J/ApJ/792/76 Lensed z∼6-8 galaxies behind CLASH clusters (Bradley+, 2014)
CLASH: a census of magnified star-forming galaxies at z ∼ 6-8.
Bradley L.D., Zitrin A., Coe D., Bouwens R., Postman M., Balestra I.,
Grillo C., Monna A., Rosati P., Seitz S., Host O., Lemze D., Moustakas J.,
Moustakas L.A., Shu X., Zheng W., Broadhurst T., Carrasco M., Jouvel S.,
Koekemoer A., Medezinski E., Meneghetti M., Nonino M., Smit R., Umetsu K.,
Bartelmann M., Benitez N., Donahue M., Ford H., Infante L.,
Jimenez-Teja Y., Kelson D., Lahav O., Maoz D., Melchior P., Merten J.,
Molino A.
<Astrophys. J., 792, 76 (2014)>
=2014ApJ...792...76B 2014ApJ...792...76B (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Gravitational lensing ; Galaxies, photometry ;
Photometry, HST ; Redshifts
Keywords: galaxies: evolution - galaxies: high-redshift -
gravitational lensing: strong
Abstract:
We utilize 16 band Hubble Space Telescope (HST) observations of 18
lensing clusters obtained as part of the Cluster Lensing And Supernova
survey with Hubble (CLASH) Multi-Cycle Treasury program to search for
z ∼ 6-8 galaxies. We report the discovery of 204, 45, and 13
Lyman-break galaxy candidates at z ∼ 6, z ∼ 7, and z ∼ 8,
respectively, identified from purely photometric redshift selections.
This large sample, representing nearly an order of magnitude increase
in the number of magnified star-forming galaxies at z ∼ 6-8 presented
to date, is unique in that we have observations in four WFC3/UVIS UV,
seven ACS/WFC optical, and all five WFC3/IR broadband filters, which
enable very accurate photometric redshift selections. We construct
detailed lensing models for 17 of the 18 clusters to estimate object
magnifications and to identify two new multiply lensed z ≳ 6
candidates. The median magnifications over the 17 clusters are 4, 4,
and 5 for the z ∼ 6, z ∼ 7, and z ∼ 8 samples, respectively, over an
average area of 4.5 arcmin2 per cluster. We compare our observed
number counts with expectations based on convolving "blank" field UV
luminosity functions through our cluster lens models and find rough
agreement down to ∼27 mag, where we begin to suffer significant
incompleteness. In all three redshift bins, we find a higher number
density at brighter observed magnitudes than the field predictions,
empirically demonstrating for the first time the enhanced efficiency
of lensing clusters over field surveys. Our number counts also are in
general agreement with the lensed expectations from the cluster
models, especially at z ∼ 6, where we have the best statistics.
Description:
CLASH is a 524 orbit multi-cycle treasury program to observe 25 galaxy
clusters to a total depth of 20 orbits each, incorporating archival
HST data for our cluster sample whenever possible (Postman et al.
2012, J/ApJS/199/25). Each cluster is observed using WFC3/UVIS,
ACS/WFC, and WFC3/IR to obtain imaging in 16 broadband filters
spanning from 0.2 to 1.7 um (for the throughput curves of each
filter, see Postman et al. 2012, J/ApJS/199/25 or Jouvel et al. 2014,
J/A+A/562/A86). We used SExtractor version 2.5.0 (Bertin & Arnouts
1996A&AS..117..393B 1996A&AS..117..393B) in dual-image mode to perform object detection
and photometry. For each of our 18 clusters, we constructed a
detection image by performing an inverse-variance weighted sum of the
images in all five WFC3/IR bands: Y105, J110, J125, JH140, and H160.
