MMNRAS , 1–12 (0000) Preprint 23 February 2021 Compiled using MNRAS L A TEX style file v3.0
Possible Evidence of a Universal Radio / X-ray Correlation in anear-Complete Sample of Hard X-ray Selected Seyfert Galaxies
N. Chang , (cid:63) , F. G. Xie (cid:63) , X. Liu , (cid:63) , L. C. Ho , , A.-J. Dong , , Z. H. Han , X. Wang , Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Street, Urumqi 830011, Xinjiang, China School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing, 100049, China Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, 80 Nandan Road,Shanghai 200030, China Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, Nanjing 210008, China Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, China Department of Astronomy, School of Physics, Peking University, Beijing 100871, China Guizhou Provincial Key Laboratory of Radio Astronomy and Data Processing, Guizhou Normal University, Guiyang 550001, China Physics and Electronic Engineering Department, Xinjiang Normal University, Urumqi 830000, China
Accepted XXX. Received YYY; in original form ZZZ
ABSTRACT
Because the disc–jet coupling likely depends on various properties of sources probed, the sample control is always an importantbut challenging task. In this work, we re-analyzed the
INTEGRAL hard X-ray-selected sample of Seyfert galaxies. We onlyconsider sources that have measurements in black hole mass, and luminosities in radio and X-rays. Our final sample includes64 (out of the original 79) sources, consists of both bright AGNs and low-luminosity ones. The 2-10 keV X-ray Eddingtonratio L X / L Edd locates in the range between ∼ − . and ∼ − . . We first find that, because of the similarity in the L HX / L X distribution, the X-ray origin of radio-loud Seyferts may be the same to that of radio-quiet ones, where we attribute to the hotaccretion flow (or similarly, the corona). We then investigate the connections between luminosities in radio and X-rays. Sinceour sample su ff ers a selection bias of a black hole mass M BH dependence on L X / L Edd , we focus on the correlation slope ξ X between the radio (at 1.4 GHz) and X-ray luminosities in Eddington unit, i.e. ( L R / L Edd ) ∝ ( L X / L Edd ) ξ X . We classify the sourcesaccording to various properties, i.e. 1) Seyfert classification, 2) radio loudness, and 3) radio morphology. We find that, despitethese di ff erences in classification, all the sources in our sample are consistent with a universal correlation slope ξ X (note thatthe normalization may be di ff erent), with ξ X = . ± .
10. This is unexpected, considering various possible radio emitters inradio-quiet systems. For the jet (either relativistic and well collimated, or sub-relativistic and weakly collimated) interpretation,our result may suggest a common / universal but to be identified jet launching mechanism among all the Seyfert galaxies, whileproperties like black hole spin and magnetic field strength only play secondary roles. We further estimate the jet productione ffi ciency η jet of Seyfert galaxies, which is η jet ≈ . + . − . × − on average. We also find that η jet increases as the system goesfainter. Alternative scenarios for the radio emission in radio-quiet systems are also discussed. Key words: galaxies: active – galaxies: Seyfert – radio continuum: galaxies – accretion: accretion discs
Almost every galaxy contains a supermassive black hole (BH) at itscenter (Kormendy & Ho 2013). Among most of the cosmic time theBH remains quiet; only over a short period of 10 − yrs (e.g.,Kau ff mann & Haechnelt 2000; Martini & Weinberg 2001; Condonet al. 2013), the BH is fed with a su ffi cient amount of gas / materialand the system becomes active and luminous, i.e. enter a phase so-called the active galactic nucleus (AGN). It is now widely acceptedthat the AGN and its host galaxy are tightly connected, i.e. thehost galaxy provides the feed for the accretion, while the energyand momentum driven by the AGN will also impact the dynamics (cid:63) E-mail: [email protected] (NC), [email protected] (FGX),[email protected] (XL) of the gas (consequently, the star formation) within the galaxy (forreviews, see e.g., Fabian 2012; Kormendy & Ho 2013; Heckman &Best 2014).The structure of AGN is admittedly complex. Emission at di ff er-ent wavebands may originate from di ff erent physical components ordi ff erent spatial locations (see e.g., Ho 2008; Heckman & Best 2014for reviews), i.e. continuum radiation in radio, optical-ultraviolet(UV), and hard X-rays originates from, respectively, the relativisticjet, the cold accretion disc and the corona (or hot accretion flow incase of low-luminosity AGNs, here we use them interchangeably).The highly collimated jet, which propagates from sub-pc up to Mpcscales, may play a crucial role in the BH-host galaxy co-evolution(e.g., Croton et al. 2006; Heckman & Best 2014), although it remainsinclusive on its basic physics, e.g., its composition and the launch-ing and acceleration / deceleration mechanisms (see e.g., Harris & © a r X i v : . [ a s t r o - ph . H E ] F e b N. Chang et al.
Krawczynski 2006; Tchekhovskoy 2015; Davis & Tchekhovskoy2020 for summaries, and Parfrey, Philippov & Cerutti 2019; Chen &Zhang 2020 for recent progress). Statistically, as the systems becomefainter, the fraction of radio-loud AGNs increases (Ho 2008), whichagrees with observations in black hole binaries (Fender et al.2009). Observationally jets in AGNs are diverse in both power andmorphology (Padovani 2016; Panessa et al. 2019; Chiaraluce et al.2020). Depending on the radio-to-optical luminosity ratio, the AGNscan be separated into two main classes. The minorities are radio-loud(RL), where the jet is highly relativistic and well collimated (forreviews, see e.g., Harris & Krawczynski 2006; Blandford, Meier, &Readhead 2019; Hardcastle & Croston 2020). Based on their large-scale radio morphology, the RL AGNs can be further classified toFR I or II (Fanaro ff & Riley 1974). The rest majorities are radio-quiet (RQ), where the radio emission is compact, without clear well-collimated structure in high-resolution observations. The origin ofthe radio emission in RQ AGNs is still under debate, a significantfraction of the large-scale radio emission may originate from stellarprocesses, or from interactions between AGN wind and interstellarmedium (e.g., Condon 1992; Padovani et al. 2015; Panessa et al.2019; Chiaraluce et al. 2020). Even for the compact radio core (ofRQ systems) investigated in this work, the origin is still inclusive,either a weak jet adopted here, or nuclear activities related to starformation (e.g., Laor & Behar 2008; Bonchi et al. 2013; Baek etal. 2019; Smith et al. 2020). Under the jet interpretation, the jetvelocity is low (e.g., non-relativistic) and the collimation of jet ispoor. Despite these observational di ff erences, it is argued that jetamong these systems may be governed by the same physics (Chen& Zhang 2020).For the investigation of the connection of the jet and the accretionflow (more clearly, the hot accretion flow. See Yuan & Narayan2014 for a review) in AGNs and BH X-ray binaries (BHBs), atight linear relationship in logarithmic space among the BH mass M BH , and the radio (monochromatic, L R = ν L ν at e.g. 1.4 GHz)and X-ray (integrated, i.e. L X = (cid:82) L ν d ν in e.g. the 2–10 keV band)luminosities has been discovered (e.g., Merloni et al. 2003; Falckeet al. 2004; Panessa et al. 2007; Li, Wu & Wang 2008; G¨ultekinet al. 2009, 2019; Burlon et al. 2013; Liu et al. 2016; Inoue et al.2017; Qian et al. 2018). It is also called the ”fundamental plane” (FP)of BH activity. Motivated by accretion theory (see this suggestionin Xie & Yuan 2017), we consider the FP in a revised space, i.e.