“JEANS? The legendary super-team? Of course I’ve heard of them. Who hasn’t?”
— Everybody, 2027
This day will forever be known as the landmark of the first ever blog post by the legendary super-team JEANS. Bards will sing of our legacy, and our names will be met with glorious fanfare, a hardly worthy testimony to the immense scientific contribution we have made for the betterment of mankind for the centuries that are so blessed to follow. My name is Fal, and welcome to our blog.
–= Members of the Criterion
I am christened the unflattering title of Errors and Communications lead, and serve a wide range of supporting roles within the team including public outreach, coding and data processing. My direct superior is Iestyn, the esteemed Project Lead, and my colleagues are Gethin, Nathan, Anton and Nick.
Gethin is responsible for acquisitions and the technological aspect of our affairs, and hence operates as our Coding Lead.
Nathan is the Administrator, and oversees the co-ordination of meetings, and keeps stringent records of our activities.
Anton is the “Theory Lead”
And finally, Nick is the logician in our ranks, taking charge of the processes involving data handling, earning him the title of Data Lead.
–= Initiation
Galaxies are large scale, gravitationally bound systems of stars, dust and gas that form a significant part of the universe. They are subject to a multitude of properties that characterise them, as well as provide indication of their evolution paths and constituents. The twines between the colour of a galaxy and its morphology have been studied since the 1930s, whereupon the works of Morgan & Mayall and E.P. Hubble, astronomers such as I. Strateva have built a model describing the colour dependence on dominant stellar populations. It now falls upon us to answer a further question, concerning the variation in star formation rate across cosmic time.
In lieu of our discussions commencing Week 11, we decided to aim towards the route of connecting morphology with star formation rate, and observe this relation over a cosmic timescale. This, I would like to emphasize, is definitely not because almost all of us had just finished a 363 Lab Report on the same topic in the leading days. It wasn’t. We all decided to purvey the blogs of former years (As you, dear reader, are likely doing too), as well as read one paper on this idea in advance of Week 12’s team meeting.
This meeting was incredibly fruitful. We emerged with an overall scope of the project, as well as discrete tasks that could be done within labs. The conclusions we wanted to draw, the hypotheses we wanted to pose. The summary of the project was decided as follows:
—
Hypothesis: Star formation rate increases over redshift independent of morphology, metallicity, and density.
Study: Split into three overarching questions:
- Morphology binaries (Spiral/elliptical, Featured/Featureless, Barred Spiral/Natural Spiral) plotted on axes of SFR and Redshift
- Metallicity and Density extremes (Extremely low/Extremely high) plotted on axes of SFR and Redshift
- Tidally formed barred spirals and Isolation formed barred spirals plotted on axes of SFR and Redshift
Conclusions: Expect to disprove hypothesis by showing clear distinctions between all trend dichotomies. Aim to explain increases of SFR qualitatively by considering the processes in, for example, metal poor/rich stars – extend this idea over all categories.
—
With this initial plan in mind, I organised a presentation, and we showed off our ideas on the Wednesday of Week 12. Our feedback told us to reduce our scope in some areas, but the principles remained unchanged. And thus, after two more meetings in which we discussed papers in detail and allocated discrete tasks for all members, we tackled the first lab on the Tuesday of Week 13.
–= Execution
“The greatest contributions to astrophysics and fashion since sliced bread.”
— Darren Jean, The Gethin Hughes Observatory, Stanford University 2033
From this point, we split into two sub-teams. The Low-RS team comprised of Gethin and Nathan tackled low-redshift data sourced from the SDSS. Moreover, they took charge of processing Galaxy Zoo data in order to match morphology with the data points from other catalogues. Team High-RS was formed of Nick and Anton, and had the task of gleaning results in the high-redshift limit of z=0.6 to 1. They used data from COSMOS and LEGA-C. Iestyn made sure everyone knows what to do. My role was to determine necessary uncertainties for both teams, produce a program to filter unwanted LEGA-C rows, and then scout out the expected data results for the first task to determine if it was worth pursuing.
In the Galaxy Zoo data, we came across a problem – how to determine which weighting fraction to use. The Galaxy Zoo is a project whereupon the public is called to contribute their own time to help categorise galaxies in a database. In this respect, there is plenty of scope for errors; different voting policies between individuals. Therefore, weightings are used in order to minimise bias and get the best representation for the correct categorisation of things. It falls upon us to determine the correct weightings to use, but we had no leads.
Gethin then had the idea of doing the experiment ourselves, and comparing with Galaxy Zoo results to determine the weighting that matches our views with the public opinion. In this way, by collecting data with N=50 from all JEANS members, we can essentially choose from the public sample the weighting that our team (on average) deems to be correct. A random sample of galaxies were selected from the database, and each member sat down to classify them over the course of the lab. Nathan did the entire experiment wrong and ruined everything. Sorry, I meant, Nathan decided to represent the very likely case that a fraction of the public would misinterpret the instructions and acted accordingly. In any case, the data we collected was wonderfully interpreted by Gethin, who then produced the accurate weighting fraction to be used in our processing.
