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ABSTRACT: This paper describes the design and implementation of a facility simulator
for the 4 metre Multi-Object Spectroscopic Telescope (4MOST) project, a new
survey instrument proposed for the ESO VISTA telescope. The 4MOST Facility
Simulator (4FS) has several roles, firstly to optimise the design of the
instrument, secondly to devise a survey strategy for the wide field design
reference surveys that are proposed for 4MOST, and thirdly to verify that
4MOST, as designed, can indeed achieve its primary science goals. We describe
the overall structure of the 4FS, together with details of some important 4FS
subsystems. We present the initial results from the 4FS which illustrate
clearly the value of having a functioning facility simulator very early in the
conceptual design phase of this large project.
08/2012;
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ABSTRACT: We present here photometric redshift confirmation of the presence of large-scale structure around the z= 1.82 quasi-stellar object (QSO) RX J0941, which shows an overdensity of submillimetre (submm) sources. Radio imaging confirms the presence of the submm sources and pinpoints their likely optical near-infrared (NIR) counterparts. Four of the five submm sources present in this field (including the QSO) have counterparts with redshifts compatible with z= 1.82. We show that our photometric redshifts are robust against the use of different spectral templates. We have measured the galaxy stellar mass of the submm galaxies from their rest-frame K-band luminosity obtaining log(M*/M⊙) ∼ 11.5 ± 0.2, slightly larger than the Schechter mass of present-day galaxies, and hence indicating that most of the stellar mass is already formed. We present optical-to-radio spectral energy distributions (SEDs) of the five Submillimetre Common-User Bolometer Array (SCUBA) sources. The emission of RX J0941 is dominated by reprocessed active galactic nucleus (AGN) emission in the observed mid-IR (MIR) range, while the starburst contribution completely dominates in the submm range. The SEDs of the other three counterparts are compatible with a dominant starburst contribution above ∼24 μm, with star formation rates ∼2000 M⊙ yr−1, central dust masses log(Mdust/M⊙) ∼ 9 ± 0.5 and hence central gas masses log(Mgas/M⊙) ∼ 10.7. There is very little room for an AGN contribution. From X-ray upper limits and the observed 24 μm flux, we derive a maximum 2–10 keV X-ray luminosity of 1044 erg s−1 for any putative AGN, even if they are heavily obscured. This in turn points to relatively small black holes with log(M•/M⊙) ≲ 8 and hence stellar-to-black hole mass ratios about 1 order of magnitude higher than those observed in the present Universe: most of their central black hole masses are still to be accreted. Local stellar-to-black hole mass ratios can be reached if ∼1.3 per cent of the available nuclear gas mass is accreted.
Monthly Notices of the Royal Astronomical Society 03/2011; 413(4):2791 - 2807. · 4.90 Impact Factor
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ABSTRACT: We present here photometric redshift confirmation of the presence of large
scale structure around the z=1.82 QSO RXJ0941, which shows an overdensity of
submm sources. Radio imaging confirms the presence of the submm sources and
pinpoints their likely optical-NIR counterparts. Four of the five submm sources
present in this field (including the QSO) have counterparts with redshifts
compatible with z=1.82. We show that our photometric redshifts are robust
against the use of different spectral templates. We have measured the galaxy
stellar mass of the submm galaxies from their rest-frame K-band luminosity
obtaining log(M*/Msun)~11.5+-0.2, slightly larger than the Schechter mass of
present day galaxies, and hence indicating that most of the stellar mass is
already formed. We present optical-to-radio spectral energy distributions
(SEDs) of the five SCUBA sources. The emission of RXJ0941 is dominated by
reprocessed AGN emission in the observed MIR range, while the starburst
contribution completely dominates in the submm range. The SEDs of the other
three counterparts are compatible with a dominant starburst contribution above
~24um, with star formation rates SFR~2000Msun/yr, central dust masses
log(Mdust/Msun)~9+-0.5 and hence central gas masses log(Mgas/Msun)~10.7. There
is very little room for an AGN contribution. From X-ray upper limits and the
observed 24um flux, we derive a maximum 2-10keV X-ray luminosity of 1e44 erg/s
for any putative AGN, even if they are heavily obscured. This in turn points to
relatively small black holes with log(MBH/Msun)<~8 and hence stellar-to-black
hole mass ratios about one order of magnitude higher than those observed in the
present Universe: most of their central black hole masses are still to be
accreted. Local stellar-to-black hole masses ratios can be reached if ~1.3% of
the available nuclear gas mass is accreted.
