J/ApJ/820/82 S2CLS: multiwavelength counterparts to SMGs (Chen+, 2016)
The SCUBA-2 Cosmology Legacy Survey: multiwavelength counterparts to
103 submillimeter galaxies in the UKIDSS-UDS field.
Chen C.-C., Smail I., Ivison R.J., Arumugam V., Almaini O., Conselice C.J.,
Geach J.E., Hartley W.G., Ma C.-J., Mortlock A., Simpson C., Simpson J.M.,
Swinbank A.M., Aretxaga I., Blain A., Chapman S.C., Dunlop J.S., Farrah D.,
Halpern M., Michalowski M.J., van der Werf P., Wilkinson A., Zavala J.A.
<Astrophys. J., 820, 82 (2016)>
=2016ApJ...820...82C 2016ApJ...820...82C (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, photometry ; Millimetric/submm sources ; Radio sources ;
Infrared sources ; Redshifts ; Surveys
Keywords: catalogs; cosmology: observations; galaxies: formation;
galaxies: high-redshift; galaxies: starburst; submillimeter: galaxies
Abstract:
We present multiwavelength identifications for the counterparts of
1088 submillimeter sources detected at 850µm in the SCUBA-2
Cosmology Legacy Survey (S2CLS) study of the UKIRT Infrared Deep Sky
Survey-Ultra-Deep Survey (UDS) field. By utilizing an Atacama Large
Millimeter Array (ALMA) pilot study on a subset of our bright SCUBA-2
sample as a training set, along with the deep optical-near-infrared
(OIR) data available in this field, we develop a novel technique,
Optical-IR Triple Color (OIRTC), using z-K, K-[3.6], [3.6]-[4.5]
colors to select the candidate submillimeter galaxy (SMG)
counterparts. By combining radio identification and the OIRTC
technique, we find counterpart candidates for 80% of the Class = 1
≥4σ SCUBA-2 sample, defined as those that are covered by both
radio and OIR imaging and the base sample for our scientific analyses.
Based on the ALMA training set, we expect the accuracy of these
identifications to be 82%±20%, with a completeness of 69%±16%,
essentially as accurate as the traditional p-value technique but with
higher completeness. We find that the fraction of SCUBA-2 sources
having candidate counterparts is lower for fainter 850µm sources,
and we argue that for follow-up observations sensitive to SMGs with
S850≳1mJy across the whole ALMA beam, the fraction with multiple
counterparts is likely to be >40% for SCUBA-2 sources at S850≳4mJy.
We find that the photometric redshift distribution for the SMGs is
well fit by a lognormal distribution, with a median redshift of
z=2.3±0.1. After accounting for the sources without any radio and/or
OIRTC counterpart, we estimate the median redshift to be z=2.6±0.1
for SMGs with S850>1mJy. We also use this new large sample to study
the clustering of SMGs and the far-infrared properties of the
unidentified submillimeter sources by stacking their Herschel SPIRE
far-infrared emission.
Description:
The SCUBA-2 data at 850um in the UDS field were taken as part of the
SCUBA-2 Cosmology Legacy Survey (S2CLS). The full data reduction steps
are described fully in J. E. Geach et al. (2016, in preparation).
In total we detect 1088 submillimeter sources at ≥3.5σ within
the region where rms noise is ≤1.3mJy/beam. We define a main sample
of 716 submillimeter sources that have ≥4.0σ, for which we
expect a false detection rate of ∼1% based on simulations and source
extractions on negative signals. We also define a supplementary sample
of 372 submillimeter sources that are detected at 3.5-4.0σ and
have a false detection rate of ∼10%. In this paper, we provide
counterpart candidates for both main and supplementary samples;
however, the scientific analyses were performed on the main sample.
We have carried out ALMA follow-up observations at 870um on 30 of
the brighter SCUBA-2 sources in a Cycle 1 project 2012.1.00090.S
(Simpson et al. 2015ApJ...807..128S 2015ApJ...807..128S, 2015ApJ...799...81S 2015ApJ...799...81S).
The K-band-based multiwavelength photometry adopted in this paper is
based on the UDS data release 8 (DR8) of the UKIRT Infrared Deep Sky
Survey (UKIDSS; Lawrence et al. 2007, see II/319).
The VLA radio observations at 1.4GHz (20cm) were carried out by the
project UDS20 (V. Arumugam et al. 2016, in preparation), which
comprises a mosaic of 14 pointings covering a total area of ∼1.3deg2
centered on the UDS.
The ∼1 square degree UDS field contains a rich set of ancillary data
(see section 2 for further details).
