arXiv subjects

Eduardo Banados

Publications and source records attributed to Eduardo Banados.

At least 19 recordsLinked to original sources

arXiv2026

To be lensed or not to be lensed: on the nature of the alleged high-z lensed quasars J0109-5424 and P170+20

We present a detailed multi-wavelength analysis of two gravitationally lensed z>6 quasar candidates: J0109-5424 and P170+20. Using JWST/NIRSpec near-infrared data from the Aether survey, we demonstrate that J0109-5424 is in fact a FeLoBAL quasar at z=2.07, exhibiting strong iron broad absorption lines that mimic the Lyman break. From the Pabeta emission line, we estimate a black hole mass of 3.9 x 10^8 Msun and a bolometric luminosity of Lbol = 7.7 x 10^45 erg/s for this quasar. Follow-up HST/ACS WFC imaging of P170+20 with the F555W filter, probing emission below the Lyman limit of the quasar, reveals a compact source located 0.09+/-0.04 arcsec from the quasar position. PSF modelling and subtraction yield no evidence for extended emission. This is inconsistent with a foreground galaxy acting as a lens. Furthermore, we obtain Gemini-South/Flamingos 2 near-infrared observations to complement the existing optical Gemini-North/GMOS spectrum of P170+20. Our spectral analysis shows that the observed spectral shape of P170+20 is consistent with a composite quasar and M-dwarf spectrum. However, this interpretation remains uncertain, as a chance alignment between an ultracool dwarf and a quasar within 0.1 arcsec would be unlikely. Overall, our findings establish J0109-5424 as an intermediate redshift source and do not favor the lensed nature of P170+20, although this possibility cannot be conclusively ruled out, highlighting the challenges of selecting lensed quasars at high redshift.

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arXiv2026

ASPIRE: The Environments and Dark Matter Halos of Luminous Quasars in the Epoch of Reionization

We present a systematic study of the environments of 25 luminous quasars at $z > 6.5$ from the ASPIRE program. Using JWST/NIRCam WFSS data, we identified 487 galaxies at $5.3 \lesssim z \lesssim 7.0$ exhibiting [OIII] emission. Among these, 122 [OIII] emitters lie within $|Δv_{\rm los}| < 1000~{\rm km~s^{-1}}$ of the quasars, corresponding to a $\sim9.4$-fold enhancement relative to the average galaxy density at other redshifts. Furthermore, we identified 16 [CII]-emitting galaxies at the quasar redshifts from ALMA mosaic observations. A cross-correlation function (CCF) analysis between quasars and [OIII]+[CII] emitters yields a cross-correlation length of $r_0^{\rm QG} = 8.68^{+0.51}_{-0.55}~h^{-1}~\mathrm{cMpc}$ and a auto-correlation of $r_0^{\rm{QQ}}=15.76^{+2.48}_{-2.70}~h^{-1}~{\rm cMpc}$, indicating that $z \sim 7$ quasars reside in dark matter halos with $M_{\rm halo} = 10^{12.27^{+0.21}_{-0.26}}~M_\odot$. Notably, the number of [OIII]-emitting galaxies at quasar redshifts varies significantly from field to field, ranging from zero to twenty, highlighting a diverse quasar environment. Remarkably, seven quasars trace significant galaxy overdensities (i.e., protoclusters), with $δ_{\rm gal} > 5$ within a volume of $V \sim 500~{\rm cMpc^3}$. We also find that $|Δv_{\rm los}|$ increases rapidly toward smaller galaxy-quasar separations in protocluster fields, consistent with galaxy kinematics around extremely massive halos in cosmological simulations. By combining JWST and ALMA data, we reveal the complex and diverse environments of these early quasars, providing robust evidence that the earliest luminous quasars are effective tracers of galaxy overdensities, albeit with substantial field-to-field variation.

