Deep XMM-Newton observations of the northern disc of M31: II. Tracing the hot interstellar medium

Aims. We use new deep XMM-Newton observations of the northern disc of M31 to trace the hot interstellar medium (ISM) in unprecedented detail and to characterise the physical properties of the X-ray emitting plasmas. Methods. We used all XMM-Newton data up to and including our new observations to produce the most detailed image yet of the hot ISM plasma in a grand design spiral galaxy such as our own. We compared the X-ray morphology to multi-wavelength studies in the literature to set it in the context of the multi-phase ISM. We performed spectral analyses on the extended emission using our new observations as they offer sufficient depth and count statistics to constrain the plasma properties. Data from the Panchromatic Hubble Andromeda Treasury were used to estimate the energy injected by massive stars and their supernovae. We compared these results to the hot gas properties. Results. The brightest emission regions were found to be correlated with populations of massive stars, notably in the 10 kpc star-forming ring. The plasma temperatures in the ring regions are ∼0.2 up to ∼0.6 keV. We suggest this emission is hot ISM heated in massive stellar clusters and superbubbles. We derived X-ray luminosities, densities, and pressures for the gas in each region. We also found large extended emission filling low density gaps in the dust morphology of the northern disc, notably between the 5 and 10 kpc star-forming rings. We propose that the hot gas was heated and expelled into the gaps by the populations of massive stars in the rings. Conclusions. It is clear that the massive stellar populations are responsible for heating the ISM to X-ray emitting temperatures, filling their surroundings, and possibly driving the hot gas into the low density regions. Overall, the morphology and spectra of the hot gas in the northern disc of M31 is similar to other galaxy discs. © 2020 ESO

Deep XMM-Newton observations of the northern disc of M 31: I. Source catalogue

Context. We carried out new observations of two fields in the star-forming northern ring of M 31 with XMM-Newton with each one of them consisting of two exposures of about 100 ks each. A previous XMM-Newton survey of the entire M 31 galaxy revealed extended diffuse X-ray emission in these regions. Aims. We study the population of X-ray sources in the northern disc of M 31 by compiling a complete list of X-ray sources down to a sensitivity limit of ∼7 × 1034 erg s-1 (0.5-2.0 keV) and improve the identification of the X-ray sources. The major objective of the observing programme was the study of the hot phase of the interstellar medium (ISM) in M 31. The analysis of the diffuse emission and the study of the ISM is presented in a separate paper. Methods. We analysed the spectral properties of all detected sources using hardness ratios and spectra if the statistics were high enough. We also checked for variability. In order to classify the sources detected in the new deep XMM-Newton observations, we cross-correlated the source list with the source catalogue of a new survey of the northern disc of M 31 carried out with the Chandra X-ray Observatory and the Hubble Space Telescope (Panchromatic Hubble Andromeda Treasury, PHAT) as well as with other existing catalogues. Results. We detected a total of 389 sources in the two fields of the northern disc of M 31 observed with XMM-Newton. We identified 43 foreground stars and candidates and 50 background sources. Based on a comparison with the results of the Chandra/PHAT survey, we classify 24 hard X-ray sources as new candidates for X-ray binaries. In total, we identified 34 X-ray binaries and candidates and 18 supernova remnants (SNRs) and candidates. We studied the spectral properties of the four brightest SNRs and confirmed five new X-ray SNRs. Three of the four SNRs, for which a spectral analysis was performed, show emission mainly below 2 keV, which is consistent with shocked ISM. The spectra of two of them also require an additional component with a higher temperature. The SNR [SPH11] 1535 has a harder spectrum and might suggest that there is a pulsar-wind nebula inside the SNR. For all SNRs in the observed fields, we measured the X-ray flux or calculated upper limits. We also carried out short-term and long-term variability studies of the X-ray sources and found five new sources showing clear variability. In addition, we studied the spectral properties of the transient source SWIFT J004420.1+413702, which shows significant variation in flux over a period of seven months (June 2015 to January 2016) and associated change in absorption. Based on the likely optical counterpart detected in the Chandra/PHAT survey, the source is classified as a low-mass X-ray binary. © ESO 2018

