The ratio of molecular to atomic gas in spiral galaxies as a function of morphological type

In order to gain an understanding of the global processes which influence cloud and star formation in disk galaxies, it is necessary to determine the relative amounts of atomic, molecular, and ionized gas both as a function of position in galaxies and from galaxy to galaxy. With observations of the CO distributions in over 200 galaxies now completed as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey (Young et al. 1989), researchers are finally in a position to determine the type dependence of the molecular content of spiral galaxies, along with the ratio of molecular to atomic gas as a function of type. Do late type spirals really have more gas than early types when the molecular gas content is included. Researchers conclude that there is more than an order of magnitude decrease in the ratio of molecular to atomic gas mass as a function of morphological type from Sa-Sd; an average Sa galaxy has more molecular than atomic gas, and an average Sc has less. Therefore, the total interstellar gas mass to blue luminosity ratio, M sub gas/L sub B, increases by less than a factor of two as a function of type from Sa-Sd. The dominant effect found is that the phase of the gas in the cool interstellar medium (ISM) varies along the Hubble sequence. Researchers suggest that the more massive and centrally concentrated galaxies are able to achieve a molecular-dominated ISM through the collection of more gas in the potential. That gas may then form molecular clouds when a critical density is exceeded. The picture which these observations support is one in which the conversion of atomic gas to molecular gas is a global process which depends on large scale dynamics (cf Wyse 1986). Among interacting and merging systems, researchers find considerable scatter in the M(H2)/M(HI) ratio, with the mean ratio similar to that in the early type galaxies. The high global ratio of molecular to atomic gas could result from the removal of HI gas, the enhanced conversion of HI into H2, or both

EDUsummIT 2011 Report from TWG3: Teacher Professional Development

A summary of the discussion and recommendations from the International Summit on ICT in Education 2011 working group on professional development of teachers

Massive low surface brightness galaxies

A multi-wavelength study of an extreme type of galaxy which will assist us in our attempts to understand the formation and evolution of galaxies was completed. In particular, a subset of low surface brightness (bar-mu(sub B) is approximately greater than 25 mag arcsec(sup -2)), giant galaxies (LSBG's) which contain large amounts of atomic gas (M(HI) is approximately greater than 10(exp 10) solar mass), have blue optical diameters similar to those of giant spiral galaxies, but which do not seem to have prodigious amounts of ongoing star formation were observed. Our sample was drawn from the first and second Palomar Sky Surveys. This population of galaxies has been largely ignored because of selection effects which make it difficult to detect optically. The question of how these massive systems differ from the higher surface brightness 'normal' spiral galaxies is addressed. Using B and R surface photometry, in conjunction with H-alpha, HI, CO-12, and far-infrared data, an attempt is made to determine if these galaxies had an early epoch of star formation that has since faded, have ongoing star formation with an unusual interplanetary magnetic field (IMF), or are perhaps galaxies which have never efficiently formed stars due to a lack of molecular clouds

Research-informed strategies to address educational challenges in a digitally networked world

This special issue represents the scholarly work that emerged from the EDUsummIT 2013. EDUsummIT is a growing and active community of researchers, policy makers and practitioners that is committed to promote research-informed strategies to effectively integrate ICT in educational policy and practice. First the background and aim of EDUsummIT is presented, followed by an overview of the contributions to this special issue

Multiple rooks of chess - a generic integral field unit deployment technique

A new field re-configuration technique, Multiple Rooks of Chess (MRC), for multiple deployable Integral Field Spectrographs has been developed. The method involves mechanical geometry as well as an optimized deployment algorithm. The geometry is found to be simple for mechanical implementation. The algorithm initially assigns the IFUs to the target objects and then devises the movement sequence based on the current and the desired IFU positions. The reconfiguration time using the suitable actuators which runs at 20 cm/s is found to be a maximum of 25 seconds for the circular DOTIFS focal plane (180 mm diameter). The Geometry Algorithm Combination (GAC) has been tested on several million mock target configurations with object-to-IFU ({\tau} ) ratio varying from 0.25 to 16. The MRC method is found to-be efficient in target acquisition in terms of field revisit and deployment time without any collision or entanglement of the fiber bundles. The efficiency of the technique does not get affected by the increase in number density of target objects. The technique is compared with other available methods based on sky coverage, flexibility and overhead time. The proposed geometry and algorithm combination is found to have an advantage in all of the aspects.Comment: 18 Pages, 13 Figures, 1 Tabl

Equatorial Magnetic Waves in the Stratified Ocean of Earth's Core

Earth’s global magnetic field envelops us all, protecting us from cosmic rays, aiding our navigation, and shielding our oxygen-rich atmosphere. Yet details about its origin, operation, and future remain unknown. Recent space-based magnetic observatories let us observe the field more precisely than ever before, and we can use these measurements to study the deep interior of the Earth and illuminate a region of our planet previously observed mainly by listening to the echoes of earthquakes. In this thesis, I use observations of changes in Earth’s magnetic field to study the structure and processes occurring near the top of Earth’s core. In particular, I examine the long-debated question of whether a stratified layer of fluid, termed by some as the stratified ocean of the core or SOC (Braginsky, 1998), lies at the top of Earth’s outer core. I first implement a model to simulate fluid motions in the SOC, which I describe in chapter two. Then, I derive the properties of a class of eastward-propagating equatorially trapped magnetic waves I term eMAC waves in chapter three and develop a statistical threshold to detect these waves in chapter four. In chapter five, I apply my statistical test to observations of Earth’s geomagnetic field and find evidence for these waves in Earth’s core. Finally, in chapter six, I propose a 20-40 km thick SOC with buoyancy strength of N ≥ 10 Ω to support the observed eMAC wave modes. I then discuss the implications of this layer, propose a double-layer SOC as a way to reconcile eMAC signals with previous observations, and enumerate possible future avenues of investigation