376 research outputs found
Aspectos sobre o dimensionamento em betão estrutural considerando-se a não-linearidade fÃÂsica
O presente trabalho apresenta aspectos sobre a aplicação de relações constitutivas não-lineares ao projeto de estruturas de concreto armado. A metodologia semi-probabilÃstica de segurança aplicada à análise não-linear, e as perspectivas do método do coeficiente global de segurança referido aos materiais, são brevemente apresentados e discutidos. Uma série de argumentos ressaltando as principais virtudes e deficiências de cada uma das metodologias são apresentados, e a abordagem de dois exemplos práticos de dimensionamento de elementos isolados ilustra a versatilidade e os possÃveis benefÃcios oferecidos pela análise não-linear
Ages and Abundances of Red Sequence Galaxies as a Function of LINER Emission Line Strength
Although the spectrum of a prototypical early-type galaxy is assumed to lack
emission lines, a substantial fraction (likely as high as 30%) of nearby red
sequence galaxy spectra contain emission lines with line ratios characteristic
of low ionization nuclear emission-line regions (LINERs). We use spectra of
~6000 galaxies from the Sloan Digital Sky Survey (SDSS) in a narrow redshift
slice (0.06 < z < 0.08) to compare the stellar populations of red sequence
galaxies with and without LINER-like emission. The spectra are binned by
internal velocity dispersion and by emission properties to produce high S/N
stacked spectra. The recent stellar population models of R. Schiavon (2007)
make it possible to measure ages, [Fe/H], and individual elemental abundance
ratios [Mg/Fe], [C/Fe], [N/Fe], and [Ca/Fe] for each of the stacked spectra. We
find that red sequence galaxies with strong LINER-like emission are
systematically 2-3.5 Gyr (10-40%) younger than their emission-free counterparts
at the same velocity dispersion. This suggests a connection between the
mechanism powering the emission (whether AGN, post-AGB stars, shocks, or
cooling flows) and more recent star formation in the galaxy. We find that mean
stellar age and [Fe/H] increase with velocity dispersion for all galaxies.
Elemental abundance [Mg/Fe] increases modestly with velocity dispersion in
agreement with previous results, and [C/Fe] and [N/Fe] increase more strongly
with velocity dispersion than does [Mg/Fe]. [Ca/Fe] appears to be roughly solar
for all galaxies. At fixed velocity dispersion, galaxies with fainter r-band
luminosities have lower [Fe/H] and older ages but similar abundance ratios
compared to brighter galaxies.Comment: 25 pages, 17 figures, Accepted for publication in ApJ as of 16 July
2007; acceptance status updated, paper unchange
And the winner is: galaxy mass
The environment is known to affect the formation and evolution of galaxies
considerably best visible through the well-known morphology-density
relationship. We study the effect of environment on the evolution of early-type
galaxies for a sample of 3,360 galaxies morphologically selected by visual
inspection from the SDSS in the redshift range 0.05<z<0.06, and analyse
luminosity-weighted age, metallicity, and alpha/Fe ratio as function of
environment and galaxy mass. We find that on average 10 per cent of early-type
galaxies are rejuvenated through minor recent star formation. This fraction
increases with both decreasing galaxy mass and decreasing environmental
density. However, the bulk of the population obeys a well-defined scaling of
age, metallicity, and alpha/Fe ratio with galaxy mass that is independent of
environment. Our results contribute to the growing evidence in the recent
literature that galaxy mass is the major driver of galaxy formation. Even the
morphology-density relationship may actually be mass-driven, as the consequence
of an environment dependent characteristic galaxy mass coupled with the fact
that late-type galaxy morphologies are more prevalent in low-mass galaxies.Comment: 5 pages, proceedings of JENAM 2010, Symposium 2: "Environment and the
formation of galaxies: 30 years later
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
A Magellan-IMACS-IFU Search for Dynamical Drivers of Nuclear Activity. I. Reduction Pipeline and Galaxy Catalog
Using the Inamori Magellan Areal Camera and Spectrograph (IMACS)
integral-field unit (IFU) on the 6.5m Magellan telescope, we have designed the
first statistically significant investigation of the two-dimensional
distribution and kinematics of ionized gas and stars in the central kiloparsec
regions of a well-matched sample of Seyfert and inactive control galaxies
selected from the Sloan Digital Sky Survey. The goals of the project are to use
the fine spatial sampling (0.2 arcsec/pixel) and large wavelength coverage
(4000-7000A) of the IMACS-IFU to search for dynamical triggers of nuclear
activity in the central region where active galactic nucleus (AGN) activity and
dynamical timescales become comparable, to identify and assess the impact of
AGN-driven outflows on the host galaxy and to provide a definitive sample of
local galaxy kinematics for comparison with future three-dimensional kinematic
studies of high-redshift systems. In this paper, we provide the first detailed
description of the procedure to reduce and calibrate data from the IMACS-IFU in
`long mode' to obtain two-dimensional maps of the distribution and kinematics
of ionized gas and stars. The sample selection criteria are presented,
observing strategy described and resulting maps of the sample galaxies
presented along with a description of the observed properties of each galaxy
and the overall observed properties of the sample.Comment: 62 pages. 41 figures. 5 tables. Accepted for publication in ApJS.
