Spectral Energy Distribution Research Articles

An alternative interpretation of magnetars’ traits deduced from the observational data on their outburst fluxes and spectra

Abstract By applying the Efron-Petrosian method to the fluxes S and distances D of the magnetars listed in the Magnetar Outburst Online Catalogue, we show that the observational data are consistent with the dependence S∝D−3/2, which characterizes the emission from the superluminally moving current sheet in the magnetosphere of a non-aligned neutron star, at substantially higher levels of significance than they are with the dependence S∝D−2. This result agrees with that previously obtained by an analysis of the data in the McGill Online Magnetar Catalog and confirms that, contrary to the currently prevalent view, magnetars’ X-ray luminosities do not exceed their spin-down luminosities. The X-ray spectra of magnetars, moreover, are congruous with the spectral energy distribution (SED) of a broadband non-thermal emission mechanism identical to that at play in rotation-powered pulsars: we show that the SED of the caustics that are generated in certain privileged directions by the magnetospheric current sheet single-handedly fits the observed spectra of 4U 0142+61, 1E 1841-045 and XTE J1810-197 over their entire breadths. Magnetars’ outbursts and their associated radio bursts are predicted to occur when, as a result of large-scale timing anomalies (such as glitches, quakes or precession), one of the privileged directions along which the radiation from the current sheet decays more slowly than predicted by the inverse-square law either swings past or oscillates across the line of sight.

AGN feeding along a one-armed spiral in NGC 4593. A study using ALMA CO(2-1) observations

We investigate active galactic nuclei (AGN) feeding through the molecular gas (CO(2-1) emission) properties of the local Seyfert 1 galaxy NGC\,4593, using Atacama Large Millimeter Array (ALMA) observations and other multi-wavelength data. Our study aims to understand the interplay between the AGN and the interstellar medium (ISM) in this galaxy, examining the role of the AGN in steering gas dynamics within its host galaxy, evaluating the energy injected into the ISM, and determining whether gas is inflowing or outflowing from the galaxy. After reducing the ALMA CO(2-1) images, we employed two models 3D-Barolo and discFit to construct a disc model and fit its emission to the ALMA data. Additionally, we used photometric data to build a spectral energy distribution (SED) and apply the CIGALE code to derive key physical properties of the AGN and its host. Our analysis reveals a complex interplay within NGC\,4593, including a clear rotational pattern, the influence of a non-axisymmetric bar potential, and a central molecular zone (CMZ)-like ring. We observe an outflow of CO(2-1) gas along the minor axis, at a distance of sim 220 pc from the nucleus. The total molecular gas mass is estimated to be $1 - 5 odot $, with non-circular motions contributing $10<!PCT!>$. Our SED analysis indicates an AGN fraction of 0.88 and a star formation rate (SFR) of 0.42 $M_ odot yr These findings highlight the complex dynamics in the centre of NGC\,4593, which are significantly influenced by the presence of the AGN. The overall physical properties of this system suggest that the AGN has a substantial impact on the evolution of NGC\,4593.

Electromagnetic signatures from accreting massive black hole binaries in time domain photometric surveys

We study spectral and time variability of accreting massive black hole binaries (MBHBs) at milli-parsec separations surrounded by a geometrically thin circumbinary disc. To this end, we present the first computation of the expected spectral energy distribution (SED) and light curves (LCs) from 3D hyper-Lagrangian resolution hydrodynamic simulations of these systems. We modelled binaries with a total mass of $10^6$ M$_ eccentricities of $e=0,\, 0.9$, and a mass ratio of $q=0.1,\, 1$. The circumbinary disc has an initial aspect ratio of 0.1, features an adiabatic equation of state, and evolves under the effect of viscous heating, black-body cooling, and self gravity. To construct the SED, we considered black-body emission from each element of the disc and we added a posteriori an X-ray corona with a luminosity proportional to that of the mini-discs that form around each individual black hole. We find significant variability of the SED, especially at high energies, which translates into LCs displaying distinctive modulations of a factor of $ 2$ in the optical and of $ 10$ in UV and X-rays. We analysed in detail the flux variability in the optical band that will be probed by the Vera Rubin Observatory (VRO). We find clear modulations on the orbital period and half of the orbital period in all systems. Only in equal-mass binaries, we find an additional, longer-timescale modulation, associated with an over-density forming at the inner edge of the circumbinary disc (commonly referred to as a lump). When considering the VRO flux limit and nominal survey duration, we find that equal-mass, circular binaries are unlikely to be identified, due to the lack of prominent peaks in their Fourier spectra. Conversely, unequal-mass and/or eccentric binaries can be singled out up to $z 0.5$ (for systems with bol $ erg s$^ $) and $z 2$ (for systems with bol $ erg s$^ $). Identifying electromagnetic signatures of MBHBs at separations of $ $ pc is of paramount importance to understand the physics of the gravitational wave (GW) sources of the future Laser Interferometer Space Antenna, and to pin down the origin of the GW background (GWB) observed in pulsar timing arrays.

