Tayyaba Zafar

Context . Face-on spiral galaxies offer a favorable geometry for studying magnetic-field structures and their impact on cosmic-ray propagation, as projection effects and structural overlap are significantly reduced. Aims . We aim to investigate the transport of cosmic-ray electrons (CREs) in the nearby face-on spiral galaxy NGC 2442 and assess how the galactic environment and magnetic-field structure influence their propagation. Methods . We combined radio continuum (RC) observations from ASKAP at 943 MHz, MeerKAT at 1.28 and 1.7 GHz, and ATCA at 5 GHz with optical H α and infrared data to characterize the galactic environment. We then compared these observations with 2D CRE transport simulations to evaluate the role of the magnetic field and the surrounding environment in shaping CRE propagation. Results . NGC 2442 exhibits an integrated RC spectrum that is steeper than those of most nearby galaxies, with spectral indices of α = −0.96 ± 0.04 for the total emission and α _nt = −1.21 ± 0.04 for the synchrotron emission over 408 MHz–5 GHz. The spectrum shows a break near 1 GHz, indicating substantial radiative aging of the CRE population. Under the equipartition assumption, we derive a mean magnetic-field strength of 10.8 µG. The RC–star formation rate smoothing analysis indicates effective CRE propagation lengths of ∼0.65–0.89 kpc at 943–1700 MHz and ∼0.44 kpc at 5 GHz, corresponding to effective diffusion coefficients on the order of 10 ²⁸ cm ² s ⁻¹ . We identify a steep-spectrum synchrotron “island” in the southeastern region, with an average synchrotron spectral index of α ∼ −1.09 and no clear H α , infrared, far-ultraviolet or near-ultraviolet counterpart, indicating that the CREs are unlikely to be injected in situ. Our 2D simulations using CRPropa show that anisotropic diffusion along ordered magnetic fields allows CREs to reach the island region much more efficiently than isotropic diffusion. Conclusions . NGC 2442 provides evidence that the combined effects of environmental disturbances and ordered magnetic fields can strongly regulate CRE propagation in disturbed spiral galaxies.

Context. X-ray flashes (XRFs) are a type of gamma-ray burst (GRB) with prompt emission predominantly below ∼30 keV and have been poorly detected by previous missions monitoring the high-energy sky. The advent of the Space-based multiband astronomical Variable Objects Monitor (SVOM), with its wide-field instrument ECLAIRs, provides a new way to detect soft X-ray transients such as XRFs, complemented by rapid onboard multiwavelength follow-up. Aims. We present photometric and spectroscopic observations of XRF 241001A detected by SVOM, a soft, subluminous, and low-energetic burst located in a poorly populated region of the Amati relation. We investigated the origin of its faint, soft high-energy emission to assess its connection to the long GRB population. Methods. We analyzed the SVOM/ECLAIRs prompt emission and modeled its afterglow emission from X-ray-to-radio. We present JWST /NIRSpec and SVOM/VT observations of the associated supernova (SN 2024aiiq), which we modeled with an Arnett radioactive decay component, and we compared its properties with previously detected GRB/SNe. Results. The event XRF 241001A is located at z = 0.573 and has a prompt emission dominated by photons below 20 keV, with a duration of T ₉₀ = 3.14 seconds. Its spectrum is consistent with both thermal and nonthermal models, each implying a low E _peak < 10 keV and E _iso ∼ 8 × 10 ⁴⁹ erg. The X-ray-to-radio afterglow modeling favors an origin from a relativistic jet viewed on-axis and supports a nonthermal origin of the prompt emission. In the optical, XRF 241001A exhibits an early blue emission, similar to that detected in some extragalactic fast X-ray transients (eFXTs) and inconsistent with the expected synchrotron emission from a relativistic jet. The JWST /NIRSpec observations firmly established its collapsar origin by revealing an SN Type Ic with broad lines, comparable to SN 1998bw and SN 2025kg-like events near maximum light and with similar properties. Conclusions. The event XRF 241001A is a soft low-luminosity collapsar event produced by a weak relativistic jet observed on-axis, supporting the view that at least part of the XRF population forms the low-energy soft tail of the long GRB population. Its observation demonstrates the potential of SVOM/ECLAIRs to probe the soft regime of the high-energy transient population that remains largely unexplored.

