46 research outputs found
Two more disk galaxies with global gas counterrotation
We report a discovery of extended counterrotating gaseous disks in early-type
disk galaxies NGC 2551 and NGC 5631. To find them, we have undertaken complex
spectral observations including integral-field spectroscopy for the central
parts of the galaxies and long-slit deep spectroscopy to probe the external
parts. The line-of-sight velocity fields have been constructed and compared to
the photometric structure of the galaxies. As a result, we have revealed
full-size counterrotating gaseous disks, the one coplanar to the stellar disk
in NGC 2551 and the other inclined to the main stellar disk in NGC 5631. We
suggest that we observe the early stages of minor-merger events which may be
two different stages of the process of lenticular galaxy formation in rather
sparse environments.Comment: 8 pages, 8 EPS figures, accepted for publication in Ap
Observational Mass-to-Light Ratio of Galaxy Systems: from Poor Groups to Rich Clusters
We study the mass-to-light ratio of galaxy systems from poor groups to rich
clusters, and present for the first time a large database for useful
comparisons with theoretical predictions. We extend a previous work, where B_j
band luminosities and optical virial masses were analyzed for a sample of 89
clusters. Here we also consider a sample of 52 more clusters, 36 poor clusters,
7 rich groups, and two catalogs, of about 500 groups each, recently identified
in the Nearby Optical Galaxy sample by using two different algorithms. We
obtain the blue luminosity and virial mass for all systems considered. We
devote a large effort to establishing the homogeneity of the resulting values,
as well as to considering comparable physical regions, i.e. those included
within the virial radius. By analyzing a fiducial, combined sample of 294
systems we find that the mass increases faster than the luminosity: the linear
fit gives M\propto L_B^{1.34 \pm 0.03}, with a tendency for a steeper increase
in the low--mass range. In agreement with the previous work, our present
results are superior owing to the much higher statistical significance and the
wider dynamical range covered (about 10^{12}-10^{15} M_solar). We present a
comparison between our results and the theoretical predictions on the relation
between M/L_B and halo mass, obtained by combining cosmological numerical
simulations and semianalytic modeling of galaxy formation.Comment: 25 pages, 12 eps figures, accepted for publication in Ap
A Spectroscopic Study of Mass Outflows in the Interacting Binary RY Scuti
The massive interacting binary RY Scuti is an important representative of an
active mass-transferring system that is changing before our eyes and which may
be an example of the formation of a Wolf-Rayet star through tidal stripping.
Utilizing new and previously published spectra, we present examples of how a
number of illustrative absorption and emission features vary during the binary
orbit. We identify spectral features associated with each component, calculate
a new, double-lined spectroscopic binary orbit, and find masses of 7.1 +/- 1.2
M_sun for the bright supergiant and 30.0 +/- 2.1 M_sun for the hidden massive
companion. Through tomographic reconstruction of the component spectra from the
composite spectra, we confirm the O9.7 Ibpe spectral class of the bright
supergiant and discover a B0.5 I spectrum associated with the hidden massive
companion; however, we suggest that the latter is actually the spectrum of the
photosphere of the accretion torus immediately surrounding the massive
companion. We describe the complex nature of the mass loss flows from the
system in the context of recent hydrodynamical models for beta Lyr, leading us
to conclude RY Scuti has matter leaving the system in two ways: 1) a bipolar
outflow from winds generated by the hidden massive companion, and 2) mass from
the bright O9.7 Ibpe supergiant flowing from the region near the L2 point to
fill out a large, dense circumbinary disk. This circumbinary disk (radius ~ 1
AU) may feed the surrounding double-toroidal nebula (radius ~ 2000 AU).Comment: 41 pages with 7 tables and 11 figures, accepted to Ap
Star Formation History at the Centers of Lenticular Galaxies with Bars and Purely Exponential Outer Disks from SAURON Data
We have investigated the stellar population properties in the central regions
of a sample of lenticular galaxies with bars and single-exponential outer
stellar disks using the data from the SAURON integral-field spectrograph
retrieved from the open Isaac Newton Group Archive. We have detected chemically
decoupled compact stellar nuclei with a metallicity twice that of the stellar
population in the bulges in seven of the eight galaxies. A starburst is
currently going on at the center of the eighth galaxy and we have failed to
determine the stellar population properties from its spectrum. The mean stellar
ages in the chemically decoupled nuclei found range from 1 to 11 Gyr. The
scenarios for the origin of both decoupled nuclei and lenticular galaxies as a
whole are discussed.Comment: 10 pages, 4 figures, a slightly edited version of the paper published
by Astronomy Letters, v. 37, no.1, 201
Results of UBV Photoelectric Observations of the Early-Type Eclipsing Binary System XZ Cep
Results of the three-colour photoelectric observation of the close binary
system XZ Cep, obtained at the Abastumani Astrophysical observatory, are
presented.Comment: 23 pages, 3 figures, 1 tebl
The Discovery of New Galaxy Members in the NGC 5044 and NGC 1052 Groups
We present the results of neutral hydrogen (HI) observations of the NGC 5044
and NGC 1052 groups, as part of a GEMS (Group Evolution Multiwavelength Study)
investigation into the formation and evolution of galaxies in nearby groups.
Two new group members have been discovered during a wide-field HI imaging
survey conducted using the ATNF Parkes telescope. These results, as well as
those from followup HI synthesis and optical imaging, are presented here.
