Radio jet–ISM interaction and positive radio-mechanical feedback in Abell 1795

Abstract

We present XSHOOTER observations with previous ALMA, MUSE and HST observations to study the nature of radio-jet triggered star formation and the interaction of radio jets with the interstellar medium in the brightest cluster galaxy (BCG) in the Abell 1795 cluster. Using HST UV data we determined an ongoing star formation rate of 9.3 M⊙ yr−1. The star formation follows the global Kennicutt-Schmidt law, however, it has a low efficiency compared to circumnuclear starbursts in nearby galaxies with an average depletion time of ∼1 Gyr. The star formation and molecular gas are offset by ∼1 kpc indicating that stars have decoupled from the gas. We detected an arc of high linewidth in ionized gas where electron densities are elevated by a factor of ∼4 suggesting a shock front driven by radio jets or peculiar motion of the BCG. An analysis of nebular emission line flux ratios suggests that the gas is predominantly ionized by star formation with a small contribution from shocks. We also calculated the velocity structure function (VSF) of the ionized and molecular gases using velocity maps to characterize turbulent motion in the gas. The ionized gas VSF suggests that the radio jets are driving supersonic turbulence in the gas. Thus radio jets can not only heat the atmosphere on large scales and may quench star formation on longer timescales while triggering star formation in positive feedback on short timescales of a few million years.

“Beads-on-a-string” Star Formation Tied to One of the Most Powerful Active Galactic Nucleus Outbursts Observed in a Cool-core Galaxy Cluster

“…Although the YSCs are separated from the molecular gas by ∼1-3 kpc, the similarity in the morphologies of the beaded star formation and the edges of the cold molecular gas suggests that the gas played a critical role in fueling the star formation. Similar offsets between star formation and cold gas have been found in the Perseus Cluster (NGC 1275), A1795, and simulations of AGN feedback (Canning et al 2014;Li et al 2015;Tamhane et al 2023). Below, we discuss the potential contributions of a cooling wake, ram pressure, and tidal interactions to the observed separation between the star formation, the BCGs, and the molecular gas.…”

“…Observations have revealed massive flows of atomic and molecular gas that appear entrained around the rims of jetblown cavities (e.g., Russell et al 2017;Tremblay et al 2018), or closely trailing behind them (e.g., Russell et al 2016;Vantyghem et al 2016), suggesting incredibly efficient coupling between the radio jets, the ICM, and the cooled multiphase gas. Given that the cooling hot plasma, warm ionized gas, cold molecular gas, and radio emission from the AGN should each retain imprints of their shared journey within the ICM, multiwavelength observational studies of cool-core clusters have become standard practice for studying the interplay between nebular emission, star formation, and AGN activity, commonly referred to as the "AGN feedback cycle" (e.g., McNamara et al 2014;O'Dea et al 2008;McDonald et al 2015;Russell et al 2017;Tremblay et al 2018;Pasini et al 2019;Ciocan et al 2021;Calzadilla et al 2022;Masterson et al 2023;Tamhane et al 2023).…”

AGN Feedback Signatures in UV Emission

“…The SFR ranged from 0.1 to 1 M ⊙ yr −1 , which could contribute to 5-30% of the total SFR in the galaxy. Recent observations, as well as simulations, suggest that both negative and positive feedback can work together and can be observed in some galaxies [44,45].…”

“…UV emission arises from massive O-, B-, and A-type stars and hence traces star-formation within the age range of 10 6 to 10 8 yr [48,49]. Recently, Tamhane et al [45] explored jet-ISM interaction in the central elliptical galaxy of the Abell 1975 cluster using multi-frequency observations. They concluded that radio jets that heat the gas on a large scale and over a large timescale can also trigger star formation through positive feedback over a shorter time scale.…”

Optical- and UV-continuum Morphologies of Compact Radio Source Hosts

“…Observational evidence of this effect on sub-galactic scale has been limited regarding both quasar-mode (Cresci et al 2015a(Cresci et al , 2015bCarniani et al 2016) and radio-mode (Salomé et al 2015;Santoro et al 2015;Zovaro et al 2020) processes, but has been growing with the advent of integral field studies of active galaxies at higher redshifts, where strong impacts of feedback are expected. The emerging picture from recent works suggests that AGN jets and outflows might be playing a double role-providing negative feedback as a fundamental large-scale mechanism that shapes the growth of an SMBH and the host, with the starburst-enhancing positive feedback acting locally and/or in episodes that occur at short timescales of a few megayears (e.g., Cresci et al 2015b;Mukherjee et al 2018;Tamhane et al 2023). However, suppression of new star formation, while inferred from thermal and kinematic properties of the ISM gas, is not straightforward to observe without comparative analysis with a control sample.…”