504 research outputs found
The globular clusters-stellar haloes connection in early type galaxies
This paper explores if, and to what an extent, the stellar populations of
early type galaxies can be traced through the colour distribution of their
globular cluster systems. The analysis, based on a galaxy sample from the Virgo
ACS data, is an extension of a previous approach that has been successful in
the cases of the giant ellipticals NGC 1399 and NGC 4486, and assumes that the
two dominant GC populations form along diffuse stellar populations sharing the
cluster chemical abundances and spatial distributions. The results show that a)
Integrated galaxy colours can be matched to within the photometric
uncertainties and are consistent with a narrow range of ages; b) The inferred
mass to luminosity ratios and stellar masses are within the range of values
available in the literature; c) Most globular cluster systems occupy a thick
plane in the volume space defined by the cluster formation efficiency, total
stellar mass and projected surface mass density. The formation efficiency
parameter of the red clusters shows a dependency with projected stellar mass
density that is absent for the blue globulars. In turn, the brightest galaxies
appear clearly detached from that plane as a possible consequence of major past
mergers; d) The stellar mass-metallicity relation is relatively shallow but
shows a slope change at . Galaxies with smaller
stellar masses show predominantly unimodal globular cluster colour
distributions. This result may indicate that less massive galaxies are not able
to retain chemically enriched intestellar matter.Comment: 19 pages, 10 figure
Starspots on the fastest rotators in the Beta Pic moving group
Aims: We carried out high-resolution spectroscopy and BV(I)_C photometric
monitoring of the two fastest late-type rotators in the nearby Beta Pictoris
moving group, HD199143 (F7V) and CD-641208 (K7V). The motivation for this work
is to investigate the rotation periods and photospheric spot patterns of these
very young stars, with a longer term view to probing the evolution of rotation
and magnetic activity during the early phases of main-sequence evolution. We
also aim to derive information on key physical parameters, such as rotational
velocity and rotation period. Methods: We applied maximum entropy (ME) and
Tikhonov regularizing (TR) criteria to derive the surface spot map
distributions of the optical modulation observed in HD199143 (F7 V) and
CD-641208 (K7V). We also used cross-correlation techniques to determine stellar
parameters such as radial velocities and rotational velocities. Lomb-Scargle
periodograms were used to obtain the rotational periods from differential
magnitude time series. Results: We find periods and inclinations of 0.356 days
and 21.5deg for HD199143, and 0.355 days and 50.1deg for CD-641208. The spot
maps of HD199143 obtained from the ME and TR methods are very similar, although
the latter gives a smoother distribution of the filling factor. Maps obtained
at two different epochs three weeks apart show a remarkable increase in spot
coverage amounting to ~7% of the surface of the photosphere over a time period
of only ~20 days. The spot maps of CD-641208 from the two methods show good
longitudinal agreement, whereas the latitude range of the spots is extended to
cover the whole visible hemisphere in the TR map. The distributions obtained
from the first light curve of HD199143 show the presence of an extended and
asymmetric active longitude with the maximum filling factor at longitude
~325degree.Comment: Accepted by A&A. 13 pages, 13 figures (4 online included), 5 Table
RACE-OC Project: Rotation and variability in young stellar associations within 100 pc
Our goal is to determine the rotational and magnetic-related activity
properties of stars at different stages of evolution. We have focussed our
attention on 6 young loose stellar associations within 100 pc and ages in the
range 8-70 Myr: TW Hydrae (~8 Myr), beta Pictoris (~10 Myr), Tucana/Horologium,
Columba, Carina (~30 Myr), and AB Doradus (~70 Myr). Additional data on alpha
