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Gas Properties (gas + property)

Distribution by Scientific Domains
Physics and Astronomy75%

Selected Abstracts

On the interstellar medium and star formation demographics of galaxies in the local universe

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2009
Matthew S. Bothwell
ABSTRACT We present a demographic analysis of integrated star formation and gas properties for a sample of galaxies representative of the overall population at z, 0. This research was undertaken in order to characterize the nature of star formation and interstellar medium (ISM) behaviour in the local Universe, and test the extent to which global star formation rates (SFRs) can be seen as dependent on the interstellar gas content. Archival 21-cm derived H i data are compiled from the literature, and are combined with CO (J =1 , 0) derived H2 masses to calculate and characterize the total gas content for a large sample of local galaxies. The distribution in stellar mass-normalized H i content is found to exhibit the noted characteristic transition at stellar masses of ,3 × 1010 M,, turning off towards low values, but no such transition is observed in the equivalent distribution of molecular gas. H, based SFRs and specific star formation rates (SSFRs) are also compiled for a large (1110) sample of local galaxies. We confirm two transitions as found in previous work: a turnover towards low SFRs at high luminosities, indicative of the quenching of SF characteristic of the red sequence; and a broadening of the SF distribution in low-luminosity dwarf galaxies, again to extremely low SFRs of <10,3 M, yr,1. However, a new finding is that while the upper luminosity transition is mirrored by the turnover in H i content, suggesting that the low SFRs of the red sequence result from a lack of available gas supply, the transition towards a large spread of SFRs in the least luminous dwarf galaxies is not matched by a prominent increase in scatter in gas content. Possible mass-dependent quenching mechanisms are discussed, along with speculations that in low-mass galaxies, the H, luminosity may not faithfully trace the SFR. [source]

Ionization, shocks and evolution of the emission-line gas of distant 3CR radio galaxies

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2000
P. N. Best
An analysis of the kinematics and ionization state of the emission-line gas of a sample of 14 3CR radio galaxies with redshifts z,1 is carried out. The data used for these studies, deep long-slit spectroscopic exposures from the William Herschel Telescope, are presented in an accompanying paper. It is found that radio sources with small linear sizes (,150 kpc) have lower ionization states, higher emission-line fluxes and broader line widths than larger radio sources. An analysis of the low-redshift sample of Baum et al. demonstrates that radio galaxies at low redshift show similar evolution in their velocity structures and emission-line ratios from small to large radio sources. The emission-line ratios of small radio sources are in agreement with theoretical shock ionization predictions, and their velocity profiles are distorted. Together with the other emission-line properties, this indicates that shocks associated with the radio source dominate the kinematics and ionization of the emission-line gas during the period that the radio source is expanding through the interstellar medium. Gas clouds are accelerated by the shocks, giving rise to the irregular velocity structures observed, whilst shock compression of emission-line gas clouds and the presence of the ionizing photons associated with the shocks combine to lower the ionization state of the emission-line gas. By contrast, in larger sources the shock fronts have passed well beyond the emission-line regions; the emission-line gas of these larger radio sources has much more settled kinematical properties, indicative of rotation, and emission-line ratios consistent with the dominant source of ionizing photons being the active galactic nucleus. This strong evolution with radio size of the emission-line gas properties of powerful radio galaxies mirrors the radio size evolution seen in the nature of the optical,ultraviolet continuum emission of these sources, implying that the continuum alignment effect is likely to be related to the same radio source shocks. [source]

The host galaxies of Compact Steep Spectrum and Gigahertz-Peaked Spectrum radio sources

ASTRONOMISCHE NACHRICHTEN, Issue 2-3 2009
J. Holt
Abstract I will review some of the developments in studies of the host galaxy properties of Compact Steep Spectrum (CSS) and Gigahertz-Peaked Spectrum (GPS) radio sources. In contrast to previous reviews structured around observational technique, I will discuss the host galaxy properties in terms of morphology, stellar content and warm gas properties and discuss how compact, young radio-loud AGN are key objects for understanding galaxy evolution (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Dynamic Modeling and Simulation of Steam Cracking Furnaces

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2007
M. Ghashghaee
Abstract The transient modeling of thermal cracking furnaces is developed. This representation is capable of describing and predicting the unsteady-state behavior of cracking furnaces during start-up. To accurately predict the heat transfer to the reactor tube, the fireside conditions are coupled with the process side. The mutual interaction of these two sections is found to be very stiff in terms of convergence of the computations. The two-dimensional transient zone model is developed for the radiative heat exchange calculation. A simplified model for the convection section is also used to predict the crossover temperature at each time increment. The main simulation outputs are the flue gas properties as well as the distributions of heat flux, refractory wall and coil skin temperatures versus time. The dynamic simulation is implemented for a conventional procedure used in the start-up run of the olefin furnaces. [source]