arXiv subjects

Huub Röttgering

Publications and source records attributed to Huub Röttgering.

At least 19 recordsLinked to original sources

arXiv2026

A dust-reddened quasar in a [C II]-luminous host at z=6.55

Most known quasars at $z>6$ were selected through their rest-frame UV emission. Only a small number of reddened quasars have been identified at these redshifts, leaving their nuclear and host-galaxy properties poorly constrained. We present JWST/NIRSpec spectroscopy and ALMA band 6 observations of the quasar J1440+0019 at $z=6.5488$, revealing its dust-reddened nature and jointly characterizing its nucleus and host galaxy. The continuum is best described by an SMC-like extinction law with $E(B-V)=0.20\pm0.03$. Three absorption systems detected in N V, Si IV, and C IV are blueshifted by approximately $900$--$3600$ km s$^{-1}$ and likely trace an ionized nuclear outflow. The broad Mg II line and extinction-corrected continuum yield a black-hole mass of $\log(M_{\rm BH}/M_\odot)=9.04\pm0.42$, a bolometric luminosity of $L_{\rm bol}\simeq1.1\times10^{47}$ erg s$^{-1}$, and an Eddington ratio of $λ_{\rm Edd}\simeq0.8$. ALMA observations further reveal its host galaxy to be among the most [C II]-luminous known at $z>6$, with $L_{\mathrm{[C II]}}=(7.21\pm0.25)\times10^9 L_\odot$. For a fiducial dust temperature of 47 K and emissivity index $β=1.6$, the dust continuum implies $L_{\rm TIR}=8.9\times10^{12} L_\odot$ and $M_{\rm dust}=4.0\times10^8 M_\odot$. The inferred dynamical mass places J1440+0019 in the region of the $M_{\rm BH}$--$M_{\rm dyn}$ plane occupied by high-redshift blue quasars. These observations reveal a moderately reddened, rapidly accreting quasar in a luminous, dust-rich host during reionization. Its measured nuclear and host-galaxy properties provide an observational reference for identifying and characterizing similar systems in future systematic searches with wide-area infrared surveys.

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arXiv2026

A Brush with Turbulence: Probing the ICM Dynamics in the Merging Toothbrush Cluster using XRISM

The Toothbrush Cluster (1RXS J0603.3+4214) is known for its northern radio relic, radio halo, and highly disturbed X-ray morphology. It shows features of both shock-driven and turbulent reacceleration, the latter of which is invoked to explain its radio halo. However, how kinetic energy from the merger is distributed into gas motions across spatial scales remains unclear. We probe the intracluster medium (ICM) dynamics in the southern, X-ray-brightest region of the cluster using a 167 ks XRISM/Resolve observation. We conduct both full-array and quadrant sub-array analyses by fitting the spectra with single and multi-component thermal models in the 3-8 keV band. The full-array spectrum favours two ICM components with a transonic line-of-sight (LOS) velocity difference of $Δv_{\mathrm{bulk}}=1635^{+165}_{-110}$ km s$^{-1}$, while the velocity dispersions are much lower, at $σ_{v,1\mathrm{D}}\sim$245-310 km s$^{-1}$. The sub-array analysis likewise reveals multiple components in at least three quadrants, with LOS bulk velocities ranging from $-2520^{+295}_{-230}$ to $+930^{+70}_{-110}$ km s$^{-1}$. The velocity dispersions remain modest at $\sim$215 km s$^{-1}$, corresponding to a turbulent pressure support of about 3-6% on scales dominating the observed line broadening. Cooler gas is detected in the NE and SW, with $kT_{\mathrm{NE}}=3.13^{+0.33}_{-0.30}$ keV and $kT_{\mathrm{SW}}=2.32^{+0.43}_{-0.37}$ keV, likely associated with a third, northern subcluster identified in weak-lensing and optical studies. Our results indicate a complex ICM kinematic structure, with evidence for at least three subclusters exhibiting supersonic bulk velocity offsets and much smaller velocity dispersions. This shows that the merger geometry has a significant line-of-sight component and may indicate that the cluster collision is relatively young, with the turbulent cascade not yet fully established.

