arXiv subjects

Torsten Böker

Publications and source records attributed to Torsten Böker.

At least 37 records · Page 2Linked to original sources

arXiv2025

The Rich JWST Spectrum of the Western Nucleus of Arp 220: Shocked Hot Core Chemistry Dominates the Inner Disk

We present full 3-28 $\mathrm{μm}$ JWST MIRI/MRS and NIRSpec/IFU spectra of the western nucleus of Arp 220, the nearest ultraluminous infrared galaxy. This nucleus has long been suggested to possibly host an embedded Compton-thick AGN. Millimeter observations of the dust continuum suggest the presence of a distinct 20 pc core with a dust temperature of $T_\mathrm{d} \gtrsim 500~\mathrm{K}$, in addition to a 100 pc circumnuclear starburst disk. However, unambiguously identifying the nature of this core is challenging, due to the immense obscuration, the nuclear starburst activity, and the nearby eastern nucleus. With the JWST integral field spectrographs, we can, for the first time, separate the two nuclei across this full wavelength range, revealing a wealth of molecular absorption features towards the western nucleus. We analyse the rovibrational bands detected at 4-22 $\mathrm{μm}$, deriving column densities and rotational temperatures for 10 distinct species. Optically thick features of C$_2$H$_2$, HCN and HNC suggest that this molecular gas is hidden behind a curtain of cooler dust, and indicate that the column densities of C$_2$H$_2$ and HCN are an order of magnitude higher than previously derived from Spitzer observations. We identify a warm HCN component with rotational temperature $T_\mathrm{rot} = 330~\mathrm{K}$, which we associate with radiative excitation by the hot inner nucleus. We propose a geometry where the detected molecular gas is located in the inner regions of the starburst disk, directly surrounding the hot 20 $\mathrm{pc}$ core. The chemical footprint of the western nucleus is reminiscent of that of hot cores, with additional evidence for shocks. Despite the molecular material's close proximity to the central source, no evidence for the presence of an AGN in the form of X-ray-driven chemistry or extreme excitation is found.

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arXiv2025

Detection of Deuterated Hydrocarbon Nanoparticles in the Whirlpool Galaxy, M51

Deuteration of hydrocarbon material, including polycyclic aromatic hydrocarbons (PAHs), has been proposed to account for the low gas-phase abundances of D in the interstellar medium. JWST spectra of four star-forming regions in M51 show an emission feature, with central wavelength $\sim$4.647$μ$m and FWHM 0.0265$μ$m, corresponding to the C-D stretching mode in aliphatic hydrocarbons. The emitting aliphatic material is estimated to have (D/H)$_{\rm aliph}\approx 0.17\pm0.02$ -- a factor $\sim$$10^4$ enrichment relative to the overall interstellar medium (ISM). On $\sim$$50\,$pc scales, deuteration levels toward four H$\,$II regions in M51 are 2-3 times higher than in the Orion Bar photodissociation region (PDR), with implications for the processes responsible for the formation and evolution of hydrocarbon nanoparticles, including PAHs. The deuteration of the aliphatic material is found to anticorrelate with helium ionization in the associated H$\,$II, suggesting that harsh FUV radiation may act to lower the deuteration of aliphatics in PDRs near massive stars. No evidence is found for deuteration of aromatic material, with (D/H)$_{\rm arom} \lesssim 0.016$: deuteration of the aliphatic material exceeds that of the aromatic material by at least a factor 10. The observed levels of deuteration may account for the depletion of D observed in the Galactic interstellar medium. If so, the $4.65μ$m feature may be detectable in absorption.

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arXiv2025

The JWST/NIRSpec view of the nuclear region in the prototypical merging galaxy NGC 6240