High-resolution version available at:
http://www.astro.ljmu.ac.uk/~pbw/IMACS-IFU/IMACS-1-highRes.pd
A Log-Quadratic Relation Between the Nuclear Black-Hole Masses and Velocity Dispersions of Galaxies
We demonstrate that a log-linear relation does not provide an adequate
description of the correlation between the masses of Super-Massive Black-Holes
(SMBH, M_bh) and the velocity dispersions of their host spheroid (sigma). An
unknown relation between log(M_bh) and log(sigma) may be expanded to second
order to obtain a log-quadratic relation of the form log(M_bh)=alpha+beta
log(sigma/200) + beta_2[log(sigma/200)]^2. We perform a Bayesian analysis using
the Nuker sample, and solve for beta, beta_2 and alpha, in addition to the
intrinsic scatter (delta). We find unbiased parameter estimates of
beta=4.2+/-0.37, beta_2=1.6+/-1.3 and delta=0.275+/-0.05. At the 80% level the
M_bh-sigma relation does not follow a uniform power-law. Indeed, over the
velocity range 70km/s<sigma<380km/s the logarithmic slope of the best fit
relation varies between 2.7 and 5.1, which should be compared with a power-law
estimate of 4.02+/-0.33. Assuming no systematic offset, single epoch virial
SMBH masses estimated for AGN follow the same log-quadratic M_bh-sigma relation
as the Nuker sample, but extend it downward in mass by an order of magnitude.
The log-quadratic term in the M_bh-sigma relation has a significant effect on
estimates of the local SMBH mass function at M_bh>10^9 solar masses, leading to
densities of SMBHs with M_bh>10^10 solar masses that are several orders of
magnitude larger than inferred from a log-linear relation. We also estimate
unbiased parameters for the SMBH-bulge mass relation. With a parameterisation
log(M_bh)=alpha_b + beta_b log(M_b/10^{11}) + beta_2b[log(M_b/10^{11})]^2, we
find beta_b=1.15+/-0.18 and beta_2b=0.12+/-0.14. We determined an intrinsic
scatter delta_b=0.41+/-0.07 which is ~50% larger than the scatter in the
M_bh-sigma relation.Comment: 21 pages, 14 figures. Replaced to correct errors in published versio
Coupling MOAO with Integral Field Spectroscopy: specifications for the VLT and the E-ELT
[Abridged] We have developed an end-to-end simulation to specify the science
requirements of a MOAO-fed integral field spectrograph on either an 8m or 42m
telescope. Our simulations re-scales observations of local galaxies or results
from numerical simulations of disk or interacting galaxies. For the current
analysis, we limit ourselves to a local disk galaxy which exhibits simple
rotation and a simulation of a merger. We have attempted to generalize our
results by introducing the simple concepts of "PSF contrast" which is the
amount of light polluting adjacent spectra which we find drives the smallest EE
at a given spatial scale. The choice of the spatial sampling is driven by the
"scale-coupling", i.e., the relationship between the IFU pixel scale and the
size of the features that need to be recovered by 3D spectroscopy in order to
understand the nature of the galaxy and its substructure. Because the dynamical
nature of galaxies are mostly reflected in their large-scale motions, a
relatively coarse spatial resolution is enough to distinguish between a
rotating disk and a major merger. Although we used a limited number of
morpho-kinematic cases, our simulations suggest that, on a 42m telescope, the
choice of an IFU pixel scale of 50-75 mas seems to be sufficient. Such a coarse
sampling has the benefit of lowering the exposure time to reach a specific
signal-to-noise as well as relaxing the performance of the MOAO system. On the
other hand, recovering the full 2D-kinematics of z~4 galaxies requires high
signal-to-noise and at least an EE of 34% in 150 mas (2 pixels of 75 mas).
Finally, we carried out a similar study at z=1.6 with a MOAO-fed spectrograph
for an 8m, and find that at least an EE of 30% at 0.25 arcsec spatial sampling
is required to understand the nature of disks and mergers.Comment: 17 pages, 20 figures, accepted for publication in the MNRA
Is NGC 3108 transforming itself from an early to late type galaxy -- an astronomical hermaphrodite?
