40 research outputs found
Line-strength indices and velocity dispersions for 148 early-type galaxies in different environments
We have derived high quality line-strength indices and velocity
dispersions for a sample of 148 early-type galaxies in different
environments. The wavelength region covered by the observations
( to 6600 Å) includes the Lick/IDS indices
H, Mg1, Mg2, Mgb, Fe5015, Fe5270, Fe5335, Fe5406,
Fe5709, Fe5782, NaD, TiO1 and TiO2. The data are intended to
address possible differences of the stellar populations of early-type
galaxies in low- and high-density environments. This paper describes
the sample properties, explains the data reduction and presents the
complete list of all the measurements. Most galaxies of the sample
(85%) had no previous measurements of any Lick/IDS indices and for
30% of the galaxies we present first-time determinations of their
velocity dispersions. Special care is taken to identify galaxies with
emission lines. We found that 62 per cent of the galaxies in the
sample have emission lines, as measured by the equivalent width of the
[OIII] 5007Å line, EW[OIII] > 0.3 Å
Gravitational potential and X-ray luminosities of early-type galaxies observed with XMM-Newton and Chandra
We study dark matter content in early-type galaxies and investigate whether
X-ray luminosities of early-type galaxies are determined by the surrounding
gravitational potential. We derived gravitational mass profiles of 22
early-type galaxies observed with XMM-Newton and Chandra. Sixteen galaxies show
constant or decreasing radial temperature profiles, and their X-ray
luminosities are consistent with kinematical energy input from stellar mass
loss. The temperature profiles of the other 6 galaxies increase with radius,
and their X-ray luminosities are significantly higher. The integrated
mass-to-light ratio of each galaxy is constant at that of stars within 0.5-1
r_e, and increases with radius, where r_e is the effective radius of a galaxy.
The scatter of the central mass-to-light ratio of galaxies was less in K-band
light. At 3r_e, the integrated mass-to-light ratios of galaxies with flat or
decreasing temperature profiles are twice the value at 0.5r_e, where the
stellar mass dominates, and at 6r_e, these increase to three times the value at
0.5r_e. This feature should reflect common dark and stellar mass distributions
in early-type galaxies: Within 3r_e, the mass of dark matter is similar to the
stellar mass, while within 6r_e, the former is larger than the latter by a
factor of two. By contrast, X-ray luminous galaxies have higher gravitational
mass in the outer regions than X-ray faint galaxies. We describe these X-ray
luminous galaxies as the central objects of large potential structures; the
presence or absence of this potential is the main source of the large scatter
in the X-ray luminosity.Comment: 22 pages, 18 figures, 6 tables, accepted for publication in A&
AGN-Induced Cavities in NGC 1399 and NGC 4649
We present an analysis of archival Chandra and VLA observations of the E0
galaxy NGC 1399 and the E2 galaxy NGC 4649 in which we investigate cavities in
the surrounding X-ray emitting medium caused by the central AGN. We calculate
the jet power required for the AGN to evacuate these cavities and find values
of ~8x10^{41} erg/s and ~14x10^{41} erg/s for the lobes of NGC 1399 and
~7x10^{41} erg/s and ~6x10^{41} erg/s for those of NGC 4649. We also calculate
the k/f values for each cavity, where k is the ratio of the total particle
energy to that of electrons radiating in the range of 10 MHz to 10 GHz, and f
is the volume filling factor of the plasma in the cavity. We find that the
values of k/f for the lobes of NGC 1399 are ~93 and ~190, and those of the
lobes of NGC 4649 are ~15000 and ~12000. We conclude that the assumed spectrum
describes the electron distribution in the lobes of NGC 1399 reasonably well,
and that there are few entrained particles. For NGC 4649, either there are many
entrained particles or the model spectrum does not accurately describe the
population of electrons.Comment: 8 pages, 2 figures, accepted for publication in MNRA
Integrated Spectroscopy of Bulge Globular Clusters and Fields. II. Implications for stellar population models and elliptical galaxies
Synthetic Lick indices (e.g. Mg_2, Fe, etc.) of Simple Stellar Population
(SSP) models are calibrated for the first time up to solar metallicity with a
sample of Milky Way globular clusters (GCs) which includes the metal rich GCs
of the Galactic bulge. This metallicity range is relevant to elliptical
galaxies. It is shown that the Bulge GCs and integrated light follow the same
