Best oral presentation：Daryl Santos

Title: Environmental Effects on AGN Activities via Extinction-free Mid-Infrared Census

Abstract:

This study focused on unveiling the relationship between star formation/active galactic nucleus (SF/AGN) activity and environment of galaxies with mid-infrared (MIR) and far-infrared (FIR) detections in the AKARI North Ecliptic Pole Wide (NEPW) field in the redshift range 0 < z < 1.5. The AKARI satellite, compared to other infrared (IR) telescopes (e.g., WISE and Spitzer), has the unique continuous 9-band filter coverage that provides more detailed photometry, thus allowing us to better characterize features that appear in the MIR. We constrained the properties of the selected galaxies using CIGALE, a spectral energy distribution (SED) fitting code. We also defined several parameters to describe the galactic environments of our sample: local galaxy density, clustercentric distance, and cluster-field galaxy classification. The AGN contribution fraction (ratio between the AGN luminosity and total IR luminosity) and the AGN number fraction (ratio of the number of AGNs over the total number of galaxies) were used as probes of AGN activity in this study. The specific star formation rates of the sample galaxies were also investigated. Both definitions of AGN activity showed consistent trends: AGN and star-formation activities decrease with denser environments only for ultra-luminous infrared galaxies (ULIRGs). This suggests that the environmental effect on quenching galactic activities is more effective in ULIRGs than less luminous galaxies. We present our current progress and possible physical explanations for our results.

Poster: https://ras.ac.uk/poster-contest/daryl-joe-d-santos

 

 

First runner up oral presentation：Y. X. Jane Yap

Title: High energy emission mechanism in blazar

Abstract:

This talk will focus on the high-energy emission mechanism of blazar, in which both the leptonic and hadronic model will be discussed. Traditionally, the one-zone leptonic synchrotron-self-Compton (SSC) is used to explain the high energy emission of blazar. On the other hand, the hadronic process receives less attention due to the complication in simulating the energy dependence of the cross section. The increased number of blazar spectrums poses a question about the origin of the high-energy emission since both models are able to reproduce most of the observations. We will discuss the radiation processes and their signatures in each model, for instance, synchrotron and SSC in the leptonic, and in the hadronic, proton-synchrotron, photo-pion process with different radiation fields, as well as gamma-ray induced pair cascades.

 

Best poster：Bo-Yan Chen

Title: Testing the existence of linear black hole mass − τ relation for LLAGN

Abstract: 

A big question for Active Galactic Nuclei (AGN) is whether there is a relation between the accretion and the mass scale of the center black hole, the emission coming from the accretion disk, the outflow and jet cross all the electromagnetic spectrum, therefore the flux variability provide a good probe to investigate the accretion and outflow physics. Previous studies found that there is a relation between power spectrum break time scale and black hole mass and luminosity in X-ray and NIR variability (McHardy et al. 2006 & Meyer et al.2009). In Submillimeter wavelength (230 GHz), Dexter et al. 2014 revealed a characteristic time scale of Sgr A* about 8 hours, which is consistent with the viscous time scale. Bower et al. 2015 investigated 413 sources in SMA calibrator list including different type of AGN and found that there seem to be a linear relationship between black hole mass and τ for low luminosity AGN (LLAGN). To exam this linear relationship for LLAGN, we monitored the light curve of six LLAGNs. For Cen A, combine the SMA calibrator list with our observation, we have the light curve spanned about 13 years. The observation spanned 40 month for M84, NGC4278, NGC4579. We also have the light curve for NGC4552 and NGC4579 which spanned about 12 month. We present the preliminary result of these light curve and the analysis of the characteristic time scale.