J/ApJ/826/114 z∼3-6 protoclusters in the CFHTLS deep fields (Toshikawa+, 2016)
A systematic survey of protoclusters at z∼3-6 in the CFHTLS deep fields.
Toshikawa J., Kashikawa N., Overzier R., Malkan M.A., Furusawa H.,
Ishikawa S., Onoue M., Ota K., Tanaka M., Niino Y., Uchiyama H.
<Astrophys. J., 826, 114-114 (2016)>
=2016ApJ...826..114T 2016ApJ...826..114T (SIMBAD/NED BibCode)
ADC_Keywords: Clusters, galaxy ; Redshifts ; Photometry, ugriz ;
Photometry, ultraviolet ; Equivalent widths
Keywords: early universe - galaxies: clusters: general -
galaxies: high-redshift - large-scale structure of universe
Abstract:
We present the discovery of three protoclusters at z∼3-4 with
spectroscopic confirmation in the Canada-France-Hawaii Telescope
Legacy Survey Deep Fields. In these fields, we investigate the
large-scale projected sky distribution of z∼3-6 Lyman-break galaxies
and identify 21 protocluster candidates from regions that are
overdense at more than 4σ overdensity significance. Based on
cosmological simulations, it is expected that more than 76% of these
candidates will evolve into a galaxy cluster of at least a halo mass
of 1014 M☉ at z=0. We perform follow-up spectroscopy for eight
of the candidates using Subaru/FOCAS, Keck II/DEIMOS, and Gemini-N/GMOS.
In total we target 462 dropout candidates and obtain 138 spectroscopic
redshifts. We confirm three real protoclusters at z=3-4 with more
than five members spectroscopically identified and find one to be an
incidental overdense region by mere chance alignment. The other four
candidate regions at z∼5-6 require more spectroscopic follow-up in
order to be conclusive. A z=3.67 protocluster, which has 11
spectroscopically confirmed members, shows a remarkable core-like
structure composed of a central small region (<0.5 physical Mpc) and
an outskirts region (∼1.0 physical Mpc). The Lyα equivalent
widths of members of the protocluster are significantly smaller than
those of field galaxies at the same redshift, while there is no
difference in the UV luminosity distributions. These results imply
that some environmental effects start operating as early as at z∼4
along with the growth of the protocluster structure. This study provides
an important benchmark for our analysis of protoclusters in the upcoming
Subaru/HSC imaging survey and its spectroscopic follow-up with the
Subaru/PFS that will detect thousands of protoclusters up to z∼6.
Description:
We made use of publicly available data from the CFHTLS (T0007:
Gwyn 2012AJ....143...38G 2012AJ....143...38G; Hudelot et al. 2012, Cat. II/317), which was
obtained with MegaCam mounted at the prime focus of the CFHT. The Deep
Fields of the CFHTLS were used in this study, which consist of four
independent fields of about 1 deg2 area each (∼4 deg2 area in total)
observed in the u*, g', r', i', and z' bands.
We selected z∼3-6 galaxy candidates using the Lyman-break technique
(u-, g-, r-, and i-dropout galaxies).
We carried out spectroscopic observations using Subaru/FOCAS
(Kashikawa et al. 2002PASJ...54..819K 2002PASJ...54..819K), Keck II/DEIMOS (Faber et al.
2003SPIE.4841.1657F 2003SPIE.4841.1657F), and Gemini-N/GMOS (Hook et al. 2004PASP..116..425H 2004PASP..116..425H).
