Research Articles (Physics)

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MIGHTEE polarization early science fields: The deep polarized sky
(Oxford University Press, 2024) Taylor, Andrew Russell; Sekhar, Srikrishna; Collier, Jordan D.
The MeerKAT International GigaHertz Tiered Extragalactic Exploration (MIGHTEE) is one of the MeerKAT large survey projects, designed to pathfind SKA key science. MIGHTEE is undertaking deep radio imaging of four well-observed fields (COSMOS, XMM-LSS, ELAIS S1, and CDFS) totaling 20 square degrees to μJy sensitivities. Broad-band imaging observations between 880 and1690 MHz yield total intensity continuum, spectro-polarimetry, and atomic hydrogen spectral imaging. Early science data from MIGHTEE are being released from initial observations of COSMOS and XMM–LSS. This paper describes the spectro-polarimetric observations, the polarization data processing of the MIGHTEE early science fields, and presents polarization data images and catalogues. The catalogues include radio spectral index, redshift information, and faraday rotation measure synthesis results for 13 267 total intensity radio sources down to a polarized intensity detection limit of ∼20 μJy bm−1. Polarized signals were detected from 324 sources. For the polarized detections, we include a catalogue of faraday depth from both faraday synthesis and Q, U fitting, as well as total intensity and polarization spectral indices. The distribution of redshift of the total radio sources and detected polarized sources are the same, with median redshifts of 0.86 and 0.82, respectively. Depolarization of the emission at longer-wavelengths is seen to increase with decreasing total-intensity spectral index, implying that depolarization is intrinsic to the radio sources. No evidence is seen for a redshift dependence of the variance of faraday depth.
Theoretical strong-line metallicity diagnostics for the JWST era
(Institute of Physics, 2024) Garg, Prerak; Dave, Romeel; Sanders, Ryan L
The ratios of strong rest-frame optical emission lines are the dominant indicators of metallicities in high-redshift galaxies. Since typical strong-line-based metallicity indicators are calibrated on auroral lines at z = 0, their applicability for galaxies in the distant Universe is unclear. In this paper, we make use of mock emission-line data from cosmological simulations to investigate the calibration of rest-frame optical emission lines as metallicity indicators at high redshift. Our model, which couples the SIMBA cosmological galaxy formation simulation with CLOUDY photoionization calculations, includes contributions from H II regions, post-asymptotic-giant-branch stars, and diffuse ionized gas (DIG). We find mild redshift evolution in the 12 indicators that we study, which implies that the dominant physical properties that evolve in our simulations do have a discernible impact on the metallicity calibrations at high redshifts. When comparing our calibrations with high-redshift auroral line observations from the James Webb Space Telescope, we find a slight offset between our model results and the observations and find that a higher ionization parameter at high redshifts can be one of the possible explanations. We explore the physics that drives the shapes of strong-line metallicity relationships and propose calibrations for hitherto unexplored low-metallicity regimes. Finally, we study the contribution of DIG to total line fluxes.
Characterization of herschel-selected strong lens candidates through HST and sub-mm/mm observations
(Oxford University Press, 2024) Borsato E.; Baker A.J.; Negrello M
We have carried out hubble space telescope (HST) snapshot observations at 1.1 μm of 281 candidate strongly lensed galaxies identified in the wide-area extragalactic surveys conducted with the Herschel space observatory. Our candidates comprise systems with flux densities at 500 μm, S500 ≥ 80 mJy. We model and subtract the surface brightness distribution for 130 systems, where we identify a candidate for the foreground lens candidate. After combining visual inspection, archival high-resolution observations, and lens subtraction, we divide the systems into different classes according to their lensing likelihood. We confirm 65 systems to be lensed. Of these, 30 are new discoveries. We successfully perform lens modelling and source reconstruction on 23 systems, where the foreground lenses are isolated galaxies and the background sources are detected in the HST images. All the systems are successfully modelled as a singular isothermal ellipsoid. The Einstein radii of the lenses and the magnifications of the background sources are consistent with previous studies. However, the background source circularized radii (between 0.34 and 1.30 kpc) are ∼3 times smaller than the ones measured in the sub-millimetre/millimetre for a similarly selected and partially overlapping sample. We compare our lenses with those in the sloan lens advanced camera for surveys (ACS) survey confirming that our lens-independent selection is more effective at picking up fainter and diffuse galaxies and group lenses. This sample represents the first step towards characterizing the near-infrared properties and stellar masses of the gravitationally lensed dusty star-forming galaxies.
