arXiv subjects

G. Trinchieri

Publications and source records attributed to G. Trinchieri.

At least 55 records · Page 3Linked to original sources

arXiv2010

The jet and counterjet of 3C 270 (NGC 4261) viewed in the X-ray with Chandra

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.

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arXiv2009

JKCS041: a colour-detected galaxy cluster at z_phot=1.9 with deep potential well as confirmed by X-ray data

[Abridged] We report the discovery of JKCS041, a massive near-infrared selected cluster of galaxies z=1.9. The cluster was originally discovered using a modified red-sequence method and was also detected in follow-up Chandra data as extended X-ray source. Optical and near-infrared imaging data alone allow us to show that the detection of JKCS041 is as secure, even in absence of the X-ray data. We investigate the possibility that JKCS041 is not a discrete galaxy cluster at z=1.9, and find other explanations to be unlikely. The X-ray detection and statistical arguments rule out the hypothesis that JKCS041 is actually a blend of groups along the line of sight, and we find that the X-ray emitting gas is too hot and dense to be a filament projected along the line of sight. The cluster has an X-ray core radius of 36.6 arcsec (about 300 kpc), an X-ray temperature of 7.4 keV, a bolometric X-ray luminosity within R500 of 7.6 10^44 erg/s, an estimated mass of M500=2.9 10^14 Msol, the latter derived under the usual (and strong) assumptions. The cluster is composed of 16.4 galaxies within 1.5 arcmin (750 kpc) brighter than K~20.7 mag. The high redshift of JKCS041 is determined from the detection colour, from the detection of the cluster in a galaxy sample formed by z_phot>1.6 galaxies and from a photometric redshift based on 11-band spectral energy distribution fitting. By means of the latter we find the cluster redshift to be 1.84<z<2.12 at 68 % confidence. Therefore, JKCS041 is a cluster of galaxies at z=1.9 with deep potential well, making it the most distant cluster with extended X-ray emission known.

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arXiv2009

Comparing GC and Field LMXBs in Elliptical Galaxies with deep Chandra and Hubble data

(abridged) We present a statistical study of the low-mass X-ray binary (LMXB) populations of three nearby, old elliptical galaxies: NGC 3379, NGC 4278, and NGC 4697. With a cumulative ~1 Ms Chandra ACIS observing time, we detect 90-170 LMXBs within the D25 ellipse of each galaxy. Cross-correlating Chandra X-ray sources and HST optical sources, we identify 75 globular cluster (GC) LMXBs and 112 field LMXBs. In the low luminosity range allowed by our deeper data (LX < 5 x 1037 erg s-1), we find a significant relative lack of GC-LMXBs, when compared with field sources. Using the co-added sample from the three galaxies, we find that the incompleteness-corrected X-ray luminosity functions (XLFs) of GC and field LMXBs differ at ~4# significance at LX < 5 x 1037 erg s-1. As previously reported, these XLFs are consistent at higher luminosities. Our observations may indicate a potential predominance of GC-LMXBs with donors evolved beyond the main sequence, when compared to current models, but their efficient formation requires relatively high initial binary fractions in clusters. The field LMXB XLF can be fitted with either a single power-law model plus a localized excess at a luminosity of 5-6 x 1037 erg s-1, or a broken power-law with a similar low-luminosity break. This XLF may be explained with NS-red-giant LMXBs, contributing to ~15% of total LMXBs population at ~5x1037 erg s-1. The difference in the GC and field XLFs is consistent with different origins and/or evolutionary paths between the two LMXB populations, although a fraction of the field sources are likely to have originated in GCs.

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arXiv2009

Small-scale systems of galaxies. IV. Searching for the faint galaxy population associated with X-ray detected isolated E+S pairs

In hierarchical evolutionary scenarios, isolated, physical pairs may represent an intermediate phase, or "way station", between collapsing groups and isolated elliptical (E) galaxies (or fossil groups). We started a comprehensive study of a sample of galaxy pairs composed of a giant E and a spiral (S) with the aim of investigating their formation/evolutionary history from observed optical and X-ray properties. Here we present VLT-VIMOS observations designed to identify faint galaxies associated with the E+S systems from candidate lists generated using photometric criteria on WFI images covering an area of ~ 0.2 h^{-1} Mpc radius around the pairs. The results are discussed in the context of the evolution of poor galaxy group associations. A comparison between the Optical Luminosity Functions (OLFs) of our E+S systems and a sample of X-ray bright poor groups suggest that the OLF of X-ray detected poor galaxy systems is not universal. The OLF of our X-ray bright systems suggests that they are more dynamically evolved than our X-ray faint sample and some X-ray bright groups in the literature. However, we suggest that the X-ray faint E+S pairs represent a phase in the dynamical evolution of some X-ray bright poor galaxy groups. The recent or ongoing interaction in which the E member of the X-ray faint pairs is involved could have decreased the luminosity of any surrounding X-ray emitting gas.

