Spatially resolved spectroscopy of the environments of explosive transients carries detailed information about the physical properties of the stellar population that gave rise to the explosion, and ...thus the progenitor itself. Here, we present new observations of ESO184-G82, the galaxy hosting the archetype of the γ-ray burst/supernova connection, GRB 980425/SN 1998bw, obtained with the integral field spectrograph MUSE mounted at the Very Large Telescope. These observations have yielded detailed maps of emission-line strength for various nebular lines along with physical parameters such as dust extinction, stellar age, and oxygen abundance on spatial scales of 160 pc. The immediate environment of GRB 980425 is young (5–8 Myr) and consistent with a mildly extinguished (AV ~ 0.1 mag) progenitor of zero-age main-sequence mass between 25 M⊙ and 40 M⊙ and an oxygen abundance 12 + log (O / H) ~ 8.2 (Z ~ 0.3 Z⊙), which is slightly lower than that of an integrated measurement of the whole galaxy (12 + log (O / H) ~ 8.3) and a prominent nearby H ii region (12 + log (O / H) ~ 8.4). This region is significantly younger than the explosion site, and we argue that a scenario in which the GRB progenitor formed in this environment and was subsequently ejected appears very unlikely. We show that empirical strong-line methods based on O iii and/or N ii are inadequate to produce accurate maps of oxygen abundance at the level of detail of our MUSE observation as these methods strongly depend on the ionization state of the gas. The metallicity gradient in ESO184-G82 is − 0.06 dex kpc-1, indicating that the typical offsets of at most few kpc for cosmological GRBs on average have a small impact on oxygen abundance measurements at higher redshift.
Context. Several issues regarding the nature of dust at high redshift remain unresolved: its composition, its production and growth mechanisms, and its effect on background sources. Aims. We provide ...a more accurate relation between dust depletion levels and dust-to-metals ratio (DTM), and to use the DTM to investigate the origin and evolution of dust in the high-redshift Universe via gamma-ray burst damped Lyman-alpha absorbers (GRB-DLAs). Methods. We use absorption-line measured metal column densities for a total of 19 GRB-DLAs, including five new GRB afterglow spectra from VLT/X-Shooter. We use the latest linear models to calculate the dust depletion strength factor in each DLA. Using these values we calculate total dust and metal column densities to determine a DTM. We explore the evolution of DTM with metallicity, and compare it to previous trends in DTM measured with different methods. Results. We find significant dust depletion in 16 of our 19 GRB-DLAs, yet 18 of the 19 have a DTM significantly lower than the Milky Way. We find that DTM is positively correlated with metallicity, which supports a dominant ISM grain-growth mode of dust formation. We find a substantial discrepancy between the dust content measured from depletion and that derived from the total V-band extinction, AV, measured by fitting the afterglow SED. We advise against using a measurement from one method to estimate that from the other until the discrepancy can be resolved.
Abstract
The number of long-duration gamma-ray burst (LGRB) host galaxies with measured metallicities and host masses has expanded sufficiently to investigate how the distributions of these ...properties change with redshift. Using the combined host galaxy metallicity sample from Graham & Fruchter and Krühler et al., we find a surprising lack of evolution in the LGRB metallicity distribution across different redshifts. In particular, the fraction of LGRB hosts with relatively high metallicity (12+log(O/H) ≥ 8.4) remains essentially constant out to
z
= 2.5. This result is at odds with the evolution in the mass–metallicity relation of typical galaxies, which become progressively more metal poor with increasing redshift. A similar result is found when converting the LGRB host galaxy mass distribution taken from the Swift GRB Host Galaxy Legacy Survey (SHOALS) sample to a corresponding metallicity distribution by applying a redshift-dependent mass–metallicity relation. The SHOALS sample is compiled using an unbiased selection function implying that the observed lack of evolution in the host galaxy high-metallicity distribution is not caused by selection effects. However, the LGRB host galaxy metallicities estimated from the stellar mass are typically a quarter dex higher at all redshifts than the metallicity we measure spectroscopically. This implies that using mass–metallicity relationships to estimate host metallicities will thus produce a substantial systematic bias.
ABSTRACT We estimate the long-duration gamma-ray burst (LGRB) progenitor rate using our recent work on the effects of environmental metallically on LGRB formation in concert with supernovae (SNe) ...statistics via an approach patterned loosely off the Drake equation. Beginning with the cosmic star formation history, we consider the expected number of broad-line Type Ic events (the SNe type associated with LGRBs) that are in low-metallicity host environments adjusted by the contribution of high-metallicity host environments at a much reduced rate. We then compare this estimate to the observed LGRB rate corrected for instrumental selection effects to provide a combined estimate of the efficiency fraction of these progenitors to produce LGRBs and the fraction of which are beamed in our direction. From this we estimate that an aligned LGRB occurs for approximately every 4000 2000 low-metallically broad-lined SNe Ic. Therefore, if one assumes a semi-nominal beaming factor of 100, then only about one such supernova out of 40 produce an LGRB. Finally, we propose an off-axis LGRB search strategy of targeting only broad-line Type Ic events that occur in low-metallicity hosts for radio observation.
