J/ApJ/817/111 HST/COS survey of z<0.9 AGNs. I. (Danforth+, 2016)
An HST/COS survey of the low-redshift intergalactic medium.
I. Survey, methodology, and overall results.
Danforth C.W., Keeney B.A., Tilton E.M., Shull J.M., Stocke J.T.,
Stevans M., Pieri M.M., Savage B.D., France K., Syphers D., Smith B.D.,
Green J.C., Froning C., Penton S.V., Osterman S.N.
<Astrophys. J., 817, 111 (2016)>
=2016ApJ...817..111D 2016ApJ...817..111D (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Spectra, ultraviolet ; Redshifts ; Surveys
Keywords: cosmological parameters; cosmology: observations;
intergalactic medium; quasars: absorption lines; surveys
Abstract:
We use high-quality, medium-resolution Hubble Space Telescope/Cosmic
Origins Spectrograph (HST/COS) observations of 82 UV-bright active
galactic nuclei (AGNs) at redshifts zAGN<0.85 to construct the
largest survey of the low-redshift intergalactic medium (IGM) to date:
5138 individual extragalactic absorption lines in HI and 25 different
metal-ion species grouped into 2611 distinct redshift systems at
zabs<0.75 covering total redshift pathlengths ΔzHI=21.7 and
ΔzOVI=14.5. Our semi-automated line-finding and measurement
technique renders the catalog as objectively defined as possible. The
cumulative column density distribution of HI systems can be
parametrized d N(>N)/dz=C14(N/1014/cm2)-(β-1), with
C14=25±1 and β=1.65±0.02. This distribution is seen to
evolve both in amplitude, C14∝(1+z)2.3±0.1, and slope
β(z)=1.75-0.31 z for z≤0.47. We observe metal lines in 418
systems, and find that the fraction of IGM absorbers detected in
metals is strongly dependent on NH1. The distribution of OVI
absorbers appears to evolve in the same sense as the Lyα forest.
We calculate contributions to Ωb from different components of
the low-z IGM and determine the Lyα decrement as a function of
redshift. IGM absorbers are analyzed via a two-point correlation
function in velocity space. We find substantial clustering of HI
absorbers on scales of Δv=50-300km/s with no significant
clustering at Δv≳1000km/s. Splitting the sample into strong and
weak absorbers, we see that most of the clustering occurs in strong,
NHI≳1013.5/cm2, metal-bearing IGM systems.
Description:
COS is the fourth-generation UV spectrograph on board HST and is
optimized for medium-resolution (R∼18000, Δv∼17km/s)
spectroscopy of point sources in the 1135-1800Å band. To constitute
our survey, we selected 82 AGN sight lines from the archive which met
the selection criteria. Most of the AGNs observed in Cycles 18-20
under the Guaranteed Time Observation programs (GTO; PI-Green) are
included, along with numerous archival data sets collected under
various Guest Observer programs. Observational and programatic details
are presented in Table 2; see also section 2.1.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 89 82 HST/COS sight lines
table2.dat 77 89 COS observation details
linelist.dat 92 11844 HST/COS linelists for all the sightlines
systems.dat 106 4930 HST/COS systems for all the sightlines
igm/* 0 88 Individual subdirectories for each sightline
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Description of file: The "igm" repertory downloaded on
http://archive.stsci.edu/prepds/igm/ and available on the FTP,
is described in detail in section 3.
