The Zooniverse

I’m delighted to announce that the latest paper based on Galaxy Zoo classifications was accepted to appear in the Monthly Notices of the Royal Astronomical Society earlier this week, and appears on the arxiv this morning (link will be here when I have it).

Usually there is a long delay between submission and acceptance of papers (something Kevin discussed on this blog in “What Happens Next – Peer Review“), but in this case the initial referee report came back after 2 days, and the paper was accepted only 2 weeks after the first submission so I never got time to post to the arxiv or write a blog post about it before it was accepted! This was certainly the smoothest and fastest referee process I’ve been through.

Here’s the title page.

So what was new about this paper was that we combined information on the morphologies (whether or not the spiral galaxies had bars) with information on the amount of atomic hydrogen gas the galaxies contained and and our main result was that galaxies with more atomic gas in them, are less likely to have a bar.

But I want to back up a bit first and tell you about where we get this information on the atomic gas content, and why it  might be interesting. As you might guess from the title of the paper it’s from something called the ALFALFA survey (and the new names in the author list for a Galaxy Zoo paper – Martha Haynes and Riccardo Giovanelli – are from Cornell University who are running this survey). Atomic hydrogen emits radio waves at a frequency of 1.4 GHz (or 21cm). This is detectable by a classic radio telescope (in what we call the “L”-band which makes up the second L of ALFALFA). In the case of ALFALFA, we use the Arecibo radio telescope (two of the “A”s in the acronym stand for Arecibo, the third is for array), which is the worlds biggest single dish radio telescope deep in the jungle of Puerto Rico.

Aerial shot of Arecibo. Credit: NAIC.

ALFALFA is a massive survey which will map the location of atomic hydrogen over basically the whole sky visible to the Arecibo radio telescope. What’s neat about a survey for something which emits as a specific frequency is that you actually get a 3D map of where the hydrogen is – both redshift and sky position! Anyway, we made use of about 40% of the survey which is already complete, and which covers about 25% of the area of the sky in which the Galaxy Zoo galaxies are found (the Sloan Digital Sky Survey Legacy Area). Adding some cuts on how face-on the galaxies are so that the bars can be identified, and to make sure the sample contains the same size galaxies right through it’s volume we ended up with 2090 galaxies with both atomic hydrogen detections and bar classifications from you guys. This is an order of magnitude larger than any similar sample! So thanks.

Atomic hydrogen is the basic building block of galaxies (after dark matter). It represents the fuel for future star formation in a galaxy – a galaxy with a lot of atomic hydrogen could in principle make a lot of new stars. Many spiral galaxies have a lot of atomic hydrogen (with perhaps as much as 10 times as much mass in hydrogen as in stars!), while a typical elliptical galaxy has very little atomic gas, and so cannot form lots of new stars.

So our observation that bars are more likely to be found in spiral galaxies with less atomic gas supports our earlier ideas about bars possibly “killing” spirals (ie. helping to stop them form stars).

Trends of bar fraction with atomic gas content, galaxy colour and how many stars are in a galaxy.

Of course it’s never quite that straightforward with galaxies. To start with correlation is not the same as causation, and to that we add that lots of things are correlated. We show some of that in the figure above. Bars are more likely in redder spirals which have more stars (“log Mstar” represents stellar mass in units relative to the mass of our Sun) and which also have less atomic gas. So the skeptical astronomer could say this has nothing to do with the gas content at all, just that the types/sizes of galaxies with less bars have more gas. To test that idea we measured the typical gas content of a spiral galaxy with a given number of stars, and from that we calculated how “deficient” or rich in atomic hydrogen any given galaxy was. Then we plotted the bar fraction against that. The convention in astronomy is to call how much less atomic hydrogen a galaxy has than normal it’s “HI deficiency” which gets bigger the less atomic hydrogen there is (from the people who brought you the magnitude scale!).

Bar fraction against how much more or less atomic gas a galaxy has than is typical for the number of stars it has. Bigger HI deficiency = less atomic gas than is normal for a galaxy’s size.

