Deriving stellar masses from SDSS

Transcription

1 Deriving stellar masses from SDSS Reference: Bruzual and Charlot 2003MNRAS B Kauffmann et al. 2003MNRAS Salim et al. 2007ApJS S Bell et al. 2003ApJS B

2 Outline! Basic idea! Stellar population synthesis model! SED fitting! M/L optical color relation! Current stellar mass estimation

3 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 ( A, 3A), Pickles (1150A-2.5micron, 5A)! Different in wavelength range, spectral resolution, etc.

4 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

5 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

6 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

7 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

8 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

9 SED fitting! Kauffmann et al (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 (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

10 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

11 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 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 average maximum Kauffmann et al Bell et al. 2001

12 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

13 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

14 Current stellar mass estimation! Correct for Internal extinction (Giovanelli et al. 95)! I = r x(r - i) ! M/L r g-r color relation (Bell et al. 2003)! M/L r = x (g r)

15 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