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arXiv:2404.06098v1 Announce Type: new Abstract: Extracting precise cosmology from weak lensing surveys requires modelling the non-linear matter power spectrum, which is suppressed at small scales due to baryonic feedback processes. However, hydrodynamical galaxy formation simulations make widely varying predictions for the amplitude and extent of this effect. We use measurements of Dark Energy Survey Year 3 weak lensing (WL) and Atacama Cosmology Telescope DR5 kinematic Sunyaev-Zel'dovich (kSZ) to jointly constrain cosmological and astrophysical baryonic feedback parameters using a flexible analytical model, `baryonification'. First, using WL only, we compare the $S_8$ constraints using baryonification to a simulation-calibrated halo model, a simulation-based emulator model and the approach of discarding WL measurements on small angular scales. We find that model flexibility can shift the value of $S_8$ and degrade the uncertainty. The kSZ provides additional constraints on the astrophysical parameters and shifts $S_8$ to $S_8=0.823^{+0.019}_{-0.020}$, a higher value than attained using the WL-only analysis. We measure the suppression of the non-linear matter power spectrum using WL + kSZ and constrain a mean feedback scenario that is more extreme than the predictions from most hydrodynamical simulations. We constrain the baryon fractions and the gas mass fractions and find them to be generally lower than inferred from X-ray observations and simulation predictions. We conclude that the WL + kSZ measurements provide a new and complementary benchmark for building a coherent picture of the impact of gas around galaxies across observations.

Nature, Published online: 10 April 2024; doi:10.1038/d41586-024-01054-z

Astronomers and enthusiasts share with Nature what dazzled them most during the moments when the Moon blocked the Sun.

A new way of interpreting the elusive mathematics of quantum mechanics could fundamentally change our understanding of reality

The expansion rate of the universe, measured by the Hubble constant, has been one of the most controversial numbers in cosmology for years, and we seem at last to be close to nailing it down

Fixed-term: The funds for this post are available for 3 years in the first instance.

The Institute of Astronomy (IoA, see: www.ast.cam.ac.uk) is a highly computer-reliant department in the School of Physical Sciences at the University of Cambridge, and is engaged in teaching and research in the fields of theoretical and observational astronomy.

There is a vacancy in the IoA's IT team for a technically competent individual who enjoys both problem solving and assisting people with IT matters. The IT team are collectively responsible for providing and/or supporting all the IT services used at the IoA, including the network, audiovisual services, servers, desktops, laptops and phones, so a broad range of skills is needed.

This role specialises in providing customer-facing support to all the IoA's staff, students and visitors, although there will be some time to work on IT projects. It requires a good knowledge of Linux, networks and audiovisual systems and services, with excellent troubleshooting and fault-finding skills. Expertise in Windows and Mac OS is desired. The role-holder will need very good written and verbal communication skills, and be able to convey information clearly to people with a range of technical understanding. The role will involve manual handling and manual dexterity and working in confined spaces.

The IoA's IT helpdesk uses a ticketing system to manage workflows, both for requests and for project work. The role holder will need to triage tickets to prioritise urgent requests, contacting other team members for assistance when appropriate. The role requires an organised, methodical approach, a rapid assimilation of information, and is best suited to those who remain calm when under pressure due to quickly changing priorities and unplanned urgent work requirements.

Much of the scientific research at the IoA is carried out on Linux computers, and candidates should detail their experience in working with Linux servers and desktops. An important part of the job is supporting the administration staff, who use Windows systems, so experience in supporting Windows and Office applications is desired. The role holder will need to acquire a thorough knowledge of the administrative processes in place at the University. Supporting the AV systems in the lecture theatre and meeting rooms will need the ability to gain a good understanding of AV systems, and the confidence to be able to resolve issues in the presence of an audience.

If this sounds like the job for you, and you would like to join the IoA's small team of IT professionals, working at a very pleasant site on Madingley Rise, please read the further particulars and apply.

Click the 'Apply' button below to register an account with our recruitment system (if you have not already) and apply online.

Please indicate the contact details of three employment-related referees, one of whom should be your most recent line manager, on the online application form and upload a full curriculum vitae (CV), and a covering letter describing how you are suited to this role.

References will be requested for shortlisted applicants only.

The closing date for applications is: 23:59 BST on 30th April 2024.

Applications will be reviewed after the closing date and interviews are provisionally planned for mid-May; more details will be shared with shortlisted candidates nearer the time.

Please refer to further particulars for full instructions. For any queries regarding the application please contact: hr@ast.cam.ac.uk.

Please quote reference LG41244 on your application and in any correspondence about this vacancy.

This role does not require screening but the successful candidate will be asked to complete and adhere to a confidentiality agreement as you will potentially have access to sensitive information.

Conversations about flexible working are encouraged at the University of Cambridge. Please feel free to discuss flexibility prior to applying (using the contact information above) or at interview if your application is successful.

The University of Cambridge thrives on the diversity of its staff and students. We have an active Equality and Diversity Committee which continually works to further the aims of the Athena SWAN charter. The University has a number of family-friendly policies and initiatives, including a returning-carer scheme, childcare costs support, university workplace nurseries, university holiday play-schemes, and a shared parental-leave policy.

The University has a responsibility to ensure that all employees are eligible to live and work in the UK.

