arXiv subjects

Peter Zeidler

Publications and source records attributed to Peter Zeidler.

At least 37 records · Page 2Linked to original sources

arXiv2024

Exploring the Mpc Environment of the Quasar ULAS J1342+0928 at z = 7.54

Theoretical models predict that z~6 quasars are hosted in the most massive halos of the underlying dark matter distribution and thus would be immersed in protoclusters of galaxies. However, observations report inconclusive results. We investigate the 1.1 pMpc2 environment of the z = 7.54 luminous quasar ULAS J1342+0928. We search for Lyman-break galaxy candidates (LBG) using deep imaging from the Hubble Space Telescope (HST) in the ACS/F814W, WFC3/F105W/F125W bands, and Spitzer/IRAC at 3.6 $μ$m and 4.5 $μ$m. We report a zphot = $7.69^{+0.33}_{-0.23}$ LBG with magF125W = 26.41 at 223 projected-pkpc from the quasar. We find no HST counterpart to one [CII]-emitter previously found with ALMA at 27 projected-pkpc and $z[CII]=7.5341\pm0.0009$ (Venemans et al. 2020). We estimate the completeness of our LBG candidates using results from CANDELS/GOODS deep blank field searches sharing a similar filter setup. We find that >50% of the z~7.5 LBGs with magF125W >25.5 are missed due to the absence of a filter redward of the Lyman-break in F105W, hindering the UV color accuracy of the candidates. We conduct a QSO-LBG clustering analysis revealing a low LBG excess of $0.46^{+1.52}_{-0.08}$ in this quasar field, consistent with an average or low-density field. Consequently, this result does not present strong evidence of an LBG overdensity around ULAS J1342+0928. Furthermore, we identify two LBG candidates with a zphot matching a confirmed z=6.84 absorber along the line-of-sight to the quasar. All these galaxy candidates are excellent targets for follow-up observations with JWST and/or ALMA to confirm their redshift and physical properties.

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arXiv2023

The VLT MUSE NFM view of outflows and externally photoevaporating discs near the Orion Bar

We present VLT/MUSE Narrow Field Mode (NFM) observations of a pair of disc-bearing young stellar objects towards the Orion Bar: 203-504 and 203-506. Both of these discs are subject to external photoevaporation, where winds are launched from their outer regions due to environmental irradiation. Intriguingly, despite having projected separation from one another of only 1.65{\arcsec} (660au at 400pc), 203-504 has a classic teardrop shaped ``proplyd'' morphology pointing towards $θ^2$Ori A (indicating irradiation by the EUV of that star, rather than $θ^1$ Ori C) but 203-506 has no ionisation front, indicating it is not irradiated by stellar EUV at all. However, 203-506 does show [CI] 8727Å and [OI] 6300Å in emission, indicating irradiation by stellar FUV. This explicitly demonstrates the importance of FUV irradiation in driving mass loss from discs. We conclude that shielding of 203-506 from EUV is most likely due to its position on the observers side of an ionized layer lying in the foreground of the Huygens Region. We demonstrate that the outflow HH 519, previously thought to be emanating from 203-504 is actually an irradiated cloud edge and identify a new compact outflow from that object approximately along our line of sight with a velocity $\sim130$\,km\,s$^{-1}$.

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arXiv2023

Discovery of dusty sub-solar mass young stellar objects in NGC 346 with JWST/NIRCam

JWST observations of NGC 346, a star-forming region in the metal-poor Small Magellanic Cloud, reveal a substantial population of sub-solar mass young stellar objects (YSOs) with IR excess. We detected $\sim$500 YSOs and pre main sequence (PMS) stars from more than 45,000 unique sources utilizing all four NIRCam wide filters with deep, high-resolution imaging, where ongoing low-mass star formation is concentrated along dust filaments. From these observations, we construct detailed near-IR colour-magnitude diagrams with which preliminary categorizations of YSO classes are made. For the youngest, most deeply-embedded objects, JWST/NIRCam reaches over 10 magnitudes below Spitzer observations at comparable wavelengths, and two magnitudes fainter than HST for more-evolved PMS sources, corresponding to $\sim$0.1 M$_\odot$. For the first time in an extragalactic environment, we detect embedded low-mass star-formation. Furthermore, evidence of IR excess and accretion suggests that dust required for rocky planet formation is present at metallicities as low as 0.2 $Z_\odot$.

