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arXiv:2404.04325v1 Announce Type: new Abstract: We describe new ultra-deep James Webb Space Telescope (JWST) NIRSpec PRISM and grating spectra for the galaxies JADES-GS-z11-0 ($z_{\mathrm{spec}} = 11.122^{+0.005}_{-0.003}$) and JADES-GS-z13-0 ($z_{\mathrm{spec}} = 13.20^{+0.03}_{-0.04}$), the most distant spectroscopically-confirmed galaxy discovered in the first year of JWST observations. The extraordinary depth of these observations (75 hours and 56 hours, respectively) provides a unique opportunity to explore the redshifts, stellar properties, UV magnitudes, and slopes for these two sources. For JADES-GS-z11-0, we find evidence for multiple emission lines, including [OII]3726,3729 and [NeIII]3869, resulting in a spectroscopic redshift we determine with 94% confidence. At this spectroscopic redshift, the Lyman-$\alpha$ break in JADES-GS-z11-0 can be fit with a damped Lyman-$\alpha$ absorber with $\log{(N_\mathrm{HI}/\mathrm{cm}^{-2})} = 22.42^{+0.093}_{-0.120}$. We present stringent upper limits on the emission line fluxes and line equivalent widths for JADES-GS-z13-0. These results demonstrate how neutral hydrogen fraction and Lyman-damping wings may impact the recovery of spectroscopic redshifts for sources like these, providing insight into the overprediction of the photometric redshifts seen for distant galaxies observed with JWST. In addition, we analyze updated NIRCam photometry to calculate the morphological properties of these resolved sources, and find a secondary source $0.3^{\prime\prime}$ south of JADES-GS-z11-0 at a similar photometric redshift, hinting at how galaxies grow through interactions in the early Universe.

arXiv:2404.03001v2 Announce Type: replace Abstract: We present the measurement of Baryon Acoustic Oscillations (BAO) from the Lyman-$\alpha$ (Ly$\alpha$) forest of high-redshift quasars with the first-year dataset of the Dark Energy Spectroscopic Instrument (DESI). Our analysis uses over $420\,000$ Ly$\alpha$ forest spectra and their correlation with the spatial distribution of more than $700\,000$ quasars. An essential facet of this work is the development of a new analysis methodology on a blinded dataset. We conducted rigorous tests using synthetic data to ensure the reliability of our methodology and findings before unblinding. Additionally, we conducted multiple data splits to assess the consistency of the results and scrutinized various analysis approaches to confirm their robustness. For a given value of the sound horizon ($r_d$), we measure the expansion at $z_{\rm eff}=2.33$ with 2\% precision, $H(z_{\rm eff}) = (239.2 \pm 4.8) (147.09~{\rm Mpc} /r_d)$ km/s/Mpc. Similarly, we present a 2.4\% measurement of the transverse comoving distance to the same redshift, $D_M(z_{\rm eff}) = (5.84 \pm 0.14) (r_d/147.09~{\rm Mpc})$ Gpc. Together with other DESI BAO measurements at lower redshifts, these results are used in a companion paper to constrain cosmological parameters.

arXiv:2404.04148v1 Announce Type: new Abstract: We report the chemical abundance pattern of GS\_3073, a galaxy at $z=5.55$ which was previously confirmed to host an overmassive active black hole, by leveraging the detection of about 40 emission lines, combining JWST/NIRSpec observations and ground-based (VLT/VIMOS) data. By using rest-frame UV emission lines, which trace high-density ($\sim 10^5~{\rm cm}^{-3}$) and highly ionized gas, we derived an abundance ratio of $\rm log(N/O) = 0.46^{+0.12}_{-0.09}$. At an estimated metallicity of $0.2~Z_{\odot}$, this is the most extreme nitrogen-rich object found by JWST thus far. In comparison, the relative carbon abundance derived from the rest-frame UV emission lines is $\rm log(C/O) = -0.30^{+0.12}_{-0.09}$, which is not significantly higher than those in local galaxies and stars with similar metallicities. We also detected coronal lines, including [FeVII]$\lambda 6087$ and potentially [FeXIV]$\lambda 5303$. We inferred a high Fe abundance of $\rm [Fe/O] \gtrsim 0.1$. Overall, the chemical abundance pattern of GS\_3073 is compatible with enrichment by super-massive stars with $M_* \gtrsim 1000~M_\odot$, ejecta from asymptotic giant branch (AGB) stars, or winds from Wolf-Rayet (WR) stars, although the WR scenario is less likely. Interestingly, when using optical emission lines which trace lower density ($\sim 10^3~{\rm cm}^{-3}$) and lower ionization gas, we found a sub-solar N/O ratio. We interpret the difference in N/O derived from UV lines and optical lines as evidence for a stratified system, where the inner and denser region is both more chemically enriched and more ionized. Taking this luminous, well-studied system as a benchmark, our results suggest that nitrogen loudness in high-$z$ galaxies is confined to the central, dense, and highly ionized region of the galaxy, while the bulk of the galaxy evolves more normally.

