Author Topic: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?  (Read 7470 times)

JeanTate

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That's NGC 5249 (DR8 ObjId 1237668623557460046) [1]

Morphologically, it's a lenticular, S0 in the Hubble/de Vaucouleurs classification scheme. Its distorted shape, and prominent dust lanes, would lead zooites to say it's likely a late-stage merger (you would think that, wouldn't you, you '100k+ GZ classifications' zooite?  ;) :D)

And the bluish tinge suggests star-formation is not quite dead yet; the spectrum can be introduced as evidence too (yes, it's a nice 'old' spectrum, but there are some 'hard to ignore' emission lines too):



Fair enough; while lenticulars are often very hard to tell from ellipticals, in this case it's not that hard, right?




NGC 2534 (DR8 ObjId 1237663916804538442) this time. Morphologically it's ... E1!  :o But clearly it's a blue elliptical, and there are hints of shells - tell-tale signs of past merger activity - so add in the obvious dust lane, and it's very likely a late-stage merger too (despite its E1 morphology).



A completely unambiguous, completely authentic typical elliptical, right? NGC 4374 (DR7 ObjId 588017704006910002; a.k.a. M84) is classified as E1 ... but with these extras: 'LINER', 'Sy 2', 'FR I', ...

Yet while you may not be able to pick out any distinct dust lanes in that SDSS image, the central part is, in fact, packed with enough dust to put the dust bunnies under a billion couches to shame tip the scales at many thousands or even tens of thousands of sols. This is an example of an elliptical with a 'nuclear' dust lane morphology. Here is a Herschel image (source [2]); at these far-infrared wavelengths, dust is what makes a galaxy shine:



I had intended to include an SDSS image of a large elliptical - preferably an NGC object - in which it is obvious that there is dust (in the elliptical itself); a non-blue one. However, while there are plenty of lenticulars with such dust - with classifications such as S0, S0/a - I couldn't find an elliptical.  :(  Also, there are images of nuclear dust (e.g. in the van Dokkum & Franx paper referenced below), but they're not SDSS. Anyway, part of my motivation for doing this OotD is my Not a dustlane? collection, in GZ Talk, which was inspired by some images of a brown splotch in the bright yellow part of some SDSS ETGs (early type galaxies; basically ellipticals and lenticulars). Here's the only one in that collection which might, as of today, be a dustlane in an elliptical, and not an artifact (AGZ0005b32; GZ4 image, then SDSS Explore one):



Anyway, it turns out that dust is surprisingly common in ellipticals, as the first couple of sentences in this paper makes clear (source):

Quote from: Leeuw et al.
Optical absorption patches, lanes, and filaments of dust have been seen in 50%80% of nearby bright elliptical galaxies (e.g., van Dokkum & Franx 1995). Observations at a range of other wavelengths have also revealed unexpected amounts of gas and dust in these galaxies (e.g., Roberts et al. 1991; Goudfrooij et al. 1994). In some objects, the dust masses estimated from optical extinction studies are a magnitude lower than masses implied by the IRAS far-infrared (FIR) fluxes, suggesting that elliptical galaxies may contain diffusely distributed dust not detected or properly accounted for in optical observations (e.g., Goudfrooij & de Jong 1995).

How did all this dust get there? Aren't ellipticals supposed to be 'dead and red' (the traditional ones, not the blue ones), where star-formation ceased long ago? And isn't it true that, left alone in the interstellar medium (ISM), dust will largely disappear after ~100 million years (a blink of a cosmic eye), being sputtered into a gas by the hot ISM plasma and cosmic rays? Yes, there will be some new dust created, as stars age and become red giants and blow smoke into the room the ISM; but that can't ever amount to much. Sure, if the nucleus is active - an AGN - it may keep things well and truly stirred up, and keep creating new dust by any of several different processes.

