arXiv subjects

Maarten Baes

Publications and source records attributed to Maarten Baes.

At least 145 records · Page 8Linked to original sources

arXiv2016

Far-infrared and dust properties of present-day galaxies in the EAGLE simulations

The EAGLE cosmological simulations reproduce the observed galaxy stellar mass function and many galaxy properties. In this work, we study the dust-related properties of present-day EAGLE galaxies through mock observations in the far-infrared and submm wavelength ranges obtained with the 3D dust radiative transfer code SKIRT. To prepare an EAGLE galaxy for radiative transfer processing, we derive a diffuse dust distribution from the gas particles and we re-sample the star-forming gas particles and the youngest star particles into star-forming regions that are assigned dedicated emission templates. We select a set of redshift-zero EAGLE galaxies that matches the K-band luminosity distribution of the galaxies in the Herschel Reference Survey (HRS), a volume-limited sample of about 300 normal galaxies in the Local Universe. We find overall agreement of the EAGLE dust scaling relations with those observed in the HRS, such as the dust-to-stellar mass ratio versus stellar mass and versus NUV-r colour relations. A discrepancy in the f_250/f_350 versus f_350/f_500 submm colour-colour relation implies that part of the simulated dust is insufficiently heated, likely because of limitations in our sub-grid model for star-forming regions. We also investigate the effect of adjusting the metal-to-dust ratio and the covering factor of the photodissociation regions surrounding the star-forming cores. We are able to constrain the important dust-related parameters in our method, informing the calculation of dust attenuation for EAGLE galaxies in the UV and optical domain.

astro-ph.GA↗

arXiv2016

Far-reaching Dust Distribution in Galaxy Disks

In most studies of dust in galaxies, dust is only detected from its emission to approximately the optical radius of the galaxy. By combining the signal of 110 spiral galaxies observed as part of the Herschel Reference Survey, we are able to improve our sensitivity by an order-of-magnitude over that for a single object. Here we report the direct detection of dust from its emission that extends out to at least twice the optical radius. We find that the distribution of dust is consistent with an exponential at all radii with a gradient of ~-1.7 dex R$_{25}^{-1}$. Our dust temperature declines linearly from ~25 K in the centre to 15 K at R$_{25}$ from where it remains constant out to ~2.0 R$_{25}$. The surface-density of dust declines with radius at a similar rate to the surface-density of stars but more slowly than the surface-density of the star-formation rate. Studies based on dust extinction and reddening of high-redshift quasars have concluded that there are substantial amounts of dust in intergalactic space. By combining our results with the number counts and angular correlation function from the SDSS, we show that with Milky Way type dust we can explain the reddening of the quasars by the dust within galactic disks alone. Given the uncertainties in the properties of any intergalactic dust, we cannot rule out its existence, but our results show that statistical investigations of the dust in galactic halos that use the reddening of high-redshift objects must take account of the dust in galactic disks.

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arXiv2016

Pinwheels in the sky, with dust: 3D modeling of the Wolf-Rayet 98a environment

The Wolf-Rayet 98a (WR 98a) system is a prime target for interferometric surveys, since its identification as a "rotating pinwheel nebulae", where infrared images display a spiral dust lane revolving with a 1.4 year periodicity. WR 98a hosts a WC9+OB star, and the presence of dust is puzzling given the extreme luminosities of Wolf-Rayet stars. We present 3D hydrodynamic models for WR 98a, where dust creation and redistribution are self-consistently incorporated. Our grid-adaptive simulations resolve details in the wind collision region at scales below one percent of the orbital separation (~4 AU), while simulating up to 1300 AU. We cover several orbital periods under conditions where the gas component alone behaves adiabatic, or is subject to effective radiative cooling. In the adiabatic case, mixing between stellar winds is effective in a well-defined spiral pattern, where optimal conditions for dust creation are met. When radiative cooling is incorporated, the interaction gets dominated by thermal instabilities along the wind collision region, and dust concentrates in clumps and filaments in a volume-filling fashion, so WR 98a must obey close to adiabatic evolutions to demonstrate the rotating pinwheel structure. We mimic Keck, ALMA or future E-ELT observations and confront photometric long-term monitoring. We predict an asymmetry in the dust distribution between leading and trailing edge of the spiral, show that ALMA and E-ELT would be able to detect fine-structure in the spiral indicative of Kelvin-Helmholtz development, and confirm the variation in photometry due to the orientation. Historic Keck images are reproduced, but their resolution is insufficient to detect the details we predict.

