199 research outputs found
The primordial environment of super massive black holes: large scale galaxy overdensities around QSOs with LBT
We investigated the presence of galaxy overdensities around four
QSOs, namely SDSS J1030+0524 (z = 6.28), SDSS J1148+5251 (z = 6.41), SDSS
J1048+4637 (z = 6.20) and SDSS J1411+1217 (z = 5.95), through deep -, -
and - band imaging obtained with the wide-field () Large
Binocular Camera (LBC) at the Large Binocular Telescope (LBT). We adopted
color-color selections within the vs plane to identify samples of
-band dropouts at the QSO redshift and measure their relative abundance and
spatial distribution in the four LBC fields, each covering
physical Mpc at . The same selection criteria were then applied to
-band selected sources in the 1 deg Subaru-XMM Newton Deep Survey
to derive the expected number of dropouts over a blank LBC-sized field
(0.14 deg). The four observed QSO fields host a number of candidates
larger than what is expected in a blank field. By defining as -band dropouts
objects with and undetected in the -band, we found
16, 10, 9, 12 dropouts in SDSS J1030+0524, SDSS J1148+5251, SDSS J1048+4637,
and SDSS J1411+1217, respectively, whereas only 4.3 such objects are expected
over a 0.14 deg blank field. This corresponds to overdensity significances
of 3.3, 1.9, 1.7, 2.5, respectively. By considering the total number of
dropouts in the four LBC fields and comparing it with what is expected in four
blank fields of 0.14 deg each, we find that high-z QSOs reside in overdense
environments at the level. This is the first direct and unambiguous
measurement of the large scale structures around QSOs. [shortened]Comment: 12 pages, 8 figures. Accepted for publication in A&
Deep R-band counts of z~3 Lyman break galaxy candidates with the LBT
Aims. We present a deep multiwavelength imaging survey (UGR) in 3 different
fields, Q0933, Q1623, and COSMOS, for a total area of ~1500arcmin^2. The data
were obtained with the Large Binocular Camera on the Large Binocular Telescope.
Methods. To select our Lyman break galaxy (LBG) candidates, we adopted the well
established and widely used color-selection criterion (U-G vs. G-R). One of the
main advantages of our survey is that it has a wider dynamic color range for
U-dropout selection than in previous studies. This allows us to fully exploit
the depth of our R-band images, obtaining a robust sample with few interlopers.
In addition, for 2 of our fields we have spectroscopic redshift information
that is needed to better estimate the completeness of our sample and interloper
fraction. Results. Our limiting magnitudes reach 27.0(AB) in the R band
(5\sigma) and 28.6(AB) in the U band (1\sigma). This dataset was used to derive
LBG candidates at z~3. We obtained a catalog with a total of 12264 sources down
to the 50% completeness magnitude limit in the R band for each field. We find a
surface density of ~3 LBG candidates arcmin^2 down to R=25.5, where
completeness is >=95% for all 3 fields. This number is higher than the original
studies, but consistent with more recent samples.Comment: in press by A&A, full LBG candidates' catalog will be available in
electronic form at the CD
Spectroscopic confirmation of two Lyman break galaxies at redshift beyond 7
We report the spectroscopic confirmation of two Lyman break galaxies at
redshift > 7. The galaxies were observed as part of an ultra-deep spectroscopic
campaign with FORS2 at the ESO/VLT for the confirmation of z~7 ``z--band
dropout'' candidates selected from our VLT/Hawk-I imaging survey. Both galaxies
show a prominent emission line at 9735A and 9858A respectively: the lines have
fluxes of ~ 1.6-1.2 x 10^(-17) erg/s/cm2 and exhibit a sharp decline on the
blue side and a tail on the red side. The asymmetry is quantitatively
comparable to the observed asymmetry in z ~ 6 Ly-alpha lines, where absorption
by neutral hydrogen in the IGM truncates the blue side of the emission line
profile. We carefully evaluate the possibility that the galaxies are instead at
lower redshift and we are observing either [OII], [OIII] or H-alpha emission:
however from the spectroscopic and the photometric data we conclude that there
are no other plausible identifications, except for Ly-alpha at redshift >7,
implying that these are two of the most robust redshift determination for
galaxies in the reionization epoch. Based on their redshifts and broad--band