Well, according to this recent paper, "Dust and Ionized Gas Association in E/S0 Galaxies with Dust Lanes: Clues to their Origin" (Finkelman et al. 2012), a lot of different clues point to a somewhat surprising conclusion: the ionized gas (plasma) often seen outside the nuclear region in ellipticals is closely associated with the dust, and the ISM in these ellipticals may be surprisingly complex in its structure and morphology (not at all like the 'thin, uniform screen' often assumed in textbooks). The paper is fairly easy to read, and the conclusion a nice, calm summary:
Quote from: Finkelman et al.
We argue that these observed relations indicate that the ionized gas and the obscuring material have the same origin, are heated by the same sources and are well mixed. We conclude that an internal origin of the dust and ionized gas in E/S0 galaxies with dust lanes is highly unlikely; the hot gas content of E/S0 galaxies is quite heterogeneous and expected to affect differently the grain size distribution, mass content and dust distribution of individual galaxies, whereas our findings are independent of the hot gas content of each galaxy. We argue also that our results are consistent with the ‘evaporation flow’ hypothesis, albeit with some uncertainty as to the exact details of the process. If the dusty gas that we observe in the optical is part of the dense material arriving from outside during an accretion or merger event, than it could survive destruction even in hot and extreme environments. Relaxed gaseous discs and chaotic filamentary structures represent in this picture different states of similar events. The frequent detection of tidal features, atomic and molecular gas and kinematically decoupled gas components in E/S0 galaxies with dust lanes support this proposed view.

Hmm, I wonder what Robaina and Masters would make of this? And maybe it might be worth somebody's while to collect elliptical-elliptical overlaps after all.  8)

[1] All galaxies in this OotD have been posted many, many times before (except for AGZ0005b32), and I'm not even going to try to find who posted each first. As they're all (but one) NGC objects, the link is to the entry in the NGC catalogue LIST

[2] Did you hear that this most magnificent of space-based observatories ran out of liquid helium, just last week, and so it's now basically just a big piece of space junk?

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #1 on: May 08, 2013, 05:40:15 am »
Please be informed about following GZ papers.:

Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes

Sugata Kaviraj, Yuan-Sen Ting, Martin Bureau, Stanislav S. Shabala, R. Mark Crockett, Joseph Silk, Chris Lintott, Arfon Smith, William C. Keel, Karen L. Masters, Kevin Schawinski, Steven P. Bamford
(Submitted on 26 Jul 2011 (v1), last revised 17 May 2012 (this version, v2))
http://arxiv.org/abs/1107.5306

Galaxy Zoo: dust lane early-type galaxies are tracers of recent, gas-rich minor mergers
Stanislav S. Shabala, Yuan-Sen Ting, Sugata Kaviraj, Chris Lintott, R. Mark Crockett, Joseph Silk, Marc Sarzi, Kevin Schawinski, Steven P. Bamford, Edd Edmondson
(Submitted on 26 Jul 2011 (v1), last revised 23 Aug 2012 (this version, v3))
http://arxiv.org/abs/1107.5310

PS: Both are in the Refs of the Finkelman et al. paper.
« Last Edit: May 08, 2013, 05:52:17 am by zutopian »

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #2 on: May 08, 2013, 08:00:16 am »
Concerning NGC 4374:
In wikipedia there is another image, where the dustlane is visible.

PS: Thank you for this interesting Object of the Day.
« Last Edit: May 08, 2013, 08:01:59 am by zutopian »

AlexandredOr

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #3 on: May 08, 2013, 02:34:05 pm »
Great OotD indeed !!
Thx Jean  :)

Baby star opening its eyes on the Universe.

JeanTate

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #4 on: May 09, 2013, 07:51:35 am »
Thanks zutopian, AlexandredOr.  :-*

Especially to you, zutopian, for giving me the chance to explain something that I don't seem to have been clear about: in this OotD I wanted to distinguish between lenticulars (given morphological codes like S0 or S0/a) and ellipticals (E1, E+, etc). Sure they're both ETGs (early-type galaxies), but lenticulars supposedly have a recognizable bulge and disk (ellipticals don't). At least, that's what I understand from reading Buta's "Galaxy Morphology".

The two GZ papers you cited are both great - and I'd read them too - but neither so much as hints at trying to distinguish ellipticals from lenticulars. For sure, S. Kaviraj and Y. S. Ting did a lot of hard eyeballing [1], but they did not try to separate the ellipticals from the lenticuars. There are six nice examples of ETGs with dustlanes, in Figure 1 of the first paper (including, by the looks of it, NGC 2534), but as they did not state which objects these are, I was unable to check to see if any are ellipticals.