Persei and the Pleiades from the literature is also considered. Rotational
periods of stars showing rotational modulation due to photospheric magnetic
activity (i.e. starspots) have been determined applying the Lomb-Scargle
periodogram technique to photometric time-series obtained by the All Sky
Automated Survey (ASAS). The magnetic activity level has been derived from the
amplitude of the V lightcurves. We detected the rotational modulation and
measured the rotation periods of 93 stars for the first time, and confirmed the
periods of 41 stars already known from the literature. For further 10 stars we
revised the period determinations by other authors. The sample was augmented
with periods of 21 additional stars retrieved from the literature. In this way,
for the first time we were able to determine largest set of rotation periods at
ages of ~8, ~10 and ~30 Myr, as well as increase by 150\% the number of known
periodic members of AB Dor.The analysis of the rotation periods in young
stellar associations, supplemented by Orion Nebula Cluster (ONC) and NGC2264
data from the literature, has allowed us to find that in the 0.6 - 1.2 solar
masses range the most significant variations of the rotation period
distribution are the spin-up between 9 and 30 Myr and the spin-down between 70
and 110 Myr. Variations between 30 and 70 Myr are rather doubtful, despite the
median period indicates a significant spin-up.Comment: Accepted by Astronomy and Astrophysic
Globular cluster systems in fossil groups: NGC6482, NGC1132 and ESO306-017
We study the globular cluster (GC) systems in three representative fossil
group galaxies: the nearest (NGC6482), the prototype (NGC1132) and the most
massive known to date (ESO306-017). This is the first systematic study of GC
systems in fossil groups. Using data obtained with the Hubble Space Telescope
Advanced Camera for Surveys in the F475W and F850LP filters, we determine the
GC color and magnitude distributions, surface number density profiles, and
specific frequencies. In all three systems, the GC color distribution is
bimodal, the GCs are spatially more extended than the starlight, and the red
population is more concentrated than the blue. The specific frequencies seem to
scale with the optical luminosities of the central galaxy and span a range
similar to that of the normal bright elliptical galaxies in rich environments.
We also analyze the galaxy surface brightness distributions to look for
deviations from the best-fit S\'ersic profiles; we find evidence of recent
dynamical interaction in all three fossil group galaxies. Using X-ray data from
the literature, we find that luminosity and metallicity appear to correlate
with the number of GCs and their mean color, respectively. Interestingly,
although NGC6482 has the lowest mass and luminosity in our sample, its GC
system has the reddest mean color, and the surrounding X-ray gas has the
highest metallicity.Comment: 16 pages, 13 figures. Accepted for publication in A&
The central dark matter content of early-type galaxies: scaling relations and connections with star formation histories
We examine correlations between the masses, sizes, and star formation
histories for a large sample of low-redshift early-type galaxies, using a
simple suite of dynamical and stellar populations models. We confirm an
anti-correlation between size and stellar age, and survey for trends with the
central content of dark matter (DM). An average relation between central DM
density and galaxy size of ~ Reff^-2 provides the first clear
indication of cuspy DM haloes in these galaxies -- akin to standard LCDM haloes
that have undergone adiabatic contraction. The DM density scales with galaxy
mass as expected, deviating from suggestions of a universal halo profile for
dwarf and late-type galaxies. We introduce a new fundamental constraint on
galaxy formation by finding that the central DM fraction decreases with stellar
age. This result is only partially explained by the size-age dependencies, and
the residual trend is in the opposite direction to basic DM halo expectations.