astro-ph.SR↗

arXiv2016

HERschel Observations of Edge-on Spirals (HEROES). III. Dust energy balance study of IC 2531

We investigate the dust energy balance for the edge-on galaxy IC 2531, one of the seven galaxies in the HEROES sample. We perform a state-of-the-art radiative transfer modelling based, for the first time, on a set of optical and near-infrared galaxy images. We show that taking into account near-infrared imaging in the modelling significantly improves the constraints on the retrieved parameters of the dust content. We confirm the result from previous studies that including a young stellar population in the modelling is important for explaining the observed stellar energy distribution. However, the discrepancy between the observed and modelled thermal emission at far-infrared wavelengths, the so-called dust energy balance problem, is still present: the model underestimates the observed fluxes by a factor of about two. We compare two different dust models, and find that dust parameters and thus the spectral energy distribution in the infrared domain are sensitive to the adopted dust model. In general, the THEMIS model reproduces the observed emission in the infrared wavelength domain better than the popular Zubko et al. BARE-GR-S model. Our study of IC 2531 is a pilot case for detailed and uniform radiative transfer modelling of the entire HEROES sample, which will shed more light on the strength and origins of the dust energy balance problem.

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arXiv2016

The interstellar medium in Andromeda's dwarf spheroidal galaxies: I. Content and origin of the interstellar dust

Dwarf spheroidal galaxies are among the most numerous galaxy population in the Universe, but their main formation and evolution channels are still not well understood. The three dwarf spheroidal satellites (NGC147, NGC185, and NGC205) of the Andromeda galaxy are characterised by very different interstellar medium (ISM) properties, which might suggest them being at different galaxy evolutionary stages. While the dust content of NGC205 has been studied in detail by De Looze et al. (2012), we present new Herschel dust continuum observations of NGC147 and NGC185. The non-detection of NGC147 in Herschel SPIRE maps puts a strong constraint on its dust mass (< 128 Msun). For NGC185, we derive a total dust mass M_d = 5.1 x 10^3 Msun, which is a factor of ~2-3 higher than that derived from ISO and Spitzer observations and confirms the need for longer wavelength observations to trace more massive cold dust reservoirs. We, furthermore, estimate the dust production by asymptotic giant branch (AGB) stars and supernovae (SNe). For NGC147, the upper limit on the dust mass is consistent with expectations of the material injected by the evolved stellar population. In NGC185 and NGC205, the observed dust content is one order of magnitude higher compared to the estimated dust production by AGBs and SNe. Efficient grain growth, and potentially longer dust survival times (3-6 Gyr) are required to account for their current dust content. Our study confirms the importance of grain growth in the gas phase to account for the current dust reservoir in galaxies.

astro-ph.GA↗

arXiv2016

The Herschel Virgo Cluster Survey. XIX. Physical properties of low luminosity FIR sources at $z <$ 0.5

The Star formation rate (SFR) is a crucial parameter to investigate galaxy evolution. At low redshift the cosmic SFR density declines smoothly, and massive active galaxies become passive, reducing their star formation activity. This implies that the bulk of the SFR density at low redshift is mainly driven by low mass objects. We investigate the properties of a sample of low luminosity Far-Infrared (FIR) sources selected at 250 microns from Pappalardo et al. (2015). We have collected data from Ultraviolet to FIR to perform a multi-wavelengths analysis. The main goal is to investigate the correlation between SFR, stellar mass, and dust mass for a galaxy population with a wide range in dust content and stellar mass, including the low mass regime that most probably dominates the SFR density at low z. We define a main sample of ~800 sources with full Spectral Energy Distribution (SED) coverage between 0.15 < lambda < 500 microns and an extended sample with ~5000 sources in which we remove the constraints on the Ultraviolet and Near-Infrared bands. We analyze both samples with two different SED fitting methods: MAGPHYS and CIGALE. In the SFR versus stellar mass plane our samples occupy a region included between local spirals and higher redshift star forming galaxies. The galaxies subsample with the higher masses (M* > 3e10 Msol) does not lie on the main sequence, but shows a small offset, as a consequence of the decreased star formation. Low mass galaxies (M* < 1e10 Msol) settle in the main sequence with SFR and stellar mass consistent with local spirals. Deep Herschel data allow the identification of a mixed galaxy population, with galaxies still in an assembly phase, or galaxies at the beginning of their passive evolution. We find that the dust luminosity is the parameter that discriminates these two galaxy populations.

