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N. J. Brassington,
G. Fabbiano,
A. Zezas,
A. Kundu,
D. -W. Kim,
T. Fragos,
A. R. King,
S. Pellegrini, G. Trinchieri,
S. Zepf,
N. J. Wright
[show abstract]
[hide abstract]
ABSTRACT: We report the spectral and temporal variability properties of 18 candidate
transient and potential transient (TC and PTC) sources detected in deep
multi-epoch Chandra observation of the nearby elliptical galaxies, NGC 3379,
NGC 4278 and NGC 4697. Only one source can be identified with a background
counterpart, leaving 17 TCs + PTCs in the galaxies. Of these, 14 are in the
galaxy field, supporting the theoretical picture that the majority of field
X-ray binaries (XRBs) will exhibit transient accretion for >75% of their
lifetime. Three sources are coincident with globular clusters (GCs), including
two high-luminosity candidate black hole (BH) XRBs, with Lx=5.4E38 erg/s, and
Lx=2.8E39 erg/s, respectively. The spectra, luminosities and temporal behavior
of these 17 sources suggest that the transient population is heterogeneous,
including neutron star (NS) and BH XRBs in both normal and high-rate accretion
modes, and super soft sources containing white dwarf binaries. Our TC and PTC
detections are noticeably fewer that the number expected from the populations
synthesis (PS) models of Fragos et al. (2009), tailored to our new Chandra
pointings of NGC 4278. We attribute this discrepancy to the PS assumption that
the transient population is composed of NS XRBs, as well as differences between
the statistical analysis and error estimates used in the model and our
observations.
06/2012;
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[show abstract]
[hide abstract]
ABSTRACT: The analysis of a deep (579 ks) Chandra ACIS pointing of the elliptical
galaxy NGC4278, which hosts a low luminosity AGN and compact radio emission,
allowed us to detect extended emission from hot gas out to a radius of \sim 5
kpc, with a 0.5--8 keV luminosity of 2.4x10^{39} erg/s. The emission is
elongated in the NE-SW direction, misaligned with respect to the stellar body,
and aligned with the ionized gas, and with the Spitzer IRAC 8\mum non-stellar
emission. The nuclear X-ray luminosity decreased by a factor of \sim 18 since
the first Chandra observation in 2005, a dimming that enabled the detection of
hot gas even at the position of the nucleus. Both in the projected and
deprojected profiles, the gas shows a significantly larger temperature (kT=0.75
keV) in the inner \sim 300 pc than in the surrounding region, where it stays at
\sim 0.3 keV, a value lower than expected from standard gas heating
assumptions. The nuclear X-ray emission is consistent with that of a low
radiative efficiency accretion flow, accreting mass at a rate close to the
Bondi one; estimates of the power of the nuclear jets require that the
accretion rate is not largely reduced with respect to the Bondi rate. Among
possibile origins for the central large hot gas temperature, such as
gravitational heating from the central massive black hole and a recent AGN
outburst, the interaction with the nuclear jets seems more likely, especially
if the latter remain confined, and heat the nuclear region frequently. The
unusual hot gas distribution on the galactic scale could be due to the
accreting cold gas triggering the cooling of the hot phase, a process also
contributing to the observed line emission from ionize gas, and to the hot gas
temperature being lower than expected; alternatively, the latter could be due
to an efficiency of the type Ia supernova energy mixing lower than usually
adopted.
