30 research outputs found
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
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 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
Discovery Of Cold, Pristine Gas Possibly Accreting Onto An Overdensity Of Star-Forming Galaxies At Redshift z ~ 1.6
We report the discovery of large amounts of cold (T ~ 10^4 K), chemically
young gas in an overdensity of galaxies at redshift z ~ 1.6 in the Great
Observatories Origins Deep Survey southern field (GOODS-S). The gas is
identified thanks to the ultra-strong Mg II absorption features it imprints in
the rest-frame UV spectra of galaxies in the background of the overdensity.
There is no evidence that the optically-thick gas is part of any massive galaxy
(i.e. M_star > 4x10^9 M_sun), but rather is associated with the overdensity;
less massive and fainter galaxies (25.5 < z_850 < 27.5 mag) have too large an
impact parameter to be causing ultra-strong absorption systems, based on our
knowledge of such systems. The lack of corresponding Fe II absorption features,
not detected even in co-added spectra, suggests that the gas is chemically more
pristine than the ISM and outflows of star-forming galaxies at similar
redshift, including those in the overdensity itself, and comparable to the most
metal-poor stars in the Milky Way halo. A crude estimate of the projected
covering factor of the high-column density gas (N_H >~ 10^20 cm-2) based on the
observed fraction of galaxies with ultra-strong absorbers is C_F ~ 0.04. A
broad, continuum absorption profile extending to the red of the interstellar Mg
II absorption line by <~ 2000 km/s is possibly detected in two independent
co-added spectra of galaxies of the overdensity, consistent with a large-scale
infall motion of the gas onto the overdensity and its galaxies. Overall, these
findings provides the first tentative evidence of accretion of cold, chemically
young gas onto galaxies at high redshift, possibly feeding their star formation
activity. The fact that the galaxies are members of a large structure, as
opposed to field galaxies, might play a significant role in our ability to
detect the accreting gas.Comment: 57 pages, 17 figures, 1 table; accepted for publication by ApJ (Aug
9, 2011); minor modifications to match the accepted versio
AlpArray-Italy: Site description and noise characterization
Within the framework of the European collaborative research initiative AlpArray (http://www.alparray.ethz. ch), the Istituto Nazionale di Geofisica e Vulcanolgia (INGV) deployed overall 20 broad-band seismic stations in Northern Italy and on two islands in the Tyrrhenian Sea (Capraia and Montecristo) during Fall-Winter 2015.
The temporary deployment (16 stations) will run for two to three years and 4 INGV National Seismic Network accelerometric sites are now equipped with additional per- manent broad-band sensors. The 16 temporary stations are equipped with REF TEK 130 digitizers and Nanometrics Trillium Compact 120 s sensors, a couple have Nanometrics Trillium 120P sensors and one a Streckeisen STS2.
For each site we describe the settings and discuss the noise levels, the site effects and the preliminary sensitivity analysis.Published39-528T. Sismologia in tempo realeJCR Journa
Color and Stellar Population Gradients in Passively Evolving Galaxies at z~2 from HST/WFC3 Deep Imaging in the Hubble Ultra Deep Field
We report the detection of color gradients in six massive (stellar mass >
10^{10} M_{sun}) and passively evolving (specific SFR < 10^{-11}/yr) galaxies
at redshift 1.3<z<2.5 identified in the HUDF using HST ACS and WFC3/IR images.
After matching different PSFs, we obtain color maps and multi-band
optical/near-IR photometry (BVizYJH) in concentric annuli, from the smallest
resolved radial (~1.7 kpc) up to several times the H-band effective radius. We
find that the inner regions of these galaxies have redder rest-frame
UV--optical colors than the outer parts. The slopes of the color gradients
mildly depend on the overall dust obscuration and rest-frame (U-V) color, with
more obscured or redder galaxies having steeper color gradients. The z~2 color
gradients are also steeper than those of local early-types. The gradient of a
single parameter (age, extinction or metallicity) cannot fully explain the
observed color gradients. Fitting spatially resolved HST seven-band photometry
to stellar population synthesis models, we find that, regardless of assumptions
for metallicity gradient, the redder inner regions of the galaxies have
slightly higher dust obscuration than the bluer outer regions, although the
magnitude depends on the assumed extinction law. The derived age gradient
depends on the assumptions for metallicity gradient. We discuss the
implications of a number of assumptions for metallicity gradient on the
formation and evolution of these galaxies. We find that the evolution of the
mass--size relationship from z~2 to z~0 cannot be driven by in--situ extended
star formation, implying that accretion or merger is mostly responsible for the
evolution. The lack of a correlation between color gradient and stellar mass
argues against the metallicity gradient predicted by the monolithic collapse,
which would require significant major mergers to evolve into the one observed
at z~0. (Abridged)Comment: Minor changes to address referee's comments, accepted by Ap
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey - The Hubble Space Telescope Observations, Imaging Data Products and Mosaics
This paper describes the Hubble Space Telescope imaging data products and
data reduction procedures for the Cosmic Assembly Near-IR Deep Extragalactic
Legacy Survey (CANDELS). This survey is designed to document the evolution of
galaxies and black holes at , and to study Type Ia SNe beyond
. Five premier multi-wavelength sky regions are selected, each with
extensive multiwavelength observations. The primary CANDELS data consist of
imaging obtained in the Wide Field Camera 3 / infrared channel (WFC3/IR) and
UVIS channel, along with the Advanced Camera for Surveys (ACS). The
