A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey
We present a new sample of the z ≥ 2 quasar spectra. It contains 102 643 spectra which were visually selected from the SDSS DR10, and includes also a subsample of 65 976 spectra for the composite spectra compilation. This sample will be used for the Lyα forest studies, and can be used for other stud...
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irk-123456789-1199372017-06-11T03:03:51Z A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey Torbaniuk, O. We present a new sample of the z ≥ 2 quasar spectra. It contains 102 643 spectra which were visually selected from the SDSS DR10, and includes also a subsample of 65 976 spectra for the composite spectra compilation. This sample will be used for the Lyα forest studies, and can be used for other studies, including those of the quasar spectral properties and the spatial distribution of quasars at z > 2. The compiled composite spectra will be used for the determination of the intrinsic spectrum in the Lyα forest studies. Those objects which were not included into the main sample and rejected during the visual examination, are 11 192 quasars with the broad absorption lines, 6 804 spectra with the damped Lyα systems, 1 248 and 493 spectra with the absorption in the Lyα and Lyβ lines, respectively. The "non-quasar" objects, including 191 candidates for blazars and 30 galaxies with starburst, as well as 617 quasar spectra with wrong redshift, 417 incomplete spectra and 1 497 spectra with low S/N ratio, were also excluded. 2015 Article A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey / O. Torbaniuk // Advances in Astronomy and Space Physics. — 2015. — Т. 5., вип. 2. — С. 84-88. — Бібліогр.: 9 назв. — англ. 2227-1481 DOI:10.17721/2227-1481.5.84-88 http://dspace.nbuv.gov.ua/handle/123456789/119937 en Advances in Astronomy and Space Physics Головна астрономічна обсерваторія НАН України |
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We present a new sample of the z ≥ 2 quasar spectra. It contains 102 643 spectra which were visually selected from the SDSS DR10, and includes also a subsample of 65 976 spectra for the composite spectra compilation. This sample will be used for the Lyα forest studies, and can be used for other studies, including those of the quasar spectral properties and the spatial distribution of quasars at z > 2. The compiled composite spectra will be used for the determination of the intrinsic spectrum in the Lyα forest studies. Those objects which were not included into the main sample and rejected during the visual examination, are 11 192 quasars with the broad absorption lines, 6 804 spectra with the damped Lyα systems, 1 248 and 493 spectra with the absorption in the Lyα and Lyβ lines, respectively. The "non-quasar" objects, including 191 candidates for blazars and 30 galaxies with starburst, as well as 617 quasar spectra with wrong redshift, 417 incomplete spectra and 1 497 spectra with low S/N ratio, were also excluded. |
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Torbaniuk, O. |
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Torbaniuk, O. A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey Advances in Astronomy and Space Physics |
| author_facet |
Torbaniuk, O. |
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Torbaniuk, O. |
| title |
A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey |
| title_short |
A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey |
| title_full |
A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey |
| title_fullStr |
A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey |
| title_full_unstemmed |
A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey |
| title_sort |
quasar sample for the lyα forest studies from the data release 10 of the sloan digital sky survey |
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Головна астрономічна обсерваторія НАН України |
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2015 |
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http://dspace.nbuv.gov.ua/handle/123456789/119937 |
| citation_txt |
A quasar sample for the Lyα forest studies from the Data Release 10 of the Sloan Digital Sky Survey / O. Torbaniuk // Advances in Astronomy and Space Physics. — 2015. — Т. 5., вип. 2. — С. 84-88. — Бібліогр.: 9 назв. — англ. |
| series |
Advances in Astronomy and Space Physics |
| work_keys_str_mv |
AT torbaniuko aquasarsampleforthelyaforeststudiesfromthedatarelease10ofthesloandigitalskysurvey AT torbaniuko quasarsampleforthelyaforeststudiesfromthedatarelease10ofthesloandigitalskysurvey |
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2025-07-08T16:56:24Z |
| last_indexed |
2025-07-08T16:56:24Z |
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A quasar sample for the Lyα forest studies
from the Data Release 10 of the Sloan Digital Sky Survey
O.Torbaniuk
∗
Advances in Astronomy and Space Physics, 5, 84-88 (2015)
O.Torbaniuk, 2015
Main Astronomical Observatory of the NAS of Ukraine, 27 Akademika Zabolotnoho Str., Kyiv 03680, Ukraine
We present a new sample of the z ≥ 2 quasar spectra. It contains 102 643 spectra which were visually selected
from the SDSS DR10, and includes also a subsample of 65 976 spectra for the composite spectra compilation. This
sample will be used for the Lyα forest studies, and can be used for other studies, including those of the quasar
spectral properties and the spatial distribution of quasars at z > 2. The compiled composite spectra will be used
for the determination of the intrinsic spectrum in the Lyα forest studies. Those objects which were not included
into the main sample and rejected during the visual examination, are 11 192 quasars with the broad absorption
lines, 6 804 spectra with the damped Lyα systems, 1 248 and 493 spectra with the absorption in the Lyα and Lyβ
lines, respectively. The �non-quasar� objects, including 191 candidates for blazars and 30 galaxies with starburst,
as well as 617 quasar spectra with wrong redshift, 417 incomplete spectra and 1 497 spectra with low S/N ratio,
were also excluded.
