LOFAR observation of beautiful galaxy, M87

I just posted the below over on the LOFAR-UK blog, but is also fits into my series of Messier Object posts - this one M87, which has a beauty in the eye of the beholder perhaps as a "boring" elliptical, but check out that jet from it's actively accreting supermassive black hole. Amazing!

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A paper appears on the arxiv today with new images of the centre of nearby elliptical galaxy M87, taken with the Dutch LOFAR stations.

M87 at Metre Wavelenghts: the LOFAR Picture, by de Gasperin et al. (A&A in press).

M87 (also known at Virgo-A) is one of the two massive elliptical galaxies found at the centre of our nearest cluster of galaxies (the Virgo cluster).

In the centre of M87 is a well know actively accreting supermassive black hole, which is emitting jets of energetic particles which emit significant amounts of radio. These jets are even (just) visible in optical images of M87 (the blue line below).

Optical image of M87 taken with Hubble Space Telescope. Scale 3x3 arcmins.  More details. 

M87 has often been a poster child for radio astronomy images. These images of the jet taken by the NRAO's VLA can be seen in many talks about radio galaxies and AGN.

M87 imaged at 90cm (300 Mhz) with the VLA. Scale 15x15 arcmin. More details. 

And especially this series of images zooming into the central regions.

For more details see the APOD entry for this image. 

The paper on the arxiv today used observations of M87 with both the HBA and LBA arrays of LOFAR. The Dutch stations only were used in this observation - adding in international stations like Chilbolton will be able to increase the resolution even further, and I will look forward to seeing that in the future.

I have extracted two of the images from the paper. This first was taken with the HBA at 140 MHz (2.1 m) and shows an area 15x15 arcmin in size (same as the VLA image above, but at wavelengths more than twice as large).

And this shows one of the many LBA images made - this one at 25 Mhz (12m) of a slightly larger sky area (21x21 arcmin). 

These new observations at lower frequencies than ever before allow scientists to better constrain the spectral shape of the radio emission from the jets, which in turn can be used to constrain the details of how the supermassive black hole in the centre of M87 is able to power these extremely extended emission regions.

Beautiful Galaxy M106

The next in my series of beautiful galaxies is inspired by today's Astronomy Picture of the Day Image.

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.  


I've cross listed this post at the Galaxy Zoo blog. 

Beautiful Galaxy M61

One of my favourite hashtags on Twitter is #bbcstargazing. During the programme I followed this to answer astronomy questions sent to it. Something I enjoyed the challenge of in 140 characters, and would love to continue if you tweet questions tagged #askastronomy.

Now the  #bbcstargazing hashtag is mostly astrophotographers posting their latest image. This morning the image being retweeted (RT) is this one of M61 taken by Daniel Marlow (@drm3107).

M61. Credit: Daniel Marlow

So it seemed like a good time for the next beautiful galaxy post - this one about M61.

Messier 61, is a bright spiral galaxy in the Southern extremity of the Virgo Cluster (our nearest large cluster of galaxies). It's notable astrophysically for having had 6 supernova observed in it, which apparently ties it with M83 as the Messier galaxy with the most observed supernova, but none of the supernova in M61 have been of the Type1a used to measure cosmological distances.

And the distance to M61 is a bit tricky to estimate. Being near the Virgo cluster whose large mass distorts the usual relationship between recessional velocity and distance you can't really just use the redshift of M61 to give it's distance, and other distance measurements listed in NED for M61 range from about 30 million - 90 million light years (10.1-35.5 Mpc). If it's at the distance of the centre of Virgo it's probably about 50 million light years away (16 Mpc).

Assuming that distance the size of M61 is quite similar to the Milky Way, and so is it's morphology. It's historical classification lists it as a weakly barred Sbc galaxy. It also host an actively accreting black hole in its centre.

Here is the Sloan Digital Sky Survey image of it:

M61: Credit SDSS

Another beautiful galaxy.

Links: LookUP on M61; SEDS on M61; NASA Extragalactic Database on M61; Wikipedia on M61.

