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Session 83 - Galaxy Evolution/Interaction.
Oral session, Wednesday, January 15
Piers 4/5,

[83.02] Galaxy Formation from Subgalactic-sized Clumps at z\simeq 2.39

S. M. Pascarelle, R. A. Windhorst (ASU), W. C. Keel (U of AL), N. Scoville, L. Armus (Caltech)

The discovery of numerous compact star-forming objects at z\simeq 2.39 in several distinct regions of the sky with the Hubble Space Telescope (HST) represents the first direct observations of what may be the building blocks of present-day luminous galaxies. The HST medium-band F410M filter (centered at 4100Åwas used with WFPC2 to image Lyman-\alpha emission at z\simeq 2.39, which along with broad-band B_F450W, V_F606W, and I_F814W images, found 18 candidates in a field surrounding the weak radio galaxy 53W002. Thus far, eight of the original 18 candidates from this field have either MMT or Keck spectroscopic confirmations, along with one possible new detection in H\alpha from CVF and K observations at the IRTF. More than a dozen additional z\simeq 2.39 candidates have been found with HST using the same method in two independent fields from recent Cycle 6 parallel WFPC2/F410M observations. Our hypothesis is that such a widespread population of subgalactic-sized clumps exists throughout the redshift range z=1-4, and provides a reservoir of building blocks for the formation of the present-epoch early-type galaxies through the process of repeated hierarchical merging (with a merger rate that was most likely higher in the past). Finding similar objects in random fields with F410M suggests that these objects are indeed ubiquitous, and are part of the high-redshift (z=1-4) faint blue galaxy population. Still, some clustering is evident because the velocity dispersion of most of the 53W002 field objects (_ <\atop^\sim 300 km/s) is much smaller than the redshift range passed by the F410M filter. This indicates that these objects, which are within a region _ <\atop^\sim 1 Mpc^2, will in fact eventually merge. We take this to suggest that such building blocks exist everywhere in the sky and trace large-scale structure that may have been ``frozen in'' shortly after the Big Bang.

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