Radio spectral properties of star-forming galaxies between 150 and 5000 MHz in the ELAIS-N1 field
(Oxford University Press, 2024) Fangxia ,An; Vaccari , Mattia; Taylor, Andrew Russell
By combining high-sensitivity LOFAR 150 MHz, uGMRT 400 MHz and 1250 MHz, GMRT 610 MHz, and VLA 5 GHz data in the ELAIS-N1 field, we study the radio spectral properties of radio-detected star-forming galaxies (SFGs) at observer-frame frequencies of 150-5000 MHz. We select ∼3500 SFGs that have both LOFAR 150 MHz and GMRT 610 MHz detections, and obtain a median two-point spectral index of α150610 = −0.51 ± 0.01. The photometric redshift of these SFGs spans z = 0.01−6.21. We also measure the two-point radio spectral indices at 150-400-610-1250 MHz and 150-610-5000 MHz, respectively, for the GMRT 610-MHz-detected SFGs, and find that, on average, the radio spectrum of SFGs is flatter at low frequency than at high frequency. At observer-frame 150-5000 MHz, we find that the radio spectrum slightly steepens with increasing stellar mass. However, we only find that the radio spectrum flattens with increasing optical depth at V band at ν ≲ 1 GHz. We suggest that spectral ageing due to the energy loss of CR electrons and thermal free-free absorption could be among the possible main physical mechanisms that drive the above two correlations, respectively. In addition, both of these mechanisms could physically explain why the radio spectrum is flatter at low frequency than at high frequency.
Astronomaly at scale: searching for anomalies amongst 4 million galaxies
(Oxford University Press, 2024) Etsebeth, Veronica; Lochner, Michelle; Walmsley M
Modern astronomical surveys are producing data sets of unprecedented size and richness, increasing the potential for high- impact scientific discovery. This possibility, coupled with the challenge of exploring a large number of sources, has led to the development of novel machine-learning-based anomaly detection approaches, such as astronomy. For the first time, we test the scalability of astronomy by applying it to almost 4 million images of galaxies from the Dark energy camera legacy survey. We use a trained deep learning algorithm to learn useful representations of the images and pass these to the anomaly detection algorithm isolation forest, coupled with astronomy's active learning method, to discover interesting sources. We find that data selection criteria have a significant impact on the trade-off between finding rare sources such as strong lenses and introducing artefacts into the data set. We demonstrate that active learning is required to identify the most interesting sources and reduce artefacts, while anomaly detection methods alone are insufficient. Using astronomy, we find 1635 anomalies among the top 2000 sources in the data set after applying active learning, including eight strong gravitational lens candidates, 1609 galaxy merger candidates, and 18 previously unidentified sources exhibiting highly unusual morphology. Our results show that by leveraging the human-machine interface, astronomy’s able to rapidly identify sources of scientific interest even in large data sets.
The cosmic baryon partition between the IGM and CGM in the SIMBA simulations
(Oxford University Press, 2024) Khrykin, Ilya S.; Davé, Romeel; Sorini, Daniele
We use the SIMBA suite of cosmological hydrodynamical simulations to investigate the importance of various stellar and active galactic nuclei (AGN) feedback mechanisms in partitioning the cosmic baryons between the intergalactic (IGM) and circumgalactic (CGM) media in the z ≤ 1 Universe. We identify the AGN jets as the most prominent mechanism for the redistribution of baryons between the IGM and CGM. In contrast to the full feedback models, deactivating AGN jets results in ≈20 per cent drop in fraction of baryons residing in the IGM and a consequent increase of CGM baryon fraction by ≈50 per cent. We find that stellar feedback modifies the partition of baryons on a 10 per cent level. We further examine the physical properties of simulated haloes in different mass bins, and their response to various feedback models. On average, a sixfold decrease in the CGM mass fraction due to the inclusion of feedback from AGN jets is detected in 1012 M☉ ≤ M200 ≤ 1014 M☉ haloes. Examination of the average radial gas density profiles of M200 > 1012 M☉ haloes reveals up to an order of magnitude decrease in gas densities due to the AGN jet feedback. We compare gas density profiles from SIMBA simulations to the predictions of the modified Navarro-Frenk-White model, and show that the latter provides a reasonable approximation within the virial radii of the full range of halo masses, but only when rescaled by the appropriate mass-dependent CGM fraction of the halo. The relative partitioning of cosmic baryons and, subsequently, the feedback models can be constrained observationally with fast radio bursts in upcoming surveys.