photometry, we derive limits on the star formation rate and on the ultraviolet
spectral slopes of the two galaxies. We argue that these two galaxies alone are
unlikely to have ionized the IGM in their surroundings.Comment: Accepted for publication in ApJL, 3 figures and one table, emulated
ap
The GOODS-MUSIC sample: a multicolour catalog of near-IR selected galaxies in the GOODS-South field
We present a high quality multiwavelength (from 0.3 to 8.0 micron) catalog of
the large and deep area in the GOODS Southern Field covered by the deep near-IR
observations obtained with the ESO VLT. The catalog is entirely based on public
data: in our analysis, we have included the F435W, F606W, F775W and F850LP ACS
images, the JHKs VLT data, the Spitzer data provided by IRAC instrument (3.6,
4.5, 5.8 and 8.0 micron), and publicly available U-band data from the 2.2ESO
and VLT-VIMOS. We describe in detail the procedures adopted to obtain this
multiwavelength catalog. In particular, we developed a specific software for
the accurate "PSF-matching" of space and ground-based images of different
resolution and depth (ConvPhot), of which we analyse performances and
limitations. We have included both z-selected, as well as Ks-selected objects,
yielding a unique, self-consistent catalog. The largest fraction of the sample
is 90% complete at z~26 or Ks~23.8 (AB scale). Finally, we cross-correlated our
data with all the spectroscopic catalogs available to date, assigning a
spectroscopic redshift to more than 1000 sources. The final catalog is made up
of 14847 objects, at least 72 of which are known stars, 68 are AGNs, and 928
galaxies with spectroscopic redshift (668 galaxies with reliable redshift
determination). We applied our photometric redshift code to this data set, and
the comparison with the spectroscopic sample shows that the quality of the
resulting photometric redshifts is excellent, with an average scatter of only
0.06. The full catalog, which we named GOODS-MUSIC (MUltiwavelength Southern
Infrared Catalog), including the spectroscopic information, is made publicly
available, together with the software specifically designed to this end.Comment: Accepted for publication in Astronomy and Astrophysics, uses aa.cls,
20 pages, 16 figures. Further information at http://lbc.oa-roma.inaf.it/good
ASTRI SST-2M prototype and mini-array simulation chain, data reduction software, and archive in the framework of the Cherenkov Telescope Array
The Cherenkov Telescope Array (CTA) is a worldwide project aimed at building
the next-generation ground-based gamma-ray observatory. Within the CTA project,
the Italian National Institute for Astrophysics (INAF) is developing an
end-to-end prototype of the CTA Small-Size Telescopes with a dual-mirror
(SST-2M) Schwarzschild-Couder configuration. The prototype, named ASTRI SST-2M,
is located at the INAF "M.C. Fracastoro" observing station in Serra La Nave
(Mt. Etna, Sicily) and is currently in the scientific and performance
validation phase. A mini-array of (at least) nine ASTRI telescopes has been
then proposed to be deployed at the Southern CTA site, by means of a
collaborative effort carried out by institutes from Italy, Brazil, and
South-Africa. The CTA/ASTRI team is developing an end-to-end software package
for the reduction of the raw data acquired with both ASTRI SST-2M prototype and
mini-array, with the aim of actively contributing to the global ongoing
activities for the official data handling system of the CTA observatory. The
group is also undertaking a massive Monte Carlo simulation data production
using the detector Monte Carlo software adopted by the CTA consortium.
Simulated data are being used to validate the simulation chain and evaluate the
ASTRI SST-2M prototype and mini-array performance. Both activities are also
carried out in the framework of the European H2020-ASTERICS (Astronomy ESFRI
and Research Infrastructure Cluster) project. A data archiving system, for both
ASTRI SST-2M prototype and mini-array, has been also developed by the CTA/ASTRI
team, as a testbed for the scientific archive of CTA. In this contribution, we
present the main components of the ASTRI data handling systems and report the
status of their development.Comment: Proceedings of the 35th International Cosmic Ray Conference (ICRC
2017), Bexco, Busan, Korea. All CTA contributions at arXiv:1709.0348
An optical and HI study of the dwarf Local Group galaxy VV124=UGC4879. A gas-poor dwarf with a stellar disk?
