MARTA: A "little" black hole hidden in a clumpy, metal-poor galaxy at z~3.8
Abstract
JWST has extended the search for accreting black holes into the high-redshift, low-mass regime. We report a low-mass black hole candidate in MARTA 3887, a clumpy, metal-poor galaxy at z=3.7694, combining deep JWST/NIRSpec spectroscopy, HST and JWST imaging, and archival VLT/MUSE data. We detect a broad Hα component with LHα,b=2.35×1041 erg s−1 and FWHM =1270+260−250 km s−1, with no [O III] counterpart of comparable width. Under a broad-line-region interpretation, virial calibrations give log(MBH/M⊙)=6.52+0.18−0.23 and λEdd=0.07, or up to 0.38 for alternative calibrations. The host comprises at least three compact clumps, with log(M⋆/M⊙)=8.16+0.09−0.10. If stellar photoionization dominates the narrow lines, the gas is highly ionized and metal poor, with 12+log(O/H)=7.68±0.04 (≃0.10 Z⊙). The inferred MBH/M⋆=2.3% lies about 2 dex above the extrapolated local relation, suggesting that black-hole growth has outpaced the assembly of the observed host. If growth began only when the first 10% of the observed stellar mass had formed (t10=92 Myr ago), a 102 M⊙ seed would require a lifetime-mean Eddington ratio ≃5.7; earlier growth or a more massive, e.g. direct-collapse, seed would allow sub-Eddington mean accretion. MUSE reveals extended Lyα emission (≃6.5-6.9 proper kpc), offset by +64+10−8 km s−1 from systemic, with a provisional escape fraction of ≃0.44. Together with a Mg II doublet ratio close to the optically thin limit and a high [O III]/[O II] ratio, this makes MARTA 3887 a laboratory to study black-hole growth, stellar assembly, and ionizing-photon escape jointly.
Related
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BibTeX
@misc{curti2026marta,
title = {{MARTA: A "little" black hole hidden in a clumpy, metal-poor galaxy at z~3.8}},
author = {Mirko Curti and Bianca Moreschini and Elisa Cataldi and Francesco Belfiore and Ivan Delvecchio and Alessandro Marconi and Filippo Mannucci and Elena Bertola and Giovanni Cresci and Anna Feltre and Roberto Maiolino and Francesca Pozzi and Letizia Scaloni and Alberto Traina and Caterina Bracci and Stefano Carniani and Carlotta Gruppioni and Giacomo Venturi and Magda Arnaboldi and Meriem Behiri and Michele Ginolfi and Mahsa Kohandel and Livia Vallini},
howpublished = {arXiv},
year = {2026},
month = nov,
doi = {10.48550/arxiv.2611.00199},
eprint = {2611.00199},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2611.00199},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - MARTA: A "little" black hole hidden in a clumpy, metal-poor galaxy at z~3.8
AU - Mirko Curti
AU - Bianca Moreschini
AU - Elisa Cataldi
AU - Francesco Belfiore
AU - Ivan Delvecchio
AU - Alessandro Marconi
AU - Filippo Mannucci
AU - Elena Bertola
AU - Giovanni Cresci
AU - Anna Feltre
AU - Roberto Maiolino
AU - Francesca Pozzi
AU - Letizia Scaloni
AU - Alberto Traina
AU - Caterina Bracci
AU - Stefano Carniani
AU - Carlotta Gruppioni
AU - Giacomo Venturi
AU - Magda Arnaboldi
AU - Meriem Behiri
AU - Michele Ginolfi
AU - Mahsa Kohandel
AU - Livia Vallini
PY - 2026
DA - 2026/11/01
PB - arXiv
DO - 10.48550/arxiv.2611.00199
UR - https://arxiv.org/abs/2611.00199
AB - JWST has extended the search for accreting black holes into the high-redshift, low-mass regime. We report a low-mass black hole candidate in MARTA 3887, a clumpy, metal-poor galaxy at z=3.7694, combining deep JWST/NIRSpec spectroscopy, HST and JWST imaging, and archival VLT/MUSE data. We detect a broad Hα component with L_Hα,b=2.35×10^41 erg s^−1 and FWHM =1270^+260_−250 km s^−1, with no [O III] counterpart of comparable width. Under a broad-line-region interpretation, virial calibrations give log(M_BH/M_⊙)=6.52^+0.18_−0.23 and λ_Edd=0.07, or up to 0.38 for alternative calibrations. The host comprises at least three compact clumps, with log(M_⋆/M_⊙)=8.16^+0.09_−0.10. If stellar photoionization dominates the narrow lines, the gas is highly ionized and metal poor, with 12+log(O/H)=7.68±0.04 (≃0.10 Z_⊙). The inferred M_BH/M_⋆=2.3% lies about 2 dex above the extrapolated local relation, suggesting that black-hole growth has outpaced the assembly of the observed host. If growth began only when the first 10% of the observed stellar mass had formed (t_10=92 Myr ago), a 10^2 M_⊙ seed would require a lifetime-mean Eddington ratio ≃5.7; earlier growth or a more massive, e.g. direct-collapse, seed would allow sub-Eddington mean accretion. MUSE reveals extended Lyα emission (≃6.5-6.9 proper kpc), offset by +64^+10_−8 km s^−1 from systemic, with a provisional escape fraction of ≃0.44. Together with a Mg II doublet ratio close to the optically thin limit and a high [O III]/[O II] ratio, this makes MARTA 3887 a laboratory to study black-hole growth, stellar assembly, and ionizing-photon escape jointly.
ER -