Probing the Broad-Line Region and the Accretion Disk in the Lensed Quasars HE 0435-1223, WFI 2033-4723, and HE 2149-2745 Using Gravitational Microlensing

Discovered by Wisotzki et al. (2002), it consists of four images of a lensed quasar at z = 1.689 and a lens galaxy at z_L = 0.455 (Morgan et al. 2005; Ofek et al. 2006). CASTLES images obtained with the Hubble Space Telescope also revealed multiple partial arcs between the images. We present spectra for the B and D images taken with MMT and VLT. Due to the symmetric distribution of the images, the time delay between images is small ($\lt 10$ days; Kochanek et al. 2006; Courbin et al. 2011).

In Figure 1 we present the continuum-subtracted spectra in the regions corresponding to the C iv, C iii], and Mg ii emission lines. The spectra are normalized to match the profiles in the region of the core of the line (see Section 3). A very interesting result in the high-ionization C iv line is the presence of a slight but systematic enhancement of the red wing ($\sim [4200,4250]$ Å range) of component D with respect to component B. A similar enhancement of the red wing is hinted at in component A (not plotted here) with respect to component B, but with less strength. C iv profiles of images B and C (not plotted here) seem to match reasonably well. In the case of the low-ionization C iii] line, the red wing of image D also seems to be brighter than that of image B, but by a small amount. Finally, the lower-ionization line Mg ii shows no significant differences between image profiles.

Zoom In Zoom Out Reset image size

Differences present at specific wavelengths in the line profiles and the dependence of its strength on the degree of ionization (decreasing in the C iv, C iii], Mg ii sequence) can be explained as microlensing acting selectively on parts of a BLR with organized kinematics. B and C would be the images less affected by differential microlensing and D the most affected.

From near-IR observations of the Hα emission line, Braibant et al. (2014) also propose microlensing to explain the differences between profiles. They found that the Hα emission line profiles of images B and C match well and that the effect of microlensing seems to be more pronounced for image D. However, their Figure 1 shows an excess in the image B profile in the blue wing relative to D (instead of the red wing excess of D that we measure). This is likely due to the different approach they followed to compare the profiles. They normalize the continuum before superposing them. Thus, their normalization factors include macro-magnification and continuum microlensing. In this way, they are mixing these two effects with line microlensing in the comparison of two emission line profiles. Following our procedure, on the contrary, continuum microlensing is removed by continuum subtraction, and macro-magnification is corrected for by normalization to the core of the emission line (assumed to be insensitive to microlensing). In fact, the renormalization of the emission-line profiles of Braibant et al. (2014) to match the core of the lines would likely result in an enhancement of the red wing of the D emission line profile with respect to that of B. In the same manner, the blue wing enhancements reported by Braibant et al. (2014) in the Mg ii emission line will also likely disappear after normalization to the line cores.

Integrating the red wing excess in C iv corresponding to image D and B in the $[4200,4250]$ Å range, we obtain the microlensing magnification associated with the region. The red wing magnification was obtained as (see Guerras et al. 2013) ${\rm{\Delta }}{m}_{{BD}}^{\mathrm{red}\,\mathrm{wing}}={({m}_{B}-{m}_{D})}_{[\mathrm{4200,4250}]}-{({m}_{B}-{m}_{D})}_{\mathrm{core}}$ $=\,(-0.12\pm 0.03)-(-0.37\pm 0.02)=(0.25\pm 0.04)$ mag.

In spite of the presence of microlensing in the red wings of some line profiles, the ratio of the line cores (see Figure 2 and Table 3) agrees within uncertainties. We obtain an average value for the emission-line ratio of ${\rm{\Delta }}{m}_{L}=\langle {m}_{B}-{m}_{D}{\rangle }_{L}\,=-0.37\pm 0.01$ mag. This confirms the expectation that the cores are not very sensitive to microlensing and that extinction is not significantly present in this lens system (in agreement with Wisotzki et al. 2003; Morgan et al. 2005).

Zoom In Zoom Out Reset image size

Table 3.  HE 0435-1223 Magnitude Differences

Region	${\lambda }_{c}$ (Å)	Windowa (Å)	${m}_{D}-{m}_{B}$ b (mag)	${m}_{D}-{m}_{B}$ c (mag)
Continuum	4170	4000–4350	−0.11 ± 0.02	⋯
	5140	4540–5550	−0.14 ± 0.01	−0.12 ± 0.02
	7560	7130–7880	−0.28 ± 0.02	−0.22 ± 0.01
Line	C ivλ1549	4170–4195	−0.37 ± 0.02	⋯
	C iv red wing	4200–4250	−0.12 ± 0.03	⋯
	C iii]λ1909	5100–5180	−0.34 ± 0.01	−0.36 ± 0.01
	Mg iiλ2800	7480–7580	−0.47 ± 0.02	−0.37 ± 0.01

Notes.

