Resolving the Galaxies within a Giant Lya Nebula: Witnessing the Formation of a Galaxy Group?

The Astrophysical Journal (Impact Factor: 5.99). 11/2011; 752(2). DOI: 10.1088/0004-637X/752/2/86
Source: arXiv


Detailed analysis of the substructure of Lya nebulae can put important
constraints on the physical mechanisms at work and the properties of galaxies
forming within them. Using high resolution HST imaging of a Lya nebula at
z~2.656, we have taken a census of the compact galaxies in the vicinity, used
optical/near-infrared colors to select system members, and put constraints on
the morphology of the spatially-extended emission. The system is characterized
by (a) a population of compact, low luminosity (~0.1 L*) sources --- 17
primarily young, small (Re~1-2 kpc), disky galaxies including an obscured AGN
--- that are all substantially offset (>20 kpc) from the line-emitting nebula;
(b) the lack of a central galaxy at or near the peak of the Lya emission; and
(c) several nearly coincident, spatially extended emission components --- Lya,
HeII, and UV continuum --- that are extremely smooth. These morphological
findings are difficult to reconcile with theoretical models that invoke
outflows, cold flows, or resonant scattering, suggesting that while all of
these physical phenomena may be occurring, they are not sufficient to explain
the powering and large extent of Lya nebulae. In addition, although the compact
galaxies within the system are irrelevant as power sources, the region is
significantly overdense relative to the field galaxy population (by at least a
factor of 4). These observations provide the first estimate of the luminosity
function of galaxies within an individual Lya nebula system, and suggest that
large Lya nebulae may be the seeds of galaxy groups or low-mass clusters.

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