Spectral Index Distribution Research Articles

Mapping the Distribution of the Magnetic Field Strength along the NGC 315 Jet

We study magnetic field strengths along the jet in NGC 315. First, we estimated the angular velocity of rotation in the jet magnetosphere by comparing the measured velocity profile of NGC 315 with the magnetohydrodynamic jet model proposed by Tomimatsu and Takahashi. Similar to the case of M87, we find that the model can reproduce the logarithmic feature of the velocity profile and suggest a slowly rotating black hole magnetosphere for NGC 315. By substituting the estimated Ω F into the jet power predicted by the Blandford–Znajek mechanism, we estimate the magnetic field strength near the event horizon of the central black hole as 5 × 103 G ≲ B H ≲ 2 × 104 G. We then estimate magnetic field strengths along the jet by comparing the spectral index distribution obtained from very long baseline interferometry (VLBI) observations with a synchrotron-emitting jet model. Then we constrain the magnetic field strength at a deprojected distance z from the black hole to be in the range 0.06 G ≲ B(z) ≲ 0.9 G for 5.2 × 103 r g ≲ z ≲ 4.9 × 104 r g , where r g represents the gravitational radius. By combining the obtained field strengths at the event horizon and the downstream section of the jet, we find that the accretion flow at the jet base is consistent with a magnetically arrested disk. We discuss a comparison of the jet power and the magnetic flux anchored to the event horizon in NGC 315 and M87.

Constraining the hadronic properties of star-forming galaxies above 1 GeV with 15-years Fermi-LAT data

Star-forming and starburst galaxies (SFGs and SBGs) are considered to be powerful emitters of non-thermal γ-rays and neutrinos, due to their intense phases of star-formation activity, which should confine high-energy Cosmic-Rays (CRs) inside their environments. On this regard, the Fermi-LAT collaboration has found a correlation between the γ-ray and infrared luminosities for a sample of local sources. Yet, the physics behind these non-thermal emission is still under debate. We provide novel constraints on the tight relation between γ-rays and star formation rate (SFR) exploiting 15 years of public Fermi-LAT data. Thus, we probe the calorimetric fraction Fcal of high-energy protons in SFGs and SBGs, namely, the fraction of high-energy protons actually producing high-energy γ-rays and neutrinos. Further, we extrapolate this information to their diffuse γ-ray and neutrino emissions constraining their contribution to the extra-galactic gamma-ray background (EGB) and the diffuse neutrino flux. Using the publicly-available fermitools, we analyse 15.3 years of γ-ray between 1-1000 GeV data for 70 sources, 56 of which were not previously detected. We relate this emission to a theoretical model for SBGs in order to constrain Fcal for each source and then study its correlation with the star formation rate of the sources. Firstly, we find at 4σ level an indication of γ-ray emission for other two SBGs, namely M 83 and NGC 1365. By contrast, we find that, even with the new description of background, the significance for the γ-ray emission of M 33 (initially reported as discovered) still stands at ~ 4σ (as already reported by previous works).Along with previous findings, the flux of each detected source is consistent with a ~ E -2.3/2.4 spectrum, compatible with the injected CR flux inferred in the Milky-Way. We also notice that the correlation between Fcal and the SFR is in accordance with the expected scaling relation for CR escape dominated by advection. We remark that undiscovered sources strongly constrain Fcal at 95% CL, providing fundamental information when we interpret the results as common properties of SFGs and SBGs. Finally, we find that these sources might contribute (12 ± 3)% to the EGB, while the corresponding diffuse neutrino flux strongly depends on the spectral index distribution along the source class.

Population synthesis models indicate a need for early and ubiquitous disk substructures