Using JADES NIRCam photometry to investigate the dependence of stellar mass inferences on the IMF in the early universe

The detection of numerous and relatively bright galaxies at redshifts z > 9 has prompted new investigations into the star-forming properties of high-redshift galaxies. Using local forms of the initial mass function (IMF) to estimate stellar masses of these galaxies from their light output leads to galaxy masses that are at the limit allowed for the state of the Lambda Cold Dark Matter (ΛCDM) Universe at their redshift. We explore how varying the IMF assumed in studies of galaxies in the early universe changes the inferred values for the stellar masses of these galaxies. We infer galaxy properties with the spectral energy distribution (SED) fitting code Prospector using varying IMF parameterizations for a sample of 102 galaxies with photometry from the James Webb Space Telescope, JWST Advanced Deep Extragalactic Survey that are spectroscopically confirmed to be at [Formula: see text], with additional photometry from the JWST Extragalactic Medium Band Survey for twenty-one of the galaxies. We demonstrate that models with stellar masses reduced by a factor of three or more do not affect the modeled SED.

A Nançay Radio Telescope study of the hyperactive repeating FRB 20220912A

Abstract The repeating fast radio burst source FRB 20220912A was remarkably active in the weeks after its discovery. Here we report 696 bursts detected with the Nançay Radio Telescope (NRT) as part of the Extragalactic Coherent Light from Astrophysical Transients (ÉCLAT) monitoring campaign. We present 68 observations, conducted from October 2022 to April 2023, with a total duration of 61 hours and an event rate peaking at $75^{+10}_{-9}$ bursts per hour above a fluence threshold of 0.59 Jy ms in the 1.2 − 1.7-GHz band. Most bursts in the sample occur towards the bottom of the observing band. They follow a bimodal wait-time distribution, with peaks at 33.4 ms and 67.0 s. We find a roughly constant dispersion measure (DM) over time (δDM ≲ 2 pc cm−3) when taking into account ‘sad-trombone’ drift, with a mean drift rate of −8.8 MHz ms−1. Nonetheless, we confirm small ∼0.3 pc cm−3 DM variations using microshot structure, while finding that microstructure is rare in our sample – despite the 16 μs time resolution of the data. The cumulative spectral energy distribution shows more high-energy bursts (Eν ≳ 1031 erg Hz−1) than would be expected from a simple power-law distribution. The burst rate per observation appears Poissonian, but the full set of observations is better modelled by a Weibull distribution, showing clustering. We discuss the various observational similarities that FRB 20220912A shares with other (hyper)active repeaters, which as a group are beginning to show a common set of phenomenological traits that provide multiple useful dimensions for their quantitative comparison and modelling.

JWST/NIRSpec spectroscopy of intermediate-mass quiescent galaxies at z ∼ 3–4

Abstract We present the analysis of three intermediate-mass quiescent galaxies (QGs) with stellar masses of ∼1010 M⊙ at redshifts z ∼ 3–4 using NIRSpec low-resolution spectroscopy. Utilising the SED fitting code BAGPIPES, we confirm these target galaxies are consistent with quiescent population, with their specific star formation rates (sSFR) falling below 2-dex the star-forming main sequence at the same redshifts. Additionally, we identify these QGs to be less massive than those discovered in previous works, particularly prior to the JWST era. Two of our target galaxies exhibit the potentially-blended Hα+[N ii] emission line within their spectra with S/N > 5. We discuss whether this feature comes from an Active Galactic Nucleus (AGN) or star formation although future high-resolution spectroscopy is required to reach a conclusion. One of the target galaxies is covered by JWST/NIRCam imaging of the PRIMER survey. Using the 2D profile fitting code Galfit, we examine its morphology, revealing a disc-like profile with a Sérsic index of n = 1.1 ± 0.1. On the size–mass relation, we find a potential distinction between less-massive (log10(M*/M⊙) < 10.3) and massive (log10(M*/M⊙) > 10.3) QGs in their evolutionary pathways. The derived quenching timescales for our targets are less than 1 Gyr. This may result from these galaxies being quenched by AGN feedback, supporting the AGN scenario of the emission line features.

