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Talking About S pectrum. Hou Saiyu 04/01/2014 Note: Four digital numbers referring to wavelength in unit of angstrom here. outline. Introduction Properties Important spectrum in astronomy AGN spectrum. outline. Introduction Properties Important spectrum in astronomy
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Talking About Spectrum HouSaiyu 04/01/2014 Note: Four digital numbers referring to wavelength in unit of angstrom here
outline • Introduction • Properties • Important spectrum in astronomy • AGN spectrum
outline • Introduction • Properties • Important spectrum in astronomy • AGN spectrum
outline • Introduction • Properties • Important spectrum in astronomy • AGN spectrum
Forbidden Lines • Dipoleradiation, selectionrules • Meta stable state • Collisionde-excitation • Energy level life time • Critical density • Transition probabilities ~ 1 in 109
Forbidden Line Examples Highest vacuum on earth <1000 atoms/cm3 http://www.astr.ua.edu/keel/galaxies/emission.html
Semi Forbidden Line • eg. CIII]1909, NIII]1750, OIII]1663,NIV]1486 • Electric dipole transition, but ΔS ≠0 • CaI] λ65733P1 1S0 • Transition probabilities ~1 in 106
Broadening • Thermal Doppler Broadening • Collision Broadening • Rotational Broadening Δ λ/λ = v/c • Natural Broadening • Turbulent Broadening • Zeeman Splitting • … www.astronomy.gatech.edu/Courses/Phys3021/Lectures/pdf/Line_Broadening.pdf
ThermalBroadening http://astronomy.swin.edu.au/cosmos/t/thermal+doppler+broadening
Rotational Broadening http://astronomy.nju.edu.cn/~lixd/GA/AT4/AT404/HTML/AT40404.htm
Double Horned Line Profile Broad, asymmetric line profile with a sharp cutoff at high E
Broadening Estimate: For hydrogen atoms in the Solar photosphere (T=5770K), Hα656.3nm broadening 0.04nm • The concept of Equivalent Width(EW) and Fullwidthathalfmaxium (FWHM) http://www.mssl.ucl.ac.uk/www_astro/agn/agn_rixos.html
Reverberation Mapping • GM = f RBLR(ΔV)2 • ΔV measured from Doppler broadening of the gaseous emission lines • Measuring Black Hole Mass http://ned.ipac.caltech.edu/level5/Sept09/Gaskell/Gaskell3.html
outline • Introduction • Properties • Important spectrum in astronomy • AGN spectrum
LymanαForest http://www.astr.ua.edu/keel/agn/forest.html
Mg II absorption line Useful in finding galaxies with a background quasar http://astronomy.nmsu.edu/cwc/Research/MgIIreview/mgii-over.html
H 21 cm Line http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/h21.html • the birth of spectral-line radio astronomy • Mapping the rotation curve of the Galaxy • probe the "dark ages" from recombination to reionization • SETI: searching for extraterrestrial civilizations
[OIII] line [OIII] 5006.843/4958.911 intensity ratio • strongest narrow line in AGNs at optical band • high abundance of doubly charged oxygen ions • isolated from other optical spectrum • Useful in studying NLR
outline • Introduction • Properties • Important spectrum in astronomy • AGN spectrum
AGN Spectrum http://www.astro.caltech.edu/~george/ay127/Ay127_AGN.pdf
http://en.wikipedia.org/wiki/Blazar RadioGalaxy/Seyfert2 Quasar/Seyfert1 Blazar
NLR: Keplerian orbital speeds of the clouds much smaller => lines are narrow Spatially resolvable Narrow permitted/forbidden Lines No bright continuum from the obscured central engine, except infrared and X-ray Broad permitted lines Narrow Forbidden Lines Bright continuumfrom central engine http://abyss.uoregon.edu/~js/ast123/lectures/lec12.html
Seyfert 1 & Seyfert 2 Type 1.2, 1.5, 1.8 and 1.9 Seyfert galaxies, due to H spectrum FWHMs~500km/s FWHMs~5000km/s Osterbrock, D. Astrophysics of Gaseous Nebulae and Active Galactic Nuclei
Spectrum of a typical quasar Lyα1216 Quasar=quasi-stellar radio source http://loke.as.arizona.edu/~ckulesa/camp/spectroscopy_examples.html
Why νFν ~ ν plot • Power law spectrumFν~ ν-α • In case α=1, νFν ~ ν diagram: horizontal • In case α=0, νFν ~ ν diagram: proportional • Quasar α=0~1 • Convenient
Featureless non-thermal continuum O[III] Hβ Hβ O[III] http://www.astr.ua.edu/keel/agn/spectra.html
DiagnosticLineRatios R. Cid Fernandeset al. 2010
VariabilityofAGNin various spectral domains Seyfert I http://www.astr.ua.edu/keel/agn/vary.html