Sylvain Veilleux

We present new Keck Cosmic Web Imager (KCWI) observations of the central few kiloparsecs of NGC 1275, 2023ascl.soft01019Nvthe brightest cluster galaxy of the Perseus Cluster. These integral field spectroscopic data reveal a warm-ionized outflow traced by H β and the [O III ] doublet extending out to ∼2.5 kpc from the nucleus. The warm-ionized outflow has an [O III ]-derived v ₅₀ of up to ∼570 km s ⁻¹ , w ₈₀ of up to 3780 km s ⁻¹ , and H β -derived outflowing mass of (2.7 ± 0.3) × 10 ⁶ M _⊙ . Our H β -derived warm-ionized outflowing mass rate of 2.7 ± 0.7 M _⊙ yr ⁻¹ is comparable to the estimated cold molecular disk accretion rate of 1−10 M _⊙ yr ⁻¹ , which could be a sign of self-regulation between the parsec-scale cold gas feeding the active galactic nucleus (AGN) and the warm wind accelerated out to kiloparsec scales. In the host galaxy, we detect an enhancement in the [O III ]/H β ratio in the direction of the receding jet, which may imply jet interaction with the host interstellar medium. The outflow component also shows a clear enhancement of [O III ]/H β that positively correlates with w ₈₀ and v ₅₀ , indicative of AGN influence and/or fast shocks. Both the outflow and host galaxy [O III ]/H β ratio decrease with increasing distance from the center, showing that the influence of the AGN is confined to the central ∼2 kpc. These results are the first resolved measurements of a kiloparsec-scale ionized wind in NGC 1275 and provide a view into how both jets and winds contribute to the feedback cycles in complex cool core cluster systems.

We report the discovery of ‘the Step’, a dense protocluster at z = 3 revealed by JWST/NIRISS Wide-Field Slitless Spectroscopy (WFSS) of the field around the luminous quasar and starburst SDSSJ165202.64+172852.3. The protocluster contains at least 18 member galaxies and exhibits signs of two substructures in the 3D position-velocity space – notably a distinctive step-like distribution, from which the nickname is derived. We propose that the Step may be undergoing a merger of two halos, which could also explain the unusually large velocity span (700–850 km/s) between galaxies along the densest line of sight. This sightline contains four (seven) galaxies within projected distances of 20 (70) kpc from the quasar. Within a 320×230 kpc ² region, we find ten galaxies (including the quasar), consistent with a remarkably dense protocluster core. We derive a galaxy overdensity of a factor of >100 in this core and > 15 in the full field (1 Mpc ² ), making it one of the densest structures known at this redshift, and a very massive halo of 13.1 < log M _halo / M _⊙ < 13.8, which suggests the structure could potentially evolve into a massive, Coma-like cluster at z = 0. Compared to the field, the star-forming galaxies in the Step appear to show slightly elevated levels of star formation activity. Yet, we find two quiescent galaxies (log M _⋆ / M _⊙ ∼ 10.2, 10.4 ± 0.8) with strong continuum breaks and no evidence of ongoing star formation. Compared to other protoclusters at z = 3, the Step structure exhibits broadly similar or slightly suppressed star-forming activity for its halo mass. We also identify two new active galactic nucleus (AGN) candidates based on optical line ratios and find tentative evidence of an enhanced AGN fraction (10–20%) with respect to the field. The protocluster constitutes one of an emerging number of maturing structures at 2 ⩽ z ⩽ 4 that host both star-forming and quenched galaxies. This redshift regime may thus be a key transitional epoch for cluster studies, where overdensities transition from being the most active sites of star formation in the early Universe towards shaping the massive passive ellipticals seen in the cores of today’s clusters.