06/2012;
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[show abstract]
[hide abstract]
ABSTRACT: Seyfert's Sextet (a.k.a HCG 79) is one of the most compact and isolated
galaxy groups in the local Universe. It shows a prominent diffuse light
component that accounts for ~50% of the total observed light. This likely
indicates that the group is in an advanced evolutionary phase, which would
predict a significant hot gaseous component. Previous X-ray observations had
suggested a low luminosity for this system, but with large uncertainties and
poor resolution. We present the results from a deep (70 ks), high resolution
Chandra observation of Seyfert's Sextet, requested with the aim of separating
the X-ray emission associated with the individual galaxies from that of a more
extended inter-galactic component. We discuss the spatial and spectral
characteristics of this group we derive with those of a few similar systems
also studied in the X-ray band. The high resolution X-ray image indicates that
the majority of the detected emission does not arise in the compact group but
is concentrated towards the NW and corresponds to what appears to be a
background galaxy cluster. The emission from the group alone has a total
luminosity of ~1x10^40 erg/s in the (0.5-5) keV band. Most of the luminosity
can be attributed to the individual sources in the galaxies, and only ~2x10^39
erg/s is due to a gaseous component. However, we find that this component is
also mostly associated with the individual galaxies of the Sextet, leaving
little or no residual in a truly IGM component. The extremely low luminosity of
the diffuse emission in Seyfert's Sextet might be related to its small total
mass.
04/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present an analysis of the Globular Cluster (GC) population of the
elliptical galaxy NGC 4261 based on HST WFPC2 data in the B, V and I bands. We
study the spatial distribution of the GCs in order to probe the anisotropy in
the azimuthal distribution of the discrete X-ray sources in the galaxy revealed
by Chandra images (Zezas et al. 2003). The luminosity function of our GC sample
(complete at the 90% level for V_mag = 23.8 mag) peaks at V_mag = 25.1
(-0.6)(+1.0) mag, which corresponds to a distance consistent with previous
measurements. The colour distribution can be interpreted as being the
superposition of a blue and red GC component with average colours V-I = 1.01
(-0.06)(+0.06) mag and 1.27 (-0.08)(+0.06) mag, respectively. This is
consistent with a bimodal colour distribution typical of elliptical galaxies.
The red GC's radial profile is steeper than that of the galaxy surface
brightness, while the profile of the blue subpopulation looks more consistent
with it. The most striking finding is the significant asymmetry in the
azimuthal distribution of the GC population about a NE-SW direction. The lack
of any obvious feature in the morphology of the galaxy suggests that the
asymmetry could be the result of an interaction or a merger.
01/2012;
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G. Fabbiano,
N. J. Brassington,
L. Lentati,
L. Angelini,
R. L. Davies,
J. Gallagher,
V. Kalogera,
D.-W. Kim,
A. R. King,
A. Kundu,
S. Pellegrini,
A. J. Richings, G. Trinchieri,
A. Zezas,
and S. Zepf
[show abstract]
[hide abstract]
ABSTRACT: We report a detailed spectral analysis of the population of low-mass X-ray binaries (LMXBs) detected in the elliptical galaxy NGC 4278 with Chandra. Seven luminous sources were studied individually, four in globular clusters (GCs) and three in the stellar field. The range of (0.3-8 keV) L X for these sources is ~(3-8) × 1038 erg s–1, suggesting that they may be black hole binaries (BHBs). Fitting the data with either single thermal accretion disk or power-law (PO) models results in best-fit temperatures of ~0.7-1.7 keV and Γ ~ 1.2-2.0, consistent with those measured in Galactic BHBs. Comparison of our results with simulations allows us to discriminate between disk and power-law-dominated emission, pointing to spectral/luminosity variability, reminiscent of Galactic BHBs. The BH masses derived from a comparison of our spectral results with the L X ~ T 4 in relation of Galactic BHBs are in the 5-15 M ☉ range, as observed in the Milky Way. The analysis of joint spectra of sources selected in three luminosity ranges (L X ≥ 1.5 × 1038 erg s–1, 6 × 1037ergs–1 ≤ L X < 1.5 × 1038 erg s–1, and L X < 6 × 1037 erg s–1) suggests that while the high-luminosity sources have prominent thermal disk emission components, power-law components are likely to be important in the mid- and low-luminosity spectra. Comparing low-luminosity average spectra, we find a relatively larger N H in the GC spectrum; we speculate that this may point to either a metallicity effect or to intrinsic physical differences between field and GC accreting binaries. Analysis of average sample properties uncovers a previously unreported L X-R G correlation (where R G is the galactocentric radius) in the GC-LMXB sample, implying richer LMXB populations in more central GCs. No such trend is seen in the field LMXB sample. We can exclude that the GC L X-R G correlation is the by-product of a luminosity effect and suggest that it may be related to the presence of more compact GCs at smaller galactocentric radii, fostering more efficient binary formation.
