168 research outputs found
Mid-Infrared Spectroscopic Properties of Ultra-Luminous Infrared Quasars
We analyse mid-infrared (MIR) spectroscopic properties for 19 ultra-luminous
infrared quasars (IR QSOs) in the local universe based on the spectra from the
Infrared Spectrograph on board the Spitzer Space Telescope. The MIR properties
of IR QSOs are compared with those of optically-selected Palomar-Green QSOs (PG
QSOs) and ultra-luminous infrared galaxies (ULIRGs). The average MIR spectral
features from ~ 5 to 30um, including the spectral slopes, 6.2um PAH emission
strengths and [NeII] 12.81um luminosities of IR QSOs, differ from those of PG
QSOs. In contrast, IR QSOs and ULIRGs have comparable PAH and [NeII]
luminosities. These results are consistent with IR QSOs being at a transitional
stage from ULIRGs to classical QSOs. We also find that the colour index
alpha(30, 15) is a good indicator of the relative contribution of starbursts to
AGNs for all QSOs. Correlations between the [NeII] 12.81um and PAH 6.2um
luminosities and those between the [NeII], PAH with 60um luminosities for
ULIRGs and IR QSOs indicate that both [NeII] and PAH luminosities are
approximate star formation rate indicators for IR QSOs and starburst-dominated
galaxies; the scatters are, however, quite large (~ 0.7 to 0.8 dex). Finally
the correlation between the EW(PAH 6.2um) and outflow velocities suggests that
star formation activities are suppressed by feedback from AGNs and/or
supernovae.Comment: 19 pages, 8 figures, 6 tables, accepted for publication in MNRA
Observing Supermassive Black Holes across cosmic time: from phenomenology to physics
In the last decade, a combination of high sensitivity, high spatial
resolution observations and of coordinated multi-wavelength surveys has
revolutionized our view of extra-galactic black hole (BH) astrophysics. We now
know that supermassive black holes reside in the nuclei of almost every galaxy,
grow over cosmological times by accreting matter, interact and merge with each
other, and in the process liberate enormous amounts of energy that influence
dramatically the evolution of the surrounding gas and stars, providing a
powerful self-regulatory mechanism for galaxy formation. The different
energetic phenomena associated to growing black holes and Active Galactic
Nuclei (AGN), their cosmological evolution and the observational techniques
used to unveil them, are the subject of this chapter. In particular, I will
focus my attention on the connection between the theory of high-energy
astrophysical processes giving rise to the observed emission in AGN, the
observable imprints they leave at different wavelengths, and the methods used
to uncover them in a statistically robust way. I will show how such a combined
effort of theorists and observers have led us to unveil most of the SMBH growth
over a large fraction of the age of the Universe, but that nagging
uncertainties remain, preventing us from fully understating the exact role of
black holes in the complex process of galaxy and large-scale structure
formation, assembly and evolution.Comment: 46 pages, 21 figures. This review article appears as a chapter in the
book: "Astrophysical Black Holes", Haardt, F., Gorini, V., Moschella, U and
Treves A. (Eds), 2015, Springer International Publishing AG, Cha
Obscured and powerful AGN and starburst activities at z~3.5
We report the discovery of two sources at z=3.867 and z=3.427 that exhibit
powerful starburst and AGN activities. They benefit from data from radio to X
rays from the CFHTLS-D1/SWIRE/XMDS surveys. Follow-up optical and near-infrared
spectroscopy, and millimeter IRAM/MAMBO observations are also available. We
performed an analysis of their spectral energy distributions to understand the
origin of their emission and constrain their luminosities. A comparison with
other composite systems at similar redshifts from the literature is also
presented. The AGN and starburst bolometric luminosities are ~10^13 Lsun. The
AGN emission dominates at X ray, optical, mid-infrared wavelengths, and
probably in the radio. The starburst emission dominates in the far-infrared.