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table3.dat 98 914 *Candidate submillimeter galaxy (SMG) counterparts
of the main SCUBA-2 sources
table4.dat 98 425 *Candidate submillimeter galaxy (SMG) counterparts
of the supplementary SCUBA-2 sources
--------------------------------------------------------------------------------
Note on table3.dat and table4.dat: The main sample includes sources detected
at ≥4σ with an expected false detection rate of ∼1% whereas the
supplementary sample includes sources detected at 3.5-4σ with a flase
detection rate of ∼10%.
--------------------------------------------------------------------------------
See also:
II/319 : UKIDSS-DR9 LAS, GCS and DXS Surveys (Lawrence+ 2012)
J/ApJ/812/43 : ALMA 870um obs. of HerMES galaxies (Bussmann+, 2015)
J/MNRAS/442/577 : Selected ALESS SMGs radio properties (Thomson+, 2014)
J/MNRAS/440/3462 : AzTEC/ASTE 1.1mm survey of SSA22 (Umehata+, 2014)
J/MNRAS/436/1919 : SCUBA observations of COSMOS galaxies (Casey+, 2013)
J/MNRAS/431/194 : Selecting IRAC counterparts to SMGs (Alberts+, 2013)
J/ApJ/768/91 : ALMA observations of LESS submm galaxies (Hodge+, 2013)
J/MNRAS/426/1845 : AzTEC survey of the SHADES fields. II. (Michalowski+, 2012)
J/MNRAS/421/3060 : Subaru/XMM Deep Field radio imaging. III. (Simpson+, 2012)
J/MNRAS/415/1479 : LESS photometric redshift survey (Wardlow+, 2011)
J/MNRAS/413/2314 : Radio & mid-IR counterpart of submm galaxies (Biggs+, 2011)
J/MNRAS/405/2260 : GOODS-S field AzTEC/ASTE Deep 1.1mm imaging (Scott+, 2010)
J/ApJ/707/1201 : LABOCA ECDFS Submillimeter Survey (LESS) (Weiss+, 2009)
J/ApJS/179/124 : Subaru/XMM-Newton deep survey (SXDS) III. (Ueda+, 2008)
J/ApJS/179/95 : VLA survey of CDF-S. II. (Mainieri+, 2008)
J/MNRAS/380/199 : SCUBA Half-Degree Extragalactic Survey. III (Ivison+, 2007)
J/MNRAS/372/741 : SXDF 100µJy catalogue (Simpson+, 2006)
J/ApJ/622/772 : Redshift survey of submillimeter galaxies (Chapman+, 2005)
J/ApJ/606/664 : MAMBO sources near NTT Deep Field (Dannerbauer+, 2004)
Byte-by-byte Description of file: table[34].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- ID Short S2CLS identifier (UDS.NNNN)
10- 17 F8.5 deg RAdeg SMG Right Ascension in decimal degrees (J2000)
19- 26 F8.5 deg DEdeg SMG Declination in decimal degrees (J2000)
28 I1 --- Class [1/3] Class (1)
30 I1 --- N [0/5] Number of counterpart candidates
32- 34 A3 --- CCID Counterpart candidate identifier (IDN)
36 A1 --- f_CCID [*] Flag on CCID (2)
38- 45 F8.5 deg RARdeg ? Radio Right Ascension (J2000)
47- 54 F8.5 deg DERdeg ? Radio Declination (J2000)
56- 63 F8.5 deg RAKdeg ? UKIDSS K-band Right Ascension (J2000)
65- 72 F8.5 deg DEKdeg ? UKIDSS K-band Declination (J2000)
74- 77 F4.2 --- z [0.2/6.5]? Photometric redshift
79- 82 F4.2 --- E_z [0.01/2.6]? Upper uncertainty in z
84- 87 F4.2 --- e_z [0.01/1.9]? Lower uncertainty in z
89- 93 F5.3 --- p [0/0.11]? The p-value for radio selected
counterparts
95- 98 F4.2 --- [0.05/0.5]? Mean submillimeter galaxy (SMG)
fraction (fi,OIRTC=Ni,SMG/Ni) (3)
--------------------------------------------------------------------------------
Note (1): Class code as follows:
1 = within the search radius of 8.7" from the SCUBA-2 position, sources that
are covered by the radio imaging, and also qualified for the Optical-IR
Triple Color (OIRTC) technique (having at least two color measurements
among z-K, K-[3.6], [3.6]-[4.5]).
2 = sources that are only covered by the radio imaging, but lack the coverage
necessary for the OIRTC technique (or only have it in part of the region
within the search radius).
3 = sources that are not covered by the radio imaging and not covered by the
OIRTC technique either (or only covered in part of the region within the
search radius).
Note (2):
* = Counterpart that is confirmed by ALMA observations
(Simpson et al. 2015ApJ...807..128S 2015ApJ...807..128S).
Note (3): Of candidates selected purely based on the OIRTC technique, see
Section 3.3 for the definition of this quantity.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 31-May-2016