The ALMA-CRISTAL survey: Dust temperature and physical conditions of the interstellar medium in a typical galaxy at z=5.66

We present new $ rest =77$ mu m dust continuum observations from the Atacama Large Millimeter/submillimeter Array of HZ10 (CRISTAL-22). This dusty main sequence galaxy at $z$=5.66 was observed as part of the Resolved Ism in STar-forming Alma Large program (CRISTAL). The high angular resolution of the ALMA Band 7 and new Band 9 data ($ ''.4$) reveals the complex structure of HZ10, which comprises two main components (HZ10-C and HZ10-W), along with a bridge-like dusty emission between them (i.e., "the bridge"). Using a modified blackbody function to model the dust spectral energy distribution (SED), we constrained the physical conditions of the interstellar medium (ISM) and its variations among the different components identified in HZ10. We find that HZ10-W (the more UV-obscured component) has an SED dust temperature of $T_ SED $sim 51.2$ K; this was found to be sim 5 K higher (which is statistically insignificant; i.e., less than 1sigma ) than that of the central component and previous global estimations for HZ10. Our new ALMA data allow us to reduce the uncertainties of global SED $ measurements by a factor of sim 2.3, compared to previous studies. The HZ10 components have (FIR) luminosity ratios and FIR surface densities values that are consistent with local starburst galaxies. However, HZ10-W shows a lower CII /FIR ratio compared to the other two components (albeit still within the uncertainties), which may suggest a harder radiation field destroying polycyclic aromatic hydrocarbon associated with emission (e.g., active galactic nuclei or young stellar populations). While HZ10-C appears to follow the tight IRX-$ UV $ relation seen in local UV-selected starburst galaxies and high-$z$ star-forming galaxies, we find that both HZ10-W and the bridge depart from this relation and are well described by dust-screen models with holes in front of a hard UV radiation field. This suggests that the UV emission, which is likely coming from young stellar populations, is strongly attenuated in the "dustier" components of the HZ10 system.

Varying linear polarisation in the dust-free gamma-ray burst 210610B

Context. Long gamma-ray bursts (GRBs) are produced by the collapse of some very massive stars, that emit ultra-relativistic jets. When the jets collide with the interstellar medium they decelerate and generate the so-called afterglow emission, which has been observed to be polarised. Aims. We study the polarimetric evolution of the GRB 210610B afterglow, at z = 1.1341. This allows us to evaluate the role of geometric and/or magnetic mechanisms in the GRB afterglow polarisation. Methods. We observed GRB 210610B using imaging polarimetry with CAFOS on the 2.2 m Calar Alto Telescope and FORS2 on the 4 × 8.1 m Very Large Telescope. Complementary optical spectroscopy was obtained with OSIRIS on the 10.4 m Gran Telescopio Canarias. We studied the GRB light-curve from X-rays to the optical bands and the Spectral Energy Distribution (SED). This allowed us to strongly constrain the line-of-sight extinction. Finally, we studied the GRB host galaxy using optical to NIR data to fit the SED and derive its integrated properties. Results. GRB 210610B had a bright afterglow with a negligible line-of-sight extinction. Polarimetry was obtained at three epochs: during an early plateau phase, at the time when the light curve breaks, and after the light curve steepened. We observe an initial polarisation of ∼4% that goes to zero at the time of the break, and it then again increases to ∼2%, with a change in the position angle of 54 ± 9 deg. The spectrum shows features with very low equivalent widths. This indicate a small amount of material in the line of sight within the host. Conclusions. The lack of dust and the low amount of material in the line of sight to GRB 210610B allowed us to study the intrinsic polarisation of the GRB optical afterglow. The GRB polarisation signals are consistent with ordered magnetic fields in refreshed shock or/and hydrodynamics-scale turbulent fields in the forward shock.

