| 1. |
- Cormier, D., et al.
(författare)
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The molecular gas reservoir of 6 low-metallicity galaxies from the Herschel Dwarf Galaxy Survey A ground-based follow-up survey of CO(1-0), CO(2-1), and CO(3-2)
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 564
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Tidskriftsartikel (refereegranskat)abstract
- Context. Observations of nearby starburst and spiral galaxies have revealed that molecular gas is the driver of star formation. However, some nearby low-metallicity dwarf galaxies are actively forming stars, but CO, the most common tracer of this reservoir, is faint, leaving us with a puzzle about how star formation proceeds in these environments. Aims. We aim to quantify the molecular gas reservoir in a subset of 6 galaxies from the Herschel Dwarf Galaxy Survey with newly acquired CO data and to link this reservoir to the observed star formation activity. Methods. We present CO(1-0), CO(2-1), and CO(3-2) observations obtained at the ATNE Mopra 22-m, APEX, and IRAM 30-m telescopes, as well as [CII] 157 mu m and [OI] 63 mu m observations obtained with the Herschel/PACS spectrometer in the 6 low-metallicity dwarf galaxies: Haro 11, Mrk 1089, Mrk 930, NGC 4861, NGC 625, and UM 311. We derived their molecular gas masses from several methods, including using the CO-to-H-2 conversion factor X-CO (both Galactic and metallicity-scaled values) and dust measurements. The molecular and atomic gas reservoirs were compared to the star formation activity. We also constrained the physical conditions of the molecular clouds using the non-LTE code RADEX and the spectral synthesis code Cloudy. Results. We detect CO in 5 of the 6 galaxies, including first detections in Haro 11 (Z similar to 0.4 Z(circle dot)), Mrk 930 (0.2 Z(circle dot)), and UM 311 (0.5 Z(circle dot)), but CO remains undetected in NGC 4861 (0.2 Z(circle dot)). The CO luminosities are low, while [CII] is bright in these galaxies, resulting in [CII]/CO(1-0) >= 10 000. Our dwarf galaxies are in relatively good agreement with the Schmidt-Kennicutt relation for total gas. They show short molecular depletion timescales, even when considering metallicity-scaled X-CO factors. Those galaxies are dominated by their HI gas, except Haro 11, which has high star formation efficiency and is dominated by ionized and molecular gas. We determine the mass of each ISM phase in Haro 11 using Cloudy and estimate an equivalent X-CO factor that is 10 times higher than the Galactic value. Overall, our results confirm the emerging picture that CO suffers from significant selective photodissociation in low-metallicity dwarf galaxies.
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| 2. |
- Meixner, Margaret, et al.
(författare)
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Herschel and ALMA measurements of dust and molecules in supernova 1987A
- 2013
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Ingår i: Proceedings of Science. - 1824-8039. ; Part F113823
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Konferensbidrag (refereegranskat)abstract
- Dust production by supernovae is important in the dust life cycle of a galaxy. The explosion of SN 1987A was the nearest SN detected in the last 400 years, allowing us detailed studies of contemporary evolution of a supernova for the first time. In 2011, Matsuura et al. reported 0.4-0.7 M of dust in SN 1987A based on Herschel HERITAGE survey data, which is surprisingly large compared to prior measurements of supernovae. In this paper, we present our follow-up studies of this important discovery about SN 1987A using the Herschel Space Observatory and the Atacama Large Millimeter Array (ALMA). We highlight two important results, the detection of cold molecular gas and dust in the ejected material of SN 1987A. Our results suggest that SNe are significant producers of dust and molecules, as well as heavy elements, driving chemical evolution of galaxies.
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| 3. |
- Matsuura, M., et al.
(författare)
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Herschel Detects a Massive Dust Reservoir in Supernova 1987A
- 2011
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 333:6047, s. 1258-1261
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Tidskriftsartikel (refereegranskat)abstract
- We report far-infrared and submillimeter observations of supernova 1987A, the star whose explosion was observed on 23 February 1987 in the Large Magellanic Cloud, a galaxy located 160,000 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of about 17 to 23 kelvin at a rate of about 220 times the luminosity of the Sun. The intensity and spectral energy distribution of the emission suggest a dust mass of about 0.4 to 0.7 times the mass of the Sun. The radiation must originate from the supernova ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts.
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| 4. |
- Decin, L., et al.
(författare)
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Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles. I. Theoretical model - Mass-loss history unravelled in VY CMa
- 2006
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 456:2, s. 549-563
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Tidskriftsartikel (refereegranskat)abstract
- Context: Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). The gas and dust ejected during this phase are a major source in the mass budget of the interstellar medium. Recent studies have pointed towards the importance of variations in the mass-loss history of such objects.Aims: By modelling the full line profile of low excitation CO lines emitted in the circumstellar envelope, we can study the mass-loss history of AGB stars.Methods: We have developed a non-LTE radiative transfer code, which calculates the velocity structure and gas kinetic temperature of the envelope in a self-consistent way. The resulting structure of the envelope provides the input for the molecular line radiative calculations which are evaluated in the comoving frame. The code allows for the implementation of modulations in the mass-loss rate. This code has been benchmarked against other radiative transfer codes and is shown to perform well and efficiently.Results: We illustrate the effects of varying mass-loss rates in case of a superwind phase. The model is applied to the well-studied case of VY CMa. We show that both the observed integrated line strengths as the spectral structure present in the observed line profiles, unambiguously demonstrate that this source underwent a phase of high mass loss (~3.2 × 10-4 Mȯ yr-1) some 1000 yr ago. This phase took place for some 100 yr, and was preceded by a low mass-loss phase (~1 × 10-6 Mȯ yr-1) taking some 800 yr. The current mass-loss rate is estimated to be in the order of 8 × 10-5 Mȯ yr-1.Conclusions: In this paper, we demonstrate that both the relative strength of the CO rotational line profiles and the (non)-occurrence of spectral structure in the profile offer strong diagnostics to pinpoint the mass-loss history.
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| 5. |
- Decin, L., et al.
(författare)
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Probing the Mass-Loss History of VY CMa
- 2008
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Ingår i: Mass Loss from Stars and the Evolution of Stellar Clusters, Proceedings of conference in Lunteren May-June 2006, The Netherlands, eds. A. de Koter, L.J. Smith, L.B.F.M. Waters, ASP Conference Series, San Francisco. ; 388, s. 159-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Mass loss plays a dominant role in the evolution of low mass stars while they are on the Asymptotic Giant Branch (AGB). Recent studies have hinted towards the importance of time variability of the mass-loss rates of such objects. Likewise, more massive stars (MZAMS ⪆ 8 Msun) may pass through a red supergiant phase and lose mass in a similar manner. By modelling the full line profiles of low excitation CO transitions emitted in the circumstellar envelope (CSE), we have studied the mass-loss history of the well-studied supergiant VY CMa. We show that this source underwent a phase of high mass loss (˜ 2.8 × 10-4 Msun/yr) some 1000 yr ago, lasting some 100 yr, followed by a low mass-loss phase (˜ 1 × 10-6 Msun/yr) taking some 800 yr. The current mass-loss rate is estimated to be in the order of 1 × 10-4 Msun/yr.
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| 6. |
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