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arXiv2022

The internal line-of-sight kinematics of NGC 346: the rotation of the core region

We present the stellar radial velocity analysis of the central 1x1' of the young massive Small Magellanic Cloud star cluster NGC 346. Using VLT/MUSE integral field spectroscopy in combination with Hubble Space Telescope photometry we extract 103 spectra of cluster member stars suited to measure accurate line-of-sight kinematics. The cluster member stars show two distinct velocity groups at v1 = -3.3 (+0.3/-0.2) km/s and v2 = 2.6 (+0.1/-0.1) km/s, relative to the systemic velocity of 165.5+/-0.2 km/s, and hint for a third group at v3 = 9.4 (+0.1/-0.1 km/s. We show that there is neither a correlation between the velocity groups and the spatial location of the stars, nor their locus on optical color-magnitude diagrams, which makes the stellar velocity a key parameter to separate individual stellar components in such a young star cluster. Velocity group 2 shows clear rotation with Omega2 = -0.4 +/- 0.1 1/Myr, corresponding to -4.9+/-0.7 km/s at radial distance of 10 pc from the center, a possible remnant of the formation process of NGC 346 through the hierarchical collapse of the giant molecular cloud. The ionizing gas has lost any natal kinematic imprint and shows clear expansion, driven by far ultra violet fluxes and stellar winds of the numerous OB stars in the cluster center. The size of this expanding bubble and its expansion velocity of 7.9 km/s is in excellent agreement with the estimate that the latest star formation episode occurred about two million years ago.

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arXiv2022

The In-Flight Noise Performance of the JWST/NIRSpec Detector System

The Near-Infrared Spectrograph (NIRSpec) is one the four focal plane instruments on the James Webb Space Telescope (JWST) which was launched on December 25, 2021. We present the in-flight status and performance of NIRSpec's detector system as derived from the instrument commissioning data. The instrument features two 2048 x 2048 HAWAII-2RG sensor chip assemblies (SCAs) that are operated at a temperature of about 42.8 K and are read out via a pair of SIDECAR ASICs. NIRSpec supports "Improved Reference Sampling and Subtraction" (IRS2) readout mode that was designed to meet NIRSpec's stringent noise requirements and to reduce 1/f and correlated noise. In addition, NIRSpec features subarrays optimized for bright object time series observations, e.g. for the observation of exoplanet transit around bright host stars. We focus on the dark signal as well as the read and total noise performance of the detectors.

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arXiv2022

In-flight performance and calibration of the Grating Wheel Assembly sensors (NIRSpec/JWST)

The Near-Infrared Spectrograph (NIRSpec) on board of the James Webb Space Telescope will be the first multi-object spectrograph in space offering ~250,000 configurable micro-shutters, apart from being equipped with an integral field unit and fixed slits. At its heart, the NIRSpec grating wheel assembly is a cryogenic mechanism equipped with six dispersion gratings, a prism, and a mirror. The finite angular positioning repeatability of the wheel causes small but measurable displacements of the light beam on the focal plane, precluding a static solution to predict the light-path. To address that, two magneto-resistive position sensors are used to measure the tip and tilt displacement of the selected GWA element each time the wheel is rotated. The calibration of these sensors is a crucial component of the model-based approach used for NIRSpec for calibration, spectral extraction, and target placement in the micro-shutters. In this paper, we present the results of the evolution of the GWA sensors performance and calibration from ground to space environments.

