arXiv subjects

Fabian Walter

Publications and source records attributed to Fabian Walter.

At least 37 records · Page 2Linked to original sources

arXiv2026

Aether-SHELLQs: JWST integral-field spectroscopy of candidate obscured quasars at z ~ 6

We present James Webb Space Telescope (JWST) NIRSpec integral field unit (IFU) observations of six galaxies at $z \sim 6$, obtained as part of the Aether project (General Observers program 5645). The targets were originally identified by the Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) survey, as candidate obscured quasars with luminous ($\gtrsim10^{43}$ erg s$^{-1}$) but narrow ($\lesssim500$ km s$^{-1}$) Ly$α$ emission. Two objects exhibit a broad component in their Balmer lines (FWHM $>3000$ km s$^{-1}$), indicating the presence of active galactic nuclei (AGNs), while the remaining four show similar profiles in permitted and forbidden lines. Combining these data with similar SHELLQs objects reported previously, we find that the presence of broad lines is strongly correlated with Ly$α$ luminosity ($L_{\rm Lyα}$); the inferred AGN fraction is $>$77 % and $<$15 % above and below $L_{\rm Lyα} =10^{44}$ erg s$^{-1}$, respectively. Dust-extinction corrections inferred from the Balmer decrement would imply unrealistically high Ly$α$ luminosities, suggesting that the line-emitting gas consists of multiple zones. The IFU data reveal diverse spatial structures. The AGN hosts are compact, whereas the other galaxies show extended ionized gas on scales up to 10 kpc and star formation rates of 60 - 600 $M_\odot$ yr$^{-1}$. One of the extended objects exhibits a signature of rotation, while most of the others show little ordered kinematics, with velocity widths (FWHM) up to 200 - 300 km s$^{-1}$. These objects populate the intermediate luminosity regime between classical luminous quasars and the low-luminosity AGNs discovered by JWST, including Little Red Dots, potentially linking the two populations.

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arXiv2026

A $z \sim$ 6.2 Quasar on the Local M$_{\rm BH}$-$σ_{\rm \ast}$ Relation Quenching Its Host Galaxy from the Aether Survey

We report JWST/NIRSpec integral field unit (IFU) observations of the quasar J1512$+$4422 at $z \sim 6.2$ from the Aether survey. At $\sim$900 Myr after the Big Bang, this object already lies on the $M_{\rm BH}$-$σ_\ast$ relation found in the local universe, with an $M_{\rm BH} \simeq 8.9\times10^8\,M_\odot$ and a stellar velocity dispersion $σ_\ast \simeq 288$ km s$^{-1}$. We detect an outflow with a velocity of $\sim$478 km s$^{-1}$ in the nuclear region, which likely extends to $\sim$3.2 kpc in projection and has a median velocity of $\sim$352 km s$^{-1}$. The outflow dynamical time scale ($\sim$ 9 Myr) is consistent with the time scale of the current quenching process based on the star formation history as reported previously. The total mass outflow rate (92.6$^{+92.6}_{-74.1}$ M$_{\odot}$ yr$^{-1}$) is larger than the current star formation rate (0.9$^{+3.8}_{-0.8}$ or 4.3$^{+5.8}_{-3.7}$ M$_{\odot}$ yr$^{-1}$), and the total kinetic energy outflow rate (0.6$^{+0.6}_{-0.5}$\% of quasar luminosity) meets the threshold for negative quasar feedback as suggested by simulations. These results suggest that the outflow is capable of suppressing/quenching the star formation activity within the host galaxy. Furthermore, J1512$+$4422 exhibits $σ_\ast$, stellar mass and size similar to those of $z \gtrsim$ 3 quiescent/post-starburst galaxies, implying a link between the two. Overall, for objects like J1512$+$4422, the evolution of their SMBHs and host galaxies appears to be tightly coupled within the first billion years. The quasar feedback likely plays a critical role in both placing them on the $M_{\rm BH}$--$σ_\ast$ relation and quenching.