^aIntegration window. ^bMMT data. ^cVLT archive data.

Download table as:  ASCIITypeset image

Continuum observations also indicate that, in contrast with B, A and D are affected by microlensing. Courbin et al. (2011) conclude that the B image is the least affected by stellar microlensing while A is affected by strong microlensing variations. Wisotzki et al. (2003) found evidence of chromatic microlensing in the D component (0.07 mag) between 2001 December and 2002 September. Using light curves in the R filter, Kochanek et al. (2006) also observed microlensing in D (relative to A) of ∼0.1 mag yr⁻¹. Mosquera et al. (2011) obtained light curves with narrowband filters in 2007 October, observing a chromaticity between the bluest (Str-b) and the reddest (I-band) filters of ${\rm{\Delta }}{m}_{I-b}=0.20\pm 0.09$ mag affecting the A component. Ricci et al. (2011) observed the system in the i, V, R bands in two epochs, concluding that image A is probably affected by microlensing.

In Figure 2 we show the continuum ratio values available from the literature and those obtained from the spectra used in the present work. In the wavelength region between Mg ii and C iv all these data consistently depict a linear trend with a variable gap with respect to the no-microlensing baseline defined by the emission-line ratios of about 0.1 and 0.3 mag, respectively, at the red (Mg ii) and blue (C iv) ends. From C iv toward the UV, the broadband data available seem to fit in this linear trend, albeit with a large scatter. From Mg ii toward the IR, the chromaticity disappears, and with the exception of the outlying K-band data from Fadely & Keeton (2011), the broadband data seem to concentrate around a constant offset of ∼0.18 mag with respect to the baseline defined by the emission-line ratios.

Following the method described in Section 3, we will use these wavelength-dependent microlensing measurements to estimate the size and temperature profile of the accretion disk. To make the problem manageable, we will consider that the global behavior of the continuum can be defined by two straight lines, one independent of λ to describe the data redder than Mg ii, and the other one following the almost linear dependence of microlensing with ${\lambda }^{-1}$ from Mg ii toward the blue (see Figure 3). We will take three points corresponding in wavelength to the F160W band, 8100 Å (from spectroscopic continuum), and u' band (see Table 4) to describe the global dependence of microlensing with wavelength in the simplest possible way. In Figure 4 we show the 2D joint probability distribution function (PDF) of r_s and p conditioned to these three microlensing measurements. The resulting estimates are ${r}_{s}={13}_{-4}^{+5}$ lt-day at ${\lambda }_{0}=1310\,\mathring{\rm A}$ and $p=1.2\pm 0.6$ ($1\sigma$ level), using uniform logarithmic and linear priors for the size and p, respectively. The estimated size (${r}_{s}={7}_{-2}^{+3}$ lt-day or ${r}_{1/2}={9}_{-3}^{+4}$ lt-day, scaled to $0.3\,{M}_{\odot }$) is in agreement with the average size estimated by Jiménez-Vicente et al. (2014) (${r}_{s}={4.8}_{-2.7}^{+6.2}$ lt-day at 1026 Å), and it is consistent with the results in Blackburne et al. (2011) ($\mathrm{log}({r}_{1/2}/\mathrm{cm})=16.09\pm 0.19$ or ${4.8}_{-1.7}^{+2.6}$ lt-day at 1208 Å). This is also consistent with sizes predicted by the black hole–mass size correlation (Morgan et al. 2010; ${r}_{s}={2.3}_{-0.5}^{+0.8}$ at 2500 Å for ${M}_{\mathrm{BH}}={10}^{9}\,{M}_{\odot }$). However, this size is large compared to predictions based on flux variations (Mosquera et al. 2011; ${r}_{s}=0.76\times {10}^{15}\,\mathrm{cm}$ or 0.3 lt-day at 3027 Å), and recent results using R-band light curves (Blackburne et al. 2014; $\mathrm{log}({r}_{s}/\mathrm{cm})={15.23}_{-0.33}^{+0.34}$ or ${0.7}_{-0.4}^{+0.8}$ lt-day at 3027 Å). Our results for p are in agreement with previous results (ranging from 0.55 ± 0.49 in Blackburne et al. [2011] to 1.3 ± 0.6 in Jiménez-Vicente et al. [2014]). Notice that these results match those of Jiménez-Vicente et al. (2014), although those were estimated using pair B − A.

