Ildar Khabibullin’s research while affiliated with Technical University of Munich and other places

Diffuse radio emission in galaxy clusters is a tracer of ultra-relativistic particles and μG-level magnetic fields, and is thought to be triggered by cluster merger events. In the distant Universe (i.e. z>0.6), such sources have been observed only in a handful of systems, and their study is important to understand the evolution of large-scale magnetic fields over the cosmic time. Previous studies of nine Planck clusters up to z∼0.9 suggest a fast amplification of cluster-scale magnetic fields, at least up to half of the current Universe's age, and steep spectrum cluster scale emission, in line with particle re-acceleration due to turbulence. In this paper, we investigate the presence of diffuse radio emission in a larger sample of galaxy clusters reaching even higher redshifts (i.e. z≳1). We selected clusters from the Massive and Distant Clusters of WISE Survey (MaDCoWS) with richness λ_ >40 covering the area of the second data release of the LOFAR Two-Meter Sky Survey (LoTSS-DR2) at 144 MHz. These selected clusters are in the redshift range $0.78-1.53$ (with a median value of 1.05). We detect the possible presence of diffuse radio emission, with the largest linear sizes of $350-500$ kpc, in five out of the 56 clusters in our sample. If this diffuse radio emission is due to a radio halo, these radio sources lie on or above the scatter of the P_ν-M_500 radio halo correlations (at 150 MHz and 1.4 GHz) found at z<0.6, depending on the mass assumed. We also find that these radio sources are at the limit of the detection by LoTSS, and therefore deeper observations are important for future studies.

Diffuse radio emission in galaxy clusters is a tracer of ultra-relativistic particles and $\mu$G-level magnetic fields, and is thought to be triggered by cluster merger events. In the distant Universe (i.e. $z>0.6$), such sources have been observed only in a handful of systems, and their study is important to understand the evolution of large-scale magnetic fields over the cosmic time. Previous studies of nine {\it Planck} clusters up to $z\sim0.9$ suggest a fast amplification of cluster-scale magnetic fields, at least up to half of the current Universe's age, and steep spectrum cluster scale emission, in line with particle re-acceleration due to turbulence. In this paper, we investigate the presence of diffuse radio emission in a larger sample of galaxy clusters reaching even higher redshifts (i.e. $z\gtrsim1$). We selected clusters from the Massive and Distant Clusters of {\it WISE} Survey (MaDCoWS) with richness $\lambda_{15}>40$ covering the area of the second data release of the LOFAR Two-Meter Sky Survey (LoTSS-DR2) at 144 MHz. These selected clusters are in the redshift range $0.78-1.53$ (with a median value of 1.05). We detect the possible presence of diffuse radio emission, with the largest linear sizes of $350-500$ kpc, in 5 out of the 56 clusters in our sample. If this diffuse radio emission is due to a radio halo, these radio sources lie on or above the scatter of the $P_\nu-M_{500}$ radio halo correlations (at 150 MHz and 1.4 GHz) found at $z<0.6$, depending on the mass assumed. We also find that these radio sources are at the limit of the detection by LoTSS, and therefore deeper observations will be important for future studies.

Nest200047 is a clear example of multiple radio bubbles from an Active Galactic Nucleus (AGN) in a galaxy group, featuring non-thermal filaments likely shaped by buoyancy, gas motions, and stabilized by magnetic fields. This study presents high-quality data obtained from uGMRT, MeerKAT, and VLA, alongside existing LOFAR data, to analyze the system's morphology and spectrum over a broad frequency range (53-1518 MHz). Our findings reveal new filamentary emission in the inner 60 kpc, surrounding and extending from the inner bubbles and jets, suggesting complex dynamical evolution of the non-thermal plasma in the group core. The filaments have widths of a few kpc and lengths from tens to hundreds of kpc, with a steep and curved radio spectrum ($\rm \alpha=1\sim2$). They exhibit a constant spectral index profile along their length, implying particles are either (re-)accelerated together or move at super-Alfvenic speeds. Spectral aging analysis yields jet active times between 50 and 100 Myr with short inactive phases, suggesting continuous energy injection typical of AGN feedback in galaxy groups. This study highlights the potential of combining high-quality radio data to understand recurrent jet activity and feedback, with implications for future research with the SKA observatory.

Superclusters are the most massive structures in the universe. To what degree they are actually bound against an accelerating expansion of the background is of significant cosmological and astrophysical interest. In this study, we introduce a cross matched set of superclusters from the SLOW constrained simulations of the local (z<0.05) universe. Identifying the superclusters provides estimates on the efficacy of the constraints in reproducing the local large-scale structure accurately. The simulated counterparts can help identifying possible future observational targets containing interesting features such as bridges between pre-merging and merging galaxy clusters and collapsing filaments and provide comparisons for current observations. By determining the collapse volumes for the superclusters we further elucidate the dynamics of cluster-cluster interactions in those regions. Using catalogs of local superclusters and the most massive simulated clusters, we search for counterparts of supercluster members of six regions. We evaluate the significance of these detections by comparing their geometries to supercluster regions in random simulations. We then run an N-body version of the simulation into the far future and determine which of the member clusters are gravitationally bound to the host superclusters. Furthermore we compute masses and density contrasts for the collapse regions. We demonstrate the SLOW simulation of the local universe to accurately reproduce local supercluster regions in mass of their members and three-dimensional geometrical arrangement. We furthermore find the bound regions of the local superclusters consistent in size and density contrast with previous theoretical studies. This will allow to connect future numerical zoom-in studies of the clusters to the large scale environments and specifically the supercluster environments these local galaxy clusters evolve in.

