Evidence of widespread degradation of gene control regions in hominid genomes

Although sequences containing regulatory elements located close to protein-coding genes are often only weakly conserved during evolution, comparisons of rodent genomes have implied that these sequences are subject to some selective constraints. Evolutionary conservation is particularly apparent upstream of coding sequences and in first introns, regions that are enriched for regulatory elements. By comparing the human and chimpanzee genomes, we show here that there is almost no evidence for conservation in these regions in hominids. Furthermore, we show that gene expression is diverging more rapidly in hominids than in murids per unit of neutral sequence divergence. By combining data on polymorphism levels in human noncoding DNA and the corresponding human¿chimpanzee divergence, we show that the proportion of adaptive substitutions in these regions in hominids is very low. It therefore seems likely that the lack of conservation and increased rate of gene expression divergence are caused by a reduction in the effectiveness of natural selection against deleterious mutations because of the low effective population sizes of hominids. This has resulted in the accumulation of a large number of deleterious mutations in sequences containing gene control elements and hence a widespread degradation of the genome during the evolution of humans and chimpanzees

Influence of Cooled Interstellar Gas on the Fundamental Plane for Elliptical Galaxies

We explore the possibly important influence of cooled interstellar gas on the fundamental plane of elliptical galaxies. Interstellar cooling is described by a parameterized sink term in the equation of continuity. Parameters that give the best fits to the X-ray observations of NGC 4472 are used as a template for the radial distribution of interstellar cooling in structurally homologous elliptical galaxies of lower mass. Gas that cools within an effective radius can contribute an additional 10 - 30 percent to the mass of the old stellar population. If the cooled gas forms into stars of very low mass, $\ll M_{\odot}$, as is commonly assumed, the cooled mass is optically dark. As a result, the mass to light ratios determined from stellar velocities systematically overestimate that of the old stellar population. Moreover, the total mass and spatial distribution of the optically dark young stellar population does not scale homologously with galactic luminosity or radius and the total stellar mass to light ratio varies with galactic radius. We investigate the non-homologous perturbations of cooled gas on the mass to light ratio for several idealized homologous elliptical galaxies and show that they appear to be incompatible with the observed thinness of the fundamental plane. If optically luminous young stars formed from the cooled gas, the disturbance of the fundamental plane would be lessened.Comment: 10 pages with 2 figures; accepted by Astrophysical Journa

Tomography of Collisionless Stellar Systems

In this paper the concept of tomography of a collisionless stellar system of general shape is introduced, and a generalization of the Projected Virial Theorem is obtained. Applying the tomographic procedure we then derive a new family of virial equations which coincides with the already known ones for spherically symmetric systems. This result is obtained without any use of explicit expressions for the line-of-sight velocity dispersion, or spherical coordinate system.Comment: BAP-06-1994-016-OAB. 7 pages, postscript file. In press on Celestial Mechanic

Dynamical friction in multi-component evolving globular clusters

We use the Chandrasekhar formalism and direct N-body simulations to study the effect of dynamical friction on a test object only slightly more massive than the field stars, orbiting a spherically symmetric background of particles with a mass spectrum. The main goal is to verify whether the dynamical friction time (t_DF) develops a non-monotonic radial-dependence that could explain the bimodality of the Blue Straggler radial distributions observed in globular clusters. In these systems, in fact, relaxation effects lead to a mass and velocity radial segregation of the different mass components, so that mass-spectrum effects on t_DF are expected to be dependent on radius. We find that, in spite of the presence of different masses, t_DF is always a monotonic function of radius, at all evolutionary times and independently of the initial concentration of the simulated cluster. This because the radial dependence of t_DF is largely dominated by the total mass density profile of the background stars (which is monotonically decreasing with radius). Hence, a progressive temporal erosion of the BSS population at larger and larger distances from the cluster center remains the simplest and the most likely explanation of the shape of the observed BSS radial distributions, as suggested in previous works. We also confirm the theoretical expectation that approximating a multi-mass globular cluster as made of (averaged) equal-mass stars can lead to significant overestimates of t_DF within the half-mass radius.Comment: In press on Ap

Radiative feedback from massive black holes in elliptical galaxies. AGN flaring and central starburst fueled by recycled gas

The importance of the radiative feedback from massive black holes at the centers of elliptical galaxies is not in doubt, given the well established relations among electromagnetic output, black hole mass and galaxy optical luminosity. We show how this AGN radiative output affects the hot ISM of an isolated elliptical galaxy with the aid of a high-resolution hydrodynamical code, where the cooling and heating functions include photoionization plus Compton heating. We find that radiative heating is a key factor in the self-regulated coevolution of massive black holes and their host galaxies and that 1) the mass accumulated by the central black hole is limited by feedback to the range observed today, and 2) relaxation instabilities occur so that duty cycles are small enough (~0.03) to account for the very small fraction of massive ellipticals observed to be in the "on" -QSO- phase, when the accretion luminosity approaches the Eddington luminosity. The duty cycle of the hot bubbles inflated at the galaxy center during major accretion episodes is of the order of 0.1-0.4. Major accretion episodes caused by cooling flows in the recycled gas produced by normal stellar evolution trigger nuclear starbursts coincident with AGN flaring. During such episodes the central sources are often obscured; but overall, in the bursting phase (1<z<3), the duty cycle of the black hole in its "on" phase is of the order of percents and it is unobscured approximately one-third of the time. Mechanical energy output from non-relativistic gas winds integrates to 2.3 10^{59} erg, with most of it caused by broadline AGN outflows. [abridged]Comment: ApJ resubmitted. 48 pages, 14 figures (some of them new, bitmapped, low resolution). New references added, typos correcte

The Mass Assembly History of Spheroidal Galaxies: Did Newly-Formed Systems Arise Via Major Mergers?

