Search

We use the photoionization codecloudy to determine both the location and the kinematics of the optical forbidden, high-ionization line (hereafter, FHIL) emitting gas in the narrow line Seyfert 1 galaxy Ark 564. The results of our models are compared with the observed properties of these emission lines to produce a physical model that is used to explain both the kinematics and the source of this gas. The main features of this model are that the FHIL emitting gas is launched from the putative dusty torus and is quickly accelerated to its terminal velocity of a few hundred km s−1. Iron-carrying grains are destroyed during this initial acceleration. This velocity is maintained by a balance between radiative forces and gravity in this super-Eddington source. Eventually the outflow is slowed at large radii by the gravitational forces of and interactions with the host galaxy. In this model, FHIL emission traces the transition between the active galactic nucleus (AGN) and bulge zones of influence. [ABSTRACT FROM AUTHOR]

Based on a new spectroscopic sample observed using the William Herschel Telescope, we examine the kinematic properties of the various emission-line regions in narrow-line Seyfert 1 galaxies (NLS1s) by modelling their profiles using multiple component fits. We interpret these results by comparison with velocity components observed for different lines species covered in the same spectrum, and equivalent components measured in the spectra of some broad-line Seyfert 1s and a representative Seyfert 2 galaxy. We find that the fits to the Hα and Hβ line profiles in NLS1s require an additional broad (≳3000 km s−1) component that might correspond to a suppressed broad-line region (BLR) with similar kinematics to those of typical broad-line Seyfert 1s. From the profiles of the forbidden high-ionization lines (FHILs) in NLS1s, we find evidence that they appear to trace an ‘intermediate’ velocity region with kinematics between the standard broad and narrow-line regions. Weaker evidence of this region is also present in the profiles of the permitted Balmer lines. Finally, we note that despite having similar ionization potentials, the relative intensities of the highly ionized lines of [Fe x]λ6374 and [Fe xi]λ7892 show considerable dispersion from one galaxy to another. The interpretation of this requires further modelling, but suggests the possibility of using the ratio as a diagnostic to constrain the physical conditions of the FHIL emitting region and possibly the shape of the spectral energy distribution in the vicinity of 200 eV. This spectral region is very difficult to observe directly due to photoelectric absorption both in our Galaxy and intrinsic to the source. [ABSTRACT FROM AUTHOR]

We present the global X-ray properties of the point source population in the grand-design spiral galaxy M101, as seen withXMM–Newton. 108 X-ray sources are detected within the D25 ellipse of M101, of which∼24 are estimated to be background galaxies. Multiwavelength cross-correlations show that 20 sources are coincident with H iiregions and/or supernova remnants (SNRs), seven have identified/candidate background galaxy counterparts, six are coincident with foreground stars and one has a radio counterpart. While the spectral and timing properties of the brightest sources were presented by Jenkins et al., here we apply an X-ray colour classification scheme to split the entire source population into different types, i.e. X-ray binaries (XRBs), SNRs, absorbed sources, background sources and supersoft sources (SSSs). Approximately 60 per cent of the population can be classified as XRBs, although there is source contamination from background active galactic nuclei (AGN) in this category as they have similar spectral shapes in the X-ray regime. 15 sources have X-ray colours consistent with SNRs, three of which correlate with known SNR/H iiradio sources. Another two are promising new candidates for SNRs, one is unidentified, and the remainder are a mixture of foreground stars, bright soft XRBs and AGN candidates. We also detect 14 candidate SSSs, with significant detections in the softest X-ray band (0.3–1 keV) only. 16 sources display short-term variability during theXMM–Newtonobservation, twelve of which fall into the XRB category, giving additional evidence of their accreting nature. Using archivalChandraandROSATHigh Resolution Imager data, we find that∼40 per cent of theXMMsources show long-term variability over a baseline of up to∼10 yr, and eight sources display potential transient behaviour between observations. Sources with significant flux variations between theXMMandChandraobservations show a mixture of softening and hardening with increasing luminosity. The spectral and timing properties of the sources coincident with M101 confirm that its X-ray source population is dominated by accreting XRBs. [ABSTRACT FROM AUTHOR]

We present XMM-Newton EPIC observations of the two nearby starburst merger galaxies NGC 3256 and NGC 3310. The broad-band (0.3–10 keV) integrated X-ray emission from both galaxies shows evidence of multiphase thermal plasmas plus an underlying hard non- thermal power-law continuum. NGC 3256 is well fitted with a model comprising two MEKAL components (kT = 0.6⁄0.9 keV) plus a hard power law (Γ = 2), while NGC 3310 has cooler MEKAL components (kT = 0.3⁄0.6 keV) and a harder power-law tail (Γ = 1.8). Chandra observations of both galaxies reveal the presence of numerous discrete sources embedded in the diffuse emission, which dominate the emission above ∼2 keV and are likely to be the source of the power-law emission. The thermal components show a trend of increasing absorption with higher temperature, suggesting that the hottest plasmas arise from supernova-heated gas within the discs of the galaxies, while the cooler components arise from outflowing galactic winds interacting with the ambient interstellar medium. We find no strong evidence for an active galactic nucleus in either galaxy. [ABSTRACT FROM AUTHOR]