Zoom In Zoom Out Reset image size

Zoom In Zoom Out Reset image size

Table 4.  HE 0435-1223 Chromatic Microlensing

${\lambda }_{c}$ (Å)	${\rm{\Delta }}{m}_{C}-{\rm{\Delta }}{m}_{L}$ a (mag)
3522	0.39 ± 0.1
8100	0.12 ± 0.1
15500	0.11 ± 0.1

Note.

^aDifference between the magnitude difference in the continuum and in the emission-line cores ${({m}_{D}-{m}_{B})}_{C}-{({m}_{D}-{m}_{B})}_{L}$ for MMT and VLT continuum data and including the CASTLES F160W band data (see text).

Download table as:  ASCIITypeset image

We follow the same procedure (Guerras et al. 2013) to estimate the size of the C iv emitting region affected by microlensing. In this case, we only calculate the size of the region at the C iv wavelength. We obtained ${r}_{s}={10}_{-7}^{+15}$ lt-day. This size is in agreement with that of the region emitting the blue continuum, indicating that the microlensed C iv emission likely arises close to the accretion disk.

This is a quadruply imaged quasar (${z}_{S}=1.664\pm 0.002$ by our estimation) discovered by Morgan et al. (2004) lensed by a galaxy at z_L = 0.66 (Eigenbrod et al. 2006; Ofek et al. 2006). We present new spectra for components B and C, which are separated $2\buildrel{\prime\prime}\over{.} 1$. Vuissoz et al. (2008) found a time delay of ${\rm{\Delta }}{t}_{{BC}}\sim {62.6}_{-2.3}^{+4.1}$ days, in agreement with values estimated by Morgan et al. (2005).

In Figure 5 we plot the continuum-subtracted spectra for images B and C in the regions corresponding to the C iii] and Mg ii emission lines. The spectra have been normalized to match the profiles in the region of the core of the line (see Section 3). A very interesting result is the significant enhancement (of the B image compared to the C image) of a bump-like feature present in the blue wing of the C iii] line, coincident with an Al iii emission line typical of quasar spectra. Careful inspection of our spectra reveals that there is another bump-like feature in the red wing of the C iii] line that also appears to be brighter in B than in C.

Zoom In Zoom Out Reset image size

At a much lower intensity, two microlensed bumps with a separation of about ∼200 Å are also noticeable at both sides of the Mg ii emission lines. In the Morgan et al. (2004) spectra, the C iii] emission line profiles also show a relative enhancement of the B image with respect to C. This was interpreted as evidence of microlensing by Sluse et al. (2012), who indicated that the excess might also be due to microlensing of the Al iii or Si iii] lines blended with the blue wing of C iii]. Unfortunately, the signal-to-noise ratio spectra of the red side of C iii] and of the C iv lines are not sufficient to look for further evidence of these features.

Integrating the bump excess corresponding to image B in the [4930, 5000] Å and [5160, 5250] Å ranges, we obtain the microlensing magnification associated with the region generating the blue/red wing as (see Guerras et al. 2013) ${\rm{\Delta }}{m}_{{CB}}^{\mathrm{blue},\mathrm{red}}={({m}_{C}-{m}_{B})}_{\mathrm{blue},\mathrm{red}}-{({m}_{C}-{m}_{B})}_{\mathrm{core}}$. We obtain consistent microlensing estimates for both bumps: ${\rm{\Delta }}{m}^{\mathrm{blue}}=0.17\pm 0.02$ mag and ${\rm{\Delta }}{m}^{\mathrm{red}}=0.22\pm 0.03$ mag. The presence of the two bumps with similar enhancements on both sides of the line suggests a common origin for both structures (as an alternative to a microlensed Al iii line). In several AGNs (see Popović et al. 2004, and references therein) the presence of these features in the wings of a broad-emission line (BEL), which remind us of the double-peak characteristic of kinematics confined in a plane, have been interpreted as evidence of the accretion disk surrounding the massive central black hole. Both elements, the separation between the bumps of ∼250 Å ($\sim {\rm{15,000}}\,\mathrm{km}\,{{\rm{s}}}^{-1}$) and the fact that only the bumps are microlensed, would be in agreement with the hypothesis that these features arise from an inner, compact region of the BLR, likely residing on the accretion disk. An alternative possibility is that the bumps arise from a region with biconical geometry (Abajas et al. 2007).

In Figure 6 (Table 5) we present the emission-line and continuum ratios for our data and for other data in the literature. The emission-line ratios from Sluse et al. (2012) and from our data agree within uncertainties and show no evidence of chromaticity. We obtain an average value for the emission-line ratio of ${\rm{\Delta }}{m}_{L}=-0.01\pm 0.02$ mag (we have not considered the discrepant emission-line ratios from Morgan et al. [2004], because they have been obtained integrating in a window of 200 Å).

