1,575 research outputs found
The role of quenching time in the evolution of the mass-size relation of passive galaxies from the WISP survey
We analyze how passive galaxies at z 1.5 populate the mass-size plane
as a function of their stellar age, to understand if the observed size growth
with time can be explained with the appearance of larger quenched galaxies at
lower redshift. We use a sample of 32 passive galaxies extracted from the Wide
Field Camera 3 Infrared Spectroscopic Parallel (WISP) survey with spectroscopic
redshift 1.3 z 2.05, specific star-formation rates lower
than 0.01 Gyr, and stellar masses above 4.5 10
M. All galaxies have spectrally determined stellar ages from fitting of
their rest-frame optical spectra and photometry with stellar population models.
When dividing our sample into young (age 2.1 Gyr) and old (age 2.1
Gyr) galaxies we do not find a significant trend in the distributions of the
difference between the observed radius and the one predicted by the mass-size
relation. This result indicates that the relation between the galaxy age and
its distance from the mass-size relation, if it exists, is rather shallow, with
a slope alpha -0.6. At face value, this finding suggests that
multiple dry and/or wet minor mergers, rather than the appearance of newly
quenched galaxies, are mainly responsible for the observed time evolution of
the mass-size relation in passive galaxies.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figures, 1 tabl
The Circumnuclear Ring of Ionized Gas in NGC3593
We present the results of narrow-band Halpha+NII imaging of the early-type
spiral NGC3593 in combination with a study of the flux radial profiles of the
NII (lambda: 654.80, 658.34 nm), Halpha, and SII (lambda: 671.65, 673.08 nm)
emission lines along its major axis. The galaxy is known to contain two
counterrotating stellar discs of different size and luminosity. We find that
the Halpha emission mainly derives from a small central region of 57 arcsec x
25 arcsec. It consists of a filamentary pattern with a central ring. This has a
diameter of about 17 arcsec (~ 0.6/h kpc) and it contributes about half of the
total Halpha flux. The ring is interpreted as the result of the interaction
between the acquired retrograde gas which later formed the smaller
counterrotating stellar disc and the pre-existing prograde gas of the galaxy.Comment: Accepted for pubblication in Astronomy and Astrophysics; one latex
file (corsini.tex), and 2 encapsulated postscript figures
(corsini_fig1.ps,corsini_fig2.ps). To be compiled with aa.cls latex2e macro
style (pslatex option): 6 pages after latex compilatio
Thirty years after - dramatic change in the coastal marine habitats of Kos Island (Greece), 1981-2013.
Results of recent fieldwork were compared with data collected in 1981, taken as a reference condition. Surveys were conducted with the same method (time-based visual census along random paths), in the same sites, by the same people. Semi-quantitative inventories of conspicuous species were analysed by univariate and multivariate techniques. Available information on the main potential stressors indicated that a regime shift has occurred in these 30+ years: sea surface temperature rose by1-2°C, human pressure grew impressively, and invasion by several alien species took place. Consistently, a phase shift occurred in the biological communities. Of the 120 conspicuous species found in total, only 51 were common to both surveys; 31 species ('losses') were found in 1981 but not again in 2013, 38 ('gains') were found exclusively in 2013, 16 ('winners') increased their abundance, 8 ('losers') got scarcer, and 27 underwent little or no change. Gains included 7 alien, 2 nitrophilic, and 7 thermophilic species. Multivariate analysis evidenced biotic homogenisation in 2013 and huge change in rocky reef habitats. The once flourishing algal forests have disappeared to leave space to sponges and wide areas of bare substratum. This has most probably been the result of overgrazing by alien herbivorous fishes (Siganus luridus and S. rivulatus), whose establishment and spread has been favoured by seawater warming; the synergic action of local human impacts was also evidenced
The bulge-disk orthogonal decoupling in galaxies: NGC 4698 and NGC 4672
We report the case of the geometrical and kinematical decoupling between the
bulge and the disk of the Sa galaxy NGC 4698. The R-band isophotal map of this
spiral shows that the bulge structure is elongated perpendicularly to the major
axis of the disk. At the same time a central stellar velocity gradient is found
along the major axis of the bulge. We also present the Sa NGC 4672 as good
