4,554 research outputs found
Mass Distribution in Hickson Compact Groups of Galaxies
This study presents the mass distribution for a sample of 18 late-type
galaxies in nine Hickson Compact Groups. We used rotation curves from high
resolution 2D velocity fields of Fabry-Perot observations and J-band photometry
from the 2MASS survey, in order to determine the dark halo and the visible
matter distributions. The study compares two halo density profile, an
isothermal core-like distribution and a cuspy one. We also compare their
visible and dark matter distributions with those of galaxies belonging to
cluster and field galaxies coming from two samples: 40 cluster galaxies of
Barnes et al (2004) and 35 field galaxies of Spano et al. (2008). The central
halo surface density is found to be constant with respect to the total absolute
magnitude similar to what is found for the isolated galaxies. This suggests
that the halo density is independent to galaxy type and environment. We have
found that core-like density profiles fit better the rotation curves than
cuspy-like ones. No major differences have been found between field, cluster
and compact group galaxies with respect to their dark halo density profiles.Comment: 35 pages, 21 figures. Accept for publication in Astronomical Journa
GHASP: an H{\alpha} kinematic survey of spiral and irregular galaxies -- IX. The NIR, stellar and baryonic Tully-Fisher relations
We studied, for the first time, the near infrared, stellar and baryonic
Tully-Fisher relations for a sample of field galaxies taken from an homogeneous
Fabry-Perot sample of galaxies (the GHASP survey). The main advantage of GHASP
over other samples is that maximum rotational velocities were estimated from 2D
velocity fields, avoiding assumptions about the inclination and position angle
of the galaxies. By combining these data with 2MASS photometry, optical colors,
HI masses and different mass-to-light ratio estimators, we found a slope of
4.48\pm0.38 and 3.64\pm0.28 for the stellar and baryonic Tully-Fisher relation,
respectively. We found that these values do not change significantly when
different mass-to-light ratios recipes were used. We also point out, for the
first time, that rising rotation curves as well as asymmetric rotation curves
show a larger dispersion in the Tully-Fisher relation than flat ones or than
symmetric ones. Using the baryonic mass and the optical radius of galaxies, we
found that the surface baryonic mass density is almost constant for all the
galaxies of this sample. In this study we also emphasize the presence of a
break in the NIR Tully-Fisher relation at M(H,K)\sim-20 and we confirm that
late-type galaxies present higher total-to-baryonic mass ratios than early-type
spirals, suggesting that supernova feedback is actually an important issue in
late-type spirals. Due to the well defined sample selection criteria and the
homogeneity of the data analysis, the Tully-Fisher relation for GHASP galaxies
can be used as a reference for the study of this relation in other environments
and at higher redshifts.Comment: 16 pages, 6 figures. Accepted for publication in MNRA
A flat faint end of the Fornax cluster galaxy luminosity function
We analyse the photometric properties of the early-type Fornax cluster dwarf
galaxy population (M_V>-17 mag), based on a wide field imaging study of the
central cluster area in V and I band-passes with IMACS/Magellan at Las Campanas
Observatory. We create a fiducial sample of ~100 Fornax cluster dwarf
ellipticals (dEs) with -16.6<M_V<-8.8 mag in the following three steps: (1) To
verify cluster membership, we measured I-band surface brightness fluctuations
(SBF) distances to candidate dEs known from previous surveys; (2) We
re-assessed morphological classifications for those candidate dEs that are too
faint for SBF detection; and (3) We searched for new candidate dEs in the
size-luminosity regime close to the resolution limit of previous surveys. The
resulting fiducial dE sample follows a well-defined surface brightness -
magnitude relation, showing that Fornax dEs are about 40% larger than Local
Group dEs. The sample also defines a colour-magnitude relation similar to that
of Local Group dEs. The early-type dwarf galaxy luminosity function in Fornax
has a very flat faint end slope alpha = -1.1 +/- 0.1. We compare the number of
dwarfs per unit mass with those in other environments and find that the Fornax
cluster fits well into a general trend of a lack of high-mass dwarfs in more
massive environments.Comment: 5 pages, 4 figures, to appear in the proceedings of IAU Symposium 244
'Dark galaxies and lost baryons', Cambridge University Press, editors J. I.
Davies & M. D. Disne
Star formation in low density HI gas around the Elliptical Galaxy NGC2865
Interacting galaxies surrounded by HI tidal debris are ideal sites for the
study of young clusters and tidal galaxy formation. The process that triggers
star formation in the low-density environments outside galaxies is still an
open question. New clusters and galaxies of tidal origin are expected to have
high metallicities for their luminosities. Spectroscopy of such objects is,
however, at the limit of what can be done with existing 8-10m class telescopes,
which has prevented statistical studies of these objects. NGC2865 is an
UV-bright merging elliptical galaxy with shells and extended HI tails. The
regions observed in this work were previously detected using multi-slit imaging
spectroscopy. We obtain new multislit spectroscopy of six young star-forming
regions around NGC2865, to determine their redshifts and metallicities. The six
emission-line regions are located 16-40 kpc from NGC2865 and they have similar
redshifts. They have ages of ~10Myears and an average metallicity of
12+log(O/H) ~ 8.6, suggesting a tidal origin for the regions. It is noted that
they coincide with an extended HI tail, which has projected density of N
< 10 cm, and displays a low surface brightness counterpart. These
regions may represent the youngest of the three populations of star clusters
already identified in NGC2865. The high, nearly-solar, oxygen abundances found
for the six regions in the vicinity of NGC2865 suggest that they were formed by
pre-enriched material from the parent galaxy, from gas removed during the last
major merger. Given the mass and the location of the HII regions, we can
speculate that these young star-forming regions are potential precursors of
globular clusters that will be part of the halo of NGC2865 in the future. Our
result supports the use of the multi-slit imaging spectroscopy as a useful tool
for finding nearly-formed stellar systems around galaxies.Comment: 7 pages, 2 figures accepted in A&
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