Probing broad absorption line quasar outflows: X-ray insights

Energetic outflows appear to occur in conjunction with active mass accretion onto supermassive black holes. These outflows are most readily observed in the 10% of quasars with broad absorption lines, where the observer’s line of sight passes through the wind. Until fairly recently, the paucity of X-ray data from these objects was notable, but now sensitive hard-band missions such as Chandra and XMM-Newton are routinely detecting broad absorption line quasars. The X-ray regime offers qualitatively new information for the understanding of these objects, and these new results must be taken into account in theoretical modeling of quasar winds.     

Cosmic-ray antiprotons in the galaxy

A key issue in fundamental physics is the nature of non-baryonic dark matter in the universe. Among the candidates proposed by the particle physics community are neutralinos whose annihilation in the Galactic halo can produce antiprotons with a characteristic spectrum. Several balloon and space borne experiments have been actively looking to detect the neutralino signature in cosmic antiprotons. This task is however hampered by the existence of a secondary “background” flux of antiprotons produced in the interactions of cosmic-ray particles in the interstellar medium. A notable difficulty is that a self-consistent and complete model of cosmic-ray propagation in the Galaxy has thus far been elusive. When subtracting the secondary background from the observed data, it is therefore critical that all viable models of secondary cosmic-ray antiproton propagation be thoroughly examined, and all uncertainties stemming from plurality of the models be duly considered. In this paper we concentrate on three particular models of Diffusion, Galactic Wind, and Distributed Stochastic Reacceleration, and discuss the predicted antiproton spectrum in each model.     

ROSAT observations of galaxy clusters and cosmological implications

Clusters of galaxies are filled with a hot teneous plasma which is emitting soft X-rays over very extended regions. The ROSAT observatory with its high resolution and high sensitivity X-ray telescope allows to image nearby clusters in great detail and is therefore ideally suited to study the structure and morphology of galaxy clusters. In particular the distribution of the intracluster gas can be mapped, some information on the temperature structure of the gas can be obtained, the gravitational mass can be infered, and the dynamical state of the clusters can be investigated. Results of such studies for some nearby clusters as Virgo, Perseus and Coma are presented. Gas mass fractions of the total gravitational mass of the cluster in excess of 10 to 15% are infered from X-ray observations where the cluster emission can be traced out to an Abell radius (3 Mpc). If these values are taken to be representative for the matter composition in the Universe it has interesting consequences for cosmology as for example for the nucleosythesis models and the mean density of the Universe.     

The X-ray structure of nearby galaxy clusters

The combination of the large effective area and the very low internal background of the ROSAT Position Sensitive Proportional Counter provides an extremely sensitive instrument for the study of diffuse X-ray sources. In this paper we review new results on the X-ray structure of nearby clusters as measured with ROSAT. Substructure is a common feature in these objects. Such structure provides evidence that clusters have formed relatively recently through mergers of relatively large subunits. This behavior is predicted by hierarchical formation theories in a dense universe.     

Compact X-ray sources in nearby galaxy nuclei

We have found compact, near-nuclear X-ray sources in 21 (54%) of a complete sample of 39 nearby face-on spiral and elliptical galaxies with available ROSAT HRI data. ROSAT X-ray luminosities (0.2 – 2.4 keV) of these compact X-ray sources are ∼10³⁷ – 10⁴⁰ erg s⁻¹. The mean displacement between the location of the compact X-ray source and the optical photometric center of the galaxy is ∼390 pc. ASCA spectra of six of the 21 galaxies show the presence of a hard component with relatively steep (Γ ≈ 2.5) spectral slope. A multicolor disk blackbody plus power-law model fits the data from the spiral galaxies well, suggesting that the X-ray objects in these galaxies may be similar to a black hole candidate (BHC) in its soft (high) state. ASCA data from the elliptical galaxies indicate that hot (kT ≈ 0.7 keV) gas dominates the emission. The fact that the spectral slope of the spiral galaxy sources is steeper than in normal type 1 active galactic nuclei (AGNs) and that relatively low absorbing columns (N_H ≈ 10²¹ cm⁻²) were found to the power-law component indicates that these objects are somehow geometrically and/or physically different from AGNs in normal active galaxies. The X-ray sources in the spiral galaxies may be BHCs, low-luminosity AGNs, or possibly X-ray luminous supernovae. We estimate the black hole masses of the X-ray sources in the spiral galaxies (if they are BHCs or AGNs) to be ∼10²–10³ M_⊙. The X-ray sources in the elliptical galaxies may be BHCs, AGNs or young X-ray supernova also.     