The estimated star formation rates range from 500 to 3000Msun/yr. The AGN
near-infrared and X ray emissions are heavily obscured in both sources with an
estimated dust extinction Av>4, and Compton-thick gas column densities. The two
sources are the most obscured and most luminous AGNs detected at millimeter
wavelengths currently known. The sources presented in this work are heavily
obscured QSOs, but their properties are not fully explained by the standard AGN
unification model. In one source, the ultraviolet and optical spectra suggest
the presence of outflowing gas and shocks, and both sources show emission from
hot dust, most likely in the vicinity of the nucleus. Evidence of moderate
AGN-driven radio activity is found in both sources. The two sources lie on the
local M_BH-M_bulge relation. To remain on this relation, their star formation
rate has to decrease. Our results support evolutionary models that invoke radio
feedback as star formation quenching mechanism, and suggest that such a
mechanism might play a major role also in powerful AGNs.Comment: Accepted for publication in Astronomy & Astrophysics (12 pages; 6
figures); replaced version includes minor language editing and revised
reference
Seeking legitimacy through CSR: Institutional Pressures and Corporate Responses of Multinationals in Sri Lanka
Arguably, the corporate social responsibility (CSR) practices of multinational enterprises (MNEs) are influenced by a wide range of both internal and external factors. Perhaps most critical among the exogenous forces operating on MNEs are those exerted by state and other key institutional actors in host countries. Crucially, academic research conducted to date offers little data about how MNEs use their CSR activities to strategically manage their relationship with those actors in order to gain legitimisation advantages in host countries. This paper addresses that gap by exploring interactions between external institutional pressures and firm-level CSR activities, which take the form of community initiatives, to examine how MNEs develop their legitimacy-seeking policies and practices. In focusing on a developing country, Sri Lanka, this paper provides valuable insights into how MNEs instrumentally utilise community initiatives in a country where relationship-building with governmental and other powerful non-governmental actors can be vitally important for the long-term viability of the business. Drawing on neo-institutional theory and CSR literature, this paper examines and contributes to the embryonic but emerging debate about the instrumental and political implications of CSR. The evidence presented and discussed here reveals the extent to which, and the reasons why, MNEs engage in complex legitimacy-seeking relationships with Sri Lankan institutions
Planck 2013 results. XXII. Constraints on inflation
We analyse the implications of the Planck data for cosmic inflation. The Planck nominal mission temperature anisotropy measurements, combined with the WMAP large-angle polarization, constrain the scalar spectral index to be ns = 0:9603 _ 0:0073, ruling out exact scale invariance at over 5_: Planck establishes an upper bound on the tensor-to-scalar ratio of r < 0:11 (95% CL). The Planck data thus shrink the space of allowed standard inflationary models, preferring potentials with V00 < 0. Exponential potential models, the simplest hybrid inflationary models, and monomial potential models of degree n _ 2 do not provide a good fit to the data. Planck does not find statistically significant running of the scalar spectral index, obtaining dns=dln k = 0:0134 _ 0:0090. We verify these conclusions through a numerical analysis, which makes no slowroll approximation, and carry out a Bayesian parameter estimation and model-selection analysis for a number of inflationary models including monomial, natural, and hilltop potentials. For each model, we present the Planck constraints on the parameters of the potential and explore several possibilities for the post-inflationary entropy generation epoch, thus obtaining nontrivial data-driven constraints. We also present a direct reconstruction of the observable range of the inflaton potential. Unless a quartic term is allowed in the potential, we find results consistent with second-order slow-roll predictions. We also investigate whether the primordial power spectrum contains any features. We find that models with a parameterized oscillatory feature improve the fit by __2 e_ _ 10; however, Bayesian evidence does not prefer these models. We constrain several single-field inflation models with generalized Lagrangians by combining power spectrum data with Planck bounds on fNL. Planck constrains with unprecedented accuracy the amplitude and possible correlation (with the adiabatic mode) of non-decaying isocurvature fluctuations. The fractional primordial contributions of cold dark matter (CDM) isocurvature modes of the types expected in the curvaton and axion scenarios have upper bounds of 0.25% and 3.9% (95% CL), respectively. In models with arbitrarily correlated CDM or neutrino isocurvature modes, an anticorrelated isocurvature component can improve the _2 e_ by approximately 4 as a result of slightly lowering the theoretical prediction for the ` <_ 40 multipoles relative to the higher multipoles. Nonetheless, the data are consistent with adiabatic initial conditions
Chemical genetics strategy identifies an HCV NS5A inhibitor with a potent clinical effect. Nature
The worldwide prevalence of chronic hepatitis C virus (HCV) infection is estimated to be approaching 200 million people We designed a mechanistically unbiased approach based on chemical genetics to identify chemical starting points for interfering with HCV replication. Our differentiating strategy centred on the identification of compounds functionally distinct from those acting on the traditional targets of antiviral research in this field, the NS3 protease and the NS5B RNA-dependent RNA polymerase 10 . BMS-858 formed the basis of an extensive series of chemical refinements that focused on improving antiviral potency, broadening inhibitory activity to encompass the HCV 1a genotype, and optimizing for oral bioavailability and sustained pharmacokinetic properties. After defining symmetry as an important contributor to antiviral activity 10 , a discovery that preceded the disclosure of structural information (see below), we subsequently identified BMS-79005