MeerKAT observations of herschel protocluster candidates
(Oxford University Press , 2024) Ding Y. ; Leeuw, Lerothodi L. ; Clements, D.L.
High-redshift protoclusters consisting of dusty starbursts are thought to play an important role in galaxy evolution. Their dusty nature makes them bright in the far-infrared (FIR)/submm but difficult to find in optical/near-infrared (NIR) surveys. Radio observations are an excellent way to study these dusty starbursts, as dust is transparent in the radio and there is a tight correlation between the FIR and radio emission of a galaxy. Here, we present MeerKAT 1.28 GHz radio imaging of three Herschel candidate protoclusters, with a synthesized beam size of ∼ 7.5 arcsec × 6.6 arcsec and a central thermal noise down to 4.35 μJy beam-1. Our source counts are consistent with other radio counts with no evidence of overdensities. Around 95 per cent of the Herschel sources have 1.28 GHz IDs. Using the Herschel250 μm primary beam size as the searching radius, we find 54.2 per cent Herschel sources have multiple 1.28 GHz IDs. Our average FIR-radio correlation coefficient q250μm is 2.33 ± 0.26. Adding q250μm as a new constraint, the probability of finding chance-aligned sources is reduced by a factor of ∼ 6, but with the risk of discarding true identifications of radio-loud/quiet sources. With accurate MeerKAT positions, we cross-match our Herschel sources to optical/NIR data followed by photometric redshift estimations. By removing z > 1 sources, the density contrasts of two of the candidate protoclusters increase, suggestive of them being real protoclusters at z > 1. There is also potentially a 0.9 > z > 1.2 overdensity associated with one candidate protocluster. In summary, photometric redshifts from radio-optical cross-identifications have provided some tentative evidence of overdensities aligning with two of the candidate protoclusters
MeerKAT observations of pair-plasma induced birefringence in the double pulsar eclipses
(Oxford University Press, 2024) Lower M.E; Serylak, Maciej ; Kramer M.
PSR J0737−3039A/B is unique among double neutron star systems. Its near-perfect edge-on orbit causes the fast spinning pulsar A to be eclipsed by the magnetic field of the slow spinning pulsar B. Using high-sensitivity MeerKAT radio observations combined with updated constraints on the system geometry, we studied the impact of these eclipses on the incident polarization properties of pulsar A. Averaging light curves together after correcting for the rotation of pulsar B revealed enormous amounts of circular polarization and rapid changes in the linear polarization position angle, which occur at phases where emission from pulsar A is partially transmitted through the magnetosphere of pulsar B. These behaviours confirm that the eclipse mechanism is the result of synchrotron absorption in a relativistic pair-plasma confined to the closed-field region of pulsar B’s truncated dipolar magnetic field. We demonstrate that changes in circular polarization handedness throughout the eclipses are directly tied to the average line of sight magnetic field direction of pulsar B, from which we unambiguously determine the complete magnetic and viewing geometry of the pulsar.
Learning the universe: GalactISM simulations of resolved star formation and galactic outflows across main sequence and quenched galactic environments
(Institute of Physics, 2024) Hassan Sultan; Jeffreson Sarah M.R.; Ostriker Eve C.; Kim Chang-Goo
We present a suite of six high-resolution chemodynamical simulations of isolated galaxies, spanning observed disk-dominated environments on the star-forming main sequence, as well as quenched, bulge-dominated environments. We compare and contrast the physics driving star formation and stellar feedback among the galaxies, with a view to modeling these processes in cosmological simulations. We find that the mass loading of galactic outflows is coupled to the clustering of supernova explosions, which varies strongly with the rate of galactic rotation Ω = vcirc/R via the Toomre length, leading to smoother gas disks in the bulge-dominated galaxies. This sets an equation of state in the star-forming gas that also varies strongly with Ω, so that the bulge-dominated galaxies have higher midplane densities, lower velocity dispersions, and higher molecular gas fractions than their main-sequence counterparts. The star formation rate in five out of six galaxies is independent of Ω and is consistent with regulation by the midplane gas pressure alone. In the sixth galaxy, which has the most centrally concentrated bulge and thus the highest Ω, we reproduce dynamical suppression of the star formation efficiency in agreement with observations. This produces a transition away from pressure-regulated star formation.
