arXiv subjects

Klaudia Protušová

Publications and source records attributed to Klaudia Protušová.

10 recordsLinked to original sources

arXiv2026

Deep X-ray View of a Distant Protocluster Anchored by a Quasar at $z=6.63$: No Evidence for Enhanced X-ray AGN Activity

Whether dense environments accelerate SMBH growth during cosmic reionization remains uncertain because X-ray constraints on $z>6$ protoclusters are rare. We analyze $\sim865$ ks of Chandra observations of J0910-0414 quasar field, a massive protocluster at $z=6.63$. We construct a catalog of 251 X-ray sources and search for AGN among 21 spectroscopically confirmed members, excluding the central quasar. This is the first systematic X-ray AGN census in a $z>6$ protocluster; none of the members is individually detected. Stacking all members ($\sim17$ Ms total exposure) yields no significant signal and limits the average rest-frame 2-10 keV luminosity to $\langle L_{\rm 2-10~keV}\rangle\leq9.54\times10^{42}~\rm erg~s^{-1}$. The null result gives a central 90% Jeffreys upper bound of $f_{\rm AGN}<0.09$. After accounting for the spatially varying sensitivity, the field Compton-thin X-ray luminosity function predicts $N_{\rm exp,field}=0.0356$ AGN in the surveyed volume. Assuming the overdensity profile of AGNs in this protocluster is the same as that of galaxies determined by Wang et al. (2024), the expected AGN count becomes $N_{\rm exp}=0.131$. Zero detections then imply a one-sided 90% upper limit of $η_{\rm rel}<17.5$ on any additional X-ray AGN enhancement beyond that associated with the galaxy overdensity. Although $η_{\rm rel}<17.5$ permits more than an order-of-magnitude enhancement, the data show no significant excess of X-ray-detectable AGN in J0910-0414 protocluster. The present X-ray data may miss heavily obscured, intrinsically X-ray-weak, or intermittently accreting SMBHs; the non-detection therefore does not rule out AGNs among the member galaxies.

astro-ph.GA↗

arXiv2026

Nearly pristine gas in a galaxy 1 billion years after the Big Bang

Excitation of carbon and oxygen ions is the primary mechanism by which collapsing gas clouds dissipate heat to form new stars. At early cosmic times, in galaxies with chemically pristine gas, many stars are expected to have masses far larger than the mass of our sun due to the deficit in these elements. We searched for ultra-metal-poor galaxies using their spectroscopic absorption signatures in front of bright background quasars, employing the new GHOST high-resolution spectrograph. Here we report the discovery of the first galaxy containing a reservoir of neutral hydrogen gas with metallicity below the ultra-metal-poor threshold: with a measured carbon-to-hydrogen ratio 11,000 times lower than the Sun, it is the most pristine ever found by a factor of four. UMP-DLA-1 is the only known galaxy with measured carbon and oxygen abundances too low to enable efficient formation of stars with solar mass or below. The low metallicity alone therefore guarantees a top-heavy stellar population, providing a direct view of the chemical composition imprinted by massive low-metallicity stars that perished long before the present day: an elevated oxygen-to-carbon ratio. The abundance pattern of UMP-DLA-1 is likely a close representation of the atomic yields of first- or early second-generation stars.

astro-ph.GA↗

arXiv2026

$\textit{Nāpōwawā`enakaulua}$: a close quasar pair at cosmic dawn in the Aether survey

We present the discovery and first characterization of $\textit{Nāpōwawā`enakaulua}$: the most compact known quasar pair candidate in the Epoch of Reionization, with a projected separation of only $0.98^{\prime\prime}$ ($\approx 5.56$ pkpc at $z \sim 6.08$) and a velocity offset of $Δv \simeq 15 \text{ km s}^{-1}$. Using spectroscopy from JWST/NIRSpec IFU, as part of the $\textit{Aether survey}$, Gemini/GNIRS and GMOS we characterize the continuum and emission line properties of the two quasars, enabling constraints on their black hole masses ($M_{\text{BH}} \simeq 1.5 \times 10^9$ and $4.0 \times 10^8\,M_\odot$), accretion states ($λ_{\text{Edd}} \simeq 1.23$ and $1.07$), and systemic redshifts ($z_{\rm sys} \simeq 6.0781$ and $6.0785$). We place this pair in the cosmological context by comparing the chance of occurrence to extrapolations of high-$z$ quasar clustering measurements at larger scales, resulting in a $\sim 2-3$ order of magnitude excess with respect to expectations. This excess hints at an underlying population of merger-triggered quasar pairs at cosmic dawn or to a denser-than-average galactic environment. $\textit{Nāpōwawā`enakaulua}$ thus represents a crucial signpost to investigate the mass assembly of the first massive galaxies and black holes.

