Skip to main content

Posts

Showing posts from October, 2015

Isolated galaxies and AMIGA

Galaxy evolution is a tug of war between the nature of the galaxy (morphology, mass, etc) and nurturing environment of the galaxy (major or minor mergers, ram stripping, etc) and to understand it, we need to understand when nature rules over nurture or otherwise. An interesting way to resolve this question is to study isolated galaxies - isolated in the sense that there are hardly any galaxies in their vicinity. The qualitative 'hardly any' was quantified to create the Catalog of Isolated Galaxies (in 1973) and then revised by the AMIGA people for a more up-to-date study. Understanding the evolution of isolated galaxies inherently tells us more about the role that the nature of the galaxy plays in it's evolution.

Today, I was reading up on some interesting papers by the AMIGA people, all three on the HI (neutral Hydrogen) profiles of select isolated galaxies. The three papers can be found here, here and here. I came across this survey recently and only today, as I was rev…

Katheryn's Wheel and colliding galaxies

The first thing that you should note about this work (available here) is that it has almost been a decade in the making. The peculiar object, named Katheryn's Wheel, was first discovered in 2005/6 and the authors have been performing follow up observations and digging up archival data on the object ever since. After first being discovered in the optical region, the authors dug up Near Infrared, Mid Infrared, Far Infrared and Radio observations. The authors also pursued follow up spectroscopic observations of specific regions of the object.

I think I should take a step back to give you a look at the bigger picture. Every once in a while, we see galaxies interacting. I'm sure you've heard by now that our own Milky way galaxy and Andromeda are on a path to collide sometime over the next billion years and will end up being one big mess of stars and gas. Similarly, in the past, a lot of galaxies have interacted with our Milky way galaxy. And if we look out into space, we will …

First science from New Horizons of Pluto

The first official scientific publication from the data New Horizons has sent back to us got published last week and it's open access, available here. In my opinion, it's fairly accessible to the layman or one who's familiar with the basics of geology and basic science.

Broadly speaking, the paper talks about their observations of Pluto and it's three moons Charon, Hydra and Nix. Towards the end of the paper, they also talk about upper limits on size of possibly undiscovered moons and the the properties of a ring system, if any is present while still undetected. Going into the details, they talk about the changes in albedo (reflectivity of a surface) on Pluto's and Charon's surfaces and what the reasons might be. There are also numerous surface features, from ridges to valleys, from craters to mountains, from glaciers to possible sublimation pits. The paper discusses these diverse geological features and their possible origins. The paper also talks about the a…

Sifting through photographs : The comet 17P/Holmes' orbit from images on the WWW

I watched this video a long long time ago, where Dr. David W. Hogg using images publicly available on the internet to do science. Case in point is this paper they published where they tried understanding the trajectory of the comet 17P/Holmes from astrophotographers' images online. They searched for images of the comet, after it brightened and public interest in it had gone up. They then tagged the images to know what part of the sky they were looking at using astrometry.net. They then did some math, which I will hopefully understand one day, to weigh different images depending on their authenticity and how their metadata of when the images were taken was compared with their predictions of when the comet was in the field of view of the picture. One day. They were, in fact, finally able to reconstruct the orbit of the comet, albeit a slight error.

The video mentioned above gives more examples of such, including one awesome example where they rediscover stellar tidal streams observ…

FIGGS : The Faint Irregular Galaxy GMRT Survey

For those who don't know, GMRT stands for the Gaint Meter-wave Radio Telescope. Meter because it observed radiation with wavelength of about a meter or about 300 MHz. Ohkay, with that out of the way, let's talk about the actual paper.

