Download or read book Multiwavelength Analyses of Mid Infrared Selected Active Galactic Nuclei written by Anson Lam and published by . This book was released on 2018 with total page 211 pages. Available in PDF, EPUB and Kindle. Book excerpt: Traditional methods of identifying active galactic nuclei (AGNs) rely on UV and optical color criteria, but these methods exclude AGNs that are highly optically obscured by surrounding dust. This bias causes underestimates in the number of obscured AGNs in the Universe, and is problematic for our understanding of galaxy evolution and computing luminosity functions. Since much of the radiation absorbed by dust is re-radiated in the IR, mid-IR color selection provides a much more robust method of identifying AGNs that is not biased against highly dust obscured galaxies. The Wide-field Infrared Survey Explorer (WISE) has provided an all-sky mid-IR survey in four passbands, and the photometry from this catalog can be used to identify AGN candidates. We select AGNs from the catalog using a WISE $W1-W2>0.8$ color cut, and perform follow-up observations with the Keck DEIMOS optical spectrograph for redshift and emission line measurements. We spectroscopically confirm that mid-IR color selection does indeed identify obscured AGNs that are missed by the largest existing optical surveys, and targeted observations are necessary to find these objects. Combining WISE data with the AKARI far-IR all-sky catalog, we also perform SED analysis to characterize the physical properties of dusty AGNs and their surrounding obscuring medium. Using only photometry, we are able to extract a number of physical properties (ex. dust temperature and masses) without the need for time and resource-intensive spectroscopy. Finally, we test the effects of using different SED and color criteria to select different populations of AGNs from the 3D-HST catalog and compute their luminosity functions. We find that SED fitting can identify a large number of AGNs that are missed by traditional color selection methods, and this can potentially increase the sample size of AGNs available for analysis by several factors.

Download or read book Multi wavelength Analysis of Active Galactic Nuclei and Host Galaxies Physical Properties written by Mojegan Azadi and published by . This book was released on 2017 with total page 209 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this dissertation we study the properties of active galactic nuclei (AGN), which are powered by the accretion activity of supermassive black holes residing at the centers of galaxies. While observations propose that growth of AGN and galaxies are globally tied, we investigate whether this connection exists in individual galaxies. We also investigate various AGN selection techniques and star formation rate (SFR) estimates using multi-wavelength data from Chandra, Spitzer and rest-frame optical spectra from the Keck telescope. We find that combining multi-wavelength identification techniques provides a more complete AGN sample, as each selection method suffers from selection biases. In particular, all selection techniques are biased against identifying AGN in lower mass galaxies. Once stellar mass selection biases are taken into account, we find that AGN reside in galaxies with similar physical properties (i.e., SFR) as inactive galaxies. We find that while AGN are prevalent in both star-forming and quiescent galaxies, AGN of a given accretion rate are more likely to reside in star-forming galaxies. The probability of fueling an AGN does not strongly depend on SFR for a star-forming galaxy, though it decreases when star formation is shut down in quiescent galaxies. We also find no evidence for a strong correlation between SFR or stellar mass of the host galaxy and AGN luminosity. These results indicate that while both AGN and galaxy growth are reliant on the same fuel, enhanced star formation activity does not necessarily go hand-in-hand with increased AGN activity. While the star formation activity of galaxies can be traced with various indicators, our investigations indicate that extrapolations from mid-infrared data using calibrations based on local galaxies overestimates SFRs at higher redshift. We show that a combination of mid-infrared and far-infrared data provide a more reliable SFR estimation than the mid-infrared data alone. We also find that the robustness of UV-based SFRs depends on the extinction correction method used. We find a relatively small fraction of z ∼ 2 galaxies have SFRs from infrared observations that are elevated relative to other SFR tracers, and we do not find any contribution from AGN in this excess.

Download or read book Multiwavelength Analysis of the Active Galactic Nuclei s Feedback on the Evolution of Quasar Host Galaxies written by Aishwarya Girdhar and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The X ray Background written by Xavier Barcons and published by Cambridge University Press. This book was released on 1992-07-31 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt: A review of the current observational knowledge and understanding of the cosmic X-ray background.

