J/A+A/641/A102 Milky Way nuclear star cluster HKs photometry (Schoedel+, 2020)
The Milky Way's nuclear star cluster: Old, metal-rich, and cuspy.
Structure and star formation history from deep imaging.
Schoedel R., Nogueras-Lara F., Gallego-Cano E., Shahzamanian B.,
Gallego-Calvente A.T., Gardini A.
<Astron. Astrophys. 641, A102 (2020)>
=2020A&A...641A.102S 2020A&A...641A.102S (SIMBAD/NED BibCode)
ADC_Keywords: Galactic center ; Photometry, infrared ; Associations, stellar
Keywords: techniques: high angular resolution - methods: observational -
Galaxy: center
Abstract:
The environment of Sagittarius A* (Sgr A*), the central black hole of
the Milky Way, is the only place in the Universe where we can
currently study the interaction between a nuclear star cluster and a
massive black hole and infer the properties of a nuclear cluster from
observations of individual stars. This work aims to explore the star
formation history of the nuclear cluster and the structure of the
innermost stellar cusp around Sgr A*. We combined and analysed multi
epoch high quality AO observations. For the region close to Sgr A* we
apply the speckle holography technique to the AO data and obtain
images that are ≥50% complete down to Ks∼19 within a projected radius
of 5" around Sgr A*. We used $H$-band images to derive extinction
maps. We provide Ks photometry for roughly 39000 stars and H-band
photometry for ∼11000 stars within a field of about 40"x40", centred
on Sgr A*. In addition, we provide Ks photometry of ∼3000 stars in a
very deep central field of 10"x10", centred on Sgr A*. We find that
the Ks luminosity function (KLF) is rather homogeneous within the
studied field and does not show any significant changes as a function
of distance from the central black hole on scales of a few 0.1pc. By
fitting theoretical luminosity functions to the KLF, we derive the
star formation history of the nuclear star cluster. We find that about
80% of the original star formation took place 10Gyr ago or longer,
followed by a largely quiescent phase that lasted for more than 5Gyr.
We clearly detect the presence of intermediate-age stars of about 3Gyr
in age. This event makes up about 15% of the originally formed stellar
mass of the cluster. A few percent of the stellar mass formed in the
past few 100Myr. Our results appear to be inconsistent with a
quasi-continuous star formation history. The mean metallicity of the
stars is consistent with being slightly super solar. The stellar
density increases exponentially towards Sgr A* at all magnitudes
between Ks=15-19. We also show that the precise properties of the
stellar cusp around Sgr A* are hard to determine because the star
formation history suggests that the star counts can be significantly
contaminated, at all magnitudes, by stars that are too young to be
dynamically relaxed. We find that the probability of observing any
young (non-millisecond) pulsar in a tight orbit around Sgr A* and
beamed towards Earth is very low. We argue that typical globular
clusters, such as they are observed in and around the Milky Way today,
have probably not contributed to the nuclear cluster's mass in any
significant way. The nuclear cluster may have formed following major
merger events in the early history of the Milky Way.
