M58 is a strongly barred galaxy and a bright member of the Virgo cluster with a similar mass to the Milky Way. It is located in proximity to M87 near the center of the Virgo cluster. It is one of the most gas poor galaxies known presumably due to its location near the center of the rich Virgo cluster. It is a well known phenomenon that galaxies located deep within crowded clusters often display profound deficiencies in their neutral gas content compared to galaxies in less crowded environments. The gas loss is explained by several factors including tidal stripping by galaxy-galaxy interactions and a phenomenon known as "ram-pressure" where a galaxy moving through the dense intergalactic gas of a rich cluster has much of its interstellar gas stripped from it. The gas deficiency parameter is a strong signature of a galaxy's membership in a rich cluster and its location relative to the center of the cluster.
M58 is in a class of galaxies known as LINERs (Low Ionization Emission Line Regions). Normal galaxies display only stellar spectra from their nucleus which arise from old population II stars normally distributed throughout the nucleus and bulge. A subset of galaxies display peculiar spectra from their nucleus that is either nonstellar in origin or from hot and massive population I stars not normally found in the central region. Active galaxies (galaxies containing an active galactic nucleus or AGN) are the classic nonstellar emitters as their central mass accreting black holes release prodigious amounts of energy at a large range of wavelengths. LINERs represent a class of galaxies that lie between the normal exclusively stellar emitting galaxy nuclei and those with an AGN.
LINERs display low excitation optical line spectra from their nucleus that is believed not to arise from normal stars. One third to perhaps one half of all galaxies fall into this category. The nature of the central engine in LINERs has been under debate by astronomers for several decades. LINERs make up a diverse group of galaxies and can be associated with a number of different nuclear phenomenon including a low level active galactic nucleus (low luminosity AGN), hot massive population I stars within nuclear starbursts, cloud-cloud collisions in galaxy mergers, and shock fronts. Some astronomers have further divided LINERs into AGN-LINERs and non-AGN-LINERs based on their infrared characteristics. For unknown reasons LINER phenomenon is often associated with dust enshrouded galaxies like M58 which emit much of their energy in the infrared.
So what is the nature of M58's nonstellar nuclear spectra? M58 is known as an active galaxy with a Seyfert type nucleus. As is typical of Seyfert galaxies, M58 possesses a central jet phenomenon in its nucleus presumably due to a mass accreting central black hole. To confuse matters more M58 also shows evidence of both recent and older nuclear starburst regions. It appears that M58's LINER characteristics arise almost solely from its AGN which places it into the class of AGN-LINERs.
Nuclear starbursts are often the consequence of gas inflows into the nucleus from bar induced torques. In M58's case however the younger and more central nuclear starburst was created by a different process. Presumably the interaction of the central jet with ambient gas clouds in the nucleus produced the right conditions to form massive stars. The older starburst located further out in the circumnuclear region, was likely formed in the traditional manner.