Hierarchical star cluster assembly boosts intermediate-mass black hole formation

Observations and high-resolution hydrodynamical simulations indicate that massive star clusters assemble hierarchically from sub-clusters with a universal power-law cluster mass function. We study the consequences of such assembly for the formation of intermediate-mass black holes (IMBHs) and massive black hole (MBH) seeds at low metallicities (1% of the solar value) with our updated direct N-body code BIFROST in simulations up to N = 2.35 million stars. The GPU -accelerated code BIFROST is based on the hierarchical fourth-order forward integrator. Few-body systems are treated using secular and regularized techniques including post-Newtonian equations of motion up to order PN3 .5 and gravitational-wave recoil kicks for merging BHs. Stellar evolution is provided by the fast population synthesis code SEVN . IMBHs with masses up to 2200 solar masses form rapidly mainly via the collapse of very massive stars (VMSs) assembled through repeated collisions of massive stars followed by growth through tidal disruption events (TDEs) and BH mergers. Later the IMB Hs form subsystems resulting in gravitational-wave BH-BH, IMBH -BH and IMBH -IMBH mergers with a 1000 solar mass gravitational-wave detection being the observable prediction. Our simulations indicate that the hierarchical formation of massive star clusters in metal poor environments naturally results in formation of potential seeds for supermassive black holes.

• Speaker: Antti Rantala (MPA)
• Wednesday 22 May 2024, 11:30-12:30
• Venue: Martin Ryle Meeting Room, KICC + Online.
• Series: Kavli Institute for Cosmology Seminars; organiser: Alison Wilson.

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Inside Astronomically Realistic Black Holes

I will use a real-time general relativistic Black Hole Flight Similator to show what really happens inside astronomically realistic black holes. The inner horizon of a rotating black hole is the most violent place in the Universe, easily reaching and surpassing energy densities attained in the Big Bang. What does Nature do at this extraordinary place?

• Speaker: Prof. Andrew Hamilton (University of Colorado Boulder)
• Thursday 16 May 2024, 16:00-17:00
• Venue: Hoyle Lecture Theatre, Institute of Astronomy.
• Series: Institute of Astronomy Colloquia; organiser: eb694.

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KICC Special Seminar (Title TBC)

Abstract not available

• Speaker: Tsevi Mazeh (Tel Aviv)
• Tuesday 07 May 2024, 11:30-12:30
• Venue: Hoyle Lecture Theatre + ONLINE - Details will be sent by email.
• Series: Kavli Institute for Cosmology Seminars; organiser: Alison Wilson.

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Title to be confirmed

Abstract not available

• Speaker: Arjen van der Wel (Ghent University)
• Friday 07 June 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Modelling supermassive black holes: accretion, spin evolution, jets and winds

Abstract not available

• Speaker: Martin Bourne (IoA)
• Friday 21 June 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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arXiv:2308.12991v3 Announce Type: replace Abstract: We present the photometric and spectroscopic evolution of SN 2022oqm, a nearby multi-peaked hydrogen- and helium-weak calcium-rich transient (CaRT). SN 2022oqm was detected 13.1 kpc from its host galaxy, the face-on spiral galaxy NGC 5875. Extensive spectroscopic coverage reveals an early hot (T >= 40,000 K) continuum and carbon features observed $\sim$1~day after discovery, SN Ic-like photospheric-phase spectra, and strong forbidden calcium emission starting 38 days after discovery. SN 2022oqm has a relatively high peak luminosity (MB = -17 mag) for (CaRTs), making it an outlier in the population. We determine that three power sources are necessary to explain the light curve (LC), with each corresponding to a distinct peak. The first peak is powered by an expanding blackbody with a power law luminosity, suggesting shock cooling by circumstellar material (CSM). Subsequent LC evolution is powered by a double radioactive decay model, consistent with two sources of photons diffusing through optically thick ejecta. From the LC, we derive an ejecta mass and 56Ni mass of ~0.6 solar masses and ~0.09 solar masses. Spectroscopic modeling suggests 0.6 solar masses of ejecta, and with well-mixed Fe-peak elements throughout. We discuss several physical origins for SN 2022oqm and find either a surprisingly massive white dwarf progenitor or a peculiar stripped envelope model could explain SN 2022oqm. A stripped envelope explosion inside a dense, hydrogen- and helium-poor CSM, akin to SNe Icn, but with a large 56Ni mass and small CSM mass could explain SN 2022oqm. Alternatively, helium detonation on an unexpectedly massive white dwarf could also explain SN 2022oqm.