A3COSMOS: Dust mass function and dust mass density at 0.5 < z < 6

Context. Although dust in galaxies represents only a few percent of the total baryonic mass, it plays a crucial role in the physical processes occurring in galaxies. Studying the dust content of galaxies, particularly at high z, is therefore crucial for understanding the link between dust production, obscured star formation, and the build-up of galaxy stellar mass. Aims. We study the dust properties (mass and temperature) of the largest Atacama Large Millimeter/submillimeter Array (ALMA)-selected sample of star-forming galaxies available from the archive (A3COSMOS), and we derive the dust mass function and dust mass density of galaxies from z = 0.5 − 6. Methods. We fit the spectral energy distribution (SED) with the CIGALE code to constrain the dust mass and temperature of the A3COSMOS galaxy sample based on the UV-to-near-infrared photometric coverage of each galaxy combined with the ALMA (and Herschel when available) coverage of the Rayleigh-Jeans tail of their dust-continuum emission. We then computed and fit the dust mass function by combining the A3COSMOS and the most recent Herschel samples in order to obtain the best estimate of the integrated dust mass density up to z ∼ 6. Results. The dust masses in galaxies in A3COSMOS lie between ∼108 and ∼109.5 M⊙. From the SED fitting, we were also able to derive a dust temperature. The distribution of the dust temperature peaks at ∼30 − 35 K. The dust mass function at z = 0.5 − 6 evolves with an increase in M* and a decrease in the number density (Φ*), and it agrees well with literature estimates. The dust mass density decreases smoothly in its evolution from z ∼ 0.5 to z ∼ 6, which is steeper than what is found by models at z ≳ 2.

The Northern Cross Fast Radio Burst project

Context. Fast radio bursts (FRBs) are energetic, millisecond-duration radio pulses observed at extragalactic distances and whose origins are still a subject of heated debate. A fraction of the FRB population have shown repeating bursts, however it’s still unclear whether these represent a distinct class of sources. Aims. We investigated the bursting behaviour of FRB 20220912A, one of the most active repeating FRBs known thus far. In particular, we focused on its burst energy distribution, linked to the source energetics, and its emission spectrum, with the latter directly related to the underlying emission mechanism. Methods. We monitored FRB 20220912A at 408 MHz with the Northern Cross radio telescope and at 1.4 GHz using the 32-m Medicina Grueff radio telescope. Additionally, we conducted 1.2 GHz observations taken with the upgraded Giant Meter Wave Radio Telescope (uGMRT) searching for a persistent radio source coincident with FRB 20220912A, and included high energy observations in the 0.3–10 keV, 0.4–100 MeV and 0.03–30 GeV energy range. Results. We report 16 new bursts from FRB 20220912A at 408 MHz during the period between October 16th 2022 and December 31st 2023. Their cumulative spectral energy distribution follows a power law with slope αE = −1.3 ± 0.2 and we measured a repetition rate of 0.19 ± 0.03 hr−1 for bursts having a fluence of ℱ ≥ 17 Jy ms. Furthermore, we report no detections at 1.4 GHz for ℱ ≥ 20 Jy ms. These non-detections imply an upper limit of β < −2.3, with β being the 408 MHz – 1.4 GHz spectral index of FRB 20220912A. This is inconsistent with positive β values found for the only two known cases in which an FRB has been detected in separate spectral bands. We find that FRB 20220912A shows a decline of four orders of magnitude in its bursting activity at 1.4 GHz over a timescale of one year, while remaining active at 408 MHz. The cumulative spectral energy distribution (SED) shows a flattening for spectral energy Eν ≥ 1031 erg Hz−1, a feature seen thus far in only two hyperactive repeaters. In particular, we highlight a strong similarity between FRB 20220912A and FRB 20201124A, with respect to both the energy and repetition rate ranges. We also find a radio continuum source with 240 ± 36 μJy flux density at 1.2 GHz, centered on the FRB 20220912A coordinates. Finally, we place an upper limit on the γ to radio burst efficiency η to be η < 1.5 × 109 at 99.7% confidence level, in the 0.4–30 MeV energy range. Conclusions. The strong similarity between the cumulative energy distributions of FRB 20220912A and FRB 20201124A indicate that bursts from these sources are generated via similar emission mechanisms. Our upper limit on β suggests that the spectrum of FRB 20220912A is intrinsically narrow-band. The radio continuum source detected at 1.2 GHz is likely due to a star formation environment surrounding the FRB, given the absence of a source compact on millisecond scales brighter than 48 μJy beam−1. Finally, the upper limit on the ratio between the γ and radio burst fluence disfavours a giant flare origin for the radio bursts unlike observed for the Galactic magnetar SGR 1806-20.