Key words: quasars: general, methods: data analysis, catalogues
introduction
One of the main observational tools allowing to
study the matter distribution in the Universe is the
analysis of Lyα forest lines in the spectra of dis-
tant (z > 2) quasars. This forest is a set of the
absorption Lyα (1215.6Å) lines blueward of the in-
trinsic quasar emission Lyα line. It is a result of
the absorption of the quasar light by the neutral
intergalactic hydrogen in the �laments distributed
along the line of sight, thus there is a bunch of ab-
sorption lines with di�erent redshifts instead of one
line. The distribution of the transmission (the value
characterising transparency of intergalactic medium
(IGM) in the Lyα line) �uctuations in the Lyα line,
which is based on the two-point statistics, gives the
information about the matter distribution on the in-
tergalactic scales. Such studies are conducted with
two types of data: small samples of high-resolution
spectra (obtained using the echelle spectrographs at
VLT etc.) and large samples of medium-resolution
spectra mainly from the Sloan Digital Sky Survey
(SDSS). Both have their pros and cons and should
supplement each other in the overall picture.
Several steps to obtain values of the transmission
�uctuations from the raw spectral data imply sev-
eral sources of inaccuracy of the �nal result. For
example, one of the main problems is the determi-
nation of the intrinsic spectrum of a quasar. This
is being done using di�erent techniques by di�erent
authors. Up to date almost all known studies of the
Lyα forest from the SDSS have been done only by
the SDSS collaboration [1, 4, 5, 6]. Consequently, it
is necessary to conduct independent studies for the
veri�cation of the results. For this purpose we com-
piled a new sample of the quasar spectra from the
Tenth Data Release of SDSS (SDSS DR10). In this
paper we describe the sample selection criteria and
characteristics.
Our sample will be used for two interrelated tasks:
the compilation of the composite spectra and the
study of the matter distribution on the intergalac-
tic scales using the Lyα forest. Hence an additional
sample of spectra with the relatively high S/N-ratio
was compiled from the main one for the Lyα for-
est studies. The composite spectra are the averaged
spectra of a certain type of objects. The main pur-
pose of the composite spectra compilation is the in-
crease of the S/N ratio, which allows to distinguish
spectral features not seen in the individual spectra
having low S/N ratios. Averaging over a sample of
spectra yields also elimination of the separate inter-
galactic absorption lines, i. e. the Lyα forest, and
results in a general �ux reduction within the Lyα
forest region. The mean transmission can be found
from the value of the latter.
The subsample compiled for the composite spec-
tra production will also be used for studying the
spectral properties of quasars and relations between
them, that can shed light on the quasar physics. For
example, in our previous studies with the smaller
sample of quasar spectra from SDSS DR7, we showed
that there is no correlation between the spectral in-
dex αλ and the monochromatic luminosity at 1450Å,
∗el.torbaniuk@gmail.com
84
Advances in Astronomy and Space Physics O.Torbaniuk
log l1450 [2]. We also found that there is a dependence
of the emission line equivalent width on spectral in-
dex (correlation or anti-correlation) for some of the
lines, mostly for those for which the Baldwin e�ect
is detected, and that there is no dependence between
the virial mass of the central supermassive black hole
of a quasar and its spectral index αλ [8, 9].
the data and spectra selection
We used the SDSS DR10 quasar catalogue [3] that
contains 166 583 objects within the redshift range
0.053 < z < 5.855. Firstly, all objects with redshifts
z > 2.0 and the redshift determination con�dence
level > 0.9 were selected, since the region of Lyα
forest is observed at these redshifts. The resulting
preliminary sample contains 125 132 objects.
