73 research outputs found
Demography of obscured and unobscured AGN: prospects for a Wide Field X-ray Telescope
We discuss some of the main open issues in the evolution of Active Galactic
Nuclei which can be solved by the sensitive, wide area surveys to be performed
by the proposed Wide Field X-ray Telescope mission.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in
Bologna, Italy, Nov. 25-26 2009. To appear in Memorie della Societa'
Astronomica Italiana 2010 (arXiv:1010.5889
Mining the SDSS archive. I. Photometric redshifts in the nearby universe
We present a supervised neural network approach to the determination of
photometric redshifts. The method was tuned to match the characteristics of the
Sloan Digital Sky Survey and it exploits the spectroscopic redshifts provided
by this unique survey. In order to train, validate and test the networks we
used two galaxy samples drawn from the SDSS spectroscopic dataset: the general
galaxy sample (GG) and the luminous red galaxies subsample (LRG). The method
consists of a two steps approach. In the first step, objects are classified in
nearby (z<0.25) and distant (0.25<z<0.50). In the second step two different
networks are separately trained on objects belonging to the two redshift
ranges. Using a standard MLP operated in a Bayesian framework, the optimal
architectures were found to require 1 hidden layer of 24 (24) and 24 (25)
neurons for the GG (LRG) sample. The presence of systematic deviations was then
corrected by interpolating the resulting redshifts. The final results on the GG
dataset give a robust sigma_z = 0.0208 over the redshift range [0.01, 0.48] and
sigma_z = 0.0197 and sigma_z = 0.0238 for the nearby and distant samples
respectively. For the LRG subsample we find a robust sigma_z = 0.0164 over the
whole range, and sigma_z = 0.0160, sigma_z = 0.0183 for the nearby and distant
samples respectively. After training, the networks have been applied to all
objects in the SDSS Table GALAXY matching the same selection criteria adopted
to build the base of knowledge, and photometric redshifts for ca. 30 million
galaxies having z<0.5 were derived. A catalogue containing photometric
redshifts for the LRG subsample was also produced.Comment: 45 pages, 14 figures, accepted for publication is the Astrophysical
Journa
High-Redshift Extremely Red Objects in the Hubble Space Telescope Ultra Deep Field Revealed by the GOODS Infrared Array Camera Observations
Using early data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope, taken for the Great Observatories Origins Deep Survey (GOODS), we identify and study objects that are well detected at 3.6 m but are very faint (and in some cases, invisible) in the Hubble Ultra Deep Field (HUDF) ACS and NICMOS images andinverydeepVLT Ks-band imaging. We select a sample of 17 objects with f(3:6 m)=f(z850) > 20. The analysis of their spectral energy distributions (SEDs) from 0.4 to 8.0 m shows that the majority of these objects cannot be satisfactorily explained without a well-evolved stellar population.We find thatmost of themcan be well fitted by a simple two-component model, where the primary component represents a massive, old population that dominates the strong IR emission, while the secondary component represents a low-amplitude, on-going star formation process that accounts for the weak optical fluxes. Their estimated photometric redshifts (zp) range from
1.6 to 2.9 with the median at zp ÂŒ 2:4. For the simple star formation histories considered here, their corresponding stellarmasses range from (0.1â1.6) ; 1011 M for a Chabrier initialmass function ( IMF). Their median rest-frame Ks-band absolute magnitude is 22.9 maginthe AB system,or 1:5 ; L(K) for present-day elliptical galaxies. In the scenario of pure luminosity evolution, such objects may be direct progenitors for at least 14%â51% of the
local population of early type galaxies. Because of the small cosmic volume of the HUDF, however, this simple estimate could be affected by other effects, such as cosmic variance and the strong clustering of massive galaxies. A full analysis of the entire GOODS area is now under way to assess such effects
Unveiling the Nature of Giant Ellipticals and their Stellar Halos with the VST
