1,127 research outputs found
A statistical analysis of the characteristics of pigmented skin lesions using epiluminescence microscopy
Due to the fact that not all pigmented skin lesions (PSL) can be diagnosed solely by their clinical appearance, additional criteria are required to optimize the clinical diagnosis of atypical nevus and melanoma. Epiluminescence microscopy is a non-invasive in vivo examination that often helps to improved the accuracy of clinical diagnosis of such lesions. Years of experience have indicated some differential epiluminescent patterns for benign and malignant PSI, but there is some controversy about certain borderline lesions for which histological examination is always necessary. In our study we performed a statistical analysis of data concerning 183 PSI, to determine characteristics significantly associated with these lesions allowing identification of epiluminescent criteria suggestive of atypical nevus and malignant melanoma. Using he chi-quadro test and stepwise regression logistic model, we identified the following epiluminescent pattern as a risk factor for atypical nevus and malignant melanoma: irregular pigment network, presence of capillaries, irregular and abrupt ending of overall pigmentation, irregular brown globules and irregular shape and size of black dots
The PEP survey: clustering of infrared-selected galaxies and structure formation at z~2 in the GOODS South
ABRIDGED-This paper presents the first direct estimate of the 3D clustering
properties of far-infrared sources up to z~3. This has been possible thanks to
the Pacs Evolutionary Probe (PEP) survey of the GOODS South field performed
with the PACS instrument onboard the Herschel Satellite. An analysis of the
two-point correlation function over the whole redshift range spanned by the
data reports for the correlation length, r_0~6.3 Mpc and r_0~6.7 Mpc,
respectively at 100um and 160um, corresponding to dark matter halo masses
M>~10^{12.4} M_sun. Objects at z~2 instead seem to be more strongly clustered,
with r_0~19 Mpc and r_0~17 Mpc in the two considered PACS channels. This
dramatic increase of the correlation length between z~1 and z~2 is connected
with the presence of a wide, M>~10^{14} M_sun, filamentary structure which
includes more than 50% of the sources detected at z~2. An investigation of the
properties of such sources indicates the possibility for boosted star-forming
activity in those which reside within the overdense environment with respect of
more isolated galaxies found in the same redshift range. Lastly, we also
present our results on the evolution of the relationship between luminous and
dark matter in star-forming galaxies between z~1 and z~2. We find that the
increase of (average) stellar mass in galaxies between z~1 and z~2 is
about a factor 10 lower than that of the dark matter haloes hosting such
objects ([z~1]/[z~2] ~ 0.4 vs M_{halo}[z~1]/M_{halo}[z~2] ~ 0.04). Our
findings agree with the evolutionary picture of downsizing whereby massive
galaxies at z~2 were more actively forming stars than their z~1 counterparts,
while at the same time contained a lower fraction of their mass in the form of
luminous matter.Comment: 14 pages, 8 figures, MNRAS accepte
Evolution in the bias of faint radio sources to z ~ 2.2
Quantifying how the baryonic matter traces the underlying dark matter distribution is key to both understanding galaxy formation and our ability to constrain the cosmological model. Using the cross-correlation function of radio and near-infrared galaxies, we present a large-scale clustering analysis of radio galaxies to z ~ 2.2. We measure the angular auto-correlation function of Ks90μJy to infer linear bias of radio galaxies in four redshift bins. We find that the bias evolves from b = 0.57 ± 0.06 at z ~ 0.3 to 8.55 ± 3.11 at z ~ 2.2. Furthermore, we separate the radio sources into subsamples to determine how the bias is dependent on the radio luminosity, and find a bias which is significantly higher than predicted by the simulations of Wilman et al., and consistent with the lower luminosity but more abundant FR-I population having a similar bias to the highly luminous but rare FR-IIs. Our results are suggestive of a higher mass, particularly for FR-I sources than assumed in simulations, especially towards higher redshift.Peer reviewe
On the thermal footsteps of Neutralino relic gases
Current literature suggests that neutralinos are the dominant cold dark
matter particle species. Assuming the microcanonical definition of entropy, we
examine the local entropy per particle produced between the ``freeze out'' era
to the present. An ``entropy consistency'' criterion emerges by comparing this
entropy with the entropy per particle of actual galactic structures given in
terms of dynamical halo variables. We apply this criterion to the cases when
neutralinos are mosly b-inos and mostly higgsinos, in conjunction with the
usual ``abundance'' criterion requiring that present neutralino relic density
complies with 0.1 < \Omega_{\chic{\tilde\chi^0_1}} < 0.3 for .