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arXiv2026

Quasar Impostors: Two Extremely UV-Bright ($M_{\rm UV}\approx-23.5$) Reionisation-Epoch Galaxies Powered by Very Massive Stars

The extreme bright end of the galaxy UV luminosity function during reionisation remains poorly constrained, particularly where the galaxy and quasar luminosity functions overlap and source classification becomes ambiguous. We present JWST/NIRSpec and ALMA Band-6 observations of J1450-0144 ($z=6.627$) and J1429-0104 ($z=6.796$), two $M_{\rm UV}\simeq-23.5$ sources originally classified as faint quasars by SHELLQs. NIRSpec reveals blue UV continua, strong P Cygni profiles in N V, Si IV, and C IV, broad He II $\lambda1640$ emission with rest-frame equivalent widths of $8.8\pm1.2$ and $3.7\pm1.1$ Å, respectively, and narrow nebular lines, reclassifying both as extremely UV-luminous galaxies. Standard population-synthesis models cannot simultaneously reproduce the strong He II and wind features, whereas models incorporating very massive stars (VMS; $M\gtrsim100\,M_\odot$) with dedicated wind prescriptions can. These models favor a star-formation duration of 2-4 Myr for J1450-0144, with a broader allowed range for J1429-0104, stellar masses of $\log(M_\star/M_\odot)\approx9.2$-$9.9$, and star-formation rates of $\simeq300$-$540\,M_\odot\,{\rm yr}^{-1}$. Under the same VMS wind models, equivalent-width diagnostics imply $M_{\rm up}\gtrsim225\,M_\odot$ for J1429-0104, while J1450-0144 lies beyond even the $M_{\rm up}=475\,M_\odot$ grid. ALMA detects luminous [C II] 158 $μ$m emission in both systems, with $L_{\rm [CII]}\approx0.8$ and $4.1\times10^{9}\,L_\odot$, respectively. J1429-0104 additionally shows bright dust continuum, with both [C II] and dust offset by $\sim5.4$ kpc from its UV emission. These sources demonstrate that VMS can power some of the most UV-luminous galaxies at cosmic dawn and show that source classifications, and hence the inferred demographics of both galaxies and quasars in the crossover regime, need revisiting.

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arXiv2026

A first systematic study of [OIII] 88$μ$m at $z>8$: two luminous oxygen lines and a powerful ionized outflow in the first 600 million years

We present deep ALMA Band 7 observations of the [OIII] $88μ$m line and underlying dust continuum emission in four UV-bright, gravitationally lensed (magnification $μ= 1.4-3.8$), JWST-selected galaxies at $z = 8.5 - 10.3$, with observed magnitudes $-22.5 \lesssim M_\mathrm{UV} \lesssim -20.5$. [OIII] $88μ$m is confidently detected in UNCOVER-10646 at $z=8.5080 \pm 0.0011$ ($15σ$) and DHZ1 at $z=9.3113 \pm 0.0006$ ($6σ$), with both being intrinsically luminous systems [$L_\text{[OIII]} = (1.1 - 1.6) \times 10^9\,L_\odot$] that follow the local [OIII]-SFR relation. [OIII] $88μ$m remains undetected in the two $z>10$ targets, including in the $z=10.07$ X-ray AGN UHZ1, where we obtain a deep limit of $L_\text{[OIII]} < 6 \times 10^7\,L_\odot$. Dust emission is not detected in any individual source nor in a stack ($<3σ$). The high S/N [OIII] $88μ$m detection in UNCOVER-10646 uniquely reveals an additional broad component ($\mathrm{FWHM} = 1366_{-329}^{+473}\,\mathrm{km/s}$; $Δ\mathrm{BIC}\approx20$) indicative of an ionized outflow. We infer a high outflow rate of $\dot{M}_\mathrm{out} = 128_{-46}^{+80}\,M_\odot\,\mathrm{yr}^{-1}$, corresponding to a mass loading factor $η= \dot{M}_\mathrm{out}/\mathrm{SFR} = 2.9_{-1.0}^{+1.8}$ that matches or exceeds theoretical predictions and JWST-based studies of ionized outflows at high redshift. While high-resolution ALMA follow-up is required to confirm and spatially resolve the outflow, this first systematic study at $z>8$ highlights the unique diagnostic power of [OIII] $88μ$m in characterizing galaxies in the early Universe.