The Astrophysical Journal 12/2010; 725(2):1824. · 6.02 Impact Factor
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G. Fabbiano,
N. J. Brassington,
L. Lentati,
L. Angelini,
R. L. Davies,
J. Gallagher,
V. Kalogera,
D W Kim,
A. R. King,
A. Kundu,
S. Pellegrini,
A. J. Richings, G Trinchieri,
A. Zezas,
S. Zepf
[show abstract]
[hide abstract]
ABSTRACT: We report a detailed spectral analysis of the population of low-mass X-ray binaries (LMXBs) detected in the elliptical galaxy NGC~4278 with Chandra. Seven luminous sources were studied individually, four in globular clusters (GCs), and three in the stellar field. The range of (0.3-8 keV) $L_X$ for these sources suggests that they may be black hole binaries (BHBs). Comparison of our results with simulations allows us to discriminate between disk and power-law dominated emission, pointing to spectral/luminosity variability, reminiscent of Galactic BHBs. The BH masses derived from a comparison of our spectral results with the $L_X \sim T^4_{in}$ relation of Galactic BHBs are in the 5-15 $M_{\odot}$ range, as observed in the Milky Way. The analysis of joint spectra of sources selected in three luminosity ranges suggests that while the high luminosity sources have prominent thermal disk emission components, power-law components are likely to be important in the mid and low-luminosity spectra. Comparing low-luminosity average spectra, we find a relatively larger $N_H$ in the GC spectrum; we speculate that this may point to either a metallicity effect, or to intrinsic physical differences between field and GC accreting binaries. Analysis of average sample properties uncover a previously unreported $L_X - R_G$ correlation (where $R_G$ is the galactocentric radius) in the GC-LMXB sample, implying richer LMXB populations in more central GCs. No such trend is seen in the field LMXB sample. We can exclude that the GC $L_X - R_G$ correlation is the by-product of a luminosity effect, and suggest that it may be related to the presence of more compact GCs at smaller galactocentric radii, fostering more efficient binary formation. Comment: Accepted for publication in ApJ
10/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: The radio source 3C 270, hosted by NGC 4261, is the brightest known example of counterjet X-ray emission from a low-power radio galaxy. We report on the X-ray emission of the jet and counterjet from 130 ks of Chandra data. We argue that the X-ray emission is synchrotron radiation and that the internal properties of the jet and counterjet are remarkably similar. We find a smooth connection in X-ray hardness and X-ray to radio ratio between the jet and one of the X-ray components within the core spectrum. We observe wedge-like depressions in diffuse X-ray surface brightness surrounding the jets, and interpret them as regions where an aged population of electrons provides pressure to balance the interstellar medium of NGC 4261. About 20% of the mass of the interstellar medium has been displaced by the radio source. Treating 3C 270 as a twin-jet system, we find an interesting agreement between the ratio of jet-to-counterjet length in X-rays and that expected if X-rays are observed over the distance that an outflow from the core would have traveled in ~6x10^4 yr. X-ray synchrotron loss times are shorter than this, and we suggest that most particle acceleration arises as a result of turbulence and dissipation in a stratified flow. We speculate that an episode of activity in the central engine beginning ~6x10^4 yr ago has led to an increased velocity shear. This has enhanced the ability of the jet plasma to accelerate electrons to X-ray-synchrotron-emitting energies, forming the X-ray jet and counterjet that we see today. Comment: Accepted for publication in the MNRAS. 12 pages, 10 figs (some in color).Some figures reduced in quality
06/2010;
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N. J. Brassington,
G. Fabbiano,
S. Blake,
A. Zezas,
L. Angelini,
R. L. Davies,
J. Gallagher,
V. Kalogera,