Anyway you can see we still see a clear trend, which demonstrates that it’s likely to be the atomic gas driving the correlation. Where a galaxy is richer in atomic hydrogen than normal it’s less likely to host a bar, and vice versa. Very atomic hydrogen rich galaxies which are massive and have bars are really quite rare!

Here are some examples of low and high mass galaxies which are gas rich or poor and with or without bars.

Example images.

I made images of the whole sample we use available here.

At the end of the paper we put forward three possible explanations for the correlation, all of which fit in with the observations we presented. It’s possible that the bars are causing the atomic gas in galaxies to be used up faster – “killing” the galaxy. The bar does this by driving the gas to the centre of the galaxy where it gets denser, turns into molecular hydrogen and from that stars (but only in the centre). It’s also possible (based on dynamical studies of galaxies) that gas slows down the formation of a bar in a spiral galaxy, and/or destroys the bar. Finally it’s possible that as a galaxy interacts with its neighbours, a bar gets triggered and its gas gets stripped (ie. the correlation between the two is caused by an external process). We’ll need to do more work to figure out which of these (or which combination of them) is the most important.

To my mind the most interesting result was a hint that if a gas rich galaxy does (rarely) host a bar, it’s optically redder than similar galaxies without bars. It’s just possible that bars hold back infall of gas from the outer regions of a spiral galaxy and slow down star formation over all in that galaxy. That idea needs testing, but if it’s true it’s saying that an internal structure like a bar plays an important role in the global star formation history of a galaxy.

Anyway thanks again for the classifications, and I hope the above made at least some sense!

In June 2012 people all over the world will watch the planet Venus transit across the Sun. Planet Hunters is all about spotting planets as they move across the face of a star so we thought it would be good to share the event with everyone. Venus will pass directly between the Earth and Sun on the night of June 5th and the morning of June 6th. This historic event can be seen from many parts of the world and will not happen again for 105 years!

As the map above shows, most people will only see part of the transit. With the help of the GLORIA team, we’ll be showing a live feed of the whole event on the Planet Hunters site. The webcast is being streamed from Tromsø, Sapporo and Cairns and will feature commentary in English and Spanish during the key parts of the event.

Check out our guide to the Transit of Venus, which we’ll update as we approach the event itself. It covers a basic history of the transits, and include information on when and where to see it. It also links to other useful resources for the event, including a Transit Guide from the GLORIA group, and the NASA observers handbook links. We hope you’ll try to see the transit when it happens, but if you’re unable to for some reason, then the webcast means that you can still be a part of this last-chance astronomical event.

Fresh off the telescope, here’s a first view of the “Voorwerpje” gas clouds around the Seyfert galaxy Markarian 1498. Its nucleus, shown in our Lick and Kitt Peak spectra, is a type 1 Seyfert, meaning that we see the broad-line region of gas very close to the central black hole, moving at high velocity. Those data showed highly-ionized gas to a radius of at least 20 kiloparsecs (65,000 light-years). Its nucleus is too dim to account for the ionization of the extended gas clouds, which landed it a spot in our list of seven objects for the Hubble proposal. Getting these data now was an unexpected treat – they were originally scheduled to be taken next November. As another bonus, the good people at the Space Telescope Science Institute just last week implemented the software to deal with charge-transfer problems in the Advanced Camera CCDs, right in the pipeline, improving the image quality a lot (it took months to get to this point with the Hanny’s Voorwerp data). And here it is, Markarian 1498 in a combination of [O III] emission (green) and Hα (red):

This is… interesting. From the few of these galaxies where we have data so far, loops of ionized gas near the nucleus may be a recurring theme. I could add speculations on what we’re seeing in Mkn 1498 – but for now, I’ll just let everyone enjoy the spectacle.

Today we have a guest post by Jules, fellow Planet Hunter and zooite who attended the ZooCon1. Jules is a lead moderator and blogger for the Solar Stormwatch and Moon Zoo forums as well as a volunteer on the Zooniverse Advisory Board.