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arXiv2026

Radio-detected Lya emitters at 1.88 < z < 3.52: AGN fraction and Lya emission

Lya emitters (LAEs) are galaxies with strong Lya emission, tracing early star formation and ionizing radiation. Their connection to active galactic nuclei (AGNs) is key to understanding the mechanisms behind (extended) Lya emission. In this work, we measure the fraction of LAEs identified as radio-emitting AGN (fAGN,radio) and the fraction of radio sources that exhibit Lya emission (fLya) to investigate the connection between radio AGN activity and Lya emission at 1.88 < z < 3.52. We identify 928 sources detected in both the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX) and the LOw Frequency ARray (LOFAR) surveys. These matches are drawn from 55,109 spectroscopically confirmed LAEs and 27,625 radio sources. After applying completeness corrections, we obtain fAGN,radio = 1.77 $\pm$ 0.04% and fLya = 18.15 $\pm$ 0.14%. The fraction fAGN,radio increases from 0.4 $\pm$ 0.1% to 9.7 $\pm$ 1.3% with increasing Lya luminosity, while fLya rises from 0.7 $\pm$ 0.1% to 55.8 $\pm$ 14.5% with radio luminosity. `LAEs with radio AGN' and `optical AGN with Lya emission' show similar radio luminosities above the AGN threshold, although optical AGN have higher Lya luminosities. We find no significant correlation between Lya luminosity and either radio luminosity or spectral index. Lya line width increases with Lya luminosity but shows no correlation with radio size. Our results show that most Lya emission at 1.88 < z < 3.52 is powered by star formation, with radio AGN activity confined to a small luminous subset (1.77 $\pm$ 0.04%). The absence of correlations between Lya and radio properties suggests that Lya emission is governed primarily by host-galaxy gas properties rather than direct AGN jet coupling.

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arXiv2026

JWST observes the assembly of a massive galaxy at z~4

We present JWST observations of the radio galaxy TGSSJ1530+1049, spectroscopically confirmed at $z=4.0$. NIRCam images and NIRSpec/IFU spectroscopy (R=2700) show that TGSSJ1530+1049 is part of one of the densest-known structures of continuum and line-emitting objects found at these redshifts. NIRCam images show a number of distinct continuum objects and evidence of interactions traced by diffuse emission, and the NIRSpec IFU cube reveals further strong line emitting regions. We identify six continuum and four additional strong H$α$ emitting sources with weaker or no underlying continuum within the 3x3 arcsec IFU field. From spatial alignment with high-resolution radio data and emission line profiles, the radio AGN host galaxy is clearly identified. The bright H$α$ emission (but not the optical components) is distributed remarkably linearly along the radio axis, suggestive of a biconical illumination zone by a central obscured AGN. The emission line kinematics indicate jet-gas interactions on scales of a few kpc. However, due to large relative velocities and presence of underlying continuum, the alignment with the radio structure appears to be, at least partly, caused by a particular configuration of interacting galaxies. At least four objects within a 10x10 (projected) kpc$^2$ area which includes the radio source have high stellar masses ($\log(M_\star/M_\odot)>10.3$) and star formation rates in the range $70-163\,M_\odot$ yr$^{-1}$. Using a stellar mass-based analysis, we predict a total dark matter halo mass of $\approx10^{13} M_\odot$. Based on the physical separations and velocity differences between the galaxies, it is expected that these galaxies will merge to form a massive galaxy within a few Gyr. The system qualitatively resembles the forming brightest cluster galaxies in cosmological simulations that form early through a rapid succession of mergers.

