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Universite Provence Th`Ese UNIVERSITE DE PROVENCE (Aix-Marseille I) THESE` pour obtenir le titre de Docteur en Sciences de l'Universit¶ede Provence Sp¶ecialit¶e: Rayonnement et Plasmas pr¶esent¶eepar Anabela CARDOSO GONC»ALVES ETUDE¶ SPECTROSCOPIQUE DES NOYAUX ACTIFS DE GALAXIES A` (( SPECTRE DE TRANSITION )) Th`esesoumise aux rapporteurs : Mme Suzy Collin Mme Thaisa Storchi Bergmann Soutenue le 27 septembre 1999, devant le jury compos¶ede : Mme Brigitte Rocca-Volmerange Pr¶esident Mme Suzy Collin Rapporteur M. Georges Courtes` Examinateur Mme Lise Deharveng Examinateur M. Daniel Kunth Examinateur M. Philippe Veron¶ Directeur de th`ese CENTRE NATIONAL DE LA RECHERCHE SCIENTIFIQUE - OBSERVATOIRE DE HAUTE PROVENCE Abstract Galaxy nuclei often show emission lines; they were classi¯ed in several categories on the basis of the intensity ratios of particular optical lines: Seyferts 1 and 2, LINERs and H ii regions; these categories correspond to di®erent excitation conditions. However, a number of objects have intermediate line ratios which do not make it possible to classify them unambiguously in one or the other of these categories. With the aim of clarifying the nature of the \transition spectra" objects, we carried out spectroscopic observations in the visible of a great number of them; the majority of the observations have been made using the spectrograph CARELEC, attached to the Cassegrain focus of the 1,93 m telescope of the Haute{Provence Observatory. The results of this work constitute the bulk of the manuscript presented here. Our observations of 61 objects with a \transition spectrum" showed that they ¯t into a simple classi¯cation scheme; indeed, the spectrum of the majority of them results from the simultaneous presence on the slit of the spectrograph of two di®erent emissive regions (in general, a H ii region and a Seyfert{type cloud) | what we call a \composite spectrum". Being so, no \intermediary" excitation mechanism, nor evolutionary scenario, is necessary to explain their characteristics. Among the objects with composite spectra studied two, particularly interesting, drew our attention and are presented separately: NGC 5252 and KUG 1031+398. Our study of NGC 5252 is based on observations carried out with both the Hubble space telescope and the 1,93 m telescope; it revealed the simultaneous presence, in this object, of a LINER and a Seyfert{type cloud. This suggests that, at least in this galaxy, the LINER{type emission could be due to an ionizing source of non{stellar origin. Ne- vertheless, the LINERs constitute a class of objects very poorly known: True AGNs or galaxies whose emission is not due to a central engine, but entirely of stellar origin? The debate is still open. KUG 1031+398 is a Narrow Line Seyfert 1 galaxy for which an emission region inter- mediate between the Broad Line Region and the Narrow Line Region was reported. Our observations do not con¯rm the presence of an intermediate region in this galaxy, the only one for which a \¯rm" detection has been published. The existence of such an emission region remains, therefore, to be proven. Table des mati`eres 1 Introduction g¶en¶erale 1 1.1 Historique . 1 1.2 Motivation de ce travail . 6 1.3 Structure du manuscrit . 7 2 Les noyaux actifs de galaxie 9 2.1 La famille des AGNs . 9 2.2 Caract¶eristiquesobservationnelles de quelques classes . 10 2.3 Le mod`elestandard . 13 2.4 Le mod`eled'uni¯cation . 16 3 Les instruments 19 3.1 Le t¶elescope de 1,93 m de l'OHP . 19 3.2 Le t¶elescope de 3,60 m de l'ESO . 25 3.3 Le t¶elescope spatial Hubble . 26 3.4 Le t¶elescope de 2,60 m du BAO . 31 3.5 Le t¶elescope de Schmidt du BAO . 33 4 Les observations 35 4.1 Description des observations . 35 4.2 Pr¶eparationde la nuit d'observation . 38 4.3 Acquisition des donn¶ees . 40 4.4 D¶epouillement des donn¶ees. 45 5 Les AGNs `a (( spectre de transition )) 49 5.1 Les m¶ecanismesd'¶emissiondans les objets extra{galactiques . 49 5.2 Les diagrammes de diagnostic . 50 5.3 Les objets `a (( spectre de transition )) ..................... 54 5.4 Ajustement des raies en ¶emissiondans le visible . 58 5.5 Observations `ad'autres longueurs d'onde . 59 Miscellaneous observations of active galactic nuclei II 117 AGNs with composite spectra 117 AGNs with composite spectra II. Additional data 117 III 6 NGC 5252 et les LINERs 117 6.1 NGC 5252 . 117 6.2 Les galaxies h^otesdes LINERs . 119 6.3 Les m¶ecanismesd'excitation dans les LINERs . 120 6.4 Les AGNs `araies larges complexes (double{peaked pro¯les) . 123 NGC 5252 | a Liner undercover 132 7 KUG 1031+398 et la ILR 133 7.1 La r¶egiond'¶emission (( interm¶ediaire )) (ILR) . 133 7.2 KUG 1031+398 . 134 The emission{line spectrum of KUG 1031+398 and the ILR 143 8 La compl¶etudedu BQS 143 8.1 La fonction de luminosit¶edes quasars . 