Observations of diffuse starlight in the outskirts of galaxies provide fundamental constraints on the cosmological context of galaxy assembly in the Lambda Cold Dark Matter model, which predicts that galaxies grow through a combination of in-situ star formation and accretion of stars from other galaxies. Accreted stars are expected to dominate in the outer parts of galaxies. Since dynamical timescales are longer in these regions, substructures related to accretion, such as streams and shells, can persist over many Gyr. In this work we use extremely deep g- and i-band images of six massive early- type galaxies (ETGs) from the VEGAS survey to constrain the properties of their accreted stellar components. The wide field of view of OmegaCAM on the VLT Survey Telescope (VST) also allows us to investigate the properties of small stellar systems (such as globular clusters, ultra-compact dwarfs and satellite galaxies) in the halos of our galaxies. By fitting light profiles, and comparing the results to simulations of elliptical galaxy assembly, we have identified signatures of a transition between relaxed and unrelaxed accreted components and can constrain the balance between in-situ and accreted stars
Galaxy populations in the Hydra i cluster from the VEGAS survey:I. Optical properties of a large sample of dwarf galaxies
At ~50 Mpc, the Hydra I cluster of galaxies is among the closest cluster in
the z=0 Universe, and an ideal environment to study dwarf galaxy properties in
a cluster environment. We exploit deep imaging data of the Hydra I cluster to
construct a new photometric catalog of dwarf galaxies in the cluster core,
which is then used to derive properties of the Hydra I cluster dwarf galaxies
population as well as to compare with other clusters. Moreover, we investigate
the dependency of dwarf galaxy properties on their surrounding environment. The
new Hydra I dwarf catalog contains 317 galaxies with luminosity between
-18.5<<-11.5 mag, a semi-major axis larger than ~200 pc (a=0.84 arcsec),
of which 202 are new detections, previously unknown dwarf galaxies in the Hydra
I central region. We estimate that our detection efficiency reaches 50% at the
limiting magnitude =-11.5 mag, and at the mean effective surface
brightness =26.5 mag/. We present the standard
scaling relations for dwarf galaxies and compare them with other nearby
clusters. We find that there are no observational differences for dwarfs
scaling relations in clusters of different sizes. We study the spatial
distribution of galaxies, finding evidence for the presence of substructures
within half the virial radius. We also find that mid- and high-luminosity
dwarfs (<-14.5 mag) become on average redder toward the cluster center,
and that they have a mild increase in with increasing clustercentric
distance, similar to what is observed for the Fornax cluster. No clear
clustercentric trends are reported with surface brightness and S\'ersic index.
Considering galaxies in the same magnitude-bins, we find that for high and
mid-luminosity dwarfs (<-13.5 mag) the g-r color is redder for the
brighter surface brightness and higher S\'ersic n index objects.Comment: Accepted for publication in A&A. 25 pages, 21 figure
X-Ray Spectral Analyses of AGNs from the 7Ms Chandra Deep Field-South Survey: The Distribution, Variability, and Evolutions of AGN Obscuration
We present a detailed spectral analysis of the brightest active galactic nuclei (AGNs) 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 2â21 months. With this approach, we not only present the power-law slopes, column densities , observed fluxes, and absorption-corrected 2â10 keV luminosities L X for our sample of AGNs, but also identify significant spectral variabilities among them on timescales of years. We find that the 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 can be well explained by the continuum suppression with increasing . Accounting for the sample incompleteness and bias, we measure the intrinsic distribution of for the CDF-S AGN population and present reselected subsamples that are complete with respect to . The -complete subsamples enable us to decouple the dependences of on L X and on redshift. Combining our data with those from C-COSMOS, we confirm the anticorrelation between the average 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
Looking into the faintEst WIth MUSE (LEWIS): on the nature of ultra-diffuse galaxies in the Hydra-I cluster.I. Project description and preliminary results
Looking into the faintEst WIth MUSE (LEWIS) is an ESO large observing
programme aimed at obtaining the first homogeneous integral-field spectroscopic
survey of 30 extremely low-surface brightness (LSB) galaxies in the Hydra I
cluster of galaxies, with MUSE at ESO-VLT. The majority of LSB galaxies in the
sample (22 in total) are ultra-diffuse galaxies (UDGs). The distribution of
systemic velocities Vsys ranges between 2317 km/s and 5198 km/s and is centred
