J/ApJ/833/270 HI-selected-Lyman limit system metallicities (Glidden+, 2016)
Predominantly low metallicities measured in a stratified sample of Lyman limit
systems at z=3.7.
Glidden A., Cooper T.J., Cooksey K.L., Simcoe R.A., O'Meara J.M.
<Astrophys. J., 833, 270-270 (2016)>
=2016ApJ...833..270G 2016ApJ...833..270G (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Redshifts ; Spectroscopy ; Abundances
Keywords: galaxies: evolution; galaxies: high-redshift; intergalactic medium;
quasars: absorption lines
Abstract:
We measured metallicities for 33 z=3.4-4.2 absorption line systems
drawn from a sample of HI-selected-Lyman limit systems (LLSs)
identified in Sloan Digital Sky Survey (SDSS) quasar spectra and
stratified based on metal line features. We obtained higher-resolution
spectra with the Keck Echellette Spectrograph and Imager, selecting
targets according to our stratification scheme in an effort to fully
sample the LLS population metallicity distribution. We established a
plausible range of HI column densities and measured column densities
(or limits) for ions of carbon, silicon, and aluminum, finding
ionization-corrected metallicities or upper limits. Interestingly, our
ionization models were better constrained with enhanced
α-to-aluminum abundances, with a median abundance ratio of
[α/Al]=0.3. Measured metallicities were generally low, ranging
from [M/H]=-3 to -1.68, with even lower metallicities likely for some
systems with upper limits. Using survival statistics to incorporate
limits, we constructed the cumulative distribution function (CDF) for
LLS metallicities. Recent models of galaxy evolution propose that
galaxies replenish their gas from the low-metallicity intergalactic
medium (IGM) via high-density HI "flows" and eject enriched
interstellar gas via outflows. Thus, there has been some expectation
that LLSs at the peak of cosmic star formation (z∼3) might have a
bimodal metallicity distribution. We modeled our CDF as a mix of two
Gaussian distributions, one reflecting the metallicity of the IGM and
the other representative of the interstellar medium of star-forming
galaxies. This bimodal distribution yielded a poor fit. A single
Gaussian distribution better represented the sample with a low mean
metallicity of [M/H]~-2.5.
Description:
Our sample of 33 HI-selected-Lyman limit systems (LLSs) is a subset of
the 194 LLSs with zLLS≥3.3 and N_HI≥17.5cm-2 found in SDSS DR7
by Prochaska+ (2010, J/ApJ/718/392).
We observed the quasars toward which these 33 LLSs were identified,
using the Keck Echellette Spectrograph and Imager (ESI) on UT January
17-18 and UT 2015 April 19 using 0.75" slits. ESI covers the optical
spectrum from 0.39-1.1 microns and, with 0.75" slits, has a resolution
of (full-width at half-maximum) FWHM∼50km/s (SDSS spectra have
FWHM∼150km/s). Observational details are listed in Table 1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 130 33 Details for the Keck/ESI observations
table2.dat 84 273 Metal column densities
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See also:
J/ApJS/221/2 : Keck+Magellan survey for LLSs. III. (Prochaska+, 2015)
J/ApJ/775/78 : Lyman limit absorption systems in z∼3 QSOs (Fumagalli+, 2013)
J/ApJ/770/138 : Metallicities of Lyman limit systems and DLA (Lehner+, 2013)
J/ApJ/765/137 : HST survey for Lyman limit systems. II. (O'Meara+, 2013)
J/ApJ/755/89 : Metallicities of damped Lyα systems (Rafelski+, 2012)
J/ApJ/736/48 : 48 Lyman break galaxies at z∼3 in HUDF (Rafelski+, 2011)
J/ApJ/718/392 : SDSS Lyman limit systems at z∼3.5 (Prochaska+, 2010)