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arXiv2026

Detection of an Extended Ly$α$ Halo around a $\textit{z}=6.64$ Broad Absorption Line Quasar with the Keck Cosmic Web Imager

We present the first results from a program searching for extended Ly$α$ halos around high redshift ($ z \gtrsim 6.5$) quasars using the red channel of the Keck Cosmic Web Imager (KCWI). Our observations reveal a Ly$α$ halo extending to $\simeq11$ pkpc around the $z=6.64$ broad absorption line quasar J0910$-$0414. The Ly$α$ velocity field displays a rotation-like gradient, and the gas velocity dispersion is consistent with gravitationally dominated motion ($σ_{\mathrm{Lyα}}<300$ km s$^{-1}$). Comparison with the $[\mathrm{C\;II}]$ kinematics of the host galaxy core from ALMA observations shows that the Ly$α$-emitting gas extends over a much larger region, shows distinct kinematics, and has a smaller velocity dispersion ($σ_{\mathrm{Lyα}} \simeq 0.6σ_{\mathrm{[C\;II]}}$). The Ly$α$ spectral region of the quasar is largely obscured by a deep $\mathrm{N\;V}$ absorption trough, and as a result, roughly $55\%$ of the total Ly$α$ flux is from the extended halo. These observations demonstrate the potential of KCWI for probing the cool gas reservoir that fuels the growth of quasars and their hosts in the epoch of reionization.

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arXiv2026

Extreme Galaxy-scale Outflows Are Frequent among Luminous Early Quasars

The existence of abundant post-starburst/quiescent galaxies just $\sim$1-2 Gyrs after the Big Bang challenges our current paradigm of galaxy evolution. Cosmological simulations suggest that quasar feedback is likely the most promising mechanism responsible for such rapid quenching. Here we report a high detection rate (6/27) of exceptionally fast and powerful galaxy-scale outflows traced by [O III] emission in z $\sim$ 5-6 luminous quasars as revealed by the James Webb Space Telescope (JWST), with velocity up to $\sim$8400 km s$^{-1}$ and order-of-magnitude kinetic energy outflow rates up to $\sim$260% the observed quasar bolometric luminosities. This fraction is $>$3.9 and $\sim$8.8 times of those in comparison samples at z $\sim$ 1.5-3.5 and z $<$ 1, respectively. These extreme outflows are comparable to or even faster than the most rapid [O III] outflows reported at z $\lesssim$ 3, and could reach the circumgalactic medium (CGM) or even the intergalactic medium (IGM). The average kinetic energy outflow rate of our sample is more than 2 dex higher than those of the lower-redshift comparison samples. The substantially higher frequency of outflows with energetics well above the threshold for negative feedback in our sample strongly suggests that quasar feedback plays a significant role in efficiently quenching/regulating early massive galaxies.

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arXiv2026

Observations of Early Black Holes Before and After JWST

These notes are from three lectures given at the 54th Saas-Fee Advanced Course of the Swiss Society of Astrophysics and Astronomy in January 2025. This chapter reviews the dramatic evolution in our understanding of supermassive black holes in the first billion years, from ground-based discoveries to recent space-based infrared observations with JWST. Section 1 introduces AGN and quasars to contextualise observations at the highest redshifts. Section 2 reviews the pre-JWST understanding of early quasars, including personal accounts of how key discoveries were made. Section 3 examines how JWST is transforming the field, from black hole mass measurements and host galaxy characterisation to large-scale environmental studies, and identifies emerging directions.

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arXiv2026

The Advanced X-ray Imaging Satellite (AXIS) Community Science Book

The AXIS Community Science Book represents the collective effort of 592 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles 138 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks.

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arXiv2025

Kiloparsec-Scale Alignment of a Radio Jet with Cool Gas and Dust in a z~6 Quasar

We present high-angular resolution (0.068", ~400pc) ALMA imaging of the [CII] line and dust continuum emission of PSO J352.4034-15.3373, a radio-loud quasar at z=5.83. The observations reveal a remarkably close match between the orientation of the [CII] and thermal dust emission mapped by ALMA, and radio synchrotron emission of a radio jet previously mapped by the VLBA. This narrow alignment extends over ~4kpc, reminiscent of the well-studied 'alignment effect' in lower-redshift radio galaxies. The [CII] kinematics show a linear increase in velocity with galactocentric radii up to ~200 km/s at r=2kpc, consistent with bulk motions within the galaxy potential, and not relativistic jet motions. The kinematics and respective morphologies are consistent with a picture in which the relativistic jet injects energy into the interstellar medium (potentially leading to subsequent star formation), giving rise to the observed alignment and significant (> 100 km/s) [CII] velocity dispersion within the host galaxy on kiloparsec scales. Indeed, the astonishingly close alignment and narrow linearity of the radio jet with the [CII] and dust emission are hard to conceive without some fundamental relationship between the two.

