The Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function

Abstract

Astronomy & AstrophysicsThe Arches cluster out to its tidal radius: dynamical mass segregation and the effect of the extinction law on the stellar mass function , ABSTRACTThe Galactic center is the most active site of star formation in the Milky Way, where particularly high-mass stars have formed very recently and are still forming today. However, since we are looking at the Galactic center through the Galactic disk, knowledge of extinction is crucial when studying this region. The Arches cluster is a young, massive starburst cluster near the Galactic center. We observed the Arches cluster out to its tidal radius using K s -band imaging obtained with NAOS/CONICA at the VLT combined with Subaru/CISCO J-band data to gain a full understanding of the cluster mass distribution. We show that the determination of the mass of the most massive star in the Arches cluster, which had been used in previous studies to establish an upper mass limit for the star formation process in the Milky Way, strongly depends on the assumed slope of the extinction law. Assuming the two regimes of widely used infrared extinction laws, we show that the difference can reach up to 30% for individually derived stellar masses and ∆A Ks ∼ 1 magnitude in acquired K s -band extinction, while the present-day mass function slope changes by ∼0.17 dex. The presentday mass function slope derived assuming the more recent extinction law increases from a flat slope of α Nishi = −1.50 ± 0.35 in the core (r < 0.2 pc) to α Nishi = −2.21 ± 0.27 in the intermediate annulus (0.2 < r < 0.4 pc), where the Salpeter slope is -2.3. The mass function steepens to α Nishi = −3.21 ± 0.30 in the outer annulus (0.4 < r < 1.5 pc), indicating that the outer cluster region is depleted of high-mass stars. This picture is consistent with mass segregation owing to the dynamical evolution of the cluster.

The ATLASGAL survey: The sample of young massive cluster progenitors

“…Known (proto)clusters from the literature are labelled with magenta stars, as are the estimated initial clump mass at half-radius for the galactic (super) star clusters like the Orion Nebula Cluster (ONC, e.g. Da Rio et al 2012) and Arches (Habibi et al 2013), following Tan et al (2014). The approximate distance limit for detecting sources corresponding to cores, clumps, and cloud fragments is shown as a dotted line (Bergin & Tafalla 2007).…”

Circumstellar discs in Galactic centre clusters: Disc-bearing B-type stars in the Quintuplet and Arches clusters

“…Both clusters are host to a rich population of more than 100 massive O-and B-type stars (Liermann et al 2009;Martins et al 2008). From the extrapolation of the observed stellar mass function, they have estimated photometric masses of about 10 4 M (Habibi et al 2013;Hußmann et al 2012). According to dynamical simulations, the underlying stellar mass is suggested to be as high as 4 × 10 4 M for the Arches cluster (Harfst et al 2010).…”

Young stars in the Galactic center

“…They suggest that this is consistent with a cluster that was originally born with a "normal" and uniform IMF that subsequently evolved through mass-segregation into the present-day, radially-dependent mass function we observe today. Habibi et al (2013) show that the integrated mass above 1 M and within 0.4 pc extrapolated with a Salpeter IMF only slightly exceeds the dynamical mass reported by Clarkson et al (2012), when an updated radial density profile is used. However, including stars below 1 M with a "normal" mass-function (which breaks at 0.5 M ) may exceed the measured dynamical mass.…”

“…] or a "normal" index with a cut-off at relatively high masses (e.g., 2 M , bottom-light). However, recent results from Habibi et al (2013) covering a much larger cluster extent (but without proper motion membership selection) suggest that the mass-function powerlaw index steepens dramatically at larger radii. They suggest that this is consistent with a cluster that was originally born with a "normal" and uniform IMF that subsequently evolved through mass-segregation into the present-day, radially-dependent mass function we observe today.…”