The joint application of both criteria reveals that a better fitting occurs for
the b-ino channels, hence the latter seem to be favoured over the higgsino
channels. The suggested methodology can be applied to test other annihilation
channels of the neutralino, as well as other particle candidates of thermal
gases relics.Comment: LaTex AIP style, 8 pages including 1 figure. Final version to appear
in Proceedings of the Mexican School of Astrophysics (EMA), Guanajuato,
M\'exico, July 31 - August 7, 200
The Angular Three-Point Correlation Function in the Quasilinear Regime
We calculate the normalized angular three-point correlation function (3PCF),
, as well as the normalized angular skewness, , assuming the
small-angle approximation, for a biased mass distribution in flat and open
cold-dark-matter (CDM) models with Gaussian initial conditions. The
leading-order perturbative results incorporate the explicit dependence on the
cosmological parameters, the shape of the CDM transfer function, the linear
evolution of the power spectrum, the form of redshift distribution function,
and linear and nonlinear biasing, which may be evolving. Results are presented
for different redshift distributions, including that appropriate for the APM
Galaxy Survey, as well as for a survey with a mean redshift of (such as the VLA FIRST Survey). Qualitatively, many of the results found for
and are similar to those obtained in a related treatment of the
spatial skewness and 3PCF (Buchalter & Kamionkowski 1999), such as a
leading-order correction to the standard result for in the case of
nonlinear bias (as defined for unsmoothed density fields), and the sensitivity
of the configuration dependence of to both cosmological and biasing models.
We show that since angular CFs are sensitive to clustering over a range of
redshifts, the various evolutionary dependences included in our predictions
imply that measurements of in a deep survey might better discriminate
between models with different histories, such as evolving vs. non-evolving
bias, that can have similar spatial CFs at low redshift. Our calculations
employ a derived equation---valid for open, closed, and flat models---for
obtaining the angular bispectrum from the spatial bispectrum in the small-angle
approximation.Comment: 45 pages, including 11 Figures, submitted to the Astrophysical
Journa
Constraints on the Clustering, Biasing and Redshift Distribution of Radio Sources
We discuss how different theoretical predictions for the variance
of the distribution of radio sources can be matched to measurements from the
FIRST survey at different flux limits. The predictions are given by the
integration of models for the angular correlation function for
three different functional forms of the redshift distribution , different
spatial correlation functions and by different evolutions of the bias
with redshift. We also consider the two cases of open and flat Universes.
Although the predicted show substantial differences due to
differences in the 's, these differences are not significant compared to
the uncertainties in the current observations. It turns out that the best fit
is provided by models with constant biasing at all times, although the
difference between models with epoch-independent bias and models with bias that
evolves linearly with redshift is not very large. All models with strong
evolution of bias with epoch are ruled out. As a further step we directly
calculated at 3mJy from the catalogue and matched it with our
models for the angular correlation function in the hypothesis that the
clustering signal comes from two different populations, namely AGN-powered
sources and starbursting galaxies. The results are consistent with a scenario
for hierarchical clustering where the fainter starbursting galaxies trace the
mass at all epochs, while brighter AGN's are strongly biased, with
evolving linearly with redshift, as suggested by some theories of galaxy
formation and evolution.Comment: 14 pages, 12 figures, version to appear on MNRA
The lesser role of starbursts for star formation at z=2
Two main modes of star formation are know to control the growth of galaxies:
a relatively steady one in disk-like galaxies, defining a tight star formation
rate (SFR)-stellar mass sequence, and a starburst mode in outliers to such a
sequence which is generally interpreted as driven by merging. Such starburst
galaxies are rare but have much higher SFRs, and it is of interest to establish
the relative importance of these two modes. PACS/Herschel observations over the
whole COSMOS and GOODS-South fields, in conjunction with previous
optical/near-IR data, have allowed us to accurately quantify for the first time
the relative contribution of the two modes to the global SFR density in the
redshift interval 1.5<z<2.5, i.e., at the cosmic peak of the star formation
activity. The logarithmic distributions of galaxy SFRs at fixed stellar mass
are well described by Gaussians, with starburst galaxies representing only a
relatively minor deviation that becomes apparent for SFRs more than 4 times
higher than on the main sequence. Such starburst galaxies represent only 2% of