Merger events are thought to be an important phase in the assembly of massive galaxies. At the same time, Active Galactic Nuclei (AGN) play a fundamental role in the evolution of their star formation histories. Both phenomena can be observed at work in NGC 6240, a local prototypical merger, classified as an UltraLuminous InfraRed Galaxy (ULIRG) thanks to its elevated infrared luminosity. Interestingly, NGC 6240 hosts two AGN separated by 1.5''(~ 735 pc), detected in both X-ray and radio band. Taking advantage of the unprecedented sensitivity and wavelength coverage provided by the Integral Field Unit (IFU) of the NIRSpec instrument onboard JWST, we observed the nuclear region of NGC 6240 in a FoV of 3.7'' x 3.7''(1.9 x 1.9 kpc^2), to investigate gas kinematics and InterStellar Medium (ISM) properties with a high spatial resolution of ~ 0.1'' (or ~ 50 pc). We separated the different gas kinematic components through multi-Gaussian fitting and studied the excitation properties of the ISM from the NIR diagnostic diagram based on the H_2 1-0 S(1)/BrGamma and [Fe II]1.257micron/PaBeta lines ratios. We isolated the ionization cones of the two nuclei, and detected coronal lines emission from both of them. Using H_2 line ratios, we found that the molecular hydrogen gas is excited mostly by thermal processes. We computed a hot molecular gas mass of 1.3 x 10^5 M_sun and an ionized gas mass in the range of 10^5 - 10^7 M_sun. We studied with unprecedented spatial resolution and sensitivity the kinematics of the molecular and ionized gas phases. We revealed the complex structure of the molecular gas and found a blueshifted outflow near the Southern nucleus, together with filaments connecting a highly redshifted H_2 cloud with the two nuclei. We speculate on the possible nature of this H_2 cloud and propose two possible scenarios: either outflowing gas, or a tidal cloud falling onto the nuclei.

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arXiv2025

GOALS-JWST: The Warm Molecular Outflows of the Merging Starburst Galaxy NGC 3256

We present James Webb Space Telescope (JWST) Integral Field Spectrograph observations of NGC 3256, a local infrared-luminous late-stage merging system with two nuclei roughly 1$\;\rm{kpc}$ apart, both of which have evidence of cold molecular outflows. Using JWST/NIRSpec and MIRI datasets, we investigate this morphologically complex system on spatial scales of $<$100$\;\rm{pc}$, where we focus on the warm molecular H$_2$ gas surrounding the nuclei. We detect collimated outflowing warm H$_2$ gas originating from the southern nucleus, though we do not find significant outflowing H$_2$ gas surrounding the northern nucleus. We measure maximum intrinsic outflow velocities of $\sim$1,000$\;\rm{km}\;\rm{s}^{-1}$, which extend out to a distance of 0.7$\;\rm{kpc}$. Based on H$_2$ S(7)/S(1) ratios, we find a larger fraction of warmer gas near the S nucleus, which decreases with increasing distance from the nucleus, signifying the southern nucleus as a primary source of H$_2$ heating. The gas mass of the warm H$_2$ outflow component is estimated to be $M\rm{_{warm,out}}=(1.4\pm0.2)\times10^6\;\rm{M}_{\odot}$, as much as 6$\%$ of the cold H$_2$ mass estimated using ALMA CO data. The outflow time scale is about $7\times10^5\;\rm{yr}$, resulting in a mass outflow rate $\dot{M}\rm{_{warm,out}}=2.0\pm0.8\;\rm{M}_{\odot}\;\rm{yr}^{-1}$ and kinetic power $P\rm{_{warm,out}}\;\sim\;4\times10^{41}\;\rm{erg}\;\rm{s}^{-1}$. Lastly, regions within our 3.0"x3.0" NIRSpec data where the outflowing gas reside show high [Fe II]/Pa$β$ and H$_2$/Br$γ$ line ratios, indicate enhanced mechanical heating caused by the outflows. The fluxes and ratios of Polycyclic Aromatic Hydrocarbons (PAH) in these regions are not significantly different compared to those elsewhere in the disk, suggesting the outflows may not significantly alter the PAH ionization state or grain size.

