Search for extra dimensions in the diphoton final state with ATLAS

The large difference between the Planck scale and the electroweak scale, known as the hierarchy problem, has been addressed in some models through the existence of extra spatial dimensions. A search for evidence of extra spatial dimensions has been performed, through an analysis of the diphoton final state in data recorded in 2011 with the ATLAS detector at the CERN Large Hadron Collider. The analysis uses a dataset of 2.12 fb-1 of proton-proton collisions at sqrts=7 TeV. The diphoton invariant mass spectrum is observed to be in good agreement with the expected Standard Model (SM) background. We set 95 CL lower limits on the fundamental Planck scale in the context of the Arkani-Hamed, Dimopoulos, Dvali model (ADD) and on the lightest Kaluza Klein (KK) excitation mass in the context of the Randall-Sundrum model (RS).Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011), Paris, France, November 14-18 2011, 3 pages, 3 figure

The nearby universe observed in far-infrared and in ultraviolet: an analysis of the dust attenuation and the star formation activity

We discuss the dust attenuation and the star formation rates in the nearby universe obtained from a comparison of far-infrared (IRAS) and ultraviolet (GALEX) observations. The ratio of the dust to UV flux ratio is used to derive the dust attenuation: this dust attenuation is found to increase with the luminosity of the galaxies and from z=0 to z=1. The slope of the UV continuum is found to be a very poor tracer of the dust attenuation in "normal" galaxies. Galaxies selected by their UV emission are found to be rather quiescent with a recent star formation rate equal to only 25-30% of the past averaged one. Galaxies selected in FIR appear slightly more active in star formation.Comment: 10 pages, invited conference, The Spectral Energy Distribution of Gas Rich Galaxies: Confronting Models with Data Heidelberg, Germany October 4-8, 200

What Controls the Star Formation in Luminous Starburst Mergers ?

In order to understand what controls the star formation process in luminous starburst mergers (e.g., NGC 6240, Arp 220, and so on), we investigate observational properties of two samples of high-luminosity starburst galaxies mapped in CO($J$=1--0) independently using both the Owens Valley Radio Observatory (Scoville et al. 1991) and the IRAM interferometer (Downes & Solomon 1998). We find that the surface density of far-infrared luminosity, $\Sigma$(FIR), is proportional linearly to the H$_2$ surface mass density, $\Sigma$(H$_2$), for the two samples; $\Sigma$(FIR) $\propto \Sigma$(H$_2$)$^{1.01\pm0.06}$ with a correlation coefficient of 0.96. It is often considered that $\Sigma$(FIR) provides a good measure of the star formation rate per unit area, $\Sigma$(SFR). It is also known that molecular gas is dominated in circumnuclear regions in the luminous starburst mergers; i.e., $\Sigma$(gas) $\simeq \Sigma$(H$_2$). Therefore, the above relationship suggests a star formation law; $\Sigma$(SFR) $\propto \Sigma$(gas). We suggest that this star formation law favors the gravitational instability scenario rather than the cloud-cloud collision one.Comment: 14 pages, 2 figures. The Astrophysical Journal (Letters), in pres

The Evolution of the Visible and Hidden Star Formation in the Universe: Implication from the Luminosity Functions at FUV and FIR

Based on GALEX and IRAS/Spitzer datasets, we have found that both FUV and FIR luminosity functions (LFs) show a strong evolution from z=0 to z=1, but the FIR LF evolves much stronger than the FUV one. Consequently, the FIR/FUV luminosity density ratio increases from 4 (z=0) to 15 (z=1). It means that more than 80% of the star-forming activity in the Universe is hidden by dust at z=1. To explore this issue further, we have performed a combined analysis of the galaxy sample in FUV and FIR. For the Local Universe we used GALEX-IRAS sample, whereas at z=1 we used the Lyman-break galaxy sample selected by GALEX bands constructed by Burgarella et al. (2005), which is known to be representative of visible (i.e., non-obscured) star-forming galaxies at z=1. From these datasets, we constructed the LFs of the FUV-selected galaxies by the survival analysis to, take into account the upper-limit data properly. We discovered that the FIR LF of the Lyman-break galaxies show a significant evolution comparing with the local FIR LF, but it is a factor of 2-3 lower than the global FIR LF (Le Floc'h et al. 2005). This indicates that the evolution of visible galaxies is not strong enough to explain the drastic evolution of the FIR LF. Namely, a FIR-luminous, rapidly diminishing population of galaxies is required.Comment: 4 pages, 4 figures, conference proceedings of "At the Edge of the Universe", Sintra 9-13 October 200

