Institute of Astronomy

The surprising relationship between Lyman break galaxy spectroscopic features, environment, and kinematics

SpeakerTalk DateTalk Series
Jeff Cooke (Swinburne)15 July 2011Institute of Astronomy Galaxies Discussion Group


I will present results from our program investigating the spatial distribution of LBGs exhibiting
different spectroscopic features that has uncovered direct links to their environment and kinematics.
Motivated by our recent work investigating interacting z$\sim$3 LBGs, we divide the LBG population
into two sub-types: one that exhibits dominant Lyman-alpha absorption and broad/strong interstellar
features (termed aLBGs) and one that exhibits dominant Lyman-alpha emission and weak/narrow
interstellar features (eLBGs). We use a novel broadband color-magnitude technique, tested using
$\sim$1000 Keck spectra, to generate highly pure and large ($\sim$10000) photometric samples of aLBGs and
eLBGs in the Canada-France-Hawaii Telescope Legacy Survey Deep fields. The large numbers
enable a detailed investigation of the spatial distributions of the two LBG sub-types from large to
very small scales using their two-point correlation functions. We see a highly significant difference
in the behavior of the two auto-correlation functions indicating that aLBGs typically reside in proto-
groups, whereas eLBGs typically reside in the field. In addition, an anti-correlation component in
the aLBG/eLBG cross-correlation further signifies the intrinsic differences in spatial locations of the
two sub-types. The observed bimodality in the full LBG population - highlighted by these two sub-
populations - appears to trace the early formation of the red sequence and blue cloud of galaxies
observed locally. Finally, and equally surprising, analysis of IFU studies of z$\sim$2-3 LBGs compiled
from the literature find that aLBGs are best fit to disk models and eLBGs to interacting/merging and
compact dispersion dominated systems.


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