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arXiv2009

The HI content of early-type galaxies from the ALFALFA survey. II. The case of low density environments

We present the analysis of the HI content of a sample of early-type galaxies (ETGs) in low-density environments (LDEs) using the data set provided by the Arecibo Legacy Fast ALFA (ALFALFA) survey. We compare their properties to the sample in the Virgo cluster that we studied in a previous paper (di Serego Alighieri et al. 2007, Paper I). We have selected a sample of 62 nearby ETGs (V< 3000 km/s) in an area of the sky where the ALFALFA data are already available (8h -17). In both cases it is 10 times higher than that of the Virgo cluster. The presence of gas can be related to a recent star formation activity: 60% of all ETGs with HI have optical emission line ratios typical of star-forming galaxies and blue colours suggesting the presence of young stellar populations, especially in the dwarf subsample. We show that the HI detection rate of ETGs depends both on the environment and mass. The fraction of early-type systems with neutral hydrogen is higher in more massive objects when compared to early-type dwarfs. The ETGs in LDEs seem to have more heterogeneous properties than their Virgo cluster counterparts, since they are able to retain a cold interstellar gas component and to support star formation activity even at recent epochs.

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arXiv2009

The Very Local Universe in X-rays

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.

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arXiv2009

Deep Chandra Monitoring Observations of NGC 4278: Catalog of Source Properties

We present the properties of the discrete X-ray sources detected in our monitoring program of the globular cluster (GC) rich elliptical galaxy, NGC 4278, observed with Chandra ACIS-S in six separate pointings, resulting in a co-added exposure of 458-ks. From this deep observation, 236 sources have been detected within the region overlapped by all observations, 180 of which lie within the D25 ellipse of the galaxy. These 236 sources range in Lx from 3.5E36 erg/s (with 3sigma upper limit <1E37 erg/s) to ~2E40 erg/s, including the central nuclear source which has been classified as a LINER. From optical data, 39 X-ray sources have been determined to be coincident with a globular cluster, these sources tend to have high X-ray luminosity, with ten of these sources exhibiting Lx>1E38 erg/s. From X-ray source photometry, it has been determined that the majority of the 236 point sources that have well constrained colors, have values that are consistent with typical LMXB spectra, with 29 of these sources expected to be background objects from the logN-logS relation. There are 103 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. 3 of these sources have been identified as transient candidates, with a further 3 possible transients. Spectral variations have also been identified in the majority of the source population, where a diverse range of variability has been identified, indicating that there are many different source classes located within this galaxy.

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arXiv2009

Transient Low-Mass X-Ray Binary Populations in Elliptical Galaxies NGC 3379 and NGC 4278

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.

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arXiv2008

Obscured and powerful AGN and starburst activities at z~3.5

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.

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arXiv2008

XMM-Newton observations of the diffuse X-ray emission in the starburst galaxy NGC 253

Aims: We present a study of the diffuse X-ray emission in the halo and the disc of the starburst galaxy NGC 253. Methods: After removing point-like sources, we analysed XMM-Newton images, hardness ratio maps and spectra from several regions in the halo and the disc. We introduce a method to produce vignetting corrected images from the EPIC pn data, and we developed a procedure that allows a correct background treatment for low surface brightness spectra, using a local background, together with closed filter observations. Results: Most of the emission from the halo is at energies below 1 keV. In the disc, also emission at higher energies is present. The extent of the diffuse emission along the major axis of the disc is 13.6 kpc. The halo resembles a horn structure and reaches out to ~9 kpc perpendicular to the disc. Disc regions that cover star forming regions, like spiral arms, show harder spectra than regions with lower star forming activity. Models for spectral fits of the disc regions need at least three components: two thermal plasmas with solar abundances plus a power law and galactic foreground absorption. Temperatures are between 0.1 and 0.3 keV and between 0.3 and 0.9 keV for the soft and the hard component, respectively. The power law component may indicate an unresolved contribution from X-ray binaries in the disc. The halo emission is not uniform, neither spatially nor spectrally. The southeastern halo is softer than the northwestern halo. To model the spectra in the halo, we needed two thermal plasmas with solar abundances plus galactic foreground absorption. Temperatures are around 0.1 and 0.3 keV. A comparison between X-ray and UV emission shows that both originate from the same regions.

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arXiv2008

Discovery of Hot Gas in Outflow in NGC3379

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.

