stellar population results from nfps: age and metallicity along the red sequence

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  • Stellar population results from NFPS:Age and Metallicity along the Red SequenceRussell 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)

  • NFPS Primer Aims: Cosmic flows measure large-scale bulk flow at 150 h-1 Mpc with random, systematic and sampling errors < 100 km/s via FP measurements of an all-sky sample of ~100 nearby (z < 0.06) rich clustersEarly-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)

  • R and B band FOV 40 - 1 degree (CTIO 4m MOSAIC; KPNO 4m/0.9m MOSAIC; CFH12k)Seeing
  • Red Sequence of Cluster GalaxiesRed-sequence galaxies dominate the stellar content of rich clusters .

    Is the red-sequence a sequence of age or metallicity?

  • Thomas et al. (2005) Typical literature results for early-type galaxies

  • Co-added spectra, binned by sigma to S/N ~ 200 @ 5000A Co-added NFPS red-sequence spectra

  • Co-added spectra binned by sigma to S/N ~200 demonstrate the impressive regularity of the stellar populations of cluster red-sequence galaxies.

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

  • 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.Initial comparison with the Thomas et al. models Increasing age, [Z/H], [/Fe] with increasing

  • Grid Inversion MethodThomas 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.

  • 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 ~ 0.67 0.15[Z/H] ~ 0.48 0.05[a/Fe] ~ 0.35 0.05

  • 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.

  • 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.Deficiency of Red Sequence galaxies in high redshift clusters

  • e.g. GALFORM

    filled: B/T > 0.6open: 0.4< B/T < 0.6

    Kuntschner et al. 2002Predicted Age Trends from ModelsFieldCluster

  • Predicted [/Fe] trends from ModelsThomas, Maraston & Bender (2002)

  • CaveatsSample selection:Red, emission-free cluster galaxiesNo selection by morphological typeResults 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.Understand star formation history of bulge and disk componentsGALEX, CFHT u*, K-band imagingMorphologies from CFHT sub-arcsec imagingEnvironmental effectsTrends with cluster mass, radiusTo Do

  • 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 galaxiesthe red sequence was assembled slowly over cosmic history with the ~ 50 km/s galaxies only reaching the red sequence about 4 Gyr agothese results are incompatible with the generic predictions from the hierarchical galaxy formation models

  • Results do not depend strongly on morphological type

  • Map the line strength trends into [/Fe], [Fe/H] and ages, via the Thomas et al. models.

  • NFPS Primer

    Supported through NOAO Survey Program (50+ nights) data collection is now completeFP data for 30-70 red-sequence galaxies per cluster (