(log( L R / L Edd ) , log( L X / L Edd ) , log M BH ) and re-express it as,log( L R / L Edd ) = ξ X log( L X / L Edd ) + ξ M log M BH + const .. (1)Here L Edd = . × ( M BH / M (cid:12) ) erg s − is the Eddingtonluminosity. L R / L Edd and L X / L Edd define the Eddington ratios inradio and X-rays, respectively. We focus on the dependence onthe luminosity (i.e. slope parameter ξ X ), but not on the BH mass(i.e. ξ M ). It is found that a majority of sources follow a “standard” ξ X ≈ . ± . Note that there are at least two types of jets, one is continuous / steady andthe other is transient / episodic shown as discrete blobs, see e.g., Fender et al.(2009) for the classification of these two types of jets in BHBs. There mayalso exist a third type of jet (e.g., Xie, Yan & Wu 2020; Zdziarski et al. 2020and references therein). In the FP studies only the continuous / steady jets areconsidered. Observationally, individual sources may have a large scatterto the FP. Such scatter can be due to e ff ects of, among others, the(combination of) BH spin (Miller et al. 2009; ¨Unal & Loeb 2020),the strength of the magnetic field (Blandford & Znajek 1977; Sikoraet al. 2007; Li & Xie 2017), the Doppler beaming e ff ect (Li, Wu &Wang 2008), and the environment (van Velzen & Falcke 2013).Ever since its discovery, deviations to the standard FP in ξ X areobserved in di ff erent classes of systems, e.g., the radio-loud AGNs(e.g., Wang, Wu & Kong 2006; Panessa et al. 2007; Li, Wu &Wang 2008; de Gasperin et al. 2011), and the narrow-line Seyfert1 galaxies (e.g., Yao et al. 2018). Such deviation is also observed inBHBs (e.g., Coriat et al. 2011; Corbel et al. 2013; Xie, Yan & Wu2020). It is thus clear that ξ X depends on the sample compilation,and its value may hint on the accretion mode of individual (type) ofsources (e.g., Heinz & Sunyaev 2003; Xie & Yuan 2016; Xie, Yan& Wu 2020). Indeed, theoretically we can link the radio and X-rayluminosities to the dimensionless mass accretion rate ˙ m as (see e.g.,¨Unal & Loeb 2020) L R / L Edd ∝ ˙ m γ , and L X / L Edd ∝ ˙ m κ , (2)where γ ≈ . − . γ and κ characterize respectively, the radiative e ffi ciencies of jet and hotaccretion flow, i.e. L R / ( ˙ Mc ) ∝ ˙ m γ − and L X / ( ˙ Mc ) ∝ ˙ m κ − .Physically the observation of ξ X then measures the value of γ/κ ≈ (1 . − . /κ . If we additionally estimate the jet power as P jet ∝ L / (Willott et al. 1999; Cavagnolo et al. 2010; Su et al. 2017), then theFP also provides information on the connection between powers inaccretion and ejection, which can then used to probe the e ffi ciencyof converting accretion power into ejection (e.g., Inoue et al. 2017;Rusinek et al. 2020; Soares & Nemmen 2020; W´ojtowicz et al.2020).With the advantage of free from absorption, the > ∼
10 keV hardX-rays provide a more direct measurement of the accretion power(especially of the hot accretion flow, which tightly correlates withjet). An unbiased hard X-ray selected sample, e.g., the
INTE-GRAL / IBIS selected sample of Panessa et al. 2015 (hereafter P15;see Section 2.1), will then be of great importance in the disc–jetcoupling investigation. Most sources in the P15 Seyfert sample have L X / L Edd > ∼ − , i.e. they belong to bright AGNs, and only a limitednumber of sources belong to low-luminosity ones ( L X / L Edd < ∼ − ).It is known that bright AGNs and low-luminosity ones are distinctivein their accretion physics (Ho 2008; Heckman & Best 2014).Theoretically bright AGNs are powered by cold accretion disk (e.g.,Shakura-Sunyaev disc [SSD], Shakura & Sunyaev 1973), whilelow-luminosity AGNs are powered by hot accretion flow (Yuan &Narayan 2014).P15 focused on correlations among luminosities of their absolutevalues (e.g., L R and L X ), but not the Eddington normalized ones(e.g., L R / L Edd and L X / L Edd ), thus di ff erences in accretion physics are As stated above, the origin of radio emission in RQ AGNs is questioned inrecent years (e.g., Bonchi et al. 2013; Baek et al. 2019; Smith et al. 2020, seePanessa et al. 2019 for a review), where they argue the contributions fromnuclear star formation, outflow, corona and jet are of comparable importancein many RQ AGNs. Dimensionless accretion rate ˙ m is defined as ˙ m = ˙ M / ˙ M Edd , i.e. themass accretion rate ˙ M normalized by the Eddington accretion rate ˙ M Edd = L Edd / c .MNRAS000
INTE-GRAL / IBIS selected sample of Panessa et al. 2015 (hereafter P15;see Section 2.1), will then be of great importance in the disc–jetcoupling investigation. Most sources in the P15 Seyfert sample have L X / L Edd > ∼ − , i.e. they belong to bright AGNs, and only a limitednumber of sources belong to low-luminosity ones ( L X / L Edd < ∼ − ).It is known that bright AGNs and low-luminosity ones are distinctivein their accretion physics (Ho 2008; Heckman & Best 2014).Theoretically bright AGNs are powered by cold accretion disk (e.g.,Shakura-Sunyaev disc [SSD], Shakura & Sunyaev 1973), whilelow-luminosity AGNs are powered by hot accretion flow (Yuan &Narayan 2014).P15 focused on correlations among luminosities of their absolutevalues (e.g., L R and L X ), but not the Eddington normalized ones(e.g., L R / L Edd and L X / L Edd ), thus di ff erences in accretion physics are As stated above, the origin of radio emission in RQ AGNs is questioned inrecent years (e.g., Bonchi et al. 2013; Baek et al. 2019; Smith et al. 2020, seePanessa et al. 2019 for a review), where they argue the contributions fromnuclear star formation, outflow, corona and jet are of comparable importancein many RQ AGNs. Dimensionless accretion rate ˙ m is defined as ˙ m = ˙ M / ˙ M Edd , i.e. themass accretion rate ˙ M normalized by the Eddington accretion rate ˙ M Edd = L Edd / c .MNRAS000 , 1–12 (0000) niversal RX Correlation in Seyferts − − − − Log ( L X /L Edd ) L og ( M B H ) Sy 1s | RQSy 2s | RQSy 1s | RLSy 2s | RL − − − − Log ( L X /L Edd ) L og ( L HX / L X ) Sy 1s | RQSy 2s | RQSy 1s | RLSy 2s | RL Figure 1.