If you have been following my blog posts, you will understand why studying faint, irregular, dwarf galaxies is important. Faint dwarf galaxies have very low mass and understanding them will help us understand galaxy formation and evolution in the low mass case. Another interesting thing I learnt from the paper, that should've been obvious to me earlier, is that the gravitational force keeping the (gas in the) galaxy together is about the same as that produced by a few supernovae. The reason they are irregular makes sense now because once these galaxies start forming their first stars, which then go on to explode, the galaxy's gas gets pushed out by the explosions. Also interesting is figure 12 from the paper, that tells us that most of t…

Decadal vision document, Astronomy & Astrophysics - Indian Academy of Sciences & Astronomical Society of India

Decadal reports are used as a sort of a road map, a review of the current trends in the field, of what the field is moving towards in the next decade and recommendations put forth which can be used by the governing bodies to dispatch funds appropriately. I have come across decadal reports by the American Astronomical Society (AAS) and by the Astronomical Society of Australia (ASA) but only now have I come across one by the Astronomical Society of India (ASI)
Decadal vision document : Astronomy & Astrophysics (PDF file, 27 MB)
I skipped right to the recommendations part and I had my mind blown. Let me give you a brief summary of the recommendations put forth by the committee.
1. Bringing together the community to consolidate work and form Autonomous Working Groups spanning the astronomical research being carried out. The groups can bring together astronomers working on theory, observations and simulations to give a holistic picture. Working groups also help foster younger talent an…

This week's pocket reading list : Week 2 of Oct

Chinese scientists row over long-sought protein that senses magnetism : If you don't know already, all(?) birds and some animals can sense magnetic fields. Birds use the Earth's magnetic field to be able to migrate long distances. This article is about the story of how one researcher discovered the exact protein that the animal body uses to detect magnetic fields and how another researcher from a neighboring institution apparently broke an agreement between the two to wait for the first one to publish. Collaborations are commonplace in academia, more so now than ever before, and the legal ramifications of such collaborations where a large amount of money (and of course pride) is (are) involved are still in murky waters.

Curiosity wheel damage: The problem and solutions : I hope you know that NASA put a new (yes, there have been ones before it) rover on Mars called Curiosity and it's been there for over an year now if I'm correct. If you know about Curiosity, you probabl…

New born stars and the State-of-the-art.

If large cameras and telescope capable of probing the low surface brightness objects in the sky is one end of the state-of-the-art in astronomy, the following work would be the state-of-the-art at the other end of the spectrum. While surveys focusing on looking at all of the objects in the sky, choosing speed and number of astronomical objects found over spatial resolution, there are telescopes used specifically to study objects at the highest spatial resolution.

The paper (found here) talks about a narrow, edge-on disk resolved around the star HD 106906 using the SPHERE instrument on the VLT telescope. Note that I used to word resolved and not detected. For an astronomer, those two words are vastly different. The same way dark matter is discovered but not yet observed, astronomers knew that the aforementioned star had a dusty disk around it. How you ask? Well, for starters, if you have dust in front of a light source, the light source looks dimmer. Secondly, whatever light that the …

Maarten Schmidt and Jayant V. Narlikar : An Astronomer's life.

Well, I guess, if I'm being pedantic, Dr. Jayant V. Narlikar is more of a cosmologist and Dr. Maarten Schmidt is the astronomer, I guess. Moving that aside, they are two heavy weights in their respective professions and we younguns have a lot to learn from them.

I came across this autobiography (of sorts) of Dr. Maarten Schmidt wrote for the Astronomy & Astrophysics Annual Reviews journal, It's a beautiful account of his professional life as an astronomers, where all he traveled for the job and a historical perspective on what many astronomical concepts we now consider to be set in stone.

While I read the earlier article a long time back, I am only now coming around to post it here because I read this other biography [1] of Dr. Jayant V. Narlikar and his work by one of his colleagues Dr. Naresh Dadhich. You probably know Dr. Narlikar as one of those scientists who came up with the steady state theory of the universe, you know that theory that competed with the Hot big ban…

The TMT, India and the Indian astronomical community.