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arXiv2026

Lyα Nebulae in HETDEX: The Largest Statistical Census Bridging Lyα Halos and Blobs across Cosmic Noon

The Hobby-Eberly Dark Energy Experiment (HETDEX) is an untargeted ~540 deg^2 spectroscopic survey of Lyα emission in the 1.9 < z < 3.5 Universe. In surface brightness, this survey reaches 1σ Lyα sensitivities of approximately 2-5 x 10^-18 erg s^-1 cm^-2 arcsec^-2, allowing large samples of extended Lyα nebulae (LAN) to be studied. We selected a sample of 70,691 Lyα-emitting galaxies (LAEs) with an emission-line signal-to-noise ratio greater than 6 and modeled the Lyα emission as a point-source component with an optional exponential envelope. Half (~47.5%) of the LAE sample (33,612 objects) exhibits significant extended emission and is best fit by the two-component model. The fraction of resolved sources increases with Lyα flux and luminosity. Their isophotal areas range from 10-130 arcsec^2 (median 15 arcsec^2), with integrated Lyα fluxes from 6-2000 x 10^-17 erg s^-1 cm^-2 (median 20 x 10^-17 erg s^-1 cm^-2). Comparison between point-spread-function-weighted and isophotal flux measurements shows that the HETDEX pipeline underestimates the total Lyα flux by ~30% on average, reflecting the substantial halo contribution in extended sources. Approximately 420 LANs are found per deg^2 over 79.5 deg^2 of non-contiguous sky. About 12% of resolved sources show active galactic nuclei signatures and are bright in Lyα and continuum. The remaining 88% span a wide range of morphologies and often lack continuum counterparts. Exponential scale lengths show no strong correlation with Lyα flux or luminosity (median 11.6 +/- 1.9 kpc). Only 2.9% of the full S/N > 6 LAE population with ancillary data have radio counterparts, but 64% of those are found to be extended, with the radio fraction increasing with Lyα size.

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arXiv2025

Detection of [OIII]88$μ$m in JADES-GS-z14-0 at z=14.1793

We report the first successful ALMA follow-up observations of a secure $z > 10$ JWST-selected galaxy, by robustly detecting ($6.6σ$) the [OIII]$_{88μm}\,$ line in JADES-GS-z14-0 (hereafter GS-z14). The ALMA detection yields a spectroscopic redshift of $z=14.1793\pm0.0007$, and increases the precision on the prior redshift measurement of $z=14.32_{-0.20}^{+0.08}$ from NIRSpec by $\gtrsim$180$\times$. Moreover, the redshift is consistent with that previously determined from a tentative detection ($3.6σ$) of CIII]$_{1907,1909}$ ($z=14.178\pm0.013$), solidifying the redshift determination via multiple line detections. We measure a line luminosity of $L_\mathrm{[OIII]88} = (2.1 \pm 0.5)\times10^8\,L_\odot$, placing GS-z14 at the lower end, but within the scatter of, the local $L_\mathrm{[OIII]88}$-star formation rate relation. No dust continuum from GS-z14 is detected, suggesting an upper limit on the dust-to-stellar mass ratio of $< 2 \times 10^{-3}$, consistent with dust production from supernovae with a yield $y_d < 0.3\,M_\odot$. Combining a previous JWST/MIRI photometric measurement of the [OIII]$λλ$4959,5007$\mathrm{\mathring{A}}$ and H$β$ lines with Cloudy models, we find GS-z14 to be surprisingly metal-enriched ($Z\sim0.05 - 0.2\,Z_\odot$) a mere $300\,\mathrm{Myr}$ after the Big Bang. The detection of a bright oxygen line in GS-z14 thus reinforces the notion that galaxies in the early Universe undergo rapid evolution.