In these observations, eight protocluster candidates from z∼3 to z∼6 were
observed in total (two at each redshift). All these observations were
conducted with Multi-Object Spectroscopy (MOS) mode.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
sources.dat 54 8 Overview of the Protocluster Candidates
in Table 4 (from Table 2 of the paper)
table4.dat 125 138 Observed Properties of All Spectroscopically
Confirmed Dropout Galaxies
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See also:
II/317 : The CFHTLS Survey (T0007 release) (Hudelot+ 2012)
J/ApJ/648/7 : Lyα emitters at z=6.5 in Subaru Deep Field
(Kashikawa+, 2006)
J/A+A/494/845 : Galaxy clusters in the CFHTLS (Grove+, 2009)
J/A+A/509/A81 : Candidate clusters detected in six CFHTLS fields (Adami+, 2010)
J/A+A/535/A65 : Galaxy clusters in the 4 CFHTLS Wide fields (Durret+, 2011)
J/A+A/572/A41 : VUDS Dicovery of a high-redshift protocluster (Lemaux+, 2014)
J/ApJ/799/60 : X-ray galaxy clusters in the CFHTLS fields (Mirkazemi+, 2015)
J/ApJ/823/11 : Candidate Lyα emitting galaxies at z∼3.8 (Dey+, 2016)
Byte-by-byte Description of file: sources.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Name Protocluster candidate name (DNADNN)
8- 9 I2 h RAh Hour of Right Ascension (J2000)
11- 12 I2 min RAm Minute of Right Ascension (J2000)
14- 17 F4.1 s RAs Second of Right Ascension (J2000)
19 A1 --- DE- Sign of the Declination (J2000)
20- 21 I2 deg DEd Degree of Declination (J2000)
23- 24 I2 arcmin DEm Arcminute of Declination (J2000)
26- 29 F4.1 arcsec DEs Arcsecond of Declination (J2000)
31- 32 A2 --- Field [D1 D3 D4] CFHTLS field
34- 42 A9 --- Pop Galaxy population
44- 46 F3.1 --- ODens Overdensity significance (in σ unit)
48- 50 I3 --- Ngal Number of dropout galaxies within 3 arcmin
radius from its overdensity peak
52- 54 A3 --- Spec [Yes] Protocluster candidate observed by
follow-up spectroscopy are marked as "Yes"
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Name Protocluster candidate name (DNADNN)
8- 9 I2 --- ID [1/42] Dropout galaxy identifier
11- 12 I2 h RAh Hour of Right Ascension (J2000)
14- 15 I2 min RAm Minute of Right Ascension (J2000)
17- 22 F6.3 s RAs Second of Right Ascension (J2000)
24 A1 --- DE- Sign of the Declination (J2000)
25- 26 I2 deg DEd Degree of Declination (J2000)
28- 29 I2 arcmin DEm Arcminute of Declination (J2000)
31- 35 F5.2 arcsec DEs Arcsecond of Declination (J2000)
37- 41 F5.2 mag mag Apparent aperture magnitude of detection band
(1)
43- 46 F4.2 mag e_mag Uncertainty in mag
48- 52 F5.3 --- z Redshift
54- 58 F5.3 --- E_z Upper limit uncertainty in z
60- 64 F5.3 --- e_z Lower limit uncertainty in z
66- 71 F6.2 mag UVMag UV absolute magnitude at 1300Å in
the rest frame
73- 76 F4.2 mag e_UVMag Uncertainty in UVMag
78- 83 F6.2 10-21W/m2 FLya Observed Lyα line flux
(in 10-18erg/s/cm2)
85- 88 F4.2 10-21W/m2 e_FLya Uncertainty in FLya
90- 94 F5.2 10+35W LLya Lyα luminosity (in 1042erg/s)
96- 99 F4.2 10+35W e_LLya Uncertainty in LLya
101-106 F6.2 0.1nm EW0 Rest-frame Lyα equivalent width (Å)
108-113 F6.2 0.1nm e_EW0 Uncertainty in EW0
115-119 F5.2 0.1nm Sw Weighted skewness (Å)
121-125 F5.2 0.1nm e_Sw Uncertainty in Sw
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Note (1): The apparent aperture magnitude of detection band is i' band for
u-, g-, and r-dropout, and z' band for i-dropout galaxies.
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History:
From electronic version of the journal
(End) Tiphaine Pouvreau [CDS] 02-Mar-2018