2,079 research outputs found
Age, metallicity and star formation history of spheroidal galaxies in cluster at z~1.2
We present the analysis, based on spectra collected at the Large Binocular
Telescope, of the stellar populations in seven spheroidal galaxies in the
cluster XLSSJ0223 at 1.22. The aim is to constrain the epoch of their
formation and their star formation history. Using absorption line strenghts and
full spectral fitting, we derive for the stellar populations of the seven
spheroids a median age =2.40.6 Gyr, corresponding to a median
formation redshift $\sim2.6_{-0.5}^{+0.7}$ (lookback time =
11$_{-1.0}^{+0.6}$ Gyr). We find a significant scatter in age, showing that
massive spheroids, at least in our targeted cluster, are not coeval. The median
metallicity is [Z/H]=0.09$\pm$0.16, as for early-types in clusters at
0$<z<<\sigma_e_{dyn}\Sigma_e_{dyn}\Sigma_e_{dyn}\Sigma_ez\sim1.3$, i.e.
more massive spheroids are more metal rich, have lower stellar mass density and
tend to be older than lower-mass galaxies.Comment: 16 pages, 6 figures, 6 tables, published on MNRA
The Kinematics of Kepler's Supernova Remnant as revealed by Chandra
I determine the expansion of the supernova remnant of SN1604 (Kepler's
supernova) based on archival Chandra ACIS-S observations made in 2000 and 2006.
The measurements were done in several distinct energy bands, and were made for
the remnant as a whole, and for six individual sectors. The average expansion
parameter indicates that the remnant expands as , but there
are significant differences in different parts of the remnant: the bright
northwestern part expands as , whereas the rest of the
remnant's expansion shows an expansion . The latter is
consistent with an explosion in which the outer part of the ejecta has a
negative power law slope for density () of , or with
an exponential density profile(). The expansion
parameter in the southern region, in conjunction with the shock radius,
indicate a rather low value (<5E50 erg) for the explosion energy of SN1604 for
a distance of 4 kpc. An higher explosion energy is consistent with the results,
if the distance is larger.
The filament in the eastern part of the remnant, which is dominated by X-ray
synchrotron radiation seems to mark a region with a fast shock speed , corresponding to a shock velocity of v= 4200 km/s, for a distance to
SN1604 of 4 kpc. This is consistent with the idea that X-ray synchrotron
emission requires shock velocities in excess of ~2000 km/s.
The X-ray based expansion measurements reported are consistent with results
based on optical and radio measurements, but disagree with previous X-ray
measurements based on ROSAT and Einstein observations.Comment: Accepted for publication in ApJ. This new version is the accepted
version, which differs mainly in the discussion sectio
The Kormendy relation of massive elliptical galaxies at z~1.5. Evidence for size evolution ?
We present the morphological analysis based on HST-NIC2 (0.075 arcsec/pixel)
images in the F160W filter of a sample of 9 massive field (> 10^{11} M_\odot)
galaxies spectroscopically classified as early-types at 1.2<z<1.7. Our analysis
shows that all of them are bulge dominated systems. In particular, 6 of them
are well fitted by a de Vaucouleurs profile (n=4) suggesting that they can be
considered pure elliptical galaxies. The remaining 3 galaxies are better fitted
by a Sersic profile with index 1.9<n<2.3 suggesting that a disk-like component
could contribute up to 30% to the total light of these galaxies. We derived the
effective radius R_e and the mean surface brightness within R_e of our
galaxies and we compared them with those of early-types at lower redshifts. We
find that the surface brightness of our galaxies should get fainter by
2.5 mag from z~1.5 to z~0 to match the surface brightness of the local
ellipticals with comparable R_e, i.e. the local Kormendy relation. Luminosity
evolution without morphological changes can only explain half of this effect,
as the maximum dimming expected for an elliptical galaxy is ~1.6 mag in this
redshift range. Thus, other parameters, possibly structural, may undergo
evolution and play an important role in reconciling models and observations.