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arXiv2026

Little Red Dot $-$ Host Galaxy $=$ Black Hole Star: A Gas-Enshrouded Heart at the Center of Every Little Red Dot

The central engines of Little Red Dots (LRDs) may be ``black hole stars" (BH*s), early stages of black hole growth characterized by dense gas envelopes. So far, the most direct evidence for BH*s comes from a handful of sources where the host galaxy is completely outshone as suggested by their remarkably steep Balmer breaks. Here we present a novel scheme to disentangle BH*s from their host galaxies assuming that the [OIII]5008Å line arises exclusively from the host. Using a sample of 98 LRDs ($z$~$2-9$) with high quality NIRSpec/PRISM spectra, we demonstrate that the host-subtracted median stack displays a Balmer break $>2\times$ stronger than massive quiescent galaxies, with the rest-optical continuum resembling a blackbody-like SED ($T_{\rm{eff}}$~$4050$ K, $\log(L_{\rm{bol}})$~$43.9$ erg s$^{-1}$, $R_{\rm{eff}}$~$1300$ au). We measure a steep Balmer decrement (H$α$/H$β>10$) and numerous density-sensitive features (e.g., FeII, HeI, OI). These are hallmark signatures of dense gas envelopes, providing population-level evidence that BH*s indeed power LRDs. In the median LRD, BH*s account for $\sim20\%$ of the UV emission, $\sim50\%$ at the Balmer break, and $\sim90\%$ at wavelengths longer than H$α$ with the remainder arising from the host. BH*s preferentially reside in low-mass galaxies ($M_{\rm{\star}}$~$10^{8}\,{\rm M}_{\rm{\odot}}$) undergoing recent starbursts, as evidenced by extreme emission line EWs (e.g., [OIII]5008Å~$1100$Å, CIII]~$12$Å), thereby favoring BH* origins linked to star-formation. We show V-shaped LRD selections are biased to high BH*/host fractions ($\gtrsim60\%$ at 5500Å) -- less dominant BH*s may be powering JWST's blue broad-line AGN. We find BH*s are so commonplace and transient (duty cycle $\sim1\%$, lifetime $\sim10$ Myrs) that every massive black hole may have once shone as a BH*.

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arXiv2026

CO(7-6) and [C I](2-1) survey in z > 6 quasars

High-redshift ($z\gtrsim6$) quasars trace the earliest supermassive black holes and intense star formation, offering key laboratories for black hole-galaxy evolution at cosmic dawn. While far-infrared studies have revealed large dust reservoirs and strong [C II] emission, the physical conditions and molecular gas content of their ISM remain uncertain. We present ALMA Band 3 observations of the redshifted CO(7-6) and [C I](2-1) emission lines and dust continuum in a sample of 18 quasars at $z \sim 6$. We detected CO(7-6) in 15/18, [C I](2-1) in 6/18, and continuum in 13/18 sources. Line luminosities and continuum fluxes were used to estimate molecular gas masses from CO, [C I], and dust, and a hierarchical Bayesian cross-calibration of all four tracers yielded consistent per-source $M_{\rm H_2}$ estimates and conversion factors. Comparison with PDR and XDR model grids using the $L_{\rm [CII]}/L_{\rm [CI]}$ and $L_{\rm CO(7--6)}/L_{\rm TIR}$ ratios suggests gas densities of $n > 10^4$ cm$^{-3}$ and radiation fields of $G_0 \sim 10^3$--$10^4$ for sources consistent with PDR solutions, while many quasars fall outside the model parameter space. The $L'_{\rm CO(7-6)}/L'_{\rm [CI](2-1)}$ ratio indicates that a large fraction of the molecular gas resides in a warm and highly excited phase. Together these results suggest that classical PDR heating alone cannot explain the observed line ratios and that additional volumetric processes such as X-ray irradiation, turbulence and shocks, or enhanced cosmic-ray heating likely influence the excitation of the cold ISM. They demonstrate the power of multi-line diagnostics in revealing the excitation and structure of the cold ISM in early quasar host galaxies and highlight the need for joint analysis of CO, [C I], [C II], and dust emission to characterize star formation and AGN-driven heating at cosmic dawn.

