Three-Dimensional Numerical Simulations of Thermal-Gravitational Instability in Protogalactic Halo Environment

We study thermal-gravitational instability in simplified models for protogalactic halos using three-dimensional hydrodynamic simulations. The simulations followed the evolution of gas with radiative cooling down to T = 10^4 K, background heating, and self-gravity. Then cooled and condensed clouds were identified and their physical properties were examined in detail. During early stage clouds start to form around initial density peaks by thermal instability. Small clouds appear first and they are pressure-bound. Subsequently, the clouds grow through compression by the background pressure as well as gravitational infall. During late stage cloud-cloud collisions become important, and clouds grow mostly through gravitational merging. Gravitationally bound clouds with mass M_c > ~6 X 10^6 Msun are found in the late stage. They are approximately in virial equilibrium and have radius R_c = \~150 - 200 pc. Those clouds have gained angular momentum through tidal torque as well as merging, so they have large angular momentum with the spin parameter ~ 0.3. The clouds formed in a denser background tend to have smaller spin parameters. We discuss briefly the implications of our results on the formation of protoglobular cluster clouds in protogalactic halos. (abridged)Comment: To appear in ApJ 20 September 2005, v631 1 issue. Pdf with full resolution figures can be downloaded from http://canopus.cnu.ac.kr/ryu/baeketal.pd

Effects of Rotation on Thermal-Gravitational Instability in the Protogalactic Disk Environment

Thermal-gravitational instability (TGI) is studied in the protogalactic environment. We extend our previous work, where we found that dense clumps first form out of hot background gas by thermal instability and later a small fraction of them grow to virialized clouds of mass M_c >~ 6X10^6 M_sun by gravitational infall and merging. But these clouds have large angular momentum, so they would be difficult, if not impossible, to further evolve into globular clusters. In this paper, through three-dimensional hydrodynamic simulations in a uniformly rotating frame, we explore if the Coriolis force due to rotation in protogalactic disk regions can hinder binary merging and reduce angular momentum of the clouds formed. With rotation comparable to the Galactic rotation at the Solar circle, the Coriolis force is smaller than the pressure force during the early thermal instability stage. So the properties of clumps formed by thermal instability are not affected noticeably by rotation, except increased angular momentum. However, during later stage the Coriolis force becomes dominant over the gravity, and hence the further growth to gravitationally bound clouds by gravitational infall and merging is prohibited. Our results show that the Coriolis force effectively destroys the picture of cloud formation via TGI, rather than alleviate the problem of large angular momentum.Comment: To appear in ApJ Lett. (June 1, 2006, v643n2). Pdf with full resolution figures can be downloaded from http://canopus.cnu.ac.kr/ryu/baeketal.pd

Numerical Simulations of a Protostellar Outflow Colliding with a Dense Molecular Cloud

High-resolution SiO observations of the NGC 1333 IRAS 4A star-forming region showed a highly collimated outflow with a substantial deflection. The deflection was suggested to be caused by the interactions of the outflow and a dense cloud core. To investigate the deflection process of protostellar outflows, we have carried out three-dimensional hydrodynamic simulations of the collision of an outflow with a dense cloud. Assuming a power-law type density distribution of the obstructing cloud, the numerical experiments show that the deflection angle is mainly determined by the impact parameter and the density contrast between the outflow and the cloud. The deflection angle is, however, relatively insensitive to the velocity of the outflow. Using a numerical model with physical conditions that are particularly suitable for the IRAS 4A system, we produce a column-density image and a position-velocity diagram along the outflow, and they are consistent with the observations. Based on our numerical simulations, if we assume that the initial density and the velocity of the outflow are \sim 10 \cm3 and \sim 100 \kms, the densities of the dense core and ambient medium in the IRAS 4A system are most likely to be \sim 10^5 \cm3 and \sim 10^2 \cm3, respectively. We therefore demonstrate through numerical simulations that the directional variability of the IRAS 4A outflow can be explained reasonably well using the collision model.Comment: 19 pages, 7 figures, Submitted to ApJ, High resolution version has been uploaded at http://arcsec.sejong.ac.kr/~chbae

