arXiv subjects

Pierre Ferruit

Publications and source records attributed to Pierre Ferruit.

33 records · Page 2Linked to original sources

arXiv2018

Simulating and interpreting deep observations in the Hubble Ultra Deep Field with the JWST/NIRSpec low-resolution 'prism'

The James Webb Space Telescope (JWST) will enable the detection of optical emission lines in galaxies spanning a broad range of luminosities out to redshifts z>10. Measurements of key galaxy properties, such as star formation rate and metallicity, through these observations will provide unique insight into, e.g., the role of feedback from stars and active galactic nuclei (AGNs) in regulating galaxy evolution, the co-evolution of AGNs and host galaxies, the physical origin of the 'main sequence' of star-forming galaxies and the contribution by star-forming galaxies to cosmic reionization. We present an original framework to simulate and analyse observations performed with the Near Infrared Spectrograph (NIRSpec) on board JWST. We use the BEAGLE tool (BayEsian Analysis of GaLaxy sEds) to build a semi-empirical catalogue of galaxy spectra based on photometric spectral energy distributions (SEDs) of dropout galaxies in the Hubble Ultra Deep Field (HUDF). We demonstrate that the resulting catalogue of galaxy spectra satisfies different types of observational constraints on high redshift galaxies, and use it as input to simulate NIRSpec/prism (R~100) observations. We show that a single 'deep' (~100 ks) NIRSpec/prism pointing in the HUDF will enable S/N>3 detections of multiple optical emission lines in ~30 (~60) galaxies at z>6 (z~4-6) down to m_F160W<30 AB mag. Such observations will allow measurements of galaxy star formation rates, ionization parameters and gas-phase metallicities within factors of 1.5, mass-to-light ratios within a factor of 2, galaxy ages within a factor of 3 and V-band attenuation optical depths with a precision of 0.3.

astro-ph.GA↗

arXiv2018

Preparing the NIRSpec/JWST science data calibration: from ground testing to sky

The Near-Infrared Spectrograph (NIRSpec) is one of four instruments aboard the James Webb Space Telescope (JWST). NIRSpec is developed by ESA with AIRBUS Defence & Space as prime contractor. The calibration of its various observing modes is a fundamental step to achieve the mission science goals and provide users with the best quality data from early on in the mission. Extensive testing of NIRSpec on the ground, aided by a detailed model of the instrument, allow us to derive initial corrections for the foreseeable calibrations. We present a snapshot of the current calibration scheme that will be revisited once JWST is in orbit.

astro-ph.IM↗

arXiv2018

The JWST Extragalactic Mock Catalog: Modeling galaxy populations from the UV through the near-IR over thirteen billion years of cosmic history

We present an original phenomenological model to describe the evolution of galaxy number counts, morphologies, and spectral energy distributions across a wide range of redshifts (0.2 6]. Our model follows observed mass and luminosity functions of both star-forming and quiescent galaxies, and reproduces the redshift evolution of colors, sizes, star-formation and chemical properties of the observed galaxy population. Unlike other existing approaches, our model includes a self-consistent treatment of stellar and photoionized gas emission and dust attenuation based on the BEAGLE tool. The mock galaxy catalogs generated with our new model can be used to simulate and optimize extragalactic surveys with future facilities such as the James Webb Space Telescope (JWST), and to enable critical assessments of analysis procedures, interpretation tools, and measurement systematics for both photometric and spectroscopic data. As a first application of this work, we make predictions for the upcoming JWST Advanced Deep Extragalactic Survey (JADES), a joint program of the JWST/NIRCam and NIRSpec Guaranteed Time Observations teams. We show that JADES will detect, with NIRCam imaging, thousands of galaxies at z>6, and tens at z>10 at m_AB<30 (5-sigma) within the 236 arcmin^2 of the survey. The JADES data will enable accurate constraints on the evolution of the UV luminosity function at z>8, and resolve the current debate about the rate of evolution of galaxies at z>8. Ready to use mock catalogs and software to generate new realizations are publicly available as the JAdes extraGalactic Ultradeep Artificial Realizations (JAGUAR) package.

astro-ph.GA↗

arXiv2016

A model-based approach to the spatial and spectral calibration of NIRSpec onboard JWST

Context: The NIRSpec instrument for the James Webb Space Telescope (JWST) can be operated in multiobject (MOS), long-slit, and integral field (IFU) mode with spectral resolutions from 100 to 2700. Its MOS mode uses about a quarter of a million individually addressable minislits for object selection, covering a field of view of $\sim$9 $\mathrm{arcmin}^2$. Aims: The pipeline used to extract wavelength-calibrated spectra from NIRSpec detector images relies heavily on a model of NIRSpec optical geometry. We demonstrate how dedicated calibration data from a small subset of NIRSpec modes and apertures can be used to optimize this parametric model to the necessary levels of fidelity. Methods: Following an iterative procedure, the initial fiducial values of the model parameters are manually adjusted and then automatically optimized, so that the model predicted location of the images and spectral lines from the fixed slits, the IFU, and a small subset of the MOS apertures matches their measured location in the main optical planes of the instrument. Results: The NIRSpec parametric model is able to reproduce the spatial and spectral position of the input spectra with high fidelity. The intrinsic accuracy (1-sigma, RMS) of the model, as measured from the extracted calibration spectra, is better than 1/10 of a pixel along the spatial direction and better than 1/20 of a resolution element in the spectral direction for all of the grating-based spectral modes. This is fully consistent with the corresponding allocation in the spatial and spectral calibration budgets of NIRSpec.

astro-ph.IM↗

arXiv2015

Solar System Observations with the James Webb Space Telescope

The James Webb Space Telescope will enable a wealth of new scientific investigations in the near- and mid-infrared, with sensitivity and spatial/spectral resolution greatly surpassing its predecessors. In this paper, we focus upon Solar System science facilitated by JWST, discussing the most current information available concerning JWST instrument properties and observing techniques relevant to planetary science. We also present numerous example observing scenarios for a wide variety of Solar System targets to illustrate the potential of JWST science to the Solar System community. This paper updates and supersedes the Solar System white paper published by the JWST Project in 2010 (Lunine et al., 2010). It is based both on that paper and on a workshop held at the annual meeting of the Division for Planetary Sciences in Reno, NV in 2012.

astro-ph.EP↗

arXiv2015

Unique Spectroscopy and Imaging of Mars with JWST

In this document, we summarize the main capabilities of the James Webb Space Telescope (JWST) for performing observations of Mars. The distinctive vantage point of JWST at the Sun-Earth Lagrange point (L2) will allow sampling the full observable disk, permitting the study of short-term phenomena, diurnal processes (across the East-West axis) and latitudinal processes between the hemispheres (including seasonal effects) with excellent spatial resolutions (0.07 arcsec at 2 μm). Spectroscopic observations will be achievable in the 0.7-5 μm spectral region with NIRSpec at a maximum resolving power of 2700, and with 8000 in the 1-1.25 μm range. Imaging will be attainable with NIRCam at 4.3 μm and with two narrow filters near 2 μm, while the nightside will be accessible with several filters in the 0.5 to 2 μm. Such a powerful suite of instruments will be a major asset for the exploration and characterization of Mars. Some science cases include the mapping of the water D/H ratio, investigations of the Martian mesosphere via the characterization of the non-LTE CO$_2$ emission at 4.3 μm, studies of chemical transport via observations of the O$_2$ nightglow at 1.27 μm, high cadence mapping of the variability dust and water ice clouds, and sensitive searches for trace species and hydrated features on the Martian surface. In-flight characterization of the instruments may allow for additional science opportunities.

astro-ph.IM↗

arXiv2014

Observations of Transiting Exoplanets with the James Webb Space Telescope (JWST), Publications of the Astronomical Society of the Pacific (PASP), December 2014

This article summarizes a workshop held on March, 2014, on the potential of the James Webb Space Telescope (JWST) to revolutionize our knowledge of the physical properties of exoplanets through transit observations. JWST's unique combination of high sensitivity and broad wavelength coverage will enable the accurate measurement of transits with high signal-to-noise. Most importantly, JWST spectroscopy will investigate planetary atmospheres to determine atomic and molecular compositions, to probe vertical and horizontal structure, and to follow dynamical evolution, i.e. exoplanet weather. JWST will sample a diverse population of planets of varying masses and densities in a wide variety of environments characterized by a range of host star masses and metallicities, orbital semi-major axes and eccentricities. A broad program of exoplanet science could use a substantial fraction of the overall JWST mission.

