Katarzyna Malek

Context . Ultra-diffuse galaxies (UDGs) in the field, gravitationally isolated from galaxy clusters, are faint systems that remain poorly represented in the literature due to lack of spectroscopic confirmation and the difficulty of obtaining high signal-to-noise emission-line measurements. Aims . We present a spectroscopic study of 17 blue UDG candidates in the field using optical emission lines to confirm their ultra-diffuse nature and characterise their physical properties. Methods . Data were collected using the MODS instrument at the Large Binocular Telescope Observatory and the MISTRAL instrument at the Observatoire de Haute-Provence. Using the software pandora EZ , we derived spectroscopic redshifts ( z _spec ) for our field UDG candidates. We then computed their effective radii ( r _eff ) and central surface brightnesses (µ _0,g ). We measured the H α and H β emission line fluxes in the 17 spectra and derived star formation rates (SFRs) from the line-luminosity relation. We performed forced photometry on our sample to obtain photometric fluxes and applied an aperture correction on the H α integrated fluxes, propagating the correction to the derived SFRs. Using colour relations and estimated dust attenuation, we then computed stellar masses (M _∗ ) and corrected the SFRs accordingly. Finally, we placed our sample on the star-forming main sequence, comparing its distribution with that of local star-forming galaxies. Two sources were further examined as potential giant low surface brightness galaxies (GLSBGs). Results . In our samples, we identify nine confirmed UDGs, eight other low surface-brightness galaxies (LSBGs), including one GLSBG. The z _spec of our field UDGs span a range of 0.015–0.037. Their r _eff ranges from 1.69–4.99 kpc, and their µ _{0 ,g} range from 24.05–24.98 mag arcsec ⁻² . Consistent with previous studies, the galaxies exhibit low to moderate dust content, with an average V-band attenuation of 0.29 mag . The spectroscopically confirmed UDGs presented in this work, after aperture correction, exhibit −2.95 ≤ log (SFR) ≤−1.60 M _⊙ yr ⁻¹ as an upper limit and 7.20 ≤ log (M _∗ ) ≤ 8.08 M _⊙ . These values place them along the star-forming main sequence. Conclusions . Our results indicate that blue field UDGs are characterised by heterogeneous dust attenuation and occupy the same region of the star formation–stellar mass plane as dwarf LSBGs. This is consistent with the broader population of local star-forming galaxies and indicates no distinct global star-forming behaviour.

Context. Measuring the expansion rate of the Universe is a central challenge in cosmology, particularly due to the persistent statistically significant discrepancy between the measurements of the Hubble constant, H ₀ , obtained using early- and late-time probes, commonly known as the Hubble tension. Independent and robust methods are therefore essential to validate existing measurements and assess potential systematic effects. Aims. We employed the cosmic chronometer (CC) approach, which uses the differential age evolution of quiescent galaxies to measure the Hubble parameter H ( z ) without assuming an underlying cosmological model. In contrast to previous CC studies, we restricted our analysis to relics – ultra-compact massive galaxies (UCMGs) hosting the oldest stellar populations – thereby minimising uncertainties related to star formation history and merger history. Methods. We selected a sample of 189 relic galaxies in the redshift range 0.07 ≤ z ≤ 0.22 from the E-INSPIRE UCMG catalogue. Using the D _n 4000 spectral index of relic galaxies and its redshift evolution, combined with MILES stellar population synthesis models, we derived the differential age relation required to infer H ( z ). We accounted not only for metallicity effects but also for the impact of α -element enhancement, which has not been explicitly propagated into the systematic uncertainty budget of the D _n 4000 CC method. Results. We obtain an independent measurement of H ( z = 0.15) = 85 ± 53 km s ⁻¹ Mpc ⁻¹ . Although the total uncertainty remains large and dominated by statistical limitations, the systematic component is 13% (8.7% when α enrichment is not propagated), among the tightest estimates in current CC studies. We find that α enrichment plays a major role in the systematic error budget, particularly in the high-metallicity regime, and must be properly accounted for in future analyses. Conclusions. We demonstrate the proof of concept that relic galaxies provide a promising pathway to reduce systematic uncertainties in the CC method. The statistical uncertainties, which dominate the error budget, can be significantly reduced by the increase of data volume expected during the next years with Euclid , the Vera C. Rubin Observatory, DESI, and 4MOST.

