the star formation histories of disk galaxies

The Star Formation Histories of Disk The Star Formation Histories of Disk GalaxiesGalaxies

The Star Formation Histories of Disk The Star Formation Histories of Disk GalaxiesGalaxies

Knut OlsenKnut Olsen

Collaborators: Bob Blum, Andrew Collaborators: Bob Blum, Andrew Stephens, Tim Davidge, Phil Massey, Steve Stephens, Tim Davidge, Phil Massey, Steve

Strom, François Rigaut, and Joss Bland-Strom, François Rigaut, and Joss Bland-HawthornHawthorn

Science with Giant Telescopes: Public Science with Giant Telescopes: Public Participation in TMT and GMTParticipation in TMT and GMT

Chicago, June 16, 2008Chicago, June 16, 2008

Knut OlsenKnut Olsen

Collaborators: Bob Blum, Andrew Collaborators: Bob Blum, Andrew Stephens, Tim Davidge, Phil Massey, Steve Stephens, Tim Davidge, Phil Massey, Steve

Strom, François Rigaut, and Joss Bland-Strom, François Rigaut, and Joss Bland-HawthornHawthorn

Science with Giant Telescopes: Public Science with Giant Telescopes: Public Participation in TMT and GMTParticipation in TMT and GMT

Chicago, June 16, 2008Chicago, June 16, 2008

T.A.Rector and B.A.Wolpa/NOAO/AURA/NSF

Juneau et al. (2005)

Benson et al. (2007)

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Stockton et al. (2004)

Motivation IMotivation IMotivation IMotivation I– Many lines of evidence showing that massive galaxies form the bulk of their stars at high redshift, earlier than less massive galaxies

– More massive galaxies have heavier contribution from spheroidal components, reinforcing the idea that bulges and elliptical galaxies are old, and disks are accreted later

– Massive disk galaxies also exist at high redshift; may be the galaxies that form massive spheroids?

Dark matter Gas Stars

Motivation IIMotivation IIMotivation IIMotivation II

Abadi et al. (2003)

320 kpc

40 kpc

The observed Universe vs. a simulated one (Springel, Frenk, & White 2006)

– Hierarchical structure formation does an excellent job of describing large scale structure; history of build-up of dark matter, however, appears different than that of the observed stellar mass buildup

– Galaxy formation is complex and non-linear, depending on processes operating on a huge range of scales

– Star formation histories of simulated disks are sensitive to the input physics, e.g. feedback from stars and merging, as well as to the mass of the parent galaxy

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•Feedback inhibits rapid collapse of gas

•Feedback regulates star formation

•Introduces dependence on galaxy mass

•Also expect dependence on environment

Robertson et al. (2004)



Governato et al. (2007)

ApproachApproachMilky Way bulge from near- and mid-IR photometry (van Loon et al. 2003): old stars dominate

The M31 halo with HST (Brown et al. 2007): old and intermediate-age populations

A summary of Local Group dwarf star formation histories (Grebel & Gallagher 2004): variety is the rule

Why ELTs?Why ELTs?

1. Need a representative sample of morphological types of galaxies

2. Need to sample orders of magnitude in the range of environmental densities

Both argue for getting out to 10 Mpc and beyond

With high surface brightnesses and faint sources, need to consider both sensitivity and crowding

From Tully group catalog

V I

Crowding introduces photometric error through luminosity fluctuations within a single resolution element of the telescope due to the unresolved stellar sources in that element.

Modeling crowdingModeling crowding

To calculate the effects of crowding on magnitudes and colors, we need only consider the Poisson statistics of the luminosity functions (e.g. Tonry & Schneider 1988)

For magnitudes:

For colors:

hi

8 8

Crowding limits for current and future Crowding limits for current and future telescopestelescopes

Crowding limits for current and future Crowding limits for current and future telescopestelescopes

Magnitudes at which 10% photometry is possible in regions of surface brightness V=22, K=19 for galaxies at the indicated distances.

HST (optical) Gemini North 30-m (near-IR)30-m (I and J)

Using avg

How big an ELT do we need?

How big an ELT do we need?

