686 research outputs found
Density waves and star formation in grand design spirals
HII regions in the arms of spiral galaxies are indicators of recent
star-forming processes. They may have been caused by the passage of the density
wave or simply created by other means near the arms. The study of these regions
may give us clues to clarifying the controversy over the existence of a
triggering scenario, as proposed in the density wave theory. Using H
direct imaging, we characterize the HII regions from a sample of three grand
design galaxies: NGC5457, NGC628 and NGC6946. Broad band images in R and I were
used to determine the position of the arms. The HII regions found to be
associated with arms were selected for the study. The age and the star
formation rate of these HII regions was obtained using measures on the
H line. The distance between the current position of the selected HII
regions and the position they would have if they had been created in the centre
of the arm is calculated. A parameter, T, which measures whether a region was
created in the arm or in the disc, is defined. With the help of the T parameter
we determine that the majority of regions were formed some time after the
passage of the density wave, with the regions located `behind the arm' (in the
direction of the rotation of the galaxy) the zone they should have occupied had
they been formed in the centre of the arm. The presence of the large number of
regions created after the passage of the arm may be explained by the effect of
the density wave, which helps to create the star-forming regions after its
passage. There is clear evidence of triggering for NGC5457 and a co-rotation
radius is proposed. A more modest triggering seems to exist for NGC628 and non
significant evidence of triggering are found for NGC6946.Comment: 10 pages, 20 figures, accepted for publication in A&
The density of states approach for the simulation of finite density quantum field theories
10 pages, 6 figures, talk at at DISCRETE2014, King's College London, December 2014Finite density quantum field theories have evaded first principle Monte-Carlo simulations due to the notorious sign-problem. The partition function of such theories appears as the Fourier transform of the generalised density-of-states, which is the probability distribution of the imaginary part of the action. With the advent of Wang-Landau type simulation techniques and recent advances, the density-of-states can be calculated over many hundreds of orders of magnitude. Current research addresses the question whether the achieved precision is high enough to reliably extract the finite density partition function, which is exponentially suppressed with the volume. In my talk, I review the state-of-play for the high precision calculations of the density-of-states as well as the recent progress for obtaining reliable results from highly oscillating integrals. I will review recent progress for the quantum field theory for which results can be obtained from the simulation of the dual theory, which appears to free of a sign problem
The density of states approach at finite chemical potential: a numerical study of the Bose gas
7 pages, 3 figures, LATTICE 2015Recently, a novel algorithm for computing the density of states in statistical systems and quantum field theories has been proposed. The same method can be applied to theories at finite density affected by the notorious sign problem, reducing a high-dimensional oscillating integral to a more tractable one-dimensional one. As an example we applied the method to the relativistic Bose gas
Herschel Far-IR counterparts of SDSS galaxies: Analysis of commonly used Star Formation Rate estimates
We study a hundred of galaxies from the spectroscopic Sloan Digital Sky
Survey with individual detections in the Far-Infrared Herschel PACS bands (100
or 160 m) and in the GALEX Far-UltraViolet band up to z0.4 in the
COSMOS and Lockman Hole fields. The galaxies are divided into 4 spectral and 4
morphological types. For the star forming and unclassifiable galaxies we
calculate dust extinctions from the UV slope, the H/H ratio and
the ratio. There is a tight correlation between the
dust extinction and both and metallicity. We calculate
SFR and compare it with other SFR estimates (H, UV, SDSS)
finding a very good agreement between them with smaller dispersions than
typical SFR uncertainties. We study the effect of mass and metallicity, finding
that it is only significant at high masses for SFR. For the AGN and
composite galaxies we find a tight correlation between SFR and L
(0.29), while the dispersion in the SFR - L relation is
larger (0.57). The galaxies follow the prescriptions of the
Fundamental Plane in the M-Z-SFR space.Comment: 24 pages, 23 figures, accepted for publication in MNRA
Acinar cell carcinoma of the pancreas with thyroid-like follicular features: first description of a new diagnostic challenging subtype.