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arXiv2025

WIggle Corrector Kit for NIRSpEc Data: WICKED

The point-spread function of the integral-field unit (IFU) mode of the JWST's NIRSpec is heavily under-sampled, creating resampling noise seen as low-frequency sinusoidal-like artifacts, or "wiggles". These artifacts in the data are not corrected in the JWST data pipeline, and significantly impact the science that can be achieved at a single-pixel level. We present WICKED (WIggle Corrector Kit for NIRSpEc Data), a tool designed to empirically remove wiggles. WICKED uses the Fast Fourier Transform to identify wiggle-affected spaxels across the data cube. Spectra are modeled with a mix of integrated aperture and annular templates, a power-law, and a second-degree polynomial. The method works across all medium- and high-resolution NIRSpec gratings: F070LP, F100LP, F170LP, and F290LP. WICKED can recover the true overall spectral shape up to a factor of 3.5x better compared to uncorrected spectra. It recovers the equivalent width of absorption lines within 5% of the true value-~3x better than uncorrected spectra and ~2x better than other methods. WICKED significantly improves kinematic measurements, recovering the line-of-sight velocity (LOSV) within 1% of the true value -- more than 100x better than uncorrected spectra at S/N ~40. As a case study, we applied WICKED to G235H/F170LP IFU data of the elliptical galaxy NGC5128, finding good agreement with previous studies. In wiggle-affected regions, the uncorrected spectrum showed stellar LOSV and velocity dispersion differences compared to the WICKED-cleaned spectrum, of ~17x and ~36x larger than the estimated uncertainties, respectively. Wiggles in NIRSpec IFU data can introduce severe biases in spectral shape, line measurements, and kinematics to values larger than the typical uncertainties. WICKED provides a robust, user-friendly solution, enabling precise single-pixel studies and maximizing JWST's potential.

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arXiv2025

GA-NIFS: High number of dual active galactic nuclei at z~3

Merger events can trigger gas accretion onto supermassive black holes (SMBHs) located at the centre of galaxies, and form close pairs of AGN. The fraction of AGN in pairs offers critical insights into the dynamics of galaxy interactions, SMBH growth, and their co-evolution with host galaxies. However, the identification of dual AGN is difficult, as it requires high-quality spatial and spectral data; hence, only very few pairs have been found in the distant Universe so far. This study aims to provide a first observational estimate of the fraction of dual AGN at 2<z<6 by analysing a sample of 16 AGN observed with JWST/NIRSpec IFS, as part of the GA-NIFS survey. For two AGN in our sample, we also incorporate archival VLT/MUSE data to expand the search area. We searched for nearby companion galaxies and emission-line sources within the ~20x20 kpc field of view of the NIRSpec data cubes, extending up to ~50 kpc using the MUSE data cubes. We analysed the spectra of such emitters to determine their physical and kinematic properties. We report the serendipitous discovery of a triple AGN and four dual AGN (two of which considered as candidates), with projected separations in the range 3-28 kpc. Their AGN classification is mainly based on standard optical emission line flux ratios, as observed with JWST/NIRSpec, and is complemented with additional multi-wavelength diagnostics. The identification of these 3-5 multiple AGN out of the 16 AGN systems in GA-NIFS (i.e. ~20-30%) suggests they might be more common than previously thought based on other observational campaigns. Moreover, our inferred fraction of dual AGN moderately exceeds predictions from cosmological simulations that mimic our observational criteria (~10%). This work highlights the exceptional capabilities of NIRSpec for detecting distant dual AGN, and prompts new investigations to constrain their fraction across cosmic time.

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arXiv2025

GA-NIFS: JWST/NIRSpec IFS view of the z~3.5 galaxy GS5001 and its close environment at the core of a large-scale overdensity

We present JWST NIRSpec observations in IFS mode of the galaxy GS5001 at redshift z=3.47, the central member of a candidate protocluster in the GOODS-S field. The data cover a field of view (FoV) of 4''$\times$4'' (~$30\times30$~kpc$^2$) and were obtained as part of the GA-NIFS GTO program. The observations include both high (R~2700) and low (R~100) spectral resolution data, spanning the rest-frame wavelength ranges 3700-6780A and 1300-11850A, respectively. We analyse the spatially resolved ionised gas kinematics and interstellar medium properties, including obscuration, gas metallicity, excitation, ionisation parameter, and electron density. In addition to the main galaxy (GS5001), the NIRSpec FoV covers three components in the south, with velocities blue-shifted by -150 km/s with respect to the main galaxy, and another source in the north redshifted by ~200 km/s. Optical line ratio diagnostics indicate star formation ionisation and electron densities of ~500 cm$^{-3}$ across all sources in the FoV. The gas-phase metallicity in the main galaxy is 12+log(O/H) $= 8.45\pm0.04$, and slightly lower in the companions (12+log(O/H)$ = 8.34-8.42$), consistent with the mass-metallicity relation at $z\sim3$. We find peculiar line ratios (high log [NII]/H$α$, low log [OIII]/H$β$) in the northern part of GS5001. These could be attributed to either higher metallicity, or to shocks resulting from the interaction of the main galaxy with the northern source. We identify a spatially resolved outflow in the main galaxy, with an extension of about 3 kpc. We find maximum outflow velocities of ~400 km/s, an outflow mass of $(1.7\pm0.4)\times 10^8$ M$_{\odot}$, a mass outflow rate of $23\pm5$ M$_{\odot}$ yr$^{-1}$ and a mass loading factor of 0.23. These properties are compatible with star formation being the driver of the outflow.