Now I could, myself, have simply clicked on the link, in the ADS page recording this paper, the one that reads "NED Objects" and gone through the 352 objects one by one ... except, of course, I couldn't!  :o Why? Because there is no such link!!  :o :o

OK, getting desperate now; how about I download the GZ2 catalog, and repeat what S. Kaviraj and Y. S. Ting did (restricting my search to just those with z < 0.07)? Uh uh, that won't work either.

You, dear reader, do know why I can't do this, don't you? And it's not just me; no ordinary zooite can do this.  :o :o :o And that's despite the fact that the first paper appeared, as a preprint, in July 2011 (and was published in MNRAS in June 2012). Oh, and good luck getting hold of the actual published paper (not the preprint): "If you would like to purchase short-term access you must have a personal account. Please sign in with your personal user name and password or Register to obtain a user name name and password for free. You may access this article for 1 day for US$25.00." [2]

[1] "Around 19000 GZ2 galaxies in the redshift range 0.01< z <0.1 are flagged as containing a dust feature by at least one GZ2 user. Each galaxy in this sample was visually re-inspected by S. Kaviraj and Y. S. Ting to determine ..."

[2] Of course, there's an extensive list of "Published Papers" on the Zooniverse ("Real Science Online") site (here). And "Galaxy Zoo: dust lane early-type galaxies are tracers of recent gas-rich minor mergers, Shabala+ 2012." is one of the 35 Galaxy Zoo papers listed there. There's even a link next to, "Available here". Guess where it takes you?  :P

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #5 on: May 09, 2013, 10:07:53 am »
Why isn't a table given in the GZ paper, where the objids of the 352 ETGs are listed? I also would like to know them.:
The objids of the images in Figure 1 and the objids of the other ETGs.
« Last Edit: May 09, 2013, 10:41:21 am by zutopian »

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #6 on: May 09, 2013, 12:08:37 pm »
Here is a related forum topic.:

Dust lanes in 'non-spiral' galaxies:
http://www.galaxyzooforum.org/index.php?topic=272856.0



« Last Edit: May 09, 2013, 12:21:48 pm by zutopian »

JeanTate

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #7 on: May 09, 2013, 03:21:23 pm »
"The Atlas3D project - VII. A new look at the morphology of nearby galaxies: the kinematic morphology-density relation", Cappellari et al. (2011):

Quote from: Cappellari
We look at the morphology of fast and slow rotator early-type galaxies. Edge-on fast rotators are lenticular galaxies. They appear like spiral galaxies with the gas and dust removed, and in some cases are flat ellipticals with disky isophotes. Fast rotators are often barred and span the same full range of bulge fractions as spiral galaxies. The slow rotators are rounder and are generally consistent with being genuine, namely spheroidal-like, elliptical galaxies. We propose a revision to the tuning-fork diagram by Hubble as it gives a misleading description of ETGs. We study for the first time the kinematic morphology-density T-Sigma relation using fast and slow rotators to replace lenticulars and ellipticals. We find that our relation is cleaner than using classic morphology. Slow rotators are nearly absent at the lowest density environments [f(SR)<2%] and generally constitute a small fraction [f(SR)~4%] of the total galaxy population in the environments explored by our survey, with the exception of the densest core of the Virgo cluster [f(SR)~20%]. We find a clean log-linear relation between the fraction f(Sp) of spiral galaxies and the local galaxy surface density. The existence of a smooth kinematic T-Sigma relation in the field excludes processes related to the cluster environment as main contributors to the apparent conversion of spirals into fast-rotators in low-density environments. It shows that the segregation is driven by local effects at the small-group scale. Only at the largest densities in the Virgo core does the f(Sp) relation break down and steepens sharply, while the fraction of slow-rotators starts to significantly increase. This suggests that a different mechanism is at work there. (Abridged)

Translation: an awful lot of galaxies which are, morphologically, elliptical are, in fact, disk galaxies ... just like lenticulars are disk galaxies!  :o  8)

Note: a spiral (galaxy) is, quintessentially, a disk galaxy; its key structural feature is the disk (the arms are nice, and quite separate, structural features).

