Papers by Vincenzo Mainieri
Monthly Notices of the Royal Astronomical Society: Letters
Many active galactic nuclei (AGN) surveys rely on optical emission line signatures for robust sou... more Many active galactic nuclei (AGN) surveys rely on optical emission line signatures for robust source classification. There are, however, examples of luminous AGN candidates lacking such signatures, including those from the narrow-line region, which are expected to be less susceptible to classical nuclear (torus) obscuration. Here, we seek to formalize this subpopulation of AGN with a prototypical candidate, SDSS J075139.06+402810.9. This shows infrared (IR) colours typical for AGN, an optical spectrum dominated by an early type galaxy continuum, an [O iii] λ5007Å limiting flux about two dex below Type 2 quasars at similar IR power, and a k-corrected 12 $\mu$m quasar-like luminosity of ∼ 1045 erg s−1. These characteristics are not consistent with jet and host galaxy dilution. A potential scenario to explain this AGN quiescence in the optical is a sky-covering ‘cocoon’ of obscuring material, such that the AGN ionizing radiation is unable to escape and excite gas on kpc scales. Alterna...
The Astrophysical Journal Supplement Series
We present a detailed spectral analysis of the brightest Active Galactic Nuclei (AGN) identified ... more We present a detailed spectral analysis of the brightest Active Galactic Nuclei (AGN) identified in the 7Ms Chandra Deep Field South (CDF-S) survey over a time span of 16 years. Using a model of an intrinsically absorbed power-law plus reflection, with possible soft excess and narrow Fe Kα line, we perform a systematic X-ray spectral analysis, both on the total 7Ms exposure and in four different periods with lengths of 2-21 months. With this approach, we not only present the power-law slopes, column densities N H , observed fluxes, and absorption-corrected 2-10 keV luminosities L X for our sample of AGNs, but also identify significant spectral variabilities among them on time scales of years. We find that the N H variabilities can be ascribed to two different types of mechanisms, either flux-driven or flux-independent. We also find that the correlation between the narrow Fe line EW and N H can be well explained by the continuum suppression with increasing N H. Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of N H for the CDF-S AGN population and present reselected subsamples which are complete with respect to N H. The N H-complete subsamples enable us to decouple the dependences of N H on L X and on redshift. Combining our data with that from C-COSMOS, we confirm the anti-correlation between the average N H and L X of AGN, and find a significant increase of the AGN obscured fraction with redshift at any luminosity. The obscured fraction can be described as f obscured ≈ 0.42 (1 + z) 0.60 .
Ground-based and Airborne Instrumentation for Astronomy VI, 2016
Bulletin of the American Astronomical Society, 2009
The detailed X-ray spectral analysis of sources in the Chandra Deep Field South, allows us to stu... more The detailed X-ray spectral analysis of sources in the Chandra Deep Field South, allows us to study the distribution of intrinsic obscuration among AGN. The Mid-InfraRed data from Spitzer reveals that no proposed mid-IR color selection will identify all the X-ray AGN. In addition, IRAC color-color criteria in the literature select the CDF-S X-ray sources with 22-31% reliability and 2-5% completeness.
We present the evolutionary properties and luminosity functions of the radio sources belonging to... more We present the evolutionary properties and luminosity functions of the radio sources belonging to the Chandra Deep Field South VLA survey, which reaches a flux density limit at 1.4 GHz of 43 µJy at the field center and redshift ∼ 5, and which includes the first radio-selected complete sample of radio-quiet active galactic nuclei (AGN). We use a new, comprehensive classification scheme based on radio, farand near-IR, optical, and X-ray data to disentangle star-forming galaxies from AGN and radio-quiet from radio-loud AGN. We confirm our previous result that star-forming galaxies become dominant only below 0.1 mJy. The sub-millijansky radio sky turns out to be a complex mix of star-forming galaxies and radio-quiet AGN evolving at a similar, strong rate; non-evolving low-luminosity radio galaxies; and declining radio powerful (P 3 × 10 24 W Hz −1) AGN. Our results suggest that radio emission from radio-quiet AGN is closely related to star formation. The detection of compact, high brightness temperature cores in several nearby radio-quiet AGN can be explained by the coexistence of two components, one non-evolving and AGN-related and one evolving and star-formation-related. Radio-quiet AGN are an important class of sub-millijansky sources, accounting for ∼ 30% of the sample and ∼ 60% of all AGN, and outnumbering radio-loud AGN at 0.1 mJy. This implies that future, large area sub-millijansky surveys, given the appropriate ancillary multi-wavelength data, have the potential of being able to assemble vast samples of radio-quiet AGN bypassing the problems of obscuration, which plague the optical and soft X-ray bands.
