165 research outputs found
The AMIGA sample of isolated galaxies: VIII. The rate of asymmetric HI profiles in spiral galaxies
(abridged) Measures of the HI properties of a galaxy are among the most
sensitive interaction diagnostic at our disposal. We report here on a study of
HI profile asymmetries (e.g., lopsidedness) in a sample of some of the most
isolated galaxies in the local Universe. This presents us with an excellent
opportunity to quantify the range of intrinsic HI asymmetries and provides us
with a zero-point calibration for evaluating these measurements in less
isolated samples. We characterize the HI profile asymmetries and search for
correlations between HI asymmetry and their environments, as well as their
optical and far infrared (FIR) properties. We use high signal-to-noise global
HI profiles for galaxies in the AMIGA project (http://amiga.iaa.csic.es). We
restrict our study to N=166 galaxies with accurate measures of the HI shape
properties. We quantify asymmetries using a flux ratio parameter. The asymmetry
parameter distribution of our isolated sample is well described by a Gaussian
model. The width of the distribution is sigma=0.13, and could be even smaller
(sigma=0.11) if instrumental errors are reduced. Only 2% of our carefully
vetted isolated galaxies sample show an asymmetry in excess of 3sigma. By using
this sample we minimize environmental effects as confirmed by the lack of
correlation between HI asymmetry and tidal force (one-on-one interactions) and
neighbor galaxy number density. On the other hand, field galaxy samples show
wider distributions and deviate from a Gaussian curve. As a result we find
higher asymmetry rates (~10-20%) in such samples. We find evidence that the
spiral arm strength is inversely correlated with the HI asymmetry. We also find
an excess of FIR luminous galaxies with larger HI asymmetries that may be
spirals associated with hidden accretion events. Our sample presents the
smallest fraction of asymmetric HI profiles compared with any other yet
studied.Comment: 18 pages, 17 figures, accepted for publication in A&
AMIGA project: Active galaxies in a complete sample of isolated galaxies
The project AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies)
provides a statistically significant sample of the most isolated galaxies in
the northern sky. Such a control sample is necessary to understand the role of
the environment in evolution and galaxy properties like the interstellar medium
(ISM), star formation and nuclear activity. The data is publicly released under
a VO interface at http://amiga.iaa.es/. One of our main goals is the study of
nuclear activity in non-interacting galaxies using different methods. We focus
on the well known radiocontinuum-far infrared (FIR) correlation in order to
findradio-excess galaxies which are candidates to host an active galactic
nucleus (AGN) and FIR colours to find obscured AGN candidates. We looked for
the existing information on nuclear activity in the V\'eron-Cetty catalogue and
in the NASA Extragalactic Database (NED). We also used the nuclear spectra from
the Sloan Digital Sky Survey which allow us to determine the possible presence
of an AGN and to study the properties of the underlying stellar populations. We
produced a final catalogue of AGN-candidate galaxies which will provide a
baseline for the study of the nuclear activity depending on the environment. We
find that the fraction of FIR selected AGN-candidates ranges between 7% and
20%. There are no radio-excess galaxies in our sample above a factor 5 of radio
excess which is the lowest rate found in comparison with other samples in
denser environments. Finally, we obtained a fraction of about 22% of AGN using
the optical spectra, a significant fraction for a sample of isolated galaxies.
