Research

On the basis of its ongoing multi-colour surveys, CADIS and COMBO-17, the survey team at MPIA has gained unique experience in how the pseudo-spectra obtained for each object via the imaging observations in more than a dozen medium band filters can be used to extract spectral-type and redshifts for a large sample of faint galaxies, stars and QSOs. For instance, in the 1 square degree currently covered by COMBO-17 we have secured classifications and redshifts for >10,000 galactic stars, 50,000 galaxies, and almost 1000 QSOs/AGNs.

Both by spectroscopic control observations and extensive Monte-Carlo simulations, we could prove that the medium-band technique is capable of improving the redshift accuracy of conventional photometric redshift methods by almost a factor of 10 (c.f. Wolf, Meisenheimer and Röser, 2001 and Wolf et al, 2001).

Thus medium-size survey telescopes (2-4m) with their square-degree field-of-view are able to deliver datasets of galaxies and QSOs which are for many cosmological applications equivalent or superior to those which will be obtained by extensive spectroscopic surveys planned at 8 to 10-m class telescopes. (VIRMOS, DEEP). When employed at large telescopes this technique can reach as deep as I>25 which is well beyond the capability of spectroscopic surveys.

Recently, 120 orbits with the ACS have been allocated to the COMBO-17 team and collaborators at the STScI for imaging one entire COMBO field (Chandra Deep Field S) in order to get morphological parameters for 10,000 galaxies down to R = 24 and out to z = 1.2.

The MPIA node will deliver:

• The largest available sample of faint galaxies 18 < R < 24 with complete redshift and SED information out to z = 1.2. This will be used to study and understand the galaxy evolution between z = 1.2 and today.
• An (almost) unbiased sample of faint AGNs and QSOs out to redshifts z ~ 5. When combined with the much larger but shallower 2dF QSO sample new insights in quasar evolution should be possible.
• A catalogue of 10,000 galaxies with redshift, accurate SED and morphological parameters based on a resolution of < 1 kpc out to redschift z = 1.2.
• Further develop the muti-colour technique both by investigating optimum combinations of red optical and NIR bands which are essential to probe the poorly explored but cosmologically extremely relevant galaxy redshifts, z>1. Additionally, the library of template spectra will be extended such that redshift errors caused by the mismatch between templates and real galaxy spectra are minimised.
• Distribute experience and software throughout the network in order to enable an optimum design of future surveys.

1. Star-formation history of the universe since the H-alpha luminosity (and with some caution the [OII]lambda 3727 luminosity) provides the best measure of the actual star-formation rate which is much less affected by extinction than the UV continuum.
2. The abundance of primeval galaxies which form their first generation of massive stars from primordial material and stand out by their very strong Lyman-alpha line.

• Carry out emission line surveys at the Calar Alto telescopes, with the MPG/ESO 2.2-m WFI and with the VLT.
• Provide emission-line selected galaxy samples both at intermediate (z<1.2) and very high redshift (z>5). These will complement the continuum selected galaxy samples.
• Design and promote narrow-band surveys with the next generation of survey telescopes (VST, VISTA).
• model the formation and spectral properties of Lyman-alpha bright primaeval galaxies at very high redshift.

Key staff

Most relevant recent references

Applications

• galaxy evolution between z = 2 and today,
• the connection between AGN activity and galaxy evolution,
• large scale structure and its influence on galaxy/star formation,
• data analysis methods for imaging surveys

The address for applications is: