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Register a new userThe U.S. ISO Key Project on Quasars
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Eric Hooper
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Observations for the U.S. key project on quasars using ISO were completed in April when the satellites cryogen supply expired. This proceeding presents an update of the project, including information on the final sample, a discussion of some of the data reduction challenges and current efforts to meet them, plus a comparison of preliminary results with IRAS fluxes.
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The U.S. ISO Key Project on quasar spectral energy distributions seeks to better understand the very broad-band emission features of quasars from radio to X-rays. A key element of this project is observations of 72 quasars with the ISOPHOT instrument at 8 bands, from 5 to 200 microns. The sample was chosen to span a wide range of redshifts and quasar types. This paper presents an overview of the analysis and reduction techniques, as well as general trends within the data set (comparisons with IRAS fluxes, uncertainties as a function of background sky brightness, and an analysis of vignetting corrections in chopped observing mode). A more detailed look at a few objects in the sample is presented in Wilkes et al. 1999, astro-ph/9902084.
In this contribution we schematically summarize a number of ongoing, coordinated spectro-photometric projects devoted to the study of the stellar population properties in Omega Cen. All of these investigations are part of a global comprehensive project led by our team to address the complex formation history of stars in this cluster.
We perform a survey of the X-ray properties of 41 objects from the WISE/SDSS selected Hyper-luminous (WISSH) quasars sample, composed by 86 broad-line quasars (QSOs) with bolometric luminosity $L_{Bol}geq 2times 10^{47},erg, s^{-1}$, at z~2-4. All but 3 QSOs show unabsorbed 2-10 keV luminosities $L_{2-10}geq10^{45} ,erg ,s^{-1}$. Thanks to their extreme radiative output across the Mid-IR-to-X-ray range, WISSH QSOs offer the opportunity to significantly extend and validate the existing relations involving $L_{2-10}$. We study $L_{2-10}$ as a function of (i) X-ray-to-Optical (X/O) flux ratio, (ii) mid-IR luminosity ($L_{MIR}$), (iii) $L_{Bol}$ as well as (iv) $alpha_{OX}$ vs. the 2500$mathring{A}$ luminosity. We find that WISSH QSOs show very low X/O(<0.1) compared to typical AGN values; $L_{2-10}/L_{MIR}$ ratios significantly smaller than those derived for AGN with lower luminosity; large X-ray bolometric corrections $k_{rm Bol,X}sim$ 100-1000; and steep $-2<alpha_{OX}<-1.7$. These results lead to a scenario where the X-ray emission of hyper-luminous quasars is relatively weaker compared to lower-luminosity AGN. Models predict that such an X-ray weakness can be relevant for the acceleration of powerful high-ionization emission line-driven winds, commonly detected in the UV spectra of WISSH QSOs, which can in turn perturb the X-ray corona and weaken its emission. Accordingly, hyper-luminous QSOs represent the ideal laboratory to study the link between the AGN energy output and wind acceleration. Additionally, WISSH QSOs show very large BH masses ($log[M_{rm BH}/M_{odot}]$>9.5). This enables a more robust modeling of the $Gamma-M_{BH}$ relation by increasing the statistics at high masses. We derive a flatter $Gamma$ dependence than previously found over the broad range 5 <$log(M_{rm BH}/M_{odot})$ < 11.
Studying the coupling between the energy output produced by the central quasar and the host galaxy is fundamental to fully understand galaxy evolution. Quasar feedback is indeed supposed to dramatically affect the galaxy properties by depositing large amounts of energy and momentum into the ISM. In order to gain further insights on this process, we study the SEDs of sources at the brightest end of the quasar luminosity function, for which the feedback mechanism is supposed to be at its maximum. We model the rest-frame UV-to-FIR SEDs of 16 WISE-SDSS Selected Hyper-luminous (WISSH) quasars at 1.8 < z < 4.6 disentangling the different emission components and deriving physical parameters of both the nuclear component and the host galaxy. We also use a radiative transfer code to account for the contribution of the quasar-related emission to the FIR fluxes. Most SEDs are well described by a standard combination of accretion disk+torus and cold dust emission. However, about 30% of them require an additional emission component in the NIR, with temperatures peaking at 750K, which indicates the presence of a hotter dust component in these powerful quasars. We measure extreme values of both AGN bolometric luminosity (LBOL > 10^47 erg/s) and SFR (up to 2000 Msun/yr). A new relation between quasar and star-formation luminosity is derived (LSF propto LQSO^(0.73)) by combining several Herschel-detected quasar samples from z=0 to 4. Future observations will be crucial to measure the molecular gas content in these systems, probe the impact between quasar-driven outflows and on-going star-formation, and reveal the presence of merger signatures in their host galaxies.
We present the specifications of the MeerKAT Karoo Array Telescope, the South African Square Kilometre Array Precursor. Some of the key science for MeerKAT is described in this document. We invite the community to submit proposals for Large Key Projects.
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