The disc-like host galaxies of radio-loud narrow-line Seyfert 1s

Until recently, relativistic jets were ubiquitously found to be launched from giant elliptical galaxies. However, the detection by the Fermi-LAT of gamma-ray emission from radio-loud narrow-line Seyfert 1 (RL-NLSy1) galaxies raised doubts on this relation. Here, we morphologically characterize a sample of 29 RL-NLSy1s (including 12 gamma-emitters, gamma-NLSy1s) in order to find clues on the conditions needed by active galactic nuclei (AGNs) to produce relativistic jets. We use deep near-infrared images from the Nordic Optical Telescope and the ESO VLT to analyse the surface brightness distribution of the galaxies in the sample. We detected 72 per cent of the hosts (24 per cent classified as gamma-NLSy1s). Although we cannot rule out that some RL-NLSy1s are hosted by dispersion-supported systems, our findings strongly indicate that RL-NLSy1 hosts are preferentially disc galaxies. 52 per cent of the resolved hosts (77 per cent non-gamma-emitters and 20 per cent gamma-emitters) show bars with morphological properties (long and weak) consistent with models that promote gas inflows, which might trigger nuclear activity. The extremely red bulges of the gamma-NLSy1s, and features that suggest minor mergers in 75 per cent of their hosts, might hint to the necessary conditions for gamma-rays to be produced. Among the features that suggest mergers in our sample, we find six galaxies that show offset stellar bulges with respect to their AGNs. When we plot the nuclear versus the bulge magnitude, RL-NLSy1s locate in the low-luminosity end of flat spectrum radio quasars, suggesting a similar accretion mode between these two AGN types

Flare-like Variability of the Mg~II λ\lambda2798 \AA\ Emission Line and UV Fe~II band in the Blazar CTA~102

We report on the detection of a statistically significant flare-like event in the Mg~II~$\lambda$ 2798~\AA\ emission line and the UV~Fe~II band of CTA~102 during the outburst of autumn 2017. The ratio between the maximum and minimum of $\lambda$3000~\AA\ continuum flux for the observation period ($2010-2017$) is 179$\pm$15. Respectively, the max/min ratios 8.1$\pm$10.5 and 34.0$\pm$45.5 confirmed the variability of the Mg~II emission line and of the Fe~II band. The highest levels of emission lines fluxes recorded coincide with a superluminal jet component traversing through a stationary component located at $\sim$0.1 mas from the 43 GHz core. Additionally, comparing the Mg~II line profile in the minimum of activity against the one in the maximum, we found that the latter is broader and blue-shifted. As a result of these findings, we can conclude that the non-thermal continuum emission produced by material in the jet moving at relativistic speeds is related to the broad emission line fluctuations. In consequence, these fluctuations are also linked to the presence of broad-line region (BLR) clouds located at $\sim$25 pc from the central engine, outside from the inner parsec, where the canonical BLR is located. Our results suggest that during strong activity in CTA~102, the source of non-thermal emission and broad-line clouds outside the inner parsec introduces uncertainties in the estimates of black hole (BH) mass. Therefore, it is important to estimate the BH mass, using single-epoch or reverberation mapping techniques, only with spectra where the continuum luminosity is dominated by the accretion disk.Comment: 15 pages, 6 figures, 2 tables, accepted for publication in Ap

A 3-Dimensional study of the Local Environment of Bright IRAS Galaxies: The AGN/Starburst connection

We present a 3-dimensional study of the local ($\leq 100 h^{-1}$ kpc) and the large scale ($\leq$ 1 $h^{-1}$ Mpc) environment of Bright IRAS Galaxies (BIRGs). For this purpose we use 87 BIRGs located at high galactic latitudes (with 0.008$\leq z \leq$0.018) as well as a control sample of non-active galaxies having the same morphological, redshift and diameter size distributions as the corresponding BIRG sample. Using the Center for Astrophysics (CfA2) and Southern Sky Redshift Survey (SSRS) galaxy catalogues ($m_b\lesssim 15.5$)as well as our own spectroscopic observations ($m_b\lesssim19.0$) for a subsample of the original BIRG sample, we find that the fraction of BIRGs with a close neighbor is significantly higher than that of their control sample. Comparing with a related analysis of Sy1 and Sy2 galaxies of Koulouridis et al. (2006) we find that BIRGs have a similar environment as Sy2s, although the fraction of BIRGs with a bright close neighbor is even higher than that of Sy2 galaxies. An additional analysis of the relation between FIR colors and the type of activity of each BIRG shows a significant difference between the colors of strongly-interacting and non-interacting starbursts and a resemblance between the colors of non-interacting starbursts and Sy2s. Our results support the view where close interactions can drive molecular clouds towards the galactic center, triggering starburst activity and obscuring the nuclear activity. When the close neighbor moves away, starburst activity is reduced with the simultaneous appearance of an obscured (type 2) AGN. Finally, the complete disentanglement of the pair gives birth to an unobscured (type 1) AGN.Comment: Accepted for publication in The Astrophysical Journal,10 pages, 4 figure