1,318 research outputs found
Measuring the low mass end of the Mbh - sigma relation
We show that high quality laser guide star (LGS) adaptive optics (AO)
observations of nearby early-type galaxies are possible when the tip-tilt
correction is done by guiding on nuclei while the focus compensation due to the
changing distance to the sodium layer is made 'open loop'. We achieve
corrections such that 40% of flux comes from R<0.2 arcsec. To measure a black
hole mass (Mbh) one needs integral field observations of both high spatial
resolution and large field of view. With these data it is possible to determine
the lower limit to Mbh even if the spatial resolution of the observations are
up to a few times larger than the sphere of influence of the black hole.Comment: 4 pages, 2 figures, LaTeX. To appear in "Hunting for the Dark: The
Hidden Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P.
Debattista and C.C. Popescu, AIP Conf. Ser., in pres
Do Job Security Guarantees Work?
We investigate the effect of employer job security guarantees on employee perceptions of job security. Using linked employer-employee data from the 1998 British Workplace Employee Relations Survey, we find job security guarantees reduce employee perceptions of job insecurity. This finding is robust to endogenous selection of job security guarantees by employers engaging in organisational change and workforce reductions. Furthermore, there is no evidence that increased job security through job guarantees results in greater work
intensification, stress, or lower job satisfaction
Monster black holes
A combination of ground-based and spacecraft observations has uncovered two
black holes of 10 billion solar masses in the nearby Universe. The finding
sheds light on how these cosmic monsters co-evolve with galaxies.Comment: 2 pages, 1 figure, LaTeX. Published in Nature "News & Views
The Mass Assembly History of Spheroidal Galaxies: Did Newly-Formed Systems Arise Via Major Mergers?
We examine the properties of a morphologically-selected sample of 0.4<z<1.0
spheroidal galaxies in the GOODS fields in order to ascertain whether their
increase in abundance with time arises primarily from mergers. To address this
question we determine scaling relations between the dynamical mass determined
from stellar velocity dispersions, and the stellar mass determined from optical
and infrared photometry. We exploit these relations across the larger sample
for which we have stellar masses in order to construct the first statistically
robust estimate of the evolving dynamical mass function over 0<z<1. The trends
observed match those seen in the stellar mass functions of Bundy et al. 2005
regarding the top-down growth in the abundance of spheroidal galaxies. By
referencing our dynamical masses to the halo virial mass we compare the growth
rate in the abundance of spheroidals to that predicted by the assembly of dark
matter halos. Our comparisons demonstrate that major mergers do not fully
account for the appearance of new spheroidals since z~1 and that additional
mechanisms, such as morphological transformations, are required to drive the
observed evolution.Comment: Accepted to ApJL; New version corrects the Millennium merger
predictions--further details at
http://www.astro.utoronto.ca/~bundy/millennium
Fast and slow rotators in the densest environments: a FLAMES/GIRAFFE IFS study of galaxies in Abell 1689 at z=0.183
We present FLAMES/GIRAFFE integral field spectroscopy of 30 galaxies in the
massive cluster Abell 1689 at z = 0.183. Conducting an analysis similar to that
of ATLAS3D, we extend the baseline of the kinematic morphology-density relation
by an order of magnitude in projected density and show that it is possible to
use existing instruments to identify slow and fast rotators beyond the local
Universe. We find 4.5 +- 1.0 slow rotators with a distribution in magnitude
similar to those in the Virgo cluster. The overall slow rotator fraction of our
Abell 1689 sample is 0.15 +- 0.03, the same as in Virgo using our selection
criteria. This suggests that the fraction of slow rotators in a cluster is not
strongly dependent on its density. However, within Abell 1689, we find that the
fraction of slow rotators increases towards the centre, as was also found in
the Virgo cluster.Comment: Accepted by MNRA
An Oxford SWIFT Integral Field Spectroscopy study of 14 early-type galaxies in the Coma cluster
As a demonstration of the capabilities of the new Oxford SWIFT integral field
spectrograph, we present first observations for a set of 14 early-type galaxies
in the core of the Coma cluster. Our data consist of I- and z-band spatially
resolved spectroscopy obtained with the Oxford SWIFT spectrograph, combined
with r-band photometry from the SDSS archive for 14 early- type galaxies. We
derive spatially resolved kinematics for all objects from observations of the
calcium triplet absorption features at \sim 8500 {AA} . Using this kinematic
information we classify galaxies as either Fast Rotators or Slow Rotators. We
compare the fraction of fast and slow rotators in our sample, representing the
densest environment in the nearby Universe, to results from the ATLAS3D survey,
finding the slow rotator fraction is \sim 50 per cent larger in the core of the
Coma cluster than in the Virgo cluster or field, a 1.2 {\sigma} increase given
our selection criteria. Comparing our sample to the Virgo cluster core only
(which is 24 times less dense than the Coma core) we find no evidence of an
increase in the slow rotator fraction. Combining measurements of the effective
velocity dispersion {\sigma_e} with the photometric data we determine the
Fundamental Plane for our sample of galaxies. We find the use of the average
velocity dispersion within 1 effective radius, {\sigma_e}, reduces the
residuals by 13 per cent with respect to comparable studies using central
velocity dispersions, consistent with other recent integral field Fundamental
Plane determinations.Comment: 7 pages, 4 figures, in pres
