arXiv subjects

Maya Merhi

Publications and source records attributed to Maya Merhi.

3 recordsLinked to original sources

arXiv2022

Forming Stars in a Dual AGN Host: Molecular and Ionized Gas in the Nearby, Luminous Infrared Merger, Mrk 266

We present star formation rates based on cold and ionized gas measurements of Mrk 266 (NGC 5256), a system composed of two colliding gas-rich galaxies, each hosting an active galactic nucleus. Using $^{12}$CO (1-0) observations with the Combined Array for Research in Millimeter-Wave Astronomy (CARMA), we find a total H$_2$ mass in the central region of $1.1\pm0.3\times10^{10}$ $M_\odot$ which leads to a possible future star formation rate of $25\pm10 M_\odot$ yr$^{-1}$. With the Fourier Transform Spectrograph (SITELLE) on the Canada-France-Hawaii Telescope, we measure an integrated H$\alpha$ luminosity and estimate a present-day star formation rate of $15\pm2 M_\odot$ yr$^{-1}$ in the core of the system (avoiding the two active nuclei). These results confirm that Mrk 266 is an intermediate stage merger with a relatively high recent star formation rate and enough molecular gas to sustain it for a few hundred million years. Inflowing gas associated with the merger may have triggered both the starburst episode and two AGN but the two galaxy components differ: the region around the SW nucleus appears to be more active than the NE nucleus, which seems relatively quiet. We speculate that this difference may originate in the properties of the interstellar medium in the two systems.

astro-ph.GA↗

arXiv2021

Information Operations in Turkey: Manufacturing Resilience with Free Twitter Accounts

Following the 2016 US elections Twitter launched their Information Operations (IO) hub where they archive account activity connected to state linked information operations. In June 2020, Twitter took down and released a set of accounts linked to Turkey's ruling political party (AKP). We investigate these accounts in the aftermath of the takedown to explore whether AKP-linked operations are ongoing and to understand the strategies they use to remain resilient to disruption. We collect live accounts that appear to be part of the same network, ~30% of which have been suspended by Twitter since our collection. We create a BERT-based classifier that shows similarity between these two networks, develop a taxonomy to categorize these accounts, find direct sequel accounts between the Turkish takedown and the live accounts, and find evidence that Turkish IO actors deliberately construct their network to withstand large-scale shutdown by utilizing explicit and implicit signals of coordination. We compare our findings from the Turkish operation to Russian and Chinese IO on Twitter and find that Turkey's IO utilizes a unique group structure to remain resilient. Our work highlights the fundamental imbalance between IO actors quickly and easily creating free accounts and the social media platforms spending significant resources on detection and removal, and contributes novel findings about Turkish IO on Twitter.

cs.SI↗

arXiv2020

Molecular Gas Heating and Modified Dust Properties in Active Galaxies: Growing Black Holes or Tidal Shocks?

We investigate if and how growing super-massive black holes (SMBH) known as Active Galactic Nuclei (AGN) and gravitational interactions affect the warm molecular gas and dust of galaxies. Our analysis focuses on the morphologies and warm ISM properties of 630 galaxies at z < 0.1. We use grizy images from the Pan-STARRS survey to classify the galaxies into mergers, early mergers, and non-mergers. We use MIR spectroscopic measurements of emission from rotational H2 transitions, dust and PAH features, and silicate emission or absorption lines at 9.7 microns to study how gravitational interactions impact the warm ISM in AGN and non-AGN hosts. We find that in AGN-hosts, the ISM is warmer, the ratios of H2 to PAHs are larger, the PAH emission line ratios and silicate strengths have a wider range of values than in non-AGN hosts. We find some statistical differences between the H2 emission of mergers and non-mergers, but those differences are less statistically significant than those between AGN and non-AGN hosts.

astro-ph.GA↗