Astron Astrophys, 2004
Using deep VLT/ISAAC near-infrared imaging data, we derive the Ks-band luminosity function (LF) o... more Using deep VLT/ISAAC near-infrared imaging data, we derive the Ks-band luminosity function (LF) of the z = 1.237 massive X-ray luminous cluster of galaxies RDCS J1252.9−2927. Photometric redshifts, derived from deep multi-wavelength BV RIzJKs data, and calibrated using a large subset of galaxies with spectroscopic redshifts, are used to separate the cluster galaxy population from the foreground and background field galaxy population. This allows for a simultaneous determination of the characteristic magnitude K * s and faint end slope α of the LF without having to make an uncertain statistical background subtraction. The derived LF is well represented by the Schechter function with K * s = 18.54 +0.45 −0.55 and α = −0.64 +0.27 −0.25. The shape of the bright end of the derived LF is similar to that measured at similar restframe wavelengths (in the z-band) in local clusters, but the characteristic magnitude is brighter by ∆M * z = −1.40 +0.49 −0.58 magnitudes. The derived α is similar to the value derived in the Ks-band in the z = 1 cluster of galaxies MG2016+112 but is shallower (at the 2.2σ level) than the value measured at similar restframe wavelength (in the z-band) in clusters in the local universe. The brightening of the characteristic magnitude and lack of evolution in the shape of the bright end of the LF suggests that the massive cluster ellipticals that dominate the bright end of the LF were already in place at z = 1.237, while the flattening of the faint end slope suggest that clusters at z ∼ 1 contains relatively smaller fractions of low mass galaxies than clusters in the local universe. The results presented in this paper are a challenge for semi analytical hierarchical models of galaxy formation which predict the characteristic magnitude to grow fainter and the faint end slope to steepen with redshift as the massive galaxies break up into their progenitors. The observed evolution is consistent with a scenario in which clusters are composed of a population of massive galaxies which formed at high redshift (z ≫ 1) and subsequently evolved passively, and a population of lower mass galaxies which are gradually accreted from the field, primarily at lower redshift (z < 1).
Eprint Arxiv Astro Ph 0202211, Feb 11, 2002
We present the results of the X-ray spectral analysis of the deep survey obtained with the XMM-Ne... more We present the results of the X-ray spectral analysis of the deep survey obtained with the XMM-Newton observatory on the Lockman Hole. The X-ray data and the cumulative source counts were reported by Hasinger et al. (2001). Our sample contains 104 sources with a count limit of 70 of which 55 have redshift identification. The redshift distribution peaks at z ∼ 0.8, with a strong excess of low z AGN and a deficiency of sources at z > 2 compared to population synthesis models for the X-ray background. The type 2 (obscured) AGN have weaker soft X-ray and optical fluxes. They cluster around z ∼ 1. There is a clear separation between the classical/type 1 AGN and the obscured/type 2 ones in several diagnostics involving X-ray colour, X-ray flux, optical/near IR colour and optical brightness. Using the z subsample, we show that this separation between the AGN populations is a consequence of different absorption column densities. The two populations have the same average spectral index, Γ ∼ 1.9. At the 70 count detection limit, there is also a strong overlap between the two populations in hard X-ray flux and near IR brightness. These diagnostics should enable the classification of obscured/type 2 AGN very faint optically.
ABSTRACT The coalescence of two SMBHs in galaxy major merger gives rise to the strongest Gravitat... more ABSTRACT The coalescence of two SMBHs in galaxy major merger gives rise to the strongest Gravitational Wave (GW) events in the universe. Typically, the GW emission is asymmetric and causes the newly merged single SMBH to displace from the galaxy center of few parsecs. Under particular condition of BH spin and mass ratio, the SMBH can gain a significant velocity (up to ~5000km/s) and it may be displaced by several kpc. If the SMBH is ejected from the galaxy, or even if wanders through the halo for several Gyrs, it will continue to shine for 10^6-10^7 yr, until it exhausts the fuel and is no longer recognizable as an active SMBH. The partial or total absence of the SMBH from the galaxy center has strong implications on the SF history of the galaxy. Despite predicted by theoretical models of structure formation, GW recoiling SMBHs are very hard to detect. The recoils with high probability have a very small velocity resulting in undetectable offsets, those with low probability can escape easily from the galaxy and not been recognized as such. We discovered in the COSMOS survey CID-42 (z=0.359), the best candidate recoiling SMBH to date, just caught when still active. CID-42 clearly shows both the presence of two compact sources, ~2.5 kpc embedded in the same galaxy in HST imaging, and a ~1100km/s velocity offset between the narrow and broad components of Hα, in 3 optical spectra. High resolution Chandra data were crucial to resolve the X-ray emission from the two optical sources and determines the AGN activity level of each. The results clearly favor the recoiling scenario for this source. Models &amp; simulations have been developed to explain the observed properties of CID-42.