astro-ph.GA↗

arXiv2016

Composite biasing in Monte Carlo radiative transfer

Biasing or importance sampling is a powerful technique in Monte Carlo radiative transfer, and can be applied in different forms to increase the accuracy and efficiency of simulations. One of the drawbacks of the use of biasing is the potential introduction of large weight factors. We discuss a general strategy, composite biasing, to suppress the appearance of large weight factors. We use this composite biasing approach for two different problems faced by current state-of-the-art Monte Carlo radiative transfer codes: the generation of photon packages from multiple components, and the penetration of radiation through high optical depth barriers. In both cases, the implementation of the relevant algorithms is trivial and does not interfere with any other optimisation techniques. Through simple test models, we demonstrate the general applicability, accuracy and efficiency of the composite biasing approach. In particular, for the penetration of high optical depths, the gain in efficiency is spectacular for the specific problems that we consider: in simulations with composite path length stretching, high accuracy results are obtained even for simulations with modest numbers of photon packages, while simulations without biasing cannot reach convergence, even with a huge number of photon packages.

astro-ph.IM↗

arXiv2016

The nature of the UV halo around the spiral galaxy NGC 3628

Thanks to deep UV observations with GALEX and Swift, diffuse UV haloes have recently been discovered around galaxies. Based on UV-optical colours, it has been advocated that the UV haloes around spiral galaxies are due to UV radiation emitted from the disc and scattered off dust grains at high latitudes. Detailed UV radiative transfer models that take into account scattering and absorption can explain the morphology of the UV haloes, and they require the presence of an additional thick dust disc next the to traditional thin disc for half of the galaxies in their sample. We test whether such an additional thick dust disc agrees with the observed infrared emission in NGC 3628, an edge-on galaxy with a clear signature of a thick dust disc. We extend the far-ultraviolet radiative transfer models to full-scale panchromatic models. Our model, which contains no fine-tuning, can almost perfectly reproduce the observed spectral energy distribution from UV to mm wavelengths. These results corroborate the interpretation of the extended UV emission in NGC 3628 as scattering off dust grains, and hence of the presence of a substantial amount of diffuse extra-planar dust. A significant caveat, however, is the geometrical simplicity and non-uniqueness of our model: other models with a different geometrical setting could lead to a similar spectral energy distribution. More detailed radiative transfer simulations that compare the model results to images from UV to submm wavelengths are a way to break this degeneracy, as are UV polarisation measurements.

astro-ph.GA↗

arXiv2015

H-ATLAS/GAMA: Quantifying the Morphological Evolution of the Galaxy Population Using Cosmic Calorimetry

Using results from the Herschel Astrophysical Terrahertz Large-Area Survey and the Galaxy and Mass Assembly project, we show that, for galaxy masses above approximately 1.0e8 solar masses, 51% of the stellar mass-density in the local Universe is in early-type galaxies (ETGs: Sersic n > 2.5) while 89% of the rate of production of stellar mass-density is occurring in late-type galaxies (LTGs: Sersic n < 2.5). From this zero-redshift benchmark, we have used a calorimetric technique to quantify the importance of the morphological transformation of galaxies over the history of the Universe. The extragalactic background radiation contains all the energy generated by nuclear fusion in stars since the Big Bang. By resolving this background radiation into individual galaxies using the deepest far-infrared survey with the Herschel Space Observatory and a deep near-infrared/optical survey with the Hubble Space Telescope (HST), and using measurements of the Sersic index of these galaxies derived from the HST images, we estimate that approximately 83% of the stellar mass-density formed over the history of the Universe occurred in LTGs. The difference between this and the fraction of the stellar mass-density that is in LTGs today implies there must have been a major transformation of LTGs into ETGs after the formation of most of the stars.

astro-ph.GA↗

arXiv2015

Benchmarking the Calculation of Stochastic Heating and Emissivity of Dust Grains in the Context of Radiative Transfer Simulations

