348 research outputs found
Probing the Low Mass X-ray Binaries/Globular Cluster connection in NGC1399
We present a wide field study of the Globular Clusters/Low Mass X-ray
Binaries connection in the cD elliptical NGC1399, combining HST/ACS and Chandra
high resolution data. We find evidence that LMXB formation likelihood is
influenced by GCs structural parameters, in addition to the well known effects
of mass and metallicity, independently from galactocentric distance.Comment: in press in the Proceedings of the X-ray 2009 Conference, 7-11
September 2009, Bologna, Ital
The Fornax Deep Survey with VST. VIII. Connecting the accretion history with the cluster density
This work is based on deep multi-band (g, r, i) data from the Fornax Deep
Survey with VST. We analyse the surface brightness profiles of the 19 bright
ETGs inside the virial radius of the Fornax cluster. The main aim of this work
is to identify signatures of accretion onto galaxies by studying the presence
of outer stellar halos, and understand their nature and occurrence. Our
analysis also provides a new and accurate estimate of the intra-cluster light
inside the virial radius of Fornax. We performed multi-component fits to the
azimuthally averaged surface brightness profiles available for all sample
galaxies. This allows to quantify the relative weight of all components in the
galaxy structure that contribute to the total light. In addition, we derived
the average g-i colours in each component identified by the fit, as well as the
azimuthally averaged g-i colour profiles, to correlate them with the stellar
mass of each galaxy and the location inside the cluster. We find that in the
most massive and reddest ETGs the fraction of light in, probably accreted,
halos is much larger than in the other galaxies. Less-massive galaxies have an
accreted mass fraction lower than 30%, bluer colours and reside in the
low-density regions of the cluster. Inside the virial radius of the cluster,
the total luminosity of the intra-cluster light, compared with the total
luminosity of all cluster members, is about 34%. Inside the Fornax cluster
there is a clear correlation between the amount of accreted material in the
stellar halos of galaxies and the density of the environment in which those
galaxies reside. By comparing this quantity with theoretical predictions and
previous observational estimates, there is a clear indication that the driving
factor for the accretion process is the total stellar mass of the galaxy, in
agreement with the hierarchical accretion scenario.Comment: 18 pages, 10 figures. Accepted for publication in A&
Variability-selected low-luminosity active galactic nuclei candidates in the 7 Ms Chandra Deep Field-South
In deep X-ray surveys, active galactic nuclei (AGNs) with a broad range of
luminosities have been identified. However, cosmologically distant
low-luminosity AGN (LLAGN, erg s)
identification still poses a challenge due to significant contamination from
host galaxies. Based on the 7 Ms Chandra Deep Field-South (CDF-S) survey, the
longest timescale ( years) deep X-ray survey to date, we utilize an
X-ray variability selection technique to search for LLAGNs that remain
unidentified among the CDF-S X-ray sources. We find 13 variable sources from
110 unclassified CDF-S X-ray sources. Except for one source which could be an
ultraluminous X-ray source, the variability of the remaining 12 sources is most
likely due to accreting supermassive black holes. These 12 AGN candidates have
low intrinsic X-ray luminosities, with a median value of erg
s. They are generally not heavily obscured, with an average effective
power-law photon index of 1.8. The fraction of variable AGNs in the CDF-S is
independent of X-ray luminosity and is only restricted by the total number of
observed net counts, confirming previous findings that X-ray variability is a
near-ubiquitous property of AGNs over a wide range of luminosities. There is an
anti-correlation between X-ray luminosity and variability amplitude for
high-luminosity AGNs, but as the luminosity drops to erg
s, the variability amplitude no longer appears dependent on the
luminosity. The entire observed luminosity-variability trend can be roughly
reproduced by an empirical AGN variability model based on a broken power-law
power spectral density function.Comment: 18 pages, 11 figures, accepted for publication in Ap
Gauging the dark matter fraction in a S0 galaxy at z=0.47 through gravitational lensing from deep HST/ACS imaging