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arXiv2025

Deep Constraints on [CII]158$μ$m in JADES-GS-z14-0: Further Evidence for a Galaxy with Low Gas Content at z=14.2

We present deep ALMA observations targeting the [CII]$_{158μm}\,$ line in JADES-GS-z14-0, the most distant known galaxy at z=14.1793. We do not detect the [CII]$_{158μm}\,$ line in our deep observations, implying a luminosity of $<$6$\times10^7$ L$_{\odot}$ (3$σ$) for the target. Comparing this with the detected [OIII]$_{88μm}\,$ line, we constrain the [OIII]/[CII] ratio to be $>$3.5, significantly improving our probe of the ionization parameter $U$. The observed ratio is higher than analogues in the local universe, but consistent with galaxies at $z\approx6$-9. Through ISM modeling, we infer extreme ionizing conditions with log(U)$>-$2.0, likely requiring a young stellar population. Our modeling also indicates a relatively low gas density ($51_{-32}^{+116}$ cm$^{-3}$), significantly lower than expected from lower redshift trends. We infer a relatively high gas-phase metallicity (16$\pm$6\% solar) consistent with previous results and implying a rapid build-up of metals. Finally, using [CII]$_{158μm}\,$ as a molecular/cold gas mass tracer, we infer a low gas fraction ($f_\mathrm{gas} < 0.77$), consistent with previous estimates of the dynamical mass from [OIII]$_{88μm}\,$. Combined with the low observed gas density, lack of dust and high ionization parameter, this suggests strong feedback processes are playing an important role in the evolution of this galaxy. Our observations show that JADES-GS-z14-0 is a rapidly evolving galaxy with extreme ISM conditions, shedding light on the earliest phases of galaxy formation.

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arXiv2024

Radio AGN jet alignment: Radio and Optical Position Angle of Radio Galaxies

It is well established that AGNs play an important role in the evolution of galaxies. These AGNs can be linked to the accretion processes onto massive black holes and past merger events in their host galaxies, which may lead to different alignments of the jets with respect to the host galaxies. This paper presents a study of the PA differences between radio and optical images of radio AGNs based on the LoTSS DR2, the FIRST, the DESI Legacy Imaging Surveys and the SDSS. We assessed PA measurement biases in the data and classified the radio AGNs based on the radio luminosity and infrared colour from the WISE. This resulted in the largest yet published sample of 3682 radio AGNs with reliable radio and optical PA measurements. The PA difference (dPA) distributions for the radio AGN sample show a prominent minor-axis alignment tendency. Based on some simple assumptions, we simulated the projection effect to estimate the intrinsic jet-galaxy alignment. The observed dPA distribution can be well described by a two-component jet-alignment model in which one component is more aligned with the minor axis of the host galaxy than the other. The fitting results indicate that the jet alignment is dependent on radio luminosity and the shape of the host galaxies, with the jets being more likely to be aligned with the minor axis of the galaxy for lower radio luminosity and for optically more elongated radio AGNs. The minor-axis alignment of the entire sample may suggest a coherent accretion model present in most AGN host galaxies, while a considerable number of luminous radio-AGN with massive host galaxies might have undergone an accretion according to the chaotic model or past merger events.

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arXiv2024

Widespread AGN feedback in a forming brightest cluster galaxy at $z=4.1$ unveiled by JWST

We present rest-frame optical spectroscopy using JWST/NIRSpec IFU for the radio galaxy TN J1338-1942 at z=4.1, one of the most luminous galaxies in the early Universe with powerful extended radio jets. Previous observations showed evidence for strong, large-scale outflows on the basis of its large (~150 kpc) halo detected in Ly-alpha, and high velocity [O II] emission features detected in ground-based IFU data. Our NIRSpec/IFU observations spatially resolve the emission line properties across the host galaxy in great detail. We find at least five concentrations of line emission, coinciding with discrete continuum features previously detected in imaging from HST and JWST, over an extent of ~2'' (~15 kpc). The spectral diagnostics enabled by NIRSpec unambiguously trace the activity of the obscured AGN plus interaction between the interstellar medium and the radio jet as the dominant mechanisms for the ionization state and kinematics of the gas in the system. A secondary region of very high ionization lies at roughly 5 kpc distance from the nucleus, and within the context of an expanding cocoon enveloping the radio lobe, this may be explained by strong shock-ionization of the entrained gas. However, it could also signal the presence of a second obscured AGN, which may also offer an explanation for an intriguing outflow feature seen perpendicular to the radio axis. The presence of a dual SMBH system in this galaxy would support that large galaxies in the early Universe quickly accumulated their mass through the merging of smaller units (each with their own SMBH), at the centers of large overdensities. The inferred black hole mass to stellar mass ratio of 0.01-0.1 for TNJ1338 points to a more rapid assembly of black holes compared to the stellar mass of galaxies at high redshifts, consistent with other recent observations.

