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Measuring the properties of QSO broad-line regions with the GMOS IFU.

Measuring the properties of QSO broad-line regions with the GMOS IFU. Randall Wayth with Matt O'Dowd & Rachel Webster. Outline. Motivation Introduction to 2237+0305 Observations & Data reduction Emission line flux ratios Microlensing of QSO emission regions

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Measuring the properties of QSO broad-line regions with the GMOS IFU.

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  1. Measuring the properties of QSO broad-line regions with the GMOS IFU. Randall Wayth withMatt O'Dowd & Rachel Webster.

  2. Outline • Motivation • Introduction to 2237+0305 • Observations & Data reduction • Emission line flux ratios • Microlensing of QSO emission regions • Constraints on emitting region size

  3. Motivation - QSO emission regions • QSO continuum/line emission regions are too small to resolve • Reverberation mapping suggests they are very small • Gravitational lensing magnifies objects. If a source is resolved in a lensed image, then we can directly determine its true size & surface brightness • If not resolved, then microlensing should create different magnifications for the continuum and broad-line regions of the QSO.

  4. 2237+0305 • Barred spiral (Sbc) galaxy at low redshift (z=0.04) lensing z=1.69 radio quiet QSO. • Four images of QSO formed around galaxy bulge with separation ~1-2 arcsec • Lensing offers unique opportunity to study • QSO continuum and emission line region size/structure • Properties of dark matter halo (shape, cuspiness, clumpiness) • Mass function of galaxy bulge stars, and more...

  5. 2237+0305 N E 15 second r-band acquisition image

  6. 2237+0305 Same image, different contrast

  7. 2237+0305 Galaxy centre B D C A QSO image labels follow Yee (1988)

  8. Is the CIII] emission region in 2237+0305 resolved? • Mediavilla et al. (1998) claimed seeing an arc of resolved CIII] emission using INTEGRAL IFU on WHT. (0.5” separation, rectangular array, 0.45” fibre diameter) • If real, we can “undo” the effects of lensing and create a true image of the emission region. From Mediavilla et al. (1998) ApJ 503 L27

  9. Sky Object Data - GMOS IFU • IFU is a hexagonal lenslet array with separation 0.2” • R400 grating in “one slit” mode. Useful wavelength range ~500-850nm. Object coverage is 5”x3”. • 8 x 30min exposures taken on 16/17 July, 2002. We use 5 of the 8 frames. Seeing 0.6”

  10. Aims • Confirm/refute existence of arc of emission • If real, make an image of the QSO BELR! • If not real, examine effect of lensing on the relative strengths of continuum and broad-line emission from the QSO

  11. Data CIII] QSO spectrum MgII D A B C Galaxy spectrum

  12. Line flux extraction CIII] line MgII line Continuum

  13. Images of the broad-line flux • Subtracting surrounding continuum from the emission lines leaves the line flux • Subtraction is quite clean • Notice difference in brightness of QSO images Arc or PSF overlap? MgII – emission line CIII] continuum MgII continuum CIII] - emission line

  14. PSF modelling & subtraction • We are looking for a faint arc, so we need to create an accurate PSF and subtract the QSO images. • Method • combine line images for the 5 good frames • define a mask around each QSO image including a region which is uncontaminated by other images • cut out, rescale and combine sections from each image • use this PSF, to subtract QSO images, iterate a few times

  15. PSF model Combined PSF (MgII) Uncontaminated regions

  16. Line images with QSOs subtracted MgII CIII] Unresolved! - No arc in MgII or CIII]! Peak residual ~10%

  17. Microlensing and the BELR • Microlensing by stars in the lens galaxy's bulge project a network of “caustics” onto the QSO. • Parts of the source crossing caustics (red/yellow) are highly magnified. • The QSO can be differentially magnified depending on its size relative to the caustic network. Microlensing caustic network Image courtesy Joachim Wambsganss

  18. Microlensing and the BELR • Small source = no differential magnification • All parts of the source are equally magnified

  19. Microlensing and the BELR • Medium source = differential magnification! • If the QSO's continuum region is much smaller than the BELR, then the continuum should be more highly magnified.

  20. Flux ratios Galaxy centre B D C • Extinction corrected flux ratios for continuum and broad-lines are certainly different! • Without microlensing, all images should have approx same magnitude, so BELR is also microlensed. • Because MgII and CIII] lines have same flux ratio, they must be similar size. • BELR size ~0.06pc based on simulations of Wyithe et. al 2002 (MNRAS 331) A

  21. Next: de-dispersed spectral ratios • After correcting for atmospheric dispersion, take ratios of image spectra • Broad-line magnifications clearly visible • Shape of continuum is a function of source morphology, microlensing and extinction • Shape/location of lines depends on BELR structure! C/A D/A B/A 8000 6000 5000 7000

  22. Summary • Using GMOS-N IFU we have taken the best spectroscopic data of 2237+0305 to date • We find no arc of emission in either the CIII] or MgII line, contrary to previous claims • Magnification ratios of the images in both the continuum and broad-lines show microlensing • BELR is measured from flux ratios to be ~0.06pc. This estimate will improve using de-dispersed data. • MNRAS 359 561 (2005)

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