GalaxyLF - Galaxy Luminosity Function(LF Φ What are the...

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Unformatted text preview: 7/11/11 Galaxy Luminosity Function (LF) - Φ- What are the relative numbers of galaxies of different luminosities? δN = Φ(L) δL δV δN is the # of galaxies that are located in volume δV with luminosities between L and L+δL Φ(L) has units # galaxies/(luminosity interval*volume) Can also be written in terms of absolute magnitude ν = Φ(M) dM ∞-∞ Field Galaxy LF • measure apparent brightness of galaxies in some sample (i.e. field) • convert apparent to absolute magnitude from estimated distance • apply k-correction if z is more than ~0.1 • divide # of galaxies in each magnitude/luminosity interval by volume of space surveyed • note that V is greater for intrinsically brighter galaxies in a survey with fixed apparent magnitude limit 7/11/11 Problems: • Malmquist Bias in magnitude limited surveys • Distance estimate uncertainties • enhancements (clusters/walls) and voids in galaxy distribution (for a given magnitude, N can depend on spatial distribution as much as Φ) Field LF reveals 1) # density of galaxies declines w/increasing L 2) decline increases sharply at some characteristic luminosity L Schechter (1976) found LF well described by Φ(L) = Φ*/L* (L/L*)α exp(- L/L*) this is the SLF α Φ* = 5.5 x 10-3 galaxies/Mpc3 L* = 2 x 1010 Lsun M*B = -20.4 α = -1.07±0.07 (Efstathiou, Ellis, & Peterson 1988) 7/11/11 Results from SDSS (Blanton et al. 2001) for z < 0.2 Φ* = 7.4 x 10-3 galaxies/Mpc3 M*B = -20.8 α = -1.26 ± 0.05 S&G give results from 2dF survey L* = 2 x 1010 Lsun M*B = -20.5 Move to K-band (IR) to avoid domination of light by star forming regions and sample more “typical” stars Φ* = 5.5 x 10-3 galaxies/Mpc3 L* = 2 x 1010 Lsun M*K = -23.8 α = -0.9 ± 0.2 (Gardner at al. 1997) 2MASS (Kochanek et al. 2001) Φ* = 4.1 x 10-3 galaxies/Mpc3 L* = 2 x 1010 Lsun M*K = -23.4 α = -1.09 ± 0.06 ∞ Even though different wavelengths are dominated by different stellar types, LFs are virtually the same in optical and infrared. 7/11/11 Remarks about SLF • works for all galaxies lumped together; individual galaxy types not as well fit • Milky Way and Andromeda are close to or just fainter than L* • galaxies with L ≥ 3L* are very rare • SLF predicts too many galaxies at low L (as L & 0, N & ∞) Calculate total # of galaxies in some volume whose luminosity exceeds L N(>L) = Φ(L’) dL’ = Φ* xα e-x dx = Φ* Γ(1+α)...
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GalaxyLF - Galaxy Luminosity Function(LF Φ What are the...

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