J/MNRAS/440/2810 Galaxy luminosity function at z ≃ 7 (Bowler+, 2014)
The bright end of the galaxy luminosity function at z ≃ 7:
before the onset of mass quenching?
Bowler R.A.A., Dunlop J.S., McLure R.J., Rogers A.B., McCracken H.J.,
Milvang-Jensen B., Furusawa H., Fynbo J.P.U., Taniguchi Y., Afonso J.,
Bremer M.N., Le Fevre O.
<Mon. Not. R. Astron. Soc., 440, 2810-2842 (2014)>
=2014MNRAS.440.2810B 2014MNRAS.440.2810B (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, photometry ; Redshifts
Keywords: galaxies: evolution - galaxies: formation - galaxies: high-redshift
Abstract:
We present the results of a new search for bright star-forming
galaxies at redshift z≃7 within the UltraVISTA second data release
(DR2) and UKIDSS (UKIRT Infrared Deep Sky Survey) UDS (Ultra Deep
Survey) DR10 data, which together provide 1.65deg2 of near-infrared
imaging with overlapping optical and Spitzer data. Using a full
photometric redshift analysis, to identify high-redshift galaxies and
reject contaminants, we have selected a sample of 34 luminous
(-22.7<MUV←21.2) galaxies with 6.5<z<7.5. Crucially, the deeper
imaging provided by UltraVISTA DR2 confirms all of the robust objects
previously uncovered by Bowler et al., validating our selection
technique. Our new expanded galaxy sample includes the most massive
galaxies known at z≃7, with M*≃1010M☉, and the majority are
resolved, consistent with larger sizes (r1/2≃1-1.5kpc) than
displayed by less massive galaxies. From our final robust sample, we
determine the form of the bright end of the rest-frame UV galaxy
luminosity function (LF) at z≃7, providing strong evidence that it
does not decline as steeply as predicted by the Schechter-function fit
to fainter data. We exclude the possibility that this is due to either
gravitational lensing, or significant contamination of our galaxy
sample by active galactic nuclei (AGN). Rather, our results favour a
double power-law form for the galaxy LF at high redshift, or, more
interestingly, an LF which simply follows the form of the dark matter
halo mass function at bright magnitudes. This suggests that the
physical mechanism which inhibits star formation activity in massive
galaxies (i.e. AGN feedback or some other form of 'mass quenching')
has yet to impact on the observable galaxy LF at z≃7, a conclusion
supported by the estimated masses of our brightest galaxies which have
only just reached a mass comparable to the critical 'quenching mass'
of M*≃1010.2M☉ derived from studies of the mass
function of star-forming galaxies at lower redshift.
Description:
The two multiwavelength survey fields analysed in this paper contain a
wealth of observations from X-ray to radio wavelengths.
The analysis presented in this paper relies on the DR1 and DR2 of the
ongoing UltraVISTA survey,1 which consists of Y, J, H and Ks imaging
with the Visible and Infrared Camera (VIRCAM) on the VISTA telescope
within the Cosmological Evolution Survey (COSMOS) field. The DR1,
described in detail by McCracken et al. (2012A&A...544A.156M 2012A&A...544A.156M, Cat.
J/A+A/544/A156), provided near-infrared imaging over the maximum area
of the programme covering 1.5deg2. DR2 provides deeper data in
strips that cover ∼70 per cent of the full field as shown in Fig.
1. Integration times for the DR2 Y, J, H and Ks bands range from 29 to
82 h per pixel, compared with 11 to 14h per pixel from DR1.
Throughout this paper, we refer to the DR2 imaging within the strips
as the 'ultradeep' part of the survey, and the DR1 imaging over the
full field as the 'deep' part.
In this study, we use the 10th data release (DR10) of near-infrared
imaging in the UDS field, from the UKIDSS (Lawrence et al.,
2007MNRAS.379.1599L 2007MNRAS.379.1599L, Cat. II/314). The UKIDSS UDS consists of deep
imaging (mAB∼25, 5σ) in the J, H and K bands over a total area
of 0.8deg2 centred on RA=02:17:48, DE=-05:05:57 (J2000).
DR10 was made public in January 2013 and is available on the Wide
Field Camera science archive.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 145 34 The photometry for the sources in our final
UltraVISTA and UDS samples
table3.dat 80 34 The best-fitting photometric redshift and model
parameters for the DR2 UltraVISTA and UDS samples
table4.dat 80 34 The physical properties of the galaxies in our z∼7
sample derived from the best-fitting SED models
tableb1.dat 121 10 The DR2 UltraVISTA magnitudes for the 10 galaxy
candidates presented in Bowler et al.
