The Nearest Giant Ellipticals:

Rosetta Stones or Fool’s Gold?

A hypothesis or theory is clear, decisive, and positive, but it is believed by no one but the man who created it. Experimental findings, on the other hand, are messy, inexact things which are believed by everyone except the man who did that work.

Harlow Shapley

NGC 5128 (Centaurus group)

NGC 3377 (Leo group)

NGC 3379 (Leo group)

W.E.H.

SDSS

In these three galaxies ….

Old halo and bulge RGB stars are readily accessible with HST imaging

(V,I) photometry works well (high metallicity sensitivity and takes full advantage of the optical cameras)

Interpolate within RGB tracks (calibrated onto the Milky Way globular cluster grid)

Fast, efficient way to derive first-order Metallicity Distribution Function

NGC 5128

Unique chance to study a halo population in an E/S0 giant at close range

d = 3.8 Mpc from several standard candles:

TRGB, PNLF, SBF, Cepheids

Metallicity Age

“20 kpc field”

Allocated in Cycle 5, mid-1994

Exposures taken August 1997!

Harris, Harris, & Poole 1999, AJ 117, 855

Harris, Poole, & Harris 1998, AJ 116, 2866

Previous work:

More fields ….

7’ 8.0 kpc = 1.4 Reff

18’ 20 kpc = 3.7 Reff

27’ 30 kpc = 5.4 Reff

33’ 37 kpc = 6.7 Reff

deepest, with ACS

Peng, Ford & Freeman 2002

More fields ….

7’ 8.0 kpc = 1.4 Reff

18’ 20 kpc = 3.7 Reff

27’ 30 kpc = 5.4 Reff

33’ 37 kpc = 6.7 Reff

Malin 1983

Harris & Harris 2000, 2002

Metal-rich all the way out!

Rejkuba, Greggio, Harris, Harris & Peng 2005

Mean age = 8.5 Gy

NGC 3377

MV = -19.9

38.5 ksec V, 22.3 ksec I

field center at 12 kpc

(1.5 5.2 Reff )

Leo Group ellipticals: d = 10.5 Mpc

NGC 3379

MV = -20.9

38.5 ksec V, 22.3 ksec I

field center at 33 kpc

(10.3 13.6 Reff )

Harris, Harris, Layden & Stetson 2007, AJ in press

Harris, Harris, Layden & Wehner 2007, submitted

NGC 3377

NGC 3377

Entirely old, simple formation history, intermediate metallicity

No trace of metallicity gradient!

NGC 3379

ACS

NICMOS fields

Gregg et al. (2004) – old and high-Z

Textbook standard giant elliptical! “A walking advertisement for the deVaucouleurs law” (Statler & Smecker-Hane 1999)

DeVaucouleurs & Capaccioli 1979 (“note close agreement with r1/4 law”)

NGC 3379

ACS

NGC 3379V filter cutoff

2-stage chemical evolution

Are we seeing the “true” metal-poor halo for Z < 0.2 ?

Are we seeing the region of transition to the classic metal-poor halo?

-5.6

-2.4

Are we seeing the region of transition to the classic metal-poor halo?

Why didn’t we see it in the others?

Are we looking at two distinct components ?? (bulge + halo)

NGC 3377 1.5 5.2 Reff

NGC 3379 10.3 13.6 Reff

NGC 5128 1.4 6.7 Reff

Should we expect to find the transition starting routinely around 12 Reff ?

Kalirai et al. 2006 &&

M31 halo Z-gradient Metal-poor past R > 10 Reff

Kalirai et al. 2006 &&

Metal-poor past R > 10 Reff

Williams et al. 2007

Virgo ICM stars

Increasing luminosity of host galaxy

NGC 5128 Cycle 15 – ACS target fields at R = 70, 110, 140 kpc

(13, 20, 25 Reff)

- Finding them in the first place is hard. Field is at intermediate latitude (b = 19o), thus field contamination by both foreground stars and faint background galaxies is very significant

- Low SN = 2 (1500 GC’s total), thus “signal” is low

- Nearby (D = 4 Mpc), thus GCS is very dilute against the field

- Observing runs are always plagued by bad weather, bad seeing, or instrument failure [this includes HST]

What about the globular cluster population? N5128 permits detailed comparison

VERY DIFFICULT TO WORK WITH:

~450 clusters now known, 340 with radial velocities

Woodley et al. 2007, AJ, in press: kinematics & dynamics

Radial velocity measurements

Hi-res imaging (HST, Gemini, VLT, Magellan)

G.Harris et al. 2004 CMT1 database

(C-T1)0 metallicity

Metallicity distribution function

SN = 0.85 +- 0.12 SN = 4.2 +- 0.6

Metallicity distribution function

5)(

)(

MRS

MPS

N

N

The new “specific frequency problem” !

SN = 0.85 +- 0.12 SN = 4.2 +- 0.6

Probably a common feature of gE galaxies.

Assuming the low-metallicity clusters formed in massive pregalactic dwarfs, did they form –

-preferentially early relative to the field stars, followed by truncation of star formation?

-at ~5 x higher efficiency?

Harris & Harris 2002

Beasley et al. 2002

Jordan et al. 2004

Rhode et al. 2005

Major star formation phase of the gE

courtesy Thomas Puzia

Age estimates from Lick indices: Beasley et al. 2007

Highest-metallicity GCs appear 6-8 Gy old. cf. Rejkuba && halo-star mean age of 8.5 Gy

But -- Great majority > 10 Gy

Gemini GMOS study of inner GC population

Preliminary !!

Woodley, Harris, Harris, Geisler, Gomez, & Puzia 2007

N5128: GC kinematics

Woodley et al. 2007, astro-ph/0704.1189

Blue, MP Red, MR

Woodley et al. 2007

GCS PNeNGC 5128 NGC 3379

Romanowsky et al. 2003 Bergond et al. 2006

M87: Cote et al. 2001

Dynamical connection of a giant central galaxy with its surroundings

NGC 5128: Woodley 2006, AJ 132, 2424

There appears to be good reason to think that the metal-rich globular clusters and the main population of stars in E galaxies formed together

and

We may now have reason to think that the metal-poor globular clusters and the (more elusive) metal-poor halo stars formed together as well (but in a different ratio).

But are these generalizations risky? Prospects for continuing the halo-star studies are great if we can get HST back with WFC3 (or ACS) … more extended coverage of N5128, 3379, plus Virgo, Fornax E’s and many others.

Stellar populations are what happen when galaxy populations run out !

All depends on keeping the eye steadily fixed on the facts of nature, and so receiving their images as they are. For God forbid that we should give out a dream of our own imagination for a pattern of the world.

Francis Bacon (1623)

There appears to be good reason to think that the metal-rich globular clusters and the main population of stars in E galaxies formed together

and

We may now have reason to think that the metal-poor globular clusters and the (more elusive) metal-poor halo stars formed together as well (but in a different ratio).