The nature of absorption-selected galaxies and their connection to the general galaxy population have been open issues for more than three decades, with little information available on their gas ...properties. Here we show, using detections of carbon monoxide emission with the Atacama Large Millimeter/submillimeter Array, that five of seven high-metallicity, absorption-selected galaxies at intermediate redshifts, z 0.5-0.8, have large molecular gas masses, MMol (0.6-8.2) × 1010 M and high molecular gas fractions (fMol MMol/(M* + MMol) 0.29-0.87). Their modest star formation rates (SFRs), (0.3-9.5) M yr−1, then imply long gas depletion timescales, (3-120) Gyr. The high-metallicity absorption-selected galaxies at z 0.5-0.8 appear distinct from populations of star-forming galaxies at both z 1.3-2.5, during the peak of star formation activity in the Universe, and lower redshifts, z 0.05. Their relatively low SFRs, despite the large molecular gas reservoirs, may indicate a transition in the nature of star formation at intermediate redshifts, z 0.7.
Context.
GRB 211106A and GRB 211227A are two recent gamma-ray bursts (GRBs) whose initial X-ray position enabled us to possibly associate them with bright, low-redshift galaxies (
z
< 0.7). The ...prompt emission properties suggest that GRB 211106A is a genuine short-duration GRB and GRB 211227A is a short GRB with extended emission. Therefore, they are likely to be produced by a compact binary merger. However, a classification based solely on the prompt emission properties can be misleading.
Aims.
The possibility of having two short GRBs occurring in the local Universe makes them ideal targets for the search of associated kilonova (KN) emission and for detailed studies of the host galaxy properties.
Methods.
We carried out deep optical and near-infrared (NIR) follow-up with the ESO-VLT FORS2, HAWK-I, and MUSE instruments for GRB 211106A and with ESO-VLT FORS2 and X-shooter for GRB 211227A, starting from hours after the X-ray afterglow discovery up to days later. We performed photometric analysis to look for afterglow and KN emissions associated with the bursts, together with imaging and spectroscopic observations of the host galaxy candidates. We compared the results obtained from the optical/NIR observations with the available
Swift
X-Ray Telescope (XRT) and others high-energy data of both events.
Results.
For both GRBs we placed deep limits to the optical/NIR afterglow and KN emission. We identified their associated host galaxies, GRB 211106A at a photometric redshift
z
= 0.64, GRB 211227A at a spectroscopic
z
= 0.228. From MUSE and X-shooter spectra we derived the host galaxy properties, which turned out to be consistent with short GRBs typical hosts. We also compared the properties of GRB 211106A and GRB 211227A with those of the short GRBs belonging to the S-BAT4 sample, here extended up to December 2021, in order to further investigate the nature of these two bursts.
Conclusions.
Our study of the prompt and afterglow phase of the two GRBs, together with the analysis of their associated host galaxies, allows us to confirm the classification of GRB 211106A as a short GRB, and GRB 211227A as a short GRB with extended emission. The absence of an optical/NIR counterpart down to deep magnitude limits is likely due to high local extinction for GRB 211106A and a peculiarly faint kilonova for GRB 211227A.
Context. The extreme brightness of gamma-ray burst (GRB) afterglows and their simple spectral shape make them ideal beacons to study the interstellar medium of their host galaxies through absorption ...line spectroscopy at almost any redshift. Aims. We describe the distribution of rest-frame equivalent widths (EWs) of the most prominent absorption features in GRB afterglow spectra, providing the means to compare individual spectra to the sample and identify its peculiarities. Methods. Using 69 low-resolution GRB afterglow spectra, we conduct a study of the rest-frame EWs distribution of features with an average rest-frame EW larger than 0.5 Å. To compare an individual GRB with the sample, we develop EW diagrams as a graphical tool, and we give a catalogue with diagrams for the 69 spectra. We introduce a line strength parameter (LSP) that allows us to quantify the strength of the absorption features in a GRB spectrum as compared to the sample by a single number. Using the distributions of EWs of single-species features, we derive the distribution of their column densities by a curve of growth (CoG) fit. Results. We find correlations between the LSP and the extinction of the GRB, the UV brightness of the host galaxies and the neutral hydrogen column density. However, we see no significant evolution of the LSP with the redshift. There is a weak correlation between the ionisation of the absorbers and the energy of the GRB, indicating that, either the GRB event is responsible for part of the ionisation, or that galaxies with high-ionisation media produce more energetic GRBs. Spectral features in GRB spectra are, on average, 2.5 times stronger than those seen in QSO intervening damped Lyman-α (DLA) systems and slightly more ionised. In particular we find a larger excess in the EW of C ivλλ1549 relative to QSO DLAs, which could be related to an excess of Wolf-Rayet stars in the environments of GRBs. From the CoG fitting we obtain an average number of components in the absorption features of GRBs of 6.00-1.25+1.00. The most extreme ionisation ratios in our sample are found for GRBs with low neutral hydrogen column density, which could be related to ionisation by the GRB emission.
