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Institute of Astronomy

 

SIDE-real: Truncated marginal neural ratio estimation for Supernova Ia Dust Extinction with real data

Recent IoA Publications - Wed, 13/03/2024 - 14:00
arXiv:2403.07871v1 Announce Type: new Abstract: We present the first fully simulation-based hierarchical analysis of the light curves of a population of low-redshift type Ia supernovae (SNae Ia). Our hardware-accelerated forward model, released in the Python package slicsim, includes stochastic variations of each SN's spectral flux distribution (based on the pre-trained BayeSN model), extinction from dust in the host and in the Milky Way, redshift, and realistic instrumental noise. By utilising truncated marginal neural ratio estimation (TMNRE), a neural network-enabled simulation-based inference technique, we implicitly marginalise over 4000 latent variables (for a set of $\approx 100$ SNae Ia) to efficiently infer SN Ia absolute magnitudes and host-galaxy dust properties at the population level while also constraining the parameters of individual objects. Amortisation of the inference procedure allows us to obtain coverage guarantees for our results through Bayesian validation and frequentist calibration. Furthermore, we show a detailed comparison to full likelihood-based inference, implemented through Hamiltonian Monte Carlo, on simulated data and then apply TMNRE to the light curves of 86 SNae Ia from the Carnegie Supernova Project, deriving marginal posteriors in excellent agreement with previous work. Given its ability to accommodate arbitrarily complex extensions to the forward model -- e.g. different populations based on host properties, redshift evolution, complicated photometric redshift estimates, selection effects, and non-Ia contamination -- without significant modifications to the inference procedure, TMNRE has the potential to become the tool of choice for cosmological parameter inference from future, large SN Ia samples.

Hawai`i Supernova Flows: A Peculiar Velocity Survey Using Over a Thousand Supernovae in the Near-Infrared

Recent IoA Publications - Tue, 12/03/2024 - 14:06
arXiv:2403.05620v1 Announce Type: new Abstract: We introduce the Hawai`i Supernova Flows project and present summary statistics of the first 1218 astronomical transients observed, 669 of which are spectroscopically classified Type Ia Supernovae (SNe Ia). Our project is designed to obtain systematics-limited distances to SNe Ia while consuming minimal dedicated observational resources. This growing sample will provide increasing resolution into peculiar velocities as a function of position on the sky and redshift, allowing us to more accurately map the structure of dark matter. This can be used to derive cosmological parameters such as $\sigma_8$ and can be compared with large scale flow maps from other methods such as luminosity-line width or luminosity-velocity dispersion correlations in galaxies. Additionally, our photometry will provide a valuable test bed for analyses of SNe Ia incorporating near-infrared data. In this survey paper, we describe the methodology used to select targets, collect and reduce data, and calculate distances.

Fri 15 Mar 13:00: Fully general Cauchy evolution of asymptotically AdS spacetimes: the non-linear instability of Kerr-AdS

Next External Talks - Tue, 12/03/2024 - 10:56
Fully general Cauchy evolution of asymptotically AdS spacetimes: the non-linear instability of Kerr-AdS

In addition to being at the core of the widely employed AdS/CFT correspondence, asymptotically anti-de Sitter (AdS) spacetimes with reflective boundary conditions can serve as the arena for a range of strong gravity effects: arbitrarily small perturbations are bound to remain in the bulk, where they continue to interact and typically become sizeable. Initially, I will review a numerical scheme that enables the Cauchy evolution of these spacetimes to be performed in full generality. Then, I will present the first simulations of the trapping mechanism occurring in the exterior of a Kerr-AdS black hole. This mechanism has been conjectured to cause a non-linear instability, the existence of which remains a topic of debate. The simulations offer insights into this debate, providing new perspectives on the non-linear instability of Kerr-AdS.

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Categories: Talks

PHANGS-HST catalogs for $\sim$100,000 star clusters and compact associations in 38 galaxies: I. Observed properties