(2012MNRAS.426.2772B 2012MNRAS.426.2772B)
tableb2.dat 78 10 The best-fitting photometric redshift parameters
and galaxies sizes derived from the improved
UltraVISTA DR2 imaging of the 10 galaxy candidates
presented in Bowler et al. (2012MNRAS.426.2772B 2012MNRAS.426.2772B)
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- ID [2103/583226] ID number
8- 9 I2 h RAh Right ascension (J2000)
11- 12 I2 min RAm Right ascension (J2000)
14- 18 F5.2 s RAs Right ascension (J2000)
20 A1 --- DE- Declination sign (J2000)
21- 22 I2 deg DEd Declination (J2000)
24- 25 I2 arcmin DEm Declination (J2000)
27- 30 F4.1 arcsec DEs Declination (J2000)
32 A1 --- l_z'mag Limit flag on z'mag
33- 36 F4.1 mag z'mag UKIRT z' magnitude (1)
38- 40 F3.1 mag E_z'mag ? Error on z'mag (upper value)
42- 44 F3.1 mag e_z'mag ? Error on z'mag (lower value)
46 A1 --- l_NB921 Limit flag on l_NB921
47- 50 F4.1 mag NB921 ?=- UKIRT NB921 magnitude (1)
52- 54 F3.1 mag E_NB921 ? Error on NB921 (upper value)
56- 58 F3.1 mag e_NB921 ? Error on NB921 (lower value)
60- 63 F4.1 mag Ymag UKIRT Y magnitude (1)
65- 67 F3.1 mag E_Ymag Error on Ymag (upper value)
69- 71 F3.1 mag e_Ymag Error on Ymag (lower value)
73 A1 --- l_Jmag Limit flag on Jmag
74- 77 F4.1 mag Jmag ? UKIRT J magnitude (1)
79- 81 F3.1 mag E_Jmag ? Error on Jmag (upper value)
83- 85 F3.1 mag e_Jmag ? Error on Jmag (lower value)
87 A1 --- l_Hmag Limit flag on Hmag
88- 91 F4.1 mag Hmag ? UKIRT H magnitude (1)
93- 95 F3.1 mag E_Hmag ? Error on Hmag (upper value)
97- 99 F3.1 mag e_Hmag ? Error on Hmag (lower value)
101 A1 --- l_Kmag Limit flag on Kmag
102-105 F4.1 mag Kmag ? UKIRT K magnitude (1)
107-109 F3.1 mag E_Kmag ? Error on Kmag (upper value)
111-113 F3.1 mag e_Kmag ? Error on Kmag (lower value)
115 A1 --- l_[3.6] Limit flag on [3.6]
116-119 F4.1 mag [3.6] ? Spitzer/IRAC 3.6um magnitude (1)
121-123 F3.1 mag E_[3.6] ? Error on [3.6] (upper value)
125-127 F3.1 mag e_[3.6] ? Error on [3.6] (lower value)
129 A1 --- l_[4.5] Limit flag on [4.5]
130-133 F4.1 mag [4.5] ? Spitzer/IRAC 4.5um magnitude (1)
135-137 F3.1 mag E_[4.5] ? Error on [4.5] (upper value)
139-141 F3.1 mag e_[4.5] ? Error on [4.5] (lower value)
144 A1 --- B12 Bowler et al. (2012MNRAS.426.2772B 2012MNRAS.426.2772B) galaxy
number or H for 'Himiko' galaxy from
Ouchi et al. (2013ApJ...778..102O 2013ApJ...778..102O)
145 A1 --- fc [+] + indicates that the [3.6] and [4.5]
photometry is confused
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Note (1): The magnitudes presented here were based on 1.8-arcsec diameter
circular apertures except for the Spitzer/IRAC channels where 2.8-arcsec
diameter circular apertures were used. The photometry has been corrected to
the 84 per cent enclosed flux level using the appropriate point-source
correction. Where the flux is below 2σ significance, as defined by the
local depth derived for each object, we replaced the magnitude with the
limiting 2σ magnitude. The errors displayed were derived from the median
absolute deviation of the fluxes from the closest 200 blank sky apertures.
