| 1. |
- Michalowski, Michal J., et al.
(author)
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Molecular gas masses of gamma-ray burst host galaxies
- 2018
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 617
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Journal article (peer-reviewed)abstract
- Context. Long gamma-ray bursts (GRBs) can potentially be used as a tool to study star formation and recent gas accretion onto galaxies. However, the information about gas properties of GRB hosts is scarce. In particular, very few carbon monoxide (CO) line detections of individual GRB hosts have been reported. It has also been suggested that GRB hosts have lower molecular gas masses than expected from their star formation rates (SFRs). Aims. The objectives of this paper are to analyse molecular gas properties of the first substantial sample of GRB hosts and test whether they are deficient in molecular gas. Methods. We obtained CO(2-1) observations of seven GRB hosts with the APEX and IRAM 30 m telescopes. We analysed these data together with all other hosts with previous CO observations. From these observations we calculated the molecular gas masses of these galaxies and compared them with the expected values based on their SFRs and metallicities. Reults. We obtained detections for 3 GRB hosts (980425, 080207, and 111005A) and upper limits for the remaining 4 (031203, 060505, 060814, and 100316D). In our entire sample of 12 CO-observed GRB hosts, 3 are clearly deficient in molecular gas, even taking into account their metallicity (980425, 060814, and 080517). Four others are close to the best-fit line for other star-forming galaxies on the SFR-M-H2 plot (051022, 060505, 080207, and 100316D). One host is clearly molecule rich (111005A). Finally, the data for 4 GRB hosts are not deep enough to judge whether they are molecule deficient (000418, 030329, 031203, and 090423). The median value of the molecular gas depletion time, M-H2/SFR, of GRB hosts is similar to 0.3 dex below that of other star-forming galaxies, but this result has low statistical significance. A Kolmogorov-Smirnov test performed on M-H2/SFR shows an only similar to 2 sigma difference between GRB hosts and other galaxies. This difference can partly be explained by metallicity effects, since the significance decreases to similar to 1 sigma for M-H2/SFR versus metallicity. Conclusions. We found that any molecular gas deficiency of GRB hosts has low statistical significance and that it can be attributed to their lower metallicities; and thus the sample of GRB hosts has molecular properties that are consistent with those of other galaxies, and they can be treated as representative star-forming galaxies. However, the molecular gas deficiency can be strong for GRB hosts if they exhibit higher excitations and/or a lower CO-to-H-2 conversion factor than we assume, which would lead to lower molecular gas masses than we derive. Given the concentration of atomic gas recently found close to GRB and supernova sites, indicating recent gas inflow, our results about the weak molecular deficiency imply that such an inflow does not enhance the SFRs significantly, or that atomic gas converts efficiently into the molecular phase, which fuels star formation. Only if the analysis of a larger GRB host sample reveals molecular deficiency (especially close to the GRB position) would this support the hypothesis of star formation that is directly fuelled by atomic gas.
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| 2. |
- Akins, Hollis B., et al.
(author)
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ALMA Reveals Extended Cool Gas and Hot Ionized Outflows in a Typical Star-forming Galaxy at Z=7.13
- 2022
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In: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 934:1
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Journal article (peer-reviewed)abstract
- We present spatially resolved morphological properties of [C II] 158 mu m, [O III] 88 mu m, dust, and rest-frame ultraviolet (UV) continuum emission for A1689-zD1, a strongly lensed, sub-L* galaxy at z = 7.13, by utilizing deep Atacama Large Millimeter/submillimeter Array (ALMA) and Hubble Space Telescope (HST) observations. While the [O III] line and UV continuum are compact, the [C II] line is extended up to a radius of r similar to 12 kpc. Using multi-band rest-frame far-infrared continuum data ranging from 52 to 400 mu m, we find an average dust temperature and emissivity index of Tdust=41-14+17 beta=1.7-0.7+1.1 6 galaxies.
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| 3. |
- Thöne, Christina C., et al.
(author)
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NGC 2770 : A Supernova Ib Factory?
- 2009
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 698:2, s. 1307-1320
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Journal article (peer-reviewed)abstract
- NGC 2770 has been the host of three supernovae (SNe) of Type Ib during the last ten years, SN 1999eh, SN 2007uy, and SN 2008D. SN 2008D attracted special attention due to the serendipitous discovery of an associated X-ray transient. In this paper, we study the properties of NGC 2770 and specifically the three SN sites to investigate whether this galaxy is in any way peculiar to cause a high frequency of SNe Ib. We model the global spectral energy distribution of the galaxy from broadband data and derive a star formation and SN rate comparable to the values of the Milky Way. We further study the galaxy using longslit spectroscopy covering the major axis and the three SN sites. From the spectroscopic study we find subsolar metallicities for the SN sites, a high extinction and a moderate star formation rate. In a high-resolution spectrum, we also detect diffuse interstellar bands in the line of sight toward SN 2008D. A comparison of NGC 2770 to the global properties of a galaxy sample with high SN occurrence (>= 3 SN in the last 100 years) suggests that NGC 2770 is not particularly destined to produce such an enhancement of observed SNe. Its properties are also very different from gamma-ray burst host galaxies. Statistical considerations on SN Ib detection rates give a probability of ~1.5% to find a galaxy with three Ib SNe detected in ten years. The high number of rare Ib SNe in this galaxy is therefore likely to be a coincidence rather than special properties of the galaxy itself. NGC 2770 has a small irregular companion, NGC 2770B, which is highly star-forming, has a very low mass and one of the lowest metallicities detected in the nearby universe as derived from longslit spectroscopy. In the most metal poor part, we even detect Wolf-Rayet (WR) features, which is at odds with most current models of WR stars which require high metallicities. Based on observations with the Nordic Optical Telescope, ESO proposal 080.D-0526, the GALEX and NED databases.
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| 4. |
- Nadolny, Jakub, et al.
(author)
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Main Sequence to Starburst Transitioning Galaxies : Gamma-Ray Burst Hosts at z ∼ 2
- 2023
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 952:2
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Journal article (peer-reviewed)abstract
- Star-forming galaxies populate a main sequence (MS), a well-defined relation between stellar mass (M*) and star formation rate (SFR). Starburst (SB) galaxies lie significantly above the relation, whereas quenched galaxies lie below the sequence. In order to study the evolution of galaxies on the SFR–M* plane and its connection to the gas content, we use the fact that recent episodes of star formation can be pinpointed by the existence of gamma-ray bursts (GRBs). Here we present sensitive [C i] nondetections of z ∼ 2 ultraluminous infrared (ULIRG) GRB host galaxies. We find that our GRB hosts have similar molecular masses to those of other ULIRGs. However, unlike other ULIRGs, the GRB hosts are located at the MS or only a factor of a few above it. Hence, our GRB hosts are caught in the transition toward the SB phase. This is further supported by the estimated depletion times, which are similar to those of other transitioning galaxies. The GRB hosts are [C i]-dark galaxies, defined as having a [C i]/CO temperature brightness ratio of <0.1. Such a low [C i]/CO ratio has been found in high-density environments (nH > 104 cm−3) where CO is shielded from photodissociation, leading to underabundances of [C i]. This is consistent with the merger process that is indeed suggested for our GRB hosts by their morphologies.
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