No abstract

We use a large sample of galaxies from the Two Micron All Sky Survey (2MASS) and the Sloan Digital Sky Survey (SDSS) to calculate galaxy luminosity and stellar mass functions in the local universe. We estimate corrections for passband shifting and galaxy evolution, as well as present-day stellar mass-to-light (M/L) ratios, by fitting the optical-near-infrared galaxy data with simple models. Accounting for the 8% galaxy overdensity in the SDSS early data release region, the optical and near-infrared luminosity functions we construct for this sample agree with most recent literature optical and near-infrared determinations within the uncertainties. We argue that 2MASS is biased against low surface brightness galaxies and use SDSS plus our knowledge of stellar populations to estimate the '' true '' K-band luminosity function. This has a steeper faint end slope and a slightly higher overall luminosity density than the direct estimate. Furthermore, assuming a universally applicable stellar initial mass function (IMF), we find good agreement between the stellar mass function we derive from the 2MASS/SDSS data and that derived by Cole et al. The faint end slope for the stellar mass function is steeper than À1.1, reflecting the low stellar M/L ratios characteristic of low-mass galaxies. We estimate an upper limit to the stellar mass density in the local universe à h ¼ 2:0 AE 0:6  10 À3 by assuming an IMF as rich in low-mass stars as allowed by observations of galaxy dynamics in the local universe. The stellar mass density may be lower than this value if a different IMF with fewer low-mass stars is assumed. Finally, we examine type-dependence in the optical and near-infrared luminosity functions and the stellar mass function. In agreement with previous work, we find that the characteristic luminosity or mass of early-type galaxies is larger than for later types, and the faint end slope is steeper for later types than for earlier types. Accounting for typing uncertainties, we estimate that at least half, and perhaps as much as 3/4, of the stellar mass in the universe is in early-type galaxies. As an aid to workers in the field, we present in an Appendix the relationship between model stellar M/L ratios and colors in SDSS/2MASS passbands, an updated discussion of near-infrared stellar M/L ratio estimates, and the volume-corrected distribution of g-and K-band stellar M/L ratios as a function of stellar mass.

We present the first all-sky view of the Sagittarius (Sgr) dwarf galaxy mapped by M giant star tracers detected in the complete Two Micron All-Sky Survey (2MASS).Near infrared photometry of Sgr's prominent M giant population permits an unprecedentedly clear view of the center of Sgr. The main body is fit with a King profile of limiting major axis radius 30 • -substantially larger than previously found or assumed -beyond which is a prominent break in the density profile from stars in its tidal tails; thus the Sgr radial profile resembles that of Galactic dSph satellites. Adopting traditional methods for analyzing dSph light profiles, we determine the brightness of the main body of Sgr to be M V = −13.27 (the brightest of the known Galactic dSph galaxies) and the total Sgr mass-to-light ratio to be 25 in solar units. However, we regard the latter result with suspicion and argue that much of the observed structure beyond the King fit core radius (224 arcmin) may be outside the actual Sgr tidal radius as the former dwarf spiral/irregular satellite undergoes catastrophic disruption over its past last orbit. The M giant distribution of Sgr exhibits a central density cusp at the same location as, but not due to, the old stars constituting the globular cluster M54.A striking trailing tidal tail is found to extend from the Sgr center and arc across the South Galactic Hemisphere with approximately constant density and mean distance varying from ∼ 20−40 kpc. A prominent leading debris arm extends from the Sgr center northward of the Galactic plane to an apoGalacticon ∼ 45 kpc from the Sun, then turns towards the North Galactic Cap (NGC) from where it descends back towards the Galactic plane, becomes foreshortened and at brighter magnitudes covers the NGC. The leading and trailing Sgr tails lie along a well-defined orbital plane about the Galactic Center. The Sun lies within a kiloparsec of that plane and near the path of leading Sgr debris; thus, it is possible that former Sgr stars are near or in the solar neighborhood.We discuss the implications of this new view of the Sgr galaxy and its entrails for the character of the Sgr orbit, mass, mass-loss rate, and contribution of stars to the Milky Way halo. The minimal precession displayed by the Sgr tidal debris along its inclinded orbit supports the notion of a nearly spherical Galactic potential. The number of M -2giants in the Sgr tails is at least 15% that contained within the King limiting radius of the main Sgr body. The fact that M giants, presumably formed within the past few gigayears in the Sgr nucleus, are nevertheless so widespread along the Sgr tidal arms not only places limits on the dynamical age of these arms but poses a timing problem that bears on the recent binding energy of the Sgr core and that is most naturally explained by recent and catastrophic mass loss. Sgr appears to contribute more than 75% of the high latitude, halo M giants, despite substantial reservoirs of M giants in the Magellanic Clouds. No evidence of extended M giant tidal debris from the ...

No abstract

Recent observations have shown that globular clusters contain a significant binary population. This is a dramatic change from the conventional view of even a decade ago, which held that globular clusters formed without any binaries at all, since the observed X-ray binaries were understood to be formed through dynamical capture. Over the last few years, a number of different observational techniques have resulted in the detection of a substantial number of binaries most of which are believed to be primordial. When the many selection effects are taken into account, these detections translate into a binary abundance in globular clusters that may be somewhat smaller than those in the Galactic disk and halo, but not by a large factor. Within the current uncertainties, it is even possible that the primordial binary abundance in globular clusters is comparable to that in the Galactic disk. We discuss different successful optical search techniques, based on radial-velocity variables, photometric variables, and the positions of stars in the color-magnitude diagram. In addition, we review searches in other wavelengths, which have turned up low-mass X-ray binaries and more recently a variety of radio 981

No abstract

No abstract

No abstract