candidate of a spiral hosting a bulge and a disk orthogonally decoupled with
respect to one other. This decoupling of the two fundamental components of a
visible galaxy suggests that the disk could represent a second event in the
history of early-type spirals.Comment: 4 pages, 3 figures (LaTeX, cupconf.sty). To appear in "The Formation
of Bulges" C. M. Carollo, H. C. Ferguson, R. F. G. Wyse (eds.), Cambridge
University Pres
The Bulge-Disk Orthogonal Decoupling in Galaxies: NGC 4698
The R-band isophotal map of the Sa galaxy NGC 4698 shows that the inner
region of the bulge structure is elongated perpendicularly to the major axis of
the disk, this is also true for the outer parts of the bulge if a parametric
photometric decomposition is adopted. At the same time the stellar component is
characterized by an inner velocity gradient and a central zero-velocity plateau
along the minor and major axis of the disk respectively. This remarkable
geometric and kinematic decoupling suggests that a second event occurred in the
formation history of this galaxy.Comment: 12 pages, LaTex, with 4 PostScript figures. Accepted for publication
in The Astrophysical Journal Letter
On the relation between circular velocity and central velocity dispersion in high and low surface brightness galaxies
In order to investigate the correlation between the circular velocity Vc and
the central velocity dispersion of the spheroidal component sigma_c, we
analyzed these quantities for a sample of 40 high surface brightness disc
galaxies (hereafter HSB), 8 giant low surface brightness spiral galaxies
(hereafter LSB), and 24 elliptical galaxies characterized by flat rotation
curves. We find that the Vc-sigma_c relation is descri ed by a linear law out
to velocity dispersions as low as sigma_c~50km/s, while in previous works a
power law was adopted for galaxies with sigma_c>80k/ms.
Elliptical galaxies with Vc based on dynamical models or directly derived
from the HI rotation curves follow the same relation as the HSB galaxies in the
Vc-sigma_c plane. On the contrary, the LSB galaxies follow a different
relation, since most of them show either higher Vc (or lower sigma_c) with
respect to the HSB galaxies. This argues against the relevance of baryon
collapse in the radial density profile of the dark matter haloes of LSB
galaxies. (abridged)Comment: 18 pages, 4 figures, ApJ in pres
Simulations of nanocrystals under pressure: Combining electronic enthalpy and linear-scaling density-functional theory.
We present an implementation in a linear-scaling density-functional theory
code of an electronic enthalpy method, which has been found to be natural and
efficient for the ab initio calculation of finite systems under hydrostatic
pressure. Based on a definition of the system volume as that enclosed within an
electronic density isosurface [Phys. Rev. Lett., 94, 145501 (2005)], it
supports both geometry optimizations and molecular dynamics simulations. We
introduce an approach for calibrating the parameters defining the volume in the
context of geometry optimizations and discuss their significance. Results in
good agreement with simulations using explicit solvents are obtained,
validating our approach. Size-dependent pressure-induced structural
transformations and variations in the energy gap of hydrogenated silicon
nanocrystals are investigated, including one comparable in size to recent
experiments. A detailed analysis of the polyamorphic transformations reveals
three types of amorphous structures and their persistence on depressurization
is assessed.Comment: 11 pages and 13 figures (accepted for publication by The Journal of
Chemical Physics on the 29th of July 2013
Study of the Feasibility of an X-Ray Free Electron Laser with a 15 GeV CLIC Beam
This note presents a study of the feasibility of a Free Electron Laser (FEL) using an electron beam from the Compact Linear Collider (CLIC). We first show that, with the nominal CLIC layout, the energy spread at 15 GeV would be too large to allow FEL saturation in an undulator of reasonable length. An alternative scheme was studied, with a dedicated source, with a by-pass of the damping rings and with magnetic compression between the various acceleration stages. With this scheme, the energy spread of the CLIC beam can be reduced from 1.5% to 0.1%, but the emittance is much larger and, although the power gain is better than in the nominal case, FEL saturation is still not reached. We show that the energy spread or the transverse emittance would have to be reduced by another order of magnitude in order to obtain FEL saturation
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