Author Topic: Thursday July 12 2012; Meet BigFoot  (Read 8683 times)

PeterD

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Thursday July 12 2012; Meet BigFoot
« on: July 12, 2012, 07:36:12 am »



Meet BigFoot



AHZ4000098, Survey number 90001759, COMBO-17 06803, GEMS J033133.08-280048.9 ; Mag 22.76; a redshift of approx ~ 0.125, Chandra Deep Field South

AHZ4000098 was originally posted by djj  on the  Irregular Galaxies list and by Oswego9050 in Favourite Images and re-posted by djj on the Caterpillar list .
After a remark by Elizabeth that it "looks like a big foot" it rapidly became "BigFoot". Given the names that astronomers apply to objects that they don't much resemble [think Sombrero, Pinwheel, Cigar and above all the constellations], BigFoot at least is appropriate :-)

So what is it? The best bet is that it is a member of a group of objects called "Cluster Clump" galaxies (Elmegreene et al.. 2008, ApJ, 688, 67 ) which is what some of the  caterpillars may be. Cluster Clumps are believed to be an early stage in the formation of classical types of galaxies, principally spirals. Clumpy and Irregular galaxies may form as much as 50% 0f the population for z > 1.

In the Cluster Clump model the cloud of matter that will one day form the galaxy begins the process of local accretion and forms several nuclei, which start to form stars and in turn eventually coalesce to form the core and disk of the spiral. The individual blobs that you see are these star-forming nuclei. There is evidence that a class of similar-looking objects at higher z (z >> 1) may contain black holes at their centres (  see Schawinski et al 2011 ) - this is the formal version of  the talk zookeeperKevin gave at the Oxford GZ gathering) but for BigFoot to have BHs present would imply the much more recent creation of BH seeds than is widely believed.

Another recent paper discusses other mechanisms in star-forming, low-mass galaxies ("green peas") in the same redshift range as BigFoot ( z~0.1 - 0.3). It suggests that in the GPs there is rapid star-forming activity taking place and they have identified multiple turbulent knots with projected separations of between 0.4 and ~1 kpc. Interestingly they claim to be able to identify multiple (3 - 6) such clumps in GPs.


BigFoot's blue "cloud" is probably a mixture of independent stars and gas lit by the nuclei. The Caterpillars List contains a number of similar objects, as does the Irregulars List but one of the most striking things about BigFoot is that it contains so many nuclei. We have counted 14. Typically on the Caterpillars List the number of nuclei is between 1 and 7, with the commonest being 2 or 3. Not all the clumps are of equal brightness, some in the ball of the foot and at the heel being substantially less conspicuous than those elsewhere, which might be explained by a variety of mechanisms.

Overall BigFoot measures about 2.3" or about 2.29 kpc/5,300ly across (on standard assumptions and taking z = 0.13). The average diameter of a nucleus is a little under 0.2" or about 0.45kpc and the area of the whole including the outlier is about 3.4 sq. arcsec or about 17.8M pc2 The inter-clump separation ranges from about 0.38"(0.87 kpc/2800ly) between the "big" and "first" toes and about 0.1" (0.25 kpc/820ly) towards the heel. These values are in a very similar range to those mentioned above.

Unfortunately  we don't have any spectra for BigFoot, other than the 24-point SED in NED, so at present finding out a great deal more about it is difficult. On the basis of measurements made to date, it is not a radio, X-ray or other source.

....and BigFoot's Big Brother

Just as I was putting this OoTD to bed, Elizabeth posted me this. The picture was originally posted by wakaleo on August 06, 2007 587735666394661050....



SDSS 16434337+33011269 available in DR8 here The original image looks a bit more foot-like and like BigFoot.

At first sight it looks structurally very similar, with a number of nuclei. But, this one has two feet(?) and a denser cloud surrounding the nuclei.

Is there any physical similarity? Perhaps, but only perhaps.

"BigFoot_2" is a lot closer and is bigger.