Just back from the very first #zoocon1 in Chicago. I attended as a volunteer on the Zooniverse Advisory Board. As Meg said it was a chance for the science teams from new projects to meet with and learn from representatives of current projects and for everybody to meet up with Zooniverse techies and developers. It made sense then for some of the “old hands” to present an overview of their own projects. Meg’s Planet Hunters talk was particularly interesting as it highlighted the value of Talk and the great collaborative work being done there by volunteers.

A brief foray into data reduction showed the kind of work necessary to make the clicks usable. For example, there are 5,508 stars with possible transits. Removing all pulsating stars, which can be mistaken for transits, reduced the number of candidates to 3,404. Further examination of these transits reduced the pool further to 77 transit candidates – a much more manageable number.

Here’s Meg in action demonstrating the light curves of different sized planets.

The discoveries Meg highlighted included a slide showing 4 planet candidates missed by Kepler one of which is being re-investigated because of the work done by Planet Hunters. Kepler 16, the circumbinary system, also got a mention as did the impressive volunteer-led analysis on cataclysmic variables and heartbeat stars.

Old Weather, Mergers and the Milky Way Project were also put in the spotlight. Afterwards someone from one of the new projects told me how amazed they were that volunteers would want to do more than just click and another told me that they found the Planet Hunters story particularly inspiring and wanted to know how Planet Hunters had attracted these “awesome people.”

Well that’s Citizen Science for you. Volunteers come with a great mix of interests, skills and the knack of finding treasure!

The ‘Lake of Death’ (Lacus Mortis) lies in the northeastern part of the Moon, north of Mare Serenitatis, and is either an ancient crater or a basin, which has been flooded by lava. It is about 150 km in diameter with the crater Burg, which was formed less than a million years ago, situated approximately in the centre. Lacus Mortis was named by selenographer Giovanni Riccioli in 1651 but he gave no reason for its strange name.

Lacus Mortis also contains one of the few “true” faults found on the Moon and you can see it (marked with an orange arrow) in the image below starting at the southern boundary of Lacus Mortis and going north before finally turning into a rille. (See the first link under Useful Links for more images of the fault).
The western half of Lacus Mortis also contains several rilles, the main one of which is Rimae Burg which is over a 100 km in length and is a graben. Where this rille crosses the boundary between Lacus Mortis and the highlands in the southwest, there are some volcanic cones – see link #4 under Useful Links for more information.

[ACT-REACT Image]

ACT-REACT Link

A larger image containing feature names will be found here: LROC Context Image

Burg crater, within Lacus Mortis, is worth exploring as it has many boulder tracks and some nice landslide textures on the western crater wall. See links #2 and #3 under Useful Links for more information.

Strip: M113778346LE
Boulder tracks within Burg crater

Landslide textures from inner wall of Burg crater, western side.

Useful Links

A true fault in Lacus Mortis: Lacus Mortis Fault

Boulder tracks within Burg crater: A Gathering in Lacus Mortis

Description of Burg crater: Not your average complex crater

Volcanic domes: Volcanoes in the Lake of Death

A mystery! Tidbits of Strangeness

All credit for this entry goes to forum regular kodemunkey who wrote this article:

Hello, and welcome to what will hopefully be the first of many IOTW posts from me.

I was exploring the LRO Data using the WMS Browser and I came across Maginus crater.

(Maginus crater, as seen in the WMS browser, latitude -48.992774 longitude -5.149416)

This is what Wikipedia has to say about the crater:

Maginus is an ancient lunar impact crater located in the southern highlands to the southeast of the prominent crater Tycho. It is a large formation almost three quarters the diameter of Clavius, which lies to the southwest. Just to the north of Maginus is the smaller crater Proctor, and to the southeast is Deluc.

The rim of Maginus is heavily eroded, with impact-formed incisions, and multiple overlapping craters across the eastern side. The wall is broken through in the southeast by Maginus C, a worn crater. Little remains of the original features that formed the rim of Maginus, and it no longer possesses an outer rampart. The floor is relatively flat, with a pair of low central peaks.

The thing about Maginus that interested me at the time was the unnamed crater near Maginus A, as it has a lot of NAC frame coverage. I’m certain that like me you prefer to look at areas with a lot of coverage, if only out of sheer nosiness!