correlation between Mg and Fe indices of elliptical galaxies, showing weaker Fe
indices at given Mg indices with respect to models that assume solar-scaled
abundances. This similarity is the robust empirical evidence for enhanced
alpha/Fe ratios in the stellar populations of elliptical galaxies, since the
globular clusters are independently known to be alpha-enhanced. The uniqueness
of this alpha-overabundance solution is checked by exploring the whole range of
model ingredients. We argue that the standard models reproduce the Mg-Fe
correlation at low metallicities because the stellar templates used in the
synthesis are the alpha-enhanced stars of the galactic Halo. These same models,
however, fail to recover the Mg-Fe pattern of Bulge clusters and ellipticals at
high metallicities because the high-metallicity templates are disk stars, which
are not alpha-enhanced. The new SSP models by Thomas, Maraston & Bender (2002)
which incorporate the dependence on alpha/Fe reproduce the Mg and Fe indices of
GCs at all metallicities, with alpha/Fe=+0.3, which is in agreement with
spectroscopic abundance determinations. The Balmer indices (Hbeta, Hdelta,
Hgamma) are very well calibrated, provided the Horizontal Branch morphology is
taken into account. In particular, we reproduce the Balmer lines of NGC 6388
and NGC 6441, which are metal-rich GCs with a tail of warm Horizontal Branch
stars. {Abridged}Comment: 19 pages, 13 figures, Astronomy and Astrophysics in press. Only minor
changes after the referee repor
Nearby early-type galaxies with ionized gas. III. Analysis of line-strength indices with new stellar population models
In this paper we study the underlying stellar population of a sample of 65
nearby early-type galaxies predominantly located in low density environments.
Ages, metallicities and [alpha/Fe] ratios have been derived through the
comparison of Lick indices measured at different galacto-centric distances with
new SSP models which account for the presence of alpha/Fe enhancement. The SSPs
cover a wide range of ages, metallicities and [alpha/Fe] ratios. To derive the
stellar population parameters we have devised an algorithm based on the
probability density function. We derive a large spread in age ((1-15) Gyrs).
Age does not show any significant trend with central velocity dispersion
sigma_c but E galaxies appear on average older than S0. On the contrary, an
increasing trend of metallicity and [alpha/Fe] with sigma_c is observed,
testifying that the chemical enrichment was more efficient and the duration of
the star formation shorter in more massive galaxies. We have also sought for
possible correlations with the local galaxy density but neither metallicity nor
alpha-enhancement show clear trends. However we find that while low density
environments (LDE) contain very young objects (from 1 to 4 Gyr), none of the
galaxies in the higher density environments (HDE) is younger than 5 Gyrs.
Considering the lack of environmental effect on the [alpha/Fe] ratio and the
high value of [alpha/Fe] in some young massive objects, we argue that young
galaxies in LDE are more likely due to recent rejuvenation episodes. By
comparing the number of rejuvenated objects with the total number of galaxies
in our sample, and by means of simple two-SSP component models, we estimate
that, on average, the rejuvenation episodes do not involve more than 25 % of
the total galaxy mass.Comment: Final version as it will appear in A&A. Typos in the Abstract and
Conclusions have been correcte
Stellar Populations of Bulges in 14 Cluster Disc Galaxies
‘The definitive version is available at www.blackwell-synergy.com.’ Copyright Blackwell Publishing / RAS. DOI: 10.1111/j.1365-2966.2008.13566.xPeer reviewe
The radio properties of a complete, X-ray selected sample of nearby, massive elliptical galaxies
We investigate the radio properties of a complete sample of nearby, massive,
X-ray bright elliptical and S0 galaxies. Our sample contains 18 galaxies with
ROSAT All-Sky Survey X-ray fluxes Fx_(0.1-2.4 keV) > 3 x 10^(-12) erg/s/cm^2,
within a distance of 100 Mpc. For these galaxies, we have complete (18/18) VLA
radio and Chandra X-ray coverage. Nuclear radio emission is detected from 17/18
of the galaxies. Ten of the galaxies exhibit extended radio emission; of these
ten, all but one also exhibit clear evidence of interaction of the radio source
with the surrounding, X-ray emitting gas. Among the seven galaxies with
unresolved radio sources, one has clear, and one has small, cavity-like
features in the Chandra X-ray images; a third has a disturbed X-ray morphology.
