J/ApJ/843/41 HST/WFC3 obs. of z∼2-8 galaxies in 4 HFF clusters (Bouwens+, 2017)
Extremely small sizes for faint z∼2-8 galaxies in the Hubble Frontier Fields:
a key input for establishing their volume density and UV emissivity.
Bouwens R.J., Illingworth G.D., Oesch P.A., Atek H., Lam D., Stefanon M.
<Astrophys. J., 843, 41 (2017)>
=2017ApJ...843...41B 2017ApJ...843...41B
ADC_Keywords: Clusters, galaxy ; Photometry, HST ; Galaxies, IR ; Redshifts
Keywords: galaxies: evolution; galaxies: high-redshift
Abstract:
We provide the first observational constraints on the sizes of the
faintest galaxies lensed by the Hubble Frontier Fields (HFF) clusters.
Ionizing radiation from faint galaxies likely drives cosmic
reionization, and the HFF initiative provides a key opportunity to
find such galaxies. However, we cannot assess their ionizing
emissivity without a robust measurement of their sizes, since this is
key to quantifying both their prevalence and the faint- end slope to
the UV luminosity function. Here we provide the first size constraints
with two new techniques. The first utilizes the fact that the
detectability of highly magnified galaxies as a function of shear is
very dependent on a galaxy's size. Only the most compact galaxies
remain detectable in high-shear regions (versus a larger detectable
size range for low shear), a phenomenon we quantify using simulations.
Remarkably, however, no correlation is found between the surface
density of faint galaxies and the predicted shear, using 87
high-magnification (µ=10-100) z∼2-8 galaxies seen behind the first
four HFF clusters. This can only be the case if faint (~-15mag)
galaxies have significantly smaller sizes than more luminous galaxies,
i.e., ≲30mas or 160-240pc. As a second size probe, we rotate and
stack 26 faint high-magnification sources along the major shear axis.
Less elongation is found even for objects with an intrinsic half-light
radius of 10mas. Together, these results indicate that extremely faint
z∼2-8 galaxies have near point-source profiles (half-light radii
<30mas and perhaps 5-10mas). These results suggest smaller
completeness corrections and hence shallower faint-end slopes for the
z∼2-8 LFs than derived in some recent studies (by Δα≳0.1-0.3).
Description:
We base the present study on the v1.0 reductions of the HST
observations over the first four HFF clusters Abell 2744, MACS0416,
MACS0717, and MACS1149 (A. Koekemoer et al. 2017, in preparation).
These data include at least 18, 10, 42, 34, 12, 10, and 24 orbits of
F435W, F606W, F814W, F105W, F125W, F140W, and F160W observations. The
FWHM of the PSF in the F105W, F125W, F140W, and F160W WFC3/IR
observations is typically ∼0.16"-0.17".
We also make use of our own reduction of the HST WFC3/UVIS F275W and
F336W observations available over Abell 2744, MACS0717, and MACS1149.
These observations include eight orbits of data in the F275W and F336W
bands.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . this file
table1.dat 26 4 Samples of high-magnification µ=10-100 z=2-8
galaxies found over the first four HFF clusters
table2.dat 98 236 Coordinates and other measured properties of z∼2-8
sources
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/ApJ/612/L93 : Candidates of z∼5.5-7 galaxies in the HST-UDF (Yan+, 2004)
J/AJ/132/1729 : HUDF BVI-dropout sources (Beckwith+, 2006)
J/ApJ/754/83 : UV continuum for z∼4-7 star-forming gal. (Bouwens+, 2012)
J/ApJ/756/164 : UV galaxies in CANDELS from z=8 to z=4 (Finkelstein+, 2012)
J/MNRAS/432/2696 : Galaxy luminosity function at z = 7-9 (McLure+, 2013)
J/ApJ/762/L30 : MCS J0416.1-2403 strong lensing analysis (Zitrin+, 2013)
J/ApJ/793/115 : UV-continuum slopes beta for z∼4-8 galaxies (Bouwens+, 2014)
J/MNRAS/444/268 : HST Frontier Fields clusters (Richard+, 2014)
J/ApJ/800/18 : HST/WFC3 obs. of z∼7-8 galaxies in A2744 (Atek+, 2015)
J/ApJ/803/34 : z∼4-10 galaxies from HST legacy fields (Bouwens+, 2015)
J/ApJ/810/71 : UV mag of cand. galaxies at 3~<z~<8.5 (Finkelstein+, 2015)
J/MNRAS/452/1437 : Abell 2744 strong-lensing analysis (Jauzac+, 2015)
J/ApJS/219/15 : Morphologies of z=0-10 galaxies with HST (Shibuya+, 2015)
J/ApJ/801/44 : HST lensing analysis of the CLASH sample (Zitrin+, 2015)
J/A+A/590/A31 : ASTRODEEP Frontier Fields Catalogues (Merlin+, 2016)
J/ApJ/835/113 : Gal. ≳6 from the Hubble Frontier Fields (Livermore+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Cluster Cluster identification
12- 13 I2 --- z2 [2/15]? Number of galaxies with z∼2
15- 16 I2 --- z3 [2/10]? Number of galaxies with z∼3
18- 19 I2 --- z5 [2/10] Number of galaxies with z∼5
21- 22 I2 --- z6 [1/7] Number of galaxies with z∼6
24- 24 I1 --- z7 [0/3] Number of galaxies with z∼7
26- 26 I1 --- z8 [0/2] Number of galaxies with z∼8
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 10 A10 --- Cluster Cluster identification as in table 1;
column added by CDS
12- 28 A17 --- ID Source ID
29- 29 A1 --- HMagS Member of high magnification sample (1)
31- 32 I2 h RAh Hour of Right Ascension (J2000)
34- 35 I2 min RAm Minute of Right Ascension (J2000)
37- 42 F6.3 s RAs Second of Right Ascension (J2000)
44- 44 A1 --- DE- Sign of the Declination (J2000)
45- 46 I2 deg DEd Degree of Declination (J2000)
48- 49 I2 arcmin DEm Arcminute of Declination (J2000)
51- 55 F5.2 arcsec DEs Arcsecond of Declination (J2000)
57- 61 F5.2 mag F160mag [24.6/30.2] Measured HST WFC3 F160W AB magnitude
63- 68 F6.2 mag F160Mag [-21.5/-12.2] Absolute F160W-band AB magnitude
70- 73 F4.2 --- zphot [1.5/7.7] Photometric redshift estimate
75- 80 F6.2 --- magf [1/145] Magnification factor (median of the
four parametric models)
82- 86 F5.2 --- shff [1/47] Shear factor (median of the available
models)
88- 92 F5.3 kpc rhl [0.0/2.7]? Circularized half-light radius
estimate after correction for lensing
94- 98 F5.3 kpc e_rhl [0.0/4.3]? Uncertainty in rhl
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Note (1):
* = Member of high magnification sample presented in Figure 1/Table 1.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 28-Feb-2018