Archive for weak gravitational lensing

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, The Universe and Stuff with tags , , , , , on May 26, 2023 by telescoper

It’s time to announce yet another new paper at the Open Journal of Astrophysics. This one was published yesterday (25th May).

The latest paper is the 18th paper so far in Volume 6 (2023) and the 83rd in all. With this one we have now published more papers in 2023 than we did in all of last year. With significantly less than half the year gone, and a large number of papers in the pipeline, I think it’s quite likely we will exceed a total of 100 papers by the end of 2023.

The primary classification for this paper is Cosmology and Nongalactic Astrophysics and its title is “The Effect of Splashback on Weak Lensing Mass Estimates of Galaxy Clusters and Groups”. For the uninitiated  “Splashback” of infalling material produces features in the radial density profile of galaxy clusters. This paper discusses the effect of this on cluster masses derived from weak lensing measurements.

The authors, most of whom have multiple affiliations, are: Yuanyuan Zhang (NOIRLab, Tucson, AZ, USA), Susmita Adhikari (IISER, Pune, India), Matteo Costanzi (Univ. Trieste, Italy) and Josh Frieman, Jim Annis & Chihway Chang (Univ. Chicago, IL, USA).

Here is a screen grab of the overlay which includes the  abstract:

 

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper, along with all other astrophysics and cosmology research papers worth reading, on the arXiv here.

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , on May 18, 2023 by telescoper

It’s time to announce yet another new paper at the Open Journal of Astrophysics. This one was published yesterday (17th May).

The latest paper is the 17th paper so far in Volume 6 (2023) and the 82nd in all. With this one we have now published as many papers so far in 2023 as we did in all of last year. With significantly less than half the year gone, and a large number of papers in the pipeline, I think it’s quite likely we will exceed a total of 100 papers by the end of 2023. How’s that for cosmic acceleration?

The primary classification for this paper is Instrumentation and Methods for Astrophysics and its title is “Deep-field Metacalibration”. This article describes a technique that reduces the pixel noise in estimators of weak gravitational lensing shear signals by using a deeper imaging survey for calibration.

The authors are Zhuoqi (“Jackie”) Zhang (University of Chicago, IL, USA), Erin Sheldon (Brookhaven National Laboratory, NY, USA), and Matthew Becker (Argonne National Laborary, IL, USA).

Here is a screen grab of the overlay which includes the  abstract:

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper, along with all other astrophysics and cosmology research papers worth reading, on the arXiv here.

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The Euclid Launch Kit!

Posted in The Universe and Stuff with tags , , , , , on May 17, 2023 by telescoper

As the launch of the European Space Agency’s Euclid mission approaches, though we don’t know official launch date yet, the associated publicity machines are ramping up for the big occasion. The latest bit of merch is the Euclid Launch Kit.

Sadly, this does not allow you to build your own Falcon 9 launcher which is what I inferred from the name. What it is is an interactive PDF file that allows you to navigate around and learn things about the satellite, its orbit, its instruments and the science case. I think it’s pretty good. You can download it here. It’s over 100 MB though, so beware if you have a very slow connection.

To whet your appetite, here some graphics extracted from the launch kit. You can click on the tiles to make them bigger.

The two science images relate to weak gravitational lensing and baryon acoustic oscillations; for more details you can click on the relevant links.

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, The Universe and Stuff with tags , , , , on May 16, 2023 by telescoper

It’s time to announce yet another new paper at the Open Journal of Astrophysics. In fact it’s a little overdue, because we published this one on Friday 12th May, but I just got round to posting it on here.

The latest paper is the 16th paper so far in Volume 6 (2023) and the 81st in all. The primary classification for this paper is Instrumentation and Methods for Astrophysics and its title is “Metadetection Weak Lensing for the Vera C. Rubin Observatory“. I added the link to Wikipedia myself for those who might be unfamiliar with the Rubin Observatory.

The authors are Erin Sheldon (Brookhaven National Laboratory, NY, USA), Matthew Becker (Argonne National Laborary, IL, USA), Michael Jarvis (University of Pennsylvania, PA) and Robert Armstrong (Lawrence Livermore National Laboratory, CA) – all in the USA – and the LSST Dark Energy Science Collaboration, who have published a significant number of publications with OJAp. In fact, we’ll have another one in a day or two.

Here is a screen grab of the overlay which includes the  abstract:

 

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper, along with all other astrophysics and cosmology research papers worth reading, on the arXiv here

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New Publication at the Open Journal of Astrophysics

Posted in OJAp Papers, Open Access, The Universe and Stuff with tags , , , , , on February 8, 2023 by telescoper

We’re on a bit of a roll at the Open Journal of Astrophysics and it’s time to announce yet another paper. We actually published this one yesterday (7th February 2023), which makes it two in two days. I don’t think we’ll keep up that rate but we have seen a big increase in submissions recently and these are working their way through the system very nicely. We aim to publish accepted papers within a day of the revised version appearing on arXiv.

