1 Quantitative Spektroskopie von AGN Spektrallinien in AGN, Beobachtete Ph ¨ anomene im ¨ Uberblick Breite Emissionslinien: Charakteristikum von AGN-Spektren; speziell Seyfert 1-Galaxien und ” Typ 1“-Quasaren. • Linienbreiten Δλ/λ fast immer > 10 -3 (als Dopplergeschwindigkeit ausgedr¨ uckt: v r > 1500 km/s) • Wasserstoff-Linien (Balmer-, Paschen-, Lyman-Serien), aber auch Linien von Mg + , Fe + ,C 2+ ,C 3+ , Si 3+ ,N 5+ ,O 5+ , ... • Super-breite Linie von Fe 0 (∼ 100 000 km/s) in einigen AGN gefunden • Linienleuchtkraft korreliert mit Kontinuumsleuchtkraft Variabilit¨ at der Kontinuumshelligkeit gefolgt von Linienfluss Schmale Emissionslinien: Zus¨ atzlich zu breiten Linien in Sy 1 / Q 1; einzige Linienform in Sy 2 und Q 2. • Linienbreiten entsprechen v r ∼ 100–300 km/s • Gleiche Linien wie in Planetarischen Nebeln, H ii-Regionen, Starburst- Galaxien • Auff¨ alliges Nebeneinander sehr verschiedener Ionisationsstufen (z.B. O 0 und O 2+ ; Fe 6+ und Fe 13+ . • ¨ Ubergang zwischen schmalen und breiten Linien nicht kontinuierlich! ⇒ Broad Line Region (BLR) und Narrow Line Region (NLR) zwei physikalisch verschiedene Bereiche. Absorptionslinien: Bekannt vor allem intergalaktische Absorptionslinien; hier geht es um intrinsische Absorption! • Spezieller Objekttyp: Broad Absorption Line Quasars (BAL-Quasare) • Schmale Absorptionslinien vor allem im UV von Seyfert-Galaxien • Absorptionskanten in AGN-R¨ ontgenspektren; St¨ arke oft zeitvariabel
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Quantitative Spektroskopie von AGN · 2006. 6. 29. · 1 Quantitative Spektroskopie von AGN Spektrallinien in AGN, Beobachtete Ph anomene im Ub erblick Breite Emissionslinien: Charakteristikum
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Quantitative Spektroskopie von AGN
Spektrallinien in AGN,
Beobachtete Phanomene im Uberblick
Breite Emissionslinien: Charakteristikum von AGN-Spektren;
Ionisationspotentiale einiger wichtiger Elemente und Ionisationsstufen
(alle Angaben in eV):
Element i → ii ii → iii iii → iv iv → v v → vi vi → vii vii → viii
H 13.6
He 24.6 54.4
C 11.2 24.4 47.9 64.5 392.1 490.0
N 14.5 29.6 47.4 77.5 97.9 552.1 667.0
O 13.6 35.1 54.9 77.4 113.9 138.1 739.3
Ne 21.6 41.0 63.5 97.1 126.2 157.9 207.4
Mg 7.6 15.0 80.1 109.3 141.3 186.8 225.0
Si 8.2 16.3 33.5 45.1 166.8 205.3 246.5
S 10.4 23.3 34.8 47.2 72.6 88.1 280.9
Fe 7.9 16.2 30.7 54.8 75.0 99.1 125.0
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within 0>5 of each other, proving that possible spatial strati-fication of different emission zones is insignificant. The over-all positional uncertainty between the PN and RGSinstruments is less than the absolute pointing uncertainty ofthe telescope of 400, implying a robust upper limit on the lineshift uncertainty of 8 mA (120 km s�1 at 20 A).
Significant velocity blueshifts from roughly 0 to 600 kms�1 have been measured from the RGS spectrum (Table 1).Line blueshifts of each ionic line series are fairly consistent.Longer wavelength lines appear to have higher blueshifts.Overall, the observed blueshifts are comparable to blue-shifts of optical/UV emission lines (Grimes, Kriss, & Espey1999; Kraemer & Crenshaw 2000a), although in contrast tothese observations, we find no evidence for any significantredshifts.
The widths we measure are similarly due to intrinsicvelocity distributions at the source. A Chandra image ofNGC 1068 (Young, Wilson, & Shopbell 2001) shows evi-dence for weak extended emission on scales of tens of arc-seconds (Fig. 3). The effect of spatial broadening in the RGSspectrum for this source, characterized by a strongly peakedcentral component and weak extended emission, is negli-gible (A. Rasmussen 2001, private communication). There-fore, any excess broadening of particular lines can only bedue to velocity distributions at the source. Measured veloc-ity widths are also presented in Table 1. All widths lie in therange �obs
v ¼ 300–700 km s�1, which is consistent with theline widths associated with the narrow-line–emitting regionsobserved in the UV (Grimes et al. 1999).
