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Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Mapping formation pathways of nuclear star clusters across galaxies

Francesca Pinna, Isabel Pérez, Anna Ferré-Mateu, Begoña García Lorenzo, Alessandra Mastrobuono Battisti, Abbas Askar, Michael Beasley, Bahar Bidaran, Ana L. Chies-Santos, Sébastien Comerón, Kristen C. Dage, Adriana de Lorenzo-Cáceres, Katja Fahrion, Jesús Falcón Barroso, Anja Feldmeier-Krause, Emma Fernández Alvar, Nils Hoyer, Rubén García Benito, Rosa M. Gonzalez Delgado, Ignacio Martín Navarro, Cristina Ramos Almeida, Patricia Sánchez Blázquez, Rubén Sánchez Janssen, Alexandre Vazdekis

TL;DR

This paper argues that the majority of nuclear star clusters (NSCs) reside in the Northern sky, necessitating a 30-m-class telescope in the North to perform a comprehensive, spatially resolved survey of NSCs beyond the local volume. It outlines a program to map parsec-scale kinematics and stellar populations for hundreds of NSCs across a broad range of host galaxies, enabling discrimination between in situ formation and cluster inspiral, and tying NSC growth to galaxy evolution. The work emphasizes detecting intermediate-mass black holes (IMBHs) via dynamical measurements within the black hole spheres of influence to constrain the low-mass end of MBH–host scaling relations and the MBH occupation fraction. Achieving these goals requires milliarcsecond resolution with adaptive optics, high PSF stability, and spectral resolution above 8000, underscoring that a 30–40 m Northern telescope is the essential capability for advancing NSC physics and their coevolution with host galaxies.

Abstract

Nuclear star clusters (NSCs) are dense, compact stellar systems only a few parsecs across, located at galaxy centers. Their small sizes make them difficult to resolve spatially. NSCs often coexist with massive black holes, and both trace the dynamical state and evolution of their host galaxies. Dense stellar environments such as NSCs are also ideal sites for forming intermediate-mass black holes (IMBHs). To date, spatially resolved NSC properties, crucial for reconstructing dynamical and star-formation histories, have only been obtained for galaxies within 5 Mpc, using the highest-resolution instruments on the current class of very large telescopes. This severely limits spectroscopic studies, and a systematic, unbiased survey has never been accomplished. Because the vast majority of known NSCs are located in the Northern Hemisphere, only a 30-m-class telescope in the North can provide the statistical power needed to study their physical properties and measure the mass of coexisting central black holes. We propose leveraging the capabilities of a 30-m-class Northern telescope to obtain the first comprehensive, spatially resolved survey of NSCs, finally allowing us to unveil their formation pathways and their yet unknown connection with central massive black holes.

Why the Northern Hemisphere Needs a 30-40 m Telescope and the Science at Stake: Mapping formation pathways of nuclear star clusters across galaxies

TL;DR

This paper argues that the majority of nuclear star clusters (NSCs) reside in the Northern sky, necessitating a 30-m-class telescope in the North to perform a comprehensive, spatially resolved survey of NSCs beyond the local volume. It outlines a program to map parsec-scale kinematics and stellar populations for hundreds of NSCs across a broad range of host galaxies, enabling discrimination between in situ formation and cluster inspiral, and tying NSC growth to galaxy evolution. The work emphasizes detecting intermediate-mass black holes (IMBHs) via dynamical measurements within the black hole spheres of influence to constrain the low-mass end of MBH–host scaling relations and the MBH occupation fraction. Achieving these goals requires milliarcsecond resolution with adaptive optics, high PSF stability, and spectral resolution above 8000, underscoring that a 30–40 m Northern telescope is the essential capability for advancing NSC physics and their coevolution with host galaxies.

Abstract

Nuclear star clusters (NSCs) are dense, compact stellar systems only a few parsecs across, located at galaxy centers. Their small sizes make them difficult to resolve spatially. NSCs often coexist with massive black holes, and both trace the dynamical state and evolution of their host galaxies. Dense stellar environments such as NSCs are also ideal sites for forming intermediate-mass black holes (IMBHs). To date, spatially resolved NSC properties, crucial for reconstructing dynamical and star-formation histories, have only been obtained for galaxies within 5 Mpc, using the highest-resolution instruments on the current class of very large telescopes. This severely limits spectroscopic studies, and a systematic, unbiased survey has never been accomplished. Because the vast majority of known NSCs are located in the Northern Hemisphere, only a 30-m-class telescope in the North can provide the statistical power needed to study their physical properties and measure the mass of coexisting central black holes. We propose leveraging the capabilities of a 30-m-class Northern telescope to obtain the first comprehensive, spatially resolved survey of NSCs, finally allowing us to unveil their formation pathways and their yet unknown connection with central massive black holes.

Paper Structure

This paper contains 5 sections, 1 figure.

Table of Contents

  1. Introduction and Motivation
  2. The Science Challenge
  3. Detailed zoom-in analysis of NSC
  4. Revealing hidden IMBHs and expanding direct BH measurements
  5. Capability Requirements

Figures (1)

  • Figure 1: Left panel: Stellar kinematic maps of the NSC in M 32 adapted from Pinna2021. From left to right, from top to bottom, mean velocity $V$, velocity dispersion $\sigma$, skewness $h_3$ and kurtosis $h_4$. Isophotes are shown in black and the NSC effective-radius ellipse in dashed green. Right panel: BH mass versus stellar masses of NSCs and a variety of galaxy types, from the low mass ultracompact dwarfs, to the most massive systems, adapted from FerreMateu2021.