We define an appropriate problem for benchmarking dust emissivity calculations in the context of radiative transfer (RT) simulations, specifically including the emission from stochastically heated dust grains. Our aim is to provide a self-contained guide for implementors of such functionality, and to offer insights in the effects of the various approximations and heuristics implemented by the participating codes to accelerate the calculations. The benchmark problem definition includes the optical and calorimetric material properties, and the grain size distributions, for a typical astronomical dust mixture with silicate, graphite and PAH components; a series of analytically defined radiation fields to which the dust population is to be exposed; and instructions for the desired output. We process this problem using six RT codes participating in this benchmark effort, and compare the results to a reference solution computed with the publicly available dust emission code DustEM. The participating codes implement different heuristics to keep the calculation time at an acceptable level. We study the effects of these mechanisms on the calculated solutions, and report on the level of (dis)agreement between the participating codes. For all but the most extreme input fields, we find agreement within 10% across the important wavelength range from 3 to 1000 micron. We conclude that the relevant modules in RT codes can and do produce fairly consistent results for the emissivity spectra of stochastically heated dust grains.

astro-ph.IM↗

arXiv2015

Herschel-ATLAS: The Surprising Diversity of Dust-Selected Galaxies in the Local Submillimetre Universe

We present the properties of the first 250 $μ$m blind sample of nearby galaxies (15 < D < 46 Mpc) containing 42 objects from the Herschel Astrophysical Terahertz Large Area Survey (H-ATLAS). Herschel's sensitivity probes the faint end of the dust luminosity function for the first time, spanning a range of stellar mass (7.4 < log$_{10}$ M$_{\star}$ < 11.3 M$_{\odot}$), star formation activity (-11.8 < log$_{10}$ SSFR < -8.9 yr$^{-1}$), gas fraction (3-96 per cent), and colour (0.6 < FUV-Ks < 7.0 mag). The median cold dust temperature is 14.6 K, colder than in the Herschel Reference Survey (18.5 K) and Planck Early Release Compact Source Catalogue 17.7 K. The mean dust-to-stellar mass ratio in our sample is higher than these surveys by factors of 3.7 and 1.8, with a dust mass volume density of (3.7 $\pm$ 0.7) x 10$^{5}$ M$_{\odot}$ Mpc$^{-3}$. Counter-intuitively, we find that the more dust rich a galaxy, the lower its UV attenuation. Over half of our dust-selected sample are very blue in FUV-Ks colour, with irregular and/or highly flocculent morphology, these galaxies account for only 6 per cent of the sample's stellar mass but contain over 35 per cent of the dust mass. They are the most actively star forming galaxies in the sample, with the highest gas fractions and lowest UV attenuation. They also appear to be in an early stage of converting their gas into stars, providing valuable insights into the chemical evolution of young galaxies.

astro-ph.GA↗

arXiv2015

SKIRT: the design of a suite of input models for Monte Carlo radiative transfer simulations

The Monte Carlo method is the most popular technique to perform radiative transfer simulations in a general 3D geometry. The algorithms behind and acceleration techniques for Monte Carlo radiative transfer are discussed extensively in the literature, and many different Monte Carlo codes are publicly available. On the contrary, the design of a suite of components that can be used for the distribution of sources and sinks in radiative transfer codes has received very little attention. The availability of such models, with different degrees of complexity, has many benefits. For example, they can serve as toy models to test new physical ingredients, or as parameterised models for inverse radiative transfer fitting. For 3D Monte Carlo codes, this requires algorithms to efficiently generate random positions from 3D density distributions. We describe the design of a flexible suite of components for the Monte Carlo radiative transfer code SKIRT. The design is based on a combination of basic building blocks (which can be either analytical toy models or numerical models defined on grids or a set of particles) and the extensive use of decorators that combine and alter these building blocks to more complex structures. For a number of decorators, e.g. those that add spiral structure or clumpiness, we provide a detailed description of the algorithms that can be used to generate random positions. Advantages of this decorator-based design include code transparency, the avoidance of code duplication, and an increase in code maintainability. Moreover, since decorators can be chained without problems, very complex models can easily be constructed out of simple building blocks. Finally, based on a number of test simulations, we demonstrate that our design using customised random position generators is superior to a simpler design based on a generic black-box random position generator.

astro-ph.IM↗

arXiv2015

Dust energy balance study of two edge-on spiral galaxies in the Herschel-ATLAS survey