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arXiv2026

JWST Observations of Starbursts: Molecular Hydrogen Excitation and Disequilibrium in M82

Emission from the pure rotational transitions of H$_2$ traces warm molecular gas, providing insight into its temperature distribution and local heating conditions. We have extended previous power-law H$_2$ temperature models to account for differential extinction by dust as well as non-equilibrium ortho-to-para-H$_2$ ratios (OPR). The turbulent environment of the M82 starburst offers a unique opportunity to study H$_2$ out of equilibrium conditions, using ~15 pc spatially resolved measurements from MIRI/MRS on JWST. With extensive detections of H$_2$ S(1)-S(7), we use our model to assess spatial variations in local heating conditions of molecular gas across a ~500 pc region of the M82 central starburst. The average slope of the recovered H$_2$ power law temperature distribution is consistent with prior studies, and the slope strongly anti-correlates with relative [Fe II]/H$_2$ S(1)-S(2) strength, pointing to the importance of shock-heating. Our models indicate that the OPR is, on average, about half of its equilibrium value. This suppression is attributed to cloud mixing timescales which are short compared to timescales for spin conversion, with molecular gas remembering its ''cooler past''. By accounting for OPR disequilibrium, we can identify instances of recent and rapid heating to better understand the flow of energy through the interstellar medium and track its thermal history.

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arXiv2026

JWST Observations of Starbursts: Dust Processing in the M82 Superwind

We present JWST MIRI and NIRCam imaging of the inner ~5 kpc of the M82 superwind at 0.05-0.375'' (~0.9-6.5 pc) resolution. Targeted filters probe emission from polycyclic aromatic hydrocarbons (PAHs; F335M, F360M, F770W, F1130W) and continuum (F250M, F360M). The images reveal a network of cool wind filaments traced by PAHs. PAH surface brightness declines with the inverse square of distance to the midplane, suggesting that the incident radiation field from the starburst drives the observed PAH intensity out to 2.5 kpc. The 3.3/11.3 and 3.3/7.7 band ratios show uniformity with distance from the starburst, though comparisons with mid-IR dust emission models indicate a modest shift toward larger PAHs. Outside the disk, 11.3/7.7 increases moderately, reflecting that PAHs become more neutral with distance from the starburst as they are exposed to a declining radiation field and ionization parameter. Overall, PAHs in the wind are consistent with standard-to-large sizes and standard-to-high ionization states. Including Spitzer and Herschel data, PAH abundance (qPAH) is set at ~1% in the starburst and remains unchanging out to 5 kpc off the disk. This flat qPAH profile suggests that PAHs are shielded from the hot wind, perhaps residing in the surface layers of cool clouds, with possible replenishment from cloud interiors and enrichment of the halo from previous bursts. In this picture, clouds are not dense enough to promote PAH growth, and they likely undergo radiative cooling and mixing with the hot phase to survive the gauntlet for at least ~20 Myr.

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arXiv2026

Nowhere Left to Hide: Uncovering All of the Massive Young Embedded Star Clusters in the Antennae with JWST

The Antennae galaxies merger produces the brightest infrared emission of any galaxy within ~20 Mpc, mostly from intense star formation taking place in supergiant molecular cloud complexes in the overlap region. Here, we present new, high-resolution NIRCam and MIRI images of the Antennae galaxies taken with the F150W, F187N, F335M, F360M, F410M, and F770W filters on JWST to search for the predicted but as-yet-undiscovered population of deeply embedded, optically obscured star clusters. We identify a population of 45 sources, 40 previously unknown, with high Bralpha/Halpha and Paalpha/Halpha flux ratios which are likely very young clusters still embedded or just emerging from their natal cocoons, and estimate their age, extinction (A_V), and mass. We find that all are extremely young (< 2.5 Myr), have A_V between 2 and 10 mag, and masses between ~ 10^4 and several x 10^6~Msun. We believe we have now uncovered all clusters with M > 3 x 10^4 Msun and A_V > 2 mag in the Antennae. While our sample represents a small fraction(~15%) of clusters younger than 3~Myr by number, it dominates the ionizing photon luminosity across the galaxy pair (~60%). We find elevated H_2/PAH ratios of the ISM surrounding the most massive pair of embedded clusters, supporting the idea that merger-induced shock-heated gas play an important role in the formation of extremely massive clusters.

