Search Results (61)

The study of high-redshift active galactic nuclei (AGN) and their small-scale environment is necessary to investigate the different processes that control and influence the evolution of massive galaxies. In this paper we present a case study of cid_1253 ($z=2.15$) and its companion galaxy using archive CO(3–2) and 340 GHz continuum observations with the Atacama Large Millimeter/submillimeter Array, supplemented by multi-wavelength photometry. Previous studies treated the system as a whole, without separating its components in order to match large-beam infrared observations. Our goal is to study cid_1253 and its companion separately by re-analysing the available archive data of the system. Based on our analysis, the companion galaxy is not only more gas-rich ($M_{{\mathrm{H}}_2}\sim {10}^{11}{\mathrm{M}}_{\odot }$) but also has a higher dust mass, indicative of obscured star formation. Moreover, as cid_1253 is not detected at 340 GHz, it is possible that a large fraction of the unresolved, Herschel-detected infrared emission is associated with the companion, rather than cid_1253. The presented case study highlights the need to be more cautious with blended sources before drawing our conclusions and the necessity of high-resolution observations. Full article

Measuring supermassive black hole (SMBH) masses is fundamental to understanding active galactic nuclei (AGN) and their coevolution with host galaxies. Among existing techniques, H₂O megamaser observations with Very Long Baseline Interferometry (VLBI) provide the most direct and geometric determinations of SMBH masses by tracing molecular gas in sub-parsec Keplerian disks. Over the past two decades, the Megamaser Cosmology Project (MCP) has surveyed thousands of nearby AGNs and obtained high-sensitivity VLBI maps of dozens of maser disks that lead to accurate SMBH masses with uncertainties typically below 10%. In this paper, we present a comprehensive review that summarizes the essential elements required to obtain accurate black hole masses with the H₂O megamaser technique—including the physical conditions for maser excitation, observational requirements, disk modeling, and sources of SMBH mass uncertainty—and we discuss the implications of maser-based measurements for exploring SMBH demographics. In particular, we will show that maser-derived black hole masses, largely free from the systematic biases of stellar or gas-dynamical methods, provide critical anchors at the low-mass end of the SMBH population (M_BH∼10⁷M_⊙), and reveal possible deviations from the canonical M_BH–σ_∗ relation. With forthcoming spectroscopic surveys and advances in millimeter/submillimeter VLBI, the maser technique promises to extend precise dynamical mass measurements to both larger local samples and high-redshift galaxies. Full article

Radio-loud high-redshift quasars (RHRQs) provide crucial insights into the evolution of relativistic jets and their connection to the growth of supermassive black holes. Beyond the extensively studied population at $z\ge 5$, the cosmic morning epoch ($3\lesssim z\lesssim 5$) marks the peak of active galactic nucleus (AGN) activity and black hole accretion, yet remains relatively unexplored. In this work, we compiled the radio high-redshift quasar catalog (RHzQCat) by cross-matching the SDSS DR16Q catalog with four major radio surveys—FIRST, NVSS, RACS, and GLEAM. Our tier-based cross-matching framework and visual validation ensured reliable source identification across surveys with diverse beam sizes. The catalog included 1629 reliable and 315 candidate RHRQs, with radio luminosities uniformly spanning ${10}^{25.5}$–${10}^{29.3}$ W Hz⁻¹. About 95% of the confirmed sources exhibited compact morphologies, consistent with Doppler-boosted or young AGN populations at high redshifts. Our catalog increases the number of known RHRQs at $z\ge 3$ by an order of magnitude, representing the largest and most homogeneous catalog of radio quasars at cosmic morning, filling the observational gap between the early ($z>6$) and local Universe. It provides a robust reference for future statistical studies of jet evolution, AGN feedback, and cosmic magnetism with next-generation facilities such as the Square Kilometer Array (SKA). Full article

