Considering Galaxy spectra as multidimensional vectors, we use the k-means algorithm and the minimum spanning tree to show that the data in the Sloan Digital Sky Survey do not fill the entire space but are confined to a manifold with very low dimensionality. More precisely, all the spectra can be described in terms of only two degrees of freedom

The CHilean Automatic Supernova sEarch (CHASE) project began in 2007 with the goal to discover young, nearby southern supernovae in order to (1) better understand the physics of exploding stars and their progenitors, and (2) refine the methods to derive extragalactic distances. During the first four years of operation, CHASE has produced more than

Comparison between microlensing on quasars observed and simulated makes it possible to draw conclusions about physical parameters such as source size, quasar brightness profile, mass distribution of the lens, abundance and mass of microlenses, and relative transverse velocity between source and lens. By simulating magnification maps for different

We now consider the environment of quasars in the widest possible sense, from the circumnuclear regions to very large scales of hundreds of kiloparsecs. The circumgalactic environment of nearby quasars has been widely studied since the late 1960s in an attempt to test its influence on the triggering of nuclear activity. The underlying hypothesis is

Most of the questions in this chapter deal with sources that do not show the "classical" broad emission-line spectrum that characterizes the majority of known AGNs at high and low redshift. If that majority represents a "parent population" of AGNs, is the apparent absence of broad lines a result of obscuration, orientation, or different physical

After almost one century since their definition, the origin of lenticular galaxies is still a matter of debate. Several formation processes have been proposed in order to explain the wide variety of their observational properties. These properties could indicate that the class of lenticulars is a family formed by galaxies with different formations