1,190 research outputs found
On breaking the age-metallicity degeneracy in early-type galaxies: Outflows versus Star Formation Efficiency
A simple model of chemical enrichment in cluster early-type galaxies is
presented where the main parameters driving the formation of the stellar
component are reduced to four: infall timescale (tf), formation epoch (zF),
star formation efficiency (Ceff) and fraction of gas ejected in outflows
(Bout). We find that only variations in Bout or Ceff can account for the
colour-magnitude relation, so that the most luminous galaxies had low values of
ejected gas and high efficiencies. The combination of chemical enrichment
tracks with population synthesis models is used to explore the correlation
between mass-to-light ratios and masses. A significant slope mismatch is found
between stellar and total M/L ratios, which cannot be explained by an age
spread and implies a non-linear correlation between total and stellar mass. The
sequences driven by star formation efficiency and outflows are shown to predict
different trends at high redshift. Measurement of the dependence of the tilt of
the fundamental plane on redshift will break the degeneracy between outflows
and star formation efficiency, which will enable us to determine whether the
colour-magnitude relation is controlled by age or metallicity.Comment: 8 pages, 5 figures. To be published in MNRA
Out-of-plane thermopower of strongly correlated layered systems: an application to Bi_2(Sr,La)_2CaCu_2O_{8+\delta}
We calculate the out-of-plane thermopower in a quasi-two dimensional system,
and argue that this quantity is an effective probe of the asymmetry of the
single-particle spectral function. We find that the temperature and doping
dependence of the out-of-plane thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}
single crystals is broadly consistent with the behavior of the spectral
function determined from ARPES and tunneling experiments. We also investigate
the relationship between out-of-plane thermopower and entropy in a quasi-two
dimensional material. We present experimental evidence that at moderate
temperatures, there is a qualitative correspondence between the out-of-plane
thermopower in Bi_2(Sr,La)_2CaCu_2O_{8+\delta}, and the entropy obtained from
specific heat measurements. Finally, we argue that the derivative of the
entropy with respect to particle number may be the more appropriate quantity to
compare with the thermopower, rather than the entropy per particle.Comment: 11 pages, 5 figures. v2: substantially rewritten, including a more
detailed analysis of the relationship between thermopower and entrop
Type Ia supernovae and the formation history of early-type galaxies
Using the standard prescription for the rates of supernovae type II and type
Ia, we compare the predictions of a simple model of star formation in galaxies
with the observed radial gradients of abundance ratios in a sample of
early-type galaxies to infer the relative contribution of each type of
supernova. The data suggests a correlation between the fractional contribution
of Type Ia to the chemical enrichment of the stellar populations (1-xi) and
central velocity dispersion of order 1-xi ~ -0.16log sigma_0+0.40, so that the
type Ia contribution in stars ranges from a negligible amount in massive
galaxies up to 10% in low-mass systems. Our model is parametrized by a star
formation timescale (t_SF) which controls the duration of the starburst. A
correlation with galaxy radius as a power law (t_SF ~ r^beta) translates into a
radial gradient of the abundance ratios. The data implies a wide range of
formation scenarios for a simple model that fixes the luminosity profile,
ranging from inside-out (beta=2), to outside-in formation (beta=-1), as is
consistent with numerical simulations of elliptical galaxy formation. An
alternative scenario that links t_SF to the dynamical timescale favours
inside-out formation over a smaller range. In both cases, massive galaxies are
predicted to have undergone a more extended period of star formation in the
outer regions with respect to their low-mass counterparts.Comment: Accepted for publication in MNRAS. 8 pages with 5 embedded color EPS
figure
Comments on "Limits on Dark Matter Using Ancient Mica"
To appear in Phys. Rev. Lett. together with the author's Reply.Comment: Compressed PostScript (filename.ps.Z), 3 pages, no figure
A SuperMassive Black Hole Fundamental Plane for Ellipticals
We obtain the coefficients of a new fundamental plane for supermassive black
holes at the centers of elliptical galaxies, involving measured central black
hole mass and photometric parameters which define the light distribution. The
galaxies are tightly distributed around this mass fundamental plane, with
improvement in the rms residual over those obtained from the \mbh-\sigma and
\mbh-L relations. This implies a strong multidimensional link between the
central massive black hole formation and global photometric properties of
elliptical galaxies and provides an improved estimate of black hole mass from
galaxy data.Comment: Accepted for publication in ApJ Letter
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