Bump Strength Research Articles

Measuring the Dust Attenuation Curves of SINGS/KINGFISH Galaxies Using Swift/UVOT Photometry

We present Swift/Ultraviolet Optical Telescope (UVOT) integrated light photometry of the Spitzer Infrared Nearby Galaxies Survey (SINGS) and the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH) samples of nearby galaxies. Combining the Swift/UVOT data with archival photometry, we investigate a variety of dust attenuation curves derived using MCSED, a flexible spectral energy distribution (SED) fitting code. We fit the panchromatic data using three different star formation history (SFH) parameterizations: a decaying exponential, a double power law, and a piecewise function with breaks at physically motivated ages. We find that the average attenuation law of the sample changes slightly based on the SFH assumed. Specifically, the exponential SFH leads to the shallowest attenuation curves. Using simulated data, we also find the exponential SFH fails to outperform the more complex SFHs. Finally, we find a systematic offset in the derived bump strength between SED fits with and without UVOT data, where the inclusion of UVOT data leads to smaller bump strengths, highlighting the importance of the UVOT data. This discrepancy is not seen in fits to mock photometry. Understanding dust attenuation in the local universe is key to understanding high-redshift objects where rest-frame far-infrared data are unavailable.

Discovery of a Radio-loud Narrow-line Seyfert 1 Galaxy at z = 0.9 Reddened with a Strong 2175 Å Bump

We present a broadband spectrophotometric analysis of an unusual quasar, SDSS J160558.86+474300.1, at z = 0.9, found in a systematic search for reddened radio-loud narrow-line Seyfert 1 galaxies (NLS1s). J1605+4743 qualifies for the conventional definition of an NLS1 in its permitted emission line widths and Hβ/[O iii] flux ratio. It also shows strong Fe ii emissions. J1605+4743 has a steep radio spectrum. With a radio loudness of ∼150 (70) before (after) reddening correction, it is among the most radio-loud NLS1s discovered. In addition, the blueshifted emission lines are also found to be weak, suggesting that it can be an exotic “wind-dominated” Seyfert similar to weak-line quasars, especially the ones with strong reddening. As an extreme hybrid central engine, its environment and host galaxy become rather intriguing. We discover in it a proximate 2175 Å absorber with a bump strength similar to the average value of 2175 Å absorbers in the Milky Way, which we suspect can be intrinsic to the quasar. In addition, the quasar seems to have enhanced instead of suppressed star formation at a rate of ≳94 M ⊙ yr−1. The combination of these unusual properties, i.e., the unique extinction, strong Fe ii and [O ii] lines, weak [O iii], Mg ii, and Balmer lines, and large radio loudness, might hold important clues to accretion physics, the formation/destruction of dust grains in the environment of active galactic nuclei, and possibly also the coevolution of supermassive black holes and their host galaxies in general.

Newly discovered Ca ii absorbers in the early Universe: statistics, element abundances, and dust

ABSTRACT We report discoveries of 165 new quasar Ca ii absorbers from the Sloan Digital Sky Survey (SDSS) Data Releases 7 and 12. Our ca ii rest-frame equivalent width distribution supports the weak and strong subpopulations, split at ${W}^{\lambda 3934}_{0}=0.7$ Å. Comparison of both populations’ dust depletion shows clear consistency for weak absorber association with halo-type gas in the Milky Way (MW), while strong absorbers have environments consistent with halo and disc-type gas. We probed our high-redshift Ca ii absorbers for 2175 Å dust bumps, discovering 12 2175 Å dust absorbers (2DAs). This clearly shows that some Ca ii absorbers follow the Large Magellanic Cloud (LMC) extinction law rather than the Small Magellanic Cloud extinction law. About 33 per cent of our strong Ca ii absorbers exhibit the 2175 Å dust bump, while only 6 per cent of weak Ca ii absorbers show this bump. 2DA detection further supports the theory that strong Ca ii absorbers are associated with disc components and are dustier than the weak population. Comparing average Ca ii absorber dust depletion patterns to that of Damped Ly α absorbers (DLAs), Mg ii absorbers, and 2DAs shows that Ca ii absorbers generally have environments with more dust than DLAs and Mg ii absorbers, but less dust than 2DAs. Comparing 2175 Å dust bump strengths from different samples and also the MW and LMC, the bump strength appears to grow stronger as the redshift decreases, indicating dust growth and the global chemical enrichment of galaxies in the Universe over time.

