Among the key parameters defining the interstellar media (ISM) of galaxies is the fraction of the metals that are locked up in dust: the metals-to-dust ratio. This ratio bears not only on the ISM and ...its evolution, but also particularly on the origin of cosmic dust. We combine extinction and abundance data from γ-ray burst (GRB) afterglows with similar data from quasar (QSO) foreground absorbers, as well as from multiply-imaged galaxy-lensed QSOs, to determine the metals-to-dust ratios for lines of sight through a wide diversity of galaxies from blue, dwarf starbursts to massive ellipticals, across a vast range of redshifts z = 0.1–6.3, and nearly three orders of magnitude of column density and metal abundance. The GRB and lensed QSO extinction methods are the most reliable that are available outside the Local Group (LG), allowing absolute extinction measurements. We thus determine the metals-to-dust ratio in a unique way, providing direct determinations of in situ gas and dust columns without recourse to assumptions with large uncertainties. We find that the metals-to-dust ratios in these systems are surprisingly close to the value for the LG, with a mean value of 1021.2 cm-2 AV mag-1 and a standard deviation of 0.3 dex, compared to the Galactic value of 1021.3 cm-2Av mag-1 (in units of the Galactic gas-to-dust ratio). There is no evidence of deviation from this mean ratio as a function of metallicity, even down to our lowest metallicity of 0.01 Z/Z⊙. The lack of any obvious dependence of the metals-to-dust ratio on column density, galaxy type or age, redshift, or metallicity indicates a close correspondence between the formation of the metals and the formation of dust. Any delay between the formation of metals and dust must be shorter than the typical metal-enrichment times of these galaxies, i.e. shorter than a few Myr. Formation of the bulk of the dust in low mass stars is therefore ruled out by these data at any cosmic epoch. Furthermore, dust destruction must not dominate over formation/growth in virtually any galaxy environment. The close correlation between metals and dust is a natural consequence of the formation of the bulk of cosmic dust in supernovae. Grain growth in the ISM, if it is to be the dominant cosmic dust formation mechanism, is strongly constrained by these data to operate on very short timescales.
Long-duration Gamma-ray bursts (GRBs) are excellent probes to study dust extinction due to their occurrence in star-forming regions and having simple synchrotron emission spectra. Inclusion of ...spectroscopic data to the GRB X-ray to the infrared spectral energy distribution (SED) could better define the continuum and confirm extinction feature. A preliminary SED analysis of GRB afterglows targeted with the VLT/X-Shooter spectrograph finds that all the 60% of extinguished bursts fit-well with featureless extinction curves. The longer wavelength coverage from ultraviolet to the near-infrared of X-Shooter helps to derive individual extinction curves and determine the total-to-selective extinction, RV precisely, suggesting extinction curves steeper (with a mean of RV=2.66±0.10) than the Small Magellanic Cloud. Moreover, addition of more data to the study of dust-to-metals ratios in GRB afterglows, quasar absorbers, and multiply lensed galaxies still shows the dust-to-metals ratios close to the Galactic value (with a mean value of log −21.2cm−2mag−1), hinting short time delay between metals and dust formation. Such studies demonstrate the strength of using GRB afterglows to study dust origin and its properties the from low to high redshift Universe.
•Long GRBs, associated with the death of massive stars, have power-law spectra, and occur up to the epoch of reionization.•These advantages make GRBs potentially unique and effective probes to study dust extinction over broad range of redshifts.•This work constitutes X-ray to optical spectroscopic spectral energy distributions of GRBs to determine the dust extinction.•The 2175Å bump is also seen in GRBs suggesting diverse environments from young, low-mass to the evolved, massive galaxies.•Various dust laws hints grains varying from silicates to carbonaceous. A decrease in dust content at high redshift is seen.
ABSTRACT
Periodic quasars are candidates for binary supermassive black holes (BSBHs) efficiently emitting low-frequency gravitational waves. Recently, ∼150 candidates were identified from optical ...synoptic surveys. However, they may be false positives caused by stochastic quasar variability given the few cycles covered (typically 1.5). To independently test the binary hypothesis, we search for evidence of truncated or gapped circumbinary accretion discs (CBDs) in their spectral energy distributions (SEDs). Our work is motivated by CBD simulations that predict flux deficits as cut-offs from central cavities opened by secondaries or notches from minidiscs around both BHs. We find that candidate periodic quasars show SEDs similar to those of control quasars matched in redshift and luminosity. While seven of 138 candidates show a blue cut-off in the IR–optical–UV SED, six of which may represent CBDs with central cavities, the red SED fraction is similar to that in control quasars, suggesting no correlation between periodicity and SED anomaly. Alternatively, dust reddening may cause red SEDs. The fraction of extremely radio-loud quasars, e.g. blazars (with R > 100), is tentatively higher than that in control quasars (at 2.5σ). Our results suggest that, assuming most periodic candidates are robust, IR–optical–UV SEDs of CBDs are similar to those of accretion discs of single BHs, if the periodicity is driven by BSBHs; the higher blazar fraction may signal precessing radio jets. Alternatively, most current candidate periodic quasars identified from few-cycle light curves may be false positives. Their tentatively higher blazar fraction and lower Eddington ratios may both be caused by selection biases.
