Fuelling, evolution, and diversity of active galactic nuclei in dwarf galaxies: Insights from star formation and black hole scaling relations

¹ Instituto de Fisica de Cantabria (CSIC-Universidad de Cantabria), Avenida de los Castros, 39005 Santander, Spain
² Instituto de Astrofísica de Canarias, Vía Láctea, 38205 La Laguna, Tenerife, Spain
³ Instituto de Astrofísica de Canarias (IAC); Departamento de Astrofísica, Universidad de La Laguna (ULL), 38200 La Laguna, Tenerife, Spain

^⋆ Corresponding author: gmountrichas@gmail.com

Received: 28 May 2025
Accepted: 20 August 2025

Abstract

We investigated the star formation activity and black hole scaling relations in a sample of 1 451 active galactic nuclei (AGNs) hosted by dwarf galaxies (log(M_⋆/M_⊙) < 10) at 0.5 < z < 0.9, drawn from the VIPERS survey. The sample comprises Seyferts and low-ionization nuclear emission-line regions (LINERs) identified through emission-line diagnostics, as well as IR-selected AGNs based on WISE mid-IR colours. Using the normalized star formation rate (SFR_norm), defined as the ratio of the SFR of a galaxy hosting an AGN to the median SFR of star-forming galaxies of similar stellar masses and redshifts, we compared AGN hosts to a control sample of non-AGN star-forming galaxies. We examined how SFR_norm varies with AGN power (L[OIII]), black hole mass (M_BH), local environment, and stellar population age. We also analysed the M_BH–M_⋆ relation and the evolution of the M_BH/M_⋆ ratio, incorporating comparisons to X-ray AGNs and high-redshift quasars (z > 4). We note that black hole masses have been estimated from narrow-line diagnostics, which introduce significant scatter and can carry substantial uncertainties for individual sources, though they remain useful for identifying statistical trends. Our key findings are: (i) All AGN populations show suppressed star formation at low AGN luminosities, with SFR_norm rising above unity at different luminosity thresholds depending on AGN type. (ii) LINERs show flat SFR_norm trends with M_BH, remaining broadly consistent with unity. Seyferts display a mild increase with M_BH, while IR AGNs show a more pronounced positive trend. (iii) LINERs have older stellar populations than Seyferts. (iv) At fixed stellar mass, Seyferts host more massive black holes than LINERs, with IR AGNs falling in between. (v) The M_BH/M_⋆ ratio is elevated relative to local scaling relations and remains approximately constant with redshift over 0.5 < z < 0.9, in agreement with high-z AGN measurements. (vi) The ratio decreases with stellar mass up to log(M_⋆/M_⊙)∼11, beyond which it flattens towards values consistent with those of local, inactive galaxies; this trend is clearest for Seyferts and IR AGNs, while LINERs show no clear dependence. These results suggest that AGNs in dwarf galaxies follow diverse evolutionary pathways, shaped by gas availability, feedback, and selection effects.