3.4. Radiative Recombination Continua
The spectrum also includes very distinctive radiativerecombination continua (RRCs) for H-like and He-like C,N, and O, which are produced when electrons recombinedirectly to the ground state of these highly ionized species.RRCs are broad features for hot, collisionally ionizedplasma but are narrow, prominent features for cooler pho-toionized plasma. The narrow width of these RRCs pro-vides a direct measure of the recombining electrontemperature (Liedahl & Paerels 1996; Liedahl 1999).
For those RRCs that are clearly detected (C v, C vi, N vi,N vii, O vii, and O viii), we were able to determine accuratetemperatures from the RRC profile itself (Table 2). Theunblended RRCs (on the short-wavelength side) of C v andO vii provide the best temperature determinations. For theother RRCs, the dominant source of uncertainty comesfrom blending with other nearby lines. All temperatures areconsistent with the conservative range of kTe � a few eV.These temperatures imply velocity broadening of all fea-tures by �10 km s�1. This broadening is much lower thanthe observed broadening of �400 km s�1, implying theimportance of bulk and/or turbulent cloud velocities.
Higher temperatures of kTe ¼ 20–30 eV were inferredfrom the broad, polarized, electron-scattered optical lines(Miller, Goodrich, & Mathews 1991), but these tempera-tures are really only upper limits since nonthermal broaden-ing due to bulk and/or turbulent cloud velocities, asobserved in the X-ray, could also be present.
Fig. 1.—Effective area–corrected, first-order RGS 1 (red ) andRGS 2 (blue) spectra of NGC 1068 shifted to its rest frame (z ¼ 0:00379). The spectral discon-tinuities are due to chip gaps in the CCDarrays, bad pixels, and the previous inflight loss of one CCD for RGS 2 (� � 20–24 A). Line labeling indicates the finalstate ion. All H-like (�) andHe-like (r, i, and f ) principal order lines are labeled for each ion with the corresponding RRC edges indicated as well. Additionally,resonance transitions (np!1s) are labeled as � through � (short for Ly�–Ly� and He�–He�). Several Fe L-shell transitions are listed as well. Unlabeled fea-tures at longer wavelengths (e.g., � ¼ 27:45, 27.92, 30.4, 31.0, 34.0–34.6, and 36.38 A) are likely due to L-shell transitions in mid-Z elements. Line blueshiftsare especially noticeable at longer wavelength.
734 KINKHABWALA ET AL. Vol. 575
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Photoionisierte Gasnebel
Literatur: D.E. Osterbrock, Astrophysics of Gaseous Nebulae and Active Ga-
lactic Nuclei, University Science Books, 1989.
Beobachtungen liefern starke Hinweise auf Photoionisation:
• Leuchtkrafte der breiten Emissionslinien korreliert mit Kontinuum.
• Breite Emissionslinien in Sy 1 sind variabel, wobei Lichtkurven ahnlich
denen im Kontinuum, mit Zeitverschiebung ∆t
⇒ Photoionisation durch UV-Kontinuum;
lineare Ausdehnung rBLR ∼ c∆t.
• Schmale Emissionslinien zwar nicht variabel ⇒ rNLR � rBLR,
aber in nahen Seyfert-Galaxien: NLR hat oft konusformige Geometrie
⇒ Abschattung der Zentralquelle durch”Torus“
⇒ Nur moglich bei Photoionisation!
• Fur ausgedehnte NLR in Galaxien aber nicht in jedem Fall sichergestellt,
dass nicht auch Stoßionisation (Schocks) relevant.
Folgende Betrachtungen sind im Prinzip fur breite und schmale Emissionslinien
gleichermaßen gultig:
Betrachte zunachst reines Wasserstoffgas mit Dichte nH , ionisiert durch UV-
Photonen aus Zentralquelle, mit
QH =∫ ∞
νH
Lν
hνdν
wobei hνH = 13.6 eV; λH = c/νH = 91.2 nm.
Definition: Ionisationsparameter im Abstand r,
U =QH
4πr2 c nh,
= Anzahl ionisierender Photonen pro H-Atom.
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Korrelation zwischen Hα-Leuchtkraft und absoluter Helligkeit im Ruhesystem-
B-Band (d.h. ∼ Kontinuumsleuchtkraft) fur eine Stichprobe von Quasaren und
Bedeutende Entdeckung 1995 und nachfolgend: Einige AGN haben extrem brei-
te (∆v ' 100 000 km/s) Emissionslinie im Rontgenspektrum. Maximum koinzi-
dent mit Fe0 Kα, Form aber stark asymmetrisch, langwelliger Flugel erheblich
rotverschoben. Interpretation: Entstehung durch”Wolke“ in stark relativisti-
schem Potential bei r ' RS. Vermutlich physikalisch starkste Evidenz fur Exi-
stenz schwarzer Locher in Galaxienzentren.
Allerdings kein universales Phanomen – viele AGN haben relativ schmale Fe0
Kα-Linien ⇒ Entstehung bei r � RS.
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Go to high resolution image (144kb)
FIG. 7. The time-averaged iron line profile observed in the Seyfert galaxy NGC 3516, obtained from along ASCA observation (Nandra et al. 1999). It shows a broad red tail as well as a resonant absorptionfeature around 5.4 keV.
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