Zoom In Zoom Out Reset image size

Table 5.  WFI 2033-4723 Magnitude Differences

Region	${\lambda }_{c}$ (Å)	Windowa (Å)	${m}_{C}-{m}_{B}$ b (mag)
Continuum	5140	4700–5450	0.30 ± 0.01
	7560	7200–7800	0.30 ± 0.01
Line	C iii]λ1909	5060–5100	−0.02 ± 0.01
	C iii] blue wing	4930–5000	0.17 ± 0.02
	C iii] red wing	5160–5250	0.22 ± 0.03
	Mg iiλ2800	7430–7470	0.03 ± 0.01

Notes.

^aIntegration window. ^bVLT data.

Download table as:  ASCIITypeset image

Table 6.  WFI 2033-4723 Chromatic Microlensing

${\lambda }_{c}$ (Å)	${\rm{\Delta }}{m}_{C}-{\rm{\Delta }}{m}_{L}$ a (mag)
4300	0.29 ± 0.04
5500	0.31 ± 0.01
8700	0.34 ± 0.01
5439	0.31 ± 0.04
8012	0.19 ± 0.1
15500	0.07 ± 0.03
3522	0.28 ± 0.01
5500	0.17 ± 0.01
8500	0.11 ± 0.01
3522	0.70 ± 0.03
9114	0.26 ± 0.02
16500	0.13 ± 0.03

Note.

^aDifference between the magnitude difference in the continuum and in the emission-line cores ${({m}_{C}-{m}_{B})}_{C}-{({m}_{C}-{m}_{B})}_{L}$ for (a) VLT data, (b) CASTLES data, (c) reanalysis of Sluse et al. (2012) deconvolved spectra + Morgan et al. (2004) + Vuissoz et al. (2008) (see the text), and (d) Blackburne et al. (2011) data.

Download table as:  ASCIITypeset image

The continuum ratios, however, show a great change in amplitude at bluer wavelengths (i.e., chromaticity), showing a varying slope from 2003 to 2008, which can be explained by microlensing magnification of image B (Table 6, Figure 7). This trend is better seen if we group the data around four slopes that correspond to different epochs or observations (green, red, blue, and black in Figure 7). In 2008 the slope of the chromaticity changes, which likely requires a combination of microlensing in both components to be explained if a small size for the blue emission is assumed.

Zoom In Zoom Out Reset image size

Following the method described in Section 3, we estimate the size, r_s, and the logarithmic slope, p, of the size dependence with wavelength for each one of the four epochs described above (Table 5). In Figure 8 we present the PDF of r_s and p for each one of the epochs and the combined PDF. Notice that the slope in our continuum data is small (meaning small chromaticity within our error bars; black squares in Figure 7), i.e., parameters are largely unconstrained for this epoch (Figure 8 (a)). The resulting estimates for the combined PDF are ${r}_{s}={10}_{-2}^{+3}$ lt-day (log prior) at ${\lambda }_{0}=1310\,\mathring{\rm A}$ and $p=0.8\pm 0.2$ (linear prior). This disk size value (${r}_{s}={6}_{-1}^{+2}$ lt-day or ${r}_{1/2}={7}_{-1}^{+2}$ lt-day, scaled to $0.3\,{M}_{\odot }$) is in agreement with the average size estimated by Jiménez-Vicente et al. (2014) (${r}_{s}={4.8}_{-2.7}^{+6.2}$ lt-day at 1026 Å) and Morgan et al. (2010) (${r}_{s}={2.3}_{-0.5}^{+0.8}$ at 2500 Å for ${M}_{\mathrm{BH}}={10}^{9}\,{M}_{\odot }$). However, we cannot reconcile our results (r_s and p) with those of Blackburne et al. (2011) (${r}_{1/2}={19.8}_{-5.9}^{+8.2}$ lt-day at 1233 Å, using $0.3\,{{\rm{M}}}_{\odot }$ microlenses, $p=-0.63\pm 0.52$). Although these last authors obtain size estimates that decrease with wavelength, they do not rule out positive values for p and suggest that the anomalous flux ratios might be caused by unusual caustic patterns.