Context. Large millimeter surveys of star-forming regions enable the study of entire populations of planet-forming disks and reveal correlations between their observable properties. The ever-increasing number of these surveys has led to a flourishing of population study, a valuable tool and approach that is spreading in ever more fields. Population studies of disks have shown that the correlation between disk size and millimeter flux could be explained either through disks with strong substructure, or alternatively by the effects of radial inward drift of growing dust particles. Aims. This study aims to constrain the parameters and initial conditions of planet-forming disks and address the question of the need for the presence of substructures in disks and, if needed, their predicted characteristics, based on the large samples of disk sizes, millimeter fluxes, and spectral indices available. Methods. We performed a population synthesis of the continuum emission of disks, exploiting a two-population model (two-pop-py), considering the influence of viscous evolution, dust growth, fragmentation, and transport, varying the initial conditions of the disk and substructure to find the best match with the observed distributions. Disks both with and without substructure have been examined. We obtained the simulated population distribution for the disk sizes, millimeter fluxes, and spectral indices by post-processing the resulting disk profiles (surface density, maximum grain size, and disk temperature). Results. We show that the observed distributions of spectral indices, sizes, and luminosities together can be best reproduced by disks with significant substructure; namely, a perturbation that is strong enough to be able to trap particles, that is formed early in the evolution of the disk, and that is within 0.4 Myr. Agreement is reached by relatively high initial disk masses (10−2.3 M⋆ ⩽ Mdisk ⩽ 10−0.5 M⋆) and moderate levels of turbulence (10−3.5 ⩽ α ⩽ 10−2.5). Other disk parameters play a weaker role. Only opacities with a high absorption efficiency can reproduce the observed spectral indices. Conclusions. Disk population synthesis is a precious tool for investigating and constraining the parameters and initial conditions of planet-forming disks. The generally low observed spectral indices call for significant substructure, like that which planets in the mass range of Saturn to a few Jupiters would induce, to already be present before 0.4 Myr. Our results indicate that substructure, which so far has only been assessed in individual disks, is likely ubiquitous and extends to the whole population, and imply that most “smooth” disks hide unresolved substructure.

Unveiling the Small-scale Jets in the Rapidly Growing Supermassive Black Hole IZw1

Accretion of black holes at near-Eddington or super-Eddington rates represents the most powerful episode driving black hole growth, potentially occurring across various types of objects. However, the physics governing accretion and jet–disk coupling in such states remains unclear, primarily due to the difficulty in detecting associated jets, which may emit extremely weakly or exhibit episodic behavior. Only a few near/super-Eddington systems have demonstrated radio activity, and it remains uncertain whether jets exist and what their properties are in super-Eddington active galactic nuclei (AGNs) and ultraluminous X-ray sources. This uncertainty stems mainly from the complex radio emission mix, which includes contributions from jets, star formation activity, photoionized gas, accretion disk wind, and coronal activity. In this work, we conducted high-resolution, very long baseline interferometry observations to investigate jets in the highly accreting narrow-line Seyfert I system I Zw 1. Our observations successfully revealed small-scale jets (with a linear size of ∼45 pc) at both 1.5 and 5 GHz, based on the high radio brightness temperature, radio morphology, and spectral index distribution. Additionally, the parsec-scale jet observed in I Zw 1 displays a knotted morphology reminiscent of other sources accreting at similar rates. In summary, the high accretion rates and jet properties observed in the AGN I Zw 1 may support the AGN/X-ray binary analogy in this extreme state.

Spectral Index Distribution of Various Scale Components in Supernova Remnant Cassiopeia A

Cassiopeia A (Cas A) is a well-known candidate for studying cosmic-ray acceleration, in which compact features of various scales have attracted much attention. Based on observations by the Very Large Array of Cas A at 6 cm and 21 cm, we measure the spectral index distribution of various scale components using the observation of the 1998 epoch. We decompose its total density image into nine scale components, and map the temperature spectral index distribution of each component, which ranges from −2.48 ± 0.01 to −2.91 ± 0.05. We find that the spectral indices increase from the small scale to large scale components. A damped post-shock magnetic field model with a strength larger than ∼200 μG and a damping length scale less than ∼10% of the remnant radius can account for the spectral index variation naturally.

A Giant Metrewave Radio Telescope survey of radio-loud broad absorption line quasars

ABSTRACT A substantial fraction of quasars display broad absorption lines (BALs) in their rest-frame ultraviolet spectra. While the origin of BALs is thought to be related to the accretion disc wind, it remains unclear whether the observed ratio of BAL to non-BAL quasars is a result of orientation. We conducted observations of 48 BAL quasars and the same number of non-BAL quasars at 322 MHz using the Giant Metrewave Radio Telescope. Combined with previous flux measurements ranging from MHz to GHz frequencies, we compared continuum radio spectra between the two quasar groups. These data offer insights into low-frequency radio properties that have been difficult to investigate with previous observations only at GHz frequencies. Our results show that 73 ± 13 per cent of the BAL quasars exhibit steep or peaked spectra, a higher proportion than the 44 ± 14 per cent observed in the non-BAL quasars. In contrast, there are no discernible differences between the two quasar groups in the radio luminosity, peak frequency, and spectral index distributions of sources with steep or peaked spectra and sources with flat or inverted spectra. Generally, as the jet axis and line of sight become closer to parallel, quasars exhibit flat or inverted spectra rather than steep or peaked spectra. Therefore, these results suggest that BAL quasars are more frequently observed farther from the jet axis than non-BAL quasars. However, given that a certain proportion of BAL quasars exhibit flat or inverted spectra, more than the simple orientation scenario is required to elucidate the radio properties of BAL quasars.

