J/ApJ/754/83 UV continuum for z∼4-7 star-forming galaxies (Bouwens+, 2012)
UV-continuum slopes at z∼4-7 from the HUDF09+ERS+CANDELS observations:
discovery of a well-defined UV color-magnitude relationship for z≥ 4
star-forming galaxies.
Bouwens R.J., Illingworth G.D., Oesch P.A., Franx M., Labbe I., Trenti M.,
van Dokkum P., Carollo C.M., Gonzalez V., Smit R., Magee D.
<Astrophys. J., 754, 83 (2012)>
=2012ApJ...754...83B 2012ApJ...754...83B
ADC_Keywords: Galaxies, photometry ; Magnitudes, absolute ; Ultraviolet
Keywords: galaxies: evolution; galaxies: high-redshift
Abstract:
Ultra-deep Advanced Camera for Surveys (ACS) and WFC3/IR HUDF+HUDF09
data, along with the wide-area GOODS+ERS+CANDELS data over the CDF-S
GOODS field, are used to measure UV colors, expressed as the
UV-continuum slope β, of star-forming galaxies over a wide range
of luminosity (0.1L*z=3 to 2L*z=3) at high redshift (z∼7 to z∼4).
β is measured using all ACS and WFC3/IR passbands uncontaminated
by Lyα and spectral breaks. Extensive tests show that our β
measurements are only subject to minimal biases. Using a different
selection procedure, Dunlop et al. (2012MNRAS.420..901D 2012MNRAS.420..901D) recently
found large biases in their β measurements. To reconcile these
different results, we simulated both approaches and found that β
measurements for faint sources are subject to large biases if the same
passbands are used both to select the sources and to measure β.
High-redshift galaxies show a well-defined rest-frame UV
color-magnitude (CM) relationship that becomes systematically bluer
toward fainter UV luminosities. No evolution is seen in the slope of
the UV CM relationship in the first 1.5 Gyr, though there is a small
evolution in the zero point to redder colors from z∼7 to z∼4. This
suggests that galaxies are evolving along a well-defined sequence in
the LUV-color (β) plane (a "star-forming sequence"?). Dust
appears to be the principal factor driving changes in the UV color
β with luminosity. These new larger β samples lead to
improved dust extinction estimates at z∼4-7 and confirm that the
extinction is essentially zero at low luminosities and high redshifts.
Inclusion of the new dust extinction results leads to (1) excellent
agreement between the star formation rate (SFR) density at z∼4-8 and
that inferred from the stellar mass density; and (2) to higher
specific star formation rates (SSFRs) at z≳4, suggesting that the
SSFR may evolve modestly (by factors of ∼2) from z∼4-7 to z∼2.
Description:
Here, we utilize two primary data sets to examine the UV-continuum
slope β distribution of galaxies from z∼7 to z∼4: (1) the
ultra-deep ACS+WFC3/IR observations over the three HUDF09 fields
(Bouwens et al. 2010ApJ...709L.133B 2010ApJ...709L.133B; Bouwens et al.
2011ApJ...737...90B 2011ApJ...737...90B; Oesch et al. 2010ApJ...709L..16O 2010ApJ...709L..16O) and (2) the
wide-area ACS+WFC3/IR observations taken over the CDF-South GOODS
field as a result of Early Release Science and CANDELS programs
(Windhorst et al. 2011ApJS..193...27W 2011ApJS..193...27W; Giavalisco et al. 2004,
Cat. II/261; Grogin et al. 2011ApJS..197...35G 2011ApJS..197...35G; Koekemoer et al.
2011ApJS..197...36K 2011ApJS..197...36K). Figure 1 shows the layout of these observations
over the CDF-South GOODS area.
At present, the full two years of WFC3/IR observations (all 192 orbits
from the HUDF09 GO11563 program) have been obtained over the three
HUDF09 fields. The WFC3/IR observations over the HUDF include some 111
orbits of observations - while the HUDF09-1 and HUDF09-2 fields
include 33 orbits and 48 orbits of observations, respectively. See
section 2 for further details.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table8.dat 46 2518 *A complete list of the UV-continuum slopes β
we measure for sources in our z∼4, z∼5, z∼6, and
z∼7 samples from the HUDF09+ERS+CANDELS data sets
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Note on table8.dat: Samples were selected using the B, V, i, and z dropout
selection criteria given in Section 3.2 of the paper. Note that a small
fraction of the sources in our sample have very red UV-continuum slopes
β, i.e, >0.5, and therefore may not be at high redshifts (since this
would imply that the apparent break at ∼1 micron in their SEDs may not be
due to absorption by neutral hydrogen, but due to their overall spectral
shape). However, these sources essentially have no effect, i.e.,
δ-β≲0.01, on the biweight-mean beta's we report.
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
II/261 : GOODS initial results (Giavalisco+, 2004)
II/258 : Hubble Ultra Deep Field Catalog (UDF) (STScI, 2004)
J/A+A/556/A55 : Multi-color phot. of star-forming galaxies (Ilbert+, 2013)
J/ApJS/206/10 : CANDELS multiwavelength catalog (Galametz+, 2013)
J/A+A/545/A141 : UV selected sources in the GOODS-S field (Buat+, 2012)
J/ApJS/203/24 : Structural parameters of CANDELS galaxies (van der Wel+, 2012)
J/ApJ/742/3 : Photometric catalogs for ECDF-S and CDF-N (Rafferty+, 2011)
J/ApJ/743/146 : HST/WFC3 observations in HUDF and GOODS-S (Cameron+, 2011)
J/ApJ/738/69 : SEDs of galaxies at 3.8<z<5 in GOODS (Shim+, 2011)
J/AJ/141/14 : HST WFC3 ERS : emission-line galaxies (Straughn+, 2011)
J/MNRAS/418/2074 : Robust sample of galaxies at 6.0<z<8.7 (Mclure+, 2011)
J/ApJ/704/548 : Photometric properties of galaxies at z=4-6 (Overzier+, 2009)
J/AJ/132/1729 : Hubble Ultra Deep Field BVI-dropout sources (Beckwith+, 2006)
J/AJ/132/926 : Galaxies in the Hubble Ultra Deep Field (Coe+, 2006)
J/ApJ/653/53 : z∼6 galaxies UV luminosity function (Bouwens+, 2006)
Byte-by-byte Description of file: table8.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh [3] Hour of Right Ascension (J2000)
4- 5 I2 min RAm [32/33] Minute of Right Ascension (J2000)
7- 11 F5.2 s RAs Second of Right Ascension (J2000)
13 A1 --- DE- [-] Sign of the Declination (J2000)
14- 15 I2 deg DEd [27] Degree of Declination (J2000)
17- 18 I2 arcmin DEm [39/57] Arcminute of Declination (J2000)
20- 24 F5.2 arcsec DEs Arcsecond of Declination (J2000)
26- 31 F6.2 mag UVMag [-23/-16] Absolute AB magnitude in the
rest-frame UV
33- 37 F5.2 --- beta [-6.4/2.7] UV-continuum slope β
39- 42 F4.2 --- e_beta [0.1/2.1] UV-continuum slope beta uncertainty
44 I1 --- [4-7] Mean redshift of the sample (1)
46 A1 --- dset Data Set (2)
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Note (1): The mean redshift of the sample in which the source was found.
Note (2): The data set from which the source was selected and in which its
UV-continuum slope β was derived as follows:
1 = HUDF09 (WFC3/IR HUDF);
2 = HUDF09-1 (WFC3/IR P12);
3 = HUDF09-2 (WFC3/IR P34);
4 = CANDELS/ERS.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 04-Mar-2014