Cosmic evolution of grain size distribution in galaxies using the ν2GC semi-analytical model

ABSTRACT We investigate the cosmological evolution of interstellar dust with a semi-analytical galaxy formation model (ν2GC), focusing on the evolution of grain size distribution. The model predicts the statistical properties of dust mass and grain size distribution in galaxies across cosmic history. We confirm that the model reproduces the relation between dust-to-gas ratio and metallicity in the local Universe, and that the grain size distributions of the Milky Way (MW)-like sample become similar to the so-called Mathis, Rumpl & Nordsieck (MRN) distribution that reproduces the observed MW extinction curve. Our model, however, tends to overpredict the dust mass function at the massive end at redshift z ≲ 0.8 while it reproduces the abundance of dusty galaxies at higher redshifts. We also examine the correlation between grain size distribution and galaxy properties (metallicity, specific star formation rate, gas fraction, and stellar mass), and observe a clear trend of large-grain-dominated, small-grain-dominated, and MRN-like grain size distributions from unevolved to evolved stages. As a consequence, the extinction curve shapes are flat, steep, and intermediate (MW-like) from the unevolved to evolved phases. At a fixed metallicity, the grain size distribution tends to have larger fractions of small grains at lower redshift; accordingly, the extinction curve tends to be steeper at lower redshift. We also predict that supersolar-metallicity objects at high redshift have flat extinction curves with weak 2175 Å bump strength.

Detecting PAHs in high-z galaxies in proxy: modelling physical conditions in an extremely strong damped Lyman α absorber towards QSO SDSS J1143+1420 at z = 2.323

ABSTRACT We explore indirect methods to detect polycyclic aromatic hydrocarbons (PAHs) in gas-rich, absorption-selected galaxies at high redshift. We look at the optical X-Shooter observations of an intervening, extremely strong damped Lyman α absorber (or ESDLA, with log [N(H i) ≳ 21.7)] towards QSO SDSS J1143+1420 at redshift, zESDLA = 2.323. Literature studies have shown that this ESDLA contains signatures of dust and diffuse molecular hydrogen and it was specifically chosen for our study due to its close spatial proximity (impact parameter, $\rm \rho = 0.6\, \pm \, 0.3$kpc) with its associated galaxy. There is no direct detection of PAHs emission in the limited observations of infrared spectra along this sightline. Hence, we use cloudy numerical simulation modelling to indirectly probe the presence of PAHs in the ESDLA. We note that PAHs need to be included in the models to reproduce the observed column densities of warm H2 and C i. Thus, we infer the presence of PAHs indirectly in our ESDLA, with an abundance of PAH/H = 10−7.046. We also measure a low 2175 Å bump strength (E$\rm _{bump}\, \sim$0.03–0.19 mag) relative to star-forming galaxies by modelling extinction of quasar QSO spectra by dust at the absorber rest frame. This is consistent with the low PAH abundance obtained indirectly using cloudy modelling. Our study highlights the usage of cloudy modelling to indirectly detect PAH in high-redshift gas-rich absorption-selected galaxies.

Investigation Into Chemistry and Performance of No-Clean Flux in Fine Pitch Flip-Chip Package