We examine the properties of a morphologically-selected sample of 0.4<z<1.0 spheroidal galaxies in the GOODS fields in order to ascertain whether their increase in abundance with time arises primarily from mergers. To address this question we determine scaling relations between the dynamical mass determined from stellar velocity dispersions, and the stellar mass determined from optical and infrared photometry. We exploit these relations across the larger sample for which we have stellar masses in order to construct the first statistically robust estimate of the evolving dynamical mass function over 0<z<1. The trends observed match those seen in the stellar mass functions of Bundy et al. 2005 regarding the top-down growth in the abundance of spheroidal galaxies. By referencing our dynamical masses to the halo virial mass we compare the growth rate in the abundance of spheroidals to that predicted by the assembly of dark matter halos. Our comparisons demonstrate that major mergers do not fully account for the appearance of new spheroidals since z~1 and that additional mechanisms, such as morphological transformations, are required to drive the observed evolution.Comment: Accepted to ApJL; New version corrects the Millennium merger predictions--further details at http://www.astro.utoronto.ca/~bundy/millennium

Hydrostatic models for the rotation of extra-planar gas in disk galaxies

We show that fluid stationary models are able to reproduce the observed, negative vertical gradient of the rotation velocity of the extra-planar gas in spiral galaxies. We have constructed models based on the simple condition that the pressure of the medium does not depend on density alone (baroclinic instead of barotropic solutions: isodensity and isothermal surfaces do not coincide). As an illustration, we have successfully applied our method to reproduce the observed velocity gradient of the lagging gaseous halo of NGC 891. The fluid stationary models discussed here can describe a hot homogeneous medium as well as a "gas" made of discrete, cold HI clouds with an isotropic velocity dispersion distribution. Although the method presented here generates a density and velocity field consistent with observational constraints, the stability of these configurations remains an open question.Comment: 12 pages, 9 figures. Accepted for publication in Astronomy and Astrophysic

The Tilt of the Fundamental Plane: Three-quarters Structural Nonhomology, One-quarter Stellar Population

The variation of the mass-to-light ratios M/L of early type galaxies as function of their luminosities L is investigated. It is shown that the tilt beta=0.27 (in the B--band) of the fundamental plane relation M/L ~ L^{beta} can be understood as a combination of two effects: about one-quarter (i.e. dbeta =0.07) is a result of systematic variations of the stellar population properties with increasing luminosity. The remaining three-quarters (i.e. dbeta =0.2) can be completely attributed to nonhomology effects that lead to a systematic change of the surface brightness profiles with increasing luminosity. Consequently, the observed tilt in the K-band (beta=0.17) where stellar population effects are negligible, is explained by nonhomology effects alone. After correcting for nonhomology, the mean value of the mass-to-light ratio of elliptical galaxies (M/L_B) is 7.1+-2.8 (1 sigma scatter).Comment: 8 pages, 3 figures, ApJL, 600, 39, minor changes made to match the published versio

Embodied CO2 analysis of a secondary school

This paper describes the process, challenges and results of a carbon profiling tool used as part of the design process at White Design Associates. The paper first explores the need amongst designers for a carbon profiling tool to enable and encourage a focus on carbon reduction, as a key element in the fight against global warming. Next it describes the methodology adopted by White Design Associates to develop a tool to be used throughout the building design process, to inform design decisions, and begin to quantify the climate change impact of the finished building. Examples from the most recent iteration of the tool, used during the construction of John Ferneley College, illustrate the development of the tool, the challenges that were faced, and the "headline" results of the analysis. It also illustrates how White Design incorporated the results into the curriculum through web updates and highlights the Carbon Stacks visualisation tool

Morphological Dependence of MIR Properties of SDSS Galaxies in the Spitzer SWIRE Survey

We explore the correlation between morphological types and mid-infrared (MIR) properties of an optically flux-limited sample of 154 galaxies from the Forth Data Release (DR4) of Sloan Digital Sky Survey (SDSS), cross-correlated with Spitzer SWIRE (Spitzer Wide-Area InfraRed Extragalactic Survey) fields of ELAIS-N1, ELAIS-N2 and Lockman Hole. Aperture photometry is performed on the SDSS and Spitzer images to obtain optical and MIR properties. The morphological classifications are given based on both visual inspection and bulge-disk decomposition on SDSS g- and r-band images. The average bulge-to-total ratio (B/T) is a smooth function over different morphological types. Both the 8um(dust) and 24um(dust) luminosities and their relative luminosity ratios to 3.6um (MIR dust-to-star ratios) present obvious correlations with both the Hubble T-type and B/T. The early-type galaxies notably differ from the late-types in the MIR properties, especially in the MIR dust-to-star ratios. It is suggested that the MIR dust-to-star ratio is an effective way to separate the early-type galaxies from the late-type ones. Based on the tight correlation between the stellar mass and the 3.6um luminosity, we have derived a formula to calculate the stellar mass from the latter. We have also investigated the MIR properties of both edge-on galaxies and barred galaxies in our sample. Since they present similar MIR properties to the other sample galaxies, they do not influence the MIR properties obtained for the entire sample.Comment: Accepted for publication by AJ. 18 pages, 14 figures, and 4 table