Bibcode
Laporte, N.; Streblyanska, A.; Kim, S.; Pelló, R.; Bauer, F. E.; Bina, D.; Brammer, G.; De Leo, M. A.; Infante, L.; Pérez-Fournon, I.
Bibliographical reference
Astronomy and Astrophysics, Volume 575, id.A92, 10 pp.
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3
2015
Journal
Citations
50
Refereed citations
42
Description
Context. The Hubble Space Telescope (HST) Frontier Fields (HFFs) project
started at the end of 2013 with the aim of providing extremely deep
images of six massive galaxy clusters. One of the main goals of this
program is to push several telescopes to their limits to provide the
best current view of the earliest stages of the Universe. The analysis
of the initial data has already demonstrated the huge capabilities of
the program. Aims: We present a detailed analysis of z ~ 8
objects behind the HFFs lensing cluster, MACSJ0416.1-2403, combining
0.3-1.6 μm imaging from HST, ground-based Ks imaging from
VLT HAWK-I, and 3.6 μm and 4.5 μm Spitzer Space Telescope. The
images probe to 5σ depths of ≈29 AB for HST, 25.6 AB for
HAWK-I, and ≈0.310 and 0.391 μJy at 3.6 and 4.5 μm,
respectively. With these datasets, we assess the photometric properties
of z ~ 8 galaxies in this field, as well as their distribution in
luminosity, to unprecedented sensitivity. Methods: We applied the
classical Lyman break (LB) technique, which combines non detection
criteria in bands blueward of the Lyman break at z ~ 8 and
color-selection in bands redward of the break. To avoid contamination by
mid-z interlopers, we required a strong break between optical and
near-infrared data. We determined the photometric properties of z ~ 8
selected candidates using spectral energy distribution (SED)-fitting
with standard library templates. The luminosity function at z ~ 8 is
computed using a Monte-Carlo method taking advantage of the SED-fitting
results. A piece of cautionary information is gleaned from new deep
optical photometry of a previously identified z ~ 8 galaxy in this
cluster, which is now firmly detected as a mid-z interloper with a
strong ≈1.5 mag Balmer break (between F606W and F125W). Using the SED
of this interloper, we estimated the contamination rate of our
MACSJ0416.1-2403 sample, and that of previous samples in Abell 2744 that
were based on HFF data, we highlight the dangers of pushing the LB
technique too close to the photometry limits. Results: Our
selection reliably recovers four objects with mF160W ranging
from 26.0 to 27.9 AB that are located in modest-amplification regions
(μ < 2.4). Two of the objects display a secondary break between
the IRAC 3.6 μm and 4.5 μm bands, which could be associated to the
Balmer break or emission lines at z ~ 8. The SED-fitting analysis
suggests that all of these objects favor high-z solutions with no
reliable secondary solutions. The candidates generally have star
formation rates around ~10 M⊙/yr and sizes ranging from
0.2 to 0.5 kpc, which agrees well with previous observations and
expectations for objects in the early Universe. The sample size and
luminosity distribution are consistent with previous findings.
Related projects
Formation and Evolution of Galaxies: Observations in Infrared and other Wavelengths
This IAC research group carries out several extragalactic projects in different spectral ranges, using space as well as ground-based telescopes, to study the cosmological evolution of galaxies and the origin of nuclear activity in active galaxies. The group is a member of the international consortium which built the SPIRE instrument for the
Ismael
Pérez Fournon