Its redshift is 0.031 and it covers an area of about 200 arcsec2 (10arcsec x 20arcsec) [including the outlier/"second foot"] which at that redshift is about  72 M pc2. On that basis it is about four times the area of BigFoot. It's also a good deal brighter: the absolute magnitude of BigFoot_1 is -16.05; that of BigFoot_2 is -17.88. The measured flux is about ten times greater, too.

But for this one we have a spectrum!



with a very strong OII line.

SDSS lists it as a star-forming galaxy. From the spectrum, roughly1 T~2.5 X 104Kelvin from [OIII] and from [SII] Ne~5 x 104

As we noted above there isn't a spectrum for BigFoot_1 itself. It would be nice to use what data we can extract from BigFoot_2 to understand BigFoot_1. Unfortunately...

That leaves some open questions:

(i) is BigFoot a Caterpillar*?

(ii) Is it a Clump Cluster?

(iii)What is the relationship between Caterpillars and Clumps and Green Peas, if any?

(iv) Are the any of the above covered by what zookeeperKevin has shown in the paper mentioned above?

(v) Can we extended any of what we understand about cluster, clumps and peas to throw light on the others?

(vi) What is the relationship between Bigfoot_1 and BigFoot_2?

...to none of which we have an answer. But GZH  just might help to make some suggestions. As is so often the case, we need more data!!



1 My rapid calcs from DR8 data.


* For more on Caterpillars see the Caterpillar list
« Last Edit: July 15, 2012, 07:44:16 am by PeterD »

AlexandredOr

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #1 on: July 12, 2012, 09:25:10 am »

Baby star opening its eyes on the Universe.

djj

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #2 on: July 12, 2012, 12:03:40 pm »
Great OotD !  ;) :) :D :)

Big Foot certainly gets around ;D!  Your OOTD should run and run, Peter ::) 8).

Alice

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #3 on: July 12, 2012, 01:05:59 pm »
Bigfoot is the life and sole of the party. ;D ;D ;D

PeterD

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #4 on: July 12, 2012, 01:27:45 pm »
with puns like that I don't know that I should say it, but thanks guys!

mitch

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #5 on: July 12, 2012, 03:17:16 pm »
Mother always said, don't be a heel
Really interesting OOTD, Peter - Thanks  8) 8) 8)

djj

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #6 on: July 12, 2012, 05:00:27 pm »
While we're on the subject of feet, this was posted in W&W/Proto-spirals by LankyYankee and in Stunning/Irregulars by Watchingthesky:


http://cas.sdss.org/astro/en/tools/explore/obj.asp?id=587741816788877393
Two bright feet, one faint one ;D

However, the spectrum seems characteristic of one of Budgieye's Blue Peas


KWillett

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #7 on: July 12, 2012, 06:24:03 pm »
This is a really neat OOTD, Peter (and photogenic to boot). Always fun to have links from astrophysics to cryptozoology - I remember an example from a couple of years ago that found another Bigfoot slightly closer to home. See http://blogs.discovermagazine.com/badastronomy/2008/01/21/speaking-of-dumb-mars-claims/

(i) is BigFoot a Caterpillar*?

(ii) Is it a Clump Cluster?

(iii)What is the relationship between Caterpillars and Clumps and Green Peas, if any?

          I'll combine questions i-iii somewhat. I don't consider there to be a significant distinction between caterpillars and the clump cluster galaxies. As many of you know (and has been mentioned on the other threads), the leading theories for these galaxies are that they're gas-rich clumps in a disk. The ones we observe at this stage are beginning to interact gravitationally, losing angular momentum and falling to the center of the galaxy where they'll contribute to bulge formation. Analysis of both chain-type galaxies and clump clusters from Hubble surveys, especially the deep field, suggest that they are the same type of object viewed from different orientations (eg, Dalcanton et al. 1996 http://arxiv.org/abs/astro-ph/9604157; Elmegreen et al. 2005 http://arxiv.org/abs/astro-ph/0508216). However, if we had enough collections of clump galaxies with different colors or big velocity dispersions above a normal disk plane, that might not be true for all the galaxies we've been classifying.