J/ApJ/648/L97 : SDSS QSOs supersolar super-Lyman limit syst. (Prochaska+ 2006)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 14 A14 --- ID QSO Identifier
16 A1 --- f_ID [ab] Flag on ID (1)
18- 19 I2 h RAh Hour of Right Ascension (J2000)
21- 22 I2 min RAm Minute of Right Ascension (J2000)
24- 28 F5.2 s RAs Second of Right Ascension (J2000)
30 A1 --- DE- Sign of the Declination (J2000)
31- 32 I2 deg DEd Degree of Declination (J2000)
34- 35 I2 arcmin DEm Arcminute of Declination (J2000)
37- 40 F4.1 arcsec DEs Arcsecond of Declination (J2000)
42- 46 F5.3 --- zqso [3.6/4.4] QSO redshift
48- 52 F5.3 --- zlls [3.3/4.2] LLS redshift
54 I1 --- Tier [1/3] Tier number (1=no metals) (2)
56- 67 A12 s Exp Exposure time
69- 73 F5.2 [cm-2] logHIl [17/20] Lower limit on log H I column density
75- 79 F5.2 [cm-2] logHIu [17/20] Upper limit on log H I column density
81 A1 --- l_Z Limit flag on Z
82- 86 F5.2 [-] Z [-3.6/-1.6] Metallicity
88- 91 F4.2 [-] e_Z [0.08/0.5]? Lower limit uncertainty in Z
93- 96 F4.2 [-] E_Z [0.08/0.5]? Upper limit uncertainty in Z
98 A1 --- l_logU Limit flag on logU
99-103 F5.2 [-] logU [-3/-1.3] Ionization parameter
105-108 F4.2 [-] e_logU [0.06/0.3]? Lower limit uncertainty in logU
110-113 F4.2 [-] E_logU [0.06/0.3]? Upper limit uncertainty in logU
115 A1 --- l_Ratio Limit flag on Ratio
116-120 F5.2 [-] Ratio [-1.4/0.8]? Log α/Al ratio
122-125 F4.2 [-] e_Ratio [0.09/0.2]? Lower limit uncertainty in Ratio
127-130 F4.2 [-] E_Ratio [0.09/0.2]? Upper limit uncertainty in Ratio
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Note (1): Flag as follows:
a = Denotes a partial HI-selected-Lyman limit system (LLS).
b = Observed during 18 degrees twilight.
Note (2): Our sample of 33 HI-selected-Lyman limit systems (LLSs) were grouped
into three "tiers" based on the prominence of their metal absorption
lines upon visual inspection of the SDSS spectra. The tiers are
classified as no metals (Tier 1; 27% of the 194),
possible metals (2; 15%), and obvious metals (3; 58%).
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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- 14 A14 --- ID QSO Identifier
16- 20 F5.3 --- zspec [3.3/4.2] Spectroscopic redshift (1)
22- 26 F5.2 [cm-2] logNl [17/19.8] Log lower limit of H I column density
28- 32 F5.2 [cm-2] logNu [17.6/20] Log upper limit of H I column density
34- 39 A6 --- Ion Ion identifier
41- 44 I4 0.1nm lambda [1260/1862]? Rest wavelength of Ion; Angstroms
46 A1 --- l_logN Limit flag on logN
48- 54 F7.4 [cm-2] logN [11.5/14.8]? Log column density (2)
56- 59 F4.2 [cm-2] e_logN [0.01/0.4]? Uncertainty in logN
61 A1 --- l_logNa Limit flag on logNa
63- 67 F5.2 [cm-2] logNa [11.5/14.8]? Log adopted column density (3)
69- 73 F5.3 [cm-2] e_logNa [0.004/0.3]? Uncertainty in logNa
75- 79 F5.2 [cm-2] logNp [11.6/15.8]? Log predicted column density (4)
81- 84 F4.2 [cm-2] e_logNp [0.05/0.5]? Uncertainty in logNp
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Note (1): Errors to the redshift were generally on the order of 1e-3.
Note (2): Measured using the apparent optical depth method.
Note (3): For saturated lines, we use lower limits. For non-detections, we
use 3-σ upper limits.
Note (4): As predicted by the Cloudy model using the ionization and metallicity
parameters obtained via MCMC modeling.
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History:
From electronic version of the journal
References:
Cooper et al. Paper I. 2015ApJ...812...58C 2015ApJ...812...58C
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-May-2017