Acinar cell carcinomas (ACCs) of the pancreas are a heterogeneous group of neoplasms showing a wide spectrum of morphological features including acinar, solid, glandular, and trabecular architecture. In addition, uncommon cytological aspects have recently been described and include oncocytic, spindle, clear, and pleomorphic cell types. This wide histological spectrum represents a challenge in the diagnostic task for pathologists. Molecular mechanisms involved in the onset and progression of ACCs are not completely known, but, in general, they differ from those observed in ductal adenocarcinomas or neuroendocrine neoplasms of the pancreas and frequently include alterations in the APC/β-catenin pathway. In the present paper, we describe a new variant of ACC showing thyroid-like follicular features and CTNNB1 mutation. This phenotype needs to be included in the spectrum of morphological presentation of ACC
Unveiling Far-Infrared Counterparts of Bright Submillimeter Galaxies Using PACS Imaging
We present a search for Herschel-PACS counterparts of dust-obscured,
high-redshift objects previously selected at submillimeter and millimeter
wavelengths in the Great Observatories Origins Deep Survey North field. We
detect 22 of 56 submillimeter galaxies (39%) with a SNR of >=3 at 100 micron
down to 3.0 mJy, and/or at 160 micron down to 5.7 mJy. The fraction of SMGs
seen at 160 micron is higher than that at 100 micron. About 50% of
radio-identified SMGs are associated with PACS sources. We find a trend between
the SCUBA/PACS flux ratio and redshift, suggesting that these flux ratios could
be used as a coarse redshift indicator. PACS undetected submm/mm selected
sources tend to lie at higher redshifts than the PACS detected ones. A total of
12 sources (21% of our SMG sample) remain unidentified and the fact that they
are blank fields at Herschel-PACS and VLA 20 cm wavelength may imply higher
redshifts for them than for the average SMG population (e.g., z>3-4). The
Herschel-PACS imaging of these dust-obscured starbursts at high-redshifts
suggests that their far-infrared spectral energy distributions have
significantly different shapes than template libraries of local infrared
galaxies.Comment: 6 pages, 4 figures. ApJ Letters in pres
PACS-Herschel FIR detections of Lyman-alpha emitters at 2.0<z<3.5
In this work we analyze the physical properties of a sample of 56
spectroscopically selected star-forming (SF) Ly emitting galaxies at
2.0z3.5 using both a spectral energy distribution (SED)
fitting procedure from rest-frame UV to mid-IR and direct 160m
observations taken with the Photodetector Array Camera & Spectrometer (PACS)
instrument onboard \emph{Herschel Space Observatory}. We define LAEs as those
Ly emitting galaxies whose rest-frame Ly equivalent widths
(Ly EW) are above 20\AA, the typical threshold in
narrow-band searches. Ly emitting galaxies with Ly
EW are called non-LAEs. As a result of an individual SED fitting
for each object, we find that the studied sample of LAEs contains galaxies with
ages mostly below 100Myr and a wide variety of dust attenuations, SFRs, and
stellar masses. The heterogeneity in the physical properties is also seen in
the morphology, ranging from bulge-like galaxies to highly clumpy systems. In
this way, we find that LAEs at 2.0z3.5 are very diverse,
and do not have a bimodal nature, as suggested in previous works. Furthermore,
the main difference between LAEs and non-LAEs is their dust attenuation,
because LAEs are not as dusty as non-LAEs. On the FIR side, four galaxies of
the sample (two LAEs and two non-LAEs) have PACS-FIR counterparts. Their total
IR luminosity place all of them in the ULIRG regime and are all dusty objects,
with A4mag. This is an indication from direct FIR
measurements that dust and Ly emission are not mutually exclusive. This
population of red and dusty LAEs is not seen at z0.3, suggesting an
evolution with redshift of the IR nature of galaxies selected via their
Ly emission.Comment: Accepted for publication in A&
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