EVIDENCE FOR WARPED DISKS OF YOUNG STARS IN THE GALACTIC CENTER

“The quantity p(χ2, 1) = 1 − Erf( √ χ2/2) denotes the probability to observe by chance a value of χ2 or larger, even for a correct model (Yao et al. 2006).”

“At a distance of about 8 kpc (Eisenhauer et al. 2003b; Gillessen et al. 2009; Ghez et al. 2008; Gronewegen et al. 2008; Trippe et al. 2008), processes in the GC can be studied at much higher resolution compared to any other galactic nucleus.”

“We define the significance for each bin of the sky map as (see Equation (10a) of Li & Ma 1983): significance = observed density − mean density of isotropic stars rms density of isotropic stars .”

“It is associated with the compact radio source Sgr A*, which must be a massive black hole, beyond any reasonable doubt (Schödel et al. 2002; Ghez et al. 2005; Gillessen et al. 2009).”

“It is also interesting to note a well known example of another warped nuclear disk surrounding a supermassive black hole in another galaxy; the maser disk observation of NGC 4258 (Miyoshi et al. 1995; Herrnstein et al. 1996).”

“For each star we assigned effective temperatures derived from spectral types using the effective temperature scales of Martins et al. (2005) for O stars and Crowther et al. (2006) for B supergiants.”

“The Galactic center (GC) is a uniquely accessible laboratory for studying the properties and evolution of galactic nuclei (for reviews, see, e.g., Genzel & Townes 1987; Morris & Serabyn 1996; Mezger et al. 1996; Alexander 2005).”

“R) stars (Forrest et al. 1987; Allen et al. 1990; Krabbe et al. 1991; Najarro et al. 1994; Krabbe et al. 1995; Blum et al. 1995; Tamblyn et al. 1996; Najarro et al. 1997; Genzel et al. 2003; Ghez et al. 2003; Paumard et al. 2006; Martins et al. 2007) with an estimated age of about 6×106 years.”

“…(Krabbe et al. 1995), including massive young stars in one and possibly two disks with diameters of 1– 2 arcmin rotating around the SMBH (Paumard et al. 2006, Bartko et al. 2009) and a remarkable concentration of B stars within 1 arcsec of the SMBH, the so-called S stars (Eckart et al. 1995).”

“In situ star formation from dense gas accretion disks is favored over the inspiraling star cluster scenario (see e.g. Bartko et al. 2009).”

“…both observations and theory suggest that it is top-heavy in extreme environments like the Galactic Centre and starburst galaxies (e.g. Padoan, Nordlund & Jones 1997; Baugh et al. 2005; Klessen, Spaans & Jappsen 2007; Maness et al. 2007; Bartko et al. 2009; Dabringhausen, Kroupa & Baumgardt 2009).”

“To estimate the number of binaries crossing the accretion disk of radius Rdisk, we assume that the orbital eccentricity of the CoM of the binary is drawn from an isotropic thermal distribution with f (e) = 12 e and a strongly mass segregated number density n(a) ∝ a−2.5, which is also consistent with the massive O star…”

“This is in perfect agreement with what Bartko et al. (2009) and Yelda et al. (2014) find.”

“Interestingly this common orbit shows a similar orientation and angular momentum direction as the clockwise stellar disk and the G2 object (Ω ≈ 99◦, i ≈ 129◦, Bartko et al. 2009; Genzel et al. 2010; Gillessen et al. 2012; Pfuhl et al. 2015; Plewa et al. 2017).”

“Paumard et al. (2006) and Bartko et al. (2009) find evidence for a counter-clockwise structure, perhaps a second disk in a dissolving state.”

“…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…”

“Bottom panel: Distribution of EKL-induced mergers and GWonly mergers for merger time versus . the disk of massive stars (Bartko et al. 2009; Lu et al. 2009).”

“We use only stars which have been spectroscopically identified as early-type (Paumard et al. 2006; Bartko et al. 2009).”

“The young stars are arranged in a non-isotropic pattern and at least 50% of them are located in a rotating disk (see Bartko et al. 2009; Lu et al. 2009). ar X iv :0 91 2.”

“About 50% of the few million-year-old stars in the central parsec of the GC do not form part of the clockwise disc and appear to be distributed in a more isotropic way - or form part of a less-well defined disc/streamer (Bartko et al. 2009; Lu et al. 2009).”

