ISM properties in hydrodynamic galaxy simulations: Turbulence cascades, cloud formation, role of gravity and feedback

We study the properties of ISM substructure and turbulence in hydrodynamic (AMR) galaxy simulations with resolutions up to 0.8 pc and 5x10^3 Msun. We analyse the power spectrum of the density distribution, and various components of the velocity field. We show that the disk thickness is about the average Jeans scale length, and is mainly regulated by gravitational instabilities. From this scale of energy injection, a turbulence cascade towards small-scale is observed, with almost isotropic small-scale motions. On scales larger than the disk thickness, density waves are observed, but there is also a full range of substructures with chaotic and strongly non-isotropic gas velocity dispersions. The power spectrum of vorticity in an LMC-sized model suggests that an inverse cascade of turbulence might be present, although energy input over a wide range of scales in the coupled gaseous+stellar fluid could also explain this quasi-2D regime on scales larger than the disk scale height. Similar regimes of gas turbulence are also found in massive high-redshift disks with high gas fractions. Disk properties and ISM turbulence appear to be mainly regulated by gravitational processes, both on large scales and inside dense clouds. Star formation feedback is however essential to maintain the ISM in a steady state by balancing a systematic gas dissipation into dense and small clumps. Our galaxy simulations employ a thermal model based on a barotropic Equation of State (EoS) aimed at modelling the equilibrium of gas between various heating and cooling processes. Denser gas is typically colder in this approach, which is shown to correctly reproduce the density structures of a star-forming, turbulent, unstable and cloudy ISM down to scales of a few parsecs.Comment: MNRAS in pres

Paper Session II-C - NASA\u27s Hydrogen Research at Florida Universities

For the past two years, the State University System (SUS) of Florida has been conducting hydrogen research for NASA. The general objective of the hydrogen research is to support hydrogen utilization within NASA\u27s space exploration and space launch activities. These research awards are slightly under $8 million per fiscal year and are co-managed by the University of Central Florida and the University of Florida and, on the NASA side, by NASA\u27s Glenn Research Center and Kennedy Space Center. The hydrogen research is conducted by six universities within the Florida University System. These universities are the University of Central Florida, University of Florida, Florida State University, University of South Florida, Florida International University, and the University of West Florida. This unique research program teams Florida\u27s talented university researchers with NASA Glenn, the nation\u27s premier space research facility, and NASA Kennedy, the nation\u27s premier space launch facility, to form a powerful partnership. The specific research areas being investigated are densified propellant usage, hydrogen production and transport at Kennedy Space Center, development of hydrogen sensor and safety technologies, Pad A and B storage tank losses at Kennedy Space Center, hydrogen operating systems, and education and outreach. The research is extremely important to Florida because hydrogen is the fuel of space vehicles; it is important to Florida\u27s spaceport activities, a$ 5 billion dollar per year industry; and hydrogen will play an important role in Florida\u27s and the nation\u27s move towards a hydrogen economy. As a note to the nation\u27s moving towards a hydrogen economy, Florida has already developed a cooperative partnership called the Florida Hydrogen Partnership to assist in this important activity. This presentation will discuss the research program and the benefits of the research to NASA. It will also consider the spin-off technology benefits for terrestrial applications. The presentation fo Howing this one, by the University of Florida, will give additional and more specific details on the programs being conducted under this research

ISM properties in hydrodynamic galaxy simulations: turbulence cascades, cloud formation, role of gravity and feedback

We study the properties of interstellar medium (ISM) substructure and turbulence in hydrodynamic [adaptive mesh refinement (AMR)] galaxy simulations with resolutions up to 0.8 pc and 5 × 103 M⊙. We analyse the power spectrum of the density distribution, and various components of the velocity field. We show that the disc thickness is about the average Jeans scalelength, and is mainly regulated by gravitational instabilities. From this scale of energy injection, a turbulence cascade towards small scale is observed, with almost isotropic small-scale motions. On scales larger than the disc thickness, density waves are observed, but there is also a full range of substructures with chaotic and strongly non-isotropic gas velocity dispersions. The power spectrum of vorticity in a Large Magellanic Cloud sized model suggests that an inverse cascade of turbulence might be present, although energy input over a wide range of scales in the coupled gaseous+stellar fluid could also explain this quasi-two-dimensional regime on scales larger than the disc scaleheight. Similar regimes of gas turbulence are also found in massive high-redshift discs with high gas fractions. Disc properties and ISM turbulence appear to be mainly regulated by gravitational processes, both on large scales and inside dense clouds. Star formation feedback is however essential to maintain the ISM in a steady state by balancing a systematic gas dissipation into dense and small clumps. Our galaxy simulations employ a thermal model based on a barotropic equation of state aimed at modelling the equilibrium of gas between various heating and cooling processes. Denser gas is typically colder in this approach, which is shown to correctly reproduce the density structures of a star-forming, turbulent, unstable and cloudy ISM down to scales of a few parsec

NASA Hydrogen Research at Florida Universities, Program Year 2003

This document presents the final report for the NASA Hydrogen Research at Florida Universities project for program year 2003. This multiyear hydrogen research program has positioned Florida to become a major player in future NASA space and space launch projects. The program is funded by grants from NASA Glenn Research Center with the objective of supporting NASA's hydrogen-related space, space launch and aeronautical research activities. The program conducts over 40 individual projects covering the areas of cryogenics, storage, production, sensors, fuel cells, power and education. At the agency side, this program is managed by NASA Glenn Research Center and at the university side, co-managed by FSEC and the University of Florida with research being conducted by FSEC and seven Florida universities: Florida International University, Florida State University, Florida A&M University, University of Central Florida, University of South Florida, University of West Florida and University of Florida. For detailed information, see the documents section of www.hydrogenresearch.org. This program has teamed these universities with the nation's premier space research center, NASA Glenn, and the nation's premier space launch facility, NASA Kennedy Space Center. It should be noted that the NASA Hydrogen Research at Florida Universities program has provided a shining example and a conduit for seven Florida universities within the SUS to work collaboratively to address a major problem of national interest, hydrogen energy and the future of energy supply in the U.S

Variation of Galactic Bar Length with Amplitude and Density as Evidence for Bar Growth over a Hubble Time

K_s-band images of 20 barred galaxies show an increase in the peak amplitude of the normalized m=2 Fourier component with the R_25-normalized radius at this peak. This implies that longer bars have higher $m=2$ amplitudes. The long bars also correlate with an increased density in the central parts of the disks, as measured by the luminosity inside 0.25R_25 divided by the cube of this radius in kpc. Because denser galaxies evolve faster, these correlations suggest that bars grow in length and amplitude over a Hubble time with the fastest evolution occurring in the densest galaxies. All but three of the sample have early-type flat bars; there is no clear correlation between the correlated quantities and the Hubble type.Comment: ApJ Letters, 670, L97, preprint is 7 pages, 4 figure