Star formation efficiency across large-scale galactic environments
(Oxford University Press, 2024) Ghodsi, Laya; Davé, Romeel; Man, Allison W.S.
Environmental effects on the formation and evolution of galaxies have been one of the leading questions in galaxy studies during the past few decades. In this work, we investigate the relationship between the star formation activity of galaxies and their environmental matter density using the cosmological hydrodynamic simulation SIMBA. The galactic star formation activity indicators that we explore include the star formation efficiency (SFE), specific star formation rate (sSFR), and molecular hydrogen mass fraction (fH∗2 ), and the environment is considered as the large-scale environmental matter density, calculated based on the stellar mass of nearby galaxies on a 1 h−1 Mpc grid using the cloud in cell method. Our sample includes galaxies with 9 < log MM0∗ at 0 < z < 4, divided into three stellar mass bins to disentangle the effects of stellar mass and environment on the star formation activity of galaxies. For low- to intermediate-mass galaxies at low redshifts (z < 1.5), we find that the star formation efficiency of those in high-density regions are ∼0.3 dex lower than those in low-density regions. However, there is no significant environmental dependence of the star formation efficiency for massive galaxies over all our redshift range, and low- to intermediate-mass galaxies at high redshifts (z > 1.5). We present a scaling relation for the depletion time of cold molecular hydrogen (tdepl = 1/SFE) as a function of galaxy parameters including environmental density. Our findings provide a framework for quantifying the environmental effects on the star formation activities of galaxies as a function of stellar mass and redshift. The most significant environmental dependence is seen at later cosmic times (z < 1.5) and towards lower stellar masses (9 < log MM0∗ < 10). Future large galaxy surveys can use this framework to look for the environmental dependence of the star formation activity and examine our predictions.
Radio-optical synergies at high redshift to constrain primordial non-gaussianity
(Institute of Physics, 2024) Squarotti, Matilde Barberi; Maartens, Roy; Camera, Stefano
We apply the multi-tracer technique to test the possibility of improved constraints on the amplitude of local primordial non-Gaussianity, fNL, in the cosmic large-scale structure. A precise measurement of fNL is difficult because the effects of non-Gaussianity mostly arise on the largest scales, which are heavily affected by the low statistical sampling commonly referred to as cosmic variance. The multi-tracer approach suppresses cosmic variance and we implement it by combining the information from next-generation galaxy surveys in the optical/near-infrared band and neutral hydrogen (Hi) intensity mapping surveys in the radio band. High-redshift surveys enhance the precision on fNL, due to the larger available volume, and Hi intensity mapping surveys can naturally reach high redshifts. In order to extend the redshift coverage of a galaxy survey, we consider different emission-line galaxy populations, focusing on the Hα line at low redshift and on oxygen lines at higher redshift. By doing so, we cover a wide redshift range 1 ≲ z ≲ 4. To assess the capability of our approach, we implement a synthetic-data analysis by means of Markov chain Monte Carlo sampling of the (cosmological+nuisance) parameter posterior, to evaluate the constraints on fNL obtained in different survey configurations. We find significant improvements from the multi-tracer technique: the full data set leads to a precision of σ(fNL) < 1.
Bayesian estimation of cross-coupling and reflection systematics in 21cm array visibility data
(Oxford University Press , 2024) Murphy Geoff G.; Bull Philip; Santos Mario G.
Observations with radio arrays that target the 21-cm signal originating from the early Universe suffer from a variety of systematic effects. An important class of these is reflections and spurious couplings between antennas. We apply a Hamiltonian Monte Carlo sampler to the modelling and mitigation of these systematics in simulated Hydrogen Epoch of Reionization Array (HERA) data. This method allows us to form statistical uncertainty estimates for both our models and the recovered visibilities, which is an important ingredient in establishing robust upper limits on the epoch of reionization (EoR) power spectrum. In cases where the noise is large compared to the EoR signal, this approach can constrain the systematics well enough to mitigate them down to the noise level for both systematics studied. Incoherently averaging the recovered power spectra can further reduce the noise and improve recovery. Where the noise level is lower than the EoR, our modelling can mitigate the majority of the reflections and coupling with there being only a minor level of residual systematics. Our approach performs similarly to existing filtering/fitting techniques used in the HERA pipeline, but with the added benefit of rigorously propagating uncertainties. In all cases it does not significantly attenuate the underlying signal.
