199 research outputs found
New response functions for absorption-line indices from high-resolution spectra
Basing on the huge library of 1-A resolution spectra calculated by Munari et
al. over a large range of logT, log g, [Fe/H] and both for solar and a-enhanced
abundance ratios [a/Fe], we present theoretical absorption-line indices on the
Lick system. First we derive the so-called response functions (RFs) of Tripicco
& Bell for a wide range of logT, log g, [Fe/H] and [a/Fe]=+0.4 dex. The RFs are
commonly used to correct indices with solar [a/Fe] ratios to indices with
[a/Fe]>0. Not only the RFs vary with the type of star but also with the
metallicity. Secondly, with the aid of this and the fitting functions (FFs) of
Worthey et al., we derive the indices for single stellar populations and
compare them with those obtained by previous authors, e.g. Tantalo & Chiosi.
The new RFs not only supersede the old ones by Tripicco & Bell, but also show
that Hb increases with the degree of enhancement in agreement with the results
by Tantalo & Chiosi. The new indices for single stellar populations are used to
derive with aid of the recursive Minimum Distance method the age, metallicity
and degree of enhancement of a sample of Galactic Globular Clusters for which
these key parameters have been independently derived from the Colour-Magnitude
Diagram and/or spectroscopic studies. The agreement is remarkably good.Comment: 18 pages, to appear in Astronomy & Astrophysic
Modelling galaxy spectra in presence of interstellar dust. I. The model of ISM and the library of dusty SSPs
In this paper, the first of a series of two devoted to modelling the spectra
of galaxies of different morphological type in presence of dust, we present our
description of the dust both in the diffuse ISM and the molecular clouds. Our
model for the dust takes into account three components, i.e. graphite,
silicates and polycyclic aromatic hydrocarbons. We consider and adapt to our
aims two prescriptions for the size distribution of the dust grains and two
models for the emission of the dusty ISM. We cross-check the emission and
extinction models of the ISM by calculating the extinction curves and the
emission for the typical environments of the Milky Way and the Large and Small
Magellanic Clouds and by comparing the results with the observational data. The
final model we have adopted is an hybrid one which stems from combining the
analysis of Guhathakurta et al (1989) for the emission of graphite and
silicates and Puget et al. (1985) for the PAH emission, and using the
distribution law of Weingartner et al. (2001a) and the ionization model for
PAHs of Weingartner et al. (2001b). We apply the model to calculate the SED of
SSPs of different age and chemical composition, which may be severely affected
by dust in young, massive stars while they are still embedded in their parental
MCs. We use the "Ray Tracing" method to solve the problem of radiative transfer
and to calculate libraries of SSP SEDs. Particular care is paid to model the
contribution from PAHs, introducing different abundances of C in the population
of very small carbonaceous grains (VSGs) and different ionization states in
PAHs. The SEDs of young SSPs are then compared with observational data of star
forming regions of four local galaxies successfully reproducing their SEDs from
the UV-optical regions to the mid and far infrared.Comment: 24 pages, 29 figure
Remarks on the Gauge Dependence of the RI/MOM Renormalization Procedure
The RI/MOM non-perturbative renormalization scheme is studied on the lattice
in SU(3) quenched QCD with Wilson fermions. The gauge dependence of some
fermion bilinear renormalization constants is discussed by comparing data which
have been gauge-fixed in two different realizations of the Landau gauge and in
a generic covariant gauge. The very good agreement between the various sets of
results and the theory indicates that the numerical uncertainty induced by the
lattice gauge-fixing procedure is moderate and below the statistical errors.Comment: 11 pages, 3 figure
Measurements of Far-UV Emission from Elliptical Galaxies at z=0.375
The ``UV upturn'' is a sharp rise in spectra of elliptical galaxies shortward
of rest-frame 2500 A. It is a ubiquitous phenomenon in nearby giant elliptical
galaxies, and is thought to arise primarily from low-mass evolved stars on the