We report the results of a programme of dual-epoch Chandra ACIS-S observations of five ultraluminous X-ray sources (ULXs) in nearby spiral galaxies. All five ULXs are detected as unresolved, point-like X-ray sources by Chandra, though two have faded below the 1039 erg s−1 luminosity threshold used to first designate these sources as ULXs. Using this same criterion, we detect three further ULXs within the imaged regions of the galaxies. The ULXs appear to be related to the star-forming regions of the galaxies, indicating that even in normal spiral galaxies the ULX population is predominantly associated with young stellar populations. A detailed study of the Chandra ACIS-S spectra of six of the ULXs shows that five are better described by a power-law continuum than a multicolour disc blackbody model, though there is evidence for additional very soft components to two of the power-law continua. The measured photon indices in four out of five cases are consistent with the low/hard state in black hole binaries, contrary to the suggestion that power-law-dominated spectra of ULXs originate in the very high state. A simple interpretation of this is that we are observing accretion on to intermediate-mass black holes, though we might also be observing a spectral state unique to very high mass accretion rates in stellar-mass black hole systems. Short-term flux variability is only detected in one of two epochs for two of the ULXs, with the lack of this characteristic arguing that the X-ray emission of this sample of ULXs is not dominated by relativistically beamed jets. The observational characteristics of this small sample suggest that ULXs are a distinctly heterogeneous source class. [ABSTRACT FROM AUTHOR]

ABSTRACT We report the results of an observation of a large-diameter (110 pc) supernova remnant (SNR) found to encircle the position of the ultraluminous X-ray source (ULX) IC 342 X-1. The inferred initial energy input to the SNR is at least 2–3 times greater than the canonical energy for an ‘ordinary’ SNR. Two regions on the inside of the shell are bright in [Oiii]λ5007 emission, possibly as the result of X-ray photoionization by the ULX. If this is the case, then the morphology of this nebulosity implies that the X-ray emission from the ULX is anisotropic. The presence of the ULX, most probably a black hole X-ray binary, within an unusually energetic SNR suggests that we may be observing the aftermath of a gamma-ray burst, although other origins for the energetic nebula are discussed. [ABSTRACT FROM AUTHOR]

We report the results of a 20-ks Chandra ACIS-S observation of the galaxy pair NGC 4485/4490. This is an interacting system containing a late-type spiral with an enhanced star formation rate (NGC 4490), and an irregular companion that possesses a disturbed morphology. A total of 29 discrete X-ray sources are found coincident with NGC 4490, but only one is found within NGC 4485. The sources range in observed X-ray luminosity from ∼ 2 × 10[sup 37] to 4 × 10[sup 39] erg s[sup -1]. The more luminous sources appear, on average, to be spectrally harder than the fainter sources, an effect that is attributable to increased absorption in their spectra. Extensive diffuse X-ray emission is detected coincident with the disc of NGC 4490, and in the tidal tail of NGC 4485, which appears to be thermal in nature and hence the signature of a hot interstellar medium in both galaxies. However, the diffuse component accounts for only ∼10 per cent of the total X-ray luminosity of the system (2 × 10[sup 40] erg s[sup -1], 0.5-8 keV), which arises predominantly in a handful of the brightest discrete sources. This diffuse emission fraction is unusually low for a galaxy pair which has many characteristics that would lead it to be classified as a starburst system, possibly as a consequence of the small gravitational potential well of the system. The discrete source population, on the other hand, is similar to that observed in other starburst systems, possessing a flat luminosity function slope of ∼ -0.6 and a total of six ultraluminous X-ray sources (ULX). Five of the ULX are identified as probable black hole X-ray binary systems, and the sixth (which is coincident with a radio continuum source) is identified as an X-ray luminous supernova remnant. The ULX all lie in star formation regions, providing further evidence of the link between the ULX phenomenon and active star formation. Importantly, this shows that even in star-forming regions, the ULX... [ABSTRACT FROM AUTHOR]

We present high spatial resolution X-ray Chandra HRC and HST WFPC2 Hα observations of the prototypical infrared-luminous galaxy NGC 6240. The central region of this system shows a remarkably complex morphology, with filaments and loops observed in the optical and X-rays. The total X-ray luminosity is dominated by the extended emission. Both nuclei are clearly detected in the HRC image and both appear to be extended. The energetics of the nuclei imply that the southern nucleus is the more plausible counterpart to the obscured active galactic nucleus. The overall spectral energy distribution of the galaxy is in good agreement with a blend of starburst and AGN components that have similar bolometric luminosities, Lbol ∼ 5 × 10[sup 45] erg s[sup -1], with the starburst dominating the observed continuum in the nearinfrared (K band), optical and soft X-ray bands. [ABSTRACT FROM AUTHOR]

Details XMM-Newton observations and spectral fitting of two high-redshift, luminous, narrow-line radio galaxies, B3 0731+438 and 3C 257. X-ray continua well fitted by a partial covering model with intrinsically unabsorbed and absorbed power-law components; Spectral models indicating that both objects harbor highly obscured nuclei; Large intrinsic luminosities seen.