Two-Micron Galactic Survey Research Articles

Inversion of stellar statistics equation for the Galactic bulge

A method based on Lucy's iterative algorithm is developed to invert the equation of stellar statistics for the Galactic bulge and is then applied to the K-band star counts from the Two-Micron Galactic Survey in a number of off-plane regions (10°>|b|>2°, |l|<15°). The top end of the K-band luminosity function is derived and the morphology of the stellar density function is fitted to triaxial ellipsoids, assuming a non-variable luminosity function within the bulge. The results, which have already been outlined by López-Corredoira et al., are shown in this paper with a full explanation of the steps of the inversion: the luminosity function shows a sharp decrease brighter than MK=−8.0 mag when compared with the disc population; the bulge fits triaxial ellipsoids with the major axis in the Galactic plane at an angle with the line of sight to the Galactic centre of 12° in the first quadrant; the axial ratios are 1:0.54:0.33, and the distance of the Sun from the centre of the triaxial ellipsoid is 7860 pc. The major-minor axial ratio of the ellipsoids is found not to be constant, the best fit to the gradient being Kz=(8.4±1.7)×exp(−t/(2000±920) pc), where t is the distance along the major axis of the ellipsoid in parsecs. However, the interpretation of this is controversial. An eccentricity of the true density-ellipsoid gradient and a population gradient are two possible explanations. The best fit for the stellar density, for 1300 pc<t<3000 pc, is calculated for both cases, assuming an ellipsoidal distribution with constant axial ratios, and when Kz is allowed to vary. From these, the total number of bulge stars is ∼3×1010 or ∼4×1010, respectively.

A Major Star Formation Region in the Receding Tip of the Stellar Galactic Bar

We present an analysis of the optical spectroscopy of 58 stars in the Galactic plane at l=27°, where a prominent excess in the flux distribution and star counts have been observed in several spectral regions, in particular in the Two-Micron Galactic Survey (TMGS) catalog. The sources were selected from the TMGS to have a K magnitude brighter than +5 mag and to be within 2° of the Galactic plane. More than 60% of the spectra correspond to stars of luminosity class I, and a significant proportion of the remainder are very late and fast-evolving giants. This very high concentration of young sources points to the existence of a major star formation region in the Galactic plane, located just inside the assumed origin of the Scutum spiral arm. Such regions can form because of the concentrations of shocked gas where a galactic bar meets a spiral arm, as is observed at the ends of the bars of face-on external galaxies. Thus, the presence of a massive star formation region is very strong supporting evidence for the presence of a bar in our Galaxy.

A two-micron Galactic survey

The first results are presented here of the Two-Micron Galactic Survey (TMGS). The TMGS is the most sensitive near-infrared survey of the Galactic plane yet attempted on a large scale. The Galactic plane has been drift-scanned in several regions over the areas −5° < l < 30°, |b| ≤ 15° and 30° < l < 180°, |b| ≤ 5°. The discussion in this paper concentrates mainly on three extensively mapped areas centred on δ = −1°, −23° and −30°, covering a total of 138 deg 2 of sky. The survey is complete in the areas covered to magnitude m K ≃ + 9.8 mag. So far, a total area of 255 deg 2 has been mapped and 470 000 objects have been detected, the majority of these in the Galactic plane and with no known visible counterparts

Cross-correlation of the two micron galactic survey with IRAS

The Two Micron Galactic Survey (TMGS) is described by Calbet et al. (this symposium) and Mahoney et al. (1990). It has been cross-correlated with the IRAS point source catalogue (IRPS) using a 15-arcsec search radius, and preliminary results are presented here.

Preliminary results of the two micron galactic survey

We present the first results of the Two-Micron Galactic Survey (TMGS). The sources are concentrated on the Galactic plane, the width of the distribution increasing between 0° and 30° longitude. Several obscuration lanes are seen, showing that K-band absorption can be high and patchy.