Radio morphology–accretion mode link in Fanaroff–Riley type II low-excitation radio galaxies

Abstract

Fanaroff-Riley II low-excitation radio galaxies (FRII-LERGs) are characterized by weak nuclear excitation on pc-scales and by properties typical of powerful FRIIs (defined as high-excitation, hereafter HERGs/BLRGs) on kp-scales. Since a link between the accretion properties and the power of the produced jets is expected both from theory and observations, their nature is still debated. In this work we investigate the X-ray properties of a complete sample of 19 FRII-LERGs belonging to the 3CR catalog, exploiting Chandra and XMM-Newton archival data. We also analyze 32 FRII-HERGs/BLRGs with Chandra data as a control sample. We compared FRII-LERG and FRII-HERG/BLRG X-ray properties and optical data available in literature to obtain a wide outlook of their behavior. The low accretion rate estimates for FRII-LERGs, from both X-ray and optical bands, allow us to firmly reject the hypothesis for that they are the highly obscured counterpart of powerful FRII-HERGs/BLRGs. Therefore, at least two hypothesis can be invoked to explain the FRII-LERGs nature: (i) they are evolving from classical FRIIs because of the depletion of accreting cold gas in the nuclear region, while the extended radio emission is the heritage of a past efficiently accreting activity; (ii) they are an intrinsically distinct class of objects with respect to classical FRIs/FRIIs. Surprisingly, in this direction a correlation between accretion rates and environmental richness is found in our sample. The richer the environment, the more inefficient is the accretion. In this framework, the FRII-LERGs are intermediate between FRIs and FRII-HERGs/BLRGs both in terms of accretion rate and environment.

The MURALES survey

“…This morphology is reminiscent of what is often observed in type 2 Seyfert galaxies (e.g., Tadhunter & Tsvetanov 1989), and it is indicative of circumnuclear selective obscuration, as postulated by the unified model (UM) of AGN (Antonucci 1993). The lack of broad lines in Coma A (Buttiglione et al 2010) and the high column density derived from the nuclear X-ray spectrum (Worrall et al 2016;Macconi et al 2020) are in line with the idea that our view toward its nucleus intercepts regions of high absorption. However, the angular size of the bicone is smaller (∼ 18 • ± 5 • ) than predicted by the UM estimate: based the relative number of 3CR RGs with z < 0.3 with without broad lines in their optical spectra.…”

Jet collimation in NGC 315 and other nearby AGN

“…This is the average value found byMacconi et al (2020) in highexcitation radio galaxies. The median is L X /L Edd = 6.7e−4.A67, page 8 of 20…”

“…Since this optical classification is not available in the literature for all the sources in our sample, in order to adopt a uniform criterion we con-sider instead the X-ray luminosity L X as a proxy of the accretion activity. Following the work of Macconi et al (2020), who have investigated the X-ray properties of a large sample of highexcitation (HERG) and low-excitation (LERG) radio galaxies, we assume a ratio L X /L Edd = 1.1e−3 4 as the limit above (below) which the source is classified as HEG (LEG). This method is applied to all the radio galaxies and to the NLSy1; the BL Lacs are instead assumed to be LEG since they form the beamed parent population of LERG.…”

The eMERLIN and EVN View of FR 0 Radio Galaxies

“…Since an affinity between the nuclear properties of FR 0s and FR Is has been clearly assessed [64,72,73] and low-power RGs have been found to be the scaled-down version of FR Is (e.g., [28,43,53,99,100]), it is plausible to search for a general connection between the jet and accretion strength of a population of low-and high-power RGs with comparable properties: hosted in massive ETGs and characterized by a LINER spectrum (we excluded the FR II LINERs, because the nature of their central engine and its relation to the FR I LINERs is still not fully understood [11,101,102]). With the purpose of building such a sample of local (z < 0.05) LINER-type RL AGNs, we collected VLBI, VLBA, EVN, and eMERLIN data at 1.4 GHz and 5 GHz available from the literature ([O III] line emission from [44,103]); see Figure 5 for: LINERs from the Palomar sample of nearby galaxies [104] (green circles, from [28,[105][106][107]), which appear as unresolved cores or core-jet structures at JVLA scales in the radio band and were classified as RL by [43]; 3C/FR Is (all LINERs, open upwards triangles, from [107][108][109][110]); and core galaxies (open downward triangles, from [28]), which have LINER spectra and are known to be miniature FR Is [100].…”