Feed aggregator

Problems with (our) galaxy formation simulations and some new angles

Stellar feedback is a crucial component in controlling the baryon cycle in galaxies. However, it is not very clear how this can be done without assuming exotic models of stellar feedback. In this talk I will first discuss why we have not been very successful in producing realistic galaxies in our simulations, and present some attempts to solve this problem. I will also discuss how Lyman alpha profiles can potentially be used to place some constraints on cosmological simulations with cosmic ray feedback. This talk is intended to be thought-provoking rather than a collection of success stories.

• Speaker: Taysun Kimm (Yonsei)
• Thursday 08 February 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

The Crafoord Prize in Astronomy The Crafoord Prize in Astronomy 2024 is awarded to Douglas Gough , University of Cambridge, UK, Jørgen Christensen-Dalsgaard , Aarhus University, Denmark, and Conny Aerts , KU Leuven, Belgium “for developing the methods of asteroseismology and their application to the study of the interior...

Title to be confirmed

Abstract not available

• Speaker: Xuejian (Jacob) Shen (MIT)
• Friday 28 June 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

Title to be confirmed

Abstract not available

• Speaker: Roger de Belsunce (LBNL)
• Monday 18 March 2024, 13:00-14:00
• Venue: CMS, Pav. B, CTC Common Room (B1.19) [Potter Room].
• Series: Cosmology Lunch; organiser: Fiona McCarthy.

Add to your calendar or Include in your list

Title to be confirmed

Abstract not available

• Speaker: Trevor Mendel (ANU)
• Friday 19 April 2024, 11:30-12:30
• Venue: Ryle seminar room + online.
• Series: Galaxies Discussion Group; organiser: Sandro Tacchella.

Add to your calendar or Include in your list

Title to be confirmed

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.

Add to your calendar or Include in your list

Photoevaporation from Exoplanet Atmospheres: Understanding the Role of Stellar Winds and Considering Water-rich Atmospheres

The atmospheres of close-in exoplanets are extremely vulnerable to the effects of stellar UV to X-ray radiation. Photoevaporation can significantly alter planetary atmospheres or even strip them entirely, potentially rendering a planet uninhabitable. Understanding how these atmospheres evolve, persist, or fade away remains a fundamental challenge. In this talk, I will discuss two distinct but interconnected areas of photoevaporative research.

Firstly, I will discuss the interaction between the stellar wind and photoevaporating atmospheres. I will present 3D magnetohydrodynamic simulations of the interaction between the stellar wind and the photoevaporating outflow of a planet orbiting an M dwarf. This analysis reveals a diverse range of magnetosphere morphologies and plasma distributions due to the wind-outflow interaction. I consider how these changing morphologies might impact observable hydrogen Lyman-alpha signatures during planetary transits.

In the second part, I will delve into our current understanding of photoevaporation from water-rich atmospheres. Conventional analytic approaches often oversimplify the process, assuming two scenarios: the escape of only lighter hydrogen, or the dragging of oxygen along with escaping hydrogen. These two scenarios lead to two end cases: a planet that has retained its water-rich atmosphere or a planet which has lost its atmosphere, becoming dry and desiccated. I will challenge these oversimplifications by presenting results from a novel 1D multifluid hydrodynamic model of photoevaporation from a water-rich atmosphere, which shows oxygen escape should no longer be described by a simple on/off switch but instead requires careful modelling.

Room changed

• Speaker: Laura Harbach (Imperial)
• Tuesday 06 February 2024, 13:00-14:00
• Venue: Hoyle Committee Room + ONLINE - Details to be sent by email.
• Series: Exoplanet Seminars; organiser: Dr Emily Sandford.

Add to your calendar or Include in your list

The INSPIRE project has built the largest sample of ultra-compact massive galaxies (UCMGs) at 0.1<z<0.4 and obtained their star formation histories (SFHs). Due to their preserved very old stellar populations, relics are the perfect systems to constrain the earliest epochs of mass assembly in the Universe and the formation of massive early-type galaxies. The goal of this work is to investigate whether a correlation exists between the degree of relicness (DoR), quantifying the fraction of stellar mass formed at z>2, and the other stellar population parameters.We use the Full-Index-Fitting method to fit the INSPIRE spectra to single stellar population (SSP) models. This allows us to measure, for the first time, the low-mass end slope of the IMF, as well as stellar metallicity [M/H], [Mg/Fe], [Ti/Fe] and [Na/Fe] ratios, and study correlations between them and the DoR. Similarly to normal-sized galaxies, UCMGs with larger stellar masses have overall higher metallicities. We found a correlation between the low-mass end of the IMF slope and the DoR, that, however, breaks down for systems with a more extended SFH. An even stronger dependency is found between the IMF and the fraction of mass formed at high-z. At equal velocity dispersion and metallicity, galaxies with a higher DoR have a dwarf-richer IMF than that of low-DoR counterparts. This might indicate that the cosmic epoch and formation mechanisms influence the fragmentation of the star formation cloud and hence might be the explanation for IMF variations detected in massive ETGs.

