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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 (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) 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:
FileName Lrecl Records Explanations
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
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
Bytes Format Units Label Explanations
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
Note (1): Notes as follows: c = Ebeling et al. (2007ApJ...661L..33E) d = High-magnification cluster e = Hubble Frontier Fields (HFF) cluster f = Ebeling et al. (2010MNRAS.407...83E) h = Mann & Ebeling (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.
Byte-by-byte Description of file: table4.dat table5.dat table6.dat table7.dat
Bytes Format Units Label Explanations
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)
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). g = Quadruply lensed galaxy at z∼6.2 (Zitrin et al. 2012ApJ...747L...9Z). h = Zitrin et al. (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) 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) 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). 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), 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.
History: From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 06-Apr-2017
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