EDP Sciences
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Issue
A&A
Volume 544, August 2012
Article Number A62
Number of page(s) 28
Section Extragalactic astronomy
DOI https://doi.org/10.1051/0004-6361/201219125
Published online 26 July 2012

Online material

Appendix A: Effect of intrinsic variability on the MmD

thumbnail Fig. A.1

Application of the MmD method for H β & [O III] for mock lensed quasars simulated based on spectro-photometric monitoring data of Palomar-Green quasars. For each pair of spectra separated by a delay Δt, the continuum of one of the spectra has been artificially microlensed by μ = 1.5 and M = 1 has been assumed. For legibility, only the fraction F (red solid line) and the reference spectrum (blue dotted line) are shown. Each row corresponds to a different object. The time-delay between the pairs of spectra is increasing from panel a) to d). For each panel, we provide M retrieved with the decomposition, the variability in the continuum ϵc and in the line ϵl.

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The MmD technique described in Sect. 4.1 should ideally be applied to pairs of spectra separated by the time-delay in order correct for any effect introduced by intrinsic variability. Hereafter, we investigate how intrinsic variability may affect the MmD technique applied to spectra obtained at a single epoch. For this purpose, we have decided to create mock lensed systems based on existing spectra of quasars observed at several epochs. The principle of our simulation is to pick pairs of spectra of an object at two different epochs t1,t2. A pair of spectra simulates the single-epoch spectra of two images of a macro-lensed quasar with a time delay Δt = t1 − t2 and M = 1. Then, we amplify the continuum of one image to simulate microlensing and apply the MmD. Since only the continuum is microlensed, we do not expect emission lines or part of them in F, except possible contamination due to intrinsic variability.

Specifically, we proceeded as follows. First, we used publicly available reverberation mapping data8 of Palomar-Green quasars. In this database, we choose pairs of spectra of the same object separated by a delay Δt in the ranges (a) 1–20 days, (2) 20–40 days, (3) 40–60 days, (4) 60–100 days. Second, we artificially microlensed the continuum of the first spectrum by a factor μ = 1.5. Third, we applied the MmD, estimating automatically A and choosing M to minimize the flux in F at the position of the H β line9. Note that we had to restrict ourselves to pairs of spectra obtained with the same instrumental setup to avoid spurious line deformation introduced by variable spectral resolution. We show in Fig. A.1 the result of this procedure at the position of the H β line for PG0052 (RBLR ~ 134 light days), PG0953 (RBLR ~ 151 light days), PG1613 (RBLR ~ 39 light days), PG0026 (RBLR ~ 113 light days). We also report the measured fractional variation of the continuum (ϵc) and of the line (ϵl) during Δt. This figure illustrates that in general the deformations of the emission lines caused by intrinsic variability are too weak to mimic microlensing and introduce a significant signal above the continuum

in F at the location of H β. When the delay becomes large (typically  > 40 days), it happens that a weak signal is detected in the emission lines (e.g. panel (c) and (d) for PG0052, panel (c) for PG0026). This happens when ϵl is large and when it differs significantly from ϵc. From this figure, it seems that differences of ϵl and ϵc by more than 10% are needed to introduce noticeable line deformations in the decomposition. In order to derive how frequent this situation appears, we have calculated ϵl/ϵc as a function of Δt for the objects of the sample of Kaspi et al. (2000). We did not find a clear change of ϵl/ϵc nor of the standard deviation σϵ with the size of the BLR. Therefore, we report in Table A.1 the average value of ϵl/ϵc together with the average value of σϵ. We see in Table A.1 that ϵl/ϵc is in average equal to 1 with a scatter <10% on periods corresponding to a time delay <50 days. Since most of our targets have Δt < 50 days (13 out of 17 targets), we may safely conclude that statistically, intrinsic variability is unlikely to mimic microlensing of the broad lines for such time-delays. The situation might be less favourable for the objects with Δt > 50 days, but only two out of four of these systems (Q1355-2257 and WFI 2033-4723) show possible microlensing of the emission lines.