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arXiv2022

Astrometric and Wavelength Calibration of the NIRSpec Instrument during Commissioning using a model-based approach

The NIRSpec instrument for the James Webb Space Telescope (JWST) is a highly versatile near-infrared spectrograph that can be operated in various observing modes, slit apertures, and spectral resolutions. Obtaining dedicated calibration data for all possible combinations of aperture and disperser is an intractable task. We have therefore developed a procedure to derive a highly realistic model of the instrument's optical geometry across the entire field of view, using calibration data acquired through only a subset of NIRSpec apertures, which nevertheless allows the light paths within the spectrograph to be accurately computed for all apertures and all observing modes. This parametric instrument model thus provides the basis for the extraction of wavelength-calibrated spectra from any NIRSpec exposure, regardless of observing mode or aperture used. Optimizing the NIRSpec instrument model and deriving its final wavelength and astrometric calibration was one of the most crucial elements of the NIRSpec commissioning phase. Here, we describe the process of re-fitting the NIRSpec instrument model with in-orbit commissioning data, and present its final performance in terms of wavelength accuracy and astrometric calibration.

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arXiv2022

In-flight performance of the NIRSpec Micro Shutter Array

The NIRSpec instrument on the James Webb Space Telescope (JWST) brings the first multi-object spectrograph (MOS) into space, enabled by a programmable Micro Shutter Array (MSA) of ~250,000 individual apertures. During the 6-month Commissioning period, the MSA performed admirably, completing ~800 reconfigurations with an average success rate of ~96% for commanding shutters open in science-like patterns. We show that 82.5% of the unvignetted shutter population is usable for science, with electrical short masking now the primary cause of inoperable apertures. In response, we propose a plan to recheck existing shorts during nominal operations, which is expected to reduce the number of affected shutters. We also present a full assessment of the Failed Open and Failed Closed shutter populations, which both show a marginal increase in line with predictions from ground testing. We suggest an amendment to the Failed Closed shutter flagging scheme to improve flexibility for MSA configuration planning. Overall, the NIRSpec MSA performed very well during Commissioning, and the MOS mode was declared ready for science operations on schedule.

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arXiv2022

In-orbit Commissioning of the Near-Infrared Spectrograph on the James Webb Space Telescope

The Near-Infrared Spectrograph (NIRSpec) is one of the four focal plane instruments on the James Webb Space Telescope which was launched on Dec. 25, 2021. We present an overview of the as-run NIRSpec commissioning campaign, with particular emphasis on the sequence of activities that led to the verification of all hardware components of NIRSpec. We also discuss the mechanical, thermal, and operational performance of NIRSpec, as well as the readiness of all NIRSpec observing modes for use in the upcoming JWST science program.

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arXiv2021

The impact of pre-supernova feedback and its dependence on environment

Integral field units enable resolved studies of a large number of star-forming regions across entire nearby galaxies, providing insight on the conversion of gas into stars and the feedback from the emerging stellar populations over unprecedented dynamic ranges in terms of spatial scale, star-forming region properties, and environments. We use the VLT/MUSE legacy data set covering the central $35$ arcmin$^{2}$ (${\sim}12$ kpc$^{2}$) of the nearby galaxy NGC 300 to quantify the effect of stellar feedback as a function of the local galactic environment. We extract spectra from emission line regions identified within dendrograms, combine emission line ratios and line widths to distinguish between HII regions, planetary nebulae, and supernova remnants, and compute their ionised gas properties, gas-phase oxygen abundances, and feedback-related pressure terms. For the HII regions, we find that the direct radiation pressure ($P_\mathrm{dir}$) and the pressure of the ionised gas ($P_{HII}$) weakly increase towards larger galactocentric radii, i.e. along the galaxy's (negative) abundance and (positive) extinction gradients. While the increase of $P_{HII}$ with galactocentric radius is likely due to higher photon fluxes from lower-metallicity stellar populations, we find that the increase of $P_\mathrm{dir}$ is likely driven by the combination of higher photon fluxes and enhanced dust content at larger galactocentric radii. In light of the above, we investigate the effect of increased pre-supernova feedback at larger galactocentric distances (lower metallicities and increased dust mass surface density) on the ISM, finding that supernovae at lower metallicities expand into lower-density environments, thereby enhancing the impact of supernova feedback.

