Measuring galaxy sizes is essential for understanding how they were formed and evolved across time. However, traditional methods based on l ight concentration or isophotal densities often lack a clear physical meaning. A recent study from Trujillo+20 explores a more physically motivated definition: the radius R 1, where the stellar surface density falls to 1 solar masses per parsec square —roughly the threshold for gas to form stars in galaxies like the Milky Way. In this work, Arjona-Gálvez+25 uses over 1,000 galaxies from several state-of-the-art cosmological simulations (AURIGA, HESTIA

We present, for the first time, model spectra of single-age, single-metallicity stellar populations computed with the E-MILES evolutionary synthesis code incorporating an environment-dependent, variable galaxy-wide initial mass function (gwIMF). This gwIMF, calculated using the GalIMF code, is rooted in the integrated galactic initial mass function (IGIMF) theory, which predicts IMF variations as a function of the star formation rate and the metallicity. By coupling these two codes, we generated a comprehensive library of single-burst stellar population spectra uniquely sensitive to gwIMF

In the standard cosmological model (𝜦CDM), galaxies are merely the visible "tips of the icebergs," residing within massive, invisible cocoons of dark matter known as haloes. While these haloes dictate the evolution and motion of galaxies, measuring their true size and mass has long been one of the most challenging tasks in astrophysics. A new study published in Astronomy & Astrophysics by Claudio Dalla Vecchia and Ignacio Trujillo from the Instituto de Astrofísica de Canarias (IAC) proposes a breakthrough: a physically motivated definition of a galaxy’s edge that acts as a precision "ruler"