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arXiv2023

COALAS II. Extended molecular gas reservoirs are common in a distant, forming galaxy cluster

This paper presents the results of 475 hours of interferometric observations with the Australia Telescope Compact Array towards the Spiderweb protocluster at $z=2.16$. We search for large, extended molecular gas reservoirs among 46 previously detected CO(1-0) emitters, employing a customised method we developed. Based on the CO emission images and position-velocity diagrams, as well as the ranking of sources using a binary weighting of six different criteria, we have identified 14 robust and 7 tentative candidates that exhibit large extended molecular gas reservoirs. These extended reservoirs are defined as having sizes greater than 40 kpc or super-galactic scale. This result suggests a high frequency of extended gas reservoirs, comprising at least $30 \%$ of our CO-selected sample. An environmental study of the candidates is carried out based on N-th nearest neighbour and we find that the large molecular gas reservoirs tend to exist in denser regions. The spatial distribution of our candidates is mainly centred on the core region of the Spiderweb protocluster. The performance and adaptability of our method are discussed. We found 13 (potentially) extended gas reservoirs located in nine galaxy (proto)clusters from the literature. We noticed that large extended molecular gas reservoirs surrounding (normal) star-forming galaxies in protoclusters are rare. This may be attributable to the lack of observations low-J CO transitions and the lack of quantitative analyses of molecular gas morphologies. The large gas reservoirs in the Spiderweb protocluster are a potential source of the intracluster medium seen in low redshift Virgo- or Coma-like galaxy clusters.

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arXiv2023

MaNGA integral-field stellar kinematics of LoTSS radio galaxies: Luminous radio galaxies tend to be slow rotators

The radio jets of an active galactic nucleus (AGN) can heat up the gas around a host galaxy and quench star formation activity. The presence of a radio jet could be related to the evolutionary path of the host galaxy and may be imprinted in the morphology and kinematics of the galaxy. In this work, we use data from the Sloan Digital Sky Survey's Mapping Nearby Galaxies at Apache Point Observatory survey and the Low Frequency Array (LOFAR) Two-Metre Sky Survey as well as the National Radio Astronomy Observatory (NRAO) the Karl G. Jansky Very Large Array (VLA) Sky Survey and the Faint Images of the Radio Sky at Twenty Centimeter survey. We combine these integral field spectroscopic data and radio data to study the link between stellar kinematics and radio AGNs. We find that the luminosity-weighted stellar angular momentum $λ_{Re}$ is tightly related to the range of radio luminosity and the fraction of radio AGNs F radio present in galaxies, as high-luminosity radio AGNs are only in galaxies with a small $λ_{Re}$, and the $F_{radio}$ at a fixed stellar mass decreases with $λ_{Re}$. These results indicate that galaxies with stronger random stellar motions with respect to the ordered motions might be better breeding grounds for powerful radio AGNs. This would also imply that the merger events of galaxies are important in the triggering of powerful radio jets in our sample.

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arXiv2022

(Re)Solving Reionization with Lyα: How Bright Lyα Emitters account for the $z\approx2-8$ Cosmic Ionizing Background

