1,403 research outputs found
Obscured accretion from AGN surveys
No full textRecent models of super-massive black hole (SMBH) and host galaxy joint evolution predict the presence of a key phase where accretion, traced by obscured Active Galactic Nuclei (AGN) emission, is coupled with powerful star formation. Then feedback processes likely self-regulate the SMBH growth and quench the star-formation activity. AGN in this important evolutionary phase have been revealed in the last decade via surveys at different wavelengths. On the one hand, moderate-to-deep X-ray surveys have allowed a systematic search for heavily obscured AGN, up to very high redshifts (z≈5). On the other hand, infrared/optical surveys have been invaluable in offering complementary methods to select obscured AGN also in cases where the nuclear X-ray emission below 10 keV is largely hidden to our view. In this review I will present my personal perspective of the field of obscured accretion from AGN surveys
Observatorio de bibliometría y cienciometría USTA Métricas de autor FICHA BIBLIOMÉTRICA Cristian Fernando Tellez Piñerez
No full textInforme de las métricas de autor del Dr. Cristian Fernando Tellez Piñerez de las
publicaciones indexadas en Google Académico cuyo objetivo es entregar un insumo
para el fortalecimiento de las capacidades y potencialidades de los autores de la
Universidad Santo Tomás en el posicionamiento y visibilidad de sus publicaciones.Report of the author metrics Cristian Fernando Tellez Piñerez of the publications
indexed in Google Scholar whose objective is to provide an input for the
strengthening of the capacities and potentialities of the authors of the Santo Tomás
University in the positioning and visibility of their publications.http://unidadinvestigacion.usta.edu.c
Imports under a foreign exchange constraint
No full textThe traditional model of import behavior -- which looks only at the gross domestic product (GDP) and real import prices as explanatory variables -- failed to predict or explain the developing countries'import slumps in the early 1980's. This paper expands on a more useful model, the Hemphill, which incorporates the traditional variables (relative prices and domestic income) with the variables introduced by Hemphill (foreign exchange receipts and international reserves). Section 2 of this paper discusses the theoretical models in the present study. The traditional model, used here as a benchmark, is presented first, and is later extended to include foreign exchange constraints. Section 3 presents the empirical estimates of the general import models that include foreign constraints, and two special cases, the Hemphill and benchmark models, using pooled, cross-section time series. Section 4 concludes that policy makers must look at the policies that affect GDP and prices and the availability of foreign exchange when trying to estimate import behavior in developing countries.Economic Theory&Research,Environmental Economics&Policies,Economic Stabilization,Inequality,Geographical Information Systems
Exploratory X-Ray Monitoring of Luminous Radio-quiet Quasars at High Redshift: No Evidence for Evolution in X-Ray Variability
No full textWe report on the second installment of an X-ray monitoring project of seven luminous radio-quiet quasars (RQQs). New Chandra observations of four of these, at 4.10 ≤ z ≤ 4.35, yield a total of six X-ray epochs per source, with temporal baselines of ∼850-1600 days in the rest frame. These data provide the best X-ray light curves for RQQs at z > 4 to date, enabling qualitative investigations of the X-ray variability behavior of such sources for the first time. On average, these sources follow the trend of decreasing variability amplitude with increasing luminosity, and there is no evidence for X-ray variability increasing toward higher redshifts, in contrast with earlier predictions of potential evolutionary scenarios. An ensemble variability structure function reveals that their variability level remains relatively flat across ≈20-1000 days in the rest frame and it is generally lower than that of three similarly luminous RQQs at 1.33 ≤ z ≤ 2.74 over the same temporal range. We discuss possible explanations for the increased variability of the lower-redshift subsample and, in particular, whether higher accretion rates play a leading role. Near-simultaneous optical monitoring of the sources at 4.10 ≤ z ≤ 4.35 indicates that none is variable on ≈1 day timescales, although flux variations of up to ∼25% are observed on ≈100 day timescales, typical of RQQs at similar redshifts. Significant optical-X-ray spectral slope variations observed in two of these sources are consistent with the levels observed in luminous RQQs and are dominated by X-ray variations. © 2017. The American Astronomical Society. All rights reserved
Detection of a radio-filled X-ray cavity within the interstellar medium of NGC 5141
No full textWe present the first Chandra detection of a single X-ray cavity within the interstellar medium of the small Fanaroff-Riley type I radio galaxy NGC 5141. The X-ray surface brightness depression, located ≈4 kpc away from the galaxy center, is projected on the northern radio lobe, which is completely contained within the galaxy. The thermal gas surrounding the cavity, which extends to ≃20 kpc, has a bolometric X-ray luminosity (0.1–100 keV) of LX ≈ 2 × 1040 erg s−1 and a temperature of kT ≈ 0.8 keV. We calculated the total energy (Ecav = 4PV ≈ 1055 erg) required to inflate the cavity and its age (tcav ≈ 9 Myrs), assuming that it is filled with relativistic particles and rises buoyantly. The inferred total cavity power is as low as Pcav = Ecav/tcav ≈ 6 × 1040 erg s−1, which is the lowest one among the radio-filled systems. Comparing Pcav to the bolometric X-ray luminosity (i.e., the cooling luminosity), we conclude that NGC 5141’s central active galactic nucleus can heat the interstellar medium and balance its cooling luminosity, confirming that the Pcav − Lcool relation, mainly tested on groups and clusters, also works for such a low-power system
Type II quasar candidates in the Sloan Digital Sky Survey: evidence for X-ray obscuration
No full textCONSTRAINING THE TRUE NATURE OF AN EXOTIC BINARY IN THE CORE OF NGC 6624
No full textWe report on the identification of the optical counterpart to Star1, the exotic object serendipitously discovered by Deutsch et al. in the core of the Galactic globular cluster NGC 6624. Star1 has been classified by Deutsch et al. as either a quiescent cataclysmic variable or a low-mass X-ray binary. Deutsch et al. proposed StarA as a possible optical counterpart to this object. We used high-resolution images obtained with the Hubble Space Telescope to perform a variability analysis of the stars close to the nominal position of Star1. While no variability was detected for StarA, we found another star, referred to here as COM_Star1, showing a clear sinusoidal light modulation with amplitude Δm F435W ~ 0.7 mag and an orbital period of P orb ~ 98 minutes. The shape of the light curve is likely caused by strong irradiation by the primary heating of one hemisphere of the companion, thus suggesting a quite hot primary
Investigating the Complex X-Ray Spectrum of a Broad-Line 2MASS Red Quasar: XMM-Newton Observation of FTM 0830+3759
No full textPhysics Laboratory at Home During the COVID-19 Pandemic
No full textThe pandemic triggered by the SARS-CoV-2 virus has produced worldwide interruptions of face-to-face teaching activity in both schools and universities. In It-
aly, the quarantine began in the second half of February 2020 and lasted for all the second semester of lectures. The Univer- sity of Bologna, where all the authors of the present article are based, developed and activated several interfaces necessary
to efficiently deliver online teaching courses with the utmost speed. The framework used by the authors is based on a com- mon platform, Microsoft TEAMS, available to all teachers at Bologna University
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