99 research outputs found
Evolution of Galaxy morphologies in Clusters
We have studied the evolution of galaxian morphologies from ground-based,
good-seeing images of 9 clusters at z=0.09-0.25. The comparison of our data
with those relative to higher redshift clusters (Dressler et al. 1997) allowed
us to trace for the first time the evolution of the morphological mix at a
look-back time of 2-4 Gyr, finding a dependence of the observed evolutionary
trends on the cluster properties.Comment: 4 pages with 2 figures in Latex-Kluwer style. To be published in the
proceedings of the Granada Euroconference "The Evolution of
Galaxies.I-Observational Clues
Circumnuclear structure and kinematics in the active galaxy NGC 6951
A study is presented of the central structure and kinematics of the galaxy
NGC 6951, by means of broad band B'IJK images and high resolution high
dispersion longslit spectroscopy, together with archival HST WFPC2 V and
NICMOS2 J and H images. We find that there is evidence of two modes of star
formation, in bursts and continuously. The equivalent width of the CaII triplet
absorption lines show that, in the metal rich central region, the continuum is
dominated by a population of red supergiants. The gaseous and stellar
kinematics along three slit position angles, suggest the existence of a
hierarchy of disks within disks, whose dynamics are decoupled at the two ILRs,
that we find at 180 pc and at 1100 pc. This is supported by the structure seen
in the high resolution HST images. The nucleus is spatially resolved within a
radius of 1.5 arcsec, just inside the innermost ILR. Outside the iILR, the
stellar CaT velocity profile is resolved into two components, associated with
the bar and the disk. Several results indicate that this is a dynamically old
system. It is thus possible that a nuclear bar has existed in NGC 6951 that
drove the gas towards the nucleus, as in the bars within bars scenario, but
that this bar has already dissolved by the gas accumulated within the
circumnuclear region. We discuss the possibility that the kinematical component
inside the iILR could be due to a nuclear outflow produced by the combined
effects of SN and SN remnants, or to a nuclear disk, as in the disk within disk
scenario that we propose for the fueling of the AGN in NGC 6951.Comment: 14 pages, 16 figures. Accepted for publication in Astronomy and
Astrophysics. High resolution images in
http://www.iaa.es/~eperez/research/degas.htm
The complex velocity distribution of galaxies in Abell 1689: implications for mass modelling
The Abell 1689 galaxy cluster has recently become a subject of intensive
study. Thanks to its intermediate redshift (z=0.183) its mass distribution can
be reconstructed using numerous methods including gravitational lensing, galaxy
kinematics and X-ray imaging. The methods used to yield conflicting mass
estimates in the past and recently the cluster mass distribution has been
claimed to be in conflict with standard CDM scenarios due to rather large
concentration and steep mass profile obtained from detailed studies of
Broadhurst et al. using lensing. By studying in detail the kinematics of about
200 galaxies with measured redshifts in the vicinity of the cluster we show
that the cluster is probably surrounded by a few structures, quite distant from
each other, but aligned along the line of sight. We support our arguments by
referring to cosmological N-body simulations and showing explicitly that
distant, non-interacting haloes can produce entangled multi-peak line-of-sight
velocity distributions similar to that in A1689. We conclude that it is
difficult to estimate the cluster mass reliably from galaxy kinematics, but the
value we obtain after applying a simple cut-off in velocity agrees roughly with
the mass estimated from lensing. The complicated mass distribution around the
cluster may however increase the uncertainty in the determination of the
density profile shape obtained with weak lensing.Comment: 5 pages, 4 figures, revised version accepted for publication in MNRAS
Letter
On the use of scaling relations for the Tolman test
The use of relations between structural parameters of early type galaxies to
perform the Tolman test is reconsidered. Scaling relations such as the FP or
the Kormendy relation, require the transformation from angular to metric sizes,
to compare the relation at different z values. This transformation depends on
the assumed world model: galaxies of a given angular size, at a given z, are
larger (in kpc) in a non-expanding universe than in an expanding one.
