Tags: #physics

Each of the two searchable webpages has a link to the other, as well as to the source data. The webpages are self-contained with all the data included in the html file, which contains the javascript code for the searches and the CSS for styling.

The original purpose in doing this was because many of the submissions were not on the arXiv, and I wanted to see what else was available and also so the PDF file link were all on one page. In addition, though, the search feature has been very useful.

The webpages are coded with simple html and javascript (javascript must be enabled to view the data). The webpage search input box shows the syntax:

Use * for AND search, : keyword1*keyword2

Use | for OR search: keyword1|keyword2

For NOT, use — (2 hyphens) after 1st keyword: keyword1—keyword2

¹APC: Activity, Project, or State of the Profession Consideration

HashTags: #astrophysics #cosmology #physics

Link to the Conference Program page

Youtube recorded videos (~ 2-½ hours each day): Day 1 | Day 2 | Day 3 | Day 4 | Day 5 |

There are at least 2 people who have created an index of each day's talks with links to key sections of each talk, along with some commentary.

One was created by me and is a thread at the cosmology subreddit. Links to each day: Day 1 | Day 2 | Day 3 | Day 4 | Day 5 |

The other was created by conference participant and panelist Behnam Javamardi, available on his blog: Day 1 | Day 2 | Day 3 | Day 4 | Day 5 |

There is also a twitter #H02020 hashtag, which has some additional coverage.

If I come across additional reference materials on this conference, I will add them to this post.

Tags: #Cosmology #H0 #Talks

I'd like to point out an excellent overview talk from this program by Raphael Flauger on Feb. 28 that reviews Hubble measurement physics and results from each of the major determination methods and discusses current status on Hubble tension. The video for Flauger's talk is here. That page does not have the talk slides (at least not yet anyway) but the slides are available in PDF format here. Update: the slides are also now available on the KITP video page. Here is a PDF of the slides.

In the cosmology subreddit that I'm a member of, there are frequent questions from those who have a grasp of the basics and are keenly interested in learning more about cosmology but do not work in the field themselves. I especially want to give a shout-out about this talk to that group. It's an excellent and reasonably accessible review of a key trending problem-area needing resolution for there to be a better understanding of whether adjustments are needed to the ΛCDM standard model of cosmology. This overview talk very clearly summarizes what would otherwise take hours and hours of digging to get. The rest of the program has very good material but some of it is rather specialized and deep.

A recent discussion in this reddit thread contrasted differing takes within the community on whether inflation preceded or followed the big bang. There are various reasons for this, some of it having to do with the history and evolution of what is meant by the term 'big bang', which was also explored in this earlier thread.

Here are comments from the overview page for this KITP program on this: “inflation not only explains the large-scale homogeneity and isotropy of the Universe, but also provides a causal mechanism that results in the seeds for the subsequent growth of structure. However, what happens after inflation remains poorly understood. The end of inflation must provide a hot Big Bang, also known as reheating, which eventually must lead to a thermal bath of Standard Model particles, dark matter, and any additional Beyond the Standard Model (BSM) sectors, at least by the time of nucleosynthesis.”

Tags: #Cosmology #H0 #Talks

Updates since this was originally posted:

• [2109.04451] The Atacama Cosmology Telescope: Constraints on Pre-Recombination Early Dark Energy , J. Colin Hill, et. al. Colin presents these results in a colloquium talk on 09-Sep-2021.
• In [2009.10740] Early dark energy is not excluded by current large-scale structure data a rebuttal is made and the authors “suggest that EDE still provides a potential resolution to the Hubble tension and that it is worthwhile to test the predictions of EDE with future data-sets and further study its theoretical possibilities.”
• Lead author Colin Hill was interviewed in a Cosmology Talk episode by Shaun Hotchkiss: Early dark energy doesn't make cosmology concordant again. Links to key parts of the video are available at the talk page.
• A detailed review of this paper was posted by cosmologist Sunny Vagnozzi on his blog here
• Follow-up paper: [2006.11235] Constraining Early Dark Energy with Large-Scale Structure, by Mikhail M. Ivanov, Evan McDonough, J. Colin Hill, Marko Simonović, Michael W. Toomey, Stephon Alexander, Matias Zaldarriaga. An astrobites article about it.

Background

Going back at least several years [1], but increasingly since late-2018 [2-7], there has been growing theoretical interest for the Hubble tension issue that suggests new physics models may be needed for the early universe prior to recombination that do not cause changes to late time cosmology, since that is tightly-constrained [4, 8].

For example, papers [2, 5] propose models for a new form of early dark energy (EDE) present at z ≳ 3000 that then dilutes away, resulting in a reduced sound horizon at decoupling. This results in a larger inferred $H_0$ value from CMB data versus Planck results, thus reducing the disparity between early and late time $H_0$ results.

These EDE proposals for resolving $H_0$ tension were characterized as being somewhere on the spectrum between “most plausible” [3] to “least unlikely” [4].

