Stellar population results from NFPS:

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Stellar population results from NFPS Age and
Metallicity along the Red Sequence
Russell Smith (Waterloo), Jenica Nelan
(Dartmouth), Mike Hudson (Waterloo), Steve Moore
(Durham), Stephen Quinney (Durham), John Lucey
(Durham), Gary Wegner (Dartmouth), David Schade
(CADC), Justin Malecki (Waterloo), Jonathan Ford
(Waterloo), Jeff Stevenson (Waterloo), Nick
Suntzeff (CTIO)
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NFPS Primer
Aims Cosmic flows measure large-scale bulk
flow at 150 h-1 Mpc with random, systematic and
sampling errors lt 100 km/s via FP measurements of
an all-sky sample of 100 nearby (z lt 0.06) rich
clusters Early-type galaxy properties in
clusters benchmark sample of 4000 galaxies
with very high quality, homogenous photometric
and spectroscopic data Supported through NOAO
Survey Program (50 4m nights) hence the NOAO FP
Survey (NFPS) Smith et al. 2004, AJ, 128, 1558
(NFPS-I) Nelan et al. 2005, AJ, in press
(NFPS-II)
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Photometry

• R and B band
• FOV 40 - 1 degree (CTIO 4m MOSAIC KPNO 4m/0.9m
  MOSAIC CFH12k)
• Seeing lt1 arcsec better for more distant
  clusters (CTIO/CFHT)
• FP photometric parameters (Re, SBe)
• Morphologies (bulge/disk decomposition with GIM2D)

Spectroscopy

• Spectroscopy follow-up for 30-70
  colour-magnitude selected cluster members
• WIYN 3.5mHYDRA CTIO 4mHYDRA, 2 hours per
  field
• FWHM 3Å Median S/N is only 22 per Å (but we
  have 4000!)
• Overlap and multiple observations (crucial)
• Redshifts, velocity dispersions, linestrength
  indices

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Red Sequence of Cluster Galaxies

• Red-sequence galaxies dominate the stellar
  content of rich clusters .
• Is the red-sequence a sequence of age or
  metallicity?

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Typical literature results for early-type galaxies
Thomas et al. (2005)
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Co-added spectra, binned by sigma to S/N 200 _at_
5000A
Co-added NFPS red-sequence spectra
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Co-added spectra binned by sigma to S/N 200
demonstrate the impressive regularity of the
stellar populations of cluster red-sequence
galaxies.
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Sigma trends

• All absorption-line indices show significant
  variations with sigma
• Usual trends seen.
• Balmer lines negative, all others positive.
• (Emission-line galaxies excluded)
• Average in five bins.

Best fit (solid lines). Predictions from our
derived solution (dashed lines).

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Initial comparison with the Thomas et al. models
Grids Thomas et al. alpha-enhanced single
stellar population (SSP) models account for
non-solar chemical abundances.
Squares binned NFPS values (each the average of
700 galaxies), size increases with sigma value.
Increasing age, Z/H, ?/Fe with increasing s
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• Grid Inversion Method
• Thomas et al. models predict variations of each
  linestrength index with age, Z/H, a/Fe for
  each binned data point.
• Note errors on binned points.
• Thick lines show the average relations.
• Shaded regions indicate the maximum internal
  scatter.

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• Scaling Relationships for the Red Sequence
• Simultaneous comparison of slopes of 12
  linestrength-index vs sigma relations to models
  .
• yields mean age, Z/H, a/Fe variations for
  nuclear regions along the red-sequence. (red
  lines)
• Age s 0.67 0.15
• Z/H s 0.48 0.05
• a/Fe s 0.35 0.05

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• General trends in good agreement with other work
  in clusters (Trager et al., Caldwell et al.,
  Thomas et al.) and in groups/field (Proctor et
  al., Denicolo et al.) but with much greater
  resolution.
• H? absorption NFPS sub-sample gives the same
  result (Smith 2005).

Stars in large galaxies formed early and quickly
(high ?/Fe). Stars in small galaxies formed, on
average, much later. Simplest interpretation
down-sizing onto the red sequence.
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Deficiency of Red Sequence galaxies in high
redshift clusters

• De Lucia et al. (2004) data for clusters at z
  0.75 shows a 50 deficit of faint (0.1-0.4 L)
  red-sequence members which is approximately
  consistent with our result.

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Predicted Age Trends from Models

• e.g. GALFORM
• filled B/T gt 0.6
• open 0.4lt B/T lt 0.6
• Kuntschner et al. 2002

Field
Cluster
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Predicted ?/Fe trends from Models
Thomas, Maraston Bender (2002)
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Caveats

• Sample selection
• Red, emission-free cluster galaxies
• No selection by morphological type
• Results are for nuclear regions ( 0.5 kpc)
• Ages, metallicities are means of the red-sequence
  at a given velocity dispersion assuming a SSP
  model. This does not necessarily imply that their
  star formation histories were actually single
  bursts, e.g. frosting model may be able to
  produce the observed trends.

To Do

• Understand star formation history of bulge and
  disk components
• GALEX, CFHT u, K-band imaging
• Morphologies from CFHT sub-arcsec imaging
• Environmental effects
• Trends with cluster mass, radius

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Conclusions

• From the detailed analysis of 4000 spectra from
  red sequence galaxies in low redshift clusters we
  conclude that
• more massive galaxies on the red sequence are
  older, have higher overall metallicity, and have
  higher high ?/Fe than the lower mass galaxies
• the red sequence was assembled slowly over cosmic
  history with the s 50 km/s galaxies only
  reaching the red sequence about 4 Gyr ago
• these results are incompatible with the generic
  predictions from the hierarchical galaxy
  formation models

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• Results do not depend strongly on morphological
  type

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Map the line strength trends into ?/Fe, Fe/H
and ages, via the Thomas et al. models.
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NFPS Primer

• Supported through NOAO Survey Program (50
  nights)
• data collection is now complete
• FP data for 30-70 red-sequence galaxies per
  cluster (lt3 distance errors per cluster)
  plus some field ellipticals out to z 0.2.
• provides benchmark sample of 4000 local cluster
  E/S0 galaxies with very high quality photometric
  and spectroscopic data
• the final SDSS sample of local cluster early-type
  galaxies will only be 1/3 size of NFP and will
  have poorer image quality. NFP
  sample has B/T ratios accurate to 10
• an extremely powerful dataset to investigate many
  key aspects of local cluster early-type
  (red-sequence) galaxies
• first NFP paper published, Smith et al. 2004,
  AJ, 128, 1558, second Nelan et al. 2005, in
  press.