Recent works have demonstrated a surprisingly small variation of the dust-to-metals ratio in different environments and a correlation between dust extinction and the density of stars. Naively, one ...would interpret these findings as strong evidence of cosmic dust being produced mainly by stars. But other observational evidence suggest that there is a significant variation of the dust-to-metals ratio with metallicity. As we demonstrate in this paper, a simple star-dust scenario is problematic also in the sense that it requires that destruction of dust in the interstellar medium (e.g. due to passage of supernova shocks) must be highly inefficient. We suggest a model where stellar dust production is indeed efficient, but where interstellar dust growth is equally important and acts as a replenishment mechanism which can counteract the effects of dust destruction. This model appears to resolve the seemingly contradictive observations, given that the ratio of the effective (stellar) dust and metal yields is not universal and thus may change from one environment to another, depending on metallicity.
Because of their brightness, gamma-ray burst (GRB) afterglows are viable targets for investigating the dust content in their host galaxies. Simple intrinsic spectral shapes of GRB afterglows allow us ...to derive the dust extinction. Recently, the extinction data of GRB afterglows are compiled up to redshift z = 6.3, in combination with hydrogen column densities and metallicities. This data set enables us to investigate the relation between dust-to-gas ratio and metallicity out to high redshift for a wide metallicity range. By applying our evolution models of dust content in galaxies, we find that the dust-to-gas ratios derived from GRB afterglow extinction data are excessively high such that they can be explained with a fraction of gas-phase metals condensed into dust (f
in) ∼ 1, while theoretical calculations on dust formation in the wind of asymptotic giant branch stars and in the ejecta of Type II supernovae suggest a much more moderate condensation efficiency (f
in ∼ 0.1). Efficient dust growth in dense clouds has difficulty in explaining the excessive dust-to-gas ratio at metallicities Z/Z < , where is the star formation efficiency of the dense clouds. However, if is as small as 0.01, the dust-to-gas ratio at Z ∼ 10−2 Z can be explained with nH 106 cm−3. Therefore, a dense environment hosting dust growth is required to explain the large fraction of metals condensed into dust, but such clouds should have low star formation efficiencies to avoid rapid metal enrichment by stars.
We analyse a sample of 16 absorption systems intrinsic to long-duration gamma-ray burst (GRB) host galaxies at z ≳ 2 for which the metallicities are known. We compare the relation between the ...metallicity and cold gas velocity width for this sample to that of the QSO-DLAs (quasi-stellar object–damped Lyman α), and find complete agreement. We then compare the redshift evolution of the mass–metallicity relation of our sample to that of QSO-DLAs and find that also GRB hosts favour a late onset of this evolution, around a redshift of ≈2.6. We compute predicted stellar masses for the GRB host galaxies using the prescription determined from QSO-DLA samples and compare the measured stellar masses for the four hosts where stellar masses have been determined from spectral energy distribution (SED) fits. We find excellent agreement and conclude that, on basis of all available data and tests, long-duration GRB-DLA hosts and intervening QSO-DLAs are consistent with being drawn from the same underlying population. GRB host galaxies and QSO-DLAs are found to have different impact parameter distributions and we briefly discuss how this may affect statistical samples. The impact parameter distribution has two effects. First, any metallicity gradient will shift the measured metallicity away from the metallicity in the centre of the galaxy, and secondly, the path of the sightline through different parts of the potential well of the dark matter halo will cause different velocity fields to be sampled. We report evidence suggesting that this second effect may have been detected.
Abstract
Early optical observations of gamma-ray bursts can significantly contribute to the study of the central engine and physical processes therein. However, of the thousands observed so far, only ...a few have data at optical wavelengths in the first minutes after the onset of the prompt emission. Here we report on GRB 190106A, whose afterglow was observed in optical bands just 36 s after the Swift/BAT trigger, i.e., during the prompt emission phase. The early optical afterglow exhibits a bimodal structure followed by a normal decay, with a faster decay after ∼
T
0
+ 1 day. We present optical photometric and spectroscopic observations of GRB 190106A. We derive the redshift via metal absorption lines from Xinglong 2.16 m/BFOSC spectroscopic observations. From the BFOSC spectrum, we measure
z
= 1.861 ± 0.002. The double-peak optical light curve is a significant feature predicted by the reverse-forward external-shock model. The shallow decay followed by a normal decay in both the X-ray and optical light curves is well explained with the standard forward-shock model with late-time energy injection. Therefore, GRB 190106A offers a case study for GRB emission from both reverse and forward shocks.
Soft X-ray absorption in excess of Galactic is observed in the afterglows of most gamma-ray bursts (GRBs), but the correct solution to its origin has not been arrived at after more than a decade of ...work, preventing its use as resolve this long-standing problem and find that absorption by He in the GRB's host H II region is responsible for most of the absorption. We conclude that the absorption of X-rays in GRB afterglows is caused by He in the H II region hosting the GRB. While dust is destroyed and metals are stripped of all of their electrons by the GRB to great distances, the abundance of He saturates the He-ionizing UV continuum much closer to the GRB, allowing it to remain in the neutral or singly-ionized state. Helium X-ray absorption explains the correlation with total gas, the lack of strong evolution with redshift, as well as the absence of dust, metal or hydrogen absorption features in the optical-UV spectra.
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