## Abstract

Understanding the nature of distant Lyα nebulae, aka "blobs," and connecting them to their present-day descendants requires constraining their number density, clustering, and large-scale environment. To measure these basic quantities, we conduct a deep narrowband imaging survey in four different fields, Chandra Deep Field South (CDFS), Chandra Deep Field North (CDFN), and two COSMOS subfields, for a total survey area of 1.2 deg ^{2}. We discover 25 blobs at z = 2.3 with Lyα luminosities of L_{Lyα}= (0.7-8) x 10^{43} erg s^{-1} and isophotal areas of A_{iso} = 10-60 □′′. The transition from compact Lyα emitters (LAEs; A^{iso} ∼ a few □′′) to extended Lyα blobs (A_{iso} > 10 □′′) is continuous, suggesting a single family perhaps governed by similar emission mechanisms. Surprisingly, most blobs (16/25) are in one survey field, the CDFS. The six brightest, largest blobs with L _{ly α} ≳ 1.5 x 10^{43} erg s^{-1} and A _{iso} > 16 □′′ lie only in the CDFS. These large, bright blobs have a field-to-field variance of σ_{υ} ≳ 1.5 (150%) about their number density n ∼1.0^{+1.8}_{0.6} x 10^{-5} Mpc^{-3}. This variance is large, significantly higher than that of unresolved LAEs (σ_{υ} ∼ 0.3 or 30%), and can adversely affect comparisons of blob number densities and luminosity functions (LFs) among different surveys. Our deep, blind survey allows us to construct a reliable blob LF We compare the statistics of our blobs with dark matter halos in a 1 h^{-1} Gpc cosmological N-body simulation. At z = 2.3, n implies that each bright, large blob could occupy a halo of M _{halo} ≳10^{13} M_{⊙} if most halos have detectable blobs. The predicted variance in n is consistent with that observed and corresponds to a bias of ∼7. Blob halos lie at the high end of the halo mass distribution at z = 2.3 and are likely to evolve into the ∼10 ^{14} M_{⊙} halos typical of galaxy clusters today. On larger scales of ∼10 comoving Mpc, blobs cluster where compact LAEs cluster, indicating that blobs lie in coherent, highly overdense structures.

Original language | English |
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Pages (from-to) | 1654-1671 |

Number of pages | 18 |

Journal | Astrophysical Journal |

Volume | 719 |

Issue number | 2 |

DOIs | |

Publication status | Published - 20 Aug 2010 |

## Keywords

- Galaxies: formation
- Galaxies: high-redshift
- Intergalactic medium