| 1. |
- Aalto, Susanne, 1964
(författare)
-
Molecules as tracers of galaxy evolution
- 2012
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 8:5287, s. 199-208
-
Konferensbidrag (refereegranskat)abstract
- Studying the molecular phase of the interstellar medium in galaxies is fundamental for the understandingof the onset and evolution of star formation and the growth of supermassive black holes. Wecan use molecules as observational tools exploiting them as tracers of chemical, physical and dynamicalconditions. In this short review, key molecules (e.g. HCN, HCO+, HNC, HC3N, CN, H3O+) in identifyingthe nature of buried activity and its evolution are discussed including some standard astrochemical scenarios.Furthermore, we can use IR excited molecular emission to probe the very inner regions of luminousinfrared galaxies (LIRGs) allowing us to get past the optically thick dust barrier of the compact obscurednuclei, e.g. in the dusty LIRG NGC4418. High resolution studies are often necessary to separate effectsof excitation and radiative transport from those of chemistry - one example is absorption and effects ofstimulated emission in the ULIRG Arp220. Finally, molecular gas in large scale galactic outflows is brieflydiscussed.
|
|
| 2. |
- Aalto, Susanne, 1964, et al.
(författare)
-
OH megamaser emission in the outflow of the luminous infrared galaxy Zw049.057
- 2022
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 18, s. 40-44
-
Konferensbidrag (refereegranskat)abstract
- High resolution (0.”26 × 0.”13 (70 × 35 pc)) L-band (18 cm) OH megamaser (OHM) e-Merlin observations of the LIRG Zw049.057 show that the emission is emerging from a low velocity outflowing structure - which is foreground to a fast, dense and collimated molecular outflow detected by ALMA. The extremely dusty compact obscured nucleus (CON) of Zw049.057 has no (or only little) OHM emission associated with it - possibly because of too high number densities that quench the OHM. In contrast we detect 6 cm H2CO emission primarily from the CON-region. We suggest that the OHM-region of Zw049.057 is not directly associated with star formation, but instead occurs in a wide-angle, slow outflow that surrounds the fast and dense outflow. The OHM is pumped by IR emission that likely stems from activities in the nucleus. We briefly discuss how OHM emission can be used as a probe of LIRG-CON galaxies.
|
|
| 3. |
- Aalto, Susanne, 1964
(författare)
-
Physical conditions and chemistry of molecular gas in galactic centers
- 2014
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 9:S303, s. 15-28
-
Tidskriftsartikel (refereegranskat)abstract
- Studying the molecular phase of the interstellar medium in galaxy nuclei is fundamental for the understanding of the onset and evolution of star formation and the growth of supermassive black holes. We can use molecules as observational tools exploiting them as tracers of chemical, physical and dynamical conditions. The molecular physical conditions in galaxy centers show large variety among galaxies, but in general the average gas densities (traced by e.g.HCN) and temperatures (probed by e.g. H2CO, NH3) are greater than in their disks. Molecular gas and dust is being funneled to the centers of galaxies by spiral arms, bars, and interactions - and one example of this is the minor merger NGC1614. Gas surface densities are also greaterin galaxy nuclei and in extreme cases they become orders of magnitudes larger than what we find in the center of our own Milky Way. We can use IR excited molecular emission to probe the very inner regions of galaxies with deeply obscured nuclei where N(H2)>10^24 cm-2 -for example in the luminous infrared galaxy (LIRG) NGC4418. Abundances of key molecules such as HCN, HCO+, HNC, HC3N, CN, H3O+,are important tools in identifying the nature of buried activity and its evolution. Standard astrochemical scenarios (including X-ray Dominated regions (XDRs) and Photon Dominated Regions (PDRs)) are briefly discussed in this review and how we can use molecules to distinguish between them. High resolution studies are often necessaryto separate effects of excitation and radiative transfer from those of chemistry - one example is absorption and effects of stimulated emission in the ULIRG Arp220. The nuclear activity in luminous galaxies often drives outflows and winds and in some cases molecular gas is being entrained in the outflows. Sometimes the molecular gas is carrying the bulk of the momentum.We can study the structure and physical conditions of the molecular gas to constrain the mass outflow rates and the evolution and nature of the driving source and two examples are discussed here: NGC1377 and Mrk231
|
|
| 4. |
- Alves, F. O., et al.
(författare)
-
The magnetic field of IRAS 16293-2422 as traced by shock-induced H2O masers
- 2012
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 8:5287, s. 74-78
-
Konferensbidrag (refereegranskat)abstract
- H2O masers are important magnetic field tracers in very high density gas. We show one of the first magnetic field determinations at such high density in a low-mass protostar: IRAS 16293-2422. We used the Very Large Array (VLA) to carry out spectro-polarimetric observations of the 22 GHz Zeeman emission of H2O masers. A blend of at least three maser features can be inferred from our data. They are excited in zones of compressed gas produced by shocks between the outflows ejected by this source and the ambient gas. The post-shock particle density is in the range 1 - 3 × 109 cmt−3, and the line-of-sight component of the magnetic field is estimated as ~ 113 mG. The outflow dynamics is likely magnetically dominated.
|
|
| 5. |
- Amada, Kei, et al.
