J/ApJ/770/138 Metallicities of Lyman limit systems and DLA (Lehner+, 2013)
The bimodal metallicity distribution of the cool circumgalactic medium at z≲1.
Lehner N., Howk J.C., Tripp T.M., Tumlinson J., Prochaska J.X.,
O'Meara J.M., Thom C., Werk J.K., Fox A.J., Ribaudo J.
<Astrophys. J., 770, 138 (2013)>
=2013ApJ...770..138L 2013ApJ...770..138L
ADC_Keywords: QSOs ; Redshifts ; Abundances ; H I data
Keywords: cosmology: observations; galaxies: abundances; galaxies: halos;
galaxies: kinematics and dynamics
Abstract:
We assess the metal content of the cool (∼104K) circumgalactic
medium (CGM) about galaxies at z≲1 using an H I-selected sample of 28
Lyman limit systems (LLS; defined here as absorbers with
16.2≲logNHI≲18.5) observed in absorption against background QSOs
by the Cosmic Origins Spectrograph on board the Hubble Space
Telescope. The NHI selection avoids metallicity biases inherent in
many previous studies of the low-redshift CGM. We compare the column
densities of weakly ionized metal species (e.g., O II, Si II, Mg II)
to NHI in the strongest H I component of each absorber. We find that
the metallicity distribution of the LLS (and hence the cool CGM) is
bimodal with metal-poor and metal-rich branches peaking at [X/H]≃-1.6
and -0.3 (or about 2.5% and 50% solar metallicities). The cool CGM
probed by these LLS is predominantly ionized. The metal-rich branch of
the population likely traces winds, recycled outflows, and tidally
stripped gas; the metal-poor branch has properties consistent with
cold accretion streams thought to be a major source of fresh gas for
star forming galaxies. Both branches have a nearly equal number of
absorbers. Our results thus demonstrate there is a significant mass of
previously undiscovered cold metal-poor gas and confirm the presence
of metal enriched gas in the CGM of z≲1 galaxies.
Description:
We searched for the Lyman limit systems (LLS) in four high resolution
HST Cosmic Origins Spectrograph (COS) programs: 11520 ("COS-GTO: QSO
Absorbers, Galaxies and Large-scale Structures in the Local Universe",
PI Green), 11598 ("How Galaxies Acquire their Gas: A Map of Multiphase
Accretion and Feedback in Gaseous Galaxy Halos", a.k.a. the
"COS-Halos" program, PI: Tumlinson), 11692 ("The LMC as a QSO
Absorption Line System", PI: Howk), 11741 ("Probing Warm-Hot
Intergalactic Gas at 0.5<z<1.3 with a Blind Survey for OVI, NeVIII,
MgX, and SiXII Absorption Systems, PI: Tripp). The resolution of the
COS G130M and G160M gratings is R∼17000.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 90 84 Summary of the metallicity of the Lyman limit
systems (LLS), super-LLS, and DLA at z≳1
table2.dat 57 152 Adopted column densities
refs.dat 72 34 References
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See also:
B/hst : HST Archived Exposures Catalog (STScI, 2007)
J/MNRAS/434/1765 : Catalog of galaxies around PKS 0405-123 (Johnson+, 2013)
J/ApJ/755/89 : Metallicities of damped Lyα systems (Rafelski+, 2012)
J/ApJ/740/91 : Lyα & OVI in galaxies around quasars (Prochaska+, 2011)
J/ApJ/736/42 : HST QSO Catalog (Ribaudo+, 2011)
J/ApJS/193/28 : Galaxy survey around 20 UV-bright quasars (Prochaska+, 2011)
J/ApJ/721/1 : Keck ESI observations of Lyα systems (Penprase+, 2010)
J/ApJ/714/1521 : Spectroscopy of galaxies around distant QSOs (Chen+, 2010)
J/ApJ/710/613 : Broad HI absorbers (Danforth+, 2010)
J/ApJ/700/1299 : Gas-phase element depletions in the ISM (Jenkins, 2009)
J/ApJS/182/378 : HI and OVI absorbers in nearby Universe (Wakker+, 2009)
J/ApJ/676/262 : PKS1302-102 intergalactic absorption system (Cooksey+, 2008)
J/ApJS/168/213 : Ionization states and cooling efficiencies (Gnat+, 2007)
J/ApJ/636/610 : Damped Lyα systems at z<1.65 (Rao+, 2006)
J/MNRAS/367/1261 : Redshift survey in 15 quasar fields (Morris+, 2006)
J/ApJS/164/1 : IGM absorbers toward HE 0226-4110 (Lehner+, 2006)
J/ApJ/617/718 : Atomic data and EW for PKS 0405-123 (Prochaska+, 2004)
J/ApJ/599/116 : UV properties of absorbed quasars (Vestergaard+, 2003)
J/ApJS/155/351 : Absorption toward PG 1116+215 (Sembach+, 2004)
J/ApJ/513/168 : HST observations of carbon in spiral galaxies (Garnett+, 1999)
J/ApJ/508/200 : QSO low-z Lyα absorbers (Tripp+, 1998)
J/ApJ/475/469 : Composite HST Spectrum of Quasars (Zheng+ 1997)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 4 A4 --- Type Object type: LLS, SLLS or DLA (1)
6- 16 A11 --- QSO QSO name
18- 23 F6.4 --- zabs [0.006/1.1] Redshift of the absorber
