J/ApJ/736/133 Spitzer-IRS study of massive YSOs in galactic center (An+, 2011)
Massive young stellar objects in the Galactic Center.
I. Spectroscopic identification from Spitzer Infrared Spectrograph observations.
An D., Ramirez S.V., Sellgren K., Arendt R.G., Boogert A.C.A.,
Robitaille T.P., Schultheis M., Cotera A.S., Smith H.A., Stolovy S.R.
<Astrophys. J., 736, 133 (2011)>
=2011ApJ...736..133A 2011ApJ...736..133A
ADC_Keywords: Photometry, infrared ; Abundances ; Spectroscopy ; Extinction ;
YSOs
Keywords: Galaxy: nucleus - infrared: ISM - ISM: molecules - stars: formation
Abstract:
We present results from our spectroscopic study, using the Infrared
Spectrograph (IRS) on board the Spitzer Space Telescope, designed to
identify massive young stellar objects (YSOs) in the Galactic center
(GC). Our sample of 107 YSO candidates was selected based on Infrared
Array Camera (IRAC) colors from the high spatial resolution, high
sensitivity Spitzer/IRAC images in the Central Molecular Zone, which
spans the central ∼300pc region of the Milky Way. We obtained IRS
spectra over 5-35um using both high- and low-resolution IRS modules.
We spectroscopically identify massive YSOs by the presence of a 15.4um
shoulder on the absorption profile of 15um CO2 ice, suggestive of
CO2 ice mixed with CH3OH ice on grains. This 15.4um shoulder is
clearly observed in 16 sources and possibly observed in an additional
19 sources. We show that nine massive YSOs also reveal molecular
gas-phase absorption from CO2, C2H2, and/or HCN, which traces
warm and dense gas in YSOs. Our results provide the first
spectroscopic census of the massive YSO population in the GC. We fit
YSO models to the observed spectral energy distributions and find YSO
masses of 8-23M☉, which generally agree with the masses derived
from observed radio continuum emission. We find that about 50% of
photometrically identified YSOs are confirmed with our spectroscopic
study. This implies a preliminary star formation rate of
∼0.07M_☉/yr at the GC.
Description:
Our 107 spectroscopic targets (Table 1) were selected from the GC
point-source catalog (Ramirez et al. 2008, Cat. II/295) extracted from
the Infrared Array Camera (IRAC) images of the Central Molecular Zone
(CMZ) made using the IRAC on board the Spitzer Space Telescope. These
images cover 280x200pc in the four IRAC channels (3.6um, 4.5um, 5.8um,
and 8.0um) with uniform high sensitivity and spatial resolution ∼2".
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 59 107 Infrared Spectrograph (IRS) sample of candidate YSOs
table2.dat 114 35 Data reduction summary for YSOs and possible YSOs
table3.dat 97 40 CO2 ice decomposition for YSOs and possible YSOs
table4.dat 96 9 Gas-phase absorption features of YSOs and possible
YSOs
table5.dat 32 35 AV for GC YSOs and possible YSOs
table6.dat 85 35 Photometric properties of YSOs and possible YSOs
table7.dat 63 35 SED fitting results and mass estimates from
radio continuum
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See also:
II/293 : GLIMPSE Source Catalog (I + II + 3D) (IPAC 2008)
II/295 : Spitzer IRAC survey of the galactic center (Ramirez+, 2008)
J/A+A/530/A72 : Fermi sources with massive YSO associations (Munar-Adrover+,
2011)
J/ApJ/702/178 : YSOs in the central 400pc of the Galaxy (Yusef-Zadeh+, 2009)
