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Abstract We present high-resolution Karl G. Jansky Very Large Array observations of the 22 GHz H2O maser line in the extended Sagittarius B2 cloud. We detect 499 H2O masers across the observed velocities between −39 and 172 km s−1. To investigate the nature of the masers, we analyze their spatial distribution and crossmatch with catalogs of HIIregions and protostellar cores. 62% of masers are associated with protostellar cores and 32% with HIIregions. The nature of the remaining 6% of sources was not established but is likely associated with protostellar cores. Based on the spatial extent of the groups of masers, we classify them as either outflow-associated or young stellar object (YSO)–associated. We identify 144 unique sites of maser emission: 23 are associated with HIIregions and 94 with protostellar cores, of which 33 are associated with protostellar outflows and 18 with YSOs. The outflow-associated H2O maser emission is confined to within <2000 au of the central continuum source, despite shocked SiO emission extending over tens of thousands of astronomical units. The YSO-associated masers show a lack of detections at 5 < Vrel < 30 km s−1, which we suggest may be due to maser self-absorption. We show how H2O masers trace the large-scale material flow in Sgr B2 North, also seen in SiO and millimeter continuum emission. Finally, we find that protostellar cores with associated H2O masers tend to have brighter 3 mm continuum emission on average, although there is no strong correlation between maser brightness and continuum flux.
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H 3 + absorption and emission in local (U)LIRGs with JWST/NIRSpec: Evidence for high H 2 ionization rates
We study the 3.4 − 4.4 μm fundamental rovibrational band of H3+, a key tracer of the ionization of the molecular interstellar medium (ISM), in a sample of 12 local (d < 400 Mpc) (ultra)luminous infrared galaxies ((U)LIRGs) observed with JWST/NIRSpec. TheP,Q, andRbranches of the band are detected in 13 out of 20 analyzed regions within these (U)LIRGs, which increases the number of extragalactic H3+detections by a factor of 6. For the first time in the ISM, the H3+band is observed in emission; we detect this emission in three regions. In the remaining ten regions, the band is seen in absorption. The absorptions are produced toward the 3.4 − 4.4 μm hot dust continuum rather than toward the stellar continuum, indicating that they likely originate in clouds associated with the dust continuum source. The H3+band is undetected in Seyfert-like (U)LIRGs where the mildly obscured X-ray radiation from the active galactic nuclei might limit the abundance of this molecule. For the detections, the H3+abundances,N(H3+)/NH = (0.5 − 5.5)×10−7, imply relatively high ionization rates,ζH2, of between 3 × 10−16and > 4 × 10−15s−1, which are likely associated with high-energy cosmic rays. In half of the targets, the absorptions are blueshifted by 50–180 km s−1, which is lower than the molecular outflow velocities measured using other tracers such as OH 119 μm or rotational CO lines. This suggests that H3+traces gas close to the outflow-launching sites before it has been fully accelerated. We used nonlocal thermodynamic equilibrium models to investigate the physical conditions of these clouds. In seven out of ten objects, the H3+excitation is consistent with inelastic collisions with H2in warm translucent molecular clouds (Tkin ∼ 250–500 K andn(H2) ∼102 − 3cm−3). In three objects, dominant infrared pumping excitation is required to explain the absorptions from the (3,0) and (2,1) levels of H3+detected for the first time in the ISM.
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- Award ID(s):
- 2142300
- PAR ID:
- 10569721
- Publisher / Repository:
- Astronomy and Astrophysics
- Date Published:
- Journal Name:
- Astronomy & Astrophysics
- Volume:
- 689
- ISSN:
- 0004-6361
- Page Range / eLocation ID:
- L12
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1051/0004-6361/202451741