Dark matter in very poor galaxy groups

We have analyzed a sample of 7000 galaxies in the Local Supercluster (LS) (V < 3100 km/s) selected from the LEDA database [Makarov, D.I., Karachentsev, I.D. A new catalogue of multiple galaxies in the local supercluster small galaxy groups. Small Galaxy Groups ASP Confer. Ser. 209, 40–46, 2000]. We have derived physical properties of poor LS groups selected by dynamical and 3D-Voronoi tessellation methods. Median values of mass-to-luminosity ratios for poor LS groups selected by these methods are 50 M_⊙/L_⊙ and 34 M_⊙/L_⊙, respectively. Physical parameters of LS galaxy triplets in comparison with other samples were evaluated. We suggest that the Dressler effect is present even in such poor groups as galaxy triplets. The data suggest that dark matter haloes are associated with the individual galaxies for LS triplets, which we find are dynamically younger systems. This contrasts with the properties of the Interacting and Northern & Southern triplet samples. For these two samples, the data suggest that the dark matter resides in a common halo. The median values of the mass-to-luminosity ratios for LS triplets, Northern & Southern triplets, and Interacting triplets are 35 M_⊙/L_⊙, 47 M_⊙/L_⊙, and 13 M_⊙/L_⊙, respectively.     

Reverberation time lags in the high luminosity quasar PG 1247+267

Virial estimates of the black hole mass in the center of AGNs, derived from single-epoch observations of luminosity and emission line widths, are now available for several thousands of objects at all redshifts and luminosities, so that studies of the cosmological evolution of the AGN mass function are becoming possible. These estimates are based on the empirical luminosity-size relation measured through reverberation mapping at low redshifts and luminosities. For this reason the spectrophotometric monitoring of 4 luminous quasars was started in 2003, with the 1.8 m telescope of the Asiago Observatory. To measure the reverberation time lag we adopt a method, recently introduced by Zu et al. (2011), which takes advantage of the available statistical information on variability autocorrelation and makes simple assumptions on the continuum-emission line transfer function. We present the estimate of the broad line region size for the quasar PG 1247+267, which is the most luminous object with reverberation measures to date. Virial products computed for C iv and C iii] emission lines provide consistent results. A possible flattening of the size-luminosity relation for C iv at high luminosity is suggested.     

Sunyaev-Zel'dovich effect and the dust emission in the galaxy clusters

It is shown that if the dust is present in the hot intergalactic gas, the galaxy cluster must be very bright source of far infrared emission. This emission can be observed by modern IR astronomy methods. At the same time, taking realistic assumptions about the intergalactic dust nature, it is impossible to explain negative results of the attempts made at observational detecting the Sunyaev-Zel'dovich effect in the centimeter wavelength region as the compensation of the expected decrements by the dust grains emission.     

Millimeter-wave spectroscopy and mapping of quasar hosts,and the status of ULIRGS as Quasar 2s

It is becoming possible to detect high redshift quasars in various molecular lines, and to show by mapping lensed objects that the strong dust and molecular emission arises in warm dense ∼ 100 pc-scale “tori.” The properties of ULIRGS, at least those with AGN-like narrow line regions, are very similar, as expected in the hidden quasar hypothesis. Several of the latter are in fact confirmed as “Quasar 2s” by spectropolarimetry. I argue against claims that the source of the majority of the luminosity has been determined in any ULIRG or Scuba sources.     

BAX: a dedicated X-rays galaxy clusters database

We present BAX, Base de Données amas de galaxies X (http://webast.ast.obs-mip.fr/bax), a project aiming at building a comprehensive database dedicated to X-rays clusters of galaxies allowing detailed information retrieval. BAX provides the user with basic data published in the literature on X-rays clusters of galaxies as well as with information concerning the physical properties in the X-rays domain or at other wavelengths. BAX allows individual studies on selected clusters as well as building up homogenous samples, from known X-rays clusters for which selection criteria are chosen through web interfaces. We expect BAX to become a useful tool for astronomy community in order to optimize the cluster science return using data from both ground based facilities like MEGACAM (CFHT), VIRMOS (VLT) and space missions like XMM, Chandra and Planck.     

X-ray and radio observations of the galaxy cluster 3C 129

The galaxy cluster 3C 129 contains two radio galaxies, the prototypical head tail radio galaxy 3C 129 and the weaker radio galaxy 3C 129.1. The tail of the first radio galaxy extends over more than 15′ across the sky. In this paper, we report on Chandra spectroscopy observations of the galaxy cluster, complemented by new and archival radio data taken with the Very Large Array (VLA) at 0.33, 1.4, 5, and 8 GHz and by HI-observations performed with the dominion radio astrophysical observatory (DRAO). We describe the Chandra results on the properties of the Intra-Cluster Medium (ICM) and discuss extended X-ray emission detected from the host galaxy of the radio galaxy 3C 129.1 and from the inner jet of the radio galaxy 3C 129. Finally, we report on the results of an ICM/radio plasma pressure balance study along the tail of the radio galaxy 3C 129.     

