J/ApJ/765/47 Lyman-break galaxies and LAEs at z∼3 (Nestor+, 2013)
A refined estimate of the ionizing emissivity from galaxies at z ≃ 3:
spectroscopic follow-up in the SSA22a field.
Nestor D.B., Shapley A.E., Kornei K.A., Steidel C.C., Siana B.
<Astrophys. J., 765, 47 (2013)>
=2013ApJ...765...47N 2013ApJ...765...47N
ADC_Keywords: Galaxies, spectra ; Redshifts ; Magnitudes ; Ultraviolet
Keywords: cosmology: observations; diffuse radiation; galaxies: high-redshift;
intergalactic medium
Abstract:
We investigate the contribution of star-forming galaxies to the
ionizing background at z∼3, building on previous work based on
narrowband (NB3640) imaging in the SSA22a field. We use new Keck/LRIS
spectra of Lyman break galaxies (LBGs) and narrowband-selected
Lyα emitters (LAEs) to measure redshifts for 16 LBGs and 87 LAEs
at z>3.055, such that our NB3640 imaging probes the Lyman-continuum
(LyC) region. When we include the existing set of spectroscopically
confirmed LBGs, our total sample with z>3.055 consists of 41 LBGs and
91 LAEs, of which 9 LBGs and 20 LAEs are detected in our NB3640 image.
With our combined imaging and spectroscopic data sets, we critically
investigate the origin of NB3640 emission for detected LBGs and LAEs.
We remove from our samples three LBGs and three LAEs with
spectroscopic evidence of contamination of their NB3640 flux by
foreground galaxies and statistically model the effects of additional,
unidentified foreground contaminants. The resulting contamination and
LyC-detection rates, respectively, are 62%±13% and 8%±3% for our
LBG sample, and 47%±10% and 12%±2% for our LAE sample. The
corresponding ratios of non-ionizing UV to LyC flux density, corrected
for intergalactic medium (IGM) attenuation, are 18.0+34.8-7.4 for
LBGs and 3.7+2.5-1.1 for LAEs. We use these ratios to estimate the
total contribution of star-forming galaxies to the ionizing background
and the hydrogen photoionization rate in the IGM, finding values
larger than, but consistent with, those measured in the Lyα
forest. Finally, the measured UV to LyC flux-density ratios imply
model-dependent LyC escape fractions of fLyCesc∼5%-7% for our LBG
sample and fLyCesc∼10%-30% for our fainter LAE sample.
Description:
Our analyses make use of deep multiband imaging available in the
SSA22a field. These data, which are described in detail in Nestor et
al. (2011, J/ApJ/736/18), include ground-based broad B-, V-, and
R-band images and narrowband images with effective wavelengths at
λ∼3640Å and λ∼4980å. The NB3640 and part of the
NB4980 data were obtained using the Keck/LRIS imaging spectrograph.
We performed spectroscopy in the SSA22a field using both shallow and
deep observations. Nine shallow slit masks were observed over the
course of five observing runs in 2009 June, 2009 September, 2010 July,
2010 August, and 2011 May. A single deep mask was observed in 2010
August. Typical exposure times for the shallow masks were 5400s,
while the deep mask was observed for 23700s.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 75 42 z>3.055 Lyman break galaxies (LBGs) sample
table3.dat 80 130 Summary of Lyα emitters (LAEs) data
--------------------------------------------------------------------------------
See also:
J/MNRAS/418/2074 : Robust sample of galaxies at 6.0<z<8.7 (Mclure+, 2011)
J/ApJ/736/31 : HETDEX pilot survey. II. 1.9<z<3.8 LAEs (Blanc+, 2011)
J/ApJ/736/18 : Lyman-continuum emission in SSA22 field (Nestor+, 2011)
J/MNRAS/401/1521 : Lyman break galaxies stellar masses at z∼3 (Magdis+, 2010)
J/ApJS/176/301 : Subaru/XMM-Newton deep survey IV. (SXDS) (Ouchi+, 2008)
J/ApJ/667/79 : Lyα emission-line galaxies at z=3.1 (Gronwall+, 2007)
J/ApJ/592/728 : Lyman break galaxies at redshift z∼3 (Steidel+, 2003)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 8 A8 --- LBG Lyman-Break Galaxy identification
(<SAS-LBG SSA22a-AANN> in Simbad)
10 A1 --- f_LBG [f] Redshift not available (1)
12- 13 I2 h RAh [22] Hour of right ascension (J2000)
15- 16 I2 min RAm [17] Minute of right ascension (J2000)