PSR J1227−6208 and its massive white dwarf companion: pulsar emission analysis, timing update, and mass measurements
(EDP Sciences, 2024) i Bernadich, Miquel Colom; Serylak, Maciej; Krishnan, Vivek Venkatraman
PSR J1227−6208 is a 34.53-ms recycled pulsar with a massive companion. This system has long been suspected to belong to the emerging class of massive recycled pulsar−ONeMg white dwarf systems such as PSR J2222−0137, PSR J1528−3146, and J1439−5501. Here, we present an updated emission and timing analysis with more than 11 years of combined Parkes and MeerKAT data, including 19 hours of high-frequency data from the newly installed MeerKAT S-band receivers. We measure a scattering timescale of 1.22 ms at 1 GHz with a flat scattering index of 3.33 < β < 3.62, and a mean flux density of 0.53−0.62 mJy at 1 GHz with a steep spectral index of 2.06 < α < 2.35. Around 15% of the emission is linearly and circularly polarised, but the polarisation angle does not follow the rotating vector model. Thanks to the sensitivity of MeerKAT, we successfully measure a rate of periastron advance of [Formula Presented], and a Shapiro delay with an orthometric amplitude of h3 = 3.6 ± 0.5 µs and an orthometric ratio of ς = 0.85 ± 0.05. The main source of uncertainty in our timing analysis is chromatic correlated dispersion measure noise, which we model as a power law in the Fourier space thanks to the large frequency coverage provided by the Parkes UWL receiver. Assuming general relativity and accounting for the measurements across all the implemented timing noise models, the total mass, companion mass, pulsar mass, and inclination angle are constrained at [Formula Presented], and 77.5 < i/deg < 80.3. We also constrain the longitude of ascending node to either Ωa = 266 ± 78 deg or Ωa = 86 ± 78 deg. We argue against a neutron star nature of the companion based on the very low orbital eccentric of the system (e = 1.15 × 10−3), and instead classify the companion of PSR J1227−6208 as a rare, massive ONeMg white dwarf close to the Chandrasekhar limit.
Analytical gaussian process cosmography: unveiling insights into matter-energy density parameter at present
(Springer Nature, 2024) Dinda, Bikash Ranjan
In this study, we introduce a novel analytical Gaussian Process (GP) cosmography methodology, leveraging the differentiable properties of GPs to derive key cosmological quantities analytically. Our approach combines cosmic chronometer (CC) Hubble parameter data with growth rate (f) observations to constrain the Ωm0 parameter, offering insights into the underlying dynamics of the Universe. By formulating a consistency relation independent of specific cosmological models, we analyze under a flat FLRW metric and first-order Newtonian perturbation theory framework. Our analytical approach simplifies the process of Gaussian Process regression (GPR), providing a more efficient means of handling large datasets while offering deeper interpretability of results. We demonstrate the effectiveness of our methodology by deriving precise constraints on Ωm0h2, revealing Ωm0h2=0.139±0.017. Moreover, leveraging H0 observations, we further constrain Ωm0, uncovering an inverse correlation between mean H0 and Ωm0. Our investigation offers a proof of concept for analytical GP cosmography, highlighting the advantages of analytical methods in cosmological parameter estimation.
Hydrogen epoch of reionization array (HERA) phase ii deployment and commissioning
(IOP science, 2024) Berkhout, Lindsay M; Bull, Philip ; Jacobs, Daniel C
This paper presents the design and deployment of the Hydrogen Epoch of Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements of the Epoch of Reionization. First results from the phase I array are published as of early 2022, and deployment of the phase II system is nearing completion. We describe the design of the phase II system and discuss progress on commissioning and future upgrades. As HERA is a designated Square Kilometre Array pathfinder instrument, we also show a number of “case studies” that investigate systematics seen while commissioning the phase II system, which may be of use in the design and operation of future arrays. Common pathologies are likely to manifest in similar ways across instruments, and many of these sources of contamination can be mitigated once the source is identified.