This study investigates the chemistry and performance of two commercial no-clean fluxes (NCFs) ii.e., NC-1 and NC-2. One water-soluble (WS) flux was also studied for comparison. Chemistry of these fluxes and their residues was studied using the Fourier transmission infrared (FTIR) spectroscopy. Thermal behavior of the flux was evaluated using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Hygroscopicity of the residue was determined using water contact angle on residue-contaminated substrates. These fluxes were used to prepare fine pitch (<inline-formula> <tex-math notation="LaTeX">$150~\mu \text{m}$ </tex-math></inline-formula>) flip-chip package (<inline-formula> <tex-math notation="LaTeX">$17\times17$ </tex-math></inline-formula> mm²) containing solder bump and copper pillar. Performance of each flux was evaluated using wettability of preprinted SAC-305 solder on copper substrate. Die pull strength of solder bump was evaluated and failure mode was analyzed using scanning electron microscopy (SEM). FTIR results showed that carboxylic acids, tertiary amine, and ether were present in NC-1. Carboxylic acid, secondary amide, and ether were observed in NC-2. WS showed the presence of carboxylic acid, secondary amine, ether, and alcohol. Residue showed the presence of carboxylic acid and amine in NC-1 and only amide in NC-2. Evaporation of certain monocarboxylic acids and ether solvent in NCF led to minimal residue compared to WS. Residue of WS was highly hygroscopic compared to N CF. Wetting of solder bump prepared by using NC-1 and NC-2 was better than WS, which is related to flux chemistry. Consequently, higher die pull strength was observed for N CF.

Effect of rapid thermal shock cycle on the thermomechanical reliability of 20Sn-80Pb solder bumps

The influence of rapid thermal shock(RTS) cycles on 20Sn-80Pb solder bumps was studied. In the study, 20Sn-80Pb solder bumps were prepared by desktop nitrogen lead-free reflow soldering machine. The prepared 20Sn-80Pb solder bumps were used for RTS test in the temperature rang of 0°C ~ 150°C. One cycle of RTS is 24 seconds, and the temperature rise and fall rate of RTS is 12.5 C/s. The result indicated that when the cycle of RTS reached 1500T (here T is cycle, the same below), the shear strength of Sn-80Pb solder bump dropped by drastically 48.6%. Whereas, when the cycle of RTS reached 5500T, 20Sn-80Pb solder bumps’ shear strength decreased to 18.35 MPa, which increased by 7.5% compared with that of l6.97 MPa at 4500T. With the increase of RTS cycles, 20Sn-80Pb solder bumps’ shear strength was a decreasing trend and the fracture mechanism changed from ductile fracture to ductile-brittle mixed fracture, which could be subject to the thickening of the interfaical IMCs and the stress concentration caused by the growth of interfacial IMCs. To understand the changes of the mechanical properties of 20Sn-80Pb solder bumps, the influences of RTS on the crack and interfacial IMC of 20Sn-80Pb solder bumps were studied in details.

The origin of the dust extinction curve in milky way-like galaxies

ABSTRACT We develop a cosmological model for the evolution of dust grains in galaxies with a distribution of sizes in order to understand the origin of the Milky Way dust extinction curve. Our model considers the formation of active dust in evolved stars, growth by accretion and coagulation, and destruction processes via shattering, sputtering, and astration in the ISM of galaxies over cosmic time. Our main results follow. Galaxies in our cosmological model with masses comparable to the Milky Way’s at z ∼ 0 exhibit a diverse range of extinction laws, though with slopes and bump strengths comparable to the range observed in the Galaxy. The progenitors of the Milky Way have steeper slopes, and only flatten to slopes comparable to the Galaxy at z ∼ 1. This owes to increased grain growth rates at late times/in high-metallicity environments driving up the ratio of large to small grains, with a secondary dependence on the graphite-to-silicate ratio evolution. The UV bump strengths depend primarily on the graphite-to-silicate ratio, and remain broadly constant in MW-like galaxies between z = 3 and z = 0, though show slight variability. Our models span comparable regions of bump-slope space as sightlines in the Galaxy do, though there is a lack of clear relationship between the model slopes and bump strengths owing to variations among galaxies in the graphite-to-silicate ratio. Our model provides a novel framework to study the origins and variations of dust extinction curves in galaxies over cosmic time.