We carry out a careful analysis of the notion of observation of distant events in a curved Universe. This leads us to hypothesise that all measurements of our physical environment are performed with respect to a representation referential that obeys the rules of Euclidean geometry. In curved spacetime geometries, this creates a distortion of metric quantities which affects the wavelength of photons incoming from distant sources. We show that, at the scale of our galaxy, this effect is too small to be experimentally detected. At a cosmological scale, however, and in the context of the Einstein Universe, we show that it becomes measurable and offers a simple alternative explanation for most modern cosmological observations. In particular, we predict a redshift which increases as a function of the source’s distance, in a way that is consistent with Supernovae data, and the existence of a Cosmic Microwave Background whose characteristics align with the ones measured by the Planck mission. Furthermore, it accounts for the presence of well-formed galactic structures in the high-redshift Universe, as recently detected by the James Webb Space Telescope. Full article

STRange and Odd Morphology Extragalactic Radio Sources (STROMERSs) is a new category of radio galaxies that shows extremely peculiar anatomy. A purely manual visual search is carried out for the identification of such interesting sources. We reported a total of 108 STROMERS sources from the LOFAR Two-meter Sky Survey second data release (LoTSS DR2) at 144 MHz. The host galaxies are found ∼94% of the sources. We studied the radio and optical properties of the sources. Redshifts were found in 76% of sources with known host galaxies. The redshifts of STROMERS range from 0.0015 to 1.6599 and peak at 0.15. Among the reported STROMERS sources, there are 17 giant radio galaxies (GRG) with a linear size of greater than 700 kpc. Among them, only five GRGs are new, which is a small fraction of the population of GRGs from LoTSS DR2 data. The source ILTJ164117.44 +380208.4 has the highest linear size, approximately 1.8 Mpc. To study the reasons behind these interesting morphologies, we studied the galaxy cluster environment of each candidate within a 1 Mpc search radius. We found that 53% of STROMERS candidates are associated with cluster environments with known redshifts. The source ILTJ150956.65+332642.9 is associated with a high mass galaxy cluster Abell 2034 with mass a 7.57 $\times {10}^{14}{M}_{\odot }$. We also propose that the merger scenario is one of the reasons for the formation of STROMERS in the paper. Full article

The formation and evolution of galaxies and other astrophysical objects have become of great interest, especially since the launch of the James Webb Space Telescope in 2021. The mass, size, and density of objects in the early universe appear to be drastically different from those predicted by the standard cosmology—the $\mathsf{\Lambda }$CDM model. This work shows that the mass–size–density evolution is not surprising when we use the CCC+TL cosmology, which is based on the concepts of covarying coupling constants in an expanding universe and the tired light effect contributing to the observed redshift. This model is consistent with supernovae Pantheon+ data, the angular size of the cosmic dawn galaxies, BAO, CMB sound horizon, galaxy formation time scales, time dilation, galaxy rotation curves, etc., and does not have the coincidence problem. The effective radii $r_e$ of the objects are larger in the new model by $r_e\propto {\left(1+z\right)}^{0.93}$. Thus, the object size evolution in different studies, estimated as $r_e\propto {\left(1+z\right)}^s$ with $s=-1.0$ ± $0.3$, is modified to $r_e\propto {\left(1+z\right)}^{s+0.93}$, the dynamical mass by ${\left(1+z\right)}^{0.93},$ and number density by ${\left(1+z\right)}^{-2.80}$. The luminosity modification increases slowly with $z$ to 1.8 at $z=20$. Thus, the stellar mass increase is modest, and the luminosity and stellar density decrease are mainly due to the larger object size in the new model. Since the aging of the universe is stretched in the new model, its temporal evolution is much slower (e.g., at $z=10$, the age is about a dex longer); stars, black holes, and galaxies do not have to form at unrealistic rates. Full article

This paper aims to explore whether astrophysical observations, primarily galaxy rotation curves, result from covarying coupling constants (CCC) rather than from dark matter. We have shown in earlier papers that cosmological observations, such as supernovae type 1a (Pantheon+), the small size of galaxies at cosmic dawn, baryon acoustic oscillations (BAO), the sound horizon in the cosmic microwave background (CMB), and time dilation effect, can be easily accounted for without requiring dark energy and dark matter when coupling constants are permitted to evolve in an expanding Universe, as predicted by Dirac, and the redshift is considered jointly due to the Universe’s expansion and Zwicky’s tired light (TL) effect. Here, we show that the CCC parameter α is responsible for generating the illusion of dark matter and dark energy, which we call α-matter and α-energy, and is influenced by the baryonic matter density distribution. While cosmologically α is a constant determined for the homogenous and isotropic Universe, e.g., by fitting Pantheon+ data, it can vary locally due to the extreme anisotropy of the matter distribution. Thus, in high baryonic density regions, one expects α-matter and α-energy densities to be relatively low and vice versa. We present its application to a few galaxy rotation curves from the SPARC database and find the results promising. Full article

