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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Water and hydroxyl in luminous infrared galaxies: Spectroscopic observations and modelling [Elektronisk resurs]
No full textMany luminous infrared galaxies (LIRGs) contain compact obscured nuclei (CONs) where luminosities in excess of 10^9 Lsun emerge from inside dusty regions smaller than 100 pc in diameter. Due to the obscuring material in these regions, the nature of the nuclear power source cannot be determined using direct observations in the optical or IR. In addition, extreme column densities towards the central regions might render these objects heavily Compton-thick, blocking even X-rays originating in the nucleus. It is nevertheless important to reveal and understand the nature of the source behind the high luminosity as this may aid our understanding of the evolution of, and connection between, starbursts and active galactic nuclei (AGN). This thesis describes the ongoing observational and theoretical work to use far-infrared and submillimeter molecular lines to study the central regions of CONs. From excitation analysis, it is possible to construct models of the molecular lines that probe these regions. These models can then constrain the nature of the buried power source. Observations of the LIRG Zw 049.057, obtained with the Herschel Space Observatory, are presented. These observations reveal a rich spectrum of highly excited water (H2O) and hydroxyl (OH), species that couple very well to the intense far-infrared radiation field in the centre of this galaxy. The results of our radiative transfer modelling indicate that Zw 049.057 hosts an optically thick, dusty core with a surface brightness of 10^13-10^14 Lsun kpc^-2 and a column density of molecular hydrogen (H2) approaching 10^25 cm^-2. A surface brightness this high in the central parsecs of a galaxy is expected to arise from a compact starburst or an active galactic nucleus, neither of which can be ruled out based on these results
Water and hydroxyl in luminous infrared galaxies: Spectroscopic observations and modelling
No full textMany luminous infrared galaxies (LIRGs) contain compact obscured nuclei (CONs) where luminosities in excess of 10^9 Lsun emerge from inside dusty regions smaller than 100 pc in diameter. Due to the obscuring material in these regions, the nature of the nuclear power source cannot be determined using direct observations in the optical or IR. In addition, extreme column densities towards the central regions might render these objects heavily Compton-thick, blocking even X-rays originating in the nucleus. It is nevertheless important to reveal and understand the nature of the source behind the high luminosity as this may aid our understanding of the evolution of, and connection between, starbursts and active galactic nuclei (AGN).
This thesis describes the ongoing observational and theoretical work to use far-infrared and submillimeter molecular lines to study the central regions of CONs. From excitation analysis, it is possible to construct models of the molecular lines that probe these regions. These models can then constrain the nature of the buried power source.
Observations of the LIRG Zw 049.057, obtained with the Herschel Space Observatory, are presented. These observations reveal a rich spectrum of highly excited water (H2O) and hydroxyl (OH), species that couple very well to the intense far-infrared radiation field in the centre of this galaxy. The results of our radiative transfer modelling indicate that Zw 049.057 hosts an optically thick, dusty core with a surface brightness of 10^13-10^14 Lsun kpc^-2 and a column density of molecular hydrogen (H2) approaching 10^25 cm^-2. A surface brightness this high in the central parsecs of a galaxy is expected to arise from a compact starburst or an active galactic nucleus, neither of which can be ruled out based on these results
Molecular observations of obscured galaxy nuclei