arXiv:2404.03557v1 Announce Type: new Abstract: Analysis of microwave sky signals, such as the cosmic microwave background, often requires component separation with multi-frequency methods, where different signals are isolated by their frequency behaviors. Many so-called "blind" methods, such as the internal linear combination (ILC), make minimal assumptions about the spatial distribution of the signal or contaminants, and only assume knowledge of the frequency dependence of the signal. The ILC is a minimum-variance linear combination of the measured frequency maps. In the case of Gaussian, statistically isotropic fields, this is the optimal linear combination, as the variance is the only statistic of interest. However, in many cases the signal we wish to isolate, or the foregrounds we wish to remove, are non-Gaussian and/or statistically anisotropic (in particular for Galactic foregrounds). In such cases, it is possible that machine learning (ML) techniques can be used to exploit the non-Gaussian features of the foregrounds and thereby improve component separation. However, many ML techniques require the use of complex, difficult-to-interpret operations on the data. We propose a hybrid method whereby we train an ML model using only combinations of the data that $\textit{do not contain the signal}$, and combine the resulting ML-predicted foreground estimate with the ILC solution to reduce the error from the ILC. We demonstrate our methods on simulations of extragalactic temperature and Galactic polarization foregrounds, and show that our ML model can exploit non-Gaussian features, such as point sources and spatially-varying spectral indices, to produce lower-variance maps than ILC - eg, reducing the variance of the B-mode residual by factors of up to 5 - while preserving the signal of interest in an unbiased manner. Moreover, we often find improved performance when applying our model to foreground models on which it was not trained.

TBD

Abstract not available

• Speaker: Tsevi Mazeh (Tel Aviv)
• Tuesday 07 May 2024, 11:30-12:30
• Venue: Hoyle Lecture Theatre + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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arXiv:2404.03002v1 Announce Type: new Abstract: We present cosmological results from the measurement of baryon acoustic oscillations (BAO) in galaxy, quasar and Lyman-$\alpha$ forest tracers from the first year of observations from the Dark Energy Spectroscopic Instrument (DESI), to be released in the DESI Data Release 1. DESI BAO provide robust measurements of the transverse comoving distance and Hubble rate, or their combination, relative to the sound horizon, in seven redshift bins from over 6 million extragalactic objects in the redshift range $0.1-1$ and $w_a0$ $(\sum m_\nu>0.059)$ eV prior. These neutrino-mass constraints are substantially relaxed in models beyond $\Lambda$CDM. [Abridged.]

arXiv:2404.03001v1 Announce Type: new Abstract: We present the measurement of Baryon Acoustic Oscillations (BAO) from the Lyman-$\alpha$ (Ly$\alpha$) forest of high-redshift quasars with the first-year dataset of the Dark Energy Spectroscopic Instrument (DESI). Our analysis uses over $420\,000$ Ly$\alpha$ forest spectra and their correlation with the spatial distribution of more than $700\,000$ quasars. An essential facet of this work is the development of a new analysis methodology on a blinded dataset. We conducted rigorous tests using synthetic data to ensure the reliability of our methodology and findings before unblinding. Additionally, we conducted multiple data splits to assess the consistency of the results and scrutinized various analysis approaches to confirm their robustness. For a given value of the sound horizon ($r_d$), we measure the expansion at $z_{\rm eff}=2.33$ with 2\% precision, $H(z_{\rm eff}) = (239.2 \pm 4.8) (147.09~{\rm Mpc} /r_d)$ km/s/Mpc. Similarly, we present a 2.4\% measurement of the transverse comoving distance to the same redshift, $D_M(z_{\rm eff}) = (5.84 \pm 0.14) (r_d/147.09~{\rm Mpc})$ Gpc. Together with other DESI BAO measurements at lower redshifts, these results are used in a companion paper to constrain cosmological parameters.

