1. Current Topics: Lyman Break Galaxies - Lecture 4 Current Topics Lyman Break Galaxies Dr Elizabeth Stanway (E.R.Stanway@Bristol.ac.uk)

2. Current Topics: Lyman Break Galaxies - Lecture 4 Topic Summary Star Forming Galaxies and the Lyman-  Line Lyman Break Galaxies at z<4 Lyman Break Galaxies at z>4 Lyman Break Galaxies at z>7 Reionisation, SFH and Luminosity Functions

3. Current Topics: Lyman Break Galaxies - Lecture 4 Ground vs Space-Based Surveys HST can reach objects 0.7-1mag (2-3 times) fainter in the same length of time Ground-based 8m telescopes have larger fields of view (by a factor of about 4) So which is more efficient at finding high-z galaxies? The faint end of the Schecter Luminosity function (L<<L*) can be approximated as power law (i.e. N(L)  L  dA dz) So N 8m /N HST =(L 8m /L HST )  (A 8m /A HST )  If  is steeper than about -1.2, then HST always wins (I.e depth is more useful than area) HST has higher resolution, but 8m telescopes are ‘cheaper’

4. Current Topics: Lyman Break Galaxies - Lecture 4 Surveys of z>4 LBGs GOODS (The Great Observatories Origins Deep Survey) Hubble Space Telescope V-drops I-drops Z-drops SDF/SXDFSubaru 8m telescope V-drops R-drops I-drops BDF/ERGSESO Very Large Telescopes (8m) R-drops I-drops Z-drops Cluster Lensing Surveys Keck / HST I-drops Z-drops J-drops UKIDSSUK Infrared Telescope (4m) I-drops Z-drops Y-drops J-drops

5. Current Topics: Lyman Break Galaxies - Lecture 4 Stellar populations As at z=3, most information is derived from SED fitting. Unconfused Spitzer data is essential for this at z>4 Detailed results are model dependent General results are model independent Verma et al, 2007

6. Current Topics: Lyman Break Galaxies - Lecture 4 Old Stars at z=6 Sometimes both a new starburst and an old population are needed to fit a galaxy As at z=3, some stars seem as old as the universe, but time scales are shorter, so the constraints are tighter SFR  e -t/  Eyles et al, 2005

7. Current Topics: Lyman Break Galaxies - Lecture 4 Old Stars at z~6 Sometimes both a new starburst and an old population are needed to fit a galaxy As at z=3, some stars seem as old as the universe, but time scales are shorter, so the constraints are tighter z=5.83 Too Young for Ly  line Older than universe

8. Current Topics: Lyman Break Galaxies - Lecture 4 Comparisons with z=3 Using a z~5 HST v-drop sample GOODS field => extremely deep Using an SMC (i.e. low metallicity) extinction law Using Spitzer data

9. Current Topics: Lyman Break Galaxies - Lecture 4 Comparisons with z=3 Age: At z=3, age~300Myr At z=5, age~30Myr If Z=Z , then age~3Myr  Galaxies are younger (Verma et al 2007) Log (Age) fraction

10. Current Topics: Lyman Break Galaxies - Lecture 4 Comparisons with z=3 Stellar Mass: At z=3, mass~10 10 M  At z=5, Mass ~ 2x10 9 M  Independent of metallicity  Galaxies are smaller (Verma et al 2007) Log (Mass) fraction

11. Current Topics: Lyman Break Galaxies - Lecture 4 Comparisons with z=3 Star Formation Rate: At z=3, SFR~50M  /yr At z=5, SFR ~ 50M  /yr If Z=Z , SFR~600M  /yr => Galaxies are forming stars at about the same rate Log (SFR) fraction

12. Current Topics: Lyman Break Galaxies - Lecture 4 Comparisons with z=3 Dust: At z=3, Av~0.6 mags At z=5, Av ~ 0.3 mags If Z=Z , Av~0.6 mags => High z galaxies are less dusty Av fraction

13. Current Topics: Lyman Break Galaxies - Lecture 4 Sizes and Morphologies Galaxies at high-z have a smaller projected size. Most of this is due to evolution in physical size rather than angular scale factor Up to z~5, the size evolution is as expected for a fixed mass Morphologies are often irregular and complex Ferguson et al 2004

14. Current Topics: Lyman Break Galaxies - Lecture 4 Sizes and Morphologies Galaxies at high-z have a smaller projected size. Most of this is due to evolution in physical size rather than angular scale factor Up to z~5, the size evolution is as expected for a fixed mass Morphologies are often irregular and complex

15. Current Topics: Lyman Break Galaxies - Lecture 4 Spectroscopy at z~5 Spectroscopy at z~5 is challenging, but not impossible In 5 hours on an 8m telescope get good S/N on lines and reasonable detections of continuum flux The night sky is growing brighter but is still reasonable

