Tracing the dynamical and structural complexity of spiral galaxy centres

arXiv (Cornell University)

Abstract

The formation of late-type galaxies has traditionally been described via two pathways: one producing pressure-supported classical bulges, the other rotationally supported pseudo-bulges. Early studies relied on photometric decompositions assuming an exponential disk extrapolated inwards. Recent high-resolution observations, however, reveal a far more complex landscape in disk galaxy centres. We investigated the morphology of central stellar components in intermediate-to-massive spiral galaxies, focusing on disentangling cold, warm, and hot orbital contributions, critically reassessing the standard approach of extrapolating the exponential disk profile inwards. We developed GLANCE (Galactic archaeoLogy via chronochemicAl and dyNamiCal modElling), a tool for photometric, chronochemical, and dynamical galaxy analysis, applied to 8 high-resolution MUSE galaxies to derive stellar population properties and decompose orbits into cold, warm, hot, and counter-rotating (CR) components. We uncovered remarkable structural diversity in the dynamically cold central component: one galaxy displays an exponential profile throughout, while the majority exhibit either a pronounced central drop resembling a doughnut-shaped structure or a compact inner disk significantly steeper than the outer disk. Most galaxies hosting nuclear disks are classifiable as classical bulges - hot, old, red, high bulge-to-total ratio - contrasting with galaxies showing a central cold-component deficit. Beyond the bulge, cold plus warm orbit contributions remain below the total, indicating non-negligible hot or CR orbits with Sérsic indexes consistently above unity. These results highlight the composite nature of disk galaxy centres and the need for decomposition methods that avoid extrapolating the outer disk inwards, requiring large IFS samples across a broad mass range, complemented by simulations such as IllustrisTNG50.

Authors 10

1. Iris Breda

   University of Vienna

   Affiliation as printed

   Dep. of Astrophysics , University of Vienna , Türkenschanzstraße 17 , 1180 , Vienna , Austria

2. Glenn van de Ven

   University of Vienna

   Affiliation as printed

   Dep. of Astrophysics , University of Vienna , Türkenschanzstraße 17 , 1180 , Vienna , Austria

3. Sabine Thater

   University of Vienna

   Affiliation as printed

   Dep. of Astrophysics , University of Vienna , Türkenschanzstraße 17 , 1180 , Vienna , Austria

4. J. Falcón-Barroso

   Universidad de La Laguna · Instituto de Astrofísica de Canarias

   Affiliation as printed

   Dep. de Astrofísica , Universidad de La Laguna , Av. del Astrofísico Francisco Sánchez s/n , E-38206 , La Laguna , Tenerife , Spain

   Instituto de Astrofísica de Canarias , Calle Vía Láctea s/n , E-38205 , La Laguna , Tenerife , Spain

5. Prashin Jethwa

   University of Vienna

   Affiliation as printed

   Dep. of Astrophysics , University of Vienna , Türkenschanzstraße 17 , 1180 , Vienna , Austria

6. Masato Onodera

   The Graduate University for Advanced Studies, SOKENDAI · National Astronomical Observatory of Japan

   Affiliation as printed

   Graduate Institute for Advanced Studies , SOKENDAI , 2-21-1 Osawa , Mitaka , Tokyo 181-8588 , Japan

   Subaru Telescope , National Astronomical Observatory of Japan , 650 N Aohoku Pl , Hilo , HI96720 , Japan

7. Joop Schaye Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300 RA Leiden , the Netherlands

8. J. Brinchmann

   Universidade do Porto

   Affiliation as printed

   Dep. de Física e Astronomia , Faculdade de Ciências , Rua do Campo Alegre , 4169-007 Porto , Portugal

9. B. Ziegler

   University of Vienna · Durham University

   Affiliation as printed

   Centre for Extragalactic Astronomy , Department of Physics , Durham University , South Road , Durham DH1 3LE , UK

   Dep. of Astrophysics , University of Vienna , Türkenschanzstraße 17 , 1180 , Vienna , Austria

10. Federica Mauro

    University of Vienna

    Affiliation as printed

    Dep. of Astrophysics , University of Vienna , Türkenschanzstraße 17 , 1180 , Vienna , Austria