349 research outputs found
Extragalactic planetary nebulae as mass tracers: biases in the estimate of dynamical quantities
Planetary Nebulae (PNe) are very important kinematical tracers of the outer
regions of early-type galaxies, where the integrated light techniques fail.
Under ad hoc assumptions, they allow measurements of rotation velocity and
velocity dispersion profile from descrete radial velocity fields. We present
the results on the precision allowed by different set of radial velocity
samples, discuss the hypotheses in the analysis of descrete velocity fields and
their impact on the inferred kinematics of the stellar population.Comment: 4 pages, 2 figures. To appear on ``Galaxy Dynamics: from Early
Universe to the Present'', ASP Conf. Ser., F. Combes, G.A. Mamon and V.
Charmandaris (eds.
Pulse Shape Analysis with scintillating bolometers
Among the detectors used for rare event searches, such as neutrinoless Double
Beta Decay (0DBD) and Dark Matter experiments, bolometers are very
promising because of their favorable properties (excellent energy resolution,
high detector efficiency, a wide choice of different materials used as
absorber, ...). However, up to now, the actual interesting possibility to
identify the interacting particle, and thus to greatly reduce the background,
can be fulfilled only with a double read-out (i.e. the simultaneous and
independent read out of heat and scintillation light or heat and ionization).
This double read-out could greatly complicate the assembly of a huge,
multi-detector array, such as CUORE and EURECA. The possibility to recognize
the interacting particle through the shape of the thermal pulse is then clearly
a very interesting opportunity.
While detailed analyses of the signal time development in purely thermal
detectors have not produced so far interesting results, similar analyses on
macro-bolometers (10-500 g) built with scintillating crystals showed that
it is possible to distinguish between an electron or -ray and an
particle interaction (i.e. the main source of background for 0DBD
experiments based on the bolometric technique). Results on pulse shape analysis
of a CaMoO crystal operated as bolometer is reported as an example. An
explanation of this behavior, based on the energy partition in the heat and
scintillation channels, is also presented.Comment: Presented at the 14th International Workshop on Low Temperature
Detectors, proceedings to be published in the Journal of Low Temperature
Physic
The Kinematics of Intracluster Planetary Nebulae and the On-Going Subcluster Merger in the Coma Cluster Core
The Coma cluster is the richest and most compact of the nearby clusters, yet
there is growing evidence that its formation is still on-going. With a new
multi-slit imaging spectroscopy technique pioneered at the 8.2 m Subaru
telescope and FOCAS, we have detected and measured the line-of-sight velocities
of 37 intracluster planetary nebulae associated with the diffuse stellar
population of stars in the Coma cluster core, at 100 Mpc distance. We detect
clear velocity substructures within a 6 arcmin diameter field. A substructure
is present at ~5000 km/s, probably from in-fall of a galaxy group, while the
main intracluster stellar component is centered around ~6500 km/s, ~700 km/s
offset from the nearby cD galaxy NGC 4874. The kinematics and morphology of the
intracluster stars show that the cluster core is in a highly dynamically
evolving state. In combination with galaxy redshift and X-ray data this argues
strongly that the cluster is currently in the midst of a subcluster merger,
where the NGC 4874 subcluster core may still be self-bound, while the NGC 4889
subcluster core has probably dissolved. The NGC 4889 subcluster is likely to
have fallen into Coma from the eastern A2199 filament, in a direction nearly in
the plane of the sky, meeting the NGC 4874 subcluster arriving from the west.
The two inner subcluster cores are presently beyond their first and second
close passage, during which the elongated distribution of diffuse light has
been created. We predict the kinematic signature expected in this scenario, and
argue that the extended western X-ray arc recently discovered traces the arc
shock generated by the collision between the two subcluster gas halos. Any
preexisting cooling core region would have been heated by the subcluster
collision.Comment: Astronomy & Astrophysics, in press, 9 pages, 5 figure
Diffuse Light in Hickson Compact Groups: The Dynamically Young System HCG 44
Compact groups are associations of a few galaxies in which the environment
plays an important role in galaxy evolution. The low group velocity dispersion
favors tidal interactions and mergers, which may bring stars from galaxies to
the diffuse intragroup light. Numerical simulations of galaxy clusters in
hierarchical cosmologies show that the amount of the diffuse light increases
with the dynamical evolution of the cluster. We search for diffuse light in the
galaxy group HCG 44 in order to determine its luminosity and luminosity
fraction. Combining with literature data, we aim to constrain the dynamical
status of Hickson compact groups. We use Intra Group planetary nebulae (IGPNe)
as tracers of diffuse light. These are detected by the so-called on band-off
band technique. We found 12 emission line objects in HCG 44, none of them
associated with the galaxies of the group. 6/12 emission line objects are
consistent with being IGPNe in HCG 44, but are also consistent with being
Ly background galaxies. Thus we derive an upper limit to the diffuse
light fraction in HCG 44 of 4.7%. We find a correlation between the fraction of
elliptical galaxies and the amount of diffuse light in Hickson compact groups.
