Ionized gas probes the influence of massive stars on their environment. The Cygnus X region (d~1.5 kpc) is one of the most massive star forming complexes in our Galaxy, in which the Cyg OB2 ...association (age of 3-5 Myr and stellar mass \(2 \times 10^{4}\) M\(_{\odot}\)) has a dominant influence. We observe the Cygnus X region at 148 MHz using the Low Frequency Array (LOFAR) and take into account short-spacing information during image deconvolution. Together with data from the Canadian Galactic Plane Survey, we investigate the morphology, distribution, and physical conditions of low-density ionized gas in a \(4^{\circ} \times 4^{\circ}\) (100 pc \(\times\) 100 pc) region at a resolution of 2' (0.9 pc). The Galactic radio emission in the region analyzed is almost entirely thermal (free-free) at 148 MHz, with emission measures of \(10^3 < EM~{\rmpc~cm^{-6}} < 10^6\). As filamentary structure is a prominent feature of the emission, we use DisPerSE and FilChap to identify filamentary ridges and characterize their radial (\(EM\)) profiles. The distribution of radial profiles has a characteristic width of 4.3 pc and a power-law distribution (\(\beta = -1.8 \pm 0.1\)) in peak \(EM\) down to our completeness limit of 4200 pc cm\(^{-6}\). The electron densities of the filamentary structure range from \(10 < n_e~{\rmcm^{-3}} < 400\) with a median value of 35 cm\(^{-3}\), remarkably similar to N II surveys of ionized gas. Cyg OB2 may ionize at most two-thirds of the total ionized gas and the ionized gas in filaments. More than half of the filamentary structures are likely photoevaporating surfaces flowing into a surrounding diffuse (~5 cm\(^{-3}\)) medium. However, this is likely not the case for all ionized gas ridges. A characteristic width in the distribution of ionized gas points to the stellar winds of Cyg OB2 creating a fraction of the ionized filaments through swept-up ionized gas or dissipated turbulence.
If the interstellar medium (ISM) in a galaxy is driven into the nuclear region, it will change the evolution of the galaxy. Although it is generally assumed that bars are efficient at driving the ISM ...to smaller radii, how the characteristics of a bar affect the inflow has never been examined in detail. In this paper we investigate how various bar characteristics affect the ability of the bar to drive the ISM to smaller radii. We model the ISM using high- resolution hydrodynamic simulations and are able to show that weak bars have almost no effect on the radial distribution of the ISM. We also find that for all bar strengths, bars are only able to drive gas down to a radius where a ring forms. Inside of this ring there is very little net inflow. When a nuclear ring forms the bar becomes very efficient at driving gas down to the inner kiloparsec. Alternatively, when no nuclear ring forms, gas forms a ring at the largest nonlooping orbit whose major axis is parallel to the major axis of the bar (x sub(1) orbit). For all but the thinnest bars, this ring is far from the nuclear region. We term this type of ring an x sub(1) ring and show that inner rings are a subset of x sub(1) rings and form when there are no looping x sub(1) orbits. In this case, the gas accumulates at the largest x sub(1) orbit inside of the looping 4 : 1 orbits. We also show that the one-dimensional measure of bar strength based on the maximum nonaxisymmetric force, Q sub(b), is degenerate with several bar characteristics that control orbit family transitions. Because these orbit transitions determine where and whether rings form, and it is ring formation that is the ultimate result of bar- driven inflow, Q sub(b) is not a useful metric for determining the effect of a bar on the evolution of a galaxy.
As observations of molecular gas in galaxies are pushed to lower star formation rate (SFR) galaxies at higher redshifts, it is becoming increasingly important to understand the conditions of the gas ...in these systems to properly infer their molecular gas content. The rotational transitions of the carbon monoxide (CO) molecule provide an excellent probe of the gas excitation conditions in these galaxies. In this paper, we present the results from the gas excitation sample of the Evolution of molecular Gas in Normal Galaxies (EGNoG) survey at the Combined Array for Research in Millimeter-wave Astronomy (CARMA). This subset of the full EGNoG sample consists of four galaxies at z Almost-Equal-To 0.3 with SFRs of 40-65 M {sub Sun} yr{sup -1} and stellar masses of Almost-Equal-To 2 Multiplication-Sign 10{sup 11} M {sub Sun }. Using the 3 mm and 1 mm bands at CARMA, we observe both the CO(J = 1 {yields} 0) and CO(J = 3 {yields} 2) transitions in these four galaxies in order to probe the excitation of the molecular gas. We report robust detections of both lines in three galaxies (and an upper limit on the fourth), with an average line ratio, r {sub 31} = L'{sub CO(3-2)}/L'{sub CO(1-0)}, of 0.46 {+-} 0.07 (with systematic errors {approx}< 40%), which implies sub-thermal excitation of the CO(J = 3 {yields} 2) line. We conclude that the excitation of the gas in these massive, highly star-forming galaxies is consistent with normal star-forming galaxies such as local spirals, not starbursting systems like local ultraluminous infrared galaxies. Since the EGNoG gas excitation sample galaxies are selected from the main sequence (MS) of star-forming galaxies, we suggest that this result is applicable to studies of MS galaxies at intermediate and high redshifts, supporting the assumptions made in studies that find molecular gas fractions in star-forming galaxies at z {approx} 1-2 to be an order of magnitude larger than what is observed locally.
Asplenic patients are at increased risk for the development of overwhelming postsplenectomy infection (OPSI) syndrome. It is believed that adequate immunization, antimicrobial prophylaxis, as well as ...appropriate education concerning risks on severe infection lead to the decreased incidence of OPSI. The aim of this study was to analyze the methods used to prevent OPSI in trauma patients splenectomized before the age of 18.
