The environment of AGN dwarf galaxies at z ∼ 0.7 from the VIPERS survey

Abstract

Dwarf galaxies are ideal laboratories to study the relationship between the environment and AGN activity. However, the type of environments in which dwarf galaxies hosting AGN reside is still unclear and limited to low-redshift studies ($\rm {z<0.5}$). We use the VIMOS Public Extragalactic Redshift Survey (VIPERS) to investigate, for the first time, their environments at $0.5<\rm {z}<0.9$. We select a sample of 12,942 low-mass ($\rm {log}(M_\mathrm{*}/M_{\odot })\le 10$) galaxies and use the emission-line diagnostic diagram to identify AGN. We characterise their local environments as the galaxy density contrast, δ, derived from the fifth nearest neighbour method. Our work demonstrates that AGN and non-AGN dwarf galaxies reside in similar environments at intermediate redshift suggesting that the environment is not an important factor in triggering AGN activity already since $\rm {z=0.9}$. Dwarf galaxies show a strong preference for low-density environments, independently of whether they host an AGN or not. Their properties do not change when moving to denser environments, suggesting that dwarf galaxies are not gas-enriched due to environmental effects. Moreover, AGN presence does not alter host properties supporting the scenario that AGN feedback does not impact the star formation of the host. Lastly, AGN are found to host over-massive black holes. This is the first study of dwarf galaxies hosting AGN at $\rm {z>0.5}$. The next generation of deep surveys will reveal whether or not such lack of environmental trends is common also for faint higher-redshift dwarf galaxy populations.

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

“…We show the corresponding histograms of the first, third, and tenth closest projected separations in Figure 10 as examples, and the histograms of our active dwarf galaxies do not visually show large differences from those of the comparison sample. Indeed, we found that our sources and the comparison samples do not show statistically significant differences for any of the separations, as also found in Davis et al (2022) and Siudek et al (2023). Therefore, environmental effects are not significantly responsible for the presence of AGNs in dwarf galaxies.…”

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

“…A larger sample would be needed to confirm such a tendency. We note that a statistical study of the environment of AGN dwarf galaxies out to z ∼ 0.9 was recently performed by Siudek et al (2023), finding that dwarf galaxies prefer lowdensity environments independently of whether they host an AGN or not. This is in agreement with the absence of a significant dependence between AGN activity and environment found for dwarf galaxies at lower redshifts (e.g., Bradford et al 2018;Kristensen et al 2020;Manzano-King & Canalizo 2020;Davis et al 2022).…”

“…Such seed black holes should be found in local dwarf galaxies if they have not grown much through mergers and accretion (Mezcua 2019), where they can be detected as AGN. In the past years several efforts have been made to detect such AGN dwarf galaxies out to z ∼ 1 (Mezcua et al 2018a(Mezcua et al , 2019Halevi et al 2019;Siudek et al 2023); however, the scarce number of high-z sources and for which a black hole mass estimate is available has prevented making a direct connection between them and the early universe seed black holes. In this Letter we have reported the finding of a sample of seven AGN dwarf galaxies out to z ∼ 0.9 and with black hole masses >10 7 M e derived from the width of broad emission lines.…”

“…Four of such sources have confirmed spectroscopic redshifts, one at z = 1.18 and another at z = 1.82 (Mezcua et al 2019), which constitute the redshift record-holders for an AGN in a dwarf galaxy. Siudek et al (2023) have recently identified a sample of 4315 AGN dwarf galaxies at 0.5 < z < 0.9 using the VIMOS Public Extragalactic Redshift Survey (VIPERS), carried out with the VIMOS spectrograph on the ∼8 m Very Large Telescope (Scodeggio et al 2018). Using correlations based on the luminosity of narrow [O III] and Hβ emission lines (i.e., Baron & Ménard 2019), the authors report a median black hole mass for their sample of log M BH = 8.2 M e .…”

Overmassive Black Holes at Cosmic Noon: Linking the Local and the High-redshift Universe

“…Recently, Siudek et al (2023) identified a sample of 4315 AGN in dwarf galaxies at 0.5 <z < 0.9, the largest of its kind. The average BH mass of this sample is log M BH = 8.2 M e , derived from correlations between narrow emission lines (Baron & Ménard 2019).…”