Aims.
We investigate electron temperature (
T
e
) and gas-phase oxygen abundance (
Z
Te
) measurements for galaxies in the local Universe (
z
< 0.25). Our sample comprises spectra from a total of ...264 emission-line systems, ranging from individual H
II
regions to whole galaxies, including 23 composite H
II
regions from star-forming main sequence galaxies in the MaNGA survey.
Methods.
We utilise 130 of these systems with directly measurable
T
e
(O
II
) to calibrate a new metallicity-dependent
T
e
(O
III
)–
T
e
(O
II
) relation that provides a better representation of our varied dataset than existing relations from the literature. We also provide an alternative
T
e
(O
III
)–
T
e
(N
II
) calibration. This new
T
e
method is then used to obtain accurate
Z
Te
estimates and form the mass – metallicity relation (MZR) for a sample of 118 local galaxies.
Results.
We find that all the
T
e
(O
III
)–
T
e
(O
II
) relations considered here systematically under-estimate
Z
Te
for low-ionisation systems by up to 0.6 dex. We determine that this is due to such systems having an intrinsically higher O
+
abundance than O
++
abundance, rendering
Z
Te
estimates based only on O
III
lines inaccurate. We therefore provide an empirical correction based on strong emission lines to account for this bias when using our new
T
e
(O
III
)–
T
e
(O
III
) and
T
e
(O
III
)–
T
e
(N
II
) relations. This allows for accurate metallicities (1
σ
= 0.08 dex) to be derived for any low-redshift system with an O
III
λ
4363 detection, regardless of its physical size or ionisation state. The MZR formed from our dataset is in very good agreement with those formed from direct measurements of metal recombination lines and blue supergiant absorption lines, in contrast to most other
T
e
-based and strong-line-based MZRs. Our new
T
e
method therefore provides an accurate and precise way of obtaining
Z
Te
for a large and diverse range of star-forming systems in the local Universe.
We present and analyse an extensive dataset of the superluminous supernova (SLSN) LSQ14mo (z = 0.256), consisting of a multi-colour light curve from −30 d to +70 d in the rest-frame (relative to ...maximum light) and a series of six spectra from PESSTO covering −7 d to +50 d. This is among the densest spectroscopic coverage, and best-constrained rising light curve, for a fast-declining hydrogen-poor SLSN. The bolometric light curve can be reproduced with a millisecond magnetar model with ~ 4 M⊙ ejecta mass, and the temperature and velocity evolution is also suggestive of a magnetar as the power source. Spectral modelling indicates that the SN ejected ~ 6 M⊙ of CO-rich material with a kinetic energy of ~7 × 1051 erg, and suggests a partially thermalised additional source of luminosity between −2 d and +22 d. This may be due to interaction with a shell of material originating from pre-explosion mass loss. We further present a detailed analysis of the host galaxy system of LSQ14mo. PESSTO and GROND imaging show three spatially resolved bright regions, and we used the VLT and FORS2 to obtain a deep (five-hour exposure) spectra of the SN position and the three star-forming regions, which are at a similar redshift. The FORS2 spectrum at + 300 days shows no trace of SN emission lines and we place limits on the strength of O i from comparisons with other Ic supernovae. The deep spectra provides a unique chance to investigate spatial variations in the host star-formation activity and metallicity. The specific star-formation rate is similar in all three components,as is the presence of a young stellar population. However, the position of LSQ14mo exhibits a lower metallicity, with 12 + log (O/H) = 8.2 in both the R23 and N2 scales (corresponding to ~0.3 Z⊙ ). We propose that the three bright regions in the host system are interacting, which could induce gas flows triggering star formation in low-metallicity regions.
Motivated by the anomalous dust-to-metal ratios derived in the literature for gamma -ray burst (GRB) damped Lyman- alpha absorbers (DLAs), we measure these ratios using the dust-depletion pattern ...observed in UV/optical afterglow spectra associated with the interstellar medium (ISM) at the GRB host-galaxy redshifts. Our sample consists of 20 GRB absorbers and a comparison sample of 72 DLAs toward quasars (QSOs) with redshift 1.2 < z < 4.0 and down to Z = 0.002 Z# metallicities. The dust-to-metal ratio in QSO- and GRB-DLAs increases both with metallicity and metal column density, spanning ~10-110% of the Galactic value and pointing to a nonuniversal dust-to-metal ratio. The dust extinction AV increases steeply with the column density of iron in dust, N(Fe)dust, calculated from relative metal abundances, confirming that dust extinction is mostly occurring in the host galaxy ISM. Most GRB-DLAs display log N(Fe)dust > 14.7, above which several QSO-DLAs reveal molecular hydrogen, making GRB-DLAs promising candidates for molecular detection and study.