Origin of the Very High Energy Gamma Rays in the Low-luminosity Active Galactic Nucleus NGC 4278

NGC 4278, a low-luminosity active galactic nucleus, is generally classified as a low-ionization nuclear emission-line region (LINER). Recently, it has been reported to be associated with a very high energy γ-ray source 1LHAASO J1219+2915 in the first Large High Altitude Air Shower Observatory source catalog. However, no associated counterpart has been detected by analyzing the data collected by the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. By analyzing its X-ray observation data from Swift-XRT, we find that NGC 4278 is in a high-flux state on MJD 59546, with the X-ray flux more than one order of magnitude higher than that observed ∼11.7 yr earlier by Chandra. Interestingly, this Swift-XRT observation was conducted during the active phase of the γ-ray source 1LHAASO J1219+2915. We propose that the detection of very high energy γ-rays from NGC 4278 may be attributed to the presence of an active nucleus in its center. To reproduce the spectral energy distribution (SED) of NGC 4278, we employ a one-zone leptonic model, typically used for fitting broadband SEDs of BL Lacs, and find that a smaller magnetic field strength is required than that of typical TeV BL Lacs. Furthermore, NGC 4278 exhibits significantly lower luminosity in both radio and TeV bands when compared with typical TeV BL Lacs. In the radio luminosity versus Eddington ratio plane, NGC 4278 shows greater similarity to Seyfert galaxies and LINERs than to BL Lacs; however, it still roughly follows the extension toward lower luminosity seen in BL Lacs.

Unraveling the Hybrid Origins of the X-Ray Nonthermal Emission from IGR J17091–3624

We present a comprehensive study based on multiwavelength observations from the NuSTAR, NICER, Swift, Fermi, NEOWISE, and ATCA telescopes during the 2022 outburst of the black-hole X-ray binary IGR J17091–3624. Our investigation concentrates on the heartbeat-like variability in the X-ray emission, with the aim of using it as a tool to unravel the origin of the nonthermal emission during the heartbeat state. Through X-ray timing and spectral analysis, we observe that the heartbeat-like variability correlates with changes in the disk temperature, supporting the disk radiation pressure instability scenario. Moreover, in addition to a Comptonization component, our time-averaged and phase-resolved spectroscopy reveal the presence of a power-law component that varies independently from the disk component. Combined with the radio–X-ray spectral energy distribution fitting, our results suggest that the power-law component could originate from synchrotron self-Compton radiation in the jet, which requires a strong magnetic field of about B = (0.3–3.5) × 106 G. Additionally, assuming that IGR J17091-3624 and GRS 1915 + 105 share the same radio–X-ray correlation coefficient during both the hard and the heartbeat states, we obtain a distance of 13.7 ± 2.3 kpc for IGR J17091–3624.

Host Galaxy Properties of Gamma-Ray Bursts Involving Neutron Star Binary Mergers and Their Impact on Kilonovae Rates

In the upcoming gravitational-wave (GW) observing runs, identifying host galaxies is crucial as it provides essential redshift information and enables the use of GW events as standard sirens. However, pinpointing host galaxies remains challenging due to the large localization uncertainties and the rapidly fading nature of their optical counterparts. Analyzing the host galaxies of short gamma-ray bursts (sGRBs) offers an alternative approach to deepen our understanding of the environments where binary neutron stars (BNS) primarily merge. This study compiles archival photometric data for the host galaxies of 76 sGRBs and four hybrid GRBs that are long GRBs accompanied by kilonova-like signals. We use this data to evaluate their physical properties through spectral energy distribution fitting. To assess the characteristics of the host galaxies, we utilized a volume-limited sample (z < 0.5) from the COSMOS field as a control group. Contrary to expectations that the BNS merger rate is proportional to host stellar mass, the short and hybrid GRB population appears less massive than the mass-weighted distribution of the control sample. Instead, we propose a formulation for the expected BNS merger rate from a galaxy as log(nBNSGyr-1)=0.86×log(M*/M⊙) + 0.44×log(sSFRyr-1)+0.857 , which optimally explains the deviation between the stellar mass distributions of the GRB host galaxies and the control sample. These insights provide a strategic framework for targeted GW follow-ups and enhance our ability to identify potential host galaxies for future GW events.