Massive clusters of galaxies are very rare in the observable Universe. Mergers of such clusters observed close to pericenter passage are even rarer. Here, we report on one such case: The massive ($\,M_ and hot ($kT keV $) cluster CL0238.3+2005 at$z = 0.42$. For this cluster, we combined X-ray data from SRG/eROSITA and Chandra optical images from DESI, and spectroscopy from the BTA and RTT-150 telescopes. The X-ray and optical morphologies suggest an ongoing merger with a projected separation of the subhalos of$ kpc $. We conclude that the merger axis is most likely neither close to the line of sight nor to the sky plane. We compare CL0238 with the two well-known clusters MACS0416 and the Bullet and conclude that CL0238 corresponds to an intermediate phase between the pre-merging MACS0416 cluster and the post-merger Bullet cluster. Namely, this cluster recently (only$ Gyr $ ago) experienced an almost head-on merger. We argue that this "just after" system is a very rare case and an excellent target for lensing, the Sunyaev-Zeldovich effect, and X-ray studies that can constrain properties ranging from dynamics of mergers to self-interacting dark matter, and plasma effects in the intracluster medium that are associated with shock waves, for instance, electron-ion equilibration efficiency and relativistic particle acceleration.

Aims. Detecting diffuse synchrotron emission from the cosmic web is still a challenge for current radio telescopes. We aim to make predictions about the detectability of cosmic web filaments from simulations. Methods. We present the first cosmological magnetohydrodynamic simulation of a 500 h ⁻¹ c Mpc volume with an on-the-fly spectral cosmic ray (CR) model. This allows us to follow the evolution of populations of CR electrons and protons within every resolution element of the simulation. We modeled CR injection at shocks, while accounting for adiabatic changes to the CR population and high-energy-loss processes of electrons. The synchrotron emission was then calculated from the aged electron population, using the simulated magnetic field, as well as different models for the origin and amplification of magnetic fields. We used constrained initial conditions, which closely resemble the local Universe, and compared the results of the cosmological volume to a zoom-in simulation of the Coma cluster, to study the impact of resolution and turbulent reacceleration of CRs on the results. Results. We find a consistent injection of CRs at accretion shocks onto cosmic web filaments and galaxy clusters. This leads to diffuse emission from filaments of the order S ν ≈ 0.1 μJy beam ⁻¹ for a potential LOFAR observation at 144 MHz, when assuming the most optimistic magnetic field model. The flux can be increased by up to two orders of magnitude for different choices of CR injection parameters. This can bring the flux within a factor of ten of the current limits for direct detection. We find a spectral index of the simulated synchrotron emission from filaments of α ≈ −1.0 to –1.5 in the LOFAR band.

We argue that the North Polar Spur (NPS) and many less prominent structures are formed by gaseous metal-rich plumes associated with star-forming regions (SFRs). The SFRs located at the tangent to the 3-5 kpc rings might be particularly relevant to the NPS. A multi-temperature mixture of gaseous components and cosmic rays rises above the Galactic disk under the action of their initial momentum and buoyancy. Eventually, the plume velocity becomes equal to that of the ambient gas, which rotates with different angular speeds than the stars in the disk. As a result, the plumes acquire characteristic bent shapes. An ad hoc model of plumes' trajectories shows an interesting resemblance to the morphology of structures seen in the radio continuum and X-rays.

