Jet-induced star formation in 3C 285 and Minkowski’s Object

Abstract

How efficiently star formation proceeds in galaxies is still an open question. Recent studies suggest that active galactic nucleus (AGN) can regulate the gas accretion and thus slow down star formation (negative feedback). However, evidence of AGN positive feedback has also been observed in a few radio galaxies (e.g. Centaurus A, Minkowski's Object, 3C 285, and the higher redshift 4C 41.17). Here we present CO observations of 3C 285 and Minkowski's Object, which are examples of jet-induced star formation. A spot (named 3C 285/09.6 in the present paper) aligned with the 3C 285 radio jet at a projected distance of ∼70 kpc from the galaxy centre shows star formation that is detected in optical emission. Minkowski's Object is located along the jet of NGC 541 and also shows star formation. Knowing the distribution of molecular gas along the jets is a way to study the physical processes at play in the AGN interaction with the intergalactic medium. We observed CO lines in 3C 285, NGC 541, 3C 285/09.6, and Minkowski's Object with the IRAM 30 m telescope. In the central galaxies, the spectra present a double-horn profile, typical of a rotation pattern, from which we are able to estimate the molecular gas density profile of the galaxy. The molecular gas appears to be in a compact reservoir, which could be evidence of an early phase of the gas accretion after a recent merger event in 3C 285. No kinematic signature of a molecular outflow is detected by the 30 m telescope. Interestingly, 3C 285/09.6 and Minkowski's Object are not detected in CO. The cold gas mass upper limits are consistent with a star formation induced by the compression of dense ambient material by the jet. The depletion time scales in 3C 285/09.6 and Minkowski's Object are of the order of and even shorter than what is found in 3C 285, NGC 541, and local spiral galaxies (10 9 yr). The upper limit of the molecular gas surface density in 3C 285/09.6 at least follows a Schmidt-Kennicutt law if the emitting region is very compact, as suggested by the Hα emission, while Minkowski's Object is found to have a much higher star formation efficiency lower limit (very short depletion time). Higher sensitivity is necessary to detect CO in the star-forming spots, and higher spatial resolution is required to map the emission in these jet-induced star-forming regions.

Further evidence for a quasar-driven jet impacting its neighbour galaxy: The saga of HE0450-2958 continues

“…It should be mentioned, however, that the probability of two extremely short-lived and rare events such as (iii) and (iv) happening simultaneously in the same system without any causal connection seems small. Intriguingly, the SF efficiency we have re-estimated based on our new JLVA continuum data is also comparable to that found for Minkowski's Object (depletion time <20 Myr; Salomé, Salomé & Combes 2015).…”

Numerical Simulations of a Jet–Cloud Collision and Starburst: Application to Minkowski’s Object

“…(S.F.R. = 0.47M yr −1 or L Hα = 5.9 × 10 40 erg s −1 ; Salomé et al 2015). In fact, we overshoot the observed S.F.R.…”

A free-form mass model of the Hubble Frontier Fields cluster AS1063 (RXC J2248.7−4431) with over one hundred constraints

“…Similar examples are known of such linear alignment of galaxies spanning nearly 20 kpc at redshift of z=3 (Rauch et al 2013). Also in the local universe there are examples of star forming regions that are being triggered by jets and be found as far as 20 kpc (van Breugel et al 1985) or even 70 kpc (Salomé, Salomé & Combes 2015) from the AGN. None of the central knots of system 14 (in the 3 multiple images) show any excess X-rays in Chandra data despite being magnified by factors between 2.5 and 6.5 implying in this scenario that the AGN is weak or in a quiescent state.…”