A common feature of hierarchical galaxy formation models is the process of
"inverse" morphological transformation: a bulge dominated galaxy accretes a gas
disk, dramatically reducing the system's bulge-to-disk mass ratio. During their
formation, present day galaxies may execute many such cycles across the Hubble
diagram. A good candidate for such a "hermaphrodite" galaxy is NGC 3108: a
dust-lane early-type galaxy which has a large amount of HI gas distributed in a
large scale disk. We present narrow band H_alpha and R-band imaging, and
compare the results with the HI distribution. The emission is in two
components: a nuclear bar and an extended disk component which coincides with
the HI distribution. This suggests that a stellar disk is currently being
formed out of the HI gas. The spatial distributions of the H_alpha and HI
emission and the HII regions are consistent with a barred spiral structure,
extending some 20 kpc in radius. We measure an extinction- corrected SFR of
0.42 Msun/yr. The luminosity function of the HII regions is similar to other
spiral galaxies, with a power law index of -2.1, suggesting that the star
formation mechanism is similar to other spiral galaxies. We measured the
current disk mass and find that it is too massive to have been formed by the
current SFR over the last few Gyr. It is likely that the SFR in NGC 3108 was
higher in the past. With the current SFR, the disk in NGC 3108 will grow to be
~6.2x10^9 Msun in stellar mass within the next 5.5 Gyr. While this is
substantial, the disk will be insignificant compared with the large bulge mass:
the final stellar mass disk-to-bulge ratio will be ~0.02. NGC 3108 will fail to
transform into anything resembling a spiral without a boost in the SFR and
additional supply of gas.Comment: 9 pages, 3 figures, accepted for publication in MNRA
The stellar population histories of early-type galaxies. III. The Coma Cluster
We present stellar population parameters of twelve early-type galaxies (ETGs)
in the Coma Cluster based on spectra obtained using the Low Resolution Imaging
Spectrograph on the Keck II Telescope. Our data allow us to examine in detail
the zero-point and scatter in their stellar population properties. Our ETGs
have SSP-equivalent ages of on average 5-8 Gyr with the models used here, with
the oldest galaxies having ages of ~10 Gyr old. This average age is identical
to the mean age of field ETGs. Our ETGs span a large range in velocity
dispersion but are consistent with being drawn from a population with a single
age. Specifically, ten of the twelve ETGs are consistent within their formal
errors of having the same age, 5.2+/-0.2 Gyr, over a factor of more than 750 in
mass. We therefore find no evidence for downsizing of the stellar populations
of ETGs in the core of the Coma Cluster. We suggest that Coma Cluster ETGs may
have formed the majority of their mass at high redshifts but suffered small but
detectable star formation events at z~0.1-0.3. Previous detections of
'downsizing' from stellar populations of local ETGs may not reflect the same
downsizing seen in lookback studies of RSGs, as the young ages of the local
ETGs represent only a small fraction of their total masses. (abridged)Comment: 49 pages, 20 figures (19 EPS, 1 JPEG). MNRAS, in press. For version
with full resolution of Fig. 1 see
http://www.astro.rug.nl/~sctrager/coma.pdf; for Table 2, see
http://www.astro.rug.nl/~sctrager/coma_table2.pdf; for Table B3, see
http://www.astro.rug.nl/~sctrager/coma_tableB3.pd
The HI content of Early-Type Galaxies from the ALFALFA survey I. Catalogued HI sources in the Virgo cluster
Aims: We are using the Arecibo Legacy Fast ALFA survey (ALFALFA), which is
covering 17% of the sky at 21 cm, to study the HI content of Early-Type
galaxies (ETG) in an unbiased way. The aim is to get an overall picture of the
hot, warm and cold ISM of ETG, as a function of galaxy mass and environment, to
understand its origin and fate, and to relate it to the formation and evolution
history of these objects. Methods: This paper deals with the first part of our
study, which is devoted to the 8-16 deg. declination strip in the Virgo
cluster. In this sky region, using the Virgo Cluster Catalogue (VCC), we have
defined an optical sample of 939 ETG, 457 of which are brighter than the VCC
completeness limit at B_T=18.0. We have correlated this optical sample with the
catalogue of detected HI sources from ALFALFA. Results: Out of the 389 ETG from
the VCC with B_T<=18.0, outside the 1 deg. region of poor HI detection around
M87, and corrected for background contamination of VCC galaxies without a known
radial velocity, only 9 galaxies (2.3%) are detected in HI with a completeness
limit of 3.5 and 7.6 x 10^7 Mo of HI for dwarf and giant ETG, respectively. In
addition 4 VCC ETG with fainter magnitudes are also detected. Our HI detection
rate is lower than previously claimed. The majority of the detected ETG appear
to have peculiar morphology and to be located near the edges of the Virgo
cluster. Conclusions: Our preliminary conclusion is that cluster ETG contain
very little neutral gas, with the exceptions of a few peculiar dwarf galaxies
at the edge of the ETG classification and of very few larger ETG, where the
cold gas could have a recent external origin.Comment: Accepted for publication in Astronomy and Astrophysics; 6 pages, 3
figure
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