J/ApJ/869/123 Keck Lyman continuum spectroscopic survey (KLCS) (Steidel+, 2018)
The Keck Lyman continuum spectroscopic survey (KLCS): the emergent ionizing
spectrum of galaxies at z∼3.
Steidel C.C., Bogosavljevic M., Shapley A.E., Reddy N.A., Rudie G.C.,
Pettini M., Trainor R.F., Strom A.L.
<Astrophys. J., 869, 123 (2018)>
=2018ApJ...869..123S 2018ApJ...869..123S
ADC_Keywords: Surveys; Galaxies, spectra; Redshifts; Colors; Ultraviolet;
Photometry, SDSS; Equivalent widths; Intergalactic medium
Keywords: cosmology: observations ; galaxies: evolution ;
galaxies: high-redshift ; intergalactic medium ; ultraviolet: galaxies
Abstract:
We present results of a deep spectroscopic survey quantifying the
statistics of the escape of ionizing radiation from star-forming
galaxies at z∼3. We measure the ratio of ionizing to non-ionizing UV
flux density <f900/f1500>obs, where f900 is the mean flux
density evaluated over the range [880,910]Å. We quantify the
emergent ratio of ionizing to non-ionizing UV flux density by
analyzing high signal-to-noise ratio composite spectra formed from
subsamples with common observed properties and numbers sufficient to
reduce the statistical uncertainty in the modeled IGM+CGM correction
to obtain precise values of <f900/f1500>out, including a
full-sample average <f900/f1500>out_=0.057±0.006. We show that
<f900/f1500>out increases monotonically with Wλ(Lyα),
inducing an inverse correlation with UV luminosity as a by-product. We
fit the composite spectra using stellar spectral synthesis together
with models of the ISM in which a fraction fc of the stellar
continuum is covered by gas with column density NHI. We show that
the composite spectra simultaneously constrain the intrinsic
properties of the stars (L900/L1500)int along with fc, NHI,
E(B-V), and fesc,abs, the absolute escape fraction of ionizing
photons. We find a sample-averaged fesc,abs=0.09±0.01, with
subsamples falling along a linear relation
<fesc,abs≳0.75[Wλ(Lyα)/110Å]. Using the far-UV
luminosity function, the distribution function n(W(Lyα)), and
the relationship between Wλ(Lyα) and <f900/f1500>out,
we estimate the total ionizing emissivity of z∼3 star-forming galaxies
with Muv≤-19.5, which exceeds the contribution of quasi-stellar
objects by a factor of ∼3, and accounts for ∼50% of the total
εLyC at z∼3 estimated using indirect methods.
Description:
The observations were conducted over the course of six separate
observing runs using low resolution imaging spectrometer (LRIS) on the
Keck I 10m telescope between 2006 December and 2008 June. The total
integration time per slit mask was between 8.2 and 12.8hr.
The average resolving power is R∼800 (LRIS-B; ∼3200-5000Å) and
R∼1400 (LRIS-R; ∼5000-7200Å).
A total of 136 galaxies was observed, in nine independent fields using
10 different slit masks.
The selection of z∼3 Lyman-break galaxies (LBGs) in all nine of the
Keck Lyman continuum spectroscopic survey (KLCS) fields was based on
photometric selection using the three-band (Un,G,{R}) photometric
system described in detail by Steidel+ (2003, J/ApJ/592/728).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 115 124 The final Keck Lyman Continuum Spectroscopic
(KLCS) sample
table3.dat 38 15 Objects with individual Lyman continuum (LyC)
detections
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See also:
III/116 : Spectrophotometric Standards (Massey+ 1988)
J/ApJ/592/728 : Lyman break galaxies at redshift z∼3 (Steidel+, 2003)
J/ApJ/667/79 : Lyα emission-line galaxies at z=3.1 (Gronwall+, 2007)
J/ApJ/671/1227 : Lyα galaxies at z∼4.5 (Dawson+, 2007)
