16.01.2020
Joint journal club
Michaela Kraus will present the following paper: "The evolution of red supergiant mass-loss rates" Beasor et al., 2018, MNRAS 475, 55 https://ui.adsabs.harvard.edu/abs/2018MNRAS.475...55B/abstract and Rhys Taylor will talk about this paper on the size of Ultra Diffuse Galaxies possibly being hugely overestimated: "Are ultra-diffuse galaxies Milky Way-sized?" Chamba et al., 2020, A&A 633, L3 https://arxiv.org/abs/2001.02691
08.04.2020
Restarting radio activity in a hard X-ray selected sample
Radio activity is episodic in nature and radio galaxies witness such activity. However, the duration and the duty cycle of the jet activity is not known, notwithstanding its importance in the context of radio galaxy evolution and feedback to the environment. Due to their large scale and old age, Giant Radio Galaxies (GRG) are ideal targets to study the duty cycle of radio activity. However, GRG usually constitute only a small fraction of sources in radio surveys and a systematic study of the occurrence of restarting activity is still missing. Cross-correlating the INTEGRAL+Swift AGN population with radio catalogues (NVSS, FIRST, SUMSS), we found that 22% of the sources are GRG (a factor four higher than those selected from radio catalogues). Remarkably, all of the sources in the sample show signs of restarting radio activity. The X-ray properties are consistent with this scenario, the nuclei being in a high-accretion, high-luminosity state. I will discuss in details the multi-frequency evidence of restarting activity in this sample.
30.04.2020
Joint Journal Club
Meeting ID: 96137754167 Password: 7089 Meeting link: https://zoom.us/j/96137754167 Scheduled time: 30/04/2020 10:30 CEST (08:30 UTC) Duration: 150 minutes Julieta will present the paper: "Low-frequency gravity waves in blue supergiants revealed by high-precision space photometry by Bowman et al., https://arxiv.org/abs/1905.02120 Pavel will review the paper: "A Link Between Ram Pressure Stripping and Active Galactic Nuclei" by Ricarte et al., https://arxiv.org/abs/2003.05950
11.05.2020
Do stellar-mass and super-massive black holes have similar dining habits?
We compare the relationship between the luminosity of the accretion disc and corona in AGN and X-ray binaries in their radiatively efficient (and non-jetted) phases. The observed scatter in the log Ldisc - log Lcorona plane of XRBs is high (~0.43 dex) and significantly larger than in AGN (~0.30). On the other hand, we also find that XRBs and AGN show different accretion rate and power-law index distributions, with the latter in particular being broader and softer in XRBs. Remarkably, once similarly broad photon index and accretion rate distributions are selected, the AGN sample overlaps nicely with XRBs observations in the mass-normalised log Ldisc - log Lcorona plane, with a scatter of ~0.30-0.33 dex in both cases. This indicates that a mass-scaling of properties might hold after all, with our results being consistent with the disc-corona systems in AGNs and XRBs exhibiting the same physical processes, albeit under different conditions for instance in terms of temperature, optical depth and/or electron energy distribution in the corona, heating-cooling balance, coronal geometry and/or black hole spin.
27.05.2020
Radio Galaxies flavours: how accretion and environment can make the difference
In radio galaxies a correlation between accretion onto supermassive black hole and jet production is expected from both theoretical and obervational works. However, there is a population of radio galaxies that seems to break the classical accretion-ejection scheme. They are defined FRII-LERG and are characterized by strong jets (typical of FRII sources) up to hundreds of kpc, but inefficient accretion engine on pc-scales, testified by their NLR optical spectra. In order to understand their nature, in our work we analyzed all the FRII-LERG sources (19) belonging to the 3CR catalog with X-ray data available (both Chandra and XMM-Newton) with z<0.3. We then analyzed all classical FRII (32) from the same catalog classified both in radio and in optical band as a control sample. We compared X-ray results of FRII-LERG with classical FRII and also FRI, which data are taken from literature. Hence, we matched X-ray analysis with radio and optical data available in literature for all three populations. From our work two scenarios are the most plausible to explain FRII-LERG nature: they could be evolved FRII or they could be a distinct class of sources, inhabiting intermediate environments. Surprisingly, in the latter direction we found a general anti-correlation between accretion rate (measured both from optical and X-ray band) and extra-galactic environment.