The cosmic ionizing emissivity from star-forming galaxies has long been anchored to UV luminosity functions. Here we introduce an emissivity framework based on Ly$α$ emitters (LAEs), which naturally hones in on the subset of galaxies responsible for the ionizing background due to the intimate connection between the production and escape of Ly$α$ and LyC photons. Using constraints on the escape fractions of bright LAEs ($L_{\rm{Lyα}}>0.2 L^{*}$) at $z\approx2$ obtained from resolved Ly$α$ profiles, and arguing for their redshift-invariance, we show that: (i) quasars and LAEs together reproduce the relatively flat emissivity at $z\approx2-6$, which is non-trivial given the strong evolution in both the star-formation density and quasar number density at these epochs and (ii) LAEs produce late and rapid reionization between $z\approx6-9$ under plausible assumptions. Within this framework, the $>10\times$ rise in the UV population-averaged $f_{\rm{esc}}$ between $z\approx3-7$ naturally arises due to the same phenomena that drive the growing Ly$α$ emitter fraction with redshift. Generally, a LAE dominated emissivity yields a peak in the distribution of the ionizing budget with UV luminosity as reported in latest simulations. Using our adopted parameters ($f_{\rm{esc}}=50\%$, $ξ_{\rm{ion}}=10^{25.9}$ Hz erg$^{-1}$ for half the bright LAEs), a highly ionizing minority of galaxies with $M_{\rm UV}<-17$ accounts for the entire ionizing budget from star-forming galaxies. Rapid flashes of LyC from such rare galaxies produce a "disco" ionizing background. We conclude proposing tests to further develop our suggested Ly$α$-anchored formalism.

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arXiv2022

ALMA as a Redshift Machine: Using [CII] to Efficiently Confirm Galaxies in the Epoch of Reionization

The [CII]$_{158μm}$ line has long been proposed as a promising line to spectroscopically confirm galaxies in the epoch of reionization. In this paper we present the results of new ALMA observations spectral scanning for [CII] in six particularly luminous Lyman Break Galaxies at $z\sim7$. The six sources were drawn from a sample of bright $z\sim7$ galaxies identified using the wide-area optical, near-IR, and Spitzer/IRAC data over the COSMOS/UltraVISTA field and were targeted on the basis of tight constraints on their redshifts from their IRAC [3.6]-[4.5] colors. We detect significant ($>9σ$) [CII] lines in three of our six targets ($50\%$) co-spatial with the rest-$UV$ emission from the ground/space-based near-IR imaging. The luminosities of the [CII] lines lie in the range $5.6$ to $8.8\times10^{8}L_{\odot}$, consistent with the local [CII]-SFR relation. Meanwhile, their [CII]/$L_{IR}\sim1-3\times10^{-3}$ ratios are slightly elevated compared to local (U)LIRGS. This could be due to lower dust-to-gas or dust-to-metal ratios. We also find that our sources display a large kinematic diversity, with one source showing signs of rotation, one source a likely major merger and one dispersion dominated source that might contain a bright star-forming clump. Our results highlight the effectiveness of spectral scans with ALMA in spectroscopically confirming luminous galaxies in the epoch of reionization, something that is being be applied on a significantly larger sample in the on-going REBELS large program.

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arXiv2021

The Synchrony of Production & Escape: Half the Bright Ly$α$ Emitters at $z\approx2$ have Lyman Continuum Escape Fractions $\approx50\%$

The ionizing photon escape fraction (LyC $f_{\rm{esc}}$) of star-forming galaxies is the single greatest unknown in the reionization budget. Stochastic sightline effects prohibit the direct separation of LyC leakers from non-leakers at significant redshift. Here we circumvent this uncertainty by inferring $f_{\rm{esc}}$ with resolved (R>4000) LyA profiles from the X-SHOOTER LyA survey at z=2 (XLS-z2). We select leakers ($f_{\rm{esc}}>20$%) and non-leakers ($f_{\rm{esc}}<5$%) from a representative sample of $>0.2 L^{*}$ LyA emitters (LAEs). With median stacked spectra of these subsets covering 1000-8000 Å (rest-frame) we investigate the conditions for LyC $f_{\rm{esc}}$. We find the following differences between leakers vs. non-leakers: (i) strong nebular CIV and HeII emission vs. non-detections, (ii) O32~8.5 vs. ~3, (iii) Ha/Hb indicating no dust vs. E(B-V)~0.3, (iv) MgII emission close to the systemic velocity vs. redshifted, optically thick MgII, (v) LyA $f_{\rm{esc}}$ of ~50% vs. ~10%. The extreme EWs in leakers (O3+Hb~1100 Å) constrain the characteristic timescale of LyC escape to ~3-10 Myr bursts when short-lived stars with the hardest ionizing spectra shine. The defining traits of leakers -- extremely ionizing stellar populations, low column densities, a dust-free, high ionization state ISM -- occur simultaneously in the $f_{\rm{esc}}>20\%$ stack, suggesting they are causally connected, and motivating why indicators like O32 may suffice to constrain $f_{\rm{esc}}$ at z>6 with JWST. The leakers comprise half our sample, have a median LyC $f_{\rm{esc}}$~50%, and an ionising production efficiency $\log({ξ_{\rm{ion}}/\rm{Hz\ erg^{-1}}})$~25.9. These results show LAEs -- the type of galaxies rare at z=2, but that become the norm at higher redshift -- are highly efficient ionizers, with extreme $ξ_{\rm{ion}}$ and prolific $f_{\rm{esc}}$ occurring in sync. (ABRIDGED)