Table A.1

Average value of fractional variation of the H β line and of the continuum (ϵl/ϵc) on periods Δt (Col. 1), for the sample of reverberation mapped quasars of published in Kaspi et al. (2000).

Appendix B: MmD applied to a simulated spectrum

Similarly to the example of MmD applied to HE 0435-1223 in Sect. 4.2, we show in Fig. B.1, the MmD applied to mock spectra roughly mimicking our spectra of HE 0435-1223. The mock spectra of HE 0435-1223 are defined in the following way: (B.1)where Fc is the continuum emission, (Eb, Ea) are gaussian emission profiles centered on (λEb, λEa) = (2798, 2803)    Å and with (FWHMEb,FWHMEa) = (5700, 2500) km s-1. In this equation, the macro model magnification ℳ and the micro-magnification μ (for the continuum) and μl (for the line) of individual images have been written explicitly. These quantities have been chosen arbitrarily such that M = ℳB/ℳD = 6.46/4.39 = 1.47 (matching the macro-model), μ = μB/μD = 0.74/0.9 = 0.82, and . We used a different micro-magnification factor in the line and in the continuum to account for the fact that lines are emitted in a region larger than the continuum (i.e. μl closer to 1 than μc). We have also added a fake atmospheric absorption to the spectra of B and D in order to increase the similarity with the observed spectrum of H 0435-1223. Despite the similarity with the data, the model of the emission line of Eq. (B.1) should be considered only for illustration purpose. The MmD applied to these spectra is the same as the one discussed in Sect. 4.2. In absence of noise, the value M = 1.47 and μ = 0.82 are retrieved. The component F shows that a red fraction of the emission line (corresponding to our input component Ea) is retrieved as microlensed, in agreement with our input model.

thumbnail Fig. B.1

Macro-micro decomposition (MmD) applied to simulated spectra of HE 0435-1223 mimicking the observed data. The decomposition is similar to the one showed in Fig. 3. The bottom panel shows FM for three different values of A and an arbitrary value of M. The best value of A is A ~ 1.2 because it leads to FM = 0 in the continuum regions blueward and redward of the emission line. The upper panel shows the decomposition for 3 different values of M. The best value is M = 1.47 because it minimizes the emission in the line, keeping the flux above the apparent local continuum depicted as a dotted black line.

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Appendix C: Characteristics of the main sample

We provide hereafter detailed notes about the characteristics of the spectra of each object of the main sample. For each target we discuss i) the quality of the deconvolution, which might introduce spurious signal; ii) the chromatic changes observed in the spectra; iii) the microlensing-induced deformation of the emission lines, when a deformation is observed; and iv) important results from literature which shed light on the source of chromaticity and confirm/infirm our flux ratio measurements. We provide in Fig. C.1, the spectral flux ratios between the pairs of images and we discuss in the text four origins for the chromatic changes in the spectral ratios: differential extinction (DE), chromatic microlensing (CML), contamination by the lens (LC), or intrinsic variability (IV). In order to quantify the possible systematic error on our estimate of M caused by intrinsic variability, we also provide in Table C.1 the amplitude of variation Δm of an object over the time-spent of the time-delay. This quantity has been derived using the g-band structure functions (divided in 6 bins of MBH and L, cf. their Eq. (2) and Table 3) of Wilhite et al. (2008) and the black hole masses and luminosities of Table 3. In the following, the references to the NIR flux ratios from literature are not systematically given. They can be found in Table 5.

(a) HE0047-1756: deconvolution: the deconvolution is slightly less good than for other systems. The total flux left in the residual under the QSO images never exceeds 0.1% of the flux of the QSO image. Although this is a very small amount of flux, this appears as a systematic feature suggesting that the PSF is less representative of the QSO images than in other systems.