A Gamma-Ray Flare from TXS 1508+572: Characterizing the Jet of a z = 4.31 Blazar in the Early Universe

Blazars can be detected from very large distances due to their high luminosity. However, the detection of γ-ray emission of blazars beyond z = 3 has only been confirmed for a small number of sources. Such observations probe the growth of supermassive black holes close to the peak of star formation in the history of galaxy evolution. As a result from a continuous monitoring of a sample of 80 z > 3 blazars with the Fermi Large Area Telescope (Fermi-LAT), we present the first detection of a γ-ray flare from the z = 4.31 blazar TXS 1508+572. This source showed high γ-ray activity from 2022 February to August, reaching a peak luminosity comparable to the most luminous flares ever detected with Fermi-LAT. We conducted a multiwavelength observing campaign involving XMM-Newton, the Neil Gehrels Swift Observatory, the Effelsberg 100 m radio telescope, and the Very Long Baseline Array. In addition, we make use of the monitoring programs by the Zwicky Transient Facility and the Near-Earth Object Wide-field Infrared Survey Explorer at optical and infrared wavelengths, respectively. We find that the source is particularly variable in the infrared band on daily timescales. The spectral energy distribution collected during our campaign is well described by a one-zone leptonic model, with the γ-ray flare originating from an increase of external Compton emission as a result of a fresh injection of accelerated electrons.

A new census of dust and polycyclic aromatic hydrocarbons at z = 0.7–2 with JWST MIRI

Aims. This paper utilises the James Webb Space Telescope (JWST) Mid-Infrared Instrument (MIRI) to extend the observational studies of dust and polycyclic aromatic hydrocarbon (PAH) emission to a new mass and star formation rate (SFR) parameter space beyond our local Universe. The combination of fully sampled spectral energy distributions (SEDs) with multiple mid-infrared (mid-IR) bands and the unprecedented sensitivity of MIRI allows us to investigate dust obscuration and PAH behaviour from z = 0.7 up to z = 2 in typical main-sequence galaxies. Our focus is on constraining the evolution of PAH strength and the dust-obscured luminosity fraction before and during cosmic noon, the epoch of peak star formation activity in the Universe. Methods. In this study, we utilise MIRI multi-band imaging data from the SMILES survey (5 to 25 μm), complemented with NIRCam photometry from the JADES survey (1 to 5 μm), available HST photometry (0.4 to 0.9 μm), and spectroscopic redshifts from the FRESCO and JADES surveys in GOODS-S for 443 star-forming (without dominant active galactic nucleus (AGN)) galaxies at z = 0.7 − 2.0. This redshift range was chosen to ensure that the MIRI data cover mid-IR dust emission. Our methodology involved employing ultraviolet (UV) to IR energy balance SED fitting to robustly constrain the fraction of dust mass in PAHs and dust-obscured luminosity. Additionally, we inferred dust sizes from MIRI 15 μm imaging data, enhancing our understanding of the physical characteristics of dust within these galaxies. Results. We find a strong correlation between the fraction of dust in PAHs (PAH fraction, qPAH) with stellar mass. Moreover, the sub-sample with robust qPAH measurements (N = 216) shows a similar behaviour between qPAH and gas-phase metallicity to that at z ∼ 0, suggesting a universal relation: qPAH is constant (∼3.4%) above a metallicity of Z ∼ 0.5 Z⊙ and decreases to &lt; 1% at metallicities ≲0.3 Z⊙. This indicates that metallicity is a good indicator of the interstellar medium properties that affect the balance between the formation and destruction of PAHs. The lack of a redshift evolution from z ∼ 0 − 2 also implies that above Z ∼ 0.5 Z⊙ the PAH emission effectively traces obscured luminosity and the previous locally calibrated PAH-SFR calibrations remain applicable in this metallicity regime. We observe a strong correlation between the obscured UV luminosity fraction (ratio of obscured to total luminosity) and stellar mass. Above the stellar mass of M* &gt; 5 × 109 M⊙, on average, more than half of the emitted luminosity is obscured, while there exists a non-negligible population of lower-mass galaxies with &gt; 50% obscured fractions. At a fixed mass, the obscured fraction correlates with SFR surface density. This is a result of higher dust covering fractions in galaxies with more compact star-forming regions. Similarly, galaxies with high IRX (IR to UV luminosity) at a given mass or UV continuum slope (β) tend to have higher ΣSFR and shallower attenuation curves, owing to their higher effective dust optical depths and more compact star-forming regions.