J1320-1427, a new member of the NGC 5044 Group, has an HI mass of
M_HI=1.05e9Msun and M_HI/L_B=1.65 Msun/Lsun, with a radial velocity of
v=2750km/s. The optical galaxy is characterised by two regions of star
formation, surrounded by an extended, diffuse halo. J0249-0806, the new member
of the NGC 1052 Group, has M_HI=5.4e8Msun, M_HI/L_R=1.13 Msun/Lsun and
v=1450km/s. The optical image reveals a low surface brightness galaxy. We
interpret both of these galaxies as irregular type, with J0249-0806 possibly
undergoing first infall into the NGC 1052 group.Comment: Accepted for publication in MNRAS. 21 pages, 13 figures. Also
available with high-resolution figures at
http://www.astro.livjm.ac.uk/~npfm/Papers/mmb04.ps.g
Spatial clustering in the ESO-Sculptor Survey: two-point correlation functions by galaxy type at redshifts 0.1 - 0.5
We calculate the spatial two-point auto and cross-correlation functions for
the 765 galaxies with Rc<21.5 and 0.1<z<0.51 in the ESO-Sculptor survey, and
explore the segregation effects among the populations of giant (early-type,
late spiral) and dwarf (dE, dI) galaxies. At separation of 0.3 h^-1 Mpc, pairs
of early-type galaxies dominate the clustering over all the other types of
pairs. At intermediate scales, 0.3-5 h^-1 Mpc, mixed pairs of dwarf and giant
galaxies contribute equally as pairs of giant galaxies, whereas the latter
dominate at ~10 h^-1 Mpc. We detect the signature of the transition between the
1-halo and 2-halo regimes which is expected in the scenario of galaxy formation
by hierarchical merging of dark matter halos. The early-type galaxies largely
outdo the late spiral galaxies in their 1-halo component, whereas the 2-halo
components of both giant populations are comparable. The dwarf galaxies have an
intermediate 1-halo component between the 2 giant galaxy types, and their
2-halo component is weak and consistent with null clustering. The present
analysis indicates that the early-type galaxies are preferentially located near
the centers of the most massive halos, whereas late spiral galaxies tend to
occupy their outskirts or the centers of less massive halos. This analysis also
unveils new results on the spatial distribution of dwarf galaxies: at the scale
at which they significantly cluster inside the halos (<0.3 h^-1 Mpc), they are
poorly mixed with the late spiral galaxies, and appear preferentially as
satellites of early-type galaxies.Comment: Astronomy & Astrophysics, in press. 29 pages, 15 color figures, 3
table
Frequency and properties of bars in cluster and field galaxies at intermediate redshifts
We present a study of large-scale bars in field and cluster environments out
to redshifts of ~0.8 using a final sample of 945 moderately inclined disk
galaxies drawn from the EDisCS project. We characterize bars and their host
galaxies and look for relations between the presence of a bar and the
properties of the underlying disk. We investigate whether the fraction and
properties of bars in clusters are different from their counterparts in the
field. The total optical bar fraction in the redshift range z=0.4-0.8 (median
z=0.60), averaged over the entire sample, is 25% (20% for strong bars). For the
cluster and field subsamples, we measure bar fractions of 24% and 29%,
respectively. We find that bars in clusters are on average longer than in the
field and preferentially found close to the cluster center, where the bar
fraction is somewhat higher (~31%) than at larger distances (~18%). These
findings however rely on a relatively small subsample and might be affected by
small number statistics. In agreement with local studies, we find that
disk-dominated galaxies have a higher optical bar fraction (~45%) than
bulge-dominated galaxies (~15%). This result is based on Hubble types and
effective radii and does not change with redshift. The latter finding implies
that bar formation or dissolution is strongly connected to the emergence of the
morphological structure of a disk and is typically accompanied by a transition
in the Hubble type. (abridged)Comment: 17 pages, accepted for publication in A&
FAUST observations of UV sources toward the Virgo cluster
We analyze three UV images covering a 100 square degree field toward the
Virgo cluster,obtained by the FAUST space experiment. We detect 191 sources to
a signal-to-noise ratio of 4.4 and identify 94% of them. Most sources have
optical counterparts in existing catalogs and about half are identified as
galaxies. Some sources with no listed counterpart were observed at the Wise
Observatory. We present the results of low resolution visible spectrophotometry
and discuss the foreground 101 stellar sources and the 76 detected galaxies,
both in the cluster and in the fore- or background. We derive conclusions on
star-formation properties of galaxies and on the total UV flux from discrete
and diffuse sources in the cluster. We test for the presence of intra-cluster
dust, determine the clustering properties of UV emitting galaxies, and derive
the UV luminosity function of Virgo galaxies.Comment: 60 pages, LaTeX (including 5 Tables) + 8 PostScript figures. To
appear in "The Astrophysical Journal
Metallicity and age gradients in round elliptical galaxies
We probe the stellar population age and metallicity distributions in nearby
elliptical galaxies over the largest extension to date. Long-slit spectroscopy
is made by using the spectrograph SCORPIO of the 6-m telescope of the Special
Astrophysical Observatory of the Russian Academy of Sciencies. The Lick indices
H-beta, Mg b, Fe5270, and Fe5335 are calculated along the slit up to radii of
1.3 to 3r_e in 4 galaxies and up to 0.5r_e in the fifth one. The comparison
with evolutionary synthesis models of simple stellar populations allows us to
disentangle age and metallicity and to measure both. We have found that the
mean stellar age is constant along the radius only in one galaxy out of 5. The
other 4 galaxies demonstrate quite different behaviour of the mean stellar age:
the outer parts are older than the centres in 3 cases and younger - in one
case. The metallicity gradients cannot be approximated by a single power law
over the full radial extension in 4 galaxies of 5. The inner metallicity
gradients within 0.5r_e are all rather steep, steeper than -0.4 metallicity dex
per radius dex, and are inconsistent with the origin of the elliptical galaxies
by a major merger.Comment: 12 pages, 12 figures, accepted to Astronomy and Astrophysics, fig 11
in low resolution versio