CONGRuENTS (COsmic-ray, Neutrino, Gamma-ray and Radio Non-Thermal Spectra) – II. Population-level correlations between galactic infrared, radio, and γ-ray emission

ABSTRACT Galaxies obey a number of empirical correlations between their radio, γ-ray, and infrared emission, but the physical origins of these correlations remain uncertain. Here, we use the CONGRuENTS model for broad-band non-thermal emission from star-forming galaxies, which self-consistently calculates energy-dependent transport and non-thermal emission from cosmic ray hadrons and leptons, to predict radio and γ-ray emission for a synthetic galaxy population with properties drawn from a large deep-field survey. We show that our synthetic galaxies reproduce observed relations such as the far infrared (FIR)–radio correlation, the FIR–γ correlation, and the distribution of radio spectral indices, and we use the model to explain the physical origins of these relations. Our results show that the FIR–radio correlation arises because the amount of cosmic ray electron power ultimately radiated as synchrotron emission varies only weakly with galaxy star formation rate as a result of the constraints imposed on gas properties by hydrostatic balance and turbulent dynamo action; the same physics dictates the extent of proton calorimetry in different galaxies, and thus sets the FIR–γ–ray correlation. We further show that galactic radio spectral indices result primarily from competition between thermal free–free emission and energy-dependent loss of cosmic ray electrons to bremsstrahlung and escape into galactic haloes, with shaping of the spectrum by inverse Compton, synchrotron, and ionization processes typically playing a subdominant role. In addition to explaining existing observations, we use our analysis to predict a heretofore unseen correlation between the curvature of galaxies’ radio spectra and their pion-driven γ-ray emission, a prediction that will be testable with upcoming facilities.

Evolution of Magnetic Field of the Quasar 1604+159 at parsec Scale

We have analyzed the total intensity, spectral index, linear polarization, and rotation measure (RM) distributions at the parsec scale for the quasar 1604+159. The source was observed at 5.0, 8.4, and 15.4 GHz in 2002 and 4.6, 5.1, 6.0, 7.8, 12.2, 15.2, and 43.9 GHz in 2020 with the American Very Long Baseline Array (VLBA). Combining the polarization results of Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments at 15 GHz from 2009 to 2013, we studied the evolution of magnetic field at the parsec scale for the source. We detected a core-jet structure. The jet extends to the distance of ∼25 mas from the core at a direction of ∼66° north by east. The shape of the jet derived from 15 GHz data varies slightly with time and could be described by a straight line. Based on the linear polarization distribution in 2002, we divided the source structure into the central region and the jet region. In the jet region, we find the polarized emission varies with time. The flatter spectral index values and electric vector position angle direction indicate the possible existence of shocks, contributing to the variation of polarization in the jet with time. In the central region, the derived core shift index k r values indicate that the core in 2002 is close to the equipartition case, while it deviated from the case in 2020. The measured magnetic field strength in 2020 is 2 orders of magnitude lower than that in 2002. We detected transverse RM gradients, evidence of a helical magnetic field, in the core. The polarized emission orients in general toward the jet direction in the core. At 15 GHz, in the place close to the jet base, the polarization direction changes significantly with time from perpendicular to parallel to the jet direction. The evolution of RM and magnetic field structure are potential reasons for the observed polarization change. The core ∣RM∣ in 2020 increases with frequency following a power law with index a = 2.7 ± 0.5, suggesting a fast electron density falloff in the medium with distance from the jet base.