We present the discovery and characterization of two warm mini-Neptunes transiting the K3V star TOI-815 in a K-M binary system. Analysis of the spectra and rotation period reveal it to be a young star with an age of $200^{+400}_{-200}$Myr. TOI-815b has a 11.2-day period and a radius of 2.94$\pm$0.05$\it{R_{\rm\mathrm{\oplus}}}$ with transits observed by TESS, CHEOPS, ASTEP, and LCOGT. The outer planet, TOI-815c, has a radius of 2.62$\pm$0.10$\it{R_{\rm\mathrm{\oplus}}}$, based on observations of three non-consecutive transits with TESS, while targeted CHEOPS photometry and radial velocity follow-up with ESPRESSO were required to confirm the 35-day period. ESPRESSO confirmed the planetary nature of both planets and measured masses of 7.6$\pm$1.5 $\it{M_{\rm \mathrm{\oplus}}}$ ($\rho_\mathrm{P}$=1.64$^{+0.33}_{-0.31}$gcm$^{-3}$) and 23.5$\pm$2.4$\it{M_{\rm\mathrm{\oplus}}}$ ($\rho_\mathrm{P}$=7.2$^{+1.1}_{-1.0}$gcm$^{-3}$) respectively. Thus, the planets have very different masses, unlike the usual similarity of masses in compact multi-planet systems. Moreover, our statistical analysis of mini-Neptunes orbiting FGK stars suggests that weakly irradiated planets tend to have higher bulk densities compared to those suffering strong irradiation. This could be ascribed to their cooler atmospheres, which are more compressed and denser. Internal structure modeling of TOI-815b suggests it likely has a H-He atmosphere constituting a few percent of the total planet mass, or higher if the planet is assumed to have no water. In contrast, the measured mass and radius of TOI-815c can be explained without invoking any atmosphere, challenging planetary formation theories. Finally, we infer from our measurements that the star is viewed close to pole-on, which implies a spin-orbit misalignment at the 3$\sigma$ level.

Astronomers have, for the first time, made a direct measurement of the mass of a distant black hole, one so far away that light from its surroundings took 11 billion years to reach us. The team, led by Taro Shimizu at the Max Planck Institute for Extraterrestrial Physics in Germany, found the black hole, called J0920, to have a mass of about 320 million times that of the Sun. This achievement, described in a paper published today in Nature, has been made possible thanks to GRAVITY+, a series of ongoing upgrades to ESO’s Very Large Telescope Interferometer (VLTI) and its GRAVITY instrument.

To directly measure the mass of a black hole, astronomers use telescopes to track the movement of gas and stars around it. The faster these move, the more mass is encased within the material’s orbit. This technique has been used to measure the mass of nearby black holes, including the one at the centre of the Milky Way. At very remote distances, however, this motion is extremely hard to observe. This means similar direct measurements of the mass of distant black holes, which provide a window into a period in the history of the Universe when galaxies and black holes were rapidly growing, have not been possible until now.

The direct measurement of J0920’s mass was only possible with the first set of GRAVITY+ improvements. These upgrades have allowed astronomers to observe the faint, distant gas around the black hole with greater accuracy than ever before by using a technique called wide-field, off-axis fringe tracking. Measuring the mass of J0920 accurately is a first step to help astronomers understand how black holes and galaxies grew together at a time when the Universe was only a couple of billion years old and galaxies were still forming. For J0920, the new mass measurement reveals the black hole is about four times less massive than expected given the mass of its host galaxy; this indicates a delay in the growth of the black hole compared to the surrounding galaxy.

GRAVITY+ uses interferometry to combine the light arriving at the four 8-metre Unit Telescopes (UTs) that are part of VLTI. Once completed, it will include upgraded adaptive optics technology that will enable better correction of the blur caused by the Earth’s atmosphere and improve the contrast of observations. GRAVITY+ will also implement one new laser guide star on each of UT1-3, and will make use of one of the lasers currently installed on UT4, to observe fainter and more distant objects than currently possible.