PCR and Omics Based Techniques to Study the Diversity, Ecology and Biology of Anaerobic Fungi:Insights, Challenges, and Opportunities

Anaerobic fungi (phylum Neocallimastigomycota) are common inhabitants of the digestive tract of mammalian herbivores, and in the rumen, can account for up to 20% of the microbial biomass. Anaerobic fungi play a primary role in the degradation of lignocellulosic plant material. They also have a syntrophic interaction with methanogenic archaea, which increases their fiber degradation activity. To date, nine anaerobic fungal genera have been described, with further novel taxonomic groupings known to exist based on culture-independent molecular surveys. However, the true extent of their diversity may be even more extensively underestimated as anaerobic fungi continue being discovered in yet unexplored gut and non-gut environments. Additionally many studies are now known to have used primers that provide incomplete coverage of the Neocallimastigomycota. For ecological studies the internal transcribed spacer 1 region (ITS1) has been the taxonomic marker of choice, but due to various limitations the large subunit rRNA (LSU) is now being increasingly used. How the continued expansion of our knowledge regarding anaerobic fungal diversity will impact on our understanding of their biology and ecological role remains unclear; particularly as it is becoming apparent that anaerobic fungi display niche differentiation. As a consequence, there is a need to move beyond the broad generalization of anaerobic fungi as fiber-degraders, and explore the fundamental differences that underpin their ability to exist in distinct ecological niches. Application of genomics, transcriptomics, proteomics and metabolomics to their study in pure/mixed cultures and environmental samples will be invaluable in this process. To date the genomes and transcriptomes of several characterized anaerobic fungal isolates have been successfully generated. In contrast, the application of proteomics and metabolomics to anaerobic fungal analysis is still in its infancy. A central problem for all analyses, however, is the limited functional annotation of anaerobic fungal sequence data. There is therefore an urgent need to expand information held within publicly available reference databases. Once this challenge is overcome, along with improved sample collection and extraction, the application of these techniques will be key in furthering our understanding of the ecological role and impact of anaerobic fungi in the wide range of environments they inhabit

Cross-National Differences in Victimization : Disentangling the Impact of Composition and Context

Varying rates of criminal victimization across countries are assumed to be the outcome of countrylevel structural constraints that determine the supply ofmotivated o¡enders, as well as the differential composition within countries of suitable targets and capable guardianship. However, previous empirical tests of these ‘compositional’ and ‘contextual’ explanations of cross-national di¡erences have been performed upon macro-level crime data due to the unavailability of comparable individual-level data across countries. This limitation has had two important consequences for cross-national crime research. First, micro-/meso-level mechanisms underlying cross-national differences cannot be truly inferred from macro-level data. Secondly, the e¡ects of contextual measures (e.g. income inequality) on crime are uncontrolled for compositional heterogeneity. In this paper, these limitations are overcome by analysing individual-level victimization data across 18 countries from the International CrimeVictims Survey. Results from multi-level analyses on theft and violent victimization indicate that the national level of income inequality is positively related to risk, independent of compositional (i.e. micro- and meso-level) di¡erences. Furthermore, crossnational variation in victimization rates is not only shaped by di¡erences in national context, but also by varying composition. More speci¢cally, countries had higher crime rates the more they consisted of urban residents and regions with lowaverage social cohesion.

A Holistic Perspective on the Dynamics of G035.39-00.33 : The Interplay between Gas and Magnetic Fields

