Large Fraction Of Gas Research Articles

Modelling feedback from stars and black holes in galaxy mergers

We describe techniques for incorporating feedback from star formation and black hole (BH) accretion into simulations of isolated and merging galaxies. At present, the details of these processes cannot be resolved in simulations on galactic scales. Our basic approach therefore involves forming coarse-grained representations of the properties of the interstellar medium (ISM) and BH accretion starting from basic physical assumptions, so that the impact of these effects can be included on resolved scales. We illustrate our method using a multiphase description of star-forming gas. Feedback from star formation pressurizes highly overdense gas, altering its effective equation of state (EOS). We show that this allows the construction of stable galaxy models with much larger gas fractions than possible in earlier numerical work. We extend the model by including a treatment of gas accretion onto central supermassive BHs in galaxies. Assuming thermal coupling of a small fraction of the bolometric luminosity of accreting BHs to the surrounding gas, we show how this feedback regulates the growth of BHs. In gas-rich mergers of galaxies, we observe a complex interplay between starbursts and central active galactic nuclei (AGN) activity when the tidal interaction triggers intense nuclear inflows of gas. Once an accreting supermassive BH has grown to a critical size, feedback terminates its further growth and expels gas from the central region in a powerful quasar-driven wind. Our simulation methodology is therefore able to address the coupled processes of gas dynamics, star formation and BH accretion during the formation of galaxies.

AWM 4 - an isothermal cluster observed with XMM-Newton

We present an analysis of an XMM-Newton observation of the poor cluster AWM 4. The cluster is relaxed and its X-ray halo is regular with no apparent substructure. Azimuthally averaged radial spectral profiles suggest that the cluster is isothermal to a radius of at least 160 kpc, with no evidence of a central cooling region. Spectral mapping shows some significant temperature and abundance substructure, but no evidence of strong cooling in the cluster core. Abundance increases in the core, but not to the extent expected, and we find some indication of gas mixing. Modelling the three-dimensional properties of the system, we show that ongoing heating by an active galactic nuclei (AGN) in the dominant elliptical, NGC 6051, is likely to be responsible for the lack of cooling. We also compare AWM 4 to MKW 4, a cluster of similar mass observed recently with XMM-Newton. While the two systems have similar gravitational mass profiles, MKW 4 has a cool core and a somewhat steeper gas density profile, which leads to a lower core entropy. AWM 4 has a considerably larger gas fraction at 0.1R 200 , and we show that these differences result from the difference in mass between the two dominant galaxies and the activity cycles of their AGN. We estimate the energy required to raise the temperature profile of MKW 4 to match that of AWM 4 to be 9 x 10 58 erg or 3 x 10 43 erg s -1 for 100 Myr, comparable to the likely power output of the AGN in AWM 4.

Gas in Groups and Clusters of Galaxies

Groups and clusters contain a large fraction of hot gas which emits X-ray radiation. This gas yields information on the dynamical state and on the total mass of these systems. X-ray spectra show that heavy elements are present in the gas. As these metals must have been produced in the cluster/group galaxies and later transported into the gas, the metallicity is a good tracer for the transport processes. Several possible processes, that transport gas from the small potential wells of the galaxies into the clusters and groups, are discussed.

Effects of Type II and Type Ia Supernovae Feedback on the Chemodynamical Evolution of Elliptical Galaxies

We numerically investigate the dynamical and chemical processes of the formation of elliptical galaxies in a cold dark matter (CDM) universe, in order to understand the origin of the mass-dependence of the photometric properties of elliptical galaxies. Our three-dimensional TREE N-body/SPH numerical simulations of elliptical galaxy formation take into account both Type II (SNe II) and Type Ia (SNe Ia) supernovae (SNe) and follow the time evolution of the abundances of several chemical elements (C, O, Ne, Mg, Si, and Fe). Moreover we compare different strengths of SNe feedback.In combination with stellar population synthesis, we derive the photometric properties of simulation end-products, including the magnitude, color, half-light radius, and abundance ratios, and compare them with the observed scaling relations directly and quantitatively. We find that the extremely strong influence of SNe is required to reproduce the observed color-magnitude relation (CMR), where we assume each SN yields energy of 4x10^51 ergs and that 90% of this energy is ejected as kinetic feedback. The feedback affects the evolution of lower mass systems more strongly and induces the galactic wind by which a larger fraction of gas is blown out in a lower mass system. Finally higher mass systems become more metal rich and have redder colors than lower mass systems. We emphasize based on our simulation results that the galactic wind is triggered mainly by SNe Ia rather than SNe II. In addition we examined the Kormendy relation, which prescribes the size of elliptical galaxies, and the [Mg/Fe]--magnitude relation, which provides a strong constraint on the star formation history.