Recent IoA Publications - Mon, 11/03/2024 - 11:17
arXiv:2403.04901v1 Announce Type: new Abstract: We present the largest catalog to-date of star clusters and compact associations in nearby galaxies. We have performed a V-band-selected census of clusters across the 38 spiral galaxies of the PHANGS-HST Treasury Survey, and measured integrated, aperture-corrected NUV-U-B-V-I photometry. This work has resulted in uniform catalogs that contain $\sim$20,000 clusters and compact associations which have passed human inspection and morphological classification, and a larger sample of $\sim$100,000 classified by neural network models. Here, we report on the observed properties of these samples, and demonstrate that tremendous insight can be gained from just the observed properties of clusters, even in the absence of their transformation into physical quantities. In particular, we show the utility of the UBVI color-color diagram, and the three principal features revealed by the PHANGS-HST cluster sample: the young cluster locus, the middle-age plume, and the old globular cluster clump. We present an atlas of maps of the 2D spatial distribution of clusters and compact associations in the context of the molecular clouds from PHANGS-ALMA. We explore new ways of understanding this large dataset in a multi-scale context by bringing together once-separate techniques for the characterization of clusters (color-color diagrams and spatial distributions) and their parent galaxies (galaxy morphology and location relative to the galaxy main sequence). A companion paper presents the physical properties: ages, masses, and dust reddenings derived using improved spectral energy distribution (SED) fitting techniques.

VIRA: An Exoplanet Atmospheric Retrieval Framework for JWST Transmission Spectroscopy

Recent IoA Publications - Mon, 11/03/2024 - 10:57
arXiv:2403.04825v1 Announce Type: new Abstract: JWST observations are leading to important new insights into exoplanetary atmospheres through transmission spectroscopy. In order to harness the full potential of the broad spectral range and high sensitivity of JWST, atmospheric retrievals of exoplanets require a high level of robustness and accuracy in the underlying models. We present the VIRA retrieval framework which implements a range of modelling and inference capabilities motivated by early JWST observations of exoplanet transmission spectra. This includes three complementary approaches to modelling atmospheric composition, three atmospheric aerosol models, including a physically-motivated Mie scattering approach, and consideration of correlated noise. VIRA enables a cascading retrieval architecture involving a sequence of retrievals with increasing sophistication. We demonstrate VIRA using a JWST transmission spectrum of the hot Saturn WASP-39 b in the $\sim$1-5 $\mu$m range. In addition to confirming prior chemical inferences, we retrieve molecular abundances for H$_2$O, CO, CO$_2$, SO$_2$ and H$_2$S, resulting in super-solar elemental abundances of log(O/H)=$-2.0\pm0.2$, log(C/H)=$-2.1\pm0.2$ and log(S/H)=$-3.6\pm0.2$, along with C/O and S/O ratios of $0.83^{+0.05}_{-0.07}$ and $0.029^{+0.012}_{-0.009}$, respectively, in the free chemistry case. The abundances correspond to $20.1^{+10.5}_{-8.1}\times$, $28.2^{+16.3}_{-12.1}\times$ and $20.8^{+10.3}_{-7.5}\times$ solar values for O/H, C/H and S/H, respectively, compared to C/H $= 8.67\pm0.35 \times$ solar for Saturn. Our results demonstrate how JWST transmission spectroscopy combined with retrieval frameworks like VIRA can measure multi-elemental abundances for giant exoplanets and enable comparative characterisation with solar system planets.

Wed 13 Mar 13:15: A new convection scheme for exoplanet atmospheres

IoA Institute of Astronomy Talk Lists - Mon, 11/03/2024 - 09:43
A new convection scheme for exoplanet atmospheres

Convection is an essential process for transporting heat and moisture in planetary atmospheres. The standard Earth picture of moist convection rising from the surface is only one of a number of modes of convection. Notably, convection in atmospheres with a high condensible mass fraction (non-dilute atmospheres), or with a lighter background gas than the condensible species (e.g. water convection in a hydrogen dominated atmosphere) – acts very differently and can be much weaker or even shut down entirely in the latter case. Here I present a new mass-flux scheme which can capture these variations and simulate convection in a wide range of parameter space for use in 3D climate models. A validation using the case of Trappist-1 e is presented.

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Wed 13 Mar 13:15: A new convection scheme for exoplanet atmospheres

Next Wednesday Seminars - Mon, 11/03/2024 - 09:43
A new convection scheme for exoplanet atmospheres

Convection is an essential process for transporting heat and moisture in planetary atmospheres. The standard Earth picture of moist convection rising from the surface is only one of a number of modes of convection. Notably, convection in atmospheres with a high condensible mass fraction (non-dilute atmospheres), or with a lighter background gas than the condensible species (e.g. water convection in a hydrogen dominated atmosphere) – acts very differently and can be much weaker or even shut down entirely in the latter case. Here I present a new mass-flux scheme which can capture these variations and simulate convection in a wide range of parameter space for use in 3D climate models. A validation using the case of Trappist-1 e is presented.

