143 research outputs found
Orthogonally Decoupled Variational Gaussian Processes
Gaussian processes (GPs) provide a powerful non-parametric framework for reasoning over functions. Despite appealing theory, its superlinear computational and memory complexities have presented a long-standing challenge. State-of-the-art sparse variational inference methods trade modeling accuracy against complexity. However, the complexities of these methods still scale superlinearly in the number of basis functions, implying that that sparse GP methods are able to learn from large datasets only when a small model is used. Recently, a decoupled approach was proposed that removes the unnecessary coupling between the complexities of modeling the mean and the covariance functions of a GP. It achieves a linear complexity in the number of mean parameters, so an expressive posterior mean function can be modeled. While promising, this approach suffers from optimization difficulties due to ill-conditioning and non-convexity. In this work, we propose an alternative decoupled parametrization. It adopts an orthogonal basis in the mean function to model the residues that cannot be learned by the standard coupled approach. Therefore, our method extends, rather than replaces, the coupled approach to achieve strictly better performance. This construction admits a straightforward natural gradient update rule, so the structure of the information manifold that is lost during decoupling can be leveraged to speed up learning. Empirically, our algorithm demonstrates significantly faster convergence in multiple experiments
A Detailed Study of Photometric Redshifts for GOODS-South Galaxies
We use the deepest and the most comprehensive photometric data currently
available for GOODS-South galaxies to measure their photometric redshifts. The
photometry includes VLT/VIMOS (U-band), HST/ACS (F435W, F606W, F775W, and
F850LP bands), VLT/ISAAC (J-, H-, and Ks-bands), and four Spitzer/IRAC channels
(3.6, 4.5, 5.8, and 8.0 micron). The catalog is selected in the z-band (F850LP)
and photometry in each band is carried out using the recently completed TFIT
algorithm, which performs PSF matched photometry uniformly across different
instruments and filters, despite large variations in PSFs and pixel scales.
Photometric redshifts are derived using the GOODZ code, which is based on the
template fitting method using priors. The code also implements "training" of
the template SED set, using available spectroscopic redshifts in order to
minimize systematic differences between the templates and the SEDs of the
observed galaxies. Our final catalog covers an area of 153 sq. arcmin and
includes photometric redshifts for a total of 32,505 objects. The scatter
between our estimated photometric and spectroscopic redshifts is sigma=0.040
with 3.7% outliers to the full z-band depth of our catalog, decreasing to
sigma=0.039 and 2.1% outliers at a magnitude limit m(z)<24.5. This is
consistent with the best results previously published for GOODS-S galaxies,
however, the present catalog is the deepest yet available and provides
photometric redshifts for significantly more objects to deeper flux limits and
higher redshifts than earlier works. Furthermore, we show that the photometric
redshifts estimated here for galaxies selected as dropouts are consistent with
those expected based on the Lyman break technique.Comment: 62 pages, 21 figures. Minor changes to match version to be published
in Ap
The Progenitors of the Compact Early-Type Galaxies at High-Redshift
We use GOODS and CANDELS images to identify progenitors of massive (log M >
10 Msun) compact "early-type" galaxies (ETGs) at z~1.6. Since merging and
accretion increase the size of the stellar component of galaxies, if the
progenitors are among known star-forming galaxies, these must be compact
themselves. We select candidate progenitors among compact Lyman-break galaxies
at z~3 based on their mass, SFR and central stellar density and find that these
account for a large fraction of, and possibly all, compact ETGs at z~1.6. We
find that the average far-UV SED of the candidates is redder than that of the
non-candidates, but the optical and mid-IR SED are the same, implying that the
redder UV of the candidates is inconsistent with larger dust obscuration, and
consistent with more evolved (aging) star-formation. This is in line with other
evidence that compactness is a sensitive predictor of passivity among
high-redshift massive galaxies. We also find that the light distribution of
both the compact ETGs and their candidate progenitors does not show any
extended "halos" surrounding the compact "core", both in individual images and
in stacks. We argue that this is generally inconsistent with the morphology of
merger remnants, even if gas-rich, as predicted by N-body simulations. This
suggests that the compact ETGs formed via highly dissipative, mostly gaseous
accretion of units whose stellar components are very small and undetected in
the HST images, with their stellar mass assembling in-situ, and that they have
not experienced any major merging until the epoch of observations at z~1.6.Comment: 25 pages, 20 figures; Accepted for publication in Ap
Static and dynamic evaluation of pelvic floor disorders with an open low-field tilting magnet.
