Velocity dispersion and the stellar population in the central 1.2 parsecs of the Galaxy

Sellgren, K.; Mcginn, M. T.; Becklin, E. E.; Hall, Donald N. B.

doi:10.1086/169039

Cited by 135 publications

(102 citation statements)

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“…the projected density increases with the distance to the center. This flattening or even inversion of the projected surface density profile of the late-type stars combined with the steeply increasing density of early-type stars towards Sgr A* explains the dip in CO band head absorption strength found in early spectroscopic observations of low spatial resolution (Allen et al 1990;Sellgren et al 1990;Haller et al 1996). We discuss this in detail in Sect.…”

Section: Structure Of the Clustermentioning

confidence: 69%

“…This has been observed first as a drop in CO absorption strength towards Sgr A* in seeing-limited observations (Allen et al 1990;Sellgren et al 1990;Haller et al 1996). Two explanations have been discussed for this: a significantly lower density of late type stars in the central few arcseconds and/or the presence of a large number of bright early type stars.…”

Section: Introductionmentioning

confidence: 90%

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Composition of the galactic center star cluster

Buchholz

Schödel

Eckart

2009

A&A

173

339

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Context. The GC is the closest galactic nucleus, offering the unique possibility of studying the population of a dense stellar cluster surrounding an SMBH. Aims. The goals of this work are to develop a new method of separating early and late type stellar components of a dense stellar cluster based on narrow band filters, applying it to the central parsec of the GC, and conducting a population analysis of this area. Methods. We use AO assisted observations obtained at the ESO VLT in the NIR H-band and 7 intermediate bands covering the NIR K-band. A comparison of the resulting SEDs with a blackbody of variable extinction then allows us to determine the presence and strength of a CO absorption feature to distinguish between early and late type stars.Results. This new method is suitable for classifying K giants (and later), as well as B2 main sequence (and earlier) stars that are brighter than 15.5 mag in the K band in the central parsec. Compared to previous spectroscopic investigations that are limited to 13-14 mag, this represents a major improvement in the depth of the observations and reduces the needed observation time. Extremely red objects and foreground sources can also be reliably removed from the sample. Comparison to sources of known classification indicates that the method has an accuracy of better than ∼87%. We classify 312 stars as early type candidates out of a sample of 5914 sources. Several results, such as the shape of the KLF and the spatial distribution of both early and late type stars, confirm and extend previous works. The distribution of the early type stars can be fitted with a steep power law (β 1 = −1.49 ± 0.12), alternatively with a broken power law, β 1−10 = −1.08 ± 0.12, β 10−20 = −3.46 ± 0.58, since we find a drop in the early type density at ∼10 . We also detect early type candidates outside of 0.5 pc in significant numbers for the first time. The late type density function shows an inversion in the inner 6 , with a power-law slope of β R<6 = 0.17 ± 0.09. The late type KLF has a power-law slope of 0.30 ± 0.01, closely resembling the KLF obtained for the bulge of the Milky Way. The early type KLF has a much flatter slope of (0.14 ± 0.02). Our results agree best with an in-situ star formation scenario.

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Section: Structure Of the Clustermentioning

confidence: 69%

Section: Introductionmentioning

confidence: 90%

Composition of the galactic center star cluster

Buchholz

Schödel

Eckart

2009

A&A

173

339

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“…Low-luminosity stars have a greater contribution from low-mass, old stars than more luminous stars. In addition, it has long been known that the strength of the 2.3 km CO index decreases in the inner 10@@ around Sgr A* (Sellgren et al 1990 ;Haller et al 1996), indicating a remarkable change in the stellar population. However, it is not clear at present whether this change of the CO index is a result of a change in the distribution of masses or ages of the stars or is due to the di †erent environment in the Galactic center (for example, the envelopes of supergiants may be destroyed by the ambient radiation Ðeld).…”

Section: Observable Consequencesmentioning

confidence: 99%

A Cluster of Black Holes at the Galactic Center

Miralda-Escudé

Gould

2000

ApJ

220

241

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If the stellar population of the bulge contains black holes formed in the Ðnal core collapse of ordinary stars with then about 25,000 stellar mass black holes should have migrated by dynamical M Z 30 M _ , friction into the central parsec of the Milky Way, forming a black hole cluster around the central supermassive black hole. These black holes can be captured by the central black hole when they randomly reach a highly eccentric orbit due to relaxation, either by direct capture (when their Newtonian peribothron is less than 4 Schwarzschild radii) or after losing orbital energy through gravitational waves. The overall depletion timescale is D30 Gyr, so most of the 25,000 black holes remain in the central cluster today. The presence of this black hole cluster would have several observable consequences. First, the low-mass, old stellar population should have been expelled from the region occupied by the black hole cluster as a result of relaxation, implying a core in the proÐle of solar-mass red giants with a radius of D2 pc (i.e., 1@). The observed central density cusp (which has a core radius of only a few arcseconds) should be composed primarily of young Gyr) stars. Second, Ñares from stars being captured by ([1 supermassive black holes in other galaxies should be rarer than usually expected because the older stars will have been expelled from the central regions by the black hole clusters of those galaxies. Third, the young Gyr) stars found at distances D3È10 pc from the Galactic center should be preferentially on ([2 highly eccentric orbits. Fourth, if future high-resolution K-band images reveal sources microlensed by the Milky WayÏs central black hole, then the cluster black holes could give rise to secondary ("" planetlike ÏÏ) perturbations on the main event.

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“…Alternative scenarios include late-type stars rejuvenated by collisions or optically thick atmospheres of 10 M black holes. The drop in the CO index within the central 5 00 and the replacement of late-type stars by the bright and hot stars was discussed by Lacy, Townes, & Hollenbach (1982), Phinney (1989), Sellgren et al (1990), in the context of stellar collisions and external photoionization as two possible mechanisms for removing late-type stars in the core. A more recent analysis of the stellar populations and evolution in the environment of the central stellar cluster is given by Genzel et al (2003).…”

Section: Introductionmentioning

confidence: 99%

Young Stars at the Center of the Milky Way?

Eckart

Moultaka

Viehmann

et al. 2004

ApJ

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We present results from the first diffraction-limited images of the Galactic center (GC) at 1.6, 2.1, and 3.8 m with the new adaptive optics (AO) camera NAOS/CONICA at the ESO Very Large Telescope, as well as 3-4 m low-resolution spectroscopy. We have discovered a small (0.13 lt-yr diameter) cluster of compact sources about 0B5 north of IRS 13 with strong IR excesses due to T > 500 K dust. The nature of the sources is unclear. They may be a cluster of highly extincted stars that heat the local environment of the minispiral. We also consider an explanation that involves the presence of young stars at evolutionary stages between young stellar objects and Herbig Ae/Be objects with ages of about 0.1 to 1 million yr. This scenario would imply more recent star formation in the GC than previously suspected. The AO observations also resolve the central IRS 13 complex. In addition to the previously known bright stars E1 and E2, the K-and L 0 -band images for the first time resolve object E3 into two components, E3N and E3c. The latter one is closest to the 7 mm Very Large Array radio continuum source found at the location of the IRS 13 complex. E3c may be associated with a strong stellar wind or a dusty Wolf-Rayet-like star at that location.

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Velocity dispersion and the stellar population in the central 1.2 parsecs of the Galaxy

Cited by 135 publications

References 0 publications

Composition of the galactic center star cluster

Composition of the galactic center star cluster

A Cluster of Black Holes at the Galactic Center

Young Stars at the Center of the Milky Way?

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