Galaxy Zoo only accounted for low redshift unfortunately. Therefore, in order to progress with the plan, Team High-RS needed to use Galaxy Zoo CANDELS. Nick matched LEGA-C and COSMOS data, but found that only 70 data points were present in both GZC and LEGA-C. We chose to use that over COSMOS anyway because it had more documentation. 70 data points, we decided, were enough for our purposes.
The final hours of this first lab were spent producing our first graph, at least to a preliminary level. Myself and Nick independently worked on graphs of SFR in featured and featureless galaxies over galactic time. Nick made the distinction of the morphologies at the cost of only having 70 data points, whereas I kept in all the data points, including those past the desired redshift range, in order to scout our future results. Together, we found that, it is indeed the case that there is a difference in trend between featured and featureless galaxies, and also that there is a clear SFR exponent in the high redshift region.
Well, that’s all for this update. Thanks for sticking with us thus far and I hope I haven’t bored any of you to death. Next week’s blog post will feature an actual banner and group photo! And some astrophysics.
See you lovely fellas in the next one!
JEANS Blog – 05/FEB/22
–= Update the First
“I wish for my very good looking daughter to marry one of those lovely gentlemen from that super-team JEANS”
— An incredibly wealthy family, ASAP please
Reporting for Just Examining AstroNomical Systems, Fal here!
This week, we’re proud to report we made great progress. A general overview goes as follows; the first result is drawing to a close, meaning that next week, our loyal readers will have a final graph to behold/worship. This graph concerns the variation of morphology and mass with SFR over cosmic time. Our software framework is complete for this task, meaning that future data is expected to be simply plug & play with minimal changes. We have finally gleaned an adequate method for determining uncertainties in SFR, at the blood cost of ~8 months off poor Gethin’s lifespan. And finally, the initial pages of our report has come to sustain the tender touch of the JEANS pen; the structure is complete and the introduction, data and methods sections are completed to a perfunctory level. We deem ourselves to be ahead of the planned schedule, with optimistic outlooks for the coming weeks.
It’s been a productive, at times hectic, week. The biggest problem for us thus far has been the SFR errors, which after so long we’ve finally come to a resolution about. Dr. Sobral helped up find a paper that outlined a calculation for SFR, which we’re going to take as gospel. (We will lose members in an accident if we have to go through SFR uncertainties any more). We also found a processed dataset from SDSS made by the “Portsmouth Group”, who are quite usefully anonymous in citings and references. But, this data set does include errors in SFR in the bands we need, therefore, for the sake of progress and our own sweet skin, we shall move on.
Nick’s code for long range redshift has been leveraged for the Low-RS team’s use, for the sake of consistency in format. I worked with him to determine parameter limits so we could shave off the less useful data points; quite representative of this notion was how we filtered out all data points with magnitude in any band (that we are working with) above 22 mag. This is because fainter galaxies have greater flux uncertainties, and we don’t like that.
I was responsible for starting the report in preparation for the first wave of results. To this end, I purveyed the works of previous years to make sure what we’re doing doesn’t stand out like a sore thumb. Then, I designed the structure of our report accordingly and spent the lab writing precursory paragraphs.
Some issues came up in the plotting for both teams – firstly, since we were advancing science at an unprecedented rate, God himself felt threatened and decided to crash Nick’s python. Moreover, team High-RS had three graphs with roughly 40 data points between them, quite contrasting with Team Low-RS’ corresponding single graph with 3000 data points. We’re working on this, and will fix it before it’s time to start the second and third projects.
We’ve also begun scouting out the next tasks – Iestyn identified the next route as determining the density and overdensity relations with SFR over cosmic time. I’m on errors for the overdensity and on a completely unrelated note I need counselling.
The expectation for next week is that our first and second projects are done, the report has quality writing and citations for the introduction and data sections, and Anton becomes the CEO of Cisco Telecommunications. Please look forward to our next update!
JEANS Update 1 – 11/FEB/22
–= Update the Second
Reporting for Just Examining AstroNomical Systems, Fal here!
Blog post is late? What happened to the routine Saturday updates that I’d hammered into the rituals of all JEANS apostles? Well, there’s a good reason for that and its because we finished the project just now and I wanted to stretch this update to include the ending.
As predicted in the first weeks, we’d done all the heavy lifting and the rest of our project has been for the most part, plug and play. The data hashing, reduction pipeline and analysis were completed this past week-and-a-half for the remaining two projects. Indeed quite the testimony to our incredible efficiency, efficacy and variegation.
So, before I present the results, let’s review what’s happened in the macroscopic context of the project.
–= The Ascent
“Why have all the other teams taken their group photos in front of the telescope and we got ours at Greggs”
– someone in my team
Initially, we’d identified three conjectures to investigate. These were;
- Morphology binaries (Spiral/elliptical, Featured/Featureless, Barred Spiral/Natural Spiral)
- Metallicity and Density extremes (Extremely low/Extremely high)
- Tidally formed barred spirals and Isolation formed barred spirals
These did not all survive the test of time. Along the way, the march of progress did discriminate between the viabilities, the insightfulness and the amount of available documentation, screw you COSMOS, and as a result, we had to adapt as we went. Our final setup was:
- Morphology binaries (Spiral/Barred/Elliptical, Featured/Featureless)
- Overdensity extremes
- Mass bins
So, let’s review our process.