The latest paper is the 6th paper in Volume 6 (2023) as well as the 71st in all. This one is another one for the folder marked Cosmology and Nongalactic Astrophysics. The title is “Almanac: Weak Lensing power spectra and map inference on the masked sphere”. The nub of the problem addressed by this paper is that the usual statistical analysis of data presented in projection on the sky involves spherical harmonics, which are orthogonal functions on the celestial sphere, but when the sky is not completely covered (i.e. part of it is masked), these functions are not orthogonal on what remains.

The authors of this paper are Arthur Loureiro (University of Edinburgh, UK), Lorne Whiteway (University College London, UK), Elena Selentin (Leiden University, NL), Javier Silva Lafaurie (Leiden University, NL), Andrew Jaffe (Imperial College London, UK) and Alan Heavens (Imperial College London, UK)

Here is a screen grab of the overlay which includes the  abstract:

 

You can click on the image of the overlay to make it larger should you wish to do so. You can find the officially accepted version of the paper on the arXiv here.

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More from the Dark Energy Survey

Posted in Astrohype, The Universe and Stuff with tags , , , , , , on May 28, 2021 by telescoper

To much media interest the Dark Energy Survey team yesterday released 11 new papers based on the analysis of their 3-year data. You can find the papers together with short descriptions here. There’s even a little video about the Dark Energy Survey here:

The official press release summarizes the results as follows:

Scientists measured that the way matter is distributed throughout the universe is consistent with predictions in the standard cosmological model, the best current model of the universe.

This contrasts a bit with the BBC’s version:

The results are a surprise because they show that it is slightly smoother and more spread out than the current best theories predict.

The observation appears to stray from Einstein’s theory of general relativity – posing a conundrum for researchers.

The reason for this appears to be that the BBC story focusses on the weak lensing paper (found here; I’ll add a link to the arXiv version if and when it appears there). The abstract is here:

The parameter S8 is a (slightly) rescaled version of the more familiar parameter σ8  – which quantifies the matter-density fluctuations on a scale of 8 h-1 Mpc – as defined in the abstract; cosmic shear is particularly sensitive to this parameter.

The key figure showing the alleged “tension” with Planck is here:

The companion paper referred to in the above abstract (found here has an abstract that concludes with the words (my emphasis).

We find a 2.3σ difference between our S8 result and that of Planck (2018), indicating no statistically significant tension, and additionally find our results to be in qualitative agreement with current weak lensing surveys (KiDS-1000 and HSC).

So, although certain people have decided to hype up a statistically insignificant l discrepancy, everything basically fits the standard model…

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The Most Ancient Heavens

Posted in Art, Biographical, Poetry, The Universe and Stuff with tags , , , , , , , , on March 21, 2019 by telescoper

So here I am, in that London, getting ready for the start of a two-day conference at the Royal Astronomical Society on cosmology, large-scale structure, and weak gravitational lensing, to celebrate the work of Professor Alan Heavens, on (or near) the occasion of his 60th birthday. Yes, it is a great name for an astronomer.

I was honoured to be invited to give a talk at this meeting, though my immediate reaction when I was told about was `But he can’t be sixty! He’s only a few years older than me…oh.’ I gather I’m supposed to say something funny after the conference dinner tomorrow night too.

Courtesy of alphabetical order it looks like I’m top of the bill!

Anyway, I’ve known Alan since I was a research student, i.e. over thirty years, and we’re co-authors on 13 papers (all of them since 2011). I’m looking forward to the HeavensFest not only for the scientific programme (which looks excellent) but also for the purpose of celebrating an old friend and colleague.

Just to clear up a couple of artistic points.

First, the title of the meeting, The Most Ancient Heavens, is taken from Ode to Duty by William Wordsworth.

Second, the image on the conference programme shown above is a pastiche of The Creation of Alan Adam which is part of the ceiling of the Sistine Chapel painted by Michelangelo di Lodovico Buonarroti Simoni, known to his friends as Michelangelo. Apparently he worked flat out painting this enormous fresco. It was agony but the ecstasy kept him going. I’ve often wondered (a) who did the floor of the Sistine Chapel and (b) how could Michelangelo create such great art when it was so clearly extremely cold? Anyway, I think that is a picture of Alan at high redshift on the far right, next to the man with beard who at least had the good sense to wear a nightie to spare his embarrassment.

Anyway, that’s all for now. I must be going. Time for a stroll down to Piccadilly.

Update: you can find a bunch of pictures of this conference here.

