted for publication in The Astronomical Journa

The Galactic Distribution of Large HI Shells

We report the discovery of nineteen new HI shells in the Southern Galactic Plane Survey (SGPS). These shells, which range in radius from 40 pc to 1 kpc, were found in the low resolution Parkes portion of the SGPS dataset, covering Galactic longitudes l=253 deg to l=358 deg. Here we give the properties of individual shells, including positions, physical dimensions, energetics, masses, and possible associations. We also examine the distribution of these shells in the Milky Way and find that several of the shells are located between the spiral arms of the Galaxy. We offer possible explanations for this effect, in particular that the density gradient away from spiral arms, combined with the many generations of sequential star formation required to create large shells, could lead to a preferential placement of shells on the trailing edges of spiral arms. Spiral density wave theory is used in order to derive the magnitude of the density gradient behind spiral arms. We find that the density gradient away from spiral arms is comparable to that out of the Galactic plane and therefore suggest that this may lead to exaggerated shell expansion away from spiral arms and into interarm regions.Comment: 25 pages, 20 embedded EPS figures, uses emulateapj.sty, to appear in the Astrophysical Journa

Two Large HI Shells in the Outer Galaxy near l=279 degrees

As part of a survey of HI 21-cm emission in the Southern Milky Way, we have detected two large shells in the interstellar neutral hydrogen near l=279 deg. The center velocities are +36 and +59 km/s, which puts the shells at kinematic distances of 7 and 10 kpc. The larger shell is about 610 pc in diameter and very empty, with density contrast of at least 15 between the middle and the shell walls. It has expansion velocity of about 20 km/s and swept up mass of several million solar masses. The energy indicated by the expansion may be as high as 2.4 X 10^53 ergs. We estimate its age to be 15 to 20 million years. The smaller shell has diameter of about 400 pc, expansion velocity about 10 km/s and swept up mass of about 10^6 solar masses. Morphologically both regions appear to be shells, with high density regions mostly surrounding the voids, although the first appears to have channels of low density which connect with the halo above and below the HI layer. They lie on the edge of the Carina arm, which suggests that they may be expanding horizontally into the interarm region as well as vertically out of the disk. If this interpretation is correct, this is the first detection of an HI chimney which has blown out of both sides of the disk.Comment: 21 pages, 14 jpeg figures, accepted for publication in A

Observational Manifestations of the First Protogalaxies in the 21 cm Line

The absorption properties of the first low-mass protogalaxies (mini-halos) forming at high redshifts in the 21-cm line of atomic hydrogen are considered. The absorption properties of these protogalaxies are shown to depend strongly on both their mass and evolutionary status. The optical depths in the line reach $\sim$0.1-0.2 for small impact parameters of the line of sight. When a protogalaxy being compressed, the influence of gas accretion can be seen manifested in a non-monotonic frequency dependence of the optical depth. The absorption characteristics in the 21-cm line are determined by the thermal and dynamical evolution of the gas in protogalaxies. Since the theoretical line width in the observer's reference frame is 1-6 kHz and the expected separation between lines 8.4 kHz, the lines from low mass protogalaxies can be resolved using ongoing and future low frequency interferometers.Comment: 12 pages, 5 figure

Эффективность действия биорегуляторов из Verbascum densiflorum Bertol. на процессы развития овощных культур

Relevance. Increasing the resistance of vegetable plants to unfavorable growing conditions with the use of growth regulators that actively affect the seed quality, increase the survival rate of seedlings, stimulate the setting, formation and maturation of the crop is a significant reserve for increasing productivity with the already achieved level of intensification of their production.Material and methods. The effect of verbascosides obtained by exhaustive extraction with 60% aqueous ethyl alcohol from the aboveground part of Verbascum densiflorum Bertol. (Scrophulariaceae) was studied on the germination, growth, development and yield of tomatoes, cucumbers, onions and white cabbage. Before sowing, the seeds were soaked in an aqueous solution of verbascosides for 15-20 minutes, followed by drying to flowability at the rate of 0.5-0.8 liters of solution per 1 kg of seeds.Results. It is shown, that possessing phytoregulatory activity and influencing the metabolic and synthetic reactions of plants, these compounds, applied exogenously, stimulate the seed germination energy and total germination of vegetable crops, provide simultaneous appearance of seedlings and optimal plant density, accelerate the growth dynamics of plants assimilation surface and fruit mass. Reducing the consequences of stresses arising in the process of plant growth and development, they thereby contribute to increasing plant resistance, productivity and improving the commercial quality of the products. The ability of these compounds to improve the production process of vegetable crops, depending on the type and variety of vegetables was established. Their highest stimulating effect was determined on cabbage variants, where the yield exceeded the control by 34.3%. The performed studies and obtained results allow to recommend the pre-sowing seed treatment with a 0.01% solution of biological active substances from Verbascum densiflorum Bertol. as an element in technology of growing vegetable.Актуальность. Повышение устойчивости овощных растений к неблагоприятным условиям произрастания с использованием регуляторов роста, активно влияющих на посевные качества семян, повышающих приживаемость рассады, стимулирующих завязываемость, формирование и созревание урожая является существенным резервом увеличения урожайности при уже достигнутом уровне интенсификации их производства.Материал и методика. Изучено влияние суммы вербаскозидов, полученной методом исчерпывающей экстракции 60% водным этиловым спиртом из надземной части Verbascum densiflorum Bertol. (сем. Scrophulariaceae), на всхожесть, рост, развитие и урожайность томата, огурца, лука репчатого и капусты белокочанной. Перед посевом семена замачивали в водном растворе вербаскозидов в течение 15-20 мин. с последующей подсушкой до сыпучести из расчета 0,5-0,8 л раствора на 1 кг семян.Результаты. Показано, что, обладая фиторегуляторной активностью и влияя на метаболические и синтетические реакции растений, данные соединения при экзогенном применении стимулируют энергию прорастания и всхожесть семян овощных культур, обеспечивают дружное появление всходов и оптимальную густоту стояния, ускоряют динамику нарастания ассимиляционной поверхности растений и массы плодов. Уменьшая последствия стрессов, возникающих в процессе роста и развития, они тем самым способствуют повышению устойчивости растений, урожайности и улучшению товарного качества получаемой продукции. Установлена способность вербаскозидов совершенствовать продукционный процесс овощных культур в зависимости от вида и сорта последних. Самое высокое стимулирующее их действие выявлено в вариантах на капусте, где урожайность превысила контроль на 34,3%. Выполненные исследования и полученные результаты позволяют рекомендовать предпосевную обработку семян 0,01%-ным раствором суммы биологических активных веществ из Verbascum densiflorum Bertol. в качестве элемента в технологии выращивания овощных культур

