In:
The Astrophysical Journal, American Astronomical Society, Vol. 930, No. 1 ( 2022-05-01), p. 16-
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 2.3 μ m, 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 H 2 O ice column densities ( N 〉 2 × 10 18 cm −2 ), and six of them also reveal CH 3 OH 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 (≲0.02 M ⊙ yr −1 ), reinforcing the previous claim on the suppressed star-formation activity in the CMZ. Our data also indicate that the strong “shoulder” CO 2 ice absorption at 15.4 μ m observed in YSO candidates in the previous paper arises from CH 3 OH-rich ice grains having a large CO 2 concentration [ N (CO 2 )/ N (CH 3 OH) ≈ 1/3].
Type of Medium:
Online Resource
ISSN:
0004-637X
,
1538-4357
DOI:
10.3847/1538-4357/ac5d51
Language:
Unknown
Publisher:
American Astronomical Society
Publication Date:
2022
detail.hit.zdb_id:
2207648-7
detail.hit.zdb_id:
1473835-1
SSG:
16,12
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