on the mean velocity of Hydra I (Vsys = 3683 46 km/s). Considering the
mean velocity and the velocity dispersion of the cluster, 17 out of 20 targets
are confirmed cluster members. To assess the quality of the data and
demonstrate the feasibility of the science goals, we report the preliminary
results obtained for one of the sample galaxies, UDG11. For this target, we
derived the stellar kinematics, including the 2-dimensional maps of
line-of-sight velocity and velocity dispersion, constrained age and
metallicity, and studied the globular cluster (GC) population hosted by the
UDG. Results are compared with the available measurements for UDGs and dwarf
galaxies in literature. By fitting the stacked spectrum inside one effective
radius, we find that UDG11 has a velocity dispersion km/s,
it is old ( Gyr), metal-poor ([M/H]=-1.170.11 dex) and has a total
dynamical mass-to-light ratio M, comparable to those observed for
classical dwarf galaxies. The spatially resolved stellar kinematics maps
suggest that UDG11 does not show a significant velocity gradient along either
major or minor photometric axes. We find two GCs kinematically associated with
UDG11. The estimated total number of GCs in UDG11, corrected for the
spectroscopic completeness limit, is , which
corresponds to a GC specific frequency of .Comment: Accepted for publication in Astronomy and Astrophysic
VizieR Online Data Catalog: The Fornax Deep Survey with the VST. IX. (Cantiello+, 2020)
We derive ugri photometry of ~1.7 million sources over the ~21 square degree area of the Fornax Deep Survey (FDS) centered on the bright galaxy NGC1399 (fds.dat). For a wider area, of ~27 square degrees extending in the direction of NGC1316, we provide gri photometry for ~3.1 million sources (fdsex.dat). The identification of compact sources, globular clusters (GC) and ultra compact dwarf galaxies (UCD), is obtained from a combination of photometric and morphometric selection criteria taking as reference the properties of confirmed GCs and UCDs in the literature. The master tables of GC and UCD are also provided. (4 data files)
The XMM-SERVS Survey: XMM-Newton Point-source Catalogs for the W-CDF-S and ELAIS-S1 Fields
We present the X-ray point-source catalogs in two of the XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS) fields, W-CDF-S (4.6 deg2) and ELAIS-S1 (3.2 deg2), aiming to fill the gap between deep pencil-beam X-ray surveys and shallow X-ray surveys over large areas. The W-CDF-S and ELAIS-S1 regions were targeted with 2.3 and 1.0 Ms of XMM-Newton observations, respectively; 1.8 and 0.9 Ms exposures remain after flare filtering. The survey in W-CDF-S has a flux limit of 1.0 Ă 10â14 erg cmâ2 sâ1 over 90% of its area in the 0.5â10 keV band; 4053 sources are detected in total. The survey in ELAIS-S1 has a flux limit of 1.3 Ă 10â14 erg cmâ2 sâ1 over 90% of its area in the 0.5â10 keV band; 2630 sources are detected in total. Reliable optical-to-IR multiwavelength counterpart candidates are identified for â89% of the sources in W-CDF-S and â87% of the sources in ELAIS-S1. A total of 3129 sources in W-CDF-S and 1957 sources in ELAIS-S1 are classified as active galactic nuclei (AGNs). We also provide photometric redshifts for X-ray sources; â84% of the 3319/2001 sources in W-CDF-S/ELAIS-S1 with optical-to-near-IR forced photometry available have either spectroscopic redshifts or high-quality photometric redshifts. The completion of the XMM-Newton observations in the W-CDF-S and ELAIS-S1 fields marks the end of the XMM-SERVS survey data gathering. The â12,000 pointlike X-ray sources detected in the whole â13 deg2 XMM-SERVS survey will benefit future large-sample AGN studies
VizieR Online Data Catalog: Chandra Deep Field-South survey: 7Ms sources (Luo+, 2017)
The 7Ms CDF-S contains 102 Chandra ACIS-I observations, with a total cleaned exposure time of 6.727Ms, taken in four separate epochs of time. The basic information on these observations is listed in Table 1. There were 48 recent observations acquired between 2014 June 9 and 2016 March 24, which constitute the last 3Ms of exposure of the 7Ms CDF-S. The first 1Ms of exposure consists of 11 observations taken between 1999 and 2000 (Giacconi+ 2002, J/ApJS/139/369; Rosati+ 2002ApJ...566..667R; Alexander+ 2003, J/AJ/126/539), the next 1Ms of exposure consists of 12 observations taken in 2007 (Luo+ 2008, J/ApJS/179/19), and another 2Ms of exposure includes 31 observations in 2010 (Xue+ 2011, J/ApJS/195/10). The total area covered by the 7Ms CDF-S is 484.2arcmin2. (3 data files)
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