01/2011;
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ABSTRACT: We present the results of a multi‐wavelength analysis of the properties of a sample of 86 X‐ray selected AGN. X‐ray flux and optical magnitude are strongly correlated in broad‐line AGN (BLAGN) as expected from the unified model. Narrow emission line galaxies (NELGs), however, display a wide range in optical brightnesses for a given X‐ray flux, which we attribute to varying amounts of obscuration and host galaxy contamination. We find that more luminous AGN and increasingly softer X‐ray AGN show redder mid infrared power law slopes in their spectra between 3.6 and 8 μm. The power law slope between 3.6 and 24 μm is however uncorrelated with X‐ray luminosity and X‐ray spectral index.
AIP Conference Proceedings. 07/2010; 1248(1):463-464.
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ABSTRACT: In this paper we examine the contribution of galaxies with different infrared (IR) spectral energy distributions (SEDs) to the comoving infrared luminosity density, a proxy for the comoving star formation rate (SFR) density. We characterise galaxies as having either a cold or hot IR SED depending upon whether the rest-frame wavelength of their peak IR energy output is above or below 90um. Our work is based on a far-IR selected sample both in the local Universe and at high redshift, the former consisting of IRAS 60um-selected galaxies at z<0.07 and the latter of Spitzer 70um selected galaxies across 0.1<z<1. We find that the total IR luminosity densities for each redshift/luminosity bin agree well with results derived from other deep mid/far-IR surveys. At z<0.07 we observe the previously known results: that moderate luminosity galaxies (L_IR<10^11 Lsun) dominate the total luminosity density and that the fraction of cold galaxies decreases with increasing luminosity, becoming negligible at the highest luminosities. Conversely, above z=0.1 we find that luminous IR galaxies (L_IR>10^11 Lsun), the majority of which are cold, dominate the IR luminosity density. We therefore infer that cold galaxies dominate the IR luminosity density across the whole 0<z<1 range, hence appear to be the main driver behind the increase in SFR density up to z~1 whereas local luminous galaxies are not, on the whole, representative of the high redshift population. Comment: 5 pages, 3 figures, accepted for publication in MNRAS
11/2009;
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ABSTRACT: In order to examine the far-IR/radio correlation at high redshift we have studied the Spitzer 70um/far-infrared (far-IR) properties of sub-mJy radio sources from the 13^H XMM-Newton/Chandra Deep Field by redshift and galaxy type: active galactic nucleus (AGN) or star forming galaxy (SFG). We directly detect 70um counterparts (at >3sigma significance) for 22.5% (92/408) of the radio sources, while for the rest we perform stacking analysis by redshift and galaxy type. For the sources detected at 70um we find that the median and scatter of the observed flux density ratio, q70, are similar to previous results in the literature, but with a slight decrease in q70 towards higher redshifts. Of the radio sources detected at 70um 8/92 were already classified as AGN, but two of which maybe SFGs. For the stacked sources we obtain a detection for the SFGs at every redshift bin which implies they have mean flux densities a factor ~5 below the original 70um detection limit. For the stacked AGN we obtain a detection only in our highest redshift bin (1<~z<~5) where we may be sampling hot dust associated with the AGN at rest-frame 12-35um. The combined observed mean value of q70 for the SFGs (detected and non-detected at 70um) decreases gradually with redshift, consistent with tracks derived from empirical spectral energy distributions (SEDs) of local SFGs. Upon closer inspection and when comparing with tracks of appropriate luminosity, the values of q70 broadly agree at low redshift. However, at z~1, the observed q70 (for ULIRGs) is 2sigma below the value seen for local ULIRGs tracks, implying a difference in the SED between local and z~1 ULIRGs. At higher redshifts, the convergence of the tracks and the higher uncertainties in q70 do not allow us to determine if such a difference persists. Comment: 10 pages, 4 figures, accepted for publication in MNRAS