Remote microwave plasma source for cleaning chemical vapor deposition chambers: Technology for reducing global warming gas emissions

The semiconductor industry uses a large amount of perfluoro compounds (PFCs), and their impact on global warming has become a major environmental concern. In the semiconductor industry, PFC are used to periodically remove deposits from the chamber walls of chemical vapor deposition (CVD) reactors after film deposition. These chamber clean processes account for typically 50%–70% of the PFC usage in a semiconductor wafer fabrication site, the rest being mainly used for wafer-etching processes. With a conventional parallel plate radio frequency (rf) plasma reactor, the PFC gas utilization is incomplete and a large fraction of unreacted gas can be emitted in the atmosphere. This paper describes a microwave plasma source that provides as high as 99.9% utilization removal efficiency (URE) of the reactant gas (NF3) during chamber clean. This technology brings the million metric tons carbon equivalent (MMTCE) of a chamber clean to negligible levels and also enhances the chamber clean efficiency and the system throughput. Here we review the requirements for the manufacturability of a remote plasma clean process. Gaseous Fourier transform infrared and quadrupole mass spectroscopy techniques have been used to characterize the clean process, the by-products of the reaction, and the efficiency in reducing the MMTCE of CVD chamber cleans.

Molecular Gas and Star Formation in Interacting and Isolated Galaxies

The results of the FCRAO Extragalactic CO Survey are used to examine the trends regarding the molecular gas distribution, the star formation efficiency, and the global gas surface densities (HI and H2) in galaxies as a function of environment. Relative to a sample of isolated Sbc-Scd galaxies, the strongly interacting galaxies have more compact gas distributions, a higher mean value for the global star formation efficiency, and a larger fraction of gas in molecular form. Not only is the molecular gas redistributed during interactions, but evidence is presented for an enhanced conversion of atomic to molecular gas as well.

Damped Lya systems at high redshift and models of protogalactic discs

We employ observationally determined intrinsic velocity widths and column densities of damped Lyman alpha (Lyα) systems at high redshift to investigate the distribution of baryons in protogalaxies within the context of a standard cold dark matter (CDM) model. We proceed under the assumption that damped Lyα systems represent a population of cold, rotationally supported, protogalactic discs, and that the abundance of dark matter haloes is well approximated by a CDM model with critical density and vanishing cosmological constant. Using conditional cross-sections to observe a damped system with a given velocity width and column density, we compare observationally inferred velocity width and column density distributions to the corresponding theoretically determined distributions for a variety of disc parameters and CDM normalizations. In general, we find that the observations cannot be reproduced by the models for most disc parameters and CDM normalizations. Whereas the column density distribution favours small discs with large neutral gas fraction, the velocity width distribution favours large and thick discs with small neutral gas fraction. The possible resolutions of this problem in the context of this CDM model may be (1) an increased contribution of rapidly rotating discs within massive dark matter haloes to damped Lya absorption, or (2) the abandoning of simple disc models within this CDM model for damped Lya systems at high redshift. Here the first possibility may be achieved by supposing that damped Lya system formation occurs only in haloes with fairly large circular velocities, and the second possibility may result from a large contribution of mergers and double discs to damped Lya absorption at high redshift.

The evolution of X-ray clusters in a cold plus hot dark matter universe

We present the first self-consistently computed results on the evolution of X-ray properties of galaxy clusters in a Cold + Hot Dark Matter (CHDM) model. We have performed a hydrodynamic plus N-body simulation for the COBE-compatible CHDM model with standard mass components: Omega(hot) = 0.3, Omega(cold) = 0.6 and Omega(baryon) = 0.1 (h = 0.5). In contrast with the CDM model, which fails to reproduce the observed temperature distribution function dN/dT (Bryan et al. 1994b), the CHDM model fits the observational dN/dT quite well. Our results on X-ray luminosity are less firm but even more intriguing. We find that the resulting X-ray luminosity functions at redshifts z = 0.0, 0.2, 0.4, 0.7 are well fit by observations, where they overlap. The fact that both temperatures and luminosities provide a reasonable fit to the available observational data indicates that, unless we are missing some essential physics, there is neither room nor need for a large fraction of gas in rich clusters: 10% (or less) in baryons is sufficient to explain their X-ray properties. We also see a tight correlation between X-ray luminosity and gas temperature.