Related papers: Low-mass X-ray binaries indicate a top-heavy stell…
We examine the cosmic evolution of a stellar initial mass function (IMF) in galaxies that varies with the Jeans mass in the interstellar medium, paying particular attention to the K-band stellar mass to light ratio (M/L_K) of present-epoch…
We present a new study of deep star counts in the Local Group dwarf spheroidal (dSph) in Ursa Minor. Both the luminosity function (LF) and the colour-magnitude diagram (CMD) of the unevolved stars are compared with the LF and CMD of the…
From a study of the integrated light properties of 200 globular clusters (GCs) in M31, Strader et al. found that the mass-to-light ratios are lower than what is expected from simple stellar population (SSP) models with a `canonical' stellar…
Observed variations in the IMF are reviewed with an emphasis on environmental density. The remote field IMF studied in the LMC by several authors is clearly steeper than most cluster IMFs, which have slopes close to the Salpeter value.…
High mass X-ray binaries (HMXBs) may have had a significant impact on the heating of the intergalactic medium in the early universe. Study of HMXBs in nearby, low metallicity galaxies that are local analogues to early galaxies can help us…
The luminosities of ultraluminous X-ray sources (ULXs) require an exotic solution with either super-critical accretion modes onto stellar mass black holes or sub-critical accretion onto intermediate mass black holes (IMBHs) being invoked.…
It is well established that the [alpha/Fe] ratios in elliptical galaxies increase with galaxy mass. This relation holds also for early-type dwarf galaxies, although it seems to steepen at low masses. The [alpha/Fe] vs. mass relation can be…
A universal stellar initial mass function (IMF) should not be expected from theoretical models of star formation, but little conclusive observational evidence for a variable IMF has been uncovered. In this paper, a parameterization of the…
Observations of the stellar initial mass function are reviewed. The flattening at low mass is evidence for a characteristic mass in star formation, which could be the minimum stellar mass for the onset of deuterium burning or the thermal…
Star formation in the early Universe has left its imprint on the chemistry of observable stars in galaxies. We derive elemental abundances and the slope of the low-mass end of the initial mass function (IMF) for a sample of 25 very massive…
Mass models for a sample of 18 late-type dwarf and low surface brightness galaxies show that in almost all cases the contribution of the stellar disks to the rotation curves can be scaled to explain most of the observed rotation curves out…
A thorough search for Ultraluminous X-ray source candidates within the Local Volume is made. The search spatially matches potential ULXs detected in X-ray images or cataloged in the literature with galaxies tabulated in the Catalog of…
The stellar initial mass function (IMF) seems to be variable and not universal, as argued in the literature in the last three decades. Several relations among the low-mass end of the IMF slope and other stellar population, photometric or…
Ultra-luminous X-ray sources (ULXs) are off-nuclear point sources in nearby galaxies with luminosities well exceeding the Eddington limit for stellar-mass objects. It has been recognized after the discovery of pulsating ULXs (PULXs) that a…
Theoretical models have had difficulty matching the observed number density of sub-millimeter galaxies (SMGs), causing some authors (e.g., Baugh et al. 2005) to suggest that SMGs provide evidence for a top-heavy initial mass function (IMF).…
We review recent advances in our understanding of the origin of the initial mass function (IMF). We emphasize the use of numerical simulations to investigate how each physical process involved in star formation affects the resulting IMF. We…
The X-ray emission from the faintest X-ray elliptical and S0 galaxies is characterized by a hard ~5 keV component, and a very soft ~0.2 keV component. The hard component has generally been regarded as the integrated emission from low mass…
Ultraluminous X-ray sources (ULXs) are bright extragalactic sources with X-ray luminosities above 10^39 erg/s powered by accretion onto compact objects. According to the first studies performed with XMM-Newton ULXs seemed to be excellent…
We analyse intermediate-resolution VLT FLAMES/Giraffe spectra of six ultra-compact dwarf (UCD) galaxies in the Fornax cluster. We obtained velocity dispersions and stellar population properties by full spectral fitting against PEGASE.HR…
Strong gravitational lensing can provide accurate measurements of the stellar mass-to-light ratio $\Upsilon$ in low-redshift ($z$ $\lesssim$ 0.05) early-type galaxies, and hence probe for possible variations in the stellar initial mass…