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arXiv2024

A blazar in the epoch of reionization

Relativistic jets are thought to play a crucial role in the formation and evolution of massive galaxies and supermassive black holes. Blazars, which are quasars with jets aligned along our line of sight, provide insights into the jetted population and have been observed up to redshifts of z=6.1. Here, we report the discovery and multi-wavelength characterization of the blazar VLASS J041009.05-013919.88 at z=7 (Universe's age ~750 Myr), powered by a ~7x10^8 Msun black hole. The presence of this high-redshift blazar implies a large population of similar but unaligned jetted sources in the early Universe. Our findings suggest two possible scenarios: in one, the jet in J0410-0139 is intrinsically low-power but appears highly luminous due to relativistic beaming, suggesting that most UV-bright quasars at this redshift host jets. Alternatively, if J0410-0139 represents an intrinsically powerful radio source, there should be hundreds to thousands of radio-quiet quasars at z~7 with properties similar to J0410-0139, a prediction in tension with observed quasar densities based on their UV luminosity function. These results support the hypothesis that rapid black hole growth in the early Universe may be driven by jet-enhanced or obscured super-Eddington accretion, potentially playing a key role in forming massive black holes during the epoch of reionization.

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arXiv2024

No Redshift Evolution in the Fe II/Mg II Flux Ratios of Quasars across Cosmic Time

The Fe II/Mg II emission line flux ratio in quasar spectra serves as a proxy for the relative Fe to alpha-element abundances in the broad line regions of quasars. Due to the expected different enrichment timescales of the two elements, they can be used as a cosmic clock in the early Universe. We present a study of the Fe II/Mg II ratios in a sample of luminous quasars exploiting high-quality near-IR spectra taken primarily by the XQR-30 program with VLT XSHOOTER. These quasars have a median bolometric luminosity of log(L_bol[erg s^-1])~47.3 and cover a redshift range of z=6.0-6.6. The median value of the measured Fe II/Mg II ratios is ~7.9 with a normalized median absolute deviation of ~2.2. In order to trace the cosmic evolution of Fe II/Mg II in an unbiased manner, we select two comparison samples of quasars with similar luminosities and high-quality spectra from the literature, one at intermediate redshifts (z=3.5-4.8) and the other at low redshifts (z=1.0-2.0). We perform the same spectral analysis for all these quasars, including the usage of the same iron template, the same spectral fitting method, and the same wavelength fitting windows. We find no significant redshift evolution in the Fe II/Mg II ratio over the wide redshift range from z=1 to 6.6. The result is consistent with previous studies and supports the scenario of a rapid iron enrichment in the vicinity of accreting supermassive black holes at high redshift.

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arXiv2024

Far-Infrared and [CII] observations of a z=7 blazar

We present millimeter observations of the host galaxy of the most distant blazar known, VLASSJ041009.05-013919.88 (hereafter J0410-0139) at z=7, using ALMA and NOEMA observations. The ALMA data reveal a 2e42 erg/s [CII] 158um emission line at z=6.9964 with a [CII]-inferred star-formation rate of 58 Msun/yr. We estimate a dynamical mass of 4.6e9 Msun, implying a black hole mass to host a dynamical mass ratio of 0.15. The 238 GHz continuum (rest-frame IR) decreased by ~33% from the NOEMA to the ALMA observations taken ~10 months apart. The VLA 3-10 GHz radio flux densities showed a ~37% decrease in a similar time frame, suggesting a causal connection. At face value, J0410-0139 would have the lowest [CII]-to-IR luminosity ratio of a z>5.7 quasar reported to date (~1e-4). However, if only <20% of the measured IR luminosity were due to thermal emission from dust, the [CII]-to-IR luminosity ratio would be typical of (U)LIRGS, and the star formation rates derived from [CII] and IR luminosities would be consistent. These results provide further evidence that synchrotron emission significantly contributes to the observed rest-frame IR emission of J0410-0139, similar to what has been reported in some radio-loud AGN at z<1.

