Gas flows are an important aspect of feedback and the regulation of star formation in galaxies. Nearby starburst galaxies and luminous infrared galaxies (LIRGs) provide extreme environments, where feedback and the changes due to it can be studied in great detail. Understanding the gas flows in these galaxies will help us to understand galaxy evolution better. I will present the results from my recently completed PhD thesis. We studied the resolved gas flows in a sample of 12 nearby (0.0073 ≤ z ≤ 0.0374) starburst galaxies and luminous infrared galaxies in the SUperNovae and starBurst in the InfraReD (SUNBIRD) survey with long-slit spectra from the Southern African Large Telescope. We found evidence of ionized and neutral non-circular gas flows (which includes outflows, inflows and extraplanar gas) in all 12 galaxies at varying velocities. No previous measurements of gas flows had been made for five galaxies (ESO 428-G023, ESO 550-IG025, IRAS 18293-3413, NGC 1819 and NGC 3508). The non-circular gas flow velocities of the 12 galaxies range between 35-182 km/s for the ionized gas and 61-403 km/s for the neutral gas and originate from the nucleus for most of the galaxies. Our results also showed that none of the gas flows are strong enough to leave the galaxies and could possibly cool down to form more stars. This suggests that for these starburst galaxies and LIRGs, even though their star-formation rate is enhanced and gas is flowing outwards, star formation is not necessarily quenched by this, and could continue in the future via the galactic fountain model.

The formation and evolution of the ultra-diffuse galaxies (UDGs) continue to remain a puzzle. Similarities and differences in the morphological and the kinematical properties of the UDGs with their possible precursors, namely low-surface brightness (LSB), L*-type high-surface brightness (HSB) and dwarf galaxies, may provide crucial constraints on their origin and evolution. To investigate the possible formation scenario of the UDGs, we selected samples of UDGs, LSBs, HSBs and dwarfs from the TNG50-1 sub-box of the IllustrisTNG simulation. We studied individual galaxy cutouts to evaluate the intrinsic shapes of their dark-matter (DM) and stellar components, orbital and kinematical properties related to their stellar velocity dispersion. Further, we constructed mock integral-field spectroscopic data using the SimSpin code to extract the stellar kinematic moment maps. We find that the isolated UDGs are prolate rotators similar to the dwarf population, while the tidally bound UDGs can exhibit both prolate- and oblate-rotating shapes. The DM and stellar velocity anisotropy properties of the UDGs suggest that they reside in a cored, dwarf-like halo and may be classified by early-type galaxies. Finally, the stellar kinematic properties suggest that both the UDGs and the dwarfs are slow-rotators having low to nearly no-rotations in contrast to the late-type, disc-dominated, fast-rotating LSBs and HSBs. Therefore, we may conclude that the UDGs and the dwarfs possibly have a common dynamical lineage.

Isolated stellar-mass black holes traversing dense regions of the interstellar medium, such as molecular clouds, are expected to accrete ambient gas. This accretion process can ionize surrounding gas, carving out a low-density ionized cavity within the cloud. The accreting black holes may also possess accretion discs and jets, producing cosmic rays and triggering hadronic and leptonic interactions. In this work, we show that the number of black holes residing in molecular clouds is proportional to the size of the cloud and we estimate the specific black-hole number density to be $\sim 1.2 \times 10 ^{-5}$ per solar mass of cloud, i.e., at least 10 black holes in massive molecular clouds with mass $8.4 \times 10^5$ solar mass. We then estimate the accretion process by Bondi–Hoyle–Lyttleton accretion and the effects brought about on the cloud structures, such as the formation of ionization cavities, and on the production of energetic particles. We show that the accretion rate log($\dot{M}$) [g/s] can reach up to 18 and the ionization cavity can reach up to 1 pc, occupying a substantial region of smaller molecular clouds. We discuss the consequences of the presence of ionization cavities in molecular clouds of different sizes, hence the implications for (i) cloud fragmentation and star formation and (ii) the inhomogeneity in the cloud environment for cosmic-ray transport in molecular clouds.

