HC3 N as a Diagnostic Tool for Activity in Galaxies
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Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Publicerad
2009
Författare
Lindberg, Johan
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The aim of this thesis is to discuss a small survey of extragalactic measurements of HC3N, as well as present results of unpublished HC3N measurements in galaxies. These data have been compared with HCN and HNC data from the literature and from new observations, thus giving estimates of line ratios between these three molecules in about 15 galaxies. This can help understanding the evolution of active galaxies, and also make it easier to distinguish galaxies powered by starbursts from those powered by active galactic nuclei (AGN). Our spectral line observations have been made with the IRAM, SEST, OSO 20 m and JCMT telescopes between 2001 and 2008. Among the new HC3N data, detections of HC3N in six galaxies with no earlier detections are reported. Three new detections of HNC and one new detection of HCN are also reported. The detection of HC3N in IRAS 17208-0014 is the most distant detection of this molecule yet reported. The formation of HC3N is discussed, and the theory that HC3N is formed from C2H2 on the grains reacting with CN is supported by the data. The HC3N line ratios are compared with other parameters important to star formation and AGN activity. A tentative correlation between HC3N and PAH (polycyclic aromatic hydrocarbons) emission is reported, as well as a tentative correlation between HC3N and the depth of silicate absorption. A preliminary definition “HC3N-luminous galaxy”, based on the HC3N/HCN ratio, is made, and most HC3N-luminous galaxies seem to be galaxies with deeply obscured cores and (U)LIRGs - (ultra-)luminous infrared galaxies. Many of them also seem to have OH megamaser activity. A possible explanation is that both HC3N and OH megamasers need warm dust for their excitation. Alternatively, the dust offers protection against UV destruction. This work will be adapted into an article for Astronomy and Astrophysics during the autumn/winter of 2009.
Beskrivning
Ämne/nyckelord
Astronomi, astrofysik och kosmologi , Astronomy, Astrophysics and Cosmology