TELAMON: Effelsberg monitoring of AGN jets with very-high-energy astroparticle emission

Aims. We introduce the TELAMON program which is using the Effelsberg 100-m telescope to monitor the radio spectra of active galactic nuclei (AGN) under scrutiny in astroparticle physics, specifically TeV blazars and candidate neutrino-associated AGN. Here, we present and characterize our main sample of TeV-detected blazars. Methods. We analyzed the data sample from the first ∼2.5 yr of observations between August 2020 and February 2023 in the range from 14 GHz to 45 GHz. During this pilot phase, we observed all 59 TeV-detected blazars in the Northern Hemisphere (i.e., Dec > 0°) known at the time of observation. We discuss the basic data reduction and calibration procedures used for all TELAMON data and introduce a sub-band averaging method used to calculate average light curves for the sources in our sample. Results. The TeV-selected sources in our sample exhibit a median flux density of 0.12 Jy at 20 mm, 0.20 Jy at 14 mm, and 0.60 Jy at 7 mm. The spectrum for most of the sources is consistent with a flat radio spectrum and we found a median spectral index (S(ν)∝να) of α = −0.11. Our results on flux density and spectral index are consistent with previous studies of TeV-selected blazars. Compared to the GeV-selected F-GAMMA sample, TELAMON sources are significantly fainter in the radio band. This is consistent with the double-humped spectrum of blazars being shifted towards higher frequencies for TeV-emitters (in particular for high-synchrotron peaked BL Lac type objects), which results in a lower radio flux density. The spectral index distribution of our TeV-selected blazar sample is not significantly different from the GeV-selected F-GAMMA sample. Moreover, we present a strategy to track the light curve evolution of sources in our sample for future variability and correlation analysis.

Coupled nonlinear drift and IAWs in streaming O–H plasma of upper ionosphere

Nonlinear structures formed by the coupled drift wave (DW) and ion acoustic waves (IAWs) are studied in a magnetized inhomogeneous collisionless bi-ion plasma with ions shear flow along the ambient magnetic field B=B0ẑ. The electrons are assumed to follow double spectral index (r, q) distribution in which r shows the flat top nature, while q is responsible for the shape of the distribution at the tail. A nonlinear differential equation is derived, and its solutions in the form of double layers (DLs) and solitons are obtained in different limits. It is pointed out that the presence of (0.4%) protons in the oxygen plasma of ionosphere should not be ignored because acoustic speeds corresponding to oxygen and hydrogen ions have small ratio of about four and drift wave frequency may lie in the same range. It is found that only the rarefactive solitons can be formed by the nonlinear DW and IAWs in the inhomogeneous oxygen hydrogen (O–H) plasma. However, the theoretical model predicts that both compressive and rarefactive DLs may be formed. The linear instabilities of low-frequency electrostatic waves due to field-aligned shear flow of ions have also been investigated.

Probing diffuse radio emission in bridges between galaxy clusters with uGMRT

Aims. Recent X-ray and Sunyaev–Zeldovich (SZ) observations have detected thermal emission between early-stage merging galaxy clusters. The main purpose of this work is to investigate the properties of the non-thermal emission in the interacting cluster pairs Abell 0399-Abell 0401 and Abell 21-PSZ2 G114.9. Methods. These two unique cluster pairs have been found in an interacting state. In both cases, their connection along a filament is supported by an SZ effect detected by the Planck satellite and, in the special case of Abell 0399-Abell 0401, the presence of a radio bridge has been already confirmed by LOFAR observations at 140 MHz. Here, we analyse new high-sensitivity, wideband (250–500 MHz) uGMRT data of these two systems and describe an injection procedure to place limits on the spectrum of Abell 0399-Abell 0401 and on the radio emission between Abell 21-PSZ2 G114.9. Results. In both cases, the low-surface-brightness diffuse emission is not detected in Band 3 (250–500 MHz). For the A399-A401 pair, we are able to constrain the steep spectral index of the bridge emission to be α > 2.2 with a 95% confidence level between 140 MHz and 400 MHz. We also detect a small patch of the bridge with a flatter spectral index, which may suggest a variable spectral index distribution across the bridge area. For the A21-PSZ2 G114.9 pair, we are able to place an upper limit on the flux density of the bridge emission with two different methods, finding at the central frequency of 383 MHz a conservative value of fu1 < 260 mJy at a 95% confidence level, and a lower value of fu2 < 125 mJy at an 80% confidence level, based on visual inspection and a morphological criterion. Conclusions. Our work provides a constraint on the spectrum in the bridge A399-A401 that disfavours shock acceleration as the main mechanism for the radio emission. The methods that we propose for the limits on the radio emission in the A21-PSZ2 G114.9 system represent a first step towards a systematic study of these sources.