16. Current Topics: Lyman Break Galaxies - Lecture 4 Spectroscopy at z~6 Spectroscopy at z~6 is extremely difficult Sources are typically 1 mag fainter at z=6 than at z=5 Continuum is only detected in exceptional or lensed galaxies 35 hours with Gemini 6 hours with Keck

17. Current Topics: Lyman Break Galaxies - Lecture 4 The Rest-Ultraviolet Rest-UV slope is an age indicator: –young=blue, old=red But many z~5 galaxies seem too blue Line emitters No Ly  lines Too Blue

18. Current Topics: Lyman Break Galaxies - Lecture 4 The Rest-Ultraviolet Steep Rest-UV slope (blue of f  -2 ) could indicate zero age, Pop III, top-heavy initial mass function … => New physics! Interpretation still unclear Line emitters No Ly  lines Too Blue

19. Current Topics: Lyman Break Galaxies - Lecture 4 Lyman-  Equivalent Widths i’-drops (DEIMOS) At z~5 the distribution of Lyman-a line strengths is similar to that at z~3 At z~6 see more high EW lines - selection function? More hot stars? Dust effects? New physics? 50% of z>5 sources have EW>0Å 25% have EW>30Å z~6 z~5

20. Current Topics: Lyman Break Galaxies - Lecture 4 Other spectral lines and outflows Stacking together ~50 z~5 galaxies, can start to see other lines: CIV, SiIV and OI are starting to be visible Velocity offsets => similar winds to z~3 Work still in progress! SIVOI

21. Current Topics: Lyman Break Galaxies - Lecture 4 Other spectral lines and outflows In a few lensed cases, can identify lines in individual spectra This example is 6x the typical z~5 LBG brightness It is also lensed! Strong interstellar lines No Ly  => older than typical, more dusty or more evolved Psychotic cases like this can’t really describe the whole population Dow-Hygelund et al, 2005

22. Current Topics: Lyman Break Galaxies - Lecture 4 Non-LBGs at z=5-6 As at z=3, LBGs don’t show the whole picture at z=5 Some star forming sources are going to be too faint to be detected as LBGs –Narrowband detected galaxies (LAEs) –Lensed galaxies –GRB Host galaxies Some galaxies won’t be star forming –Sub-mm galaxies –DLAs –Molecular Line Emitter galaxies

23. Current Topics: Lyman Break Galaxies - Lecture 4 The Whole Picture at z=5? How many galaxies at these redshifts are UV-dark? Searching z=5 LBG clusters for UV-dark material might be the way forward Initial results are promising - z=5 CO emission detected near z=5 LBGs (Stanway et al, 2008) If typical, similar galaxies could contribute a significant fraction of the total galaxy mass in high- z clusters and a large amount of obscured star formation.

24. Current Topics: Lyman Break Galaxies - Lecture 4 Future Millimeter Observations The Atacama Large Millimeter Array (ALMA) begins commissioning this year It will be fully online by about 2013 It observes at mm and sub- mm wavelengths 80 telescopes at 5000m Will be sensitive to dust emission, CO and other strong emission lines (e.g. [CII]) to very high z

25. Current Topics: Lyman Break Galaxies - Lecture 4 Gamma-Ray Bursts Some star formation will be going on in galaxies too faint to detect as LBGs Where massive stars are forming, some small number can go supernova In certain circumstances, supernovae are associated with extraordinarily luminous, highly beamed flashes of gamma rays These are known as Gamma Ray Bursts (GRBs) and can be used as tracers of low mass star formation At high redshifts, a GRB will show up as a dropout (i.e. selected like an LBG), but will fade rapidly with time The most distant objects known in the Universe are GRBs (z=8.3)

26. Current Topics: Lyman Break Galaxies - Lecture 4 Lensing as a tool at high redshift In rare cases, can use intervening galaxy clusters as gravitational lenses - gives spatial information, boosted signal-to-noise, near-IR spectroscopy 2 known strongly lensed LBGs at z~5 Only provides information on rare sources - not average sources Requires lens reconstruction Swinbank et al (2009) z=4.9

27. Current Topics: Lyman Break Galaxies - Lecture 4 LBGs at z>6 Beyond z=6, the Lyman break moves into the infrared Resolution and sensitivity are poor Need lensing to stand realistic chance of detecting objects from ground NO spectroscopically confirmed galaxies beyond z=6.96 z=6.5 candidate

28. Current Topics: Lyman Break Galaxies - Lecture 4 Lensed LBGs at z>7 z=7.6 candidate galaxy z-drop J-drop 100 Myr old No dust Lensed Bradley et al 2008

29. Current Topics: Lyman Break Galaxies - Lecture 4 HST and WFC3 In 2009 HST was serviced and a new camera was installed: WFC3 This gave HST much better resolution, field of view and sensitivity in the near- infrared Can now effectively extend the LBG technique to higher redshifts Spectroscopic follow-up remains a problem