Context . Radio continuum emission has the potential to be useful as an extinction-free tracer of star formation. However, the relation between the radio continuum luminosity and star formation rate (SFR) is potentially limited by various effects such as cosmic-ray transport, free-free absorption, and cosmic-ray electron energy losses. Aims . We aim to calibrate the radio-SFR relation in a sample of nearby galaxies ranging from dwarf to spiral galaxies, covering nearly five orders of magnitude in terms of the SFR range. We include both global and local measurements from individual and spatially resolved, kiloparsec-sized galaxies, respectively. Methods . We measured the radio continuum luminosities at 144 MHz using observations with the LOw Frequency ARray (LOFAR) and measured the radio spectral indices using ancillary 1.4 GHz data. We selected 70 nearby (distance d < 30 Mpc) galaxies, 15 of which were used for local measurements. Taking advantage of their rich ancillary data, we carried out a study of the radio-SFR relation using the total infrared (TIR), mid-infrared (MIR), H α , and far-ultraviolet (FUV) as complementary SFR tracers. About a third of our sample is made up of at least moderately star-forming edge-on galaxies with the remaining ones chosen to form a representative sample of a wide range of morphological types and SFR values. Results . For the first time, we show that the radio luminosity ( L ₁₄₄ ), the SFR, and the radio spectral index ( α ) define a ‘fundamental plane’ in the [log( L ₁₄₄ ), log(SFR), α ] space. This enables us to define a unified radio-SFR relation that is applicable to both for global and local data when using the radio spectral index as a secondary parameter. Conclusions . A unified radio-SFR relation for both global and local data could serve as a litmus test for galaxy simulations that include the effect of cosmic rays and magnetic fields. It also strengthens the case for using the radio-SFR relation as an extinction-free tracer of star formation.

We investigate X-shaped radio galaxies (XRGs) with optical double-peaked narrow emission lines (DPNELs) as potential hosts of dual or binary supermassive black holes (SMBHs). Using available optical spectra from the Sloan Digital Sky Survey and the Dark Energy Spectroscopy Instrument survey, we identify 55 DPNEL sources among a sample of 187 XRGs. We find that the occurrence of [O iii ] DPNELs in XRGs is ∼30%, which is substantially higher than the ∼1% observed in the general galaxy population. Using optical (involving [O iii ] λ 5007, H α , H β , [N ii ] λ 6584, and [S ii ] λλ 6716, 6731) and mid-infrared diagnostic diagrams, we found that both components are predominantly powered by active galactic nuclei (AGNs), implying a ∼95% probability of hosting dual-AGN systems. In comparison, a stellar-mass-, color-, and redshift-matched control sample of non-XRG DPNEL galaxies shows a lower dual-AGN fraction, which depends strongly on radio luminosity, rising from 25% in radio-undetected galaxies to 54% in radio-detected galaxies, and reaching 95% in radio-bright XRGs and FR II radio galaxies. Interestingly, more than 30% of DPNEL XRGs have companion galaxies, supporting a merger-driven origin for these systems. Finally, we analyze parsec-scale radio structure in seven XRGs using Very Long Baseline Array (VLBA) observations at 1.4, 4.3, and 7.6 GHz, resolving the core in only one source. Nevertheless, flat radio spectral indices, AGN-like emission-line properties, and radio–optical VLBA–Gaia positional offsets found in five cases together support the interpretation that XRGs are strong dual/binary-AGN candidates.

Decomposing the contributions of active galactic nuclei (AGNs) from their host galaxies is essential for identifying AGN-dominated galaxies and accurately deriving key physical properties of both supermassive black holes (SMBHs) and their host galaxies, such as black hole accretion rates, stellar masses, and star formation rates. However, decomposing AGN contributions from multi-wavelength photometry remains challenging due to inherent parameter degeneracies in spectral energy distribution (SED) fitting. We establish a unified framework for estimating AGN contribution fractions (f_ AGN ) and host galaxy properties by combining complementary AGN diagnostics: SED decomposition from two independent SED-fitting codes (CIGALE and GRAHSP) and deep learning (DL)-based imaging decomposition. We applied SED decomposition to galaxies in the COSMOS-Web field using multi-wavelength photometry (ultraviolet to far-infrared) and calculated the AGN-to-host galaxy flux ratio (f_ AGN ^ SED ) in the JWST/NIRCam F150W filter. We then compared these SED-fitting derived AGN fractions with those obtained from image decomposition using DL (f_ AGN ^ DL ). Strong agreement is found for AGN-negligible galaxies across all methods: ∼82% are identified as such by both SED codes (f_ AGN ^ SED <0.1), and ∼87% of these also show minimal AGN contribution in the DL model. This high concordance demonstrates that current methods reliably identify pure galaxy systems in most cases. However, for potential AGN-dominant galaxies, large discrepancies emerge. Only 2.7% of galaxies show consistent significant AGN identification between SED codes, and merely ∼7.6% of these also exhibit a significant AGN fraction in DL estimation. Forcing DL AGN fraction constraints into SED fitting generally works for SED-significant but imaging-negligible cases, whereas it fails for around 30% of SED-negligible but imaging-significant cases. In summary, our results highlight the degeneracies inherent in current SED-fitting methods based on empirical observations or theoretical templates and demonstrate the power of incorporating independent morphological information to break these degeneracies. We present a more robust framework combining morphological information from high-fidelity imaging from surveys such as the James Webb Space Telescope (JWST) and , enabling improved AGN–host galaxy decomposition and more reliable measurements of both AGN and galaxy properties. Euclid