          The relation to the Green Peas is less clear. Peas do show clumpy structure related to star-forming clouds in the high-resolution HST images, and on similar size scales of a few kpc across for the whole galaxy. The main questions you suggest really come down to stellar mass and metallicity, for me - we know that Peas really are metal poor, and a good test of whether these are similar beasts would be to carefully measure the nitrogen/oxygen and oxygen/hydrogen ratio in these galaxies. Stellar masses also would give us an indication of where they fall compared to Bigfoot.

The number of clumps is intriguing, especially if this is really a high number for clump-cluster galaxies. Simulations like the one in the Elmegreen paper do show numbers of clumps in the disk that are on the order of a dozen or so. More clumps would indicate either that the disk is more massive (and producing more star-forming clumps as a result), or that the mass function of the gas isn't doing what we predict. One likely way of reconciling this with predictions is to change the magnitude of effects like supernovae, black hole/AGN feedback, or star formation. Counting clumps like this is important - if anyone has higher-multiplicity numbers that they've seen in a caterpillar or clump cluster galaxy, let us know!

As PeterD suggests, more data is always useful for this. I'd especially like to see if we can get rest-frame infrared observations of Bigfoot-type galaxies, which are better at revealing older stars that are making up the majority of the growing bulge. Hubble and the new images we'll be getting in upcoming Zoos will hopefully provide analogues to this.

Great discussion - let's keep it going!

- Kyle Willett
GZ science team

elizabeth

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #8 on: July 12, 2012, 06:30:09 pm »
 ;D  8) 8) OOTD

Infinity

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #9 on: July 13, 2012, 01:17:55 pm »
That's one giant step... 8)

c_cld

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #10 on: July 13, 2012, 03:45:30 pm »
archetypal “clumpy irregular” galaxy NGC 7673

Kinematics and Structure of the Starburst Galaxy NGC 7673 Redshift:  0.011368
SDSS J232741.04+233520.3 1237678579288637459

previous post by elizabeth in "Gotta love these blues " http://www.galaxyzooforum.org/index.php?topic=204.msg535631#msg535631


from HLA hst_06870_02_wfpc2_f814w_f555w_wf
« Last Edit: July 13, 2012, 03:47:41 pm by c_cld »

PeterD

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #11 on: July 13, 2012, 05:50:45 pm »

          I'll combine questions i-iii somewhat. I don't consider there to be a significant distinction between caterpillars and the clump cluster galaxies. As many of you know (and has been mentioned on the other threads), the leading theories for these galaxies are that they're gas-rich clumps in a disk. The ones we observe at this stage are beginning to interact gravitationally, losing angular momentum and falling to the center of the galaxy where they'll contribute to bulge formation. Analysis of both chain-type galaxies and clump clusters from Hubble surveys, especially the deep field, suggest that they are the same type of object viewed from different orientations (eg, Dalcanton et al. 1996 http://arxiv.org/abs/astro-ph/9604157; Elmegreen et al. 2005 http://arxiv.org/abs/astro-ph/0508216). However, if we had enough collections of clump galaxies with different colors or big velocity dispersions above a normal disk plane, that might not be true for all the galaxies we've been classifying.


OK let me take up this thread. I started "collecting" Caterpillars - or as I call them Blue Blobby Objects (BBOs) - in part  because I couldn't see what they (BBOs) are - and partly because I have always been interested in irregulars and LSBGs in particular. There must be a number of them that do fit into the Elmegreene classification, perhaps even the majority of them. However as you can see from the Caterpillars thread there are a number of them that are don't appear co-planar, unless you assume that you are "looking straight down" on them. and indeed where the association is not as tight as the Elomegreene papers would suggest. Unfortunately for most of these objects - and in fact I can only think of one or two exceptions - there is no significant spectroscopic data at least at first glance. Asa result it is dfifficult to say what they are, what their masses are and so on. There is hope however that work such as Kevin's (referred to above) may be able to provide at least some of the information we need to understand what these BBOs are. As I said more data is always needed.



