Galactic Astronomy 銀河物理学特論 I
overview
• Contents:
1. Statistical properties of galaxies in the local universe
•
Stellar properties of galaxies
•
Emission line diagnostics of galaxies (藤井(慎))
Tremonti et al. 2004, ApJ, 613, 898
•
Morphological properties of galaxies (馬渡)
•
Dynamical structure of galaxies (小室)
•
Dependence of galaxy properties on “environment” (本間)
•
Multi-wavelength view of galaxies (IR, 藤井(淳))
2. Active galaxies and super massive black holes in the local universe
•
Relation between bulges and super massive black holes of galaxies (前林)
•
Unified model of Active Galactic Nuclei
3. Observations of galaxies in the distant (high-redshift universe)
•
Searching for distant galaxies, method (大野)
•
Luminosity function of galaxies and its evolution (鶴指)
•
Stellar mass function of galaxies (本田)
•
Chemical evolution of galaxies (Kogawa)
•
Evolution of dynamical properties of galaxies (Akhlaghi)
•
Co-evolution of galaxies and super massive black holes
4. Observational astronomy in future
Galactic Astronomy
銀河物理学特論 I
Lecture 1-2: Emission line diagnostics of galaxies
Seminar: Tremonti et al. 2004, ApJ, 613, 898
Lecture:
2011/10/17
Regions of ionized gas 1: HII regions in M51 galaxy
Regions of ionized gas 2: Narrow-line region around Active
Galactic Nuclei
Emission line spectra
：
Ratios between lines vary with ionization source, temperature, density, metallicity,
extinction, and so on.
[OI]
Ionization source = 10,000K star
Electron density = 1000cm-3
Electron temperature = 7,000-25,000K
Ionization source = 100,000K star
Electron density = 1000cm-3
Electron temperature = 10,000K
Ionization source = power-law continuum
-> Various ionization levels, [OI], [OII], [OIII]
Electron density = 1000cm-3
Electron temperature = 10,000K
Emission line diagnostics
：
Ratios between lines vary with ionization source, temperature, density, metallicity,
extinction, and so on.
Ionization source : Young stars or AGN ?
Line flux = amount of ionization photons
# of young stars = star formation rate
luminosity of AGN = black hole mass accretion rate
Ionization parameter : gas density vs. photon density
Metallicity (金属量) : X/H, O/H, Fe/H
(Electron) density : n_e
(Electron) temperature : T_e = ionization level
Dust extinction : from Balmer decrement
Collisional excitation, metastable state (準安定準位), and forbidden
lines (禁制線):
case with Oxygen-atom and Oxygen-ion
Upper levels have different energy:
Electron temperature can be determined
with the flux ratio of these lines, if electron
density is lower than critical density.
Upper levels are close ~ doublet:
Electron density can be estimated with
the flux ratio of these lines if electron
density is lower than critical density.
Estimation of electron density
Electron density can be determined with transitions between doublet and
ground state.
Collisional excitation and spontaneous emission, ratio determined
by “statistical weight” (統計的重み) of each state
Critical density for each forbidden
line.
Collisional excitation and collisional deexcitation, ratio determined by “statistical
weight” + “transition probability (遷移確率)”
小暮 智一 “星間物理学”
Estimation of electron temperature:
小暮 智一 “星間物理学”
Estimating metallicity (O/H ) : bese-line
Metallicity (O/H abundance ratio) of gas-component of galaxies can be estimated with
collisionally excited forbidden lines.
[OII] 3729/3726, [SII] 6716/6731 -> Electron density
[OIII] (4959+5007) / 4363 -> Electron temperature
[OIII] / Hb + Te + ne -> O++ / H+
[OII] / Hb + Te + ne -> O+ / H+
O++ / H+ + O+ / H+ -> O / H (assuming ionized region)
Sample: O/H vs. y, and y of the early universe
O/H abudances are compared with y (=He/H) determined from ratio between
recombination lines
HeI / Hb -> y+ = He+ / H+
HeII / Hb -> y++ = He++ / H+
x(He+) / x(H+) = 1 (ionization fraction is similar for H, He)
(smaller if log[(O+/S+)/(O++/S++)]>0.7)
-> y+ + y++ = y (number fraction)
He mass fraction Y = 4y[1-20(O/H)] / (1+4y)
Pagel et al. 1992, MNRAS, 255,325
Estimation of metallicity
： “Bright line method 1”
Ratio between summed flux of multiple ionization states and flux of Balmer line.
R23 = ( f([OIII]4959,5007) + f([OII]3727,3729) ) / f(Hb), but two-valued function in the low-metallicity range
S23 = ( f([SIII]9069,9532 + f([SII]6717,6731) ) / f(Hb), but two-valued function in the wide metallictiy range.
Kewley & Dopita 2002, ApJS, 142, 35
(Originally from Pagel et al. 1980, MNRAS, 193, 219)
Estimation of metallicity
： “Bright line method 2”
Metallicity estimation with one line ratio：
[NII]6584 / [OII]3726,3729
(affected by dust extinction)
[NII]6584 / [SII]6717,6731
(Saturation at low metallicity, degenerate with ionization parameter).
[NII]6584 / [OIII]5007 (saturation at low metallicity, degenerate with ionization parameter, affected by
dust extinction)
Kewley & Dopita 2002, ApJS, 142, 35
Metallicity determination ： “Bright line method 3”
Metallicity determination only with f([NII6584) / f(Ha).
Kewley & Dopita 2002, ApJS, 142, 35
Metallicity determination with various line ratios:
Maiolino et al. 2008, A&A, 488, 463
Chemical evolution model of galaxies: “1-zone”, “closed-box” model
• Instantaneous Recycling Approximation = Stars are formed but soon
(simultaneously) exploded, a fraction is kept as stellar remnants (lock-up as
white dwarfs, black-holes, long-lived stars) and the remaining fraction is
returned to the interstellar space (stellar wind, super nova remnants) as
metal enriched gas.
• 1-zone model = Mtotal(t) = Mgas(t) + Mstar(t) = constant, no-infall, nooutflow.
• With these assumptions, the gas metallicity abundance (Z(t)) increases with
the stellar mass fraction (Mstar(t)/(Mtotal(t))
Metal mass in gas = Mgas(t) * Z(t)
Yield = P= Mgas(t) * dZ(t) / dMstar(t) : gas metallicity increase with star
formation
In “closed-box” mode, Z(t) = - P ln( Mgas(t) / Mtotal(t) )