Ly-α imaging of GRB host galaxy fields

Ly-α emission is indicative of on-going star formation in a dust-poor environment. Ly-α imaging of GRB hosts will therefore provide information about both the star formation rate and the dust-content of the host galaxies. Both of these parameters are central to our understanding of GRB progenitors and of how the environments affect the propagation of afterglow emission out of host galaxies. We have started a program aimed at imaging high redshift (z>2) host galaxies of GRBs at the Ly-α line from neutral hydrogen. This work is done in collaboration with the Copenhagen GRB-group (of which I am part) and several other people.
The first attempt we did in this direction was a project targetting the fields of GRB 000310C and GRB 000926 both a z=2.04. Here is a figure showing the HST image of the host galaxy of GRB 000926 taken by the CalTech group (published in ApJ by Castro et al. 2003). The contours show the Ly-α emission from the same object as detected in a deep narrow band image taken at the NOT in May and August 2001 (click on the image to get the paper):


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Besides the host galaxy of GRB 000926 we detected almost 20 other candidate z=2.04 Ly-α emitters in the two fields. The figure here shows some of the best candidates.

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Our second project targeted the host of GRB 011211 at redshift z=2.14. In ESO observing period 70 we observed this field in a similar way using the New Technology telescope. Again the host was detected as a moderately strong Ly-α emitter. The figure below shows the HST/STIS image of the host with the contours of the Ly-α emission overplotted.



Six other galaxies with significant excess emission in the narrow filter most likely due to Ly-α emission at z=2.14 were detected in the field. The six galaxies and the host can be seen in the next figure.



In period 71 we had time to observe the field of GRB 020124 with FORS1 on the Very Large Telescope and later we used the NOT to study the fields of GRB021004 and GRB030226. The results were published in MNRAS in 2005. We are currently observing a large sample of hosts to infer how common Ly-α emission is in a statistically significant sample.

Publications:

  • Deep Ly-α imaging of two z=2.04 GRB host galaxy fields

    - Authors: Fynbo J.P.U., Møller P., Thomsen B., Hjorth J., Gorosabel J., Andersen M.I., Egholm M.P., Holland S., Jensen B.L., Pedersen H., Weidinger M.
    - A&A, 388, 425-438 (2002)

    - text and figures

  • Ly-α emission from GRB host galaxies

    - Authors: Fynbo J.P.U., Møller P., Thomsen B., Hjorth J., Gorosabel J., Andersen M.I., Egholm M.P., Holland S., Jensen B.L., Pedersen H., Weidinger M.
    - to appear in the proceedings of Roma 2002 GRB workshop

    - text and figures

  • On the Ly-α emission from gamma-ray burst host galaxies: evidence for low metallicities

    - Authors: Fynbo J.P.U., Jakobsson P., Møller P., Hjorth J., Thomsen B., Andersen M.I., Fruchter A.S., Gorosabel J., Holland S.T., Ledoux C., Pedersen H., Rhoads J., Weidinger M., Wijers R.A.M.J.
    - A&A Letters, 406, L63-L66 (2003)

  • Ly-alpha and UV emission from high-redshift GRB hosts: To what extent do GRBs trace star formation?

    - Authors: Jakobsson P., Bjørnsson G., Fynbo J. P. U., et al.
    - MNRAS, 362, 245 (2005)

    - text and figures