Interpreting Galaxies across Cosmic Time with Binary Population Synthesis Models Elizabeth Stanway Warwick (UK) with J J Eldridge (Auckland, NZ) and others
Putting Warwick on the Map WARWICK! London @WarwickAstro
Population Synthesis Models Studying distant, small or faint galaxies often means interpreting very incomplete data. We may only have broadband photometry, or a few strong emission lines. Interpreting these requires context from: Comparison populations Good theoretical models
Stellar Population Synthesis Stars
Stellar Population Synthesis Stars Gas & Dust in Galaxy Intergalactic Gas Clouds Atmosphere & Telescope
Stellar Population Synthesis Stars Gas & Dust in Galaxy Intergalactic Gas Clouds Parameters: Ages, Metal content, Masses & Types Geometry Number, Distribution Atmosphere & Telescope
So what s missing Sana, de Mink et al. (2012)
Binary Population And Spectral Synthesis 15,000 detailed stellar evolution models. Can be used to study a broad range of astrophysical systems: stars, supernovae, clusters and galaxies. BPASS.AUCKLAND.AC.NZ Next-gen models (>100,000 models, more masses, more metallicities, rotation?) hopefully 2015-2016ish... (Eldridge & Stanway 2009, 2012)
Ionising Spectra Binary pathways lead to more massive and WR stars in a stellar population at late times The resulting spectrum is hotter with a bluer ultraviolet spectrum Plot from Steidel et al 2014
Ionising Spectra 1 The stellar spectral slope (before nebular effects) from SSP models at log(age/yr)=7.5 0 BPASS (continuous) UV Slope, -1 BC03-2 BPASS (instant) -3 0.000 0.005 0.010 0.015 0.020 0.025 Metallicity, Z
Emission Line Diagnostics The ratio of optical emission line strengths provides information on the hardness of the ionizing radiation field 1.5 z>2 galaxies 1.0 log 10 (OIII/Hbeta) Log ([OIII] / Hβ) 0.5 0.0-0.5-1.0 8 9 10 11 log 10 (Mass) Log (Mass) SDSS galaxies Masters et al 2014 Schenker et al 2013
Emission Line Diagnostics The ratio of optical emission line strengths provides information on the hardness of the ionizing radiation field log 10 (OIII/Hbeta) Log ([OIII] / Hβ) 1.5 1.0 0.5 0.0-0.5-1.0 Local Analogues to z>4 galaxies 8 9 10 11 log 10 (Mass) Log (Mass) SDSS galaxies Stanway et al, 2014, MNRAS 444 3466
Emission Line Diagnostics The ratio of optical emission line strengths provides information on the hardness of the ionizing radiation field log 10 (OIII/Hbeta) Log ([OIII] / Hβ) 1.5 1.0 0.5 0.0-0.5-1.0 Local Analogues to z>4 galaxies See talk by Steph Greis on Thursday! 8 9 10 11 log 10 (Mass) Log (Mass) SDSS galaxies Stanway et al, 2014, MNRAS 444 3466
Emission Line Diagnostics 1.5 1.0 z>2 galaxies Local Analogues log 10 ( [O III]/H ) Log ([OIII] / Hβ) 0.5 0.0-0.5-1.0 0.5 1.0 1.5 2.0 2.5 3.0 log 10 (EW H ) Log (Hβ EW) Stanway et al, 2014, MNRAS 444 3466
Emission Line Diagnostics 1.5 1.0 z>2 galaxies Local Analogues log 10 ( [O III]/H ) Log ([OIII] / Hβ) 0.5 0.0-0.5-1.0 0.5 1.0 1.5 2.0 2.5 3.0 log 10 (EW H ) Log (Hβ EW) Stanway et al, 2014, MNRAS 444 3466
Emission Line Diagnostics z>2 galaxies binary - instant 1.0 0.020 0.008 Z log 10 ( [O III]/H ) Log ([OIII] / Hβ) 0.5 0.0 0.001-0.5-1.0-0.8-0.6-0.4-0.2 0.0 0.2 0.4 log 10 ( [O II]/[O III] ) Log ([OII] / [OIII]) Local Analogues Stanway et al, 2014, MNRAS 444 3466
Emission Line Diagnostics 1.5 1.0 Binary, Z=0.08, instantaneous burst log(gas density) -4-3 -2-1 0 1 2 3 4 log 10 ( [O III]/H ) Log ([OIII] / Hβ) 0.5 0.0-0.5-1.0 6.0 6.5 7.0 7.5 8.0 8.5 log 10 (Age in years) Log (Age) Stanway et al, 2014, MNRAS 444 3466
Reconsidering line classifications 1.0 0.8 Baldwin, Phillips & Terlevich 1981, Kauffmann et al 2003 0.6 log 10 ( [O III]/H ) 0.4 0.2 0.0 Star Forming AGN -0.2 Composite -0.4-1.0-0.8-0.6-0.4-0.2 0.0 0.2 0.4 log 10 ( [N II]/H )