Brown dwarfs are unique laboratories for studying the physics of cool atmospheres, the low-mass end of star formation, and the transition between stars and giant planets. Their spectra encode the effects of temperature, gravity, metallicity, clouds, and disequilibrium chemistry, but identifying and characterizing the coldest brown dwarfs remains challenging, particularly at faint magnitudes in deep extragalactic surveys. We aim to establish the nature and atmospheric properties of COSMOS2025 ID 639188, hereafter Shabgard, a compact source previously selected as a brown-dwarf candidate from COSMOS-Web photometry on the basis of its point-source morphology and T/Y-dwarf-like NIRCam colors. In this work, we characterize this source using serendipitous JWST/NIRCam F444W wide-field slitless spectroscopy from COSMOS-3D. We extract its local-background-subtracted, profile-weighted 4.05–4.85 μ m spectrum, combine it with COSMOS2025 NIRCam photometry, compare the data with six atmosphere-model families, and measure its motion using multi-epoch NIRCam imaging. The LOWZ atmosphere-grid fit, based on principal component analysis (PCA) interpolation and Markov Chain Monte Carlo (MCMC) sampling, gives T eff = 718 . 6 − 10.2 + 10.6 K and [ M / H ] = − 1.0 0 − 0.08 + 0.07 , favoring a cool, subsolar-metallicity atmosphere characteristic of the late-T/Y transition. A fixed-atmosphere molecular-opacity test strongly favors a contribution from CH ₄ to the observed 4–5 μ m spectral shape. The restricted wavelength coverage, however, prevents a molecule-by-molecule abundance determination. Model-dependent physical estimates span approximately 23–52 M _Jup and 140–180 pc. We measure a proper motion of ∣ μ ∣ = 89.2 ± 0.4 mas yr ⁻¹ , while the LOWZ MCMC flux scaling gives a distance of 176 . 2 − 17.8 + 18.4 pc, supporting the interpretation of Shabgard as a Galactic brown dwarf. Together, these results support its classification as a cool, metal-poor brown dwarf and demonstrate the ability of JWST deep-field surveys to discover and characterize faint Galactic substellar objects.

Context . The evolution of galaxies from cosmic noon to the present day provides a key window through which to probe the balance between early, rapid bulge formation and prolonged disk growth. In this context, the epoch at z ~ 0.3 (intermediate redshift) marks a crucial transitional phase between the peak of cosmic star formation and the predominantly quiescent local Universe, where these processes can be directly observed. Aims . In this work, we examine the spatially resolved stellar populations of 34 galaxies at z ~ 0.3 to quantify radial gradients in age, stellar metallicity, and star formation activity, and disentangle the distinct evolutionary pathways of inner and outer galactic components. Methods . We utilised MUSE integral-field spectroscopy data cubes from the MAGPI survey at redshifts of 0.28 < z < 0.35. Stellar population properties were derived using the spectral synthesis codes FADO and Starlight , and radial profiles were constructed by fitting isophotal annuli to the galaxy continuum emission, thereby preserving galaxy morphology and enabling the separation between components. We further reconstructed star formation histories and cumulative mass assembly curves for inner and outer regions. Results . We find pronounced negative radial gradients in age and negative to flat gradients in stellar metallicity. Inner regions are systematically older and more metal-rich than their surrounding outskirts, with age differences of up to 3–4 Gyr in the most massive systems. H α equivalent width profiles reveal centrally suppressed specific star formation in most galaxies, consistent with inside-out quenching. Star formation histories and mass assembly curves demonstrate that galaxy cores formed 80% of their stellar mass rapidly, within the first 2–3 Gyr of cosmic time; while areas outside 1 R _eff assembled more gradually and sustained star formation to later epochs. These findings support a scenario in which early dissipative processes and mergers dominate inner formation. At the same time, outskirts evolve primarily through extended, secular star formation, establishing the centrally concentrated quenching and inside-out growth that link high-redshift systems to the quiescent galaxies of the local Universe.

We report the detection of a clumpy, blue-dominated Lyman- α (Ly α ) emission at z = 3.066 located in the heart of a cosmic web filament in the MUSE eXtremely Deep Field (MXDF). It is spatially associated with the formation of two compact star-forming regions revealed by deep JWST/NIRCam imaging. Gas accretion in these regions is indicated by the blue-dominated Ly α profiles, spectral signatures that are rarely observed. Radiative transfer simulations of the Ly α profile using a clumpy multiphase model suggest a radial inflow of gas clumps with a velocity of ∼100 km/s. Embedded in this Ly α structure, the associated main galaxy dominates the stellar mass budget, while the two compact ultra-low-mass systems (log( M _★ / M _⊙ ) = 6.3 − 6.9) have formed the bulk of their stellar mass in less than 7 Myr. These two components also have high specific star-formation rates and elevated ionisation parameters, consistent with recent bursty star formation. This system provides compelling observational evidence of how gas accretion, most likely from the cosmic web, can induce starbursts in ultra-low-mass galaxies.