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arXiv2021

The young massive star cluster Westerlund 2 observed with MUSE. III. A cluster in motion -- the complex internal dynamics

Analyzing the dynamical state of nearby young massive star clusters is essential understanding star cluster formation and evolution during their earliest stages. In this work we analyze the stellar and gas kinematics of the young massive star cluster Westerlund 2 (Wd2) using data from the integral field unit MUSE and complement them with proper motions from the Gaia DR2. The mean gas radial velocity of $15.9\,{\rm km}\,{\rm s}^{-1}$ agrees with the assumption that Wd2 is the result of a cloud-cloud collision. The gas motions show the expansion of the HII region, driven by the radiation from the many OB stars in the cluster center. The velocity profile of the cluster member stars reveal an increasing velocity dispersion with decreasing stellar mass and that the low-mass stars show five distinct velocity groups. Based on their spatial correlation with the cluster's two clumps, we concluded that this is the imprint of the initial cloud collapse that formed Wd2. A thorough analysis of the dynamical state of Wd2, which determines a dynamical mass range of $M_{\rm dyn,Wd2} = (7.5 \pm 1.9)\cdot10^4 - (4.4 \pm 1.1)\cdot10^5\,{\rm M}_\odot$ and exceeds the photometric mass by at least a factor of two leads to the conclusion that Wd2 is not massive enough to remain gravitationally bound. Additionally we also identify 22 runaway candidates with peculiar velocities between 30 and $546\,{\rm km}\,{\rm s}^{-1}$.

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arXiv2020

Stellar Parameter Determination from Photometry using Invertible Neural Networks

Photometric surveys with the Hubble Space Telescope (HST) allow us to study stellar populations with high resolution and deep coverage, with estimates of the physical parameters of the constituent stars being typically obtained by comparing the survey data with adequate stellar evolutionary models. This is a highly non-trivial task due to effects such as differential extinction, photometric errors, low filter coverage, or uncertainties in the stellar evolution calculations. These introduce degeneracies that are difficult to detect and break. To improve this situation, we introduce a novel deep learning approach, called conditional invertible neural network (cINN), to solve the inverse problem of predicting physical parameters from photometry on an individual star basis and to obtain the full posterior distributions. We build a carefully curated synthetic training data set derived from the PARSEC stellar evolution models to predict stellar age, initial/current mass, luminosity, effective temperature and surface gravity. We perform tests on synthetic data from the MIST and Dartmouth models, and benchmark our approach on HST data of two well-studied stellar clusters, Westerlund 2 and NGC 6397. For the synthetic data we find overall excellent performance, and note that age is the most difficult parameter to constrain. For the benchmark clusters we retrieve reasonable results and confirm previous findings for Westerlund 2 on cluster age ($1.04_{-0.90}^{+8.48}\,\mathrm{Myr} $), mass segregation, and the stellar initial mass function. For NGC 6397 we recover plausible estimates for masses, luminosities and temperatures, however, discrepancies between stellar evolution models and observations prevent an acceptable recovery of age for old stars.

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arXiv2020

Star clusters near and far; tracing star formation across cosmic time

Star clusters are fundamental units of stellar feedback and unique tracers of their host galactic properties. In this review, we will first focus on their constituents, i.e.\ detailed insight into their stellar populations and their surrounding ionised, warm, neutral, and molecular gas. We, then, move beyond the Local Group to review star cluster populations at various evolutionary stages, and in diverse galactic environmental conditions accessible in the local Universe. At high redshift, where conditions for cluster formation and evolution are more extreme, we are only able to observe the integrated light of a handful of objects that we believe will become globular clusters. We therefore discuss how numerical and analytical methods, informed by the observed properties of cluster populations in the local Universe, are used to develop sophisticated simulations potentially capable of disentangling the genetic map of galaxy formation and assembly that is carried by globular cluster populations.