Chromaticity: the ratio B/A shows a monotonic decrease with increasing wavelength. This chromatic change is not due to contamination by the flux of the lensing galaxy. Indeed, in order to reconcile the shape of the spectrum in A & B, one has to invoke a contamination of A (the brightest image) by  ~ 4 times the measured flux of G and a contamination 10 times smaller for image B. Therefore, the two most likely explanations are DE with (M(blue), M(red), μ) = (0.231, 0.220, 1.173) and CML with (M, μ(blue), μ(red)) = (0.220, 1.260, 1.170).

Broad Lines: whatever the origin of the chromatic changes, the blue wing of Mg II  is microlensed. Microlensing of the blue wing of C III]  is also tentatively observed but this is more uncertain owing to the proximity of this line from the red edge of the spectrum.

Notes: the observed monotonic decrease of B/A was also reported in the discovery spectra of Wisotzki et al. (2004). For these spectra, obtained in Dec. 2001 and Sept. 2002, we measure A = 0.347 ± 0.002 and M = 0.24 ± 0.02 at the wavelength of C III]. The different value of A found in our spectra is caused by time-variable microlensing. On the other hand, M is compatible with our measurement, confirming that intrinsic variability may not be too large. The H-band flux ratio from Chantry et al. (2010), does not follow the chromatic variation of M observed in the spectra and is found 0.1 mag smaller than the value derived at the level of C III]. This may be explained by intrinsic variability (Δm ~ 0.07 mag) and/or microlensing of the H-band continuum.

(b) Q0142-100: deconvolution: because of the inaccurate PSF, residual signal above the noise is visible in the deconvolved image. However, this flux amounts only to 0.02–0.2% of the total flux in the lensed images. The flux of the lens galaxy G, located only  ~ 0.4″ from B, reaches 20% of the flux in image B in the red part of the spectrum. This could lead to significant contamination of image B by the lensing galaxy G.

Chromaticity: there is no differential ML between the continuum and the emission lines however the two spectra do not superimpose once scaled with the same magnification factor. This chromatic effect is probably caused by residual contamination of image B by flux from the lens since only  ~ 13% of the observed flux of G is needed to explain the observed chromatic trend. Intrinsic variability could also play a role. We discard DE because it involves a larger reddening of image A which is farther away from the galaxy than image B.

Notes: our flux ratio is in good agreement with those obtained by Fadely & Keeton (2011) in the K- and L′-bands. Koptelova et al. (2010) measured flux changes by 0.1 mag over a period of 100 days,which probably explain the flux ratio differences with H-band (Lehár et al. 2000). Color differences associated to IV might also play a role and have been reported for this system by Koptelova et al. (2010). The study of the extinction in the lensed images by Østman et al. (2008) disfavours significant extinction in this system, in disagreement with Falco et al. (1999); Elíasdóttir et al. (2006).

(c) SDSS J0246-0825: deconvolution: the deconvolution is very good. The small systematic residual detectable in the vicinity of the brightest lensed image A contributes to less than 0.05% of the flux of A.

Chromaticity: the observed chromatic trend in B/A is compatible with DE (M(blue) = 0.32, M(red) = 0.34, μ = 0.76) or with CML (M = 0.34, μ(blue) = 0.73, μ(red) = 0.76). Contamination of image A by the host galaxy, unveiled as a ring feature close to A in Inada et al. (2005) is plausible but is probably very low due to the slit clipping and to the relative faintness of this feature.

thumbnail Fig. C.1

Flux ratio for all the image pairs of our main sample.

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Broad lines: whatever the origin of the chromatic changes, the broad component of C III] is microlensed but ML of Mg II is more tentative.

Notes: there is a good agreement between our spectral-based estimate of M and the H- and L-band flux ratios (Inada et al. 2005; Fadely & Keeton 2011). The agreement in the K-band is slightly less good but still marginally consistent with the other measurements (Fadely & Keeton 2011).

(d) HE 0435-1223: deconvolution: very good results are obtained with the deconvolution. The lensing galaxy is relatively bright compared to the lensed images (only 4 times fainter than the flux of the lensed images above 6500 Å) and we may not exclude contamination of the latter by the lens. The symmetric location of the lensed images aside the lensing galaxy and their similar brightnesses however argue against large differential effects (i.e. if contamination takes place, the spectra of A & D should be corrupted the same way by the lens).