The upgrades to GRAVITY+ are being implemented incrementally, to ensure that there are limited disruptions to the scientific operations of the VLTI. This also allows for astronomers to continually test the performance of GRAVITY+ as it comes online. The full set of upgrades is anticipated to be completed in 2025. The new features will benefit all present and future VLTI instruments and the scientists who use them.

More Information

This research was presented in a paper to appear in Nature titled “A dynamical measurement of the supermassive black hole mass in a quasar 11 billion years ago”.

The team is composed of R. Abuter (European Southern Observatory, Garching, Germany [ESO]), F. Allouche (Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, France [Lagrange]), A. Amorim (Universidade de Lisboa - Faculdade de Ciências, Portugal and Centro de Astrofísica e Gravitação, IST, Universidade de Lisboa, Portugal [CENTRA]), C. Bailet (Lagrange), A. Berdeu (Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, France [LESIA]), J. P. Berger (Univ. Grenoble Alpes, CNRS, France [UGA]), P. Berio (Lagrange), A. Bigioli (Institute of Astronomy, KU Leuven, Belgium [KU Leuven]), O. Boebion (Lagrange), M.-L. Bolzer (Max Planck Institute for Extraterrestrial Physics, Germany [MPE], Department of Physics, Technical University Munich, Germany [TUM] and Univ. Lyon, ENS de Lyon, CNRS, Centre de Recherche Astrophysique de Lyon, France [CRAL]), H. Bonnet (ESO), G. Bourdarot (MPE), P. Bourget (European Southern Observatory, Chile [ESO Chile]), W. Brandner (Max Planck Institute for Astronomy, Germany [MPIA]), Y. Cao (MPE), R. Conzelman (ESO), M. Comin (ESO), Y. Clénet (LESIA), B. Courtney-Barrer (ESO Chile and Research School of Astronomy and Astrophysics, College of Science, Australian National University, Australia [ANU]), R. Davies (MPE), D. Defrère (KU Leuven), A. Delboulbé (UGA), F. Delplancke-Ströbele (ESO), R. Dembet (LESIA), J. Dexter (Department of Astrophysical & Planetary Sciences, JILA, University of Colorado, USA), P. T. de Zeeuw (Leiden University, The Netherlands), A. Drescher (MPE), A. Eckart (Max Planck Institute for Radio Astronomy, Germany [MPIfR] and 1st Institute of Physics, University of Cologne, Germany [Cologne]), C. Édouard (LESIA), F. Eisenhauer (MPE), M. Fabricius (MPE), H. Feuchtgruber (MPE), G. Finger (MPE), N. M. Förster Schreiber (MPE), P. Garcia (Faculdade de Engenharia, Universidade do Porto, Portugal [FEUP] and CENTRA), R. Garcia Lopez (School of Physics, University College Dublin, Ireland), F. Gao (MPIfR), E. Gendron (LESIA), R. Genzel (MPE and Departments of Physics and Astronomy, University of California, USA), J.P. Gil (ESO Chile), S. Gillessen (MPE), T. Gomes (CENTRA and FEUP), F. Gonté (ESO), C. Gouvret (Lagrange), P. Guajardo (ESO Chile), S. Guieu (IPAG), W. Hackenberg (ESO), N. Haddad (ESO Chile), M. Hartl (MPE), X. Haubois (ESO Chile), F. Haußmann (MPE), G. Heißel (LESIA and Advanced Concepts Team, European Space Agency, TEC-SF, ESTEC, The Netherlands), T. Henning (MPIA), S. Hippler (MPIA), S.F. Hönig (School of Physics & Astronomy, University of Southampton, UK [Southampton]), M. Horrobin (Cologne), N. Hubin (ESO), E. Jacqmart (Lagrange), L. Jocou (IPAG), A. Kaufer (ESO Chile), P. Kervella (LESIA), J. Kolb (ESO), H. Korhonen (ESO Chile), S. Lacour (ESO and LESIA), S. Lagarde (Lagrange), O. Lai (Lagrange), V. Lapeyrère (LESIA), R. Laugier (KU Leuven), J.-B. Le Bouquin (IPAG), J. Leftley (Lagrange), P. Léna (LESIA), S. Lewis (ESO), D. Liu (MPE), B. Lopez (Lagrange), D. Lutz (MPE), Y. Magnard (IPAG), F. Mang (MPE and TUM), A. Marcotto (Lagrange), D. Maurel (IPAG), A. Mérand (ESO), F. Millour (Lagrange), N. More (MPE), H. Netzer (School of Physics and Astronomy, Tel Aviv University, Israel [TAU]), H. Nowacki (IPAG), M. Nowak (Institute of Astronomy, University of Cambridge, UK), S. Oberti (ESO), T. Ott (MPE), L. Pallanca (ESO Chile), T. Paumard (LESIA), K. Perraut (IPAG), G. Perrin (LESIA), R. Petrov (Lagrange), O. Pfuhl (ESO), N. Pourré (IPAG), S. Rabien (MPE), C. Rau (MPE), M. Riquelme (ESO), S. Robbe-Dubois (Lagrange), S. Rochat (IPAG), M. Salman (KU Leuven), J. Sanchez-Bermudez (Instituto de Astronomía, Universidad Nacional Autónoma de México, Mexico and MPIA), D.J.D. Santos (MPE), S. Scheithauer (MPIA), M. Schöller (ESO), J. Schubert (MPE), N. Schuhler (ESO Chile), J. Shangguan (MPE), P. Shchekaturov (ESO), T.T. Shimizu (MPE), A. Sevin (LESIA), F. Soulez (CRAL), A. Spang (Lagrange), E. Stadler (IPAG), A. Sternberg (TAU and Center for Computational Astrophysics, Flatiron Institute, USA), C. Straubmeier (Cologne), E. Sturm (MPE), C. Sykes (Southampton), L.J. Tacconi (MPE), K.R.W. Tristram (ESO Chile), F. Vincent (LESIA), S. von Fellenberg (MPIfR), S. Uysal (MPE), F. Widmann (MPE), E. Wieprecht (MPE), E. Wiezorrek (MPE), J. Woillez (ESO), and G. Zins (ESO).