Multiple Emission Regions in Jets of the Low-Luminosity Active Galactic Nucleus in NGC 4278

The Large High Altitude Air Shower Observatory (LHAASO) has detected very-high-energy gamma rays from the low-ionization nuclear emission-line region galaxy NGC 4278, which has a low-luminosity active galactic nucleus (LLAGN) and symmetric, mildly relativistic S-shaped twin jets detected by radio observations. Few LLAGNs have been detected in gamma rays due to their faintness. Earlier, several radio-emitting components were detected in the jets of NGC 4278. We model their radio emission with synchrotron emission of ultra-relativistic electrons to estimate the strength of the magnetic field inside these components within a time-dependent framework after including the ages of the different components. We show that the synchrotron and synchrotron self-Compton emission by these components cannot explain the Swift X-ray data and the LHAASO gamma-ray data from NGC 4278. We suggest that a separate component in one of the jets is responsible for the high-energy emission, whose age, size, magnetic field, and the spectrum of the ultra-relativistic electrons inside it have been estimated after fitting the multiwavelength data of NGC 4278 with the sum of the spectral energy distributions from the radio components and the high-energy component. We note that the radio components of NGC 4278 are larger than the high-energy component, which has also been observed in several high-luminosity active galactic nuclei.

Ubiquitous radio emission in quasars: predominant AGN origin and a connection to jets, dust, and winds

We present a comprehensive study of the physical origin of radio emission in optical quasars at redshifts $z&lt;2.5$. We focus particularly on the associations between compact radio emission, dust reddening, and outflows identified in our earlier work. Leveraging the deepest low-frequency radio data available to date (LoTSS Deep DR1), we achieve radio detection fractions of up to 94&lt;!PCT!&gt;, demonstrating the virtual ubiquity of radio emission in quasars, and a continuous distribution in radio loudness. Through our analysis of radio properties, combined with spectral energy distribution modelling of deep multiwavelength photometry, we establish that the primary source of radio emission in quasars is the active galactic nucleus (AGN), rather than star formation. Modelling the dust reddening of the accretion disc emission shows a continuous increase in radio detection in quasars as a function of the reddening parameter E(B-V) suggesting a causal link between radio emission and dust reddening. Confirming previous findings, we observe that the radio excess in red quasars is most pronounced for sources with compact radio morphologies and intermediate radio loudness. We find a significant increase in Oiii and Civ outflow velocities for red quasars not seen in our control sample, with particularly powerful Oiii winds in those around the threshold from radio-quiet to radio-loud. Based on the combined characterisation of radio, reddening, and outflow properties in our sample, we favour a model in which the compact radio emission observed in quasars originates in compact radio jets and their interaction with a dusty, circumnuclear environment. In particular, our results align with the theory that jet-induced winds and shocks resulting from this interaction are the origin of the enhanced radio emission in red quasars. Further investigation of this model is crucial for advancing our understanding of quasar feedback mechanisms and their role in galaxy evolution.

Lyman Continuum Leakers at z > 3 in the GOODS-S Field: Starburst or Not?