Short duration gamma-ray bursts (SGRBs) are thought to be related to the violent merger of compact objects, such as neutron stars or black holes, which makes them promising sources of gravitational ...waves. The detection of a "kilonova"- likesignature associated to the Swift-detected GRB 130603B has suggested that this event is the result of a compact object merger. Our knowledge on SGRB has been, until now, mostly based on the absence of supernova signatures and the analysis of the host galaxies to which they cannot always be securely associated. Further progress has been significantly hampered by the faintness and rapid fading of their optical counterparts (afterglows), which has so far precluded spectroscopy of such events. Afterglow spectroscopy is the key tool to firmly determine the distance at which the burst was produced, crucial to understand its physics, and study its local environment. The merger is not associated with the most star-forming region of the galaxy; however, it did occur in a dense region, implying a rapid merger or a low natal kick velocity for the compact object binary.
Evolved asymptotic giant branch (AGB) stars and Type Ia supernovae (SNe) are important contributors to the elements that form dust in the interstellar medium of galaxies, in particular, carbon and ...iron. However, they require at least a Gyr to start producing these elements, therefore, a change in dust quantity or properties may appear at high redshifts. In this work, we use extinction of γ-ray burst (GRB) afterglows as a tool to look for variations in dust properties at z ≥ 3. We use a spectroscopically selected sample of GRB afterglows observed with the VLT/X-shooter instrument to determine extinction curves out to high redshifts. We present 10 new z ≥ 3 X-shooter GRBs of which six are dusty. Combining these with individual extinction curves of three previously known z ≥ 3 GRBs, we find an average extinction curve consistent with the SMC-Bar. A comparison with spectroscopically selected GRBs at all redshifts indicates a drop in visual extinction (AV) at z > 3.5 with no moderate or high-extinction bursts. We check for observational bias using template spectra and find that GRBs up to z ∼ 8 are detectable with X-shooter up to AV ∼ 0.3 mag. Although other biases are noted, a uniformly low dust content above z > 3.5 indicates a real drop, suggesting a transition in dust properties and/or available dust building blocks. The remarkable increase in dust content at z < 3.5 could arise due to carbon and possibly iron production by the first carbon-rich AGB and Type Ia SNe, respectively. Alternatively, z > 3.5 dust drop could be the result of low stellar masses of GRB host galaxies.
Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A, from which we can ...measure metallicity, chemical abundance patterns, dust-to-metals ratio (DTM), and extinction of the GRB host galaxy at z = 5.0. The host absorption system is a damped Ly alpha absorber with a very large neutral hydrogen column density of log N(H I)/cm super(-2) = 22.30 + or - 0.06 and a metallicity of S/H = -1.70 + or - 0.10. It is the highest-redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z = 5.0 system as the GRB host galaxy and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with A sub(V) = 0.11 + or - 0.04 mag, and the host galaxy has a DTM that is consistent with being equal to or lower than typical values in the Local Group.
The Cambrian Miaolingian Series strata are continuously exposed in the North China Platform and contain diverse sedimentary phenomena, including substantial with oncoid-rich units. Limestone samples ...from the Zhangxia Formation in the Sandaogou section were collected to characterise unique macroscale to microscale sedimentary characteristics of the marine carbonate oncoids. In the oncolitic beds (∼4.5 m thick), the individual size of oncoids gradually increases from bottom to top. The oncoid morphology and the presence of a nucleus and laminae in thin-sections are used to classify these oncoids into three types (concentric laminar, lateral growth and multicore oncoids). As evidenced by scanning electron microscopy and energy-dispersive X-ray observations, Girvanella are abundant inside these oncoids and are associated with nanospheres, framboidal pyrite, and spherical and filamentous microbial fossils, confirming the biogenicity of the studied oncoids. These results suggest that the oncolitic-oolitic limestone formed in an upward-shallowing marine environment caused by a forced regression process that resulted in a decrease in accommodation space in a fourth-order sequence. Thus, the conditions became increasingly suitable for the development of cyanobacteria-dominated microbial mats and large oncoids. The late stage of the depositional setting and elevated solar radiation resulted in the formation of the growth termination surface.