Reconsidering line classifications 1.0 0.8 0.020 0.008 0.6 log 10 ( [O III]/H ) 0.4 0.2 0.0 Star Forming AGN -0.2 Composite -0.4-1.0-0.8-0.6-0.4-0.2 0.0 0.2 0.4 log 10 ( [N II]/H )
GRB Host 080517 GRBs are the most luminous explosions in the Universe They (probably) end the lives of very massive stars GRB 080517 occurred at unusually low redshift (z=0.09) Its spectrum shows emission lines (i.e. recent star formation) (Stanway et al 2015 MNRAS 446 3911 Stanway et al 2015 ApJ 798 L7) This may be triggered by a neighbour at the same redshift 12 10 F / x 10-16 ergs/s/cm 2 /A 8 6 4 2 0 4000 5000 6000 7000 Wavelength/A
GRB Host 080517 FUV NUV g r i J H Ks W1 W2 W3 W4 GRB 080517 occurred at unusually low redshift (z=0.09) It also appears to be extremely red in the infrared (out to 22µm) Based on radio, emission lines, UV continuum and infrared, we estimate a star formation rate of ~16 M /yr
GRB Host 080517 10-1 Maraston (2005) Stellar Population models + Dust Best single model At least one dusty component Flux / Jy 10-2 10-3 10-4 10-5 10 3 10 4 10 5 10 6 Wavelength / Angstroms Stanway et al 2015 MNRAS 446 3911
GRB Host 080517 Flux / Jy 10-1 10-2 10-3 10-4 10-5 BPASS Stellar Population models + Dust 500 Myr Burst A V = 0.16 ± 0.02 Log (M/M ) = 9.58 ± 0.16 0.1% of mass in young stars Best fit single model Additional star forming component 10 3 10 4 10 5 10 6 Wavelength / Angstroms Stanway et al 2015 MNRAS 446 3911
Plans for Development Modifications to stellar populations: Secondary star treatment White dwarfs and accretion Building multiple stellar populations Metallicity evolution
Plans for Development Modifications due to wider environment Gas geometries and densities Radio continuum from supernovae and their remnants Self-consistent treatment of dust emission in infrared Star formation histories and metallicities
Conclusions Binary evolution pathways are particularly important for massive stars and young starbursts, and for low metallicities These are particularly important at high redshift and in the rest-frame UV. Incorporating these in stellar population synthesis models can match observed properties of galaxy populations Our BPASS models include detailed binary models bpass.auckland.ac.uk These are under ongoing development
Conclusions Binary evolution pathways are particularly important for massive stars and young starbursts, and for low metallicities These are particularly important at high redshift and in the rest-frame UV. Incorporating these in stellar population synthesis models can match observed properties of galaxy populations Our BPASS models include detailed binary models watch this bpass.auckland.ac.uk These are under ongoing development space!
Case Study: z=3 Spectra C IV He II C IV He II Fitting the Shapley et al (2003) composite, we find good matches to the stellar component at low metallicities (Eldridge & Stanway, 2012, MNRAS, 419, 479)
Case Study: z=3 Spectra BPASS fitting reveals the variety of z~2-3 galaxies: z=2-3 galaxy BPASS metallicity Reduced [C/O]? Needs QHE? Previous metallicity Previous [C/O] Composite 7.6-8.5 7.7-8.7 0.2 BX 418 7.6-8.2 7.7-8.1 0.2 8 o clock arc Cosmic Eye 7.6-8.2 8.3-8.6 8.2-8.5 ~8.3 cb58 8.2-8.5 ~8.4 Cosmic Horseshoe 8.2-8.5 ~8.4 (Eldridge & Stanway, 2012, MNRAS, 419, 479)
Case Study: Core-collapse supernovae Supernova Observations Single stars Mix Binaries Type II 71±9% 85% 71% 63% Type Ib/c 29±6% 15% 29% 37%
Case Study: Core-collapse supernovae Single stars Binaries Eldridge et al. (2013, 2014)
Extended LBA sample 1.5 1.0 log 10 (OIII/Hbeta) 0.5 0.0-0.5-1.0 8 9 10 11 log 10 (Mass)