Context . The supernova remnant (SNR) candidate G310.7-5.4 was identified as a faint shell in the MGPS-2 survey. We followed up on it with multi-wavelength observations, confirming it to be an SNR at a high Galactic latitude that shows spatially coinciding γ -ray emission. Aims . We conducted the first detailed investigation of the radio emission from the G310.7-5.4 region, aiming to characterise the radio structure, polarisation measurements, and the coinciding GeV emission. Methods . We used recent radio continuum observations at 943.5 MHz from the EMU and POSSUM surveys with ASKAP, as well as 16.5 years of Fermi -LAT observations. We furthermore considered the multi-wavelength context of the object by investigating observations previously conducted with other instruments, such as IR and X-ray surveys. Results . We confirm that G310.7-5.4 is indeed an SNR, which we have dubbed Abeona. We detect the presence of a faint, extended (30′ diameter) bilateral radio shell with an ASKAP radio flux density of 1.5 _−0.1 ^+1.5 Jy with no obvious IR counterparts. With a radio surface brightness of about 2.4 _−0.1 ^+2.4 × 10 ⁻²² W m ⁻² Hz ⁻¹ sr ⁻¹ , it is one of the faintest radio SNRs known. The northern part of the shell shows linearly polarised radio emission, which is characteristic of synchrotron emission in SNRs. The physical size of the SNR is estimated to be around 42 ₋₂₁ ⁺⁴² pc, which would correspond to a distance of around 4.9 _−2.5 ^+4.9 kpc. Furthermore, the spatially coincident γ -ray source 4FGL J1413.9-6705 shows an energy flux of (1.26 ± 0.35) × 10 ⁻⁶ MeV cm ⁻² s ⁻¹ with a significance of 5.7 σ between 100 MeV and 100 GeV. We placed Abeona in context with other known high-latitude SNRs with γ -ray counterparts and compared their observational properties. Conclusions . New radio surveys are discovering a population of faint high-Galactic-latitude SNRs with GeV counterparts in isolated environments. More sensitive observations with the CTAO in the next few years should provide valuable insights into particle acceleration and escape in these important cosmic ray accelerators.

The stellar initial mass function (IMF) is a fundamental ingredient in galaxy evolution, linking observed integrated light to stellar masses, star-formation rates, and chemical enrichment histories. Constraining the full IMF shape beyond the Milky Way remains challenging, as most studies focus either on the low-mass end of quiescent galaxies or the high-mass end of star-forming galaxies. Here we present the first simultaneous analysis of both ends of the stellar initial mass function (IMF) in 214 star-forming galaxies from the Hector survey (z ∼ 0.01–0.07). We estimate the low-mass end slope ( α _low ) using a stellar population approach that fits IMF-sensitive absorption features with extended star formation histories, while the high-mass end slope ( α _high ) is derived via the Kennicutt diagnostic, which compares the observed H α equivalent width and g – r colour with stellar population synthesis models. We find substantial diversity in IMF shapes, with galaxies spanning combinations of bottom-heavy/light and top-heavy/light slopes. A weak but statistically robust correlation between the low- and high-mass IMF slopes is observed, but partial correlation analysis indicates that this apparent link is largely driven by their mutual dependence on stellar mass and metallicity. Both IMF slopes show significant correlations with stellar mass, star formation activity (traced by H α luminosity and surface density), and stellar metallicity ([M/H]). In general, higher stellar mass, stronger star formation activity, and higher metallicity are associated with both bottom-heavy and top-heavy IMFs. We find that the full IMF shape seems to be modulated by total stellar mass. Partial correlation analysis reveals that α _low is primarily driven by [M/H], whereas α _high is mainly linked to stellar mass and recent star formation. Because α _low traces the IMF over long-term averages and α _high captures only recent (≲ 10 Myr) star formation, the processes shaping each end likely occur over different and possibly decoupled timescales. Our findings challenge the universality of the IMF and emphasise the need for galaxy evolution and stellar population models to incorporate a flexible IMF prescription. Accounting for these variations is essential to build an IMF-consistent picture of galaxy evolution across cosmic time.