The thing that first caught my eye about the crater was this large, and probably quite deep crack:

The next thing to catch my eye are these huge boulders which are blocking the flow of material down the slope.

These things are quite large, probably at least the size of a house, I wonder where they came from?

Sources and more information:
http://bit.ly/M59Okp

http://bit.ly/JFj1Tt

NAC frame: http://bit.ly/JFj29H

Your task, should you choose to accept it (even if you don’t ) is to try and figure out how the boulders came to be in their present positions.

Long time Zookeeper Steven Bamford has made a new website on which you can easilly write any words you like from the galaxy alphabet.He’s called the website: My Galaxies – Write in Starlight!

Enjoy!

Today we have a guest post by fellow Planet Hunter Daryll (nighthawk_black) updating us on the search for dwarf novae and cataclysmic variables. Daryll’s here to talk about a dwarf nova candidate found in PH Talk.

Hi Planet Hunters,

Following the guest post from GO Director Martin Still, a review of light some light curves discussed on PH Talk turned up  an interesting target somewhat similar to the serendipitous Dwarf Nova known as NIK 1. First noted by myself and several volunteers as a possible cataclysmic, we believe this to be another SU UMA type variant with over 50 quasi-periodic brightness changes observed and a defined superoutburst,  in the public Q6 data.

The activity is not visible in all quarters. An examination of the accompanying target pixel files (these are files created by the Kepler processing pipeline that show the brightness over time for each of the pixels that are added up to make a Kepler light curve and those surrounding that don’t go into making the light curve – they can help you see if the features in the Kepler light curve come from the target star or something nearby that is contaminating the target’s star aperture) reveal that the true source of the dwarf nova candidate lies in the background and likely originates from an adjacent source tagged as KID-11412049, leaving how much activity we see in the original light curve dependent on the differing aperture pixel masks used for each Quarterly roll. Unfortunately it does not appear to be an eclipsing arrangement nor has it displayed any transiting circumbinary companions.

We asked the science team to take a look at this star and they think it looks like a good dwarf nova candidate. The PH science team has applied for Directors Discretionary Time seeking additional observations in the coming Quarter (we’re all waiting to hear back if the Planet Hunters proposal has been approved) to learn more about this system including its outburst supercycle, accretion disc stability and component compositions. Early analysis indicates high mass transfer with a notably short orbital period of 76 minutes; a GALEX survey shows this location also appears to be associated with a UV source.

Screening out background binaries from transit candidates is something the community has gotten pretty sharp at and I believe more of Martin’s missing Dwarf Nova will turn up. If confirmed, this will be the 5th Superoutbursting DN in the Kepler FOV and the 17th total, so well done and keep up the eagle-eyed hunting!

A little while ago Sarah Fitzmaurice, a work experience student at Zooniverse Oxford, spent a week working with the Milky Way Project database. She did some fun things with the data, including plotting the locations of many of the bubbles according to their distance from us. For many, the current canonical view of our own Galaxy comes from a combination of data sources, compiled by Robert Hurt, working at NASA JPL. The image is shown below, and you may recognise it: we use it as our Twitter/Facebook avatar. It is an artist’s impression based on several data sources and guided by astronomers.

The Milky Way may be our home in the Universe but we know startlingly little about it. On key missing piece of information for many objects in our Galaxy is their distance from us. From the Spitzer data alone, we do not know the distance to the bubbles in the MWP. For our first Data Release paper, we compared the MWP Bubble catalogue to known objects, some with distances, and this allowed us to find  out how far way some of the bubbles are. This enables us to investigate how large and sometimes how massive they may be.

During her work experience week, Sarah plotted the bubbles with known distances onto Robert Hurt’s map of the Milky Way. The result is shown below. The bubbles are marked with crosses, and the size of the cross shows the relative size of the bubble. The distances to these bubbles were derived by comparing them to a known set of radio sources that are expected to look like bubbles in Spitzer data.