Distributions of BH mass M BH (left panel) and the 20-100 keV to 2-10 keV X-ray flux ratio L HX / L X (right panel) versus 2-10 keV X-ray Eddingtonratio L X / L Edd . In both panels, the open and filled separate sources in their radio loudness, i.e. open for radio-loud (RL) and filled for radio-quiet (RQ); whilethe color and shape define their optical properties, i.e. green circles for Seyfert 1s (labelled Sy 1s) and orange triangles for Seyfert 2s (labelled Sy 2s). The solidcurve in the left panel shows a simple power-law fit with M BH ∝ ( L X / L Edd ) − . ± . . not directly demonstrated. In this work, we reanalyze the completehard-X-ray selected Seyfert galaxy sample of P15, with an emphasison comparison between di ff erent type of sources (radio loud versusradio quiet, Seyfert 1s versus Seyfert 2s, etc). For tens of sources weupdate their measurements in black hole mass and radio luminosity.This work is organized as follows. In Section 2, we briefly introducethe sample, with a focus on those updates compared to P15. Thestatistical method is also introduced here. Then in Section 3 wepresent our results in detail, where we compare properties amongdi ff erent subsamples. Section 4 is devoted to discussions of ourresults and the final Section 5 provides a brief summary. Throughoutthis work, the distances are derived based on a flat cold dark mattercosmology ( Λ CDM cosmology) with the Hubble constant H =
70 km s − Mpc − and the mass density fraction parameter Ω M = . Our parent sample comes from P15, who compiled a completesample of moderately bright AGNs, selected at hard X-rays (20-100 keV) from the third
INTEGRAL / IBIS survey. The sensitivityof
INTEGRAL / IBIS above 20 keV is better than a few mCrab.Blazars are excluded in this sample, in order to avoid strong Dopplerboosting e ff ect (thus the luminosities measured are far away fromtheir intrinsic values). The absorption-corrected 2-10 keV X-ray fluxis from Malizia et al. (2009), where they gather from literature.The radio data of the P15 sample mainly come from the NRAOVLA Sky Survey (NVSS; Condon et al. 1998) at 1.4 GHz, whosesensitivity is about 0 .
45 mJy beam − . Additional complements arefrom the Sydney University Molonglo Sky Survey (SUMSS; Bocket al. 1999) at 843 MHz. In total there are 79 Seyfert galaxies inthe P15 sample, among which 46 are Seyfert 1s (Seyfert 1-1.5, alsoinclude 6 narrow-line AGNs) and 33 are Seyfert 2s (Seyfert 1.9-2.0).For our investigation, detections / measurements of M BH , L R , and L X are necessary. We complement the M BH of some sources fromother literature. For those that lack M BH estimation (noted as “2”in the column 6 of Table 1), we follow Graham (2007) to estimatetheir M BH as log( M BH / M (cid:12) ) = − . ± . × ( M K + + . ± . M K is obtained from Two-Micron All-Sky Survey (2MASS) throughSIMBAD. This above empirical relationship has a total scatter of0.33 dex in M BH (Graham 2007), similar to those derived basedon other methods. We exclude from our final sample sources thatlack detections / measurements of either M BH , L R , or L X . We furtherexamined their radio fluxes at 1.4 GHz, to consider only the radioemission from the nuclei / core region. This is crucial for thoseresolved ones with extended structures. For those resolved ones, ifpossible, their nuclear radio emission at 1.4 GHz is then derivedfrom higher-resolution (compared to VLA) VLBI observations atfrequencies specified below, assuming a radio spectrum F ν ∝ ν − α with α = . α measurements, i.e. NGC 1275 ( α = − .
51, Kim etal. 2019) and NGC 5506 ( α = − .
06, Middelberg et al. 2004).Compared to P15, sources that have their radio fluxes updated are:NGC 1275 (based on VLBI observations at 43 GHz, Kim et al.2019), NGC 3783 (1.6 GHz, Orienti & Prieto 2010), NGC 4151 (5GHz, Nagar et al. 2005), NGC 4388 (1.6 GHz, Giroletti & Panessa2009), NGC 5506 (1.6 GHz, Middelberg et al. 2004), 3C 390.3 (5GHz, Dodson et al. 2008), Cyg A (1.34 GHz, Struve & Conway2010) and 4C 74.26 (2.3 GHz, Bourda et al. 2011).To summarize, of the original 79 AGNs in P15, 9 (4) are excludeddue to the lack of radio (BH mass) measurements. The other2 are also excluded, who are only detected marginally or su ff erbackground contamination in radio. Our final sample includes 64sources, among which 35 are Seyfert 1s (Seyfert 1-1.5, 4 narrow-line Seyfert 1s are also included) and 29 are Seyfert 2s (Seyfert 1.9-2.0). We list in Table 1 the basic properties of our sample, includingtheir Seyfert classification, redshift, black hole mass and the methodadopted in its measurement, X-ray luminosities in 2-10 keV ( L X )and 20-100 keV ( L HX ; from INTEGRAL / IBIS, see P15), and radioluminosities at 1.4 GHz. Their radio morphology and the size ofthe radio core at 1.4 GHz (NVSS) or 0.8 GHz (SUMSS) are alsoprovided for reference.Figure 1 shows the basic properties of our sample. In both panels,the optical property is defined by the color and the shape, i.e. the http://simbad.u-strasbg.fr/simbad/ very long baseline interferometry, e.g., the Very Long Baseline Array (VLBA) and the
European VLBI Network (EVN).MNRAS , 1–12 (0000)
N. Chang et al.
Table 1.
Basic properties of the
INTEGRAL / IBIS hard-X-ray selected Seyfert sample
Name Class z Log( M BH ) M BH Method Ref. Log( L X ) Log( L HX ) Log( L R ) Radio Mor. (cid:63) D maj (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11)IGR J00333 + < +
62 Sy 1 0.044 8.1 WL 4 43.87 44.41 40.3 U < < +
411 Sy 1 0.136 8.8 M K K +
17 Sy 1.5 0.0179 7.0 RM 1 43.23 43.62 37.75 S 8.484MCG + < < K ∗ < K ∗ K ∗ < ∗ < K ∗ < ∗ < ∗ ∗ < ∗ < K ∗ ∗ K ∗ < K ∗ ∗ < ∗ ∗ < + < < +
81 Sy 1 0.084 8.8 WL 1 44.25 44.77 40.71 R 701.6IGR J21247 + + + < < < + K Notes:
Column 1 – source name; Column 2 – Seyfert classification; Column 3 – redshift; Column 4 – BH mass, Column 5 and 6 – measurement methodand reference for BH mass; Columns 7 and 8 – X-ray luminosities in 2-10 keV ( L X ) and 20-100 keV ( L HX ); Column 9 – radio luminosities at 1.4 GHz;Column 10 – radio morphology; Column 11 – length of half the major axis of the radio core. M BH in unit M (cid:12) , luminosities in unit erg s − , and D maj inunit kpc. BH mass measurement method (Column 5).
RM: reverberation mapping; S: from stellar velocity dispersion; GR: from gas velocity and size of the broad-line region; WL: from the line width and luminosity of broad emission lines (e.g., H β , H α , Pa β ), sometimes the luminosity may be that at 5100Å; G: fromgas velocity dispersions (through e.g., [O III ] or [Ne
III ]); M K : from K-band magnitude / luminosity of either the whole host galaxy or the stellar bulge; Refences for BH mass (Column 6). / BAT AGN Spectroscopic Survey: . References for L R (Column 7). (a) Kim et al. (2019); (b) Orienti & Prieto (2010); (c) Nagar et al. (2005); (d) Giroletti & Panessa (2009); (e) Middelberget al. (2004); (f) Dodson et al. (2008); (g) Struve & Conway (2010); (h) Bourda et al. (2011). The rest L R measurements are directly from P15. (cid:63) The symbol of the radio morphology (see P15 for details).
