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We present an updated repository of sub-mJy extragalactic radio source counts between 150 MHz and 10 GHz, incorporating recent advances in radio surveys and observational techniques. By compiling and refining previous datasets, we provide a comprehensive catalog that enhances the understanding of faint radio-source populations, including Dusty Star-Forming Galaxies (DSFGs) and Radio-Quiet Active Galactic Nuclei (RQAGNs), from intermediate to high redshifts. Our analysis accounts for observational biases, such as resolution effects and Eddington bias, ensuring improved accuracy in flux-density estimations. We also discuss the implications of new-generation radio telescopes, such as the Square-Kilometer Array Observatory (SKAO) and its precursors and pathfinders, to further resolve these populations. Our collection contributes to constraining evolutionary models of radio sources, highlighting the increasing role of polarization studies in distinguishing different classes. This work serves as a key reference for future deep radio surveys targeting the faintest end of the extragalactic radio sky.

The question of at which energy the transition from galactic to extra-galactic cosmic rays takes place has been a long-standing conundrum in cosmic ray physics. The sun stands out as the closest and clearest astrophysical accelerator of cosmic rays, while other objects within and beyond the galaxy remain enigmatic. It is probable that the cosmic ray spectrum and mass components from these celestial sources share similarities, offering a novel approach to study their origin. In this study, we perform joint analysis of spectra and mass in the energy range from MeV to 10 EeV, and find the following: (1) lnA demonstrates three clear peaks, tagging component transition; (2) a critical variable Δ is adopted to define the location of the transition; (3) for protons, the knee is located at ∼1.8 PeV, and the boundary between the galaxy and extra-galaxy occurs at ∼60 PeV, marked by a spectral dip; and (4) the all-particle spectrum exhibits hardening at ∼60 PeV due to the contribution of nearby galaxies, and the extra-galaxy dominates ∼0.8 EeV. We hope the LHAASO experiment can perform spectral measurements of individual species to validate these specific observations.

The dominant fraction of the extragalactic γ-ray sources are blazars, active galactic nuclei with jets inclined ata small angle to the line of sight. Apart from blazars, a few dozen narrow-line Seyfert 1 galaxies (NLS1) and a number of radio galaxies are associated with γ-ray sources. The identification of γ-ray sources requires multiwavelength follow-up observations since several candidates could reside within the relatively large γ-ray localisation area. The γ-ray source 4FGL 0959.6+4606 was originally associated with a radio galaxy. However, follow-up multiwavelength work suggested a nearby NLS1 as the more probable origin of the γ-ray emission. We performed high-resolution very long baseline interferometry (VLBI) observation at 5 GHz of both proposed counterparts of 4FGL 0959.6+4606. We clearly detected the NLS1 source SDSS J095909.51+460014.3 with relativistically boosted jet emission. On the other hand, we did not detect milliarcsecond-scale compact emission in the radio galaxy 2MASX J09591976+4603515. Our VLBI imaging results suggest that the NLS1 object is the origin of the γ-ray emission in 4FGL 0959.6+4606.

Cepheids have been the cornerstone of the extragalactic distance scale for a century. With high-quality data, these luminous supergiants exhibit a small dispersion in their Leavitt (period–luminosity) relation, particularly at longer wavelengths, and few methods rival the precision possible with Cepheid distances. In these proceedings, we present an overview of major observational programs pertaining to the Cepheid extragalactic distance scale, its progress and remaining challenges. In addition, we present preliminary new results on Cepheids from the James Webb Space Telescope (JWST). The launch of JWST has opened a new chapter in the measurement of extragalactic distances and the Hubble constant. JWST offers a resolution three times that of the Hubble Space Telescope (HST) with nearly 10 times the sensitivity. It has been suggested that the discrepancy in the value of the Hubble constant based on Cepheids compared to that inferred from measurements of the cosmic microwave background requires new and additional physics beyond the standard cosmological model. JWST observations will be critical in reducing remaining systematics in the Cepheid measurements and for confirming if new physics is indeed required. Early JWST data for the galaxy, NGC 7250 show a decrease in scatter in the Cepheid Leavitt law by a factor of two relative to existing HST data and demonstrate that crowding/blending effects are a significant issue in a galaxy as close as 20 Mpc.

Ultra Long Period Cepheids are becoming a very interesting and important topic thanks to the contribution that they can give to understanding the current tension existing between the early-universe and local Hubble constant measurements. These bright pulsating variables are observable up to cosmological distances (larger than 100 Mpc) allowing us, in principle, to measure the Hubble constant without the need for secondary indicators, thus reducing the possible systematic errors in the calibration of the extragalactic distance scale. The Ultra Long Period Cepheids also represent a useful tool for obtaining information on the star formation history of the host galaxy and a challenge for the evolutionary and pulsational models, particularly in the very metal poor regime. In this paper, the largest known ULP sample, consisting of 72 objects, including 10 new candidates, is analyzed to give an observational and theoretical overview of their role as distance indicators and of their evolutionary properties.