          The relation to the Green Peas is less clear. Peas do show clumpy structure related to star-forming clouds in the high-resolution HST images, and on similar size scales of a few kpc across for the whole galaxy. The main questions you suggest really come down to stellar mass and metallicity, for me - we know that Peas really are metal poor, and a good test of whether these are similar beasts would be to carefully measure the nitrogen/oxygen and oxygen/hydrogen ratio in these galaxies. Stellar masses also would give us an indication of where they fall compared to Bigfoot.

The number of clumps is intriguing, especially if this is really a high number for clump-cluster galaxies.


It is a high number for BBOs. In the eighty or so objects that I have identified in my own BBO list and measured, the number of blobs in BigFoot is exceptional.


Simulations like the one in the Elmegreen paper do show numbers of clumps in the disk that are on the order of a dozen or so. More clumps would indicate either that the disk is more massive (and producing more star-forming clumps as a result), or that the mass function of the gas isn't doing what we predict.


Does the Elmegreen model  or the simulations impose a limit on the number of clumps that appear, upper or lower bounds?


One likely way of reconciling this with predictions is to change the magnitude of effects like supernovae, black hole/AGN feedback, or star formation. Counting clumps like this is important - if anyone has higher-multiplicity numbers that they've seen in a caterpillar or clump cluster galaxy, let us know!


There are exceptions with higher counts but as far as I recall they are already clearly forming galaxies


I'd especially like to see if we can get rest-frame infrared observations of Bigfoot-type galaxies, which are better at revealing older stars that are making up the majority of the growing bulge. Hubble and the new images we'll be getting in upcoming Zoos will hopefully provide analogues to this.

Great discussion - let's keep it going!

- Kyle Willett
GZ science team

Am always happy to talk about these and BBOs. Got to go. I have a flight to catch at 5am!!!

will try and catch up tomorrow or Sunday

PeterD

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #12 on: July 17, 2012, 01:01:25 pm »
...
The number of clumps is intriguing, especially if this is really a high number for clump-cluster galaxies.


It is a high number for BBOs. In the eighty or so objects that I have identified in my own BBO list and measured, the number of blobs in BigFoot is exceptional.


Simulations like the one in the Elmegreen paper do show numbers of clumps in the disk that are on the order of a dozen or so. More clumps would indicate either that the disk is more massive (and producing more star-forming clumps as a result), or that the mass function of the gas isn't doing what we predict.




One likely way of reconciling this with predictions is to change the magnitude of effects like supernovae, black hole/AGN feedback, or star formation. Counting clumps like this is important - if anyone has higher-multiplicity numbers that they've seen in a caterpillar or clump cluster galaxy, let us know!


There are exceptions with higher counts but as far as I recall they are already clearly forming galaxies

will try and catch up tomorrow or Sunday

Well it took till Tuesday, but this is supposed to be a holiday :)

so

Galaxies with higher number of clump counts:



http://www.galaxyzoo.org/examine/AHZ20010by

though not perhaps the prettiest, or




are certainly SFGs on their way to being spirals or something.

But is something like:



http://www.galaxyzoo.org/examine/AHZ2000cod

the same sort of thing? or is



http://www.galaxyzoo.org/examine/AHZ400036p

or:



http://www.galaxyzoo.org/examine/AHZ2001r1o

? The third and fourth would fit in the caterpillar zoo, the fifth is a possible.

I am not sure that BigFoot is a caterpillar. It certainly intrigued me enough to write an OoTD though.

Peter

Alice

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #13 on: July 17, 2012, 01:06:11 pm »
Just popped in to see how things are running. I'm so glad you're still keeping us on our toes. :D 8) ;D

PeterD

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Re: Thursday July 12 2012; Meet BigFoot
« Reply #14 on: July 18, 2012, 02:12:58 pm »
Just popped in to see how things are running. I'm so glad you're still keeping us on our toes. :D 8) ;D

I think that a "cheesy grin" sums it up! ;D