25- 29 F5.2 [cm-2] logNHI [16.1/21.7] HI column density
31- 34 F4.2 [cm-2] E_logNHI [0.02/0.3] Positive error on logNHI
36- 39 F4.2 [cm-2] e_logNHI [0.02/0.3] Negative error on logNHI
41 A1 --- l_[X/H] Limit flag on [X/H]
43- 47 F5.2 [Sun] [X/H] [-2/0.7] Metallicity (2)
48 A1 --- u_[X/H] [:] Uncertainty flag on [X/H] (3)
50- 53 F4.2 [Sun] e_[X/H] ? Uncertainty on [X/H]
55- 56 A2 --- l_logU [≤> ] Limit flag on logU
58- 61 F4.1 [-] logU [-5.2/-2]? Log of ionization parameter U (3)
63 A1 --- l_rho Limit flag on rho
65- 68 I4 kpc rho [6/3238]? Impact parameter ρ (3)
70- 88 A19 --- Ref Reference(s) (see refs.dat file)
90 A1 --- n_Ref Remarks on absorber (4)
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Note (1): Sets are:
LLS = Lyman limit systems (LLS) with 16.2≤logNHI<19
SLLS = Super-LLS with 19≤logNHI<20.3
DLA = Damped Lyα absorber with logNHI>20.3
Note (2): For the LLS, the metallicity is estimated from α elements
(e.g., O, Mg, Si). For the SLLS and DLA, the metallicities were estimated
from Zn, except those estimated by Bat12 (2012ApJ...744...93B 2012ApJ...744...93B)
and Tri05 (2005ApJ...619..714T 2005ApJ...619..714T) where X is an α element.
Note (3): U is the ionization parameter derived from the Cloudy simulations
and ρ is the impact parameter to generally the closest galaxy
(there might be evidence of other galaxies within 150kpc, e.g. Jenkins
et al. 2005ApJ...623..767J 2005ApJ...623..767J; Kacprzak et al. 2012MNRAS.427.3029K 2012MNRAS.427.3029K). For
the SLLS with logNHI≲19.7 and no U value, no ionization correction
was estimated. For these absorbers, ionization corrections may be
necessary, and we emphasize this uncertainty by a colon and adopt the
measured value as an upper limit.
Note (4): Flag as follows:
a = This absorber was analyzed by Thom et al. (2011ApJ...736....1T 2011ApJ...736....1T), but no
error was given on NHI and 1σ upper limits were used to estimate
the metallicity. Using HI926, 920, 919, 918, we re-estimated NHI; we
also re-estimated the metallicity using 3σ upper limits. Our and
Thom et al. results are consistent within 1σ.
b = As this absorber was pre-selected on MgII absorption it is not included in
our sample of HI-selected LLS.
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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- 11 A11 --- QSO QSO name (1)
13- 18 F6.4 --- zabs Redshift from absorption lines
20 A1 --- r_zabs [bc] Origin of z (2)
22- 27 A6 --- Ion Species identifier
29- 32 A4 --- l_logN Limit flag on logN (3)
33- 37 F5.2 [cm-2] logN Log column density
39- 42 F4.2 [cm-2] E_logN ? Uncertainty in logN (4)
44- 47 F4.2 [cm-2] e_logN ? Lower limit uncertainty in logN (4)
48 A1 --- u_logN [:] Uncertainty flag in logN
50- 53 I4 km/s v1 Lower velocity of the integration of the
Na(v) profile
55- 57 I3 km/s v2 Upper velocity of the integration of the
Na(v) profile
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Note (1): The reader should refer to the Appendix for a description of each
of these absorbers (in particular for the complete information about
the velocity structure).
Note (2): Flag as follows:
b = C IV, Si IV, and Al II are from STIS E230M data.
c = The analysis of PG1216+069 is based on both COS and STIS E140M data;
see Appendix for details.
Note (3): the symbols are:
* ">" indicates that the absorption profile is saturated.
* "≥" indicates that the absorption profile might be saturated
* "<" indicates that there is no detection at the 3σ level.
* "≤" indicates that the profile might be contaminated by an
unrelated absorber.
Note (4): Values for both e_logN and E_logN indicate asymmetric uncertainties
with e_logN and E_logN being the lower and upper limits, respectively.
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Byte-by-byte Description of file: refs.dat
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Bytes Format Units Label Explanations
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1- 6 A6 --- Ref Reference code
8- 26 A19 --- BibCode Bibcode
28- 52 A25 --- Aut Author's name(s)
54- 72 A19 --- Comm Comment (VizieR catalog reference)
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History:
* 13-Jan-2015: From electronic version of the journal
* 27-Feb-2015:
-- in table1, for PG1522+101, zabs corrected from 0.7292 into 0.7289
-- in table2, for PKS0552-640, zabs corrected from 0.3415 into 0.3451
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 13-Jan-2015