We test the validity of the cosmic distance duality relation (CDDR) by combining angular diameter distance and luminosity distance measurements from recent cosmological observations. For the angular diameter distance, we use data from transverse baryon acoustic oscillations and galaxy clusters. On the other hand, the luminosity distance is obtained from Type Ia supernovae in the Pantheon+ sample and from quasar catalogs. To reduce the large dispersion in quasar luminosity distances, we apply a selection criterion based on their deviation from the $\mathrm{\Lambda }$CDM model and implement a binning procedure to suppress statistical noise. We reconstruct the CDDR using Gaussian Processes, a non-parametric supervised machine learning method. Our results show no significant deviation from the CDDR within the $2\sigma$ confidence level across the redshift range explored, supporting its validity even at high redshifts. Full article

The real nature of little red dots (LRDs), a class of very compact galaxies in the early Universe recently discovered by the James Webb Space Telescope, is still poorly understood. The most popular theories competing to interpret the phenomena include active galactic nuclei and enhanced star formation in dusty galaxies. To date, however, neither model gives a completely satisfactory explanation to the population as a whole; thus, alternative theories have arisen, including tidal disruption events (TDEs). By considering observational constraints on the radio emission of LRDs, we discuss whether TDEs are adequate alternatives solving these high-redshift enigmas. We utilise radio flux density upper limits from LRD stacking analyses, TDE peak radio luminosities, and volumetric density estimates. We find that the characteristic values of flux densities and luminosities allow radio-quiet TDEs as the underlying process of LRDs in any case, while the less common radio-loud TDEs are compatible with the model under special constraints only. Considering other factors, such as volumetric density estimates, delayed and long-term radio flares of TDEs, and cosmological time dilation, TDEs appear to be a plausible explanation for LRDs from the radio point of view. Full article

Weak lensing magnification probes the correlation between galaxies and the underlying matter field in a similar fashion to galaxy–galaxy lensing shear. Although it has long been sidelined in favor of the latter on the grounds of poorer performance in terms of statistical significance, the provision of a large sample of high-redshift submillimeter galaxies by the Herschel observatory has transformed the landscape of cosmic magnification due to their optimal physical properties for magnification analyses. This review aims to summarize the core principles and unique advantages of the cosmic magnification of high-redshift submillimeter galaxies and discuss recent results applied to cosmological inference. The outlook and challenges of this observable are also outlined, with a focus on the ample scope for exploration and its potential to emerge as a competitive independent cosmological probe. Full article

The presence of Active Galaxy Nuclei (AGN) can affect the morphological classification of galaxies. This work aims to determine how the contribution of AGN affects the most-used morphological parameters down to the redshift of z ∼ 2 in COSMOS-like conditions. We use a sample of >2000 local non-active galaxies, with a well-known visual morphological classification, and add an AGN as an unresolved component that contributes to the total galaxy flux with 5–75%. We moved all the galaxies to lower magnitudes (higher redshifts) to map the conditions in the COSMOS field, and we measured six morphological parameters. The greatest impact on morphology occurs when considering the combined effect of magnitude, redshift, and AGN, with spiral galaxies being the most affected. In general, all the concentration parameters change significantly if the AGN contribution is >25% and the magnitude > 23. We find that the GINI coefficient is the most stable in terms of AGN and magnitude/redshift, followed by the moment of light (M20), Conselice–Bershady (CCON), and finally the Abraham (CABR) concentration indexes. We find that, when using morphological parameters, the combination of CABR, CCON, and asymmetry is the most effective in classifying active galaxies at high-redshift, followed by a combination of CABR and GINI. Full article