You can see that the bubbles generally follow the distribution of spiral arms and that it is easier to see the bubbles nearby than those farther away. This is good because it is roughly what we expect. This map also allows us to easily spot the isolated, nearby or most-distant bubbles in the project. Much of Sarah’s week was spent looking at each of the interesting bubbles and finding out some more about them.

Although there may well be more distant bubbles in the catalogue, Sarah’s map provides a candidate for ‘most distant bubble’ in the MWP. It is one of a pair of bubbles located on the far side of the Perseus arm, almost 45,000 light years away from the Sun – in the top part of the above image.

Using the new MWP coordinates tool we can take a look at this distant object, and two nice images of it are shown below. Our ‘most distant bubble’ is actually located within another larger, clearer bubble, the image of this is also given. This is a line-of-sight effect and they are not necessarily near each other.

This bubble is located literally on the other side of our Galaxy and is roughly 15 light years across. The fact that the two bubbles are positioned on top of each other makes it hard to decide which one is farther away. There are many more instances where bubbles lie on top of each other where it would be impossible to decide which is actually on top of which. The nebulous material of which these objects are made makes them hard to disentangle. In this case there are stars and IR objects on top of the smaller bubble that make it easier to pick out the nearer and farther bubble.

In this case, the distance value is derived from a radio source that we expect to be associated with a bubble. Both of these bubbles lie at roughly the correct position to be associated with the radio source. Since we know the radio source is very far away, we can say that the smaller bubble is most likely the object associated with the radio source.

These kinds of confusing caveats are one of the things that make Galactic astronomy difficult and challenging. For these reasons, this might be the most distant bubble we know of in the MWP – or it might not. Either way, this awesome little bubble has provided the opportunity to discuss the ways that we determine the distances to objects in the MWP catalogue, and how doing astronomy in our cosmic backyard is tricky territory indeed.

Image credit: Michael Parrish

Greetings from Adler Planetarium in Chicago. I’m at the first Zooniverse Science Conference. I’m here representing the Planet Hunters science team.  At this conference science teams from the current and upcoming Zooniverse projects and the Zooniverse development team have gathered together to talk citizen science.  It’s been a great two days of  presented talks and discussions. This is the first time that teams from across the Zooniverse projects have come together. I’ve really enjoyed talking to the scientists from the different projects, and what I’ve been really impressed with is the cool and wide-ranging science that is being done in the Zooniverse.  I’ve been hearing about the exciting future projects and new tools and features the Zooniverse is working on. This morning I shared the highlights from Planet Hunters and how I’m going from clicks to planet candidates.  It was great to highlight all the science we’ve done and will be doing in the future with your classifications on Planet Hunters. I focused on my search for short period planets from the Quarter 1 classifications (on a side note – I got a response from the referee for my paper. I’ve revised the manuscript and the paper is back with the referee. Hopefully soon it will be accepted for publication by the Journal).

Cheers,

~Meg

I was embarrassed to discover today that I never got around to writing a full blog post explaining our work studying the properties of the red spirals, as I promised way back in October 2009. Chris wrote a lovely post about it “Red Spirals at Night, Astronomers Delight“, and in my defense new science results from Zoo2, and a few other small (tiny people) things distracted me.

I won’t go back to explaining the whole thing again now, but one thing missing on the blog is the colour magnitude diagram which demonstrates how we shifted through thousands of galaxies (with your help) to find just 294 truly red, disc dominated and face-on spirals.

A colour magnitude diagram is one of the favourite plots of extragalactic astronomers these days. That’s because galaxies fall into two distinct regions on it which are linked to their evolution. You can see that in the grey scale contours below which is illustrating the location of all of the galaxies we started with from Galaxy Zoo. The plot shows astronomical colour up the y-axis (in this case (g-r) colour), with what astronomers call red being up and blue dow. Along the x-axis is absolute magnitude – or astronomers version of how luminous (how many stars effectively) the galaxy is. Bigger and brighter is to the right.

So you see the greyscale indicating a “red sequence” at the top, and a “blue cloud” at the bottom. In both cases brighter galaxies are redder.

