J/MNRAS/476/4965 Weak metal line absorbers sample (Muzahid+, 2018)
COS-Weak: probing the CGM using analogues of weak Mg II absorbers at z < 0.3.
Muzahid S., Fonseca G., Roberts A., Rosenwasser B., Richter P.,
Narayanan A., Churchill C., Charlton J.
<Mon. Not. R. Astron. Soc., 476, 4965-4986 (2018)>
=2018MNRAS.476.4965M 2018MNRAS.476.4965M (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Redshifts
Keywords: galaxies: formation - galaxies: haloes - quasar: absorption line
Abstract:
We present a sample of 34 weak metal line absorbers at z<0.3 selected
by the simultaneous >3σ detections of the SiIIλ1260 and
CIIλ1334 absorption lines, with Wr(SiII)<0.2 Å and
Wr(CII)<0.3Å, in archival HST/COS spectra. Our sample increases
the number of known low-z 'weak absorbers' by a factor of >5. The
column densities of HI and low-ionization metal lines obtained from
Voigt profile fitting are used to build simple photoionization models.
The inferred densities and line-of-sight thicknesses of the absorbers
are in the ranges of -3.3<lognH/cm-3←2.4 and ∼1pc-50kpc (median
~=500pc), respectively. Most importantly, 85 per cent (50 per cent) of
these absorbers show a metallicity of [Si/H]>-1.0(0.0). The fraction
of systems showing near-/supersolar metallicity in our sample is
significantly higher than in the HI-selected sample of Wotta et al.,
and the galaxy-selected sample of Prochaska et al., of absorbers
probing the circum-galactic medium at similar redshift. A search for
galaxies has revealed a significant galaxy-overdensity around these
weak absorbers compared to random positions with a median impact
parameter of 166 kpc from the nearest galaxy. Moreover, we find the
presence of multiple galaxies in ~=80 per cent of the cases,
suggesting group environments. The observed dN/dz of 0.8±0.2
indicates that such metal-enriched, compact, dense structures are
ubiquitous in the haloes of low-z group galaxies. We suggest that
these are transient structures that are related to galactic outflows
and/or stripping of metal-rich gas from galaxies.
Description:
We have searched for weak MgII analogues in 363 medium resolution,
far-UV (FUV) spectra of active galactic nuclei (AGNs)/quasars (QSOs)
observed with the Hubble Space Telescope/Cosmic Origins Spectrograph
(HST/COS). These spectra were available in the public HST archive
before 2016 February. Note that all these spectra were obtained under
programs prior to the HST Cycle-22. The properties of COS and its
in-flight operations are discussed in Osterman et al.
(2011Ap&SS.335..257O 2011Ap&SS.335..257O) and Green et al. (2012ApJ...744...60G 2012ApJ...744...60G). We have
used only spectra that were obtained with the medium resolution
(R∼20000) FUV COS gratings (i.e. G130M and/or G160M).
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 76 296 List of QSO spectra with S/N>5 per pixel
searched for weak MgII analogs
tableb2.dat 70 67 List of QSO spectra with S/N<5 per pixel
that are not used in this study
tableb3.dat 84 48 List of strong CII/SiII systems. These systems
are not part of the sample studied here
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Byte-by-byte Description of file: tableb1.dat tableb2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 16 A16 --- QSO QSO name sorted by increasing RA
18- 26 F9.5 deg RAdeg Right ascension (J2000)
28- 36 F9.5 deg DEdeg Declination (J2000)
38- 42 F5.3 --- zqso QSO redshift
44 I1 --- Gratings COS gratings used for observations (G1)
46- 50 F5.3 --- zmin Minimum search redshift
52- 56 F5.3 --- zmax Maximum search redshift
58- 59 I2 --- S/NG130M ?=-1 S/N of the G130M data estimated near
1400Å (-1 when data are not available)
61- 62 I2 --- S/NG160M ?=-1 S/N of the G160M data estimated near
1600Å (-1 when data are not available)
64 I1 --- Flag [0/2] Spectrum flag (G2)
66- 76 A11 --- PID HST proposal ID(s)
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Byte-by-byte Description of file: tableb3.dat
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Bytes Format Units Label Explanations
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1- 16 A16 --- QSO QSO name
18- 26 F9.5 deg RAdeg Right ascension (J2000)
28- 36 F9.5 deg DEdeg Declination (J2000)
38- 42 F5.3 --- zqso QSO redshift
44- 50 F7.5 --- zabs Absorption redshift
52 I1 --- Gratings COS gratings used for observations (G1)
54- 58 F5.3 --- zmin Minimum search redshift
60- 64 F5.3 --- zmax Maximum search redshift
66- 67 I2 --- S/NG130M S/N of the G130M data estimated near 1400Å
69- 70 I2 --- S/NG160M ?=-1 S/N of the G160M data estimated near
1600Å. S/N is -1 when data are not available
72 I1 --- Flag [0/2] Spectrum flag (G2)
74- 84 A11 --- PID HST proposal ID(s)
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Global notes:
Note (G1): Gratings code as follows:
1 = G130M
2 = G160M
3 = G130M+160M
Note (G2): Spectrum flag as follows:
1 = part of the statistical sample
2 = not part of the statistical sample
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 04-May-2021