A Method for Spatial Deconvolution of Spectra

Courbin, F.; Magain, Pierre; Kirkove, Murielle; Sohy, Sandrine

doi:10.1086/308291

Cited by 53 publications

(55 citation statements)

References 6 publications

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“…In this way, a spectral point spread function (PSF) is measured simultaneously with the quasar. This is crucial for the spatial deconvolution of the data to work efficiently (Courbin et al 2000) and to clearly separate the quasar spectrum from that of the putative envelope.…”

Section: Sample and Observationsmentioning

confidence: 99%

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Spectroscopy of extended Lyαenvelopes aroundz = 4.5 quasars

North¹,

Courbin²,

Eigenbrod³

et al. 2012

A&A

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What are the frequency, shape, kinematics, and luminosity of Lyα envelopes surrounding radio-quiet quasars at high redshift, and is the luminosity of these envelopes related to that of the quasar or not? As a first step towards answering these questions, we have searched for Lyα envelopes around six radio-quiet quasars at z ∼ 4.5, using deep spectra taken with the FORS2 spectrograph attached to the UT1 of the Very Large Telescope (VLT). Using the multi-slit mode allows us to observe several point spread function stars simultaneously with the quasar, and to remove the point-like emission from the quasar, unveiling the faint underlying Lyα envelope with unprecedented depth. An envelope is detected around four of the six quasars, which suggests that these envelopes are very frequent. Their diameter varies in the range 26 < ∼ d < ∼ 64 kpc, their surface brightness in the range 3 × 10 −19 < ∼ μ < ∼ 2 × 10 −17 erg s −1 cm −2 arcsec −2 , and their luminosity in the range 10 42 < ∼ L(Lyα) < ∼ 10 44 erg s −1 . Their shape may be strongly asymmetric. The Lyα emission line full width at half maximum (FWHM) is 900 < FWHM < 2200 km s −1 and its luminosity correlates with that of the broad line region (BLR) of the quasar, with the notable exception of BR2237-0607, the brightest object in our sample. The same holds for the relation between the envelope Lyα luminosity and the ionizing luminosity of the quasar. While the deep slit spectroscopy presented in this paper is very efficient at detecting very faint Lyα envelopes, narrow-band imaging is now needed to measure accurately their spatial extent, radial luminosity profile, and total luminosity. These observables are crucial to help us discriminate between the three possible radiation processes responsible for the envelope emission: (i) cold accretion, (ii) fluorescence induced by the quasar, and (iii) scattering of the BLR photons by cool gas.

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Section: Sample and Observationsmentioning

confidence: 99%

“…We spatially deconvolved the spectra following the method described in Courbin et al (2000), which is an adaptation to spectroscopy of the "MCS" image deconvolution algorithm (Magain et al 1998). The results of this deconvolution are displayed in Fig.…”

Section: Reduction and Spatial Deconvolutionmentioning

confidence: 99%

Spectroscopy of extended Lyαenvelopes aroundz = 4.5 quasars

North¹,

Courbin²,

Eigenbrod³

et al. 2012

A&A

Self Cite

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show abstract

“…0.025−1.0 of the standard deviation of the Gaussian convolving function). For all of these simulations, the noise level is fixed to produce SNR = 220 (similar to that in the simulations of Courbin et al 2000 for comparison of the two methods). .…”

Section: Figmentioning

confidence: 99%

“…To provide a direct comparison with previous methods, we adopt exactly the same problem considered by Courbin et al (2000) for a second test. This consists of a quasar and a star with a featureless continuum (see Courbin et al 2000, Sect. 3.1).…”

Section: Example Bmentioning

confidence: 99%

On the spectroastrometric separation of binary point-source fluxes

Porter¹,

Oudmaijer

Baines

2004

A&A

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Abstract. Spectroastrometry is a technique which has the potential to resolve flux distributions on scales of milliarcseconds. In this study, we examine the application of spectroastrometry to binary point sources which are spatially unresolved due to the observational point spread function convolution. The technique uses measurements with sub-pixel accuracy of the position centroid of high signal-to-noise long-slit spectrum observations. With the objects in the binary contributing fractionally more or less at different wavelengths (particularly across spectral lines), the variation of the position centroid with wavelength provides some information on the spatial distribution of the flux. We examine the width of the flux distribution in the spatial direction, and present its relation to the ratio of the fluxes of the two components of the binary. Measurement of three observables (total flux, position centroid and flux distribution width) at each wavelength allows a unique separation of the total flux into its component parts even though the angular separation of the binary is smaller than the observations' point-spread function. This is because we have three relevant observables for three unknowns (the two fluxes, and the angular separation of the binary), which therefore generates a closed problem. This is a wholly different technique than conventional deconvolution methods, which produce information on angular sizes of the sampling scale. Spectroastrometry can produce information on smaller scales than conventional deconvolution, and is successful in separating fluxes in a binary object with a separation of less than one pixel. We present an analysis of the errors involved in making binary object spectroastrometric measurements and the separation method, and highlight necessary observing methodology.

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“…The analysis of M05, both for their Hubble Space Telescope (HST ) images and ground-based spectra, rely on highly specialized deconvolution methods developed by these authors (Magain et al 1998;Courbin et al 2000). While we do not call into question the reliability of M05's analysis, given the wide-spread interest that their results have generated it would be worthwhile to confirm them independently, preferably using a different technique.…”

Section: Introductionmentioning

confidence: 99%

The Host Galaxy of the Quasar HE 0450−2958

Kim

Peng

et al. 2007

ApJ

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A recent study suggests that the quasar HE 0450À2958 is hosted by a galaxy substantially fainter than that inferred from the correlation between black hole mass and bulge luminosity. As this result has significant bearings on galaxy and black hole evolution, we revisit the issue by performing an independent analysis of the data, using a two-dimensional image fitting technique. We indeed find no evidence of a host galaxy either, but due to the brightness of the quasar and uncertainties in the point-spread function, the limits are fairly weak. To derive an upper limit on the host galaxy luminosity, we perform simulations to deblend the quasar from the host under conditions similar to those actually observed. We find that the host galaxy has an absolute magnitude upper limit of À20 P M V P À21, in good agreement with the previous determination. Since this limit is consistent with the value predicted from the current best estimate of the black hole mass, there is no compelling evidence that the quasar HE 0450À2958 has an abnormally underluminous host galaxy. We also show that, contrary to previous claims, the companion galaxy to HE 0450À2958 should not be regarded as an ultraluminous infrared galaxy.

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A Method for Spatial Deconvolution of Spectra

Cited by 53 publications

References 6 publications

Spectroscopy of extended Lyαenvelopes aroundz = 4.5 quasars

Spectroscopy of extended Lyαenvelopes aroundz = 4.5 quasars

On the spectroastrometric separation of binary point-source fluxes

The Host Galaxy of the Quasar HE 0450−2958

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