The second step was the visual inspection of the
preliminary sample. This is needed because SDSS
is an automatic survey and may contain the �non-
quasar� objects (stars, supernovae, normal galaxies
etc.) as well as the spectra with the too low signal-
to-noise (S/N) ratio or the spectral peculiarities un-
wanted in the Lyα forest studies (e. g., BAL, DLA).
Low S/N means that the noise is so high, that one
can distinguish not more than one emission line; the
value of S/N ratio in these cases is usually less than
three.
In addition to the 30 normal or starburst galaxies
and 191 blazar candidates, 1 497 spectra with very
low S/N-ratio (which does not allow to classify the
object type), 617 quasars with wrong redshifts, and
417 incomplete spectra, we excluded the quasar spec-
tra with the Broad Absorption Lines (BAL) and the
Damped Lyα-systems during the visual inspection.
These two latter types of spectra were excluded be-
cause of some di�culties in using them for the Lyα
forest studies. For the BAL quasars it is not easy to
use the automatic methods of the intrinsic spectrum
�tting, and the presence of the intrinsic absorption in
the Lyα forest region complicates the separation of
the IGM absorption. The DLA-systems are the ab-
sorption features with the zero transparency in the
Lyα line.
To compile a subsample for the composite spectra
production we excluded the following spectra from
the main one: those with the absorption in the Lyα
and Lyβ lines (1 248 and 493, respectively) and also
the spectra with the narrow absorption lines redward
of the Lyα emission line (36 666 spectra). The latter
are most likely the strong metallic absorption lines
from IGM which have sporadic nature and can in-
troduce additional uncertainties into the composite
spectrum both within the Lyα forest and outside of
it.
The following samples are obtained: the sample
for Lyα forest studies containing 102 643 spectra (ex-
amples of spectra with z = 2.45, 3.64, 4.34, 5.42 are
presented in Fig. 1) and the sample for composites
containing 65 976 spectra (see Fig. 2). Both samples
are presented as an online table at the AASP web-
page. Table 1 presents a part of this table with an
example of ten quasars. The last column indicates
to which sample the object belongs to (note, that
the �composite� means that a given object belongs
to both samples). In addition, the following objects
were selected: 11 192 BAL-quasars (Fig. 3(a)), 6 804
quasars with DLA (Fig. 3(b)). Examples of the spec-
tra with the absorption in the intrinsic Lyα and Lyβ
emission lines are presented in Fig. 4(a) and (b), re-
spectively.
additional sample reduction
Since the main purpose of the selected sample is
the study of the Lyα forest requiring as high S/N
ratio as possible, some additional reduction was ap-
plied for both samples. For this purpose some pre-
liminary data processing was carried out �rst. The
spectra were smoothed with a simple moving average
by three points.
The next step is the normalisation of each spec-
trum, which is needed for the compilation of the
composite spectra. Each spectrum was normalized
to the mean (arithmetic) �ux in all the pixels within
the rest wavelength range 1450-1470Å. This range is
located blueward of the Civ emission line and is usu-
ally considered to be free of emission and absorption
lines. For further study we used only the spectra
with the RMS of the normalisation constant A less
than 10%, resulting in the samples of 42 140 spec-
tra (the sample for the Lyα forest study) and 21 868
spectra (for the composites). The redshift distribu-
tions of the preliminary, main and composite samples
before and after the imposition of the conditions with
a normalisation constant A are shown in Fig. 5.
results and conclusions
We compiled a new sample of quasar spectra from
the SDSS DR10 sample [3] of 166 583 objects. Out of
this sample, we have visually selected 102 643 �true�
quasars, excluding 11 192 quasars with BAL, 6 804
spectra with DLA, 1 248 and 493 spectra with ab-
sorption in Lyα and Lyβ lines, respectively. Also
there were excluded �non-quasar� objects, namely
191 candidates to blazars and 30 galaxies with star-
bursts. From the main sample we also excluded 617
quasar spectra with wrong redshifts, 417 incomplete
spectra and 1 497 spectra with low S/N ratio.
From the main sample, containing 102 643 spec-
tra, we compiled additional subsample for making
the composite spectra. This subsample contains
65 976 quasar spectra and does not include the spec-
tra with narrow absorption lines redward of the
quasar Lyα line.