Context. The James Webb Space Telescope (JWST) enables the identification of quiescent galaxies out to early epochs, offering a transformative view of their evolution. However, the photometric selection of quiescent galaxy candidates (QGCs) and the derivation of their key physical quantities, such as stellar masses (M _★ ) and dust attenuation, remain highly sensitive to the assumed star formation histories (SFHs), where dust–age degeneracies and modelling choices continue to stand as a major source of uncertainty. Aims. We aim to quantify how the inclusion of JWST/MIRI data and different SFH models impacts the selection and characterisation of QGCs. We test the robustness of the physical properties inferred from the spectral energy distribution (SED) fitting, such as M _★ , age, star formation rate (SFR), and dust attenuation (A _V ). We study how these parameters impact the quiescence criteria of the galaxies across cosmic time. Methods. We performed SED fittings for ∼13 000 galaxies at z ≤ 6 from the CEERS/MIRI fields with a ≤20 optical to mid-infrared broadband coverage. We implemented three SFH prescriptions: a flexible delayed model, a non-parametric model, and an extended regulator model. For each SFH, we compared the results obtained with and without MIRI photometry and dust emission models. We evaluated the impact of these configurations on both the number of QGCs, selected on the basis of their rest-frame UVJ colours, specific SFR, and main-sequence offset, as well as on their key physical properties, such as M _★ , A _V , and stellar ages. Results. The number of selected QGCs varied significantly, with the SFH ranging from 70 to 100 out of a mass-complete sample of ∼5000 galaxies, depending on the model. This number increased to 103–180 when MIRI data were included, driven by improved constraints on both dust attenuation and M _★ . We found a strong correlation between A _V and M _★ of QGCs at z ≤ 2.5, with massive galaxies (M _★ ∼ 10 ¹¹ M _⊙ ) shown to be ∼ 1.5 − 4 times more attenuated than low-mass galaxies (M _★ ∼ 10 ⁹ M _⊙ ). Regardless of the SFH, ∼13% of QGCs exhibit significant attenuation (A _V > 0.5) in support of recent JWST results on dust-rich quiescent galaxy candidates.

Context. Although the population of quasars evolved significantly in the past, the properties of quasars as physical objects are supposed to remain almost unchanged, which makes quasars promising candidates for cosmological tests. The X–UV luminosity relation in particular is widely used for this purpose. However, the potential of other spectral domains for this purpose remains open. Aims. The aim of the analysis we present is to test the parameter space in order to build a well behaving OPT-IR correlation that could serve as a cosmological probe. The main objective is to calibrate the OPT-IR luminosity relation for quasars, focusing on accurate estimations of dusty torus and accretion disk luminosities. We analyzed contaminations related to host galaxies, particularly from polar dust, the interstellar medium, and stellar emission that affect the optical and infrared. Methods. We used a sample of nearly 400 quasars with photometrical observations and spectroscopical redshift divided into four redshift bins (0.7–2.4). Full spectral energy distribution (SED) fitting was performed with the CIGALE code, and results were compared with simplified photometric luminosity estimates. The impact of non-active galactic nucleus components and the role of polar dust in the fitting process were assessed. Results. We show that for sources with a disk luminosity above 10 ⁴⁵ [erg s ⁻¹ ], the photometric estimates are consistent with SED-based values. While polar dust contributes marginally to luminosity, its presence significantly alters SED fitting, particularly the torus opening angle and cold dust properties. In the optical domain, stellar emission is the dominant contamination. In the infrared, disk emission and cold dust play major roles. We propose two empirical calibrations for the OPT–IR relation. Conclusions. We conclude that the optical band is dominated by the accretion disk component above 10 ⁴⁵ or 10 ⁴⁶ [erg s ⁻¹ ] depending on redshift, while IR luminosity is dominated by the dusty torus emission above 1.6 × 10 ⁴⁵ or 2 × 10 ⁴⁶ [erg s ⁻¹ ] depending on the redshift. In this high-luminosity regime, simplified photometric methods yield reliable disk and torus luminosity estimates.

