VLA Observations of the Cambridge-Cambridge Rosat Survey

Ciliegi, P.; Elvis, M.; Wilkes, Belinda; Boyle, B. J.; McMahon, R. G.; Maccacaro, T.

doi:10.1007/978-94-009-0295-4_195

Cited by 10 publications

(22 citation statements)

References 5 publications

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“…On the other hand, the distribution of α OX of the hard sources is similar to that found in other AGN surveys (e.g. Wilkes et al 1994; Ciliegi et al 1995), with the majority of sources having .…”

Section: Resultssupporting

confidence: 84%

“…This is a large radio loud fraction per cent where errors are the Poisson 68 per cent confidence interval, Gehrels 1986) of the BLAGN, NELGs and galaxies compared to the fraction found in normal ROSAT surveys without spectral selection, e.g. Ciliegi et al (1995) found that only two of the eighty Cambridge–Cambridge ROSAT Serendipity Survey (CRSS) AGN and NELGs per cent) are radio loud. On the other hand, the distribution of α OX of the hard sources is similar to that found in other AGN surveys (e.g.…”

Section: Resultsmentioning

confidence: 97%

“…per cent in the EMSS, Della Ceca et al 1994) compared to fainter soft X‐ray surveys (e.g. per cent in the CRSS, Ciliegi et al 1995).…”

Section: Discussionmentioning

confidence: 96%

“…Schmidt et al (1998) argued that the NELGs are also AGN, but with low luminosity or obscured broad line regions. On an average, faint NELGs have harder X‐ray spectra with , Almaini et al 1996, Romero Colmenero et al 1996) than the broad line AGN which have mean (Ciliegi et al 1997, Mittaz et al 1999).…”

Section: Introductionmentioning

confidence: 99%

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A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources

Page

Mittaz

Carrera

2001

Monthly Notices of the Royal Astronomical Society

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We have surveyed 188 ROSAT Position Sensitive Proportional Counter (PSPC) fields for X‐ray sources with hard spectra (α<0.5); such sources must be major contributors to the X‐ray background at faint fluxes. In this paper we present optical identifications for 62 of these sources: 28 active galactic nuclei (AGN) which show broad lines in their optical spectra (BLAGN), 13 narrow emission line galaxies (NELGs), five galaxies with no visible emission lines, eight clusters and eight Galactic stars. The BLAGN, NELGs and galaxies have similar distributions of X‐ray flux and spectra. Their ROSAT spectra are consistent with their being AGN obscured by columns of 20.5< log(NH/cm−2)<23. The hard spectrum BLAGN have a distribution of X‐ray to optical ratios which is similar to that found for AGN from soft X‐ray surveys (1<αOX<2). However, a relatively large proportion (15 per cent) of the BLAGN, NELGs and galaxies are radio loud. This could be because the radio jets in these objects produce intrinsically hard X‐ray emission, or if their hardness is caused by absorption, it could be because radio‐loud objects are more X‐ray luminous than radio‐quiet objects. The eight hard sources identified as clusters of galaxies are the brightest, and softest group of sources and hence clusters are unlikely to be an important component of the hard, faint population. We propose that BLAGN are likely to constitute a significant fraction of the faint, hard, 0.5–2 keV population and could be important to reproducing the shape of the X‐ray background, because they are the most numerous type of object in our sample (comprising almost half the identified sources), and because all our high redshift (z>1) identified hard sources have broad lines.

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Section: Resultssupporting

confidence: 84%

Section: Resultsmentioning

confidence: 97%

“…per cent in the EMSS, Della Ceca et al 1994) compared to fainter soft X‐ray surveys (e.g. per cent in the CRSS, Ciliegi et al 1995).…”

Section: Discussionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources

Page

Mittaz

Carrera

2001

Monthly Notices of the Royal Astronomical Society

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“…For dilution of the nuclear spectrum by galaxy starlight to explain the optical characteristics of these sources, their nuclear components must have optical/X‐ray flux ratios which are smaller than the average for BLAGN. This however, is quite plausible if AGN with L 2–10 < 10 43 erg s −1 have a similar intrinsic scatter of optical/X‐ray flux ratios to the scatter found in more luminous BLAGN (∼0.5 dex; Ciliegi et al 1995). The lack of NELGs and galaxies to the right‐hand side of the dashed‐line region of Fig.…”