We present a detailed study of the dwarf galaxy VV124, recently recognized as
a isolated member of the Local Group. We have obtained deep (r=26.5) wide-field
g,r photometry of individual stars with the LBT under sub-arcsec seeing
conditions. The Color-Magnitude Diagram suggests that the stellar content of
the galaxy is dominated by an old, metal-poor population, with a significant
metallicity spread. A very clean detection of the RGB tip allows us to derive
an accurate distance of D=1.3 +/- 0.1 Mpc. Combining surface photometry with
star counts, we are able to trace the surface brightness profile of VV124 out
to ~ 5' = 1.9 kpc radius (where mu_r=30 mag/arcsec^2), showing that it is much
more extended than previously believed. Moreover, the surface density map
reveals the presence of two symmetric flattened wings emanating from the
central elongated spheroid and aligned with its major axis, resembling a
stellar disk seen nearly edge-on. We also present HI observations obtained with
the WSRT, the first ever of this object. A total amount of 10^6 M_sun of HI gas
is detected in VV124. Compared to the total luminosity, this gives a value of
M_HI/L_V=0.11, which is particularly low for isolated Local Group dwarfs. The
spatial distribution of the gas does not correlate with the observed stellar
wings. The systemic velocity of the HI in the region superposed to the stellar
main body of the galaxy is V_h=-25 km/s. The velocity field shows substructures
typical of galaxies of this size but no sign of rotation. The HI spectra
indicates the presence of a two-phase interstellar medium, again typical of
many dwarf galaxies.Comment: Accepted for publication in A&A. 19 pages, 20 reduced-resolution
figures, pdflatex, A&A style. The full resolution pdf file can be be
downloaded from http://www.bo.astro.it/SGR
A low escape fraction of ionizing photons of L>L* Lyman break galaxies at z=3.3
We present an upper limit for the relative escape fraction (f_{esc}^{rel}) of
ionizing radiation at z~3.3 using a sample of 11 Lyman Break Galaxies (LBGs)
with deep imaging in the U band obtained with the Large Binocular Camera,
mounted on the prime focus of the Large Binocular Telescope. We selected 11
LBGs with secure redshift in the range 3.27<z<3.35, from 3 independent fields.
We stacked the images of our sources in the R and U band, which correspond to
an effective rest-frame wavelength of 1500\AA and 900\AA respectively,
obtaining a limit in the U band image of >=30.7(AB)mag at 1 sigma. We derive a
1 sigma upper limit of f_{esc}^{rel}~5%, which is one of the lowest values
found in the literature so far at z~3.3. Assuming that the upper limit for the
escape fraction that we derived from our sample holds for all galaxies at this
redshift, the hydrogen ionization rate that we obtain (Gamma_{-12}<0.3 s^{-1})
is not enough to keep the IGM ionized and a substantial contribution to the UV
background by faint AGNs is required. Since our sample is clearly still limited
in size, larger z~3 LBG samples, at similar or even greater depths are
necessary to confirm these results on a more firm statistical basis.Comment: 15 pages, 2 figures, 1 table, accepted for publication in Ap
Physical properties of z~4 LBGs: differences between galaxies with and without Ly-alpha emission
We have analysed the physical properties of z~4 Lyman Break Galaxies observed
in the GOODS-S survey, in order to investigate the possible differences between
galaxies where the Ly-alpha is present in emission, and those where the line is
absent or in absorption. The objects have been selected from their optical
color and then spectroscopically confirmed by Vanzella et al. (2005). From the
public spectra we assessed the nature of the Ly-alpha emission and divided the
sample into galaxies with Ly-alpha in emission and objects without Ly-alpha
line (i.e. either absent or in absorption). We have then used the complete
photometry, from U band to mid infrared from the GOODS-MUSIC database, to study
the observational properties of the galaxies, such as UV spectral slopes and
optical to mid-infrared colors, and the possible differences between the two
samples. Finally through standard spectral fitting tecniques we have determined
the physical properties of the galaxies, such as total stellar mass, stellar
ages and so on, and again we have studied the possible differences between the
two samples. Our results indicate that LBG with Ly-alpha in emission are on
average a much younger and less massive population than the LBGs without
Ly-alpha emission. Both populations are forming stars very actively and are
relatively dust free, although those with line emission seem to be even less
dusty on average. We briefly discuss these results in the context of recent
models for the evolution of Lyman break galaxies and Ly-alpha emitters.Comment: Accepted for publication in A&A. Uses aa.cls, 6 pages, 3 figure
The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study
We used a proper combination of multiband high-resolution and wide field
multi-wavelength observations collected at three different telescopes (HST, LBT
and CFHT) to probe Blue Straggler Star (BSS) populations in the globular
cluster M53. Almost 200 BSS have been identified over the entire cluster
extension. The radial distribution of these stars has been found to be bimodal
(similarly to that of several other clusters) with a prominent dip at ~60'' (~2
r_c) from the cluster center. This value turns out to be a factor of two
smaller than the radius of avoidance (r_avoid, the radius within which all the
stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects
in an Hubble time). While in most of the clusters with a bimodal BSS radial
distribution, r_avoid has been found to be located in the region of the
observed minimum, this is the second case (after NGC6388) where this
discrepancy is noted. This evidence suggests that in a few clusters the
dynamical friction seems to be somehow less efficient than expected.
We have also used this data base to construct the radial star density profile
of the cluster: this is the most extended and accurate radial profile ever
published for this cluster, including detailed star counts in the very inner
region. The star density profile is reproduced by a standard King Model with an
extended core (~25'') and a modest value of the concentration parameter
(c=1.58). A deviation from the model is noted in the most external region of
the cluster (at r>6.5' from the center). This feature needs to be further
investigated in order to address the possible presence of a tidal tail in this
cluster.Comment: 25 pages, 9 figures, accepted for publication on Ap
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