D W Kim,
A. R. King,
A. Kundu, G Trinchieri,
S. Zepf
[show abstract]
[hide abstract]
ABSTRACT: From a deep multi-epoch Chandra observation of the elliptical galaxy NGC 3379 we report the spectral properties of eight luminous LMXBs (LX>1.2E38 erg/s). We also present a set of spectral simulations, produced to aid the interpretation of low-count single-component spectral modeling. These simulations demonstrate that it is possible to infer the spectral states of X-ray binaries from these simple models and thereby constrain the properties of the source. Of the eight LMXBs studied, three reside within globular clusters, and one is a confirmed field source. Due to the nature of the luminosity cut all sources are either neutron star binaries emitting at or above the Eddington luminosity or black hole binaries. The spectra from these sources are well described by single-component models, with parameters consistent with Galactic LMXB observations, where hard-state sources have a range in photon index of 1.5-1.9 and thermally dominated sources have inner disc temperatures between ~0.7-1.55 keV. The large variability observed in the brightest globular cluster source (LX>4E38 erg/s) suggests the presence of a black hole binary. At its most luminous this source is observed in a thermally dominated state with kT=1.5 keV, consistent with a black hole mass of ~4 Msol. This observation provides further evidence that globular clusters are able to retain such massive binaries. We also observed a source transitioning from a bright state (LX~1E39 erg/s), with prominent thermal and non-thermal components, to a less luminous hard state (LX=3.8E38 erg/s, Gamma=1.85). In its high flux emission this source exhibits a cool-disc component of ~0.14 keV, similar to spectra observed in some ultraluminous X-ray sources. Such a similarity indicates a possible link between `normal' stellar mass black holes in a high accretion state and ULXs. Comment: Accepted to ApJ; 24 pages with 17 figures. Replacement includes additional simulations and a decision tree summarizing the simulation results
03/2010;
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[show abstract]
[hide abstract]
ABSTRACT: The Wide Field X-ray Telescope (WFXT) will perform three very sensitive
X-ray surveys (0.3-4 keV band), 100, 3000, and 20000 sq. deg, with a
constant 5-10" PSF over the 1 degree field of view (FOV). These surveys
will detect 105 normal galaxies that will allow, for the
first time, a statistical study of their X-ray properties. Correlation
between WFXT surveys and optical wide-area surveys such as Pan-STARRS
and LSST will give redshift, galaxy type and environment information and
help to identify low-luminosity AGN. Such a large sample will allow
galaxies to be divided into various subsamples, e.g., based on optical
properties, to test the impact of these properties on the X-ray
luminosity function and scaling of X-ray luminosity with star-formation
rate and stellar mass. WFXT will likely survey the Virgo Cluster,
mapping the cluster galaxies and their interaction with the ICM with
unprecedented sensitivity. The Magellanic Clouds should be observed
fairly often in the course of the surveys (given their proximity to the
South Ecliptic Pole), resulting in excellent monitoring of the binary
population which in turn will constrain their accretion physics. The
large FOV and low background of WFXT will allow diffuse emission in the
Magellanic Clouds and large local group galaxies such as M31 to be
studied in detail and compared with models of the hot ISM in galaxies.
Repeated WFXT visits to Local Group galaxies will also be essential for
gaining a complete census of transient X-ray sources such as white-dwarf
super-soft sources, with the wide WFXT survey reaching a depth of
1035-36 ergs/s at 1 Mpc. These surveys will therefore vastly
improve our understanding of the evolution of binary stellar
populations, heating of the ISM, and the evolution of X-ray emission
from galaxies.
12/2009; 42:520.
