J/ApJ/808/106 NIR spectroscopic obs. in the Galactic Center (Stostad+, 2015)
Mapping the outer edge of the young stellar cluster in the Galactic Center.
Stostad M., Do T., Murray N., Lu J.R., Yelda S., Ghez A.
<Astrophys. J., 808, 106 (2015)>
=2015ApJ...808..106S 2015ApJ...808..106S (SIMBAD/NED BibCode)
ADC_Keywords: Photometry, infrared ; Equivalent widths ; Extinction
Keywords: Galaxy: center; stars: early-type; stars: formation; stars: late-type;
techniques: high angular resolution; techniques: spectroscopic
Abstract:
We present new near-infrared spectroscopic observations of the outer
edges of the young stellar cluster around the supermassive black hole
at the Galactic center. The observations show a break in the surface
density profile of young stars at ∼13" (0.52pc). These observations
spectroscopically confirm previous suggestions of a break based on
photometry. Using Gemini North's Near-Infrared Integral Field
Spectrometer, we are able to detect and separate early- and late-type
stars with a 75% completeness at Ks=15.5. We sample a region with
radii between 7" and 23" (0.28-0.92pc) from Sgr A* and present new
spectral classifications of 144 stars brighter than Ks=15.5, where
140 stars are late-type (>1Gyr) and only four stars are early-type
(young, 4-6Myr). A broken power-law fit of the early-type surface
density matches well with our data and previously published values.
The projected surface density of late-type stars is also measured and
found to be consistent with previous results. We find that the
observed early-type surface-density profile is inconsistent with the
theory of young stars originating from a tightly bound infalling
cluster, as no significant trail of young stars is found at radii
above 13". We also note that either a simple disk instability
criterion or a cloud-cloud collision could explain the location of the
outer edge, though we lack information to make conclusive remarks on
either alternative. If this break in surface density represents an
edge to the young stellar cluster, it would set an important scale for
the most recent episode of star formation at the Galactic center.
Description:
Observations were obtained with Gemini-North's Near-Infrared Integral
Field Spectrometer (NIFS) between 2012 May and 2014 May with natural
guide star and laser guide star adaptive optics. NIFS provides a
wavelength spectrum in the K band (1.965-2.430um) and a spectral
resolution ∼5000 with a typical spatial resolution of 115-165mas.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 97 6 NIFS observations of early-type stars
table3.dat 97 310 NIFS observations of late-type stars
table4.dat 60 55 NIFS observations of stars without spectral
identification
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See also:
J/A+A/584/A2 : KMOS view of the Galactic centre. I. (Feldmeier-Krause+, 2015)
J/ApJ/779/L6 : 3D kinematic obs. of stars in Galactic Centre (Do+, 2013)
J/ApJ/764/154 : Stellar populations in the central 0.5pc. I. (Do+, 2013)
J/A+A/549/A57 : Young, massive star candidates in Sgr A* (Nishiyama+, 2013)
J/A+A/511/A18 : NIR obs. of stars near SgrA* (Schoedel+, 2010)
J/ApJ/703/1323 : Star spectroscopy in the Galaxy's nuclear cluster (Do+ 2009)
J/ApJ/697/1741 : Warped disks of YSOs in Galactic center (Bartko+, 2009)
J/A+A/499/483 : NIR obs. of sources in galactic center (Buchholz+, 2009)
J/ApJ/670/1115 : IRS spectra at 38 positions in Gal. Center (Simpson+, 2007)
J/ApJ/643/1011 : Early-type stars in the center of the Galaxy (Paumard+, 2006)
Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Stellar identifier
11- 20 A10 "Y/M/D" Date Date of the observation
22- 25 F4.1 mag Ksmag [10.7/18.7] The KS band magnitude
27 A1 --- f_Ksmag [b] Flag on Ksmag (G1)
29- 33 F5.2 arcsec oRA Right Ascension offset (G2)
35- 39 F5.2 arcsec oDE Declination offset (G2)
41- 45 F5.2 arcsec Rad [7.7/22.8] Projected radius from Sgr A*
47 A1 --- l_SNR Limit flag on SNR
48- 50 I3 --- SNR [3/141] Signal-to-Noise
52- 55 F4.1 0.1nm EW2.29 [0/17.4]? Equivalent width of CO 2.2935 micron
feature (1)
57- 59 F3.1 0.1nm e_EW2.29 [0.1/3]? Uncertainty in EW2.2935 (1)
61- 64 F4.1 0.1nm EW2.32 [0.7/30]? Equivalent width of CO 2.3227 micron
feature (1)
66- 68 F3.1 0.1nm e_EW2.32 [0.1/2]? Uncertainty in EW2.3227 (1)
70- 73 F4.1 0.1nm EWNaI [-0.3/10.8]? Equivalent width of Na I line
(only for table 3) (1)
75- 77 F3.1 0.1nm e_EWNaI [0.1/2]? Uncertainty in EWNaI (1)
79- 81 F3.1 0.1nm EWBrg [0.7/2.5]? Equivalent width of Brγ line
(only for table 2) (2)
83- 85 F3.1 0.1nm e_EWBrg [0.3/2]? Uncertainty in EWBrg (2)
87- 90 F4.2 mag AKs [2.3/3] The KS band extinction
92 A1 --- C? Contamination? Y/N
94- 97 A4 --- Fig Figure number in the online set images;
column added by CDS
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Note (1): In units of Angstroms.
Note (2): Brγ EW is difficult to determine due to, among other things,
systematics stemming from the subtraction of local Brγ emission.
We attempt to capture this uncertainty in our errors by combining the
dispersion of Brγ EW for late-type stars at the same magnitude
with the SNR-based random uncertainty. In units of Angstroms.
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
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1- 9 A9 --- Name Stellar identifier
11- 20 A10 "Y/M/D" Date Date of the observation
22- 25 F4.1 mag Ksmag [14.7/20.6]? The KS band magnitude
27 A1 --- f_Ksmag [bc] Flag on Ksmag (G1)
29- 33 F5.2 arcsec oRA Right Ascension offset (G2)
35- 39 F5.2 arcsec oDE Declination offset (G2)
41- 45 F5.2 arcsec Rad [7.7/22.1] Projected radius from Sgr A*
47 A1 --- l_SNR Limit flag on SNR
49- 50 I2 --- SNR [0/40] Signal-to-Noise
52- 55 F4.2 mag AKs [2.3/3] The KS band extinction
57- 60 A4 --- Fig Figure number in the online set images;
column added by CDS
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Global notes:
Note (G1): Flag on Ksmag as follows:
b = Star could not be crossmatched to Schodel et al. (2010, J/A+A/511/A18).
KS magnitude estimated from the NIFS data.
c = Star could not be crossmatched to Schodel et al. (2010, J/A+A/511/A18)
and was too faint for magnitude approximation.
Note (G2): Offsets in projected distance from Sgr A*
(RA offset is positive to the east).
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 30-Nov-2015