Radio Catalogues Research Articles

A multi-frequency, multi-epoch radio continuum study of the Arches cluster with the Very Large Array

Context. The Arches cluster, one of the most massive clusters in the Milky Way, is located about 30 pc in projection from the central massive black hole Sagittarius A* at a distance of ≈8 kpc from Earth. With its high mass, young age, and location in the Galaxy’s most extreme star forming environment, the Arches is an extraordinary laboratory for studying massive stars and clusters. Aims. Our objective is to improve our knowledge of the properties of massive stars and the Arches cluster through high-angular-resolution radio continuum studies. Methods. We observed the Arches cluster with the Karl G. Jansky Very Large Array in the C- and X-bands (central frequencies of 6 and 10 GHz respectively) in two epochs at C-band and five epochs at X-band throughout 2016, 2018, and 2022, covering time spans ranging from 22 days to 6 years. We used the A-configuration to achieve the highest possible angular resolution and cross-matched the detected point-sources with stars detected in the infrared, using proper motion catalogues to ensure cluster membership. Results. We report the most extensive radio point-source catalogue of the cluster to date, with a total of 25 radio detections (7 more than the most recent study). We also created the deepest (2.5 μJy in X-band) images of the cluster so far in the 4 to 12 GHz frequency range. Most of our stellar radio sources (12 out of 18) show a positive spectral index, indicating that the dominant emission process is free-free thermal radiation, which probably originates from stellar winds. We find that radio variability is more frequent than what was inferred from previous observations, and affects up to 60% of the sources associated with bright stellar counterparts, with two of them, F18 and F26, showing extreme flux variability. We propose four of our detections (F6, F18, F19, and F26) as primary candidates for colliding-wind binaries (CWBs) based on their consistent flat-to-negative spectral index. We classify F7, F9, F12, F14, and F55 as CWB binary candidates based on their high flux and/or spectral index variability, and X-ray counterparts. Thus, we infer a 14/23 ≈ 61% multiplicity fraction for the radio stars of the Arches cluster when combining our findings with recent infrared radial velocity studies.

A new model for the extragalactic radio sky at low frequency calibrated using the LOFAR Two-metre Survey

Abstract Building the radio sky template are crucial for detecting the 21 cm emission line signal from the Epoch of Reionization (EoR), as well as for other cosmological research endeavors. Utilizing data from the LOFAR Two-meter Sky Survey (LoTSS) at 150 MHz, we recalibrated the luminosity function for various types of radio sources, including High Excitation Radio Galaxies (HERGs), Low Excitation Radio Galaxies (LERGs), Radio-Quiet Active Galactic Nuclei (RQ-AGNs), and Star-Forming Galaxies (SFGs). We subsequently updated the Tiered Radio Extragalactic Continuum Simulation (T-RECS) code to generate refined mock radio source catalogues. The simulated source counts from this work align more closely with observed data at redshifts greater than z > 4. Additionally, the differential source counts in total intensity within the flux density range of 0.1 − 1 mJy closely mirror actual observations. Due to our model incorporating a lower number of faint sources compared to T-RECS, it predicts a reduced power spectrum for point sources, suggesting a potential advantage in studies in low frequency band.

1-arcsecond imaging of the ELAIS-N1 field at 144MHz using the LoTSS survey with the international LOFAR telescope