06/2009;
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ABSTRACT: We show that the far-IR properties of distant Luminous and Ultraluminous InfraRed Galaxies (LIRGs and ULIRGs) are on average divergent from analogous sources in the local Universe. Our analysis is based on Spitzer MIPS and IRAC data of L_IR>10^10 L_solar, 70um-selected objects in the 0.1<z<2 redshift range and supported by a comparison with the IRAS Bright Galaxy Sample. The majority of the objects in our sample are described by Spectral Energy Distributions (SEDs) which peak at longer wavelengths than local sources of equivalent total infrared luminosity. This shift in SED peak wavelength implies a noticeable change in the dust and/or star-forming properties from z~0 to the early Universe, tending towards lower dust temperatures, indicative of strong evolution in the cold dust, `cirrus', component. We show that these objects are potentially the missing link between the well-studied local IR-luminous galaxies, Spitzer IR populations and SCUBA sources -- the z<1 counterparts of the cold z>1 SubMillimetre Galaxies (SMGs) discovered in blank-field submillimetre surveys. The Herschel Space Observatory is well placed to fully characterise the nature of these objects, as its coverage extends over a major part of the far-IR/submm SED for a wide redshift range. Comment: 13 pages, 7 figures, accepted for publication in MNRAS
05/2009;
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ABSTRACT: Broad absorption line quasars (commonly termed BALQSOs) contain the most dramatic examples of AGN-driven winds. The high absorbing columns in these winds, ~10^24 cm^-2, ensure that BALQSOs are generally X-ray faint. This high X-ray absorption means that almost all BALQSOs have been discovered through optical surveys, and so what little we know about their X-ray properties is derived from very bright optically-selected sources. A small number of X-ray selected BALQSOs (XBALQSOs) have, however, recently been found in deep X-ray survey fields. In this paper we investigate the X-ray and rest-frame UV properties of five XBALQSOs for which we have obtained XMM-Newton EPIC X-ray spectra and deep optical imaging and spectroscopy. We find that, although the XBALQSOs have an alpha_ox steeper by ~0.5 than normal QSOs, their median alpha_ox is nevertheless flatter by 0.30 than that of a comparable sample of optically selected BALQSOs (OBALQSOs). We rule out the possibility that the higher X-ray to optical flux ratio is due to intrinsic optical extinction. We find that the amount of X-ray and UV absorption due to the wind in XBALQSOs is similar, or perhaps greater than, the corresponding wind absorption in OBALQSOs, so the flatter alpha_ox cannot be a result of weaker wind absorption. We conclude that these XBALQSOs have intrinsically higher X-ray to optical flux ratios than the OBALQSO sample with which we compare them.
09/2008;
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ABSTRACT: We have used several different methods (radio morphology, radio spectral index, mid-IR to radio and near-IR to radio flux density ratios) to discriminate between AGN and SFGs in faint, sub-mJy radio surveys. We find that the latter two methods are the most powerful with current multi-wavelength data, but that future radio surveys with eMERLIN, LOFAR etc. (and ultimately the SKA) will greatly increase the power of the morphology and spectral index methods. As an example of the science possible we derive the IR luminosity density from the radio-selected SFGs using the radio/IR luminosity correlation. We also examine the contribution by luminosity to the total IR luminosity density and find evidence that fraction of LIRGs remains constant or decreases above z=1 while the relative fraction of ULIRGs continues to increase up to z=2.5.