Listeria monocytogenes survey in cubed cooked ham packaged in modified atmosphere and bioprotective effect of selected lactic acid bacteria
The aim of this work was to study the presence of Listeria monocytogenes, as well as the potential activity of two bioprotective cultures (Lyocarni BOX-74 and Lyocarni BOX-57), versus a mix of three L. monocytogenes strains that were intentionally inoculated in cooked cubed ham, packaged in Modified Atmosphere Packaging and stored at different temperatures. The bioprotective cultures limit L. monocytogenes growth in cubed cooked ham stored either at 4\u25e6 C for 60 days and at 4\u25e6 C for 20 days and at 8\u25e6 C for 40 days. The inhibition at 8\u25e6 C is particularly useful for industrial cooked meat products, considering there are often thermal abuse conditions (8\u25e6 C) in the supermarkets. Both the starters can eliminate L. monocytogenes risk and maintain the products safe, despite the thermal abuse conditions. In addition, both culture starters grew without producing perceptible sensory variations in the samples, as demonstrated by the panel of the untrained tasters. The bioprotective LAB produced neither off-odours and off-flavours, nor white/viscous patinas, slime, discoloration or browning. Therefore, according to the obtained data, and despite the fact that cooked cubed ham did not show pH 64 4.4 or aw 64 0.92, or pH 64 5.0 and aw 64 0.94, as cited in the EC Regulation 2073/2005. It can be scientifically stated that cubes of cooked ham with the addition of bioprotective starters cultures do not constitute a favourable substrate for L. monocytogenes growth. Consequently, these products can easily fall into category 1.3 (ready-to-eat foods that are not favourable to L. monocytogenes growth, other than those for infants and for special medical purposes), in which a maximum concentration of L. monocytogenes of 100 CFU g 121 is allowed
Determination of masses of the central black holes in NGC524 and NGC2549 using Laser Guide Star Adaptive Optics
[abridged] We present observations of NGC524 and NGC2549 with LGS AO obtained
at GEMINI North telescope using the NIFS IFU in the K band. The purpose of
these observations, together with previously obtained observations with the
SAURON IFU, is to determine the masses (Mbh) of the supermassive black holes
(SMBH). The targeted galaxies were chosen to have central light profiles
showing a core (NGC524) and a cusp (NGC2549), to probe the feasibility of using
the galaxy centre as the NGS required for LGS AO. We employ an innovative `open
loop' technique. The data have spatial resolution of 0.23" and 0.17" FWHM,
showing that high quality LGS AO observations of these objects are possible. We
construct axisymmetric three-integral dynamical models which are constrained
with both the NIFS and SAURON data. The best fitting models yield Mbh=(8.3 +2.7
-1.3) x 10^8 Msun for NGC524 and Mbh=(1.4 +0.2 -1.3) x 10^7 Msun for NGC2549
(all errors are at the 3 sigma CL). We demonstrate that the wide-field SAURON
data play a crucial role in the M/L determination increasing the accuracy of
M/L by a factor of at least 5, and constraining the upper limits on Mbh. The
NIFS data are crucial in constraining the lower limits of Mbh and in
combination with the large scale data reducing the uncertainty by a factor of 2
or more. We find that the orbital structure of NGC524 shows significant
tangential anisotropy, while at larger radii both galaxies are consistent with
having almost perfectly oblate velocity ellipsoids. Tangential anisotropy in
NGC524 coincides with the size of SMBH sphere of influence and the core region
in the light profile. We test the accuracy to which Mbh can be measured using
seeings obtained from typical LGS AO observations, and conclude that for a
typical conditions and Mbh the expected uncertainty is of the order of 50%.Comment: 19 pages, 14 figure
Spectroscopic evidence of distinct stellar populations in the counter-rotating stellar disks of NGC 3593 and NGC 4550
We present the results of integral-field spectroscopic observations of the
two disk galaxies NGC 3593 and NGC 4550 obtained with VIMOS/VLT. Both galaxies
are known to host 2 counter-rotating stellar disks, with the ionized gas
co-rotating with one of them. We measured in each galaxy the ionized gas
kinematics and metallicity, and the surface brightness, kinematics, mass
surface density, and the stellar populations of the 2 stellar components to
constrain the formation scenario of these peculiar galaxies. We applied a novel
spectroscopic decomposition technique to both galaxies, to separate the
relative contribution of the 2 counter-rotating stellar and one ionized-gas
components to the observed spectrum. We measured the kinematics and the line
strengths of the Lick indices of the 2 counter-rotating stellar components. We
modeled the data of each stellar component with single stellar population
models that account for the alpha/Fe overabundance. In both galaxies we
successfully separated the main from the secondary stellar component that is
less massive and rotates in the same direction of the ionized-gas component.
The 2 stellar components have exponential surface-brightness profiles. In both
galaxies, the two counter-rotating stellar components have different stellar
populations: the secondary stellar disk is younger, more metal poor, and more
alpha-enhanced than the main galaxy stellar disk. Our findings rule out an
internal origin of the secondary stellar component and favor a scenario where
it formed from gas accreted on retrograde orbits from the environment fueling
an in situ outside-in rapid star formation. The event occurred ~ 2 Gyr ago in
NGC 3593, and ~ 7 Gyr ago in NGC 4550. The binary galaxy merger scenario cannot
be ruled out, and a larger sample is required to statistically determine which
is the most efficient mechanism to build counter-rotating stellar disks
(abridged).Comment: 13 pages, 9 figures, accepted for publication in Astronomy and
Astrophysic
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