We present the third data release of the LOFAR Two-metre Sky Survey (LoTSS-DR3). The survey images cover 88% of the northern sky and were created from 12 950 h of data (18.6 PB) accumulated over 10.5 years. Producing the images took 20 million core hours of processing through direction-independent and direction-dependent calibration pipelines that correct for instrumental effects as well as spatially and temporally varying ionospheric distortions. In our 120–168 MHz continuum mosaic images with an angular resolution of 6″ (9″ below declination 10°) we catalogue 13 667 877 sources, formed from 16 943 656 Gaussian components. The scatter in the astrometric precision approximately follows the expected noise-like behaviour but with an additional systematic component of at least 0.24″ that is likely due to calibration imperfections. The random flux density scale error is 6%, while the systematic offset was previously shown to be within 2%. The median sensitivity of our mosaics is 92 μJy beam ⁻¹ , improving to 68 μJy beam ⁻¹ at high observing elevations, but degrading to 183 μJy beam ⁻¹ at the celestial equator due to station area projection effects. Completeness simulations, accounting for realistic source models, time- and bandwidth-smearing effects, and astrometric errors, indicate that we detect more than 95% of compact sources with integrated flux densities exceeding 9 times the local root mean square (RMS) noise. However, the recovered source counts in a particular integrated flux density bin do not match the injected counts until flux densities exceed 45 times the local RMS noise. The Euclidean-normalised differential source counts derived from the survey constrain the radio source population over five orders of magnitude and are in good agreement with previous deep and wide-area surveys. All data products are publicly available, including catalogues, individual-field Stokes I , Q , U , and V images, mosaicked Stokes I images, and uv data with associated direction-dependent calibration solutions.

Aims. Extended-UV (XUV) galaxies are galaxies that present an extended outer ultraviolet disk. Although some giant low surface brightness (GLSB) galaxies are also XUV, their relation has been seldom studied. This work aims to determine whether a sample of nine XUV galaxies can be classified as GLSB galaxies, by analyzing their photometric properties in deep optical images. Methods. The method presented here used optical data from the Dark Energy Survey to construct surface brightness profiles for each galaxy. We defined a characteristic UV radius to examine the XUV disks. We fitted the surface brightness profiles using simple exponential functions, and compared the extracted parameters with the literature to identify possible GLSB galaxies. We also examined other diagnostics, including color profiles. Results. The analysis of the optical surface brightness profiles of XUV galaxies reveals that they can be classified into three different families. One third meet the GLSB criteria in terms of diffuseness, another third are regular, and the remaining have a stronger decline in the outer disk than in the inner disk, which is opposite to the characteristics of GLSB galaxies. The color profile allowed us to distinguish one galaxy, NGC1140, and speculate that it is the result of a rare dwarf-dwarf merger.

Context. Ongoing and upcoming large spectroscopic surveys are drastically increasing the number of observed quasar spectra, making the development of fast and accurate automated methods to estimate spectral continua necessary. Aims. This study evaluates the performance of three neural networks (NNs) – an autoencoder, a convolutional NN (CNN), and a U-Net – in predicting quasar continua within the rest frame wavelength range of 1020 Å to 2000 Å. The ability to generalize and predict galaxy continua within the range of 3500 Å to 5500 Å is also tested. Methods. We evaluated the performance of these architectures using the absolute fractional flux error (AFFE) on a library of mock quasar spectra for the WEAVE survey and on real data from the early data release observations of the Dark Energy Spectroscopic Instrument (DESI) and the VIMOS Public Extragalactic Redshift Survey (VIPERS). Results. The autoencoder outperforms U-Net, achieving a median AFFE of 0.009 for quasars. The best model also effectively recovers the Lyα optical depth evolution in the DESI quasar spectra. With minimal optimization, the same architectures can be generalized to the galaxy case, with the autoencoder reaching a median AFFE of 0.014 and reproducing the D4000n break in DESI and VIPERS galaxies.