More Clues to Galaxy Formation: Massive Globular Clusters, Stochastic Self-Enrichment, and Mass/Metallicity Correlations - PowerPoint PPT Presentation

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More Clues to Galaxy Formation: Massive Globular Clusters, Stochastic Self-Enrichment, and Mass/Metallicity Correlations

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More Clues to Galaxy Formation: Massive Globular Clusters, Stochastic Self-Enrichment, and Mass/Metallicity Correlations NGC 4696 HST/ACS Harris && 2006 – PowerPoint PPT presentation

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Title: More Clues to Galaxy Formation: Massive Globular Clusters, Stochastic Self-Enrichment, and Mass/Metallicity Correlations


1
More Clues to Galaxy Formation Massive Globular
Clusters, Stochastic Self-Enrichment, and
Mass/Metallicity Correlations
NGC 4696
HST/ACS
Harris 2006
2
Young massive star clusters (YMCs) forming at
105 M0 in starburst dwarfs today
Starburst dwarf NGC 5253 (ESO/HST)
3
Bimodal or not?
Harris 2008
Harris 2006
4
Bimodal or not?
Harris 2008
Harris 2006
5
Serious questions persist!
Is this effect caused by --- (1) A gradual shift
of the blue sequence to redder color at higher
luminosity? (Mass/Metallicity relation) (2) The
disappearance of bimodality altogether at the
highest masses? (Threshold enrichment effect) (3)
An artifact of photometric measurement
procedures? (i.e. not real)
If its a true, physical MMR then Z M1/2
at high mass, and it may smoothly connect upward
to the UCD regime. Does it continue to low
mass? Why no red-sequence MMR? Is it present
in all galaxies? What is its astrophysical
origin?
6
The systematic properties of globular clusters
begin to change for M gt 2 x 106 M0
- Appearance of the MMR
7
The basic feature of bimodality is a first-order
and (probably) universal effect. The MMR is a
second-order effect and harder to trace. Though
new, much confusion already exists
Category 1 MMR is present and measurable
M87, NGC 1399, several other BCGs and
gEs Category 2 MMR is not present
M49 any others? Category 3 presence of MMR
not decidable GC sample too small or does not
extend to high enough luminosity
Milky Way M31 dwarf galaxies most spirals
GC-poor Es
8
Most galaxies do not have clusters in the 106
107 M0 range
1 strong MMR
2 no MMR
3 Not decidable
Milky Way GCs
MV
Fe/H
9
First, lets get the measurements straightened
out.
NGC 5128 d3.8 Mpc Globular clusters are easily
resolved at lt1 seeing Photometry must account
for individually different scale sizes GC
profile as seen on image PSF Intrinsic
GC profile
rh 1 5 parsecs averages 3 pc ? 0.3 width
10
NGC 3311/3309 (A1060) d 50 Mpc
2 rh 6 pc ? 0.025 fwhm(PSF) 0.5 ?
starlike! psf-fitting photometry is fine
Several regimes determined by distance no single
photometric method is suitable for all regimes
Gemini-S GMOS, Wehner Harris
11
4 distinguishable regimes compare fwhm of
stellar PSF with intrinsic cluster size D ( 2
rh), half-light diameter Well resolved
D gtgt fwhm(PSF) Partially resolved
D fwhm Marginally resolved D 0.1
0.3 fwhm Unresolved (starlike) D lt 0.1 fwhm
All this is subject to S/N considerations
12
HST/ACS Imaging program for BCGs
NGC 1407 Eridanus d23 Mpc MV
-22.35 NGC 3258 Antlia 41 Mpc
-21.87 NGC 3268 Antlia 41
Mpc -21.96 NGC 3348 CfA69
41 Mpc -22.13 NGC 4696 Centaurus
42 Mpc -23.31 NGC 7626 Pegasus I
49 Mpc -22.58 (M87 Virgo
16 Mpc -22.4)
(Partial list biggest GCSs out of 12 studied)
D 6 pc at d 40 Mpc ? half-light
profile width 0.03 compare PSF fwhm 0.1 ?
marginally resolved
13
  • Photometric technique
  • Uniform catalog of detected objects with DAOPHOT
  • Construct PSF from average of many bright
    starlike objects
  • For each individual source, convolve PSF with
    King30 model GC profile and vary D(model) to
    obtain best match (ISHAPE Larsen 1999)
  • finally, use fixed-aperture photometry corrected
    for profile width to obtain final magnitude in
    each band

ISHAPE sample fits 1 px 0.05 HST/ACS
S/N441 fwhm a1.3 px b/a 0.91
S/N24 fwhm a0.82 px b/a 0.50
S/N108 starlike
14
Growth curves for simulated GC profiles convolved
with PSF ISHAPE ? solve for best-fit D Measure
magnitude through 2.5-px aperture, corrected back
to the growth curve for a starlike profile
15
More tests
Measured size a not affected by modestly
elliptical shape
b/a, q returned correctly for a gt 0.1 PSF
16
Full, profile-corrected aperture photometry for 6
supergiant ellipticals
Previous PSF-fitting data (Harris 2006)
  • Trend lines
  • blue and red?
  • linear slope? or top end only?
  • how steep?

N12000 brighter than MI -8. Largest sample in
existence!
17
RMIX fits of bimodal gaussians within selected
magnitude intervals forces two modes into the
solution, but (a) less affected by field
contamination, (b) avoids the strong assumption
imposed by a linear fit
18
The top end uni- or bi-modal?
19
A detour the measured cluster sizes
20
Trends (?) versus galactocentric distance and
metallicity projection effects, or intrinsic?
Low-metallicity GCs average larger size at any
galactocentric zone
21
The MMR is not due to an unaccounted-for
size-mass relation.
22
What is responsible for the metallicity
distribution function (MDF)?
Bailin Harris 2008
Is a proto-GC - PRE-enriched from the surrounding
GMC gas? - internally SELF-enriched by its own
SNe within the first few Myr? - stochastic? (can
self-enrichment be responsible for the internal
dispersion of the MDF?)
23
NSN 1 per 100 M0
Stochastic self-enrichment fails to explain the
MDF dispersion at any cluster mass higher than
104 M0
24
Two additional, major factors to add - reff
M1/2 at high mass - fZ is a strong function
of M(init) and thus reff as well
25
Combined effects of pre-enrichment,
self-enrichment, and mass/radius relation
26
  • Basic features of the model
  • No MMR for cluster masses lt 106 M0 (i.e.,
    sequences vertical)
  • Very metal-poor, very massive GCs should be rare
    (anywhere)
  • blue and red sequence converge at high-mass end
  • Similar red-sequence MMR should exist at top
    end, but smaller amplitude
  • Internal dispersion and mean metallicity of each
    mode driven by pre-enrichment

27
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