Next GZ Hangout: Friday, 22nd March, 15:30 GMT
Next Galaxy Zoo Hangout: Friday, the 22nd of March, 2013, 3:30 p.m. GMT (time zones are currently weird since the US has sprung forward but Europe has not, so that’s 4:30 p.m. Central European Time, 11:30 a.m. Eastern Daylight Time, 8:30 a.m. Pacific Daylight Time).
Want to contribute for our next hangout? Post your questions & comments below and/or feel free to tweet them @galaxyzoo or post them on Facebook.
During the chat, if we use a science term you aren’t familiar with, please use the Jargon Gong by tweeting us with a GONG (example: “@galaxyzoo GONG SPS template fitting“); we’ll be happy to explain!
Update: view the video here!
Galaxy Zoo 
Jean Tate says : March 8, 2013 at 9:05 pm
Thank you Bill, Brooke, Karen, Kevin, and Kyle. For (yet another) great Live Chat, and for having a go at answering my question.
I will have to play that part again, but from what I heard (and understood), estimating galaxies’ stellar masses from photometry is (or can be) a very convoluted process, involving a great many steps and assumptions (well, the full chain – from reduced photometry to estimates – is; in practice, I expect one can simple download a package, plug in the data, turn the handle, and out pops a result, nicely tied up with comforting sigma bows). And that one of the key assumptions concerns the IMF, a nice functional form that is, in fact, very poorly grounded in direct observational data.
Food for much thought.
In a future Live Chat, I do hope you can address Tom Freethesouls Zolotor’s question. If I may, I’ll add to it this: what have x-ray observatories such as XMM-Newton and Chandra, and IR ones such as WISE, Spitzer, Herschel and ALMA (both also a sub-mm/mm observatories) so far revealed about FHBs?
Thank you Tom, for quoting my comment.
I’ve been doing some reading on IMFs, and it would seem it’s a very active area of research!
For example, A Substantial Population of Low Mass Stars in Luminous Elliptical Galaxies, by van Dokkum and Conroy, report results of a very cool set of observations. Low-mass, main sequence stars are extremely hard to detect, as stars, beyond a few hundred (thousand?) pc in our own galaxy. You’d think they’d be impossible to detect in other galaxies, yet van Dokkum and Conroy were able to estimate the number of – and hence combined mass of – just such stars in eight ETGs (four in the Virgo and four in the Coma cluster)! Very clever.
If indeed these low-mass stars contribute “>60% of the total stellar mass“, I wonder how that affects the estimates of stellar mass, obtained using SDSS photometry?
Cappellari et al. (2012), in A systematic variation of the stellar initial mass function in early-type galaxies, report “unambiguous evidence for a strong systematic variation of the IMF in early-type galaxies as a function of their stellar mass-to-light ratio, producing differences up to a factor of three in mass” (they have some very nice, colorful diagrams!). I wonder where estimates of stellar mass, obtained using SDSS photometry, lie in this range?
In The stellar and sub-stellar IMF of simple and composite populations – a very long document – Kroupa et al. (2012) talk about the IGIMF (integrated galactic IMF).
To be clear: yes, there are questions in my last comment; but they are more rhetorical than ones I’d like the team to answer. 🙂
The team’s time, on the Live Chat, is limited, and there are quite a few other questions, already asked, not yet answered … 😉
Will future telescopes help to reveal more of what these FHB galaxies really are?
@Kevin: clouds are *grey*!! Clouds – water clouds, ice clouds – mere dim the Sun; they don’t make it appear redder!
Hi Jean,
The atmosphere actually does redden. Outside the Earth’s atmosphere the Sun is a slightly bluer color (more greenish than all the way to the blue part of the spectrum), but we see it as yellow through the atmosphere. The effect is increased at sunset, when the sun looks much, much redder.
Yes, but – unless I missed it – Kevin specifically said “clouds”, as in the white fluffy (streaky, etc) things. Clouds – at least liquid or solid (icy) clouds – are grey, aren’t they? The thicker the clouds, the darker they appear, whether directly overhead or on the horizon (really high ones – noctilucent – not counted, nor dust clouds). And when the Sun ‘goes behind a cloud’, it dims, but does not change (apparent) color.
This Hong Kong Observatory webpage has, I think, a good explanation: Colours of Clouds. In a nutshell, “the size of water droplets or ice crystals inside the clouds (about 10µm or larger) are much larger than visible wavelengths, so all visible wavelengths are scattered about equally by such particles […] and it is called “Mie scattering”. This type of scattering of light of all colors is different from the type of color-selective scattering (Rayleigh scattering) which gives the blue color of the sky.”
The ‘dust extinction’ that was discussed in the Live Chat is much closer to Rayleigh scattering than to Mie scattering, isn’t it? Because the dust grains which cause interstellar extinction are comparable, in size, the wavelengths of light optical astronomers observe in, aren’t they?
@Bill: what about background galaxies from the Andromeda Project?