A rich nearby cluster in Sagittarius

Abstract

In a series of ESO Messenger and Comptes Rendu papers (1978 - 1985), Terzan, Bernard, and Ju discovered some 45 diffuse objects in the general direction of the Galactic Bulge, viz., Sagittarius bright cloud B, α range 17^h04^m – 17^h42^m, δ range -24° to -33°. This region, centered near 1_(II) ~358°, b_(II) ~ +7°, has a patchy, but obviously very heavy extinction (we estimate A_v > 3^m – 4^m). These TBJ objects are a mixed bag; in the discovery papers, some were tentatively classified as galaxies, some as possible globular clusters, others as planetary nebulae. During an imaging search for obscured globular clusters, one of us (SGD) obtained images of 14 of them. Out of those, two turned out to be probable globular clusters (TJ 5 and TJ 23), one planetary nebula. (TBJ 41), and the rest were obviously galaxies. A dozen of the remaining objects may be classified as galaxies from their appearance on the SRC/I sky survey films. The magnitudes of detected galaxies are typically in the range R ~17^m – 18^m, within 10 - 20 arcsec apertures (the measurements are difficult and still very preliminary, because of the heavy stellar foreground). The occurrence of so many background galaxies in a. relatively small and heavily obscured area is remarkable. These objects must be luminous ellipticals and/or bright S0 or Sp bulges: anything with a lower surface brightness would not be detected through the heavy extinction and foreground. (None of the TBJ galaxies and possible galaxies a.re detected in the IRAS PSC, which corroborates their identification as early types.) Thus, this concentration of galaxies must be just the very tip of an iceberg. Terzan et al. apparently discovered a major rich cluster, hidden behind the Galactic Bulge, in the heart of "zone of avoidance".

Files

Additional details