Get PDFIt is becoming evident that some (ultra)luminous infrared galaxies ((U)LIRGs) contain compact obscured nuclei (CONs) where luminosities in excess of 10^9 L☉ emerge from inside dusty regions smaller than 100 pc in diameter. Due to the obscured nature of these objects, their inner regions are hidden from examination using optical or infrared lines. In addition, extreme column densities (≳10^24 cm^-2) towards the central regions might render them heavily Compton-thick, blocking even X-rays originating in the nuclei. It is nevertheless important to reveal and understand the nature of the sources behind the high luminosities, as well as their connection to the host galaxies, as this may aid our understanding of galaxy evolution and the connection between starbursts and active galactic nuclei (AGN). <br /><br />This thesis describes observational efforts at far-infrared, (sub)millimeter, and radio wavelengths, with a focus on molecular line emission and absorption, combined with theoretical work, to investigate the central regions of CONs. Far-infrared and submillimeter observations of the LIRGs Zw 049.057 and Arp 299A, and the ULIRG IRAS 13120-5453 obtained with the <em>Herschel</em> Space Observatory as well as interferometric (sub)millimeter and radio observations of Zw 049.057 obtained with current state of the art interferometers are presented. Based on the <em>Herschel</em> observations, which targeted spectral lines of water (H2O) and hydroxyl (OH), we construct radiative transfer models in order to constrain the physical conditions in the three galaxies. In this way we find that both Zw~049.057 and Arp~299A host compact obscured nuclei, while IRAS 13120-5453 does not. It is however still difficult to determine the nature of the power sources in the two CONs, and high angular resolution observations of tracers that are able to probe highly enshrouded and compact regions are definitely required in order to do this. The <em>Herschel</em> observations also included signatures of inflowing gas in both Zw 049.057 and Arp 299A as well as a tentative signature of outflowing gas in Zw 049.057. The interferometric follow-up observations of Zw 049.057 further revealed a nuclear molecular outflow detected both in radio absorption lines of OH and (sub)millimeter emission lines of CO. We interpret this combination of in- and outflowing gas motions close to the nucleus as evidence that these objects are in a short transition phase, close to the onset of strong feedback from the nucleus. The study of CONs might thus be essential for our understanding of the global evolution of galaxies
Molecular observations of obscured galaxy nuclei [Elektronisk resurs]
No full textIt is becoming evident that some (ultra)luminous infrared galaxies ((U)LIRGs) contain compact obscured nuclei (CONs) where luminosities in excess of 10^9 L☉ emerge from inside dusty regions smaller than 100 pc in diameter. Due to the obscured nature of these objects, their inner regions are hidden from examination using optical or infrared lines. In addition, extreme column densities (≳10^24 cm^-2) towards the central regions might render them heavily Compton-thick, blocking even X-rays originating in the nuclei. It is nevertheless important to reveal and understand the nature of the sources behind the high luminosities, as well as their connection to the host galaxies, as this may aid our understanding of galaxy evolution and the connection between starbursts and active galactic nuclei (AGN). This thesis describes observational efforts at far-infrared, (sub)millimeter, and radio wavelengths, with a focus on molecular line emission and absorption, combined with theoretical work, to investigate the central regions of CONs. Far-infrared and submillimeter observations of the LIRGs Zw 049.057 and Arp 299A, and the ULIRG IRAS 13120-5453 obtained with the Herschel Space Observatory as well as interferometric (sub)millimeter and radio observations of Zw 049.057 obtained with current state of the art interferometers are presented. Based on the Herschel observations, which targeted spectral lines of water (H2O) and hydroxyl (OH), we construct radiative transfer models in order to constrain the physical conditions in the three galaxies. In this way we find that both Zw~049.057 and Arp~299A host compact obscured nuclei, while IRAS 13120-5453 does not. It is however still difficult to determine the nature of the power sources in the two CONs, and high angular resolution observations of tracers that are able to probe highly enshrouded and compact regions are definitely required in order to do this. The Herschel observations also included signatures of inflowing gas in both Zw 049.057 and Arp 299A as well as a tentative signature of outflowing gas in Zw 049.057. The interferometric follow-up observations of Zw 049.057 further revealed a nuclear molecular outflow detected both in radio absorption lines of OH and (sub)millimeter emission lines of CO. We interpret this combination of in- and outflowing gas motions close to the nucleus as evidence that these objects are in a short transition phase, close to the onset of strong feedback from the nucleus. The study of CONs might thus be essential for our understanding of the global evolution of galaxies
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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