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arXiv2024

A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): Impact of Galaxies on the CGM Metal Enrichment at z > 6 Using the JWST and VLT

We characterize the multiphase circumgalactic medium and galaxy properties at z = 6.0-6.5 in four quasar fields from the James Webb Space Telescope A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE) program. We use the Very Large Telescope/X-shooter spectra of quasar J0305-3150 to identify one new metal absorber at z = 6.2713 with multiple transitions (OI, MgI, FeII and CII). They are combined with the published absorbing systems in Davies et al. (2023a) at the same redshift range to form of a sample of nine metal absorbers at z = 6.03 to 6.49. We identify eight galaxies within 1000 km s$^{-1}$ and 350 kpc around the absorbing gas from the ASPIRE spectroscopic data, with their redshifts secured by [OIII]($λλ$4959, 5007) doublets and H$β$ emission lines. Our spectral energy distribution fitting indicates that the absorbing galaxies have stellar mass ranging from 10$^{7.2}$ to 10$^{8.8}M_{\odot}$ and metallicity between 0.02 and 0.4 solar. Notably, the z = 6.2713 system in the J0305-3150 field resides in a galaxy overdensity region, which contains two (tentatively) merging galaxies within 350 kpc and seven galaxies within 1 Mpc. We measure the relative abundances of $α$ elements to iron ([$α$/Fe]) and find that the CGM gas in the most overdense region exhibits a lower [$α$/Fe] ratio. Our modeling of the galaxy's chemical abundance favors a top-heavy stellar initial mass function, and hints that we may be witnessing the contribution of the first generation Population III stars to the CGM at the end of reionization epoch.

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arXiv2024

Recognizing Blazars Using Radio Morphology from the VLA Sky Survey

Blazars are radio-loud Active Galactic Nuclei (AGN) whose jets have a very small angle to our line of sight. Observationally, the radio emission are mostly compact or a compact-core with a 1-sided jet. With 2.5$^{\prime\prime}$ resolution at 3 GHz, the Very Large Array Sky Survey (VLASS) enables us to resolve the structure of some blazar candidates in the sky north of Decl. $-40$ deg. We introduce an algorithm to classify radio sources as either blazar-like or non-blazar-like based on their morphology in the VLASS images. We apply our algorithm to three existing catalogs, including one of known blazars (Roma-BzCAT) and two of blazar candidates identified by WISE colors and radio emission (WIBRaLS, KDEBLLACS). We show that in all three catalogs, there are objects with morphology inconsistent with being blazars. Considering all the catalogs, more than 12% of the candidates are unlikely to be blazars, based on this analysis. Notably, we show that 3% of the Roma-BzCAT "confirmed" blazars could be a misclassification based on their VLASS morphology. The resulting table with all sources and their radio morphological classification is available online.