Using K=22 mag arcsec-2

– The main sequence and its turnoff is the most fundamental indicator of stellar age and metallicity, but the stars are faint and extremely crowded

– More advanced phases of stellar evolution can also be used to determine the ages and metallicities of populations of stars, at the expense of more uncertain theoretical modeling

Current Systems: the Bulge and Disk Current Systems: the Bulge and Disk of M31 with Gemini N and of M31 with Gemini N and

NIRI+AltairNIRI+Altair

Current Systems: the Bulge and Disk Current Systems: the Bulge and Disk of M31 with Gemini N and of M31 with Gemini N and

NIRI+AltairNIRI+Altair

•Nearby:Nearby:

Can study Can study entireentire star formation star formation history from its resolved starshistory from its resolved stars

Complementary to studies of galaxies Complementary to studies of galaxies with z > 0.5, which are limited to with z > 0.5, which are limited to integrated broadband photometry or IFU integrated broadband photometry or IFU spectroscopyspectroscopy

•Extragalactic:Extragalactic:

Can easily trace contributions Can easily trace contributions from different galactic from different galactic componentscomponents

Milky Way produces important Milky Way produces important constraints on the stellar populations of constraints on the stellar populations of galactic components, but from large and galactic components, but from large and heterogeneous datasetsheterogeneous datasets

Local Group Survey (Massey et al. 2002) image

Bulge 1: 520s J, 480s H, 880s K

0.”15 J, 0.”09 H, 0.”09 K

Bulge 2: 320s J, 320s H, 1040s K

0.”11 J, 0.”085 H, 0.”09 K

Disk 1: 960s J, 960s H, 3480s K

0.”11 J, 0.”09 H, 0.”10 K

Disk 2: 540s H, 3420s K

0.”059 H (~30% Strehl), 0.”066 K (~40% Strehl)

ObservationsObservationsObservationsObservations

Gemini N+Altair/NIRI SV observations, 18-19 Nov 2003 (one night photometric)

Disk 2 field observed 14 Sep 2006: 0.´´2 - 0.´´3 seeing, photometric

NIRI/Altair provided near diffraction-limited imaging in HK over 22.´´5 22.´´5 field

We also include published HST/NICMOS data from Stephens et al. (2003)

AnalysisAnalysis

•Usefully measure stars as faint as MK = -4 to -5 (includes TRGB) in bulge and inner disk (published in Davidge et al. (2005) and Olsen et al. (2006) )

•Disk 2 field reaches level of horizontal branch

PhotometryPhotometryPhotometryPhotometry

•PSF-fitting photometry with DAOPHOT/ALLSTAR

Fits the core of the PSF (0.”44 diameter), neglecting the halo

•Corrections applied to account for:

-difference between PSF and aperture magnitudes out to a diameter of 0.”66 (30 pixels): ~0.3 mags

-difference between 0.”66 diameter aperture magnitudes and 4.”4 diameter aperture magnitudes: ~0.4 - 0.6 mags

-spatial variability of the aperture correction

-transformation of magnitudes to standard system

Photometric error analysisPhotometric error analysisPhotometric error analysisPhotometric error analysis

Bulge 2 field

•Completeness and photometric errors calculated from extensive Monte Carlo simulations

•Both simulations and analytical crowding calculation (Olsen, Blum, & Rigaut 2003) indicate that crowding dominates errors for bulge and inner disk; do not go as deep as expected in Disk 2 field

•Restrict analysis to magnitudes with >50% completeness

Disk 2 field

Deriving the population mixDeriving the population mixDeriving the population mixDeriving the population mix•Build models from isochrones (Girardi et al. 2002):

Age = 1, 3, 5, 10 Gyr; Z=0.0001, 0.0004, 0.001, 0.008, 0.019, 0.03; Salpeter IMF for bulge and inner disk; finer age grid for Disk 2 field

•Apply photometric errors and incompleteness to models

•Fit model mix to LFs using maximum likelihood analysis (Dolphin 1997, Olsen 1999, Dolphin 2002); assume E(H-K) from IRAS/ISO; solve age and Z; (m-M)0 = 24.45

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Fit to LF: P ~ 6 - 17%

ResultsResultsResultsResults

Example: two fields with Bulge/Disk ~ 1

Fits are dominated by the oldest populations

M31’s Bulge and Inner Disk M31’s Bulge and Inner Disk Population BoxPopulation Box

M31’s Bulge and Inner Disk M31’s Bulge and Inner Disk Population BoxPopulation Box

•Old ages, nearly solar metallicities dominate

•Metal-poor intermediate-age populations are probably spurious

•Luminosity-weighted age, [Fe/H] = 8 Gyr, 0.0 (-0.5)

•Mass-weighted age, [Fe/H] = 8.3 Gyr, 0.0 (-0.4)

Radial TrendsRadial TrendsRadial TrendsRadial Trends

•Both bulge and disk are dominated by older stars

•The bulge has nearly solar metallicity, in agreement with other studies

•The lower disk metallicities are in general agreement with other studies

The Disk 2 FieldThe Disk 2 FieldThe Disk 2 FieldThe Disk 2 Field

•30% of stellar mass formed within last ~100-300 Myr: prominent signature from the 10 kpc ring!

