REVIEW
Lens-Aided Multi-Angle Spectroscopy (LAMAS) Reveals Small-Scale Outflow Structure in Quasars
Astrophysics · Submitted 1 Mar 2006 · 91 references
Pith's verdict: A plausible hypothesis paper with a genuinely new observational idea, but the key smooth absorber is inferred from a stacking artifact, not detected.
T0 · AI review
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Referee report
The paper
The paper claims
This paper claims that lensed quasar sightlines expose small-scale structure in quasar outflows, making the blue-wing changes in SDSS J1004+4112 transient gaps in a smooth, patchy wind.
The reading
What carries the argument
The central mechanism is lens-aided multi-angle spectroscopy (LAMAS): gravitational lensing converts the image separation $\theta$ into an angular difference $\Delta\varphi$ between sightlines as seen from the quasar nucleus, so each image samples a slightly different cut through the outflow. The paper uses this geometry with the relation $a_L \sim R_a\theta$ for the lateral absorber size, compares the observed ratio spectra to ratios constructed by adding 15–25% of a BAL composite to a non-BAL composite to argue that the differences look absorptive, and invokes variability of the blue wing with timescale $\sim 43$ days to estimate a transverse size $a_V \sim 4\times 10^{15}$ cm. The two size scales, together with covering-fraction constraints, bracket the absorber structure at roughly $10^{15}$ cm.
Extended reading notes
Core claim
On the paper's own terms, the discovery is that spectroscopic differences between lensed quasar images can carry direct information about the transverse structure of quasar outflows. The paper argues that all four images of SDSS J1004+4112 are viewed through a warm, disk-driven wind that is smooth in velocity but spatially clumped or filamentary; component A's sightline pierces a persistently thinner part of the flow, and the blue-wing C IV enhancements observed there are gaps that open and close as the rotating flow evolves. The same effect is claimed to explain some UV and X-ray variability in AGN generally, and the measured angular separations, combined with absorber-distance estimates, imply absorber structures about $10^{15}$ cm across.
Load-bearing premise
The load-bearing premise is that quasar outflows contain an absorbing component that is smooth and broad in velocity, so it produces no visible BAL troughs, yet is spatially clumpy or filamentary, so different sightlines can see different columns and transient gaps.
Editorial extensions
If this is right
- Spectroscopic differences in other lensed quasars may be attributable to LAMAS rather than microlensing or time-delay variability.
- Outflows carry fine structure on angular scales of arcseconds as seen from the nucleus, with lateral sizes near $10^{15}$ cm.
- Smooth, broad, low-column absorption may be present in most or all quasar spectra even where no BAL troughs are visible.
- Variable absorption in rotating, clumpy outflows can account for some fraction of observed UV and X-ray variability in AGN.
- X-ray observations of SDSS J1004+4112 should show component A with a lower absorbing column and larger $f_X/f_{\rm opt}$ than components B–D.
Reading between the lines
- Beyond the paper: if smooth broad absorption is ubiquitous, then every quasar spectrum is mildly self-absorbed, and measurements of emission-line asymmetry, particularly in C IV, may need to be corrected for this before interpreting them as intrinsic wind geometry.
- Beyond the paper: the LAMAS picture implies that wide-separation lenses with multiple epochs should be monitored simultaneously; if blue-wing events are intrinsic variability, they should appear in other components at the time-delay offset, while LAMAS predicts they are confined to a single sightline.
- Beyond the paper: the $\sim 10^{15}$ cm structure size, together with the covering-fraction lower bound of $\sim 10$ pc for the absorber distance, places the absorbing region between the broad emission line region and the dusty torus, a location that future X-ray grating observations of lensed quasars could test directly.
- Beyond the paper: one could search for the predicted ubiquitous smooth absorption by stacking high signal-to-noise spectra of “non-BAL” quasars and looking for shallow, broad residual absorption features after subtracting a continuum and emission-line model.