Download or read book Probing the Physics of Active Galactic Nuclei by Multiwavelength Monitoring written by Bradley M. Peterson and published by . This book was released on 2001 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: Annotation Papers from a June 2000 meeting discuss multiwavelength monitoring methods for studying active galactic nuclei, the potential of dedicated facilities for multiwavelength monitoring, and future multiwavelength programs. Some topics discussed are multiwavelength observations of blazars, time delays of blazar flares observed at different wavebands, low radiative-efficiency accretion flows, spectrochronography, and variability of the intrinsic UV absorption lines in Seyfert galaxies. Other topics are the variable diffuse continuum emission of broad-line clouds, the MIDEX concept, and the mission. Peterson teaches astronomy at The Ohio State University. This volume lacks a subject index. Annotation c. Book News, Inc., Portland, OR (booknews.com)

Download or read book Mid infrared Interferometry of Nearby Active Galactic Nuclei written by Konrad R. W. Tristram and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Multiwavelength Spectroscopy of Active Galactic Nuclei written by Michiel Kolman and published by . This book was released on 1992 with total page 296 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Multi wavelength Studies of Active Galactic Nuclei on Parsec and Kiloparsec Scales written by Juan Carlos Algaba and published by . This book was released on 2010 with total page 177 pages. Available in PDF, EPUB and Kindle. Book excerpt: Although the continua of radio-loud Active Galactic Nuclei (AGN) are typically dominated by synchrotron radiation over virtually the entire spectrum, it is not clear whether the radio and higher-frequency emission originate in the same or different parts of the jet. In some inhomogeneous synchrotron source models for blazars, the radio and UV-optical-IR (UVOIR) emission may be co-spatial, depending on the model parameters considered. Indeed, several different radio{u2013}optical correlations based on polarization data have been found recently, suggesting that the optical and radio polarization may be closely related, and that the corresponding emission regions may be cospatial. My joint analysis of optical and 15+22+43 GHz VLBA polarization data for a sample of about 40 AGNs shows that, after correction for the inferred VLBA core Faraday rotations, most BL Lac objects and some quasars have aligned VLBA-core and optical polarizations, although many quasars also show no obvious relationship between their VLBA-core and optical polarization angles. This apparently indicates that not all AGNs have co-spatial regions of optical and radio emission in their jets. However, another possibility was that some of the 15{u2013}43 GHz VLBA cores have Faraday rotations of the order of several tens of thousand of rad/m2, which were not properly fit using our three-frequency data due to n {u00D7} _ ambiguities in the observed polarization angles, leading to incorrect subtraction of the effects of the core Faraday rotation, and so incorrect {u2018}zero-wavelength{u2019} radio polarization angles. With this is mind, I obtained additional observations for 8 of the 40 AGN, this time at 12+15+22+24+43 GHz, chosen in such a way that we should be able to discern between various possible scenarios. My results indicate that, although some VLBI radio cores have comparatively high rotation measures, this cannot explain the misalignments found between the radio core and optical VLBI polarization angles. I performed a series of analyse to check if this could be explained by other physical processes or properties occurring in the AGN, such as degree of polarization, magnetic field intensity or presence of detectable {u2013}ray emission. No clear differences between the properties of sources with aligned and misaligned radio-core and optical polarization angles was found. The emission from AGN is mostly synchrotron in origin, making it natural that the degree of circular polarization (CP) is low, less than a percent. For this reason, the detection of CP is a non trivial task. However, using recently developed new techniques, I have performed circular polarization analysis on some of my sources. The results indicate that the degree of CP tends to increase with frequency, with the spectral index being either flat or inverted, _ _ +1, which can be explained with a Blandford-Königl jet model. Using the measured intensity, spectral indices and magnetic fields derived from the measured core shift, I have derived the degree of order of the magnetic field required to explain if this observed CP is generated by the synchrotron mechanism. The implied degrees of order of the magnetic field are too high in most cases for the CP to be synchrotron in origin, requiring a substantial (possible dominant) contribution from Faraday conversion of linear to circular polarizaton. A kilo-Parsec multiwavelength study has also been performed on the source PKS 0521{u2013}365. This AGN has been classified as a HYMOR (Hybrid morphology radio source) and has a jet which is clearly detectable over a wide frequency band, ranging from radio to X-rays. This has allowed me to perform a study of its physical properties over radio, near infra-red, optical and X-rays bands, thus obtaining valuable information about its morphology, spectral energy distribution and magnetic field. The data here supports the hypothesis that PKS0521-36 is intermediate between an FRI and FRII source, agreeing with unified scenarios in which the differences between these classes can be understood on a physical basis.