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arXiv2026

Life After the Quasar: Overmassive Black Holes and Remnant Ionised Bubbles in and Around Two z~6.6 Galaxies

Supermassive black holes (SMBH, $M_{\rm{BH}} > 10^8 M_\odot$) powering luminous quasars already exist one billion years after the Big Bang, yet their connection to their star-forming host galaxies, their relation to the general galaxy population and their contribution to Reionisation remains deeply enigmatic. JWST is finding numerous Active Galactic Nuclei (AGN) in high-redshift galaxies with black hole masses that appear to be over-massive compared to their host's stellar mass, but rarely as massive as those found in luminous quasars. Here we report JWST/NIRSpec observations revealing overmassive SMBH in two ultra-luminous Lyman-$α$ emitters at $z\sim6.6$ that exhibit rare double-peaked Lyman-alpha profiles. The broad Balmer lines indicate black hole masses $M_{\rm{BH}}\simeq 2\times10^8 M_\odot$, matching that found in faint $z\sim 6-7$ quasars, and very high BH-to-stellar-mass ratio ($\sim 0.1-0.2$) that exceed the local relation by a factor $\sim$400-800. Stellar population modelling favours young ages ($<50$ Myr), inconsistent with the sustained average Eddington-rate accretion required to reach the observed BH masses by $z=6.6$. The double-peak Lyman-$α$ profiles require a large ionised bubble and high photoionisation rate that is consistent with the ionising output of quasars powered by black holes of similar mass, thus constraining the cessation of the last quasar episode to $<1$ Myr. We interpret both systems as post-quasar galaxies in which AGN feedback has delayed stellar mass assembly, and propose that episodic quasar activity partially explains the unexpected prevalence of large ionised bubbles deep into the Epoch of Reionisation.

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arXiv2026

Spatially resolved metallicity and ionization in the merging system Gz9p3 at z=9.3

Studying the interstellar medium (ISM) in merging high-redshift galaxies is crucial for understanding early galaxy assembly, star formation, and black hole growth, predicted by hierarchical $Λ$CDM models. Deep imaging and spatially resolved spectroscopy with JWST enable unprecedented insight into these processes, even for galaxies in the Epoch of Reionization. We present NIRSpec and MIRI integral field spectroscopy and MIRI imaging of the merging galaxy Gz9p3 at z=9.3 of the UV and optical rest-frame showing a clumpy morphology in the continuum as well as line emission covering the entire galaxy over a range of 5 kpc from the central clump to the tail region. We analyze the integrated spectrum as well as different apertures in the galaxy allowing a spatially resolved characterization of the ionized ISM of this galaxy. We compare our measurements with archival NIRCam imaging and ALMA data. We measure a total star formation rate of 13.4 $\pm$ 1.8 Msun yr$^{-1}$, a metallicity of 12+log(O/H) = 7.84 $\pm$ 0.05 and $ξ_{ion}$= 25.4 $\pm$ 0.1 erg$^{-1}$ Hz and a burstiness parameter of 0.9 $\pm$ 0.1 for the integrated spectrum. We find large spatial differences in these parameters between the central clump and the tail region. The optical [OIII] emission peaks in the main galaxy, the far-infrared [OIII] emission peaks towards the tail, indicating different physical conditions in the ISM of the tail and main galaxy. This study presents the spatially resolved ISM analyses of a galaxy at z>9, revealing nebular line emission and strong spatial variations in star formation, metallicity, physical conditions, and ionizing efficiency. The results indicate a recent, metal-poor starburst in a tail alongside a more evolved, enriched central clump with evidence for extreme excitation. This demonstrates the power of spatially resolved JWST spectroscopy of galaxies in the Epoch of Reionization.