We present the first wide area ($2.5 deg ^2$) LOFAR high band antenna image at a resolution of $1.2 with a median noise of $ Jy beam $. It was made from an 8-hour International LOFAR Telescope (ILT) observation of the ELAIS-N1 field at frequencies ranging from 120 to 168\,MHz with the most up-to-date ILT imaging methods. This intermediate resolution falls between the highest possible resolution (0.3 achievable by using all ILT baselines and the standard 6-arcsecond resolution in the LOFAR Two-meter Sky Survey (LoTSS) image products utilising the LOFAR Dutch baselines only. This is the first demonstration of the feasibility of imaging using the ILT at a resolution of sim 1 which provides unique information on source morphology at scales that fall below the surface brightness limits at higher resolutions. The total calibration and imaging computational time is approximately 52,000 core hours, which is nearly five times more than required to produce a $6 resolution image. We also present a radio source catalogue containing 2263 sources detected over the $2.5 deg ^2$ image of the ELAIS-N1 field, with a peak intensity threshold of $5.5 The catalogue has been cross-matched with the LoTSS deep ELAIS-N1 field radio catalogue, and its flux density and positional accuracy have been investigated and corrected accordingly. We find that sim 80<!PCT!> of sources that we expect to be detectable based on their peak brightness in the LoTSS $6 resolution image are detected in this image, which is approximately a factor of two higher than for $0.3 resolution imaging in the Lockman Hole, implying there is a wealth of information on these intermediate scales.

A global view on star formation: The GLOSTAR Galactic plane survey

Context. The GLObal view on STAR formation in the Milky Way (GLOSTAR) survey studies star formation with the Very Large Array (VLA) and the Effelsberg 100 meter radio telescope in the Galactic plane between −2° < ℓ < 60° and |b| < 1°, and the Cygnus X region (76° < ℓ < 83° and −1° < b < 2°), with unprecedented sensitivity in both flux density (1σ ~50 μJy beam−1) and the capability of detecting emission with angular scales in the range from 1.″0 to the largest radio structures in the Galaxy on the order of a few degrees in size. Aims. Here, we provide a complete GLOSTAR-VLA D-configuration radio source catalog for the part of the Galactic disk covered. A catalog for the “pilot region” between 28° < ℓ < 36° has been published in a previous paper and here we present the complementary catalog for the area within 2° < ℓ < 28°, 36° < ℓ < 60° and |b| < 1°. Methods. Observations were taken with the VLA in a 4–8 GHz band to image 100 square degrees of the inner Galactic disk at a reference frequency of 5.8 GHz, using a total of 260 h of telescope time. We determined spectral indices (α; Sν ∝ να) inside the observed band and in the frequency range of 1.4–5.8 GHz by complementing our results with those from The HI/OH/Recombination line survey of the inner Milky Way (THOR), which covers 1–2 GHz. Results. The final images have an angular resolution of 18″ and an average sensitivity of 123 μJy beam−1. The sensitivity is better (~60 μJy beam−1) in areas free of extended emission. The complementary Galactic disk catalog presented in this work consists of 11 211 radio sources. Of these, 1965 are known large-scale structure sources such as star-forming region complexes, well-known supernova remnants (SNRs), SNR candidates, or parts thereof. The remaining 9227 are discrete individual sources. Source parameters–namely flux densities, sizes, spectral indices, and classifications-are reported. We identify 769 H II region candidates, 359 of which have been newly classified as such. The mean value of spectral indices of 225 H II regions is +0.14 ± 0.02, consistent with most of them emitting optically thin thermal radio emission. Combining our results with the previously published catalog of the pilot region, the final GLOSTAR-VLA D-configuration catalog contains 12 981 radio sources.

Tomographic redshift dipole: testing the cosmological principle

The cosmological principle posits that the universe is statistically homogeneous and isotropic on large scales, implying all matter shares the same rest frame. This principle suggests that velocity estimates of our motion from various sources should agree with the cosmic microwave background (CMB) dipole's inferred velocity of 370 km/s. Yet, for over two decades, analyses of radio galaxy and quasar catalogs have found velocities at odds with the CMB dipole, with tensions up to 5σ. In a blind analysis of BOSS and eBOSS spectroscopic data from galaxies and quasars across 0.2 < z < 2.2, we applied a novel dipole estimator for a tomographic approach, robustly correcting biases and quantifying uncertainties with realistic mock catalogs. Our findings with eBOSS data (0.6 < z < 2.2), indicating a velocity of 196+92 -79-79 km/s, demonstrate a 2σ agreement with the CMB dipole when considering the full 3D vector distribution and a 3-to-6σ tension with previous number count studies. This result supports the cosmological principle, emphasizing the consistency of our motion with the CMB across vast cosmic distances. On the other hand, the BOSS data revealed potential unmodeled systematics; the estimator could not be minimized using the LOWZ set (0.2 < z < 0.4), and the CMASS set (0.4 < z < 0.6) presented results that pointed towards the southern hemisphere, conflicting with the CMB dipole. Addressing the disparities with earlier number count analyses and understanding possible systematics in spectroscopic measurements will be essential to further validate the cosmological principle.