We present a multiwavelength analysis of a young bubble in the nuclear starburst of NGC 253 using new JWST MIRI–MRS observations together with archival ALMA (100, 350, 690 GHz) and Chandra data. The MIRI maps reveal a prominent bubble-like structure in both ionized and molecular emission lines. The bubble is spatially coincident with one of the least embedded massive young clusters detected with ALMA, suggesting that the cluster is driving the expansion. We measure a radius of ∼11.5 ± 3.4 pc and an expansion velocity of ∼90 ± 44 km s ⁻¹ , implying a dynamical age of ∼0.1 ± 0.1 Myr. Using RADEX modeling of multiple CO transitions, we infer a molecular mass in the range of (1.3 ± 0.3) × 10 ⁴ to (2.8 ± 0.8) × 10 ⁵ M _⊙ . We derive a kinetic energy on the order 10 ⁵¹⁻⁵² erg, consistent with mechanical input from Wolf–Rayet stellar winds or supernovae in a ∼10 ⁶ M _⊙ cluster. The existence of a large population of Wolf–Rayet stars or past supernovae is supported by the presence of coincident X-ray emission. Our results provide direct evidence that individual clusters in a nuclear environment can carve out coherent structures on parsec scales and inject significant energy and momentum into the surrounding interstellar medium, which can contribute to the nuclear outflow in NGC 253.

We present an analysis of dust kinematics in the local starburst galaxies M82 (NGC 3034) and NGC 253 using polycyclic aromatic hydrocarbon (PAH) features observed with JWST/MIRI spectroscopy. We are able to produce high-quality velocity maps of the 5.2, 6.2, and 11.3 μ m PAH features, as well as numerous lines of molecular gas via H ₂ rotational transitions and ionized gas from [Ne ii ] and H recombination lines. Given the field of view and inclination, we trace a rotating disk in M82 where we observe a steep rise in the velocities followed by flattening, typical of galaxy rotation curves. In NGC 253, however, the 6.2 and 11.3 μ m PAH features trace the launching region of the outflow, firmly within the starburst region. We find the ionized gas also shows outflow contributions in NGC 253 while the warm molecular gas is dominated by rotation. Additionally, the molecular gas outflow velocities are lower than the ionized gas, with the 11.3 μ m PAH feature consistent with the ionized gas rather than the molecular gas. We therefore suggest that PAHs are more closely associated with the ionized gas rather than the molecular at the base of the galaxy outflow, whereas larger-scale imaging shows comparable morphology between PAHs and H I . The 6.2 μ m PAH feature has an even higher outflow velocity for both galaxies, possibly suggesting preferential ionization of the PAHs within the faster-moving hot phase of the base of the outflow.

Tidal disruption events (TDEs) have traditionally been discovered in optical sky surveys through targeted searches of nuclear transients. However, it is expected that some TDEs will occur outside the galaxy nucleus, arising from wandering black holes (BHs) originating in galaxy mergers. Here, we present observations of TDE 2025abcr, the first optical TDE discovered in the outskirts of a host galaxy. The TDE was identified by a custom “off-nuclear” implementation of the machine learning classifier tdescore , which classifies new ZTF transients based on their lightcurves. Follow-up observations confirm that TDE 2025abcr is a TDE-H+He, occurring 9 . ″ 5 (9.3 kpc projected distance) from the nucleus of a massive galaxy ( M _⋆ = 10 ^11.18±0.03 M _⊙ ) with a central BH mass of 10 ^8.82±0.65 M _⊙ . TDE 2025abcr itself was likely disrupted by a much lighter BH (10 ^6.09±0.53 M _⊙ , as estimated with peak luminosity scaling relations). The BH was either dynamically ejected from the nucleus or lies at the center of a very faint tidally stripped dwarf galaxy undergoing a minor merger. Late-time observations of TDE 2025abcr could confirm the origin of this apparent “wandering” BH. The rate of highly offset (≳3 kpc) TDEs can be constrained to <10% of the nuclear TDE rate, but our discovery implies that many dozens of similar sources will be detected by the Vera C. Rubin Observatory each year with resolvable offsets.