30. Current Topics: Lyman Break Galaxies - Lecture 4 LBGs at Higher Redshifts WFC3 on HST can find z-drops (z~7), Y-drops (z~8) and maybe J-drops (z~10) but can’t confirm them

31. Current Topics: Lyman Break Galaxies - Lecture 4 LBGs at Higher Redshifts Bunker et al (2009), see also Bouwens+ Oesch+ Castellano+ Wilkins+ etc, etc (About 20 papers in Sep-Dec 2009) z’-drop candidates at z~7

32. Current Topics: Lyman Break Galaxies - Lecture 4 Size Evolution to z>7 Galaxies at z=7 continue to get smaller This scales as size  (1+z) -1.12 ± 0.17, consistent with constant comoving sizes Most z=7 candidates very compact (Oesch et al 2010)

33. Current Topics: Lyman Break Galaxies - Lecture 4 The Rest UV spectral Slope AGN have spectra described by a power law, L    i.e L    In the rest-frame ultraviolet, star forming galaxies also show power- law spectra The slope of the power law depends on the temperature of the emitting source This power law slope can be measured using broadband photometry z’ YJH Magnitude gives the flux in J and H => f J and f H Know the central wavelengths of J and H => J and H L J /L H = f J /f H  ( J      z=7 galaxy

34. Current Topics: Lyman Break Galaxies - Lecture 4 The Rest UV spectral Slope z’ YJH z=7 galaxy AB mag = -2.5 log(f )-48.6- App. mag, defined in f J-H = -2.5 log(f J )-48.6 - (-2.5 log(f H )-48.6)- Colour is  (mag) J-H = -2.5 log (f J /f H ) = -2.5 log ( ( J       - Using spectral index J-H = -2.5 (-  -2) log ( J    Simplifying J-H = 0.16 magnitudes L J /L H = f J /f H  ( J      Example: A source has a spectral slope  =-2.5 - calculate the J-H colour in AB mags, given central wavelengths of 1.2  m and 1.6  m for J and H respectively

35. Current Topics: Lyman Break Galaxies - Lecture 4 Rest-UV Spectral Slope AGN have  ≈-1 at all redshifts Zero-age, star forming galaxies with normal stellar populations have  ≈-2 Dust or age will make this slope redder (i.e. shallower) Within the LBG population the spectral slope is seen to evolve with z => age evolution? Dust evolution? Bouwens et al (2010)

36. Current Topics: Lyman Break Galaxies - Lecture 4 Rest-UV slope at z = 7 - 8 At z~7, candidate galaxies are very blue, particularly faint galaxies  < -3 is very hard to explain with any ‘normal’ (Population II) stellar population Bouwens et al (2010)

37. Current Topics: Lyman Break Galaxies - Lecture 4 Rest-UV slope at z = 7 - 8 Pop III stars are defined as having very low or zero metallicity With no metals, they have fewer ways to emit radiation (i.e. cool down) They can become hotter, and more massive (supported by radiation pressure) Hotter galaxies have bluer spectral slopes Bouwens et al (2010)  < -3 slopes may indicate that z=7 galaxies have very low metallicity

38. Current Topics: Lyman Break Galaxies - Lecture 4 Cosmic Evolution of Star Formation Propertyz=1-3z=5-6z>7 Age~200 Myr~50 MyrMay be younger Massfew x 10 10 M  ~10 9 M  No data Metallicity0.3-0.5 Z  ~0.2 Z  May be very low - Pop III Size (half light radius) 1.5-2 kpc~1kpc scales as comoving ~0.5 kpc M*-21.1z=5 : -20.7 z=5 : -20.2 -19.9? Faint end Slope-1.6may be steeperNo data DustE(B-V)~0.2Probably less dustyNo data Star Formation Rate ~30 M  /yr

39. Current Topics: Lyman Break Galaxies - Lecture 4 Ensemble Properties of LBGs At z=2-4, you can study individual galaxies in detail At z=5-6, and more so at z>7, this becomes much harder Studying an individual galaxy only tells you about its immediate environment By looking about the ensemble properties of galaxies you can study the universe as a whole => observational cosmology By using a common selection method (LBGs), you are comparing like-for-like across cosmic time => Insights into galaxy formation, the star formation histoy of the Universe and Reionisation

40. Current Topics: Lyman Break Galaxies - Lecture 4 Lecture Summary LBGs at z>4 are significantly harder to find than those at z<4 LBGs at z~6 are a lot harder than z~5 With increasing redshift see: –Decreasing metallicity –Decreasing dust extinction –Decreasing age –Decreasing mass These traits extend to z~7-8 Very blue rest-UV spectra are hinting at changes in the nature of star formation But, as at z=3, LBGs are not the whole story