J/MNRAS/506/4389 Thermal parameters of the IGM at 2 ≤ z ≤ 4 (Gaikwad+, 2021)
A consistent and robust measurement of the thermal state of the IGM
at 2 ≤ z ≤ 4 from a large sample of Lyα forest spectra:
evidence for late and rapid He II reionization.
Gaikwad P., Srianand R., Haehnelt M.G., Choudhury T.R.
<Mon. Not. R. Astron. Soc. 506, 4389-4412 (2021)>
=2021MNRAS.506.4389G 2021MNRAS.506.4389G (SIMBAD/NED BibCode)
ADC_Keywords: QSOs ; Intergalactic medium ; Optical ; Infrared ; Line Profiles ;
Spectroscopy ; Redshifts
Keywords: methods: numerical - intergalactic medium -
quasars: absorption lines - large-scale structure of Universe
Abstract:
We characterize the thermal state of the intergalactic medium (IGM) in
10 redshift bins in the range 2 ≤ z ≤ 4 with a sample of 103
high-resolution, high S/N Lyα forest spectra using four
different flux distribution statistics. Our measurements are
calibrated with mock spectra from a large suite of hydrodynamical
simulations post-processed with our thermal IGM evolution code cite,
finely sampling amplitude, and slope of the expected
temperature-density relation. The thermal parameters inferred from our
measurements of the flux power spectrum, Doppler parameter
distribution, as well as wavelet and curvature statistics agree well
within their respective errors and all clearly show the peak in
temperature and minimum in slope of the temperature density relation
expected from He II reionization. Combining our measurements from the
different flux statistics gives T0 = (14750 ± 1322) K for the
peak temperature at mean density and a corresponding minimum slope
γ = 1.225 ± 0.120. The peak in the temperature evolution
occurs around z ≃ 3, in agreement with previous measurements that had
suggested the presence of such a peak, albeit with a large scatter.
Using CITE, we also calculate the thermal state of the IGM predicted
by five widely used (spatially homogeneous) UV-background models. The
rather rapid thermal evolution inferred by our measurements is well
reproduced by two of the models, if we assume (physically well
motivated) non-equilibrium evolution with photoheating rates that are
reduced by a moderate factor of ∼0.7-0.8. The other three models
predict He II reionization to be more extended with a higher
temperature peak occurring somewhat earlier than our measurements
suggest.
Description:
The main aim of this work is to obtain a consistent measurement of
thermal parameters using the larger data sets that have become
publicly available recently. Thanks to compilations like kodiaq dr2
(O'Meara et al. 2015AJ....150..111O 2015AJ....150..111O, Cat. J/AJ/150/111,
O'Meara et al. 2017AJ....154..114O 2017AJ....154..114O, Cat. J/AJ/154/114, from KECK/HIRES
archival data) and UVES squad dr1 (Murphy et al. 2019MNRAS.482.3458M 2019MNRAS.482.3458M,
Cat. J/MNRAS/482/3458, from VLT/UVES archival data), large samples of
QSO spectra with high resolution (∼6 km/s adequate to resolve the
thermally broadened Lyα absorption lines) and high
signal-to-noise ratio (S/N) are now available for analysis. These
samples have dramatically increased the number of available QSO
spectra that have been reduced and continuum normalized using uniform
techniques.
The sample consists of 300 QSO spectra with emission redshifts
z ≤ 5.3. All available spectra are continuum normalized and the
data product provides normalized flux and the associated error as a
function of wavelength. Many of these QSOs were observed more than
once with different exposure times. We co-added all the spectra using
the procedure described in online supplementary Appendix A. In total,
there are 214 QSO spectra that cover the Lyα forest in the
range 1.9 ≤ z ≤ 4. We manually checked all the co-added spectra and
excluded spectra if one or more of the following criteria are
satisfied: (i) sightline does not (partially or fully) contain
Lyα forest in the redshift range 1.9 ≤ z ≤ 4, (ii)
sightline contains Damped Lyα (DLA) or sub-DLA systems, (iii)
the sightline contains large spectral gaps (see online supplementary
Appendix A for details), or (iv) the median S/N per pixel along the
sightlines is smaller than 5. After excluding the QSO spectra with
above criteria, the resulting sample consists of 104 QSO spectra as
the tableqso.dat shoes.