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A. Ptak,
E. Feigelson,
Y. -H. Chu,
K. Kuntz,
A. Zezas,
S. Snowden,
D. de Martino, G Trinchieri,
G. Fabbiano,
W. Forman, [......],
M. Donahue,
K. Flannagan,
R. Gilli,
C Jones,
N. Miller,
G. Pareschi,
P. Rosati,
D Schneider,
P. Tozzi,
A. Vikhlinin
[show abstract]
[hide abstract]
ABSTRACT: While the exceptional sensitivity of Chandra and XMM-Newton has resulted in revolutionary studies of the Galactic neighborhood in the soft (<10 keV) X-ray band, there are many open questions. We discuss these issues and how they would be addressed by very wide-area (> 100 sq. deg.) X-ray surveys.
03/2009;
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T. Fragos,
V. Kalogera,
B. Willems,
K. Belczynski,
G. Fabbiano,
N. J. Brassington,
D W Kim,
L. Angelini,
R. L. Davies,
J. S. Gallagher,
A. R. King,
S. Pellegrini, G Trinchieri,
S. E. Zepf,
A. Zezas
[show abstract]
[hide abstract]
ABSTRACT: We propose a physically motivated and self-consistent prescription for the modeling of transient neutron star (NS) low-mass X-ray binary (LMXB) properties, such as duty cycle (DC), outburst duration and recurrence time. We apply this prescription to the population synthesis (PS) models of field LMXBs presented by Fragos et al. (2008), and compare the transient LMXB population to the Chandra X-ray survey of the two elliptical galaxies NGC 3379 and NGC 4278, which revealed several transient sources (Brassington et al., 2008, 2009). We are able to exclude models with a constant DC for all transient systems, while models with a variable DC based on the properties of each system are consistent with the observed transient populations. We predict that the majority of the observed transient sources in these two galaxies are LMXBs with red giant donors. Our comparison suggests that LMXBs formed through evolution of primordial field binaries are dominant in globular cluster (GC) poor elliptical galaxies, while they still have a significant contribution in GC rich ones. Comment: 12 pages, 3 figures, submitted to The Astrophysical Journal Letters
01/2009;
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G. Trinchieri,
S. Pellegrini,
G. Fabbiano,
R. Fu,
N. J. Brassington,
A. Zezas,
D.-W. Kim,
J. Gallagher,
L. Angelini,
R. L. Davies,
V. Kalogera,
A. R. King,
and S. Zepf
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a faint (LX ~ 4 ± 1.5 × 1037 ergs s−1, 0.5-2 keV), outflowing gaseous hot interstellar medium (ISM) in NGC 3379. This represents the lowest X-ray luminosity ever measured from a hot phase of the ISM in a nearby early-type galaxy. The discovery of the hot ISM in a very deep Chandra observation was possible thanks to its unique spectral and spatial signatures, which distinguish it from the integrated stellar X-ray emission, responsible for most of the unresolved emission in the Chandra data. This hot component is found in a region of ~800 pc in radius at the center of the galaxy and has a total mass M ~ 3 ± 1 × 105 M☉. Independent theoretical prediction of the characteristics of an ISM in this galaxy, based on the intrinsic properties of NGC 3379, reproduce well the observed luminosity, temperature, and radial distribution and mass of the hot gas, and indicate that the gas is in an outflowing phase, predicted by models but not observed in any system so far.
The Astrophysical Journal 12/2008; 688(2):1000. · 6.02 Impact Factor
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G. Fabbiano,
D.-W. Kim,
T. Fragos,
V. Kalogera,
A. R. King,
L. Angelini,
R. L. Davies,
J. S. Gallagher,
S. Pellegrini, G. Trinchieri,
S. E. Zepf,
and A. Zezas
[show abstract]
[hide abstract]
ABSTRACT: We report recent Chandra observations of the ULX in the elliptical galaxy NGC 3379 that clearly detect two flux variability cycles. Comparing these data with the Chandra observation of ~5 years ago, we measure a flux modulation with a period of ~12.6 hr. Moreover, we find that the emission undergoes a correlated spectral modulation, becoming softer at low flux. We argue that our results establish this source as a ULX binary in NGC 3379. Given the old stellar population of this galaxy, the ULX is likely to be a soft transient; however, historical X-ray sampling suggests that the current "on" phase has lasted ~10 yr. We discuss our results in terms of ADC and wind-feedback models. If the flux modulation is orbital, we can constrain the donor mass and orbital period at the onset of mass transfer within 1.15-1.4 M☉ and 12.5-17 hr, respectively. The duration of the mass transfer phase so far is probably ~1 Gyr, and the binary has been a soft X-ray transient throughout this time. These constraints are insensitive to the mass of the accretor.