“If they do exist, they likely formed from a relatively recent episode of star formation, which there is plenty of observational evidence to support (Bartko et al. 2009).”

“For example, Bartko et al. (2009) reported a bimodal eccentricity distribution for the disk, which is difficult to explain dynamically.”

“…al. 2008) and a nuclear star cluster (MNSC ∼ 3 × 107 M⊙ Genzel et al. 1996; Schödel et al. 2007; Trippe et al. 2008) that contains stars of many ages and in different substructures including disks of young stars in the immediate vicinity of the black hole (e.g. Lu et al. 2009; Bartko et al. 2009).”

“There exists tentative evidence for a secondary counterclockwise disk made up of stars similar in their photometric, spectroscopic and kinematic properties (e.g. Paumard et al. 2006; Bartko et al. 2009).”

“…of the supermassive black hole and studies of its surrounding stellar population (e.g., Eckart & Genzel 1997; Ghez et al. 1998, 2005; Genzel et al. 2003; Paumard et al. 2006; Stolte et al. 2008; Bartko et al. 2009; Lu et al. 2009; Clarkson et al. 2012; Meyer et al. 2012; Yelda et al. 2014).”

“It is possible that a Bahcall–Wolf cusp is present but that the stellar luminosity function changes inside ∼0.5 pc, such that the brightest stars are missing (Buchholz et al. 2009; Do et al. 2009; Bartko et al. 2009b).”

“(Bartko et al. 2009; Lu et al. 2009) provides compelling indications that star formation can occur in-situ in a circumnuclear disk.”

“We followed the method of Bartko et al. (2009), who used statistical arguments to infer the 3D distribution of a stellar population out of the 3D velocity and projected distance distribution.”

“In the Milky Way’s center, the distribution of massive young stars does not represent such a relaxed profile, but forms a clockwise disk structure with a number density distribution n(r)∼r−2.9, which is steeper than the model assumed in (Bartko et al. 2009; Yelda et al. 2014).”

“Proper motions and radial velocities are available for most of these stars (Bartko et al. 2009).”

“…et al. 2003; Pfuhl et al. 2011), but in the central ∼0.5 pc there exists an additional stellar component in the form of hot, young stars (4−8 Myr e.g. Paumard et al. 2006; Lu et al. 2009; Bartko et al. 2009), and stars of intermediate age (∼ 100 Myr, e.g. Krabbe et al. 1995; Pfuhl et al. 2011).”

“Although unusual, we can not rule out that such a top-heavy IMF might exist in the center of NGC 1266, given the likely presence of a top-heavy IMF in the center of the Milky Way (Maness et al. 2007; Bartko et al. 2009).”

“…approximately 10′′×7.2′′ east of the survey reported in Do (2010), along the major axis of the projected disk plane of the clockwise disk of young stars at a PA of 105 degrees, as measured by Lu et al. (2009) (see also Levin & Beloborodov 2003; Paumard et al. 2006; Bartko et al. 2009; Yelda 2012).”

“A major outburst might also have occurred as a by-product of the event that formed the ∼100 massive, young O- and Wolf–Rayet stars that have been found within the central 0.1 pc (Genzel et al. 2003; Ghez et al. 2005; Bartko et al. 2009).”

“There is observational evidence for the existence of a second, less massive counter-clockwise disk comprising stars with similar age and kinematic properties as in the clockwise disk (Paumard et al. 2006; Bartko et al. 2009, 2010).”

“Furthermore, the cluster of stars around Sgr A∗ is known to have substructure in the form of a coherently rotating small disc of young stars (the so-called clock-wise or CW disc) (Levin & Beloborodov 2003; Paumard et al. 2006; Bartko et al. 2009; Yelda et al. 2014; Gillessen et al. 2017).”

“Between 20% to 50% of the young WR/O stars lie in a warped, clockwise rotating disk at radii 1′′ < r < 12′′ (Paumard et al. 2006; Bartko et al. 2009; Lu et al. 2009; Yelda et al. 2014).”

