arXiv subjects

D. Langeroodi

Publications and source records attributed to D. Langeroodi.

At least 19 recordsLinked to original sources

arXiv2026

PRISMS. U37126, a very blue, ISM-naked starburst at z=10.255 with nearly 100% Lyman continuum escape fraction

We present very deep (~11h) JWST/MIRI low-resolution spectroscopy of the rest-frame optical emission of U37126, a UV-bright (M_UV ~ -20), mildly lensed ($μ\simeq 2.2$) galaxy at z=10.255. The continuum emission is well detected in both NIRSpec and MIRI spectra, yet no nebular recombination or metal emission lines are observed (EW(Hbeta+[OIII])<300A and EW(Halpha)<400A, at 3sigma). Combined with the exceptionally blue UV continuum slope, beta_UV ~ -2.9, and weak/flat Balmer break, these constraints indicate a stellar population dominated by very young and massive stars with a strongly suppressed nebular contribution. Comparisons with synthetic stellar population models indicate that U37126 requires both a very high ionizing photon production efficiency, log(Xi_ion / Hz erg^-1) ~ 25.75, and a nearly unit LyC escape fraction, of fesc>86% (3sigma) based on Halpha flux limit and fesc=0.94+/-0.06 derived independently from SED fitting. The best-fit SED yields a (de-lensed) stellar mass of Mstar ~ 10^7.8 Msun and a star-formation rate of SFR~10Msun/yr (sSFR~160 Gyr^-1), that along with its very compact size, reff~61pc, yields very high stellar mass and star-formation-rate surface densities, Sigma_M ~ 3x10^3 Msun/pc^2 and Sigma_SFR ~ 400 Msun/yr/kpc^2. Together with the lack of detectable nebular emission, these properties suggest that U37126 is undergoing an ``ISM-naked'' starburst phase, possibly driven by an extremely efficient gas-to-star conversion followed by strong feedback that has cleared the remaining gas from its stellar core, allowing most LyC photons to escape. Finally, we show that even a small fraction of galaxies like U37126 (~ 3%-6%), with extreme LyC production and escape, could contribute disproportionately (~ 50%-100%) to the ionizing photon budget during cosmic reionization.

astro-ph.GA↗

arXiv2026

JWST Reveals Two Overmassive Black Hole Candidates in Dwarf Galaxies at z $\approx$ 0.7: Pushing Black Hole Searches into the Dwarf-Galaxy Regime

We report the discovery and characterization of two compact galaxies, Pelias and Neleus, at z ~ 0.71 and z ~ 0.75, identified in MACS J0416.1-2403 and GOODS-North. Both exhibit unusual spectral energy distributions (SEDs), with very blue rest-frame UV-optical emission and a steep rise toward near- and mid-infrared wavelengths. JWST/NIRISS and JWST/NIRSpec spectroscopy show strong rest-frame optical lines ([O III] 4959,5007 and Halpha) with extreme equivalent widths (>= 1000 Angstrom), indicating young burst-dominated populations with low metallicities (Z ~ 0.1-0.4 Zsun), low dust attenuation (Av ~ 0.2 mag), and stellar masses of Mstar ~ 10^7 Msun. Nonetheless, JWST/MIRI photometry reveals a strong mid-infrared excess that cannot be explained by stellar populations or star-formation-heated dust alone, requiring a hot-dust component most naturally associated with a deeply embedded active galactic nucleus (AGN). SED modelling yields log10(Lbol [erg/s]) ~ 43.7-44.0, implying black hole masses of log10(MBH [Msun]) ~ 5.7-6.7 under the assumption of Eddington-limited accretion. Given the very low stellar masses of the hosts, this corresponds to black-hole-to-stellar mass ratios of about 6-60%, well above the extrapolation of local scaling relations. The lack of X-ray detections suggests that the accretion may be either heavily obscured or intrinsically X-ray weak. Their SEDs also resemble those of Blue Excess Hot Dust Obscured Galaxies and show the characteristic V-shaped continuum seen in Little Red Dots, although with the inflection occurring at redder wavelengths.