We investigate the star-forming properties of 23 Lyman continuum (LyC) leakers at z > 3 in the Great Observatories Origins Deep Survey-South field based on a systematic review of LyC observations from the literature. Using data from the Hubble Space Telescope and the James Webb Space Telescope, we construct the spectral energy distributions for these LyC leakers, covering the spectrum from rest-frame ultraviolet to near-infrared. Through the application of a unified modeling approach, we measure the ultraviolet slope (β), star formation rate, and stellar mass for these LyC leakers in a consistent manner. These high-redshift LyC leakers demonstrate statistically blue UV-continuum slopes (β), which is consistent with their high escape fraction of LyC photons. We find that these high-redshift LyC leakers span a wide range of specific star formation rate ( log(sSFR /yr) from −8.6 to −6.7). Ten of these LyC leakers are located on the star formation main sequence, instead of all being in the starburst mode. The results indicate that intense bursts of star formation are not necessarily required for the leakage of LyC photons for galaxies at z > 3.

UNCOVER NIRSpec/PRISM Spectroscopy Unveils Evidence of Early Core Formation in a Massive, Centrally Dusty Quiescent Galaxy at z spec = 3.97

We report the spectroscopic confirmation of a massive ( log(M⋆/M⊙)=10.34±0.070.06 ), Hubble Space Telescope–dark (m F150W − m F444W = 3.6) quiescent galaxy at z spec = 3.97 in the UNCOVER survey. NIRSpec/PRISM spectroscopy and a nondetection in deep Atacama Large Millimeter/submillimeter Array imaging surprisingly reveals that the galaxy is consistent with a low (<10 M ⊙ yr−1) star formation rate (SFR) despite evidence for moderate dust attenuation. The F444W image is well modeled with a two-component Sérsic fit that favors a compact, r e ∼ 200 pc, n ∼ 2.9 component and a more extended, r e ∼ 1.6 kpc, n ∼ 1.7 component. The galaxy exhibits strong color gradients: the inner regions are significantly redder than the outskirts. Spectral energy distribution models that reproduce both the red colors and low SFR in the center of UNCOVER 18407 require both significant (A v ∼ 1.4 mag) dust attenuation and a stellar mass-weighted age of 900 Myr, implying 50% of the stars in the core already formed by z = 7.5. Using spatially resolved annular mass-to-light measurements enabled by the galaxy’s moderate magnification ( μ=2.12±0.010.05 ) to reconstruct a radial mass profile from the best-fitting two-component Sérsic model, we infer a total mass-weighted reff=0.74±0.170.22 kpc and log (Σ1kpc[M⊙kpc-2])=9.65±0.150.12 . The early formation of a dense, low SFR, and dusty core embedded in a less attenuated stellar envelope suggests an evolutionary link between the earliest-forming massive galaxies and their elliptical descendants. Furthermore, the disparity between the global, integrated dust properties and the spatially resolved gradients highlights the importance of accounting for radially varying stellar populations when characterizing the early growth of galaxy structure.

JADES + JEMS: A Detailed Look at the Buildup of Central Stellar Cores and Suppression of Star Formation in Galaxies at Redshifts 3 < z < 4.5

We present a spatially resolved study of stellar populations in six galaxies with stellar masses M * ∼ 1010 M ☉ at z ∼ 3.7 using 14-filter James Webb Space Telescope (JWST)/NIRCam imaging from the JADES and JEMS surveys. The six galaxies are visually selected to have clumpy substructures with distinct colors over rest frame 3600−4100 Å, including a red, dominant stellar core that is close to their stellar-light centroids. With 23-filter photometry from the Hubble Space Telescope to JWST, we measure the stellar-population properties of individual structural components via spectral energy distribution fitting using Prospector. We find that the central stellar cores are ≳2 times more massive than the Toomre mass, indicating they may not form via single in situ fragmentation. The stellar cores have stellar ages of 0.4−0.7 Gyr that are similar to the timescale of clump inward migration due to dynamical friction, suggesting that they likely instead formed through the coalescence of giant stellar clumps. While they have not yet quenched, the six galaxies are below the star-forming main sequence by 0.2−0.7 dex. Within each galaxy, we find that the specific star formation rate is lower in the central stellar core, and the stellar-mass surface density of the core is already similar to quenched galaxies of the same masses and redshifts. Meanwhile, the stellar ages of the cores are either comparable to or younger than the extended, smooth parts of the galaxies. Our findings are consistent with model predictions of the gas-rich compaction scenario for the buildup of galaxies’ central regions at high redshifts. We are likely witnessing the coeval formation of dense central cores, along with the onset of galaxy-wide quenching at z > 3.