1. The Optical Sky Background

2. The Optical Sky. I: the V – I band

3. The Optical Sky. II: the R - I band

4. The Optical Sky. III: the I - Z band

5. The Optical Sky. IV: the z – J band

6. The Optical Sky. V

7. The Near-IR Sky Background

8. The Sky OH Emission Lines

9. The Sky OH Emission lines

10. The Near-IR Sky
The traditional J, H and K bands defined by the atmospheric absorption
At some wavelengths, the atmosphere is blocking the radiation. If those wavelengths are crucial, space observations are required

11. Observational tactics

12. Cosmic Volumes. I Luminosity function F(L) = f* • exp(-L/L*) • (L/L*)a
f* ~ to Mpc-3
L* ~ 1011 to 1012 LO or to 1045 erg/sec
a ~ -1.0 to -1.2 (optical);-1.4 to –1.8 (UV)
Luminosity density
L = ∫ dL • L • f* • exp(-L/L*) • (L/L*)a ~ L* • f*

13. Cosmic Volumes. II Maximum Volume Vmax = A • ∫ f(z) • dV(z)/dz • z
A ~ survey area
f(z) survey redshift distribution function
Effective Volume: the volume visible to you using a galaxy with luminosity L
Veff(L) = V(L) = A • ∫ f(z; L) • dV(z)/dz • z
When measuring luminosity function: V(L)/ Vmax
Always remember COSMIC VARIANCE

14. Cosmic Volumes. III At z = 3
1 arcsec ~ 3 kpc (physical) ~ 10.2 kpc (comoving)
10 arcmin ~ 1.8 Mpc (physical) ~ 7.2 Mpc (comoving)
At z=3, dz ~ 1
dR(z=3) ~ 500 Mpc
FWHM = 100 Å corresponds to dz = 0.08 or
DR = 40 Mpc

15. Survey Options Spectroscopy Slit or slitless spectroscopy
Objective prism imaging
Photometry (imaging)
Narrow band filters
Tunable filters
A cost-benefit analysis of any survey designed should be done in light of the desired scientific goals to achieve

16. Emission Line Surveys Lecture 3
Mauro Giavalisco
Space Telescope Science Institute
University of Massachusetts, Amherst1
1From January 2007

17. Observing Strategies: Slit Spectroscopy
dispersed images of targets through slit or slits. Can be blind or targeted (targets pre-selected according to some selection criteria)
PROs:
High sensitivity
Large radial velocity/redshift coverage
Easy selection of spectral coverage
Easy trade off b/w spectral resolution, sensitivity and coverage
CONs:
Very limited spatial coverage
Data acquisition of medium complexity
Data reduction and analysis of medium complexity
Very costly if large volumes of space need to be covered: cost driven by number of individual slit(s)-mask exposures

18. Observing Strategies: Slitless Spectroscopy
dispersed images through a dispersive spectral element (prism, grism, grating). Blind surveys
PROs:
Large spatial coverage
Large radial velocity/redshift coverage
Relatively large spectral coverage
Trade off b/w spectral resolution and coverage
Easy data acquisition
CONs:
Low sensitivity (high background)
Complex data reduction and analysis
Some spatial coverage losses due to spectra overlapping
Exposure times longer than slit spectroscopy

19. Observing Strategies: Narrow-Band Imaging
Photometry or “narrow” band imaging: images through a set of filters selected to measure emission line flux and continuum flux density
PROs:
Large spatial coverage
Spatial mapping of emission line regions
Easy data acquisition
Easy data reduction and analysis
CONs:
Limited spectral (radial velocity/redshift) coverage
Increasing spectral coverage (broader filters) decreases sensitivity
Exposure times longer than slit spectroscopy (but shorter than slitless one)
Accurate measure of continuum costly (several bands needed)

20. Emission-line surveys
Targeted surveys: “a-priory” knowledge of redshift or radial velocity:
Narrow-band imaging:
Best option if coverage of area of sky required. Examples:
Galaxy cluster, supercluster candidates
Slit spectroscopy:
Best sensitivity. Examples:
Galaxies causing QSO or GRB absorption systems

21. Strategy of Emission-line surveys
Blind surveys: no “a-priory” knowledge of redshift or radial velocity:
Narrow-band imaging:
Useful if large volume density of sources suspected and if large sensitivity can be achieved. Examples:
Distant galaxy searches
Slitless spectroscopy:
Good option if high sensitivity can be achieved (e.g. from space). Examples:
Distant galaxies searches
Slit spectroscopy:
Good option if very high sensitivity required and small volumes OK (esp. from ground). Examples:
DLA galaxies (redshift can be highly unconstrained)
host galaxies of faded GRBs

22. Survey Design: Narrow-Band Imaging
Emission line detected as excess flux in in-band images compared to off-band images, which measure continuum flux density (essentially, color selection)
In-band images generally obtained through narrow-band spectral elements (solid-state or Fabry-Perot tunable filters). For broad lines and/or large Wl, medium band elements OK.
Off-band images can be either through narrow-band elements (one required; two preferable) or medium and broad-band ones
Best photometric accuracy reached using multiple narrow-band elements. Usually costly
Final sensitivity of the survey is the ability to detect excess flux, not just S/N in in-band images: need to achieve accurate continuum measure to have sensitivity to lines with weak Wl.
Uncertainty on continuum flux density (due to SED scatter and limited “spectral resolution” of using filters, not just S/N of narrow-band image is crucial, especially for weak Wl

23. Observational Strategies: How to Choose Filters
Matsuda et al.

24. Narrow-Band Imaging: Blind Surveys
Rhoads et al.

25. Slitless Spectroscopy (space): Blind Surveys
Rhoads et al.
McCarthy et al. (1999)

26. Slitless Spectroscopy (space): Blind Surveys
Rhoads et al.
McCarthy et al. (1999)

27. Slitless Spectroscopy (space): Blind Surveys
McCarthy et al. (1999)

28. Slitless Spectroscopy (space): Blind Surveys
McCarthy et al. (1999)

29. Slit Spectroscopy: Targeted Surveys
DLAs in the
spectrum of
QSOs
McCarthy et al. (1999)

30. Slit Spectroscopy: Targeted Surveys
DLAs in the
spectrum of
QSOs

31. Slit Spectroscopy: Targeted Surveys
DLAs in the
spectrum of
QSOs

32. Slit Spectroscopy: Targeted Surveys
DLAs in the
spectrum of
QSOs

33. Slit Spectroscopy: Targeted Surveys
DLAs in the
spectrum of
QSOs

34. Lya Surveys: Early Galaxies
Originally designed to find star-forming galaxies at very high redshifts (Partridge Peebles 1967)
ready my ARAA paper (Giavalisco 2002)
Early surveys essentially unsuccesful
Koo & Kron (1980)
Djorgovski et al. (1985)
Lowenthal et al (1990); Thompson et al. (1995)
First to be found by Lya were (steep spectrum) radio galaxies
Spinrad & Djorgovski 1984a,b; Spinrad et al.\ 1985
Significant results came with advent of 8-m class telescopes
Rhoads et al. (2000)
Taniguchi et al., Ouchi et al. , Matsuda et al. Shimasaku et al.

35. Lya Surveys
Today, Lya surveys mostly useful to complement continuum-based searches:
Fainter continuum levels
Trace LSS, clustering, clusters
Spatial mapping of emitting regions
Constraints on reionization