A Formation Mechanism for “Wrong Way” Radio Relics

Radio relics are typically found to be arc-like regions of synchrotron emission in the outskirts of merging galaxy clusters, bowing out from the cluster center. In most cases they show synchrotron spectra that steepen toward the cluster center, indicating that they are caused by relativistic electrons being accelerated at outward traveling merger shocks. A number of radio relics break with this ideal picture and show morphologies that are bent the opposite way and show spectral index distributions that do not follow expectations from the ideal picture. We propose that these “wrong way” relics can form when an outward traveling shock wave is bent inward by an infalling galaxy cluster or group. We test this in an ultra-high-resolution zoom-in simulation of a massive galaxy cluster with an on-the-fly spectral cosmic-ray model. This allows us to study not only the synchrotron emission at colliding shocks, but also their synchrotron spectra to address the open question of relics with strongly varying spectral indices over the relic surface.

Understanding the broad-band emission process of 3C 279 through long term spectral analysis

ABSTRACT The long term broad-band spectral study of Flat Spectrum Radio Quasars during different flux states has the potential to infer the emission mechanisms and the cause of spectral variations. To scrutinize this, we performed a detailed broad-band spectral analysis of 3C 279 using simultaneous Swift-XRT/UVOT and Fermi-LAT observations spanning from 2008 August to 2022 June. We also supplement this with the simultaneous NuSTAR observations of the source. The optical/UV, X-ray, and γ-ray spectra were individually fitted by a power law to study the long term variation in the flux and the spectral indices. A combined spectral fit of simultaneous optical/UV and X-ray spectra was also performed to obtain the transition energy at which the spectral energy distribution is minimum. The correlation analysis suggests that the long term spectral variations of the source are mainly associated with the variations in the low energy index and the break energy of the broken power-law electron distribution which is responsible for the broad-band emission. The flux distribution of the source represents a lognormal variability while the γ-ray flux distribution showed a clear double lognormal behaviour. The spectral index distributions were again normal except for γ-ray which showed a double-Gaussian behaviour. This indicates that the lognormal variability of the source may be associated with the normal variations in the spectral index. The broad-band spectral fit of the source using synchrotron and inverse Compton processes indicates different emission processes are active at optical/UV, X-ray, and γ-ray energies.

Deciphering the radio–star formation correlation on kpc scales

The relation between the resolved star formation rate (SFR) per unit area and the nonthermal radio continuum emission is studied in 21 Virgo cluster galaxies and the two nearby spiral galaxies, NGC 6946 and M 51. For the interpretation and understanding of our results, we used a 3D model where star formation, 2D cosmic-ray (CR) propagation, and the physics of synchrotron emission are included. Based on the linear correlation between the SFR per unit area and the synchrotron emission and its scatter, radio-bright and radio-dim regions can be robustly defined for our sample of spiral galaxies. We identified CR diffusion or streaming as the physical causes of radio-bright regions of unperturbed symmetric spiral galaxies as NGC 6946. The enhanced magnetic field in the region of interstellar medium (ISM) compression via ram pressure is responsible for the southwestern radio-bright region in NGC 4501. We identified the probable causes of radio-bright regions in several galaxies as CR transport, via either gravitational tides (M 51) or galactic winds (NGC 4532) or ram pressure stripping (NGC 4330 and NGC 4522). Three galaxies are overall radio dim: NGC 4298, NGC 4535, and NGC 4567. Based on our model of synchrotron-emitting disks, we suggest that the overall radio-dim galaxies have a significantly lower magnetic field than expected by equipartition between the magnetic and turbulent energy densities. We suggest that this is linked to the difference between the timescales of the variation in the SFR and the small-scale dynamo. In NGC 4535, shear motions increase the total magnetic field strength via the induction equation, which leads to enhanced synchrotron emission with respect to the SFR in an otherwise radio-dim galactic disk. Radio-bright regions frequently coincide with asymmetric ridges of polarized radio continuum emission, and we found a clear albeit moderate correlation between the polarized radio continuum emission and the radio/SFR ratio. When compression or shear motions of the ISM are present in the galactic disk, the radio-bright regions are linked to the commonly observed asymmetric ridges of polarized radio continuum emission and represent a useful tool for the interaction diagnostics. The magnetic field is enhanced (as observed in NGC 4535 and NGC 4501) and ordered by these ISM compression and shear motions. Whereas the enhancement of the magnetic field is rather modest and does not significantly influence the radio-SFR correlation, the main effect of ISM compression and shear motions is the ordering of the magnetic field, which significantly affects the CR transport. Cosmic-ray energy losses and transport also affect the spectral index, which we measured between 4.85 and 1.4 GHz. The influence of CR losses and transport on the spectral index distribution with respect to the synchrotron/SFR ratio is discussed with the help of model calculations. Based on our results, we propose a scenario for the interplay between star formation, CR electrons, and magnetic fields in spiral galaxies.