06/2008;
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ABSTRACT: Discerning the exact nature of the sub-mJy radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep ground based optical follow-up and observations from the Spitzer Space Telescope we are able to disentangle the radio-selected Active Galactic Nuclei (AGN) and Star Forming Galaxy (SFG) populations for the first time in a deep multi-frequency VLA/MERLIN Survey of the 13^H XMM-Newton/Chandra Deep Field. The discrimination diagnostics include radio morphology, radio spectral index, radio/near-IR and mid-IR/radio flux density ratios. We are now able to calculate the extragalactic Euclidean normalised source counts separately for AGN and SFGs. We find that while SFGs dominate at the faintest flux densities and account for the majority of the up-turn in the counts, AGN still make up around one quarter of the counts at ~5 uJy (1.4 GHz). Using radio luminosity as an unobscured star formation rate (SFR) measure we are then able to examine the comoving SFR density of the Universe up to z=3 which agrees well with measures at other wavelengths. We find a rough correlation of SFR with stellar mass for both the sample presented here and a sample of local radio-selected SFGs from the 6df-NVSS survey. This work also confirms the existence of, and provides alternative evidence for, the evolution of distribution of star formation by galaxy mass: ``downsizing''. As both these samples are SFR-selected, this result suggests that there is a maximum SFR for a given galaxy that depends linearly on its stellar mass. The low ``characteristic times'' (inverse specific SFR) of the SFGs in our sample are similar to those of the 6dF-NVSS sample, implying that most of these sources are in a current phase of enhanced star formation. Comment: 15 pages, 10 figures, MNRAS, in press, Figure A1 included as gif to save space, paper with full resolution figure available here: http://web.ipac.caltech.edu/staff/seymour/13hr_sfr_final.pdf
02/2008;
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ABSTRACT: We present the results of a deep 610 MHz survey conducted as part of a
study into the radio spectral properties of the faint radio population.
We have observed the 1^H XMM/Chandra survey area with the GMRT. To a
5σ detection limit of 283 μJy we detect 222 sources within a
survey area of diameter 64 arcmin. We compute the 610 MHz source counts
and compare them to those at other radio wavelengths. The well know
flattening of the Euclidean-normalised 1.4 GHz source counts below
˜2 mJy, usually explained by a population of starburst galaxies
undergoing luminosity evolution, is seen for the first time at 610 MHz.
The 610 MHz source counts can be modelled by the same populations that
explain the 1.4 GHz source counts, assuming a spectral index of 0.8 for
the starburst galaxies and the steep spectrum AGN population. We find a
similar dependence of luminosity evolution on redshift for the starburst
galaxies at 610MHz as is found at 1.4 GHz (i.e. `Q'=
2.3+0.3-0.5). A preliminary reduction of deeper
observations gives spectral indices for ˜60 sources, ˜20 of
which are candidate ultra steep spectrum sources.
11/2007; 380:275.
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ABSTRACT: The best way to constrain Active Galactic Nuclei (AGN) absorption
properties over a wide range of luminosity and redshift is by examining
the extragalactic X-ray population. In the very deep XMM-Newton
observations of the Chandra Deep Field South (CDFS), there are >300
X-ray detections, 84% of which have redshift estimates, and nearly all
of which are AGN. This AGN sample spans more than four decades in
intrinsic luminosity. We determine the absorbing column densities and
intrinsic luminosities of these AGN using a Monte-Carlo method, which
exploits the wide bandpass (0.2--10 keV), and high throughput of
XMM-Newton. A detailed simulation scheme is then used to compare the
X-ray properties of the sources with the predictions of a number of
theoretical AGN population models. We find that the observed AGN
absorption distribution exhibits no strong dependence on either
luminosity or redshift. The best matching population model contains AGN
having a wide range of absorbing columns, with the heavily absorbed AGN
outnumbering the unabsorbed objects by 3:1. In particular, our results
are consistent with there being a large population of heavily absorbed
(N_H >1022 cm-2), intrinsically luminous (L_X
> 1044 erg s-1) AGN.
11/2007; 380:145.