Probabilistic and progressive deblended far-infrared and sub-millimetre point source catalogues

Context.Single-dish far-infrared (far-IR) and sub-millimetre (sub-mm) point source catalogues and their connections with galaxy catalogues at other wavelengths are of paramount importance to studying galaxy evolution. However, due to the large mismatch in spatial resolution, cross-matching galaxies detected at different wavelengths is not straightforward.Aims.This work aims to develop the next-generation deblended far-IR and sub-mm catalogues in deep extragalactic survey fields, by extracting photometry at the positions of known sources. We present the first application of our methodology in the COSMOS field.Methods.Our progressive deblending used the Monte Carlo Markov chain (MCMC)-based Bayesian probabilistic framework known as XID+. The deblending process started from theSpitzer/MIPS 24 μm data, using an initial prior list composed of sources selected from the COSMOS2020 catalogue and radio catalogues from the VLA and the MeerKAT surveys, based on spectral energy distribution (SED) modelling which predicts fluxes of the known sources at the deblending wavelength. To speed up flux prediction, we made use of a neural network-based emulator. After deblending the 24 μm data, we proceeded to theHerschelPACS (100 and 160 μm) and SPIRE wavebands (250, 350 and 500 μm). Each time we constructed a tailor-made prior list based on the predicted fluxes of the known sources, taking into account the deblended photometry from the previous steps.Results.Using simulated far-IR and sub-mm sky, we detailed the performance of our deblending pipeline. After validation with simulations, we then deblended the real observations from 24 to 500 μm and compared with blindly extracted catalogues and previous versions of deblended catalogues. As an additional test, we deblended the SCUBA-2 850 μm map and compared our deblended fluxes with ALMA measurements, demonstrating a higher level of flux accuracy compared to previous results. We publicly release our XID+ deblended point source catalogues, including best estimates and posterior probability distribution functions. These deblended long-wavelength data, which are cross-matched with multi-band photometry by construction, are crucial for studies such as deriving the fraction of dust-obscured star formation and better separation of quiescent galaxies from dusty star-forming galaxies.

Heavily obscured AGN detection: A radio versus X-ray challenge

Context. In the supermassive black hole (SMBH)-galaxy coevolution scenario, heavily obscured active galactic nuclei (AGN) represent a fundamental phase of SMBH growth during which most of the BH mass is accreted and the scaling relations with the host galaxy are set. Obscured nuclei are thought to constitute a major fraction of the whole AGN population, but their statistics and evolution across cosmic time are still highly uncertain. Therefore, it is pivotal to identify new ways to detect this vast and hidden population of growing SMBHs. A promising way to select heavily obscured AGN is through radio emission, which is largely unaffected by obscuration and can be used as a proxy for nuclear activity. Aims. In this work, we study the AGN radio detection effectiveness in the major deep extragalactic surveys, considering different AGN obscuration levels, redshift, and AGN bolometric luminosities. We particularly focus on comparing their radio and X-ray detectability, making predictions for present and future radio surveys. Methods. We extrapolated the predictions of the AGN population synthesis model of the cosmic X-ray background (CXB) to the radio band, by deriving the 1.4 GHz luminosity functions of unobscured (i.e., with hydrogen column densities log NH &lt; 22), obscured (22 &lt; log NH &lt; 24), and Compton-thick (CTK, log NH &gt; 24) AGN. We then used these functions to forecast the number of detectable AGN based on the area, flux limit, and completeness of a given radio survey and compare it with the AGN number resulting from X-ray predictions. Results. When applied to deep extragalactic fields covered both by radio and X-ray observations, we show that, while X-ray selection is generally more effective in detecting unobscured AGN, the surface density of CTK AGN radio detected is on average ten times larger than the X-ray one, and even greater at high redshifts, considering the current surveys and facilities. Our results suggest that thousands of CTK AGN are already present in current radio catalogs, but most of them escaped any detection in the corresponding X-ray observations. We also present expectations for the number of AGN to be detected by the Square Kilometer Array Observatory (SKAO) in its future deep and wide radio continuum surveys, finding that it will be able to detect more than 2000 AGN at z &gt; 6 and tens of them at z &gt; 10, more than half of which are expected to be CTK.