We conclude that the environment plays a crucial and direct role in triggering
radio nuclear activity and not only via the density-morphology or the
density-luminosity relations.Comment: 4 pages, 1 figure, proceedings of the contributed talk given at the
conference "Galaxies in Isolation: Exploring Nature vs. Nurture" held in
Granada, May 12-15, 200
Setting the normalcy level of HI properties in isolated galaxies
Studying the atomic gas (HI) properties of the most isolated galaxies is
essential to quantify the effect that the environment exerts on this sensitive
component of the interstellar medium. We observed and compiled HI data for a
well defined sample of ~ 800 galaxies in the Catalog of Isolated Galaxies, as
part of the AMIGA project (Analysis of the ISM in Isolated GAlaxies,
http://amiga.iaa.es), which enlarges considerably previous samples used to
quantify the HI deficiency in galaxies located in denser environments. By
studying the shape of 182 HI profiles, we revisited the usually accepted result
that, independently of the environment, more than half of the galaxies present
a perturbed HI disk. In isolated galaxies this would certainly be a striking
result if these are supposed to be the most relaxed systems, and has
implications in the relaxation time scales of HI disks and the nature of the
most frequent perturbing mechanisms in galaxies. Our sample likely exhibits the
lowest HI asymmetry level in the local Universe. We found that other field
samples present an excess of ~ 20% more asymmetric HI profiles than that in
CIG. Still a small percentage of galaxies in our sample present large
asymmetries. Follow-up high resolution VLA maps give insight into the origin of
such asymmetries.Comment: 4 pages, 2 figures, Conference 'Galaxies in Isolation: Exploring
Nature vs. Nurture', Granada, 12-15 May 2009. To be published in the ASP
Conference Serie
Search For Companions Of Nearby Isolated Galaxies
The radial velocities are measured for 45 galaxies located in the
neighborhoods of 29 likely isolated galaxies in a new catalog. We find that
about 85% of these galaxies actually are well isolated objects. 4% of nearby
galaxies with V_LG<3500 km/s are this kind of cosmic "orphan".Comment: 7 pages, 2 figure
The AMIGA sample of isolated galaxies - II. Morphological refinement
We present a complete POSS II-based refinement of the optical morphologies
for galaxies in the Karatchenseva's Catalog of Isolated Galaxies that forms the
basis of the AMIGA project. Comparison with independent classifications made
for an SDSS overlap sample of more than 200 galaxies confirms the reliability
of the early vs. late-type discrimination and the accuracy of spiral subtypes
within DeltaT = 1-2. CCD images taken at the OSN were also used to solve
ambiguities. 193 galaxies are flagged for the presence of nearby companions or
signs of distortion likely due to interaction. This most isolated sample of
galaxies in the local Universe is dominated by 2 populations: 1) 82% spirals
(Sa-Sd) with the bulk being luminous systems with small bulges (63% between
types Sb-Sc) and 2) a significant population of early-type E-S0 galaxies (14%).
Most of the types later than Sd are low luminosity galaxies concentrated in the
local supercluster where isolation is difficult to evaluate. The late-type
spiral majority of the sample spans a luminosity range M_B-corr = -18 to -22
mag. Few of the E/S0 population are more luminous than -21.0 marking an absence
of, an often sought, super L* merger (eg fossil elliptical) population. The
rarity of high luminosity systems results in a fainter derived M* for this
population compared to the spiral optical luminosity function (OLF). The E-S0
population is from 0.2 to 0.6 mag fainter depending how the sample is defined.