The local background was measured within a rectangular annulus
(default width 24 pixels) and sources were required to be detected at
>1σ significance over a minimum area of nine contiguous pixels.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 93 18 Observational Details for the Cluster Sample
table4.dat 133 196 Lensed z∼6 Candidates Identified Behind
17 CLASH Clusters
table5.dat 133 43 Lensed z∼7 Candidates Identified Behind
17 CLASH Clusters
table6.dat 133 12 Lensed z∼8 Candidates Identified Behind
17 CLASH Clusters
table7.dat 133 21 Lensed Candidates Identified Behind
RXJ1532.9+3021
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See also:
J/ApJS/199/25 : CLASH sources for MACS1149.6+2223 (Postman+, 2012)
J/A+A/562/A86 : CLASH. Photometric + photo-z catalog (Jouvel+, 2014)
J/ApJ/801/44 : HST lensing analysis of the CLASH sample (Zitrin+, 2015)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- Cluster Cluster Name
18- 22 A5 --- n_Cluster Notes on Cluster (1)
24- 31 A8 --- Alias Shortened cluster names used in the paper
33- 34 I2 h RAh Rigth ascension (J2000) (2)
36- 37 I2 min RAm Rigth ascension (J2000) (2)
39- 43 F5.2 s RAs Rigth ascension (J2000) (2)
44 A1 --- n_RAs [g] Note on position (3)
46 A1 --- DE- Declination sign (J2000) (2)
47- 48 I2 deg DEd Declination (J2000) (2)
50- 51 I2 arcmin DEm Declination (J2000) (2)
53- 56 F4.1 arcsec DEs Declination (J2000) (2)
57 A1 --- n_DEs [g] Note on position (3)
59- 63 F5.3 --- z Cluster redshift
65- 69 F5.3 mag E(B-V) Reddening
71- 81 A11 "date" Start.Date Observation starting date
83- 93 A11 "date" End.Date Observation ending date
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Note (1): Notes as follows:
c = Ebeling et al. (2007ApJ...661L..33E 2007ApJ...661L..33E)
d = High-magnification cluster
e = Hubble Frontier Fields (HFF) cluster
f = Ebeling et al. (2010MNRAS.407...83E 2010MNRAS.407...83E)
h = Mann & Ebeling (2012MNRAS.420.2120M 2012MNRAS.420.2120M)
Note (2): Cluster coordinates derived from X-ray data, except where noted.
Note (3): g when cluster coordinates derived from optical data.
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Byte-by-byte Description of file: table4.dat table5.dat table6.dat table7.dat
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Bytes Format Units Label Explanations
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1- 13 A13 --- ID Object identifier (1)
14- 18 A5 --- f_ID Flag on ID (2)
20- 30 F11.7 deg RAdeg Right Ascension in decimal degrees (J2000)
32- 42 F11.7 deg DEdeg Declination in decimal degrees (J2000)
44 A1 --- l_I814mag Limit flag on I814mag
45- 48 F4.1 mag I814mag The HST I band AB magnitude; 0.814 microns
50- 53 F4.2 mag e_I814mag ? Uncertainty in I814mag
55 A1 --- l_z850mag Limit flag on z850mag
56- 59 F4.1 mag z850mag The HST z band AB magnitude; 0.850 microns
61- 64 F4.2 mag e_z850mag ? Uncertainty in z850mag
66- 69 F4.1 mag Y105mag ? The HST Y band AB magnitude; 1.05 microns
71- 74 F4.2 mag e_Y105mag ? Uncertainty in Y105mag
76- 79 F4.1 mag Y110mag ? The HST Y band AB magnitude; 1.10 microns
81- 84 F4.2 mag e_Y110mag ? Uncertainty in Y110mag
86- 89 F4.1 mag J125mag ? The HST J band AB magnitude 1.25 microns
91- 94 F4.2 mag e_J125mag ? Uncertainty in J125mag
96- 99 F4.1 mag J140mag ? The HST J band AB magnitude; 1.40 microns
101-104 F4.2 mag e_J140mag ? Uncertainty in J140mag
106-109 F4.1 mag H160mag The HST H band AB magnitude; 1.60 microns
111-114 F4.2 mag e_H160mag Uncertainty in H160mag
116-118 F3.1 --- zphot Photometric redshift (3)
120-122 F3.1 --- E_zphot Upper limit uncertainty in zphot
124-126 F3.1 --- e_zphot Lower limit uncertainty in zphot
128 A1 --- l_mu Limit flag on mu
129-133 F5.1 --- mu Magnification (4)
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Note (1): Object identified as Alias-NNNN.