A search for AGN sources of the IceCube diffuse neutrino flux

The origin of the diffuse astrophysical neutrino flux measured by the IceCube Observatory remains largely unknown.Although NGC 1068 and TXS 0506+056 have been identified as potential neutrino sources, the diffuse flux of neutrinos must have additional sources that have not yet been identified.Here we investigate potential correlations between IceCube's neutrino events and the Fermi and MOJAVE source catalogs, using the publicly-available IceCube data set. We perform three separate spatially-dependent, energy-dependent, and time-dependent searches, and find no statistically significant sources outside of NGC 1068. We find that, under the most optimistic assumptions of a spectral index of 2.0 and a neutrino flux uncorrelated with the gamma ray flux, no more than 13% of IceCube's neutrino flux originates from blazars over the whole sky. Then, using an energy-dependent likelihood analysis, the limit on neutrinos originating from blazars reduces to 9% in the Northern hemisphere under the same spectral index and flux assumptions. Finally, we set limits on individual sources from the MOJAVE radio catalog after finding no statistically significant time-flaring sources.

Searching for magnetar binaries disrupted by core-collapse supernovae

ABSTRACT Core-collapse supernovae (CCSNe) are considered the primary magnetar formation channel, with 15 magnetars associated with supernova remnants (SNRs). A large fraction of these should occur in massive stellar binaries that are disrupted by the explosion, meaning that $\sim 45~{{\ \rm per\ cent}}$ of magnetars should be nearby high-velocity stars. Here, we conduct a multiwavelength search for unbound stars, magnetar binaries, and SNR shells using public optical (uvgrizy bands), infrared (J, H, K, and Ks bands), and radio (888 MHz, 1.4 GHz, and 3 GHz) catalogues. We use Monte Carlo analyses of candidates to estimate the probability of association with a given magnetar based on their proximity, distance, proper motion, and magnitude. In addition to recovering a proposed magnetar binary, a proposed unbound binary, and 13 of 15 magnetar SNRs, we identify two new candidate unbound systems: an OB star from the Gaia catalogue we associate with SGR J1822.3−1606, and an X-ray pulsar we associate with 3XMM J185246.6 + 003317. Using a Markov Chain Monte Carlo simulation that assumes all magnetars descend from CCSNe, we constrain the fraction of magnetars with unbound companions to $5\lesssim f_u \lesssim 24~{{\ \rm per\ cent}}$, which disagrees with neutron star population synthesis results. Alternate formation channels are unlikely to wholly account for the lack of unbound binaries as this would require $31\lesssim f_{nc} \lesssim 66~{{\ \rm per\ cent}}$ of magnetars to descend from such channels. Our results support a high fraction ($48\lesssim f_m \lesssim 86~{{\ \rm per\ cent}}$) of pre-CCSN mergers, which can amplify fossil magnetic fields to preferentially form magnetars.