Title to be confirmed

Abstract not available

• Speaker: Sinan Deger (KICC)
• Friday 31 May 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

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arXiv:2404.05488v1 Announce Type: new Abstract: We present new results on PHL 5038AB, a widely separated binary system composed of a white dwarf and a brown dwarf, refining the white and brown dwarf parameters and determining the binary separation to be $66^{+12}_{-24}$~AU. New spectra of the white dwarf show calcium absorption lines suggesting the hydrogen-rich atmosphere is weakly polluted, inferring the presence of planetesimals in the system, which we determine are in an S-type orbit around the white dwarf in orbits closer than 17-32 AU. We do not detect any infrared excess that would indicate the presence of a disc, suggesting all dust present has either been totally accreted or is optically thin. In this system, we suggest the metal pollution in the white dwarf atmosphere can be directly attributed to the presence of the brown dwarf companion disrupting the orbits of planetesimals within the system.

arXiv:2404.04508v1 Announce Type: new Abstract: Most debris discs consist of a gas-poor, cold dust belt located tens to hundreds of astronomical units away from the host star. Many cold dust belts exhibit distinct structures attributed to the dynamic interaction of planetary systems. Moreover, in a few systems, additional warm components can be found closer to the central star, resembling the asteroid belt or zodiacal dust in our Solar System. In this work, we investigate the structure of the disc surrounding the nearby F2V star HD 105211, which has a warm excess and a potential asymmetry in the cold belt. We applied the CASA pipeline to obtain the ALMA 1.3 mm continuum images. Then we constructed the SED and performed MCMC simulations to fit a model to the ALMA visibility data. To characterise the disc asymmetry, we analysed the ALMA images of two individual observation blocks and compared them to the previous Herschel images. Our modelling reveals that the disc is a narrow ring (23.6+-4.6 au) with low eccentricity positioned at a distance of 133.7+-1.6 au from the central star, which differs from the broad disc (100+-20 au) starting at an inner edge of 87+-2.5 au, inferred from the Herschel images. We found that both observation blocks show excess emission at the stellar position, while OB1 shows an offset between the star and the phase centre, and OB2 shows brightness clumps. We used a two-temperature model to fit the infrared SED and used the ALMA detection to constrain the warm component to a nearly pure blackbody model. The relatively low ratio of actual radius to blackbody radius of the HD105211 debris disc indicates that this system is depleted in small grains, which could indicate that it is dynamically cold. The excess emission from the stellar position suggests that there should be a warm mm-sized dust component close to the star, for which we suggest two possible origins: in situ asteroid belt or comet delivery.

On 8 April, a total solar eclipse passed over Mexico, the US and Canada – here are some of the most stunning images

arXiv:2404.03776v1 Announce Type: new Abstract: With four companions at separations from 16 to 71 au, HR 8799 is a unique target for direct imaging, presenting an opportunity for the comparative study of exoplanets with a shared formation history. Combining new VLTI/GRAVITY observations obtained within the ExoGRAVITY program with archival data, we perform a systematic atmospheric characterisation of all four planets. We explore different levels of model flexibility to understand the temperature structure, chemistry and clouds of each planet using both petitRADTRANS atmospheric retrievals and fits to self-consistent radiative-convective equilibrium models. Using Bayesian Model Averaging to combine multiple retrievals, we find that the HR 8799 planets are highly enriched in metals, with [M/H] $\gtrsim$1, and have stellar to super-stellar C/O ratios. The C/O ratio increases with increasing separation from $0.55^{+0.12}_{-0.10}$ for d to $0.78^{+0.03}_{-0.04}$ for b, with the exception of the innermost planet which has a C/O ratio of $0.87\pm0.03$. By retrieving a quench pressure and using a disequilibrium chemistry model we derive vertical mixing strengths compatible with predictions for high-metallicity, self-luminous atmospheres. Bayesian evidence comparisons strongly favour the presence of HCN in HR 8799 c and e, as well as CH$_{4}$ in HR 8799 c, with detections at $>5\sigma$ confidence. All of the planets are cloudy, with no evidence for patchiness. The clouds of c, d and e are best fit by silicate clouds lying above a deep iron cloud layer, while the clouds of the cooler HR 8799 b are more likely composed of Na$_{2}$S. With well defined atmospheric properties, future exploration of this system is well positioned to unveil further detail in these planets, extending our understanding of the composition, structure, and formation history of these siblings.

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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One total solar eclipse changed physics forever – and even to this day these celestial phenomena are astonishing viewers and teaching us crucial lessons about the universe

Stephen Hawking and Jacob Bekenstein calculated the entropy of a black hole in the 1970s, but it took physicists until now to figure out the quantum effects that make the formula work

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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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:2404.02303v2 Announce Type: replace Abstract: In this third paper of a series, we study the kinematics of the ionised gas and stars, calculating the dynamical masses of the circumnuclear star-forming regions in the ring of of the face-on spiral NGC 7742. We have used high spectral resolution data from the MEGARA instrument attached to the Gran Telescopio Canarias (GTC) to measure the kinematical components of the nebular emission lines of selected HII regions and the stellar velocity dispersions from the CaT absorption lines that allow the derivation of the associated cluster virialized masses. The emission line profiles show two different kinematical components: a narrow one with velocity dispersion $\sim$ 10 km/s and a broad one with velocity dispersion similar to those found for the stellar absorption lines. The derived star cluster dynamical masses range from 2.5 $\times$ 10$^6$ to 10.0 $\times$ 10$^7$ M$_\odot$. The comparison of gas and stellar velocity dispersions suggests a scenario where the clusters have formed simultaneously in a first star formation episode with a fraction of the stellar evolution feedback remaining trapped in the cluster, subject to the same gravitational potential as the cluster stars. Between 0.15 and 7.07 % of the total dynamical mass of the cluster would have cooled down and formed a new, younger, population of stars, responsible for the ionisation of the gas currently observed.

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.