Findings from this New Paper

This new paper by Colin Hill et al analyzed these EDE models in relation to a number of data set combinations, including large scale structure data. In particular, the EDE proposals run into problems with LSS data. If interested, you can read the details but here's some of their summary conclusions:

“We conclude that the EDE scenario is, at best, no more likely to be concordant with all current cosmological data sets than ΛCDM, and appears unlikely to resolve the $H_0$ tension.” (pg1)

“There is no sign of concordance amongst these data sets: the LSS data pull the parameters in the opposite direction to that required to simultaneously fit the CMB and SH0ES data.” (pg 26)

“Taken in conjunction, these results paint a bleak picture for the viability of the EDE scenario as a candidateto restore cosmological concordance. More generally, it is likely that any model that attempts to decrease the sound horizon by increasing H(z) through a new dark-energy-like component that is active at early times will encounter the problems identified here. All such models, insofar as they can accommodate a close fit to both the CMB and SH0ES measurement, will do so at the cost of a shift in ΛCDM parameters that is not compatible with LSS data.” (pg 27)

“In the absence of significant shifts with respect to current LSS data, it seems unlikely that these next-generation data sets (WFIRST, DESI, VRO, etc) will reverse the negative trajectory we have seen here in the evidence for EDE as LSS data are included in the analysis.” (pg 27) -—

[1] [1607.05617] The trouble with $H_0$ [2] [1811.04083] Early Dark Energy Can Resolve The Hubble Tension [3] [1907.10625] Tensions between the Early and the Late Universe [4] [1908.03663] The Hubble Hunter's Guide [5] [1908.06995] Oscillating scalar fields and the Hubble tension: a resolution with novel signatures [6] [1911.11760] Early dark energy from massive neutrinos — a natural resolution of the Hubble tension. Some reactions to this paper in this thread . [7] The subject paper lists additional EDE proposals, see page 26 for additional references. [8] “there is not much freedom in changing the expansion history from that of a standard ΛCDM model below z ∼ 2: the guardrails offered by SNe and BAO do not allow this.” [1, pg 7]

Tags: #Cosmology #DE #H0

January 2020: In new paper arXiv: 2001.09213, the MCP reports an updated $H_0$ value of 73.9 ± 3.0 based on improved distance measurements for 4 of the 6 systems they previously reported on. MCP researchers Braatz, Pesce, Condon, Reid, et al teamed up with SH0ES team members Scolnic and Riess for this paper. Here is a clip of Figure 1 from the paper. Additional details in this reddit thread.

July 2019: video and slides of a presentation by Mark Reid at the KITP-UCSB conference Tensions between the Early and the Late Universe on July 16, 2019: H0: NGC 4258 and the Megamaser Cosmology Project -—

This post is about the paper Science with the ngVLA: H2O Megamaser Cosmology, which was posted on the arXiv preprint server in Oct. 2018.

What's This About? A recent comment by one of the people I regularly follow (who writes excellent posts on astronomy/cosmology topics) mentioned this NRAO key project as providing direct geometric measurements of the Hubble Constant (H_0) independent of the Cosmic Microwave Background (CMB) and standard candle methods. The megamaser method gives angular diameter distances to water megamasers¹ in the nuclear regions of host active galaxies within ~0.1 pc of the SMBH. The galaxies are typically well into the Hubble flow at between 50 – 200 Mpc distance. This slide compares the distances to various studied megamasers to those for Cepheids. As indicated in the slide, these megamaser distances can be used to calibrate other distance methods.

Not being familiar with this MCP project but finding it of interest, I've tried to integrate and summarize some reading on it into this mini-overview, non-expert's report.

What Are They? These H₂O megamasers being studied are a special type of astrophysical maser originating in a flat accretion disk, with warm (~400 K) dense gas clouds, in Keplerian motion orbiting the SMBHs of host active galaxies. They produce stimulated coherent emission at 22 GHz from collisionally excited transitions between rotational energy levels of ortho-states of water². Typical rotation velocities are ~500 km s^-1. Megamasers have a large isotropic luminosity, typically 10³ solar luminosities. A radio continuum background source is needed to provide the radiation that's amplified by the maser.

What facilities are currently involved? “The MCP uses the most sensitive suite of telescopes working today at 22 GHz, including the GBT for surveys and spectral monitoring observations, and the High Sensitivity Array (the VLBA, GBT, VLA, and 100-m Effelsberg telescope) to map maser disk systems.” [quote source]

What's Involved in Measuring the Distances? Multiple steps, e.g.: (1) survey with the GBT to identify the rare, edge-on disk megamasers needed for this method (this maximizes the gain length as described in footnote¹ references), (2) image the sub-parsec disks with the High Sensitivity Array, (3) with the GBT, monitor spectral drifts in maser lines (red vs blue shifting) from centripetal accelerations of the clouds as they orbit the central BH, (4) VLBI observations for rotation curve mapping, and (5) modeling the disk dynamics. Basically, the distance to the galaxy is measured by comparing the observed angular radius of the maser's orbit to its measured linear distance from the black hole (see this visual slide and further informational details in footnote¹).

