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Register a new userResolving the Ultra-Luminous X-ray Sources in the Ly$alpha$ Emitting Galaxy Haro 11
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Lyman continuum and line emission are thought to be important agents in the reionization of the early universe. Haro 11 is a rare example of a local galaxy in which Ly$alpha$ and continuum emission have escaped without being absorbed or scattered by ambient gas and dust, potentially as a consequence of feedback from its X-ray sources. We build on our previous Chandra analysis of Haro 11 by analyzing three new observations. Our subpixel spatial analysis reveals that the two previously known X-ray sources are each better modelled as ensembles of at least 2 unresolved point sources. The spatial variability of these components reveals X1 as a dynamical system where one luminous X-ray source ($L_{rm X} sim 10^{41}$ erg s$^{-1}$) fades as a secondary source begins to flare. These might be intermediate mass black holes or low luminosity active galactic nuclei near the center of the galaxy in the process of merging. Optical emission line diagnostics drawn from the literature suggest that while the galaxy as a whole is consistent with starburst signatures of ionization, the individual regions wherein the X-ray sources reside are more consistent with AGN/composite classification. The sources in X2 exhibit some degree of flux variability. X2a dominates the flux of this region during most observations ($L_{rm X} sim 6 times 10^{40}$ erg s$^{-1}$), and gives the only evidence in the galaxy of a soft Ultra-Luminous X-ray source capable of high energy winds, which we suggest are responsible for allowing the coincident Ly$alpha$ emission to escape.
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Low-metallicity (Z <~ 0.05 Zsun) massive (>~40 Msun) stars might end their life by directly collapsing into massive black holes (BHs, 30 <~ m_BH/Msun <~ 80). More than ~10^5 massive BHs might have been generated via this mechanism in the metal-poor ring galaxy Cartwheel, during the last ~10^7 yr. We show that such BHs might power most of the ultra-luminous X-ray sources (ULXs) observed in the Cartwheel. We also consider a sample of ULX-rich galaxies and we find a possible anti-correlation between the number of ULXs per galaxy and the metallicity in these galaxies. However, the data are not sufficient to draw any robust conclusions about this anti-correlation, and further studies are required.
Many upcoming surveys, particularly in the radio and optical domains, are designed to probe either the temporal and/or the spatial variability of a range of astronomical objects. In the light of these high resolution surveys, we review the subject of ultra-luminous X-ray (ULX) sources, which are thought to be accreting black holes for the most part. We also discuss the sub-class of ULXs known as the hyper-luminous X-ray sources, which may be accreting intermediate mass black holes. We focus on some of the open questions that will be addressed with the new facilities, such as the mass of the black hole in ULXs, their temporal variability and the nature of the state changes, their surrounding nebulae and the nature of the region in which ULXs reside.
We present far infrared (FIR) spectroscopy of the luminous blue compact galaxy (BCG) Haro 11 (ESO 350-IG38) obtained with the ISO Long Wavelength Spectrometer (LWS) in low resolution mode. This metal poor dwarf merger is an extremely hot IRAS source with a high [CII]158um/CO(1-0) flux ratio. We discuss the balance between dust and line cooling in the photodissociated regions (PDR), in particular the role of the [CII] line, and derive the basic properties of the PDR gas. While samples of other starburst galaxies show a correlation between the [CII]/FIR flux ratio and the IRAS f60/f100 ratio, Haro 11 deviates significantly from this relationship being brighter in [CII] than average. We propose that the relationship is caused by an increasing optical depth with increasing IRAS temperature but that the low metallicity and the extreme starburst properties of Haro 11 allow the medium to be thin despite its high f60/f100 ratio, explaining the [CII] excess. This leaves room for a more optimistic view on the possibilities to detect massive starforming mergers at high redshifts, using the [CII] line.
Ultra-luminous X-ray sources (ULXs) are off-nuclear X-ray sources in nearby galaxies with X-ray luminosities $geq$ 10$^{39}$ erg s$^{-1}$. The measurement of the black hole (BH) masses of ULXs is a long-standing problem. Here we estimate BH masses in a sample of ULXs with XMM-Newton observations using two different mass indicators, the X-ray photon index and X-ray variability amplitude based on the correlations established for active galactic nuclei (AGNs). The BH masses estimated from the two methods are compared and discussed. We find that some extreme high-luminosity ($L_{rm X} >5times10^{40}$ erg s$^{-1}$) ULXs contain the BH of 10$^{4}$-10$^{5}$ $M_odot$. The results from X-ray variability amplitude are in conflict with those from X-ray photon indices for ULXs with lower luminosities. This suggests that these ULXs generally accrete at rates different from those of X-ray luminous AGNs, or they have different power spectral densities of X-ray variability. We conclude that most of ULXs accrete at super-Eddington rate, thus harbor stellar-mass BH.
The nature of ultra-luminous X-ray sources (ULXs), which are off-nuclear extragalactic X-ray sources that exceed the Eddington luminosity for a stellar-mass black hole, is still largely unknown. They might be black hole X-ray binaries in a super-Eddington accretion state, possibly with significant beaming of their emission, or they might harbor a black hole of intermediate mass (10^2 to 10^5 solar masses). Due to the enormous amount of energy radiated, ULXs can have strong interactions with their environment, particularly if the emission is not beamed and if they host a massive black hole. We present early results of a project that uses archival Herschel infrared observations of galaxies hosting bright ULXs in order to constrain the nature of the environment surrounding the ULXs and possible interactions. We already observe a spatial correlation between ULXs and dense clouds of cold material, that will be quantified in subsequent work. Those observations will allow us to test the similarities with the environment of Galactic high mass X-ray binaries. This project will also shed light on the nature of the host galaxies, and the possible factors that could favor the presence of a ULX in a galaxy.
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