H \alpha spectral line profiles

Starting from ground zero, the H \alpha (Balmer) emission line is observed at a wavelength of 656.3 NM. It is one of the most prominent emission lines observed in galaxies and it was one of the lines that I was looking for with Prof. Jeremy Mould as part of a summer project. Over the course of our work, we found something interesting. Given the differences in inclination of galaxies (from our point of view i.e face-on or side-on point of view), differences in distribution of gas in the galaxy and the galaxy's rotation curve, the shape of the H \alpha line differs a lot! In the lab, it'd be a simple Gaussian function but in practice, it ends up being a sum of multiple Gaussian functions with different mean and variance. Interestingly, it might happen that the spectral line has two peaks instead of one.

Think of a case where you are observing a galaxy side-on i.e one of the arms of the galaxy is moving towards you and the other, moving away. Using the same principle as Doppler shift of sound, light from two arms of the galaxy will be blue-shifted and red-shifted about the central wavelength. A lopsided or biased gas distribution in the galaxy i.e more gas away from the central region also helps such a profile, along with a large rotation curve. Such double peaked profiles are usually observed in the HI emission line profiles of galaxies.

My intentions now are to simulate such a double-peaked profile by assuming an inclination, a gas distribution and a rotation curve. I am of the idea that the double-peaked profile in itself might reveal interesting features about a galaxy using relevant models. I have a thesis by a Erica Nelson as reference on 'HI line profiles of galaxies : Tilted ring models'. I could try extend this to understand how the H \alpha line would look under similar assumptions. This is an interesting tangent of my project that I would like to pursue ...

Popular posts from this blog

Arxiv author affiliations using Python

So, I wanted to get author affiliation information from papers on arXiv. arXiv provides with an API to bulk query their database and get information. Following that, I look for the attribute 'arxiv:affiliation' in the html data. Here's the code - import urllib from BeautifulSoup import BeautifulStoneSoup   url = 'http://export.arxiv.org/api/query?search_query=all:astro&start=0&max_results=1000'   data = urllib.urlopen(url).read() soup = BeautifulStoneSoup(data) #print(soup.prettify()) #list = soup.findAll('arxiv:affiliation') #for i in range(len(list)): #        print list[i].contents   test = [tag.string for tag in soup.findAll('arxiv:aiffiliation')] Now, the problem I'm having is that I'm getting affiliation of all authors which I want to split into sets of affiliations of authors of a paper, which I'm stuck on at the moment. Once I get that part, I can move on to the next part of this pet project, displaying these
Read more

Farewell to Enthought

I started my professional career at Enthought , at the Pune office in India, on Feb 29, 2016. Over the course of eight long years, I spent time at the Austin office in the US, the Cambridge office in the UK, and I worked remotely from India. I was let go on March 27, 2024 . I had an unbelievably great time. I had three amazing mentors - Pankaj Pandey, Senganal Thirunavukkarasu, and Mark Dickinson. Pankaj mentored me in my first year at Enthought. I started paying attention to the craft of software after working with him. Senganal started mentoring me in my second year at Enthought, and continues to mentor me, even after the both of us have moved on from Enthought. He instilled professionalism in me, ensuring that the code I wrote produced precise scientific results, and that I tackled the known unknown aspects of a project first, to ensure timely communication about project progress. I was eager to manage people at the time and Senganal made me realize that I didn't want to manage
Read more

Elementary (particle physics), my dear Watson

Ground Control to Major Tom:  Shruti Patel checking in. Since my dear friend and fellow-physicist Rahul Poruri is homeward bound, and shall remain there for a week, I'm stepping in to continue his tradition of daily posts to Astronut . Even as I write, I'm not quite sure what this post is going to be about, so please forgive me for occasional rants and digressions.  By the way Rahul, I totally resent you for the name of this blog- I'm never going to start my own blog because there's no way I'll come up with a name as cool as Astronut! For now, I shall try and be happy with being a guest writer! Before I begin, a little bit on who I am and what I do; so that you can trust that my general views on science- particle physics in particular- are not entirely baseless. I graduated with a masters in Physics from IIT Madras in July this year, and I'm currently working towards (an eventual) PhD with the Theory Group at the Deutsches Electronen-Synchrotron (DESY)
Read more