astro-ph.GA↗

arXiv2026

Extreme Enrichment at Cosmic Dawn: Three FeII-Strong Quasars at z > 6 from the JWST Aether survey

We present three outliers on the quasar main sequence at z>6, as revealed by JWST/NIRSpec IFU observations from the Aether survey, a program targeting ~200 quasars at cosmic dawn. The quasars, J0216-5226, J0320-3521, and J1429+5447, exhibit exceptionally strong FeII emission and weak H$β$ and [OIII] lines, indicating rapid chemical enrichment within the first Gyr of cosmic history. Their FeII strengths ($R_{\rm{FeII},\lambda4570} \equiv \rm{EW}_{\rm{FeII}}/\rm{EW}_{\rm{H}β}$) range between ~2.5-3.6, placing them among the top ~3% of SDSS quasars at ($0\lesssim z\lesssim 1$). The H$α$ emission lines of J0216-5226 and J1429+5447 imply black hole masses of $\sim1-7\times10^9$ M$_{\odot}$ with $λ_{\rm{Edd}}\sim0.1-0.6$, comparable to typical high-z quasars, although virial black hole masses may be systematically overestimated in strong FeII emitters. In contrast, J0320-3521 hosts a lower mass black hole of $\sim0.2-2\times10^9$ M$_{\odot}$, suggesting possible super-Eddington rate accretion with $λ_{\rm{Edd}}$~0.5-6.0. The IFU data of J0320-3521 reveal a distinct emission-line region at a projected distance of ~1.5 kpc, consistent with either an interacting companion or ionized gas associated to the quasar. We further identify a complex environment around J1429+5447, including two candidate companion galaxies or extended ionized gas structures. These quasars with bright emission-line regions, J0320-3521 and J1429+5447, are radio-loud sources, while J0216-5226 remains undetected in radio ($R_{5\rm{GHz,} \,3σ}\lesssim4$). Together, these results confirm previous findings that highly enriched, rapidly growing black holes were already in place at cosmic dawn. Despite the small sample size, our results further highlight the diversity in environment and radio-jet properties among quasars that otherwise share the same extreme region of the quasar fundamental plane.

astro-ph.GA↗

arXiv2026

Broad Paschen lines as black hole mass tracers: A reverberation mapping calibration

Single-epoch (SE) black hole mass estimators based on rest-frame ultraviolet or optical broad lines can be limited by dust attenuation or wavelength coverage. We calibrate estimators based on broad Paschen P$α$ and P$β$ directly against reverberation mapping (RM) masses. We obtained LBT/LUCI near-infrared spectra of 27 SDSS-RM quasars and combined them with archival Paschen measurements for AGNs with RM masses. After continuum subtraction, we measured line luminosities and full widths at half maximum (FWHMs) using multi-component and single-Gaussian profile models. We fitted $\log(M_{\rm BH}/M_\odot)=a+b\log(L/10^{41}\,{\rm erg\,s^{-1}})+c\log({\rm FWHM}/10^3\,{\rm km\,s^{-1}})$, including intrinsic scatter. The fiducial relations use photometrically corrected line luminosities and FWHMs of the combined broad profiles. For P$α$, we obtain $(a,b,c)=(6.86^{+0.24}_{-0.25},0.47^{+0.11}_{-0.10},1.24^{+0.49}_{-0.48})$ with an intrinsic scatter of $0.28^{+0.08}_{-0.06}$ dex. For P$β$, we obtain $(7.00\pm0.24,0.48^{+0.10}_{-0.09},0.91^{+0.46}_{-0.47})$ with a scatter of $0.32^{+0.08}_{-0.06}$ dex. Relations using single-Gaussian widths, 5100 Å continuum luminosities, or fixed virial slopes have scatters consistent within the uncertainties. These relations provide complementary mass estimators when ultraviolet or optical broad lines are attenuated or unavailable. They should be applied within the parameter ranges of the calibration sample and remain subject to the systematic uncertainty associated with the RM virial factor.

astro-ph.GA↗

arXiv2025

A close look at the black hole masses and hot dusty toruses of the first quasars with MIRI-MRS

