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Near-infrared spectroscopic observations of massive young stellar object candidates in the central molecular zone

Nandakumar, G. LU ; Schultheis, M.; Feldmeier-Krause, A.; Schödel, R.; Neumayer, N.; Matteucci, F.; Ryde, N. LU ; Rojas-Arriagada, A. and Tej, A. (2018) In Astronomy and Astrophysics 609.
Abstract

Context. The central molecular zone (CMZ) is a ∼200 pc region around the Galactic centre. The study of star formation in the central part of the Milky Way is of great interest as it provides a template for the closest galactic nuclei. Aims. We present a spectroscopic follow-up of photometrically selected young stellar object (YSO) candidates in the CMZ of the Galactic centre. Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate (SFR) in the CMZ. Methods. We obtained KMOS low-resolution near-infrared spectra (R ∼ 4000) between 2.0 and 2.5 μm of sources, many of which have been previously identified by mid-infrared photometric criteria as... (More)

Context. The central molecular zone (CMZ) is a ∼200 pc region around the Galactic centre. The study of star formation in the central part of the Milky Way is of great interest as it provides a template for the closest galactic nuclei. Aims. We present a spectroscopic follow-up of photometrically selected young stellar object (YSO) candidates in the CMZ of the Galactic centre. Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate (SFR) in the CMZ. Methods. We obtained KMOS low-resolution near-infrared spectra (R ∼ 4000) between 2.0 and 2.5 μm of sources, many of which have been previously identified by mid-infrared photometric criteria as massive YSOs in the Galactic centre. Our final sample consists of 91 stars with good signal-To-noise ratio. We separated YSOs from cool late-Type stars based on spectral features of CO and Brγ at 2.3 μm and 2.16 μm, respectively. We made use of spectral energy distribution (SED) model fits to the observed photometric data points from 1.25 to 24 μm to estimate approximate masses for the YSOs. Results. Using the spectroscopically identified YSOs in our sample, we confirm that existing colour-colour diagrams and colour-magnitude diagrams are unable to efficiently separate YSOs and cool late-Type stars. In addition, we define a new colour-colour criterion that separates YSOs from cool late-Type stars in the H-KS vs. H -[8.0] diagram. We use this new criterion to identify YSO candidates in the |l| < 1.5, |b| < 0.5, region and use model SED fits to estimate their approximate masses. By assuming an appropriate initial mass function (IMF) and extrapolating the stellar IMF down to lower masses, we determine a SFR of ∼ 0.046 ± 0.026 M yr-1 assuming an average age of 0.75 ± 0.25 Myr for the YSOs. This value is lower than estimates found using the YSO counting method in the literature. Conclusions. Our SFR estimate in the CMZ agrees with the previous estimates from various methods and reaffirms that star formation in the CMZ is proceeding at a lower rate than predicted by various star forming models.

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organization
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type
Contribution to journal
publication status
published
subject
keywords
Galaxy: center, Galaxy: stellar content, Hertzsprung-Russell and C-M diagrams, Stars: formation, Stars: massive, Stars: pre-main sequence
in
Astronomy and Astrophysics
volume
609
publisher
EDP Sciences
external identifiers
  • scopus:85042522347
ISSN
0004-6361
DOI
10.1051/0004-6361/201731918
language
English
LU publication?
yes
id
9beb1b62-9622-42fe-8994-d1c8f718350a
date added to LUP
2018-03-09 09:01:06
date last changed
2018-05-29 11:53:31
@article{9beb1b62-9622-42fe-8994-d1c8f718350a,
  abstract     = {<p>Context. The central molecular zone (CMZ) is a ∼200 pc region around the Galactic centre. The study of star formation in the central part of the Milky Way is of great interest as it provides a template for the closest galactic nuclei. Aims. We present a spectroscopic follow-up of photometrically selected young stellar object (YSO) candidates in the CMZ of the Galactic centre. Our goal is to quantify the contamination of this YSO sample by reddened giant stars with circumstellar envelopes and to determine the star formation rate (SFR) in the CMZ. Methods. We obtained KMOS low-resolution near-infrared spectra (R ∼ 4000) between 2.0 and 2.5 μm of sources, many of which have been previously identified by mid-infrared photometric criteria as massive YSOs in the Galactic centre. Our final sample consists of 91 stars with good signal-To-noise ratio. We separated YSOs from cool late-Type stars based on spectral features of CO and Brγ at 2.3 μm and 2.16 μm, respectively. We made use of spectral energy distribution (SED) model fits to the observed photometric data points from 1.25 to 24 μm to estimate approximate masses for the YSOs. Results. Using the spectroscopically identified YSOs in our sample, we confirm that existing colour-colour diagrams and colour-magnitude diagrams are unable to efficiently separate YSOs and cool late-Type stars. In addition, we define a new colour-colour criterion that separates YSOs from cool late-Type stars in the H-K<sub>S</sub> vs. H -[8.0] diagram. We use this new criterion to identify YSO candidates in the |l| &lt; 1.5, |b| &lt; 0.5, region and use model SED fits to estimate their approximate masses. By assuming an appropriate initial mass function (IMF) and extrapolating the stellar IMF down to lower masses, we determine a SFR of ∼ 0.046 ± 0.026 M<sub>⊙</sub> yr<sup>-1</sup> assuming an average age of 0.75 ± 0.25 Myr for the YSOs. This value is lower than estimates found using the YSO counting method in the literature. Conclusions. Our SFR estimate in the CMZ agrees with the previous estimates from various methods and reaffirms that star formation in the CMZ is proceeding at a lower rate than predicted by various star forming models.</p>},
  articleno    = {A109},
  author       = {Nandakumar, G. and Schultheis, M. and Feldmeier-Krause, A. and Schödel, R. and Neumayer, N. and Matteucci, F. and Ryde, N. and Rojas-Arriagada, A. and Tej, A.},
  issn         = {0004-6361},
  keyword      = {Galaxy: center,Galaxy: stellar content,Hertzsprung-Russell and C-M diagrams,Stars: formation,Stars: massive,Stars: pre-main sequence},
  language     = {eng},
  month        = {01},
  publisher    = {EDP Sciences},
  series       = {Astronomy and Astrophysics},
  title        = {Near-infrared spectroscopic observations of massive young stellar object candidates in the central molecular zone},
  url          = {http://dx.doi.org/10.1051/0004-6361/201731918},
  volume       = {609},
  year         = {2018},
}