Context . The existence of axion quark nuggets is a potential consequence of the axion field, which provides a possible solution to the charge-conjugation parity violation in quantum chromodynamics. In addition to explaining the cosmological discrepancy of matter-antimatter asymmetry and a visible-to-dark-matter ratio of Ω dark /Ω visible ≃ 5, these composite compact objects are expected to represent a potentially ubiquitous electromagnetic background radiation by interacting with ordinary baryonic matter. We conducted an in-depth analysis of axion quark nugget-baryonic matter interactions in the environment of the intracluster medium in the constrained cosmological Simulation of the LOcal Web (SLOW). Aims . Here, we aim to provide upper limit predictions on electromagnetic counterparts of axion quark nuggets in the environment of galaxy clusters by inferring their thermal and non-thermal emission spectrum originating from axion quark nugget-cluster gas interactions. Methods . We analyzed the emission of axion quark nuggets in a large sample of 161 simulated galaxy clusters using the SLOW simulation. These clusters are divided into a sub-sample of 150 galaxy clusters, ordered in five mass bins ranging from 0.8 to 31.7 × 10 ¹⁴ M ⊙ , along with 11 cross-identified galaxy clusters from observations. We investigated dark matter-baryonic matter interactions in galaxy clusters in their present stage at the redshift of z = 0 by assuming all dark matter consists of axion quark nuggets. The resulting electromagnetic signatures were compared to thermal Bremsstrahlung and non-thermal cosmic ray (CR) synchrotron emission in each galaxy cluster. We further investigated individual frequency bands imitating the observable range of the WMAP, Planck , Euclid , and XRISM telescopes for the most promising cross-identified galaxy clusters hosting detectable signatures of axion quark nugget emission. Results . We observed a positive excess in the low- and high-energy frequency windows, where thermal and non-thermal axion quark nugget emission can significantly contribute to (or even outshine) the emission of the intracluster medium (ICM) in frequencies up to ν T ≲ 3842.19 GHz and ν T ϵ [3.97, 10.99] × 10 ¹⁰ GHz, respectively. Emission signatures of axion quark nuggets are found to be observable if CR synchrotron emission of individual clusters is sufficiently low. The degeneracy in the parameters contributing to an emission excess makes it challenging to offer predictions with respect to pinpointing specific regions of a positive axion quark nugget excess; however, a general increase in the total galaxy cluster emission is expected based on this dark matter model. Axion quark nuggets constitute an increment of 4.80% of the total galaxy cluster emission in the low-energy regime of ν T ≲ 3842.19 GHz for a selection of cross-identified galaxy clusters. We propose that the Fornax and Virgo clusters represent the most promising candidates in the search for axion quark nugget emission signatures. Conclusions . The results from our simulations point towards the possibility of detecting an axion quark nugget excess in galaxy clusters in observations if their signatures can be sufficiently disentangled from the ICM radiation. While this model proposes a promising explanation for the composition of dark matter, with the potential to have this outcome verified by observations, we propose further changes that are aimed at refining our methods. Our ultimate goal is to identify the extracted electromagnetic counterparts of axion quark nuggets with even greater precision in the near future.

Massive clusters of galaxies are very rare in the observable Universe. Even rarer are mergers of such clusters observed close to pericenter passage. Here, we report on one such case: a massive (~ $10^{15}\,M_\odot$) and hot (kT ~ 10 keV) cluster CL0238.3+2005 at $z\approx 0.42$. For this cluster, we combine X-ray data from SRG/eROSITA and Chandra, optical images from DESI, and spectroscopy from BTA and RTT-150 telescopes. The X-ray and optical morphologies suggest an ongoing merger with the projected separation of subhalos of $\sim 200$ kpc. The line-of-sight velocity of galaxies tentatively associated with the two merging halos differs by 2000-3000 km/s. We conclude that, most plausibly, the merger axis is neither close to the line of sight nor to the sky plane. We compare CL0238 with two well-known clusters MACS0416 and Bullet, and conclude that CL0238 corresponds to an intermediate phase between the pre-merging MACS0416 cluster and the post-merger Bullet cluster. Namely, this cluster has recently (only $\lesssim 0.1$ Gyr ago) experienced an almost head-on merger. We argue that this "just after" system is a very rare case and an excellent target for lensing, Sunyaev-Zeldovich effect, and X-ray studies that can constrain properties ranging from dynamics of mergers to self-interacting dark matter, and plasma effects in intracluster medium that are associated with shock waves, e.g., electron-ion equilibration efficiency and relativistic particle acceleration.

(Abridged) Core-collapse supernova remnants (SNRs) display complex morphologies and asymmetries, reflecting anisotropies from the explosion and early interactions with the circumstellar medium (CSM). Spectral analysis of these remnants can provide critical insights into supernova (SN) engine dynamics, the nature of progenitor stars, and the final stages of stellar evolution, including mass-loss mechanisms in the millennia leading up to the SN. This white paper evaluates the potential of the Line Emission Mapper (LEM), an advanced X-ray probe concept proposed in response to NASA 2023 APEX call, to deliver high-resolution spectra of SNRs. Such capabilities would allow detailed analysis of parent SNe and progenitor stars, currently beyond our possibilities. We employed a hydrodynamic model that simulates the evolution of a neutrino-driven SN from core-collapse to a 2000-year-old mature remnant. This model successfully replicates the large-scale properties of Cassiopeia A at an age of about 350 years. Using this model, we synthesized mock LEM spectra from different regions of the SNR, considering factors like line shifts and broadening due to plasma bulk motion and thermal ion motion, deviations from ionization and temperature equilibrium, and interstellar medium absorption. Analyzing these mock spectra with standard tools revealed LEM impressive capabilities. We demonstrated that fitting these spectra with plasma models accurately recovers the line-of-sight velocity of the ejecta, enabling 3D structure exploration of shocked ejecta, similar to optical methods. LEM also distinguishes between Doppler and thermal broadening of ion lines and measures ion temperatures near the limb of SNRs, providing insights into ion heating at shock fronts and cooling in post-shock flows. This study highlights LEM potential to advance our understanding of core-collapse SN dynamics and related processes.