Download or read book Mid infrared properties of local active galactic nuclei written by Daniel Asmus and published by . This book was released on 2012 with total page 203 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Infrared Investigations of Star Formation Suppression in X Ray Selected Active Galactic Nuclei written by Arianna Brown and published by . This book was released on 2017 with total page 55 pages. Available in PDF, EPUB and Kindle. Book excerpt: We now know that most galaxies play host to a supermassive black hole that resides at their centers. When the black hole is actively consuming dust and gas over long periods of time, it emits radiation at every wavelength, becomes brighter than the host galaxy and is commonly known as an active galactic nuclei (AGN). Some scientists believe AGNs play an important role in suppressing their host galaxy's star formation rate (SFR) by heating up, consuming and/or blasting away the cool gas and dust necessary to create stars. This mechanism is theorized as a critical step in AGN and galaxy evolutionary models in order to create the local universe we see today. Efforts to observe this effect suffer from several limitations including but not limited to low number statistics for powerful (LAGN > 1044.8 erg/s) AGN and single-band photometric estimations for star formation rates. In this work, we aim to overcome those limitations by estimating spectral energy distributions and SFRs for 550 AGN detected in the Chandra XBootes X-Ray Survey. We use available infrared data from the Spitzer Space Telescope, Herschel Space Observatory and NOAO's Mayall and Blanco telescopes to calculate SFRs corrected for mid to far-infrared contribution from heated dusty tori surrounding AGNs. We reproduce trends found in similar studies: when averaging the highly variable AGN activity in bins of more steady SFRs, we find a positive linear correlation for intermediate redshift (0.5

Download or read book Multi Wavelength Continuum Emission of AGN written by T.J.-L. Courvoisier and published by Springer. This book was released on 1994-05-14 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active Galactic Nuclei radiate over the electro-magnetic spectrum from radio waves to gamma rays. Understanding the physics of these objects therefore requires the synthesis of results from many different domains of Astronomy. It was the aim of the conference "Active Galactic Nuclei across the Electromagnetic Spectrum" to provide a forum where this exchange could take place. Some 300 astronomers participated to the conference, 250 of them presented results either as oral papers or in the form of posters. Observations in all domains of the electro magnetic spectrum in which astronomical observations can be made from the ground or from space were presented. Many theoretical contributions were also given. There has been a tremendous growth in the number and quality of Astronomical obser vations in many spectral domains over the past several years. Students of Active Galactic Nuclei have been particularly keen to make use of the available facilities (both space born and on the ground), often in a very organised way, in order to obtain repeated simultane ous data covering large bands of the spectrum. This approach has produced a qualitatively new set of data for understanding the physics of Active Galactic Nuclei. The task of the meeting was to review this data in a coherent way.