Constraints on the dust extinction law of the Galaxy with Swift/UVOT, Gaia, and 2MASS

ABSTRACT We explore variations of the dust extinction law of the Milky Way by selecting stars from the Swift/UVOT Serendipitous Source Catalogue, cross-matched with Gaia DR2 and 2MASS to produce a sample of 10 452 stars out to ∼4 kpc with photometry covering a wide spectral window. The near ultraviolet passbands optimally encompass the 2175 Å bump, so that we can simultaneously fit the net extinction, quoted in the V band (AV), the steepness of the wavelength dependence (δ), and the bump strength (Eb). The methodology compares the observed magnitudes with theoretical stellar atmospheres from the models of Coelho. Significant correlations are found between these parameters, related to variations in dust composition that are complementary to similar scaling relations found in the more complex dust attenuation law of galaxies – that also depend on the distribution of dust among the stellar populations within the galaxy. We recover the strong anticorrelation between AV and Galactic latitude, as well as a weaker bump strength at higher extinction. δ is also found to correlate with latitude, with steeper laws towards the Galactic plane. Our results suggest that variations in the attenuation law of galaxies cannot be fully explained by dust geometry.

The 2175 Å Dust Feature in Star-forming Galaxies at 1.3 ≤ z ≤ 1.8: The Dependence on Stellar Mass and Specific Star Formation Rate

Abstract We present direct spectroscopic measurements of the broad 2175 Å absorption feature in 505 star-forming main-sequence galaxies at 1.3 ≤ z ≤ 1.8 using individual and stacked spectra from the zCOSMOS-deep survey. Significant 2175 Å excess absorption features of moderate strength are measured, especially in the composite spectra. The excess absorption is well described by a Drude profile. The bump amplitude expressed in units of k(λ) = A(λ)/E(B − V), relative to the featureless Calzetti et al. law, has a range B k ≈ 0.2–0.8. The bump amplitude decreases with the specific star formation rate (sSFR), while it increases moderately with the stellar mass. However, a comparison with local “starburst” galaxies shows that the high-redshift main-sequence galaxies have stronger bump features, despite having a higher sSFR than the local sample. Plotting the bump strength against the Δ logsSFR ≡ log SFR / SFR MS relative to the main sequence, however, brings the two samples into much better concordance. This may indicate that it is the recent star formation history of the galaxies that determines the bump strength through the destruction of small carbonaceous grains by supernovae and intense radiation fields coupled with the time delay of ∼1 Gyr in the appearance of carbon-rich asymptotic giant branch stars.

Dust Attenuation Curves at z ∼ 0.8 from LEGA-C: Precise Constraints on the Slope and 2175Å Bump Strength

Abstract We present a novel approach to measure the attenuation curves of 485 individual star-forming galaxies with &gt; 1010 M⊙ based on deep optical spectra from the VLT/VIMOS LEGA-C survey and multiband photometry in the COSMOS field. Most importantly, we find that the attenuation curves in the rest-frame 3000–4500 Å range are typically almost twice as steep as the Milky Way, LMC, SMC, and Calzetti attenuation curves, which is in agreement with recent studies of the integrated light of present-day galaxies. The attenuation at 4500 Å and the slope strongly correlate with the galaxy inclination: face-on galaxies show less attenuation and steeper curves compared to edge-on galaxies, suggesting that geometric effects dominate observed variations in attenuation. Our new method produces 2175 Å UV bump detections for 260 individual galaxies. Even though obvious correlations between UV bump strength and global galaxy properties are absent, strong UV bumps are most often seen in face-on, lower-mass galaxies (10 &lt; log10(M */M ⊙) &lt; 10.5) with low overall attenuation. Finally, we produce a typical attenuation curve for star-forming galaxies at z ∼ 0.8; this prescription represents the effect of dust on the integrated spectral energy distributions of high-redshift galaxies more accurately than commonly used attenuation laws.

