The X-ray spectra of the extragalactic sources in the Einstein extended medium sensitivity survey

Maccacaro, T.; Gioia, I. M.; Wolter, A.; Zamorani, G.; Stocke, John T.

doi:10.1086/166127

Cited by 398 publications

(442 citation statements)

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“…Finally, a useful parameter used to discriminate between different classes of X-ray sources is the X-ray-to-optical flux ratio (see Maccacaro et al 1988, hereafter X/O). In this paper, we defined the X-ray to optical flux ratio using the observed X-ray flux in the 0.5−4.5 keV energy range and the optical r(S DS S ) band flux (for the appropriate conversion factors see Fukugita et al 1995).…”

Section: Optical Versus X-ray Propertiesmentioning

confidence: 99%

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1 s

Castelló-Mor

Barcons

Ballo

et al. 2012

A&A

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Context. The optical and ultraviolet emission lines of galaxies are widely used to distinguish star-forming (SF) galaxies from active galactic nuclei (AGNs). However, this type of diagnostic has some associated uncertainties, because AGNs can be of low luminosity and/or heavily obscured, and the optical emission lines may be dominated by a stellar component. On the other hand, and despite its limitations, X-ray emission can be used as a reliable tracer of luminous AGNs. Several well-studied examples exist where the optical diagnostics are indicative of SF galaxy, but the X-ray properties reveal the presence of an AGN. Aims. We aim to characterize the nature of galaxies whose optical emission line diagnostics are consistent with star formation, but whose X-ray properties strongly point towards the presence of an AGN. Understanding these sources is of particular importance in assessing the completeness of AGN samples derived from large galaxy surveys, selected solely on the basis of their optical spectral properties. Methods. We construct a large sample of 211 narrow emission line galaxies (NELGs, which have full widths at half maximum (FWHMs) H β emission line <1200 km s −1 ) from the SDSS-DR7 galaxy spectroscopic catalogue, for which we are able to construct a classical diagnostic diagram, [OIII]/H β versus [NII]/H α (hence z < 0.4), and that are also detected in the 2−10 keV X-ray band and present in the 2XMM X-ray source catalogue. This sample offers a large database by which to investigate potential mismatches between optical diagnostics and X-ray emission. Results. Among these 211 objects, which based on our selection criteria all are all at z < 0.4, we find that 145 galaxies are diagnosed as AGNs, having 2−10 keV X-ray luminosities that span a wide range, from 10 40 erg/s to above 10 44 erg/s. Out of the remaining 66 galaxies, which are instead diagnosed as "star-forming", we find a bimodal distribution in which 28 have X-ray luminosities in excess of 10 42 erg/s, large thickness parameters (T = F 2−10 keV /F [OIII] > 1) and large X-ray to optical flux ratios (X/O > 0.1), while the rest are consistent with being simply starforming galaxies. Those 28 galaxies exhibit the broadest H β line widths (FWHMs from ∼300 to 1200 km s −1 ), and their X-ray spectrum is steeper than average and often displays a soft excess. Conclusions. We therefore conclude that the population of X-ray luminous NELGs with optical lines consistent with those of a starforming galaxy (which represent 19% of our whole sample) is largely dominated by narrow line Seyfert 1s (NLS1s). The occurrence of such sources in the overall optically selected sample is small (<2%), hence the contamination of optically selected galaxies by NLS1s is very small.

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Section: Optical Versus X-ray Propertiesmentioning

confidence: 99%

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1 s

Castelló-Mor

Barcons

Ballo

et al. 2012

A&A

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“…To obtain astrometrically-corrected positions we selected optical sources, with proper-motion corrected positions, from the USNO-B1.0 catalogue (Monet et al 2003), and checked that only one optical source was in the error circle of the corresponding X-ray source. We only accepted sources correlating with globular clusters from the Revised Bologna Catalogue (V.3.4, January 2008; Galleti et al 2004Galleti et al , 2005Galleti et al , 2006Galleti et al , 2007 or with foreground stars, characterized by their optical to X-ray flux ratio (Maccacaro et al 1988) and their hardness ratio (see Stiele et al 2008). We then used the XMMSAS task eposcorr to derive the offset of the X-ray aspect solution.…”

Section: X-ray Observations and Data Analysismentioning

confidence: 99%

The first two transient supersoft X-ray sources in M 31 globular clusters and the connection to classical novae

Henze

Pietsch

Haberl

et al. 2009

A&A

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Context. Classical novae (CNe) have been found to represent the major class of supersoft X-ray sources (SSSs) in our neighbour galaxy M 31. Aims. We determine the properties and evolution of the two first SSSs ever discovered in the M 31 globular cluster (GC) system. Methods. We have used XMM-Newton, Chandra and Swift observations of the centre region of M 31 to discover both SSSs and to determine their X-ray light curves and spectra. We performed detailed analysis of XMM-Newton EPIC PN spectra of the source in Bol 111 (SS1) using blackbody and NLTE white dwarf (WD) atmosphere models. For the SSS in Bol 194 (SS2) we used optical monitoring data to search for an optical counterpart. Results. Both GC X-ray sources were classified as SSS. We identify SS1 with the CN M31N 2007-06b recently discovered in the M 31 GC Bol 111. For SS2 we did not find evidence for a recent nova outburst and can only provide useful constraints on the time of the outburst of a hypothetical nova. Conclusions. The only known CN in a M 31 GC can be identified with the first SSS found in a M 31 GC. We discuss the impact of our observations on the nova rate for the M 31 GC system.

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“…We carried out photometry at the X-ray positions and 11 Using the same zero points as Giavalisco et al (2004). present the ACS upper limits and near-IR detections in Table 1. To further investigate the nature of these sources, we examine the relationship between their X-ray and optical fluxes (e.g., Maccacaro et al 1988;Stocke et al 1991). In Figure 2 we plot versus for all the X-ray sources, including the ACS F z 0.5-8 keV 850…”

Section: Observations and Sample Descriptionmentioning

confidence: 99%

A Possible New Population of Sources with Extreme X-Ray/Optical Ratios

Koekemoer¹,

Alexander²,

Bauer³

et al. 2004

ApJ

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We describe a possible new class of X-ray sources that have robust detections in ultradeep Chandra data yet have no detections at all in our deep multiband Great Observatories Origins Deep Survey Hubble Space Telescope Advanced Camera for Surveys (ACS) images, which represent the highest quality optical imaging obtained to date on these fields. These extreme X-ray/optical ratio sources (EXOs) have values of at least an order F /F X opt of magnitude above those generally found for other active galactic nuclei (AGNs), even those that are harbored by reddened hosts. We thus infer two possible scenarios: (1) if these sources lie at redshifts , then their z Շ 6 hosts need to be exceedingly underluminous or more reddened, compared with other known sources, or (2) if these sources lie above , such that even their Lya emission is redshifted out of the bandpass of our ACS z ∼ 6-7 filter, then their optical and X-ray fluxes can be accounted for in terms of relatively normal ∼L * hosts and z 850 moderate-luminosity AGNs.

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The X-ray spectra of the extragalactic sources in the Einstein extended medium sensitivity survey

Cited by 398 publications

References 0 publications

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1 s

The X-ray luminous galaxies optically classified as star forming are mostly narrow line Seyfert 1 s

The first two transient supersoft X-ray sources in M 31 globular clusters and the connection to classical novae

A Possible New Population of Sources with Extreme X-Ray/Optical Ratios

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