U for unresolved, S for slightly resolved, R for resolved and A for ambiguous. Here, sourceslabelled with ∗ are from the SUMSS survey, while the rest are from the NVSS survey.MNRAS000
U for unresolved, S for slightly resolved, R for resolved and A for ambiguous. Here, sourceslabelled with ∗ are from the SUMSS survey, while the rest are from the NVSS survey.MNRAS000 , 1–12 (0000) niversal RX Correlation in Seyferts Seyfert 1s are shown by green circles and the Seyfert 2s by orangetriangles. All sources in our sample is fairly bright. The X-rayEddington ratio L X / L Edd covers almost 4 orders of magnitude, i.e.between ∼ − . and ∼ − . . For an X-ray bolometric correction L bol / L X ≈
16 (e.g., Ho 2008; Netzer 2019), the Eddington ratio( λ Edd = L bol / L Edd ) of our sample then ranges between ∼ − and ∼
10. The left panel of Figure 1 shows the BH mass distribution,where we find that M BH ranges between 10 ∼ . M (cid:12) and 10 ∼ M (cid:12) ,with a clustering around 10 − M (cid:12) . Moreover, there apparently existsa negative correlation between M BH and L X / L Edd , where a simplepower-law fit suggests that M BH ∝ ( L X / L Edd ) − . ± . . Pearsoncorrelation coe ffi cient of this fitting is listed in Table 2. The lackof small M BH AGNs at the low- L X / L Edd end is because our sampleis limited by the X-ray flux; the lack of large M BH AGNs at the high- L X / L Edd end, on the other hand, is because of the cosmic evolution,i.e. galaxies in local universe, whose M BH is expected to be larger,are less active than those distant ones.We also separate radio-loud sources (open symbols in Figure1) from radio-quiet ones (filled symbols), where the X-ray radio-loudness R X is defined as R X = L R / L X (Terashima & Wilson 2003) and the RL / RQ boundary is set to R X = − . . We emphasize thatwe do not observe, in our near-complete hard X-ray selected AGNsample, the bimodal distribution of R X (see also Figure 2 of P15),suggesting that the bimodality in radio-loudness may be a selectione ff ect. Another property of our sample is that, as L X / L Edd increases,the fraction of RL sources declines significantly, i.e. there are onlytwo RL AGNs in the L X / L Edd > − regime. One is IGR J10404-4625 whose L X / L Edd ≈ .
02, and the other is IGR J21247 + L X / L Edd ≈ . As clearly shown in the left panel of Figure 1, there is a strong M BH − L X / L Edd relationship, which obviously contaminates the estimationof ξ M in Equation 1. To avoid this technical problem, we in this workaggressively omit the dependence on ξ M but focus on ξ X , i.e. weconsider the following radio / X-ray correlation in Eddington unit,log( L R / L Edd ) = ξ X log( L X / L Edd ) + const .. (3)Since most sources have a clustering of M BH at ∼ − M (cid:12) ,physically it is equivalent to the case of absorbing the impact of M BH into const . .Following Merloni et al. (2003), we statistically fit the obser-vational data through the minimization of the following quantity(hereafter the least χ approach), χ = Σ (cid:0) log( L R / L Edd ) − ξ X log( L X / L Edd ) − const . (cid:1) ( σ R , Edd log( L R / L Edd )) + ( ξ X σ X , Edd log( L X / L Edd )) . (4)Considering the non-simultaneity of the radio and X-ray fluxesused in this work, we ignore the observational uncertainties inlog( L R / L Edd ) and log( L X / L Edd ), but directly take their uncertaintiesto be σ R , Edd = . σ X , Edd = .
3, respectively (see e.g., Merloniet al. 2003; G¨ultekin et al. 2009; Xie & Yuan 2017).We note that in Equation 4 we additionally weight the uncer-tainties by luminosities in Eddington unit (i.e., L R / L Edd , L X / L Edd ).This is equivalent to an emphasis on fainter sources. We test thisrevised regression method through data sets which are manually Note that conventionally the radio loudness R is defined as the ratioof luminosities between 5 GHz radio band and the optical B-band (e.g.,Kellermann et al. 1989). − − − − Log ( L X /L Edd ) − − − L og ( L R / L E dd ) RQ | Sy 1sRQ | Sy 2sRL | Sy 1sRL | Sy 2s
Figure 2.
Radio / X-ray correlation (in Eddington units) for Seyfert galaxies,with a comparison between Seyfert 1s (the green filled circles) and Seyfert2s (the orange filled triangles). The black solid curve represents the fittingto the whole sample (see Equation 5), while the dashed curves provide thefitting results of two subsamples (see Equation 6), with the color the same tothose of the data points. generated by given parameters of ξ X , σ R , Edd and σ R , Edd . We find thatthe regression based on Equation 4 provides a better recovery of theinput ξ X value than that by original formulae of Merloni et al. (2003). L HX / L X distribution We first investigate the distribution of X-ray flux ratio L HX / L X as afunction of L X / L Edd . We caution that L HX and L X are not observedin a coordinated manner, the time interval can be as large as severalyears (Malizia et al. 2009; P15). AGNs are known to be variable onyear timescale (Ulrich, Maraschi & Urry 1997; Netzer 2008), thus L HX / L X may su ff er this non-simultaneity issue.As shown in the right panel of Figure 1, we find that most sourceshave L HX / L X ∼ −
4, despite the non-simultaneity issue. Moreover,statistically there is no dependence of the ratio L HX / L X on theX-ray luminosity L X / L Edd . Furthermore, we separate the sourcesaccording to their radio-loudness and Seyfert classification. Still,we do not observe any separation in L HX / L X between RL and RQones, nor between Seyfert 1s and Seyfert 2s. All these results mayimply that, despite the four-order-of-magnitude dynamical range in L X / L Edd , the possible change in accretion mode (i.e. cold accretionat L X / L Edd > ∼ − versus hot accretion at L X / L Edd < ∼ − ), and thehuge di ff erence in their radio loudness and / or Seyfert classification,all the sources in our sample have the same radiative mechanismand origin in X-rays. From a theoretical point of view, the mostplausible mechanism is hot accretion flow (or corona in case of coldaccretion). We note that, the jet may also dominate the X-rays in RL AGNs (Harris &Krawczynski 2006; Blandford, Meier, & Readhead 2019); and radio originmay also be diverse (Panessa et al. 2019; Chiaraluce et al. 2020). See also
Introduction . MNRAS , 1–12 (0000)
N. Chang et al. / X-ray Correlation in Seyfert Galaxies
The key motivation of this work is to investigate ξ X , i.e. the radio / X-ray correlation slope, among di ff erent types of Seyfert AGNs. Wetake three di ff erent classification methods, i.e. according to, 1) thefull width at half-maximum (FWHM) of the emission lines in opticalband, 2) the radio loudness R X , and 3) the size of radio-emission site. We first consider their di ff erences in optical emission-line proper-ties, i.e. Seyfert 1s versus Seyfert 2s. There are 35 ( ∼ ∼ L R / L Edd ) , log( L X / L Edd )) plane, where Seyfert 1sare shown by green filled circles and Seyfert 2s are shown by orangefilled triangles.Several results can be derived immediately. First, the observationsdo exhibit large scatters (see also Merloni et al. 2003; Falcke etal. 2004), i.e. at a given X-ray luminosity L X / L Edd , the nuclearradio luminosity L R / L Edd can di ff er by 2-3 orders of magnitude,and the scatter is similar among Seyfert 1s and Seyfert 2s. Thismay suggest as a piece of evidence against the AGN unificationmodel, where viewing angle is considered as the primary factor,i.e. face-on for Seyfert 1s and edge-on for Seyfert 2s (see, e.g.,Netzer 2015; Padovani et al. 2017 for a summary of additionalevidence against the unification model). Actually, we notice fromthis plot that Seyfert 1s and Seyfert 2s overlap each other in L R / L Edd ,suggesting that beaming e ff ect is not the key factor. Based on ourcurrent understanding of jet physics, we may argue that additionalfactor(s), among which likely the magnetic flux (Sikora et al. 2007)and / or the BH spin ( ¨Unal & Loeb 2020), should play dominate rolesin introducing the scatters as observed.Another result from this plot is that, the Seyfert 1s and Seyfert2s cover a similar range in both radio and X-ray luminosities (inEddington unit), although as shown in Figure 1 the Seyfert 2s areless massive in M BH compared to Seyfert 1s, especially at the bright L X / L Edd regime.We fit the data under the least χ approach. As shown by the blacksolid curve in Figure 2, the whole sample followslog( L R / L Edd ) = . + . − . log( L X / L Edd ) − . + . − . . (5)Meanwhile, the Seyfert 1s and Seyfert 2s follow, respectively,log( L R / L Edd ) = . + . − . log( L X / L Edd ) − . + . − . , (Sy 1s)log( L R / L Edd ) = . + . − . log( L X / L Edd ) − . + . − . . (Sy 2s)(6)The coe ffi cients of Pearson correlation analysis are listed in Table 2.The slopes in the two subsamples agree with each other within ∼ σ .This implies that, either orientation is not the key di ff erence betweenSeyfert 1s and Seyfert 2s (thus disfavour the AGN unificationmodel), or there is no intrinsic di ff erence in the origin of X-rayemission. We then explore the impact of radio-loudness, which is widelyconsidered as an indicator of jet beaming e ff ect. According to our Indeed some individual AGNs, so-called changing-look AGNs, can changetheir appearances in optical emission lines (i.e. between type 1 with broadlines and type 2 with only narrow lines) over several years (e.g., LaMassa etal. 2015), a period that the orientation should not vary much. − − − − Log ( L X /L Edd ) − − − − − L og ( L R / L E dd ) RLRQ
Figure 3.