ALMA CO Observations of Gamma-Ray Supernova Remnant N132D in the Large Magellanic Cloud: Possible Evidence for Shocked Molecular Clouds Illuminated by Cosmic-Ray Protons

International audienceN132D is the brightest gamma-ray supernova remnant (SNR) in the Large Magellanic Cloud (LMC). We carried out 12CO(J = 1–0, 3–2) observations toward the SNR using the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Submillimeter Telescope Experiment. We find diffuse CO emission not only at the southern edge of the SNR as previously known, but also inside the X-ray shell. We spatially resolved nine molecular clouds using ALMA with an angular resolution of 5″, corresponding to a spatial resolution of ∼1 pc at the distance of the LMC. Typical cloud sizes and masses are ∼2.0 pc and ∼100 M ⊙, respectively. High intensity ratios of CO J = 3–2/1–0 > 1.5 are seen toward the molecular clouds, indicating that shock heating has occurred. Spatially resolved X-ray spectroscopy reveals that thermal X-rays in the center of N132D are produced not only behind a molecular cloud but also in front of it. Considering the absence of a thermal component associated with the forward shock toward one molecular cloud located along the line of sight to the center of the remnant, this suggests that this particular cloud is engulfed by shock waves and is positioned on the near side of the remnant. If the hadronic process is the dominant contributor to the gamma-ray emission, the shock-engulfed clouds play a role as targets for cosmic rays. We estimate the total energy of cosmic-ray protons accelerated in N132D to be ∼0.5–3.8 × 1049 erg as a conservative lower limit, which is similar to that observed in Galactic gamma-ray SNRs

First maps of the soft X-ray diffuse background from the ROSAT XRT/PSPC all-sky survey

This paper presents an initial version of the diffuse background results from the ROSAT soft X-ray all-sky survey. These maps cover #approx# 98% of the sky in the 1/4 keV, 3/4 keV, and 1.5 keV bands, with #approx# 2 angular resolution and high sensitivity for low surface brightness extended features. The effects of non-X-ray contamination and X-rays of solar system origin have been eliminated to the greatest possible extent, but discrete X-ray sources have not been removed. The much improved angular resolution, statistical precision, and completeness of coverage of these maps reveals considerable structure over the entire 0.1 - 2.0 keV energy range that was not observed previously. The data agree well with previous all-sky surveys in terms of absolute normalization and zero point. (orig.)Available from TIB Hannover: RN 9303(335) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

ROSAT survey diffuse X-ray background maps. Paper 2

This paper presents new maps of the soft X-ray background from the ROSAT all-sky survey. These maps represent a significant improvement over the previous version in that(1) the position resolution of the PSPC has been used to improve the angular resolution from #propor to#2 to 12', (2) there are six energy bands that divide each of the previous three into two parts, and(3) the contributions of point sources have been removed to a uniform source flux level over most of the sky. These new maps will be available in electronic format in 1997. In this paper we also consider the bright emission in the general direction of the Galactic center in the 0.5-2.9 keV band, and the apparent absorption trough that runs through it along the Galactic plane. We find that while the northern hemisphere data are confused by emission from Loop I, the emission seen south of the plane is consistent with a bulge of hot gas surrounding the Galactic center (in our simple model, a cylinder with an exponential fall-off density with height above the plane). The cylinder has a radial extent of #propor to#5.6 kpc. The X-ray emitting gas has a scale height of 1.9 kpc, an in-plane electron density of #propor to#0.0035 cm"-"3, a temperature of #propor to#10"6"."6 K, a thermal pressure of #propor to#28,000 cm"-"3 K, and a total luminosity of #propor to#2 x 10"3"9 ergs s"-"1 using a collisional ionization equilibrium (CIE) plasma emission model. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman