391 research outputs found
Structure and kinematics of the peculiar galaxy NGC 128
This is a multiband photometric and spectroscopic study of the peculiar S0
galaxy NGC128. We present results from broad (B and R) and narrow band optical
CCD photometry, near (NIR) and far (FIR) infrared observations, long slit
spectroscopy, and Fabry-Perot interferometry (CIGALE). The peculiar peanut
shape morphology of the galaxy is observed both at optical and near-infrared
wavelengths. The stellar disk is thick and distorted (arc-bended), with a color
asymmetry along the major axis due to the presence of a large amount of dust,
estimated through NIR and FIR data of ~6x10^6 M_sun, in the region of
interaction with the companion galaxy NGC127. The color maps are nearly uniform
over the whole galaxy, but for the major axis asymmetry, and a small gradient
toward the center indicating the presence of a redder disk-like component. The
H_alpha image indeed reveals the existence of a tilted gaseous ``disk'' around
the center, oriented with the major axis toward the companion galaxy NGC127.
Long slit and CIGALE data confirm the presence of gas in a disk-like component
counter-rotating and inclined approximately of 50 deg. to the line of sight.
The mass of the gas disk in the inner region is ~2.7x10^4 M_sun. The stellar
velocity field is cylindrical up to the last measured points of the derived
rotation curves, while the velocity dispersion profiles are typical for an S0
galaxy, but for an extended constant behaviour along the minor axis.Comment: accepted for pubblication in A&A Supp
ACCESS - V. Dissecting ram-pressure stripping through integral-field spectroscopy and multi-band imaging
We study the case of a bright (L>L*) barred spiral galaxy from the rich
cluster A3558 in the Shapley supercluster core (z=0.05) undergoing ram-pressure
stripping. Integral-field spectroscopy, complemented by multi-band imaging,
allows us to reveal the impact of ram pressure on the interstellar medium. We
study in detail the kinematics and the physical conditions of the ionized gas
and the properties of the stellar populations. We observe one-sided extraplanar
ionized gas along the full extent of the galaxy disc. Narrow-band Halpha
imaging resolves this outflow into a complex of knots and filaments. The gas
velocity field is complex with the extraplanar gas showing signature of
rotation. In all parts of the galaxy, we find a significant contribution from
shock excitation, as well as emission powered by star formation. Shock-ionized
gas is associated with the turbulent gas outflow and highly attenuated by dust.
All these findings cover the whole phenomenology of early-stage ram-pressure
stripping. Intense, highly obscured star formation is taking place in the
nucleus, probably related to the bar, and in a region 12 kpc South-West from
the centre. In the SW region we identify a starburst characterized by a 5x
increase in the star-formation rate over the last ~100 Myr, possibly related to
the compression of the interstellar gas by the ram pressure. The scenario
suggested by the observations is supported and refined by ad hoc
N-body/hydrodynamical simulations which identify a rather narrow temporal range
for the onset of ram-pressure stripping around t~60 Myr ago, and an angle
between the galaxy rotation axis and the intra-cluster medium wind of ~45 deg.
Taking into account that the galaxy is found ~1 Mpc from the cluster centre in
a relatively low-density region, this study shows that ram-pressure stripping
still acts efficiently on massive galaxies well outside the cluster cores.Comment: 46 pages, 21 figures, accepted for publication; MNRAS 201
Cosmic dance in the Shapley Concentration Core - I. A study of the radio emission of the BCGs and tailed radio galaxies
The Shapley Concentration () covers several degrees in the
Southern Hemisphere, and includes galaxy clusters in advanced evolutionary
stage, groups of clusters in the early stages of merger, fairly massive
clusters with ongoing accretion activity, and smaller groups located in
filaments in the regions between the main clusters. With the goal to
investigate the role of cluster mergers and accretion on the radio galaxy
population, we performed a multi-wavelength study of the BCGs and of the
galaxies showing extended radio emission in the cluster complexes of Abell 3528
and Abell 3558. Our study is based on a sample of 12 galaxies. We observed the
clusters with the GMRT at 235, 325 and 610 MHz, and with the VLA at 8.46 GHz.