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ABSTRACT: We present the results of a deep 610-MHz survey of the 1HXMM–Newton/Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ∼7 arcsec and an rms noise limit of 60 μJy. To a 5σ detection limit of 300 μJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ∼2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of −0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e. ‘Q’= 2.45+0.3−0.4).
Monthly Notices of the Royal Astronomical Society 06/2007; 378(3):995 - 1006. · 4.90 Impact Factor
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ABSTRACT: We present the results of a deep 610 MHz survey of the 1^H XMM/Chandra survey area with the GMRT. The resulting maps have a resolution of ~7 arcsec and an rms noise limit of 60 microJy. To a 5 sigma detection limit of 300 microJy we detect 223 sources within a survey area of diameter 64 arcmin. We compute the 610 MHz source counts and compare them to those measured at other radio wavelengths. The well know flattening of the Euclidean-normalised 1.4 GHz source counts below ~2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610 MHz source counts can be modelled by the same populations that explain the 1.4 GHz source counts, assuming a spectral index of -0.7 for the starburst galaxies and the steep spectrum AGN population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e. 'Q'= 2.45 (+0.3,-0.4)).
05/2007;
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M. J. Page,
I Lehmann,
Th. Boller,
M. G. Watson, T. Dwelly,
S. Hess,
I. Matute,
N. S. Loaring,
S. Rosen,
H. Ziaeepour,
A. Schwope,
G. Lamer,
F. J. Carrera,
J. Tedds,
R. Della Ceca,
P. Severgnini,
R. G. McMahon,
W Yuan
[show abstract]
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ABSTRACT: We present optical and X-ray data for a sample of serendipitous XMM-Newton sources that are selected to have 0.5-2 keV vs 2-4.5 keV X-ray hardness ratios which are harder than the X-ray background. The sources have 2-4.5 keV X-ray flux >= 10^-14 cgs, and in this paper we examine a subsample of 42 optically bright (r < 21) sources; this subsample is 100 per cent spectroscopically identified. All but one of the optical counterparts are extragalactic, and we argue that the single exception, a Galactic M star, is probably a coincidental association. The X-ray spectra are consistent with heavily absorbed power laws (21.8 < log NH < 23.4), and all of them appear to be absorbed AGN. The majority of the sources show only narrow emission lines in their optical spectra, implying that they are type-2 AGN. Only a small fraction of the sources (7/42) show broad optical emission lines, and all of these have NH < 10^23 cm^-2. This implies that ratios of X-ray absorption to optical/UV extinction equivalent to > 100 times the Galactic gas-to-dust ratio are rare in AGN absorbers (at most a few percent of the population), and may be restricted to broad absorption-line QSOs. Seven objects appear to have an additional soft X-ray component in addition to the heavily absorbed power law. We consider the implications of our results in the light of the AGN unified scheme. We find that the soft components in narrow-line objects are consistent with the unified scheme provided that > 4 per cent of broad-line AGN have ionised absorbers that attenuate their soft X-ray flux by >50 per cent. In at least one of the X-ray absorbed, broad-line AGN in our sample the X-ray spectrum requires an ionised absorber, consistent with this picture. Comment: accepted for publication in MNRAS
04/2007;
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[hide abstract]
ABSTRACT: Discerning the exact nature of the faint (sub-mJy) radio population has been historically difficult due to the low luminosity of these sources at most wavelengths. Using deep observations from Chandra/XMM-Newton/Spitzer and ground based follow up we are able to disentangle the AGN and star-forming populations for the first time in a deep multi-frequency GMRT/VLA/MERLIN Survey. The many diagnostics include radio luminosity, morphology, radio to mid-IR flux density ratios, radio to optical flux density ratios and radio spectral indices. Further diagnostics, e.g. optical spectra X-ray spectra/hardness ratios, IR colours indicate the presence of the AGN {\em independent} of whether the radio emission is powered by AGN or star-formation. We are able to examine the star-formation history of the universe up to z=2.5 in a unique way based on an unbiased star-formation rate indicator, radio luminosity. This work provides an alternative perspective on the distribution of star-formation by mass, ``downsizing'' and allows us to examine the prevalence of AGN in star-bursts.