Radio / X-ray correlation (in Eddington units) for Seyfert galaxieswith di ff erent radio loudness R X . Here the green open squares are for RLAGNs and the orange filled squares for RQ ones. The fitting results are alsoshown (see Equation 7), with the color the same to that of the data points. RL / RQ separation ( R X = − . ; Terashima & Wilson 2003), 27out of 64 ( ∼ ∼ L R / L Edd , at a given X-ray luminosity L X / L Edd .We re-plot the sample in Figure 3, where RL AGNs are shownby green open squares and RQ AGNs are shown by orange filledsquares. We find that most RL AGNs in our sample are less luminousin X-rays, only two out of 27 RL AGNs ( ∼ + L X / L Edd > − . On theother hand, for the 14 bright RQ AGNs with L X / L Edd > − , thereis no preference in Seyfert types (see the left panel of Figure 1), i.e.8 sources are Seyfert 1s and the rest 6 sources are Seyfert 2s.We fit the data with least χ regression method and find that RLand RQ AGNs follow, respectively,log( L R / L Edd ) = . + . − . log( L X / L Edd ) − . + . − . , (RL AGNs)log( L R / L Edd ) = . + . − . log( L X / L Edd ) − . + . − . . (RQ AGNs)(7)The coe ffi cients of Pearson correlation analysis are listed in Table2. Again, the correlation slopes of RL and RQ AGNs are consistentwith each other at 1 σ uncertainty level,Our result of a ξ X ∼ ffi cient accretion (e.g., cold accretion)and powerful radio emission. Most previous work find that RLAGNs follow a much steeper relationship, i.e. ξ X ∼ . ξ X ) as the radio-loudnessincreases (Li, Wu & Wang 2008). In accretion theory, the standardFP is achieved when the hot accretion flow is responsible for the X-rays (Yuan & Cui 2005; Xie & Yuan 2016); the steep ξ X ∼ . L X / L Edd (cid:46) − ; Yuan, Cui & Narayan 2005; Xie & Yuan 2017),and the other is when the beaming e ff ect is su ffi ciently strong (high MNRAS , 1–12 (0000) niversal RX Correlation in Seyferts − − − − Log ( L X / L Edd ) − − − − L og ( L R / L E dd ) D maj <
30 kpc D maj >
30 kpc
Figure 4.
Radio / X-ray correlation (in Eddington units) for Seyfert galaxieswith di ff erent radio emission size. The green open pentagons and orangefilled pentagons are respectively, for sources with their radio size (length ofthe half major axis) are less or greater than 30 kpc. The fitting results are alsoshown, with the color the same to those of the data points. Doppler boosting e ff ect for the jet emission in X-rays; e.g., Panessaet al. 2007; Li, Wu & Wang 2008). In this theoretical picture, ourfinding of a universal ξ X among RL and RQ systems suggests thatthe X-rays of RL Seyferts also originate from hot accretion flow,the same as RQ Seyferts. This interpretation is also favoured by the L HX / L X distribution, as shown in Figure 1. We note that similarresults have been reported in literature. For example, based on acompilation of 13 low-excitation radio galaxies (LERGs; belong toRL AGNs in our classification), Li & Gu (2018) find the LERGs tofollow the standard ξ X correlation, not a steep one as reported in deGasperin et al. (2011). The di ff erence is that in the latter work theyalso include LERGs which have a steep radio spectrum.Finally, we caution that the RQ systems here also agree with thelinear L R / L X ∼ − relationship observed in corona-active stars,thus being explained under an AGN corona (above the SSD) model(Laor & Behar 2008; see Sec 4.1). We finally investigate the impact of the radio emission size. It isnaturally expected that, the velocity and power of jet, which can beillustrated by the radio morphology, are crucial to determining theinteraction between the jet and the host galaxy (e.g., McNamara& Nulsen 2012; Duan & Guo 2020). Again we caution that thejet interpretation of RQ AGNs may be an over-simplification, seeSec. 4.1. More than 50% sources in our sample do not show clearextended structure. The only source with FR I jet morphologyis NGC 1275, and the 5 sources with FR II jet morphology arerespectively, B3 0309 + D maj as a representativeof the radio morphology. We take observations of either NVSS (at1.4 GHz) or SUMSS (at 0.8 GHz) (see Sec. 2.1 and Table 1), anddefine jets whose D maj <
30 kpc as compact systems, and thosewhose D maj >
30 kpc as extended (or resolved) systems. Under It is well-known that jet in RL AGNs morphologically has aFanaro ff –Riley dichotomy distribution, with the core-dominate FR I jetsbeing shorter and less stable than the lobe-dominate FR II jets (Fanaro ff &Riley 1974). Table 2.
Pearson correlation analysis of each subsampleSample (No.) Pearson P null R Figure 1: log ( M BH ) vs. log ( L X / L Edd )full sample (64) − .
54 3 . × − L R / L Edd ) vs. log ( L X / L Edd )full sample (64) 0 .
66 2 . × − .
65 2 . × − .
67 3 . × − .
86 9 . × − .
91 7 . × − .
71 3 . × − .
64 1 . × − η jet ) vs. log ( L X / L Edd )full sample (64) − .