Current Status: The most complete set of H_0 results I've seen the MCP report is 67.6 ±4.0, a 6% measurement. The individual 6 measurements are shown in this slide, which also shows the distances in Mpc. A comment indicates they expect to improve the measurement to < 4%. (I've also seen a ±3% goal in several of their papers). In the slide, two of the results are shown in prep, which may explain the difference from the 69.3 ±4.2 result from their latest paper 1810.06686 which reports only 4 results.

In Extragalactic maser surveys [1802.04727] they report: “With respect to 22 GHz H₂O masers, we note that the MCP is close to completion. We can expect a final Hubble constant deduced from this survey with an uncertainty of only a few percent during the next one or two years.” (page 9) Their latest paper says their final results will be based on distances to 9 megamasers. Surveys of 3000 galaxies were necessary to identify those 9 (AGNs are required with a maser disk suitable for measurement and with an edge-on view).

What's Their Future Plan? A recent 5-page paper details their plans involving the next-generation Very Large Array: H2O Megamaser Cosmology with the ngVLA [1810.06686]. Their ultimate goal is a 1% measurement, which will (1) require a survey to identify additional megamasers – their forecast is that ngVLA can discover ~30 times more sources than the GBT, and (2) the ngVLA must have certain design features as outlined in section 6 of the paper.

An overview document on the ngVLA shows it's timeline as initiating early science in 2028 and full operations in 2034.

Are There Other Study Results from MCP? Besides its primary mission for H_0 measurements, MCP results to date include the “gold standard” most accurate method for extragalactic BH masses, (e.g., see 1801.06332), and also precise BH masses in relatively low-mass systems where the BH masses have been difficult to measure – this has important implications for galaxy evolution (e.g., see 1007.2851).

What are some other MCP references? An interesting set of slides from an NRAO presentation is Water Megamasers in Galaxies, which I recommend. The Megamaser Cosmology Project has a wiki page here.

Footnotes: ¹ For a good reference on the distance measurement techniques, see Braatz et al, Measuring the Hubble constant with observations of water-vapor megamasers. For a nice summary graphic of this geometric distance technique, see this. Also the wikipedia page has a short summary here.

² See this for a graphic showing various rotational energy level transitions of water. Also see this graphic. The particular transition of interest for megamaser study is 6₁,₆ –> 5₂,₃. For more complete data on these transitions, see Table 6 in 1510.06182. Other transitions of ortho-H20 such as at 183 GHz are also candidates, but 22 GHz is the most studied currently, and is directed at ortho-H20 rather than para-H2O: “we consider only transitions between ortho-states because these are the states for which the most extensive collisional data have been calculated, and because in a hot plasma the abundance of ortho-water will exceed that of para-water by a factor 3.” Note: these two water states “are not connected by radiative or collisional transitions.” Neufeld and Melnick 1987 ApJ 322,266. Two other good sources on the transition details is Astrophysical masers and The Physics of Water Masers observable with ALMA and SOFIA [1510.06182].

Tags: #cosmology #H0 #physics

There are 3 separate python modules for cosmology, LSS, and DM Halos. You can choose to work with any of 20 built-in cosmology models based on results from Planck18 (with or w/o BAO), Planck15, Planck13, WMAP, etc. You can also create your own cosmology model by specifying values for a minimum of 6 parameters.

A paper on it is available at https://arxiv.org/abs/1712.04512. The code is available at this BitBucket repository. You can clone the repo, or download a zip file, or you can install it using pip. Documentation with many examples in html format is available here and the docs on the 3 modules are also available as interactive, live-code Jupyter notebooks here. The html tutorials doc files are just exports from the Jupyter notebooks.

Diemer has used it on at least two of his recent papers: An accurate physical model for halo concentrations [1809.07326] Modeling the atomic-to-molecular transition in cosmological simulations of galaxy formation [1806.02341]

Diemer expects future development work to continue on the code and invites bug reports, documentation feedback, feature requests, and collaborators (see the Future Development section at the end of the 1712.04512 paper).

An entry on it has been added to the Astrophysics Source Code Library. Regarding other tools, one site I saw that has a large software availability listing is Nasa's cosmology tools webpage. There's also a wikipedia page on cosmological computational software and the astrobites guide to astrophysical software. At a CosmoTools18 school event, 11 tools were covered and videos of the lectures are available here.

I installed Colossus on both an Ubuntu and a Windows 10 machine and it ran perfectly with no glitches. I typically use Spyder3 to create and run the code and JupyterLab for the notebooks. With numpy and matplotlib, it's easy to create plots.

There's also many good cosmology calculators online, e.g., ones at ICRAR, iCosmos, and Ned Wright's.

Reddit thread on this paper. ___

Footnotes: ¹ Colossus is an acronym for COsmology, haLO, and large-Scale StrUcture toolS ² Diemer's PhD thesis summary; On the (non-)universality of halo density profiles

Tags: #cosmology #software