The Astrophysical Journal 12/2008; 650(2):879. · 6.02 Impact Factor
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M. Polletta,
M. Tajer,
L. Maraschi, G. Trinchieri,
C. J. Lonsdale,
L. Chiappetti,
S. Andreon,
M. Pierre,
O. Le Fèvre,
G. Zamorani, [......],
O. Garcet,
J. Surdej,
A. Franceschini,
D. Alloin,
D. L. Shupe,
J. A. Surace,
F. Fang,
M. Rowan-Robinson,
H. E. Smith,
and L. Tresse
[show abstract]
[hide abstract]
ABSTRACT: We present the SEDs of a hard X-ray selected sample containing 136 sources with F2-10 keV > 10-14 erg cm-2 s-1; 132 are AGNs. The sources are detected in a 1 deg2 area of the XMM-Newton Medium Deep Survey where optical data from the VVDS and CFHTLS and infrared data from the SWIRE survey are available. Based on a SED fitting technique we derive photometric redshifts with σ(1 + z) = 0.11 and 6% of outliers and identify AGN signatures in 83% of the objects. This fraction is higher than derived when a spectroscopic classification is available. The remaining 17% of AGNs show star-forming galaxy SEDs (SF class). The sources with AGN signatures are divided in two classes, AGN1 (33%) and AGN2 (50%). The AGN1 and AGN2 classes include sources whose SEDs are fitted by type 1 and type 2 AGN templates, respectively. On average, AGN1s show soft X-ray spectra, consistent with being unabsorbed, while AGN2s and SFs show hard X-ray spectra, consistent with being absorbed. The analysis of the average SEDs as a function of X-ray luminosity shows a reddening of the infrared SEDs, consistent with a decreasing contribution from the host galaxy at higher luminosities. The AGNs in the SF classes are likely obscured in the mid-infrared, as suggested by their low L3-20 μm/L ratios. We confirm the previously found correlation for AGNs between the radio luminosity and the X-ray and the mid-infrared luminosities. The X-ray-radio correlation can be used to identify heavily absorbed AGNs. However, the estimated radio fluxes for the missing AGN population responsible for the bulk of the background at E > 10 keV are too faint to be detected even in the deepest current radio surveys.
The Astrophysical Journal 12/2008; 663(1):81. · 6.02 Impact Factor
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T. Fragos,
V. Kalogera,
K. Belczynski,
G. Fabbiano,
D.-W. Kim,
N. J. Brassington,
L. Angelini,
R. L. Davies,
J. S. Gallagher,
A. R. King,
S. Pellegrini, G. Trinchieri,
S. E. Zepf,
A. Kundu,
and A. Zezas
[show abstract]
[hide abstract]
ABSTRACT: We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXBs) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code, assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLFs) of point sources in these galaxies. For the first time we explore the population XLF in luminosities below 1037 ergs s−1, as probed by the most recent observational results. We consider models for the formation and evolution of LMXBs in galactic fields with different CE efficiencies, stellar wind prescriptions, magnetic braking laws, and IMFs. We identify models that produce XLFs consistent with the observations both in shape and absolute normalization, suggesting that a primordial galactic field LMXB population can make a significant contribution to the total population of an elliptical galaxy. We also find that the treatment of the outburst luminosity of transient systems remains a crucial factor for the determination of the XLF, since the modeled populations are dominated by transient X-ray systems.