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Categories: Talks

Fri 15 Mar 11:30: Effects of primordial black holes on early star formation

IoA Institute of Astronomy Talk Lists - Mon, 11/03/2024 - 09:04
Effects of primordial black holes on early star formation

Primordial black holes (PBHs) have long been considered a promising candidate or an important component of dark matter (DM). Recent gravitational wave (GW) observations of binary black hole (BH) mergers have triggered renewed interest in PBHs in the stellar-mass (∼ 10 − 100 Msun) and supermassive regimes (∼ 107 − 1011 Msun). Although only a small fraction (≲ 1%) of dark matter in the form of PBHs is required to explain observations, these PBHs may play important roles in early structure/star formation. We use cosmological zoom-in simulations and semi-analytical models to explore the possible impact of stellar-mass PBHs on first star formation, taking into account two effects of PBHs: acceleration of structure formation and gas heating by BH accretion feedback. We find that the standard picture of first star formation is not changed by stellar-mass PBHs (allowed by existing observational constraints), and their global impact on the cosmic star formation history is likely minor. However, PBHs do alter the properties of the first star-forming halos and can potentially trigger the formation of direct-collapse BHs in atomic cooling halos. On the other hand, supermassive PBHs may play more important roles as seeds of massive structures that can explain the apparent overabundance of massive galaxies in recent JWST observations. Our tentative models and results call for future studies with improved modelling of the interactions between PBHs, particle DM, and baryons to better understand the effects of PBHs on early structure/star formation and their imprints in high-redshift observations.

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Wed 13 Mar 13:40: Constraining physics and astrophysics with multifrequency CMB data

IoA Institute of Astronomy Talk Lists - Sun, 10/03/2024 - 21:00
Constraining physics and astrophysics with multifrequency CMB data

The CMB anisotropies are measured in several microwave frequency bands. Having this frequency information allows us to separate signals that are due to different sources. We can easily make maps that are sensitive to specific frequency combinations, and in this way isolate the contribution from the primary CMB (early-Universe) and various other CMB interactions such as the Sunyaev—Zel’dovich (SZ) effect (the scattering of the CMB from electrons in the late Universe). I will talk about constraints on the SZ effect from Planck data using a new frequency-separation code, pyilc, which we use to isolate the signal while removing other late-Universe biases, in particular the infrared emission from star-forming galaxies. I will also show an application to beyond standard model interactions between the CMB and a non-trivial dark sector, and how we can use the CMB to constrain beyond-standard-model particle physics.

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Wed 13 Mar 13:40: Constraining physics and astrophysics with multifrequency CMB data

Next Wednesday Seminars - Sun, 10/03/2024 - 21:00
Constraining physics and astrophysics with multifrequency CMB data

The CMB anisotropies are measured in several microwave frequency bands. Having this frequency information allows us to separate signals that are due to different sources. We can easily make maps that are sensitive to specific frequency combinations, and in this way isolate the contribution from the primary CMB (early-Universe) and various other CMB interactions such as the Sunyaev—Zel’dovich (SZ) effect (the scattering of the CMB from electrons in the late Universe). I will talk about constraints on the SZ effect from Planck data using a new frequency-separation code, pyilc, which we use to isolate the signal while removing other late-Universe biases, in particular the infrared emission from star-forming galaxies. I will also show an application to beyond standard model interactions between the CMB and a non-trivial dark sector, and how we can use the CMB to constrain beyond-standard-model particle physics.

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Categories: Talks

Peering Into the Tendrils of NGC 604 with NASA’s Webb

Astronomy News - Sun, 10/03/2024 - 17:13
4 Min Read Peering Into the Tendrils of NGC 604 with NASA’s Webb Star-forming region NGC 604. Credits:
NASA, ESA, CSA, STScI

The formation of stars and the chaotic environments they inhabit is one of the most well-studied, but also mystery-shrouded, areas of cosmic investigation. The intricacies of these processes are now being unveiled like never before by NASA’s James Webb Space Telescope.

Two new images from Webb’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) showcase star-forming region NGC 604, located in the Triangulum galaxy (M33), 2.73 million light-years away from Earth. In these images, cavernous bubbles and stretched-out filaments of gas etch a more detailed and complete tapestry of star birth than seen in the past.

Sheltered among NGC 604’s dusty envelopes of gas are more than 200 of the hottest, most massive kinds of stars, all in the early stages of their lives. These types of stars are B-types and O-types, the latter of which can be more than 100 times the mass of our own Sun. It’s quite rare to find this concentration of them in the nearby universe. In fact, there’s no similar region within our own Milky Way galaxy.