Context. Dust is known to be produced in the envelopes of asymptotic giant branch (AGB) stars, the expanded shells of supernova (SN) remnants, and in situ grain growth within the interstellar medium ...(ISM), although the corresponding efficiency of each of these dust formation mechanisms at different redshifts remains a topic of debate. During the first Gyr after the Big Bang, it is widely believed that there was not enough time to form AGB stars in high numbers, hence the dust at this epoch is expected to be purely from SNe or subsequent grain growth in the ISM. The time period corresponding to z ~ 5−6 is thus expected to display the transition from SN-only dust to a mixture of both formation channels as is generally recognized at present. Aims. Here we aim to use afterglow observations of gamma-ray bursts (GRBs) at redshifts larger than z > 4 to derive host galaxy dust column densities along their line of sight and to test if a SN-type dust extinction curve is required for some of the bursts. Methods. We performed GRB afterglow observations with the seven-channel Gamma-Ray Optical and Near-infrared Detector (GROND) at the 2.2 m MPI telescope in La Silla, Chile (ESO), and we combined these observations with quasi-simultaneous data gathered with the XRT telescope on board the Swift satellite. Results. We increase the number of measured AV values for GRBs at z > 4 by a factor of ~2–3 and find that, in contrast to samples at mostly lower redshift, all of the GRB afterglows have a visual extinction of AV < 0.5 mag. Analysis of the GROND detection thresholds and results from a Monte Carlo simulation show that although we partly suffer from an observational bias against highly extinguished sight-lines, GRB host galaxies at 4 < z < 6 seem to contain on average less dust than at z ~ 2. Additionally, we find that all of the GRBs can be modeled with locally measured extinction curves and that the SN-like dust extinction curve, as previously found toward GRB 071025, provides a better fit for only two of the afterglow SEDs. However, because of the lack of highly extinguished sight lines and the limited wavelength coverage we cannot distinguish between the different scenarios. For the first time we also report a photometric redshift of zphot = 7.88-0.94+0.75 for GRB 100905A, making it one of the most distant GRBs known to date.
The collapsar model has proved highly successful in explaining the properties of long γ-ray bursts (GRBs), with the most direct confirmation being the detection of a supernova (SN) coincident with ...the majority of nearby long GRBs. Within this model, a long GRB is produced by the core-collapse of a metal-poor, rapidly rotating, massive star. The detection of some long GRBs in metal-rich environments, and more fundamentally the three examples of long GRBs (GRB 060505, GRB 060614 and GRB 111005A) with no coincident SN detection down to very deep limits is in strong contention with theoretical expectations. In this paper we present MUSE observations of the host galaxy of GRB 111005A, which is the most recent and compelling example yet of a SN-less, long GRB. At z = 0.01326, GRB 111005A is the third closest GRB ever detected, and second closest long duration GRB, enabling the nearby environment to be studied at a resolution of 270 pc. From the analysis of the MUSE data cube, we find GRB 111005A to have occurred within a metal-rich environment with little signs of ongoing star formation. Spectral analysis at the position of the GRB indicates the presence of an old stellar population (τ ≥ 10 Myr), which limits the mass of the GRB progenitor to MZAMS < 15 M⊙, in direct conflict with the collapsar model. Our deep limits on the presence of any SN emission combined with the environmental conditions at the position of GRB 111005A necessitate the exploration of a novel long GRB formation mechanism that is unrelated to massive stars.
We present the first uniform treatment of long duration gamma-ray burst (GRB) host galaxy detections and upper limits over the redshift range 3 < z < 5, a key epoch for observational and theoretical ...efforts to understand the processes, environments, and consequences of early cosmic star formation (SF). We contribute deep imaging observations of 13 GRB positions yielding the discovery of 8 new host galaxies. We use this data set in tandem with previously published observations of 31 further GRB positions to estimate or constrain the host galaxy rest-frame ultraviolet (UV; lambda = 1600 Angstrom) absolute magnitudes M sub(UV). We then use the combined set of 44 M sub(UV) estimates and limits to construct the M sub(UV) luminosity function (LF) for GRB host galaxies over 3 < z < 5 and compare it to expectations from Lyman break galaxy (LBG) photometric surveys with the Hubble Space Telescope. Adopting standard prescriptions for the luminosity dependence of galaxy dust obscuration (and hence, total SF rate), we find that our LF is compatible with LBG observations over a factor of 600 x in host luminosity, from M sub(UV) = -22.5 mag to >-15.6 mag, and with extrapolations of the assumed Schechter-type LF well beyond this range. We review proposed astrophysical and observational biases for our sample, and find that they are for the most part minimal. We therefore conclude, as the simplest interpretation of our results, that GRBs successfully trace UV metrics of cosmic SF over the range 3 < z < 5. Our findings suggest that GRBs provide an accurate picture of star formation processes from z approx = 3 out to the highest redshifts.
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