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #8 on: May 09, 2013, 03:48:14 pm »
"Elliptical versus lenticular" had been discussed on the forum before.:

Oblate, prolate, viewing angle, and elliptical vs lenticular
http://www.galaxyzooforum.org/index.php?topic=277843.msg468912#msg468912

Most elliptical galaxies are 'like spirals'
http://www.galaxyzooforum.org/index.php?topic=279248.msg550105#msg550105

Besides I remembered following discussion in the Newbies topic.:

(...)
Hi escholzia, my reply was simply to explain how to classify a lenticular galaxy, based on the question you asked. I was not implying that all elliptical galaxies should be classified this way and I'm sorry if I caused some confusion. It's not that we cannot agree, on the contrary, we all agree that it is incredibly difficult to differentiate between these two very common morphological types when presented to us in a certain way.
I’ll explain further and please forgive me if I cover details that you already know and understand.
(...)
« Last Edit: May 09, 2013, 03:50:54 pm by zutopian »

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #9 on: May 09, 2013, 07:20:28 pm »
Quote
Hmm, I wonder what Robaina and Masters would make of this?

Following paper was recently submitted.:

The different star-formation histories of blue and red spiral and elliptical galaxies
Rita Tojeiro (ICG, Portsmouth), Karen L. Masters (ICG, Portsmouth), Joshua Richards (Imperial College London), Will J. Percival (ICG, Portsmouth), Steven P. Bamford (Nottingham), Claudia Maraston (ICG, Portsmouth), Robert C. Nichol (ICG, Portsmouth), Ramin Skibba (University of California), Daniel Thomas (ICG, Portsmouth)
(Submitted on 14 Mar 2013)
http://arxiv.org/abs/1303.3551

PS: One of the authors is K.Masters.: There was recently announcement in GZ blog. One of the Refs is Robaina et al.
« Last Edit: May 09, 2013, 07:52:17 pm by zutopian »

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #10 on: May 09, 2013, 08:32:17 pm »
Quote
There are six nice examples of ETGs with dustlanes, in Figure 1 of the first paper (including, by the looks of it, NGC 2534), but as they did not state which objects these are, I was unable to check to see if any are ellipticals.

I recognized two of the galaxies, shown in the GZ paper.: Here are the images and the links.:


NGC 5311: http://cas.sdss.org/dr7/en/tools/explore/obj.asp?id=587736584961916937


NGC 1194: http://cas.sdss.org/dr7/en/tools/explore/obj.asp?id=588015507678887987
« Last Edit: May 09, 2013, 08:34:47 pm by zutopian »

zutopian

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #11 on: May 10, 2013, 06:02:07 am »
Here is a further galaxy, which is shown in the GZ paper.:
And one of the NED Refs of this galaxy is "Stellar Populations of Elliptical Galaxies in the Local Universe" 2010ApJ...722..491Z.:


http://cas.sdss.org/dr7/en/tools/explore/obj.asp?id=587739382070706185



 

JeanTate

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #12 on: May 10, 2013, 08:59:09 am »
NED gives the following classifications:
NGC 5311: S0/a    - a lenticuar
NGC 1194: SA0^+?  - a spiral
CGCG 137-014: (no classification) - this is the DR7 ObjId 587739382070706185 in zutopian's last post.

mlpeck

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #13 on: May 11, 2013, 02:34:18 pm »
Re NGC 1194:

I think SA0+ is a deVaucoulouers (sp) style classification meaning normal, late type S0, i.e. lenticular. On the other hand in the NED notes it is variously classified as edge on spiral with either Seyfert 1 or 2 nucleus. The SDSS spectrum looks (eyeball only) AGN-like with broad emission lines. Also if you zoom out the finder chart and display it as a negative a streamer connecting it to a companion at the same redshift is visible. The companion is classified (correctly I think) as starforming. Kind of an interesting object, but definitely not elliptical.


JeanTate

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Re: Wednesday, 8th May, 2013: Who Says Ellipticals Are Dust Free?
« Reply #14 on: June 05, 2013, 01:36:25 pm »
I may have found one myself; here's the GZ Examine view:



It's DR8 1237679476937654387, and is not in the DR7 footprint:



NED gives its ID as 2MASX J00412988+2158503, and NPM1G +21.0029; I guess the lack of an SDSS ID means they're a bit behind in adding DR8 galaxies. That it's in the 2MASS catalog suggests that it's got an ETG spectrum; but it's not in WISE (apparently), so maybe there isn't all that much dust after all.

What do you think?