Stellar Population Synthesis: Which Uncertainties Matter?

Charlie Conroy

w/ Jim Gunn(Princeton)

1. Stellar evolutiono e.g., mass-loss, rotation, binaries,

horizontal branch, blue stragglers, WR stars, TP-AGB stars

2. Stellar spectral libraries3. IMF4. Dust attenuation

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.SPS Ingredients

• Thermally-pulsating AGB stars– Double shell burning– Important especially for

ages of ~0.5-2 Gyr– Carbon star production

• Metallicity-dependent– Dynamic atmospheres– Very uncertain

• How can we constrain these uncertainties??

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.An Introduction to TP-AGB starsM

ara

ston

20

05

with TP-AGB

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.TP-AGB stars in the LMC

• Compare SSP predictions to colors of `super-star clusters’ as a function of cluster age

• Latest Padova tracks produce near-IR colors too red

• BaSTI tracks are OK

• Flexible SPS allows simple re-calibration of Padova tracks to fit the LMC cluster data

What about

calibration at other Z??

Co

nro

y & G

un

n 2

01

0

• Post-starburst (“K+A”) are galaxies that have a strong A star component in their spectrum, without H emission– Implies a significant population of ~0.3-1 Gyr old stars

• Excellent testbed for TP-AGB stars– No stochastic effects– Model testing at ~solar Z

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

TP-AGB stars in post-starburst galaxies: I

Co

nro

y & G

un

n 2

01

0

FSPS+PadovaBruzual & Charlot 2003Maraston 2005

Post-starbust spectrum

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

TP-AGB stars in post-starburst galaxies: II

Near-IR spectra of post-starburst galaxies can jointly constrain: 1. the overall luminosity in the TP-AGB phase2. the presence of carbon stars

Other near-IR features such as VO (1.06m) and H2O (1.33m) will provide additional constraints on the fraction of carbon stars

Near-IR data currently being taken for a sample of post-starburst galaxies from SDSS (w/ Mariska Kriek)

Predictions for Zsol coeval populations

Dn4000=1.2 (t=0.25 Gyr)

D n4000=1.3 (t

=0.44 Gyr)

Dn4000=1.4 (t=

0.79 Gyr)

• Attenuation curve depends on:– Size distribution of grains

• Metallicity• Intensity of UV radiation

– Geometry

• In general, we do not know what the attenuation law “should” be

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.Dust Attenuation Curves

• UV bump at 2200A is an important feature in MW and LMC extinction curves, and shows considerable variation amongst environments – Not seen in local starbursts (Calzett et al. 1994), nor in the SMC– seen in z~2 star forming galaxies, (Noll et al. 2009)

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Dust in disk-dominated, star-forming galaxies

face-on edge-on

• Consider a sample of disk-dominated star-forming galaxies at z<0.05– GALEX+SDSS+2MASS

• Consider average photometric properties in bins of inclination– Trends with inclination will

depend only on dust attenuation curve

• SEDs of star-forming, disk-dominated galaxies at z<0.05– GALEX+SDSS photometry as a function of inclination

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.UV dust attenuation at z~0

Conroy, Schiminovich, & Blanton 2010

• Clear signature of the UV bump– First detection at low redshift– Based on stacking several

hundred galaxies per inclination bin, so must be generic

– Implies that dust corrections in the UV is significantly more complicated than traditionally assumed

UV bump

• Despite impressive progress in SPS model-building, significant uncertainties remain

o However, it is possible to constrain the uncertain SPS inputs directly from observations of galaxies

• Two Examples:o TP-AGB stars in post-starburst galaxieso Dust attenuation curves in disk-dominated star-forming

galaxies

• Additional Directions:o IMF in passive Ellipticals

• Wing-Ford band at 9910A is sensitive to the dwarf/giant ratio

o High mass-loss rates at super-solar metallicity?• If (some) stars bypass the HB/AGB phase it should be

detectable in the integrated light

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.Summary