AIM:
To assess the feasibility of magnetic resonance defaecography (MRD) in pelvic floor disorders using an open tilting magnet with a 0.25 T static field and to compare the results obtained from the same patient both in supine and orthostatic positions.
MATERIALS AND METHODS:
From May 2010 to November 2011, 49 symptomatic female subjects (mean age 43.5 years) were enrolled. All the patients underwent MRD in the supine and orthostatic positions using three-dimensional (3D) hybrid contrast-enhanced (HYCE) sequences and dynamic gradient echo (GE) T1-weighted sequences. All the patients underwent conventional defaecography (CD) to correlate both results. Two radiologists evaluated the examinations; inter and intra-observer concordance was measured. The results obtained in the two positions were compared between them and with CD.
RESULTS:
The comparison between CD and MRD found statistically significant differences in the evaluation of anterior and posterior rectocoele during defaecation in both positions and of rectal prolapse under the pubo-coccygeal line (PCL) during evacuation, only in the supine position (versus MRD orthostatic: rectal prolapse p < 0.0001; anterior rectocoele p < 0.001; posterior rectocoele p = 0.008; versus CD: rectal prolapse p < 0.0001; anterior rectocoele p < 0.001; posterior rectocoele p = 0.01). The value of intra-observer intra-class correlation coefficient (ICC) ranged from good to excellent; the interobserver ICC from moderate to excellent.
CONCLUSION:
MRD is feasible with an open low-field tilting magnet, and it is more accurate in the orthostatic position than in the supine position to evaluate pelvic floor disorders
Rest-Frame UV-Optical Selected Galaxies at 2.3 ≾ z ≾ 3.5: Searching for Dusty Star-forming and Passively Evolving Galaxies
A new set of color selection criteria (VJL) analogous with the BzK method is designed to select both star-forming galaxies (SFGs) and passively evolving galaxies (PEGs) at 2.3 ≾ z ≾ 3.5 by using rest-frame UV-optical (V – J versus J – L) colors. The criteria are thoroughly tested with theoretical stellar population synthesis models and real galaxies with spectroscopic redshifts to evaluate their efficiency and contamination. We apply the well-tested VJL criteria to the HST/WFC3 Early Release Science field and study the physical properties of selected galaxies. The redshift distribution of selected SFGs peaks at z ~ 2.7, slightly lower than that of Lyman break galaxies at z ~ 3. Comparing the observed mid-infrared fluxes of selected galaxies with the prediction of pure stellar emission, we find that our VJL method is effective at selecting massive dusty SFGs that are missed by the Lyman break technique. About half of the star formation in massive (M_(star) > 10^(10) M_☉) galaxies at 2.3 ≾ z ≾ 3.5 is contributed by dusty (extinction E(B – V) > 0.4) SFGs, which, however, only account for ~20% of the number density of massive SFGs. We also use the mid-infrared fluxes to clean our PEG sample and find that galaxy size can be used as a secondary criterion to effectively eliminate the contamination of dusty SFGs. The redshift distribution of the cleaned PEG sample peaks at z ~ 2.5. We find six PEG candidates at z > 3 and discuss possible methods to distinguish them from dusty contamination. We conclude that at least part of our candidates are real PEGs at z ~ 3, implying that these types of galaxies began to form their stars at z ≳ 5. We measure the integrated stellar mass density (ISMD) of PEGs at z ~ 2.5 and set constraints on it at z > 3. We find that the ISMD grows by at least about a factor of 10 in 1 Gyr at 3 < z <5 and by another factor of 10 in the next 3.5 Gyr (1 < z < 3)
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
Bimodal Color Distribution in Hierarchical Galaxy Formation