The Dust Attenuation Law in Galaxies

Understanding the properties of dust attenuation curves in galaxies and the physical mechanisms that shape them are among the fundamental questions of extragalactic astrophysics, with great practical significance for deriving the physical properties of galaxies. Attenuation curves result from a combination of dust grain properties, dust content, and the spatial arrangement of dust and different populations of stars. In this review, we assess the state of the field, paying particular attention to extinction curves as the building blocks of attenuation laws. We introduce a quantitative framework to characterize extinction and attenuation curves, present a theoretical foundation for interpreting empirical results, overview an array of observational methods, and review observational results at low and high redshifts. Our main conclusions include the following: ▪ Attenuation curves exhibit a wide range of UV-through-optical slopes, from curves with shallow (Milky Way–like) slopes to those exceeding the slope of the Small Magellanic Cloud extinction curve. ▪ The slopes of the curves correlate strongly with the effective optical opacities, in the sense that galaxies with lower dust column density (lower visual attenuation) tend to have steeper slopes, whereas the galaxies with higher dust column density have shallower (grayer) slopes. ▪ Galaxies exhibit a range of 2175-Å UV bump strengths, including no bump, but, on average, are suppressed compared with the average Milky Way extinction curve. ▪ Theoretical studies indicate that both the correlation between the slope and the dust column as well as variations in bump strength may result from geometric and radiative transfer effects.

MCSED: A Flexible Spectral Energy Distribution Fitting Code and Its Application to z ∼ 2 Emission-line Galaxies

Abstract We present MCSED, a new spectral energy distribution (SED) fitting code that mates flexible stellar evolution calculations with the Markov Chain Monte Carlo algorithms of the software package emcee. It takes broad-, intermediate-, and narrowband photometry, emission-line fluxes, and/or absorption-line spectral indices and returns probability distributions and covariance plots for all model parameters. It includes a variety of dust attenuation curves with parameters for varying the UV slopes and bump strengths, a prescription for continuum and polycyclic aromatic hydrocarbon emission from dust, models for continuum and line emission from ionized gas, options for fixed and variable stellar metallicity, and a selection of star formation rate (SFR) histories. The code is well suited for exploring parameter interdependencies in sets of galaxies with known redshifts for which there is multiband photometry and/or spectroscopy. We apply MCSED to a sample of ∼2000 galaxies in the five CANDELS fields that were selected via their strong [O iii] λ5007 emission, and we explore the systematic behavior of their SEDs. We find that the galaxies become redder with stellar mass due to both increasing internal attenuation and a greater population of older stars. The slope of the UV extinction curve also changes with stellar mass, and at least some galaxies exhibit an extinction excess at 2175 Å. Finally, we demonstrate that below M ≲ 109 M ⊙, the shape of the star-forming galaxy main sequence is highly dependent on the galaxies’ assumed SFR history, as calculations that assume a constant SFR produce stellar masses that are ∼1 dex smaller than those found using more realistic SFR histories.

Self-consistent modelling of aromatic dust species and extinction curves in galaxy evolution

ABSTRACT We formulate and calculate the evolution of dust in a galaxy focusing on the distinction among various dust components – silicate, aromatic carbon, and non-aromatic carbon. We treat the galaxy as a one-zone object and adopt the evolution model of grain size distribution developed in our previous work. We further include aromatization and aliphatization (inverse reaction of aromatization). We regard small aromatic grains in a radius range of 3–50 Å as polycyclic aromatic hydrocarbons (PAHs). We also calculate extinction curves in a consistent manner with the abundances of silicate and aromatic and non-aromatic carbonaceous dust. Our model nicely explains the PAH abundance as a function of metallicity in nearby galaxies. The extinction curve becomes similar to the Milky Way curve at an age of ∼10 Gyr, in terms of the carbon bump strength and the far-ultraviolet slope. We also apply our model to starburst galaxies by shortening the star formation time-scale (0.5 Gyr) and increasing the dense-gas fraction (0.9), finding that the extinction curve maintains bumpless shapes (because of low aromatic fractions), which are similar to the extinction curves observed in the Small Magellanic Cloud and high-redshift quasars. Thus, our model successfully explains the variety in extinction curve shapes at low and high redshifts.

