Stellar Populations in Nearby Earlytype Galaxies

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Stellar Populations in Nearby Early-type Galaxies

• Duncan Forbes
• Swinburne University

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Scientific Motivation

• How and when did galaxies form ?
• Galaxy evolution with look-back time
• or
• Galactic Archaeology
• Use Lick absorption lines and models to derive
  stellar population parameters.

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2dFGRS

• 250,000 galaxies.
• Spectral resolution of 9.0 Å.
• Not flux or Lick system calibrated.
• S/N 50 per A for brightest galaxies
• Spectral resolution varied in an untraceable way
  with fibre and zenith distance 50 km/s vel.
  disp. errors.
• This makes Lick indices un-usable.

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6dFGS

• 50,000 galaxies so far (150,000 by Dec 2005).
• Not flux or Lick system calibrated.
• Spectral resolution 5 Å and well-defined.
• 5 of galaxies suitable for Lick analysis (ie
  early-type with S/N 30)
• Velocity dispersion error /-10 km s-1 (in
  comparison with literature values).

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Magnesium-sigma relation

• 750 6dF galaxies
• Aperture differences?
• Continuum division?

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Metallicity- Age Relation
750 galaxies
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Age - Velocity Dispersion

• No strong age-mass relation as predicted by
  hierarchical models.
• Where are young, high mass galaxies?

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SuperCosmos NED
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SuperCosmos NED

• Small SC/NED photometry
• Large Spectral estimates circles old, stars
  young
• Lines Coma cluster galaxies (Gladders 1998)

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NED and SuperCosmos R mags combined.

• Offset either models or aperture.
• Young (stars) fall slightly below main relation.

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Stellar Pops with AAOmegaRobert Proctor

• Central age, metallicity and abundance ratios for
  a very large sample.
• MOS mode, low res. gives 3700-8800 (ie all Lick
  lines), spectral resolution 4 Å.
• (1700B would give 3700-4500 and 1.5A).
• Flux and Lick standards would be useful.
• S/N 30 per A in 2hrs for B 20
• B 21 requires 7hrs (S/N 30)
• B 19 gives S/N 50 in 2hrs

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Input Catalogue?

• 6dF (2MASS) K
• 2dF (APM catalog) b
• SDSS g -5
• 2dF has 200/sq deg
• Assuming 2hr pointings or 4/night gives 1400
  galaxies per night.
• 100 nights 140,000 galaxies (20x 6dF)
• Wide range of environs and galaxy mass (sigma
  100 km/s).

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Star formation and suppression in the core of the
Shapley Supercluster Glen Mackie
Shapley Supercluster centred at 13.5 h, -31.5o
14,500 km/s (Abell 3558)
25 Abell clusters within 50 Mpc.
SSC core A3562, SC 1329-313, SC
1327-312, A3558, A3556
Venturi et al MNRAS, 314, 594
Workshop on Extragalactic AAOmega projects 18
Feb. 2005
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Star formation and suppression in the core of the
Shapley Supercluster
Questions What environmental processes drive
galaxy evolution? How is star
formation (and suppression) linked to galaxy
mass, local environment, velocity
(cluster/group) sub-structures, and the
hot intracluster medium (ICM)?

• Core of SSC provides the ultimate high(est) space
  density laboratory
• Existing data to use and build upon
• previous shallow (to MB -19) radial velocity
  studies exist (eg. Bardelli et al. 2000, 2001
  Drinkwater et al. 1999, 2004 6dF Jones et al.
  2004).
• X-ray spatial distribution and T (keV) exist
  (ROSAT XMM-Newton ASCA Hanami et al. 1999
  Akimoto et al. 2003).
• (Finoguenov et al. 2004 (XMM-Newton) suggest
  A3562 shows core oscillations due to recent
  passage of SC 1329-313.)

Workshop on Extragalactic AAOmega projects 18
Feb. 2005
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Star formation and suppression in the core of the
Shapley Supercluster
Linkage to Coma cluster Poggianti et al. (2004)
studied Coma cluster galaxies to MB -14.6.
Key result In contrast to high z (0.4)
clusters they found high luminosity,
post-starburst ka galaxies were absent in Coma,
but instead ka galaxies made up a large fraction
of the dwarf MB -17.3 population. Reason?
Intrinsic downsizing effect with epoch?
Transformation (late-type to dwarf sph/Es) due to
interaction with ICM?
Potential for SSC core region Achieve similar
Coma/Poggianti et al. spectral depth coverage
in SSC core. Poggianti et al. -20.5 14.4 B 20.9 at
Coma SSC core requires 16.2 B 22.7 at
SSC (?DM SSC-Coma 1.8 mag)
Workshop on Extragalactic AAOmega projects 18
Feb. 2005
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Star formation and suppression in the core of the
Shapley Supercluster
AAOmega In 4hrs at B22 for 1.5/2
seeing S/N (per Angstrom) (Dark) 10.8/8.0
(Grey) 6.9/5.0
with AAOmega we can do a spectral survey with
S/N5 (and probe below the giant/dwarf break) for
the vast majority of the 6 mag. sample range.

• Estimated program requirements.
• 1. Deep B,R surface photometry survey of central
  8 sq. degrees of SSC core
• WFI on AAT total 15 hrs
• 2. Galaxy candidate selection and astrometry
• 3. AAOmega spectroscopy
• 8 fields x 4hrs 32 hrs

Interested? Comments? Please
contact gmackie_at_swin.edu.au
Workshop on Extragalactic AAOmega projects 18
Feb. 2005
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Stellar Pops with AAOmegaPatricia
Sanchez-Blazquez

• 2D stellar populations eg probe SPs and galaxy
  dynamics.
• IFU mode, 580V gives 3740-5850 (ie most Lick
  lines), spectral resolution 2.5 Å.
• Field-of-view 11 x 22
• Typical nearby galaxy has R_eff 30
• Calibrate MOS fibre apertures effects.

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SAURON survey

• 72 galaxies (ie small sample)
• 4810-5350 A (ie limited Lick indices)
• FOV 33 x 41 or 9 x 11
• 4.2m WHT
• Exposure time 2hrs per galaxy

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Stellar Pops with AAOmegaPatricia
Sanchez-Blazquez

• Assuming SB 21 mag/sq at 0.3 R_eff, then
  require 3hrs to reach S/N 10 per A without
  radial binning.
• 3 galaxies per night.
• In 100 nights cover 300 early-type galaxies (4x
  SAURON survey).
• Competitive advantage for low luminosity
  galaxies, particularly in the blue (ie Balmer
  lines).

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Stellar Pops Analysis

• MILES library (Sanchez-Blazquez)
• 2-5x more stars than Lick or BC03
• much better parameter space coverage (BC03 very
  poor for solar metallicity)
• access to the latest Vazdekis SSP model

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Stellar Pops Analysis

• Multi-line fitting (Proctor)
• uses all Lick lines (not just 3-4 out of 25)
• less affected by poor fluxing, sky subtraction,
  calibration to Lick, CRs etc
• simultaneous age, metallicity, alpha element fits
• pipeline tested on 6dF spectra

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Archaeology