Furthermore, the luminosities of galaxies are expected to evolve with z in an
expanding model. These effects are shown to conspire to reduce the difference
between the predicted SB change with redshift in the expanding and non
expanding cases. We find that the predictions for the visible photometric bands
of the expanding models with passive luminosity evolution are very similar to
those of the static model till z about 1, and therefore, the test cannot
distinguish between the two world models. Recent good quality data are
consistent with the predictions from both models. In the K-band, where the
expected (model) luminosity evolutionary corrections are smaller, the
differences between the xpanding and static models amount to about 0.4 (0.8)
magnitudes at z = 0.4 (1). It is shown that, due to that small difference
between the predictions in the covered z-range, and to the paucity and
uncertainties of the relevant SB photometry, the existing K-band data is not
adequate to distinguish between the different world metrics, and cannot be yet
used to discard the static case. It is pointed out that the scaling relations
could still be used to rule out the non-evolving case if it could be shown that
the coefficients change with the redshift.Comment: Latex, 15 pages with 2 figures. To be published in ApJ Letter
Structural and dynamical modeling of WINGS clusters. I. The distribution of cluster galaxies of different morphological classes within regular and irregular clusters
[Abridged] We use the WINGS database to select a sample of 67 nearby galaxy
clusters with at least 30 spectroscopic members each. 53 of these clusters do
not show evidence of substructures in phase-space, while 14 do. We estimate the
virial radii and circular velocities of the 67 clusters by a variety of proxies
(velocity dispersion, X-ray temperature, and richness) and use these estimates
to build stack samples from these 53 and 14 clusters ('Reg' and 'Irr' stacks,
respectively). We determine the number-density and velocity-dispersion profiles
(VDPs) of E, S0, and Sp+Irr (S) galaxies in the Reg and Irr samples,
separately, and fit models to these profiles. The number density profiles of E,
S0, and S galaxies are adequately described by either a NFW or a cored King
model, both for the Reg and Irr samples, with a slight preference for the NFW
model. The spatial distribution concentration increases from the S to the S0
and to the E populations, both in the Reg and the Irr stacks, reflecting the
well-known morphology-radius relation. Reg clusters have a more concentrated
spatial distribution of E and S0 galaxies than Irr clusters, while the spatial
distributions of S galaxies in Reg and Irr clusters are similar. We propose a
new phenomenological model that provides acceptable fits to the VDP of all our
galaxy samples. The VDPs become steeper and with a higher normalization from E
to S0 to S galaxies. The S0 VDP is close to that of E galaxies in Reg clusters,
and intermediate between those of E and S galaxies in Irr clusters. Our results
suggest that S galaxies are a recently accreted cluster population, that take
less than 3 Gyr to evolve into S0 galaxies after accretion, and in doing so
modify their phase-space distribution, approaching that of cluster ellipticals.
While in Reg clusters this evolutionary process is mostly completed, it is
still ongoing in Irr clusters.Comment: A&A, in press - 11 pages, 9 figures, 4 table
Periodic very high energy γ -Ray Emission from LS I +61◦303 Observed with the magic telescope
The MAGIC collaboration has recently reported the discovery of γ -ray emission from the binary system
LS I +61◦303 in the TeV energy region. Here we present new observational results on this source in the energy range
between 300 GeV and 3 TeV. In total, 112 hr of data were taken between 2006 September and December covering
four orbital cycles of this object. This large amount of data allowed us to produce an integral flux light curve covering
for the first time all orbital phases of LS I +61◦303. In addition, we also obtained a differential energy spectrum for
two orbital phase bins covering the phase range 0.5 < φ < 0.6 and 0.6 < φ < 0.7. The photon index in the two
phase bins is consistent within the errors with an average index Γ = 2.6±0.2stat ±0.2sys. LS I +61◦303 was found
