F. Garzón

DENIS: A DEEP NEAR-INFRARED SURVEY OF THE SOUTHERN SKY

The DENIS project is the first attempt to carry out a complete digitized survey of the southern sky in the range 1–2.5µm. The main objectives of the programme and the main specifications of the camera and of the data processing stream are briefly outlined

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.

IR Star Counts in the Inner Disc

New small-scale JH star counts are presented for 4 regions on the plane between l=31° and l=15°.The colourmagnitude diagrams clearly show that there is a major giant branch at l=27° which is not present at l=31°. The distance to this feature is about 7.5 kpc with a total extinction of A V =7 mag. This giant branch is also seen at l=21° and l=15° and is consistent with there being a major bar at an angle of about 75° to the line of sight. At l=31° only features attributable to the disc can be seen and show that the extinction within the molecular ring is significantly higher than along the rest of the line of sight.

Search for star clustering: methodology and application to the Two Micron Galactic Survey

A new approach to the study of the large-scale stellar cluster distribution in the Galaxy based on two-point correlation techniques is presented. The basic formalism for this method is outlined and its applications are then investigated by the use of a simple model of cluster distribution in the Galaxy. This provides an estimate of the potentials of the two-point correlation function for indicating clustering in the measured star positions, which can be related to the presence of star clusters in the observed field. This technique is then applied to several areas of the Two Micron Galactic Survey catalogue, from which information is obtained on the distribution of clusters according to position in the Galaxy, as well as about age, density of stars, etc.

Galactic Bulge from TMGS Star Counts

The bulge of the Galaxy is analysed by inverting K-band star counts from the Two-Micron Galactic Survey in a number of off-plane regions. Assuming a non-variable luminosity function within the bulge, we derive the top end of the K-band luminosity function, which shows a sharp decrease brighter than M K = —8.0 when compared with the disc population, and the stellar density function, whose morphology is fitted to triaxial ellipsoids with the major axis in the plane at an angle with 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.

Sampling the Bar Population

The Two Micron Galactic Survey (TMGS, Garzon et al. 1993), has detected a large amount of bright sources on the Galactic plane at l = 27° (Fig. 1 left). This has been attributed to a star formation region at the end of the Galactic bar (Hammersley et al. 1994). This implies that a large number of intrinsically bright stars in K, super-giants and bright M giants, should be expected in this region. Their distance should be of about 6 kpc. Comparing the counts in this region with the neighboring ones, it can be seen that the number of bright sources detected at l = 27° should be of about 80–90% of the total. To confirm this the spectra of 51 bright TMGS sources were obtained.

The boxy bulge and stellar bar of the Milky Way

We describe the boxy bulge, long stellar bar and elliptical ring of the Galaxy. This model has largely evolved from NIR survey work by many teams and differs from other models with a monolithic ellipsoidal bulge. We maintain that the structure of the inner Galaxy can only be properly studied by adequately sampling the entire Galactic plane for |l| < 30◦, |b| < 1.5◦, and that the bulge is best studied at least 3◦ from the plane. We briefly report a slight radially outwardly increasing metallicity gradient along the bar and reaffirm de Vaucouleurs & Pence’s (1978) suggestion that the Galaxy is probably of morphological type SAB(rs)bc II.

A Method for Correcting Star Counts in Moderately Overcrowded Fields

An analytical method of correcting star counts is developed in order to eliminate the effects, to a first order approximation, of star crowding. Also, a comparison with a numerical simulation is performed which agrees with our method.

Galactic Structure and Morphology of the Milky Way from the TMGS

We discuss the Two Micron Galactic Survey, a project which has been running since 1989 at the IAC mapping extended areas of the Galactic plane and bulge with a dedicated IR camera. With the analysis made so far we can suggest the existence of a central Galactic bar, whose receding end is found at l = 27° and which is associated with a huge star formation region holding the one of most luminous IR star clusters in the Galaxy. Also the internal distribution of the stars on the plane shows that the vast majority of these belong to the young and old disc population and to a well defined internal bulge, with almost no stars found in the classical spherical distribution of the bulge, or few with high luminosity. The latter is compatible with a barred gravitational potential, which could scatter the stars from the central plane. Finally, two observational follow-up programmes dedicated to enlarging the spectral coverage and scope of the TMGS are outlined.

Extinction in the Direction of the End-of-Bar Star Formation Region

V RI CCD photometry of selected Two Micron Galactic Survey fields towards the end-of-bar star formation region between l = 18°, b = 0° and l = 27°, b = 0° has been carried out at the 1.0–m Jakobus Kapteyn Telescope on La Palma. The sources appear to be mainly G/K dwarfs at a heliocentric distance of typically 1.5 kpc with a total visible extinction (A V ) of between 2.4 and and 4.8 mag