J/ApJ/697/1741 : Warped disks of YSOs in Galactic center (Bartko+, 2009)
J/A+A/495/157 : Interstellar extinction in Galactic Center (Schultheis+, 2009)
J/ApJS/175/277 : Submillimeter-Continuum SCUBA detections (Di Francesco+, 2008)
J/ApJS/174/481 : 2LC Compact Radio Sources in the GC (Lazio+, 2008)
J/A+A/453/535 : Classification of bright mid-IR sources (Schuller+, 2006)
J/AJ/130/586 : Compact radio sources in the galactic plane (White+, 2005)
J/ApJS/155/421 : Survey of Galactic Center region at 20cm (Yusef-Zadeh+, 2004)
J/A+A/392/971 : Catalogue of bright YSO candidates in ISOGAL (Felli+, 2002)
J/ApJS/118/201 : Galactic Center 6 and 20cm survey (Lazio+, 1998)
J/ApJS/91/347 : A 5-GHz VLA Survey of the Galactic Plane (Becker+ 1994)
J/ApJS/74/181 : Small-diameter radiosources catalogue (Zoonematkermani+, 1990)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- SSTGC [244532/817663] Source identification
8- 9 I2 h RAh [17] Hour of right ascension (J2000)
11- 12 I2 min RAm [43/47] Minute of right ascension (J2000)
14- 18 F5.2 s RAs Second of right ascension (J2000)
20 A1 --- DE- [-] Sign of declination (J2000)
21- 22 I2 deg DEd [28/29] Degree of declination (J2000)
24- 25 I2 arcmin DEm Arcminute of declination (J2000)
27- 30 F4.1 arcsec DEs Arcsecond of declination (J2000)
32- 39 A8 "YYYY/MMM" Date Observation date (2008/May or 2008/Oct)
41- 45 A5 --- Us [yes/maybe/no ] This work YSO status
("yes"=YSO, "maybe"=possible YSO)
47- 49 A3 --- F02 [yes/no ] Felli et al. (2002,
Cat. J/A+A/392/971) YSO status
51- 53 A3 --- S06 [yes/no ] Schuller et al. (2006,
Cat. J/A+A/453/535) YSO status
55- 57 A3 --- Y09 [yes/no ] Yusef-Zadeh et al. (2009,
Cat. J/ApJ/702/178) YSO status
59 A1 --- f_Y09 [b] b: 4.5um excess source without a 24um
counterpart
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- SSTGC [300758/817663] Source identification
8- 10 A3 --- Mod Baseline IRS module (LL2 or SL1) (1)
12- 15 F4.2 --- SL1 ? SL1 flux scaling factor (2)
17- 20 F4.2 --- e_SL1 ? Uncertainty on SL1
22- 25 F4.2 --- SL2 ? SL2 flux scaling factor (2)
27- 30 F4.2 --- e_SL2 ? Uncertainty on SL2
32- 35 F4.2 --- SL3 ? SL3 flux scaling factor (2)
37- 40 F4.2 --- e_SL3 ? Uncertainty on SL3
42- 45 F4.2 --- LL1 ? LL1 flux scaling factor (2)
47- 50 F4.2 --- e_LL1 ? Uncertainty on LL1
52- 55 F4.2 --- LL2 ? LL2 flux scaling factor (2)
57- 60 F4.2 --- e_LL2 ? Uncertainty on LL2
62-114 A53 --- Set Excluded data set (3)
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Note (1): IRS module selected as a baseline for the flux calibration.
IRS modules are (see the text for further explanations):
* short-high (SH; 9.9-19.6um, λ/Δλ∼600),
* long-high (LH; 18.7-37.2um, λ/Δλ∼600),
* short-low (SL [first-order SL17.4-14.5um, second-order SL25.2-7.7um,
third-order SL37.3-8.7um, λ/Δλ∼60-127])
* long-low (LL [first-order LL119.5-38.0um, second-order LL214.0-21.3um,
third-order LL3 19.4-21.7um, λ/Δλ∼57-126]).
Note (2): Adopted scaling factor in each module. The value represents the
scaled flux divided by the original flux.
Note (3): Specific modules/orders that contain defective data. These were
excluded in the spectral analysis. "NSEW" denote background
observations northern/southern/eastern/western from the source target.
"Nod" represents a specific nod position for a set of target spectra.