Section: Discussionmentioning

confidence: 92%

X-ray spectra of sources in the 13HXMM–Newton/Chandra deep field

Page¹,

Loaring²,

Dwelly³

et al. 2006

Monthly Notices of the Royal Astronomical Society

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We present the X‐ray spectra of 86 optically identified sources in the 13HXMM–Newton/Chandra deep field which have >70 X‐ray counts. The majority of these sources have 2–10 keV fluxes between 10−15 and 5 × 10−14 erg cm−2 s−1. The sample consists of 50 broad‐line active galactic nuclei (BLAGN), 25 narrow emission‐line galaxies (NELGs), six absorption‐line galaxies and five Galactic stars. The majority (42/50) of the BLAGN have X‐ray spectra which are consistent with a power‐law shape. They have a mean photon index 〈Γ〉= 2.0 ± 0.1 and an intrinsic dispersion σΓ= 0.4 ± 0.1. Three of the BLAGN show curved spectra, with more emission near the high‐ and low‐energy ends of the spectrum relative to the emission in the 1–2 keV range than can be reproduced by the power‐law model. Five BLAGN show a deficit of soft X‐rays, indicating absorption. We consider a source to be significantly absorbed if a power‐law model fit is rejected with >99 per cent confidence and an absorbed power‐law model produces an acceptable fit, or if the best‐fitting power law is abnormally hard (Γ < 1). Significant absorption is more common in the NELGs (13/25) and absorption‐line galaxies (2/6) than in the BLAGN (5/50), but is not universal in any of these classes of object. The majority of the 20 absorbed sources have X‐ray spectra consistent with a simple cold photoelectric absorber, but a significant minority (6/20) require more complex models with either an additional component of soft X‐ray emitting plasma, or an ionized absorber. Of the 16 narrow emission‐ and absorption‐line galaxies which do not show evidence for X‐ray absorption, only two objects are likely to be powered by star formation, and both have 2–10 keV X‐ray luminosities of ≤ 1040 erg s−1. The X‐ray emission in the other 14 unabsorbed NELGs and galaxies is most likely powered by AGN, which are not detected in the optical because they are outshone by their luminous host galaxies. The Galactic stars show multitemperature thermal spectra which peak between 0.5 and 1 keV. Star/AGN discrimination is possible for four of the five stars solely from their X‐ray spectra.

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Deep radio imaging of the SCUBA 8-mJy survey fields: submillimetre source identifications and redshift distribution

Ivison¹,

Greve²,

Smail³

et al. 2002

Monthly Notices of the Royal Astronomical Society

335

157

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The SCUBA 8-mJy survey is the largest submillimetre (submm) extragalactic mapping survey undertaken to date, covering 260 arcmin 2 to a 4σ detection limit of 8 mJy at 850 µm, centred on the Lockman Hole and ELAIS N2 regions. Here, we present the results of new 1.4-GHz imaging of these fields, of the depth and resolution necessary to reliably identify radio counterparts for 18 of 30 submm sources, with possible detections of a further 25 per cent. Armed with this greatly improved positional information, we present and analyse new optical, near-infrared (near-IR) and XMM-Newton X-ray imaging to identify optical/IR host galaxies to half of the submm-selected sources in those fields. As many as 15 per cent of the submm sources detected at 1.4 GHz are resolved by the 1.4-arcsec beam and a further 25 per cent have more than one radio counterpart, suggesting that radio and submm emission arise from extended starbursts and that interactions are common. We note that less than a quarter of the submm-selected sample would have been recovered by targeting optically faint radio sources, underlining the selective nature of such surveys. At least 60 per cent of the radio-confirmed optical/IR host galaxies appear to be morphologically distorted; many are composite systems -red galaxies with relatively blue companions; just over one half are found to be very red (I − K > 3.3) or extremely red (I − K > 4); contrary to popular belief, most are sufficiently bright to be tackled with spectrographs on 8-m telescopes. We find one submm source which is associated with the steep-spectrum lobe of a radio galaxy, at least two more with flatter radio spectra typical of radio-loud active galactic nuclei (AGN), one of them variable. The latter is amongst four sources (≡15 per cent of the full sample) with X-ray emission consistent with obscured AGN, though the AGN would need to be Compton thick to power the observed far-IR luminosity. We exploit our well-matched radio and submm data to estimate the median redshift of the S 850 µm ∼ 8 mJy submm galaxy population. If the radio/far-IR correlation holds at high redshift, and our sample is unbiased, we derive a conservative limit of z 2.0, or 2.4 using spectral templates more representative of known submm galaxies.

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VLA Observations of the Cambridge-Cambridge Rosat Survey

Cited by 10 publications

References 5 publications

A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources

A survey of hard spectrum ROSAT sources - II. Optical identification of hard sources

X-ray spectra of sources in the 13HXMM–Newton/Chandra deep field

Deep radio imaging of the SCUBA 8-mJy survey fields: submillimetre source identifications and redshift distribution

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