Magnetic activity of radio stars based on TESS and LAMOST surveys

Aims. Stellar flares serve as crucial indicators stellar magnetic activity. Radio emissions were detectable across all stages of stellar evolution. We define radio stars in our paper as stars with radio continuum emission in the frequency region of about 1.4 - 375 GHz from the catalog published by Wendker (1995, 2015). We also include detected radio stars from the LOFAR Two-metre Sky Survey (LoTSS) and the Australian Square Kilometre Array Pathfinder (ASKAP), and VLA Sky Survey (VLASS) surveys, and present comparative discussions. We used the light curves from the Transiting Exoplanet Survey Satellite (TESS) survey coupled with low- and medium-resolution spectra from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) survey to investigate the magnetic activity and statistical properties of radio stars. Methods. We cross-matched the radio stars from the radio star catalog and the LoTSS, ASKAP, and VLASS surveys with the TESS survey. For the stars from the radio star catalog, we obtained a matched sample of 1,537 stars (hereafter Sample 1) and downloaded their TESS light curves, which include 4,001 light curves at a 120s cadence. For the stars from the LoTSS, ASKAP, and VLASS surveys, we obtain a matched sample of 98 stars (hereafter Sample 2) and downloaded their 120s TESS light curves, totaling 260. Subsequently, we employed repeated fitting techniques to distinguish stellar background light curves from flare events. For Sample 1, we successfully identify 12,155 flare events occurring on 856 stars. For Sample 2, we identify a total of 3,992 flare events on 86 stars. Furthermore, by cross-referencing our samples with the Gaia survey, the TESS Input Catalog, and the LAMOST survey, we obtain additional stellar parameters, facilitating the determination of relationships between stellar and flare parameters. Results. For stars in Sample 1, within the 12,155 flare events observed on the 856 flare-active radio stars, a majority of more than 97$&lt;!PCT!&gt;$ have durations of less than 2 hours, while for stars in Sample 2, all 3,992 flare events have a duration of less than 2 hours. We calculated the flare occurrence percentage for each flare-active radio star, observing a decrease as effective temperature increased for both Sample 1 and Sample 2. We derived values of the power-law index (for Sample 1, the alpha value is approximately 1.50pm 0.11 for single stars and 1.38pm 0.09 for binary stars, for Sample 2, the alpha value is about 1.47pm 0.11 for single stars and 1.42pm 0.09 for binary stars) for the cumulative flare frequency distribution. In both Sample 1 and Sample 2, stars with lower effective temperatures tend to exhibit increased activity. Using LAMOST spectra and the Gaia DR3 chromospheric activity index, we note that the Halpha equivalent width and Gaia Ca II IRT activity index of flare-active radio stars is significantly larger than that of nonflaring stars. An intriguing finding is our potential identification of a coronal rain candidate through asymmetry observed in the Halpha line.

Influence of sources with a spectral peak in the detection of Cosmic Dawn and Epoch of Reionization

ABSTRACT Foreground removal is one of the biggest challenges in the detection of the Cosmic Dawn (CD) and Epoch of Reionization (EoR). Various foreground subtraction techniques have been developed based on the spectral smoothness of foregrounds. However, the sources with a spectral peak (SP) at megahertz may break down the spectral smoothness at low frequencies (&amp;lt;1000 MHz). In this paper, we cross-match the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) extragalactic source catalogue with three other radio source catalogues, covering the frequency range 72 MHz–1.4 GHz, to search for sources with spectral turnover. 4423 sources from the GLEAM catalogue are identified as SP sources, representing ≈3.2 per cent of the GLEAM radio source population. We utilize the properties of SP source candidates obtained from real observations to establish simulations and test the impact of SP sources on the extraction of CD/EoR signals. We statistically compare the differences introduced by SP sources in the residuals after removing the foregrounds with three methods, which are polynomial fitting, principal component analysis, and fast independent component analysis. Our results indicate that the presence of SP sources in the foregrounds has a negligible influence on extracting the CD/EoR signal. After foreground subtraction, the contribution from SP sources to the total power in the two-dimensional power spectrum within the EoR window is approximately 3–4 orders of magnitude lower than the CD/EoR signal.