Many galaxies show strong star formation activity in their central regions. In galaxies that also host an active galactic nucleus (AGN), star formation may occur locally within the AGN accretion disk itself. Low-mass stars constitute the majority of the stellar population, and as they reach the end of their life cycles, they evolve into white dwarfs. We therefore expect to find a population of white dwarfs embedded in and comoving with the AGN accretion disk. The disk provides a dense environment in which white dwarfs can efficiently accrete gas and grow in mass. As their mass approaches the Chandrasekhar limit of 1.4 solar masses, the temperature becomes high enough to trigger runaway nuclear fusion, eventually leading to a Type Ia supernova. Type Ia supernovae are crucial both as standard candles for cosmology and as major contributors to the chemical enrichment of the universe. In this work, we investigate the population of white dwarfs in AGN disks, their mass growth through accretion, and their eventual collapse into Type Ia supernovae. We show that the accretion of white dwarfs in AGN disks is a viable channel for producing type 1a supernovae. We discuss the resulting consequences for the evolution of the AGN and its accretion disk, the chemical enrichment of galactic centers, and the universality of Type Ia supernovae as standard candles.

The quasar Eigenvector-1/Main Sequence (E1/MS) is a practical roadmap that organizes AGN spectral diversity by accretion state, letting us compare objects in a common, physically motivated trend. Past applications of the E1/MS sequence made it possible to identify the effects of intrinsic viewing angle, black hole mass, and luminosity. We propose an E1/MS-driven framework to clarify the accretion status of gamma-ray-emitting AGN with an emphasis on radio-loud narrow-line Seyfert 1s (NLSy1s) and ​Population A sources. We argue that the E1/MS context is ideal for flagging super-Eddington candidates among radio-loud NLSy1s and other Population A sources that also host relativistic jets. An optimal strategy would be to place gamma-ray AGN on E1 using optical/UV spectroscopy, to derive disk-based bolometric luminosities from line or IR reprocessing (or jet-quiet SED states), and to correct single-epoch black hole masses for orientation and radiation pressure biases. This strategy should identify super-Eddington candidates and reflect a physical link between accretion state and gamma-ray efficiency: dense broad-line region/torus photon fields in high-Eddington-ratio systems should boost the external Compton emission, whereas mass loading and radiative drag shape moderate bulk Lorentz factors in gamma-ray emitters observed with VLBI. We apply the method based on the E1/MS criteria to targets for which high-S/N optical and UV spectra as well as multi-frequency coverage are available.

Narrow-Line Seyfert 1 (NLS1) galaxies exhibit narrow permitted Hβ lines (FWHM < 2000 km/s) and strong Fe II multiplets with low black hole (BH) masses (< 10⁸M⊙) and high Eddington ratios. The BH masses and predominantly disk-like hosts suggest that NLS1s are early-stage Active Galactic Nuclei (AGN). They host the lowest-mass super-massive BHs that can launch relativistic jets and offer insights into the conditions necessary for jet formation. Available optical spectral catalogues have low S/N ratios, and classifying NLS1s using them is challenging. Using FORS2 observations of ~100 candidate NLS1s, we aim to classify the sources and perform detailed spectral modelling of Hβ, [OIII], and the Fe II pseudo-continuum using Gaussian, Lorentzian and Voigt profiles. Based on preliminary results, we found 16 changing-look AGN and a contamination fraction of ~28% in our data. We study how, in NLS1s, the broad Hβ line profile transitions from a Lorentzian to a Keplerian motion-dominated Gaussian with increasing BH mass, to determine whether this change is an essential part of intraclass evolution. By modelling the lines with Voigt profiles, we test whether the sources previously best described by Lorentzian or Gaussian functions are dominated by the turbulent or Keplerian component, respectively. In this talk, I will present the spectral analysis of NLS1s and changing-look AGN and discuss our findings and future plans.

Narrow-line Seyfert 1 galaxies (NLS1s) are a class of active galactic nuclei (AGN) and were long believed to be radio-silent and incapable of producing relativistic jets; however, recent studies have demonstrated otherwise. The Fermi Large Area Telescope (LAT) made a groundbreaking discovery by detecting gamma-ray emission from the NLS1 source PMN J0948+0022, providing clear evidence that some of these sources can host relativistic jets in this class of AGN. This challenged the idea we had of NLS1s and their diversity.