See also:
J/A+A/590/A68 : AGN data and absorption-line measurements (Richter+, 2016)
J/ApJ/814/40 : Nearby galaxy filaments with UV obs. (Wakker+, 2015)
J/MNRAS/449/3263 : Extended galaxy halo gas through HI and OVI (Johnson+, 2015)
J/ApJ/759/112 : The UV low-redshift intergalactic medium (Tilton+, 2012)
J/ApJ/740/91 : Lyα & OVI in galaxies around QSOs (Prochaska+, 2011)
J/ApJ/736/42 : HST QSO Catalog (Ribaudo+, 2011)
J/ApJ/734/65 : CI radial velocities with HST/STIS (Jenkins+, 2011)
J/ApJ/710/613 : Broad HI absorbers (Danforth+, 2010)
J/ApJ/701/1219 : Galaxy survey in 3 QSO fields (Chen+, 2009)
J/ApJS/177/39 : Survey of low-redshift OVI absorbers (Tripp+, 2008)
J/ApJ/679/194 : Low-z intergalactic medium. III. (Danforth+, 2008)
J/A+A/458/427 : Lyman alpha absorbers in 0.5<z<1.9 QSOs (Janknecht+, 2006)
J/MNRAS/335/555 : Lyman-alpha forest of 5 QSOs (Kim+, 2002)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- DirName Short sightline name corresponding to
individual subdirectory names
9- 29 A21 --- Name Sight line name
34- 35 I2 h RAh Hour of right ascension (J2000)
37- 38 I2 min RAm Minute of right ascension (J2000)
40- 44 F5.2 s RAs Second of right ascension (J2000)
48 A1 --- DE- Sign of declination (J2000)
49- 50 I2 deg DEd Degree of declination (J2000)
52- 53 I2 arcmin DEm Arcminute of declination (J2000)
55- 58 F4.1 arcsec DEs Arcsecond of declination (J2000)
61 A1 --- l_z Limit flag on z
62- 67 F6.4 --- z [0.05/0.9] AGN redshift
71- 75 F5.1 10-17W/m2/nm Flux [1/462] Median observed continuum flux in
the HST/COS FUV band
in units of 10-15erg/cm2/s/Å
79- 89 A11 --- Type AGN type
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- DirName Short sightline name corresponding to
individual subdirectory names
9- 29 A21 --- Name Name of the sight line
32- 38 A7 "Y/M" Date UT date of the observation
42- 45 F4.1 ks Exp130 [1/25]? Exposure time for G130M grism
48- 49 I2 --- S/N130 [5/78]? Median S/N per resolution element
in the G130M channel
52- 55 F4.1 ks Exp160 [0.5/18]? Exposure time for G160M grism
58- 59 I2 --- S/N160 [7/47]? Median S/N per resolution element
in the G160M channel
62- 66 I5 --- PID [11484/13008] Program number
69- 77 A9 --- PI PI name
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Byte-by-byte Description of file: linelist.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- DirName Short sightline name corresponding to
individual subdirectory names
9- 15 F7.2 0.1nm lambda [1133.4/1797.2] Observed Wavelength in Å
18- 29 A12 --- LineID Line identifier
30- 38 F9.6 --- z [-0.07/0.9] Absorber redshift
40- 43 F4.1 --- Sig [0.5/99.9]? Absorber significance level σ
45- 49 F5.1 --- S/N [1/123] S/N per resel.
51- 54 I4 0.1pm EW [0/2814] Equivalent width in mÅ
56- 58 I3 0.1pm e_EW [0/999] Equivalent width uncertainty
60- 64 F5.1 km/s b [0/150] Doppler b-parameter
66- 69 F4.1 km/s e_b [0/99.9]? b-parameter uncertainty
71 I1 --- l_logN [0/1] Limit flag on logN (1=upper limit)
73- 77 F5.2 [cm-2] logN [0/19.3]? log column density
78 A1 --- f_logN [i] i=Inf
80- 83 F4.2 [cm-2] e_logN [0/9.99]? log column density uncertainty
84 A1 --- felogN [n] n=NaN
86 I1 --- Fit [0/1] Line fit quality concerns?
88 I1 --- Lcod [0/9] Line-center optical depth τ0 (G1)
90 I1 --- ISM [0/1] ISM feature?
92 I1 --- AGN [0/1] AGN-intrinsic feature?
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Byte-by-byte Description of file: systems.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- DirName Short sightline name corresponding to
individual subdirectory names
9- 16 F8.6 --- zsys [0.001/0.7] System redshift
18- 22 F5.1 km/s DelV [12/274] System velocity half-width
24- 30 F7.2 0.1nm lambda [1134.9/1793.9] Observed wavelength
33- 44 A12 --- LineID Line identifier
46- 53 F8.6 --- zabs [0.001/0.7] Line redshift
55- 58 F4.1 --- Sig [3/99.9] Line Significance Level σ
60- 63 F4.1 --- S/N [1/87] Local S/N per resel
65- 68 I4 0.1pm EW [6/2814] Line equivalent width in mÅ
70- 72 I3 0.1pm e_EW [1/999] Equivalent width uncertainty
74- 78 F5.1 km/s b [5/150] Line b-value
80- 83 F4.1 km/s e_b [1/99.9] b-value uncertainty
85 I1 --- l_logN [0/1] Limit flag on logN (1=upper limit)
87- 91 F5.2 [cm-2] logN [11.8/19.3] Line log column density
93- 96 F4.2 [cm-2] e_logN [0.01/9.99] Log column density uncertainty
98 I1 --- Fit [0/1] Line fit quality concerns?
100 I1 --- Lcod [0/9] Line-center optical depth τ0 (G1)
102-103 I2 --- Nlsys [1/36] Number of lines in system
105-106 I2 --- Nml [0/22] Number of metal lines in system
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Global notes:
Note (G1): A line-center optical depth τ0=3 corresponds to a transmitted
flux of 5%. Given the typical S/N of 20 in the sample, we feel this is a
conservative limit on where single-line column densities can be trusted.
See section 2.5 for further explanations.
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History:
Downloaded from MAST: http://archive.stsci.edu/prepds/igm/
(End) Emmanuelle Perret [CDS] 17-May-2016