For those that have forgotten (This was definitely mentioned above already, you forgot, don’t scroll up) our data was split into two samples. Sample A was a cross-pollination of SDSS and Galaxy Zoo, and Sample B was made up of CANDELS and LEGA-C.
The way we combined the data sets was by creating a script to match by co-ordinates. Then, we worked our magic and filtered them with our amazing Deity-level spells to remove rows any with high magnitude or lots of zeros. After that, we just plotted it.
Aaaaaaaaand boom! This is where we get to this week’s progress. Four of us have had nothing to do but do lab report, which is incredibly boring to write about and presumably even more so to read. Gethin and Nick, the cheap labour of the grouppeople most suited for the coding processes, have adapted their code to incorporate new columns and produced the graphs. Anton, the noble and almighty Theory Lead (lol) did the analysis of the graphs, and the rest of us, hungry for jobs, scrabbled to transcribe it into the body of the report.
That pretty much sums up the actual work we did. Now, as for the results…
–= The Zenith
“A David, some PCs and wireless earphones. Paraphernalia of formidable agency that carved their names in the annals of history. They held the knowledge to unlock the very heart of the universe and throw open the gates to Heaven, but still they remained in the service of mankind.”
Lord Jean, Chronicler of the JEANS legacy, 2094
With over 200 years of combined research experience, the six members of the Criterion are proud to present our findings. Gaze and be awed.
Firstly, looking at the first task, we present the relations between the redshift and SFR in various mass bins. Check out our cool graphs!
Remember a few weeks back, when I talked about a “scouting plot” that I made just to test out my cool filtering script? Well, surprisingly, the little bugger made it into the big leagues, and now features in the final report! We even gave him a proper makeover, some polishing and his own name, Task 0!
Well, little Task 0 actually is quite important, and serves as kind of control case. For example, in looking at our Task 1 results, we see that the Task 0 trend is observed in all of them. A closer analysis shows that over all mass bins, barred spirals are the best star-formers. There is evidence in both high and low redshifts that spiral-type or featured galaxies are on average, better star-formers than ellipticals/smooth galaxies.
Though, it’s interesting to observe that elliptical galaxies at low redshift have far steeper gradients than the spiral-types. This implies that as we head into the higher redshift regime, then ellipticals far outperform spirals! However, when we look at our high-redshift results, we actually find that it’s certainly not the case – ellipticals, corresponding with “smooth” galaxies are still outperformed by their featured counterparts.
We think that this conflict can be explained by how elliptical galaxies at younger stages are far more active, and over time die down into quiescent stages. Sprials, on the other hand, stay active for longer but are less active in their early stages. This draws an interesting parallel with the temperature-lifetime relation for stars; the hottest stars have the shortest lifetime, and the cooler ones burn at lower luminosities for much, much longer.
For the second task, here are our results for stellar mass against SSFR at low redshift;
Here, we plot the mass against specific star formation rate (SSFR). SSFR is simply defined as SFR normalised over mass. Again, this was 100% mentioned above earlier, and you forgot, don’t scroll up. What this means is that there are diminishing returns on SFR as we look at more massive galaxies. Having normalised, it also becomes apparent that there is very little distinguishment between the three categories, with barred spirals slightly outperforming the others over all masses. We think that an explanation for this is likely the bar of the galaxy – as it rotates, the space immediately ahead of the bar’s rotation gets compressed, and therefore is more likely to meet the Jeans Criterion. In this sense, the bar is a galaxy’s own manual star forming mechanism, which is super cool. This may also help to explain the results in task one!
Finally, our findings for the third task, Overdensity’s relation to SFR over high-redshift bins.
Brave little Task 0 makes yet another presence here, confirming there’s absolutely no relationship between overdensity and redshift in this graph. The relative skew of the lines is inconsequential, and the shifts in Y are the doings of Task 0. What we do find out, though, is that lower overdensities correspond to greater star formation. This can be explained in that lower overdensities correspond to less concentration of mass within a galaxy’s bounds, and therefore more uniform distribution. This means that there’s a lot more potential area for star formation, where space may be the limiting factor. If we consider a similar galaxy with very high overdensity at the same redshift, then we should find that there are clusters with huge amounts of star formation, and the rest of the galaxy finds it hard to ever satisfy the Jeans criterion, and therefore is more or less quiescent. The net effect is that more overdensity = less star formation.
–= Epilogue
Well, that’s it from me. The next weeks are just doing writeups of all our work to this date, so I won’t bother to talk about any of it. Thanks for sticking with us. It’s been quite the ride, and I hope you’ve enjoyed reading this blog at least somewhat.
—-== The JEANS team ☆
JEANS Update 2 – 22/FEB/22
XGAL: Time travelling through the Universe 