10 research outputs found
Kinematics of gas and stars in circumnuclear star-forming regions of early type spirals
(Abbr.) We present high resolution (R~20000) spectra in the blue and the far
red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals
(NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics
of stars and ionized gas in these structures and, for the first time, the
derivation of their dynamical masses for the first two. In some cases these
regions, about 100 to 150 pc in size, are seen to be composed of several
individual star clusters with sizes between 1.5 and 4.9 pc estimated from
Hubble Space Telescope (HST) images. The stellar dispersions have been obtained
from the Calcium triplet (CaT) lines at 8494,8542,8662 \AA,
while the gas velocity dispersions have been measured by Gaussian fits to the
H and [OIII] 5007 \AA lines on the high dispersion
spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s.
We apply the virial theorem to estimate dynamical masses of the clusters,
assuming that systems are gravitationally bounded and spherically symmetric,
and using previously measured sizes. The measured values of the stellar
velocity dispersions yield dynamical masses of the order of 10 to 10
solar masses for the whole CNSFRs. Stellar and gas velocity dispersions are
found to differ by about 20 to 30 km/s with the H emission lines being
narrower than both the stellar lines and the [OIII] 5007 \AA
lines. The twice ionized oxygen, on the other hand, shows velocity dispersions
comparable to those shown by stars, in some cases, even larger. We have found
indications of the presence of two different kinematical components in the
ionized gas of the regions...Comment: 4 pages, proceeding of the meeting "Young massive star clusters -
Initial conditions and environments", Granada, Spain, 200
The colour magnitude relation for galaxies in the Coma cluster
We present a new photometric catalogue of the Coma galaxy cluster in the
Johnson U- and V- bands. We cover an area of 3360arcmin2 of sky, to a depth of
V=20 mag in a 13 arcsec diameter aperture, and produce magnitudes for ~1400
extended objects in metric apertures from 8.8 to 26arcsec diameters. The mean
internal RMS scatter in the photometry is 0.014 mag in V, and 0.026 mag in U,
for V13 < 17 mag.
We place new limits on the levels of scatter in the colour--magnitude
relation (CMR) in the Coma cluster, and investigate how the slope and scatter
of the CMR depends on galaxy morphology, luminosity and position within the
cluster. As expected, the lowest levels of scatter are found in the elliptical
galaxies, while the late type galaxies have the highest numbers of galaxies
bluewards of the CMR. We investigate whether the slope of the CMR is an
artifact of colour gradients within galaxies and, show that it persists when
the colours are measured within a diameter that scales with galaxy size.
Looking at the environmental dependence of the CMR, we find a trend of
systematically bluer galaxy colours with increasing projected cluster-centric
radius which we associate with a gradient in the mean galactic ages.Comment: 18 pages, 13 Figures. For associated data file, see
ftp://ftp.sr.bham.ac.uk/pub/ale/ComaPhot
Cold gas in elliptical galaxies
We explore the evolution of the cold gas (molecular and neutral hydrogen) of
elliptical galaxies and merger remnants ordered into a time sequence on the
basis of spectroscopic age estimates. We find that the fraction of cold gas in
early merger remnants decreases significantly for ~1-2 Gyr, but subsequent
evolution toward evolved elliptical systems sees very little change. This trend
can be attributed to an initial gas depletion by strong star-formation which
subsequently declines to quiescent rates. This explanation is consistent with
the merger picture for the formation of elliptical galaxies. We also explore
the relation between HI-to-H2 mass ratio and spectroscopic galaxy age, but find
no evidence for a statistically significant trend. This suggests little net HI
to H2 conversion for the systems in the present sample.Comment: 11 pages, 6 figures, accepted for publication by MNRA
A Catalogue and Analysis of Local Galaxy Ages and Metallicities
We have assembled a catalogue of relative ages, metallicities and abundance
ratios for about 150 local galaxies in field, group and cluster environments.
The galaxies span morphological types from cD and ellipticals, to late type
spirals. Ages and metallicities were estimated from high quality published
spectral line indices using Worthey & Ottaviani (1997) single stellar
population evolutionary models. The identification of galaxy age as a fourth
parameter in the fundamental plane (Forbes et al. 1998) is confirmed by our
larger sample of ages. We investigate trends between age and metallicity, and
with other physical parameters of the galaxies, such as ellipticity,
luminosity, and kinematic anisotropy. We demonstrate the existence of a galaxy
age-metallicity relation similar to that seen for local galactic disk stars,
whereby young galaxies have high metallicity, while old galaxies span a large
range in metallicities. We also investigate the influence of environment and
morphology on the galaxy age and metallicity, especially the predictions made
by semi-analytic hierarchical clustering models (HCM). We confirm that
non-cluster ellipticals are indeed younger on average than cluster ellipticals
as predicted by the HCM models. However we also find a trend for the more
luminous galaxies to have a higher [Mg/Fe] ratio than the lower luminosity
galaxies, which is opposite to the expectation from HCM models.Comment: 17 pages, Latex, 16 figures, 4 tables, submitted to MNRA
Colour-magnitude relations and spectral line strengths in the Coma cluster
We use the , , and spectral
absorption line indices, together with U- and V-band photometry of 101 galaxies
in the Coma cluster, to investigate how mean age and metal abundance correlate
with galaxy luminosity. In particular, we use the line index measurements to
address the origin of the colour-magnitude relation (CMR). We find that the CMR
in Coma is driven primarily by a luminosity-metallicity correlation. We
additionally show evidence for a relation between age and luminosity, in the
direction predicted by the semi-analytic hierarchical clustering models of
Kauffmann & Charlot, but this is only present in the index models,
and could be an effect of the lack of non solar abundance ratios in the Worthey
models used.
By comparing deviations from the CMR, with deviations in absorption index
from analogous `index-magnitude' relations, we find that colour deviations
bluewards of the mean relation are strongly correlated with the hydrogen Balmer
line series absorption. We show that the properties of these blue galaxies are
consistent with the presence of a young stellar population in the galaxies,
rather than with a reduced metallicity.Comment: 9 pages, 5 figures. Accepted for publication in MNRA