Chromaticity: we observe a chromatic increase of B/D with increasing wavelength, in agreement with the chromatic changes observed by Fadely & Keeton (2011) based on HST images. This trend may not be produced by contamination from the lensing galaxy because one needs a large contamination of image B (by at least 30% of the observed flux of G) and nearly no contamination of image D to mimic this effect. Because we find approximately the same microlensing factor in the blue and in the red, DE (M(blue) ~ 1.34, M(red) ~ 1.47, μ ~ 0.81) is the most natural explanation, B being more reddened than D by the dust in the lensing galaxy. Alternatively, CML may be at work (M ~ 1.47, μ(blue) ~ 0.74, μ(red) ~ 0.82).

Broad lines: whatever the origin of the chromatic changes, ML of the red wing of the C III]  and Mg II  lines is observed.

Notes: two fairly different flux ratios in K-band have been reported in literature. Fadely & Keeton (2011) reported B/D = 1.49    ±    0.12 while Blackburne et al. (2011) reported B/D = 1.27 ± 0.04. The latter estimate agrees well with the H-band and L-band flux ratios while the former one agrees with our spectroscopic estimate M = 1.47. Fadely & Keeton (2011, 2012) interpreted the K-band flux ratio as caused by microlensing. However, the simplest microlensing scenario is hard to reconcile with the non monotonic variations of B/D, if real. Additional data are needed to solve this puzzle.

(e) SDSS J0806-2006: deconvolution: the deconvolution is good but the spectra have a significantly lower signal to noise than for the other systems. The residual flux under the point-like images reaches up to 0.2% of the flux of the QSO image. The lensing galaxy is well deblended from the QSO images.

Chromaticity: the estimate of A at wavelengths shorter than C III] is uncertain due to the proximity of the noisy edge of the spectrum. Despite of this, the measurements are consistent with a flat ratio B/A in the continuum from 4000 to 8000 Å and ML affecting only the continuum emission.

Notes: our average macro-magnification ratio MBA ~ 0.435 agrees with the H- and K-band ratios (Sluse et al. 2008b; Fadely & Keeton 2011), although the latter two ratios differ by 0.16 mag, suggesting that the H-band flux is still slightly microlensed. At larger wavelengths, Fadely & Keeton (2011) find a L′-band flux ratio B/A < 0.164, suggesting that the H- and K- band continua are microlensed as well, but probably by a massive substructure.

Broad lines: they are apparently unaffected by microlensing unless M is significantly underestimated as suggested by the literature data. If this scenario is correct, the broad Mg II  and C III] emission lines should then be significantly microlensed.

(f) FBQ 0951+2635: deconvolution: the deconvolution is good. The residual flux in the vicinity of the lensed images amounts less than 0.03% of the brightest lensed image A and less than 0.2% of the flux of B. The lens galaxy is only  ~ 0.15″  ~ 4 pixels away from image B and is only  ~ 5 times fainter in the reddest part of the spectrum (i.e. >7000 Å). This might lead to residual contamination of B by the lensing galaxy. The spectral regions 7200–7400 Å and 7700–7950 Å  are unreliable due to an enhanced level of noise.

Chromaticity: despite the flat continuum flux ratio, we may not exclude possible residual contamination of image B by the lens because of the small separation between G and B. We identify ML of the continuum based only on the Mg II emission, which is not microlensed. The decomposition of the spectra around that line is however not entirely satisfactory because F under Mg II  does not show the monotonic variation expected if only the power law continuum was microlensed. This might be associated to microlensing of Fe II  or to spurious effect of contamination by the lens.

Table C.1

Time delays for the observed systems and typical flux variation expected during this time-spent.