The Shapley Supercluster, one of the largest and most massive structures in the nearby (redshift $z\le 0.1$) Universe, located approximately 200 Mpc away, is a unique laboratory for high-energy astrophysics. Galaxy clusters that comprise it are promising targets for multimessenger study due to the presence in the intracluster medium of the necessary conditions for the acceleration of cosmic rays up to ultra-high energies and the generation by them of non-thermal electromagnetic and neutrino emission. Using the Shapley Supercluster’s observational data from the recent eROSITA-DE Data Release, we recover the physical parameters of 45 X-ray luminous galaxy clusters and calculate the expected multiwavelength—from radio to very-high-energy γ-ray as well as neutrino emission, with a particular focus on hadronic interactions of accelerated cosmic ray nuclei with the nuclei of the intracluster medium. The results obtained allow verification of cluster models based on multimessenger observations of clusters, especially in $\gamma$-ray (Fermi-LAT, H.E.S.S., CTAO-South for the Shapley Supercluster case), and neutrino (Ice Cube, KM3NeT). We also estimate the ability of the Shapley Supercluster to manifest as cosmic Zevatrons and show that it can contribute to the PAO Hot Spot in the Cen A region at UHECR energies over 50 EeV. Full article

We investigate the relativistic jet of the powerful radio-emitting blazar J1429+5406 at redshift $z=3.015$. Our understanding of jet kinematics in $z\ge 3$ quasars is still rather limited, based on a sample of less than about 50 objects. The blazar J1429+5406 was observed at a high angular resolution using the method of very long baseline interferometry over more than two decades, between 1994 and 2018. These observations were conducted at five radio frequencies, covering a wide range from $1.7$ to 15 GHz. The outer jet components at ∼20–40 milliarcsecond (mas) separations from the core do not show discernible apparent motion. On the other hand, three jet components within the central 10 mas region exhibit significant proper motion in the range of (0.045–0.16) mas year⁻¹, including one that is among the fastest-moving jet components at $z\ge 3$ known to date. Based on the proper motion of the innermost jet component and the measured brightness temperature of the core, we estimated the Doppler factor, the bulk Lorentz factor, and the inclination angle of the jet with respect to the line of sight. The core brightness temperature is at least $3.6\times {10}^{11}$ K, well exceeding the equipartition limit, indicating Doppler-boosted radio emission. The low jet inclination (≲5.4°) firmly places J1429+5406 into the blazar category. Full article

The phenomenon of augmented gravity on the scale of galaxies, conventionally attributed to dark matter halos, is shown to possibly result from the incremental growth of galactic masses and radii over time. This approach elucidates the cosmological origins of the acceleration scale $a_0\approx c{H}_0/2\pi \approx {10}^{-10}$ ms⁻² at which galaxy rotation curves deviate from Keplerian behavior, with no need for new particles or modifications to the laws of gravity, i.e., it constitutes a new explanatory path beyond Cold Dark Matter (CDM) and Modified Newtonian Dynamics (MOND). Once one formally equates the energy density of the universe to the critical value ($\rho ={\rho }_c$) and the cosmic age to the reciprocal of the Hubble parameter ($t=H^{-1}$), independently of the epoch of observation, the result is the Zero-Energy condition for the cosmic fluid’s equation of state, with key repercussions for the study of dark energy since the observables can be explained in the absence of a cosmological constant. Furthermore, this mass-energy evolution framework is able to reconcile the success of CDM models in describing structure assembly at $z\lesssim 6$ with the unexpected discovery of massive objects at $z\gtrsim 10$. Models that feature a strong coupling between cosmic time and energy are favored by this analysis. Full article

The adequate choice of stellar initial mass function (IMF) is crucial when studying high-z galaxy formation and the epoch of reionization (EoR) models. We employ the semi-analytical galaxy model L-Galaxies2020 and the dark matter simulation Millennium-II, in combination with the BPASS spectral model, to investigate the effects of different stellar IMFs on the properties of high-z galaxies and their ionizing photon budget during EoR. We find that different stellar IMFs lead to different SED of high-z galaxies, and thus different ultraviolet luminosity functions (UVLF) and budgets of ionizing photons for EoR. Specifically, at $z<10$, the UVLF with Salpeter and Chabrier IMF models are closer to the observed results, while at $z>10$, the ones with a Top-Heavy model are more consistent with the JWST observations. The increase in the upper limit of star mass within stellar IMF from $100{\mathrm{M}}_{\odot }$ to $300{\mathrm{M}}_{\odot }$ results in the increase in the UVLF and the ionizing photon number density. Full article