The Formation of Galaxies, the Formation of Old Globular Clusters and the Link with High-Redshift Objects

In this paper, we are exploring the properties of old, metal-poor globular clusters in galaxies. We investigate whether their properties are related to the properties of their host galaxies, and whether we can constrain their formation. The main result is that the mean metallicities of old GC systems are found to lie in a narrow range -1.7 < [Fe/H] < -1.1 (80 % of the population). Moreover, no correlations are found between the mean metallicities and other galaxy properties which implies a GC formation independent of the host galaxies. Further, we try to identify the sites of old, metal-poor GC formation, with any currently known high redshift objects. We find that the metalicities of damped Ly$\alpha$ systems in the redshift range 1.6 < z < 4 are consistent with our GC metalicities, which suggests that these high-density neutral gas objects may be the progenitors of the old, metal-poor globular clusters.Comment: 7 pages, 6 figures, to appear in A.S.P. Conf. Series "Massive Stellar Clusters" held in Strasbourg, Nov. 8-10, 1999, eds. A. Lancon et C. Boily. The files for Figs.2 were wron

Star formation and dust extinction in nearby star forming and starburst galaxies

We study the star formation rate and dust extinction properties of a sample of nearby star forming galaxies as derived from Halpha and UV (2000 A) observations and we compare them to those of a sample of starburst galaxies. The dust extinction in Halpha is estimated from the Balmer decrement and the extinction in UV using the FIR to UV flux ratio or the attenuation law for starburst galaxies of Calzetti et al. The Halpha and UV emissions are strongly correlated with a very low scatter for the star forming objects and with a much higher scatter for the starburst galaxies. The Halpha to UV flux ratio is found larger by a factor ~ 2 for the starburst galaxies. We compare both samples with a purely UV selected sample of galaxies and we conclude that the mean Halpha and UV properties of nearby star forming galaxies are more representative of UV selected galaxies than starburst galaxies. We emphasize that the Halpha to UV flux ratio is strongly dependent on the dust extinction: the positive correlation found between F{Halpha}/F{UV}$ and F{FIR}/F{UV} vanishes when the Halpha and UV flux are corrected for dust extinction. The Halpha to UV flux ratios converted into star formation rate and combined with the Balmer decrement measurements are tentatively used to estimate the dust extinction in UV.Comment: accepted for publication in Astronomy & Astrophysic

Selection of Best Available Wastewater Treatment Technology: Case of Bahir Dar University, Gish Abay Campus, Ethiopia

Wastewater treatment in developing countries is not always sustainable due to the application of inappropriate treatment technologies. Construction of best available wastewater treatment technology is a possible solution for the improvement of environmental impact of the available treatment system (septic tank) for Gish Abay Campus, Bahir Dar University. In this study a Multi-Criteria Analysis Decision Making tool is adopted to evaluate different wastewater treatment technologies. A hybrid multiple-criteria decision making model based on the analytic hierarchy process and the technique for order of preference by similarity to ideal solution is proposed as a tool to evaluate and prioritize various wastewater treatment technologies. Wastewater treatment alternatives were evaluated according to economical, technical, environmental and social criteria in which there are ten indicators by equal weight and unequal weight scenarios. Expert responses were used in the selection of wastewater treatment technologies to form different weight matrices. Depending on the priorities of the scenario the alternatives are ranked based on their relative closeness to the ideal solution. The model is finally applied to select best available wastewater treatment technology alternative among three options of sequential batch reactor, up flow anaerobic sludge blanket, and septic tank with horizontal constructed wetland. The result of this study reveal that UASB is best available wastewater treatment alternative. Sensitivity analysis also showed that a very stable ranking with the leading alternative of up flow anaerobic sludge blanket. Keywords: waste treatment alternatives, Multi Criteria Analysis Decision, up flow anaerobic sludge blanket, Analytical Hierarchy Process. DOI: 10.7176/CER/13-4-02 Publication date:June 30th 202