KEY POINTS
Evidence of microbial origin from the oncoids of the Cambrian Miaolingian Series in the North China Platform.
Vertical variation in oncoid size and distribution coincide with geochemical data.
A shallowing depositional environment is interpreted as the reason for variation in oncoid size and formation of oncoid growth termination surfaces.
We have initiated a survey using the newly commissioned X-shooter spectrograph to target candidate relatively metal-rich damped Lyα absorbers (DLAs). Our rationale is that high-metallicity DLAs due ...to the luminosity–metallicity relation likely will have the most luminous galaxy counterparts. In addition, the spectral coverage of X-shooter allows us to search for not only Lyα emission, but also rest-frame optical emission lines. We have chosen DLAs where the strongest rest-frame optical lines (O ii, O iii, Hβ and Hα) fall in the near-infrared atmospheric transmission bands. In this first paper resulting from the survey, we report on the discovery of the galaxy counterpart of the zabs= 2.354 DLA towards the z= 2.926 quasar Q 2222−0946. This DLA is amongst the most metal-rich z > 2 DLAs studied so far at comparable redshifts and there is evidence for substantial depletion of refractory elements on to dust grains. We measure metallicities from Zn ii, Si ii, Ni ii, Mn ii and Fe ii of −0.46 ± 0.07, − 0.51 ± 0.06, − 0.85 ± 0.06, − 1.23 ± 0.06 and −0.99 ± 0.06, respectively. The galaxy is detected in the Lyα, O iiiλλ4959, 5007 and Hα emission lines at an impact parameter of about 0.8 arcsec (6 kpc at zabs= 2.354). Based on the Hα line, we infer a star formation rate of 10 M⊙ yr−1, which is a lower limit due to the possibility of slit loss. Compared to the recently determined Hα luminosity function for z= 2.2 galaxies, the DLA-galaxy counterpart has a luminosity of L∼ 0.1L*Hα. The emission-line ratios are 4.0 (Lyα/Hα) and 1.2 (O iii/Hα). In particular, the Lyα line shows clear evidence for resonant scattering effects, namely an asymmetric, redshifted (relative to the systemic redshift) component and a much weaker blueshifted component. The fact that the blueshifted component is relatively weak indicates the presence of a galactic wind. The properties of the galaxy counterpart of this DLA are consistent with the prediction that metal-rich DLAs are associated with the most luminous of the DLA-galaxy counterparts.
The chemical enrichment of dust and metals in the interstellar medium of galaxies throughout cosmic time is one of the key driving processes of galaxy evolution. Here we study the evolution of the ...gas-phase metallicities, dust-to-gas (DTG) ratios, and dust-to-metal (DTM) ratios of 36 star-forming galaxies at 1.7 < z < 6.3 probed by gamma-ray bursts (GRBs). We compiled all GRB-selected galaxies with intermediate- (ℛ = 7000) to high-resolution (ℛ > 40 000) spectroscopic data, including three new sources, for which at least one refractory (e.g., Fe) and one volatile (e.g., S or Zn) element have been detected at S/N > 3. This is to ensure that accurate abundances and dust depletion patterns can be obtained. We first derived the redshift evolution of the dust-corrected, absorption-line-based gas-phase metallicity, M/Htot, in these galaxies, for which we determine a linear relation with redshift M/Htot(z) = (−0.21 ± 0.04)z − (0.47 ± 0.14). We then examined the DTG and DTM ratios as a function of redshift and through three orders of magnitude in metallicity, quantifying the relative dust abundance both through the direct line-of-sight visual extinction, AV, and the derived depletion level. We used a novel method to derive the DTG and DTM mass ratios for each GRB sightline, summing up the mass of all the depleted elements in the dust phase. We find that the DTG and DTM mass ratios are both strongly correlated with the gas-phase metallicity and show a mild evolution with redshift as well. While these results are subject to a variety of caveats related to the physical environments and the narrow pencil-beam sightlines through the interstellar medium probed by the GRBs, they provide strong implications for studies of dust masses that aim to infer the gas and metal content of high-redshift galaxies, and particularly demonstrate the large offset from the average Galactic value in the low-metallicity, high-redshift regime.
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