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Register a new userX-ray Spectral Study of the extended emission,the Cap, located 11.6 kpc above the disk of M82
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The extended X-ray emission from the Cap region located 11 (11.6 kpc) above the disk of the starburst galaxy M82 has been observed with Suzaku and XMM-Newton. Owing to the good energy resolution and the large collecting area of the XIS on Suzaku, combined with similar properties of the EPIC instrument on XMM-Newton, we have clearly detected K-shell emission lines from O VII, O VIII, Ne X, Mg XI, Mg XII and the Fe-L complex. Two optically-thin thermal plasma components are required to fit the observed X-ray spectra. We have determined the metal abundances of O, Ne, Mg, Si and Fe in this region for the first time. Their metal abundance ratios agree well with those of metal-poor stars and the model prediction of metals synthesized by type-II supernovae, but they are not consistent with the metallicities of type-Ia supernovae. This result is support for the idea that the origin of the metals in the Cap is type-II supernovae explosions occurring in the starburst regions in the M82 galaxy. We discuss the possible contribution from sputtered dust grains to the metals in the Cap. An emission line consistent with the C VI transition of n=4 to 1 at 0.459 keV is marginally detected, although it is not statistically significant at the 99% confidence level; the presence of this line would suggest charge-exchange processes in the Cap.
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It has been proposed that the charge exchange (CX) process at the interface between hot and cool interstellar gases could contribute significantly to the observed soft X-ray emission in star forming galaxies. We analyze the XMM-Newton/RGS spectrum of M82, using a newly developed CX model combined with a single-temperature thermal plasma to characterize the volume-filling hot gas. The CX process is largely responsible for not only the strongly enhanced forbidden lines of the K$alpha$ triplets of various He-like ions, but also good fractions of the Ly$alpha$ transitions of C VI (~87%), O VIII and N VII ($gtrsim$50%) as well. In total about a quarter of the X-ray flux in the RGS 6-30 AA band originates in the CX. We infer an ion incident rate of $3times10^{51},rm{s^{-1}}$ undergoing CX at the hot and cool gas interface, and an effective area of the interface as $sim2times10^{45},{rm cm^2}$ that is one order of magnitude larger than the cross section of the global biconic outflow. With the CX contribution accounted for, the best fit temperature of the hot gas is 0.6 keV, and the metal abundances are approximately solar. We further show that the same CX/thermal plasma model also gives an excellent description of the EPIC-pn spectrum of the outflow Cap, projected at 11.6 kpc away from the galactic disk of M82. This analysis demonstrates that the CX is potentially an important contributor to the X-ray emission from starburst galaxies and also an invaluable tool to probe the interface astrophysics.
The main results from a deep X-ray observation of M82 are summarised: spatially-dependent chemical abundances, temperature structure of the gas, charge-exchange emission lines in the spectrum. We also present an update of the chemical bundances, based on a more refined extraction of spectra.
We discuss the properties and implications of a 3.7x0.9 kpc region of spatially-coincident X-ray and H-alpha emission about 11.6 kpc to the north of the galaxy M82 previously discussed by Devine and Bally (1999). The PSPC X-ray spectrum is fit by thermal plasma (kT=0.80+-0.17 keV) absorbed by only the Galactic foreground column density. We evaluate the relationship of the X-ray/H-alpha ridge to the M82 superwind. The main properties of the X-ray emission can all be explained as being due to shock-heating driven as the superwind encounters a massive ionized cloud in the halo of M82. This encounter drives a slow shock into the cloud, which contributes to the excitation of the observed H-alpha emission. At the same time, a fast bow-shock develops in the superwind just upstream of the cloud, and this produces the observed X-ray emission. This interpretation would imply that the superwind has an outflow speed of roughly 800 km/s, consistent with indirect estimates based on its general X-ray properties and the kinematics of the inner kpc-scale region of H-alpha filaments. The gas in the M82 ridge is roughly two orders-of-magnitude hotter than the minimum escape temperature at this radius, so this gas will not be retained by M82. (abridged)
We studied a time history of X-ray spectral states of a black-hole candidate, 4U 1630-47, utilizing data from a number of monitoring observations with the Rossi X-Ray Timing Explorer over 1996--2004. These observations covered five outbursts of 4U 1630-47, and most of the data recorded typical features of the high/soft states. We found that the spectra in the high/soft states can be further classified into three states. The first spectral state is explained by a concept of the standard accretion disk picture. The second state appears in the so-called very high state, where a dominant hard component is seen and the disk radius apparently becomes too small. These phenomena are explained by the effect of inverse Compton scattering of disk photons, as shown by Kubota, Makishima, & Ebisawa (2001, ApJ, 560, L147) for GRO J1655-40. The third state is characterized in such a way that the disk luminosity varies in proportion to $T_{rm in}^2$, rather than $T_{rm in}^4$, where $T_{rm in}$ is the inner-disk temperature. This state is suggested to be an optically-thick and advection-dominated slim disk, as suggested by Kubota & Makishima (2004, ApJ, 601, 428) for XTE J1550-564. The second and third states appear, with good reproducibility, when $T_{rm in}$ and the total X-ray luminosity are higher than 1.2 keV and $sim2.5times10^{38}(D/10quad{rm kpc})^2l eft[cos{theta}/(1/sqrt{3})]^{-1}$ erg s$^{-1}$, respectively, where $D$ is the distance to the object and $theta$ is the inclination angle to the disk. The present results suggest that these three spectral states commonly appear among black-hole binaries under high accretion rates.
The M49 group, resident outside the virial radius of the Virgo cluster, is falling onto the cluster from the south. We report results from deep {sl XMM-Newton} mosaic observations of M49. Its hot gas temperature is 0.8,keV at the group center and rises to 1.5,keV beyond the brightest group galaxy (BGG). The group gas extends to radii of $sim300$,kpc to the north and south. The observations reveal a cold front $sim20$,kpc north of the BGG center and an X-ray bright stripped tail 70,kpc long and 10,kpc wide to the southwest of the BGG. We argue that the atmosphere of the infalling group was slowed by its encounter with the Virgo cluster gas, causing the BGG to move forward subsonically relative to the group gas. We measure declining temperature and metallicity gradients along the stripped tail. The tail gas can be traced back to the cooler and enriched gas uplifted from the BGG center by buoyant bubbles, implying that AGN outbursts may have intensified the stripping process. We extrapolate to a virial radius of 740,kpc and derive a virial mass of $4.6times10^{13},M_odot$ for the M49 group. Its group atmosphere appears truncated and deficient when compared with isolated galaxy groups of similar temperatures. If M49 is on its first infall to Virgo, the infall region of a cluster could have profound impacts on galaxies and groups that are being accreted onto galaxy clusters. Alternatively, M49 may have already passed through Virgo once.
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