Interstellar dust in galaxies can be traced either through its extinction effects on the star light, or through its thermal emission at infrared wavelengths. Recent radiative transfer studies of several nearby edge-on galaxies have found an apparent inconsistency in the dust energy balance: the radiative transfer models that successfully explain the optical extinction underestimate the observed fluxes by an average factor of three. We investigate the dust energy balance for IC4225 and NGC5166, two edge-on spiral galaxies observed by the Herschel Space Observatory in the frame of the H-ATLAS survey. We start from models which were constrained from optical data and extend them to construct the entire spectral energy distribution of our galaxies. These predicted values are subsequently compared to the observed far-infrared fluxes. We find that including a young stellar population in the modelling is necessary as it plays a non-negligible part in the heating of the dust grains. While the modelling approach for both galaxies is nearly identical, we find two very different results. As is often seen in other edge-on spiral galaxies, the far-infrared emission of our radiative transfer model of IC4225 underestimates the observed fluxes by a factor of about three. For NGC5166 on the other hand, we find that both the predicted spectral energy distribution as well as the simulated images match the observations particularly well. We explore possible reasons for this difference and conclude that it is unlikely that one single mechanism is the cause of the dust energy balance problem in spiral galaxies. We discuss the different approaches that can be considered in order to get a conclusive answer on the origin this discrepancy.

astro-ph.GA↗

arXiv2015

G2C2 - IV: A novel approach to study the radial distributions of multiple populations in Galactic globular clusters

We use the HB morphology of 48 Galactic GCs to study the radial distributions of the different stellar populations known to exist in globular clusters. Assuming that the (extremely) blue HB stars correspond to stars enriched in Helium and light elements, we compare the radial distributions of stars selected according to colour on the HB to trace the distribution of the secondary stellar populations in globular clusters. Unlike other cases, our data show that the populations are well mixed in 80% of the cases studied. This provides some constraints on the mechanisms proposed to pollute the interstellar medium in young globular clusters.

astro-ph.GA↗

arXiv2015

G2C2-III: Structural parameters for Galactic globular clusters in SDSS passbands

We use our Galactic Globular Cluster Catalog (G2C2) photometry for 111 Galactic globular clusters (GC) in g and z, as well as r and i photometry for a subset of 60 GCs and u photometry for 22 GCs, to determine the structural parameters assuming King (1962) models. In general, the resulting core radii are in good comparison with the current literature values. However, our half-light radii are slightly lower than the literature. The concentrations (and therefore also the tidal radii) are poorly constrained mostly because of the limited radial extent of our imaging. Therefore, we extensively discuss the effects of a limited field-of-view on the derived parameters using mosaicked SDSS data, which do not suffer from this restriction. We also illustrate how red giant branch (RGB) stars in cluster cores can stochastically induce artificial peaks in the surface brightness profiles. The issues related to these bright stars are scrutinised based on both our photometry and simulated clusters. We also examine colour gradients and find that the strongest central colour gradients are caused by central RGB stars and thus not representative for the cluster light or colour distribution. We recover the known relation between the half-light radius and the Galactocentric distance in the g-band, but find a lower slope for redder filters. We did not find a correlation between the scatter on this relation and other cluster properties. We find tentative evidence for a correlation between the half-light radii and the [Fe/H], with metal-poor GCs being larger than metal-rich GCs. However, we conclude that this trend is caused by the position of the clusters in the Galaxy, with metal-rich clusters being more centrally located.

astro-ph.GA↗

arXiv2015

Extinction and nebular line properties of a Herschel-selected lensed dusty starburst AT z=1.027

We present Hubble Space Telescope (HST) WFC3 imaging and grism spectroscopy observations of the {\it Herschel}-selected gravitationally-lensed starburst galaxy HATLASJ1429-0028. The lensing system consists of an edge-on foreground disk galaxy at $z=0.218$ with a nearly complete Einstein ring of the infrared luminous galaxy at $z=1.027$. The WFC3 spectroscopy with G102 and G141 grisms, covering the wavelength range of 0.8 to 1.7 $μ$m, resulted in detections of H$α$+[NII], H$β$, [SII], and [OIII] for the background galaxy from which we measure line fluxes and ratios. The Balmer line ratio H$α$/H$β$ of $7.5 \pm 4.4$, when corrected for [NII], results in an extinction for the starburst galaxy of $E(B-V)=0.8 \pm 0.5$. The $Hα$ based star-formation rate, when corrected for extinction, is $60 \pm 50$ M$_{\odot}$ yr$^{-1}$, lower than the instantaneous star-formation rate of 390 $\pm$ 90 M$_{\odot}$ yr$^{-1}$ from the total IR luminosity. We also compare the nebular line ratios of HATLASJ1429-0028 with other star-forming and sub-mm bright galaxies. The nebular line ratios are consistent with an intrinsic ultra-luminous infrared galaxy with no evidence for excitation by an active galactic nucleus (AGN). We estimate the metallicity, $12 + log(O/H)$, of HATLASJ1429-0028 to be 8.49 $\pm$ 0.16. Such a low value is below the average relations for stellar mass vs. metallicity of galaxies at $z \sim 1$ for a galaxy with stellar mass of $\sim 2 \times 10^{11}$ M$_{\odot}$. The combination of high stellar mass, lack of AGN indicators, low metallicity, and the high star-formation rate of HATLASJ1429-0028 suggest that this galaxy is currently undergoing a rapid formation.