(författare)
-
Discovery of SiO masers in the Water Fountain source, IRAS 16552-3050
- 2022
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 18, s. 359-361
-
Konferensbidrag (refereegranskat)abstract
- We report new detections of SiO ν = 1 and ν = 2 J = 1 → 0 masers in the water fountain source IRAS 16552-3050, which was observed with the Nobeyama 45 m telescope from March 2021 to April 2023. Water fountains are evolved stars whose H2O maser spectra trace high-velocity outflows of >100 Km s-. This is the second known case of SiO masers in a water fountain, after their prototypical source, W 43A. The line-of-sight velocity of the SiO masers are blue-shifted by ∼25 km s-1 from the systemic velocity. This velocity offset imply that the SiO masers are associated with nozzle structure formed by a jet penetrating the circumstellar envelope, and that new gas blobs of the jet erupted recently. Thus, the SiO masers imply this star to be in a new evolutionary stage.
|
|
| 6. |
- Amiri, N., et al.
(författare)
-
VLBA SiO maser observations of the OH/IR star OH 44.8-2.3: magnetic field and morphology
- 2012
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 8:5287, s. 54-58
-
Konferensbidrag (refereegranskat)abstract
- We report on Very Long Baseline Array SiO maser observations of the OH/IR star OH 44.8 - 2.3. The observations show that the maser features form a ring located at a distance of 5.4 AU around the central star. The masers show high fractional linear polarization up to 100%. The polarization vectors are consistent with a dipole field morphology. Additionally, we report a tentative detection of circular polarization of 7% for the brightest maser feature. This indicates a magnetic field of 1.5 ± 0.3 G. The SiO masers and the 1612 MHz OH masers suggest a mildly preferred outflow direction in the circumstellar environment of this star. The observed polarization is consistent with magnetic field structures along the preferred outflow direction. This could indicate the possible role of the magnetic fields in shaping the circumstellar environment of this object.
|
|
| 7. |
- Ao, Y., et al.
(författare)
-
The thermal state of molecular clouds in the Galactic center: evidence for non-photon-driven heating
- 2014
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 9:S303, s. 89-91
-
Tidskriftsartikel (refereegranskat)abstract
- We have used the Atacama Pathfinder Experiment (APEX) 12 m telescope at 218 GHz to observe molecular clouds simultaneously in the J_KA,Kc=3_03→2_02,3_22→2_21,and 3_21→2_20 transitions of para-H2CO to determine kinetic temperatures of the dense gas in the central molecular zone of the Galaxy. Gas kinetic temperatures for individual molecular clouds range from 55 to 125 K or even higher. The molecular clouds at high temperatures may be heated by turbulent dissipation and/or cosmic-rays
|
|
| 8. |
|
|
| 9. |
- Azulay, R., et al.
(författare)
-
Radio Emission from Binary Stars in the AB Doradus Moving Group
- 2015
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 10, s. 117-118
-
Konferensbidrag (refereegranskat)abstract
- Precise determination of dynamical masses of pre-main-sequence stars is essential for calibrating stellar evolution models, that are widely used to derive theoretical masses of young low-mass objects. We have determined the individual masses of the pair AB Dor Ba/Bb using Australian Long Baseline Array observations and archive infrared data, as part of a larger program directed to monitor binary systems in the AB Doradus moving group. We have detected, for the first time, compact radio emission from both stars. This has allowed us to determine the orbital parameters of both the relative and absolute orbits and, consequently, their individual dynamical masses: 0.28±0.05 M⊙ and 0.25±0.05 M⊙. Comparisons of the dynamical masses with the prediction of pre-main-sequence (PMS) evolutionary models show that the models underpredict the dynamical masses of the binary components Ba and Bb by 10-30% and 10-40%, respectively.
|
|
| 10. |
- Bjerkeli, Per, 1977, et al.
(författare)
-
Resolving star and planet formation with ALMA
- 2020
-
Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 14, s. 106-110
-
Konferensbidrag (refereegranskat)abstract
- Disks around young stars are the sites of planet formation. As such, the physical and chemical structure of disks have a direct impact on the formation of planetary bodies. Outflowing winds remove angular momentum and mass and affect the disk structure and therefore potentially planet formation. Until very recently, we have lacked the facilities to provide the necessary observational tools to peer into the wind launching and planet forming regions of the young disks. Within the framework of the Resolving star formation with ALMA program, young protostellar systems are targeted with ALMA to resolve the disk formation, outflow launching and planet formation. This contribution presents the first results of the program. The first resolved images of outflow launching from a disk were recently reported towards the Class I source TMC1A (Bjerkeli et al. 2016) where we also present early evidence of grain growth (Harsono et al. 2018).
|
|
