244 research outputs found
Frontier Fields: High-Redshift Predictions and Early Results
The Frontier Fields program is obtaining deep Hubble and Spitzer Space
Telescope images of new "blank" fields and nearby fields gravitationally lensed
by massive galaxy clusters. The Hubble images of the lensed fields are
revealing nJy sources (AB mag > 31), the faintest galaxies yet observed. In
this paper, we present high-redshift (z > 6) number count predictions for the
full program and candidates in three of the first Hubble Frontier Fields
images. The full program will transform our understanding of galaxy evolution
in the first 600 million years (z > 9). Where previous programs yielded perhaps
a dozen z > 9 candidates, the Frontier Fields may yield ~70 (~6 per field). We
base this estimate on an extrapolation of luminosity functions observed between
4 < z < 8 and gravitational lensing models submitted by the community. However,
in the first two deep infrared Hubble images obtained to date, we find z ~ 8
candidates but no strong candidates at z > 9. This might suggest a deficit of
faint z > 9 galaxies as also reported in the Ultra Deep Field (even while
excesses of brighter z > 9 galaxies were reported in shallower fields). At
these redshifts, cosmic variance (field-to-field variation) is expected to be
significant (greater than +/-50%) and include clustering of early galaxies
formed in overdensities. The full Frontier Fields program will significantly
mitigate this uncertainty by observing six independent sightlines each with a
lensing cluster and nearby blank field.Comment: Submitted for publication in the Astrophysical Journal. 15 pages, 17
figure
A Redshift Survey of the Strong Lensing Cluster Abell 383
Abell 383 is a famous rich cluster (z = 0.1887) imaged extensively as a basis
for intensive strong and weak lensing studies. Nonetheless there are few
spectroscopic observations. We enable dynamical analyses by measuring 2360 new
redshifts for galaxies with r and within 50 of the
BCG (Brightest Cluster Galaxy: R.A., Decl). We apply the caustic technique to identify 275 cluster
members within 7 Mpc of the hierarchical cluster center. The BCG lies
within km s and 21 kpc of the hierarchical
cluster center; the velocity dispersion profile of the BCG appears to be an
extension of the velocity dispersion profile based on cluster members. The
distribution of cluster members on the sky corresponds impressively with the
weak lensing contours of Okabe et al. (2010) especially when the impact of
foreground and background structure is included. The values of R =
Mpc and M = M obtained by application of the caustic technique agree well
with recent completely independent lensing measures. The caustic estimate
extends direct measurement of the cluster mass profile to a radius of Mpc.Comment: 29 pages, 9 figures, ApJ accepte
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