A compact jet at the infrared heart of the prototypical low-luminosity AGN in NGC 1052

Abstract

The feeble radiative efficiency characteristic of Low-Luminosity Active Galactic Nuclei (LLAGN) is ascribed to a sub-Eddington accretion rate, typically at log(L bol /L edd ) −3. At the finest angular resolutions that are attainable nowadays using mid-infrared (mid-IR) interferometry, the prototypical LLAGN in NGC 1052 remains unresolved down to < 5 mas (0.5 pc). This is in line with non-thermal emission from a compact jet, a scenario further supported by a number of evidences: the broken power-law shape of the continuum distribution in the radio-to-UV range; the ∼ 4% degree of polarisation measured in the nuclear mid-IR continuum, together with the mild optical extinction (A V ∼ 1 mag); and the "harder when brighter" behaviour of the X-ray spectrum, indicative of self-Compton synchrotron radiation. A remarkable feature is the steepness of the IR-to-UV core continuum, characterised by a power-law index of ∼ 2.6, as compared to the canonical value of 0.7. Alternatively, to explain the interferometric data by thermal emission would require an exceptionally compact dust distribution when compared to those observed in nearby AGN, with A V 2.8 mag to account for the IR polarisation. This is in contrast with several observational evidences against a high extinction along the line of sight, including the detection of the nucleus in the UV range and the well defined shape of the power-law continuum. The case of NGC 1052 shows that compact jets can dominate the nuclear emission in LLAGN across the whole electromagnetic spectrum, a scenario that might be common among this class of active nuclei.

Accretion and jets in a low-luminosity AGN: the nucleus of NGC 1052

“…Given the BH mass of 1.5 × 10 8 M ⊙ (Woo & Urry 2002), the Eddigton luminosity is 1.8 × 10 46 erg s −1 . The bolometric luminosity estimated from the integration of the Spectral Energy Distribution (SED) is ∼ 7 × 10 42 erg s −1 (Fernández-Ontiveros et al 2019), which gives an Eddington ratio of -3.4, consistent with accretion in a radiatively inefficient mode. In this case, the optically thick, geometrically thin accretion disk is expected to be truncated and replaced by an ADAF at the centre (Quataert et al 1999).…”

Dark matter and no dark matter: on the halo mass of NGC 1052

“…Indeed, the central galaxy is dominated by old (∼ 13 Gyr) stars (Milone et al 2007). It contains a low luminosity AGN with compact jets (Fernández-Ontiveros et al 2019). Forbes et al (2001) found the GC system around NGC 1052 to be fairly typical with a bimodal colour distribution and specific frequency S N = 3.2.…”

Properties of the Obscuring Torus in NGC 1052 from Multi-epoch Broadband X-ray Spectroscopy

“…Results for LL AGN obtained from the X-ray and infrared bands are divergent and even less clear due to limited statistics (e.g., Kawamuro et al 2016;González-Martín et al 2017;Ichikawa et al 2019). Studying NGC 1052 at the highest spatial resolution available in the infrared, Fernández-Ontiveros et al (2019) concluded that jets are the more likely source of broadband infrared emission at 0.5 pc, hence finding no evidence for thermal emission from a dusty torus.…”

“…It exhibits a type 2 optical spectrum with broad lines observed in polarized light (Barth et al 1999). Studying its emission across the electromagnetic spectrum, Fernández-Ontiveros et al (2019) estimated that its bolometric luminosity (L bol ) and Eddington ratio (λ Edd = L bol /L Edd ) are around 7 × 10 42 erg s −1 and 4 × 10 −4 , respectively. The relatively low accretion rate classifies NGC 1052 as a low-luminosity AGN (LL AGN; Ho 2008), although it has previously been found to share some characteristics of typically more luminous Seyfert galaxies.…”