J/ApJ/943/137 Deep NIR Subaru phot. in Sh 2-209 HII region (Yasui+, 2023)
Mass function of a young cluster in a low-metallicity environment. Sh 2-209.
Yasui C., Kobayashi N., Saito M., Izumi N., Ikeda Y.
<Astrophys. J., 943, 137 (2023)>
=2023ApJ...943..137Y 2023ApJ...943..137Y
ADC_Keywords: H II regions; Photometry, infrared; Clusters, open
Keywords: H II regions ; Star formation ; Pre-main sequence stars ;
Low mass stars ; Infrared sources ; Open star clusters ;
Galaxy abundances ; Luminosity function ; Stellar mass functions
Abstract:
We present deep near-infrared (NIR) imaging of Sh 2-209 (S209), a
low-metallicity ([O/H]=-0.5dex) HII region in the Galaxy. From the NIR
images, combined with astrometric data from Gaia EDR3, we estimate the
distance to S209 to be 2.5kpc. This is close enough to enable us to
resolve cluster members clearly (∼1000 au separation) down to a
mass-detection limit of ∼0.1M☉, and we have identified two
star-forming clusters in S209, with individual cluster scales ∼1pc. We
employ a set of model luminosity functions to derive the underlying
initial mass functions (IMFs) and ages for both clusters. The IMFs we
obtained for both clusters exhibit slightly flat high-mass slopes
(Γ~-1.0) compared to the Salpeter IMF (Γ=-1.35), and their
break mass of ∼0.1M☉ is lower than those generally seen in the
solar neighborhood (∼0.3M☉). In particular, because the S209
main cluster is a star-forming cluster with a larger number of members
(∼1500) than the number (∼100) in regions previously studied in such
environments, it is possible for the first time to derive the IMF in a
low-metallicity environment with high accuracy over the wide mass
range of 0.1-20M☉.
Description:
We obtained deep JHKS -band images for each band with the 8.2m Subaru
telescope using the wide-field NIR camera and spectrograph, MOIRCS.
The instrument uses the Maunakea Observatory (MKO) NIR photometric
filters. We performed these observations on 2006 September 3 UT.
We also obtained short-exposure images on 2006 November 8 UT.
We centered the images of Sh2-209 at
RAJ2000=04:11:08.3,DEJ2000=+51:09:29.3, so they covered the central
region of the HII region.
Objects:
----------------------------------------------------------
RA (ICRS) DE Designation(s)
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04 11 06.7 +51 09 44 S209 = SH 2-209
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table10.dat 62 8236 Subaru/MOIRCS Sh2-209 catalog
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See also:
VII/20 : Catalogue of HII Regions (Sharpless 1959)
VII/50 : CO Radial Velocities Toward Galactic H II Regions (Blitz+ 1982)
VIII/65 : 1.4GHz NRAO VLA Sky Survey (NVSS) (Condon+ 1998)
VI/102 : Geneva stellar evolution tracks and isochrones (Lejeune+, 2001)
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
J/AJ/113/1733 : Orion Nebula Cluster population (Hillenbrand 1997)
J/A+A/337/403 : Low-mass stars evolutionary models (Baraffe+ 1998)
J/ApJ/540/1016 : K-band & NICMOS phot. of Trapezium Cluster (Luhman+, 2000)
J/ApJ/573/366 : Infrared photometry of Trapezium cluster (Muench+, 2002)
J/A+A/404/223 : 2MASS IR star clusters in the Galaxy (Bica+, 2003)
J/ApJS/161/361 : Millimeter continuum survey for protoclusters (Klein+, 2005)
J/MNRAS/373/781 : JHK photometry of faint standard stars (Leggett+, 2006)
J/ApJ/653/1226 : Physical properties of galactic HII regions (Quireza+, 2006)
J/ApJS/162/346 : Abundance gradients in the Galaxy (Rudolph+, 2006)
J/ApJ/738/27 : Galactic HII regions RRL and continuum data (Balser+, 2011)
J/AJ/150/147 : Galactic HII regions. I. Stellar distances (Foster+, 2015)
J/other/Sci/359.69 : Massive stars in 30 Dor (Schneider+, 2018)
Byte-by-byte Description of file: table10.dat
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Bytes Format Units Label Explanations
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1- 4 I4 --- Seq [1/8236] Sequential identifier
6- 14 F9.6 deg RAdeg [62.68/62.88] Right Ascension (J2000) (1)
16- 24 F9.6 deg DEdeg [51.10/51.22] Declination (J2000) (1)
26- 30 F5.2 mag Jmag [11.35/22.03]? Subaru/MOIRCS J band magnitude
32- 35 F4.2 mag e_Jmag [0/0.2]? Uncertainty in Jmag
37- 41 F5.2 mag Hmag [11.54/22.17]? Subaru/MOIRCS H band magnitude
43- 46 F4.2 mag e_Hmag [0/0.2]? Uncertainty in Hmag
48- 52 F5.2 mag Ksmag [11.38/23.56]? Subaru/MOIRCS Ks band magnitude
54- 57 F4.2 mag e_Ksmag [0/0.2]? Uncertainty in Ksmag
59- 62 A4 --- YCl Notes (2)
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Note (1): The astrometry was performed using the IRAF task of the IMCOORD
package with the 2MASS Point Source Catalog as a reference.
Note (2): Using the pseudocolor image (which combines the J, H and
Ks-band images obtained with MOIRCS), we identified enhancements in
the stellar density, compared to the surrounding area, on the
northeast and southwest sides of the field observed with MOIRCS.
Hereafter, we refer to these enhancements as the "main cluster" and
the "sub-cluster," respectively (see Figure 5 where the defined
regions of the S209 main and sub-cluster are shown as solid yellow and
dotted circles, respectively). Both clusters seem to be associated
with, or at least are located close to, IRAS objects: the main cluster
with IRAS 04073+5102 and the sub-cluster with IRAS 04073+5100. See
Section 4.
Sources in the Sh2-209 two young clusters as follows:
Main = "main cluster"; 3971 occurrences
Sub = "sub-cluster"; 998 occurrences
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 11-Dec-2024