The interplay between star formation and the nuclear environment of our Galaxy: deep X-ray observations of the Galactic centre Arches and Quintuplet clusters

Abstract

The Galactic centre (GC) provides a unique laboratory for a detailed examination of the interplay between massive star formation and the nuclear environment of our Galaxy. Here, we present a 100‐ks Chandra Advanced CCD Imaging Spectrometer (ACIS) observation of the Arches and Quintuplet star clusters. We also report on a complementary mapping of the dense molecular gas near the Arches cluster made with the Owens Valley Millimeter Array. We present a catalogue of 244 point‐like X‐ray sources detected in the observation. Their number–flux relation indicates an overpopulation of relatively bright X‐ray sources, which are apparently associated with the clusters. The sources in the core of the Arches and Quintuplet clusters are most likely extreme colliding wind massive star binaries. The diffuse X‐ray emission from the core of the Arches cluster has a spectrum showing a 6.7‐keV emission line and a surface intensity profile declining steeply with radius, indicating an origin in a cluster wind. In the outer regions near the Arches cluster, the overall diffuse X‐ray enhancement demonstrates a bow shock morphology and is prominent in the Fe Kα 6.4‐keV line emission with an equivalent width of ∼1.4 keV. Much of this enhancement may result from an ongoing collision between the cluster and the adjacent molecular cloud, which have a relative velocity ≳120 km−1. The older and less‐compact Quintuplet cluster contains much weaker X‐ray sources and diffuse emission, probably originating from low‐mass stellar objects as well as a cluster wind. However, the overall population of these objects, constrained by the observed total diffuse X‐ray luminosities, is substantially smaller than expected for both clusters, if they have normal Miller & Scalo initial mass functions. This deficiency of low‐mass objects may be a manifestation of the unique star formation environment of the GC, where high‐velocity cloud–cloud and cloud–cluster collisions are frequent.

Nonthermal particles and photons in starburst regions and superbubbles

“…Apart from the thermal diffuse emission coming from optically thin plasma at temperatures ∼ 2 keV, non-thermal X-ray emission with relatively hard photon spectral index Γ ∼ 1.4 and prominent Fe 6.4 keV K-shell line emission was revealed with a 100 ks long Chandra observation by (Wang et al 2006) at the sub-arcminute large South-Eastern extension of the Arches cluster. The lightcurves of the Fe Kshell line emission from three bright molecular knots around the Arches cluster were found by Capelli et al (2011) to be constant over 8 years of XMM-Newton ob- servations.…”

A HIGH-RESOLUTION SURVEY OF H I ABSORPTION TOWARD THE CENTRAL 200 pc OF THE GALACTIC CENTER

“…In addition to the Radio Arc region (where the Quintuplet and Arches clusters are located), the GC region is filled with sites where compact thermal radio and midinfrared sources have been observed (e.g., Sgr B, Sgr C, and at many positions along the Galactic plane; e.g., LaRosa et al 2000;Egan et al 1998) and it is likely that massive stars are either forming or have formed in these regions. In addition, the spectrum of diffuse X-ray emission in this region suggests that the ISM is being strongly influenced by massive star-forming activities (Wang et al 2002(Wang et al , 2006.…”

Discovery of X-ray flaring activity in the Arches cluster

“…The X-ray diffuse emission from the AC has been investigated in a number of published papers over the last decade (i.e. Yusef-Zadeh et al 2002;Wang et al 2006;Tsujimoto et al 2007). All these studies confirm the co-existence in the cluster of both thermal and non-thermal radiation.…”