44 2 . × − Notes:
Column 1 – sample; Column 2 and 3 – Pearson correlationcoe ffi cient and null correlation hypothesis probability; Column4 –goodness of fit, defined as ESS (Explained Sum of Squares) dividedby TSS (Total Sum of Squares). The closer the R is to 1, the betterthe fitting is. Check http://online.sfsu.edu/mbar/ECON312_files/R-squared.html for detail definition of the R . this definition, 31 Seyferts in our sample belong to the extendedcategory, and the rest 33 Seyferts belongs to the compact category.We show the results in Figure 4, where the green open pentagonsand orange filled pentagons are respectively, for sources with their D maj are less or greater than 30 kpc. Obviously there is no clearseparation in the L R / L Edd − L X / L Edd plane between systems withthese two types of radio morphologies, i.e. they overlap with eachother. Moreover, with a comparison to Figure 3, we find that thereis no direct connection between radio emission size and the radio-loudness, i.e. 11 out of 27 (41%) RL AGNs remain compact with D maj <
30 kpc; and 15 out of 37 (41%) RQ AGNs show extendedradio emission. When L X / L Edd > ∼ − , there is a weak tendencythat Seyferts with extended radio morphology are more luminousin L R / L Edd (equivalently, radio-louder) at a given L X / L Edd . But thesample size in this region is small, and such tendency disappearswhen L X / L Edd < ∼ − . We further fit the data with least χ regressionmethod and find that Seyferts with compact and extended radioemission follow respectively (see Table 2 for Pearson correlationcoe ffi cients),log( L R / L Edd ) = . + . − . log( L X / L Edd ) − . + . − . , (Compact)log( L R / L Edd ) = . + . − . log( L X / L Edd ) − . + . − . . (Extended)(8)Clearly, the correlation slopes are consistent with each other within1 σ uncertainty level.Finally, we note that we also check di ff erent choices of D maj criteria, i.e. 20 kpc or 25 kpc, and the results (not shown here) arequite similar to that reported above. One notable limitation of this work is that, we attribute in this work(a dominant fraction of) the nuclear radio emission to be from thejet component, either well-collimated or weakly-collimated. Due to
MNRAS , 1–12 (0000)
N. Chang et al. the low resolution of NVSS and large D maj in our sample, alternativecontributions indeed cannot be ruled out, especially in RQ systems.Unlike RL systems, many RQ Seyferts do not show jet-like struc-ture in high-resolution radio observations (e.g., Ulvestad, Antonucci& Barvainis 2005 and references therein): some remain unresolvedat sub-pc scale, while others are extended but lack linear (jet-like)morphology. We notice that the origin of nuclear radio and / or X-ray emission in RQ Seyferts is actually under active debate inrecent years (e.g., Bonchi et al. 2013; Baek et al. 2019; Laor etal. 2019; Smith et al. 2020; Fischer et al. 2021, and referencestherein.); alternative origins of radio emission in RQ AGNs includestar formation, AGN wind and AGN corona (see e.g., Padovani etal. 2017; Panessa et al. 2019 for reviews). Below we provide briefdiscussions on these alternative origins.One origin is the nuclear star formation activities. Active starformation processes will provide extended emission in radio andnear-infrared. Based on a VLA 22 GHz RQ AGN sample, Smithet al. (2020) report that, after core flux subtraction, AGN withcompact morphology will drop below the star formation expectation.This implies that the radio emission from nuclear star formation isstill unresolved even at 1 arcsecond resolution. Higher resolution(or at higher frequency) observations are thus necessary. However,AGN activities co-evolve with the dynamics of the circum-nuclearmedium, where a tight connection to nuclear star formation is adirect signature (e.g., Zhuang et al. 2021). In this understanding, thestar formation scenario for the non-linear radio emission awaits ad-ditional evidence. We also emphasize that the dominant mechanismfor radio emission at di ff erent frequencies might be di ff erent (e.g., instar-forming galaxies, free–free emission will become comparableimportant to synchrotron at high frequency).Another scenario proposed in literature is a hot corona (abovethe cold SSD) model for not only X-rays but also radio (Laor &Behar 2008) in the RQ systems. This model is similar to the coronain stellar systems, where a linear L R / L X ∼ − relationship isestablished (Guedel & Benz 1993). Observationally the RQ sourcesseem to be broadly consistent with this model (e.g., Smith et al. 2020and references therein). We note that our interpretation shares thesame origin of X-rays, but di ff ers in the origin of radio emission,i.e. in their model from non-thermal or hot thermal electrons inthe corona (Laor & Behar 2008; Raginski & Laor 2016), or in ourinterpretation from non-thermal electrons in the weakly-collimatedjet. One supporting evidence of wind or corona scenario is fromLi, Wu & Wang (2008), where they found that the broad lineluminosity is tight correlated with radio luminosity in RQs, i.e. theradio emission in RQs might be nearly isotropic.Our result suggests a universal radio / X-ray correlation in Seyferts,irrelevant to radio-loudness. However, the uncertainties in ξ X arestill large, thus although we favor the jet interpretation, we actuallycannot rule out any alternative scenarios, especially because all theseprocesses correlate with each other. In principle, the contribution ofnuclear star formation process can be removed from regular monitor-ing of individual sources, since the AGN and stellar processes havedi ff erent variability timescale; the corona and wind / outflow models,on the other hand, are tightly correlated to the accretion process, thuschallenge to discriminate. ffi ciency η jet One important quantity in accretion theory is the jet productione ffi ciency η jet , which characterizes the fraction of accretion powerthat enters into the relativistic jet (e.g., van Velzen & Falcke 2013;Ghisellini et al. 2014; Inoue et al. 2017; Rusinek et al. 2020; Soares & Nemmen 2020; W´ojtowicz et al. 2020). It is defined as, η jet = P jet ˙ Mc . (9)Obviously, the jet production e ffi ciency η jet will also dependent onmagnetic flux attached to jet and the BH spin. Based on a sample of ∼ ffi ciencyof η jet ≈ × − in the cold accretion disc regime, suggesting the BHspin and / or the magnetic flux are low in these systems; while basedon a sample of ∼
200 well-selected blazars with γ -ray detection,Ghisellini et al. (2014) find that their η jet ∼ − ffi ciency of Seyfert galax-ies. There are several methods to estimate the jet power (seeSoares & Nemmen 2020 for a brief summary), i.e. the radio lobeemission based on equipartition assumption (Willott et al. 1999), theradio core-shift e ff ect (Shabala, Santoso, & Godfrey 2012) and thespectrum modelling (Ghisellini et al. 2014). In this work we followthat of Willott et al. (1999) (for later updates, see e.g., Cavagnoloet al. 2010). Based on a sample of 77 RL AGNs that includes bothFR Is and IIs, they found that the jet power has a strong correlationwith the radio luminosity at 151 MHz, which can be re-expressedas P jet ≈ . × f / L R6 / erg s − ≈ . × L R6 / erg s − at1.4 GHz, if a radio spectrum F ν ∝ ν − . is adopted. The theoreticaluncertainties in P jet are absorbed in a parameter f , which we take f =