We analyze a new gravitational lens, OAC-GL J1223-1239, serendipitously found
in a deep I-band image of the Hubble Space Telescope (HST) Advanced Camera for
Surveys (ACS). The lens is a L_*, edge-on S0 galaxy at z=0.4656. The
gravitational arc has a radius of 0.42 arcsec. We have determined the total
mass and the dark matter (DM) fraction within the Einstein radius as a function
of the lensed source redshift, which is presently unknown. For z ~ 1.3, which
is in the middle of the redshift range plausible for the source according to
some external constraints, we find the central velocity dispersion to be ~180
km/s. With this value, close to that obtained by means of the Faber-Jackson
relation at the lens redshift, we compute a 30% DM fraction within the Einstein
radius (given the uncertainty in the source redshift, the allowed range for the
DM fraction is 25-35 % in our lensing model). When compared with the galaxies
in the local Universe, the lensing galaxy, OAC-GL J1223-1239 seems to fall in
the transition regime between massive DM dominated galaxies and lower-mass, DM
deficient systems.Comment: 18 pages, 5 figures; accepted for publication in Ap
The Fornax Deep Survey with VST. II. Fornax A: a two-phase assembly caught on act
As part of the Fornax Deep Survey with the ESO VLT Survey Telescope, we
present new and bands mosaics of the SW group of the Fornax cluster. It
covers an area of square degrees around the central galaxy
NGC1316. The deep photometry, the high spatial resolution of OmegaCam and the
large covered area allow us to study the galaxy structure, to trace stellar
halo formation and look at the galaxy environment. We map the surface
brightness profile out to 33arcmin (kpc ) from the galaxy
centre, down to mag arcsec and mag
arcsec. This allow us to estimate the scales of the main components
dominating the light distribution, which are the central spheroid, inside 5.5
arcmin ( kpc), and the outer stellar envelope. Data analysis suggests
that we are catching in act the second phase of the mass assembly in this
galaxy, since the accretion of smaller satellites is going on in both
components. The outer envelope of NGC1316 still hosts the remnants of the
accreted satellite galaxies that are forming the stellar halo. We discuss the
possible formation scenarios for NGC1316, by comparing the observed properties
(morphology, colors, gas content, kinematics and dynamics) with predictions
from cosmological simulations of galaxy formation. We find that {\it i)} the
central spheroid could result from at least one merging event, it could be a
pre-existing early-type disk galaxy with a lower mass companion, and {\it ii)}
the stellar envelope comes from the gradual accretion of small satellites.Comment: Accepeted for publication in Ap
GMRT HI observations of the Eridanus group of galaxies
The GMRT HI 21cm-line observations of galaxies in the Eridanus group are
presented. The Eridanus group, at a distance of ~23 Mpc, is a loose group of
\~200 galaxies. The group extends more than 10 Mpc in projection. The velocity
dispersion of the galaxies in the group is ~240 km/s. The galaxies are
clustered into different sub-groups. The overall population mix of the group is
30% (E+S0) and 70% (Sp+Irr). The observations of 57 Eridanus galaxies were
carried out with the GMRT for ~200 hour. HI emission was detected from 31
galaxies. The channel rms of ~1.0 mJy beam^{-1} was achieved for most of the
image-cubes made with 4 hour of data. The corresponding HI column density
sensitivity (3-sigma) is ~1x10^{20} cm^{-2} for a velocity-width of ~13.4 km/s.
The 3-sigma detection limit of HI mass is ~1.2x10^{7} M_sun for a line-width of
50 km/s. Total HI images, HI velocity fields, global HI line profiles, HI mass
surface densities, HI disk parameters and HI rotation curves are presented. The
velocity fields are analysed separately for the approaching and the receding
sides of the galaxies. This data will be used to study the HI and the radio
continuum properties, the Tully-Fisher relations, the dark matter halos, and
the kinematical and HI lopsidedness in galaxies.Comment: 75 pages including HI atlas; Accepted for publication in Journal of
Astroph. & Astron. March, 200
The XMM deep survey in the CDFS XI. X-ray properties of 185 bright sources
We present X-ray spectra of 185 bright sources detected in the XMM-Newton
deep survey of the Chandra Deep Field South, combining the three EPIC cameras.
