Skip to main content

Week 4 - Quasar Reddening & Celestial Projections

Having reproduced the results of the original paper and extending it, for now i'm just looking to learn tricks of the trade - automating tasks like fits file extraction and scatter plots, celestial projections of the objects, learning to make animations using matplotlib and whatnot.

A Mollweide projection of 500,000 galaxies observed by the SDSS.
A Mollweide Projection of ~300,000 quasars observed by the SDSS

NOTE : You guys can see that the projection with quasars is a lot more uniform that the projection with galaxies - there are gaps in the filled region i.e dec range +-120:180! This maybe because galaxies can only observed till z<0.5 (maybe, i'll need to verify this). Beyond this point, galaxies aren't spatially resolved anymore and they look the same as stars. Also, beyond  this redshift, galaxies become too dim to even be observed, unlike quasars which are extremely luminous! The reason the quasar projection is more uniform (i'm speculating here) is because quasars have been observed till z~10. Quasars are still not spatially resolved and they are visibly no different from stars but if we look at the spectra, you can distinguish a quasar from a star! (or the colors of the quasar, which is what my summer work has been, if you guys followed it) 

And because space isn't exactly isotropic, the probability of finding a quasar at a given (ra,dec) is higher than that of finding a galaxy simply because the number of quasars in a given patch of sky is probably higher than the number of galaxies! 

Also, apart from the gaps in the filled region, the plot is almost one-sided towards the northern sky because of where the telescope is located. SDSS is carried out using a 2.5m telescope from Apache Point Observatory, Sunspot, New Mexico - which is a latitude of 32 deg N. And the declination range of telescopes usually are +_45 from zenith, which is the projection is one-sided towards the northern sky. The same goes for the gaps in the RA range! 

Also, you should refer to the wiki page for Mollweide Projection if you haven't so far. Along with the mollweide projection, there's aitoff, hammer and lambert projections as well which seem to be commonly used for projections of spherical surfaces!

Moving on, if you guys read last week's post, in my analysis of the new data set with ~140,000 quasars, you might notice see vertical features on the color-redshift plots. This represents many-a quasars at roughly the same redshift with varying color values! And it might be interesting to study these quasars specifically as they are outliers - they are reddened! You see, in as Astronomy, the outliers are what make for interesting observations and science!
Overlapped spectra of ~25 quasars

From observations atleast, these don't seem to be BAL quasars (Broad Absorption Line) whose emissions are intrinsically reddened! But one other interesting thing i noticed about these quasars is their position

Quasars belonging to the vertical feature at z~1

Quasars belonging to the vertical feature at z~1.6

You can see that (other than for a couple of quasars) there outliers are roughly concentrated in two positions. I don't know what's so special with these positions. 

So, that's what happened last week - other than for the fact that i sat through a workshop on social sciences : quant methods and open source tools! I need to learn some stat tools to analyze my data sets and i saw this as a good opportunity! Other than that, i was trying to create an animation to visualize the way colors of a quasar vary with redshift - visualizing section 4.3 from richards et al (99) but well, that hasn't really worked out so far.  I'm also working on my project report - while compiling all of the code i've used, the references etc. 

Anyway, that's all for now. Maybe i'll find something interesting studying these quasars. Either way, i've learnt quite a few interesting things :D...

Popular posts from this blog

Animation using GNUPlot

Animation using GNUPlotI've been trying to create an animation depicting a quasar spectrum moving across the 5 SDSS pass bands with respect to redshift. It is important to visualise what emission lines are moving in and out of bands to be able to understand the color-redshift plots and the changes in it.
I've tried doing this using the animate function in matplotlib, python but i wasn't able to make it work - meaning i worked on it for a couple of days and then i gave up, not having found solutions for my problems on the internet.
And then i came across this site, where the gunn-peterson trough and the lyman alpha forest have been depicted - in a beautiful manner. And this got me interested in using js and d3 to do the animations and make it dynamic - using sliders etc.
In the meanwhile, i thought i'd look up and see if there was a way to create animations in gnuplot and whoopdedoo, what do i find but nirvana!

In the image, you see 5 static curves and one dynam…

on MOOCs.

For those of you who don't know, MOOC stands for Massively Open Online Course.

The internet is an awesome thing. It's making education free for all. Well, mostly free. But it's surprising at the width and depth of courses being offered online. And it looks like they are also having an impact on students, especially those from universities that are not top ranked. Students in all parts of the world can now get a first class education experience, thanks to courses offered by Stanford, MIT, Caltech, etc.

I'm talking about MOOCs because one of my new year resolutions is to take online courses, atleast 2 per semester (6 months). And I've chosen the following two courses on edX - Analyzing Big Data with Microsoft R Server and Data Science Essentials for now. I looked at courses on Coursera but I couldn't find any which was worthy and free. There are a lot more MOOC providers out there but let's start here. And I feel like the two courses are relevant to where I …

On programmers.

I just watched this brilliant keynote today. It's a commentary on Programmers and the software development industry/ecosystem as a whole.



I am not going to give you a tl;dr version of the talk because it is a talk that I believe everyone should watch, that everyone should learn from. Instead, I am going to give my own parallel-ish views on programmers and programming.
As pointed out in the talk, there are mythical creatures in the software development industry who are revered as gods. Guido Van Rossum, the creator of Python, was given the title Benevolent Dictator For Life (BDFL). People flock around the creators of popular languages or libraries. They are god-like to most programmers and are treated like gods. By which, I mean to say, we assume they don't have flaws. That they are infallible. That they are perfect.
And alongside this belief in the infallibility of these Gods, we believe that they were born programmers. That programming is something that people are born wit…