11,743 research outputs found
Photometric redshifts and selection of high redshift galaxies in the NTT and Hubble Deep Fields
We present and compare in this paper new photometric redshift catalogs of the
galaxies in three public fields: the NTT Deep Field, the HDF-N and the HDF-S.
Photometric redshifts have been obtained for thewhole sample, by adopting a
minimization technique on a spectral library drawn from the Bruzual
and Charlot synthesis models, with the addition of dust and intergalactic
absorption. The accuracy, determined from 125 galaxies with known spectroscopic
redshifts, is in the redshift intervals . The global redshift distribution of I-selected galaxies shows a
distinct peak at intermediate redshifts, z~0.6 at I_{AB}<26 and z~0.8 at
I_{AB}<27.5 followed by a tail extending to z~6. We also present for the first
time the redshift distribution of the total IR-selected sample to faint limits
( and ). It is found that the number density of galaxies
at 1.25<z<1.5 is ~ 0.1 /arcmin^22 at J<=21 and ~1./arcmin^2} at J<22, and drops
to 0.3/arcmin^2 (at J<22) at 1.5<z<2. The HDFs data sets are used to compare
the different results from color selection criteria and photometric redshifts
in detecting galaxies in the redshift range 3.5<z<4.5 Photometric redshifts
predict a number of high z candidates in both the HDF-N and HDF-S that is
nearly 2 times larger than color selection criteria, and it is shown that this
is primarily due to the inclusion of dusty models that were discarded in the
original color selection criteria by Madau et al 1998. In several cases, the
selection of these objects is made possible by the constraints from the IR
bands. Finally, it is shown that galactic M stars may mimic z>5 candidates in
the HDF filter set and that the 4 brightest candidates at in the HDF-S
are indeed most likely M stars. (ABRIDGED)Comment: Version accepted on July, 20, 2000. To appear on Astronomical
Journal, Nov 2000. The data and photometric redshift catalogs presented here
are available on line at http://www.mporzio.astro.it/HIGH
Phonon Properties of Knbo3 and Ktao3 from First-Principles Calculations
The frequencies of transverse-optical phonons in KNbO and
KTaO are calculated in the frozen-phonon scheme making use of the
full-potential linearized muffin-tin orbital method. The calculated frequencies
in the cubic phase of KNbO and in the tetragonal ferroelectric phase are in
good agreement with experimental data. For KTaO, the effect of lattice
volume was found to be substantial on the frequency of the soft mode, but
rather small on the relative displacement patterns of atoms in all three modes
of the symmetry. The TO frequencies in KTaO are found to be of the
order of, but somehow higher than, the corresponding frequencies in cubic
KNbO.Comment: 8 pages + 1 LaTeX figure, Revtex 3.0, SISSA-CM-94-00
A new photometric technique for the joint selection of star-forming and passive galaxies at 1.4<z<2.5
A simple two color selection based on B-, z-, and K- band photometry is
proposed for culling galaxies at 1.4<z<2.5 in K-selected samples and
classifying them as star-forming or passive systems. The method is calibrated
on the highly complete spectroscopic redshift database of the K20 survey,
verified with simulations and tested on other datasets. Requiring
BzK=(z-K)-(B-z)>-0.2 (AB) allows to select actively star-forming galaxies at
z>1.4, independently on their dust reddening. Instead, objects with BzK<-0.2
and (z-K)>2.5 (AB) colors include passively evolving galaxies at z>1.4, often
with spheroidal morphologies. Simple recipes to estimate the reddening, SFRs
and masses of BzK-selected galaxies are derived, and calibrated on K<20
galaxies. Based on their UV (reddening-corrected), X-ray and radio
luminosities, the BzK-selected star-forming galaxies with K<20 turn out to have
average SFR ~ 200 Msun yr^-1, and median reddening E(B-V)~0.4. Besides missing
the passively evolving galaxies, the UV selection appears to miss some relevant
fraction of the z~2 star-forming galaxies with K<20, and hence of the
(obscured) star-formation rate density at this redshift. The high SFRs and
masses add to other existing evidence that these z=2 star-forming galaxies may
be among the precursors of z=0 early-type galaxies. Theoretical models cannot
reproduce simultaneously the space density of both passively evolving and
highly star-forming galaxies at z=2. In view of Spitzer Space Telescope
observations, an analogous technique based on the RJL photometry is proposed to
complement the BzK selection and to identify massive galaxies at 2.5<z<4.0.
These color criteria should help in completing the census of the stellar mass
and of the star-formation rate density at high redshift (abridged).Comment: 19 pages, 17 figures, to appear on ApJ (20 December 2004 issue
Statistical GIS-based analysis of energy consumption for residential buildings in Turin (IT)
Greenhouse gas emission is an important issue and the largest source of it is from human activities and from building sectors. Therefore, the building stocks play a key role in the reduction of GHG emissions through the analysis of the energy performance of buildings, in order to understand their behavior and to identify effective models that will allow expanding investigations in vast areas as districts or cities.