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arXiv2025

GA-NIFS: Multi-phase analysis of a star-forming galaxy at $z \sim 5.5$

In this study, we present a detailed multiphase analysis of HZ4, a main-sequence star-forming galaxy at z ~ 5.5, known for being a turbulent rotating disk and having a detection of a [CII] outflow in the ALMA observations. We exploit JWST/NIRSpec observations in the integral field spectroscopy mode with low- and high-spectral resolution that allow us for the first time to spatially resolve the rest-frame UV and optical emission of the galaxy to investigate the galaxy properties. In particular, the high-resolution dataset allows us to study the kinematics of the ionized gas phase, and the conditions of the interstellar medium, such as the excitation mechanism, dust attenuation, and metallicity. The lower-spectral resolution observations allow us to study the continuum emission and infer the stellar populations' ages and properties. Our findings suggest that HZ4 is a galaxy merger rather than a rotating disk as previously inferred from lower resolution [CII] data. The merger is associated with an extended broad, blueshifted emission, potentially indicative of an outflow originating from a region of intense star formation and extending up to 4 kpc. In light of these new observations we reanalyzed the ALMA data to compare the multiphase gas properties. If we interpret the broad components seen in [CII] and [OIII]$λ$5007Ȧ as outflows, the neutral and ionized components are co-spatial, the mass loading factor of the ionized phase is significantly lower than that of the neutral phase, aligning with trends observed in multi-phase systems at lower redshifts. Nonetheless, additional observations and larger statistical samples are essential to determine the role of mergers and outflows in the early Universe and to clarify the origin of the broad emission components observed in this system.

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arXiv2025

A Spectroscopically Calibrated Prescription for Extracting PAH Flux from JWST MIRI Imaging

We introduce a prescription for estimating the flux of the 7.7 micron and 11.3 micron\ polycyclic aromatic hydrocarbon (PAH) features from broadband JWST/MIRI images. Probing PAH flux with MIRI imaging data has advantages in field of view, spatial resolution, and sensitivity compared with MIRI spectral maps, but comparisons with spectra are needed to calibrate these flux estimations over a wide variety of environments. For 267 MIRI/MRS spectra from independent regions in the four luminous infrared galaxies (LIRGs) in the Great Observatories All-sky LIRG Survey (GOALS) early release science program, we derive synthetic filter photometry and directly compare estimated PAH fluxes to those measured from detailed spectral fits. We find that for probing PAH 7.7 micron, the best combination of filters is F560W, F770W, and either F1500W or F2100W, and the best for PAH 11.3 micron is F560W, F1000W, F1130W, and F1500W. The prescription with these combinations yields predicted flux densities that typically agree with values from spectral decomposition within ~7% and ~5% for PAH 7.7 and 11.3 micron, respectively.

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arXiv2024

GA-NIFS: The highly overdense system BR1202-0725 at z $\sim$ 4.7. A double AGN with fast outflows plus eight companion galaxies

Distant quasars (QSOs) in galaxy overdensities are considered key actors in the evolution of the early Universe. In this work, we studied the kinematic and physical properties of the BR1202-0725 system at z=4.7, one of the most overdense fields known in the early Universe, consisting of a QSO, a submillimeter galaxy (SMG), and three Lyman-$α$ emitters. We used data from the JWST/NIRSpec Integral Field Unit (IFU) to analyze the rest-frame optical emission of each source in the system. We estimated a bolometric luminosity of log($L_{\rm bol}/$[erg/s]) = 47.2 $\pm$ 0.4 and a black hole mass of log($M_{\rm BH}/M_\odot$) = 10.1 $\pm$ 0.5 for the QSO, which are consistent with previous measurements obtained with ground-based observations. The NIRSpec spectra of the SMG revealed instead unexpected [OIII] and H$α$+[NII] profiles. The overall [OIII] line profile is blue-shifted by more than 700 km/s relative to the systemic velocity of the galaxy. Additionally, both the [OIII] and H$α$+[NII] lines show prominent broad (1300 km/s), blueshifted wings associated with outflowing ionized gas. The analysis of NIRSpec and X-ray observations indicates that the SMG likely hosts an accreting supermassive black hole as supported by the following results: (i) the excitation diagnostic diagram is consistent with ionization from an active galactic nucleus (AGN); (ii) the X-ray luminosity is higher than $10^{44}$ erg/s; and (iii) it hosts a fast outflow ($v_{\rm out}$ = 5000 km/s), comparable to those observed in luminous QSOs. Therefore, the QSO-SMG pair represents one of the highest-redshift double AGN to date, with a projected separation of 24 kpc. Finally, we investigated the environment of this system and found four new galaxies at the same redshift of the QSO and within a projected distance of 5 kpc from it. This overdense system includes at least ten galaxies in only 980 kpc$^2$.

