Star-formation histories
Sorour Shamshiri
with
Peter Thomas
and thanks to
Bruno Henriques
Rita Tojiero
Star- Formation Histories
Outline:
 VESPA
What is VESPA
What is the result?
 Evolution of star-formation history time-bins
 Comparison SFH between SAMs and VESPA
For different redshits
 Conclusions
What is VESPA
• An analysis to the Sloan Digital Sky Survey final spectroscopic
data release of MGS and LRG sample.
• The result is a catalogue of star formation and metallicity
histories, dust content and stellar masses of nearly 800,000
galaxies.
• VESPA is intrinsically model dependent, including the SSP
modeling, IMF or dust modeling.
Method
• VESPA solves the following problem:
• Sλ(t,Z) is the luminosity per unit wavelength of a
single stellar population of age t and metallicity Z,
per unit mass .
VESPA’s bins
• In HR bin, it is assumed a constant star formation rate
• For low-resolution , a decaying star formation history is used.
Model
• Initial mass function
– BC03 models: a Chabrier initial mass function
– Maraston (M05): with a Kroupa initial mass function
• Dust model:
– One_parameter
– Two_parameter
TBC= 0.03Gyr
VESPA: BC03 vs M05
VESPA: dust models
L-Galaxies: evolution of star-formation
history time-bins
Picture credit: Rob Yates
Comparison of models with VESPA
SFH for different redshifts
Conclusions
• We presented Star-Formation Histories for two different
versions of the L-Galaxies SA model and compared them with
observations from VESPA.
• The Guo11 and HWT12 models bracket the VESPA results:
HWT12 forms fewer stars at early times (ie high redshift) but a higher starformation rate at all subsequent times.