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arXiv2008

XMM-Newton X-ray and Optical Monitor far UV observations of NGC 7070A and ESO 2400100 shell galaxies

We present XMM-Newton X-ray observations of two shell galaxies, NGC 7070A and ESO 2400100, and far UV observations obtained with the Optical Monitor for these and for an additional shell galaxy, NGC 474, for which we also have near and far UV data from GALEX. We aim at gaining insight on the overall evolution traced by their star formation history and by their hot gas content. The X-ray and the far UV data are used to derive their X-ray spatial and spectral characteristics and their UV luminosity profiles. We use models developed ad hoc to investigate the age of the last episode of star formation from the (UV - optical) colors and line strength indices. The X-ray spatial and spectral analysis show significant differences in the two objects. A low luminosity nuclear source is the dominant component in NGC 7070A log L_X=41.7 erg s^{-1} in the 2-10 keV band. In ESO 2400100, the X-ray emission is due to a low temperature plasma with a contribution from the collective emission of individual sources. In the Optical Monitor image ESO 2400100 shows a double nucleus, one bluer than the other. This probably results from a very recent star formation event in the northern nuclear region. The extension of the UV emission is consistent with the optical extent for all galaxies, at different degrees of significance in different filters. The presence of the double nucleus, corroborated by the (UV - optical) colors and line strength indices analysis, suggests that ESO 2400100 is accreting a faint companion. We explore the evolution of the X-ray luminosity during accretion processes with time. We discuss the link between the presence of gas and age, since gas is detected either before coalescence or several Gyr (>3) after (Abridged).

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arXiv2008

Deep Chandra Monitoring Observations of NGC 3379: Catalog of Source Properties

We present the properties of the discrete X-ray sources detected in our monitoring program of the `typical' elliptical galaxy, NGC 3379, observed with Chandra ACIS-S in five separate pointings, resulting in a co-added exposure of 324-ks. From this deep observation, 132 sources have been detected within the region overlapped by all observations, 98 of which lie within the D25 ellipse of the galaxy. These 132 sources range in Lx from 6E35 erg/s (with 3sigma upper limit <4E36 erg/s) to ~2E39 erg/s, including one source with Lx>1E39 erg/s, which has been classified as a ULX. From optical data, 10 X-ray sources have been determined to be coincident with a globular cluster, these sources tend to have high X-ray luminosity, with three of these sources exhibiting Lx> 1E38 erg/s. From X-ray source photometry, it has been determined that the majority of the 132 sources that have well constrained colors, have values that are consistent with typical LMXB spectra. Additionally to this, a sub-population of 10 sources has been found to exhibit very hard spectra and it is expected that most of these sources are absorbed background AGN. There are 64 sources in this population that exhibit long-term variability, indicating that they are accreting compact objects. Five of these sources have been identified as transient candidates, with a further 3 possible transients. Spectral variations have also been identified in the majority of the source population, where a diverse range of variability has been identified, indicating that there are many different source classes located within this galaxy.

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arXiv2008

Detection of a hot intergalactic medium in the spiral-only compact group SCG0018-4854

AIMS: Compact groups of galaxies are excellent laboratories for studying galaxy interactions and their effects on the evolution of galaxies. In particular, dynamically young systems, with a large fraction of interacting, late type galaxies, have so far escaped proper studies in the X-ray band and their hot intergalactic medium properties are virtually unknown. Motivated by this lack of knowledge, we present a detailed investigation here of the X-ray properties of such a dynamically young system. METHODS: We obtained XMM-Newton observations of one spiral-only system in the new southern compact group catalogue: SCG0018-4854. We present here the results of the data analysis and discuss them in comparison with the few other similar systems also studied in the X-ray band. RESULTS: The 4 members of SCG0018-4854 emit at a level comparable to what is expected based on their optical properties. We detect the low level diffuse emission between galaxies, which is most likely due to the presence of the intergalactic medium. Compared to other spiral--only groups, this could be the coolest system detected so far, although the measurements have large uncertainties. These results indicate that high quality deep X-ray observations are needed to allow a proper study of the properties of the potential well of dynamically young systems, before more general conclusions can be drawn on their average characteristics.

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arXiv2008

Early-type galaxies with neutral hydrogen in the Virgo cluster from the ALFALFA survey

We extend our published work on the neutral hydrogen content of early-type galaxies in the Virgo cluster using the catalogue of detected sources from the ALFALFA survey, by showing the 21cm spectra of all the detected galaxies and discussing a deeper analysis of the ALFALFA datacubes, searching for lower S/N sources. A view of the multiphase interstellar medium of M86 is also presented, by comparing images of the cold, warm and hot phases.

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arXiv2008

Far UV and X-ray observation: a hot view of shell galaxies

Shell galaxies are considered the debris of recent accretion/merging episodes. Their high frequency in low density environments suggest that such episodes could drive the secular evolution for at least some fraction of the early-type galaxy population. We present here the preliminary results of ultraviolet and X-ray data for a sample of three shell galaxies, namely NGC 474, NGC 7070A and ESO 2400100. The Far UV morphology and photometry are derived using the observations obtained with the Galaxy Evolution Explorer and the XMM- Newton Optical Monitor. We aim at investigating the rejuvenation processes in the stellar population using the UV information as well as at gaining information about the possible evolution with time of the X-ray emission due interaction/merging processes.

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arXiv2008

Models for Low-Mass X-Ray Binaries in the Elliptical Galaxies NGC3379 and NGC4278: Comparison with Observations

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.

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arXiv2007

The Dearth of low-luminosity Globular Cluster LMXBs in NGC 3379

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.

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