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Talking About Spectrum Hou Saiyu 04/01/2014 Note: Four digital numbers referring to wavelength in unit of angstrom here.

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Presentation on theme: "Talking About Spectrum Hou Saiyu 04/01/2014 Note: Four digital numbers referring to wavelength in unit of angstrom here."— Presentation transcript:

1 Talking About Spectrum Hou Saiyu 04/01/2014 Note: Four digital numbers referring to wavelength in unit of angstrom here

2 outline Introduction Properties Important spectrum in astronomy AGN spectrum

3 outline Introduction Properties Important spectrum in astronomy AGN spectrum

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6 outline Introduction Properties Important spectrum in astronomy AGN spectrum

7 Forbidden Lines Dipole radiation, selection rules Meta stable state Collision de-excitation Energy level life time Critical density Transition probabilities ~ 1 in 10 9

8 Forbidden Line Examples Highest vacuum on earth <1000 atoms/cm3

9 Semi Forbidden Line eg. CIII]1909, NIII]1750, OIII]1663,NIV]1486 Electric dipole transition, but ΔS ≠0 CaI] λ P 1  1 S 0 Transition probabilities ~1 in 10 6

10 Broadening Thermal Doppler Broadening Collision Broadening Rotational Broadening Δ λ/λ = v/c Natural Broadening Turbulent Broadening Zeeman Splitting …

11 Thermal Broadening

12 Rotational Broadening

13 Double Horned Line Profile Broad, asymmetric line profile with a sharp cutoff at high E

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15 Broadening Estimate: For hydrogen atoms in the Solar photosphere (T=5770K), Hα656.3nm broadening 0.04nm The concept of Equivalent Width (EW) and Full width at half maxium ( FWHM )

16 Searching For Exoplanets

17 Reverberation Mapping GM = f R BLR (ΔV) 2 ΔV measured from Doppler broadening of the gaseous emission lines Measuring Black Hole Mass

18 Narrow  low velocity Forbidden  low material density

19 outline Introduction Properties Important spectrum in astronomy AGN spectrum

20 Lyman α Forest

21 Mg II absorption line Useful in finding galaxies with a background quasar

22 H 21 cm Line 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

23 [OIII] line strongest narrow line in AGNs at optical band high abundance of doubly charged oxygen ions isolated from other optical spectrum Useful in studying NLR [OIII] / intensity ratio [OIII] / intensity ratio

24 outline Introduction Properties Important spectrum in astronomy AGN spectrum

25 AGN Spectrum

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28 Radio Galaxy/Seyfert 2 Quasar/Seyfert 1 Blazar

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30 NLR: Keplerian orbital speeds of the clouds much smaller => lines are narrow Broad permitted lines Narrow Forbidden Lines Bright continuum from central engine Narrow permitted/forbidden Lines No bright continuum from the obscured central engine, except infrared and X-ray Spatially resolvable

31 Seyfert 1 & Seyfert 2 Osterbrock, D. Astrophysics of Gaseous Nebulae and Active Galactic Nuclei FWHMs ~5000km/s FWHMs ~500km/s Type 1.2, 1.5, 1.8 and 1.9 Seyfert galaxies, due to H spectrum

32 Spectrum of a typical quasar Lyα Quasar=quasi-stellar radio source

33 Peterson, B.M. An Introduction to Active Galactic Nuclei

34 Why ν F ν ~ ν plot Power law spectrum F ν ~ ν -α In case α=1, ν F ν ~ ν diagram: horizontal In case α=0, ν F ν ~ ν diagram: proportional Quasar α=0~1 Convenient

35 BL Lac & OVVs

36 Hβ O[III] Featureless non-thermal continuum

37 SDSS Quasar Survey

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39 Diagnostic Line Ratios R. Cid Fernandes et al. 2010

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41 Variability of AGN in various spectral domains Seyfert I

42 Thanks


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