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arXiv2021

Characterising the extended morphologies of BL Lacs at 144 MHz with LOFAR

We present a morphological and spectral study of a sample of 99 BL Lacs using the LOFAR Two-Metre Sky Survey Second Data Release (LDR2). Extended emission has been identified at gigahertz frequencies around BL Lacs, but with LDR2 it is now possible to systematically study their morphologies at 144 MHz, where more diffuse emission is expected. LDR2 reveals the presence of extended radio structures around 66/99 of the BL Lac nuclei, with angular extents ranging up to 115 arcseconds, corresponding to spatial extents of 410 kpc. The extended emission is likely to be both unbeamed diffuse emission and beamed emission associated with relativistic bulk motion in jets. The spatial extents and luminosities of the extended emission are consistent with the AGN unification scheme where BL Lacs correspond to low-excitation radio galaxies with the jet axis aligned along the line-of-sight. While extended emission is detected around the majority of BL Lacs, the median 144-1400 MHz spectral index and core dominance at 144 MHz indicate that the core component contributes ~42% on average to the total low-frequency flux density. A stronger correlation was found between the 144 MHz core flux density and the gamma-ray photon flux (r = 0.69) compared to the 144 MHz extended flux density and the gamma-ray photon flux (r = 0.42). This suggests that the radio-to-gamma-ray connection weakens at low radio frequencies because the population of particles that give rise to the gamma-ray flux are distinct from the electrons producing the diffuse synchrotron emission associated with spatially-extended features.

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arXiv2021

The X-SHOOTER Lyman-$α$ survey at z=2 (XLS-z2) I: What makes a galaxy a Lyman-$α$ emitter?

We present the first results from the X-SHOOTER Lyman-$α$ survey at $z=2$ (XLS-$z2$). XLS-$z2$ is a deep spectroscopic survey of 35 Lyman-$α$ emitters (LAEs) utilising $\approx90$ hours of exposure time with VLT/X-SHOOTER and covers rest-frame Ly$α$ to H$α$ emission with R$\approx4000$. We present the sample selection, the observations and the data reduction. Systemic redshifts are measured from rest-frame optical lines for 33/35 sources. In the stacked spectrum, our LAEs are characterised by an interstellar medium with little dust, a low metallicity and a high ionisation state. The ionising sources are young hot stars that power strong emission-lines in the optical and high ionisation lines in the UV. The LAEs exhibit clumpy UV morphologies and have outflowing kinematics with blue-shifted SiII absorption, a broad [OIII] component and a red-skewed Ly$α$ line. Typically 30 % of the Ly$α$ photons escape, of which one quarter on the blue side of the systemic velocity. A fraction of Ly$α$ photons escapes directly at the systemic suggesting clear channels enabling a $\approx10$ % escape of ionising photons, consistent with an inference based on MgII. A combination of a low effective HI column density, a low dust content and young star-burst determine whether a star forming galaxy is observed as a LAE. The first is possibly related to outflows and/or a fortunate viewing angle, while we find that the latter two in LAEs are typical for their stellar mass of 10$^9$ M$_{\odot}$.

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