mass-selected star forming galaxies and account for only 10% of the cosmic SFR
density at z~2. Only when limited to SFR>1000M(sun)/yr, off-sequence sources
significantly contribute to the SFR density (46+/-20%). We conclude that
merger-driven starbursts play a relatively minor role for the formation of
stars in galaxies, whereas they may represent a critical phase towards the
quenching of star formation and morphological transformation in galaxies.Comment: Accepted for publication in ApJ Letter
Condensate cosmology -- dark energy from dark matter
Imagine a scenario in which the dark energy forms via the condensation of
dark matter at some low redshift. The Compton wavelength therefore changes from
small to very large at the transition, unlike quintessence or metamorphosis. We
study CMB, large scale structure, supernova and radio galaxy constraints on
condensation by performing a 4 parameter likelihood analysis over the Hubble
constant and the three parameters associated with Q, the condensate field:
Omega_Q, w_f and z_t (energy density and equation of state today, and redshift
of transition). Condensation roughly interpolates between Lambda CDM (for large
z_t) and sCDM (low z_t) and provides a slightly better fit to the data than
Lambda CDM. We confirm that there is no degeneracy in the CMB between H and z_t
and discuss the implications of late-time transitions for the Lyman-alpha
forest. Finally we discuss the nonlinear phase of both condensation and
metamorphosis, which is much more interesting than in standard quintessence
models.Comment: 13 pages, 13 colour figures. Final version with discussion of TE
cross-correlation spectra for condensation and metamorphosis in light of the
WMAP result
The dust content of high-z submillimeter galaxies revealed by Herschel
We use deep observations taken with the Photodetector Array Camera and
Spectrometer (PACS), on board the Herschel satellite as part of the PACS
evolutionary probe (PEP) guaranteed project along with submm ground-based
observations to measure the dust mass of a sample of high-z submillimeter
galaxies (SMGs). We investigate their dust content relative to their stellar
and gas masses, and compare them with local star-forming galaxies. High-z SMGs
are dust rich, i.e. they have higher dust-to-stellar mass ratios compared to
local spiral galaxies (by a factor of 30) and also compared to local
ultraluminous infrared galaxies (ULIRGs, by a factor of 6). This indicates that
the large masses of gas typically hosted in SMGs have already been highly
enriched with metals and dust. Indeed, for those SMGs whose gas mass is
measured, we infer dust-to-gas ratios similar or higher than local spirals and
ULIRGs. However, similarly to other strongly star-forming galaxies in the local
Universe and at high-z, SMGs are characterized by gas metalicities lower (by a
factor of a few) than local spirals, as inferred from their optical nebular
lines, which are generally ascribed to infall of metal-poor gas. This is in
contrast with the large dust content inferred from the far-IR and submm data.
In short, the metalicity inferred from the dust mass is much higher (by more
than an order of magnitude) than that inferred from the optical nebular lines.
We discuss the possible explanations of this discrepancy and the possible
implications for the investigation of the metalicity evolution at high-z.Comment: Accepted for publication in Astronomy & Astrophysics Letters. One
reference update
The role of galaxy mass on AGN emission: a view from the VANDELS survey
We present a comparative analysis of the properties of AGN emitting at radio
and X-ray wavelengths. The study is performed on 907 X-ray AGN and 100 radio
AGN selected on the CDFS and UDS fields and makes use of new and ancillary data
available to the VANDELS collaboration. Our results indicate that the mass of
the host galaxy is a fundamental quantity which determines the level of AGN
activity at the various wavelengths. Indeed large stellar masses are found to
be connected with AGN radio emission, as virtually all radio-active AGN reside
within galaxies of M*>10^{10} Msun. Large stellar masses also seem to favour
AGN activity in the X-ray, even though X-ray AGN present a mass distribution
which is more spread out and with a non-negligible tail at M*<10^{9} Msun.
Stellar mass alone is also observed to play a fundamental role in simultaneous
radio and X-ray emission: the percentage of AGN active at both wavelengths
increases from around 1% of all X-ray AGN residing within hosts of M*<10^{11}
Msun to about 13% in more massive galaxies. In the case of radio-selected AGN,
such a percentage moves from about 15% to about 45% (but up to 80% in the
deepest fields). Neither cosmic epoch, nor radio luminosity, X-ray luminosity,
Eddington ratio or star-formation rate of the hosts are found to be connected
to an enhanced probability for joint radio+X-ray emission of AGN origin.
Furthermore, only a loose relation is observed between X-ray and radio
luminosity in those AGN which are simultaneously active at both frequencies.Comment: 18 pages, 18 figures, to appear on MNRA
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