astro-ph.IM↗

arXiv2009

OASIS integral-field spectroscopy of the central kpc in 11 Seyfert 2 galaxies

We map narrow-line regions (NLRs) of 11 nearby Seyfert 2 galaxies with the optical integral-field spectrograph OASIS mounted at CFHT. We model emission-line profiles of 5 forbidden-line doublets and 2 Balmer lines, correcting for the underlying stellar absorption by reconstructing stellar spectra with synthetic evolutionary stellar population models. For each of the 11 targets, we present 2D maps of surface brightness in the observed emission lines, diagnostic line intensity ratios, gas kinematics (mean line-of-sight velocity and velocity dispersion), electron density, and interstellar reddening, and we plot spatially resolved spectral-diagnostic diagrams. The stellar data are represented by maps of mean line-of-sight (LOS) velocities and of the relative mass fractions of the young stellar populations. The gas velocity fields in 80% of the sample exhibit twisted S-shaped isovelocity contours, which are signatures of non-circular orbits and indicate non-axisymmetric gravitational potentials, gas motions out of the galactic plane, or possible outflows and inflows. Based on the kinematic measurements, we identified a possible nuclear ring or radial gas flow in NGC 262 (Mrk 348), not reported before. Eight of the eleven observed objects exhibit strongly asymmetric or multi-component emission-line profiles, in most cases confined to an elongated region passing through the galactic centre, perpendicular to the major axis of emission.

astro-ph.CO↗

arXiv2007

Detectors for the James Webb Space Telescope Near-Infrared Spectrograph I: Readout Mode, Noise Model, and Calibration Considerations

We describe how the James Webb Space Telescope (JWST) Near-Infrared Spectrograph's (NIRSpec's) detectors will be read out, and present a model of how noise scales with the number of multiple non-destructive reads sampling-up-the-ramp. We believe that this noise model, which is validated using real and simulated test data, is applicable to most astronomical near-infrared instruments. We describe some non-ideal behaviors that have been observed in engineering grade NIRSpec detectors, and demonstrate that they are unlikely to affect NIRSpec sensitivity, operations, or calibration. These include a HAWAII-2RG reset anomaly and random telegraph noise (RTN). Using real test data, we show that the reset anomaly is: (1) very nearly noiseless and (2) can be easily calibrated out. Likewise, we show that large-amplitude RTN affects only a small and fixed population of pixels. It can therefore be tracked using standard pixel operability maps.

astro-ph↗

arXiv2005

Gas and stellar dynamics in NGC 1068. Probing the galactic gravitational potential

We present Sauron 2D spectrography of the central 1.5 kpc of the nearby Sey2 galaxy NGC1068, encompassing the well-known NIR inner bar. We have successively disentangled the respective contributions of the ionized gas and stars, thus deriving their 2D distribution and kinematics. The [OIII] and Hbeta emission lines exhibit very different spatial distribution and kinematics, the latter following inner spiral arms with clumps associated with star formation. Strong inwards streaming motions are observed in both the Hbeta and [OIII] kinematics. The stellar kinematics also exhibit clear signatures of a non-axisymmetric tumbling potential, with a twist in both the velocity and h3 fields. We re-examined the long-slit data of Shapiro et al (2003) using pPXF: a strong decoupling of h3 is revealed, and the central decrease in h4 hinted in the Sauron data is confirmed. These data also suggest that NGC1068 is a good candidate for a so-called sigma-drop. We confirm the possible presence of two pattern speeds. We also examine the stellar kinematics of bars formed in N-body+SPH simulations built from axisymmetric initial conditions. These successfully reproduce a number of properties observed in the 2D kinematics of NGC1068, and the long-slit data, showing that the kinematic signature of the NIR bar is imprinted in the stellar kinematics. The remaining differences between the models and the observed properties are mostly due to the exclusion of star formation and the lack of the primary large-scale oval/bar in the simulations. These models suggest that the inner bar could drive a significant amount of gas down to a scale of ~300 pc. This is consistent with the interpretation of the sigma-drop in NGC1068 being the result of central gas accretion followed by an episode of star formation.

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arXiv2004

Spatially Resolved Ultraviolet Spectra of the High-Velocity Nuclear Outflow of NGC 1068

We present ultraviolet emission-line maps of the narrow-line region (NLR) of NGC 1068. The maps span 115--318 nm, the biconical ionization cone, several posited jet/ISM interactions, and the compact knots whose optical spectra we reported previously resemble kinematically the quasar Associated Absorption Line systems. Across the NLR, we find that ultraviolet flux ratios are consistent with photoionization, not shock excitation, even for gas blueshifted abruptly to 3000 \kms relative to galaxy systemic velocity or for gas projected near the radio jet. The knots may be radiatively accelerated, photoablated fragments of molecular clouds.

astro-ph↗

arXiv2003

A two-arm gaseous spiral in the inner 200 pc of the early-type galaxy NGC 2974: signature of an inner bar