The RMS survey: near-IR spectroscopy of massive young stellar objects
Near-infrared H- and K-band spectra are presented for 247 objects, selected from the Red MSX Source (RMS) survey as potential young stellar objects (YSOs). 195 (âŒ80 per cent) of the targets are YSOs, of which 131 are massive YSOs (L BOL > 5Ă10 3 L â , M > 8 M â ). This is the largest spectroscopic study of massive YSOs to date, providing a valuable resource for the study of massive star formation. In this paper, we present our exploratory analysis of the data. The YSOs observed have a wide range of embeddedness (2.7 < A V < 114), demonstrating that this study covers minimally obscured objects right through to very red, dusty sources. Almost all YSOs show some evidence for emission lines, though there is a wide variety of observed properties. The most commonly detected lines are BrÎł, H 2 , fluorescent Fe ii, CO bandhead, [Fe ii] and He i 2-1 1 S- 1 P, in order of frequency of occurrence. In total, âŒ40 per cent of the YSOs display either fluorescent Fe ii 1.6878 ÎŒm or CO bandhead emission (or both), indicative of a circumstellar disc; however, no correlation of the strength of these lines with bolometric luminosity was found. We also find that âŒ60 per cent of the sources exhibit [Fe ii] or H 2 emission, indicating the presence of an outflow. Three quarters of all sources have BrÎł in emission. A good correlation with bolometric luminosity was observed for both the BrÎł and H 2 emission line strengths, covering 1 < L BOL < 3.5 Ă 10 5 L â . This suggests that the emission mechanism for these lines is the same for low-, intermediate- and high-mass YSOs, i.e. high-mass YSOs appear to resemble scaled-up versions of low-mass YSOs. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
NOF1 Encodes an Arabidopsis Protein Involved in the Control of rRNA Expression
The control of ribosomal RNA biogenesis is essential for the regulation of protein synthesis in eukaryotic cells. Here, we report the characterization of NOF1 that encodes a putative nucleolar protein involved in the control of rRNA expression in Arabidopsis. The gene has been isolated by T-DNA tagging and its function verified by the characterization of a second allele and genetic complementation of the mutants. The nof1 mutants are affected in female gametogenesis and embryo development. This result is consistent with the detection of NOF1 mRNA in all tissues throughout plant life's cycle, and preferentially in differentiating cells. Interestingly, the closely related proteins from zebra fish and yeast are also necessary for cell division and differentiation. We showed that the nof1-1 mutant displays higher rRNA expression and hypomethylation of rRNA promoter. Taken together, the results presented here demonstrated that NOF1 is an Arabidopsis gene involved in the control of rRNA expression, and suggested that it encodes a putative nucleolar protein, the function of which may be conserved in eukaryotes
Planck 2018 results. VIII. Gravitational lensing
We present measurements of the cosmic microwave background (CMB) lensing potential using the final Planck 2018 temperature and polarization data. We increase the significance of the detection of lensing in the polarization maps from 5Ï to 9Ï. Combined with temperature, lensing is detected at 40Ï4. We present an extensive set of tests of the robustness of the lensing-potential power spectrum, and construct a minimum-variance estimator likelihood over lensing multipoles 8â€Lâ€400. We find good consistency between lensing constraints and the results from the Planck CMB power spectra within the ÎCDMÎCDM model. Combined with baryon density and other weak priors, the lensing analysis alone constrains Ï8Ω0.25m=0.589±0.020 (1Ï errors). Also combining with baryon acoustic oscillation (BAO) data, we find tight individual parameter constraints, Ï8=0.811±0.019, H0=67.9+1.2â1.3kmsâ1Mpcâ1, and Ωm=0.303+0.016â0.018. Combining with Planck CMB power spectrum data, we measure Ï8 to better than 1% precision, finding Ï8=0.811±0.006. We find consistency with the lensing results from the Dark Energy Survey, and give combined lensing-only parameter constraints that are tighter than joint results using galaxy clustering. Using Planck cosmic infrared background (CIB) maps we make a combined estimate of the lensing potential over 60% of the sky with considerably more small-scale signal. We demonstrate delensing of the Planck power spectra, detecting a maximum removal of 40% of the lensing-induced power in all spectra. The improvement in the sharpening of the acoustic peaks by including both CIB and the quadratic lensing reconstruction is detected at high significance (abridged)
The Sloan Digital Sky Survey quasar catalog: tenth data release
We present the Data Release 10 Quasar (DR10Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the first 2.5 years of the survey and that are confirmed as quasars via visual inspection of the spectra, have luminosities M-i[z = 2] 2.15 (117 668) is similar to 5 times greater than the number of z > 2.15 quasars known prior to BOSS. Redshifts and FWHMs are provided for the strongest emission lines (C IV, C III, Mg II). The catalog identifies 16 461 broad absorption line quasars and gives their characteristics. For each object, the catalog presents five-band (u, g, r, i, z) CCD-based photometry with typical accuracy of 0.03 mag and information on the optical morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3600-10 500 angstrom at a spectral resolution in the range 1300 < R < 2500; the spectra can be retrieved from the SDSS Catalog Archive Server. We also provide a supplemental list of an additional 2376 quasars that have been identified among the galaxy targets of the SDSS-III/BOSS
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