The Astrophysical Journal 12/2008; 683(1):346. · 6.02 Impact Factor
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M. Polletta,
A. Omont,
S. Berta,
J. Bergeron,
C. S. Stalin,
P. Petitjean,
M. Giorgetti, G Trinchieri,
R. Srianand,
H. J. McCracken,
Y. Pei,
H. Dannerbauer
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of two sources at z=3.867 and z=3.427 that exhibit powerful starburst and AGN activities. They benefit from data from radio to X rays from the CFHTLS-D1/SWIRE/XMDS surveys. Follow-up optical and near-infrared spectroscopy, and millimeter IRAM/MAMBO observations are also available. We performed an analysis of their spectral energy distributions to understand the origin of their emission and constrain their luminosities. A comparison with other composite systems at similar redshifts from the literature is also presented. The AGN and starburst bolometric luminosities are ~10^13 Lsun. The AGN emission dominates at X ray, optical, mid-infrared wavelengths, and probably in the radio. The starburst emission dominates in the far-infrared. The estimated star formation rates range from 500 to 3000Msun/yr. The AGN near-infrared and X ray emissions are heavily obscured in both sources with an estimated dust extinction Av>4, and Compton-thick gas column densities. The two sources are the most obscured and most luminous AGNs detected at millimeter wavelengths currently known. The sources presented in this work are heavily obscured QSOs, but their properties are not fully explained by the standard AGN unification model. In one source, the ultraviolet and optical spectra suggest the presence of outflowing gas and shocks, and both sources show emission from hot dust, most likely in the vicinity of the nucleus. Evidence of moderate AGN-driven radio activity is found in both sources. The two sources lie on the local M_BH-M_bulge relation. To remain on this relation, their star formation rate has to decrease. Our results support evolutionary models that invoke radio feedback as star formation quenching mechanism, and suggest that such a mechanism might play a major role also in powerful AGNs. Comment: Accepted for publication in Astronomy & Astrophysics (12 pages; 6 figures); replaced version includes minor language editing and revised references
10/2008;
-
G Trinchieri,
S. Pellegrini,
G. Fabbiano,
R. Fu,
N. J. Brassington,
A. Zezas,
D W Kim,
J. Gallagher,
L. Angelini,
R. L. Davies,
V. Kalogera,
A. R. King,
S. Zepf
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of a faint (L_x ~ 4 10^37 erg/s, 0.5-2 keV), out-flowing gaseous hot interstellar medium (ISM) in NGC 3379. This represents the lowest X-ray luminosity ever measured from a hot phase of the ISM in a nearby early type galaxy. The discovery of the hot ISM in a very deep Chandra observation was possible thanks to its unique spectral and spatial signatures, which distinguish it from the integrated stellar X-ray emission, responsible for most of the unresolved emission in the Chandra data. This hot component is found in a region of about 800 pc in radius at the center of the galaxy and has a total mass M~ 3 10^5 solar masses. Independent theoretical prediction of the characteristics of an ISM in this galaxy, based on the intrinsic properti es of NGC 3379, reproduce well the observed luminosity, temperature, and radial distribution and mass of the hot gas, and indicate that the gas is in an outflowing phase, predicted by models but not observed in any system so far. Comment: Accepted for publication in The Astrophysical Journal
07/2008;
-
T. Fragos,
V. Kalogera,
K. Belczynski,
G. Fabbiano,
D W Kim,
N. J. Brassington,
L. Angelini,
R. L. Davies,
J. S. Gallagher,
A. R. King,
S. Pellegrini, G Trinchieri,
S. E. Zepf,
A. Zezas
[show abstract]
[hide abstract]
ABSTRACT: We present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXB) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code (Belczynski et al., 2006), assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLF) of point sources in these galaxies. For the first time we explore the population XLF down to luminosities of 3X10^36 erg/s, as probed by the most recent observational results (Kim et al., 2006). We consider models for the formation and evolution of LMXBs in galactic fields with different CE efficiencies, stellar wind prescriptions, magnetic braking laws and initial mass functions. We identify models that produce an XLF in excellent agreement with the observations both in shape and absolute normalization. We also find that the treatment of the outburst luminosity of transient systems remains a crucial factor for the determination of the XLF since the modeled populations are dominated by transient X-ray systems. Comment: 54 pages, 22 figure, submitted to The Astrophysical Journal