I am crazy about the Sloan Digital Sky Survey (SDSS). I worked on data from the SDSS for my first summer project. I learnt about SQLquery to acquire data from the SDSS's servers and I learnt Python to do the relevant data analysis. It's an unbelievable treasure trove of data and is in my opinion, the best place to start off if one is serious in pursuing a career in astronomy. Having said that, a while back I was looking at the various institutional members of the SDSS and I found out that there were NO Indian institution involved with the project. None whatsoever. Now, don't get me wrong, I'm sure that there were Indians involved in the project. I'm saying that there was no institutional support meaning that Indian universities weren't funding the project or actively building instruments for the project or had priority access to the data. And it kind of made me sad.

The good news now is the fact that India is a 10% partner in the Thirty Meter Telescope (TMT), …

Ohh my! 158 new dwarf galaxies discovered using the DECam!

Well, for starters, the DECam is the Camera on the 4-metre Blanco telescope at the CTIO (Cerro-Tololo Inter-american Observatory). It was originally designed for the DES (Dark Energy Survey) but I guess it's also being used for other astronomical observations. The authors are part of the NGFS (Next Generation Fornax Survey) efforts at the CTIO.

Coming to the paper (found here), the authors give a preliminary report of the 158 new dwarf galaxies they've discovered in the Fornax cluster central regions. There is a lot more science to come out of the data but a preliminary analysis shows that the dwarf galaxies seem to be clustered within the Fornax cluster core, clustering previous predicted in simulations. The authors also fit the surface brightness distribution for each of the dwarf galaxies found to estimate their effective radii. The dwarfs found seem to be fainter and smaller than similar ones (referred to as Ultra Diffuse Galaxies - UDGs) found in the Virgo cluster and th…

HI Rogues

As I follow the endless path, looking for references in papers, I came across this - the HI rogues gallery. It is a "Collection of maps of HI in Weird Galaxies and Weird HI in otherwise Normal Galaxies" and wow is it a beautiful collection.

The whole reason astronomers are interested in HI (neutral Hydrogen) in the universe is because it is the fundamental fuel that makes stars. Also, there's loads and loads of it in galaxies and in the Inter-galactic medium (theoretically).  And in galaxies, this HI extends wayy beyond the boundary defined by the stellar population of the galaxy. This fact can be used to understand the (baryonic) gravitational potential of the galaxy it is embedded in, and the dark matter halo it is embedded in. If you dig through the gallery, you will come across interesting examples showing intergalactic debris with no optical counterparts! This is interesting as it helps us understand the history of the galaxies, their environments and the distribut…

Dwarf galaxies and all-sky HI surveys FTW \m/

I've been coming across a lot of work, in the optical and the radio domain to identify and understand dwarf/satellite galaxies, stellar tidal streams and neutral HI (HI is neutral Hydrogen and HII is singly ionized hydrogen i.e a proton) in the universe. This is one of many such efforts (a few of which I will write about later on) where the authors used the SKA pathfinder telescope BETA/ASKAP to observe the galaxy group IC 1459. The full paper can be found here.

Let me first tell you why it's a challenge to observe neutral HI in the local universe and why these results are so interesting, IMO. All galaxies form from HI (again, neutral Hydrogen) but once the galaxy/stars start(s) forming, neutral HI close to the sources of radiation get ionized into HII. Only HI in the outer reaches of the galaxy is left unionized. And given that it's at the edge of the galaxy, it's not nearly dense enough to emit strongly. Don't get me wrong, there is still a good amount of HI in-…

Why did I not know that there was a UV telescope on the MOON!!!

Well, I got to know a couple of days back that there was a Lunar-based Ultraviolet telescope. I finally got to read the paper today (that can be found here) and it's quite interesting. For those of you who remember, the Chinese landed a Lander on the moon and tried sending a rover on the lunar surface (which quickly failed). Apparently, that Lander had a UV telescope on it.

As soon as I read the abstract, the first questions that came to my mind was when exactly they observe. If you think about it, we see the moon at night because it reflects the sun's light meaning that if it's night time for us, it is day time on the moon. The same way, if I were on the moon, I'd be able to see the earth because it will reflect the sun's light. Astronomers on earth prefer moonless nights because the night skies are darker. In the same way, the lunar based telescope had to take into account the fact that earth shines bright at night time when designing their telescope and plannin…