The Optical Sky Background The Optical Sky I

The Optical Sky Background

The Optical Sky. I: the V – I band

The Optical Sky. II: the R - I band

The Optical Sky. III: the I - Z band

The Optical Sky. IV: the z – J band

The Optical Sky. V

The Near-IR Sky Background

The Sky OH Emission Lines

The Sky OH Emission lines

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

Observational tactics

Cosmic Volumes. I n Luminosity function u F(L) = f* • exp(-L/L*) • (L/L*)a f ~ 10 -2 to 10 -3 Mpc-3 t L* ~ 1011 to 1012 LO or 1044 to 1045 erg/sec t a ~ -1. 0 to -1. 2 (optical); -1. 4 to – 1. 8 (UV) t * n Luminosity density u L = ∫ d. L • f* • exp(-L/L*) • (L/L*)a ~ L* • f*

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

Cosmic Volumes. III n At z = 3 u 1 arcsec ~ 3 kpc (physical) ~ 10. 2 kpc (comoving) u 10 arcmin ~ 1. 8 Mpc (physical) ~ 7. 2 Mpc (comoving) n At z=3, dz ~ 1 u d. R(z=3) ~ 500 Mpc n FWHM = 100 Å corresponds to dz = 0. 08 or

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

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

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

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

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

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

Strategy of Emission-line surveys n Blind surveys: no “a-priory” knowledge of redshift or radial velocity: u Narrow-band imaging: t Useful if large volume density of sources suspected and if large sensitivity can be achieved. Examples: • Distant galaxy searches u Slitless spectroscopy: t Good option if high sensitivity can be achieved (e. g. from space). Examples: • Distant galaxies searches u Slit spectroscopy: t 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

Survey Design: Narrow-Band Imaging n n n 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

Observational Strategies: How to Choose Filters Matsuda et al.

Narrow-Band Imaging: Blind Surveys Rhoads et al.

Slitless Spectroscopy (space): Blind Surveys Rhoads et al. Mc. Carthy et al. (1999)

Slitless Spectroscopy (space): Blind Surveys Mc. Carthy et al. (1999)

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

Slit Spectroscopy: Targeted Surveys DLAs in the spectrum of QSOs

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

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