Surface Photometry of  AGN

Surface photometry (SP) qantitatively describes the light distribution in extended objects. It is widely used in galaxies.

SP of galaxies is usually done by fitting ellipses to the isophotes. This is motivated by the form of the isophotes mainly in elliptical and lenticular galaxies. We get two types of output from these fits. First, this is the residual image, which is the difference between the original and the model image. Residual images are different for the different types of galaxies and can also reveal asymmetric or weak hidden structures. Second, we get radial profiles of the centre position, ellipticity, position angle, intensity, deviations from perfect elliptical isophotes and other quantities.

Magnitudes can be calculated from the sky subtracted intensity. They can be integrated magnitudes within a certain aperture, or the surface brightness at a given ellipse. Both can be transformed to a standard  photometric system with the use of standard stars.

The SP has produced up to now radial profiles of a number of parameters. A major task is to pick out of them the representative, global ones. By fitting de Vaucouleurs law, an exponential law, Sersic law or others to the galaxy surface brightness the effective radius re, the mean surface brightness Ie within re, the central intensity, the exponential disc scale factor and other physically less meaningful parameters can be derived. We can determine a given global parameter either as the extremum of the parameter profile or its value at the effective radius or the value at a certain isophote, commonly at  μ = 25 mag.arcsec-2 or by other criteria. Thus the global ellipticity, position angle, colour, colour gradient (the slope of the colour versus logr plot), etc. can be determined.

The global ellipticities and deviations from perfect elliptical isophotes can be used to derive the relative disk luminosities and the inclinations of galaxies.

The measured values of logre, log<I> logσ, where σ is the line-of-sight stellar velocity dispersion, that stand in the relation:
                                    αlogre = α log<I>β logσ  +  γ,
do not populate this 3-parameter space evenly but are limited to a thin plane - the Fundamental Plane (FP). The FP combines SP with spectroscopy.It can be used to study the evolution of galaxies as a function of redshift.

Multi-colour SP gives information about star population, dust content, geometrical parameters and mass distribution in galaxies. SP has made it possible to establish the distance scale in the Universeto and to find the existence of different  galaxy types and  study their global subsystems.

SP is a basic method in the study of distant galaxies. There exist 3 principal factors complicating the observational study of distant galaxies. The first is the cosmological dimming of surface brightness, the second is the shifted wave length of the moving object, compensated by the so-called K-correction. Both factors originate from the Universe expansion. The third one is due to evolution of galaxy characteristics with time.

Our publications - Surface Photometry

SLAVCHEVA L., MIHOV B., PETROV G., BACHEV R., IAU Symp. 194, p.87, 1999.
Spectrophotometry of selected AGN.
Seyfert galaxy Arakelian 564.
, IAU Symp. 194, p.84, 1999.
Surface photometry of barred AGN. Arakelian 564.
PETROV G., SLAVCHEVA-MIHOVA L., MIHOV B., Publ. Astron. Obs. Belgrade, 2004, 74, 1-2.
Surface photometry of NGC 5610 - A Box/Peanut Structure In An Intermediately Inclined Galaxy.

SLAVCHEVA-MIHOVA L., PETROV G., MIHOV B., Aerospace Reserch in Bulgaria, 2005, 19
Multicolour Surface Photometry Of Seyfert Galaxies: First Results
PETROV G., SLAVCHEVA L., Astrophysical Investigations, 2006, vol.7, p.76.
Surface photometry of barred AGN. Wolf Rayet galaxy NGC 6764.

Created by L.Slavcheva-Mihova, 2005