Deriving stellar masses from SDSS Reference: Bruzual and Charlot 2003MNRAS.344.1000B Kauffmann et al. 2003MNRAS.341.33 Salim et al. 2007ApJS..173..267S Bell et al. 2003ApJS..149..289B
Outline! Basic idea! Stellar population synthesis model! SED fitting! M/L optical color relation! Current stellar mass estimation
Stellar population synthesis model! Bruzual and Charlot (03, 09)! Stellar evolution prescription! Tracks from zero-age main sequence to Thermally Pulsing AGB (low or intermediate mass) or core Carbon ignition (high mass)! Padova 1994, Padova 2000, Geneva! Different in Z range, stellar mass range, treatment of opacity etc.! Stellar spectra library! Individual stellar spectra for stars at any position of the H-R diagram! BaSeL, (theoretical or semi-empirical, 91A-160micron), STELIB (3200-9500A, 3A), Pickles (1150A-2.5micron, 5A)! Different in wavelength range, spectral resolution, etc.
Stellar population synthesis model! Bruzual and Charlot! Isochrone synthesis! Any SFH can be expanded in series of instantaneous starbursts (single stellar population, SSP)! F: SED at time t of a stellar population : star formation rate S: power radiated per unit wavelength per unit initial mass by an SSP of age t and metallicity, depending on IMF (option of Chabrier of Salpeter) : metal-enrichment law
Stellar population synthesis model! Bruzual and Charlot! Evolution of color and M/L V 2.5Z Salpeter 0.2Z Chabrier, Kroupa Bruzual and Charlot 2003
Stellar population synthesis model! Bruzual and Charlot! Comparison with observations of star clusters CMD of open cluster Bruzual and Charlot 2003 CMD of globular cluster
Stellar population synthesis model! Bruzual and Charlot! Spectral evolution! FUV rise until 13Gyr caused by low-mass post-agb stars! 0.1-1Gyr: stengthening of all Balmer lines from Ha (6563A) to the Balmer continuum limit! 0.1-1Gyr: Balmer break (continuum limit at 3646A) evolved into 4000A break (arising from the prominence in cool stars of a large number of metallic lines bluewards of 4000A, sensitive to bursts during the past 1-2 Gyr) SSP model Gyr Bruzual and Charlot 2003 Model fits of SDSS EDR galaxies
Stellar population synthesis model! Bruzual and Charlot! Spectral evolution of stellar populations at ages between 1x10 5 and 2x10 10 at a resolution of 3A across 3200 to 9500A for a wide range of metallicities, lower resolution from 91A to 160micron at lower resolution.! Provide integral given SFH! Multi-component dust model (Charlot et al. 2000)! Constrain physical parameters! Other synthesis code! PEGASE! STARBURST99 Bruzual and Charlot 2003
SED fitting! Kauffmann et al. 2003 (MPA-JHU DR4)! Construct a library of models from B&C 03, Kroupa IMF! Prior: Monte Carlo realization of different SFH! + superimposed random bursts! Correct for attenuation from Ha/Hb! Z uniformly distributed from 0.25 to 2 solar! Fit to D(4000) and H (4102A) absorption line! Salim et al. 2007 (MPA-JHU DR7)! A library constructed from B&C 03, 10 5 model SEDs, Chabrier IMF! Cont SF + burst (A=M burst /M cont ~[0.03-4], duration~[30, 300]Myr)! V ~[0, 6], ~[0.1, 1]! Z ~[0.1, 2] solar! Fit to u, g, r, i, z, NUV, FUV
SED fitting! Bell et al. 2003! Data! 22,697 galaxies from SDSS EDR, 13<r<17.5! 12,085 matched to 2MASS XSC, 3965 to 2MASS PSC (2 )! K-band: bright NIR sky background, 7.8s exptime, bias against LSB! SED fitting! A gird constructed from PEGASE, diet Salpeter IMF! SFHs vary exponentially with time! A grid of 29 value, including (increasing), 1, 0, +! Assume no internal extinction!! 10 value of Z ~[0.005, 2.5] solar! Fit to u, g, r, i, z, K
M/L optical color relation! Bell et al. 2003! Tight correlation given smooth SFHs! Science justification (Bell et al. 2001)! Intrinsic scatter (~20%)! Metallicity! Aging: ~0.05 dex for an age difference of ~3 Gyr! Systematic uncertainty (~25%, 0.1dex?)! Dust cancel out within 0.1 0.2 dex! A dimming of (1.6, 1.3, 0.3) mag from face-on to edge-on in grk for massive disk galaxies! Bursts of SF~10% offset to slightly lower M/L ratio at a given color Bell et al. 2003 average maximum Kauffmann et al. 2003 Bell et al. 2001
Current stellar mass estimation! ALFALFA catalog: agc, ra, dec, z, code! diatance_catalog: distance, M HI! crosstable: objid! Query to Sloan DR7! Petro and Model magnitudes with error in 5 bands! expab_r
Current stellar mass estimation! Correct for Galactic extinction! Given (ra, dec), get E(B-V) from DIRBE map! Schlegel et al. (1998)! K-correction! Blanton's code 'sdss_kcorrect! Inputs: z, 5 bands with error
Current stellar mass estimation! Correct for Internal extinction (Giovanelli et al. 95)! I = r - 1.2444x(r - i) - 0.382! M/L r g-r color relation (Bell et al. 2003)! M/L r = -0.306 + 1.097 x (g r)
Current stellar mass estimation! Compare with MPA-JHU stellar mass catalog (DR7)! Only specobj in their catalog (~80%)! Random uncertainty! Extreme outliers! Mismatch! Problematic mags! Larger scatter in low M! Poor photometry! Distance assignment! Systematic discrepancy! Burst of SF! Internal extinction! IMF! Future work: remove trend, SED fitting