A Census of Lyman - Alpha Blobs at z 055

Project: Research project

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A recent major discovery has been that of "blobs" of Lya emission at high (z > 2) redshift (Keel et al. 1999; Steidel et al. 2000; Francis et al. 2001; Matsuda et al. 2004; Nilsson et al. 2006; Saito et al. 2006; Ouchi et al. 2008; Yang et al. 2009; Erb et aI2011). These objects are distinguished by their lack of stellar continuum emission, large physical and angular sizes (up to 20"and 160 kpc in size at z "" 3; see, e.g. Matsuda et al. 2004), and are found in regions of high galaxy density. Figure 1, from Nilsson et al. (2006), shows an example of a Lya blob (LAB) at z = 3.16 in the GOODS-S field, which has been imaged from the X-ray to mid-infrared. The only emission detected from this source is that of Lya . The limited information available on LABs makes their nature unclear. Possibilities include cooling radiation from collapsing proto galactic clouds, cold gas stream accretion onto dark matter halos, superwinds from massive starbursts, and gas photoionized by obscured or transient AGN (see the above references, and Saito et al. 2008; Geach et al. 2009, Goerdt et al. 2010). As with any new class of object, more data and larger samples are needed to narrow down the range of possibilities Although it is based on a limited amount of data, Figure 3 suggests a rapid increase in the space density of LABs, roughly as (1 + Z)3. Motivated by this, 128 images of 50 QSO fields at approximately 0.556<z <0.565 were acquired in the SwiftlUVOT UVW1 and UVW2 filters. Analysis of these fields revealed a candidate of extreme promise and unusual characteristics. Undetected in the UVW1 filter, objects A and B as seen in the right frame of Figure 2 are highly extended in the Lya ; at z"" 0.5, 1" ~ 6 kpc. Object A thus appears to be ~480 kpc in diameter, unlike any known LAB. This observation requires the UVOT UVWl and UVW2 filters, as noted above; we seek to confirm detection of anomalous objects with narrow emission in UVW2. In this proposal we describe necessary follow-up observations for these LAB candidates as a fill-in program for Swift Cycle 8. We present incomplete existing Swift UVOT data that strongly suggest the presence of a LAB as justification for follow-up.
Effective start/end date11/20/1211/19/13


  • NASA: Goddard Space Flight Center: $20,000.00

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