ABSTRACT We present a catalog and first study of the Spectra Energy Distributions (SEDs) as a fun... more ABSTRACT We present a catalog and first study of the Spectra Energy Distributions (SEDs) as a function of luminosity and redshift of 278 X-ray (XMM) selected Type 1 AGNs from the wide-field &quot;Cosmological Evolution Survey&quot; (COSMOS), all of which have deep coverage and rich sampling of frequencies from X-ray to radio and spectroscopical confirmation from Magellan (IMACS), the MMT or the SDSS. We present the average SED and the dispersion SEDs before and after corrections of broad emission line photometry, Galactic extinction, and we limit our data to the interval of 2005 2007 to minimize variations. We then study the shape of the SEDs in redshift and bolometric luminosity bins, compared with the expected effects of host galaxy contamination and intrinsic extinction. These show that high redshift and high luminosity quasars depart from the mean SEDs of Elvis et al 1994.
Astronomy and Astrophysics, Jul 8, 2002
We present the results of the X-ray spectral analysis of the first deep X-ray survey with the XMM... more We present the results of the X-ray spectral analysis of the first deep X-ray survey with the XMM-Newton observatory during Performance Verification. The X-ray data of the Lockman Hole field and the derived cumulative source counts were reported by Hasinger et al. (2001). We restrict the analysis to the sample of 98 sources with more than 70 net counts (flux limit in the [0.5-7] keV band of 1.6 × 10 −15 erg cm −2 s −1) of which 61 have redshift identification. We find no correlation between the spectral index Γ and the intrinsic absorption column density NH and, for both the Type-1 and Type-2 AGN populations, we obtain Γ ≃ 2. The progressive hardening of the mean X-ray source spectrum with decreasing flux is essentially due to an increase in intrinsic absorption. The marked separation between the two AGN populations in several diagnostics diagrams, involving X-ray colour, X-ray flux, optical/near IR colour and optical brightness, is also a consequence of different absorption column densities and enables the classification of optically faint obscured AGN. The Type-2 and obscured AGN have weaker soft X-ray and optical fluxes and redder R−K ′ colours. They follow the evolutionary tracks of their host galaxies in a color-redshift diagram. About 27% of the subsample with R−K ′ colour are EROs (R−K ′ ≥ 5) and most of these 18 X-ray selected EROs contain an obscured AGN as revealed by their high X-ray-to-optical/near IR flux ratios. There are six sources in our sample with LX[0.5-10]> 10 44 erg s −1 and log(NH) > 10 22 cm −2 : which are likely Type-2 QSOs and we thus derive a density of ∼ 69 objects of this class per square degree.
While the radio-loud, obscured quasars (the radio galaxies) have been known and studied for decad... more While the radio-loud, obscured quasars (the radio galaxies) have been known and studied for decades, new and sensitive X-ray and mid-infrared surveys are now beginning to reveal large numbers of their radio-quiet counterparts beyond the local Universe. Consequent- ly, we are approaching the compilation of a relatively complete census of AGN of all types covering a large fraction of cosmic
The Lockman Hole represents the sky area of lowest Galactic line-of-sight columns density. It was... more The Lockman Hole represents the sky area of lowest Galactic line-of-sight columns density. It was observed by the XMM-Newton X-ray observatory in 18 pointings performed between April 2000 and December 2002. The total exposure time spent on the field was 1.16Ms (EPIC pn detector; EPIC MOS detector: 1.30 Ms). The effective exposure after removal of times of high particle background is 637ks (EPIC pn detector; EPIC MOS detector: 765ks). The catalogue lists positions, count rates, fluxes, hardness ratios, and partial optical classifications of 409 X-ray point sources detected in the central 0.196{deg}2 of the field down to a detection likelihood threshold of 10 (3.9sigma). The analysis was performed using the XMM-Newton SAS data analysis package version 6.0. (1 data file).
Vizier Online Data Catalog, Aug 1, 2009
We have observed the Extended Chandra Deep Field-South (E-CDF-S) using a mosaic of six deep Very ... more We have observed the Extended Chandra Deep Field-South (E-CDF-S) using a mosaic of six deep Very Large Array (VLA) pointings at 1.4GHz. In this paper, we present the survey strategy, description of the observations, and the first data release. The observations were performed during June through September of 2007 and included from 15 to 17 "classic" VLA antennas and 6 to 11 that had been retrofitted for the Expanded VLA (EVLA). The first data release consists of a 34.1'x34.1' image and the attendant source catalog. The image achieves an rms sensitivity of 6.4{mu}Jy per 2.8"x1.6" beam in its deepest regions, with a typical sensitivity of 8uJy. The catalog is conservative in that it only lists sources with peak flux densities greater than seven times the local rms noise, yet it still contains 464 sources. Nineteen of these are complex sources consisting of multiple components. Cross matching of the catalog to prior surveys of the E-CDF-S confirms the linearity of the flux density calibration, albeit with a slight possible offset (a few percent) in scale. Improvements to the data reduction and source catalog are ongoing, and we intend to produce a second data release in 2009 January. (1 data file).
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Papers by Vincenzo Mainieri