CANDELS/Deep survey covers \sim125 square arcminutes within GOODS-N and
GOODS-S, while the remainder consists of the CANDELS/Wide survey, achieving a
total of \sim800 square arcminutes across GOODS and three additional fields
(EGS, COSMOS, and UDS). We summarize the observational aspects of the survey as
motivated by the scientific goals and present a detailed description of the
data reduction procedures and products from the survey. Our data reduction
methods utilize the most up to date calibration files and image combination
procedures. We have paid special attention to correcting a range of
instrumental effects, including CTE degradation for ACS, removal of electronic
bias-striping present in ACS data after SM4, and persistence effects and other
artifacts in WFC3/IR. For each field, we release mosaics for individual epochs
and eventual mosaics containing data from all epochs combined, to facilitate
photometric variability studies and the deepest possible photometry. A more
detailed overview of the science goals and observational design of the survey
are presented in a companion paper.Comment: 39 pages, 25 figure
CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS)
is designed to document the first third of galactic evolution, over the
approximate redshift (z) range 8--1.5. It will image >250,000 distant galaxies
using three separate cameras on the Hubble Space Telescope, from the
mid-ultraviolet to the near-infrared, and will find and measure Type Ia
supernovae at z>1.5 to test their accuracy as standardizable candles for
cosmology. Five premier multi-wavelength sky regions are selected, each with
extensive ancillary data. The use of five widely separated fields mitigates
cosmic variance and yields statistically robust and complete samples of
galaxies down to a stellar mass of 10^9 M_\odot to z \approx 2, reaching the
knee of the ultraviolet luminosity function (UVLF) of galaxies to z \approx 8.
The survey covers approximately 800 arcmin^2 and is divided into two parts. The
CANDELS/Deep survey (5\sigma\ point-source limit H=27.7 mag) covers \sim 125
arcmin^2 within GOODS-N and GOODS-S. The CANDELS/Wide survey includes GOODS and
three additional fields (EGS, COSMOS, and UDS) and covers the full area to a
5\sigma\ point-source limit of H \gtrsim 27.0 mag. Together with the Hubble
Ultra Deep Fields, the strategy creates a three-tiered "wedding cake" approach
that has proven efficient for extragalactic surveys. Data from the survey are
nonproprietary and are useful for a wide variety of science investigations. In
this paper, we describe the basic motivations for the survey, the CANDELS team
science goals and the resulting observational requirements, the field selection
and geometry, and the observing design. The Hubble data processing and products
are described in a companion paper.Comment: Submitted to Astrophysical Journal Supplement Series; Revised
version, subsequent to referee repor
Arrival angles of teleseismic fundamental mode Rayleigh waves across the AlpArray
The dense AlpArray network allows studying seismic wave propagation with high spatial resolution. Here we introduce an array approach to measure arrival angles of teleseismic Rayleigh waves. The approach combines the advantages of phase correlation as in the two-station method with array beamforming to obtain the phase-velocity vector. 20 earthquakes from the first two years of the AlpArray project are selected, and spatial patterns of arrival-angle deviations across the AlpArray are shown in maps, depending on period and earthquake location. The cause of these intriguing spatial patterns is discussed. A simple wave-propagation modelling example using an isolated anomaly and a Gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths. This indicates that arrival-angle information constitutes useful additional information on the Earth structure, beyond what is currently used in inversions
Ambient-noise tomography of the wider Vienna Basin region
We present a new 3-D shear-velocity model for the top 30 km of the crust in the wider Vienna Basin region based on surface waves extracted from ambient-noise cross-correlations. We use continuous seismic records of 63 broad-band stations of the AlpArray project to retrieve interstation Green’s functions from ambient-noise cross-correlations in the period range from 5 to 25 s. From these Green’s functions, we measure Rayleigh group traveltimes, utilizing all four components of the cross-correlation tensor, which are associated with Rayleigh waves (ZZ, RR, RZ and ZR), to exploit multiple measurements per station pair. A set of selection criteria is applied to ensure that we use high-quality recordings of fundamental Rayleigh modes. We regionalize the interstation group velocities in a 5 km × 5 km grid with an average path density of ∼20 paths per cell. From the resulting group-velocity maps, we extract local 1-D dispersion curves for each cell and invert all cells independently to retrieve the crustal shear-velocity structure of the study area. The resulting model provides a previously unachieved lateral resolution of seismic velocities in the region of ∼15 km. As major features, we image the Vienna Basin and Little Hungarian Plain as low-velocity anomalies, and the Bohemian Massif with high velocities. The edges of these features are marked with prominent velocity contrasts correlated with faults, such as the Alpine Front and Vienna Basin transfer fault system. The observed structures correlate well with surface geology, gravitational anomalies and the few known crystalline basement depths from boreholes. For depths larger than those reached by boreholes, the new model allows new insight into the complex structure of the Vienna Basin and surrounding areas, including deep low-velocity zones, which we image with previously unachieved detail. This model may be used in the future to interpret the deeper structures and tectonic evolution of the wider Vienna Basin region, evaluate natural resources, model wave propagation and improve earthquake locations, among others