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arXiv2026

JWST Spectroscopic Insights Into the Diversity of Galaxies in the First 500 Myr: Short-Lived Snapshots Along a Common Evolutionary Pathway

We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at z>10 with JWST/NIRSpec prism observations. We compare the properties of strong UV line emitters, traced by intense CIV emission, with those of more "typical" sources with weak or undetected CIV. The more typical (or "CIV-weak") sources reveal significant scatter in their CIII] line strengths, UV continuum slopes, and physical sizes, spanning CIII] equivalent widths of ~1-51 Å, UV slopes of $β$~-1.6 to -2.6, and half-light radii of ~50-1000 pc. In contrast, CIV-strong sources occupy the tail of these distributions, with CIII] EWs of 16-51 Å, UV slopes $β$<-2.5, compact morphologies ($r_{50}$<100 pc), and elevated star formation surface densities ($Σ_{SFR}$>100 $M_{\odot}yr^{-1}kpc^{-2}$). These properties suggest concentrated starbursts that temporarily outshine the host galaxy. Comparing average properties from composite spectra, we find the diversity of the sample is primarily driven by bursty star formation on very short timescales (<3 Myr), with strong CIV emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong CIV and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that AGN are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionisation models. Our results support a picture whereby brief bursts and lulls can explain the spectral diversity and early growth of bright galaxies in the first 500 Myr.

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arXiv2026

MIDIS: Strong H$β$+[OIII] Line Emitters at $z \geq 9$

We present a search for strong H$β$+[O III] emitters at $z=9.4-11.3$ in the HUDF using ultra-deep JWST/MIRI F560W imaging from the MIDIS survey. Three galaxies are identified via pronounced F560W flux excesses, consistent with strong rest-frame optical line emission. SED modelling yields rest-frame H$β$+[O III] equivalent widths of $\sim 600-1300$AA (median $\simeq 1260$AA), placing these sources among the most extreme known at these epochs. Combining these with a literature sample of 16 spectroscopically confirmed galaxies at $z\geq 9$, we find a median ${\rm EW}^{\rm Hβ+[O III]}_{\rm rest}\simeq 1300$AA, similar to values at $z\sim6-9$. We find no evidence for either a strong increase or decline in EW beyond $z\sim9$. A tentative trend of higher EW with increasing UV luminosity is observed, while no statistically significant anti-correlation with stellar mass is found. We place a first constraint on the H$β$+[O III] luminosity function at $z\simeq9-11$ ($Φ\sim10^{-3.4}\,{\rm Mpc^{-3}\,dex^{-1}}$ at $\log( L_{\rm Hβ+[OIII]}/{\rm erg\,s^{-1}})=42.5$), consistent with a decline relative to $z\sim7-8$. The MIDIS sources have $\log(ξ_{\rm ion}/{\rm Hz\,erg^{-1}})=25.1-25.4$. We find significant correlations between $ξ_{\rm ion}$ and EW and $β$, but not with UV luminosity, consistent with trends at lower redshift. These results suggest that the physical conditions governing nebular emission and ionising efficiency are already in place at $z\sim9-11$, extending trends established at $z\sim6-9$.

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arXiv2026

FEASTS and MHONGOOSE: HI Column Density Distribution at $z=0$ for $N_\mathrm{HI}>10^{17.8}\, \mathrm{cm}^{-2}$

We present the first $z=0$ HI column density distribution function, $f(N_\mathrm{HI})$, extending down to $\log (N_\mathrm{HI}/\mathrm{cm}^{-2})=17.8$. This was derived from high-sensitivity 21-cm emission-line imaging at $\sim$1 kpc resolution. At high-column-densities (19.8$< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <$21.3), our results align with earlier $z=0$ studies but benefit from 100 times greater sensitivity. Comparisons with $z\sim3$ quasar absorption-line studies reveal that $f(N_\mathrm{HI})$ at $z=0$ is systematically lower by 0.1-0.4 dex for $19.2< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <21$. However, the distributions become comparable at $17.8< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <19.2$, suggesting weak evolution in this regime. Extrapolating the length incidence ($\mathrm{d}N/\mathrm{d}X$) for $\log (N_\mathrm{HI}/\mathrm{cm}^{-2}) >17.5$ implies a covering fraction ($f_\mathrm{cov}$) of $\sim0.7$ within 1-kpc-scale HI-detected pixels at $z=0$. Notably, for $17.8< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <20$, impact parameters at a given $N_\mathrm{HI}$ are significantly lower than previous $z\sim0$ absorption-line results and TNG50 simulation predictions. This discrepancy indicates challenges in identifying galaxy counterparts for absorbers and in recovering low-column-density HI within cosmological simulations. Finally, we derive a covering fraction of 0.006 for $\log (N_\mathrm{HI}/\mathrm{cm}^{-2}) >17.8$ gas within the virial radius around Milky-Way-like galaxies. These findings provide new constraints on the baryonic flows and gaseous dynamics governing galaxy evolution.

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arXiv2026

Direct pathway to the Early Supermassive Black Holes: A Red Super-Eddington Quasar in a Massive Starburst Host at $z=7.2$

We present a panchromatic optical-mm characterization of GNz7q, a recently identified X-ray weak, rapidly growing red quasar embedded within a dusty starburst galaxy at $z=7.1899$, using the full suite of JWST/NIRCam, NIRSpec, MIRI, and archival NOEMA observations. Our deep NIRSpec/G395M spectroscopy reveals unambiguous broad Balmer emission (FWHM $=2221\pm20$kms$^{-1}$), confirming a super-Eddington accreting black hole ($λ_{\rm Edd}=2.7\pm0.4$) with a mass of $\log(M_{\rm BH}/M_{\odot})=7.55\pm0.34$, using accretion-rate corrected BH mass estimators. After subtracting the point source, we robustly detect stellar emission from the host galaxy across multiple NIRCam and MIRI filters. Out joint morphological-spectral analysis yields a stellar mass of $\log (M_*/M_\odot)=10.5\pm0.4$ and an intense star formation rate of ${\rm SFR}=330\pm97\,M_\odot\,\rm yr^{-1}$, confirming the host as a massive, dusty starburst galaxy. We find that GNz7q lies on the local $M_{\rm BH}$-$M_*$ relation ($M_{\rm BH}/M_*\simeq 0.001$) and is well positioned to evolve into the locus of massive SDSS quasars with $\log (M_{\rm BH}/M_\odot)\approx 9$ and $M_*\approx 10^{11}\,M_\odot$ at $z\sim 6$, owing to its remarkably rapid growth in both the black hole and its host galaxy. This stands in stark contrast to many recently reported JWST AGN populations at similar redshifts, including the little red dots (LRDs), whose weak or undetected star formation makes it difficult for them to grow into the massive galaxies hosting SDSS-like quasars. These results suggest that GNz7q marks as a rare, pivotal phase of early BH-galaxy co-eolution, plausibly providing a crucial direct pathway to the supermassive black hole systems within the first billion years of the Universe.

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arXiv2026

Characterising Ly$α$ damping wings at the onset of reionisation: Evidence for highly efficient star formation driven by dense, neutral gas in UV-bright galaxies at $z>9$

One of the major conundrums in contemporary extragalactic astrophysics is the apparent overabundance of a remarkable population of UV-bright galaxies at redshifts $z\gtrsim 9$. We analyse galaxies spectroscopically observed by JWST/NIRSpec Prism and confirmed to lie at $z>9$, with sufficient signal-to-noise to carefully model their rest-frame UV to optical continua and line emission. In particular, we model the damped Lyman-$α$ (Ly$α$) absorption (DLA) features of each galaxy to place observational constraints on the gas assembly of neutral atomic hydrogen (HI) onto the galaxy halos at the onset of cosmic reionisation. Based on the derived HI column densities and star-formation rate (SFR) surface densities, we show that all galaxies are highly efficient at forming stars on rapid $\sim 10-100\,$Myr depletion timescales, greatly in excess compared to the canonical local universe Kennicutt-Schmidt relation and predictions from state-of-the-art galaxy formation simulations. The dense HI gas appears to also drive the offset from the fundamental-metallicity relation of these galaxies though its dust-to-gas ratio is seemingly consistent with values derived for local galaxies except for the lowest metallicity sight-lines. Our results provide the first robust observational constraints on the impact of pristine HI gas on early galaxy assembly, and imply that a combination of highly efficient star formation and low dust obscuration can likely explain the UV-brightness of galaxies at cosmic dawn.

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arXiv2026

JWST Observations of Starbursts: PAHs Closely Trace the Cool Phase of M82's Galactic Wind

Stellar feedback drives multiphase gas outflows from starburst galaxies, but the interpretation of dust emission in these winds remains uncertain. To investigate this, we analyze new JWST mid-infrared images tracing polycyclic aromatic hydrocarbon (PAH) emission at 7.7 and 11.3~$μ$m from the outflow of the prototypical starburst M82 out to $3.2$ kpc. We find that PAH emission shows significant correlations with CO, H$α$, and X-ray emission within the outflow, though the strengths and behaviors of these correlations vary with gas phase and distance from the starburst. PAH emission correlates strongly with cold molecular gas, with PAH--CO scaling relations in the wind nearly identical to those in galaxy disks despite the very different conditions. The H$α$--PAH correlation indicates that H$α$ traces the surfaces of PAH-bearing clouds, consistent with arising from ionized layers produced by shocks. Meanwhile the PAH--X-ray correlation disappears once distance effects are controlled for past 2~kpc, suggesting that PAHs are decoupled from the hot gas and the global correlation merely reflects the large-scale structure of the outflow. The PAH-to-neutral gas ratio remains nearly flat to 2~kpc, with variations following changes in the radiation field. This implies that the product of PAH abundance and dust-to-gas ratio does not change significantly over the inner portion of the outflow. Together, these results demonstrate that PAHs robustly trace the cold phase of M82's wind, surviving well beyond the starburst and providing a powerful, high-resolution proxy for mapping the life cycle of entrained cold material in galactic outflows.

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arXiv2026

A Cosmic Miracle: A Remarkably Luminous Galaxy at $z_{\rm{spec}}=14.44$ Confirmed with JWST

JWST has revealed a stunning population of bright galaxies at surprisingly early epochs, $z>10$, where few such sources were expected. Here we present the most distant example of this class yet -- MoM-z14, a luminous ($M_{\rm{UV}}=-20.2$) source in the COSMOS field at $z_{\rm{spec}}=14.44^{+0.02}_{-0.02}$ that expands the observational frontier to a mere 280 million years after the Big Bang. The redshift is confirmed with NIRSpec/PRISM spectroscopy through a sharp Lyman-$α$ break and $\sim3σ$ detections of five rest-UV emission lines. The number density of bright $z_{\rm{spec}}\sim14-15$ sources implied by our "Mirage or Miracle" survey spanning $\sim350$ arcmin$^{2}$ is $>100\times$ larger ($182^{+329}_{-105}\times$) than pre-JWST consensus models. The high EWs of UV lines ($\sim15{-}35$ Å) signal a rising star-formation history, with a $\sim10\times$ increase in the last 5 Myr ($\rm{SFR_{\rm{5Myr}}}/\rm{SFR_{\rm{50Myr}}}=9.9^{+3.0}_{-5.8}$). The source is extremely compact (circularized $r_{\rm{e}} = 74^{+15}_{-12}$ pc), and yet elongated ($b/a=0.25^{+0.11}_{-0.06}$), suggesting an AGN is not the dominant source of UV light. The steep UV slope ($β=-2.5^{+0.2}_{-0.2}$) implies negligible dust attenuation and a young stellar population. The absence of a strong damping wing provides tentative evidence that the immediate surroundings of MoM-z14 may be partially ionized at a redshift where virtually every reionization model predicts a $\sim100\%$ neutral fraction. The nitrogen emission and highly super-solar [N/C]$>1$ hint at an abundance pattern similar to local globular clusters that may have once hosted luminous supermassive stars. Since this abundance pattern is also common among the most ancient stars born in the Milky Way, we may be directly witnessing the formation of such stars in dense clusters, connecting galaxy evolution across the entire sweep of cosmic time.

