761 research outputs found
Observing the very low-surface brightness dwarfs in a deep field in the VIRGO cluster: constraints on Dark Matter scenarios
We report the discovery of 11 very faint (r< 23), low surface brightness
({\mu}_r< 27 mag/arcsec^2) dwarf galaxies in one deep field in the Virgo
cluster, obtained by the prime focus cameras (LBC) at the Large Binocular
Telescope (LBT). These extend our previous sample to reach a total number of 27
galaxies in a field of just of 0.17 deg^2 located at a median distance of 390
kpc from the cluster center. Their association with the Virgo cluster is
supported by their separate position in the central surface brightness - total
magnitude plane with respect to the background galaxies of similar total
magnitude. For a significant fraction (26\%) of the sample the association to
the cluster is confirmed by spectroscopic follow-up. We show that the mere
abundance of satellite galaxies corresponding to our observed number in the
target field provides extremely tight constraints on Dark Matter models with
suppressed power spectrum compared to the Cold Dark Matter case, independently
of the galaxy luminosity distribution. In particular, requiring the observed
number of satellite galaxies not to exceed the predicted abundance of Dark
Matter sub-halos yields a limit m_X >3 keV at 1-{\sigma} and m_X > 2.3 keV at
2-{\sigma} confidence level for the mass of thermal Warm Dark Matter particles.
Such a limit is competitive with other limits set by the abundance of
ultra-faint satellite galaxies in the Milky Way, is completely independent of
baryon physics involved in galaxy formation, and has the potentiality for
appreciable improvements with next observations. We extend our analysis to Dark
Matter models based on sterile neutrinos, showing that our observations set
tight constraints on the combination of sterile neutrino mass m_{\nu} and
mixing parameter sin^2(2{\theta}). We discuss the robustness of our results
with respect to systematics.Comment: Accepted for publication in Astronomy & Astrophysic
The detection of ultra-faint low surface brightness dwarf galaxies in the Virgo Cluster: a Probe of Dark Matter and Baryonic Physics
We have discovered 11 ultra-faint () low surface brightness
(LSB, central surface brightness ) dwarf galaxy
candidates in one deep Virgo field of just arcmin obtained by the
Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT). Their
association with the Virgo cluster is supported by their distinct position in
the central surface brightness - total magnitude plane with respect to the
background galaxies of similar total magnitude. They have typical absolute
magnitudes and scale sizes, if at the distance of Virgo, in the range
and pc,
respectively. Their colors are consistent with a gradually declining star
formation history with a specific star formation rate of the order of
yr, i.e. 10 times lower than that of main sequence star
forming galaxies. They are older than the cluster formation age and appear
regular in morphology. They represent the faintest extremes of the population
of low luminosity LSB dwarfs that has been recently detected in wider surveys
of the Virgo cluster. Thanks to the depth of our observations we are able to
extend the Virgo luminosity function down to (corresponding to
total masses M), finding an average faint-end slope
. This relatively steep slope puts interesting constraints
on the nature of the Dark Matter and in particular on warm Dark Matter (WDM)
often invoked to solve the overprediction of the dwarf number density by the
standard CDM scenario. We derive a lower limit on the WDM particle mass
keV.Comment: accepted for publication in ApJ, 13 pages, 6 figure
UV slope of z3 bright () Lyman-break galaxies in the COSMOS field
We analyse a unique sample of 517 bright () LBGs at redshift
z3 in order to characterise the distribution of their UV slopes
and infer their dust extinction under standard assumptions. We exploited
multi-band observations over 750 arcmin of the COSMOS field that were
acquired with three different ground-based facilities: the Large Binocular
Camera (LBC) on the Large Binocular Telescope (LBT), the Suprime-Cam on the
SUBARU telescope, and the VIRCAM on the VISTA telescope (ULTRAVISTA DR2). Our
multi-band photometric catalogue is based on a new method that is designed to
maximise the signal-to-noise ratio in the estimate of accurate galaxy colours
from images with different point spread functions (PSF). We adopted an improved
selection criterion based on deep Y-band data to isolate a sample of galaxies
at to minimise selection biases. We measured the UV slopes ()
of the objects in our sample and then recovered the intrinsic probability
density function of values (PDF()), taking into account the
effect of observational uncertainties through detailed simulations. The
galaxies in our sample are characterised by mildly red UV slopes with
throughout the enitre luminosity range that is probed by
our data (). The resulting dust-corrected
star formation rate density (SFRD) is , corresponding to a contribution of about 25% to the
total SFRD at z3 under standard assumptions. Ultra-bright LBGs at match the known trends, with UV slopes being redder at decreasing redshifts,
and brighter galaxies being more highly dust extinct and more frequently
star-forming than fainter galaxies. [abridged]Comment: Matched to journal version. 11 pages, 13 figures, Astronomy &
Astrophysics in pres
The red and blue galaxy populations in the GOODS field: evidence for an excess of red dwarfs
We study the evolution of the galaxy population up to z\sim3 as a function of
its colour properties. In particular, luminosity functions and luminosity
densities have been derived as a function of redshift for the blue/late and
red/early populations. We use data from the GOODS-MUSIC catalogue which have
typical magnitude limits z<26 and Ks<23.5 for most of the sample. About 8% of
the galaxies have spectroscopic redshifts; the remaining have well calibrated
photometric redshifts derived from the extremely wide multi-wavelength coverage
in 14 bands (from the U band to the Spitzer 8 \mu m band). We have derived a
catalogue of galaxies complete in rest-frame B-band, which has been divided in
two subsamples according to their rest-frame U-V colour (or derived specific
star formation rate, SSFR) properties. We confirm a bimodality in the U-V
colour and SSFR of the galaxy sample up to z\sim 3. This bimodality is used to
compute the LFs of the blue/late and red/early subsamples. The LFs of the
blue/late and total samples are well represented by steep Schechter functions
evolving in luminosity with increasing redshifts. The volume density of the LFs
of the red/early populations decreases with increasing redshift. The shape of
the red/early LFs shows an excess of faint red dwarfs with respect to the
extrapolation of a flat Schechter function and can be represented by the sum of
two Schechter functions. Our model for galaxy formation in the hierarchical
clustering scenario, which also includes external feedback due to a diffuse UV
background, shows a general broad agreement with the LFs of both populations,
the larger discrepancies being present at the faint end for the red population.