MIGHTEE: Multi-wavelength counterparts in the COSMOS field

ABSTRACT In this paper, we combine the Early Science radio continuum data from the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE) Survey, with optical and near-infrared data and release the cross-matched catalogues. The radio data used in this work covers 0.86 deg2 of the COSMOS field, reaches a thermal noise of 1.7 μJy beam−1 and contains 6102 radio components. We visually inspect and cross-match the radio sample with optical and near-infrared data from the Hyper Suprime-Cam (HSC) and UltraVISTA surveys. This allows the properties of active galactic nuclei and star-forming populations of galaxies to be probed out to z ≈ 5. Additionally, we use the likelihood ratio method to automatically cross-match the radio and optical catalogues and compare this to the visually cross-matched catalogue. We find that 94 per cent of our radio source catalogue can be matched with this method, with a reliability of 95 per cent. We proceed to show that visual classification will still remain an essential process for the cross-matching of complex and extended radio sources. In the near future, the MIGHTEE survey will be expanded in area to cover a total of ∼20 deg2; thus the combination of automated and visual identification will be critical. We compare the redshift distribution of SFG and AGN to the SKADS and T-RECS simulations and find more AGN than predicted at z ∼ 1.

Cosmology from LOFAR Two-metre Sky Survey Data Release 2: angular clustering of radio sources

ABSTRACT Covering $\sim 5600\, \deg ^2$ to rms sensitivities of ∼70−100 $\mu$Jy beam−1, the LOFAR Two-metre Sky Survey Data Release 2 (LoTSS-DR2) provides the largest low-frequency (∼150 MHz) radio catalogue to date, making it an excellent tool for large-area radio cosmology studies. In this work, we use LoTSS-DR2 sources to investigate the angular two-point correlation function of galaxies within the survey. We discuss systematics in the data and an improved methodology for generating random catalogues, compared to that used for LoTSS-DR1, before presenting the angular clustering for ∼900 000 sources ≥1.5 mJy and a peak signal-to-noise ≥ 7.5 across ∼80 per cent of the observed area. Using the clustering, we infer the bias assuming two evolutionary models. When fitting angular scales of $0.5 \le \theta \lt 5{^\circ }$, using a linear bias model, we find LoTSS-DR2 sources are biased tracers of the underlying matter, with a bias of $b_{\rm C}= 2.14^{+0.22}_{-0.20}$ (assuming constant bias) and $b_{\rm E}(z=0)= 1.79^{+0.15}_{-0.14}$ (for an evolving model, inversely proportional to the growth factor), corresponding to $b_{\rm E}= 2.81^{+0.24}_{-0.22}$ at the median redshift of our sample, assuming the LoTSS Deep Fields redshift distribution is representative of our data. This reduces to $b_{\rm C}= 2.02^{+0.17}_{-0.16}$ and $b_{\rm E}(z=0)= 1.67^{+0.12}_{-0.12}$ when allowing preferential redshift distributions from the Deep Fields to model our data. Whilst the clustering amplitude is slightly lower than LoTSS-DR1 (≥2 mJy), our study benefits from larger samples and improved redshift estimates.

The LOFAR Two-Metre Sky Survey

The second data release of the LOFAR Two-Metre Sky Survey (LoTSS) covers 27% of the northern sky, with a total area of ~5700 deg1. The high angular resolution of LOFAR with Dutch baselines (6 arcsec) allows us to carry out optical identifications of a large fraction of the detected radio sources without further radio followup; however, the process is made more challenging by the many extended radio sources found in LOFAR images as a result of its excellent sensitivity to extended structure. In this paper we present source associations and identifications for sources in the second data release based on optical and near-infrared data, using a combination of a likelihood-ratio cross-match method developed for our first data release, our citizen science project Radio Galaxy Zoo: LOFAR, and new approaches to algorithmic optical identification, together with extensive visual inspection by astronomers. We also present spectroscopic or photometric redshifts for a large fraction of the optical identifications. In total 4 116 934 radio sources lie in the area with good optical data, of which 85% have an optical or infrared identification and 58% have a good redshift estimate. We demonstrate the quality of the dataset by comparing it with earlier optically identified radio surveys. This is by far the largest ever optically identified radio catalogue, and will permit robust statistical studies of star-forming and radio-loud active galaxies.

