J/ApJ/930/16 Massive YSOs in the GC. II. IRTF spectra (Jang+, 2022)
Massive young stellar objects in the Galactic center.
II. Seeing through the ice-rich envelopes.
Jang D., An D., Sellgren K., Ramirez S.V., Boogert A.C.A., Schultheis M.
<Astrophys. J., 930, 16 (2022)>
=2022ApJ...930...16J 2022ApJ...930...16J
ADC_Keywords: Galactic center; YSOs; Spectra, infrared; Spectral types;
Extinction
Keywords: Astrochemistry ; Galactic center ; Interstellar abundances ;
Protostars ; Ice formation ; Young stellar objects
Abstract:
To study the demographics of interstellar ices in the Central
Molecular Zone (CMZ) of the Milky Way, we obtain near-infrared spectra
of 109 red point sources using NASA IRTF/SpeX at Maunakea. We select
the sample from near- and mid-infrared photometry, including
12 objects in the previous paper of this series, to ensure that these
sources trace a large amount of absorption through clouds in each line
of sight. We find that most of the sample (100 objects) show CO
band-head absorption at 2.3µm, tagging them as red (super-) giants.
Despite the photospheric signature, however, a fraction of the sample
with L-band spectra (9/82=0.11) exhibit large H2O ice column
densities (N>2x1018cm-2), and six of them also reveal CH3OH ice
absorption. As one of such objects is identified as a young stellar
object (YSO) in our previous work, these ice-rich sight lines are
likely associated with background stars in projection to an extended
envelope of a YSO or a dense cloud core. The low frequency of such
objects in the early stage of stellar evolution implies a low
star-formation rate (≲0.02M☉/yr), reinforcing the previous
claim on the suppressed star-formation activity in the CMZ. Our data
also indicate that the strong "shoulder" CO2 ice absorption at
15.4µm observed in YSO candidates in the previous paper arises from
CH3OH-rich ice grains having a large CO2 concentration
[N(CO2)/N(CH3OH)∼1/3].
Description:
We obtained 2-4um spectra for 109 red point-like sources using SpeX, a
medium-resolution (R∼2000-2500) cross-dispersed spectrograph and
imager at the 3.0m NASA Infrared Telescope Facility (IRTF) on
Maunakea. For these objects that are potentially associated with the
Central Molecular Zone (CMZ), we carried out observing runs on UT
dates 2009-May-14--15 and 17, 2011-Jul-17--20, 2017-May-28--30,
Jun-21--23, and Jul-23--24 to collect spectra for 11, 28, and 70
science targets in 2009, 2011, and 2017, respectively. See Section 2.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table2.dat 58 109 IRTF/SpeX targets
table3.dat 105 109 Parameter estimates from spectral fitting
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See also:
II/246 : 2MASS All-Sky Catalog of Point Sources (Cutri+ 2003)
II/295 : Spitzer IRAC survey of the galactic center (Ramirez+, 2008)
II/316 : UKIDSS-DR6 Galactic Plane Survey (Lucas+ 2012)
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
VIII/96 : 6-GHz methanol multibeam maser catalogue (Caswell+, 2010-12)
VII/233 : The 2MASS Extended sources (IPAC/UMass, 2003-2006)
J/ApJS/86/713 : IR spectroscopy of ices (Hudgins+, 1993)
J/ApJS/91/347 : A 5-GHz VLA Survey of the Galactic Plane (Becker+ 1994)
J/A+A/455/971 : Organic molecules in the Gal. center (Requena-Torres+, 2006)
J/ApJ/670/1115 : IRS spectra at 38 positions in Gal. center (Simpson+, 2007)
J/ApJS/181/321 : Properties of Spitzer c2d dark clouds (Evans+, 2009)
J/ApJS/181/227 : Catalog of 24um sources toward Galactic Center (Hinz+, 2009)
J/A+A/495/157 : Interstellar extinction in Gal. Center (Schultheis+, 2009)
J/ApJ/702/178 : YSOs in the central 400pc of the Galaxy (Yusef-Zadeh+, 2009)
J/A+A/511/A18 : NIR observations of stars near SgrA* (Schoedel+, 2010)
J/ApJ/736/133 : Spitzer-IRS study of massive YSOs in gal. center (An+, 2011)
J/ApJ/737/73 : Infrared extinction toward the Gal. Centre (Fritz+, 2011)
J/AJ/149/64 : MIPSGAL 24µm point source catalog (Gutermuth+, 2015)
J/MNRAS/470/1462 : HOPS. III. Dense molecular gas properties (Longmore+, 2017)
J/ApJ/857/59 : Spitzer/IRS observations of the Gal. Center (Simpson, 2018)
J/A+A/642/A81 : APOGEE cool stars (Schultheis+, 2020)
J/A+A/653/A133 : GALACTICNUCLEUS IV. JHKs imaging (Nogueras-Lara+, 2021)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
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1- 7 A7 --- SSTGC SSTGC identifier
9- 24 A16 --- 2MASS 2MASS identifier (HHMMSSss+DDMMSSs; J2000)
26- 33 F8.4 deg GLON Galactic longitude
35- 41 F7.4 deg GLAT [-0.23/0.22] Galactic latitude
43- 53 A11 "Y/M/D" Date Observation date (UT)
55- 58 A4 --- Bands Bands ("K" or "K, L")
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Byte-by-byte Description of file: table3.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 7 A7 --- SSTGC SSTGC identifier
9- 12 F4.1 mag Av [9.5/67.6] Foreground visual extinction
14- 17 F4.1 mag e_Av [1.4/42] Av uncertainty
19- 33 A15 --- SpT Spectral type
35 A1 --- l_tau3.0 Limit flag on tau3.0
37- 40 F4.2 --- tau3.0 [0.01/4]? Optical depth of the 3um band
from solid H2O (Section 3.2)
42- 45 F4.2 --- e_tau3.0 [0.01/1]? tau3.0 uncertainty
47 A1 --- l_tau3.4 Limit flag on tau3.4
49- 52 F4.2 --- tau3.4 [0.03/0.4]? Optical depth of the 3.4um
hydrocarbon band (Section 3.3)
54- 57 F4.2 --- e_tau3.4 [0.01/0.2]? tau3.4 uncertainty
59 A1 --- l_tau3.54 Limit flag on tau3.54
61- 64 F4.2 --- tau3.54 [0.01/0.2]? Optical depth of the 3.54um
from the CH3OH band (Section 3.4)
66- 69 F4.2 --- e_tau3.54 [0.01/0.1]? tau3.54 uncertainty
71 A1 --- l_NH2O Limit flag on NH2O
73- 76 F4.2 10+18cm-2 NH2O [0.01/6.4]? H2O column density
78- 81 F4.2 10+18cm-2 e_NH2O [0.02/1.6]? NH2O uncertainty
83 A1 --- l_NCH3OH Limit flag on NCH3OH
85- 88 F4.2 10+18cm-2 NCH3OH [0.02/0.6]? CH3OH column density
90- 93 F4.2 10+18cm-2 e_NCH3OH [0.02/0.2]? NCH3OH uncertainty
95- 99 A5 --- COabs CO absorption
101- 105 A5 --- Brgam Br γ emission
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History:
From electronic version of the journal
References:
An et al. Paper I. 2011ApJ...736..133A 2011ApJ...736..133A Cat. J/ApJ/736/133
(End) Emmanuelle Perret [CDS] 14-Mar-2024