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arXiv2026

MIDIS: The identification of deep MIRI-red sources as candidates for extreme Balmer-break and line emitting galaxies at high-z

We investigate the detection and nature of 5.6~μm MIRI-red sources in the MIRI Deep Imaging Survey (MIDIS), covering 2.4~arcmin$^2$ in the Hubble Ultra Deep Field. MIDIS is the deepest JWST/MIRI survey to date, probing faint limits and enabling studies of rare high-redshift galaxy populations. We define MIRI-red sources as those detected at 5$σ$ significance in MIRI/F560W with red colors: $m_{\rm F444W} - m_{\rm F560W} \ge 0.5$. Using an empirical methodology, we estimate the purity and completeness of MIRI detections and find that a 5-sigma detection at 28.75 mag has a purity of 92\% and completeness of 54\%. We identify seven MIRI-red galaxy candidates, including an F115W dropout consistent with a high-redshift galaxy candidate. We explore possible physical origins for the MIRI-red population, including active galactic nuclei, dust-obscured galaxies, extreme emission-line galaxies, evolved stellar populations, and Little Red Dots (LRDs). Given the proximity of the F444W and F560W filters and the depth of MIDIS, MIRI-red galaxies are consistent with emission-line galaxies with $EW_0(Hα) \ge 750$ Å or $EW_0(Hβ+ [OIII]) \ge 600$ Å, or high-redshift Balmer breaks of at least 1.6. We also discuss an extreme MIRI-red galaxy undetected in F444W, a potential MIRI-only source, for which we derive $EW_0(Hα) \sim 6000$ Å and $EW_0(Hβ+ [OIII]) \sim 4000$ Å, or high-$z$ LRD analogs with Balmer breaks of 6.3. Finally, we find fewer MIRI-red detections than expected from extrapolations of the H$α$ or H$β$+[OIII] line luminosity functions, consistent with previous deep searches, while the absence of $z>10$ LRD candidates agrees with theoretical expectations for the MIDIS volume.

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arXiv2026

MIRI spectrophotometry of GN-z11: Detection and nature of an optical red continuum component

We present new MIRI F560W, F770W and F1000W imaging of GN-z11, extending the previous rest-frame coverage from 0.38 to 0.86$μ$m. We report significant detections (14$σ$) in the F560W and F770W images, and a marginal detection (3.2$σ$) in F1000W. Here, we analyse its SED combining new MIRI imaging data with archival NIRSpec/Prism and MRS spectroscopy, and NIRCam imaging. The continuum emission shows a flat energy distribution, in f$_ν$, up to 0.5$μ$m, compatible with the presence of a mixed stellar population of young (4$\pm$1 Myr) and mature (63$\pm$23 Myr) stars that also account for the [O III], H$β$ and H$α$ emission lines. The continuum at rest-frame 0.66$μ$m shows a 36$\pm$3% flux excess above the predicted flux for a mixed stellar population, pointing to the presence of an additional source contributing at these wavelengths. This excess increases to 91$\pm$28% at rest-frame 0.86$μ$m, although with a large uncertainty due to the marginal detection in the F1000W filter. We consider that hot dust emission in the dusty torus around a type 2 AGN could be responsible for the observed excess. Alternatively, this excess could be due to hot dust emission or to a photoluminiscence dust process (Extended Red Emission, ERE) under the extreme UV radiation field, as observed in some local metal-poor galaxies and in young compact starbursts. The presence of a type 1 AGN is not supported by the observed SED since high-z QSOs contribute at wavelengths above rest-frame 1$μ$m, and an additional ad-hoc red source would be required to explain the observed flux excess at 0.66 and 0.86$μ$m. Additional deep MIRI imaging covering the rest-frame near-IR are needed to confirm the flux detection at 10$μ$m with higher significance, and to discriminate between the different hot dust emission in the extreme starburst and AGN scenarios with MIRI imaging at longer wavelengths.

