Project F

Measuring IMF in high density stellar systems, i.e. relic galaxies and globular clusters

Magda Arnaboldi, Lodo Coccato, Chiara Spiniello (Oxford) & Carlos Barbosa (Univ. S. Paulo)

(email advisors)

Join us on the investigation of the stellar initial mass function (IMF) in galaxies. This is the equivalent of the DNA of a living cell, it provides a quantitative mapping of the way stars are formed, how many there are in each mass bin. We want to study how this basic ¨code¨ is set in relic galaxies and in globular clusters. These are similar high density stellar systems and their differences i.e. total mass, may be the key to unmask the physics which encodes the DNA of stellar systems.

The stellar initial mass function (IMF) seems to be variable and not universal, as argued in the literature in the last three decades. Several relations among the low-mass end of the IMF slope and other stellar population, photometrical or kinematical parameters of massive early-type galaxies (ETGs) were proposed, but a consolidated agreement on a factual cause of the observed variations has not been reached yet.

With this project we want to measure the IMF in relics galaxies, i.e. red nuggets (*) from the INvestigating Stellar Population In RElics (INSPIRE) Project, that aims at spectroscopically confirming and fully characterizing a large number of relics at 0.1<z<0.5, and the globular clusters in the bright central clusters (GCs) galaxy NGC 3311 from MUSE deep cubes. Why relics and GCs? Because they are both old and ¨passive¨ stellar systems and characterizing their mass functions will unmask the physics which determines how many stars of a given mass and luminosity are formed in a burst of star formation.

Methods: We will determine at the same time the IMF slope the other stellar population parameters (age, total metallicity, [alpha/Fe])  from full spectral fitting of optical and near-infrared high signal-to-noise spectra for GCs and relics, using the state-of-the art of single stellar population models.  We will compare the IMF slope against other stellar parameters, with the goal of assessing their relations/dependencies.

Possible Results/Outcome: We have been pioneers in demonstrating the non-universality of the low-mass end of the IMF. Moreover, recently, our group has invalidated the previously claimed direct correlation between the IMF slope and the local stellar velocity dispersion.  With the inclusion of GCs we would like to probe this relation to much lower masses, lower velocity dispersions and lower metallicity values. By comparing the IMF GCs results with the relics we hope to establish whether there is a mass, or better a luminosity threshold at which the IMF changes to bottom heavy sets in. 

(*)"red-nuggets" are formed through a very short and intense star formation episode at high redshifts (z > 2), when the universe was denser and richer in gas, and that then ended up being the central cores of today giant ellipticals.


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