143 8.2 Les relev¶esdu ciel et la recherche de quasars . 143 On the nature of the FBS blue stellar objects and the completeness of the Bright Quasar Survey 171 9 Conclusions et perspectives 171 9.1 Conclusions . 171 9.2 Perspectives . 173 Liste des articles et communications publi¶es 177 Table des ¯gures 179 Liste des tableaux 181 CHAPITRE 1 Introduction g¶en¶erale L'univers, tel qu'il nous est d¶evoil¶epar les t¶elescopes actuels, comporte plus de cent milliards de galaxies, pour la plupart dites (( normales )). Elliptiques, spirales ou irr¶eguli`eres,ces galaxies doivent leur ¶eclatau rayonnement conjoint de quelques cent milliards d'¶etoiles.D'autres existent dont le bilan ¶energ¶etiquetr`es¶elev¶eexige une explication autre qu'un rayonnement d'origine purement stellaire : ce sont des galaxies dites (( actives )). Le fait que tout ph¶enom`emed'activit¶eobserv¶edans ces objets soit associ¶eau noyau galactique a conduit `aleur d¶esignationpar le terme (( noyau actif de galaxie )), ou AGN (de l'anglais Active Galactic Nucleus); c'est l'¶etudede ces objets qui est le sujet de ce travail. Dans ce chapitre d'introduction on suivra donc l'historique des noyaux actifs de galaxie pour mieux les placer dans le contexte actuel, ainsi que les motivations `al'origine des travaux pr¶esent¶esdans ce manuscrit. 1.1 Historique Les premi`eres¶etudesobservationnelles de noyaux actifs de galaxie datent du d¶ebutdu si`ecleavec les travaux de Fath (1909). Une des questions les plus importantes `al'¶epoque ¶etaitde savoir si les (( n¶ebuleusesspirales )) 1 ¶etaient des objets proches, de nature similaire `acelle de la n¶ebuleused'Orion (c’est–`a{direde simples n¶ebuleusesgazeuses), ou si elles ¶etaient des objets lointains, constitu¶esd'un grand nombre d'¶etoilesnon r¶esolues(c’est–`a{ dire d'autres galaxies). Lors d'une ¶etudespectroscopique faite `al'Observatoire de Lick et destin¶ee`aclari¯er la nature des (( n¶ebuleusesspirales )) les plus brillantes, Fath remarqua que, alors que les (( n¶ebuleuses )) observ¶eespr¶esentaient habituellement des raies en absorption, l'une d'entre elles (NGC 1068) avait aussi six raies en ¶emission(de nos jours identi¯¶eescomme ¶etant des raies de [O ii] ¸3727, [Ne iii] ¸3896, H¯ et [O iii] ¸¸4363, 4959, 5007). Ces raies 1. Ce que l'on appelait (( n¶ebuleuse )) `al'¶epoque englobe, en fait, di®¶erents types d'objets (n¶ebuleuses gazeuses, galaxies, amas globulaires); ces (( n¶ebuleuses )) apparaissaient comme des objets faibles et di®us sur les plaques photographiques. L'on doit `al'astronome fran»caisMessier (1784), qui s'est int¶eress¶e`a ces objets dans le cadre de sa recherche de nouvelles com`etes,un catalogue contenant 103 (plus 6) (( n¶ebuleuses )). C'est Lord Rosse (1845) qui, suite `al'observation de la forme spirale de quelques unes d'entre elles, isola la classe des (( n¶ebuleusesspirales )). 2 Chapitre 1. Introduction g¶en¶erale ¶etaient ¶egalement observ¶eesdans les spectres des n¶ebuleusesplan¶etaires.Dans les ann¶ees suivantes, d'autres (( n¶ebuleuses )) pr¶esentant les m^emesraies en ¶emissionfurent signal¶ees. Elles ¯gurent dans la litt¶erature(Slipher 1917; Hubble 1926) comme ¶etant des objets du (( type n¶ebuleuseplan¶etaire )) (c'est le cas de NGC 1068, 4051 et 4151, objets aujourd'hui class¶esdans la famille des AGNs). La d¶ecouverte que ces (( n¶ebuleusesspirales )) sont e®ectivement des ensembles ind¶e- pendants d'¶etoiles,de gaz et de poussi`eres(comme la Voie Lact¶ee)est attribu¶ee`aHubble, au d¶ebutdes ann¶ees20. Ceci changea la perception que les astronomes d'antan avaient de l'univers, montrant notre galaxie comme une parmi tant d'autres, et constitue les d¶ebutsd'une nouvelle branche d'¶etudesen astronomie aujourd'hui appel¶eel'(( astronomie extragalactique )). Au fur et `amesure que de nouvelles galaxies furent d¶ecouvertes, la n¶ecessit¶ed'un sch¶emade classi¯cation convenable s'imposa; il sera bas¶esur la caract¶eristiqueobserva- tionnelle la plus accessible : la morphologie de la galaxie. Hubble ¯gure parmi les astro- nomes qui se sont consacr¶esaux ¶etudesde classi¯cation de galaxies, ayant propos¶eleur s¶eparationen trois classes principales : les galaxies irr¶eguli`eres,les elliptiques et les spi- rales. Ce sch¶emade classi¯cation est bas¶esur plusieurs crit`eres: l'importance du bulbe par rapport au disque, la r¶esolutionet la pro¶eminencedes bras spiraux, la pr¶esencede gaz et de poussi`eres,de r¶egionsionis¶eeset d'¶etoilesjeunes. Ce sch¶emasera r¶evis¶epar de Vaucouleurs qui, en 1959, introduit des types interm¶ediaireset des classi¯cations plus ¯nes; c'est ce sch¶emaqui est `ala base de la classi¯cation moderne utilis¶eecouramment aujourd'hui.
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