| Weekly Seminars for February 2014 |
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Wednesday February 19,
2014 - 4,00 pm
Sala Lauree (Physics Dept., Old Building - 1st Floor)
ICRA Seminar
Speaker: Dr. Gianluca CASTIGNANI
Institution: SISSA, Trieste Title: Low power radio galaxies as beacons for high redshift clusters of galaxies.
Abstract:
At variance with the powerful Fanaroff-Riley type II (FRII) radio sources, the great majority of low power radio sources (FRIs) are found in clusters, at least in the low redshift Universe. Our newly developed Poisson Probability Method (PPM) shows evidence that 70% of z~1-2 FRIs in COSMOS reside in groups or clusters of galaxies. This is in excellent agreement with results obtained from low redshift studies. For a few of our cluster candidates, independent information (e.g. spectroscopic redshifts, weak lensing stacking, the presence of gravitational arclets and methods based on color selection) provides further support to our results. Therefore, z>~1 FRIs are found in clusters more frequently than FRIIs at similar redshifts and they may be more effectively used than FRIIs as beacons for high-z cluster searches. Being extremely versatile and statistically robust, the PPM may be applied as an alternative method to search for high-z clusters, as well to both present and future wide field surveys such as SDSS Stripe 82, LSST, and Euclid.
N.B. - In the following link, you can find the official announcement on the Physics Department website: http://www.phys.uniroma1.it/fisica/sites/default/files/bollettini/bollettino17022014_0.pdf
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La Segreteria ICRA
c/o Dipartimento di Fisica
Sapienza Università di Roma
P.le A. Moro, 5 I - 00185 ROMA, Italy tel.: +39 06 4991 4 254 fax: +39 06 4454992 email: segreteria@icra.it
Thursday February 20,
2014 - 4,00 pm
ICRANet Pescara (conference room 1st floor)
(skype connection with "Sapienza" University of Rome)
ICRANet Seminar
Speaker: Dr. Gianluca CASTIGNANI
Institution: SISSA, Trieste Title: Black-hole mass estimates and AGN torus characterization for a homogeneous sample of bright flat-spectrum radio quasars.
Abstract:
We have selected a complete sample of flat-spectrum radio quasar from the WMAP 7-yr catalog, all with measured redshift within the SDSS area and have compared black hole mass estimates based on fitting a standard accretion disk model to the `blue bump' with with those obtained from the commonly used single epoch virial method. The sample comprises 79 objects flux limited at 1 Jy at 23 GHz, 55 of which (69%) have a clearly detected `blue bump'. Thirty-three of the 55 FSRQ have, in the literature, black hole mass estimates obtained with the virial method.
The mass estimates obtained from the two methods are well correlated. The fact that the two totally independent methods agree so closely in spite of all the potentially large uncertainties associated to each of them lends strong support to both of them. The distribution of black-hole masses for the 55 FSRQs in our sample with a well detected blue bump has a median value of ~10^9 solar masses. It declines at the low mass end, consistent with other indications that radio loud AGNs are generally associated to the most massive black holes. The distribution drops above black hole masses higher than 10^9.6 solar masses, implying that ultra-massive black holes associated to FSRQs must be rare. We find evidence of MIR emitting AGN torus for eight of the 79 FSRQs, by means of the SED fitting. They have redshifts z<1, synchrotron peak frequencies <~10^13 Hz and synchrotron luminosities <10^47 erg/s, lower than those of the other FSRQs in the sample. The fraction of FSRQs with evidence of torus increases up to 39%, if the 18 FSRQs at z ≤ 1 and with optical/UV bump are considered. Therefore, the detection of the AGN torus is favoured in those FSRQs where the specific synchrotron flux at MIR wavelengths does not overwhelm the contribution from the torus. Conversely to what found by Plotkin et al. (2012) for BL Lac sources, our results show that the AGN torus might be present in a large fraction of FSRQs.
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Icranet Secretariat
ICRANet
P.zza della Repubblica, 10
65122 Pescara (PE)
tel.: +39 085 23054200
fax: +39 085 4219252 email: secretariat@icranet.org |