The standard picture before Galaxy Zoo (ie. with small numbers of galaxies with morphological types) was that red sequence galaxies are ellipticals (or at least early-types) and you find spirals in the blue cloud. The coloured dots on this picture show the face-on spirals in the red sequence (above the line which we decided was a lower limit to be considered definitely on the red sequence). The difference colours indicate how but the bulge is in the spiral galaxy – in the end we only included in the study the green and blue points which had small bulges, since we know the bulges of spiral galaxies are red. These 294 galaxies represented just 6% of spiral galaxies of their kind.

So this is one of my favourite versions of the colour magnitude diagram.

The 15th edition of the Encyclopaedia Britannica runs to 32 large volumes, each of about 1000 pages. The million pages of logs we’ve transcribed would take up more than 30 times as much space on the shelf.

Today oldWeather has passed another remarkable milestone: we’ve now transcribed 1 million logbook pages. 1,000,000 or 10⁶ – however you write it, that’s a big number.

The logbooks have large pages, so think of a big, heavy book – let’s say a volume of the old Encyclopædia Britannica. Those have about 1000 pages each, so we’d need about 1000 such volumes to make up a million pages – more than 30 copies of the entire Encyclopaedia (15th edition).

Alternatively, consider the average American, who reads 9 books a year. If a typical book is 300 pages in length, we’ve done as much reading as that average American does in about 350 years. We haven’t been skimming the logs, either: It takes, on average, about 2 minutes to read and transcribe each log page.

So we’ve spent 2 million minutes with our collective nose in a log – a task which would have been quite impossible without the combined efforts of thousands of project participants. And what treasures we’ve found in there: As well as millions of invaluable weather observations, we’ve followed stories of war, sickness, celebration, drunkenness, heroism, tragedy, partying, … Surely a better read than any novel.

The image at the head of this post was shamelessly stolen adapted from Wikipedia.

We’re very pleased to tell you that we’ve been awarded developer time from the Citizen Science Alliance to build a new, exciting Zooniverse project to discover gravitational lenses.

What’s a gravitational lens, you might ask? When a massive galaxy or cluster of galaxies lies right in front of a more distant galaxy, the light from the background source gets deflected and focused towards us. These space-bending massive galaxies allow us to peer into the distant Universe at around 10x magnification, and to make accurate measurements of the total (dark and luminous) mass of galaxies.

As many of you know, there has been a long-running and enthusiastic search for lenses in the “weird and wonderful” part of the forum; although lens-finding was never a goal of the Galaxy Zoo project, this forum has turned up some interesting systems which we are still following up. Up until now, the GZ lens search has been quite informal: it has not been easy keeping track of all the candidates that have been suggested! Nevertheless, the Lens Hunters have done an amazing job, collecting and filtering the suggestions as they come in, and teaching themselves and each other about the astrophysics of lensing.

Impressive stuff: enough to persuade a group of professional astronomers that a specially-designed Zoo for identifying lenses could be a powerful way of analyzing the new wide-field imaging surveys that are coming online. In this Lens Zoo we will be able to provide you with new tools – designed, we hope, with you – to find new lenses more effectively. We have teamed up with astronomers from several big surveys who are eager to harness your citizen science power, and will be providing a lot of new, high quality data to be inspected. Over the next 6-10 months we’ll be working hard with the Zooniverse developers to build the Lens Zoo, and we hope you will join us for the ride: Lens Zoo needs you!

Phil, Aprajita, Anupreeta & the Lens Zoo team.

Overnight, Hubble got our first data on perhaps the most spectacular Voorwerpje host galaxy, the merging system UGC 7342. We have to wait until almost the end of the year for what we really wanted to see, the ionized gas. The telescope has particular time pressure in some parts of the sky (as if it doesn’t have extreme time pressure on everything people want to do with it), so we split the two sets of images to fit the schedule better. This time, we got data in WFC3 for two medium-width filters in the orange and deep red, selected to be essentially blind to emission from the gas. These will be used to subtract the contribution of starlight from the gas images, so we can analyze the gas properties cleanly. The emission-line images use the older ACS camera, which has a set of tunable filters which can isolate any optical wavelength we need. They come at year’s end, because we have to specify a particular range of orientation angle of the telescope to fit all the gas in their 40×80-arcsecond filter field. That, plus the requirement that the solar arrays can face the Sun directly, gives us a restricted time window.