Hypothesizing an evolution of the effective radius of galaxies we find that R_e
should increase by a factor 1.5 from z~1.5 to z~0.Comment: Accepted for publication in MNRAS, 15 pages, 8 figure
Modello coesivo per l’avanzamento di fratture mediante rilascio nodale di strutture discretizzate con elementi finiti
La simulazione numerica della propagazione di una frattura in MODO I, viaggiante ad elevatavelocità in un acciaio a comportamento duttile è realizzata attraverso un modello coesivo che governa ladistribuzione delle forze di rilascio nodale. Come noto, la ricerca di un valore di tensione all’apice non ha alcunsenso nel caso elastico; infatti, la tensione può essere valutata solo mediante fattori di campo. Nel caso elasto-plastico, incrudimento e softening di origine geometrica o legato al progressivo danneggiamento influisconodecisamente sull’andamento esponenziale del campo tensionale. È possibile comunque individuare un valore diriferimento, di entità finita, mediante estrapolazione delle tensioni elasto-plastiche nella zona di inizio softeningdella frattura. Tale grandezza può essere presa come fattore di riferimento per il calcolo delle forze di rilasciocoesive e quindi dell’energia dissipata. Nel lavoro viene discusso come determinare, dal campo di tensioneelasto-plastico locale, il valore che governa la zona coesiva al variare del T-stress
Dense, Fe-rich Ejecta in Supernova Remnants DEM L238 and DEM L249: A New Class of Type Ia Supernova?
We present observations of two LMC supernova remnants (SNRs), DEM L238 and
DEM L249, with the Chandra and XMM-Newton X-ray satellites. Bright central
emission, surrounded by a faint shell, is present in both remnants. The central
emission has an entirely thermal spectrum dominated by strong Fe L-shell lines,
with the deduced Fe abundance in excess of solar and not consistent with the
LMC abundance. This Fe overabundance leads to the conclusion that DEM L238 and
DEM L249 are remnants of thermonuclear (Type Ia) explosions. The shell emission
originates in gas swept up and heated by the blast wave. A standard Sedov
analysis implies about 50 solar masses in both swept-up shells, SNR ages
between 10,000 and 15,000 yr, low (< 0.05 cm^-3) preshock densities, and
subluminous explosions with energies of 3x10^50 ergs. The central Fe-rich
supernova ejecta are close to collisional ionization equilibrium. Their
presence is unexpected, because standard Type Ia SNR models predict faint
ejecta emission with short ionization ages. Both SNRs belong to a previously
unrecognized class of Type Ia SNRs characterized by bright interior emission.
Denser than expected ejecta and/or a dense circumstellar medium around the
progenitors are required to explain the presence of Fe-rich ejecta in these
SNRs. Substantial amounts of circumstellar gas are more likely to be present in
explosions of more massive Type Ia progenitors. DEM L238, DEM L249, and similar
SNRs could be remnants of ``prompt'' Type Ia explosions with young (~100 Myr
old) progenitors.Comment: 24 pages, 8 figures, ApJ, in pres
Extremely compact massive galaxies at z~1.4
The optical rest-frame sizes of 10 of the most massive
(~5x10^{11}h_{70}^{-2}M_sun) galaxies found in the near-infrared MUNICS survey
at 1.2<z<1.7 are analysed. Sizes were estimated both in the J and K' filters.
These massive galaxies are at least a factor of 4_{-1.0}^{+1.9} (+-1 sigma)
smaller in the rest-frame V-band than local counterparts of the same stellar
mass. Consequently, the stellar mass density of these objects is (at least) 60
times larger than massive ellipticals today. Although the stellar populations
of these objects are passively fading, their structural properties are rapidly
changing since that redshift. This observational fact disagrees with a scenario
where the more massive and passive galaxies are fully assembled at z~1.4 (i.e.
