1. Lyman Break Galaxies, Dropouts, and Photometric Z ----------------------------- Because galaxies are made of stars, we start with spectra of stars…

2. Hot O, B and A type stars. Steeply rising continua to the blue (Surf T ~ 10-30K). Dominated by absorption lines of Hydrogen (n=2 gr state). The Balmer break at 3646 angstrom marks the termination of the hydrogen Balmer series and is strongest in A-type stars. The break strength does not monotonically increase with age, but reaches a maximum in stellar populations of intermediate ages (0.3 - 1 Gyr). For very high redshift galaxies, the Lyman break (n=1) may be used.

3. Cool stars: F, G and K type. Hydrogen less prominent. Ionized metals begin to appear (H and K lines of Ca II 3933, 3968A). The 4000 angstrom break arises because of an accumulation of absorption lines of mainly ionized metals. As the opacity increases with decreasing stellar temperature, the 4000 angstrom break gets larger with older ages, and it is largest for old and metal-rich stellar populations.

4. Applying this to Galaxies The Balmer break and the 4000 angstrom break are often treated as one feature, due to their similar locations and the fact that they partially overlap. However, the breaks originate from different physical processes and behave differently as populations age. Lyman break galaxies are typically starbursting (containing young hot stars) galaxies, and are easily found at great distances by drop outs in deep photometric searches Lyman Break Galaxies LyAlpha rest =1215A, obs at 5000A

5. I-drop out galaxy, (LyA = 7800, z ~ 5.4)

6. Determining galaxy properties with broadband photometry Best-fitting Bruzual & Charlot model (dark line) for SBM03#1: an exponentially decaying star formation rate with Tau = 300 Myr, viewed 640 Myr after the onset of star formation. The stellar mass is 3.4 x 10 10 M. For this galaxy, the redshift was already known..

7. Multi-epoch star formation. The best-fitting two- component stellar population model (Salpeter IMF) for SBM03#1: a dominant 450-Myr population of mass 3.6 x 10 10 M, with some ongoing star formation activity (a burst for the last 10 Myr involving 0.7 per cent of the stellar mass).

8. Accuracy of photometric Z with/without spectra Broadband: BVIzJHK, Light gray is synthetic fit to photometry only. (NOTE: Red shift WAS known through spectral emission lines). Dark grey model uses both Spectra (Pink markings) and photometry.

9. Fitting older galaxies

10. Another old galaxy..

11. Purple: fitting the optical- to-NIR broadband photometry by linear combinations of empirical and theoretical galaxy templates (Rudnick). Green: fitting the optical- to-NIR broadband photometry from the Bruzual & Charlot models Pink: NIR continuum (pink spectra), with the optical photometry. Black dashed line: emission-line redshift, if present. Measuring Photometric Redshifts