Magnetic field plays a crucial role in shaping molecular clouds and regulating star formation, yet the complete information on the magnetic field is not well constrained owing to the limitations in observations. We study the magnetic field in the massive infrared dark cloud G035.39-00.33 from dust continuum polarization observations at 850 mu m with SCUBA-2/POL-2 at JCMT for the first time. The magnetic field tends to be perpendicular to the densest part of the main filament (F-M), whereas it has a less defined relative orientation in the rest of the structure, where it tends to be parallel to some diffuse regions. A mean plane-of-the-sky magnetic field strength of similar to 50 mu G for F-M is obtained using the Davis-Chandrasekhar-Fermi method. Based on (CO)-C-13 (1-0) line observations, we suggest a formation scenario of F-M due to large-scale (similar to 10 pc) cloud-cloud collision. Using additional NH3 line data, we estimate that F-M will be gravitationally unstable if it is only supported by thermal pressure and turbulence. The northern part of F-M, however, can be stabilized by a modest additional support from the local magnetic field. The middle and southern parts of F-M are likely unstable even if the magnetic field support is taken into account. We claim that the clumps in F-M may be supported by turbulence and magnetic fields against gravitational collapse. Finally, we identified for the first time a massive (similar to 200 M-circle dot, collapsing starless clump candidate, "c8," in G035.39-00.33. The magnetic field surrounding "c8" is likely pinched, hinting at an accretion flow along the filament.Peer reviewe

The JCMT BISTRO Survey: The Magnetic Field Strength in the Orion A Filament

We determine the magnetic field strength in the OMC 1 region of the Orion A filament via a new implementation of the Chandrasekhar-Fermi method using observations performed as part of the James Clerk Maxwell Telescope (JCMT) B-Fields In Star-Forming Region Observations (BISTRO) survey with the POL-2 instrument. We combine BISTRO data with archival SCUBA-2 and HARP observations to find a plane-of-sky magnetic field strength in OMC 1 of B_pos=6.6±4.7 mG, where δB_pos=4.7 mG represents a predominantly systematic uncertainty. We develop a new method for measuring angular dispersion, analogous to unsharp masking. We find a magnetic energy density of ~1.7×10^-7 Jm^-3 in OMC 1, comparable both to the gravitational potential energy density of OMC 1 (~10^-7 Jm^-3), and to the energy density in the Orion BN/KL outflow (~10^-7 Jm^-3). We find that neither the Alfvén velocity in OMC 1 nor the velocity of the super-Alfvénic outflow ejecta is sufficiently large for the BN/KL outflow to have caused large-scale distortion of the local magnetic field in the ~500-year lifetime of the outflow. Hence, we propose that the hour-glass field morphology in OMC 1 is caused by the distortion of a primordial cylindrically-symmetric magnetic field by the gravitational fragmentation of the filament and/or the gravitational interaction of the BN/KL and S clumps. We find that OMC 1 is currently in or near magnetically-supported equilibrium, and that the current large-scale morphology of the BN/KL outflow is regulated by the geometry of the magnetic field in OMC 1, and not vice versa

The JCMT BISTRO Survey: A Spiral Magnetic Field in a Hub-filament Structure, Monoceros R2

We present and analyze observations of polarized dust emission at 850 μm toward the central 1 7 1 pc hub-filament structure of Monoceros R2 (Mon R2). The data are obtained with SCUBA-2/POL-2 on the James Clerk Maxwell Telescope (JCMT) as part of the B-fields in Star-forming Region Observations survey. The orientations of the magnetic field follow the spiral structure of Mon R2, which are well described by an axisymmetric magnetic field model. We estimate the turbulent component of the magnetic field using the angle difference between our observations and the best-fit model of the underlying large-scale mean magnetic field. This estimate is used to calculate the magnetic field strength using the Davis–Chandrasekhar–Fermi method, for which we also obtain the distribution of volume density and velocity dispersion using a column density map derived from Herschel data and the C18O (J = 3 - 2) data taken with HARP on the JCMT, respectively. We make maps of magnetic field strengths and mass-to-flux ratios, finding that magnetic field strengths vary from 0.02 to 3.64 mG with a mean value of 1.0 \ub1 0.06 mG, and the mean critical mass-to-flux ratio is 0.47 \ub1 0.02. Additionally, the mean Alfv\ue9n Mach number is 0.35 \ub1 0.01. This suggests that, in Mon R2, the magnetic fields provide resistance against large-scale gravitational collapse, and the magnetic pressure exceeds the turbulent pressure. We also investigate the properties of each filament in Mon R2. Most of the filaments are aligned along the magnetic field direction and are magnetically subcritical