The increase in temperature of the IGM due to He II reionization
has the following main effects on the H I Lyα forest. In
what follows, we describe the statistics used in this work to measure
T0 and γ parameters. In the literature, T0 and γ have been
measured by two different kind of statistics, namely, those derived
from the transmitted Lyα flux directly and those derived by fitting
the transmitted Lyα flux with multicomponent Voigt profiles. We use
here four statistics, namely the flux spectra power (FPS), the wavelet
statistics (WS), the curvature statistics (CS), and the line width (b)
distribution of Voigt profile components to measure the thermal parameters.
Here we present the distribution functions of the four statistics in
the following tables: tablefps.dat, tablews.dat, tablecs.dat,
tableb.dat. These distribution functions help us to constrain T0 and
γ by fitting them to those obtained from the simulations (see
section 3). For more details on statistic methods, fitting
observations to simulations and errors estimations please see the
section 4. Hereafter, measurement results of thermal parameters are
synthetized in the section 5.
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
tableqso.dat 21 104 The 104 QSOs sample
tablefps.dat 37 268 *Observed Ly-alpha forest FPS statistics
extracted from KODIAQ-DR2 Sample
tablews.dat 45 3085 *Observed Ly-alpha forest WS Statistics
extracted from KODIAQ-DR2 Sample
tablecs.dat 38 361 *Observed Ly-alpha forest CS Statistics extracted
from KODIAQ-DR2 Sample
tableb.dat 49 3600 *Observed Ly-alpha forest b-parameter Statistics
extracted from KODIAQ-DR2 Sample
--------------------------------------------------------------------------------
Note on tablefps.dat: Details on Flux power spectrum in the section 4.1.1
and section 4.2 for Error estimation of Lyα statistics.
Note on tablews.dat: Details on Wavelet statistics in the section 4.1.2
and section 4.2 for Error estimation of Lyα statistics.
Note on tablecs.dat: Details on curvature statistics in the section 4.1.3
and section 4.2 for Error estimation of Lyα statistics.
Note on tableb.dat: Details on b-parameter probability distribution function
in the section 4.1.4 and section 4.2 for Error estimation of Lyα
statistics.
--------------------------------------------------------------------------------
See also:
J/AJ/150/111 : KODIAQ DR1 (O'Meara+, 2015)
J/AJ/154/114 : KODIAQ DR2 (O'Meara+, 2017)
J/MNRAS/482/3458 : UVES Spectral Quasar Absorption Database DR1 (Murphy+, 2019)
Byte-by-byte Description of file: tableqso.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 14 A14 --- QSO QSOs name (JHHMMSS+DDMMSSA) as in
KODIAQ database (1)
16- 21 F6.4 --- z [2.083/4.558] Ly-alpha emission line derived
redshift (1)
-------------------------------------------------------------------------------
Note (1): Taken from O'Meara et al. 2017AJ....154..114O 2017AJ....154..114O, Cat. J/AJ/154/114
All data spectra available on
https://www2.keck.hawaii.edu/koa/public/koa.php
-------------------------------------------------------------------------------
Byte-by-byte Description of file: tablefps.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.2 --- z Mean Redshift of the statistics
[zmin,zmax] = [zmean-0.1, zmean+0.1] (z) (1)
6- 15 E10.5 s/km k Fourier mode k of the velocity v in km/s (k)
17- 26 E10.5 --- FPS 1D Dimensionless flux power spectrum
(k*PFk/pi) (2)
28- 37 E10.5 --- e_FPS Mean uncertainty 1σ of P
(ek*PF_k/pi)
--------------------------------------------------------------------------------
Note (1): The number of zbins is 10,
zbins1 = 2.00 , nbr of z is 26
zbins2 = 2.20 , nbr of z is 27
zbins3 = 2.40 , nbr of z is 27
zbins4 = 2.60 , nbr of z is 27
zbins5 = 2.80 , nbr of z is 28
zbins6 = 3.00 , nbr of z is 27
zbins7 = 3.20 , nbr of z is 27
zbins8 = 3.40 , nbr of z is 27
zbins9 = 3.60 , nbr of z is 26
zbins10 = 3.80 , nbr of z is 26
The number of z is 268.
Note (2): We take the Fourier transform of the flux contrast
δf = (F/)-1, where is the mean flux in a given redshift
zbin.
