The "Building the Bridge" Ly-α Survey

The "Building the Bridge" Ly-α Survey was started in 2000 by Cedric Ledoux, Palle Møller, Bjarne Thomsen, Bruno Leibundgut, Ingunn Burud, and me. I am the Principle Investigator on the project. The aim of the project is to build up a sample of high redshift galaxies that reach faint enough magnitude limits to have a large overlap with the galaxies selected as Damped Ly-α Absorbers in QSO spectra. To reach such faint fluxes deep narrow band Ly-α imaging is done at the ESO Very Large Telescope in service mode (we are grateful to the Paranal science operations for excellent support during the last three years). We target the fields of three QSO absorbers at redshift around 3, namely the fields of the Q2138-4427 (absorber at z=2.85), Q1346-0322 (absorber at z=3.15) and Q1202-0725 (absorber at z=3.20). The imaging observations of the Q2138-4427 field were completed in the spring and summer of 2001. The Q1346-0322 imaging was completed in the summer of 2002. The imaging of the Q1202-0725 field was completed in the spring of 2003. The first spectroscopic follow-up run was carried out during a three nights visitor run July 2002 at the VLT. Eventhough the seeing ranged from mediocre to extremely bad ( night1, night2, night3 ) we managed to measure 41 redshifts in the Q1346-0322 and Q2138-4427 fields. A paper based on these observations is published in Astronomy & Astrophysics 2003 (see below). The spectroscopy of the final Q1202-0725 field was obtained in 2004 and the final paper from the survey was submitted in December 2008 and is now accepted for publication in Astronomy & Astrophysics (see below).

Shown below are examples of some of these extremely faint Ly-α emitting galaxies at z=2.85 in the Q2138-4427 field (in black circles) detected with 10 hours of integration on the VLT. The size of the image is only 40 times 120 arcsec and still we find 6 candidate Ly-α emitting galaxies at redshifts 2.85-2.86 (and one faint z=2.035 QSO interloper with CIV in the narrow filter). In the full 7 by 7 arcmin field of view we select about 35 candidate Ly-α emitting galaxies. Most of the candidate Ly-α emitting galaxies are extremly faint. The two bright Ly-α emitters in the lower right corner have broad band magnitudes of about R(AB)=27 and B(AB)=27.5, which means more than 2 magnitudes below the typical luminosity (L*) for Lyman-Break galaxies. Most of the LEGOs in the field are fainter than these two - about 20% are fainter than the 2-sigma limit of R(AB)=28.7 and B(AB)=28.8.

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Here are six examples of LEGOs that are extremely faint in the continuum in the field of Q1346-0322. None of these are detected above a 2-sigma level of about R(AB)=28.5.

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Sections of the the 2-dimensional VLT spectra of the same six objects are shown below (the spectrum at the bottom corresponds to the leftmost image above). Note that we serendipitously detect a neighbour to one of the six candidates (the LEGO at z=3.1305). Subsequent inspection of the images show a faint source detected at the 3-sigma level in the narrow band image, but absent in both the B and R-band images.

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Publications:

Building the bridge between Damped Ly-α Absorbers and Lyman Break galaxies

Authors: Fynbo J.P.U., Ledoux C., Møller P., Thomsen B., Burud I., Leibundgut B.
In the proceedings of the conference "Galaxy evolution: theory and observations', Eds. V. Avila-Reese, C. Firmani, C. Frenk, & C. Allen, RevMexAA SC (2002)
- text and figures


The Building the Bridge survey for z=3 Ly-α emitting galaxies I: method and first results

- Authors: Fynbo J.P.U., Ledoux C., Møller P., Thomsen B., Burud I.
- A&A, 407, 147-157 (2003)
- text and figures

The Building the Bridge survey for z=3 Ly-α emitting galaxies I: method and first results

- Authors: Grove L. F., Fynbo J.P.U., Ledoux C., Limousin M., Møller P., Nilsson K. K., Thomsen B.
- A&A, in press (2009)
- text and figures