Hints on the nature of the red dwarf population are given on the basis of their
stellar mass and spatial distributions.Comment: accepted for publication in A&A. Uses aa.cls, 13 pages, 11 figure
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
Discovery of a Quadruple Lens in CANDELS with a Record Lens Redshift z=1.53
Using spectroscopy from the Large Binocular Telescope and imaging from the
Hubble Space Telescope we discovered the first strong galaxy lens at z(lens)>1.
The lens has a secure photometric redshift of z=1.53+/-0.09 and the source is
spectroscopically confirmed at z=3.417. The Einstein radius (0.35"; 3.0 kpc)
encloses 7.6 x 10^10 Msol, with an upper limit on the dark matter fraction of
60%. The highly magnified (40x) source galaxy has a very small stellar mass
(~10^8 Msol) and shows an extremely strong [OIII]_5007A emission line (EW_0 ~
1000A) bolstering the evidence that intense starbursts among very low-mass
galaxies are common at high redshift.Comment: accepted for publication in ApJ Letter
A Photometrically Detected Forming Cluster of Galaxies at Redshift 1.6 in the GOODS Field
We report the discovery of a localized overdensity at z~1.6 in the
GOODS-South Field, presumably a poor cluster in the process of formation. The
three-dimensional galaxy density has been estimated on the basis of well
calibrated photometric redshifts from the multiband photometric GOODS-MUSIC
catalog using the (2+1)D technique. The density peak is embedded in the larger
scale overdensity of galaxies known to exist at z=1.61 in the area. The
properties of the member galaxies are compared to those of the surrounding
field and we found that the two populations are significantly different
supporting the reality of the structure. The reddest galaxies, once evolved
according to their best fit models, have colors consistent with the red
sequence of lower redshift clusters. The estimated M_200 total mass of the
cluster is in the range 1.3 x 10^14 - 5.7x 10^14 Msun, depending on the assumed
bias factor b. An upper limit for the 2-10 keV X-ray luminosity, based on the
1Ms Chandra observations, is L_X=0.5 x 10^43 erg s^-1, suggesting that the
cluster has not yet reached the virial equilibrium.Comment: 6 pages, 5 figures (1 in color), uses emulateapj.cls Latex class
file, accepted for publication in Ap
Peering through the holes: the far UV color of star-forming galaxies at z~3-4 and the escaping fraction of ionizing radiation
We aim to investigate the effect of the escaping ionizing radiation on the
color selection of high redshift galaxies and identify candidate Lyman
continuum (LyC) emitters. The intergalactic medium prescription of Inoue et
al.(2014) and galaxy synthesis models of Bruzual&Charlot (2003) have been used
to properly treat the ultraviolet stellar emission, the stochasticity of the
intergalactic transmission and mean free path in the ionizing regime. Color
tracks are computed by turning on/off the escape fraction of ionizing
radiation. At variance with recent studies, a careful treatment of IGM
transmission leads to no significant effects on the high-redshift broad-band
color selection. The decreasing mean free path of ionizing photons with
increasing redshift further diminishes the contribution of the LyC to
broad-band colors. We also demonstrate that prominent LyC sources can be
selected under suitable conditions by calculating the probability of a null
escaping ionizing radiation. The method is applied to a sample of galaxies
extracted from the GOODS-S field. A known LyC source at z=3.795 is successfully
recovered as a LyC emitter candidate and another convincing candidate at
z=3.212 is reported. A detailed analysis of the two sources (including their
variability and morphology) suggests a possible mixture of stellar and
non-stellar (AGN) contribution in the ultraviolet. Conclusions: Classical
broad-band color selection of 2.5<z<4.5 galaxies does not prevent the inclusion
of LyC emitters in the selected samples. Large fesc in relatively bright
galaxies (L>0.1L*) could be favored by the presence of a faint AGN not easily
detected at any wavelength. A hybrid stellar and non-stellar (AGN) ionizing
emission could coexist in these systems and explain the tensions found among
the UV excess and the stellar population synthesis models reported in
literature.Comment: Accepted for publication in Astronomy & Astrophysics. 13 pages, 7
figure
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
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