Gaia Data Release 3
Open Access

Table 9.

Physical quantities derived from the composite spectra of quasars from the Milliquas catalogue shown in Fig. 33.

Composite spectrum Continuum slope, αν Line+λlab (nm) λobs (nm) F/Fref(a) FWHM (nm)
0.052 ≤ z < 0.5 −0.4506 ± 0.1453 Mg IIλ279.875 280.064 ± 0.234 1.00000 ± 0.01036 8.308 ± 0.214
2571 sources Hγλ434.168 435.221 ± 0.588 0.13927 ± 0.00369 10.432 ± 0.586
= 20.8 Hβλ486.268 486.936 ± 0.081 0.46937 ± 0.00233 12.874 ± 0.131
Hαλ656.461 656.240 ± 0.010 1.27766 ± 0.00095 17.971 ± 0.035

0.5 ≤ z < 1 −0.4291 ± 0.0570 C III]λ190.873 191.144 ± 0.134 1.80831 ± 0.03931 5.583 ± 0.262
8810 sources Mg IIλ279.875 279.644 ± 0.084 1.00000 ± 0.00238 10.613 ± 0.120
= 7.0 Hγλ434.168 433.932 ± 0.048 0.25984 ± 0.00099 10.355 ± 0.123
Hβλ486.268 486.825 ± 0.042 0.53950 ± 0.00085 18.263 ± 0.082
Hαλ656.461 661.947 ± 0.100 1.36875 ± 0.00735 23.063 ± 0.684

1 ≤ z < 2 −0.6115 ± 0.0227 Lyαλ121.567 122.264 ± 0.029 1.00000 ± 0.00826 4.411 ± 0.097
20 755 sources Si IVλ139.676 139.925 ± 0.051 0.14881 ± 0.00292 3.637 ± 0.111
= 4.9 C IVλ154.906 154.636 ± 0.050 0.29494 ± 0.00154 4.477 ± 0.043
C III]λ190.873 190.124 ± 0.093 0.13300 ± 0.00039 7.729 ± 0.068
Mg IIλ279.875 280.056 ± 0.053 0.08408 ± 0.00026 8.026 ± 0.047
Hγλ434.168 433.450 ± 0.101 0.01752 ± 0.00013 11.683 ± 0.292
Hβλ486.268 490.168 ± 5.268 0.03491 ± 0.00070 23.559 ± 2.499

2 ≤ z < 3 −0.7752 ± 0.0113 O VIλ103.383 103.589 ± 0.152 0.18338 ± 0.00686 3.279 ± 0.342
9870 sources Lyαλ121.567 122.156 ± 0.022 1.00000 ± 0.00160 4.908 ± 0.024
= 5.8 Si IVλ139.676 139.738 ± 0.086 0.11467 ± 0.00068 4.927 ± 0.129
C IVλ154.906 154.465 ± 0.049 0.19586 ± 0.00041 5.854 ± 0.114
C III]λ190.873 190.589 ± 0.047 0.11133 ± 0.00107 6.742 ± 0.164
Mg IIλ279.875 279.941 ± 0.091 0.07435 ± 0.00019 9.471 ± 0.078

3 ≤ z < 4 −0.7155 ± 0.0548 O VIλ103.383 103.381 ± 0.112 0.21926 ± 0.00277 5.202 ± 0.935
929 sources Lyαλ121.567 122.398 ± 0.086 1.00000 ± 0.00489 5.591 ± 0.083
= 6.0 Si IVλ139.676 139.980 ± 0.232 0.12360 ± 0.00895 4.588 ± 0.486
C IVλ154.906 154.581 ± 0.151 0.24250 ± 0.00306 3.928 ± 0.107
C III]λ190.873 190.161 ± 0.118 0.13617 ± 0.00097 6.488 ± 0.094

0.052 ≤ z ≤ 4.358 −0.4639 ± 0.0057 O VIλ103.383 103.500 ± 0.103 0.19285 ± 0.00584 3.784 ± 0.517
42 944 sources Lyαλ121.567 122.202 ± 0.037 1.00000 ± 0.00259 5.088 ± 0.036
= 6.6 Si IVλ139.676 139.838 ± 0.141 0.11467 ± 0.00146 4.672 ± 0.139
C IVλ154.906 154.542 ± 0.052 0.21615 ± 0.00132 5.383 ± 0.066
C III]λ190.873 190.232 ± 0.056 0.11681 ± 0.00072 7.938 ± 0.097
Mg IIλ279.875 280.006 ± 0.034 0.08202 ± 0.00025 8.891 ± 0.047
Hγλ434.168 434.164 ± 0.059 0.02165 ± 0.00016 10.706 ± 0.129
Hβλ486.268 486.846 ± 0.109 0.04867 ± 0.00011 16.473 ± 0.179
Hαλ656.461 656.257 ± 0.014 0.13924 ± 0.00011 18.026 ± 0.032

Notes. The reduced chi-square, , is obtained from Eq. (C.1). The frequency continuum slope, αν, is computed from the wavelength continuum slope, αλ = −αν − 2, where the continuum is modelled through a power law of the form Cλ ∝ λαλ. In Fig. 33, the continuum is plotted as the lowest line joining the two most widely separated points in the range 121 − 600 nm without crossing the spectrum in this range. The emission line location, λobs, and maximal line flux density, F, are retrieved from the fit of a quadratic polynomial in the vicinity of the laboratory wavelength, λlab, after a local continuum has been subtracted that was computed in the same way as for αλ. The full-width at half maximum (FWHM) is retrieved from these continuum-subtracted emission lines using a linear interpolation of the spectral flux densities. All uncertainties are calculated, to first order, using the formal uncertainties on the composite spectra obtained from Eq. (C.4).

(a)

If Lyα is covered by the composite spectrum, it is used as a reference flux density, Fref, otherwise Mg II is used.

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