C.D.S. - SIMBAD4 rel 1.7 - 2020.12.02CET12:21:54

2013A&A...556A.137E - Astronomy and Astrophysics, volume 556A, 137-137 (2013/8-1)

Herschel observations of the Sagittarius B2 cores: hydrides, warm CO, and cold dust.


Abstract (from CDS):

Sagittarius B2 is one of the most massive and luminous star-forming regions in the Galaxy and shows a very rich chemistry and physical conditions similar to those in much more distant extragalactic starbursts. We present large-scale far-infrared/submillimeter photometric images and broadband spectroscopic maps taken with the PACS and SPIRE instruments onboard Herschel. High angular resolution dust images (complemented with Spitzer MIPS24 µm images) as well as atomic and molecular spectral maps were made and analyzed in order to constrain the dust properties, the gas physical conditions, and the chemical content of this unique region. The spectra towards the Sagittarius B2 star-forming cores, B2(M) and B2(N), are characterized by strong CO line emission (from J=4 to 16), emission lines from high-density tracers (HCN, HCO+, and H2S), [NII]205µm emission from ionized gas, and a large number of absorption lines from light hydride molecules (OH+, H2O+, H2O, CH+, CH, SH+, HF, NH, NH2, and NH3). The rotational population diagrams of CO suggest the presence of two different gas temperature components: an extended warm component with Trot∼50-100K, which is associated with the extended envelope, and a hotter component at Trot∼200K and Trot∼300K, which is only seen towards the B2(M) and B2(N) cores, respectively. As observed in other Galactic center clouds, such gas temperatures are significantly higher than the dust temperatures inferred from photometric images (Td≃20-30K). We determined far-IR luminosities (LFIR(M)∼5x106L and LFIR(N)∼1.1x106L) and total dust masses (Md(M)∼2300M and Md(N)∼2500M) in the cores. Non-local thermodynamic equilibrium models of the CO excitation were used to constrain the averaged gas density (n(H2)∼106cm–3) in the cores (i.e., similar or lower than the critical densities for collisional thermalization of mid- and high-J CO levels). A uniform luminosity ratio, L(CO)/LFIR~(1-3)x10–4, is measured along the extended envelope, suggesting that the same mechanism dominates the heating of the molecular gas at large scales. Sgr B2 shows extended emission from warm CO gas and cold dust, whereas only the cores show a hotter CO component. The detection of high-density molecular tracers and of strong [NII]205µm line emission towards the cores suggests that their morphology must be clumpy to allow UV radiation to escape from the inner HII regions. Together with shocks, the strong UV radiation field is likely responsible for the heating of the hot CO component. At larger scales, photodissociation regions models can explain both the observed CO line ratios and the uniform L(CO)/LFIR luminosity ratios.

Abstract Copyright:

Journal keyword(s): dust, extinction - Galaxy: center - infrared: ISM - ISM: individual objects: Sagittarius B2 - ISM: lines and bands - ISM: molecules

Simbad objects: 11

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Number of rows : 11

N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2021
1 M 82 IG 09 55 52.430 +69 40 46.93 9.61 9.30 8.41     ~ 5382 6
2 IC 4553 SyG 15 34 57.22396 +23 30 11.6084   14.76 13.88     ~ 2708 4
3 NAME Sgr A* X 17 45 40.03599 -29 00 28.1699           ~ 3545 3
4 NAME Gal Center reg 17 45 40.04 -29 00 28.1           ~ 11840 0
5 NAME Sgr B2 HII U HII 17 47 12.1 -28 22 34           ~ 4 0
6 NAME Sgr B2 HII V HII 17 47 13.2 -28 24 48           ~ 7 0
7 NAME Sgr B2 (North) Rad 17 47 20.2 -28 22 21           ~ 540 1
8 NAME Sgr B2 MoC 17 47 20.4 -28 23 07           ~ 1956 1
9 NAME Sgr B2 (South) HII 17 47 20.430 -28 23 45.06           ~ 86 0
10 NAME Sgr B2 Main Rad 17 47 20.5 -28 23 06           ~ 342 1
11 NAME Sgr B2 HII R HII 17 47 26.4 -28 22 05           ~ 10 0

    Equat.    Gal    SGal    Ecl

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