Those with large fraction of diffuse light are those with large fractions in
number and luminosity of E/S0 galaxies. We propose an evolutionary sequence for
Hickson compact groups in which the amount of diffuse light increases with the
dynamical evolution of the group.Comment: 9 pages, 4 figures, accepted for publication at A&
Mass-to-light ratios in early-type galaxies and the dark matter content
The distribution of the radial trends of the mass-to-light ratios (M/L)
within an assorted sample of early-type galaxies is discussed. Three classes of
galaxies are identified according to their M/L gradients. Two such classes are
characterized by the presence or by the absence of a radial gradient of the
dark-matter (DM) distribution. A third class contains objects which are likely
undergoing interaction; they exhibit steep M/L gradients which are possibly the
result of a wrong assumption on their equilibrium conditions. Finally, a
possible correlation between DM content and morphological types is briefly
discussed.Comment: 10 pages, 2 ps figures. To appear in the proceedings for the Sakharov
Conference of Physics (Moskow, June 2002
ZnMoO4: a promising bolometer for neutrinoless double beta decay searches
We investigate the performances of two ZnMoO4 scintillating crystals operated
as bolometers, in view of a next generation experiment to search the
neutrinoless double beta decay of Mo-100. We present the results of the alpha
vs beta/gamma discrimination, obtained through the scintillation light as well
as through the study of the shape of the thermal signal alone. The
discrimination capability obtained at the 2615 keV line of Tl-208 is 8 sigma,
using the heat-light scatter plot, while it exceeds 20 sigma using the shape of
the thermal pulse alone. The achieved FWHM energy resolution ranges from 2.4
keV (at 238 keV) to 5.7 keV (at 2615 keV). The internal radioactive
contaminations of the ZnMoO4 crystals were evaluated through a 407 hours
background measurement. The obtained limit is < 32 microBq/kg for Th-228 and
Ra-226. These values were used for a Monte Carlo simulation aimed at evaluating
the achievable background level of a possible, future array of enriched ZnMoO4
crystals.Comment: 9 pages, 8 figure
The stellar dynamics and mass of NGC 1316 using the radial velocities of planetary nebulae
We present a study of the kinematics of the outer regions of the early-type
galaxy NGC 1316, based on radial velocity measurements of 43 planetary nebulae
as well as deep integrated-light absorption line spectra. The smoothed velocity
field of NGC 1316 indicates fast rotation at a distance of 16 kpc, possibly
associated with an elongated feature orthogonal to the inner dust lanes. The
mean square stellar velocity is approximately independent of radius, and the
estimated total mass of the system is 2.6 x 10^11 M_sun within a radius of 16
kpc, implying an integrated mass-to-light ratio of M/L_B = 8.Comment: 39 pages, 14 figures, in press on The Astrophysical Journal n. 50
An instrument for low-level measurements of the leakage current from high-voltage biased detectors
Resistive Plates Chambers (RPC) are detectors biased at High-Voltage (HV) in excess of 4 kV. When fired by a particle, they develop a large signal current that can be read across a small resistance, 100 Omega or so. A characterization has been made of their ageing as a function of the behaviour of their leakage current with time. An array of 10 detectors has been developed for this purpose. We present the instrument designed and built to perform a continuous and automatic monitoring of the leakage current from each detector of the array, while the system is taking data. For the particular biasing set-up adopted, the current has been measured in series to the terminal connected to the HV of every channel. Since the small value of the currents, order of tens of nA, a special circuit solution and special precautions have been adopte
Dark-Matter Content of Early-Type Galaxies with Planetary Nebulae
We examine the dark matter properties of nearby early-type galaxies using
planetary nebulae (PNe) as mass probes. We have designed a specialised
instrument, the Planetary Nebula Spectrograph (PN.S) operating at the William
Herschel telescope, with the purpose of measuring PN velocities with best
efficiency. The primary scientific objective of this custom-built instrument is
the study of the PN kinematics in 12 ordinary round galaxies. Preliminary
results showing a dearth of dark matter in ordinary galaxies (Romanowsky et al.
2003) are now confirmed by the first complete PN.S datasets. On the other hand
early-type galaxies with a "regular" dark matter content are starting to be
observed among the brighter PN.S target sample, thus confirming a correlation
between the global dark-to-luminous mass virial ratio (f_DM=M_DM/M_star) and
the galaxy luminosity and mass.Comment: 5 pages, 2 figures. To appear in the proceedings of the IAU Symposium
244 "Dark Galaxies and Lost Baryons", Cardiff 25-29 June 2007, eds. J.I.
Davies & M.J. Disne
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