The 2-10 keV flux limit of the sample is 2e-15 erg/s/cm2. The sources are
distributed over a redshift range of z=0.1-3.8. Eleven new X-ray redshift
measurements are included. A spectral analysis was performed using a simple
model to obtain absorbing column densities, rest-frame 2-10 keV luminosities
and Fe K line properties of 180 sources at z>0.4. Obscured AGN are found to be
more abundant toward higher redshifts. Using the XMM-Newton data alone, seven
Compton-thick AGN candidates are identified, which makes the Compton-thick AGN
fraction to be ~4%. An exploratory spectral inspection method with two
rest-frame X-ray colours and an Fe line strength indicator is introduced and
tested against the results from spectral fitting. This method works reasonably
well to characterise a spectral shape and can be useful for a pre-selection of
Compton-thick AGN candidates. We found six objects exhibiting broad Fe K lines
out of 21 unobscured AGN of best data quality, implying a detection rate of
~30%. Five redshift spikes, each of which has more than six sources, are
identified in the redshift distribution of the X-ray sources. Contrary to the
overall trend, the sources at the two higher-redshift spikes at z=1.61 and
z=2.57 have puzzlingly low obscuration.Comment: Accepted for publication in Astronomy & Astrophysics. Table 1 and
Fig. 2 are available in electronic form the CDS. Typos corrected and some
language editing and references adde
Accretion, ejection and reprocessing in supermassive black holes
This is a White Paper in support of the mission concept of the Large
Observatory for X-ray Timing (LOFT), proposed as a medium-sized ESA mission. We
discuss the potential of LOFT for the study of active galactic nuclei. For a
summary, we refer to the paper.Comment: White Paper in Support of the Mission Concept of the Large
Observatory for X-ray Timin
The luminosity function of field galaxies
Schmidt's method for construction of luminosity function of galaxies is
generalized by taking into account the dependence of density of galaxies from
the distance in the near Universe. The logarithmical luminosity function (LLF)
of field galaxies depending on morphological type is constructed. We show that
the LLF for all galaxies, and also separately for elliptical and lenticular
galaxies can be presented by Schechter function in narrow area of absolute
magnitudes. The LLF of spiral galaxies was presented by Schechter function for
enough wide area of absolute magnitudes: . Spiral galaxies differ slightly by
parameter . At transition from early spirals to the late spirals parameter in
Schechter function is reduced. The reduction of mean luminosity of galaxies is
observed at transition from elliptical galaxies to lenticular galaxies, to
early spiral galaxies, and further, to late spiral galaxies, in a bright end, .
The completeness and the average density of samples of galaxies of different
morphological types are estimated. In the range the mean number density of all
galaxies is equal 0.127 Mpc-3.Comment: 14 page, 8 figures, to appear in Astrophysic
Deep Extragalactic VIsible Legacy Survey (DEVILS): Consistent multi-wavelength photometry for the DEVILS regions (COSMOS, XMMLSS & ECDFS)
The Deep Extragalactic VIsible Legacy Survey (DEVILS) is an ongoing
high-completeness, deep spectroscopic survey of 60,000 galaxies to
Y21.2 mag, over 6 deg2 in three well-studied deep extragalactic
fields: D10 (COSMOS), D02 (XMM-LSS) and D03 (ECDFS). Numerous DEVILS projects
all require consistent, uniformly-derived and state-of-the-art photometric data
with which to measure galaxy properties. Existing photometric catalogues in
these regions either use varied photometric measurement techniques for
different facilities/wavelengths leading to inconsistencies, older imaging data
and/or rely on source detection and photometry techniques with known problems.
Here we use the ProFound image analysis package and state-of-the-art imaging
datasets (including Subaru-HSC, VST-VOICE, VISTA-VIDEO and UltraVISTA-DR4) to
derive matched-source photometry in 22 bands from the FUV to 500{\mu}m. This
photometry is found to be consistent, or better, in colour-analysis to previous
approaches using fixed-size apertures (which are specifically tuned to derive
colours), but produces superior total source photometry, essential for the
derivation of stellar masses, star-formation rates, star-formation histories,
etc. Our photometric catalogue is described in detail and, after internal
DEVILS team projects, will be publicly released for use by the broader
scientific community.Comment: 33 pages, 22 figures, Accepted to MNRA
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