Massive galaxies at z > 1.5

1. Massive galaxies at z > 1.5 By Hans Buist Supervisor Scott Trager Date 22nd of june 2007

2. Outline • Introduction • Measuring distant galaxies • Lyman break method (“drop outs”) • Red galaxy method • Submillimeter method • Results from surveys • Discussing the results

3. Introduction

4. Introduction • How to measure distant galaxies? • Spectroscopy gives distance • Slow and expensive • In the recent years, new methods have been developed: • Lyman break method (“drop outs”) • Red galaxy method • Submillimeter method

5. Lyman break method • Hydrogen gas in the galaxy causes a cut-off at 912 nm • Redshifting causes the cut-off to appear in optical wavelengths (z ~ 3) • The galaxy seems to disappear when using the right filters • True distance measured by spectroscopy

6. Lyman break method

7. Image from the Palomar Hale Telescope showing UV dropouts

8. Red galaxy method • Depends on the Ballmer break (400 nm) • Found by using J-K>2.3 • Corresponds to U-V>0

9. Adelberger et al., 2004

10. Submillimeter method • Local universe: • Many galaxies emit in submm due to dust • More starformation seems to cause more dust • Much dust will cause the UV to be obscured • Submm galaxies would not be found using the Lyman break • Distant galaxies: • Metal rich ISM thought to be present • Expected to find submm galaxies

11. M82, Subaru Telescope, Japan

12. Results

13. Results for Lyman break • Lyman Break Galaxies (LBGs) • Comoving space density roughly half of current high luminosity galaxies • Spectra similar to z~0 SF galaxies: • Flat continuum • Weak or absent Ly-α emission • Prominent high-ionization stellar lines • Strong interstellar absorption lines

14. Results for Lyman break • Lyman Break Galaxies (LBGs) • Star forming rate several 10’s of solar masses per year • Show spiral arm or irregular features • Mass around 1010 solar masses

15. Results for Red galaxy method • Distant Red Galaxies (DRGs) • Quite different from LBGs: Forster Schreiber et al, ApJ, in press (astro-ph/0408077)

16. Results for Red galaxy method • Distant Red Galaxies (DRGs) • 24 μm used as indicator for starformation (SF): • 45% is detected in 24 μm • 45% is not detected in 24 μm but has other SF spectral features • 10% is not detected and has no other SF spectral features

17. DRG galaxies High starformation galaxies, obscured by dust Low starformation galaxies Old galaxies, no starformation (quiescent DRGs) Results for Red galaxy method

18. Results for Red galaxy method • DRG Starburst galaxies • Starforming rate (SFR): 150 solar mass per year • 1011 solar masses • DRG quiescent galaxies • More then 1 Gyr old • Contribute at most 10% of the total mass at high z

19. Discussion of results / Conclusion

20. Madau et al., 1996

21. Discussion of results • From the LBGs: • At around z ~ 1-2 a peak in starformation rate • At most 1/2 of the metals formed before z ~ 1

22. Discussion of results • From the LBGs: • At around z ~ 1-2 a peak in starformation rate • At most 1/2 of the metals formed before z ~ 1 • ~ 50% of the stars (=metals) are in spheroid components (i.e. galaxy halo, ellipticals) • These components formed quick (< 1Gyr) and a long time ago

23. Discussion of results • It’s very likely that the LBGs are what later becomes the spheroid component of massive spiral galaxies • Masses seem to fit • SFR is low enough to prevent the galaxy from converting its gas completely into stars and becoming an E or S0 • Timescales seem to be correct as well

24. Discussion of results • From the highly obscured DRGs: • Much higher SFR and therefore run out of gas quickly (less then a Gyr or so) • Very likely to become the big E and S0 galaxies at z ~ 0 • Masses also are 1011 Msolar

28. Discussion of results • From the qDRGs: • Are already early types and likely to remain that way • From the moderate SFR DRGs: • Probably end up as ellipticals and S0’s as well. (Are they comparable to current-day spirals?)

29. Early type galaxies Spirals DRG LBG

30. The end Questions?