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arXiv2024

GA-NIFS: A galaxy-wide outflow in a Compton-thick mini-BAL quasar at z = 3.5 probed in emission and absorption

Studying the distribution and properties of ionised gas in outflows driven by AGN is crucial for understanding the feedback mechanisms at play in extragalactic environments. In this study, we explore the connection between ionised outflows traced by rest-frame UV absorption and optical emission lines in GS133, a Compton thick AGN at z = 3.47. We combine observations from the JWST NIRSpec Integral Field Spectrograph (IFS) with archival VLT VIMOS long-slit spectroscopic data, as part of the GA-NIFS project. We perform a multi-component kinematic decomposition of the UV and optical line profiles to derive the physical properties of the absorbing and emitting gas in GS133. Our kinematic decomposition reveals two distinct components in the optical lines. The first component likely traces a rotating disk with a dynamical mass of 2e10 Msun. The second component corresponds to a galaxy-wide, bi-conical outflow, with a velocity of 1000 km/s and an extension of 3 kpc. The UV absorption lines show two outflow components, with bulk velocities v_out = -900 km/s and -1900 km/s, respectively. This characterises GS133 as a mini-BAL system. Balmer absorption lines with similar velocities are tentatively detected in the NIRSpec spectrum. Both photoionisation models and outflow energetics suggest that the ejected absorbing gas is located at 1-10 kpc from the AGN. We use 3D gas kinematic modelling to infer the orientation of the [O III] bi-conical outflow, and find that a portion of the emitting gas resides along our line of sight, suggesting that [O III] and absorbing gas clouds are partially mixed in the outflow. The derived mass-loading factor (i.e. the mass outflow rate divided by the SFR) of 1-10, and the kinetic coupling efficiency (i.e. the kinetic power divided by LAGN) of 0.1-1% per cent suggest that the outflow in GS133 provides significant feedback on galactic scales.

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arXiv2024

GA-NIFS: An extremely nitrogen-loud and chemically stratified galaxy at $z\sim 5.55$

We report the chemical abundance pattern of GS\_3073, a galaxy at $z=5.55$ which was previously confirmed to host an overmassive active black hole, by leveraging the detection of about 40 emission lines, combining JWST/NIRSpec observations and ground-based (VLT/VIMOS) data. Based on the rest-frame UV emission lines, which trace high-density ($\sim 10^5~{\rm cm}^{-3}$) and highly ionized gas, we derived an abundance ratio of $\rm log(N/O) = 0.42^{+0.13}_{-0.10}$. At an estimated metallicity of $0.2~Z_{\odot}$, this is the most extreme nitrogen-rich object found by JWST thus far. In comparison, the relative carbon abundance derived from the rest-frame UV emission lines is $\rm log(C/O) = -0.38^{+0.13}_{-0.11}$, which is not significantly higher than those in local galaxies and stars with similar metallicities. We also found potential detection of coronal lines including [FeVII]$λ6087$ and [FeXIV]$λ5303$, both blended with [CaV]. We inferred a range of Fe abundances compatible with those in local stars and galaxies. Overall, the chemical abundance pattern of GS\_3073 is compatible with enrichment by super-massive stars with $M_* \gtrsim 1000~M_\odot$, asymptotic giant branch (AGB) stars, or Wolf-Rayet (WR) stars. Interestingly, when using optical emission lines which trace lower density ($\sim 10^3~{\rm cm}^{-3}$) and lower ionization gas, we found a sub-solar N/O ratio. We interpret the difference in N/O derived from UV lines and optical lines as evidence for a stratified system, where the inner and denser region is both more chemically enriched and more ionized. Taking this luminous, well-studied system as a benchmark, our results suggest that nitrogen loudness in high-$z$ galaxies is confined to the central, dense, and highly ionized region of the galaxies, while the bulk of the galaxies evolves more normally.