The presence of supermassive black holes (SMBHs, $M_\text{BH}\sim10^9 M_\odot$) at $z>7$ remains a puzzle. While their existence appears to require exotic formation or growth processes, it is possible that BH mass estimates are incorrect due to differences from the low-$z$ quasars where BH mass scaling relations are calibrated. In this work, we employ JWST MIRI-MRS spectroscopy to measure the rest-frame optical/IR properties of the four highest-redshift known luminous type-1 quasars at $7.08\leq z<7.64$. We use three new broad lines to measure updated BH masses, H$α$, Pa$α$ and Pa$β$, finding them to be in the range $(4-15)\cdot10^8 M_\odot$. Our black hole mass estimates from all tracers agree with each other and with previous, less accurate, ground-based measurements based on MgII. The flux ratios of the H lines deviate from expectations for case A and B recombination in the same way as in $z<3$ quasars, indicating similar physical conditions in the Broad Line Region. Rest-frame near-IR continuum emission from a hot dusty torus surrounding the accretion disc is unambiguously detected in all four objects. We model the emission with SKIRTOR and constrain the inclination (face-on) and the opening angle ($θ=40-60^\circ$) of the tori. These constraints are consistent for the four objects and with expectations from luminous quasars. We estimate a total dust mass $(1-4)\cdot10^6 M_\odot$ in the tori, corresponding to $(0.2-7)\%$ of the total dust in the quasar host galaxies. Given observed accretion rates, these SMBHs will deplete their tori in only $\sim5$ Myr. Overall, we confirm that $z>7$ SMBHs in quasars could not have grown from stellar-remnant BHs if the radiative efficiency of accretion is $10\%$. We also find no evidence that inferred BH masses and accretion processes in $z>7$ quasars differ significantly from their near-identical counterparts at $z<3$.

astro-ph.GA↗

arXiv2025

JWST ASPIRE: How Did Galaxies Complete Reionization? Evidence for Excess IGM Transmission around ${\rm [O\,{\scriptstyle III}]}$ Emitters during Reionization

The spatial correlation between galaxies and the Ly$α$ forest provides insights into how galaxies reionized the Universe. Here, we present initial results on the spatial cross-correlation between [OIII] emitters and Ly$α$ forest at 5.4 6.5 QSO fields. Using data from five QSO fields, we find $2σ$ evidence for excess Ly$α$ forest transmission at ~20-40 cMpc around [OIII] emitters at z=5.86, indicating that [OIII] emitters reside within a highly ionized IGM. At smaller scales, the Ly$α$ forest is preferentially absorbed, suggesting gas overdensities around [OIII] emitters. Comparing with models including THESAN simulations, we interpret the observed cross-correlation as evidence for significant large-scale fluctuations of the IGM and the late end of reionization at z<6, characterized by ionized bubbles over 50 cMpc around [OIII] emitters. The required UV background necessitates an unseen population of faint galaxies around the [OIII] emitters. Furthermore, we find that the number of observed [OIII] emitters near individual transmission spikes is insufficient to sustain reionization in their surroundings, even assuming all [OIII] emitters harbour AGN with 100 % LyC escape fractions. Despite broad agreement, a careful analysis of ASPIRE and THESAN, using the observed host halo mass from the clustering of [OIII] emitters, suggests that the simulations underpredict the observed excess IGM transmission around [OIII] emitters, challenging our model of reionization. Potential solutions include larger ionized bubbles at z<6, more enhanced large-scale UV background or temperature fluctuations of the IGM, and possibly a patchy early onset of reionization at z>10. Current observational errors are dominated by cosmic variance, meaning future analyses of more QSO fields from JWST will improve the results.

astro-ph.GA↗

arXiv2024

A unique window into the Epoch of Reionisation: A double-peaked Lyman-$α$ emitter in the proximity zone of a quasar at $z\sim 6.6$