Download or read book Multi wavelength Observations of Active Galactic Nuclei written by Thierry Jean-Louis Courvoisier and published by . This book was released on 1994 with total page 5 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book High Resolution Mid infrared Imaging of Active Galactic Nuclei written by James Thomas Radomski and published by . This book was released on 2003 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Low Ionization Nuclear Emission Line Regions written by Rachel Dudik and published by . This book was released on 2007 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: "The horizon of the universe, once thought to extend only to the disk of the Milky Way, is now known to embrace a host of diverse galaxies, from active galaxies such as quasars and Seyfert galaxies to normal galaxies such as our own. The recent discovery that virtually all local galaxies harbor massive nuclear black holes, has provided convincing evidence that active galactic nuclei (AGNs) and normal galaxies are indeed connected. The nature of this connection and the evolutionary history connecting them, however, continues to be elusive. Low Ionization Nuclear Emission-line Regions (LINERs) are the dominant population of 'active' galaxies in our local universe and may indeed be the missing piece to the evolutionary puzzle. LINERs are dened by optical line ratios uncharacteristic of photoionization by normal main sequence stars. While classical AGNs represent at most a few percent of the galaxy population, LINERs constitute as much as 50% of the total local extragalactic population. However, despite several decades of intense research, the ionization mechanism responsible for the unusual LINER spectrum remains a mystery. What is the ionization mechanism responsible for the empirical line ratios characteristic of LINER galaxies? How do LINERs t into the overall evolution of galaxies as we know it? Are LINERs a subclass of AGN? What is the evolutionary connection, if any, between galaxies with heavy starburst activity and AGNs? The majority of LINERs are dust enshrouded and therefore very luminous in the far-infrared. The far-infrared (far-IR) luminosity to the luminosity in the optical Bband (center = 4400A), the so-called IR-brightness ratio, can be used as a gauge of the amount of dust in host galaxy. LINERs span a wide range of LFIR/LB ratios, tending predominantly toward the IR-bright end. However, the majority of research to-date has been based on optically selected samples which are partial toward IR-faint LINERs. This bias toward IR-faint galaxies could have important consequences on statistical analyses which examine the fraction of LINERs hosting AGNs. In order for an accurate picture of LINERs to emerge, IR-bright as well as IR-faint galaxies must be studied. What fraction of IR-bright LINERs are AGNs? In light of the open questions regarding these remarkable objects, the central goal of this dissertation is to carry out a systematic multi-wavelength X-ray imaging and Infrared spectroscopic survey of nearby LINERs spanning a wide range of IRbrightness ratios in order to 1) characterize the dominant energy source responsible for their optical line ratios, 2) compare the AGN detection rate in our infrared selected sample with the optically selected samples, 3) determine the luminosities, spectral characteristics and accretion properties of the AGN-LINERs and compare them with the standard active galaxies, and nally, 4) relate the host galaxies properties to the properties of the central source in an attempt to constrain the role of LINERs in galaxy evolution and formation models"--Abstract

Download or read book Multi Wavelength Continuum Emission of AGN written by T.J.-L. Courvoisier and published by Springer. This book was released on 1994-04-30 with total page 534 pages. Available in PDF, EPUB and Kindle. Book excerpt: Active Galactic Nuclei radiate over the electro-magnetic spectrum from radio waves to gamma rays. Understanding the physics of these objects therefore requires the synthesis of results from many different domains of Astronomy. It was the aim of the conference "Active Galactic Nuclei across the Electromagnetic Spectrum" to provide a forum where this exchange could take place. Some 300 astronomers participated to the conference, 250 of them presented results either as oral papers or in the form of posters. Observations in all domains of the electro magnetic spectrum in which astronomical observations can be made from the ground or from space were presented. Many theoretical contributions were also given. There has been a tremendous growth in the number and quality of Astronomical obser vations in many spectral domains over the past several years. Students of Active Galactic Nuclei have been particularly keen to make use of the available facilities (both space born and on the ground), often in a very organised way, in order to obtain repeated simultane ous data covering large bands of the spectrum. This approach has produced a qualitatively new set of data for understanding the physics of Active Galactic Nuclei. The task of the meeting was to review this data in a coherent way.

Download or read book Multi wavelength Properties of Active Galactic Nuclei written by Thierry Jean-Louis Courvoisier and published by . This book was released on 1993 with total page 7 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Physics and Evolution of Active Galactic Nuclei written by Hagai Netzer and published by Cambridge University Press. This book was released on 2013-09-16 with total page 369 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive introduction to the theory underpinning our study of active galactic nuclei and the ways we observe them.