arXiv:2404.03000v1 Announce Type: new Abstract: We present the DESI 2024 galaxy and quasar baryon acoustic oscillations (BAO) measurements using over 5.7 million unique galaxy and quasar redshifts in the range 0.1

arXiv:2404.02953v1 Announce Type: new Abstract: In the cold dark matter paradigm, our Galaxy is predicted to contain >10000 dark matter subhaloes in the $10^5-10^8M_\odot$ range which should be completely devoid of stars. Stellar streams are sensitive to the presence of these subhaloes, which can create small-scale features in streams if they pass closely enough. Modelling these encounters can therefore, potentially recover the subhalo's properties. In this work, we demonstrate this for streams generated in numerical simulations, modelled on eccentric orbits in a realistic Milky Way potential, which includes the Large Magellanic Cloud and the subhalo itself. We focus on a mock model of the ATLAS-Aliqa Uma stream and inject a $10^7 M_\odot$ subhalo, creating a similar discontinuous morphology to current observations. We then explore how well subhalo properties are recovered using mock stream observations, consisting of no observational errors, as well as assuming realistic observational setups. These setups include present day style observations, and what will be possible with 4MOST and Gaia DR5 in the future. We show that we can recover all parameters describing the impact even with uncertainties matching existing data, including subhalo positions, velocities, mass and scale radius. Modelling the subhalo on an orbit instead of assuming an impulse approximation, we greatly reduce the degeneracy between subhalo mass and velocity seen in previous works. However, we find a slight bias in the subhalo mass (~0.1 dex). This demonstrates that we should be able to reliably extract the properties of subhaloes with stellar streams in the near future.

The standard model of cosmology says that the strength of dark energy should be constant, but tentative hints are emerging that it may have weakened recently

TBD (have to move to May 7?)

Abstract not available

• Speaker: Tsevi Mazeh (Tel Aviv)
• Friday 03 May 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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Chemo-dynamical evolution of disks over cosmic time

Abstract not available

• Speaker: Emily Wisnioski (ANU)
• Friday 12 April 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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arXiv:2404.02139v2 Announce Type: replace Abstract: A bright ($m_{\rm F150W,AB}$=24 mag), $z=1.95$ supernova (SN) candidate was discovered in JWST/NIRCam imaging acquired on 2023 November 17. The SN is quintuply-imaged as a result of strong gravitational lensing by a foreground galaxy cluster, detected in three locations, and remarkably is the second lensed SN found in the same host galaxy. The previous lensed SN was called "Requiem", and therefore the new SN is named "Encore". This makes the MACS J0138.0$-$2155 cluster the first known system to produce more than one multiply-imaged SN. Moreover, both SN Requiem and SN Encore are Type Ia SNe (SNe Ia), making this the most distant case of a galaxy hosting two SNe Ia. Using parametric host fitting, we determine the probability of detecting two SNe Ia in this host galaxy over a $\sim10$ year window to be $\approx3\%$. These observations have the potential to yield a Hubble Constant ($H_0$) measurement with $\sim10\%$ precision, only the third lensed SN capable of such a result, using the three visible images of the SN. Both SN Requiem and SN Encore have a fourth image that is expected to appear within a few years of $\sim2030$, providing an unprecedented baseline for time-delay cosmography.

arXiv:2404.02333v1 Announce Type: new Abstract: JWST is producing high-quality rest-frame optical and UV spectra of faint galaxies at $z>4$ for the first time, challenging models of galaxy and stellar populations. One galaxy recently observed at $z=5.943$, GS9422, has nebular line and UV continuum emission that appears to require a high ionizing photon production efficiency. This has been explained with an exotic stellar initial mass function (IMF), 10-30x more top-heavy than a Salpeter IMF (Cameron et al. 2023). Here we suggest an alternate explanation to this exotic IMF. We use a new flexible neural net emulator for CLOUDY, Cue, to infer the shape of the ionizing spectrum directly from the observed emission line fluxes. By describing the ionizing spectrum with a piece-wise power-law, Cue is agnostic to the source of the ionizing photons. Cue finds that the ionizing radiation from GS9422 can be approximated by a double power law characterized by $\frac{Q_\mathrm{HeII}}{Q_\mathrm{H}} = -1.5$, which can be interpreted as a combination of young, metal-poor stars and a low-luminosity active galactic nucleus (AGN) with $F_{\nu} \propto \lambda ^ {2}$ in a 65%/35% ratio. This suggests a significantly lower nebular continuum contribution to the observed UV flux (24%) than a top-heavy IMF ($\gtrsim80$%), and hence, necessitates a damped Lyman-$\alpha$ absorber (DLA) to explain the continuum turnover bluewards of $\sim1400$ Angstrom. While current data cannot rule out either scenario, given the immense impact the proposed top-heavy IMF would have on models of galaxy formation, it is important to propose viable alternative explanations and to further investigate the nature of peculiar high-z nebular emitters.