Over the years, many new sources have been discovered, and my researchers have focused on analyzing these findings by systematically searching for additional gamma-ray-emitting NLS1s using data from the Fermi-LAT. For this, a series of analyses are run to evaluate the test statistic (TS) value, which provides a measure of the significance of potential detection.

This poster will present an overview of narrow-line Seyfert 1 galaxies (NLS1s), the methodology applied in this study, relevant previous findings, the analysis procedure, and the automation of code used to conduct the analysis. Current results will be discussed, highlighting the test statistic (TS) values obtained thus far. As this project represents ongoing research, additional TS values will be identified over time, culminating in a more comprehensive analysis.

Cosmic rays (CRs) are accelerated in astrophysical systems, such as starburst galaxies, active galactic nuclei and large-scale shocks. These accelerators are usually embedded in the overdense part of the cosmic web, i.e., galaxy clusters and filaments, which are threaded with magnetic fields. Many studies only model the the transport of charged particles in magnetic fields and ignore the secondary neutrons. We explored an alternative route for CR escape—assisted by temporary charge neutral particles, i.e., neutrons. These neutrons are produced in the hadronic interactions of CR protons, and with the aid of time dilation, they may traverse distances larger than galactic scales before decaying into protons. We capture this alternative CR escape channel with a stochastic Poisson term in the transport equation, which also accounts for other processes that attenuate CR flux. We model the CR escape with the neutron-assisted channel for several test cases, representing host sites being a galaxy, galaxy cluster, and filament. We find that the neutron-assisted escape channel is most efficient for ultra-high-energy cosmic rays (E >~ 1e18 eV) and may modify the energy spectrum of CRs at the highest energies. I will present our methodology for modelling CR escape and highlight the importance of incorporating the physics of neutron-assisted CR escape.

The ultra-relativistic, highly collimated jets generated by Gamma-Ray Bursts (GRBs) provide crucial insights into particle emission. These jets also reveal the physical mechanisms driving the rapid release of high-energy gamma-ray photons. We discuss time-resolved spectroscopy and flux variability for the ultra-long GRB 220627A. The analysis spans a duration exceeding 1200 seconds using Fermi telescope data. Two prompt emission episodes observed by Fermi-GBM, separated by more than 500 s, were analyzed. Due to its unique characteristics, GRB 220627A serves as an excellent source for studying particle emission processes, small-scale variability, and the properties of its central engine. To investigate gravitational lensing, the time bins of the first episode were correlated with those of the second episode. A coherent relationship was observed between flux and photon spectral distribution. This relationship was modeled using an exponentially cut-off power law model for both episodes. The MeV-to-GeV photon ratio detected by LAT is inconsistent between the two episodes. High-energy gamma-ray photons were only detected by LAT for up to 700 seconds, which further rules out gravitational lensing but suggests that the progenitor underwent a burst into an ultra-long GRB with two episodes. Our findings from spectral analysis reveal characteristics most consistent with those of an ultra-long GRB. Parameters such as isotropic energy, spectral signatures, and burst duration align with the established limits for a blue supergiant progenitor, as described in the literature.

Our understanding of jet kinematics in high-redshift (z≥3) quasars is still rather limited, based on a sample of less than about fifty objects. It is difficult to perform such measurements for multiple reasons. In this work, we present very long baseline interferometry (VLBI) observations of the surprisingly rich radio jet structure of the powerful blazar J1429+5406 at z=3.015, observed at five different frequencies (1.7–15 GHz) between 1994 and 2018. While the outer jet components at ∼20–40 milliarcsecond (mas) angular separation from the core show no apparent proper motion, three components within 10 mas distance exhibit significant proper motions of (0.045–0.16) mas year^‑1, including one that is among the fastest-moving jet components at z≥3 known to date. The core brightness temperature well exceeds the equipartition limit, indicating Doppler-boosted radio emission. Based on the proper motion of the innermost component, we derive a small jet inclination with respect to the line of sight (within about 5°), confirming the blazar nature of the source. Recently, we analysed new high-sensitivity VLBI measurements of this blazar taken by the Very Long Baseline Array in 2024. At 1.5 GHz, the radio map clearly reveals a complex, extended structure around the source, reaching up to ~400 mas, rarely, if ever, seen in a high-redshift blazar. Here, we discuss possible explanations of this peculiar radio structure.