Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.stsci.edu/hst/training/events/VO/scienceMotivation1.pdf Дата изменения: Wed Jul 5 19:37:58 2006 Дата индексирования: Sun Dec 23 05:52:04 2007 Кодировка: Поисковые слова: dark nebula

Brad Whitmore

2/21/06

NVO Study of Super Star Clusters in Nearby Galaxies ­ Proposal and Demo
B . W h itm o r e , C . H a n le y , B . C h a n , R . C h a n d a r

OUTLINE · Background and Science Goals · A Feasibility Study ­ M51 · Demo · Hands-on session (11:00 ­ 12:00)

Background
This proposal was born as a "student project" at the 2005 NVO Summer School in Aspen, which Chris Hanley, Ben Chan, (IPAC) and I all attended. We then put in a proposal as part of the first NVO Research Initiatives program ($25,000 grants). 15/42 proposals successful, 4 with STScI PI's (Ferguson, Lucas, Wadadekar, Whitmore) and 1 with a JHU PI (Heckman). The following presentation is essentially what we presented at the Aspen Summer School.

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Are They Really Globular Clusters ?
The young clusters we see in the Antennae (and other galaxies with massive young clusters) have the: · Colors · Luminosities · Sizes · Spectra · Masses (-0.2 < V-I < 0.6) (-15 < Mv < ?, power law LF with index ~ -2) (Reff ~ 4 pc) (~ 10 objects age dated at 3 - 20 Myr) (104 - 106 )

· Distributions (similar to the field stars) · Vel. Dispersions (10 - 15 km/s)

to be globular clusters with ages in the range 1 to ~ 500 Myr.

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Mergers, Starbursts, Bars, Rings, and Spirals (cont.)
Roughly 20 gas-rich mergers have now been observed in detail by HST. All show young star clusters. In addition, we find young, massive, compact clusters in:
starburst dwarf galaxies (e.g., Meurer et al., 1995), barred galaxies (Barth et al., 1995), spiral galaxies (Larsen & Richtler, 1999) Milky Way and LMC (e.g., Walborn 2000) These clusters have properties similar to those seen in the mergers, but always fewer in number, and generally fainter in luminosity. Science Question # 1 ­ Is "violent" star cluster formation different than "quiescent" star formation ?

Whitmore, 2000 If there are two different modes of star cluster formation we might expect a bimodal distribution in a plot of the magnitude of the brightest cluster in a galaxy vs. the log of the number of clusters.
V io le n t s ta r fo r m a tio n ?

Q u ie s c e n t s ta r fo r m a tio n ?

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However, the data appear to support a universal model rather than a bimodal model, with the correlation being due to statistics, not physics. However, this dataset, and reductions, were very inhomogeneous.

Whitmore, 2000

B e s t f it
M 51

Our goal is to redo this diagram: - with a uniform data set (e.g., SDSS, HST) -with uniform analysis (e.g., WESIX) - for larger dataset (e.g., N~ 100)

N e w p o in t fr o m A sp e n p r o je ct

P r e d ic t e d if u n iv e r s a l p o w e r la w , in d e x = -2

Science Question # 2 ­ What fraction of clusters are hidden by dust ? Neff & Ulvestad (2000) found that their radio sources were "near but not coincident" with the young clusters in the Antennae". It appears that this was due to a 1.2" positional offset. Once the offset was made we found that 85 % (11 of 13) of the strong radio sources have optical counterparts

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Initial Program Galaxies

Feasibility Study ­ M51
wing Holtzman et al. (1992) vations of "proto-globular" rs in NGC 1275, we ved the two extremes of the re Sequence of merging ies using HST in Cycle 2 ycle 5.

(NVO tools used)

DataScope ­ Get SDSS g-band image WESIX - Source extraction and cross matching ALADIN ­ Visualization Voplot ­ Analysis

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Photometric Calibration
Compared SDSS g-mag from sextractor to HST V-mag (Rupali Chandar) Scatter ~ 0.1mag

Analysis with VOplot
Source classification with flux concentration index (aperture mag ­ isophot mag) VOTables exported back to Aladin for various source types

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Diffuse sources Nucleus Saturated stars Clusters

Compact objects (stars)

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Compact objects (stars)

Nucleus

Saturated stars

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Diffuse sources

Clusters

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Whitmore, 2000

B e s t f it
M 51

N e w p o in t fr o m A sp e n p r o je ct

P r e d ic t e d if u n iv e r s a l p o w e r la w , in d e x = -2

Fraction of missing clusters: Red crosses = 2 mass Blue squares = clusters Fraction of 2mass sources hidden by dust (outside center) = < 45 % (15/33) NOTE: - Something different near center ! Position offsets = TBD

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Conclusions
· SDSS images can be used for this project (though will probably also try HST preview images) · M51 will fit nicely on the Mv(brightest) vs. log N diagram > further support for universal model. · NVO tools will be very useful for the project (e.g., datascope, WESIX, Aladin, VOPLOT). · Automating the program (e.g., SIAP services and OPENSKYQUERY) is feasible, but will take additional work (e.g., developing a python client for WESIX, correcting for positional offsets)

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