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Register a new userChandra observations of the X-ray luminous star-forming galaxy merger Arp~299
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We report results of a Chandra observation of the X-ray luminous star-forming galaxy Arp299 (NGC3690/IC694). We detect 18 discrete X-ray sources with luminosities above ~10^39 ergs (0.5-8.0 keV band), which contribute ~40% of the total galactic emission in this band. The remaining emission is associated with a diffuse component spatially coincident with regions of widespread star-formation. We detect X-ray emission from both nuclei. One of the discrete sources within the complex nuclear region of NGC 3690 is found to have a very hard spectrum and therefore we associate it with the origin of the AGN-like spectrum that has also been detected at high X-ray energies using Beppo-SAX.
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We present mid-infrared spectro-imaging (5 - 16 microns) observations of the infrared luminous interacting system Arp 299 (=Mrk171 =IC694+NGC3690) obtained with the ISOCAM instrument aboard ISO. Our observations show that nearly 40% of the total emission at 7 and 15 microns is diffuse, originating from the interacting disks of the galaxies. Moreover, they indicate the presence of large amounts of hot dust in the main infrared sources of the system and large extinctions toward the nuclei. While the observed spectra have an overall similar shape, mainly composed of Unidentified Infrared Bands (UIB) in the short wavelength domain, a strong continuum at ~ 13 microns and a deep silicate absorption band at 10 microns, their differences reveal the varying physical conditions of each component. For each source, the spectral energy distribution (SED) can be reproduced by a linear combination of a UIB canonical spectral template and a hot dust continuum due to a 230-300 K black body, after independently applying an extinction correction to both of them. We find that the UIB extinction does not vary much throughout the system (A_V ~ 5 mag) suggesting that most UIBs originate from less enshrouded regions. IC694 appears to dominate the infrared emission of the system and our observations support the interpretation of a deeply embedded nuclear starburst located behind an absorption of about 40 mag. The central region of NGC3690 displays a hard radiation field characterized by a [NeIII]/[NeII] ratio > 1.8. It also hosts a strong continuum from 5 to 16 microns which can be explained as thermal emission from a deeply embedded (A_V ~ 60 mag) compact source, consistent with the mid-infrared signature of an active galactic nucleus (AGN), and in agreement with recent X-ray findings.
Hot atmospheres of massive galaxies are enriched with metals. Elemental abundances measured in the X-ray band have been used to study the chemical enrichment of supernova remnants, elliptical galaxies, groups and clusters of galaxies. Here we measure the elemental abundances of the hot atmosphere of luminous infrared galaxy Arp 299 observed with XMM-Newton. To measure the abundances in the hot atmosphere, we use a multi-temperature thermal plasma model, which provides a better fit to the Reflection Grating Spectrometer data. The observed Fe/O abundance ratio is subsolar, while those of Ne/O and Mg/O are slightly above solar. Core-collapse supernovae (SNcc) are the dominant metal factory of elements like O, Ne, and Mg. We find some deviations between the observed abundance patterns and theoretical ones from a simple chemical enrichment model. One possible explanation is that massive stars with $M_{star}gtrsim23-27~M_{odot}$ might not explode as SNcc and enrich the hot atmosphere. This is in accordance with the missing massive SNcc progenitors problem, where very massive progenitors $M_{star}gtrsim18~M_{odot}$ of SNcc have not been clearly detected. It is also possible that theoretical SNcc nucleosynthesis yields of Mg/O yields are underestimated.
We present results from the cross-correlation of the spectroscopic atlas of Ho etal (1995) with the ROSAT All-Sky Survey Bright Source Catalogue, in an attempt to understand the X-ray emission mechanisms in nearby galaxies. The resulting sample of 45 galaxies consists predominantly of AGN. However, there are several starforming galaxies spanning a wide range of X-ray luminosities (~10^{38} - 10^{42} erg s^{-1}). We have analyzed ROSAT and ASCA data for the two most luminous star-forming galaxies, namely NGC3310 and NGC3690. We find that their 0.1-10 keV X-ray spectra can be fitted by a soft thermal plasma of kT$sim0.8$ keV and a harder component with kT~10-15 keV or a power-law with Gamma~1.6. These are very similar to the spectra of the archetypal star-forming galaxies NGC253 and M82.
Hyper-luminous infrared galaxies (HyLIRGs) lie at the extreme luminosity end of the IR galaxy population with $L_{rm IR}>10^{13}$L$_odot$. They are thought to be closer counterparts of the more distant sub-mm galaxies, and should therefore be optimal targets to study the most massive systems in formation. We present deep $Chandra$ observations of IRAS~F15307+3252 (100ks), a classical HyLIRG located at $z=$0.93 and hosting a radio-loud AGN ($L_{rm 1.4 GHz}sim3.5times10^{25}$ W/Hz). The $Chandra$ images reveal the presence of extended ($r=160$ kpc), asymmetric X-ray emission in the soft 0.3-2.0 keV band that has no radio counterpart. We therefore argue that the emission is of thermal origin originating from a hot intragroup or intracluster medium virializing in the potential. We find that the temperature ($sim2$ keV) and bolometric X-ray luminosity ($sim3times10^{43}$ erg s$^{-1}$) of the gas follow the expected $L_{rm X-ray}-T$ correlation for groups and clusters, and that the gas has a remarkably short cooling time of $1.2$ Gyrs. In addition, VLA radio observations reveal that the galaxy hosts an unresolved compact steep-spectrum (CSS) source, most likely indicating the presence of a young radio source similar to 3C186. We also confirm that the nucleus is dominated by a redshifted 6.4 keV Fe K$alpha$ line, strongly suggesting that the AGN is Compton-thick. Finally, Hubble images reveal an over-density of galaxies and sub-structure in the galaxy that correlates with soft X-ray emission. This could be a snapshot view of on-going groupings expected in a growing cluster environment. IRAS~F15307+3252 might therefore be a rare example of a group in the process of transforming into a cluster.
We report on simultaneous observations of the local starburst system Arp 299 with NuSTAR and Chandra, which provides the first resolved images of this galaxy up to energies of ~ 45 keV. Fitting the 3-40 keV spectrum reveals a column density of $N_{rm H}$ ~ 4 x10^{24} cm^{-2}, characteristic of a Compton-thick AGN, and a 10-30 keV luminosity of 1.2x 10^{43} ergs s^{-1}. The hard X-rays detected by NuSTAR above 10 keV are centered on the western nucleus, Arp 299-B, which previous X-ray observations have shown to be the primary source of neutral Fe-K emission. Other X-ray sources, including Arp 299-A, the eastern nucleus which is also thought to harbor an AGN, as well as X-ray binaries, contribute $lesssim 10%$ to the 10-20 keV emission from the Arp 299 system. The lack of significant emission above 10 keV other than that attributed to Arp 299-B suggests that: a) any AGN in Arp 299-A must be heavily obscured ($N_{rm H}$ > 10^{24} cm^{-2}) or have a much lower luminosity than Arp 299-B and b) the extranuclear X-ray binaries have spectra that cut-off above ~10 keV. Such soft spectra are characteristic of ultraluminous X-ray (ULX) sources observed to date by NuSTAR.
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