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arXiv2026

Shedding the envelope: JWST reveals a kiloparsec-scale [OIII]-weak Balmer shell around a z=7.64 quasar

Luminous quasars at the redshift frontier z>7 serve as stringent probes of super-massive black hole formation and they are thought to undergo much of their growth obscured by dense gas and dust in their host galaxies. Fully characterizing the symbiotic evolution of SMBHs and hosts requires rest-frame optical observations that span spatial scales from the broad-line region to the ISM and CGM. JWST now provides the necessary spatially resolved spectroscopy to do so. But the physical conditions that regulate the interplay between SMBHs and their hosts at the highest redshifts, especially the nature of early feedback phases, remain unclear. We present JWST/NIRSpec IFU observations of J0313$-$1806 at z=7.64, the most distant luminous quasar known. From the restframe optical spectrum of the unresolved quasar, we derive a black hole mass of $M_\mathrm{BH}=(1.63 \pm 0.10)\times10^9 M_\odot$ based on H$β$ and an Eddington rate of $λ=L/L_\mathrm{Edd}=0.80\pm 0.05$, consistent with previous MgII-based estimates. J0313-1806 exhibits no detectable [O III] emission on nuclear scales. Most remarkably, we detect an ionized gas shell extending out to $\sim 1.8$ kpc traced by H$β$ emission that also lacks any significant [O III], with a $3σ$ upper limit on the [O III]$ λ$5007 to H$β$ flux ratio of $\log_{10} \left( F(\mathrm{[OIII]})/F(\mathrm{H}β)\right)=-1.15$. Through photoionization modelling, we demonstrate that the extended emission is consistent with a thin, clumpy outflowing shell where [OIII] is collisionally de-excited by dense gas. We interpret this structure as a fossil remnant of a recent blowout phase, providing evidence for episodic feedback cycles in one of the earliest quasars. These findings suggest that dense ISM phases may play a crucial role in shaping the spectral properties of quasars accross cosmic time.

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arXiv2025

SHELLQs-JWST perspective on the intrinsic mass relation between supermassive black holes and their host galaxies at z > 6

The relation between the masses of supermassive black holes (SMBHs) and their host galaxies encodes information on their mode of growth, especially at the earliest epochs. The James Webb Space Telescope (JWST) has opened such investigations by detecting the host galaxies of AGN and more luminous quasars within the first billion years of the universe (z > 6). Here, we evaluate the relation between the mass of SMBHs and the total stellar mass of their host galaxies using a sample of nine quasars at 6.18 < z < 6.4 from the Subaru High-z Exploration of Low-luminosity Quasars (SHELLQs) survey with NIRCam and NIRSpec observations. We find that the observed location of these quasars in the SMBH-galaxy mass plane (log M_BH/Msun ~ 8-9; log M_*/Msun ~ 9.5-11) is consistent with a non-evolving intrinsic mass relation with dispersion (0.80_{-0.28}^{+0.23} dex) higher than the local value (~0.3-0.4 dex) of their more massive descendants. Our analysis is based on a forward model of systematics and includes a consideration of the impact of selection effects and measurement uncertainties with an assumption on the slope of the mass relation. While degeneracies between parameters persist, the best-fit solution has a reasonable AGN fraction (2.3%) of galaxies at z ~ 6 with an actively growing UV-unobscured black hole. In particular, models with a substantially higher normalisation in M_BH would require an unrealistically low intrinsic dispersion (~0.22 dex). Consequently, our results predict a large population of AGNs at lower black hole masses, as are now just starting to be discovered in focused efforts with JWST.

astro-ph.GA↗