18- 22 F5.2 s RAs [18/40] Second of right ascension (J2000)
24 A1 --- DE- [+] Sign of declination (J2000)
25- 26 I2 deg DEd [00] Degree of declination (J2000)
28- 29 I2 arcmin DEm [10/18] Arcminute of declination (J2000)
31- 34 F4.1 arcsec DEs Arcsecond of declination (J2000)
36- 40 F5.3 --- zem [3/3.4]? Lyα emission redshift
42- 46 F5.3 --- zabs [3/3.4]? Interstellar absorption redshift
48- 52 F5.2 mag Rmag [23.4/25.9] R-band magnitude
54- 58 F5.2 mag NB3640 [25.2/27]? NB3640 (LyC) magnitude
60 A1 --- f_NB3640 [e] Foreground object (1)
62- 64 F3.1 arcsec Off [0.1/2]? Spatial offset between the centroids
of the R-band and NB3640 emission
66 A1 --- l_FUV/FLy Limit flag on FUV/FLy
68- 71 F4.1 --- FUV/FLy [2/29.2]? Observed ratio in non-ionizing UV
and LyC flux densities (G1)
73- 75 F3.1 --- e_FUV/FLy [0.4/5.1]? FUV/FLy uncertainty
--------------------------------------------------------------------------------
Note (1): Flag as follows:
e = Spectrum contains evidence for the presence of a foreground object. Thus,
the NB3640 flux is likely contaminated by non-ionizing UV flux from the
interloper.
f = We were unable to determine the redshift of the LBG aug96M16, which in
Nestor et al. (2011, J/ApJ/736/18) was erroneously associated with a nearby
galaxy with zem=3.298. We have removed it from our sample but include it in
this table for completeness.
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table3.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- Seq [1/130] Running sequence number
(<[NSS2011] NNN> in Simbad)
5- 8 A4 --- LBG Object also identified as LBG
10 A1 --- f_Seq [e] Previsouly known source (1)
12- 13 I2 h RAh [22] Hour of right ascension (J2000)
15- 16 I2 min RAm [17] Minute of right ascension (J2000)
18- 22 F5.2 s RAs [18/40] Second of right ascension (J2000)
24 A1 --- DE- [+] Sign of declination (J2000)
25- 26 I2 deg DEd [00] Degree of declination (J2000)
28- 29 I2 arcmin DEm [10/18] Arcminute of declination (J2000)
31- 34 F4.1 arcsec DEs Arcsecond of declination (J2000)
36 A1 --- l_Rmag Limit flag on Rmag
38- 42 F5.2 mag Rmag [23.9/27] R-band magnitude
44 A1 --- l_NB3640 Limit flag on NB3640
46- 50 F5.2 mag NB3640 [24.7/27.3] NB3640 (LyC) magnitude
52 A1 --- f_NB3640 [fh] NB3640 is not LyC (1)
54- 56 F3.1 arcsec Off [0.1/2.2]? Spatial offset between the
centroids of R and NB3640 emission
58 A1 --- f_Off [j] Offset from BV detection (1)
60- 62 F3.1 arcsec OffA [0/1.8]? Spatial offset between the centroids
of Lyα and NB3640 emission
64 A1 --- l_FUV/FLy Limit flag on FUV/FLy
66- 69 F4.1 --- FUV/FLy [0.5/23]? Observed ratio in non-ionizing UV
and LyC flux densities (G1)
71- 73 F3.1 --- e_FUV/FLy [0.2/5.1]? FUV/FLy uncertainty
75- 79 F5.3 --- zem [3.04/3.12]? Spectroscopic redshift based on
the observed wavelength of Lyα emission
80 A1 --- f_zem [gi] LRIS spectroscopic observation (1)
--------------------------------------------------------------------------------
Note (1): Flag as follows:
e = Objects with previously known spectroscopic redshifts.
f = Spectrum contains evidence for the presence of a foreground galaxy. Thus,
we do not consider the NB3640 detection to be LyC flux.
g = Objects with LRIS spectroscopic observations but without confirmed
redshifts.
h = The redshift of this LAE is such that some non-ionizing UV flux will
contribute to the NB3640 detection, and therefore we exclude it from our
LyC detection sample.
i = Objects without LRIS spectroscopic observations.
j = Offset determined from the centroid of the BV detection.
--------------------------------------------------------------------------------
Global notes:
Note (G1): Observed ratio and uncertainty in non-ionizing UV and LyC flux
densities, inferred from the NB3640-R color. This value has not been
corrected for either contamination by foreground sources or IGM
(intergalactic) absorption.
--------------------------------------------------------------------------------
History:
From electronic version of the journal
(End) Emmanuelle Perret [CDS] 30-Oct-2014