astro-ph.GA↗

arXiv2015

Far-infrared observations of an unbiased sample of gamma-ray burst host galaxies

Gamma-ray bursts (GRBs) are the most energetic phenomena in the Universe; believed to result from the collapse and subsequent explosion of massive stars. Even though it has profound consequences for our understanding of their nature and selection biases, little is known about the dust properties of the galaxies hosting GRBs. We present analysis of the far-infrared properties of an unbiased sample of 20 \textit{BeppoSAX} and \textit{Swift} GRB host galaxies (at an average redshift of $z\,=\,3.1$) located in the {\it Herschel} Astrophysical Terahertz Large Area Survey, the {\it Herschel} Virgo Cluster Survey, the {\it Herschel} Fornax Cluster Survey, the {\it Herschel} Stripe 82 Survey and the {\it Herschel} Multi-tiered Extragalactic Survey, totalling $880$ deg$^2$, or $\sim 3$\% of the sky in total. Our sample selection is serendipitous, based only on whether the X-ray position of a GRB lies within a large-scale {\it Herschel} survey -- therefore our sample can be considered completely unbiased. Using deep data at wavelengths of 100\,--\,500$\,μ$m, we tentatively detected 1 out of 20 GRB hosts located in these fields. We constrain their dust masses and star formation rates (SFRs), and discuss these in the context of recent measurements of submillimetre galaxies and ultraluminous infrared galaxies. The average far-infrared flux of our sample gives an upper limit on SFR of $<114\,{\rm M}\odot\,\mbox{yr}^{-1}$. The detection rate of GRB hosts is consistent with that predicted assuming that GRBs trace the cosmic SFR density in an unbiased way, i.e. that the fraction of GRB hosts with $\mbox{SFR}>500\,{\rm M}\odot\,\mbox{yr}^{-1}$ is consistent with the contribution of such luminous galaxies to the cosmic star formation density.

astro-ph.HE↗

arXiv2014

Spectral and morphological analysis of the remnant of Supernova 1987A with ALMA & ATCA

We present a comprehensive spectral and morphological analysis of the remnant of Supernova (SN) 1987A with the Australia Telescope Compact Array (ATCA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The non-thermal and thermal components of the radio emission are investigated in images from 94 to 672 GHz ($λ$ 3.2 mm to 450 $μ$m), with the assistance of a high-resolution 44 GHz synchrotron template from the ATCA, and a dust template from ALMA observations at 672 GHz. An analysis of the emission distribution over the equatorial ring in images from 44 to 345 GHz highlights a gradual decrease of the east-to-west asymmetry ratio with frequency. We attribute this to the shorter synchrotron lifetime at high frequencies. Across the transition from radio to far infrared, both the synchrotron/dust-subtracted images and the spectral energy distribution (SED) suggest additional emission beside the main synchrotron component ($S_ν\proptoν^{-0.73}$) and the thermal component originating from dust grains at $T\sim22$ K. This excess could be due to free-free flux or emission from grains of colder dust. However, a second flat-spectrum synchrotron component appears to better fit the SED, implying that the emission could be attributed to a pulsar wind nebula (PWN). The residual emission is mainly localised west of the SN site, as the spectral analysis yields $-0.4\lesssimα\lesssim-0.1$ across the western regions, with $α\sim0$ around the central region. If there is a PWN in the remnant interior, these data suggest that the pulsar may be offset westward from the SN position.

astro-ph.HE↗