We complemented our study with the TGSS at 150 MHz, the SUMSS at 843 MHz and
ATCA at 1380, 1400, 2380, and 4790 MHz data. Optical imaging with ESO-VST and
mid-IR coverage with WISE are also available for the host galaxies. We found
deep differences in the properties of the radio emission of the BCGs in the two
cluster complexes. The BCGs in the A3528 complex and in A3556, which are
relaxed cool-core objects, are powerful active radio galaxies. They also
present hints of restarted activity. On the contrary, the BCGs in A3558 and
A3562, which are well known merging systems, are very faint, or quiet, in the
radio band. The optical and IR properties of the galaxies are fairly similar in
the two complexes, showing all passive red galaxies. Our study shows remarkable
differences in the radio properties of the BGCs, which we relate to the
different dynamical state of the host cluster. On the contrary, the lack of
changes between such different environments in the optical band suggests that
the dynamical state of galaxy clusters does not affect the optical counterparts
of the radio galaxies, at least over the life-time of the radio emission.Comment: 24 pages, 11 figures, accepted for publication in Astronomy &
Astrophysic
Shapley Supercluster Survey: Construction of the photometric catalogues and i-band data release
The Shapley Supercluster Survey is a multi-wavelength survey covering an area of âŒ23 degÂČ (âŒ260 MpcÂČ at z = 0.048) around the supercluster core, including nine Abell and two poor clusters, having redshifts in the range 0.045â0.050. The survey aims to investigate the role of the cluster-scale mass assembly on the evolution of galaxies, mapping the effects of the environment from the cores of the clusters to their outskirts and along the filaments. The optical (ugri) imaging acquired with OmegaCAM on the VLT Survey Telescope is essential to achieve the project goals providing accurate multi-band photometry for the galaxy population down to mâ + 6. We describe the methodology adopted to construct the optical catalogues and to separate extended and point-like sources. The catalogues reach average 5Ï limiting magnitudes within a 3 arcsec diameter aperture of ugri = [24.4,24.6,24.1,23.3] and are 93 per cent complete down to ugri = [23.8,23.8,23.5,22.0] mag, corresponding to âŒmâ r + 8.5. The data are highly uniform in terms of observing conditions and all acquired with seeing less than 1.1 arcsec full width at half-maximum. The median seeing in r band is 0.6 arcsec, corresponding to 0.56 kpc hâ»Âč 70 at z = 0.048. While the observations in the u, g and r bands are still ongoing, the i-band observations have been completed, and we present the i-band catalogue over the whole survey area. The latter is released and it will be regularly updated, through the use of the Virtual Observatory tools. This includes 734 319 sources down to i = 22.0 mag and it is the first optical homogeneous catalogue at such a depth, covering the central region of the Shapley supercluster
Age, Metallicity and Star Formation History of Cluster Galaxies at z~0.3 F
We investigate the color-magnitude distribution in the rich cluster AC 118 at
z=0.31. The sample is selected by the photometric redshift technique, allowing
to study a wide range of properties of stellar populations, and is complete in
the K-band, allowing to study these properties up to a given galaxy mass. We
use galaxy templates based on population synthesis models to translate the
physical properties of the stellar populations - formation epoch, time-scale of
star formation, and metallicity - into observed magnitudes and colors. In this
way we show that a sharp luminosity-metallicity relation is inferred without
any assumption on the galaxy formation scenario (either monolithic or
hierarchical). Our data exclude significant differences in star formation
histories along the color-magnitude relation, and therefore confirm a pure