This concentration of massive stars, combined with its relatively close distance, means NGC 604 gives astronomers an opportunity to study these objects at a fascinating time early in their life.

Image: NIRCam View NGC 604 This image from NASA’s James Webb Space Telescope’s NIRCam (Near-Infrared Camera) of star-forming region NGC 604 shows how stellar winds from bright, hot, young stars carve out cavities in surrounding gas and dust. NASA, ESA, CSA, STScI

In Webb’s near-infrared NIRCam image, the most noticeable features are tendrils and clumps of emission that appear bright red, extending out from areas that look like clearings, or large bubbles in the nebula. Stellar winds from the brightest and hottest young stars have carved out these cavities, while ultraviolet radiation ionizes the surrounding gas. This ionized hydrogen appears as a white and blue ghostly glow.

The bright orange-colored streaks in the Webb near-infrared image signify the presence of carbon-based molecules known as polycyclic aromatic hydrocarbons, or PAHs. This material plays an important role in the interstellar medium and the formation of stars and planets, but its origin is a mystery. As you travel farther from the immediate clearings of dust, the deeper red signifies molecular hydrogen. This cooler gas is a prime environment for star formation.

Webb’s exquisite resolution also provides insights into features that previously appeared unrelated to the main cloud. For example, in Webb’s image, there are two bright, young stars carving out holes in dust above the central nebula, connected through diffuse red gas. In visible-light imaging from NASA’s Hubble Space Telescope, these appeared as separate splotches.

Image: MIRI View NGC 604 This image from NASA’s James Webb Space Telescope’s MIRI (Mid-Infrared Instrument) of star-forming region NGC 604 shows how large clouds of cooler gas and dust glow in mid-infrared wavelengths. This region is home to more than 200 of the hottest, most massive kinds of stars, all in the early stages of their lives. NASA, ESA, CSA, STScI

Webb’s view in mid-infrared wavelengths also illustrates a new perspective into the diverse and dynamic activity of this region. In the MIRI view of NGC 604, there are noticeably fewer stars. This is because hot stars emit much less light at these wavelengths, while the larger clouds of cooler gas and dust glow. Some of the stars seen in this image, belonging to the surrounding galaxy, are red supergiants – stars that are cool but very large, hundreds of times the diameter of our Sun. Additionally, some of the background galaxies that appeared in the NIRCam image also fade. In the MIRI image, the blue tendrils of material signify the presence of PAHs.

NGC 604 is estimated to be around 3.5 million years old. The cloud of glowing gases extends to some 1,300 light-years across.

Video: Explore the Images Explore Webb’s images of NGC 604 with Dr Jane Rigby (Webb Senior Project Scientist). Credit: NASA

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

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Media Contacts

Laura Betzlaura.e.betz@nasa.gov, Rob Gutrorob.gutro@nasa.gov
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Christine Pulliamcpulliam@stsci.edu
Space Telescope Science Institute, Baltimore, Md.

Related Information

Hubble’s view of NGC 604

Hubble’s view of NGC 604 host galaxy Triangulum (M33)

Star Lifecycle

More Webb News – https://science.nasa.gov/mission/webb/latestnews/

More Webb Images – https://science.nasa.gov/mission/webb/multimedia/images/

Webb Mission Page – https://science.nasa.gov/mission/webb/

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Hubble Sees a Spiral Galaxy Edge-On

Astronomy News - Sat, 09/03/2024 - 16:56

1 min read

Hubble Sees a Spiral Galaxy Edge-On This NASA/ESA Hubble Space Telescope image shows NGC 4423. ESA/Hubble & NASA, M. Sun

This NASA/ESA Hubble Space Telescope image shows NGC 4423, a galaxy that lies about 55 million light-years away in the constellation Virgo. In this image, NGC 4423 appears to have quite an irregular, tubular form, so it might be surprising to find out that it is in fact a spiral galaxy. Knowing this, we can make out the denser central bulge of the galaxy, and the less crowded surrounding disk (the part that comprises the spiral arms). 

If NGC 4423 were viewed face-on it would resemble the shape that we most associate with spiral galaxies: the spectacular curving arms sweeping out from a bright center, interspersed with dimmer, darker, less populated regions. But when observing the skies, we are constrained by the relative alignments between Earth and the objects that we are observing.