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Byte-by-byte Description of file: table3.dat tableb2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- ID [2103/583226] ID number
8- 11 F4.2 --- z [6.0/7.3] Best-fitting photometric redshift
13- 16 F4.2 --- E_z Error on z (upper value)
18- 21 F4.2 --- e_z Error on z (lower value)
23- 26 F4.1 --- chi2N χ2 value for "No Lyα" case (2)
27 A1 --- f_chi2N [+] Confused IRAC photometry (3)
29- 31 F3.1 mag AVN Absorption in V band for "No Lyα" case (2)
33- 35 F3.1 [Sun] ZN [0.2/1] Z abundance for "No Lyα" case (2)
37- 40 F4.2 --- zN [6.3/7.7] Redshift for "No Lyα" case (2)
42- 45 F4.1 --- chi2W χ2 value for "With Lyα" case (2)
47- 49 I3 0.1nm EW0 Rest-frame Lyα equivalent width for
"With Lyα" case (2)
51- 53 F3.1 mag AVW [0/1] Absorption in V band for
"With Lyα" case (2)
55- 57 F3.1 [Sun] ZW [0.2/1] Z abundance for "With Lyα" case (2)
59- 60 A2 --- SpT Best-fitting stellar template
62- 66 F5.1 --- chi2 χ2 value of best-fitting stellar template
68- 70 F3.1 arcsec FWHMz' [0/9]?=- FWHM for z' band (4)
72- 74 F3.1 arcsec FWHMY [0/9]?=- FWHM for Y band (4)
76- 78 F3.1 arcsec FWHMJ [0/9]?=- FWHM for J band (4)
80 A1 --- B12 Bowler et al. (2012MNRAS.426.2772B 2012MNRAS.426.2772B,
[BDM2012] NNNNNN) galaxy number or H for
'Himiko' galaxy from Ouchi et al.
(2013ApJ...778..102O 2013ApJ...778..102O) (5)
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Note (2): Case "No Lyα" stands for continuum-only fitting.
Case "With Lyα" is when we introduce the possibility of Lyα
emission in the fits
Note (3): +: where the IRAC photometry is considered confused with a nearby
object, we exclude the [3.6] and [4.5] bands from the fitting procedure, and
present the resulting χ2 value labelled with a + to illustrate that there
are different degrees of freedom, and hence acceptable χ2 values, for
these objects.
Note (4): Where an FWHM value has been measured, corresponding to an object
selected by SExtractor in that band, it is displayed.
Note (5): The candidate labelled 'H' is Himiko, which has an extremely bright
NB921 flux that can only be well fitted with models including Lyα
emission, hence the unacceptable χ2 for continuum-only fitting.
The object 28400 has an unusually blue [3.6-4.5] colour and hence cannot be
fitted well with our templates (that do not include potential nebular
emission), and so this object has a large χ2-value.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- ID [2103/583226] Identification number
8- 11 F4.1 [Msun/yr] logM* Stellar mass (6)
13- 15 F3.1 [Msun/yr] E_logM* Error on logM (upper value)
17- 19 F3.1 [Msun/yr] e_logM* Error on logM (lower value)
21- 23 I3 Msun/yr SFR [3/250] Star formation rate (6)
25- 27 I3 Msun/yr E_SFR Error on SFR (upper value)
29- 31 I3 Msun/yr e_SFR Error on SFR (lower value)
33- 37 F5.1 Gyr-1 sSFR [0.2/100] Specific star-formation rate (6)
39- 43 F5.1 Gyr-1 E_sSFR Error on SFRs (upper value)
45- 49 F5.1 Gyr-1 e_sSFR Error on SFRs (lower value)
52- 53 I2 Msun/yr SFRUV [9/47] Star formation rate from rest-frame
UV flux (7)
55- 59 F5.1 mag M1500 [-23/-21.2] Absolute magnitude (8)
61- 64 F4.1 --- bYJHK [-4.1/-1.5]?=- Rest-frame UV slope index
β calculated by fitting a power law to
the measured YJHK photometry (9)
66- 68 F3.1 --- e_bYJHK ? rms uncertainty on bYJHK
70- 73 F4.1 --- bJHK [-3.9/-0.8]?=- Rest-frame UV slope index
β calculated by fitting a power law to
the measured JHK photometry (9)
75- 77 F3.1 --- e_bJHK ? rms uncertainty on bJHK
79 A1 --- B12 Bowler et al. (7012MNRAS.426.2772B,
[BDM2012] NNNNNN) galaxy number or H for
'Himiko' galaxy from Ouchi et al.