Notes: microlensing of the continuum in this system, at different epochs, is supported by several other studies (e.g. Schechter et al. 1998; Jakobsson et al. 2005; Muñoz et al. 2011, and reference therein). A low amplitude chromatic change of B/A from 4000 to 9000 Å  has been detected based on HST images obtained 2.5 years before our data (Muñoz et al. 2011). There is a good agreement between our spectral-based estimate of M and the radio flux ratio (which unfortunately lacks error estimates). The H-band ratio (Falco et al. 1999) is larger by about 0.2 mag compared to our estimate. This offset is hardly explained by intrinsic variability (Table C.1) and therefore suggests that the continuum is still microlensed in H-band.

(g) BRI 0952-0115: deconvolution: the deconvolution is very good. Spatially resolved narrow Ly α is visible in the background image. This emission is not produced in the QSO but in the host galaxy of this remote quasar.

Chromaticity: because of the Lyman break, we do not estimate A in both sides of the emission but only in the continuum redward of Ly α. The ratio B/A seems however flat from the blue to the red with only an imprint of the broad emission lines. Therefore, the continuum emission is microlensed.

Broad lines: our decomposition unveils ML of a significant fraction of the Ly α line. Because the flux leading to the absorption is microlensed as the continuum, the latter does not appear in FM, which unveils a (nearly) symmetric emission roughly centered on the narrow emission.

Notes: the H-band flux ratio is similar to our continuum flux ratio, and therefore supports a significant microlensing (~0.45 mag) at that wavelength. This is not a surprise as H-band corresponds to rest-frame UV emission (λ ~ 3300 Å) which is small enough to be significantly microlensed.

(h) SDSS J1138+0314: deconvolution: the deconvolution is good with some residual flux and background excess in the vicinity of image B. Its origin is possibly associated to the QSO host galaxy.

Chromaticity: there is a small chromatic change of C/B from the blue to the red part of the spectrum which is hardly explained by contamination from the lensing galaxy. The amplitude of this effect is however very small and our measurement are compatible with no CML and no DE.

Broad lines: the ML of the BLR is large in this system, isolating the narrow component of the C IV flux in the non microlensed fraction of the spectrum. The signal is less pronounced in C III]. We do not detect ML of the [He II] and [O III] λ 1663  emission. If we use the K-band flux ratio as the correct value of M, we find significant microlensing of the C III]  line.

Notes: our spectroscopic estimate of C/B differs by 0.25 mag from the K-band measurement (Blackburne et al. 2011). This is hardly explained by intrinsic variability and suggests significant reddening of image C. This also explains the H-band ratio. Alternatively, we might have underestimated the amount of microlensing in our spectra. This has to be confirmed with additional data.

(i) J1226-0006: deconvolution: during the deconvolution process, we forced the separation between the 2 lensed images and the lensing galaxy to match the HST separation in order to reduce cross-contamination. Although a good deconvolution is obtained, we keep in mind that residual contamination shouldn’t be excluded due to the small separation of the system (ΔAG  =  0.437′′, ΔAB  =  1.376′′) and of a pixel size twice larger than for the other lenses (i.e. 0.2′′/pix).

Chromaticity: there is a strong change of the flux ratio from the blue to the red. We find evidence for unproper deblending of the QSO and of the lens flux, especially below λ ≤ 6500   Å – corresponding to the 4000   Å break of the lens – where the continuum spectrum of the lens and of the QSO have similar shapes. The decomposition of the Mg II line also shows imprint of the H and K absorption bands from the lens. This effect could modify the intrinsic shape of the microlensing signal. Based on the Mg II and [O II] λ3727 Å lines, we find that only DE10 (M(blue) = 0.850, M(red) = 0.765, μ = 0.536) may cause the observed chromatic change, with image B being more reddened by the lensing galaxy. This is unexpected as the lens is closer from image A than B. Another possibility would be a color change associated to the intrinsic variability, as the time delay in system should be of the order of 25 days.

Broad lines: we observe ML of the blue component of Mg II but we are unsure of the role of the contamination by the lensing galaxy in our spectral decomposition.

Notes: the H-band flux ratio is similar to the optical flux ratio A = 0.456 but deviates significantly from our line-based estimates of M = 0.80. Although intrinsic variability and differential extinction may play a role in the explaining the discrepancy, it seems plausible that the H-band continuum is in fact microlensed nearly at the same level as the optical one.