10, following the recent calibrations by studies of X-ray cavityand hot spot in AGNs (Godfrey & Shabala 2013). We caution thatthe calibration implies that the derived jet power is a time-averaged(over the past millions of years) one, and may di ff er from the P jet ofthe current on-going accretion process (represented by L X ). We forsimplicity omit this uncertainty. We further caution that the abovejet power estimation is from RL AGNs; the application to RQ AGNsmay be aggressive and risky, with uncertainties hard to measure.However, this is the only method we currently have.The accretion power ˙ Mc can be estimated from the bolometricluminosity of hot accretion flow L bol , h10 as ˙ Mc = L bol , h /(cid:15) , where (cid:15) is the radiative e ffi ciency. For a geometrically-thin cold accretiondisc like SSD (Shakura & Sunyaev 1973), the e ffi ciency is (cid:15) SSD ≈ ffi ciency is systematicallylower than (cid:15) SSD , but its value increases as ˙ M increases (Xie & Yuan2012; Xie & Zdziarski 2019), and can be comparable to that of coldSSD at high ˙ M / ˙ M Edd end. We further estimate the L bol , h from theX-ray bolometric correction factor f X = L bol , h / L X (e.g., Ho 2008;Vasudevan & Fabian 2009). Then we can re-express Equation (9)as, η jet f X (cid:15) = P jet L X ∝ L / L X . (10)We plot in Figure 5 the relationship between L X / L Edd and thejet production e ffi ciency η jet , where the symbols are of the samemeaning to those in Figure 1. Here we statistically assume f X (cid:39) (cid:15) (cid:39)
8% (Xie & Yuan 2012). The original value of η jet f X /(cid:15) ( ≡ P jet / L X , see Equation 10) of each source is also shownin Figure 5 by its right y-axis. Several results can be derived directlyfrom this plot. First, η jet (or more accurately, η jet f X /(cid:15) ) shows a prettylarge scatter at given X-ray luminosity ( L X / L Edd ), and the scatter issimilar among RL AGNs and RQ AGNs. On the other hand, thereis a tendency that Seyfert 1s has a smaller scatter than Seyfert 2s.For the whole sample of 64 Seyferts, we find that η jet varies between10 − . and 10 − , with a mean value of <η jet > = . + . − . × − . We note Expressed as the bolometric disc luminosity, i.e. L disc , in the notation ofInoue et al. (2017).MNRAS000
8% (Xie & Yuan 2012). The original value of η jet f X /(cid:15) ( ≡ P jet / L X , see Equation 10) of each source is also shownin Figure 5 by its right y-axis. Several results can be derived directlyfrom this plot. First, η jet (or more accurately, η jet f X /(cid:15) ) shows a prettylarge scatter at given X-ray luminosity ( L X / L Edd ), and the scatter issimilar among RL AGNs and RQ AGNs. On the other hand, thereis a tendency that Seyfert 1s has a smaller scatter than Seyfert 2s.For the whole sample of 64 Seyferts, we find that η jet varies between10 − . and 10 − , with a mean value of <η jet > = . + . − . × − . We note Expressed as the bolometric disc luminosity, i.e. L disc , in the notation ofInoue et al. (2017).MNRAS000 , 1–12 (0000) niversal RX Correlation in Seyferts − − − − Log ( L X /L Edd ) − − − L og ( η j e t ) − − − Log ( L bol , h /L Edd ) − − − L og ( η j e t f x / (cid:15) ) Sy 1s | RQSy 2s | RQSy 1s | RLSy 2s | RL Figure 5.
Jet production e ffi ciency η jet as a function of the X-ray Eddingtonratio L X / L Edd (and in the upper x-axis the bolometric Eddington ratio L bol , h / L Edd ), where we assume the radiative e ffi ciency of hot accretion flow (cid:15) =
8% and the X-ray bolometric correction factor f X =
16. The right y-axisshows η jet f X /(cid:15) ≡ P jet / L X . The black solid curve represents the fitting resultto the whole sample, see Equation (12). As labelled in the plot, the symbolsare of the same meaning to those in Figure 1. that compared to the results in literature (van Velzen & Falcke 2013;Ghisellini et al. 2014; Inoue et al. 2017; Soares & Nemmen 2020;W´ojtowicz et al. 2020), the scatter is roughly consistent, but themean value derived here is at least two orders of magnitude smaller.The mean jet production e ffi ciency for RL and RQ subsamples arerespectively, <η jet > = . + . − . × − and <η jet > = . + . − . × − . Wenote that, based on a large sample of low-redshift AGNs selectedfrom the Swift / BAT, Rusinek et al. (2020) recently find a meanproduction e ffi ciency of <η jet > ≈ × − ( (cid:15)/ <η jet > is because that, about 80% of the sources in theirsample are RQ AGNs, which by definition are systems with low η jet .Second, even within this limited (but near-complete) sample ofSeyferts, a gradual decline in η jet f X /(cid:15) (and η jet ) as the system bright-ens (larger in L X / L Edd ) is also observed. Considering the positivedependence on L X / L Edd in both f X and (cid:15) (Vasudevan & Fabian2009; Xie & Yuan 2012), this implies an e ffi cient reduction in η jet ,or equivalently a jet quenching behavior, as L X / L Edd increases. Asshown in Figure 5, the whole sample follows a negative relationshiplog( η jet f X /(cid:15) ) = − . + . − . log( L X / L Edd ) − . + . − . . (11)For our adopted values of f X and (cid:15) , it can also be expressed aslog η jet = − . + . − . log( L bol , h / L Edd ) − . + . − . , (12)The results of Pearson correlation analysis are provided in Table2. We note that such a negative correlation is also observed inliterature (e.g., W´ojtowicz et al. 2020). It is also consistent with thewell-known anti-correlation between radio loudness and bolometricluminosity in AGNs (e.g., Terashima & Wilson 2003; Panessa et al.2007; Ho 2008) and BHBs (Fender et al. 2009) as well.For completeness, we include in Table 3 the estimations of themean values of η jet for di ff erent subsamples, i.e. Seyfert 1s vs.Seyfert 2s. There is no clear di ff erence in η jet among Sy 1s andSy 2s. Moreover, although the η jet of RL AGNs is about one ordermagnitude larger than that of RQ AGNs, it’s still smaller than thatreported in literature (e.g., Inoue et al. 2017; W´ojtowicz et al. 2020).Finally we caution that for RQ AGNs, not only the jet powerestimation method is uncertain, there are also debates on the radio Table 3.
Jet Production E ffi ciency η jet (and η jet f X /(cid:15) ) of INTEGRAL -SelectedSeyferts Sample (No.) <η jet f X /(cid:15)> <η jet > ( f X =
16 and (cid:15) = . + . − . × − . + . − . × − RQ (37) 1 . + . − . × − . + . − . × − RL (27) 1 . + . − . × − . + . − . × − Sy 1s (35) 2 . + . − . × − . + . − . × − Sy 2s (29) 5 . + . − . × − . + . − . × − origin. If other mechanisms play a dominant role, the jet productione ffi ciency reported above will be an over-estimation. It is known that there are distinctive di ff erences among bright AGNsand low-luminosity AGNs (e.g., Ho 2008 for a review), where theseparation is around L bol / L Edd (cid:39) (1 − L X / L Edd (cid:39) − .Direct connections or analogies between bright AGNs and BHBsin soft state (and possibly the intermediate state, see Belloni 2010for state classification in BHBs), and between low-luminosity AGNsand BHBs in hard state, are now crudely established (among others,see e.g., K¨ording, Jester, & Fender 2006; Ho 2008; Yuan & Narayan2014; Yang et al. 2015). The accretion modes in the bright AGNs andlow-luminosity AGNs correspond to, respectively, the two feedbackmodes established in AGN feedback field (Fabian 2012; Kormendy& Ho 2013; Heckman & Best 2014). The Seyfert galaxies in thiswork have an X-ray luminosity of L X ∼ (10 − − L Edd , i.e. mostof them belong to the bright AGN regime, thus may be powered bycold accretion disc (e.g., SSD, or the two-phase accretion flow, cf.Yang et al. 2015), and the rest are powered by hot accretion flow. Weemphasis that the X-rays cannot be from the SSD, but may be fromthe corona above (and below) the SSD.One unresolved puzzle in accretion theory is that, BHBs usuallystay in their soft state when L X / L Edd > ∼ − . In this state, the accre-tion is a cold SSD (Shakura & Sunyaev 1973), and the continuous jetwill usually be quenched. On the other hand, although the fractionof radio loudness declines as luminosity increases (e.g., Terashima &Wilson 2003; Ho 2008, and Sec. 4.2), a significant fraction (typically ∼ Theoretically, the jet power is determined by the BH spin and themagnetic flux near BH (Blandford & Znajek 1977; Ghisellini etal. 2014; Tchekhovskoy 2015). However, in the discrepancy amongBHBs and AGNs, the BH spin is known not to be a dominate factor.For example, even for BHBs whose BH spin is large (e.g., a > . We note that the compact jet in the soft state is also discovered recentlyin a limited number of systems and / or outbursts, e.g., Cyg X-3 (Zdziarski etal. 2018), GRS 1739–278 (Xie, Yan & Wu 2020), and Cyg X-1 (Zdziarskiet al. 2020). These observations are of crucial importance, since they find inBHBs the counterparts of RL bright AGNs (and quasars).MNRAS , 1–12 (0000) N. Chang et al.