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arXiv2024

The NIRSpec Micro-Shutter Array: Operability and Operations After Two Years of JWST Science

The Near Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope affords the astronomical community an unprecedented space-based Multi-Object Spectroscopy (MOS) capability through the use of a programmable array of micro-electro-mechanical shutters. Launched in December 2021 and commissioned along with a suite of other observatory instruments throughout the first half of 2022, NIRSpec has been carrying out scientific observations since the completion of commissioning. These observations would not be possible without a rigorous program of engineering operations to actively monitor and maintain NIRSpec's hardware health and safety and enhance instrument efficiency and performance. Although MOS is only one of the observing modes available to users, the complexity and uniqueness of the Micro-Shutter Assembly (MSA) that enables it has presented a variety of engineering challenges, including the appearance of electrical shorts that produce contaminating glow in exposures. Despite these challenges, the NIRSpec Multi-Object Spectrograph continues to perform robustly with no discernible degradation or significant reduction in capability. This paper provides an overview of the NIRSpec micro-shutter subsystem's state of health and operability and presents some of the developments that have taken place in its operation since the completion of instrument commissioning.

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arXiv2024

GA-NIFS: JWST discovers an offset AGN 740 million years after the Big Bang

A surprising finding of recent studies is the large number of Active Galactic Nuclei (AGN) associated with moderately massive black holes ($\rm \log(M_\bullet/M_\odot)\sim 6-8$), in the first billion years after the Big Bang ($z>5$). In this context, a relevant finding has been the large fraction of candidate dual AGN, both at large separations (several kpc) and in close pairs (less than a kpc), likely in the process of merging. Frequent black hole merging may be a route for black hole growth in the early Universe; however, previous findings are still tentative and indirect. We present JWST/NIRSpec-IFU observations of a galaxy at $z=7.15$ in which we find evidence for a $\rm \log(M_\bullet/M_\odot)\sim7.7$ accreting black hole, as traced by a broad component of H$β$ emission, associated with the Broad Line Region (BLR) around the black hole. This BLR is offset by 620 pc in projection from the centroid of strong rest-frame optical emission, with a velocity offset of $\sim$40 km/s. The latter region is also characterized by (narrow) nebular emission features typical of AGN, hence also likely hosting another accreting black hole, although obscured (type 2, narrow-line AGN). We exclude that the offset BLR is associated with Supernovae or massive stars, and we interpret these results as two black holes in the process of merging. This finding may be relevant for estimates of the rate and properties of gravitational wave signals from the early Universe that will be detected by future observatories like LISA.

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arXiv2024

GA-NIFS: NIRSpec reveals evidence for non-circular motions and AGN feedback in GN20

We present rest-frame optical data of the z~4 sub-millimeter galaxy GN20 obtained with JWST/NIRSpec in integral field spectroscopy (IFS) mode. The H$α$ emission is asymmetric and clumpy and extends over a projected distance of more than 15 kpc. To first order, the large-scale ionised gas kinematics are consistent with a turbulent ($σ\sim90$ km/s), rotating disc ($v_{\rm rot}\sim500$ km/s), congruent with previous studies of its molecular and ionised gas kinematics. However, we also find clear evidence for non-circular motions in the H$α$ kinematics. We discuss their possible connection with various scenarios, such as external perturbations, accretion or radial flows. In the centre of GN20, we find broad line emission (FWHM $\sim1000-2000$ km/s) in the H$α$+[N II] complex, suggestive of fast, AGN-driven winds or, alternatively, of the broad-line region of an active black hole. Elevated values of [N II]$\lambda6583$/H$α>0.4$ and EW(H$α)>6$ Å, throughout large parts of GN20 suggest that feedback from the active black hole is able to photo-ionise the interstellar medium. Our data corroborates that GN20 offers a unique opportunity to observe key processes in the evolution of the most massive present-day galaxies acting in concert, over 12 billion years ago.