We present a study of a double-peaked Ly$α$ emitter, named LAE-11, found in the proximity zone of QSO J0910-0414 at $z\sim6.6$. We use a combination of deep photometric data from Subaru Telescope, HST, and JWST with spectroscopic data from Keck/DEIMOS, NIRCam WFSS and NIRSpec MSA to characterise the ionising and general properties of the galaxy, as well as the quasar environment surrounding it. We detect Ly$α$, H$β$, [OIII] doublet, and H$α$ emission lines in the various spectral datasets. The presence of a double-peaked Ly$α$ line in the spectrum allows us to characterise the opening angle and lifetime of the QSO as $θ_Q>49.62$° and $t_Q > 3.8\times10^5$ years. LAE-11 is a fairly bright (M$_\rm{UV} = -19.84^{+0.14}_{-0.16}$), blue galaxy with a UV slope of $β= -2.61^{+0.06}_{-0.08}$. Since the galaxy is located in a quasar-ionised region, we have a unique opportunity to measure the escape fraction of Lyman Continuum photons using the un-attenuated double-peaked Ly$α$ emission profile and its equivalent width at such high redshift. We employ diagnostics which do not rely on the detection of Ly$α$ for comparison, and find that all tracers of ionising photon leakage agree within 1$σ$ uncertainty. We measure a moderate escape of Lyman Continuum photons from LAE-11 of $f_\rm{esc}^\rm{LyC} = (8 - 33)\%$. Detections of both H$α$ and H$β$ emission lines allow for separate measurements of the ionising photon production efficiency, resulting with $\log(ξ_\rm{ion}/\rm{Hz~erg^{-1}}) = 25.59\pm0.08$ and $25.65\pm0.09$, for H$α$ and H$β$, respectively. The total ionising output of LAE-11, $\log(f_\rm{esc}^\rm{LyC}ξ_\rm{ion, Hα}/\rm{Hz~erg^{-1}}) = 24.85^{+0.24}_{-0.34}$, is higher than the value of $24.3 - 24.8$ which is traditionally assumed as needed to drive Reionisation forward.

astro-ph.GA↗

arXiv2024

Signatures of warm dark matter in the cosmological density fields extracted using Machine Learning

We aim to construct a machine-learning approach that allows for a pixel-by-pixel reconstruction of the intergalactic medium (IGM) density field for various warm dark matter (WDM) models using the Lyman-alpha forest. With this regression machinery, we constrain the mass of a potential WDM particle from observed Lyman-alpha sightlines directly from the density field. We design and train a Bayesian neural network on the supervised regression task of recovering the optical depth-weighted density field $Δ_τ$ as well as its reconstruction uncertainty from the Lyman-alpha forest flux field. We utilise the Sherwood-Relics simulation suite at $4.1\leq z \leq 5.0$ as the main training and validation dataset. Leveraging the density field recovered by our neural network, we construct an inference pipeline to constrain the WDM particle masses based on the probability distribution function of the density fields. We find that our trained Bayesian neural network can accurately recover within a $1σ$ error $\geq 85\%$ of the density field pixels from a validation simulated dataset that encompasses multiple WDM and thermal models of the IGM. When predicting on Lyman-alpha skewers generated using the alternative hydrodynamical code Nyx not included in the training data, we find a $1σ$ accuracy rate $\geq 75\%$. We consider 2 samples of observed Lyman-alpha spectra from the UVES and GHOST instruments, at $z=4.4$ and $z=4.9$ respectively and fit the density fields recovered by our Bayesian neural network to constrain WDM masses. We find lower bounds on the WDM particle mass of $m_{\mathrm{WDM}} \geq 3.8$ KeV and $m_{\mathrm{WDM}} \geq 2.2$ KeV at $2σ$ confidence, respectively. We are able to match current state-of-the-art WDM particle mass constraints using up to 40 times less observational data than Markov Chain Monte Carlo techniques based on the Lyman-alpha forest power spectrum.

astro-ph.CO↗

arXiv2024

The infalling elliptical galaxy M89: The chemical composition of the AGN disturbed hot atmosphere

The chemical enrichment of X-ray-emitting hot atmospheres has hitherto been primarily studied in galaxy clusters. These studies revealed relative abundances of heavy elements that are remarkably similar to Solar. Here, we present measurements of the metal content of M89 (NGC 4552), an elliptical galaxy infalling into the Virgo cluster with a $\sim$10 kpc ram-pressure stripped X-ray tail. We take advantage of deep Chandra and XMM-Newton observations, and with particular attention to carefully modelling the spectra, we measure the O/Fe, Ne/Fe, Mg/Fe, Si/Fe and S/Fe ratios. Contrary to previous measurements in galaxy clusters, our results for the hot atmosphere of M89 suggest super-Solar abundance ratios with respect to iron (i.e. $α$/Fe > 1), similar to its stellar components. Our analysis of the active galactic nucleus (AGN) activity in this system indicates that the AGN-induced outflow could have facilitated the stripping of the original galactic atmosphere, which has been replaced with fresh stellar mass loss material with super-Solar $α$/Fe abundance ratios. Additionally, we report a new fitting bias in the RGS data of low-temperature plasma. The measured O/Fe ratios are >1$σ$ lower in multi-temperature models than a single temperature fit, leading to discrepancies in the calculations of supernova fractions derived from the metal abundances.

astro-ph.HE↗