This work analyses space heating energy performance of buildings with a multi-scale approach using the main energy related variables at building, block of buildings and district scale. The purpose of this study is to identify a simple regression model in order to evaluate the space heating energy consumption of a large part of residential buildings in Turin (IT). A cluster analysis was applied in order to find groups of buildings with similar energy consumptions and to identify the main energy-related characteristics of each group. The analysis was developed with the support of a GIS tool to evaluate the buildings characteristics and a statistical software to identify a stable model at urban scale. The identified models evidenced that the space heating energy consumption not only depends on the characteristics of the building itself, but also on the urban characteristics. At urban scale, the most influential variables were: the heating degree days, positively correlated with the space heating consumption, and the albedo that was negatively correlated. Also, socio-economic variables were utilized: the percentage of working people with a positive correlation and the percentage of young inhabitants with a negative correlation. The statistical GIS-based methodology proposed in this study is simple and then replicable to other urban contexts. This kind of analysis can be useful for policy makers in defining specific energy efficiency measures for each group of buildings to identify new more effective energy performance variables and benchmarks for the different groups of buildings and then to improve the energy performance of a city reducing energy consumptions and the relative GHG emissions
The Density of Lyman-alpha Emitters at Very High Redshift
We describe narrowband and spectroscopic searches for emission-line star
forming galaxies in the redshift range 3 to 6 with the 10 m Keck II Telescope.
These searches yield a substantial population of objects with only a single
strong (equivalent width >> 100 Angstrom) emission line, lying in the 4000 -
10,000 Angstrom range. Spectra of the objects found in narrowband-selected
samples at lambda ~5390 Angstroms and ~6741 Angstroms show that these very high
equivalent width emission lines are generally redshifted Lyman alpha 1216
Angstrom at z~3.4 and 4.5. The density of these emitters above the 5 sigma
detection limit of 1.5 e-17 ergs/cm^2/s is roughly 15,000 per square degree per
unit redshift interval at both z~3.4 and 4.5. A complementary deeper (1 sigma
\~1.0 e-18 ergs/cm^2/s) slit spectroscopic search covering a wide redshift
range but a more limited spatial area (200 square arcminutes) shows such
objects can be found over the redshift range 3 to 6, with the currently highest
redshift detected being at z=5.64. The Lyman alpha flux distribution can be
used to estimate a minimum star formation rate in the absence of reddening of
roughly 0.01 solar masses/Mpc^3/year (H_0 = 65 km/s/Mpc and q_0 = 0.5).
Corrections for reddening are likely to be no larger than a factor of two,
since observed equivalent widths are close to the maximum values obtainable
from ionization by a massive star population. Within the still significant
uncertainties, the star formation rate from the Lyman alpha-selected sample is
comparable to that of the color-break-selected samples at z~3, but may
represent an increasing fraction of the total rates at higher redshifts. This
higher-z population can be readily studied with large ground-based telescopes.Comment: 7 pages, 5 encapsulated figures; aastex, emulateapj, psfig and lscape
style files. Separate gif files for 2 gray-scale images also available at
http://www.ifa.hawaii.edu/faculty/hu/emitters.html . Added discussion of
foreground contaminants. Updated discussion of comparison with external
surveys (Sec. 5 and Fig. 5). Note: continuum break strength limits (Fig. 3
caption) are correct here -- published ApJL text has a sign erro
Probing the evolution of the near-IR luminosity function of galaxies to z ~ 3 in the Hubble Deep Field South
[Abridged] We present the rest-frame Js-band and Ks-band luminosity function
of a sample of about 300 galaxies selected in the HDF-S at Ks<23 (Vega). We use
calibrated photometric redshift together with spectroscopic redshift for 25% of
the sample. The sample has allowed to probe the evolution of the LF in the
three redshift bins [0;0.8), [0.8;1.9) and [1.9;4) centered at the median
redshift z_m ~ [0.6,1.2,3]. The values of alpha we estimate are consistent with
the local value and do not show any trend with redshift. We do not see evidence
of evolution from z=0 to z_m ~ 0.6 suggesting that the population of local
bright galaxies was already formed at z<0.8. On the contrary, we clearly detect
an evolution of the LF to z_m ~ 1.2 characterized by a brightening of M* and by
a decline of phi*. To z_m ~ 1.2 M* brightens by about 0.4-0.6 mag and phi*
decreases by a factor 2-3. This trend persists, even if at a less extent, down
to z_m ~ 3 both in the Js-band and in the Ks-band LF. The decline of the number
density of bright galaxies seen at z>0.8 suggests that a significant fraction
of them increases their stellar mass at 1<z<2-3 and that they underwent a
strong evolution in this redshift range. On the other hand, this implies also
that a significant fraction of local bright/massive galaxies was already in
place at z>3. Thus, our results suggest that the assembly of high-mass galaxies
is spread over a large redshift range and that the increase of their stellar
mass has been very efficient also at very high redshift at least for a fraction
of them.Comment: 18 pages, 21 figures, Accepted for publication in MNRA
A flash in the dark: UVES/VLT high resolution spectroscopy of GRB afterglows
We present the first high resolution (R=20000--45000, corresponding to 14
km/s at 4200A to 6.6 km/s at 9000A) observations of the optical afterglow of
Gamma Ray Bursts. GRB020813 and GRB021004 were observed by UVES@VLT 22.19 hours
and 13.52 hours after the trigger, respectively. These spectra show that the
inter--stellar matter of the GRB host galaxies is complex, with many components
contributing to each main absorption system, and spanning a total velocity
range of up to about 3000 km/s. Several narrow components are resolved down to
a width of a few tens of km/s. In the case of GRB021004 we detected both low
and high ionization lines. Combined with photoionization results obtained with
CLOUDY, the ionization parameters of the various systems are consistent with a
remarkably narrow range with no clear trend with system velocity. This can be
interpreted as due to density fluctuations on top of a regular R^-2 wind
density profile.Comment: Most figure improved, a few typos corrected, added a new subsection.
ApJ in pres
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