Strategies to observe JWST First Light objects at z=10--20 based on recent results from the HUDF XDF
Abstract
We reflect on the best observing strategies to see an optimum number of First Light objects at 10-20 with the James Webb Space Telescope (JWST), based on recent results from the Hubble Wide Field Camera 3 UltraDeep Field. First, we summarize the best available data to redshifts z<8 on how the Schechter UV Luminosity Function (LF) evolves in its faint-end slope [alpha(z)], its characteristic luminosity [M*(z)] and corresponding space density [phi*(z)], and use hierarchical models to explore how alpha(z) and phi*(z) may evolve for z>8. We use the strongly declining number of z=9-11 candidates in the HUDF-XDF compared to the large number of z=7-8 objects, to constrain the plausible range in evolution of M*(z) for z> 9. While hierarchical models suggest that alpha(z>8) converges to ~-2 and phi*(z>8) to ~< 10^-3/Mpc^3, the one plausible =10-12 candidate seen in the HUDF-XDF suggests that M*(z) may drop to fainter than M=--17.5 mag at z>10 in WMAP9/Planck cosmology. If so, this may have a significant impact on the optimal observing strategies of z>10 objects with JWST. If M*(z) and/or phi*(z) continue to decline significantly for z>9, only deep 200+-hr JWST surveys that reach to AB>31 mag will see a significant number of z>10 objects. Shallow or medium deep JWST surveys that reach to AB<30 mag will not see very many unlensed z>10 objects, since they will generally sample brighter than M* at z>10. Hence, in order to sample the brighter-end of the LF at z>10, and to average over the expected significant cosmic variance at z>10, JWST will either need to observe a larger number (>5) of deep JWST fields, and/or it will need to do a much larger number (>10-20) of medium-deep surveys on gravitational lensing foreground targets. The 6 Hubble Frontier Fields that started in 2013 are excellent lensing targets for JWST. We present a subset of 2400 galaxy groups from the GAMA spectroscopic survey to z=0.4 that have M>10^15 M_o and are sufficiently compact to also be excellent lensing targets for JWST medium-deep surveys of First Light objects at z>10.
- Publication:
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American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22324662W