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- SSTGC [300758/817663] Source identification
8- 12 F5.2 [cm-2] [Npol] [17.06/18.31] Log of gas-phase column density
(Ncol) polar
14- 17 F4.2 [cm-2] e_[Npol] Uncertainty on [Npol]
19 A1 --- l_[Napol] Limit flag on [Napol]
20- 24 F5.2 [cm-2] [Napol] [16.79/18.03] Log of Ncol apolar
26- 29 F4.2 [cm-2] e_[Napol] ? Uncertainty on [Napol]
31 A1 --- l_[Nsh] Limit flag on [Nsh]
32- 36 F5.2 [cm-2] [Nsh] [16.65/17.57] Log of Ncol shoulder
38- 41 F4.2 [cm-2] e_[Nsh] ? Uncertainty on [Nsh]
43 A1 --- l_[Nd] Limit flag on [Nd]
44- 48 F5.2 [cm-2] [Nd] [16.17/16.82] Log of Ncol diluted
50- 53 F4.2 [cm-2] e_[Nd] ? Uncertainty on [Nd]
55 A1 --- l_[Np] Limit flag on [Np]
56- 60 F5.2 [cm-2] [Np] [16.78/17.41] Log of Ncol pure
62- 65 F4.2 [cm-2] e_[Np] ? Uncertainty on [Np]
67- 71 F5.2 [cm-2] [Nt] [17.38/18.54] Log of Ncol total
73- 76 F4.2 [cm-2] e_[Nt] Uncertainty on [Nt]
78- 81 I4 --- Chi2 [99/2347] Total chi-square of the fit
83- 85 I3 --- Ntot [118/152] Number of data points used in the fit
87- 97 A11 --- Status YSO status ("yes", "maybe" or "known stars")
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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- 6 I6 --- SSTGC [524665/803471] Source identification
8- 10 I3 K TexC2 [100/400]? C2H2 excitation temperature
12- 14 I3 K e_TexC2 ? Uncertainty on TexC2
16- 19 F4.1 [cm-2] [C2H2] [15.7/16.9]? Log of C2H2 column density
21- 23 F3.1 [cm-2] e_[C2H2] ? Uncertainty on [C2H2]
25- 28 F4.1 --- C2H2 [-6.9/-5.4]? C2H2 abundance/H2 (1)
30- 32 F3.1 --- e_C2H2 ? Uncertainty on C2H2
34- 36 I3 K TexH [100/400]? HCN excitation temperature
38- 40 I3 K e_TexH ? Uncertainty on TexH
41 A1 --- f_TexH [b] 2 possible values for SSTGC 803187 (2)
43- 46 F4.1 [cm-2] [HCN] [16.4/17]? Log of HCN column density
48- 50 F3.1 [cm-2] e_[HCN] ? Uncertainty on [HCN]
51 A1 --- f_[HCN] [b] 2 possible values for SSTGC 803187 (2)
53- 56 F4.1 --- HCN [-6.4/-5.3]? HCN abundance/H2 (1)
58- 60 F3.1 --- e_HCN ? Uncertainty on HCN
62- 64 I3 K Tex [100/200] CO2 excitation temperature
66- 68 I3 K e_Tex Uncertainty on Tex
70- 73 F4.1 [cm-2] [CO2] [16.2/17.2] Log of CO2 column density
75- 77 F3.1 [cm-2] e_[CO2] ? Uncertainty on [CO2]
79- 82 F4.1 --- CO2 [-6.4/-5.1]? CO2 abundance/H2 (1)
84- 86 F3.1 --- e_CO2 ? Uncertainty on CO2
88- 91 F4.2 --- CO2g [0.02/0.15] CO2 gas to solid ratio
93- 96 F4.2 --- e_CO2g Uncertainty on CO2g
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Note (1): Abundance relative to molecular hydrogren, log(N/N[H2]).
Note (2):
b = Two local χ2 minima were found at Tex=100K, logNcol=16.4 and
Tex∼700K, logNcol∼16.7.
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Byte-by-byte Description of file: table5.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- SSTGC [300758/817663] Source identification
8- 11 F4.1 mag AvL [17.6/76.5]? Dust extinction with low-resolution
modules (SL+LL)
13- 16 F4.1 mag e_AvL ? Uncertainty on AvL
18- 21 F4.1 mag AvH [19.9/64.5] Dust extinction with high-resolution
modules (SH+LH)
23- 26 F4.1 mag e_AvH Uncertainty on AvH
28- 29 I2 mag Av0 [19/76] Foreground extinction (1)
31- 32 I2 mag e_Av0 Uncertainty on Av
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Note (1): Based on the 2MASS and IRAC color-magnitude diagrams of GC red giant
branch stars within 2' of the source (Schultheis et al. 2009,
Cat. J/A+A/495/157).
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Byte-by-byte Description of file: table6.dat
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Bytes Format Units Label Explanations
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1- 6 I6 --- SSTGC [300758/817663] Source identification
8- 12 F5.2 mag Jmag [15.33/19.06]? UKIDSS J-band magnitude (1)
14- 17 F4.2 mag e_Jmag ? Uncertainty on Jmag
19- 23 F5.2 mag Hmag ? UKIDSS H-band magnitude (1)
25- 28 F4.2 mag e_Hmag ? Uncertainty on Hmag
30- 34 F5.2 mag Kmag [10.98/16.88]? UKIDSS K-band magnitude (1)
36- 39 F4.2 mag e_Kmag ? Uncertainty on Kmag
41- 44 F4.1 mag [3.6] ? 3.6um IRAC band magnitude (2)
46- 49 F4.1 mag [4.5] ? 4.5um IRAC band magnitude (2)
51- 54 F4.1 mag [5.8] ? 5.8um IRAC band magnitude (2)
56- 58 F3.1 mag [8.0] [4.8/8.9]? 8.0um IRAC band magnitude (2)
60- 63 F4.1 mag [24] [-1.1/3.3]? 24um synthetic magnitude (3)
65 A1 --- l_F450 Limit flag on F450
66- 71 F6.1 Jy F450 [1.9/7214.4]? SCUBA 450um flux (4)
73- 75 F3.1 Jy e_F450 ? Uncertainty on F450
77- 81 F5.1 Jy F850 [0.1/326.2]? SCUBA 850um flux (4)
83- 85 F3.1 Jy e_F850 ? Uncertainty on F850
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Note (1): Aperture3 magnitudes from UKIDSS DR2 (Warren et al.