01/2007;
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ABSTRACT: We have used very deep XMM-Newton observations of the Chandra Deep Field-South to examine the spectral properties of the faint active galactic nucleus (AGN) population. Crucially, redshift measurements are available for 84% (259/309) of the XMM-Newton sample. We have calculated the absorption and intrinsic luminosities of the sample using an extensive Monte Carlo technique incorporating the specifics of the XMM-Newton observations. Twenty-three sources are found to have substantial absorption and intrinsic X-ray luminosities greater than 10^44 erg/s, putting them in the "type-2" QSO regime. We compare the redshift, luminosity and absorption distributions of our sample to the predictions of a range of AGN population models. In contrast to recent findings from ultra-deep Chandra surveys, we find that there is little evidence that the absorption distribution is dependent on either redshift or intrinsic X-ray luminosity. The pattern of absorption in our sample is best reproduced by models in which ~75% of the AGN population is heavily absorbed at all luminosities and redshifts. Comment: 24 pages, 18 figures, accepted by MNRAS
08/2006;
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M. J. Page,
N. S. Loaring, T. Dwelly,
K. O. Mason,
I. McHardy,
K. Gunn,
D. Moss,
T. Sasseen,
F. Cordova,
J. Kennea,
N. Seymour
[show abstract]
[hide abstract]
ABSTRACT: 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.
Monthly Notices of the Royal Astronomical Society 06/2006; 369(1):156 - 170. · 4.90 Impact Factor
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M. J. Page,
N. S. Loaring, T. Dwelly,
K. O. Mason,
I. McHardy,
K. Gunn,
D. Moss,
T. Sasseen,
F. Cordova,
J. Kennea,
N. Seymour
[show abstract]
[hide abstract]
ABSTRACT: We present the X-ray spectra of 86 optically-identified sources in the 13H XMM-Newton/Chandra deep field which have >70 X-ray counts. The sample consists of 50 broad line AGN, 25 narrow emission line galaxies, 6 absorption line galaxies, and 5 Galactic stars. The majority (42/50) of the broad line AGN have X-ray spectra which are consistent with a power law shape. They have a mean photon index of Gamma = 2.0 +- 0.1 and an intrinsic dispersion sigma = 0.4 +- 0.1. Five BLAGN show a deficit of soft X-rays, indicating absorption. Significant absorption is more common in the narrow emission line galaxies (13/25) and absorption line galaxies (2/6) than in the broad line AGN (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 6/20 require more complex models with either an additional component of soft X-ray emitting plasma, or an ionised absorber. Of the 16 galaxies which do not show evidence for X-ray absorption, only 2 objects are likely to be powered by star formation, and both have 2-10 keV X-ray luminosities of <= 10^40 cgs. 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 multi-temperature thermal spectra which peak between 0.5 and 1 keV. Star/AGN discrimination is possible for 4 of the 5 stars solely from their X-ray spectra. Comment: Accepted for publication in MNRAS
04/2006;
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ABSTRACT: Despite the plethora of deep (sub-mJy) radio surveys there remains considerable doubt as to the exact nature of the galaxies contributing to the source counts. Current evidence suggests that star formation in moderately luminous normal galaxies is responsible for the bulk of the emission below 1 mJy. However given the sensitivities of these surveys we would expect a fraction of these sources to be distant radio galaxies. Using deep VLA and GMRT data we have found ∼20 high-z candidate radio galaxies in two fields using the classical ultra-steep radio spectrum technique (De Breuck et al. 2000) and selecting galaxies with faint (i ′ > 25) optical counterparts. Several of these sources have X-ray detections in our deep XMM/Chandra observations and have fluxes high enough to put them in the quasar regime if they lie above redshift 3. Recently performed Spitzer GTO observations and upcoming near-infrared observations will help reveal the nature of these sources. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Astronomische Nachrichten 02/2006; 327(2‐3):278 - 281. · 1.01 Impact Factor