We analyze 91,742 reported extragalactic distance moduli and their one sigma uncertainties for 14,560 galaxies with multiple reported distances in the NED Redshift-Independent Distances database. For every ordered pair of distance moduli measurements 1 and 2 for each galaxy, we define Δ(σ)1,2, a measure for how different measurement 2 is in relation to measurement 1, as a multiple of the reported one sigma uncertainty in measurement 1. For a given set of distance moduli measurements, we take a mean of all such Δ(σ)1,2 to determine the average separation between distance moduli of any galaxy in the set as a multiple of the reported uncertainty. For normally distributed measurements, the expected value of mean Δ(σ) is 0.79. Our results are as follows. The mean Δ(σ) of 1,239,062 ordered pairs of extragalactic distance moduli for 14,560 galaxies is 2.07 corresponding to a p-value of 3.85%. This indicates a possible systematic underestimation of uncertainties in extragalactic distances. We also find that the mean reported one sigma uncertainty decreased and the mean Δ(σ) increased from 1989 to 2018. This points to increased underestimation of uncertainties with time. For the latest period from 2014 to 2018 with 14,580 reported extragalactic distance moduli for 5,406 galaxies, the mean Δ(σ) of 40,462 ordered pairs is 3.00 corresponding to a p-value of 0.27%. For 14,888 extragalactic distance moduli of 2,518 galaxies measured using Type Ia Supernovae, the mean Δ(σ) for 124,016 ordered pairs is 2.85 corresponding to a p-value of 0.44%. These results may have some implications for our confidence in cosmological parameters and models. We conclude that more liberal estimation of uncertainties in future reported extragalactic distances should be considered. The results also give a possible way out of the Hubble-Lemaitre tension by advocating for increasing the error bars on Hubble-Lemaitre constant measured via distance ladders of standard candles and rulers.

The cosmological distance ladder crucially depends on classical Cepheids (with P =3–80 days), which are primary distance indicators up to 33 Mpc. Within this volume, very few SNe Ia have been calibrated through classical Cepheids, with uncertainty related to the non-linearity and the metallicity dependence of their period–luminosity (PL) relation. Although a general consensus on these effects is still not achieved, classical Cepheids remain the most used primary distance indicators. A possible extension of these standard candles to further distances would be important. In this context, a very promising new tool is represented by the ultra-long period (ULP) Cepheids ( P ≳80 days), recently identified in star-forming galaxies. Only a small number of ULP Cepheids have been discovered so far. Here we present and analyse the properties of an updated sample of 37 ULP Cepheids observed in galaxies within a very large metallicity range of 12+log(O/H) from ∼7.2 to 9.2 dex. We find that their location in the colour-magnitude ( V − I , V ) diagram as well as their Wesenheit ( V − I ) index-period (WP) relation suggests that they are the counterparts at high luminosity of the shorter-period ( P ≲80 days) classical Cepheids. However, a complete pulsation and evolutionary theoretical scenario is needed to properly interpret the true nature of these objects. We do not confirm the flattening in the studied WP relation suggested by Bird et al. (Astrophys. J. 695:874, 2009 ). Using the whole sample, we find that ULP Cepheids lie around a WP relation similar to that of the LMC, although with a large spread (∼ 0.4 mag).

We have applied the near-infrared surface-brightness method to 111 Cepheids in the Milky Way and in the Large and the Small Magellanic Clouds determining distances and luminosities for the individual stars. We find that the K -band Period-Luminosity (PL-)relations for Milky Way and Large Magellanic Cloud Cepheids are almost identical, whereas the zero point of the Wesenheit relation depends significantly on metallicity, metal poor Cepheids being fainter. We determine empirically the relation between the projection factor, p , and pulsational period, P , used for converting the observed radial velocities into the pulsational velocities necessary for applying the near-infrared surface-brightness method. We also determine the p -factor relation on a theoretical basis and find a significantly shallower slope than from our empirical determination, suggesting that there is still some physics related to the method which deserves further investigation. Using the empirical p -factor relation we re-determine the Cepheid PL-relation in the K -band using all 111 Cepheids. We argue that this is the currently best PL-relation for distance determination being largely independent of both metallicity and reddening.

Garth Illingworth and Rychard Bouwens are studying ultra-deep imaging data from the Hubble Space Telescope have found that what may be the most distant galaxy ever seen, about 13.2 billion light-years away. The study pushed he limits of Hubble's capabilities, extending its reach back to about 480 million years after the Big Bang, when the universe was just 4% of its current age. Using infrared data gathered by Hubble's Wide Field Planetary Camera 3, they were able to see dramatic changes in galaxies over a period about 480 to 650 million years after the Big Bang.