A retrospective, single-center study of all pediatric patients sustaining blunt splenic injury (BSI) managed at our level 1 trauma center from January 1979 to March 2012 was performed. A questionnaire was sent to all the included patients to determine the level of knowledge concerning infection risks, the use of antibiotics, and compliance to vaccination recommendations. Furthermore, we investigated whether the implementation of guidelines in 2003 and 2011 resulted in higher vaccination rates.
We included 116 children with BSI. A total of 93 completed interviews were eligible for analysis, resulting in a total response rate of 80% and 1,116 patient years. Twenty-seven patients were splenectomized, and 66 patients were treated by a spleen preserving therapy (including embolization). Only two out of 27 splenectomized patients were adequately vaccinated, five patients without a spleen used prophylactic antibiotics, and about half of the asplenic patients had adequate knowledge of the risk that asplenia entails. A total of 22/27 splenectomized patients were neither adequately vaccinated nor received prophylactic antibiotics. There was no OPSI seen in our study population during the 1,116 follow-up years.
The vaccination status, the level of knowledge concerning prevention of an OPSI, and the use of prophylactic antibiotics are suboptimal in pediatric patients treated for BSI. Therefore, we created a new follow-up treatment guideline to have adequate preventive coverage to current standards for these patients.
The Astropy Project supports and fosters the development of open-source and openly developed Python packages that provide commonly needed functionality to the astronomical community. A key element of ...the Astropy Project is the core package astropy, which serves as the foundation for more specialized projects and packages. In this article, we provide an overview of the organization of the Astropy project and summarize key features in the core package, as of the recent major release, version 2.0. We then describe the project infrastructure designed to facilitate and support development for a broader ecosystem of interoperable packages. We conclude with a future outlook of planned new features and directions for the broader Astropy Project.
Numerical self-consistent equilibrium models for the perfect elliptic disc have been constructed using Schwarzschild’s linear programming method. Two solutions have been found for each model, which ...minimize and maximize the total angular momentum in the disc. This is a numerical verification of the non-uniqueness of the solutions. Distribution functions in action space have been derived. The maximum angular momentum solutions have smooth distribution functions in action space (Fig. 6), apart from an allowed discontinuity at the closed loop orbits; in a real system this might plausibly arise through dissipational formation. The minimum angular momentum solutions are all discontinuous over the marginal (unstable) orbits (Fig. 7), which indicates that these solutions are probably unphysical. The maximum angular momentum solutions have been recalculated using a direct method, and have been compared with the linear programming solutions. Various numerical effects are discussed. Associating stars with all orbits and gas with the closed elliptic orbits, mean streaming and velocity dispersion fields for the star and gas have been derived. Velocity fields for the stars and gas are projected on to the sky and are shown as such hypothetical systems would be observed. There is a significant difference in the kinematics of the stars and gas. This may have some relevance to hot ovally distorted discs with little or no figure pattern speed or to gas in a principal plane of a triaxial elliptical galaxy.
We describe the characteristics of the BIMA millimeter wave array at Hat Creek, CA. The array is an aperture synthesis instrument consisting of nine 6 m diameter antennas which may be deployed in ...three different configurations, with spacings ranging from 7 m up to 1.3 km. At an observing frequency of 100 GHz these configurations yield maps with angular resolutions of 5", 2", and O.̎4, over a 2' field.Larger fields may be mapped by using multiple pointings. For all but the oldest telescopes, the surface accuracy is ≤ 30 μM rms, and the aperture efficiency is 77% at 100 GHz. Background emission from antenna losses and spillover is very low, about 5 after subtraction of the cosmic Bv(2.1 K). Each antenna contains a single de war which accommodates up to four separate receivers. SIS mixers are cooled to 3.2 oscillator are received and separated, providing two bands extending from 70-900 MHz on each side of the first local oscillator. The correlation spectrometer covers a bandwidth of up to 800 MHz, and provides up to 2048 channels for each antenna pair. There are four independently tunable spectral windows (in each sideband), allowing simultaneous observations of several different spectral lines. The spectral resolution ranges from 6 kHz to 3 MHz. For a single 8-hr track in one configuration, the sensitivity is approximately 1 mJy/beam in the 800 MHz wide continuum. Measurements of atmospheric phase fluctuations as functions of both time and baseline have been made; these indicate that routine imaging at angular resolutions of less than 1" at 100 GHz is possible only if self-calibration or some other means of phase correction can be applied. Examples of a few recent results are included. We note that 30% of the observing time on the array is granted to visitors.
Dynamical rules for barred spiral galaxies Teuben, P. J.; Sanders, R. H.
Monthly Notices of the Royal Astronomical Society,
01/1985, Letnik:
212, Številka:
2
Journal Article
Recenzirano
Odprti dostop
Numerical integrations of 2D-orbits demonstrate that the principal family of periodic orbits in strong barred potentials is the prograde parallel family. All other families have orbit density ...distributions which are inconsistent with the imposed potential. Some important implications are discussed: (1) bars tumble in the sense of galactic rotation; (2) corotation must lie outside the bar distortion; (3) strong rapidly tumbling bars are cold, and, conversely, strong slowly tumbling bars are hot and (4) the magnitude of the bar distortion is limited to axial ratios of about 1:5, due to the onset of stochasticity well inside corotation. A small population of stars on stochastic orbits may form the more nearly axisymmetric lens structure seen in some barred galaxies.
PDF