“It was noted by Levin & Beloborodov (2003) (and later confirmed by Beloborodov et al. 2006; Lu et al. 2009; Bartko et al. 2009), however, that the velocities of some of the stars lie within a thin planar structure, which allowed them to perform a likelihood analysis to precisely determine the…”

“Interestingly, the allowed region of orbital orientations is broadly consistent with those of the stars in the clockwise stellar disk, as marked by the black cross in the figure (Gillessen et al. 2017, see also Bartko et al. 2009; Yelda et al. 2014).”

“The stellar surface density is predicted to scale as −R 2 (Lin and Pringle 1987, Levin 2007), consistent with observations within the CW disk plane (Paumard et al 2006, Lu et al 2009, Bartko et al 2009).”

“Levin (2007) suggested that the S-stars could have formed in the currently observed stellar disk in the GC (Bartko et al. 2009; Lu et al. 2009), and then migrated inward in a way similar to planetary migration.”

“»M 10disk 4– M105 extending to a distance of »R 0.4 pcdisk , of which only roughly M103 would have resulted in stars, with the remainder accreting onto SgrA* over the past10 year6 (Levin 2007; Bartko et al. 2009).”

“Only in the center (r» 0.4 pc) is the light dominated by 6Myr old stars (Forrest et al. 1987; Krabbe et al. 1991; Paumard et al. 2006; Bartko et al. 2009) with a topheavy IMF (Bartko et al. 2010; Lu et al. 2013).”

“We compared our radial velocity measurements with the data of Bartko et al. (2009) and Yelda et al. (2014).”

“…young stars orbiting the central black hole at ∼0.05 - 2 pc (Genzel et al. – 10 – – 11 – 2000; Levin & Beloborodov 2003; Paumard et al. 2006; Lu et al. 2009; Bartko et al. 2009; Yelda et al. in prep) which has been suggested as the possible origin of the gas cloud through colliding stellar winds…”

“One population, mainly O giants/supergiants and WR stars, is observed to have a disk-like structure extending from 0.5 pc inward to within 0.05 pc of the MBH (Bartko et al. 2009; Lu et al. 2013).”

“Another difference to the Keck-based work is that our new Brackett-γ based orbit continues to be coplanar with the clockwise stellar disk: It is 20° tilted with respect to the best fitting inner disk of Bartko et al. (2009), and 16° with respect to the disk orientation of Lu et al. (2009).”

“…the emission from Sgr A* is coming from the footpoints of a MAD-type jet, this is inconsistent with the orientations of the Li et al. (2013) jet or Bartko et al. (2009) clockwise disk (see extended discussion in Psaltis et al. 2015a) but aligned with the preferred axis of the intrinsic emission…”

“The orientation of the orbit is near to that of the inner part of the clockwise stellar disk (Paumard et al. 2006, Lu et al. 2009, Bartko et al. 2009).”

“The observed disk of young stars in the Galactic Centre has γ = 2.4–2.9 and the spherical component of old stars has γ = 1.2–1.75 (Bartko et al. 2009, 2010). c© 0000 RAS, MNRAS 000, 000–000 Figure 2 shows the effects of the two-level timestep refinement procedure for a cluster with amax/amin = 100.”

“The most massive stars (WR/O stars) reside in a combination of a prominent warped disk, a second disklike structure highly inclined relative to the main disk, and a more isotropic component (Paumard et al. 2006; Lu et al. 2009; Bartko et al. 2009) at a projected distance of 0.”

“…a young component, mostly concentrated in the NSC inner region and likely formed in-situ ∼ 3− 8 Myr ago, and an older population with an average age ≃ 10 Gyr (Lu et al. 2009; Bartko et al. 2009; Do et al. 2013; Lu et al. 2013; Pfuhl et al. 2011; Feldmeier-Krause et al. 2015; Minniti et al. 2016).”

“Their estimated initial mass function (IMF) is heavier than Salpeter’s one (P06; Bartko et al. 2009).”

“…stellar dynamics in the GC is complicated by the presence of many luminous young stars, which dominate the light, but are certainly not relaxed (e.g., Levin & Beloborodov 2003; Paumard et al. 2006; Bartko et al. 2009), and giants, which may be affected by hydrodynamical collisions (Alexander 1999).”

