Dynamical structure of small bulges reveals their early formation in ΛCDM paradigm

Abstract

The Λ cold dark matter (ΛCDM) paradigm of galaxy formation predicts that dense spheroidal stellar structures invariably grow at early cosmic time. These primordial spheroids evolve toward a virialized dynamical status as they finally become today's elliptical galaxies and large bulges at the center of disk galaxies. However, observations reveal that small bulges in spiral galaxies are common in the nearby universe. The prevailing belief that all small bulges form at later times from internal processes occurring in the disk represents a challenge for the ΛCDM scenario. Notably, the coevolution of bulges and central supermassive black holes (SMBHs) at early phases of galaxy evolution is also at stake. However, observations have so far not provided conclusive evidence against their possible early origin. Here, we report new observations of small bulges showing that they follow the mass-velocity dispersion relation expected for virialized systems. Contrary to previous claims, small bulges bridge the gap between massive ellipticals and globular clusters. This dynamical picture supports a scenario where systems over seven orders of magnitude in stellar mass form at early cosmic time. These results alleviate the tension between ΛCDM simulations and observations at galactic scales. We hypothesize that these small bulges are actually the low-mass descendants of compact objects observed at high redshift, also known as red nuggets, which are consistently produced in cosmological ΛCDM simulations. Therefore, this also suggests that the established coevolution of SMBHs and large bulges naturally extends to spheroids in the low-mass regime.

7 pages, 1 figure, accepted for publication in ApJL

References in corpus (13)

• Formation of Massive Galaxies at High Redshift: Cold Streams, Clumpy Disks and Compact Spheroids
• Compaction and Quenching of High-z Galaxies in Cosmological Simulations: Blue and Red Nuggets
• The AIMSS Project I: Bridging the Star Cluster - Galaxy Divide
• The Nature of UCDs: Internal Dynamics from an Expanded Sample and Homogeneous Database
• Stellar kinematics across the Hubble sequence in the CALIFA survey: General properties and aperture corrections
• Two-dimensional multi-component photometric decomposition of CALIFA galaxies
• Secular- and merger-built bulges in barred galaxies
• The Next Generation Virgo Cluster Survey. XII. Stellar Populations and Kinematics of Compact, Low-Mass Early-Type Galaxies from Gemini GMOS-IFU Spectroscopy
• The Fornax3D project: Tracing the assembly history of the cluster from the kinematic and line-strength maps
• Observational Evidence for a Dark Side to NGC5128's Globular Cluster System
• Discovery of a new M32-like "Compact Elliptical" galaxy in the halo of the Abell 496 cD galaxy
• One Plane for All: Massive Star-Forming and Quiescent Galaxies Lie on the Same Mass Fundamental Plane at z~0 and z~0.7
• A New Channel of Bulge Formation via The Destruction of Short Bars

Cited by in corpus (2)

• The Carnegie-Irvine Galaxy Survey. X. Bulges in Stellar Mass-based Scaling Relations
• From naked spheroids to disky galaxies: how do massive disk galaxies shape their morphology?