9/19/2014 Claus Leitherer: Lyman Continuum Leakage 1 Lyman Continuum Leakage in the Local Universe Claus Sanch Tim Janice Sally Roderik Leitherer Borthakur Heckman Lee Oey Overzier STScI JHU JHU STScI UMich ON

9/19/20142 Claus Leitherer: Lyman Continuum Leakage

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 3 o Can normal (non-AGN) galaxies account for the ionizing photons required for re-ionization? o Since H I is very effective in absorbing Lyman continuum photons, only a small fraction of the available photons will escape from the galaxy. o What is f esc ? o Cosmological models suggest f esc ≈ 20% is needed for reionization. Science Question

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 4 o Local galaxies are not necessarily representative of the galaxy population at high redshift. o However, they are excellent training sets for studying which factors determine f esc. Galaxy Sample

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 5 Sample 1: starburst galaxies with outflows at z ≈ 0 Lyman Continuum Leakage Candidates Sample 2: Lyman-break analogs with weak Hα emission at z ≈ 0.2 Zackrisson et al. (2013)

Lyman Continuum Escape in Local Starburst Galaxies with Outflows o Pilot study as a proof of concept; therefore the sample is driven by instrument requirements o o Preexisting UV spectra with F(1100) > 1  10  14 o o v > 10,000 km s  1   > 30 Å o o Presence of O stars from UV spectra 9/19/20146 Claus Leitherer: Lyman Continuum Leakage

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 7 o The three galaxies were observed before with FUSE (Pellerin & Robert 2007; Grimes et al. 2009; Leitet et al. 2013) o Several studies specifically targeted the Lyman continuum Galaxy Sample

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 8 Grimes et al. (2009): Tol

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 9 o ISM lines in FUSE spectra are blueshifted o Large-scale outflows driven by SNe and stellar winds o Correlates with SFR/M o Inhomogeneous ISM creates favorable conditions for Lyman continuum escape

9/19/ Claus Leitherer: Lyman Continuum Leakage

9/19/ Claus Leitherer: Lyman Continuum Leakage

9/19/ Claus Leitherer: Lyman Continuum Leakage

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 13 o Spectral region around the Lyman break o Corrected for intrinsic reddening o Restframe o ~35 Å of Lyman continuum o Geocoronal Lyman lines denoted o Dashed: model o T=20 Myr, const. SF, Kroupa IMF, Geneva models with rotation

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 14 Lyman continuum escape fractions o Total escape fractions are of order 1% or less o Consistent with optical depth and covering factor suggested by CII 1036

Local Lyman-break Analogs as Candidates for Leakage o Heckman et al. (2005): GALEX discovery of a sample of UV-bright galaxies with properties similar to those of LBG’s  Lyman-break analogs (LBA’s) o L ≈ L o L ≈ L ⊙ o o SFR ≈ 10 1 – 10 2 M ⊙ yr  1 o o z ≈ 0.2 9/19/ Claus Leitherer: Lyman Continuum Leakage

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 16 Overzier et al. (2009): HST UV+ optical imaging  actively star- forming galaxies

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 17 o Heckman et al. (2011): HST COS spectroscopy of a subsample with compact cores

Properties of J o o Hα derived SF rate significantly lower than UV+IR derived rate  density bounded or inhomogeneous? o o Lyα profile shows blueshifted emission; models suggest low  due to small covering factor o o IS absorption lines are optically thick, yet have residual intensity  picket-fence model with covering factor of 60% 9/19/ Claus Leitherer: Lyman Continuum Leakage

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 19 o COS spectrum of J (Borthakur et al. 2014) o Young starburst dominated by OB stars; consistent with profile fits to CIV 1550, NV 1240, and OVI 1035 o Predict the expected Lyman-break from models  absolute f esc

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 20 Borthakur et al. (2014): Borthakur et al. (2014): Comparison of the observed break to models Comparison of the observed break to models Dashed: /912 - Dashed: /912 - Observed: 0.9 dex Observed: 0.9 dex Model: 0.5 dex Model: 0.5 dex f esc = 0.37± 0.05 f esc = 0.37± 0.05 Accounting for dust: f esc ≈ 1% Accounting for dust: f esc ≈ 1%

Take-away Points o COS is well suited for Lyman continuum observations in the local universe. o Local star-forming galaxies are excellent training sets studying Lyman leakage. o The observed local star-forming galaxies have dust corrected escape fractions of 1% or less. o In the absence of dust absorption, the galaxies would have f esc compatible with the value required for reionization 9/19/ Claus Leitherer: Lyman Continuum Leakage

Back-up Slides 9/19/ Claus Leitherer: Lyman Continuum Leakage

Reliability of the Models o Model predicts an intrinsic Lyman break of ~0.4 dex for a standard population o Kroupa IMF, constant star formation, T=20 Myr, Geneva evolution models with rotation, spherically extended, expanding, blanketed non-LTE atmospheres o How do model assumptions and uncertainties affect the prediction? 9/19/ Claus Leitherer: Lyman Continuum Leakage

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 24 Varying the duration of the SF episode has little effect for T>5 Myr as massive stars have reached equilibrium

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 25 Varying the IMF exponent between 1.6 and 3 changes the flux level by a factor of ~100 but has a small effect on the break itself

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 26 Extended model atmospheres accounting for winds decrease the break by up to 0.15 dex

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 27 Evolution models with rotation have hotter, more luminous stars and increase the Lyman continuum flux by ~0.2 dex

9/19/2014 Claus Leitherer: Lyman Continuum Leakage 28 Chemical composition has a surprisingly small influence due to the compensating effects of atmospheres and evolution models