01/2008;
-
F. Pacaud,
M. Pierre,
C. Adami,
B. Altieri,
S. Andreon,
L. Chiappetti,
A. Detal,
P.-A. Duc,
G. Galaz,
A. Gueguen, [......],
M. N. Bremer,
O. Garcet,
C. Jean,
L. R. Jones,
O. Le Fèvre,
D. Maccagni,
A. Mazure,
D. Proust,
H. J. A. Röttgering, G. Trinchieri
[show abstract]
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ABSTRACT: We present a sample of 29 galaxy clusters from the XMM-LSS survey over an area of some 5 deg2 out to a redshift of z= 1.05. The sample clusters, which represent about half of the X-ray clusters identified in the region, follow well-defined X-ray selection criteria and are all spectroscopically confirmed. For all clusters, we provide X-ray luminosities and temperatures as well as masses, obtained from dedicated spatial and spectral fitting. The cluster distribution peaks around z= 0.3 and T= 1.5 keV, half of the objects being groups with a temperature below 2 keV. Our LX–T(z) relation points towards self-similar evolution, but does not exclude other physically plausible models. Assuming that cluster scaling laws follow self-similar evolution, our number density estimates up to z= 1 are compatible with the predictions of the concordance cosmology and with the findings of previous ROSAT surveys. Our well-monitored selection function allowed us to demonstrate that the inclusion of selection effects is essential for the correct determination of the evolution of the LX–T relation, which may explain the contradictory results from previous studies. Extensive simulations show that extending the survey area to 10 deg2 has the potential to exclude the non-evolution hypothesis, but those constraints on more refined intracluster medium models will probably be limited by the large intrinsic dispersion of the LX–T relation, whatever be the sample size. We further demonstrate that increasing the dispersion in the scaling laws increases the number of detectable clusters, hence generating further degeneracy [in addition to σ8, Ωm, LX–T(z)] in the cosmological interpretation of the cluster number counts. We provide useful empirical formulae for the cluster mass–flux and mass–count rate relations as well as a comparison between the XMM-LSS mass sensitivity and that of forthcoming Sunyaev–Zel'dovich surveys.
Monthly Notices of the Royal Astronomical Society 12/2007; 382(3):1289 - 1308. · 4.90 Impact Factor
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G. Fabbiano,
N. J. Brassington,
A. Zezas,
S. Zepf,
L. Angelini,
R. L. Davies,
J. Gallagher,
V. Kalogera,
D W Kim,
A. R. King,
A. Kundu,
S. Pellegrini, G Trinchieri
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ABSTRACT: Our campaign of deep monitoring observations with {\it Chandra} of the nearby elliptical galaxy NGC 3379 has lead to the detection of nine globular cluster (GC) and 53 field low mass X-ray binaries (LMXBs) in the joint {\it Hubble}/{\it Chandra} field of view of this galaxy. Comparing these populations, we find a highly significant lack of GC LMXBs at the low (0.3-8 keV) X-ray luminosities (in the $\sim 10^{36}$ to $\sim 4\times10^{37}$ erg s$^{-1}$ range) probed with our observations. This result conflicts with the proposition that all LMXBs are formed in GCs. This lack of low-luminosity sources in GCs is consistent with continuous LMXB formation due to stellar interactions and with the transition from persistent to transient LMXBs. The observed cut-off X-ray luminosity favors a predominance of LMXBs with main-sequence donors instead of ultra-compact binaries with white-dwarf donors; ultra-compacts could contribute significantly only if their disks are not affected by X-ray irradiation. Our results suggest that current theories of magnetic stellar wind braking may work rather better for the unevolved companions of GC LMXBs than for field LMXBs and cataclysmic variables in the Galaxy, where these companions may be somewhat evolved.
11/2007;