Uncovering bright quasars’ host galaxies at cosmic noon is challenging because of the high contrast between the quasar and its host and redshifted light, making them primarily visible in the infrared. We present JWST NIRSpec integral field unit (IFU) observations of six extremely red quasars (ERQs) at z = 2.4–2.9 and two dust-obscured quasars at lower redshifts. Using image decomposition across the spectral range, we successfully separate quasar and host galaxy continuum emission, model host morphologies, and extract spectra. The ERQs have compact host galaxies with half-light radii of 0.8−2.7 kpc and stellar masses of 10^10.4−10.9M_⊙. Their stellar masses are consistent with the average stellar mass of quasar hosts, as expected from abundance matching and clustering analysis. Most of the quasars in our sample exhibit significant spatial offsets (0.4−1.3 kpc) between the quasar and host galaxy, potentially caused by postmerger dynamics or nonuniform dust obscuration. The ERQs reside 0.5−2 dex above the local black hole–stellar mass relation, similar to other heavily obscured populations such as HotDOGs, optically selected quasars at cosmic noon, and high-redshift SMBH candidates identified with JWST. However, this “overmassive” feature might be attributed to selection bias. Compared to Hubble Space Telescope–based studies, our JWST measurements reveal more compact host galaxies, smaller Sérsic indices, and lower stellar masses, likely because of improved resolution, more accurate modeling, and minimal line contamination. These findings highlight the unique capabilities of JWST IFU in revealing quasar host galaxy properties and potential evolutionary stages of obscured quasars at cosmic noon.

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 nonequilibrium 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 anticorrelates 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.

We present new James Webb Space Telescope Mid-Infrared Instrument Medium-Resolution Spectrometer observations of the nearby ultraluminous infrared galaxy F10565+2448. These integral field spectroscopic data reveal an unresolved nuclear outflow in both warm-ionized and warm-molecular gas phases as well as a resolved blueshifted kiloparsec-scale warm-molecular outflow. The unresolved warm-ionized outflow has a mean projected velocity up to −520 km s ⁻¹ , while the unresolved warm-molecular outflow is slower at −150 km s ⁻¹ . For the resolved warm-molecular outflow, the projected mean velocity (−280 < v ₅₀ < −110 km s ⁻¹ ) is only slightly faster than the velocity of the disk (−70 < v ₅₀ < 120 km s ⁻¹ ) and, as such, likely does not exceed the estimated escape velocity of ≳300 km s ⁻¹ . The warm-molecular outflow is slightly hotter (507 ± 25 K) than the disk (329 ± 5 K), and displays areas of higher temperature and lower column density that may indicate a shock front, which we explore using the [Fe II ] 5.34 μ m/Pf α shock diagnostic. Analysis of the polycyclic aromatic hydrocarbon features reveals trends of ionization and grain size that first decrease with radius up to 1 kpc before increasing up to 3 kpc. These results bolster the picture of F10565+2448 being an active galactic nucleus (AGN)-starburst composite where both star formation and AGN-powered phenomena are required to explain the outflow energetics.

We present a kinematic study of six IR-luminous galaxies observed with the Mid-infrared Instrument Medium-resolution Spectrometer (MIRI/MRS) on board JWST. These galaxies lie at z = 0.5–0.6, midway between the present day and the peak of cosmic star formation (SF). Our sample spans a range of SF and active galactic nucleus (AGN) contributions to the mid-IR emission. We characterize the dynamical state of these IR-luminous galaxies and assess how AGN activity influences the kinematics of the interstellar medium. Using mid-IR tomic lines, we map galaxy kinematics beyond the local Universe for the first time. The spatial resolution of MIRI/MRS (3.0 kpc for 0 . ″ 46 at z ∼ 0.55) allows us to resolve the internal kinematics of our targets. We compute kinematic maps in three different emission lines ([Ar II ]6.99 μ m, [Ne II ]12.81 μ m, and H ₂ 0-0 S(5)6.91 μ m). Using the [Ar II ]6.99 μ m kinematic maps, we derive rotation curves for these sources. All galaxies exhibit ordered rotation, with V / σ ≥ 2, consistent with stable disks. Although some show minor disturbances, we find no strong evidence for recent major mergers or galaxy-wide ionized outflows. We find no correlation between V / σ and AGN fraction, suggesting AGN activity does not significantly disrupt global kinematics or that disk disruption is not required to trigger AGN. However, galaxies with higher AGN fractions show elevated central dispersions, indicating localized turbulence, possibly due to AGN feedback, stellar feedback, accretion, or bulge structure. These IR-luminous galaxies likely represent mature, rotationally supported disks, with AGN activation occurring after disk assembly.

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 μ m 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 μ m 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 ( q _PAH ) is set at ∼1% in the starburst and remains unchanging out to ±5 kpc off the disk. This flat q _PAH 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.