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arXiv2026

PRISMS. UNCOVER-26185, a metal-poor SFG at z=10.05 with no evidence for a X-ray-luminous AGN

This work presents the first results of the PRImordial galaxy Survey with MIRI Spectroscopy (PRISMS), a JWST cycle 4 program (PID 8051) aimed at the characterization of a relatively large sample of ten galaxies about 500 Myr after the Big Bang. Here, we present deep (13.9 hours) spectroscopy with the MIRI LRS of the lensed galaxy UNCOVER-26185 at a redshift of z=10.054. It is a faint UV galaxy (UV absolut magnitude of -18.83 mag) previously identified as a X-ray luminous AGN. MIRI LRS detects the H$β$+[OIII]4960,5008 complex and H$α$ emission line with a significance of 10$σ$ and 8$σ$, respectively, as well as the optical continuum emission at rest-frame 0.45 $μ$m and 0.57 $μ$m with a signal-to-noise ratio of 6-7. The UV-to-optical spectral energy distribution, combining continuum and emission lines, is compatible with: (i) a low stellar (A$_V$= 0.2) and nebular (A$_V$=0.0) extinction, (ii) a SFH composed by a young (7 Myr) starburst and an intermediate-age (65 Myr) stellar population, and (iii) a total stellar mass of 1.7$\times$10$^{8}$ M$_{\odot}$. The H$α$-derived star-formation rate is 1.3 M$_{\odot}$ yr$^{-1}$. The low optical emission line ratios locate UNCOVER-26185 as the most metal-poor (Z = 0.04 Z$_{\odot}$), and as outlier with the lowest ionization (logU=-2.5) galaxy identified so far at redshifts above 9. With no evidence of an active galactic nuclei in the rest-frame UV-to-optical spectrum, UNCOVER-26185 has the properties of a metal-poor, main-sequence star-forming galaxy at redshift 10, with ISM and ionization properties very different than those of the already studied UV-bright galaxies at redshifts beyond 10. PRISMS is starting to explore the population of intermediate-UV luminosity galaxies at z=10, covering UV absolute magnitudes in the range of -17.9 to -20.5, fainter than those of UV-bright galaxies studied so far.

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arXiv2025

MIDIS: Unveiling the Star Formation History in massive galaxies at $1<z<4.5$ with spectro-photometric analysis

We investigate the star formation histories (SFHs) of a sample of massive galaxies ($M_\star \geq 10^{10} \, M_\odot$) in the redshift range $1 < z < 4.5$. We analyze spectro-photometric data combining broadband photometry from HST and JWST with low-resolution grism spectroscopy from JWST/NIRISS, obtained as part of the MIDIS (MIRI Deep Imaging Survey) program. SFHs are derived through spectral energy distribution (SED) fitting using two independent codes, BAGPIPES and Synthesizer, under various SFH assumptions. This approach enables a comprehensive assessment of the biases introduced by different modeling choices. The inclusion of NIRISS spectroscopy, even with its low resolution, significantly improves constraints on key physical parameters, such as the mass-weighted stellar age ($t_M$) and formation redshift ($z_{\mathrm{form}}$), by narrowing their posterior distributions. The massive galaxies in our sample exhibit rapid stellar mass assembly, forming 50\% of their mass between $3 \leq z \leq 9$. The highest inferred formation redshifts are compatible with elevated star formation efficiencies ($ε$) at early epochs. Non-parametric SFHs generally imply an earlier and slower mass assembly compared to parametric forms, highlighting the sensitivity of inferred formation timescales to the chosen SFH model, particularly for galaxies at $z < 2$. Quiescent galaxies are, on average, older ($t_M \sim 1.1$ Gyr) and assembled more rapidly at earlier times than their star-forming counterparts. These findings support the ``downsizing'' scenario, in which more massive and passive systems form earlier and more efficiently.