(j) SDSS J1335+0118: deconvolution: during the deconvolution process, we forced the separation between the bright lens image A and the lens galaxy component G to be identical to the HST separation. Small residual flux left after deconvolution close to A and B amounts less than 0.03% of the QSO flux.

Chromaticity: the change of B/A from the blue to the red is incompatible with CML, as the latter has to be stronger at bluer wavelengths. Instead, we hypothesise DE (M(blue) = 0.21, M(red) = 0.23, μ = 1.396), image A being more reddened than image B. We discard the possibility that the observed chromatic trend is caused by residual contamination from the lensing galaxy as we estimate that more than 70% of the observed flux of the galaxy should contaminate image B to flatten the spectral ratio.

Broad lines: we observe ML of the red wing of C III] and of Mg II. For Mg II  and C III], there is a second (very)-broad component which is microlensed.

Notes: the photometry published by Oguri et al. (2004), associated to data obtained about 2 years before our spectra, shows a slow decrease by 0.3 mag of ΔmBA from g- to K-band, compatible with our results, but they argue this is not conclusive due to their photometric error bars. On the other hand, they find a flat spectral ratio B/A without clear imprint of the emission lines. This contrasts with our higher signal to noise spectra were we observe differential microlensing between the continuum and the emission lines. Owing to the expected IV (Table C.1), our estimate of M = 0.23 is compatible with the M = 0.29 measured in H-band. It however deviates significantly from the K-band measurement M = 0.41 (Oguri et al. 2004). To explain these ratios we have to postulate significant differential extinction. Oguri et al. (2004) observed a chromatic decrease of ΔmBA by 0.15 mag from r-band to K-band. This amount would lead to a value of M corrected from reddening M = 0.264. This still disagree with the K-band value but the two values get marginally compatible provided the effect of intrinsic variability is 50% larger than predictions from the structure function.

(k) Q1355-225711: deconvolution: during the deconvolution process, we forced the separation between the bright lens image A and the lens galaxy component G to be identical to the HST separation. The deconvolution is good but low level residual flux, up to 0.2% of the faintest image, is visible aside the faintest lensed image and the lensing galaxy. A small excess of flux appears in the background and in the PSF component of the galaxy at the wavelength of the peak of the Mg II emission. This flux is likely associated to image B but amounts less than 0.5% of the Mg II flux in that image.

Chromaticity: contrary to what is observed for the other systems, the spectral ratio B/A in the continuum does not vary in a monotonic way (Fig. C.1k). The factor A is roughly the same in the continuum for λ > 5450 Å but decreases significantly for bluer wavelengths. This trend cannot be explained by contamination from the lensing galaxy. There is significant differences between the spectra of images A & B at basically every wavelength suggesting a complex ML of the continuum and of the broad line region, including the region emitting Fe II. Because we derive a similar value of M around Mg II and C III] , it seems plausible that the chromatic change of the flux ratio in the continuum is caused by ML rather than DE although we cannot rule out the influence of the latter. The measurement of M from the [Ne V] narrow emission lines, although more uncertain, is compatible with the one obtained for Mg II.

Broad lines: we observe ML of the red wing of Mg II. The C III] line being close to the red-edge of the spectrum, we estimate A for this line in the range 4650–4680 Å. We do not find ML of that line.

Notes: our estimate of M is in rough agreement with the K-band flux ratio once we account of the possible effect of intrinsic variability (Table C.1). The difference of  ~ 0.15 mag between the H- and K-band ratios seems to be too large to be caused by intrinsic variability and is compatible with the H-band continuum affected by a small amount of microlensing. We scanned the spectra published by Morgan et al. (2003) and applied our decomposition method to these ones. We find for Mg II  (M,μ) = (0.33,0.63) and (M,μ) = (0.38,0.56) around C III]. Like in our spectra, only the red wing of Mg II  is microlensed but not C III]. The small differences on the derived values of M are easily explained by intrinsic variability.