Description:
Photometric and astrometric measurements of stars in the Galactic
Centre are presented. The data correspond to tables C1 and C2 of the
related paper. The corresponding adaptive optics imaging data were
acquired with the instrument NACO at the ESO VLT. There are two
tables: one for a large field of about 40"x40", centred approximately
on Sagittarius A* and reduced in a standard way (shift-and-add); a
second one with data extracted from a smaller image of about
9.7"x9.7", centred approximately on Sagittarius A*, created from
adaptive optics data that were processed additionally with a speckle
holography algorithm. The tables contain the coordinates of the stars
in right ascension and declination (J2000.0), the pixel positions of
the stars in the images (image sizes of 3328x3328-pixels and
720x720-pixels, respectively), Ks- and H- (for the large field) band
photometry and the related uncertainties, and a number that indicates
whether the star has been identified spectroscopically as a young,
massive star (value 1; 0 otherwise). The astrometric accuracy is
better than 0.01" and the uncertainty of the photometric zero point is
0.08mag for H and Ks.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablec1.dat 69 39053 List of detected point sources in the NACO Ks
and H-band large field mosaics
tablec2.dat 66 3336 List of detected point sources in the deep,
central NACO Ks holographic image
list.dat 133 2 List of fits images
fits/* . 2 Individual fits images
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See also:
J/A+A/502/91 : Proper motions of stars near SgrA* (Schoedel+, 2009)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/A+A/534/A117 : NIR polarimetry of sources near SgrA* (Buchholz+, 2011)
J/A+A/549/A57 : Young, massive star candidates in Sgr A* (Nishiyama+, 2013)
J/A+A/557/A82 : NIR polarimetry of Galactic center sources (Buchholz+, 2013)
J/A+A/566/A47 : Milky Way nuclear star cluster extinction map (Schoedel+ 2014)
J/A+A/584/A2 : KMOS view of the Galactic centre. I. (Feldmeier-Krause+, 2015)
J/A+A/589/A116 : Multiwavelength study of Sgr A* (Mossoux+, 2016)
J/A+A/609/A26 : Galactic Center old stars distribution (Gallego-Cano+, 2018)
J/A+A/610/A83 : GALACTICNUCLEUS JHKs imaging survey (Nogueras-Lara+, 2018)
J/A+A/631/A20 : GALACTICNUCLEUS JHKs imaging survey II (Nogueras-Lara+, 2019)
J/A+A/632/A116 : Galactic Centre proper motion catalogue (Shahzamanian+, 2019)
Byte-by-byte Description of file: tablec1.dat
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Bytes Format Units Label Explanations
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1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 13 F7.4 s RAs Right ascension (J2000)
15 A1 --- DE- Declination sign (J2000)
16- 17 I2 deg DEd Declination (J2000)
19- 20 I2 arcmin DEm Declination (J2000)
22- 28 F7.4 arcsec DEs Declination (J2000)
30- 36 F7.2 pix xpos Position in image on x-axis
38- 44 F7.2 pix ypos Position in image on y-axis
46- 50 F5.2 mag Ksmag Magnitude in NACO Ks-band
52- 55 F4.2 mag e_Ksmag Uncertainty of NACO Ks magnitude
57- 61 F5.2 mag Hmag ?=99.99 Magnitude in NACO H-band (1)
63- 67 F5.2 mag e_Hmag ?=99.99 Uncertainty of NACO H magnitude (1)
69 I1 --- Young [0/1] Flag for young, hot star (1 if true)
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Note (1): A value of 99.99 in any column means that the corresponding
measurement is not available.
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Byte-by-byte Description of file: tablec2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 2 I2 h RAh Right ascension (J2000)
4- 5 I2 min RAm Right ascension (J2000)
7- 13 F7.4 s RAs Right ascension (J2000)
15 A1 --- DE- Declination sign (J2000)
16- 17 I2 deg DEd Declination (J2000)
19- 20 I2 arcmin DEm Declination (J2000)
22- 28 F7.4 arcsec DEs Declination (J2000)
30- 35 F6.2 pix xpos Position in image on x-axis
37- 40 F4.2 pix e_xpos Uncertainty of x (pixels)
42- 47 F6.2 pix ypos Position in image on y-axis
49- 52 F4.2 pix e_ypos Uncertainty of y (pixels)
54- 58 F5.2 mag Ksmag Magnitude in NACO Ks-band
61- 64 F4.2 mag e_Ksmag Uncertainty of NACO Ks magnitude
66 I1 --- Young [0/1] Flag for young, hot star (1 if true)
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 25 F6.4 arcsec/pix scale Scale of the image
27- 30 I4 --- Nx Number of pixels along X-axis
32- 35 I4 --- Ny Number of pixels along Y-axis
37- 41 I5 Kibyte size Size of FITS file
43- 53 A11 --- FileName Name of FITS file, in subdirectory fits
55-133 A79 --- Title Title of the FITS file
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Acknowledgements:
Rainer Schoedel, rainer(at)iaa.es
(End) Patricia Vannier [CDS] 04-Aug-2020