to be variable at TeV energies on timescales of days. These new MAGIC measurements allowed us to search for
intranight variability of the very high energy emission; however, no evidence for flux variability on timescales down
to 30 min was found. To test for possible periodic structures in the light curve, we apply the formalism developed
by Lomb and Scargle to the LS I +61◦303 data taken in 2005 and 2006. We found the LS I +61◦303 data set to be
periodic with a period of (26.8 ± 0.2) days (with a post-trial chance probability of 10−7), close to the orbital period.Peer reviewe
Simultaneous multi-frequency observation of the unknown redshift blazar PG1553+113 in March-April 2008
5 páginas, 2 figuras, 3 tablas.-- El Pdf del artículo es la versión pre-print: arXiv: arXiv:0911.1088.-- MAGIC Collaboration: et al.The blazar PG 1553+113 is a well known TeV γ-ray emitter. In this paper we determine its spectral energy distribution through simultaneous multi-frequency data to study its emission processes. An extensive campaign was carried out between March and April 2008, where optical, X-ray, high-energy (HE) γ-ray, and very-high-energy (VHE) γ-ray data were obtained with the KVA, Abastumani, REM, RossiXTE/ASM, AGILE and MAGIC telescopes, respectively. We combine the data to derive the source's spectral energy distribution and interpret its double-peaked shape within the framework of a synchrotron self-Compton model.Major support
from Germany’s Bundesministerium f¨ur Bildung, Wissenschaft, Forschung
und Technologie and Max-Planck-Gesellschaft, Italy’s Istituto Nazionale di
Fisica Nucleare (INFN) and Istituto Nazionale di Astrofisica (INAF), and
Spain’s Ministerio de Ciencia e Innovacion is gratefully acknowledged. The
work was also supported by Switzerland’s ETH Research grant TH34/043,
Poland’s Ministertwo Nauki i Szkolnictwa Wy˙zszego grant N N203 390834,
and Germany’s Young Investigator Program of the Helmholtz Gemeinschaft.
This work was also supported by Georgian National Science Foundation grant
GNSF/ST07/4-180. EP acknowledges support from the Italian Space Agency
through grants ASI-INAF I/023/05/0 and ASI I/088/06/0.Peer reviewe
MAGIC observation of the GRB 080430 afterglow
6 páginas, 1 figura.-- El Pdf del artículo es la versión pre-print: arXiv:1004.3665v2.-- MAGIC Collaboration: et al.[Context]: Gamma-ray bursts are cosmological sources emitting radiation from the gamma-rays to the radio band. Substantial observational efforts have been devoted to the study of gamma-ray bursts during the prompt phase, i.e. the initial burst of high-energy radiation, and during the long-lasting afterglows. In spite of many successes in interpreting these phenomena, there are still several open key questions about the fundamental emission processes, their energetics and the environment.
[Aims]: Independently of specific gamma-ray burst theoretical recipes, spectra in the GeV/TeV range are predicted to be remarkably simple, being satisfactorily modeled with power-laws, and therefore offer a very valuable tool to probe the extragalactic background light distribution. Furthermore, the simple detection of a component at very-high energies, i.e. at ~100 GeV, would solve the ambiguity about the importance of various possible emission processes, which provide barely distinguishable scenarios at lower energies.
[Methods]: We used the results of the MAGIC telescope observation of the moderate resdhift (z ~ 0.76) GRB 080430 at energies above about 80 GeV, to evaluate the perspective for late-afterglow observations with ground based GeV/TeV telescopes.
[Results]: We obtained an upper limit of F95% CL = 5.5 × 10-11 erg cm-2 s-1 for the very-high energy emission of GRB 080430, which cannot set further constraints on the theoretical scenarios proposed for this object also due to the difficulties in modeling the low-energy afterglow. Nonetheless, our observations show that Cherenkov telescopes have already reached the required sensitivity to detect the GeV/TeV emission of GRBs at moderate redshift (z ≲ 0.8), provided the observations are carried out at early times, close to the onset of their afterglow phase.The support of the German BMBF and MPG,
the Italian INFN and Spanish MICINN is gratefully acknowledged. This work
was also supported by ETH Research Grant TH 34/043, by the Polish MNiSzW
Grant N N203 390834, and by the YIP of the Helmholtz Gemeinschaft.Peer reviewe
- …