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arXiv2025

Spatially resolved H$α$ emission in B14-65666: compact starbursts, ionizing efficiency and gas kinematics in an advanced merger at the Epoch of Reionization

We present MIRI/JWST medium resolution spectroscopy (MRS) and imaging (MIRIM) of B14-65666, a Lyman-break and interacting galaxy at redshift $z$=7.15. We detect the H$α$ line emission in this system, revealing a spatially-resolved structure of the H$α$ emitting gas, which consists of two distinct galaxies, E and W, at a projected distance of 0.4". Galaxy E is very compact in the rest-frame UV, while W galaxy is more extended, showing a clumpy structure reminiscent of a tidal tail. The total H$α$ luminosity implies that the system is forming stars at a Star Formation Rate (SFR) of 76$\pm$8 M$_{\odot}$ yr$^{-1}$ and 30$\pm$4 M$_{\odot}$ yr$^{-1}$ for E and W, respectively. The ionizing photon production efficiency is within the range measured in galaxies at similar redshifts. The high values derived for the H$α$ equivalent widths (EW) and the distinct locations of the E and W galaxies in the $\log(ζ_\mathrm{ion}$) $-$ EW (H$α$) plane, indicate that the system is dominated by a young (less than 10 Myr) stellar population. The overall spectral energy distribution suggests that in addition to a young stellar population, the two galaxies may have mature stellar population and very different dust attenuation. The derived SFR and stellar masses identify the two galaxies as going through a starburst phase. The kinematics of the ionized gas traced by the H$α$ line show a velocity difference of 175 $\pm$ 28 km s$^{-1}$ between the two components of B14-65666. The in-depth study of systems like B14-65666 reveal how galaxy mergers in the early Universe drive intense star formation, shape the interstellar medium, and influence the buildup of stellar mass, just 700 $-$ 800 Myr after the Big Bang.

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arXiv2025

MIDIS. Near-infrared rest-frame morphology of massive galaxies at $3<z<5$ in the Hubble eXtreme Deep Field

Thanks to decades of observations using the Hubble Space Telescope (HST), the structure of galaxies at redshift $z>2$ has been widely studied in the rest-frame ultraviolet regime, which traces recent star formation from young stellar populations. But, we still have little information about the spatial distribution of the older, more evolved stellar populations, constrained by the rest-frame infrared portion of the galaxies' spectral energy distribution. We present the morphological characterization of a sample of 49 massive galaxies ($\log(M_{\star}/M_{\odot})>9$) at redshift $3 3$ massive galaxies show a smooth distribution of their rest-infrared light, strongly supporting the increasing number of regular disk galaxies already in place at early epochs. On the contrary, the ultraviolet structure obtained from HST/WFC3 and JWST/NIRCam observations at $\sim1.5~μ$m is generally more irregular, catching the most recent episodes of star formation. Importantly, we find a segregation of morphologies across cosmic time, where galaxies at redshift $z>3.75$ show later-type morphologies compared to $z\sim3$ galaxies. These findings suggest a transition phase in galaxy assembly and central mass build-up, which is already taking place at $z\sim3-4$. The combined analysis of NIRCam and MIRI imaging datasets allows us to prove that the rest-frame near-infrared morphology of massive galaxies at cosmic noon is typical of compact disk galaxies with a smooth mass distribution.

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arXiv2025

Final Moments III: Explosion Properties and Progenitor Constraints of CSM-Interacting Type II Supernovae

We present analysis of the plateau and late-time phase properties of a sample of 39 Type II supernovae (SNe II) that show narrow, transient, high-ionization emission lines (i.e., "IIn-like") in their early-time spectra from interaction with confined, dense circumstellar material (CSM). Originally presented by Jacobson-Galán et al 2024a, this sample also includes multicolor light curves and spectra extending to late-time phases of 35 SNe with no evidence for IIn-like features at <2 days after first light. We measure photospheric phase light-curve properties for the distance-corrected sample and find that SNe II with IIn-like features have significantly higher luminosities and decline rates at +50 days than the comparison sample, which could be connected to inflated progenitor radii, lower ejecta mass, and/or persistent CSM interaction. However, we find no statistical evidence that the measured plateau durations and $^{56}$Ni masses of SNe II with and without IIn-like features arise from different distributions. We estimate progenitor zero-age main sequence (ZAMS) masses for all SNe with nebular spectroscopy through spectral model comparisons and find that most objects, both with and without IIn-like features, are consistent with progenitor masses <12.5 M$_{\odot}$. Combining progenitor ZAMS masses with CSM densities inferred from early-time spectra suggests multiple channels for enhanced mass loss in the final years before core collapse such as a convection-driven chromosphere or binary interaction. Finally, we find spectroscopic evidence for ongoing ejecta-CSM interaction at radii $>10^{16}$ cm, consistent with substantial progenitor mass-loss rates of $\sim 10^{-4}$--$10^{-5}$ M$_{\odot}$ yr$^{-1}$ ($v_w < 50$ km/s) in the final centuries to millennia before explosion.