MIGHTEE-H I: H I galaxy properties in the large-scale structure environment at z ∼ 0.37 from a stacking experiment
(Oxford University Press, 2024) Sinigaglia, Francesco; Elson, Ed; Vaccari, Mattia
We present the first measurement of H I mass of star-forming galaxies in different large scale structure environments from a blind survey at z ∼ 0.37. In particular, we carry out a spectral line stacking analysis considering 2875 spectra of colour-selected star-forming galaxies undetected in H I at 0.23 < z < 0.49 in the COSMOS field, extracted from the MIGHTEE-H I Early Science data cubes, acquired with the MeerKAT radio telescope. We stack galaxies belonging to different subsamples depending on three different definitions of large-scale structure environment: local galaxy overdensity, position inside the host dark matter halo (central, satellite, or isolated), and cosmic web type (field, filament, or knot). We first stack the full star-forming galaxy sample and find a robust H I detection yielding an average galaxy H I mass of MH I = (8.12 ± 0.75) × 109 M⊙ at ∼11.8σ. Next, we investigate the different subsamples finding a negligible difference in MH I as a function of the galaxy overdensity. We report an H I excess compared to the full sample in satellite galaxies (MH I = (11.31 ± 1.22) × 109, at ∼10.2σ) and in filaments (MH I = (11.62 ± 0.90) × 109. Conversely, we report non-detections for the central and knot galaxies subsamples, which appear to be H I-deficient.
The next generation deep extragalactic exploratory public (NGDEEP) survey
(American Astronomical Society, 2024) Bagley, Micaela; Davé, Romeel; Pirzkal, Nor
We present the Next Generation Deep Extragalactic Exploratory Public (NGDEEP) Survey, a deep slitless spectroscopic and imaging Cycle 1 JWST treasury survey designed to constrain feedback mechanisms in low-mass galaxies across cosmic time. NGDEEP targets the Hubble Ultra Deep Field (HUDF) with NIRISS slitless spectroscopy ( f lim , line , 5 σ ≈ 1.2 × 10−18 erg s−1 cm−2) to measure metallicities and star formation rates (SFRs) for low-mass galaxies through the peak of the cosmic SFR density (0.5 < z < 4). In parallel, NGDEEP targets the HUDF-Par2 parallel field with NIRCam ( m lim , 5 σ = 30.6 − 30.9 ) to discover galaxies to z > 12, constraining the slope of the faint end of the rest-ultraviolet luminosity function. NGDEEP overlaps with the deepest HST Advanced Camera for Surveys optical imaging in the sky, F435W in the HUDF ( m lim , F 435 W = 29.6 ) and F814W in HUDF-Par2 ( m lim , F 814 W = 30 ), making this a premier HST+JWST deep field. As a treasury survey, NGDEEP data are public immediately, and we will rapidly release data products and catalogs in the spirit of previous deep-field initiatives. In this paper we present the NGDEEP survey design, summarize the science goals, and detail plans for the public release of NGDEEP reduced data products
Rest-frame uv colors for faint galaxies at z ∼ 9–16 with the Jwst ngdeep survey
(American Astronomical Society, 2024) Morales, Alexa; Dave, Romeel; Finkelstein, Steven
We present measurements of the rest-frame UV spectral slope, β, for a sample of 36 faint star-forming galaxies at z ∼ 9-16 discovered in one of the deepest JWST NIRCam surveys to date, the Next Generation Deep Extragalactic Exploratory Public Survey. We use robust photometric measurements for UV-faint galaxies (down to M UV ∼ −16), originally published in Leung et al., and measure values of the UV spectral slope via photometric power-law fitting to both the observed photometry and stellar population models obtained through spectral energy distribution (SED) fitting with Bagpipes. We obtain a median and 68% confidence interval for β from photometric power-law fitting of β PL = − 2.7 − 0.5 + 0.5 and from SED fitting, β SED = − 2.3 − 0.1 + 0.2 for the full sample. We show that when only two to three photometric detections are available, SED fitting has a lower scatter and reduced biases than photometric power-law fitting. We quantify this bias and find that after correction the median β SED , corr = − 2.5 − 0.2 + 0.2 . We measure physical properties for our galaxies with Bagpipes and find that our faint ( M UV = − 18.1 − 0.9 + 0.7 ) sample is low in mass ( log [ M * / M ⊙ ] = 7.7 − 0.5 + 0.5 ), fairly dust-poor ( A v = 0.1 − 0.1 + 0.2 mag), and modestly young ( log [ age ] = 7.8 − 0.8 + 0.2 yr) with a median star formation rate of log ( SFR ) = − 0.3 − 0.4 + 0.4 M ⊙ yr − 1 . We find no strong evidence for ultrablue UV spectral slopes (β ∼ −3) within our sample, as would be expected for exotically metal-poor (Z/Z ⊙ < 10−3) stellar populations with very high Lyman continuum escape fractions.