Miller & Miller 2015), the jet is still quenched during soft state.Even for AGNs, it is known that many Seyferts with large BH spinare radio-quiet (Reynolds 2014), i.e. there is no direct link betweenBH spin and jet power.The only possible mechanism left relates to the magnetic flux(or somewhat equivalently, the magnetic field strength) near BH.Indeed, theoretically Heinz & Sunyaev (2003) argued that there isa M BH -dependence in the jet physics itself. In their scale invariantjet model, a larger M BH leads to a relatively stronger magnetic fieldnear the BH, which would make it easier to launch a relativistic jet.One possible prediction of this model is that, the jet velocity may belarger in a system with relatively stronger magnetic fields (i.e. largerin M BH ), where acceleration may be more e ffi cient. Observationallythere is indeed supporting evidence. In AGNs with supermassiveBHs ( M BH ∼ − M (cid:12) ) the jets are usually relativistic with Γ ∼ M BH ∼ M (cid:12) ),the jets are only mildly relativistic with Γ ∼ − M BH ∼ M (cid:12) ) the jet velocity isfairly low with Γ ∼ − ff erent to those conventional weakly magnetized ones. Besides, itis unclear why some systems can enter into such an unusual statewhile the rest cannot. The observations of Seyfert galaxies report afairly low η jet ( ∼ − ; see Figure 5 and Equation 12), which is muchlower than that predicted by MAD (e.g., Ghisellini et al. 2014). Inother words, it may suggest that the central engine of the hard X-rayselected Seyfert galaxies of P15 is magnetically “weak”, far awayfrom the highly magnetized MAD state (a similar conclusion, seealso W´ojtowicz et al. 2020 for a sample of young radio galaxies).This is totally di ff erent from those γ -ray blazars as reported inGhisellini et al. (2014), where a MAD state with nearly maximalpossible jet power is observed. We note that, although the
INTEGRAL / IBIS survey provides acomplete sample of Seyfert galaxies from hard X-rays, it is not adeep / sensitive survey. The P15 sample includes only 79 sources.This limits our capabilities to explore fainter systems. One promis-ing hard X-ray survey is done by the Swift / BAT (Koss et al. 2017),whose sensitivity is about one order of magnitude higher thanthe
INTEGRAL / IBIS survey. Investigations based on the
Swift / BATsample will definitely be helpful to this problem (see e.g., Rusineket al. 2020 for the investigation of η jet ). Most importantly, the Swift / BAT survey will enlarge the sample size of sources below 10 − in L X / L Edd and / or less massive in M BH . The first is the regime whichis more ideal to the standard so-called “radiatively-ine ffi cient” hotaccretion (Yuan & Narayan 2014), while the latter will (partially)fullfill the BH mass gap between BHBs and AGNs.As mentioned in Sec.4.1, to explore the possible physical modelsfor the radio emission in RQ AGNs, high resolution and high sensitivity radio observations are the keys to unravel the coreregion. Recently, Fischer et al. (2021) perform simultaneous radio(VLBA) and X-ray observations for 25 AGNs. Despite a lowdetection rate (36%) in radio, it allows us to explore the possiblephysical mechanism of RQs. They found AGNs in their samplejump out the FP from VLBA observations, but follow the FP fromVLA observations, which implies that this discrepancy might becontributed by extranuclear radio emissions. Sample selection / control is always an important issue in the fun-damental plane investigation (e.g., Panessa et al. 2007; Li, Wu &Wang 2008; Xie & Yuan 2017; Yao et al. 2018). In this work,we focus on a complete hard X-ray selected sample of Seyfertgalaxies originally gathered by P15. We only include sources thathave measurements / estimations of BH mass and luminosities inradio and X-rays. Our final near-complete sample includes 64 (outof the original 79) sources, among which 35 are Seyfert 1s and 29are Seyferts 2s, or 27 are RL and 37 are RQ. The dynamical rangein L X / L Edd is between ∼ − and ∼ − . . According to the typicalseparation of L X / L Edd ∼ − (e.g., Ho 2008; Yang et al. 2015), mostsources of our sample belong to bright AGNs, and a small fractionare low-luminosity ones.This near-complete hard X-ray selected sample su ff ers a strongdependence of L X / L Edd on M BH , as clearly shown in the left panelof Figure 1. We thus limit ourselves only to probe the radio / X-ray correlation in Eddington units (e.g., L R / L Edd vs. L X / L Edd ).This choice reflects our motivation to investigate the accretiontheory, where only luminosities in Eddington units are related to theaccretion mode (see Esin et al. 1997; Ho 2008; Yuan & Narayan2014).Our main results can be summarized as follows. • There is no clear di ff erence in L HX / L X (mean value, scatter,distribution) among Seyfert 1s and Seyfert 2s, and among RLSeyferts and RQ Seyferts. This may suggest a common origin ofX-rays in our sample. • The slope of the radio / X-ray correlation is almost universalamong di ff erent types of sources, i.e. it is irrelevant to the broademission line properties (Seyfert 1s or 2s), the radio loudness (RLor RQ), and the morphological size of radio emission (extended orcompact). The whole sample follows L R / L Edd ∝ ( L X / L Edd ) . ± . ,which agrees with the standard FP at 2 σ level (Merloni et al. 2003). • Under the jet origin interpretation, the average jet productione ffi ciency of Seyfert galaxies is <η jet > = . + . − . × − , whichis two orders of magnitude lower than that of RL sources ateven higher bolometric luminosities (van Velzen & Falcke 2013;Inoue et al. 2017; Soares & Nemmen 2020; W´ojtowicz et al.2020). More specificaly, we have <η jet > = . + . − . × − for RLSeyferts and <η jet > = . + . − . × − for RQ Seyferts. Besides, agradual decline in η jet as the system brightens is also evident, i.e. η jet ∝ ( L bol , h / L Edd ) − . ± . . Such jet quenching process during thebrightening phase is expected in both theory and observations. ACKNOWLEDGMENTS
We appreciate the referee for his / her detailed report and thoughtfulcomments (especially updates of radio emission in RQ systems) thatimprove our presentation. This work was supported by the NationalKey R&D Program of China (NKRDC, 2018YFA0404602), and MNRAS , 1–12 (0000) niversal RX Correlation in Seyferts the Key Laboratory of Radio Astronomy, Chinese Academy ofSciences (CAS). FGX was supported in part by National SKAProject of China No. 2020SKA0110102, the National Science Foun-dation of China (NSFC, 11873074) and the Youth Innovation Pro-motion Association of CAS. LCH was supported by NKRDC(2016YFA0400702) and NSFC (11721303 and 11991052). Thiswork has made extensive use of the NASA / IPAC ExtragalacticDatabase (NED), which is operated by the Jet Propulsion Labo-ratory, California Institute of Technology, under contract with theNASA. This research has made use of the SIMBAD database,operated at CDS, Strasbourg, France.
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