TIGER integral-field spectrography and HST/WFPC2 imaging of the E3 galaxy NGC 2974 are used to derive the kinematics of the stellar and ionized gas components in its central 500 pc. We derive a numerical two-integral distribution function from a MGE mass model using the HQ formalism. The TIGER as well as published long-slit stellar kinematics are well fitted with this self-consistent model, requiring neither the addition of a significant mass contribution from a hidden disc structure, nor the presence of a central dark mass. The data reveal the presence of a striking, highly contrasted, two-arm gaseous spiral structure within a radius of ~200 pc, corresponding to a total mass of 6.8x10^4 Msun of ionized gas. We use a deconvolved TIGER datacube to probe its kinematics at a resolution of about 0.35 arcsec. Strong departures from circular motions are observed, as well as high velocity dispersion values on the inner side of the arms. We interpret the observed gas morphology and kinematics as the signature of streaming gas flows driven by a ~540 pc diameter bar with Ome=700+/-100 km/s/kpc. This hypothesis is strongly supported by the predictions of a density wave model. This model predicts that the bar should lie at about 35 degree from the line of nodes, and implies gas inflow towards the central ~50 pc. The quadrupole pertubation due to this bar is estimated to represent less than 2% of the underlying gravitational potential. Despite its weakness, the inner bar of NGC 2974 may be able to drive some gas within a 10 pc radius. We suggest that the presence of such inner bars might be more common among early-type disk galaxies than is generally thought, and that deep high-resolution emission-line imagery may be the best way to detect such structures.

astro-ph↗

arXiv2003

Relation between source and temperature fluctuations in photoionized nebulae

The magnitude of the temperature fluctuations (t^2) required to explain the observed inconsistencies between metallicities inferred from recombination lines and from forbidden lines cannot be attained by steady-state equilibrium photoionization models. If on the other hand the nebular ionizing source was variable, the temperature fluctuations t^2 would be significantly larger. We investigate the time-dependent response of the nebular ionization and temperature structure when photoionized by a periodically varying source. We study how the asymptotic mean value, , behaves as a function of the period or amplitude of the source variability. We find that the temperature fluctuations occur only in the outer section of the nebula, close to the ionization front, within a zone corresponding to 8-20% of the ionized layer's thickness. We conclude that the amplitude of the exciting star variations required to achieve a = 0.025 (as in the Orion nebula) is unacceptably large. Source variability is therefore not a viable mechanism to explain the observed values of t^2. We reach a similar conclusion from studies of the temporal variability resulting from intermittent shadows behind opaque condensations. We find that photoionized nebulae are on average less massive but somewhat hotter in the case of cyclicly variable ionizing sources.

astro-ph↗

arXiv2001

Spatial Resolution of High-Velocity Filaments in the Narrow-Line Region of NGC 1068: Associated Absorbers Caught in Emission?

Using the HST STIS spectrograph we have obtained a grid of [O III] and H-beta emission-line spectra at 0"05x0"19 and 60 km/s (FWHM) resolution that covers much of the NLR of NGC 1068. We find emitting knots that have blueshifted radial velocities up to 3200 km/s relative to galaxy systemic, are 70-150 pc NE of the nucleus and up to 40 pc from the radio jet, emit several percent of the NLR line flux but no significant continuum, span velocity extents of up to 1250 km/s but a small fraction of the sky seen from the nucleus, coincide with a region of enhanced IR coronal-line emission, and have ionized masses $\sim$200 Msun/ne4 (ne4=10^4 cm^{-3}). We argue that the blueshifted knots are ablata from disintegrating molecular clouds that are being photoionized by the AGN, and are being accelerated readiatively by the AGN or mechanically by the radio jet. In their kinematic properties, the knots resemble the associated absorbers seen projected on the UV continua of some AGN. Between 2"5-4"5 from the nucleus, emission is redshifted relative to systemic, a pattern that we interpret as gas in the galaxy disk being pushed away from us by the NE radio lobe.

astro-ph↗

arXiv2000

The Sombrero Galaxy III. Ionised gas and dust in the central 200 pc: a nuclear bar?

We present the results of new 3D TIGER spectroscopic observations and archived HST/WFPC2 and NICMOS images of the central region of M 104. The [NII]+Ha images reveal the presence of a nuclear spiral structure, and the gaseous kinematics in the central arcsecond shows evidence for kinematical decoupling of the central peak. A straight nuclear dust lane, with a weak symmetric counterpart, is seen in the V-I and V-H colour maps. These results hint for the presence of a strong nuclear bar, that would be located inside the inner Linblad resonance of the large-scale bar discussed by Emsellem (1995).

astro-ph↗