a monolithic scenario) and points towards a dry merger scenario as the
responsible mechanism for the subsequent evolution of these galaxies.Comment: 5 pages, 2 figures, 1 table, accepted for publication in MNRAS
letter
Drawing Snow White and Animating Buzz Lightyear: Technological Toolkit Characteristics and Creativity in Cross-Disciplinary Teams
The use of technological tools to execute creative tasks is pervasive within cross-disciplinary teams, yet little attention has been paid to their role in influencing team creativity. In particular, no research has focused on how the characteristics of a team’s technological toolkit – the set of technological tools a team can draw upon to construct its actions – can affect team creativity. I propose that considering the toolkit, rather than just isolated tools, and the multiple functions played by tools is critical to understand how technology characteristics influence team creativity. I hypothesize that creativity in cross-disciplinary teams is influenced by the size and field diffusion of the team toolkit, with size having a curvilinear relationship with creativity, and diffusion having a positive relationship. Moreover, I hypothesize that these effects will be mitigated when the number of team members who are experts with the focal tool is high. I test and find support for these hypotheses in a study set in the context of the Hollywood animation industry, a knowledge-intensive industry characterized by the presence of cross-disciplinary teams using a variety of technological tools. Theoretical and practical implications of the results are discussed
Ionospheric response to the corotating interaction region-driven geomagnetic storm of October 2002
Unlike the geomagnetic storms produced by coronal mass ejections (CMEs), the storms generated by corotating interaction regions (CIRs) are not manifested by dramatic enhancements of the ring current. The CIR-driven storms are however capable of producing other phenomena typical for the magnetic storms such as relativistic particle acceleration, enhanced magnetospheric convection and ionospheric heating. This paper examines ionospheric plasma anomalies produced by a CIR-driven storm in the middle- and high-latitude ionosphere with a specific focus on the polar cap region. The moderate magnetic storm which took place on 14–17 October 2002 has been used as an example of the CIR-driven event. Four-dimensional tomographic reconstructions of the ionospheric plasma density using measurements of the total electron content along ray paths of GPS signals allow us to reveal the large-scale structure of storm-induced ionospheric anomalies. The tomographic reconstructions are compared with the data obtained by digital ionosonde located at Eureka station near the geomagnetic north pole. The morphology and dynamics of the observed ionospheric anomalies is compared qualitatively to the ionospheric anomalies produced by major CME-driven storms. It is demonstrated that the CIR-driven storm of October 2002 was able to produce ionospheric anomalies comparable to those produced by CME-driven storms of much greater Dst magnitude. This study represents an important step in linking the tomographic GPS reconstructions with the data from ground-based network of digital ionosondes
A Deep Chandra Observation of Kepler's Supernova Remnant: A Type Ia Event with Circumstellar Interaction
We present initial results of a 750 ks Chandra observation of the remnant of
Kepler's supernova of AD 1604. The strength and prominence of iron emission,
together with the absence of O-rich ejecta, demonstrate that Kepler resulted
from a thermonuclear supernova, even though evidence for circumstellar
interaction is also strong. We have analyzed spectra of over 100 small regions,
and find that they fall into three classes. (1) The vast majority show Fe L
emission between 0.7 and 1 keV and Si and S K alpha emission; we associate
these with shocked ejecta. A few of these are found at or beyond the mean blast
wave radius. (2) A very few regions show solar O/Fe abundance rations; these we
associate with shocked circumstellar medium (CSM). Otherwise O is scarce. (3) A
few regions are dominated by continuum, probably synchrotron radiation.
Finally, we find no central point source, with a limit about 100 times fainter
than the central object in Cas A. The evidence that the blast wave is
interacting with CSM may indicate a Ia explosion in a more massive progenitor.Comment: Accepted by ApJ Letter
The Luminous and Carbon-Rich Supernova 2006gz: A Double Degenerate Merger?
Spectra and light curves of SN 2006gz show the strongest signature of
unburned carbon and one of the slowest fading light curves ever seen in a type
Ia event (Delta m_15 = 0.69 +/- 0.04). The early-time Si II velocity is low,
implying it was slowed by an envelope of unburned material. Our best estimate
of the luminosity implies M_V = -19.74 and the production of ~ 1.2 M_sun of
56Ni. This suggests a super-Chandrasekhar mass progenitor. A double degenerate
merger is consistent with these observations.Comment: Accepted for publication in ApJL (5 pages, 4 figures). UBVr'i' light
curves, UVOIR light curves, and spectra available at
http://www.cfa.harvard.edu/supernova/SN2006g
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