Therefore we suggest that there may be a connection between age and halo
contraction, and that galaxies forming earlier had stronger baryonic feedback
which expanded their haloes, or else lumpier baryonic accretion that avoided
halo contraction. An alternative explanation is a lighter initial mass function
for older stellar populations.Comment: 24 pages, 23 figures. MNRAS, submitted with minor modifications
following referee report
Tonotopically Arranged Traveling Waves in the Miniature Hearing Organ of Bushcrickets
Place based frequency discrimination (tonotopy) is a fundamental property of the coiled mammalian cochlea. Sound vibrations mechanically conducted to the hearing organ manifest themselves into slow moving waves that travel along the length of the organ, also referred to as traveling waves. These traveling waves form the basis of the tonotopic frequency representation in the inner ear of mammals. However, so far, due to the secure housing of the inner ear, these waves only could be measured partially over small accessible regions of the inner ear in a living animal. Here, we demonstrate the existence of tonotopically ordered traveling waves covering most of the length of a miniature hearing organ in the leg of bushcrickets in vivo using laser Doppler vibrometery. The organ is only 1 mm long and its geometry allowed us to investigate almost the entire length with a wide range of stimuli (6 to 60 kHz). The tonotopic location of the traveling wave peak was exponentially related to stimulus frequency. The traveling wave propagated along the hearing organ from the distal (high frequency) to the proximal (low frequency) part of the leg, which is opposite to the propagation direction of incoming sound waves. In addition, we observed a non-linear compression of the velocity response to varying sound pressure levels. The waves are based on the delicate micromechanics of cellular structures different to those of mammals. Hence place based frequency discrimination by traveling waves is a physical phenomenon that presumably evolved in mammals and bushcrickets independently
MAGIC Upper Limits for two Milagro-detected, Bright Fermi Sources in the Region of SNR G65.1+0.6
We report on the observation of the region around supernova remnant G65.1+0.6
with the stand-alone MAGIC-I telescope. This region hosts the two bright GeV
gamma-ray sources 1FGL J1954.3+2836 and 1FGL J1958.6+2845. They are identified
as GeV pulsars and both have a possible counterpart detected at about 35 TeV by
the Milagro observatory. MAGIC collected 25.5 hours of good quality data, and
found no significant emission in the range around 1 TeV. We therefore report
differential flux upper limits, assuming the emission to be point-like (<0.1
deg) or within a radius of 0.3 deg. In the point-like scenario, the flux limits
around 1 TeV are at the level of 3 % and 2 % of the Crab Nebula flux, for the
two sources respectively. This implies that the Milagro emission is either
extended over a much larger area than our point spread function, or it must be
peaked at energies beyond 1 TeV, resulting in a photon index harder than 2.2 in
the TeV band.Comment: 8 pages, 3 figures, 1 tabl
Detection of very high energy gamma-ray emission from the gravitationally-lensed blazar QSO B0218+357 with the MAGIC telescopes
Context. QSO B0218+357 is a gravitationally lensed blazar located at a
redshift of 0.944. The gravitational lensing splits the emitted radiation into
two components, spatially indistinguishable by gamma-ray instruments, but
separated by a 10-12 day delay. In July 2014, QSO B0218+357 experienced a
violent flare observed by the Fermi-LAT and followed by the MAGIC telescopes.
Aims. The spectral energy distribution of QSO B0218+357 can give information on
the energetics of z ~ 1 very high energy gamma- ray sources. Moreover the
gamma-ray emission can also be used as a probe of the extragalactic background
light at z ~ 1. Methods. MAGIC performed observations of QSO B0218+357 during
the expected arrival time of the delayed component of the emission. The MAGIC
and Fermi-LAT observations were accompanied by quasi-simultaneous optical data
from the KVA telescope and X-ray observations by Swift-XRT. We construct a
multiwavelength spectral energy distribution of QSO B0218+357 and use it to
model the source. The GeV and sub-TeV data, obtained by Fermi-LAT and MAGIC,
are used to set constraints on the extragalactic background light. Results.
Very high energy gamma-ray emission was detected from the direction of QSO
B0218+357 by the MAGIC telescopes during the expected time of arrival of the
trailing component of the flare, making it the farthest very high energy
gamma-ray sources detected to date. The observed emission spans the energy
range from 65 to 175 GeV. The combined MAGIC and Fermi-LAT spectral energy
distribution of QSO B0218+357 is consistent with current extragalactic
background light models. The broad band emission can be modeled in the
framework of a two zone external Compton scenario, where the GeV emission comes
from an emission region in the jet, located outside the broad line region.Comment: 11 pages, 6 figures, accepted for publication in A&
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