extreme horizontal branch and beyond. Models suggest that the UV upturn is a
very strong function of age for these old stellar populations, increasing as
the galaxy gets older. In some models the change in UV/optical flux ratio is a
factor of 25 over timescales of less than 3 Gyr. To test the predictions for
rapid evolution of the UV upturn, we have observed a sample of normal
elliptical galaxies in the z=0.375 cluster Abell 370 with the Faint Object
Camera aboard the Hubble Space Telescope. A combination of two long-pass
filters was used to isolate wavelengths shortward of rest-frame 2700 A,
providing a measurement of the UV upturn at a lookback time of approximately 4
Gyr. Surprisingly, the four elliptical galaxies observed show a range of UV
upturn strength that is similar to that seen in nearby elliptical galaxies,
with an equivalent 1550-V color ranging from 2.9-3.4 mag. Our result is
inconsistent with some models for the UV upturn; other models are consistent
only for a high redshift of formation (z_f >= 4).Comment: 4 pages, Latex. 1 figure. To appear in ApJL. Uses emulateapj.sty and
apjfonts.sty. Revision includes minor ApJ edits & fixes typo
Flavored tetraquark spectroscopy
The recent confirmation of the charged charmonium like resonance Z(4430) by the LHCb experiment strongly suggests the existence of QCD multi quark bound states. Some preliminary results about hypothetical flavored tetraquark mesons are reported. Such states are particularly amenable to Lattice QCD studies as their interpolating operators do not overlap with those of ordinary hidden-charm mesons
Balmer and Metal Absorption Feature Gradients in M32
Spectra from MDM Observatory are used to assess Lick/IDS feature strength
gradients inside the half-light radius of the compact Local Group elliptical
galaxy M32. All but a few (of 24 measured) indices show a statistically
significant gradient. Comparing with models, the index gradients indicate a
mean age and abundance gradient in the sense that the nucleus is a factor of
2.5 younger and a factor of 0.3 dex more metal-rich than at 1 effective radius.
This conclusion is only weakly dependent on which index combinations are used
and is robust to high accuracy. Stars near the M32 nucleus have a mean age and
heavy element abundance [M/H] of (4.7 Gyr, +0.02), judging from models by
Worthey with variable abundance ratios. This result has very small formal
random errors, although, of course, there is significant age-metallicity
degeneracy along an (age, abundance) line segment from (5.0 Gyr, 0.00) to (4.5
Gyr, +0.05). An abundance pattern of [C/M]=+0.077, [N/M]=-0.13, [Mg/M]=-0.18,
[Fe/M]~0.0, and [Na/M]=+0.12 is required to fit the feature data, with a
fitting precision of about 0.01 dex. Model uncertainties make the accuracies of
these values at least twice the magnitude of the precision. Forcing
scaled-solar abundances does not change the age very much, but it increases the
rms goodness of model-data fit by a factor of 3 and broadens the allowed range
of age to Gyr. The overall abundance pattern contrasts with larger
elliptical galaxies, in which all measurable lighter elements are enhanced
relative to iron and calcium.Comment: 23 pages, 9 figures, Astronomical Journal, in pres
Mass-to-Light ratio, Initial Mass Function and chemical evolution in disc galaxies
Cosmological simulations of disc galaxy formation, when compared to the
observed Tully-Fisher relation, suggest a low Mass-to-Light (M/L) ratio for the
stellar component in spirals. We show that a number of "bottom-light" Initial
Mass Functions (IMFs) suggested independently in literature, do imply M/L
ratios as low as required, at least for late type spirals (Sbc/Sc). However the
typical M/L ratio, and correspondingly the zero-point of the Tully-Fisher
relation, is expected to vary considerably with Hubble type.
Bottom-light IMFs tend to have a metal production in excess of what is
tipically estimated for spiral galaxies. Suitable tuning of the IMF slope and
mass limits, post-supernova fallback of metals onto black holes or metal
outflows must then be invoked, to reproduce the observed chemical properties of
disc galaxies.Comment: 4 pages, 6 colour figures. To appear on PASA (refereed proceedings of
Galactic ChemoDynamics V, B.K. Gibson and D. Kawata eds.
- …