The lack of success of Ly$alpha$ searches for high-redshift z>2 field galaxies may be due to extinction by dust, suggesting that surveys based on lines of longer wavelength, particularly Hα, may be more effective. To test the dust hypothesis we have undertaken deep broad- (K') and narrow-band (5000 km s^-1, lambda=2.177mum) imaging of the field towards the quasar PHL957, in an attempt to detect Hα emission from a known galaxy of redshift z=2.313. We cover an area of 4.9 arcmin^2 (0.28h^-2Mpc^2) to a 4sigma limiting narrow-band flux f=2.7x10^-16erg cm^-2 s^-1, a factor of several deeper than previously published surveys. We detect the Hα+[NII] emission line in this galaxy at the 3.3sigma level, inferring a star formation rate of 18 h^-2 M/yr^-1. This is a factor of only a few times larger than the rate seen in some Sc galaxies today. The faint flux level reached in this work demonstrates the promise of narrow-band imaging in the near-infrared as a technique for finding normal galaxies at high redshifts.
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- March 1995
- GALAXIES: FORMATION;
- QUASARS: ABSORPTION LINES;
- QUASARS: INDIVIDUAL: PHL957;
- INFRARED: GALAXIES;
- 6 pages of LaTex using mn.sty (MNRAS style). Figure 1 is an image obtainable from the Authors by FTP. Contact email@example.com for more details. Figure 2 is a Z-compressed, uuencoded postscript graph.