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arXiv2023

A comprehensive view of the interstellar medium in a quasar host galaxy at z~6.4

Characterizing the physical conditions (density, temperature, ionization state, metallicity, etc) of the interstellar medium is critical to our understanding of the formation and evolution of galaxies. Here we present a multi-line study of the interstellar medium in the host galaxy of a quasar at z~6.4, i.e., when the universe was 840 Myr old. This galaxy is one of the most active and massive objects emerging from the dark ages, and therefore represents a benchmark for models of the early formation of massive galaxies. We used the Atacama Large Millimeter Array to target an ensemble of tracers of ionized, neutral, and molecular gas, namely the fine-structure lines: [OIII] 88$μ$m, [NII] 122$μ$m, [CII] 158$μ$m, and [CI] 370$μ$m and the rotational transitions of CO(7-6), CO(15-14), CO(16-15), and CO(19-18); OH 163.1$μ$m and 163.4$μ$m; and H$_2$O 3(0,3)-2(1,2), 3(3,1)-4(0,4), 3(3,1)-3(2,2), 4(0,4)-3(1,3), 4(3,2)-4(2,3). All the targeted fine-structure lines are detected, as are half of the targeted molecular transitions. By combining the associated line luminosities, the constraints on the dust temperature from the underlying continuum emission, and predictions from photoionization models of the interstellar medium, we find that the ionized phase accounts for about one third of the total gaseous mass budget, and is responsible for half of the total [CII] emission. It is characterized by high density (n~180 cm$^{-3}$), typical of HII regions. The spectral energy distribution of the photoionizing radiation is comparable to that emitted by B-type stars. Star formation also appears to drive the excitation of the molecular medium. We find marginal evidence for outflow-related shocks in the dense molecular phase, but not in other gas phases. This study showcases the power of multi-line investigations in unveiling the properties of the star-forming medium in galaxies at cosmic dawn.

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arXiv2022

Quasars and the Intergalactic Medium at Cosmic Dawn

Quasars at cosmic dawn provide powerful probes of the formation and growth of the earliest supermassive black holes (SMBHs) in the universe, their connections to galaxy and structure formation, and the evolution of the intergalactic medium (IGM) at the epoch of reionization (EoR). Hundreds of quasars have been discovered in the first billion years of cosmic history, with the quasar redshift frontier extended to z~7.6. Observations of quasars at cosmic dawn show that: (1) The number density of luminous quasars declines exponentially at z>5, suggesting that the earliest quasars emerge at z~10; the lack of strong evolution in their average spectral energy distribution indicates a rapid buildup of the AGN environment. (2) Billion-solar-mass BHs already exist at z>7.5; they must form and grow in less than 700 Myr, by a combination of massive early BH seeds with highly efficient and sustained accretion. (3) The rapid quasar growth is accompanied by strong star formation and feedback activity in their host galaxies, which show diverse morphological and kinetic properties, with typical dynamical mass of lower than that implied by the local BH/galaxy scaling relations. (4) HI absorption in quasar spectra probes the tail end of cosmic reionization at z~5.3-6, and indicates the EoR midpoint at 6.9 < z < 7.6 with large spatial fluctuations in IGM ionization. Observations of heavy element absorption lines suggest that the circumgalactic medium also experiences evolution in its ionization structure and metal enrichment during the EoR.

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arXiv2022

The Pan-STARRS1 z>5.6 quasar survey II: Discovery of 55 Quasars at 5.6<z<6.5

The identification of bright quasars at z>6 enables detailed studies of supermassive black holes, massive galaxies, structure formation, and the state of the intergalactic medium within the first billion years after the Big Bang. We present the spectroscopic confirmation of 55 quasars at redshifts 5.6<z<6.5 and UV magnitudes -24.5<M1450<-28.5 identified in the optical Pan-STARRS1 and near-IR VIKING surveys (48 and 7, respectively). Five of these quasars have been independently discovered in other studies. The quasar sample shows an extensive range of physical properties, including 17 objects with weak emission lines, ten broad absorption line quasars, and five with strong radio emission (radio-loud quasars). There are also a few notable sources in the sample, including a blazar candidate at z=6.23, a likely gravitationally lensed quasar at z=6.41, and a z=5.84 quasar in the outskirts of the nearby (D~3 Mpc) spiral galaxy M81. The blazar candidate remains undetected in NOEMA observations of the [CII] and underlying emission, implying a star-formation rate <30-70 Msun/yr. A significant fraction of the quasars presented here lies at the foundation of the first measurement of the z~6 quasar luminosity function from Pan-STARRS1 (introduced in a companion paper). The quasars presented here will enable further studies of the high-redshift quasar population with current and future facilities.

