AN EXTREMELY TOP-HEAVY INITIAL MASS FUNCTION IN THE GALACTIC CENTER STELLAR DISKS

By H. Bartko, Fabrice Martins, S. Trippe, T. Fritz, R. Genzel, T. Ott, F. Eisenhauer, S. Gillessen, T. Paumard, T. Alexander and 12 more. 2009

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We present new observations of the nuclear star cluster in the central parsec of the Galaxy with the adaptive optics assisted, integral field spectrograph SINFONI on the ESO/VLT. Our work allows the spectroscopic detection of early- and late-type stars to mK ⩾ 16, more than 2 mag deeper than our previous data sets. Our observations result in a total sample of 177 bona fide early-type stars. We find that most of these Wolf Rayet (WR), O-, and B-stars reside in two strongly warped disks between 0.″8 and 12″ from Sgr A*, as well as a central compact concentration (the S-star cluster) centered on Sgr A*. The later type B-stars (mK>15) in the radial interval between 0.″8 and 12″ seem to be in a more isotropic distribution outside the disks. The observed dearth of late-type stars in the central few arcseconds is puzzling, even when allowing for stellar collisions. The stellar mass function of the disk stars is extremely top heavy with a best-fit power law of dN/dm ∝ m−0.45± 0.3. WR/O-stars were formed in situ in a single star formation event ∼6 Myr ago, this mass function probably reflects the initial mass function (IMF). The mass functions of the S-stars inside 0.″8 and of the early-type stars at distances beyond 12″ are compatible with a standard Salpeter/Kroupa IMF (best-fit power law of dN/dm ∝ m−2.15± 0.3).

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/f7eb5a907dd983bb8fd497d9fb1f62945753746f

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Citations in the corpus

PS1-10jh: THE DISRUPTION OF A MAIN-SEQUENCE STAR OF NEAR-SOLAR COMPOSITION (2013, background): “While there is some evidence that the mass function around SMBHs is not well-represented by a canonical IMF (Bartko et al. 2010), it seems unlikely that the numbers of these stars could be increased by the factor of∼104–107 required to plausibly explain why the first well-resolved TDE happened to be”
Greatly Enhanced Merger Rates of Compact-object Binaries in Non-spherical Nuclear Star Clusters (2017, background): “Spectroscopic studies of the Galactic center reveal a population of ≈ 200 very massive early-type stars, including Wolf-Rayet stars and O and B type main-sequence stars, giants, and supergiants (e.g., Bartko et al. 2010; Yelda et al. 2014).”
The old Nuclear Star Cluster in the Milky Way (2014, result): “In contrast, observations by Do et al. (2009); Buchholz et al. (2009); Bartko et al. (2010) show that the distribution of old stars near the SMBH appears to have a core.”
Star formation rates and efficiencies in the Galactic Centre (2017, result): “The three caveats which may affect our measurement of the embedded stellar population mass are the MNRAS 469, 2263–2285 (2017) choice of the IMF, the sampling of the IMF and the upper mass limit of the IMF (i.e. the maximum stellar mass of the population), and are discussed below.”
Assisted inspirals of stellar mass black holes embedded in AGN discs: solving the ‘final au problem’ (2016, result): “(Bartko et al. 2010) - may be consistent with the observed population.”
SECULAR EVOLUTION OF COMPACT BINARIES NEAR MASSIVE BLACK HOLES: GRAVITATIONAL WAVE SOURCES AND OTHER EXOTICA (2012, background): “…two different values: γ = 0.5, representative of the observed distribution of stars at the Galactic center (Buchholz et al. 2009; Do et al. 2009; Bartko et al. 2010), and γ = 1.8 corresponding approximately to a nearly-relaxed configuration of stars near a dominating point-mass potential…”
On the rate of black hole binary mergers in galactic nuclei due to dynamical hardening (2017, background): “Within the core of the MW nuclear star cluster (NSC), of order a hundred OB stars rotate clockwise on the sky in a strongly warped disk ∼ 0.04- 0.6 pc from the SMBH (e.g. Levin & Beloborodov 2003; Lu et al. 2009; Bartko et al. 2010; Baruteau et al. 2011; Yelda et al. 2014; Chen & Amaro-Seoane 2015).”
A study of the gas–star formation relation over cosmic time (2010, background): “, other than in the immediate vicinity of the black hole in the Galactic Centre (Bartko et al. 2010), that significantly top-heavy IMFs are found under physical conditions similar to major mergers (Bastian, Covey & Meyer 2010).”
STELLAR POPULATIONS IN THE CENTRAL 0.5 pc OF THE GALAXY. II. THE INITIAL MASS FUNCTION (2013, background): “…for a possible warp in the clockwise disk (Bartko et al. 2009), a second face-on disk made of counter-clockwise rotating stars (Genzel et al. 2003; Bartko et al. 2009), and for subclusters of stars both on and off the disk (Maillard et al. 2004; Schödel et al. 2005; Lu et al. 2005), although the…”
Eccentric Black Hole Gravitational-wave Capture Sources in Galactic Nuclei: Distribution of Binary Parameters (2017, background): “26 This assumption is consistent with most of the supersolar-mass stars in the Galactic center with lifetimes higher than 107 years (Bartko et al. 2010), and we ignore the dynamical contributions of shorter-lived massive stars.”
Finite, Intense Accretion Bursts from Tidal Disruption of Stars on Bound Orbits (2012, background): “Theoretical calculations indicate this rate to be ∼ 10−4 − 10−6 yr−1 for Milky Way-like galaxies, and that the peak flux into the loss cone comes from parsec scales.”
Quantifying the effect of baryon physics on weak lensing tomography (2011, background): “There are both observational and and theoretical arguments to support a top-heavy IMF in those extreme conditions (e.g. Padoan et al. 1997; Baugh et al. 2005; Klessen et al. 2007; Maness et al. 2007; Dabringhausen et al. 2009; Bartko et al. 2010; Weidner et al. 2010).”
The stellar and sub-stellar IMF of simple and composite populations (2011, unknown): “(Bartko et al. 2010).”
Surface brightness profile of the Milky Way’s nuclear star cluster (2014, methodology): “…dynamics (e.g., Alexander 2006; Merritt 2006; Preto & Amaro-Seoane 2010), the distribution of the old – and therefore dynamically relaxed – stars within 0.5 pc of Sgr A* is significantly flatter than predicted by theory (Buchholz et al. 2009; Do et al. 2009; Bartko et al. 2010; Do et al. 2013).”
The effects of galaxy formation on the matter power spectrum: a challenge for precision cosmology (2011, background): “It is expected that the IMF is top-heavy at high redshift and low metallicity (e.g. Larson 1998), and both observations and theory suggest that it may be top-heavy in extreme environments like the galactic centre and starburst galaxies (e.g. Baugh et al. 2005; Bartko et al. 2010).”
Nuclear star clusters (2009, background): “5 pc (Allen et al. 1990; Krabbe et al. 1991; Ghez et al. 2003; Bartko et al. 2010; Pfuhl et al. 2011; Feldmeier-Krause et al. 2015).”