The AGN/normal galaxy connection: Summary

The connection between normal and active galaxies is reviewed, by summarizing our progress on answering nine key questions. (1) Do all galaxies contain massive dark objects (MDOs)? (2) Are these MDOs actually supermassive black holes? (3) Why are the dark objects so dark? (4) Do all galaxies contain an Active Galactic Nucleus (AGN)? (5) Are the “dwarf AGN” really AGN? (6) Does AGN activity correlate with host galaxy properties? (7) How are AGN fuelled? (8) Is AGN activity related to starburst activity? (9) How do quasars relate to galaxy formation?     

Evolution of galaxy cluster scaling from XMM-Newton observation of the galaxy clusters at z ⩾ 0.4

We present here new XMM-Newton observations of 3 relatively cool clusters at z ≈ 0.4, complemented by archival observations of 3 other clusters at similar redshift. We derived the M–T and R–T relations from the hydrostatic equation using an isothermal temperature distribution.     

Hard X-ray component in Sco X-1 spectrum: Synchrotron emission from a nano quasar

Sco X-1 is a low mass X-ray binary system and with the recent observations of a resolved radio jet, the source has been included in the list of galactic microquasars. The observed spectral data in the 2–20 keV energy band fits a thermal emission. Above 20 keV, a hard tail has been reported on occasions. During our continuing balloon borne X-ray survey in the 20–200 keV region using high sensitivity Large Area Scintillation counter Experiment, Sco X-1 was observed on two different occasions. Even though the total X-ray luminosity of the source was different, the spectral nature of the source did not show any variation. The presence of hard X-ray flux is unmistakable. We present the spectral and temporal data in the hard X-ray band and discuss the results in terms of geometrical characteristics of X-ray source and its observed temporal properties. We note that the jet activity is similar to the microquasars, however, the absence of the large magnitude abrupt changes in X-ray light curve compared to GRS1915 + 105 suggest that the quasar-like behaviour is at a nano scale.     

The entropy in groups – a clue to galaxy formation

The entropy in the hot X-ray gas in groups of galaxies is a fossil of the process of galaxy formation The amount of entropy in these low mass systems considerably exceeds that predicted from structure formation models. To explain these results requires “extra” energy which is a relic of the process of star formation and active galaxy heating. We present new XMM results on the entropy and entropy profiles. These results are inconsistent with pre-heating scenarios which have been developed to explain the entropy floor in groups but are broadly consistent with models of structure formation which include the effects of heating and/or the cooling of the gas. The total entropy in these systems provides a strong constraint on all models of galaxy and group formation, and on the poorly defined feedback process which controls the transformation of gas into stars and thus the formation of structure in the universe.     

On the origin of cosmic rays in the spiral galaxy NGC 3310

The problem of cosmic ray production in the spiral galaxy NGC 3310 is addressed by analysing and comparing optical and radio continuum data. Tentative results indicate that on global scales relativistic electrons may be produced in the shock front associated with teh density wave while on local scales extreme population I objects may be producing them. It is inferred that the same conclusions apply to all cosmic rays produced in the disk.     

A serendipitous survey for galaxy clusters by the XMM-Newton Survey Science Center

We describe the initial results of a programme to detect and identify extended X-ray sources found serendipitously in XMM-Newton observations. We have analyzed 186 EPIC-PN images at high galactic latitude with a limiting flux of 1 × 10⁻¹⁴ erg cm⁻² s⁻¹ and found 62 cluster candidates. Thanks to the enhanced sensitivity of the XMM-Newton telescopes, the new clusters found in this pilot study are on the average fainter, more compact, and more distant than those found in previous X-ray surveys. At our survey limit the surface density of clusters is about 5 deg⁻². We also present the first results of an optical follow-up programme aiming at the redshift measurement of a large sample of clusters. The results of this pilot study give a first glimpse on the potential of serendipitous cluster science with XMM-Newton based on real data. The largest, yet to be fulfilled promise is the identification of a large number of high-redshift clusters for cosmological studies up to z = 1 or 1.5.     

A multi-epoch study of the C IV absorption variability in the broad absorption line quasar APM 08279+5255

Broad absorption line (BAL) variability potentially represents a powerful tool to investigate the physical nature and the structure of gas outflows in active galactic nuclei. Most existing BAL variability studies rely on observations taken at a few epochs for samples of tens of BAL QSOs. In this study we present the first “monitoring” of a single object, APM 08279+5255, which has been observed more than 20 times since 2003. All available spectra from the literature have also been analysed, including two high resolution spectra, extending the time interval from 1998 to 2012. A relative stability of the shape of the absorption profile is found. At the same time significant variations of the equivalent width are observed. A correlation of the BAL equivalent width with the QSO luminosity is found for the first time. These results suggest that changes in the ionisation state of the gas are causing opacity changes.