(2013ApJ...778..102O 2013ApJ...778..102O)
80 A1 --- fc [+] + indicates that the [3.6] and [4.5]
photometry is confused
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Note (6): The stellar mass, SFR and sSFR were determined from the best-fitting
τ-model with the errors derived from the points with Δχ2=1
from the minimum Δχ2 value, after minimizing over all other
variables. An sSFR of 100Gyr-1 corresponds to the maximum attainable in the
set of models we use, which always corresponds to an uncertain mass estimate.
Note (7): We also present the SFRUV derived using the Madau, Pozzetti &
Dickinson (1998ApJ...498..106M 1998ApJ...498..106M) prescription, which converts the observed
rest-frame UV flux into a SFR directly. The absolute rest-frame UV magnitudes
of our galaxies were measured on the best-fitting model (corrected to total
magnitudes using a point-source correction) in the rest frame, when observed
through a top-hat filter of width Δλ=100Å centred on 1500Å.
Note (8): Note that the absolute magnitudes presented here have not been
corrected for gravitational lensing magnification, as discussed in Section 7.3.
Note (9): A missing value for β indicates that the object has large
uncertainties in one or more bands and hence a secure value could not be
obtained.
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- ID [2103/583226] ID number
8 A1 --- l_z'mag Limit flag on z'mag
9- 12 F4.1 mag z'mag UKIRT z' magnitude (1)
14- 16 F3.1 mag E_z'mag ? Error on z'mag (upper value)
18- 20 F3.1 mag e_z'mag ? Error on z'mag (lower value)
22- 23 I2 --- S/Nz' [0/16] Signal-to-noise of the z' detection
25- 28 F4.1 mag Ymag UKIRT Y magnitude (1)
30- 32 F3.1 mag E_Ymag Error on Ymag (upper value)
34- 36 F3.1 mag e_Ymag Error on Ymag (lower value)
38- 39 I2 --- S/NY [3/16] Signal-to-noise of the Y detection
41- 44 F4.1 mag Jmag UKIRT J magnitude (1)
46- 48 F3.1 mag E_Jmag Error on Jmag (upper value)
50- 52 F3.1 mag e_Jmag Error on Jmag (lower value)
54- 55 I2 --- S/NJ [2/12] Signal-to-noise of the J detection
57 A1 --- l_Hmag Limit flag on Hmag
58- 61 F4.1 mag Hmag UKIRT H magnitude (1)
63- 65 F3.1 mag E_Hmag ? Error on Hmag (upper value)
67- 69 F3.1 mag e_Hmag ? Error on Hmag (lower value)
71- 72 I2 --- S/NH [0/11] Signal-to-noise of the H detection
74 A1 --- l_Ksmag Limit flag on Ksmag
75- 78 F4.1 mag Ksmag UKIRT Ks magnitude (1)
80- 82 F3.1 mag E_Ksmag ? Error on Ksmag (upper value)
84- 86 F3.1 mag e_Ksmag ? Error on Ksmag (lower value)
88- 89 I2 --- S/NKs [0/13] Signal-to-noise of the Ks detection
91 A1 --- l_[3.6] Limit flag on [3.6]
92- 95 F4.1 mag [3.6] Spitzer/IRAC 3.6um magnitude (1)
97- 99 F3.1 mag E_[3.6] ? Error on [3.6] (upper value)
101-103 F3.1 mag e_[3.6] ? Error on [3.6] (lower value)
105 I1 --- S/N3.6 [0/5] Signal-to-noise of the 3.6um detection
107 A1 --- l_[4.5] Limit flag on [4.5]
108-111 F4.1 mag [4.5] Spitzer/IRAC 4.5um magnitude (1)
113-115 F3.1 mag E_[4.5] ? Error on [4.5] (upper value)
117-119 F3.1 mag e_[4.5] ? Error on [4.5] (lower value)
121 I1 --- S/N4.5 [0/5] Signal-to-noise of the 4.5um detection
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Note (1): The magnitudes were measured in a 1.8 arcsec diameter circular
aperture in all cases except the IRAC magnitudes which were measured in a
2.8 arcsec diameter circular aperture. All magnitudes have been corrected to
the 84 per cent enclosed flux level using appropriate point-source
corrections, and the errors presented are determined from the local error
method detailed in Section 2.3.
Where an object was detected at less than 2σ significance, the magnitude
is replaced with the 2σ local depth as an upper limit.
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 09-Feb-2015