This marks the AMIGA sample as almost unique among samples that compare early
and late-type OLFs separately. In other samples, which always involve galaxies
in higher density environments, M*(E/S0) is almost always 0.3-0.5 mag brighter
than M*(S), presumably reflecting a stronger correlation between M* and
environmental density for early-type galaxies.Comment: A&A accepted, 13 pages, 9 figures, 8 tables. Higher resolution Fig. 1
and full tables are available on the AMIGA (Analysis of the interstellar
Medium of Isolated GAlaxies) website at http://www.iaa.es/AMIGA.htm
Effects of the environment on galaxies in the Catalogue of Isolated Galaxies: physical satellites and large scale structure
We aim to identify and quantify the effects of the satellite distribution
around a sample of galaxies in the Catalogue of Isolated Galaxies (CIG), as
well as the effects of the Large Scale Structure (LSS) using the SDSS-DR9. To
recover the physically bound galaxies we focus on the satellites which are
within the escape speed of each CIG galaxy. We also propose a more conservative
method using the stacked Gaussian distribution of the velocity difference of
the neighbours. The tidal strengths affecting the primary galaxy are estimated
to quantify the effects of the local and LSS environments. We also define the
projected number density parameter at the 5 nearest neighbour to
characterise the LSS around the CIG galaxies. Out of the 386 CIG galaxies
considered in this study, at least 340 (88\% of the sample) have no physically
linked satellite. Out of the 386 CIG galaxies, 327 (85\% of the sample) have no
physical companion within a projected distance of 0.3 Mpc. The CIG galaxies are
distributed following the LSS of the local Universe, although presenting a
large heterogeneity in their degree of connection with it. A clear segregation
appears between early-type CIG galaxies with companions and isolated late-type
CIG galaxies. Isolated galaxies are in general bluer, with likely younger
stellar populations and rather high star formation with respect to older,
redder CIG galaxies with companions. Reciprocally, the satellites are redder
and with an older stellar populations around massive early-type CIG galaxies,
while they have a younger stellar content around massive late-type CIG
galaxies. This suggests that the CIG is composed of a heterogeneous population
of galaxies, sampling from old to more recent, dynamical systems of galaxies.Comment: 19 pages, 10 figures, 1 table, accepted for publication in Astronomy
& Astrophysic
HI asymmetry in the isolated galaxy CIG 85 (UGC 1547)
We present the results from the Giant Metrewave Radio Telescope (GMRT)
interferometric HI and 20 cm radio continuum observations of CIG 85, an
isolated asymmetric galaxy from the AMIGA (Analysis of the Interstellar Medium
of Isolated GAlaxies) sample. Despite being an isolated galaxy, CIG 85 showed
an appreciable optical and HI spectral asymmetry and therefore was an excellent
candidate for resolved HI studies to understand the reasons giving rise to
asymmetries in isolated galaxies. The galaxy was imaged in HI and 20 cm radio
continuum using the GMRT. For a detailed discussion of the results we also made
use of multi-wavelength data from archival SDSS, GALEX and Halpha imaging. We
find the HI in CIG 85 to have a clumpy, asymmetric distribution which in the NW
part is correlated with optical tail like features, but the HI velocity field
displays a relatively regular rotation pattern. Evaluating all the
observational evidence, we come to a conclusion that CIG 85 is most likely a
case of a disturbed spiral galaxy which now appears to have the morphology of
an irregular galaxy. Although it is currently isolated from major companions,
the observational evidence is consistent with HI asymmetries, a highly
disturbed optical disk and recent increase in star formation having been caused
by a minor merger, remnants of which are now projected in front of the optical
disk. If this is correct, the companion will be fully accreted by CIG 85 in the
near future.Comment: 10 pages, 9 figures, accepted in A&
The role of environment in triggering starburst galaxies: A sample of isolated galaxies
The project AMIGA (Analysis of the interstellar Medium of Isolated GAlaxies)
will provide a statistically significant sample of the most isolated galaxies
in the northern sky. Such a control sample is necessary to assess the role of
the environment in galaxy properties and evolution. The sample is based on the
Catalogue of Isolated Galaxies (CIG, Karachentseva, 1973) and the database will
include blue and near-infrared luminosities, far-infrared (FIR) emission,
atomic gas (HI) emission, radio continuum, and, for a redshift limited
subsample of about 200 galaxies, CO and H emission. The data will be
released and periodically updated at http://www.iaa.csic.es/AMIGA.html. Here,
we present the project and its status, as well as a preliminary analysis of the
relation between star formation activity and the environment. We found a trend
that the galaxies with asymmetric HI spectrum also tend to show an enhanced
star formation, traced by a high value of , indicating that a
perturbed gas kinematics and enhanced SF are related.Comment: 6 pages, to appear in "The Evolution of Starbursts", ed. S.
Huettemeister et al., AIP Proceeding
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