Nobunari Kashikawa

Publications (2)6.02 Total impact

• Source

  Available from: Yuichi Matsuda

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

  Moire K. M. Prescott, Arjun Dey, Mark Brodwin, Frederic H. Chaffee, Vandana Desai, Peter Eisenhardt, Emeric Le Floc'h, Buell T. Jannuzi, Nobunari Kashikawa, Yuichi Matsuda, B. T. Soifer
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  ABSTRACT: 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.
  11/2011;
• Article: The Overdense Environment of a Large Lyα Nebula at z ≈ 2.7

  Moire K. M. Prescott, Nobunari Kashikawa, Arjun Dey, and Yuichi Matsuda
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  ABSTRACT: Large nebulae ( 50 kpc) emitting strongly in Lyα (also known as Lyα "blobs") are likely signposts of ongoing massive galaxy formation. The relative rarity of these sources and their discovery in well-studied galaxy overdensities suggest that they may be associated with regions of high galaxy density. One of the largest Lyα nebulae, discovered at a redshift of z ≈ 2.7 via its strong mid-infrared emission, provides an unbiased test of this association. We have carried out a deep intermediate-band imaging survey for Lyα-emitting galaxies (LAEs) within a 30' × 26' field of view around this Lyα nebula. This is the first study of the environment of a Lyα nebula found without a priori knowledge of its surroundings. We find that the nebula is located in an overdense region, at least 20 × 50 h70−1 comoving Mpc in size, showing a factor of ~3 LAE number density enhancement relative to the edge of the field. Given the predicted number of such overdensities, we rule out the possibility of a chance coincidence at the 1% level. This study, in conjunction with previous work, provides strong confirmation of the association between the largest Lyα nebulae and overdense regions of the universe.
  The Astrophysical Journal 12/2008; 678(2):L77. · 6.02 Impact Factor