(l) WFI 2033-4723: deconvolution: the deconvolution is good. Residual flux under the point-like images is  < 0.1% of the QSO flux.

Chromaticity: the amplitude of the chromatic differences between the continuum in image B and C is small and probably caused by small uncertainties in the deblending of the QSO images and of the lens galaxy.

Broad lines: there is ML of the blue wing of C III] or/and of Si III] but no ML of the Mg II line.

Notes: our estimate of M is in excellent agreement with the H-band and K-band measurements (Vuissoz et al. 2008; Blackburne et al. 2011).

(m) HE 2149-2745: deconvolution: the deconvolution is good. Residual flux under the point-like images is  < 0.09% of the QSO flux. The background flux retrieved by the deconvolution process is probably associated to unproperly subtracted sky.

Chromaticity: the measurement of A at the level of the C IV line is difficult because of its vicinity from the blue edge of the spectrum. Our estimate of A for this line is performed in the range 5070–5120 Å where Fe II emission is minimal. There is no differential ML between the continuum and the emission lines. However the two spectra do not superimpose once scaled with the same magnification factor. First, there is a chromatic effect which may be caused by a small amount of DE, image B being more extinguished than image A, in agreement with its location closer to the lens galaxy. Intrinsic variability combined with the time delay of  ~ 103 days (Burud et al. 2002) might also explain the observed color difference. Second, the absorbed fraction of the C IV emission do not superimpose once scaled by B/A ~ 0.242. This is likely caused by time-variable broad absorption which is seen in images A and B at two different epochs separated by the time delay.

Notes: comparison of our spectra with those of Burud et al. (2002) confirm our estimate of M = 0.245 at the level of the C III] line. This value is also in agreement with the H-band flux ratio.

Appendix D: Characteristics of the extended sample

thumbnail Fig. D.1

Flux ratio for all the image pairs of our main sample.

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We summarize here the main characteristics of the extended sample of objects introduced in Sect. 2.3. We provide the spectral ratio between the image pairs in Fig. D.1. For each object, we also discuss our estimate of M from the spectra at the light of literature data (except for HE 2149-2745 which was discussed in Appendix C).

(n) SDSS J0924+0219 (zl = 0.394, zs = 1.524): the VLT-FORS spectra of images A and B, obtained in Jan. and Feb. 2005 by Eigenbrod et al. (2006a), show only a weak differential ML between the continuum and the emission lines (C III]  and Mg II) but no clear ML deformation of the lines (Fig. 4). The spectral ratio is flat over the spectral range of our spectra. On the other hand, Keeton et al. (2006) identified flux ratios in disagreement with macro model predictions in both the continuum and emission lines (Ly α, C IV  and C III]) based on low resolution spectra obtained with the Advanced Camera for Survey (ACS) on 29.05.2005. They demonstrated, based on microlensing simulations, that the observed anomalies in the image pair A − D could easily be explained by ML. Unfortunately, their spectra have insufficient spectral resolution to allow a proper investigation of the line profile differences.

Notes: the flux ratio A/B = 0.44 ± 0.04 in H-band (Eigenbrod et al. 2006a) is in good agreement with our estimate of M. Although K-band observation of this system exist (Faure et al. 2011), they were not able to derive accurate photometry of the lensed images due to the ring. No other NIR/MIR photometric data of this system are available in the literature.

(o) J1131-1231 (zl = 0.295, zs = 0.657): Sluse et al. (2007) presented single epoch spectra of this system obtained in April 2003. They identified ML of the broad emission lines for images A and C and presented MmD of the H β and Mg II  emission lines using the image pairs A − B and C − B. They also identified contamination of the spectra by flux from the host galaxy and empirically corrected for this effect. In image C, only the core of the emission line is not microlensed while microlensing affects the broad component of the lines in image A. Because of the uncertainty on the host contamination, exact values of M and μ may be more prone to systematic uncertainties12 than in other systems. Nevertheless, the microlensing of the emission lines is a robust result which qualitatively remains even if M or μ are under/over-estimated by up to 40%.

