Overmassive Black Holes in Dwarf Galaxies Out to z ∼ 0.9 in the VIPERS Survey

Abstract

Supermassive black holes (SMBHs) are thought to originate from early universe seed black holes of mass M BH ∼ 102–105 M ⊙ and grown through cosmic time. Such seeds could be powering the active galactic nuclei (AGN) found in today’s dwarf galaxies. However, probing a connection between the early seeds and local SMBHs has not yet been observationally possible. Massive black holes hosted in dwarf galaxies at intermediate redshifts, on the other hand, may represent the evolved counterparts of the seeds formed at very early times. We present a sample of seven broad-line AGN in dwarf galaxies with a spectroscopic redshift ranging from z = 0.35 to z = 0.93. The sources are drawn from the VIPERS survey as having an Large Magellanic Cloud (LMC) like stellar mass (M ∗) derived from spectral energy distribution fitting, and they are all star-forming galaxies. Six of these sources are also X-ray AGN. The AGN are powered by SMBHs of >107 M ⊙, more massive than expected from the M BH–M ∗ scaling relation of AGN. Based on semianalytical simulations, we find that these objects are likely overmassive with respect to their hosts since early times (z > 4), independently of whether they formed as heavy (∼105 M ⊙) or light (∼102 M ⊙) seed black holes. In our simulations, these objects tend to grow faster than their host galaxies, contradicting models of synchronized growth. The host galaxies are found to possibly evolve into massive systems by z ∼ 0, indicating that local SMBHs in massive galaxies could originate in dwarf galaxies hosting seed black holes at higher z.

JWST CEERS and JADES Active Galaxies at z = 4–7 Violate the Local M •–M ⋆ Relation at >3σ: Implications for Low-mass Black Holes and Seeding Models

“…Interestingly, Bogdan et al (2023) reported the discovery of a gravitationally lensed quasar at z = 10.3, with an estimated black hole mass comparable to its stellar mass, and Natarajan et al (2023) suggested its origin as a heavy black hole seed. However, the detection of overmassive black holes is not new, as it was already suggested by sporadic observations at z ∼ 6 in the pre-JWST era (see, e.g., Wang et al 2010), and, recently, even more locally (see, e.g., Mezcua et al 2023, up to z = 0.9).…”

Identification and Characterization of a Large Sample of Distant Active Dwarf Galaxies in XMM-SERVS

“…An example of a similar bias can be seen in Figure 18 of Burke et al (2022), where their M BH values of variability-selected active dwarf galaxies are 2-3 dex above the M BH −M å scaling relation. Similarly, Mezcua et al (2023) also found a sample of distant active dwarf galaxies containing overmassive MBHs. It is The error of M BH is 0.55 dex, i.e., the scatter of the scaling relation in Reines & Volonteri (2015), compared to which the M å uncertainty is negligible.…”

Merger-driven Growth of Intermediate-mass Black Holes: Constraints from Hubble Space Telescope Imaging of Hyper-luminous X-Ray Sources

“…Indeed, the luminosity threshold of 10 41 erg s −1 imposes a lower black hole mass limit (per Eddington ratio), so HLXs may represent the massive end of the IMBH distribution. We note that the predicted lower black hole mass limits will be larger if the evolution of the overall sample is dominated by a mass scaling relation with a shallower slope at low black hole masses (e.g., Mezcua 2017;Pacucci et al 2018) or if some of the black holes evolved to be over massive when compared to the scaling relations (e.g., Mezcua et al 2023;Pacucci et al 2023).…”