metallicity interpretation for its origin, with an early (z~5) formation epoch
for the bulk of stellar populations. The dispersion in the color-magnitude
diagram implies that fainter galaxies in our sample (K~18) ceased to form stars
as late as z~0.5, in agreement with the picture that these galaxies were
recently accreted into the cluster environment. The trend with redshift of the
total stellar mass shows that half of the luminous mass in AC 118 was already
formed at $z~2, but also that 20% of the stars formed at z<1.Comment: 16 pages, 10 figures. ApJ in pres
Dusty Nuclear Disks and Filaments in Early Type Galaxies
We examine the dust properties of a nearby distance-limited sample of early
type galaxies using the WFPC2 of the Hubble Space Telescope. Dust is detected
in 29 out of 67 galaxies (43%), including 12 with small nuclear dusty disks. In
a separate sample of 40 galaxies biased for the detection of dust by virtue of
their detection in the IRAS 100 micron band, dust is found in ~78% of the
galaxies, 15 of which contain dusty disks. In those galaxies with detectable
dust, the apparent mass of the dust correlates with radio and far infrared
luminosity, becoming more significant for systems with filamentary dust. A
majority of IRAS and radio detections are also associated with dusty galaxies
rather than dustless galaxies. This indicates that thermal emission from
clumpy, filamentary dust is the main source of the far-IR radiation in early
type galaxies. Dust in small disk-like morphology tends to be well aligned with
the major axis of the host galaxies, while filamentary dust appears to be more
randomly distributed with no preference for alignment with any major galactic
structure. This suggests that, if the dusty disks and filaments have a common
origin, the dust originates externally and requires time to dynamically relax
and settle in the galaxy potential in the form of compact disks. More galaxies
with visible dust than without dust display emission lines, indicative of
ionized gas, although such nuclear activity does not show a preference for
dusty disk over filamentary dust. There appears to be a weak relationship
between the mass of the dusty disks and central velocity dispersion of the
galaxy, suggesting a connection with a similar recently recognized relationship
between the latter and the black hole mass.Comment: 17 pages, including 10 figures & 7 tables, to be published in the
Astronomical Journa
The VIRMOS-VLT Deep Survey
The aim of the VIRMOS VLT Deep Survey (VVDS) is to study of the evolution of
galaxies, large scale structures and AGNs from a sample of more than 150,000
galaxies with measured redshifts in the range 0<z<5+. The VVDS will rely on the
VIMOS and NIRMOS wide field multi-object spectrographs, which the VIRMOS
consortium is delivering to ESO. Together, they offer unprecedented multiplex
capability in the wavelength range 0.37-1.8microns, allowing for large surveys
to be carried out. The VVDS has several main aspects: (1) a deep multi-color
imaging survey over 18deg^2 of more than one million galaxies, (2) a "wide"
spectroscopic survey with more than 130,000 redshifts measured for objects
brighter than IAB=22.5 over 18deg^2, (3) a "deep" survey with 50,000 redshifts
measured to IAB=24, (4) ultra-deep" surveys with several thousand redshifts
measured to IAB=25, (5) multi-wavelength observations with the VLA and XMM.Comment: 5 pages including figures; to appear in Proc. of the ESO/ECF/STSCI
"Deep Fields" workshop, Garching Oct 2000, (Publ: Springer
The VIMOS VLT Deep Survey :Evolution of the major merger rate since z~1 from spectroscopicaly confirmed galaxy pairs
From the VIMOS VLT Deep Survey we use a sample of 6447 galaxies with I_{AB} <
24 to identify 251 pairs of galaxies, each member with a secure spectroscopic
redshift, which are close in both projected separation and in velocity. We find
that at z ~ 0.9, 10.9 +/- 3.2 % of galaxies with M_B(z) < -18-Qz are in pairs
with separations dr < 20 kpc/h, dv < 500 km/s, and with dM_B < 1.5,
