First results from a large-scale proper motion study of the Galactic centre

Abstract

Proper motion studies of stars in the centre of the Milky Way have been typically limited to the Arches and Quintuplet clusters and to the central parsec. Here, we present the first results of a large-scale proper motion study of stars within several tens of parsecs of Sagittarius A* based on our 0.2 angular resolution GALACTICNUCLEUS survey (epoch 2015) combined with NICMOS/HST data from the Paschen-α survey (epoch 2008). This study will be the first extensive proper motion study of the central ∼ 36 × 16 of the Galaxy, which is not covered adequately by any of the existing astronomical surveys such as Gaia because of its extreme interstellar extinction (AV 30 mag). Proper motions can help us to disentangle the different stellar populations along the line-of-sight and interpret their properties in combination with multi-wavelength photometry from GALACTICNUCLEUS and other sources. It also allows us to infer the dynamics and interrelationship between the different stellar components (Galactic bulge, nuclear stellar disk, nuclear stellar cluster) of the Galactic Centre (GC). In particular, we use proper motions to detect co-moving groups of stars which can trace low mass or partially dissolved young clusters in the GC that can hardly be discovered by any other means. Our pilot study in this work is on a field in the nuclear bulge associated by HII regions that show the presence of young stars. We detect the first group of co-moving stars coincident with an HII region. Using colour-magnitude diagrams, we infer that the co-moving stars are consistent with being the post-main sequence stars with ages of few Myrs. Simulations show that this group of stars is a real group that can indicate the existence of a dissolving or low to intermediate mass young cluster. A census of these undiscovered clusters will ultimately help us to constrain star formation at the GC in the past few ten Myrs.

The Spiral Structure in the Solar Neighborhood

“…HII regions are the regions of ionized gas surrounding recently formed O or early B-type stars or star clusters. They have been widely detected in the Galactic disk, from the Galactic center (GC) region (Shahzamanian et al, 2019) to the far outer Galaxy (Galactocentric distances > 16 kpc, Anderson et al, 2015). As indicators of the early evolutionary stage of massive stars, HII regions have long been known as one of the primary tracers of spiral arms, and helped us to construct the commonly used picture of the Galaxy's spiral structure (e.g., Georgelin and Georgelin, 1976;Caswell and Haynes, 1987;Russeil, 2003;Hou et al, 2009;Hou and Han, 2014).…”

Constraining the population of isolated massive stars within the Central Molecular Zone

“…Of the remaining four stars only P35 and P114 have been subject to further examination; the radial velocity of the former suggests that it is a runaway, while the latter appears to have formed formed in situ (and is possibly associated with a stellar overdensity; Dong et al 2017). This implies that P35 and 114 are not part of a bound physical system; although in this regard it is interesting that P35 appears to be a member of a small group of co-moving stars, possibly the remnant of a disrupted cluster (Shahzamanian et al 2019). Given the limitations of the current analysis no further conclusions may be drawn as to the relationship of either P36 or P111 to these stars.…”

A proper motion catalogue for the Milky Way's nuclear stellar disc

“…The nuclear star cluster, the Quintuplet, and the Arches cluster are also marked. co-moving groups (e.g., Stolte et al 2008;Hosek et al 2015;Rui et al 2019a;Shahzamanian et al 2019a).…”

“…In this work we combine the 2008 H-PαS with the 2015 GNS to obtain the first proper motion catalogue for the central ∼ 36 × 15 of the NSD. We have already demonstrated this method on a small field and identified a new co-moving group in Shahzamanian et al (2019a). This This paper is structured as follows.…”