Notes: the flux ratios in K-band disagree with those derived from the narrow [O III] emission lines (Sluse et al. 2007; Sugai et al. 2007). Differential extinction is not a plausible explanation because of the lack of monotonic change of the flux ratios with wavelength and because of the lack of strong hydrogen absorption in X-ray (Chartas et al. 2009). Therefore, it is likely that the K-band flux ratio is significantly microlensed.

(p) H1413+117 (zl unknown, zs = 2.55): this system is the first broad absorption line (BAL) quasars where ML has been unambiguously observed (Angonin et al. 1990; Hutsemékers 1993). Hutsemékers et al. (2010) presented the MmD for this system at four different epochs spanning a 16-years time-range. They identified that ML was affecting mostly image D, roughly in the same way, along the time-spent of the observations. The Ly α, C IV, H β, and H α emission have been analysed. In addition to the ML in the broad absorption, they found evidence for ML of the central core of the C IV  and of the Ly α  (i.e. the wings are not microlensed), but no ML in the Balmer lines (see their Figs. 6–8). We show in Fig. 4 the decomposition for the C IV  and for the H β  lines for the spectra obtained in 2005. Chromatic changes of the flux ratios are observed in this system (Hutsemékers et al. 2010; Muñoz et al. 2011). On one hand, there is differential extinction between images A & B, and on the other hand, there is chromatic microlensing of image D consistent with microlensing of a standard accretion disk (Hutsemékers et al. 2010). Note that microlensing also affects component C (Popović & Chartas 2005), but the line profile differences are more subtle (Hutsemékers et al. 2010).

(q) HE 2149-2745 (zl = 0.603, zs = 2.033): our spectra of this system do not show evidence of ML, however, Burud et al. (2002) presented spectra of the two lensed images of this BAL quasar, obtained on 19.11.2000, where they observed chromatic changes of the continuum. They mentioned subtle differences in the line profile of C III]  but we fail to detect clear ML signature of the lines using the MmD on these spectra. The MmD is however difficult to perform because of the significant Fe II  emission blueward of C III]  and of the significant chromaticity of the spectral ratio which is sensible even on the small wavelength range covered by the line. We display in Fig. 4 the decomposition of C III]  using μ(λ) instead of the average μ between the blue and red part of the line. The chromatic changes observed in these spectra have been discussed by Burud et al. (2002) as possibly caused by differential extinction or chromatic microlensing. Although we may not rule out that differential extinction is present, we are now able to say based on the new spectra that the slope in the spectra of Burud et al. (2002) was mostly caused by CML.

(r) Q2237+0305 (zl = 0.0394, zs = 1.695): there is a clear ML of the broadest component of the C IV  and C III]  lines which

has been observed in image A over the 3 years time-spent of the spectrophotometric monitoring presented in Eigenbrod et al. (2008). This signal has been used by Sluse et al. (2011) to derive a size of the BLR in agreement with the size-luminosity relation obtained by reverberation mapping studies for other systems. Image D has been found to be affected by differential extinction. The MmD applied to the extinction corrected spectra, averaged over the first year of the monitoring (Oct. 2004 − Sept. 2005), is shown in Fig. 4.

Notes: although we originally used the lens model flux ratio A/D = 1.0 to make the MmD, we are also able to derive M empirically using the MmD. Following that procedure, we derive a very similar value of M (Table 4), but we disfavour M < 0.87 because they lead to the appearance of a clear dip, that we consider as unphysical, in the center of the F fraction of the C III] line. Falco et al. (1996) published radio flux ratios A/D = 0.77 ± 0.23 and Minezaki et al. (2009) published D/A = 0.87 ± 0.05 at 11.67 μm. These values are in good agreement with our spectroscopic estimates. We should however notice that small differences between the MIR flux ratios of Minezaki et al. (2009), Agol et al. (2009) and Agol et al. (2001), as well as chromatic changes in the MIR, suggest that a small amount of microlensing may still affect these wavelengths.


© ESO, 2012

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