Powerful relativistic jets in spiral galaxies

During the latest decades, we have observed powerful relativistic jets from active galactic nuclei (AGN), Galactic binaries (stellar mass black holes, neutron stars and cataclysmic variables), and Gamma Ray Bursts (GRBs). Supersonic jets are also visible in protostellar systems. Despite of the diffusion of jets in almost all types of accreting astrophysical systems, it seemed that galaxies made some preference: early observations of the host galaxies of AGN with relativistic jets displayed only elliptical shapes 2,26,29,38 . Only a few counterexamples (i.e. jets in spiral galaxies) were found in the past. The turning point occurred a couple of years ago with the discovery -by means of the Fermi satellite -of GeV γ rays from narrow-line Seyfert 1 galaxies (γ-NLS1) 13,14,15 . This class of AGN is composed of sources generally hosted by spiral (barred) galaxies 9,10 and, according to the common paradigm, without jets. Therefore, although some early radio observations had suggested the presence of some jet emission in a handful of cases 23,27 , the discovery of GeV γ rays was somehow a surprise. It confirmed that also this class of AGN can develop powerful relativistic jets, like blazars and radio galaxies (see Ref. 16 for a review).

Presently, seven γ-NLS1s are known and surely one of them is hosted by a spiral galaxy 40,1,16 . Work is in progress to confirm the spiral hosts for the remaining γ-NLS1s. The fact that no NLS1 is known to be at high redshift a suggests that it is very unlikely to find this type of AGN hosted by ellipticals.

The issue of the host is linked to how the mass can affect the generation and the power of the jet and was studied in the past particularly with the use of the radio loudness parameter (RL = f 5 GHz /f 440 nm ), which in turn should indicate the dominance of the synchrotron emission from the jet over the radiation from the accretion disc (e.g. Ref. 29,38). Being the blazars and radio galaxies (RL » 10) confined in a mass range of 10 8-10 M ⊙ , while Seyferts and LINERs (RL < 10) occupy the range 10 6-8 M ⊙ , it seemed that the jet needed of a large mass to be generated 29,38 . The discovery of powerful relativistic jets in γ-NLS1 is now filling the region of small masses and high radio loudness (see Ref. 17 for more details). In addition, it opens also new interesting questions on the comparison of jets in AGN and in Galactic binaries. This is the topic of the present work and is complementary to Ref. 17.

I have used the same sample of AGN in Ref. 17, made of 9 BL Lac Objects, 30 flat-spectrum radio quasars (FSRQs) and 7 γ-NLS1s. For the present work, I have added a sample of Galactic objects (X-ray Binaries, XRB), made of three stellar mass black holes (GX 339-4 6 , H1743-322 8 , V404 Cyg 7 ) and two neutron stars (Aql X-1 34 , 4U 1728- 34 33 ). For XRB, the X-ray flux measured in different bands (3 -9 keV in most of the cases), which samples the accretion radiation in Galactic objects, has been converted into the 2 -10 keV flux with webPIMMS b by using a power-law model with photon index equal to 2. Then, the values have been corrected according to Ref. 33 and scaled to the Eddington luminosity, calculated by assuming a mass of 1.4M ⊙ for neutron stars and 5.8M ⊙ , 10M ⊙ , and 11.7M ⊙ for GX 339-4 19 , H1743-322 8 , and V404 Cyg 19 , respectively.

The radio emission has been converted into jet power by assuming the classical relationship 4,28 according to which P jet ∝ L 12/17 core,radio . For the sake of simplicity and homogeneity with the AGN sample, I have used the Eq. (2) of Ref. 17, taking into account that the radio emission from jets has a rather flat spectral index (α radio ∼ 0). The luminosities have been calculated by assuming the distances and the N H reported in Refs. 8, 19, 33.

a The 13th edition of the Véron-Cetty & Véron catalogue of quasars and AGN 39 contains only NLS1s with z 1. This is also in agreement with the findings that these sources are very young 31 . b http://heasarc.gsfc.nasa.gov/Tools/w3pimms.html Powerful relativistic jets in spiral galaxies 3

As already noted in Ref. 17 (Fig. 5), the addition of γ-NLS1s to the blazars makes this sample of AGN directly comparable with a sample of jets from Galactic compact objects c . Blazars can be compared with stellar mass black holes, while γ-NLS1s occupy the region of neutron stars. Therefore, in term of relativistic jets, γ-NLS1s are the low mass counterpart of blazars so as neutron stars are the small mass version of Galactic black holes. The difference of the jet power is about 12-13 orders of magnitude, more than the mass difference between the two samples. To remove the mass dependence, I have calculated the jet power per unit mass. Then, I have searched for correlations in the two samples by using the ASURV v. 1.2 software package 30,12,25 . In the case of AGN, I obtain:

and the results for the statistical tests are: Z = 4.1 (P chance < 10 -4 ) for the Kendall’s test, while the Spearman’s meth

This content is AI-processed based on open access ArXiv data.