For further studies, to reduce the uncertainties we
used only spectra with the RMS of the normalisation
constant A less than 10%, hence the number of spec-
tra of spectra is reduced to 42 140 (the main sample)
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Advances in Astronomy and Space Physics O.Torbaniuk
Fig. 1: The quasar spectra with the redshifts z = 2.45 (a), 3.64 (b), 4.34 (c), 5.42 (d), respectively.
and 21 868 (the sample for the composite spectra).
From the latter sample we compiled 55 composite
spectra from the subsamples with the di�erent spec-
tral indices αλ and di�erent monochromatic lumi-
nosities at 1450Å, log l1450. Then we applied them
for the automatic intrinsic spectrum determination
in the spectra from the former sample using our own
technique. Details of this method and the resulting
dependence of the mean Lyα forest transmission on
the redshift will be presented elsewhere.
acknowledgement
The author is thankful to Dr. Ganna Ivashchenko
and Dr. Irina Vavilova for their invaluable help
and fruitful discussions. This work has been sup-
ported by the Target Programme of Space Research
of the NAS of Ukraine for 2013-2016 and by the Swiss
National Science Foundation grant SCOPE IZ7370-
152581.
references
[1] AndersonL., Aubourg É, Bailey S. et al. 2014, MNRAS,
441, 24
[2] IvashchenkoG., Sergijenko,O. & TorbaniukO. 2014, MN-
RAS, 437, 3343
[3] Pâris I., PetitjeanP., AubourgÉ. et al. 2014, A&A, 563,
id.A54
[4] RossA. J., Samushia L., BurdenA. et al. 2013, MNRAS,
437, 1109
[5] SánchezA.G., MontesanoF., KazinE.A. et al. 2014, MN-
RAS, 440, 2692
[6] TojeiroR., RossA. J., BurdenA. et al. 2014, MNRAS,
440, 2222
[7] TorbaniukO. & IvashchenkoG. 2014, IAU Symp., 304,
282
[8] TorbaniukO. & IvashchenkoG. 2014, in WDS'10 Proc.
Contributed Papers � Physics, 42
[9] TorbaniukO., IvashchenkoG. & SergijenkoO. 2012, in
WDS'12 Proc. Contributed Papers: Part III � Physics,
123
86
Advances in Astronomy and Space Physics O.Torbaniuk
Fig. 2: Examples of the spectra from the sample for the composite spectra (a) and the spectrum with narrow absorption
lines for the Lyα forest study (b), respectively.
Fig. 3: Examples of quasar spectra with BAL (a) and DLA (b).
Fig. 4: Quasar spectra with absorption in Lyα (a) and Lyβ (b) respectively.
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Advances in Astronomy and Space Physics O.Torbaniuk
Table 1: Example of a part of the online table. The columns contain information on the object name, plate number
(�plate�), the modi�ed Julian date of the observation night (�MJD�), number of the �ber (��ber�), right ascension
(�RA�) and declination (�DEC�) of the object, the redshift (�z�) and the value of the redshift uncertainty (�σz�). The
last column gives the name of the sample to which the object belongs (the main or the composite).
name plate mjd �ber RA DEC z σz sample
134102.26+264952.5 6002 56104 631 205.259 26.8313 2.80547 0.00044 main
094804.16+595050.5 5719 56014 436 147.017 59.8474 2.61632 0.00020 main
153209.53+130029.3 4891 55736 676 233.04 13.0081 2.46111 0.00034 main
075625.70+221613.8 4471 55617 428 119.107 22.2705 2.44233 0.00013 main
093336.98-011849.2 3767 55214 694 143.404 -1.31369 3.69452 0.00045 main
171455.63+283520.8 5000 55715 16 258.732 28.5891 2.16432 0.00110 composite
171753.56+305031.3 4998 55722 283 259.473 30.8421 2.69634 0.00044 composite
122355.11+021518.0 4752 55653 534 185.98 2.25502 2.19234 0.00038 composite
160714.29+152518.3 4072 55362 364 241.81 15.4218 2.32026 0.00072 composite
152151.73+275914.0 3851 55302 858 230.466 27.9872 2.36072 0.00019 composite
Fig. 5: The redshift distribution of quasars from the preliminary sample (dashed black line), the sample for Lya-forest
studies (grey solid line), and the sample for composite compilation (black solid line). Corresponding histograms for
Lya-forest and composite subsamples with RMS of the normalization constant A less than 10% are shown by grey and
black dotted lines, respectively.
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