An H alpha search for overdense regions at z=2.23

Y. Matsuda, Ian Smail, J. E. Geach, P. N. Best, D. Sobral, I. Tanaka, F. Nakata, K. Ohta, J. Kurk, I. Iwata, Rich Bielby, J. L. Wardlow, R. G. Bower, R. J. Ivison, T. Kodama, T. Yamada, K. Mawatari, M. Casali

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

We present the results of a narrow-band (H(2)S1, lambda(c) = 2.121 mu m, delta lambda = 0.021 mu m) imaging search with Wide Field Camera/United Kingdom Infrared Telescope for Ha emitters (HAEs) around several potential signposts of rare (similar to 10(-7)-10(-8) comoving Mpc(-3)) overdense regions at z = 2.23: an overdensity of quasi-stellar objects [QSOs; 2dF QSO Redshift Survey (2QZ) cluster], a powerful, high-redshift radio galaxy (HzRG) and a concentration of submillimetre galaxies (SMGs) and optically faint radio galaxies (OFRGs). In total, we detect 137 narrowband emitter candidates down to emission-line fluxes of 0.5-1 x 10(-16) erg s(-1) cm(-2), across a total area of 0.56 deg(2) (2.1 x 10(5) comoving Mpc(3) at z = 2.23) in these fields. The BzK colours of the emitters suggest that at least 80 per cent of our sample are likely to be HAEs at z = 2.23. This is one of the largest HAE samples known at z greater than or similar to 2. Although there is no evidence for large-scale (20 comoving Mpc) overdensities of the emitters around the targets, we find modest (similar to 3 sigma) local overdensities associated with all three targets on smaller scales (5-10 comoving Mpc). In the 2QZ cluster field, the structure appears to be connecting the QSOs, while in the HzRG and SMG/OFRG fields, the structures are seen only in the vicinities of the targets. Our results suggest that these rare targets are located in local overdensities of galaxies, rather than average density regions, although it is not clear whether these structures are likely to evolve into rare, rich clusters. The K-band magnitudes and the Ha equivalent widths of the emitters are weakly correlated with the overdensities of the emitters: emitters in overdense regions are more evolved systems compared to those in underdense regions at z = 2.23. We find several examples of extended HAEs near to the targets, including a striking example with a spatial extent of 7.5 arcsec (60 kpc at z = 2.23) in the 2QZ cluster field, suggesting that these are relatively common in overdense regions. We conclude that narrow-band Ha surveys are efficient routes to map overdense regions at high redshifts and thus to understand the relation between the growth of galaxies and their surrounding large-scale structures.

Original languageEnglish
Pages (from-to)2041-2059
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
Publication statusPublished - Sept 2011

Keywords / Materials (for Non-textual outputs)

  • galaxies: evolution
  • galaxies: formation
  • galaxies: high-redshift
  • cosmology: observations
  • early Universe


Dive into the research topics of 'An H alpha search for overdense regions at z=2.23'. Together they form a unique fingerprint.

Cite this