460 research outputs found
Perspectives on Intracluster Enrichment and the Stellar Initial Mass Function in Elliptical Galaxies
Stars formed in galaxy cluster potential wells must be responsible for the
high level of enrichment measured in the intracluster medium (ICM); however,
there is increasing tension between this truism and the parsimonious assumption
that the stars in the generally old population studied optically in cluster
galaxies emerged from the same formation sites at the same epochs. We construct
a phenomenological cluster enrichment model to demonstrate that ICM elemental
abundances are underestimated by a factor >2 for standard assumptions about the
stellar population -- a discrepancy we term the "cluster elemental abundance
paradox". Recent evidence of an elliptical galaxy IMF skewed to low masses
deepens the paradox. We quantify the adjustments to the star formation
efficiency and initial mass function (IMF), and SNIa production efficiency,
required to resolve this while being consistent with the observed ICM abundance
pattern. The necessary enhancement in metal enrichment may, in principle,
originate in the observed stellar population if a larger fraction of stars in
the supernova-progenitor mass range form from an initial mass function (IMF)
that is either bottom-light or top-heavy, with the latter in some conflict with
observed ICM abundance ratios. Other alternatives that imply more modest
revisions to the IMF, mass return and remnant fractions, and primordial
fraction, posit an increase in the fraction of 3-8 solar mass stars that
explode as SNIa or assume that there are more stars than conventionally thought
-- although the latter implies a high star formation efficiency. We discuss the
feasibility of these various solutions and the implications for the diversity
of star formation in the universe, the process of elliptical galaxy formation,
and the origin of this "hidden" source of ICM metal enrichment.Comment: 22 pages, 24 figures; uses emulateapj.cls; moderate revisions
following referee feedback (now includes author's name!); now ApJ in pres
Origin and dynamics of emission line clouds in cooling flow environments
The author suggests that since clouds are born co-moving in a turbulent intra-cluster medium (ICM), the allowed parameter space can now be opened up to a more acceptable range. Large-scale motions can be driven in the central parts of cooling flows by a number of mechanisms including the motion of the central and other galaxies, and the dissipation of advected, focussed rotational and magnetic energy. In addition to the velocity width paradox, two other paradoxes (Heckman et al. 1989) can be solved if the ICM is turbulent. Firstly, the heating source for the emission line regions has always been puzzling - line luminosities are extremely high for a given (optical or radio) galaxy luminosity compared to those in non-cooling flow galaxies, therefore a mechanism peculiar to cooling flows must be at work. However most, if not all, previously suggested heating mechanisms either fail to provide enough ionization or give the wrong line ratios, or both. The kinetic energy in the turbulence provides a natural energy source if it can be efficiently converted to cloud heat. Researchers suggest that this can be done via magneto-hydrodynamic waves through plasma slip. Secondly, while the x ray observations indicate extended mass deposition, the optical line emission is more centrally concentrated. Since many of the turbulence-inducing mechanisms are strongest in the central regions of the ICM, so is the method of heating. In other words material is dropping out everywhere but only being lit up in the center
The Abundance Pattern in the Hot ISM of NGC 4472: Insights and Anomalies
Important clues to the chemical and dynamical history of elliptical galaxies
are encoded in the abundances of heavy elements in the X-ray emitting plasma.
We derive the hot ISM abundance pattern in inner and outer regions of NGC 4472
from analysis of Suzaku spectra, supported by analysis of co-spatial XMM-Newton
spectra. The low background and relatively sharp spectral resolution of the
Suzaku XIS detectors, combined with the high luminosity and temperature in NGC
4472, enable us to derive a particularly extensive abundance pattern that
encompasses O, Ne, Mg, Al, Si, S, Ar, Ca, Fe, and Ni in both regions. We apply
simple chemical evolution models to these data, and conclude that the
abundances are best explained by a combination of alpha-element enhanced
stellar mass loss and direct injection of Type Ia supernova (SNIa) ejecta. We
thus confirm the inference, based on optical data, that the stars in elliptical
galaxies have supersolar alpha/Fe ratios, but find that that the present-day
SNIa rate is 4-6 times lower than the standard value. We find SNIa yield sets
that reproduce Ca and Ar, or Ni, but not all three simultaneously. The low
abundance of O relative to Ne and Mg implies that standard core collapse
nucleosynthesis models overproduce O by a factor of 2.Comment: 37 pages, including 23 figures, uses aastex.cls; accepted for
publication in Ap
The hot interstellar medium in NGC 1399
The first two high signal-to-noise, broad bandpass x-ray spectra of elliptical galaxies were obtained with the Broad Band X-ray Telescope (BBXRT) as part of the December 1990 Astro mission. These observations provided unprecedented information on the thermal and metallicity structure of the hot interstellar media in two ellipticals: NGC 1399, the central galaxy in the Fornax cluster, and NGC 4472, the brightest galaxy in the Virgo cluster. The finalized analysis and interpretation of the approximately 4000 sec of BBXRT data on NGC 1399 is reported
Moduli dark matter and the search for its decay line using Suzaku X-ray telescope
Light scalar fields called moduli arise from a variety of different models
involving supersymmetry and/or string theory; thus their existence is a generic
prediction of leading theories for physics beyond the standard model. They also
present a formidable, long-standing problem for cosmology. We argue that an
anthropic solution to the moduli problem exists in the case of small moduli
masses, and that it automatically leads to dark matter in the form of moduli.
The recent discovery of the 125 GeV Higgs boson implies a lower bound on the
moduli mass of about a keV. This form of dark matter is consistent with the
observed properties of structure formation, and it is amenable to detection
with the help of X-ray telescopes. We present the results of a search for such
dark matter particles using spectra extracted from the first deep X-ray
observations of the Draco and Ursa Minor dwarf spheroidal galaxies, which are
dark matter dominated systems with extreme mass-to-light ratios and low
intrinsic backgrounds. No emission line is positively detected, and we set new
constraints on the relevant new physics.Comment: 8 pages, 5 figures, revte
Dark Matter Search Using XMM-Newton Observations of Willman 1
We report the results of a search for an emission line from radiatively
decaying dark matter in the ultra-faint dwarf spheroidal galaxy Willman 1 based
on analysis of spectra extracted from XMM-Newton X-ray Observatory data. The
observation follows up our analysis of Chandra data of Willman 1 that resulted
in line flux upper limits over the Chandra bandpass and evidence of a 2.5 keV
feature at a significance below the 99% confidence threshold used to define the
limits. The higher effective area of the XMM-Newton detectors, combined with
application of recently developing methods for extended-source analysis, allow
us to derive improved constraints on the combination of mass and mixing angle
of the sterile neutrino dark matter candidate. We do not confirm the Chandra
evidence for a 2.5 keV emission line.Comment: 23 pages, including 17 figures; accepted for publication in Ap
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