We show how the observed bimodality in the color distribution of galaxies can
be explained in the framework of the hierarchical clustering picture in terms
of the interplay between the properties of the merging histories and the
feedback/star-formation processes in the progenitors of local galaxies. Using a
semi-analytic model of hierarchical galaxy formation, we compute the color
distributions of galaxies with different luminosities and compare them with the
observations. Our fiducial model matches the fundamental properties of the
observed distributions, namely: 1) the distribution of objects brighter than
M_r = -18 is clearly bimodal, with a fraction of red objects increasing with
luminosity; 2) for objects brighter than M_r = -21 the color distribution is
dominated by red objects with color u-r = 2.2-2.4; 3) the spread on the
distribution of the red population is smaller than that of the blue population;
4) the fraction of red galaxies is larger in denser environments, even for
low-luminosity objects; 5) the bimodality in the distribution persists up to z
= 1.5. We discuss the role of the different physical processes included in the
model in producing the above results.Comment: 11 pages, accepted for publication in the Astrophysical Journa
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
La rete sismica AlpArray e il contributo dell'INGV
Il progetto AlpArray (PI E. Kissling, Seismology and Geodynamics ETH) è un’iniziativa europea di collaborazione interdisciplinare sismologica e geodinamica, il cui obiettivo principale è quello di migliorare la comprensione della struttura profonda e della geodinamica delle Alpi (la catena montuosa più studiata al mondo) tramite l’acquisizione, l’analisi e l’interpretazione di dati sismologici di alta qualità.
Per ottenere delle immagini di estremo dettaglio della crosta e del mantello, AlpArray propone la realizzazione di una rete sismica a maglia il più possibile omogenea (massima distanza inter- stazione 52 km, backbone network), tramite la condivisione dei dati delle reti permanenti esistenti e l’installazione, da parte di ciascun paese partecipante, di numerose stazioni sismiche temporanee a larga banda (BB). Il progetto prevede l'installazione di circa 250 stazioni sismiche in tutta Europa, in particolare in Italia, Francia, Svizzera, Germania, Austria, Croazia, Repubblica Ceca, Bosnia, Ungheria, Slovenia e Polonia. I dati confluiranno all’interno dell’archivio europeo denominato European Integrated Data Archive (EIDA). Considerata l’estensione geografica dell’area, i partecipanti combineranno le infrastrutture esistenti per l’acquisizione dei dati, il loro trattamento, l’applicazione delle tecniche più avanzate di imaging e l’interpretazione e modellazione dei risultati, in uno sforzo transnazionale ad una scala mai realizzata prima in Europa. Si tratta quindi di un’occasione fondamentale per lo scambio di competenze tecniche e scientifiche all’avanguardia.
L’INGV, oltre a condividere i dati delle proprie stazioni permanenti nell’area di interesse, si occupa della installazione e della manutenzione sul territorio italiano di 20 nuove stazioni-BB temporanee i cui dati verranno trasmessi in tempo reale (partecipando così alla realizzazione del backbone) e coadiuva l’ETH nella ricerca dei siti italiani per altrettante stazioni svizzere e nella loro manutenzione ordinaria. L’acquisizione di una mole notevole di nuovi dati permetterà di raffinare le conoscenze sulla struttura e la composizione della litosfera e del mantello al di sotto dell’area alpina: Queste conoscenze sono anche utili ai fini della modellazione geodinamica. Il potenziamento del monitoraggio sismico aiuterà ad individuare e studiare in maggior dettaglio le aree sismogenetiche della regione alpina
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