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arXiv2020

Original use of MUSE's laser tomography adaptive optics to directly image young accreting exoplanets

We present recent results obtained with the VLT/MUSE Integral Field Spectrograph fed by the 4LGSF and its laser tomography adaptive optics module GALACSI. While this so-called narrow-field mode of MUSE was not designed to perform directly imaging of exoplanets and outflows, we show that it can be a game changer to detect and characterize young exoplanets with a prominent emission lines (i.e Hα, tracer of accretion), at moderate contrasts. These performances are achieved thanks to the combo of a near-diffraction limited PSF and a medium resolution spectrograph and a cross-correlation approach in post-processing . We discuss this in the context of ground and space, infrared and visible wavelengths, preparing for missions like JWST and WFIRST in great synergy and as pathfinder for future ELT/GSMT (Extremely Large and/or Giant Segmented Mirror Telescopes) instruments.

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arXiv2020

Stellar Feedback and Resolved Stellar IFU Spectroscopy in the nearby Spiral Galaxy NGC 300

We present MUSE Integral Field Unit (IFU) observations of five individual HII regions in two giant (>100 pc in radius) star-forming complexes in the low-metallicity ($Z$~0.33 $Z_{\odot}$) nearby (D ~ 2 Mpc) dwarf spiral galaxy NGC 300. We combine the IFU data with high spatial resolution HST photometry to demonstrate the extraction of stellar spectra and the classification of individual stars from ground-based data at the distance of 2 Mpc. For the two star-forming complexes, in which no O-type stars had previously been identified, we find a total of 13 newly identified O-type stars in the mass range 15-50 M$_{\odot}$, as well as 4 Wolf-Rayet stars. We use the derived massive stellar content to analyze the impact of stellar feedback on the HII regions. As already found for HII regions in the Magellanic Clouds, the dynamics of the analyzed NGC 300 HII regions are dominated by a combination of the pressure of the ionized gas and stellar winds. By comparing the derived ionized gas mass loading factors to the total gas mass loading factor across the NGC 300 disk, we find that the latter is an order of magnitude higher, either indicating very early evolutionary stages for these HII regions, or being a direct result of the multi-phase nature of feedback-driven bubbles. Moreover, we analyze the relation between the star formation rate and the pressure of the ionized gas as derived from small (<100 pc) scales, as both quantities are systematically overestimated when derived on galactic scales. With the wealth of ongoing and upcoming IFU instruments and programs, this study serves as a pathfinder for the systematic investigation of resolved stellar feedback in nearby galaxies, and it delivers the necessary analysis tools to enable massive stellar content and feedback studies sampling an unprecedented range of HII region properties across entire galaxies in the nearby Universe.

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arXiv2019

The young massive star cluster Westerlund 2 observed with MUSE. II. MUSEpack -- a Python package to analyze the kinematics of young star clusters

We mapped the Galactic young massive star cluster Westerlund 2 (Wd2) with the integral field spectrograph MUSE (spatial resolution: 0.2arcsec/px, spectral resolution: $Δλ$ = 1.25A, wavelength range 4600-9350A) mounted on the VLT, as part of an on-going study to measure the stellar and gas kinematics of the cluster region. In this paper we present the fully reduced dataset and introduce our new Python package "MUSEpack", which we developed to measure stellar radial velocities with an absolute precision of 1-2km/s without the necessity of a spectral template library. This novel method uses the two-dimensional spectra and an atomic transition line library to create templates around strong absorption lines for each individual star. The code runs fully automatically on multi-core machines, which makes it possible to efficiently determine stellar radial velocities of a large number of stars with the necessary precision to measure the velocity dispersion of young star clusters. MUSEpack also provides an enhanced method for removing telluric lines in crowded fields without sky exposures and a Python wrapper for ESO's data reduction pipeline. We observed Wd2 with a total of 11 short and 5 long exposures to cover the bright nebular emission and OB stars, as well as the fainter pre-main sequence stars down to ~1M$_\odot$. The survey covers an area of ~11arcmin$^2$ (15.8pc$^2$). In total, we extracted 1,725 stellar spectra with a mean S/N>5 per pixel. A typical radial velocity (RV) uncertainty of 4.78km/s, 2.92km/s, and 1.1km/s is reached for stars with a mean S/N>10, S/N>20, S/N>50 per pixel, respectively. Depending on the number of spectral lines used to measure the RVs, it is possible to reach RV accuracies of 0.9km/s, 1.3km/s, and 2.2km/s with $\geq5$, 3-4, and 1-2 spectral lines, respectively. The combined statistical uncertainty on the radial velocity measurements is 1.10km/s.