A Supernova in Beautiful Galaxy M101

After starting my series of beautiful galaxies with Messier 100 I was amused to discover this morning that M101 (The Pinwheel Galaxy) is in the astronomical news after a possible Type 1a Supernova was discovered in it yesterday. So following M100 I obviously have to do M101 this morning!

M101 as seen in a mosaic of Hubble Space Telescope images added to some ground based data. Credit: NASA and Robert Gendler. For more info see APOD. 

M101 was classified in the Hubble Atlas as an Sc galaxies with a weak bar and a partial ring around the bar before the arms emerge (SAB(rs)c). It's illustrated twice in the atlas, with the largest illustration accompanied by text which describes it as the prototype of multiple armed Sc galaxies, what we might today call a "flocculent" spiral.

 According to the "Atlas of the Messier Objects", M101 is the third largest galaxy (in angular size) in the Messier list, and is visible as an extended object even through 10x50 binoculars (presumably only from a very dark site though). It definitely seems to be a popular deep sky object for amateurs, and following the SN1a discovery the AAVSO have put out a call for their members to get observing. Some predictions suggest the supernova is still brightening and could reach 10th magnitude - only 2 magnitudes fainter than Neptune (at its brightest).

 M101 has already been an important calibrating object for the extragalactic distance ladder having had its distance measured using many of the well known methods (e.g. the Leavitt Law (Cepheids), Tip of the Red Giant Branch, the Tully-Fisher relation). The most reliable distances have ranged from 6-8 Mpc (18-24 million light years or so) making the galaxy almost twice as large as our own Milky Way.

 The addition of a Type 1a Supernova in M101 would obviously be extremely exciting as a way to further link commonly used distance indicators. SNIa are an important type of object in astronomy - they are extremely bright, and therefore observable at very large distances. Much of the evidence for the acceleration of the expansion of the universe (which indicates the need for "dark energy") comes from measurements of SN1a at very large distances which suggest that in the past the universe was expanding more slowly than it is today!

 It will be interesting to see the result of the many follow-up observations of the SN in M101 - and exciting to think they are happening (on the other side of the world of course) as I write this.

Multi-wavelength views of stuff

I just know I'm going to want to find this again to use in a public talk, and it's fantastic so I want to share. "The Earth and Friends in Multiple Wavelengths", by Rob Simpson (@orbitingfrog). Of course galaxies are my favourite, so I'm reproducing the image of M31 (the Andromeda galaxy) in here (from top left to bottom right, radio, microwave, infrared, optical, UV, Xray).

And I like flowers too - so here's a geranium in optical (left) and UV.

Thanks for the excellent post Rob.

Beautiful Galaxy M100

I stumbled across a picture of the galaxy Messier 100 (NGC 4321) this morning, and just felt inspired to share it's beauty. I might share more of these as a way for me to learn the NGC numbers of some classic galaxy examples!

 So here it is - as seen by the Sloan Digital Sky Survey.

M100 as seen by the Sloan Digital Sky Survey

The central region has been observed by HST, which is also worth a look.

The central region of M100 seen by the Hubble Space Telescope.

And I encourage you to do a Google Image Search on Messier 100 to see the vast array of beautiful images of this galaxy (PS. avoid searching on M100 if you're squeamish. Yuck!).

M100 is a classic example of a grand design spiral, meaning it has clear well defined spiral arms. And look how far round they wind - it's lovely. Its classic classification (from the RC3 as listed in NED) is as an Sbc galaxy with a weak bar and an inner ring (SAB(s)bc). Apparently it's a similar size galaxy to our own Milky Way, and has played an important role in the history of extragalactic astronomy. This object is a member of our nearest large cluster of galaxies - the Virgo Cluster, and in 1994 was the first galaxy in the Virgo Cluster to have a distance measured to it using Cepheid Variables (via the Leavitt Law, see Freedman et al. 1994) which was an important step towards a reliable measurement of the Hubble constant.

Oh, and I should put in a plug for the excellent LookUP website, by @astronomyblog (Stuart Lowe). Check out the LookUP entry for M100 - turns out it also has a very interesting black hole - possibly the youngest known, and born in the same year as me. Cool!