The Balmer continuum in the spectra of AGN
The Balmer continuum in the spectra of AGN Kovačević, J. , Popovic, L. Č. , Kollatschny, W. , Saikia, P.
Introduction In order to understand physical and kinematical properties of AGN emission regions we investigate the correlations between different spectral properties. In previuos work we found: - kinematical linkage between optical Fe II lines and Intermediate Line Region (ILR), which indicates the ILR origin of optical Fe II. - different correlations between EWs of lines (and line components) vs. Lcont. - different correlations between spectral properties in “pure AGN” sample, and composit objects (AGN + starburst) sample, which indicates different physical processes in emission regions. - etc. . . (Kovačević et al. 2010, Popović et al. 2011) Present work: extension of research to UV part of spectra! GOAL: to compare UV and optical spectral properties (specially UV Fe II lines with optical Fe II, in order to find location of their emission region, etc. )
UV pseudocontinuum 1 step: determination of the UV pseudocontinuum in the sample! Not easy because: 1. complex shape of UV pseudocontinuum: Power low + Balmer continuum (Grandi 1982) Tsuzuki et al. 2006 2. Our sample contains spectra within spectral range: 2900 A – 5500 A (SDSS) (only two continuum windows : ~4200 A and ~5100 A! Complex shape of UV pseudocontinuum cannot be fitted well!
Balmer continuum fitting: Tsuzuki et al. 2006, Sameshima et al. 2010
Balmer continuum fitting: Jin et al. 2012 Convolving Balmer continuum equation with Gaussian (FWHM Gaussian = FWHM broad Hβ)
Our model of Balmer continuum We try to make model which: - we could use for fitting spectra within 2900 A – 5500 A range (with two continuum windows). It could be done by reducing number of free parameters: calculating the intensity of Balmer continuum! - we try to make good fit near Balmer edge (3646 A)! Our model consists of: Power law + Balmer continuum (λ<3646 A) + high order Balmer lines (n=3 -400), (λ>3646 A) They are fitted by one Gaussian with the same width and shift as Hγ. The relative intensites for Balmer lines with n<50 are taken from the paper: Storey and Hummer 1995. Relative intensities for 50<n<400 are calculated using approximate formula: ≈1
Examples of fit:
Continuum window at 3000 A? 3000 A
Conclusions: The intensity of Balmer continuum near Balmer edge (~3646 A) may be well estimated using fitting result for intensity of prominant Balmer lines (for example Hγ). Model with high order Balmer lines n=3 -400, for λ>3646 A, improve the fit near Balmer edge. Majority of analysed spectra have pseudocontinuum window at ~3000 A. Calculated intensity of Balmer continuum, as well as one more continuum window (~3000 A) should enable determination of UV pseudocontinuum in 2900 A – 5500 A range. Future work: construction UV Fe II template, analysis of relationships between UV/optical spectral parameters. . . Thank you for your attention!
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