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arXiv2019

Astro2020 Science White Paper: Spatially Resolved UV Nebular Diagnostics in Star-Forming Galaxies

Diagnosing the physical and chemical conditions within star-forming galaxies (SFGs) is of paramount importance to understanding key components of galaxy formation and evolution: star-formation, gas enrichment, outflows, and accretion. Well established optical emission-line diagnostics used to discern such properties (i.e., metal content, density, strength/shape of ionizing radiation) will be observationally inaccessible for the earliest galaxies, emphasizing the need for robust, reliable interstellar medium (ISM) diagnostics at ultraviolet (UV) wavelengths. Calibrating these UV diagnostics requires a comprehensive comparison of the UV and optical emission lines in nearby SFGs. Optical integral field unit (IFU) surveys have revealed the inhomogeneous nature of the ISM in SFGs, which leads to non-systematic biases in the interpretation of unresolved sources. Spatial variations are especially important to consider at UV wavelengths, where the strongest emission features originate from only the highest excitation regions of the nebula and are challenging to distinguish from competing high-ionization sources (e.g., shocks, AGN, etc.). Since surveys collecting large-scale optical integral field unit (IFU) spectroscopy are already underway, this white paper calls for an IFU or multi-object far-UV (FUV) spectroscopic instrument with high sensitivity, high spatial resolution, and large field of view (FoV). Given the impact of large-scale optical IFU surveys over the past decade, this white paper emphasizes the scientific need for a comparable foundation of spatially-resolved far-UV spectroscopy survey of nearby galaxies that will lay the foundation of diagnostics critical to the interpretation of the distant universe.

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arXiv2018

The young massive star cluster Westerlund 2 observed with MUSE. I. First results on the cluster internal motion from stellar radial velocities

Westerlund 2 (Wd2) is the central ionizing star cluster of the \ion{H}{2} region RCW~49 and the second most massive young star cluster (${\rm M} = (3.6 \pm 0.3)\times 10^4\,{\rm M}_\odot$) in the Milky Way. Its young age ($\sim2\,$Myr) and close proximity to the Sun ($\sim 4\,$kpc) makes it a perfect target to study stars emerging from their parental gas cloud, the large number of OB-stars and their feedback onto the gas, and the gas dynamics. We combine high-resolution multi-band photometry obtained in the optical and near-infrared with the \textit{Hubble} Space Telescope (HST), and VLT/MUSE integral field spectroscopy to study the gas, the stars, and their interactions, simultaneously. In this paper we focus on a small, $64\times64\,{\rm arcsec}^2$ region North of the main cluster center, which we call the Northern Bubble (NB), a circular cavity carved into the gas of the cluster region. Using MUSE data, we determined the spectral types of 17 stars in the NB from G9III to O7.5. With the estimation of these spectral types we add 2 O and 5 B-type stars to the previously published census of 37 OB-stars in Wd2. To measure radial velocities we extracted 72 stellar spectra throughout Wd2, including the 17 of the NB, and show that the cluster member stars follow a bimodal velocity distribution centered around $(8.10 \pm 1.53)\,{\rm km}\,{\rm s}^{-1}$ and $(25.41 \pm 1.57)\,{\rm km}\,{\rm s}^{-1}$ with a dispersion of $(4.52 \pm 1.78)\,{\rm km}\,{\rm s}^{-1}$ and $(3.46 \pm 1.29)\,{\rm km}\,{\rm s}^{-1}$, respectively. These are in agreement with CO($J=1$-2) studies of RCW~49 leaving cloud-cloud collision as a viable option for the formation scenario of Wd2. The bimodal distribution is also detected in the Gaia DR2 proper motions.

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