astro-ph.HE↗

arXiv2025

The emergence of the Star Formation Main Sequence with redshift unfolded by JWST

We investigate the correlation between stellar mass (M*) and star formation rate (SFR) across the stellar mass range log10(M*/Msun)~6-11. We consider almost 50,000 star-forming galaxies at z~3-7, leveraging data from COSMOS/SMUVS, JADES/GOODS-SOUTH, and MIDIS/XDF. This is the first study spanning such a wide stellar mass range without relying on gravitational lensing effects. We locate our galaxies on the SFR-M* plane to assess how the location of galaxies in the star-formation main sequence (MS) and starburst (SB) region evolves with stellar mass and redshift. We find that the two star-forming modes tend to converge at log10(M*/Msun) < 7, with all galaxies found in the SB mode. However, deeper observations will be instrumental for reaching lower SFRs and Msun to further validate this scenario. By dissecting our galaxy sample in stellar mass and redshift, we show that the emergence of the star-formation MS is stellar-mass dependent: while in galaxies with log10(M*/Msun) > 9 the MS is already well in place at z = 5-7, for galaxies with log10(M*/Msun)~7-8 it only becomes significant at z<4. Overall, our results are in line with previous findings that the SB mode dominates amongst low stellar-mass galaxies. The earlier emergence of the MS for massive galaxies is consistent with galaxy downsizing.

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arXiv2024

Insight into the Starburst Nature of Galaxy GN-z11 with JWST MIRI Spectroscopy

This paper presents a deep MIRI/JWST medium resolution spectroscopy (MRS) covering the rest-frame optical spectrum of the GN-z11 galaxy. The [OIII]5008 and H$α$ emission lines are detected and spectroscopically resolved. The line profiles are well-modeled by a narrow Gaussian component with intrinsic FWHMs of 189$\pm$25 and 231$\pm$52 kms$^{-1}$, respectively. We do not find any evidence of a dominant broad H$α$ emission line component tracing a Broad Line Region in a type 1 active galactic nuclei (AGN). However, a broad ($\sim$430-470 kms$^{-1}$) and weak ($<$ 20-30%) H$α$ line component, tracing a minor AGN contribution in the optical, cannot be ruled out completely with the sensitivity of the present data. The physical and excitation properties of the ionized gas are consistent with a low-metallicity starburst forming stars at a rate of SFR(H$α$)$=$24 $\pm$3$M_{\odot}$yr$^{-1}$. The electron temperature of the ionized gas is $T_{\mathrm{e}}$(O$^{++}$)$=$14000$\pm$2100K, while the direct-$T_{\mathrm{e}}$ gas-phase metallicity is 12+$\log$(O/H)$=$7.91$\pm$0.07 (Z=0.17$\pm$0.03Z$_{\odot}$). The optical line ratios locate GN-z11 in the starburst or AGN region but more consistent with those of local low-metallicity starbursts and high-$z$ luminous galaxies detected at redshifts similar to GN-z11. We conclude that the MRS optical spectrum of GN-z11 is consistent with that of a massive, compact, and low-metallicity starburst galaxy. Due to its high SFR and stellar mass surface densities, close to that of the densest stellar clusters, we speculate that GN-z11 could be undergoing a feedback-free, highly efficient starburst phase. Additional JWST data are needed to validate this scenario, and other recently proposed alternatives, to explain the existence of bright compact galaxies in the early Universe.