The GRAVITY+ upgrades are designed and built by the following institutes together with ESO:

• Max Planck Institute for Extraterrestrial Physics; Max Planck Institute for Astronomy; the University of Cologne (Germany)
• Institut National des Sciences de l'Univers, French National Center for Scientific Research; Institut de Planétologie et d'Astrophysique de Grenoble; Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique; the Lagrange Laboratory; the Centre de Recherche Astrophysique de Lyon (France)
• Instituto Superior Técnico’s Centre for Astrophysics and Gravitation; University of Lisbon; University of Porto (Portugal)
• University of Southampton (UK)
• Katholieke Universiteit Leuven (Belgium)

Nature, Published online: 29 January 2024; doi:10.1038/s41586-024-07053-4

A dynamical measure of the black hole mass in a quasar 11 billion years ago

SLIM was put into hibernation after landing on the moon upside down, but it woke up when sunlight hit its solar panels

Astronomers have used the James Webb Space Telescope to take astonishingly detailed images of spiral galaxies, revealing how and where they spark star formation

After nearly three years of exploring Mars, NASA’s Ingenuity helicopter has taken its final flight – but its astounding performance is a good sign for future drones on other worlds

Light from hydrogen in the early universe has baffled astronomers, but researchers have spotted interacting galaxies that could explain how it makes its way to us

Tight relationships exist in the local universe between the central stellar properties of galaxies and the mass of their supermassive black hole. These suggest galaxies and black holes co-evolve, with the main regulation mechanism being energetic feedback from accretion onto the black hole during its quasar phase. A crucial question is how the relationship between black holes and galaxies evolves with time; a key epoch to probe this relationship is at the peaks of star formation and black hole growth 8-12 billion years ago (redshifts 1-3). Here we report a dynamical measurement of the mass of the black hole in a luminous quasar at a redshift of 2, with a look back time of 11 billion years, by spatially resolving the broad line region. We detect a 40 micro-arcsecond (0.31 pc) spatial offset between the red and blue photocenters of the H$\alpha$ line that traces the velocity gradient of a rotating broad line region. The flux and differential phase spectra are well reproduced by a thick, moderately inclined disk of gas clouds within the sphere of influence of a central black hole with a mass of 3.2x10$^{8}$ solar masses. Molecular gas data reveal a dynamical mass for the host galaxy of 6x10$^{11}$ solar masses, which indicates an under-massive black hole accreting at a super-Eddington rate. This suggests a host galaxy that grew faster than the supermassive black hole, indicating a delay between galaxy and black hole formation for some systems.

