Extragalactic globular clusters

First globular cluster discovered outside the Milky Way: M54 on Sagittarius Dwarf Elliptical Galaxy (Credit: ESA/Hubble & NASA)

First globular cluster discovered outside the Milky Way: M54 on Sagittarius Dwarf Elliptical Galaxy (Credit: ESA/Hubble & NASA)

It is well know that globular clusters (GCs) are among the oldest objects in the Universe. With typical masses between 104 - 106 M, they are easily observable in external galaxies. They are fossil records and provide powerful diagnostics in a wide range of astrophysical processes such as the nucleosynthetic processes governing chemical evolution or the star formation and assembly histories of galaxies. In particular, GCs provide important constraints on galaxy formation that are complementary to in situ studies of galaxies at medium to high redshift.

A good characterization of GC subpopulations in terms of ages and metallicities in all kind of galaxies is essential to have robust statistics and put constraints on the complex process of GC and galaxy formation. Previous detailed studies have been limited to spectroscopic works on 8 - 10 m class telescopes, but these studies are scarce and time-consuming. As a low resolution IFU, J-PLUS will constitute a revolution in this topic by providing a massive census of extragalactic GCs for thousands of nearby galaxies. The multi-filter approach will allow not only to detect GC candidates but also to characterize their stellar populations.

Searching for Globular Clusters in nearby galaxies.

Searching for Globular Clusters in nearby galaxies. (Credit: NASA, ESA and Eric Peng (Peking University, China) )

The globular cluster luminosity function (GCLF) peaks at Mv=-7.5, which translates in g=24 at Virgo Cluster distance (17 Mpc). On the other hand, J-PLUS will reach g= 23.2 (S/N=3). This will allow us to explore the bright half of the GCLF. Covering a total area of ~8500 deg2, J-PLUS will observe tens of thousands of GCs in nearby galaxies (< 20 Mpc).

The study of GCs with J-PLUS will provide an estimate of the GCs metallicity and age, allowing to split between metal rich and metal poor GCs, as well as to study the ages of these objects. In combination with the unbiased sample of host galaxy morphologies and luminosities that J-PLUS will provide, it will permit to study the correlations between the host galaxy and its GC system. Through this study we will be able to answer long standing questions such as: are there a correlation between the stellar mass of the host galaxy and the GC specific frequency (SN)? What is the cause of the slope of the color-magnitude relation? Is there a link between the red and blue GCs distributions and the bulge/halo of different host galaxy morphologies? The study of the extragalactic GCs in J-PLUS will infer new clues on the formation epoch as a function on the host galaxy type.