2007MNRAS.375..213W 2007MNRAS.375..213W).
Note (2): Systematic errors of IRAC photometry were determined to be 0.1mag,
0.1mag, 0.15mag, and 0.2mags for channels 1, 2, 3, and 4,
respectively, by comparing the Ramirez et al. (2008,
Cat. II/295) values with the measurements from the GLIMPSE II
catalog (Churchwell et al. 2009PASP..121..213C 2009PASP..121..213C).
Note (3): Synthetic photometry based on IRS spectra.
Note (4): Fluxes from SCUBA Legacy Catalogues (Di Francesco et al. 2008,
Cat. J/ApJS/175/277).
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Byte-by-byte Description of file: table7.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 I6 --- SSTGC [300758/817663] Source identification
8- 11 F4.2 [Msun] logM [0.88/1.42] Log of mass
13- 16 F4.2 [Msun] e_logM ? Uncertainty on logM
18- 21 F4.2 [Lsun] logL [2.94/4.97] Log of total luminosity
23- 26 F4.2 [Lsun] e_logL ? Uncertainty on logL
28- 31 F4.1 mag Av [20/40] ISM extinction
33- 35 F3.1 mag e_Av ? Uncertainty on Av
37- 41 F5.2 [Msun/yr] logdM/dt [-4.19/-2.24]? Envelope accretion rate
43- 46 F4.2 [Msun/yr] e_logdM/dt ? Uncertainty on logdM/dt
48- 51 F4.2 [yr] logAge [3.19/6.17] Age
53- 56 F4.2 [yr] e_logAge ? Uncertainty on logAge
58- 61 F4.2 [Msun] logMrad [1.18/1.39]? Radio modeling mass
63 I1 --- r_logMrad [1/8]? logMrad reference (1)
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Note (1): References for radio observations as follows:
1 = Yusef-Zadeh et al. 2009, Cat. J/ApJ/702/178;
2 = GPSR5 0.488-0.028, Mehringer et al. 1992ApJ...401..168M 1992ApJ...401..168M; Becker et al.
1994, Cat. J/ApJS/91/347;
3 = #8, Mehringer et al. 1992ApJ...401..168M 1992ApJ...401..168M; Mehringer 1995ApJ...454..782M 1995ApJ...454..782M;
4 = 2LC 000.563-0.044, Mehringer et al. 1992ApJ...401..168M 1992ApJ...401..168M; Yusef-Zadeh et
al. 2004, Cat. J/ApJS/155/421; Lazio & Cordes 2008, Cat. J/ApJS/174/481;
5 = GPSR5 0.602-0.037, Becker et al. 1994, Cat. J/ApJS/91/347; Lazio & Cordes
1998, Cat. J/ApJS/118/201; Yusef-Zadeh et al. 2004, Cat. J/ApJS/155/421;
Lazio & Cordes 2008, Cat. J/ApJS/174/481;
6 = 1LC 000.635-0.020, Lazio & Cordes 1998, Cat. J/ApJS/118/201; White et al.
2005, Cat. J/AJ/130/586;
7 = SGR B2 HII P, Mehringer et al. 1993ApJ...412..684M 1993ApJ...412..684M; Yusef-Zadeh et al.
2004, Cat. J/ApJS/155/421;
8 = GPSR5 0.693-0.046, Zoonematkermani et al. 1990, Cat. J/ApJS/74/181;
Becker et al. 1994, Cat. J/ApJS/91/347; Lazio & Cordes 1998,
Cat. J/ApJS/118/201; Yusef-Zadeh et al. 2004, Cat. J/ApJS/155/421; White
et al. 2005, Cat. J/AJ/130/586; Lazio & Cordes 2008, Cat. J/ApJS/174/481.
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References:
Jang et al. Paper II. 2022ApJ...930...16J 2022ApJ...930...16J Cat. J/ApJ/930/16
(End) Emmanuelle Perret [CDS] 19-Dec-2012