Zoom In Zoom Out Reset image size

Using the same procedure, we estimate a size of ${r}_{s}={11}_{-7}^{+28}$ lt-day for the region generating the emission-line bumps on both sides of the C iii] line. Under the hypothesis of a common origin for both bumps, we can take this size as the radius of the accretion disk, infer a velocity of $7500\,\mathrm{km}\,{{\rm{s}}}^{-1}$ from the separation between the bumps, and, assuming Keplerian circular rotation, estimate a mass of ${1.2}_{-0.8}^{+3.1}\times {10}^{8}\,{M}_{\odot }$ for the supermassive black hole.

HE 2149-2745 was discovered by Wisotzki et al. (1996); it consists of two images A and B separated by $1\buildrel{\prime\prime}\over{.} 70$ at ${z}_{S}=2.033\pm 0.005$. The lens galaxy is at ${z}_{L}=0.603\,\pm 0.001$ (Eigenbrod et al. 2007). Image B is separated by $0\buildrel{\prime\prime}\over{.} 34$ from the main lens galaxy. Chromatic microlensing was detected in spectra taken by Burud et al. (2002). These authors estimated a time delay of 103 ± 12 days.

In Figure 9 we present the continuum-subtracted spectra for the A and B images in the regions corresponding to the C iv, C iii], and Mg ii emission lines. The spectra match very well, after normalization using $A/B=3.5$, except for the absorption in C iv. Sluse et al. (2012) also find that the absorbed fractions of the C iv emission line do not agree once scaled, and they attribute the difference to time-variable broad absorption together with a time delay. They found a chromatic difference between the spectra ($A/B=4$ for CIII and $A/B=3.5$ for Mg ii), which they attribute to dust extinction on image B and/or intrinsic variability combined with a time delay of ∼103 days.

Zoom In Zoom Out Reset image size

Flux comparison between our spectroscopic continua and CASTLE data shows that there is contamination by the lens galaxy. We estimate (using F555W and F814W fluxes) that the contamination in the B spectra could be up to 60%, while in the deconvolved spectra it could be around 30%. In the following we will use the broadband data to obtain the magnitude difference in the continuum.

In Figure 10 (Table 7) we present the emission-line and continuum ratios for our data and for other data in the literature. The emission-line ratios show no dependence with wavelength. The continuum flux ratios, however, show chromaticity, likely induced by microlensing (Table 8, Figure 11).

Zoom In Zoom Out Reset image size

Zoom In Zoom Out Reset image size

Table 7.  HE 2149-2745 Magnitude Differences

Region	${\lambda }_{c}$ (Å)	Windowa (Å)	${m}_{B}-{m}_{A}$ b (mag)	${m}_{B}-{m}_{A}$ c (mag)
Continuum	4170	4000–4350	−0.11 ± 0.02	⋯
	5140	5000 6200	−0.14 ± 0.01	−0.12 ± 0.02
	7560	8250 8650	−0.28 ± 0.02	−0.22 ± 0.01
Line	C ivλ1549	4170–4195	−0.37 ± 0.02	⋯
	C iii]λ1909	5720 5830	−0.34 ± 0.01	−0.36 ± 0.01
	Mg iiλ2800	8480 8540	−0.47 ± 0.02	−0.37 ± 0.01

Notes.

^aIntegration window. ^bVLT data. ^cSluse et al. (2012).

Download table as:  ASCIITypeset image

Table 8.  HE 2149-2745 Chromatic Microlensing

${\lambda }_{c}$ (Å)	${\rm{\Delta }}{m}_{C}-{\rm{\Delta }}{m}_{L}$ a (mag)
4380	0.26 ± 0.06
8140	0.19 ± 0.02
38000	0.15 ± 0.01

Note.

^aDifference between the magnitude difference ${({m}_{B}-{m}_{A})}_{C}-{({m}_{B}-{m}_{A})}_{L}$ in the broadband data from CASTLES and L-band data from Fadely & Keeton (2011) and in the emission-line cores from VLT data, reanalysis of Sluse et al. (2012) deconvolved spectra, and Ks-band data from Fadely & Keeton (2011) (see the text).

Download table as:  ASCIITypeset image

Using the continuum and emission-line ratios (see Section 3), we estimate the size, r_s, and the logarithmic slope, p, of the size dependence with wavelength. In this case we have used convergence ${\kappa }_{A}=0.31$, ${\kappa }_{B}=1.25$ and shear ${\gamma }_{A}=0.32$, ${\gamma }_{B}=1.25$ (Sluse et al. 2012) to compute the magnification maps. In Figure 12 we present the 2D PDF of r_s and p. The resulting estimates are ${r}_{s}={8}_{-5}^{+11}$ lt-day (log prior) at ${\lambda }_{0}=1310$ Å and $p=0.4\pm 0.3$ (linear prior).

Zoom In Zoom Out Reset image size