Note (2): Flag as follows:
c = Unresolved object with FWHM<0.22 arcsec in the image plane. There is
a small chance that brighter unresolved candidates could be low-mass
stars even though we explored such possibilities (see Section 5.3).
d = Using LePhare, we find that these unresolved candidates have a good fit
with stellar templates, with χ2star comparable or less than
χ2galaxy.
e = While BPZ prefers a high-redshift solution, we note that LePhare
slightly prefers a low-redshift solution (z∼1) over the high-redshift
solution for these three galaxies. Given this and the possible fit
with stellar templates, these candidates should be considered less
confident than the others.
f = Spectroscopically confirmed multiply-imaged galaxy at z=6.027
Richard et al. (2011MNRAS.414L..31R 2011MNRAS.414L..31R).
g = Quadruply lensed galaxy at z∼6.2 (Zitrin et al. 2012ApJ...747L...9Z 2012ApJ...747L...9Z).
h = Zitrin et al. (2013ApJ...762L..30Z 2013ApJ...762L..30Z) report that MACS0419-0419 is part of
a visually-identified double system at zphot∼6.1. The second
candidate (at RA=04:16:09.946, DE=-24:03:45.31) fell below
our S/N threshold and thus does not appear in this catalog.
i = MACS1115-0352 and MACS1720-1114 have very blue SEDs. While our
best-fit photometric redshifts suggest that these are high-redshift
candidates, a possible alternative solution is that they could be
low-redshift extreme emission-line galaxies with rest-frame equivalent
widths of ∼2000 Angstroms (Huang et al. in prep).
j = Quadruply lensed galaxy at zphot∼5.6 (zspec=5.701)
(Zitrin et al. 2012, J/ApJ/749/97).
k = VLT/VIMOS spectroscopy confirms this galaxy at z=5.701 (see Section 5).
l = Monna et al. (2014MNRAS.438.1417M 2014MNRAS.438.1417M) found that these two candidates,
along with three others, are part of a quintuply-lensed system with
zphot∼5.9. Based on their lens model, the magnifications for
RXCJ2248-0401 and RXCJ2248-1291 (ID4 and ID3, respectively in
Monna et al. (2014MNRAS.438.1417M 2014MNRAS.438.1417M) are 2.4 ± 0.2 and 6.0 ± 1.5,
respectively.
m = In the recent Hubble Frontier Fields data, this candiate is detected in
the ultradeep optical data and therefore it is very unlikely to be a
high-redshift galaxy.
n = MACS0717-0859 and MACS0717-1730 are spectroscopically confirmed at
z=6.387 (Vanzella et al. 2014ApJ...783L..12V 2014ApJ...783L..12V).
o = Despite having a best-fit photometric redshift of zphot = 7.2, we suspect
this unresolved object is most likely a star. Based on our current
understanding of the z∼7 LF (e.g., Bouwens et al. 2011ApJ...737...90B 2011ApJ...737...90B),
the probability of detecting a slightly-magnified z∼7 galaxy with
H160=23.6 in the small area covered by the clusters in this paper is
exceedingly small. We list this candidate for completeness, but do not
use it for subsequent analysis given its suspect nature.
p = The lens models suggest that this is likely a multiple system at z∼6.5.
q = The lens models suggest that this is likely a multiple system at z∼6.6.
r = In the recent Hubble Frontier Fields data, this candidate is detected in
the ultradeep optical data and therefore it is very unlikely to be a
high-redshift galaxy.
Note (3): Photometric redshift estimate with 2σ (95%) confidence
intervals (see Section 4). Objects with large lower bounds have a secondary
peak at lower redshift (z∼1-2) that contains at least 5% of the posterior
probabilty.
Note (4): Magnification estimate from the lens models (see Section 6). Because
of uncertainties in the precise location of the critical curves, objects with
magnifications >100 are simply quoted as such. Objects outside the region
constrained by the strong lensing models have been assigned a magnification
of 1.1.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 06-Apr-2017