A Complete Spectroscopic Survey of the Milky Way Satellite Segue 1: The Darkest Galaxy

We present the results of a comprehensive Keck/DEIMOS spectroscopic survey of the ultra-faint Milky Way satellite galaxy Segue 1. We have obtained velocity measurements for 98.2% of the stars within 67 pc (10 arcmin, or 2.3 half-light radii) of the center of Segue 1 that have colors and magnitudes consistent with membership, down to a magnitude limit of r=21.7. Based on photometric, kinematic, and metallicity information, we identify 71 stars as probable Segue 1 members, including some as far out as 87 pc. After correcting for the influence of binary stars using repeated velocity measurements, we determine a velocity dispersion of 3.7^{+1.4}_{-1.1} km/s, with a corresponding mass within the half-light radius of 5.8^{+8.2}_{-3.1} x 10^5 Msun. The stellar kinematics of Segue 1 require very high mass-to-light ratios unless the system is far from dynamical equilibrium, even if the period distribution of unresolved binary stars is skewed toward implausibly short periods. With a total luminosity less than that of a single bright red giant and a V-band mass-to-light ratio of 3400 Msun/Lsun, Segue 1 is the darkest galaxy currently known. We critically re-examine recent claims that Segue 1 is a tidally disrupting star cluster and that kinematic samples are contaminated by the Sagittarius stream. The extremely low metallicities ([Fe/H] < -3) of two Segue 1 stars and the large metallicity spread among the members demonstrate conclusively that Segue 1 is a dwarf galaxy, and we find no evidence in favor of tidal effects. We also show that contamination by the Sagittarius stream has been overestimated. Segue 1 has the highest measured dark matter density of any known galaxy and will therefore be a prime testing ground for dark matter physics and galaxy formation on small scales.Comment: 24 pages, 4 tables, 11 figures (10 in color). Submitted for publication in ApJ. V3 revised according to comments from the refere

The PN.S Elliptical Galaxy Survey: the dark matter in NGC 4494

We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 PNe out to 7 effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the PNe agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside 1 Re. The velocity dispersion profile declines with radius, though not very steeply, down to ~70 km/s at the last data point. We have constructed spherical dynamical models of the system, including Jeans analyses with multi-component LCDM-motivated galaxies as well as logarithmic potentials. These models include special attention to orbital anisotropy, which we constrain using fourth-order velocity moments. Given several different sets of modelling methods and assumptions, we find consistent results for the mass profile within the radial range constrained by the data. Some dark matter (DM) is required by the data; our best-fit solution has a radially anisotropic stellar halo, a plausible stellar mass-to-light ratio, and a DM halo with an unexpectedly low central density. We find that this result does not substantially change with a flattened axisymmetric model. Taken together with other results for galaxy halo masses, we find suggestions for a puzzling pattern wherein most intermediate-luminosity galaxies have very low concentration halos, while some high-mass ellipticals have very high concentrations. We discuss some possible implications of these results for DM and galaxy formation.Comment: 29 pages, 17 figures. MNRAS, accepte

A Dynamical N-body Model for the Central Region of ω\omega Centauri

Supermassive black holes (SMBHs) are fundamental keys to understand the formation and evolution of their host galaxies. However, the formation and growth of SMBHs are not yet well understood. One of the proposed formation scenarios is the growth of SMBHs from seed intermediate-mass black holes (IMBHs, 10^2 to 10^5 M_{\odot}) formed in star clusters. In this context, and also with respect to the low mass end of the M-sigma relation for galaxies, globular clusters are in a mass range that make them ideal systems to look for IMBHs. Among Galactic star clusters, the massive cluster $\omega$ Centauri is a special target due to its central high velocity dispersion and also its multiple stellar populations. We study the central structure and dynamics of the star cluster $\omega$ Centauri to examine whether an IMBH is necessary to explain the observed velocity dispersion and surface brightness profiles. We perform direct N-body simulations to follow the dynamical evolution of $\omega$ Centauri. The simulations are compared to the most recent data-sets in order to explain the present-day conditions of the cluster and to constrain the initial conditions leading to the observed profiles. We find that starting from isotropic spherical multi-mass King models and within our canonical assumptions, a model with a central IMBH mass of 2% of the cluster stellar mass, i.e. a 5x10^4 M_{\odot} IMBH, provides a satisfactory fit to both the observed shallow cusp in surface brightness and the continuous rise towards the center of the radial velocity dispersion profile. In our isotropic spherical models, the predicted proper motion dispersion for the best-fit model is the same as the radial velocity dispersion one. (abridged)Comment: Accepted for publication in A&