Episodic accretion is one of the competing models to explain the observed luminosity spread in young stellar clusters. These short-lived high accretion events could also have a strong impact on planet formation. Observations of high-amplitude variability in young stellar objects (YSOs) due to large changes in the accretion rate provide direct observational evidence for episodic accretion. However, there are still uncertainties in the frequency of these events and if episodic accretion is universal among YSOs. To determine the frequency of outbursts in Class I YSOs, we built a large and robust sample of objects at this evolutionary stage, and searched for high-amplitude near-infrared ($\Delta K_{\rm S}>2$~mag) variability in the VIRAC2 database of the Vista Variables in the Via Lactea (VVV) survey. By complementing with near-IR (2MASS and DENIS) and mid-IR (WISE/Neo-WISE) data, we find that from $\sim$ 7000 Class I YSOs, 97 objects can be classified as eruptive variable YSOs. The duration of the outbursts vary from a few months to longer than 9 years, and cover a similar range of amplitudes. Values of $\Delta K_{\rm S}>5$~mag, however, are only observed in outbursts with duration longer than 9 years. When considering different effects of completeness and contamination we estimate that the incidence of episodic accretion in Class I YSOs is between 2\% and 3\%. Finally, we determine a recurrence timescale of long-term outbursts (a.k.a FUors) of $\tau=1.75^{+1.12}_{-0.87}$~kyr. The latter value agrees with previous estimates and is in line with the expectations of higher frequency of FUor outbursts during younger stages of evolution.

We have performed a comprehensive search of a VISTA Variables in the Via Lactea (VVV) database of 9.5 yr light curves for variable sources with $\Delta K_s \ge 4$ mag, aiming to provide a large sample of high amplitude eruptive young stellar objects (YSOs) and detect unusual or new types of infrared variable source. We find 222 variable or transient sources in the Galactic bulge and disc, most of which are new discoveries. The sample mainly comprises novae, YSOs, microlensing events, Long Period Variable stars (LPVs) and a few rare or unclassified sources. Additionally, we report the discovery of a significant population of aperiodic late-type giant stars suffering deep extinction events, strongly clustered in the Nuclear Disc of the Milky Way. We suggest that these are metal-rich stars in which radiatively driven mass loss has been enhanced by super-solar metallicity. Among the YSOs, 32/40 appear to be undergoing episodic accretion. Long-lasting YSO eruptions have a typical rise time of $\sim$2 yr, somewhat slower than the 6-12 month timescale seen in the few historical events observed on the rise. The outburst durations are usually at least 5 yr, somewhat longer than many lower amplitude VVV events detected previously. The light curves are diverse in nature, suggesting that multiple types of disc instability may occur. Eight long-duration extinction events are seen wherein the YSO dims for a year or more, attributable to inner disc structure. One binary YSO in NGC 6530 displays periodic extinction events (P=59 days) similar to KH 15D.

During the pre-main-sequence evolution, Young Stellar Objects (YSOs) assemble most of their mass during the episodic accretion process. The rarely seen FUOr-type events (FUOrs) are valuable laboratories to investigate the outbursting nature of YSOs. Here, we present multi-wavelength detection of a high-amplitude eruptive source in the young open cluster VdBH 221 with an ongoing outburst, including optical to mid-infrared time series and near-infrared spectra. The initial outburst has an exceptional amplitude of $>$6.3 mag in Gaia and 4.6 mag in $K_s$, with a peak luminosity up to 16 $L_{\odot}$ and a peak mass accretion rate of 1.4 $\times$ 10$^{-5}$ $M_\odot$ yr$^{-1}$. The optical to infrared spectral energy distribution (SED) of this object is consistent with a low-mass star (0.2$M_\odot$) with a modest extinction ($A_V < 2$ mag). A 100-d delay between optical and infrared rising stages is detected, suggesting an outside-in origin of the instability. The spectroscopic features of this object reveal a self-luminous accretion disc, very similar to FU Orionis, with a low line-of-sight extinction. Most recently, there has been a gradual increase in brightness throughout the wavelength range, possibly suggesting an enhancement of the mass accretion rate.

During the pre-main-sequence (pre-MS) evolution stage of a star, significant amounts of stellar mass are accreted during episodic accretion events, such as multi-decade FUor-type outbursts. Here, we present a near-infrared spectroscopic follow-up study of 33 high-amplitude (most with $\Delta K_s$ > 4 mag) variable sources discovered by the Vista Variables in the Via Lactea (VVV) survey. Based on the spectral features, 25 sources are classified as eruptive young stellar objects (YSOs), including 15 newly identified FUors, six with long-lasting but EXor-like bursts of magnetospheric accretion and four displaying outflow-dominated spectra. By examining the photometric behaviours of eruptive YSOs, we found most FUor-type outbursts have higher amplitudes ($\Delta K_s$ and $\Delta W2$), faster eruptive timescales and bluer infrared colours than the other outburst types. In addition, we identified seven post-main sequence variables apparently associated with deep dipping events and an eruptive star with deep AlO absorption bands resembling those seen in the V838 Mon stellar merger.