J/MNRAS/449/1536 New damped Lyα absorbers (Turnshek+, 2015)
36 new, high-probability, damped Lyα absorbers at redshift 0.42<z<0.70.
Turnshek D.A., Monier E.M., Rao S.M., Hamilton T.S., Sardane G.M., Held R.
<Mon. Not. R. Astron. Soc., 449, 1536-1544 (2015)>
=2015MNRAS.449.1536T 2015MNRAS.449.1536T (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Redshifts ; Equivalent widths
Keywords: galaxies: evolution - galaxies: formation - galaxies: ISM -
quasars: absorption lines
Abstract:
Quasar damped Lyα (DLA) absorption-line systems with redshifts
z<1.65 are used to trace neutral gas over approximately 70 percent of
the most recent history of the Universe. However, such systems fall in
the UV and are rarely found in blind UV spectroscopic surveys.
Therefore, it has been difficult to compile a moderate-sized sample of
UV DLAs in any narrow cosmic time interval. However, DLAs are easy to
identify in low-resolution spectra because they have large absorption
rest equivalent widths. We have performed an efficient strong-Mg
ii-selected survey for UV DLAs at redshifts z=[0.42,0.70] using Hubble
Space Telescope's low-resolution ACS-HRC-PR200L prism. This redshift
interval covers ∼1.8Gyr in cosmic time, i.e. t~[7.2,9.0]Gyr after the
big bang. A total of 96 strong MgII absorption-line systems identified
in Sloan Digital Sky Survey spectra were successfully observed with
the prism at the predicted UV wavelengths of Lyα absorption. We
found that 35 of the 96 systems had a significant probability of being
DLAs. One additional observed system could be a very high NHI DLA
(NHI∼2x1022atoms/cm2 or possibly higher), but since very high
NHI systems are extremely rare, it would be unusual for this system
to be a DLA given the size of our sample. Here we present information
on our prism sample, including our best estimates of NHI and errors
for the 36 systems fitted with DLA profiles. This list is valuable for
future follow-up studies of low-redshift DLAs in a small redshift
interval, although such work would clearly benefit from improved UV
spectroscopy to more accurately determine their neutral hydrogen
column densities.
Description:
Table 1 presents the sample of 109 strong-MgII absorbers observed at
the location of Lyα with HST's low-resolution ACS-HRC-PR200L
The HST observations were taken between 2005 August 9 and 2006
December 23. Each quasar observation was allocated one HST orbit.
prism.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 95 112 The observed prism sample
table2.dat 46 39 Column density measurements
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See also:
J/ApJ/636/610 : Damped Lyα systems at z<1.65 (Rao+, 2006)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 19 A19 --- QSO QSO name (JHHMMSS.ss+DDMMSS.s or HHMM+DDMMCAL)
21- 24 I4 s ExpTime ?=- Exposure time
26- 30 F5.2 mag gmag ?=- SDSS g magnitude
31 A1 --- n_gmag [*] Note on gmag
33- 37 F5.3 --- zem ?=- Emission redshift
39- 44 F6.4 --- zabs Absorption redshift
46- 50 F5.3 0.1nm W0(2796) MgII (2796Å) rest equivalent width
52- 56 F5.3 0.1nm e_W0(2796) rms uncertainty on W0(2796)
58- 62 F5.3 0.1nm W0(2803) MgII (2803Å) rest equivalent width
64- 68 F5.3 0.1nm e_W0(2803) rms uncertainty on W0(2803)
70- 75 F6.3 0.1nm W0(2852) MgI (2852Å) rest equivalent width
77- 81 F5.3 0.1nm e_W0(2852) rms uncertainty on W0(2852)
83- 87 F5.3 0.1nm W0(2600) ?=- FeII (2600Å) rest equivalent width
89- 93 F5.3 0.1nm e_W0(2600) ?=- rms uncertainty on W0(2600)
95 A1 --- Status [ABCDE] Status (1)
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Note (1): Status codes as follows:
A = high-probability DLA; see Table 2 and Figure 3)
B = weak or absent absorption at the MgII-predicted position of Ly-alpha
absorption; could possibly be a subDLA)
C = spectrum cannot be used to determine whether a DLA is present)
D = no flux visible near the MgII-predicted position of Ly-alpha absorption or
at shorter wavelengths but an extremely rare, very high-N_HI DLA cannot
be ruled out; see Table 2 and Figure 3)
E = DLA calibrator; see Table 2 and Figure 3)
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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- 19 A19 --- QSO QSO name (JHHMMSS.ss+DDMMSS.s or HHMM+DDMMCAL)
21- 26 F6.4 --- zabs Absorption redshift from MgII line
28- 29 A2 --- l_NHI [≥ ] Limit flag on NHI
30- 36 E7.2 cm-2 NHI HI column density
38- 44 E7.2 cm-2 e_NHI ? rms uncertainty on NHI
46 A1 --- Notes [abcdef] Notes (1)
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Note (1): Notes as follows:
a = J1058+6008 is a broad absorption line QSO, but no strong BAL features
are expected at the location of the DLA
b = J1110+5236 has a broad absorption feature centred near 2010Å,
which is part of a BAL system
c = The very high NHI constraint for J134050.87+642544.9 is based on the
possibility that the prism spectrum flux disappears at short wavelength
due to a strong DLA. However, such systems are expected to be extremely
rare. See the discussion in Section 3 of the text.
d = Rao et al. (2003ApJ...595...94R 2003ApJ...595...94R) report NHI=(5.0±1.0)x1020atoms/cm2
based on HST-STIS spectroscopy
e = Rao et al. (2006, Cat. J/ApJ/636/610) report
NHI=(2.1±0.3)x1020atoms/cm2 based on HST-STIS spectroscopy
f = Rao et al. (2006, Cat. J/ApJ/636/610) report
NHI=(3.5±1.2)x1021atoms/cm2 based on HST-STIS spectroscopy
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History:
From electronic version of the journal
(End) Patricia Vannier [CDS] 10-Nov-2015