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Byte-by-byte Description of file: tablews.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.2 --- z Mean Redshift of the statistics
[zmin,zmax] = [zmean-0.1, zmean+0.1] (1)
6- 11 F6.2 km/s ws Wavelet Scale related to the velocity (sn) (2)
13- 23 E11.5 [-] logAsn Logarithm of the wavelet amplitude (logASn) (3)
25- 34 E10.5 --- PDF Normalized probability distribution function of
log-wavelet amplitude (dP/logASn)
36- 45 E10.5 --- e_PDF Mean uncertainty 1σ of PDF (e_dP/logAsn)
--------------------------------------------------------------------------------
Note (1): The number of zbins is 10,
zbin1 = 2.00 , nbr of z is 329
zbin2 = 2.20 , nbr of z is 318
zbin3 = 2.40 , nbr of z is 336
zbin4 = 2.60 , nbr of z is 307
zbin5 = 2.80 , nbr of z is 310
zbin6 = 3.00 , nbr of z is 294
zbin7 = 3.20 , nbr of z is 292
zbin8 = 3.40 , nbr of z is 283
zbin9 = 3.60 , nbr of z is 337
zbin10 = 3.80 , nbr of z is 279
The number of z is 3085
Note (2): The Wavelet scales are divided as for one zbin as :
wsbin1 = 30.00 , the mean occurence of ws is 42
wsbin2 = 40.00 , the mean occurence of ws is 40
wsbin3 = 50.00 , the mean occurence of ws is 39
wsbin4 = 60.00 , the mean occurence of ws is 38
wsbin5 = 70.00 , the mean occurence of ws is 39
wsbin6 = 80.00 , the mean occurence of ws is 38
wsbin6 = 90.00 , the mean occurence of ws is 37
wsbin7 = 100.00 , the mean occurence of ws is 36
The sum of these occurence numbers is 309 which is equal to the
mean of z occurences in one zbin.
Note (3): The wavelet transform of the flux here the wavelet field ASn
(equation 2) is the convolution of the wavelet Ψ(v, sn)
(equation 1) with the transmitted Lyα flux F (see section 4.1.2
Wavelet statistics).
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Byte-by-byte Description of file: tablecs.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.2 --- z Mean Redshift of the statistics
[zmin,zmax] = [zmean-0.1, zmean+0.1] (1)
6- 16 E11.5 [-] kappa Logarithm of the curvature measure κ
(κ) (2)
18- 27 E10.5 --- PDF Normalized probability distribution function of
log-curvature (dP/dlogk)
29- 38 E10.5 --- e_PDF Mean uncertainty 1σ of PDF (e_dP/dlogk)
--------------------------------------------------------------------------------
Note (1): The number of zbins is 10,
zbins1 = 2.00 , nbr of z is 32
zbins2 = 2.20 , nbr of z is 32
zbins3 = 2.40 , nbr of z is 45
zbins4 = 2.60 , nbr of z is 34
zbins5 = 2.80 , nbr of z is 35
zbins6 = 3.00 , nbr of z is 38
zbins7 = 3.20 , nbr of z is 30
zbins8 = 3.40 , nbr of z is 38
zbins9 = 3.60 , nbr of z is 49
zbins10 = 3.80 , nbr of z is 28
The number of z is 361.
Note (2): The curvature (κ) is essentially a measure of the rate of change
of direction of a point that moves on a curve defined as the
equation 3 in section 4.1.3 Curvature statistics.
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Byte-by-byte Description of file: tableb.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 4 F4.2 --- z Mean Redshift of the statistics
[zmin,zmax] = [zmean-0.1, zmean+0.1] (z) (1)
6- 10 F5.2 [cm-2] logNHIl [12.8/14.4] Logarithm of the lower value
of H I column density NHI bin (logNHI_lower)
12- 16 F5.2 [cm-2] logNHIh [13/14.6] Logarithm of higher value of
H I column density NHI bin (logNHI_higher)
18- 27 E10.5 [km/s] logb Logarithm of the doppler b parameter (logb)
29- 38 E10.5 --- PDF Normalized probability distribution function
of log-b parameter (dP/dlogb)
40- 49 E10.5 --- e_PDF Mean uncertainty 1σ of PDF (e_dP/dlogb)
--------------------------------------------------------------------------------
Note (1): The number of zbins is 10, the occurence of z is 360 for each zbins.
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History:
From electronic version of the journal
(End) Luc Trabelsi [CDS] 26-Jun-2024