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arXiv2022

VLBA reveals the absence of a compact radio core in the radio intermediate quasar J2242+0334 at z =5.9

High-resolution imaging is crucial for exploring the origin and mechanism of radio emission in quasars, especially at high redshifts. We present 1.5 GHz Very Long Baseline Array (VLBA) images of the radio continuum emission from the radio-intermediate quasar (RIQ) J2242+0334 at $z = 5.9$. This object was previously detected at both 1.5 GHz and 3 GHz with the Karl G. Jansky Very Large Array (VLA) as a point source. However, there is no clear detection in the VLBA images at both the full resolution of 10.7 milliarcsecond (mas) $\times$ 4.5 mas (61.7 pc $\times$ 26.0 pc) and a tapered resolution of 26 mas $\times$ 21 mas (150 pc $\times$ 121 pc). This suggests that the radio emission from the quasar is diffuse on mas scales with surface brightness fainter than the $3σ$ detection limit of 40.5 $μ\rm Jy \ beam^{-1}$ in the full resolution image. The radio emission in the RIQ J2242+0334 is likely to be wind-like (i.e., diffuse) rather than in the form of collimated jets. This is different from the previous radio detections of the most luminous quasars at $z \sim$6 which are usually dominated by compact, high brightness temperature radio sources. Meanwhile, compared with RIQs at low redshifts, the case of J2242+0334 suggests that not all RIQs are beamed radio-quiet quasars. This optically faint RIQ provides an important and unique example to investigate the radio activity in the less powerful active galactic nuclei at the earliest cosmic epoch.

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arXiv2022

The Decoupled Kinematics of high-z QSO Host Galaxies and their Lya halos

We present a comparison of the interstellar medium traced by [CII] (ALMA), and ionised halo gas traced by Lya (MUSE), in and around QSO host galaxies at z~6. To date, 18 QSOs at this redshift have been studied with both MUSE and high-resolution ALMA imaging; of these, 8 objects display a Lya halo. Using datacubes matched in velocity resolution, we compare and contrast the spatial and kinematic information of the Lya halos and the host galaxies' [CII] (and dust-continuum) emission. We find that the Lya halos extend typically 3-30 times beyond the interstellar medium of the host galaxies. The majority of the Lya halos do not show ordered motion in their velocity fields, whereas most of the [CII] velocity fields do. In those cases where a velocity gradient can be measured in Lya, the kinematics do not align with those derived from the [CII] emission. This implies that the Lya emission is not tracing the outskirts of a large rotating disk that is a simple extension of the central galaxy seen in [CII] emission. It rather suggests that the kinematics of the halo gas are decoupled from those of the central galaxy. Given the scattering nature of Lya, these results need to be confirmed with JWST IFU observations that can constrain the halo kinematics further using the non-resonant Ha line.

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arXiv2022

Chemical Abundance of z~6 Quasar Broad-Line Regions in the XQR-30 Sample

The elemental abundances in the broad-line regions of high-redshift quasars trace the chemical evolution in the nuclear regions of massive galaxies in the early universe. In this work, we study metallicity-sensitive broad emission-line flux ratios in rest-frame UV spectra of 25 high-redshift (5.8 < z < 7.5) quasars observed with the VLT/X-shooter and Gemini/GNIRS instruments, ranging over $\log(M_{\rm{BH}}/M_{\odot})= 8.4-9.8$ in black hole mass and $\log(L_{\rm{bol}}/\rm{erg\, s}^{-1})= 46.7-47.7$ in bolometric luminosity. We fit individual spectra and composites generated by binning across quasar properties: bolometric luminosity, black hole mass, and blueshift of the \civ\, line, finding no redshift evolution in the emission-line ratios by comparing our high-redshift quasars to lower-redshift (2.0 < z < 5.0) results presented in the literature. Using Cloudy-based locally optimally-emitting cloud photoionisation model relations between metallicity and emission-line flux ratios, we find the observable properties of the broad emission lines to be consistent with emission from gas clouds with metallicity that are at least 2-4 times solar. Our high-redshift measurements also confirm that the blueshift of the CIV emission line is correlated with its equivalent width, which influences line ratios normalised against CIV. When accounting for the CIV blueshift, we find that the rest-frame UV emission-line flux ratios do not correlate appreciably with the black hole mass or bolometric luminosity.

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