arXiv subjects

Paul Baki

Publications and source records attributed to Paul Baki.

5 recordsLinked to original sources

arXiv2026

Synchrotron filaments in radio galaxies: rarity, stability, and environmental influences from LOFAR and ROSAT observations

We present a systematic investigation of filamentary synchrotron structures in radio galaxies, using deep 144 MHz observations from the LOFAR Two-Metre Sky Survey (LoTSS) in combination with archival ROSAT X-ray data. These narrow, collimated features, linking radio lobes and often aligned with jet axes, are rare: our visual inspection of 548 cluster-associated sources identified 12 candidates (~2.2%), of which three exhibit clearly resolved filaments suitable for detailed X-ray and synchrotron minimum pressure analysis. Minimum pressures in these filaments are consistently lower than the ambient thermal pressure derived from X-ray measurements. This disparity implies a role for external confinement in filament stability, aligning with theoretical predictions of thermal pressure support and potentially toroidal magnetic field configurations. We discuss filament formation scenarios, including relic AGN outflows, magnetic draping, and plasma instabilities. Our findings highlight the utility of filamentary structures as probes of intracluster magnetic field topology and AGN feedback, and demonstrate the need for high-resolution, multi-frequency studies to constrain their origin and evolution.

astro-ph.GA↗

arXiv2026

Determination of kinematic distances of WISE & SMGPS H II regions in the Galactic plane using SEDIGISM cloud association

One of the fundamental requirements for studying and understanding Galactic structure and massive star formation is accurate distances to H II regions. However, most distance assignments are hampered by kinematic distance ambiguity (KDA), sparse parallax measurements, and the large number of radio continuum sources lacking velocity and distance measurements. We present a kinematic distance determination method via cloud association, linking H II regions from the Wide-field Infrared Survey Explorer (WISE) catalogue and the South African Radio Astronomy Observatory (SARAO) MeerKAT Galactic Plane Survey (SMGPS) with molecular clouds from the Structure, Excitation and Dynamics of the Inner Galactic Interstellar Medium (SEDIGISM) 13CO (2-1) survey. The associations are established through spatial overlap and velocity coherence, and the molecular cloud velocity and distance are then assigned to the associated H II region. The method yields 741 H II regions with adopted CO-based systemic velocities, of which 640 have reliable kinematic distances based on the SEDIGISM distance reliability criteria. We validate the method using 329 H II regions with independent radio recombination line (RRL) velocities, finding excellent agreement with a median absolute velocity difference of 3.46km/s. Our analysis resolves ambiguous velocities for 40 H II regions with multiple WISE RRL velocity measurements. Compared to the unassociated clouds, the associated molecular clouds exhibit significantly higher masses, gas surface densities, linewidths, star formation efficiencies and dense gas fractions, and slightly lower virial parameters. This work provides a large, homogeneously-derived catalogue of H II region distances and establishes a framework for further studying massive star formation and Galactic structure in general.

astro-ph.GA↗

arXiv2024

Gas flows in the central region of the Seyfert galaxy NGC 4593 with MUSE

Understanding how gas flows into galactic centres, fuels the AGN, and is in turn expelled back through feedback processes is of great importance to appreciate the role AGN play in the growth and evolution of galaxies. We use the MUSE-AO optical spectra of the inner 7".5x 7".5 of the nearby Seyfert 1 galaxy NGC 4593 to characterise its ionised gas kinematics. We fit single-Gaussian components to the [O iii]$λ$ 5007 and [N ii]$λ$ 6583 emission lines, and double-Gaussian components to H$α$ and H$β$ to determine the main ionisation mechanism of the gas. To determine the kinematics of the ionised gas, we fit double-Gaussian components to the [O iii]$λ$ 5007 line. Based on the stellar kinematic maps, we confirm the presence of a rotating disc. For the ionised gas, we find high-velocity dispersion values of up to $\mathrm{200-250\,km\,s^{-1}}$ that show that part of the gas is highly perturbed. The dominant ionisation mechanism of the gas is AGN photoionisation, which reaches the highest values within the innermost 4arcsec (680pc) diameter of the galaxy. At larger radii, the emission line ratios correspond to values in the composite region of the BPT diagram. The broad-component of [O iii]$λ$ 5007 shows blue-shifted velocities on the east side of the central 2arcsec (340pc), which spatially coincide with a region of high velocity-dispersion. This confirms the presence of outflowing gas. We estimate a mass outflow rate and kinetic power of ${\dot{M}}\geq {0.048 \,M_\odot\,{{\rm yr}^{-1}} }$ and ${\dot{E}_{\text{kin}}} \geq 4.09 \times 10^{39} \, \text{erg} \, \text{s}^{-1}$. The derived mass outflow rate is consistent with that expected from empirical relations between mass outflow rate and AGN luminosity for a low-luminosity AGN such as NGC 4593.

astro-ph.GA↗

arXiv2023

Successful Kinetic Impact into an Asteroid for Planetary Defense

While no known asteroid poses a threat to Earth for at least the next century, the catalog of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid. A test of kinetic impact technology was identified as the highest priority space mission related to asteroid mitigation. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by DART's impact. While past missions have utilized impactors to investigate the properties of small bodies those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in Dimorphos's orbit demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.

astro-ph.EP↗

arXiv2018

Development in Astronomy and Space Science in Africa

The development of astronomy and space science in Africa has grown significantly over the past few years. These advancements make the United Nations Sustainable Development Goals more achievable, and open up the possibility of new beneficial collaborations.

astro-ph.IM↗