Detailed study of the Boötes field using 300–500 MHz uGMRT observations: source properties and radio–infrared correlations

ABSTRACT The dominant source of radio continuum emissions at low frequencies is synchrotron radiation, which originates from star-forming regions in disc galaxies and from powerful jets produced by active galactic nuclei (AGNs). We studied the Boötes field using the upgraded Giant Meterwave Radio Telescope at 400 MHz, achieving a central minimum off-source rms noise of 35 μJy beam−1 and a catalogue of 3782 sources in ∼6 deg2 of the sky. The resulting catalogue was compared to other radio frequency catalogues, and the corrected normalized differential source counts were derived. We use standard multiwavelength techniques to classify the sources in star-forming galaxies (SFGs), radio-loud AGNs, and radio-quiet (RQ) AGNs that confirm a boost in the SFG and RQ AGN populations at lower flux levels. For the first time, we investigated the properties of the radio–infrared (IR) relations at 400 MHz in this field. The $L_{\rm 400\, MHz}$–LTIR relations for SFGs were found to show a strong correlation with non-linear slope values of 1.10 ± 0.01, and variation of qTIR with z is given as qTIR = (2.19 ± 0.07) (1 + z)−0.15 ± 0.08. This indicates that the non-linearity of the radio–IR relations can be attributed to the mild variation of qTIR values with z. The derived relationships exhibit similar behaviour when applied to Low-Frequency Array at 150 MHz and also at 1.4 GHz. This emphasizes the fact that other parameters like magnetic field evolution with z or the number densities of cosmic ray electrons can play a vital role in the mild evolution of q values.

Robust Estimates of Orientation between Astrometric Catalogs

Accurately comparing two celestial reference frames based on the observed position of a number of common objects requires to detect and appropriately process outliers, lest they spuriously influence the results. It is thus of practical importance to use algorithms able to minimize the impact of those outliers when comparing radio and/or optical astrometric catalogs. In this paper, we investigate and compare the performances of some well-established and more recent robust algorithms when fitting a simple rotation vector between two reference frames. We particularly focus on two aspects: the variance of the resulting estimates, and the ability of the estimators to deal with outlying leverage points. We ran a number of Monte Carlo simulations with synthetic objects, varying their number, as well as the fraction and dispersion of outliers. Since the distribution of catalog objects in the sky is sometimes markedly nonuniform as in the case of the ICRF3 catalog, and because the position of outliers in the sky might cause issues when fitting rotation models, we also ran simulations representative of the observed distribution of objects. We compare the ICRF3 S/X, ICRF2 and Gaia EDR3 reference frames. Our results, based on the synthetic simulations and the comparison between the existing celestial frames, show that the M estimator, with a scale obtained from a least absolute deviations estimate, is the best among all the robust estimators compared.

The Predicition of Solar Flares Using Millimeter Radio Brightenings

Abstract Solar activity could have significant impacts on various Earth and near-Earth space systems, such as satellite communication and power grid systems. The prediction of solar activity and active solar events plays a major role when preparing for these disturbances. Various satellite-based instruments constantly observe the Sun. However, only a few ground-based solar instruments could provide versatile enough information for the space weather prediction. Metsähovi Radio Observatory of Aalto University (Finland) has a unique collection of millimetre (8 mm) solar radio maps over the past 40 years, and even denser observational solar radio data catalogue since 2011. About 75–80 % days yearly are covered nowadays. This gives opportunity to make statistical estimation of solar flare occurrence based on solar radio maps. In this study, we had 2253 days when both solar radio map and GOES (Geostationary Operational Environmental Satellites) classified solar flare were observed. In this work, we used solar flare classification done by the Space Weather Centre (SWC) of the National Oceanic and Atmospheric Administration (NOAA). The data were observed between 1 January 2011 and 12 September 2022. Our study shows that the maximum intensity of radio brightenings is a good indicator to tell which kind of GOES classified solar flare could be expected to happen. The article presents that intense radio brightening is needed to produce a certain GOES classified solar flare.