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arXiv2024

JWST/MIRI unveils the stellar component of the GN20 dusty galaxy overdensity at $z$=4.05

Despite the importance of the dusty star-forming galaxies (DSFGs) at $z$>2 for understanding the galaxy evolution in the early Universe, their stellar distributions traced by the near-IR emission were spatially unresolved until the arrival of the JWST. In this work we present, for the first time, a spatially-resolved morphological analysis of the rest-frame near-IR (~1.1-3.5$μ$m) emission in DSFGs traced with the JWST/MIRI. In particular, we study the mature stellar component for the three DSFGs and a Lyman-break galaxy (LBG) present in an overdensity at $z$=4.05. Moreover, we use MIRI images along with UV to (sub)-mm ancillary photometric data to model their SEDs and extract their main physical properties. The sub-arcsec resolution MIRI images have revealed that the stellar component present a wide range of morphologies, from disc-like to compact and clump-dominated structures. These near-IR structures contrast with their UV emission, which is usually diffuse and off-centered. The SED fitting analysis shows that GN20 dominates the total SFR with a value ~2500 $M_\odot$yr$^{-1}$ while GN20.2b has the highest stellar mass in the sample ($M_*$~2$\times$10$^{11}$ $M_\odot$). The two DSFGs classified as LTGs (GN20 and GN20.2a) show high specific SFR (sSFR>30 Gyr$^{-1}$) placing them above the star-forming main sequence (SFMS) at z~4 by >0.5 dex while the ETG (i.e.,GN20.2b) is compatible with the high-mass end of the main sequence. When comparing with other DSFGs in overdensities at $z$~2-7 we observe that our objects present similar SFRs, depletion times and projected separations. Nevertheless, the effective radii computed for GN20 and GN20.2a are up to two times larger than those of isolated galaxies observed in CEERS and ALMA-HUDF at similar redshifts. We interpret this difference in size as an effect of rapid growth induced by the dense environment.

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arXiv2024

MIDIS: Unveiling the Role of Strong Ha-emitters during the Epoch of Reionization with JWST

By using the ultra-deep \textit{JWST}/MIRI image at 5.6 $μm$ in the Hubble eXtreme Deep Field, we constrain the role of strong H$α$-emitters (HAEs) during Cosmic Reionization at $z\simeq7-8$. Our sample of HAEs is comprised of young ($<35\;\rm Myr$) galaxies, except for one single galaxy ($\approx 300\;\rm Myr$), with low stellar masses ($\lesssim 10^{9}\;\rm M_{\odot}$). These HAEs show a wide range of UV-$β$ slopes, with a median value of $β= -2.15\pm0.21$ which broadly correlates with stellar mass. We estimate the ionizing photon production efficiency ($ξ_{ion,0}$) of these sources (assuming $f_{esc,LyC} = 0\%$), which yields a median value $\rm log_{10}(ξ_{ion,0}/(Hz\;erg^{-1})) = 25.50^{+0.10}_{-0.12}$. We show that $ξ_{ion,0}$ positively correlates with EW$_{0}$(H$α$) and specific star formation rate (sSFR). Instead $ξ_{ion,0}$ weakly anti-correlates with stellar mass and $β$. Based on the $β$ values, we predict $f_{esc, LyC}=4\%^{+3}_{-2}$, which results in $\rm log_{10}(ξ_{ion}/(Hz\;erg^{-1})) = 25.55^{+0.11}_{-0.13}$. Considering this and related findings from the literature, we find a mild evolution of $ξ_{ion}$with redshift. Additionally, our results suggest that these HAEs require only modest escape fractions ($f_{esc, rel}$) of 6$-$15\% to reionize their surrounding intergalactic medium. By only considering the contribution of these HAEs, we estimated their total ionizing emissivity ($\dot{N}_{ion}$) as $\dot{N}_{ion} = 10^{50.53 \pm 0.45}; \text{s}^{-1}\text{Mpc}^{-3}$. When comparing their $\dot{N}_{ion}$ with "non-H$α$ emitter" galaxies across the same redshift range, we find that that strong, young, and low-mass emitters may have played an important role during Cosmic Reionization.

