Enjoy!

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 different 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.

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.

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!

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. 

That’s it for this run. But we’ll be back there late next month to really clean up the target list.

Meanwhile, there has been time to look over last night’s data and do some basic processing. Here, for example, is a quick and dirty composite image of Markarian 238 and its larger spiral companion from B and R images. The display is set to show the inner structures most clearly.

Markarian 238 and companion from Kitt Peak 2.1m images

(0710 UT, three hours later) The wind continues to howl under a frustratingly clear sky; some clouds are just appearing which may be parts of the predicted storm system. Gusts up to 83 mph (133 km/hour) have been recorded in the last hour. With the outside temperature less than 2 C, I try not to think of the wind chill.

(I’ll plan to update this over time).

And to all you cosmic partiers, happy Yuri’s Night!

(0345 UT) Got data in B and I filters on one pair, suggested particularly by JeanTate on the forum thread, but those images are pretty ugly because of stray charge from bright stars that will take some processing to fix. Now off to our best case for a spiral with extended dust and no sign of interaction to cause this.

(0507 UT) Looked at SDSS 103427.72+102506.2, still seeing evidence of dust lanes very far out in the galaxy disk. Now doing an edge-on system with dwarfish companion in front.

(0830 UT) Still working away between cloud patches. Now have data on SDSS 1002+1413, UGC 5528, NGC 3605/7. Working on NGC 4377. Reached the stage of night where Mahler seems appropriate to keep alert.

(1025 UT) Nice images of Mkn 238. Now taking a detour, Kazarian 199 for the AGN=companion Galaxy Zoo project. Data from the SARA 1m suggest [O III] clouds which might trace ionization cones, so I’m taking a closer look with the larger telescope. About 1.5 hours left in the night if I arrange the last couple of exposures with their filters in the right order.

Incoming data! This week I’m headed up to the 2.1m telescope of Kitt Peak National Observatory for more followup images of overlapping galaxies. This piece of the project traces to a serendipitous discovery in Hubble data which were intended to study the populations of stars in the outskirts of NGC 253, itself 10 million light-ears away. At the 2008 Austin meeting of the American Astronomical Society, the same one at which we saw the first spectrum of Hanny’s Voorwerp, Julianne Dalcanton of the University of Washington tracked down Benne Holwerda and me to show us this galaxy pair, which rejoices in the designation 2MASX J00482185-2507365:

HST image of backlit dwarf galaxy with dust filaments

Analysis of the dust in the smaller foreground galaxy showed something unusual – there are filaments of dust extending well beyond where we can detect the starlight in its disk. This had us looking for similar cases in the Galaxy Zoo overlap catalog, which should turn them up if any known sample will. It would be important to know whether many galaxies have such distant dust – first because it could alter calculations of how much extinction light from distant objects suffers as it passes intervening galaxies, and in addition because the connection between stars and the production of dust suggests that such galaxies have a complex history of the creation and transport of dust.

Our sample for this observing run centers on galaxy pairs broadly similar to 2MASX (what I wrote above). This kind of galaxy – small, perhaps true dwarfs, with dust in its outskirts – if common, would solve a question posed by recent statistical data from the European Space Agency’s massive Herschel infrared observatory (continuing its mission at four times the Moon’s distance as long as the liquid helium lasts). In the whole population of galaxies seen in deep surveys, some of their IR spectra would be best explained if a significant amount of their dust is so cold that it must lie far from the galaxy’s stars order not to absorb enough energy to heat it further. Our approach is to take CCD images with much longer exposures than the SDSS data, so we get better data quality in the outskirts of the galaxies and could detect dust filaments like those seen in 2MASX – whatsitsnnme.

The weather forecast at this point suggests that I may get about half of the time over our four scheduled nights (we have more next month). Watch this space for progress reports…

This sample is presented in the Galaxy Zoo 1 paper on AGN host galaxies (Schawinski et al., 2010, ApJ, 711, 284). It is a volume-limited sample of galaxies (0.02 < z < 0.05, M_z < -19.5 AB) with emission line classifications, stellar masses, velocity dispersions and GZ1 morphological classifications. When using this sample, please cite Schawinski et al. 2010 and Lintott et al. 2008, 2011.

Download here: http://galaxy-zoo-1.s3.amazonaws.com/schawinski_GZ_2010_catalogue.fits.gz

Column definitions are as follows:

• OBJID – SDSS object ID
• RA, DEC – RA and Dec in J2000
• REDSHIFT – SDSS spectroscopic redshift
• GZ1_MORPHOLOGY – Galaxy Zoo 1 morphology according to the Land et al. (2008) “clean” criterion. GZ_morphology is an integer where 1-early type, 4-late type, 0-indeterminate, 3-merger
• BPT_CLASS – 0-no emission lines, 1-SF, 2-Composite, 3-Seyfert and 4-LINER (see Schawinski et al. 2010 for details)
• U,G,R,I,Z -SDSS modelMag extinction corrected but not k-corrected
• SIGMA, SIGMA_ERR – Stellar velocity dispersion measured using GANDALF
• LOG_MSTELLAR – log of stellar mass
• L_O3 – Extinction-corrected [OIII] luminosity