A deeper look at the dust attenuation law of star-forming galaxies at high redshift

ABSTRACT A diverse range of dust attenuation laws is found in star-forming galaxies. In particular, Tress et al. (2018) studied the SHARDS survey to constrain the NUV bump strength (B) and the total-to-selective ratio (RV) of 1753 star-forming galaxies in the GOODS-N field at 1.5 &lt; z &lt; 3. We revisit here this sample to assess the implications and possible causes of the correlation found between RV and B. The UVJ bicolour plot and main sequence of star formation are scrutinized to look for clues into the observed trend. The standard boundary between quiescent and star-forming galaxies is preserved when taking into account the wide range of attenuation parameters. However, an additional degeneracy – regarding the effective attenuation law – is added to the standard loci of star-forming galaxies in the UVJ diagram. A simple phenomenological model with an age-dependent extinction (at fixed dust composition) is compatible with the observed trend between RV and B, whereby the opacity decreases with the age of the populations, resulting in a weaker NUV bump when the overall attenuation is shallower (greyer). In addition, we compare the constraints obtained by the SHARDS sample with dust models from the literature, supporting a scenario where geometry could potentially drive the correlation between RV and B.

Revealing the dust attenuation properties on resolved scales in NGC 628 with SWIFT UVOT data

ABSTRACT Understanding how dust attenuation laws vary between and within galaxies is a key question if we want to reliably measure the physical properties of galaxies at both global and local scales. To shed new light on this question, we present a detailed study of the slope and bump strength of the attenuation law in the nearby spiral galaxy NGC 628 at the resolved spatial scale of 325 pc. To do so, we have modelled a broad multiwavelength data set from the ultraviolet (UV) to the infrared (IR) with the state-of-the-art SED fitting code cigale, including SWIFT UVOT data for which we have developed a new optimized reduction pipeline. We find that the median dust attenuation curve of NGC 628 is fairly steep, but not as steep as the SMC curve, and has a sub-MW-type UV bump. We observe intriguing variations within the galaxy, with regions of high AV exhibiting a shallower attenuation curve. We argue that the flattening of the curve is due to a dominance of absorption over scattering events at higher AV. No trend between the bump strength and the IRAC 8.0 $\mu$m emission was found. However, this does not necessarily rule out polycyclic aromatic hydrocarbons as the main contributors to the UV bump.

Diversity of Galaxy Dust Attenuation Curves Drives the Scatter in the IRX–β Relation

Abstract We study the drivers of the scatter in the IR excess (IRX)–β relation using 23,000 low-redshift galaxies from the GALEX–SDSS–WISE Legacy Catalog 2 (GSWLC-2). For each galaxy, we derive, using CIGALE and the spectral energy distribution+LIR fitting technique, the slope of the dust attenuation curve and the strength of the UV bump, plus many other galaxy parameters. We find that the IRX–β scatter is driven entirely by a wide range of attenuation curves—primarily by their slopes. Once the slope and the UV bump are fixed, the scatter in the IRX–β relation vanishes. The question of the IRX–β scatter is a direct manifestation of the more fundamental question of the diversity of dust attenuation curves. The predominant role of the attenuation curve is the consequence of a narrow range of intrinsic UV slopes of star-forming (SF) galaxies. Galaxies with different specific star formation rates (sSFRs) or population ages do not show strong trends in the IRX–β diagram because their attenuation curves are, on average, similar. Similarly, there is no shift in the IRX–β locus between starbursts and normal SF galaxies, both types having, on average, steep attenuation curves. Optical opacity is identified as the strongest determinant of the attenuation curve slope and consequently of the IRX–β diversity. Despite the scatter, the use of an average IRX–β relation is justified to correct SFRs, adding a random error of ≲0.15 dex. The form of the local correspondence between IRX–β and attenuation curves is maintained at high redshifts as long as the evolution of the intrinsic UV slopes stays within a few tenths.