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Subaru and Cosmic Shear

Posted in The Universe and Stuff with tags , , , , , , on February 15, 2019 by telescoper

Up with the lark this morning I suddenly remembered I was going to do a post about a paper which actually appeared on the arXiv some time ago. Apart from the fact that it’s a very nice piece of work, the first author is Chiaki Hikage who worked with me as a postdoc about a decade ago. This paper is extremely careful and thorough, which is typical of Chiaki’s work. Its abstract is here:

The work described uses the Hyper-Suprime-Cam Subaru Telescope to probe how the large-scale structure of the Universe has evolved by looking at the statistical effect of gravitational lensing – specifically cosmic shear – as a function of redshift (which relates to look-back time). The use of redshift binning as demonstrated in this paper is often called tomography. Gravitational lensing is sensitive to all the gravitating material along the line of sight to the observer so probes dark, as well as luminous, matter.

Here’s a related graphic:

The article that reminded me of this paper is entitled New Map of Dark Matter Spanning 10 Million Galaxies Hints at a Flaw in Our Physics. Well, no it doesn’t really. Read the abstract, where you will find a clear statement that these results `do not show significant evidence for discordance’. Just a glance at the figures in the paper will convince you that is the case. Of course, that’s not to say that the full survey (which will be very much bigger; the current paper is based on just 11% of the full data set) may not reveal such discrepancies, just that analysis does not. Sadly this is yet another example of misleadingly exaggerated science reporting. There’s a lot of it about.

Incidentally, the parameter S8 is a (slightly) rescaled version of the more familiar parameter σ8  – which quantifies the matter-density fluctuations on a scale of 8 h-1 Mpc – as defined in the abstract; cosmic shear is particularly sensitive to this parameter.

Anyway, if this is what can be done with just 11%, the full survey should be a doozy!

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Cosmological Results from the Dark Energy Survey

Posted in The Universe and Stuff with tags , , , , , on August 4, 2017 by telescoper

At last the Dark Energy Survey has produced its first cosmological results. The actual papers have not yet hit the arXiv but they have been announced at a meeting in the USA and are linked to from this page.

I’ll jump straight to this one, which shows the joint constraints on S8 which is related to σ8 (a measure of the level of fluctuations in the cosmological mass distribution) via S8= σ8 (Ωm/0.3)0.5 against the cosmological density parameter, Ωm.

These constraints, derived using DES Y1 measurements of galaxy clustering, galaxy-galaxy lensing, and weak lensing cosmic shear are compared with those obtained from the cosmic microwave background using Planck data, and also combined with them to produce a joint constraint. Following usual practice, the contours are 68% and 95%  posterior probability regions.

The central values of DES and Planck values are different, but the discrepancy is only marginal. Compare this with a an equivalent diagram from a paper I discussed last year.

The KIDS analysis used to produce this plot uses only weak lensing tomography, so you can see that using additional measures reduces the viable region in this parameter space.

It’s great to see new data coming in, but at first sight it seems it is tending to confirm the predictions of the standard cosmological model, rather than providing evidence of departures from it.

Incidentally, this little video shows the extent to which the Dark Energy Survey is a global project, including some of my former colleagues at the University of Sussex!

 

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KiDS-450: Testing extensions to the standard cosmological model [CEA]

Posted in The Universe and Stuff with tags , , , on October 19, 2016 by telescoper

Since I’ve just attended a seminar in Cardiff by Catherine Heymans on exactly this work, I couldn’t resist reblogging the arXiver entry for this paper which appeared on arXiv a couple of days ago.

The key finding is that the weak lensing analysis of KIDS data (which is mainly to the distribution of matter at low redshift) does seem to be discrepant with the predictions of the standard cosmological model established by Planck (which is sensitive mainly to high-redshift fluctuations).

Could this discrepancy be interpreted as evidence of something going on beyond the standard cosmology? Read the paper to explore some possibilities!

arXiver

http://arxiv.org/abs/1610.04606

We test extensions to the standard cosmological model with weak gravitational lensing tomography using 450 deg$^2$ of imaging data from the Kilo Degree Survey (KiDS). In these extended cosmologies, which include massive neutrinos, nonzero curvature, evolving dark energy, modified gravity, and running of the scalar spectral index, we also examine the discordance between KiDS and cosmic microwave background measurements from Planck. The discordance between the two datasets is largely unaffected by a more conservative treatment of the lensing systematics and the removal of angular scales most sensitive to nonlinear physics. The only extended cosmology that simultaneously alleviates the discordance with Planck and is at least moderately favored by the data includes evolving dark energy with a time-dependent equation of state (in the form of the $w_0-w_a$ parameterization). In this model, the respective $S_8 = sigma_8 sqrt{Omega_{rm m}/0.3}$ constraints agree at the $1sigma$ level, and there is `substantial concordance’ between…

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