“They suggest that the gas cloud surrounds a low-mass star, which was scattered away from its original low-eccentricity orbit at the inner edge of the disk of young O/WR stars that is known to orbit the galactic black hole (Bartko et al. 2009; Lu et al. 2009; Yelda et al. 2012).”

“Under this assumption, the results are also in accordance with the angular momentum direction and orientation of the clockwise stellar disc and gas cloud G2 (Bartko et al. 2009; Gillessen et al. 2019; Pfuhl et al. 2015; Plewa et al. 2017).”

“This is the same coordinate system used by Bartko et al. (2009) in defining the orientations of the stellar orbits.”

“…nuclear star formation scenario, in which gas infalls into the nucleus and then transforms into stars through star formation processes (Loose et al. 1982; possibly in a disk like configuration, e.g. observations of the Milky Way NSC; Levin & Beloborodov 2003; Lu et al. 2009; Bartko et al. 2009).”

“If the central MBH is the origin of HVSs, and the stars orbiting near the MBH are concentrated in one or two disks (Levin & Beloborodov 2003; Lu et al. 2009; Bartko et al. 2009), then stars probably interact with the MBH in preferred planes.”

“…bubbles (Dobler et al. 2010; Su et al. 2010) are interpreted as resulting from a black hole accretion event; it is rich in massive young stars (Bartko et al. 2009), which likely formed in a single star burst event 6± 2 Myr ago (Paumard et al. 2006); it hosts plenty of highly energetic compact…”

“If they were from structures like the CWS disk, the semimajor axes ab−•,ini follows a power-law distribution proportional to a−2.3b−•,ini in the range of ∼ 0.04- 0.5 pc according to current observations on the CWS disk (Lu et al. 2009; Bartko et al. 2009).”

“1 (b)) is roughly αdisk = 15 ◦ in our case, compared to 70◦ inferred from observations (Bartko et al. 2009).”

“The age of T Tauri stars is also consistent with the age ( 6 ± 2 Myr; Paumard et al. 2006; Bartko et al. 2009) of the clockwise disk of young stars ranging from 0.04 pc to 0.5 pc from SgrA∗, where the source is predicted to be scattered from (Murray-Clay & Loeb 2012).”

“The chosen slope of the SF function was motivated by the observed powerlaw (Do et al. 2009; Bartko et al. 2009) distribution of young stars observed in the young stellar disk in the GC. 2.2.”

“The thickness is likely larger than 10◦ (the value for the clockwise disk) and smaller than 25◦, because a thicker disk would be invisible (Bartko et al. 2009).”

“Bartko et al. (2009) claimed detection of a bimodal eccentricity distribution within the clockwise disk.”

“Observations of the Galactic Centre revealed one or two discs of ≈ 6Myr old stars orbiting the central supermassive black hole (SMBH) at a distance of ∼0.1 pc (Levin & Beloborodov 2003; Paumard et al. 2006; Lu et al. 2006, 2009; Bartko et al. 2009).”

“The disc appears to be highly warped (Bartko et al. 2009, 2010).”

“The cloud orbital plane is inclined with respect to the observer’s line-of-sight and is roughly aligned with the well-known ring of stars around Sgr A∗ (Bartko et al. 2009; Levin & Beloborodov 2003).”

“…of the apoapsis is adopted so that the energy distribution of the binaries injected from a disk structure is consistent with the density distribution of young stellar disk recently discovered in the GC (Levin & Beloborodov 2003; Paumard et al. 2006; Lu et al. 2009; Bartko et al. 2009a).”

“It is currently unclear whether this cluster edge also represents the outer edge of the clockwise disk of young stars (Paumard et al. 2006; Bartko et al. 2009, 2010; Do et al. 2009, 2013a; Lu et al. 2009; Yelda et al. 2014).”

“The young stars outside this region contain many O-stars and present markedly different orbital properties, with a top heavy mass function and a disk (or disks) like configuration(s) (Levin & Beloborodov 2003; Lu et al. 2009; Bartko et al. 2009, 2010), and much more circular orbits.”

“This includes the presence of young stars where none were expected (e.g., Levin & Beloborodov 2003; Genzel et al. 2003; Paumard et al. 2006; Bartko et al. 2009; Lu et al. 2009; Yelda et al. 2014), a lack of old stars where many were predicted (e.g., Buchholz et al. 2009; Do et al. 2009a), and very…”