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arXiv2024

Spatially-resolved H$α$ and ionizing photon production efficiency in the lensed galaxy MACS1149-JD1 at a redshift of 9.11

We present MIRI/JWST medium-resolution spectroscopy (MRS) and imaging (MIRIM) of the lensed galaxy MACS1149-JD1 at a redshift of $z$=9.1092$\pm$0.0002 (Universe age about 530 Myr). We detect, for the first time, spatially resolved H$α$ emission in a galaxy at a redshift above nine. The structure of the H$α$ emitting gas consists of two clumps, S and N. The total H$α$ luminosity implies an instantaneous star-formation of 5.3$\pm$0.4 $M_{\odot}$ yr$^{-1}$ for solar metallicities. The ionizing photon production efficiency, $\log(ζ_\mathrm{ion})$, shows a spatially resolved structure with values of 25.55$\pm$0.03, 25.47$\pm$0.03, and 25.91$\pm$0.09 Hz erg$^{-1}$ for the integrated galaxy, and clumps S and N, respectively. The H$α$ rest-frame equivalent width, EW$_{0}$(H$α$), is 726$^{+660}_{-182}$ Ángstrom for the integrated galaxy, but presents extreme values of 531$^{+300}_{-96}$ Ángstrom and $\geq$1951 Ángstrom for clumps S and N, respectively. The spatially resolved ionizing photon production efficiency is within the range of values measured in galaxies at redshift above six, and well above the canonical value (25.2$\pm$0.1 Hz erg$^{-1}$). The extreme difference of EW$_{0}$(H$α$) for Clumps S and N indicates the presence of a recent (<5 Myrs) burst in clump N and a star formation over a larger period of time (e.g., $\sim$50 Myr) in clump S. Finally, clump S and N show very different H$α$ kinematics with velocity dispersions of 56$\pm$4 km s$^{-1}$ and 113$\pm$33 km s$^{-1}$, likely indicating the presence of outflows or increased turbulence in the clump N. The dynamical mass, $M_\mathrm{dyn}$= (2.4$\pm$0.5)$\times$10$^{9}$ $M_{\odot}$, is within the range measured with the spatially resolved [OIII]88$μ$m line.

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arXiv2024

Final Moments II: Observational Properties and Physical Modeling of CSM-Interacting Type II Supernovae

We present ultraviolet/optical/near-infrared observations and modeling of Type II supernovae (SNe II) whose early-time ($δt < 2$ days) spectra show transient, narrow emission lines from shock ionization of confined ($r < 10^{15}$ cm) circumstellar material (CSM). The observed electron-scattering broadened line profiles (i.e., IIn-like) of HI, He I/II, C III/IV, and N III/IV/V from the CSM persist on a characteristic timescale ($t_{\rm IIn}$) that marks a transition to a lower-density CSM and the emergence of Doppler-broadened features from the fast-moving SN ejecta. Our sample, the largest to date, consists of 39 SNe with early-time IIn-like features in addition to 35 "comparison" SNe with no evidence of early-time IIn-like features, all with ultraviolet observations. The total sample consists of 50 unpublished objects with 474 previously unpublished spectra and 50 multiband light curves, collected primarily through the Young Supernova Experiment and Global Supernova Project collaborations. For all sample objects, we find a significant correlation between peak ultraviolet brightness and both $t_{\rm IIn}$ and the rise time, as well as evidence for enhanced peak luminosities in SNe II with IIn-like features. We quantify mass-loss rates and CSM density for the sample through matching of peak multiband absolute magnitudes, rise times, $t_{\rm IIn}$ and optical SN spectra with a grid of radiation hydrodynamics and non-local thermodynamic equilibrium (nLTE) radiative-transfer simulations. For our grid of models, all with the same underlying explosion, there is a trend between the duration of the electron-scattering broadened line profiles and inferred mass-loss rate: $t_{\rm IIn} \approx 3.8[\dot{M}/(0.01 \textrm{M}_{\odot} \textrm{yr}^{-1})]$ days.

astro-ph.HE↗

arXiv2024

Clumpy star formation and an obscured nuclear starburst in the luminous dusty z=4 galaxy GN20 seen by MIRI/JWST