significantly larger than 3.76 +/- 1.71 % at z ~ 0.5; we find that the pair
fraction evolves as (1+z)^m with m = 2.49 +/- 0.56. For brighter galaxies with
M_B(z=0) < -18.77, the pair fraction is higher and its evolution with redshift
is somewhat flatter with m=1.88 \pm 0.40, a property also observed for galaxies
with increasing stellar masses. Early type, dry mergers, pairs increase their
relative fraction from 3 % at z ~ 0.9 to 12 % at z ~ 0.5. We find that the
merger rate evolves as N_{mg}=(9.05 +/- 3.76) * 10^{-4}) * (1+z)^{2.43 +/-
0.76}. We find that the merger rate of galaxies with M_B(z) < -18-Qz has
significantly evolved since z ~ 1. The merger rate is increasing more rapidly
with redshift for galaxies with decreasing luminosities, indicating that the
flat evolution found for bright samples is not universal. The merger rate is
also strongly dependent on the spectral type of galaxies involved, late type
mergers being more frequent in the past, while early type mergers are more
frequent today, contributing to the rise in the local density of early type
galaxies. About 20 % of the stellar mass in present day galaxies with
log(M/M_{sun}) > 9.5 has been accreted through major merging events since z ~
1, indicating that major mergers have contributed significantly to the growth
in stellar mass density of bright galaxies over the last half of the life of
the Universe.Comment: 22 pages, 19 figures, accepted in A&
The VIMOS VLT Deep Survey - First epoch VVDS-Deep survey: 11564 spectra with 17.5<=IAB<=24, and the redshift distribution over 0< z <=5
This paper presents the ``First Epoch'' sample from the VIMOS VLT Deep Survey
(VVDS). The VVDS goals, observations, data reduction with VIPGI, and redshift
measurement with KBRED are discussed. Data have been obtained with the VIsible
Multi Object Spectrograph (VIMOS) on the ESO-VLT UT3, allowing to observe ~600
slits simultaneously at R~230. A total of 11564 objects have been observed in
the VVDS-02h and VVDS-CDFS Deep fields over a total area of 0.61deg^2, selected
solely on the basis of apparent magnitude 17.5 <=I_{AB} <=24. The VVDS covers
the redshift range 0 < z <= 5. It is successfully going through the ``redshift
desert'' 1.5<z<2.2, while the range 2.2<z<2.7 remains of difficult access
because of the VVDS wavelength coverage.A total of 9677 galaxies have a
redshift measurement, 836 are stars, 90 are AGNs, and a redshift could not be
measured for 961 objects. There are 1065 galaxies with a measured redshift
z>1.4. The survey reaches a redshift measurement completeness of 78% overall
(93% including less reliable objects), with a spatial sampling of the
population of galaxies of 25% and ~30% in the VVDS-02h and VVDS-CDFS. The
redshift accuracy measured from repeated observations with VIMOS and comparison
to other surveys is ~276km/s. From this sample we present for the first time
the redshift distribution of a magnitude limited spectroscopic sample down to
IAB=24. The redshift distribution has a median of z=0.62, z=0.65, z=0.70, and
z=0.76, for magnitude limited samples with IAB<=22.5, 23, 23.5, and 24. A high
redshift tail above redshift 2 and up to redshift 5 becomes readily apparent
for IAB>23.5, probing the bright star forming population of galaxies. This
sample provides an unprecedented dataset to study galaxy evolution over 90% of
the life of the universeComment: 30 pages, accepted 22-Feb-05 in A&
NIR Follow-Up of the VVDS 02hr Field
We present a new K-band survey covering 623 arcmin in the VVDS 0226-0430
deep field down to a limiting magnitude K 20.5. We use the
spectroscopic sample extracted from this new K-band catalogue to assess the
effectiveness of optical-near infrared color selections in identifying extreme
classes of objects at high redshift.Comment: 6 pages, 4 figures. To appear in the Proceedings of the IAU Symposium
No. 235, 2006, "Galaxy Evolution across the Hubble Time", F. Combes & J.
Palous, ed
- âŠ