A Theory for the Variation of Dust Attenuation Laws in Galaxies

Abstract In this paper, we provide a physical model for the origin of variations in the shapes and bump strengths of dust attenuation laws in galaxies by combining a large suite of cosmological “zoom-in” galaxy formation simulations with 3D Monte Carlo dust radiative transfer calculations. We model galaxies over three orders of magnitude in stellar mass, ranging from Milky Way–like systems to massive galaxies at high redshift. Critically, for these calculations, we employ a constant underlying dust extinction law in all cases and examine how the role of geometry and radiative transfer effects impacts the resultant attenuation curves. Our main results follow. Despite our usage of a constant dust extinction curve, we find dramatic variations in the derived attenuation laws. The slopes of normalized attenuation laws depend primarily on the complexities of star-to-dust geometry. Increasing fractions of unobscured young stars flatten normalized curves, while increasing fractions of unobscured old stars steepen curves. Similar to the slopes of our model attenuation laws, we find dramatic variation in the 2175 Å ultraviolet bump strength, including a subset of curves with little to no bump. These bump strengths are primarily influenced by the fraction of unobscured O and B stars in our model, with the impact of scattered light having only a secondary effect. Taken together, these results lead to a natural relationship between the attenuation curve slope and 2175 Å bump strength. Finally, we apply these results to a 25 Mpc h −1 box cosmological hydrodynamic simulation in order to model the expected dispersion in attenuation laws at integer redshifts from z = 0 to 6. A significant dispersion is expected at low redshifts and decreases toward z = 6. We provide tabulated results for the best-fit median attenuation curve at all redshifts.

The 2175 Å Extinction Feature in the Optical Afterglow Spectrum of GRB 180325A at z = 2.25∗

Abstract The ultraviolet (UV) extinction feature at 2175 Å is ubiquitously observed in the Galaxy but is rarely detected at high redshifts. Here we report the spectroscopic detection of the 2175 Å bump on the sightline to the γ-ray burst (GRB) afterglow GRB 180325A at z = 2.2486, the only unambiguous detection over the past 10 years of GRB follow-up, at four different epochs with the Nordic Optical Telescope (NOT) and the Very Large Telescope (VLT)/X-shooter. Additional photometric observations of the afterglow are obtained with the Gamma-Ray burst Optical and Near-Infrared Detector (GROND). We construct the near-infrared to X-ray spectral energy distributions (SEDs) at four spectroscopic epochs. The SEDs are well described by a single power law and an extinction law with R V ≈ 4.4, A V ≈ 1.5, and the 2175 Å extinction feature. The bump strength and extinction curve are shallower than the average Galactic extinction curve. We determine a metallicity of [Zn/H] &gt; −0.98 from the VLT/X-shooter spectrum. We detect strong neutral carbon associated with the GRB with equivalent width of W r(λ 1656) = 0.85 ± 0.05. We also detect optical emission lines from the host galaxy. Based on the Hα emission-line flux, the derived dust-corrected star formation rate is ∼46 ± 4 M ⊙ yr−1 and the predicted stellar mass is log M */M ⊙ ∼ 9.3 ± 0.4, suggesting that the host galaxy is among the main-sequence star-forming galaxies.

Dust Attenuation Curves in the Local Universe: Demographics and New Laws for Star-forming Galaxies and High-redshift Analogs

Abstract We study the dust attenuation curves of 230,000 individual galaxies in the local universe, ranging from quiescent to intensely star-forming systems, using GALEX, SDSS, and WISE photometry calibrated on the Herschel ATLAS. We use a new method of constraining SED fits with infrared luminosity (SED+LIR fitting), and parameterized attenuation curves determined with the CIGALE SED-fitting code. Attenuation curve slopes and UV bump strengths are reasonably well constrained independently from one another. We find that attenuation curves exhibit a very wide range of slopes that are on average as steep as the curve slope of the Small Magellanic Cloud (SMC). The slope is a strong function of optical opacity. Opaque galaxies have shallower curves—in agreement with recent radiative transfer models. The dependence of slopes on the opacity produces an apparent dependence on stellar mass: more massive galaxies have shallower slopes. Attenuation curves exhibit a wide range of UV bump amplitudes, from none to Milky Way (MW)-like, with an average strength one-third that of the MW bump. Notably, local analogs of high-redshift galaxies have an average curve that is somewhat steeper than the SMC curve, with a modest UV bump that can be, to first order, ignored, as its effect on the near-UV magnitude is 0.1 mag. Neither the slopes nor the strengths of the UV bump depend on gas-phase metallicity. Functional forms for attenuation laws are presented for normal star-forming galaxies, high-z analogs, and quiescent galaxies. We release the catalog of associated star formation rates and stellar masses (GALEX–SDSS–WISE Legacy Catalog 2).