Spectral analysis of a parsec-scale jet in M 87: Observational constraint on the magnetic field strengths in the jet

Context. Because of its proximity and the large size of its black hole, M 87 is one of the best targets for studying the launching mechanism of active galactic nucleus jets. Currently, magnetic fields are considered to be an essential factor in the launching and accelerating of the jet. However, current observational estimates of the magnetic field strength of the M 87 jet are limited to the innermost part of the jet (≲100 rs) or to HST-1 (∼105 rs). No attempt has yet been made to measure the magnetic field strength in between. Aims. We aim to infer the magnetic field strength of the M 87 jet out to a distance of several thousand rs by tracking the distance-dependent changes in the synchrotron spectrum of the jet from high-resolution very long baseline interferometry observations. Methods. In order to obtain high-quality spectral index maps, quasi-simultaneous observations at 22 and 43 GHz were conducted using the KVN and VERA Array (KaVA) and the Very Long Baseline Array (VLBA). We compared the spectral index distributions obtained from the observations with a model and placed limits on the magnetic field strengths as a function of distance. Results. The overall spectral morphology is broadly consistent over the course of these observations. The observed synchrotron spectrum rapidly steepens from α22 − 43 GHz ∼ −0.7 at ∼2 mas to α22 − 43 GHz ∼ −2.5 at ∼6 mas. In the KaVA observations, the spectral index remains unchanged until ∼10 mas, but this trend is unclear in the VLBA observations. A spectral index model in which nonthermal electron injections inside the jet decrease with distance can adequately reproduce the observed trend. This suggests the magnetic field strength of the jet at a distance of 2−10 mas (∼900 rs − ∼4500 rs in the deprojected distance) has a range of B = (0.3−1.0 G)(z/2mas)−0.73. Extrapolating to the Event Horizon Telescope scale yields consistent results, suggesting that the majority of the magnetic flux of the jet near the black hole is preserved out to ∼4500 rs without significant dissipation.

Hirota bilinear method and multi-soliton interaction of electrostatic waves driven by cubic nonlinearity in pair-ion–electron plasmas

Multi-soliton interaction of nonlinear ion sound waves in a pair-ion–electron (PIE) plasma having non-Maxwellian electrons including Kappa, Cairns, and generalized two spectral index distribution functions is studied. To this end, a modified Korteweg–de Vries (mKdV) equation is obtained to investigate the ion-acoustic waves in a PIE plasma at a critical plasma composition. The effects of temperature and density ratios and the non-Maxwellian electron velocity distributions on the overtaking interaction of solitons are explored in detail. The results reveal that both hump (positive peak) and dip (negative peak) solitons can propagate for the physical model under consideration. Two and three-soliton interactions are presented, and the novel features of interacting compressive and rarefactive solitons are highlighted. The present investigation may be useful in laboratory plasmas where PIE plasmas have been reported.

Simulated catalogs and maps of radio galaxies at millimeter wavelengths in Websky

We present simulated millimeter-wavelength maps and catalogs of radio galaxies across the full sky that trace the nonlinear clustering and evolution of dark matter halos from the Websky simulation at z < 4.6 and M halo > 1012 m ⊙/h, and the accompanying framework for generating a new sample of radio galaxies from any halo catalog of positions, redshifts, and masses. Object fluxes are generated using a hybrid approach that combines (1) existing astrophysical halo models of radio galaxies from the literature to determine the positions and rank-ordering of the observed fluxes with (2) empirical models from the literature based on fits to the observed distribution of flux densities and (3) spectral indices drawn from an empirically-calibrated frequency-dependent distribution. The resulting population of radio galaxies is in excellent agreement with the number counts, polarization fractions, and distribution of spectral slopes from the data from observations at millimeter wavelengths from 20-200 GHz, including Planck, ALMA, SPT, and ACT. Since the radio galaxies are correlated with the existing cosmic infrared background (CIB), Compton-y (tSZ), and CMB lensing maps from Websky, our model makes new predictions for the cross-correlation power spectra and stacked profiles of radio galaxies and these other components. These simulations will be important for unbiased analysis of a wide variety of observables that are correlated with large-scale structure, such as gravitational lensing and SZ clusters.