J/A+A/498/13 : Lyman-α emitters from redshifts z∼2-3 (Nilsson+, 2009)
J/ApJ/725/394 : High-redshift Lyα emitters (Hu+, 2010)
J/ApJ/736/18 : Lyman-continuum emission at z∼3 in SSA22 field (Nestor+,2011)
J/ApJ/779/65 : Photometry of LBGs, LAEs and GNBs at z∼2.85 (Mostardi+, 2013)
J/ApJ/765/47 : Lyman-break galaxies and LAEs at z∼3 (Nestor+, 2013)
J/ApJ/795/165 : Line ratios in z∼2-3 galaxies KBSS-MOSFIRE (Steidel+,2014)
J/ApJ/803/34 : z∼4-10 galaxies from HST legacy fields (Bouwens+, 2015)
J/ApJ/810/71 : UV mag of candidate galaxies at 3~<z~<8.5 (Finkelstein+,2015)
J/ApJ/810/107 : Lyman break galaxies and LAEs HST photometry (Mostardi+,2015)
J/ApJS/221/2 : Keck+Magellan survey for LLSs. III. (Prochaska+, 2015)
J/ApJ/828/21 : ZFIRE v1.0 data release (Nanayakkara+, 2016)
J/MNRAS/465/302 : Lyman continuum leaking AGN in SSA22 field (Micheva+, 2017)
J/MNRAS/465/316 : Lyman continuum LAEs and LBGs in SSA22 field (Micheva+, 2017)
J/A+A/611/A95 : Diffuse ionized gas in the Antennae galaxy (Weilbacher+,2018)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- SAS-LBG Field+Slit based object name
16- 18 A3 --- n_SAS-LBG Flag on SAS-LBG (1)
20- 21 I2 h RAh [1/22] Hour of Right Ascension (J2000)
23- 24 I2 min RAm Minute of Right Ascension (J2000)
26- 30 F5.2 s RAs Second of Right Ascension (J2000)
31 A1 --- DE- [+] Sign of declination
32- 33 I2 deg DEd [0/52] Degree of Declination (J2000)
35- 36 I2 arcmin DEm Arcminute of Declination (J2000)
38- 42 F5.2 arcsec DEs Arcsecond of Declination (J2000)
44- 49 F6.4 --- zsys [2.7/3.6] Galaxy systemic redshift
51- 55 F5.2 mag Rmag [23.2/26] {R}-band AB magnitude
57- 60 F4.2 mag (G-R) [0.04/1.2] G-{R} color, AB magnitude(s)
62- 65 F4.2 mag (Un-G) [1.25/3.79] Un-G color, AB magnitude(s)
67- 71 F5.2 mag (G-R)0 [-0.05/1.1] Corrected G-{R} color index (2)
73- 77 F5.1 0.1nm EWLya [-34.8/153.4] Rest-frame equivalent width,
Lyα, in Angstrom units (3)
79- 84 F6.3 uJy F900 [-0.04/0.2] UV flux density at 900Å
86- 90 F5.3 uJy e_F900 [0.005/0.03] Uncertainty in F900
92- 96 F5.3 uJy F1500 [0.1/1.6] UV flux density at 900Å
98-102 F5.3 uJy e_F1500 [0.008/0.03] Uncertainty in F1500
104-109 F6.3 --- F900/F1500 [-0.09/0.6] Observed F900/F1500 flux
density ratio
111-115 F5.3 --- e_F900/F1500 [0.006/0.2] Propagated uncertainty in
F900/F1500
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Note (1):
avg = Q0933-MD75 and Q0933-D20 were observed twice, on masks q0933_L2 and
q0933_L3; weighted average measurement from the two independent spectra
Note (2): Color after correction for the intergalactic medium line blanketing
and the contribution of Lyα to the observed G band (see text).
Note (3): Rest-frame Lyα equivalent width in Angstroms, where positive
values indicate net emission.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- SAS-LBG Field+Slit based object name
16- 16 A1 --- f_SAS-LBG Object flag(s) (1)
18- 23 F6.4 --- zsys [2.8/3.5] Galaxy systemic redshift
25- 28 F4.2 --- LyC [0.3/1.5] UV luminosity, in units of
L*uv at z=3 (2)
30- 33 F4.2 --- F900/F1500 [0.05/0.6] Observed F900/F1500 flux density
ratio
35- 38 F4.2 --- e_F900/F1500 [0.01/0.1] Propagated uncertainty in
F900/F1500 (includes systematic error)
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Note (1): Flag as follow :
c = LyC detected object discussed in detail by Shapley+ 2016ApJ...826L..24S 2016ApJ...826L..24S
Note (2): Based on the R magnitude and assuming a characteristic
luminosity Luv corresponds to M_AB*(1700Å)=-21.0
(Reddy & Steide 2009ApJ...692..778R 2009ApJ...692..778R ).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Coralie FIX [CDS] 06-Nov-2019