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arXiv2024

GA-NIFS: The core of an extremely massive proto-cluster at the Epoch of Reionization probed with JWST/NIRSpec

The SPT0311-58 system resides in a massive dark matter halo at z ~ 6.9. It hosts two dusty galaxies (E and W) with a combined star formation rate of ~3500 Msun/yr. Its surrounding field exhibits an overdensity of sub-mm sources, making it a candidate proto-cluster. We use spatially-resolved spectroscopy provided by the JWST/NIRSpec Integral Field Unit (IFU) to probe a field of view (FoV) ~ 17 x 17 kpc^2 around this object. These observations have revealed ten new galaxies at z ~ 6.9, characterised by dynamical masses spanning from ~10^9 to 10^10 Msun and a range in radial velocities of ~ 1500 km/s, in addition to the already known E and W galaxies. The implied large number density, and the wide spread in velocities, indicate that SPT0311-58 is at the core of a proto-cluster, immersed in a very massive dark matter halo of ~ 5 x 10^12 Msun. Hence, it represents the most massive proto-cluster ever found at the EoR. We also study the dynamical stage of the system and find that it likely is not fully virialised. The galaxies exhibit a great diversity of properties showing a range of evolutionary stages. We derive their ongoing Ha-based unobscured SFR, and find that its contribution to the total SF varies significantly across the galaxies in the system. Their ionization conditions range from those typical of field galaxies at similar redshift recently studied with JWST to those found in more evolved objects at lower z. The metallicity spans more than 0.8 dex across the FoV, reaching nearly solar values in some cases. The detailed IFU spectroscopy of the E galaxy reveals that it is actively assembling its stellar mass, showing sub-kpc inhomogeneities, and a metallicity gradient that can be explained by accretion of low metallicity gas from the IGM. The kinematic maps indicate departures from regular rotation, high turbulence, and a possible pre-collision minor merger. (Abridged)

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arXiv2024

JWST Observations of Starbursts: Massive Star Clusters in the Central Starburst of M82

We present a near infrared (NIR) candidate star cluster catalog for the central kiloparsec of M82 based on new JWST NIRCam images. We identify star cluster candidates using the F250M filter, finding 1357 star cluster candidates with stellar masses $>10^4$ M$_\odot$. Compared to previous optical catalogs, nearly all (87%) of the candidates we identify are new. The star cluster candidates have a median intrinsic cluster radius of $\approx$1 pc and have stellar masses up to $10^6$ M$_\odot$. By comparing the color-color diagram to dust-free yggdrasil stellar population models, we estimate that the star cluster candidates have A$_{\rm V}\sim3-24$ mag, corresponding to A$_{\rm 2.5μm}\sim0.3-2.1$ mag. There is still appreciable dust extinction towards these clusters into the NIR. We measure the stellar masses of the star cluster candidates, assuming ages of 0 and 8 Myr. The slope of the resulting cluster mass function is $β=1.9\pm0.2$, in excellent agreement with studies of star clusters in other galaxies.

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arXiv2024

Local Analogs of Primordial Galaxies: In Search of Intermediate Mass Black Holes with JWST NIRSpec

Local low metallicity galaxies with signatures of possible accretion activity are ideal laboratories in which to search for the lowest mass black holes and study their impact on the host galaxy. Here we present the first JWST NIRSpec IFS observations of SDSS J120122.30+021108.3, a nearby ($z=0.00354$) extremely metal poor dwarf galaxy with no optical signatures of accretion activity but identified by WISE to have extremely red mid-infrared colors consistent with AGNs. We identify over one hundred lines between $\sim$ 1.7-5.2 microns, an unresolved nuclear continuum source with an extremely steep spectral slope consistent with hot dust from an AGN ($F_ν\approxν^{-1.5}$), and a plethora of H I, He I, and H$_2$ lines, with no lines from heavier elements, CO or ice absorption features, or PAHs.Our observations reveal that the red WISE source arises exclusively from a bright central unresolved source ($<$ 3pc) suggestive of an AGN, yet there are no He II lines or coronal lines identified in the spectrum, and, importantly, there is no evidence that the radiation field is harder in the nuclear source compared with surrounding regions. These observations can be explained with a young ($<$ 5 Myr) nuclear star cluster with stellar mass $\sim3\times 10^4$ M$_\odot$ and a deeply embedded AGN with bolometric luminosity $\sim$ $2\times10^{41}$ ergs $^{-1}$. The implied black hole mass is $\sim$ 1450 M$_\odot$, based on the Eddington limit, roughly consistent with that expected based on extrapolations of black hole galaxy scaling relations derived for more massive black holes. Longer wavelength observations are crucial to confirm this scenario.

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