1. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Constraints on Lyman continuum flux escaping from galaxies at z~3 using VLT narrow-band photometry Akio K. INOUE 1, I. IWATA, J.-M. DEHARVENG, V. BUAT, & D. BURGARELLA 1 Laboratoire d’Astrophysique de Marseille, FRANCE; akio.inoue@oamp.fr

2. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Ionization history of the universe Cosmic reionization epoch  End at z~6 (Becker et al.2001)  Start at z~17 (Kogut et al.2003) How to proceed?  What is the main ionizing source; galaxies (stars) or others?  Can the ionizing photons escape from galaxies efficiently? We will discuss the escape of Lyman continuum from galaxies.

3. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Lyman continuum escape Steidel et al.(2001) succeeded in detecting the Lyman continuum photons from galaxies at z~3, whereas all the other attempts could not detect. Spectroscopy was always adopted in the attempts, except for Malkan et al.(2003) who performed a broad-band photometry for z~1 galaxies and succeeded in obtaining the most strict upper limits on the escape fraction of Lyman continuum. Steidel et al.(2001): the composite spectrum of 29 Lyman break galaxies at z~3.4. Lyman limit

4. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Narrow-band photometry  close to the Lyman limit (smaller IGM opacity) very important for high-z galaxies  moderate sensitivity (better than spectroscopy)  select galaxies with an appropriate redshift to avoid any contamination of light above the Lyman limit. The redshift criterion for the OII+44 filter of VLT/FORS is z~3.2. Our approach Lyman limit (z=3.2) Ly 

5. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Observations After the pre-selection of galaxies in the HDF- South based on the photometric redshift catalog of Labbé et al.(2003), we performed the spectroscopy with the VLT/FORS2 to know the accurate redshifts. Because of unexpected systematic errors of the photometric redshifts, only two galaxies with an appropriate redshift were left in our sample. We spent ~11 h exposure (on-source) toward the HDFS field through the narrow-band, OII+44 (central wavelength ~372 nm), filter with the VLT/FORS1.

6. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Observational results HDFS851825 z sp 3.1703.275 OII+44 <27.4<26.6 U 300 <67.8<28.1 B 450 392182 V 606 699405 I 814 860504 HDFS85 HDFS1825 Unit of the photometric data is nJy. ID of galaxies and U, B, V, I photometric data are taken from Casertano et al.(2000). Upper limits are 2- .

7. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Definition of escape fractions Absolute escape fraction: Relative escape fraction: : intrinsic Lyman continuum (LC) flux : LC flux just outside of the galaxy : intrinsic UV flux,: UV flux just outside of the galaxy observed LC flux: observed UV flux: NOTE1: UV wavelength is set to be longer than Ly  to be free from the IGM opacity. NOTE2: f esc,rel is not restricted to less than unity.

8. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Comparison of the data at z~3 galaxiesz sp (F UV /F LC ) obs  LC IGM f esc,rel ref. HDFS853.170>24.41.32<0.46a HDFS18253.275>14.61.99<1.5a LBG composite3.4017.71.500.76b DSF2237+116 C23.319>371.41<0.33c Q0000-263 D62.961>351.04<0.24c FLY99:9573.367>3.54.63...d FLY99:8253.369>184.64...d FLY99:8243.430>124.94...d a: this work, narrow-band (OII+44) photometry; b: Steidel et al.(2001), spectroscopy; c: Giallongo et al.(2002), spectroscopy; d: broad-band (U 300 ) photometry. NOTE1: (F UV /F LC ) int is given by a population synthesis model to calculate f esc,rel. NOTE2:  IGM is calculated by a model of the mean IGM opacity.

9. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Advantages of our approach Narrow-band photometry can put the most strict constraint on the relative escape fraction for normal LBGs.  For individual galaxies, we have reached a similar level of F UV /F LC to the composite spectrum of 29 LBGs by Steidel et al.  Higher sensitivity of the broad-band U are lost by heavier IGM absorption because the effective wavelength in the source rest-frame is as short as ~700A.  Giallongo’s LBGs are ~4 times brighter than ours and Steidel’s.

10. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge To estimate absolute escape fraction Absolute escape fraction is  F LC int and  LC IGM can be estimated by a multi- color SED fitting.  “Physically” based SED fitting method: NOT just a  2 fitting. ISM dust and IGM absorption amounts, age, and SFR can be estimated from B, V, I, K data, assuming dust attenuation law (e.g. Calzetti’s law), IGM cloud number distribution (only functional shape), metallicity (e.g. 40% of solar), and constant star formation history.

11. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Physically based SED fitting A unique solution in  ISM  IGM  can be found from observed B-I and V-I because the significance of the IGM absorption is different between B and V. However, to do that, we have to know the intrinsic spectrum which depends on SFH and metallicity. Assuming a constant SFR, I-K is a good indicator of the age. Metallicity effect is secondary. dust attenuation IGM absorption B-I V-I red: Solar, blue: 1/5 Solar, green: 1/20 Solar metallicity

12. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Fitting results U B V I J HK U B V I J H K OII+44 HDFSF OII obs F OII int  OII IGM f esc 85<27.47521.2<0.12 1825<26.53931.6<0.35 Unit of flux density is nJy and upper limits are 2- . NOTE:  IGM relative to a mean one is estimated by the fitting.

13. September 6—10 2004Starburst 2004 at the Institute of Astronomy, Cambridge Conclusions We did not find any significant escape of Lyman continuum from two Lyman break galaxies (LBGs) at z~3 through the narrow-band photometry with VLT. The two LBGs have a small absolute escape fraction, less than 10—30%. For the moment, the sample size is too small to conclude that many LBGs have a small escape of Lyman continuum. Narrow-band photometry can put a stronger constraint on the escape fraction of individual normal LBGs than spectroscopy and broad- band photometry.