Spectral index distribution over radio lobes of 4C 14.11 using astrophysical data in FITS format

The goal of this paper is to investigate the flux and spectral index distribution of FR II radio galaxy 4C 14.11. We focused on the distribution of flux and spectral indices over the lobes, as well as in their hot spots. For that purpose, we used publicly available observations of this radio galaxy given at 1450 and 8440 MHz. Particularly, we used Leahy’s Atlas of radio-emitting double radio sources, Jodrell Bank Centre for Astrophysics in Manchester, as well as NASA/IPAC Extragalactic Database. We found that the non-thermal (synchrotron) radiation dominates over the areas of the lobes. Distinction between hot spots and rest of the lobes are much smaller in the spectral index than in the flux. We also found that over the inner parts of both lobes, spectral index α is flat in average and significantly higher than 1.2, indicating that 4C 14.11 is old AGN.

Search and analysis of giant radio galaxies with associated nuclei (SAGAN)

Giant radio quasars (GRQs) are radio-loud active galactic nuclei (AGN) that propel megaparsec-scale jets. In order to understand GRQs and their properties, we have compiled all known GRQs (‘the GRQ catalogue’) and a subset of small (size &lt; 700 kpc) radio quasars (SRQs) from the literature. In the process, we have found ten new Fanaroff-Riley type-II GRQs in the redshift range of 0.66 &lt; z &lt; 1.72, which we include in the GRQ catalogue. Using the above samples, we have carried out a systematic comparative study of GRQs and SRQs using optical and radio data. Our results show that the GRQs and SRQs statistically have similar spectral index and black hole mass distributions. However, SRQs have a higher radio core power, core dominance factor, total radio power, jet kinetic power, and Eddington ratio compared to GRQs. On the other hand, when compared to giant radio galaxies (GRGs), GRQs have a higher black hole mass and Eddington ratio. The high core dominance factor of SRQs is an indicator of them lying closer to the line of sight than GRQs. We also find a correlation between the accretion disc luminosity and the radio core and jet power of GRQs, which provides evidence for disc-jet coupling. Lastly, we find the distributions of Eddington ratios of GRGs and GRQs to be bi-modal, similar to that found in small radio galaxies (SRGs) and SRQs, which indicates that size is not strongly dependent on the accretion state. Using all of this, we provide a basic model for the growth of SRQs to GRQs.

ALMA High-resolution Multiband Analysis for the Protoplanetary Disk around TW Hya

Abstract We present a high-resolution (2.5 au) multiband analysis of the protoplanetary disk around TW Hya using Atacama Large Millimeter/submillimeter Array (ALMA) long baseline data at Bands 3, 4, 6, and 7. We aim to reconstruct a high-sensitivity millimeter continuum image and revisit the spectral index distribution. The imaging is performed by combining new ALMA data at Bands 4 and 6 with available archive data. Two methods are employed to reconstruct the images: multifrequency synthesis (MFS) and the fiducial image-oriented method, where each band is imaged separately and the frequency dependence is fitted pixel by pixel. We find that MFS imaging with a second-order Taylor expansion can reproduce the frequency dependence of the continuum emission between Bands 3 and 7 in a manner consistent with previous studies, and that it is a reasonable method for reconstructing the spectral index map. The image-oriented method provides a spectral index map consistent with the MFS imaging, but with a two times lower resolution. Mock observations of an intensity model were conducted to validate the images from the two methods. We find that the MFS imaging provides a high-resolution spectral index distribution with an uncertainty of &lt;10%. Using the submillimeter spectrum reproduced from our MFS images, we directly calculate the optical depth, power-law index of the dust opacity coefficient (β), and dust temperature. The derived parameters are consistent with previous works, and the enhancement of β within the intensity gaps is also confirmed, supporting a deficit of millimeter-sized grains within the gaps.