Original abstract
Spectral differences between lensed quasar image components are common. Since lensing is intrinsically achromatic, these differences are typically explained as the effect of either microlensing, or as light path time delays sampling intrinsic quasar spectral variability. Here we advance a novel third hypothesis: some spectral differences are due to small line-of-sight differences through quasar disk wind outflows. In particular, we propose that variable spectral differences seen only in component A of the widest separation lens SDSSJ1004+4112 are due to differential absorption along the sightlines. The absorber properties required by this hypothesis are akin to known broad absorption line (BAL) outflows but must have a broader, smoother velocity profile. We interpret the observed CIV emission line variability as further evidence for spatial fine structure transverse to the line of sight. Since outflows are likely to be rotating, such absorber fine structure can consistently explain some of the UV and X-ray variability seen in AGN. The implications are many: (1) Spectroscopic differences in other lensed objects may be due to this ``lens-aided multi-angle spectroscopy'' (LAMAS). (2) Outflows have fine structure on size scales of arcsec as seen from the nucleus. (3) Assuming either broad absorption line region sizes proposed in recent wind models, or typically assumed continuum emission region sizes, LAMAS and/or variability provide broadly consistent absorber sizescale estimates of about 10^15cm. (4) Very broad smooth absorption may be ubiquitous in quasar spectra, even when no obvious troughs are seen.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
Spectral differences between lensed quasar image components are common. Since lensing is intrinsically achromatic, these differences are typically explained as the effect of either microlensing, or as light path time delays sampling intrinsic quasar spectral variability. Here we advance a novel third hypothesis: some spectral differences are due to small line-of-sight differences through quasar disk wind outflows. In particular, we propose that variable spectral differences seen only in component A of the widest separation lens SDSSJ1004+4112 are due to differential absorption along the sightlines. The absorber properties required by this hypothesis are akin to known broad absorption line (BAL) outflows but must have a broader, smoother velocity profile. We interpret the observed CIV emission line variability as further evidence for spatial fine structure transverse to the line of sight. Since outflows are likely to be rotating, such absorber fine structure can consistently explain some of the UV and X-ray variability seen in AGN. The implications are many: (1) Spectroscopic differences in other lensed objects may be due to this ``lens-aided multi-angle spectroscopy'' (LAMAS). (2) Outflows have fine structure on size scales of arcsec as seen from the nucleus. (3) Assuming either broad absorption line region sizes proposed in recent wind models, or typically assumed continuum emission region sizes, LAMAS and/or variability provide broadly consistent absorber sizescale estimates of about 10^15cm. (4) Very broad smooth absorption may be ubiquitous in quasar spectra, even when no obvious troughs are seen.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Spectral differences between lensed quasar image components are common. | background 1.00 | 0.06 | 0.02 | asserted 1.00 |
| s1 | Since lensing is intrinsically achromatic, these differences are typically explained as the effect of either microlensing, or as light path time delays sampling intrinsic quasar spectral variability. | background 1.00 | 0.04 | 0.02 | asserted 0.82 |
| s2 | Here we advance a novel third hypothesis: some spectral differences are due to small line-of-sight differences through quasar disk wind outflows. | contribution 0.99 | 0.34 | 0.63 | hedged possibility 0.48 |
| s3 | In particular, we propose that variable spectral differences seen only in component A of the widest separation lens SDSSJ1004+4112 are due to differential absorption along the sightlines. | contribution 0.68 | 0.58 | 0.30 | speculative 0.60 |
| s4 | The absorber properties required by this hypothesis are akin to known broad absorption line (BAL) outflows but must have a broader, smoother velocity profile. | interpretation 0.80 | 0.40 | 0.06 | asserted 0.82 |
| s5 | We interpret the observed CIV emission line variability as further evidence for spatial fine structure transverse to the line of sight. | interpretation 0.99 | 0.69 | 0.08 | asserted 0.51 |
| s6 | Since outflows are likely to be rotating, such absorber fine structure can consistently explain some of the UV and X-ray variability seen in AGN. | interpretation 1.00 | 0.19 | 0.08 | hedged possibility 0.99 |
| s7 | The implications are many: (1) Spectroscopic differences in other lensed objects may be due to this ``lens-aided multi-angle spectroscopy'' (LAMAS). | interpretation 0.98 | 0.20 | 0.15 | hedged possibility 1.00 |
| s8 | (2) Outflows have fine structure on size scales of arcsec as seen from the nucleus. | interpretation 0.72 | 0.65 | 0.18 | asserted 0.99 |
| s9 | (3) Assuming either broad absorption line region sizes proposed in recent wind models, or typically assumed continuum emission region sizes, LAMAS and/or variability provide broadly consistent absorber sizescale estimates of about 10^15cm. | result 0.54 | 0.70 | 0.10 | hedged possibility 0.86 |
| s10 | (4) Very broad smooth absorption may be ubiquitous in quasar spectra, even when no obvious troughs are seen. | interpretation 0.97 | 0.24 | 0.11 | hedged possibility 0.57 |
What was examined, and what was not
- arXiv listing abstract v1
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Figures
Figures reproduced from arXiv:astro-ph/0603033 by the authors.
References
Discussion
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