As a reminder, here’s UGC 7342 from the SDSS data.

And here is a first look at the Hubble images, warts and all. With only the two filters in orange and deep red, the color information we get is pretty muted. Here’s the whole galaxy, shrunk 4 times from the original pixel scale to fit:

This show the companion and tidal streamers of stars. UGC 7342 itself shows shells of stars, which can be formed when a lower-mass disk galaxies merges with a more massive elliptical. With some additional velocity information, those might be able to give a time since the merger (with some tailored simulations). The elliptical reflections are from bright foreground stars outside this trimmed view; the emission-line images will at least have these in different places, using a different camera and different telescope orientation.

Zooming in 4 times to the nucleus shows that UGC 7342 has complex dust lanes crossing in front of the core. These are perpendicular to the directions where we see that distant gas is ionized by radiation from the nucleus, which is pretty common. The fact that the dust (and almost certainly associated gas) wraps at right angles to most of the structure in the galaxy is another indication that a merger took place recently enough that the situation hasn’t settled down into a long-lasting remnant.

Next up? The scheduling windows for SDSS 1510+07, NGC 5972, and the Teacup AGN all happen in overlapping spans from June to August. Bring on the bits!

Inspired by today’s Astronomy Picture of the Day Image, here’s a quick post about the beautiful nearby spiral galaxy, Messier 106 (or NGC 4258).

M106 Close Up (from APOD) Credit: Composite Image Data - Hubble Legacy Archive; Adrian Zsilavec, Michelle Qualls, Adam Block / NOAO / AURA / NSF Processing - André van der Hoeven

This is a composite Hubble Space Telescope and ground based (from NOAO) image. The ground based image was used to add colour to the high resolution single filter (ie. black and white) image from HST.

M106 has traditionally been classified as an unbarred Sb galaxies (although some astronomers claim a weak bar). In the 1960s it was discovered that if you look at M106 in radio and X-ray two additional “ghostly arms” appear, almost at right angles to the optical arms. These are explained as gas being shock heated by jets coming out of the central supermassive black hole (see Spitzer press release).

In this composite image of spiral galaxy M106 (NGC 4258), optical data from the Digitized Sky Survey is shown as yellow, radio data from the Very Large Array appears as purple, X-ray data from Chandra is coded blue, and infrared data from the Spitzer Space Telescope appears red. Credit: X-ray: NASA/CXC/Univ. of Maryland/A.S. Wilson et al.; Optical: Palomar Observatory. DSS; IR:NASA/JPL-Caltech; VLA: NRAO/AUI/NSF

Messier 106 (or NGC 4258) is an extremely important galaxy for astronomers, due to it’s role in tying down the extragalactic distance scale. A search in the NASA Extragalactic Database (NED) will reveal this galaxy has 55 separate estimates of its distance, using many of the classic methods on the Cosmic distance ladder. Most importantly, M106 was the first galaxy to have an geometric distance measure using a new method which tracked the orbits of clumps of gas moving around the supermassive black hole in its centre. This remains one of the most accurate extragalactic distances ever measured with only a 4% error (7.2+/-0.3 Mpc, or 22+/-1 million light years). The error can be so low, because the number of assumptions is small (it’s based on our knowledge of gravity), and as a geometrically estimated distance it leap frogs the lower rungs of the distance ladder.

This result was published in Nature in 1999: A geometric distance to the galaxy NGC4258 from orbital motions in a nuclear gas disk, Hernstein et al. 1999 (link includes an open access copy on the ArXiV). 

Because M106 has so many different distances estimated using so many different methods, and is anchored by the extremely accurate geometric distance, it helps us to calibrate the distances to many other galaxies. Almost all cosmological results, and any result looking at the masses, or physical sizes of galaxies need a distance estimate. 

So M106 is not only beautiful, it’s important.