Text credit: European Space Agency (ESA)


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Media Contact:

Claire Andreoli
NASA’s Goddard Space Flight CenterGreenbelt, MD
claire.andreoli@nasa.gov

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200,000 Candidate Very Metal-poor Stars in Gaia DR3 XP Spectra

Recent IoA Publications - Fri, 08/03/2024 - 16:22
arXiv:2303.17676v2 Announce Type: replace Abstract: Very metal-poor stars ($\rm[Fe/H] $ 16) and obtain 38,000/41,000 additional metal-poor candidates with purity 29\%/52\%, respectively. We make our metal-poor star catalogs publicly available, for further exploration of the metal-poor Milky Way.

Two distinct molecular cloud populations detected in massive galaxies

Recent IoA Publications - Fri, 08/03/2024 - 15:55
arXiv:2403.03974v1 Announce Type: new Abstract: We present new ALMA observations of CO, CN, CS, HCN and HCO$^{+}$ absorption seen against the bright and compact radio continuum sources of eight massive galaxies. Combined with archival observations, they reveal two distinct populations of molecular clouds, which we identify by combining CO emission and absorption profiles to unambiguously reveal each cloud's direction of motion and likely location. In galaxy disks, we see clouds with low velocity dispersions, low line of sight velocities and a lack of any systemic inflow or outflow. In galactic cores, we find high velocity dispersion clouds inflowing at up to 550 km/s. This provides observational evidence in favour of cold accretion onto galactic centres, which likely contributes to the fuelling of active galactic nuclei. We also see a wide range in the CO(2-1)/CO(1-0) ratios of the absorption lines. This is likely the combined effect of hierarchical substructure within the molecular clouds and continuum sources which vary in size with frequency.

Jupiter’s stormy surface replicated in lab

Astronomy News - Fri, 08/03/2024 - 15:53

By rotating a tank of water at 75 revolutions per minute, it’s possible to replicate some of the stunning, swirling patterns on Jupiter’s surface

How one theory ties together everything we know about the universe

Astronomy News - Fri, 08/03/2024 - 15:52

All known natural phenomena fit into just a few categories and unifying them all is quantum field theory, says physicist Matt Strassler

U.S. giant telescopes imperiled by funding limit

Astronomy News - Fri, 08/03/2024 - 15:51
Science, Volume 383, Issue 6687, Page 1038-1039, March 2024.

Astronomers detect ‘waterworld with a boiling ocean’ in deep space

Astronomy News - Fri, 08/03/2024 - 15:47

Exclusive: Significant discovery, made by James Webb telescope, provokes disagreement over conditions on planet’s surface

Astronomers have observed a distant planet that could be entirely covered in a deep water ocean, in findings that advance the search for habitable conditions beyond Earth.

The observations, by Nasa’s James Webb space telescope (JWST), revealed water vapour and chemical signatures of methane and carbon dioxide in the atmosphere of the exoplanet, which is twice Earth’s radius and about 70 light years away. This chemical mix is consistent with a water world where the ocean would span the entire surface, and a hydrogen-rich atmosphere, according to researchers from the University of Cambridge, although they do not envisage a balmy, inviting seascape.

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Fri 08 Mar 13:00: International Women's Day at the IoA

IoA Institute of Astronomy Talk Lists - Thu, 07/03/2024 - 14:50
International Women's Day at the IoA

• 13.00 pm-14.00:Keynote Speaker: Ghina Halabi

• 14.00 pm-14.45:Flash Talks: Sandro Tacchella & Alejandra Castro

• 14.45 pm-15.15:Tea, Coffee and Cake

• 15.15 pm-16.30:An Interactive Session on Recognising Accomplishments

• 16.30 pm-16.50: Flash Talk: Greg Cooke

• 16.50 pm-17.00: Closing Remarks

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Thu 07 Mar 16:00: Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy

IoA Institute of Astronomy Talk Lists - Thu, 07/03/2024 - 14:36
Eddington lecture 2024: The Dawn of Galaxy-scale Gravitational Wave Astronomy

For more than 15 years, NANO Grav and other pulsar-timing array collaborations have been carefully monitoring networks of pulsars across the Milky Way. The goal was to find a tell-tale correlation signature amid the data from all those pulsars that would signal the presence of an all-sky background of nanohertz-frequency gravitational waves, washing through the Galaxy. At the end of June 2023, the global pulsar-timing array community finally announced its evidence for this gravitational-wave background, along with a series of studies that interpreted this signal as either originating from a population of supermassive black-hole binary systems, or as relics from cosmological processes in the very early Universe. I will describe the journey up to this point (including the integral role that the IoA played), what led to the ultimate breakthrough, how this affects our knowledge of supermassive black holes and the early Universe, and what lies next for gravitational-wave astronomy at light-year wavelengths.

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