Central regions of Sersic-Pastoriza galaxies - A photographic study

Abstract

A classification scheme is proposed for the central regions of Sérsic-Pastoriza galaxies based on high resolution photographs of 50 objects in the integrated light (4000 Å-8700 Å). Structures of two different linear scales are recognized: (1) Nucleus (≲1 kpc) and (2) Perinuclear formation (~l.5 kpc). The perinuclear formation is weak in class κ while the nucleus is too faint to detect in class ι. In the intermediate classes ε and σ both the components are bright. Class ε has an elliptical perinuclear formation with little gas while the class σ consists of bright H II complexes and dust. Observations of a few galaxies in the infrared and the blue ends of the image tube response show that the nucleus is generally redder than its surroundings. Equal intensity contours and the luminosity profiles are presented for the central regions of 27 galaxies. A comparison of their axial ratios with those of the parent galaxies indicates that the perinuclear formations are prolate or barlike. The dependence of the peak surface brightness of the central formation on the size of the bar is investigated as also the dependence of the central surface brightness of the bar on the size of the bar. The following major conclusions are drawn: (1) The peak central surface brightness of the perinuclear formation varies as the square of the bar length. This relation implies that the bar induces the in fall of gas from the bar-disk region. (2) The formations of class σ move towards class ε as star formation ceases and the massive stars die. (3) The class ι differs from class σ in the intensity of the burst of star formation. Low luminosity of the parent galaxies in class ι implies less in fall of gas and higher domination of the bar potential on the perinuclear formation. Thus the class ι structures are more prolate than those of class σ. (4) The central brightness of the bars varies directly as the length of the bar.