Discovery of 20 UV-emitting SNRs in M31 with UVIT

We present the first catalog of supernova remnants (SNRs) in M31 that exhibit diffuse ultraviolet (UV) emission. UV images of M31 were obtained by the Ultraviolet Imaging Telescope (UVIT) on the AstroSat satellite, and the list of SNRs was obtained from X-ray, optical, and radio catalogs of SNRs in M31. We used the UVIT images to find SNRs with diffuse emission, omitting those too contaminated with stellar emission. A total of 20 SNRs in M31 were detected with diffuse UV emission. Fluxes in the UVIT F148W, F169M, F172M, N219M, and N279N filters are measured for these SNRs. The luminosities are compared to those computed from the spectra of seven known UV-emitting SNRs in the Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud. We find similar spectral shapes between the known and the M31 UV-emitting SNRs. The spectral shapes and the diffuse nature of the emission are good evidence that the UV emissions are dominated by line emissions, like known SNRs, and the UV is associated with the SNRs. Models are applied to the six SNRs with X-ray spectra. The main difference is that the two X-ray/UV SNRs are Type Ia and the four X-ray/non-UV SNRs are core-collapse or unknown type. A comparison of M31 SNRs in different wave bands shows that most are detected optically, similar to the case for other nearby galaxies. A total of 19 of the 20 UV-emitting SNRs are detected optically, expected because both UV and optical are from forbidden and recombination lines from shock-ionized gas.

Three New Spiral Galaxies with Active Nuclei Producing Double Radio Lobes

Double radio lobes are generally believed to be produced by active nuclei of elliptical galaxies. However, several double-lobed radio sources have been solidly found to be associated with spiral galaxies. By cross-matching ∼9 × 105 spiral galaxies selected from the Sloan Digital Sky Survey DR8 data with the full 1.4 GHz radio source catalogs of NRAO VLA Sky Survey and Faint Images of the Radio Sky at Twenty-centimeters, we identify three new spiral galaxies: J0326−0623, J1110+0321 and J1134+3046 that produce double radio lobes, and five double-lobed spirals previously known. By combining the newly discovered and all the other known cases in literature, we confirm the relation that more massive spiral galaxies could produce more powerful radio lobes. We find that most of these spiral galaxies are located in a galaxy group or a poor cluster, in which the environment is denser than in the field, and about half of them are the central brightest galaxies in their parent system. We therefore suggest that the environment is one of the key factors for a spiral to produce double radio lobes.

A powerful (and likely young) radio-loud quasar at z = 5.3

We present the discovery of PSO J191.05696+86.43172 (hereafter PSO J191+86), a new powerful radio-loud quasar (QSO) in the early Universe (z = 5.32). We discovered it by cross-matching the NRAO VLA Sky Survey (NVSS) radio catalog at 1.4 GHz with the first data release of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS PS1) in the optical. With a NVSS flux density of 74.2 mJy, PSO J191+86 is one of the brightest radio QSO discovered at z ∼ 5. The intensity of its radio emission is also confirmed by the very high value of radio loudness (R &gt; 300). The observed radio spectrum of PSO J191+86 shows a possible turnover around ∼1 GHz (i.e., ∼6 GHz in the rest frame), making it a gigahertz-peaked spectrum (GPS) source. However, variability could affect the real shape of the radio spectrum, because the data in hand were taken ∼25 years apart. By assuming a peak in the observed radio spectrum between 1 and 2 GHz (i.e., ∼6 and 13 GHz in the rest-frame) we find a linear size of the source of ∼10–30 pc and a corresponding kinetic age of 150–460 yr. This would make PSO J191+86 a newly born radio source. However, the large X-ray luminosity (5.3×1045 erg s−1), the flat X-ray photon index (ΓX = 1.32), and the optical–X-ray spectral index (αox̃ = 1.329) are typical of blazars. This could indicate that the nonthermal emission of PSO J191+86 is Doppler boosted. Further radio observations (both on arcsec and parsec scales) are necessary to better investigate the nature of this powerful radio QSO.