Using a radio luminosity limit equivalent to L_(1.4 Ghz) > 10^(23) W/Hz to
calculate the radio-loud fraction, we find that this misses the majority of the
radio detected galaxies in the sample. We determine integrated radio-to-X-ray
flux ratios for the galaxies, GRx, which are shown to span a large range
(factor of 100). We calculate the mass-weighted cooling times within 1 kpc, and
find hints for an anticorrelation with the radio luminosity. We also calculate
limits on k/f, where k is the ratio of the total particle energy to that of
relativistic electrons radiating in the range 10 MHz-10 GHz and f is the volume
filling factor of the plasma in the cavity. The k/f distribution is also broad,
reflecting previous results for larger galaxy clusters. Lowering the X-ray flux
limit, at the expense of less complete VLA and Chandra coverage, increases the
size of our sample to 42 galaxies. Nuclear radio activity is detected in at
least 34/42 of this extended sample.Comment: Accepted for publication in MNRAS, 19 pages, 11 Figures and 7 Table
XMM-Newton X-ray and Optical Monitor far UV observations of NGC 7070A and ESO 2400100 shell galaxies
We present XMM-Newton X-ray observations of two shell galaxies, NGC 7070A and
ESO 2400100, and far UV observations obtained with the Optical Monitor for
these and for an additional shell galaxy, NGC 474, for which we also have near
and far UV data from GALEX. We aim at gaining insight on the overall evolution
traced by their star formation history and by their hot gas content. The X-ray
and the far UV data are used to derive their X-ray spatial and spectral
characteristics and their UV luminosity profiles. We use models developed ad
hoc to investigate the age of the last episode of star formation from the (UV -
optical) colors and line strength indices. The X-ray spatial and spectral
analysis show significant differences in the two objects. A low luminosity
nuclear source is the dominant component in NGC 7070A log L_X=41.7 erg s^{-1}
in the 2-10 keV band. In ESO 2400100, the X-ray emission is due to a low
temperature plasma with a contribution from the collective emission of
individual sources. In the Optical Monitor image ESO 2400100 shows a double
nucleus, one bluer than the other. This probably results from a very recent
star formation event in the northern nuclear region. The extension of the UV
emission is consistent with the optical extent for all galaxies, at different
degrees of significance in different filters. The presence of the double
nucleus, corroborated by the (UV - optical) colors and line strength indices
analysis, suggests that ESO 2400100 is accreting a faint companion. We explore
the evolution of the X-ray luminosity during accretion processes with time. We
discuss the link between the presence of gas and age, since gas is detected
either before coalescence or several Gyr (>3) after (Abridged).Comment: 17 pages, 11 figures, accepted for publication in A&
Kinematic and chemical evolution of early-type galaxies
We investigate in detail 13 early-type field galaxies with 0.2<z<0.7 drawn
from the FORS Deep Field. Since the majority (9 galaxies) is at z~0.4, we
compare the field galaxies to 22 members of three rich clusters with z=0.37 to
explore possible variations caused by environmental effects. We exploit
VLT/FORS spectra (R~1200) and HST/ACS imaging to determine internal kinematics,
structures and stellar population parameters. From the Faber-Jackson and
Fundamental Plane scaling relations we deduce a modest luminosity evolution in
the B-band of 0.3-0.5mag for both samples. We compare measured Lick absorption
line strengths (Hdelta, Hgamma, Hbeta, Mg_b, & Fe5335) with evolutionary
stellar population models to derive light-averaged ages, metallicities and the
element abundance ratios Mg/Fe. We find that all these three stellar parameters
of the distant galaxies obey a scaling with velocity dispersion (mass) which is
very well consistent with the one of local nearby galaxies. In particular, the
distribution of Mg/Fe ratios of local galaxies is matched by the distant ones,
and their derived mean offset in age corresponds to the average lookback time.
This indicates that there was little chemical enrichment and no significant
star formation within the last ~5Gyr. The calculated luminosity evolution of a
simple stellar population model for the derived galaxy ages and lookback times
is in most cases very consistent with the mild brightening measured by the
scaling relations.Comment: A&A acc., 17p., 7 colour figures, comments/discussion welcome! full
resolution version available from http://www.uni-sw.gwdg.de/~bziegler
The Stimulation Time for Copulation in Purposeful Strange Matings of House Pigeons (Columba Livia L.)
The purposeful strange matings of house pigeons involved pairing 24 female and 24 male racing pigeons in special nesting cells which prevented purposeless matings. However, only 4 of the males (elites) were allowed to mate (service) with the 24 female pigeons- a mating ratio of 1:6. There were altogether 277 attempted matings in four laying periods. Out of this number 151 resulted in successful copulations (matings) whereas 126 resulted in unsuccessful matings (copulations). Successful matings (N=151) occurred between one to 35 minutes whereas the unsuccessful matings (N=126) were observed between 5 to 58 minutes. It was specifically found that over 90% of all successful copulations came within 5 minutes of introduction of female pigeons to strange elite male pigeons. 5 minutes appeared then to be the optimum time of stimulation among pigeons under purposeful strange matings