Dusty star-forming galaxies emit most of their light at far-IR to mm wavelengths as their star formation is highly obscured. Far-IR and mm observations have revealed their dust, neutral and molecular gas properties. The sensitivity of JWST at rest-frame optical and near-infrared wavelengths now allows the study of the stellar and ionized gas content. We investigate the spatially resolved distribution and kinematics of the ionized gas in GN20, a dusty star forming galaxy at $z$=4.0548. We present deep MIRI/MRS integral field spectroscopy of the near-infrared rest-frame emission of GN20. We detect spatially resolved \paa, out to a radius of 6 kpc, distributed in a clumpy morphology. The star formation rate derived from \paa\ (144 $\pm$ 9 \msunperyear) is only 7.7 $\pm 0.5 $\% of the infrared star formation rate (1860 $\pm$ 90 \msunperyear). We attribute this to very high extinction (A$_V$ = 17.2 $\pm$ 0.4 mag, or A$_{V,mixed}$ = 44 $\pm$ 3 mag), especially in the nucleus of GN20, where only faint \paa\ is detected, suggesting a deeply buried starburst. We identify four, spatially unresolved, clumps in the \paa\ emission. Based on the double peaked \paa\ profile we find that each clump consist of at least two sub-clumps. We find mass upper limits consistent with them being formed in a gravitationally unstable gaseous disk. The UV bright region of GN20 does not have any detected \paa\ emission, suggesting an age of more than 10 Myrs for this region of the galaxy. From the rotation profile of \paa\ we conclude that the gas kinematics are rotationally dominated and the $v_{rot}/σ_{m} = 3.8 \pm 1.4$ is similar to low-redshift LIRGs. We speculate that the clumps seen in GN20 could contribute to building up the inner disk and bulge of GN20.

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arXiv2023

Uncovering the MIR emission of quiescent galaxies with $JWST$

We present a study of the mid-IR (MIR) emission of quiescent galaxies (QGs) beyond the local universe. Using deep $JWST$ imaging in the SMACS-0723 cluster field we identify a mass limited ($M_{*} >10^{9}$M$_{\odot}$) sample of intermediate redshift QGs ($0.2 5 μ$m, can be attributed to different dust continuum levels and/or the presence of Polycyclic Aromatic Hydrocarbons (PAHs) features. The latter would indicate enhanced 11.3- and 12.7 $μ$m PAHs strengths with respect to those at 6.2- and 7.7$ μ$m, consistent with the observed spectra of local ellipticals and indicative of soft radiation fields. Finally, we augment the average UV-to-MIR spectrum of the population with cold dust and gas emission in the far-IR/mm and construct a panchromatic UV-to-radio SED that can serve as a template for the future exploration of the interstellar medium of $z>0$ QGs with ALMA and $JWST$.

astro-ph.GA↗

arXiv2023

JWST detection of heavy neutron capture elements in a compact object merger

The mergers of binary compact objects such as neutron stars and black holes are of central interest to several areas of astrophysics, including as the progenitors of gamma-ray bursts (GRBs), sources of high-frequency gravitational waves and likely production sites for heavy element nucleosynthesis via rapid neutron capture (the r-process). These heavy elements include some of great geophysical, biological and cultural importance, such as thorium, iodine and gold. Here we present observations of the exceptionally bright gamma-ray burst GRB 230307A. We show that GRB 230307A belongs to the class of long-duration gamma-ray bursts associated with compact object mergers, and contains a kilonova similar to AT2017gfo, associated with the gravitational-wave merger GW170817. We obtained James Webb Space Telescope mid-infrared (mid-IR) imaging and spectroscopy 29 and 61 days after the burst. The spectroscopy shows an emission line at 2.15 microns which we interpret as tellurium (atomic mass A=130), and a very red source, emitting most of its light in the mid-IR due to the production of lanthanides. These observations demonstrate that nucleosynthesis in GRBs can create r-process elements across a broad atomic mass range and play a central role in heavy element nucleosynthesis across the Universe.

astro-ph.HE↗