Dust and power: unravelling the merger-active galactic nucleus connection in the second half of cosmic history
(EDP Sciences, 2024) Davé, R.; Marca, A. La; Margalef-Bentabol, B; Wang, L.
Aims. Galaxy mergers represent a fundamental physical process under hierarchical structure formation, but their role in triggering active galactic nuclei (AGNs) is still unclear. We aim to investigate the merger-AGN connection using state-of-the-art observations and novel methods for detecting mergers and AGNs. Methods. We selected stellar mass-limited samples at redshift z < 1 from the Kilo-Degree Survey (KiDS), focussing on the KiDS-NW2 field with a wide range of multi-wavelength data. We analysed three AGN types, selected in the mid-infrared (MIR), X-ray, and via spectral energy distribution (SED) modelling. To identify mergers, we used convolutional neural networks (CNNs) trained on two cosmological simulations. We created mass- and redshift-matched control samples of non-mergers and non-AGNs. Results. We first investigated the merger-AGN connection using a binary AGN/non-AGN classification. We observed a clear AGN excess (of a factor of 2–3) in mergers with respect to non-mergers for the MIR AGNs, along with a mild excess for the X-ray and SED AGNs. This result indicates that mergers could trigger all three types, but are more connected to the MIR AGNs. About half of the MIR AGNs are in mergers but it is unclear whether mergers are the main trigger. For the X-ray and SED AGNs, mergers are unlikely to be the dominant triggering mechanism. We also explored the connection using the continuous AGN fraction fAGN parameter. Mergers exhibit a clear excess of high fAGN values relative to non-mergers, for all AGN types. We unveil the first merger fraction fmerger − fAGN relation with two distinct regimes. When the AGN is not very dominant, the relation is only mildly increasing or even flat, with the MIR AGNs showing the highest fmerger. In the regime of very dominant AGNs (fAGN ≥ 0.8), fmerger shows the same steeply rising trend with increasing fAGN for all AGN types. These trends are also seen when plotted against AGN bolometric luminosity. We conclude that mergers are most closely connected to dust-obscured AGNs, generally linked to a fast-growing phase of the supermassive black hole. Such mergers therefore stand as the main (or even the sole) fuelling mechanism of the most powerful AGNs.
Mitigating calibration errors from mutual coupling with time-domain filtering of 21 cm cosmological radio observations
(Oxford University Press, 2024) Beardsley, Adam P.; Charles, Ntsikelelo; Kern, Nicholas S.; Pascua, Robert
The 21 cm transition from neutral Hydrogen promises to be the best observational probe of the Epoch of Reionization (EoR). This has led to the construction of low-frequency radio interferometric arrays, such as the Hydrogen Epoch of Reionization Array (HERA), aimed at systematically mapping this emission for the first time. Precision calibration, however, is a requirement in 21 cm radio observations. Due to the spatial compactness of HERA, the array is prone to the effects of mutual coupling, which inevitably lead to non-smooth calibration errors that contaminate the data. When unsmooth gains are used in calibration, intrinsically spectrally smooth foreground emission begins to contaminate the data in a way that can prohibit a clean detection of the cosmological EoR signal. In this paper, we show that the effects of mutual coupling on calibration quality can be reduced by applying custom time-domain filters to the data prior to calibration. We find that more robust calibration solutions are derived when filtering in this way, which reduces the observed foreground power leakage. Specifically, we find a reduction of foreground power leakage by 2 orders of magnitude at k ≈ 0.5 h Mpc−1.

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