Questions inspired by or about the background literature.
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JeanTate
This phrase appears in Michael Zevin's summary of Yang et al.'s paper (A Detailed Evolution of E+A Galaxies into Early Types), in the Blogger page.
Is this an empirical (?) conclusion, based on the discovery of zero PSGs in cluster/group environments? Or a theoretical one? Or something else?
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JeanTate
This also comes from Michael Zevin's summary of Yang et al.'s paper (A Detailed Evolution of E+A Galaxies into Early Types), in the Blogger page:
The morphologies of PSGs in this study were very diverse, including train wrecks, barred galaxies, blue cores, and relaxed-looking disky galaxies.
In this Quench project, "barred galaxies" is one morphological choice we have, but "train wrecks", "blue cores", and "relaxed-looking disky galaxies" are not. Could one of the Quench Science Team members share the reasons/rationale behind not including these morphological classes in our project?
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JeanTate
This question was also triggered by reading Michael Zevin's summary of Yang et al.'s paper (A Detailed Evolution of E+A Galaxies into Early Types), in the Blogger page. He writes:
PSGs tend to be bulge-dominated systems. The median bulge fraction (B/T), which gives the ratio of the bulge luminosity to the total luminosity of the galaxy, was 0.59.
This seems to imply that the team ("Yang et al.") first determined that all the PSGs have distinct disk and bulge components; that none are pure ellipticals (= spheroidal?). Or perhaps that there were some such, and their B/Ts were 1.00.
Is that so?
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JeanTate
OK, now that I've read the paper itself, I have some answers to my own questions:
- yes, Yang et al. ran three profile models of surface brightness, one of which involved fitting a two-component model (bulge and disk)
- three of their PSGs could not be modeled in such a way (the model blew up); another three had unreliable results
- 'pure ellipticals' were excluded, but the non-robust three were (in the dataset which has a median B/T of 0.59)
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JeanTate
Again, answering my own questions, by reading the paper itself:
- "Three-quarters of this sample are in the field, well outside rich cluster environments"
- "First noted by Dressler&Gunn (1983) in distant (z ~ 0.4) clusters, E+A galaxies have been subsequently found to be abundant in all types of environments. At intermediate redshifts (0.3 < z < 1), the proportion of E+A galaxies appears to be a factor of 4 greater in clusters than in the field (Tran et al. 2004). In the nearby Universe, E+A galaxies have been detected mainly in the field (Zabludoff et al. 1996; Quintero et al. 2004) primarily because most galaxies do not reside in dense cluster-like environments. Indeed, the overall distribution of the local environments of E+A systems follows that of the general galaxy population as a whole (Blake et al. 2004). The fraction of E+A systems in clusters shows a rapid decline from
intermediate redshifts (z ~ 0.5) where it is typically higher than 20 per cent (e.g. Couch & Sharples 1987; Belloni et al. 1995) to less than 1 per cent in local clusters (Fabricant, McClintock & Bautz 1991)."
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JeanTate
That's from the Kaviraj et al. paper; the next sentence is:
We find that all but six of the galaxies studied in this sample have fracDev > 0.8 in the r band, which indicates that the majority of E+A galaxies in this sample are indeed spheroidal systems.
The Wong et al. paper is rather more careful in using fracDev, even citing the 2010 Masters et al. paper. However, I wonder how solid their conclusion is ("the SDSS
fracDev parameter provides a better differentiation between the early- and late-type galaxies"); for example, check out what Karen had to say in this GZ forum thread.Perhaps this parameter is better at identifying galaxies with dominant bulges (or even very prominent bars)?
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