•35% of the stellar mass appears ancient and metal-poor

Block et al. (2006): Suggest that a collision between M32 and M31 formed the rings ~210 Myr ago

An M31 Survey: 20-m

An M31 Survey: 20-m


Name r() K B/D Klim Time(s)F1 1.97 15.0 7.4 24.1 21.8Bulge1 2.05 15.1 6.7 24.1 24.9F177 2.79 15.4 5.5 24.4 38.3F174 2.59 15.4 5.3 24.4 38.3F3 3.80 15.8 3.8 24.7 66.9Bulge2 3.83 16.0 3.1 24.9 87.8F4 3.98 16.1 2.7 25.0 100F5 5.84 16.4 2.0 25.2 147F170 6.08 16.5 1.9 25.3 168Disk2 9.09 17.1 1.1 25.7 348F2 11.9 17.8 0.3 26.1 776F280 20.5 18.4 0.2 26.6 1767Disk1 56.9 19.6 0.0 27.8 17476

1 hour exposure, S/N=5:J: 28.9H: 28.0K: 27.0

KHB~23.5, KMSTO~27

An M31 Survey: 30-m

An M31 Survey: 30-m


Name r() K B/D Klim Time(s)F1 1.97 15.0 7.4 24.8 17.6Bulge1 2.05 15.1 6.7 24.9 19.7F177 2.79 15.4 5.5 25.1 27.9F174 2.59 15.4 5.3 25.1 27.9F3 3.80 15.8 3.8 25.4 44.2Bulge2 3.83 16.0 3.1 25.5 55.3F4 3.98 16.1 2.7 25.6 62.0F5 5.84 16.4 2.0 25.8 86.3F170 6.08 16.5 1.9 25.9 96.8Disk2 9.09 17.1 1.1 26.2 188F2 11.9 17.8 0.3 26.8 543F280 20.5 18.4 0.2 27.5 1732Disk1 56.9 19.6 0.0 29.1 32500


KHB~23.5, KMSTO~27

An M31 Survey: 50-m

An M31 Survey: 50-m


Name r() K B/D Klim Time(s)F1 1.97 15.0 7.4 25.6 12.8Bulge1 2.05 15.1 6.7 25.7 14.1F177 2.79 15.4 5.5 25.9 18.9F174 2.59 15.4 5.3 25.9 18.9F3 3.80 15.8 3.8 26.1 27.9Bulge2 3.83 16.0 3.1 26.2 34.4F4 3.98 16.1 2.7 26.3 38.8F5 5.84 16.4 2.0 26.6 58.6F170 6.08 16.5 1.9 26.6 68.7Disk2 9.09 17.1 1.1 27.2 194F2 11.9 17.8 0.3 28.1 849F280 20.5 18.4 0.2 28.9 4170Disk1 56.9 19.6 0.0 30.4 69500


KHB~23.5, KMSTO~27

A GMT and TMT disk galaxy program

A GMT and TMT disk galaxy program

•Imaging

GMT HRCAM and TMT IRIS broad-band imaging of ~10–100 galaxies out to 10 Mpc

~10 pointings per galaxy

Having one telescope in each hemisphere would be ideal!

•Spectroscopy

R~3500 @ 0.85 (Ca triplet) with <~0.”05 resolution is ideal for abundance gradients and velocities of RGB stars out to ~10 Mpc; TMT IRIS and IRMOS, GMT NIRMOS

High resolution R~25000 – 50000 spectroscopy will be provide important detailed abundances in the nearest galaxies; GMTNIRS, TMT NIRES and HROS (Smith talk)

Program needs 10–100 clear nights

Other FacilitiesOther Facilities

The low surface brightness regions far from galaxy centers are ideal places to study the late accretion histories of disk galaxies; needs wide fields (LSST, PanSTARRS), excellent site (PILOT), and deep imaging (JWST)







Bland-Hawthorn et al. (2005)

Ibata et al. (2007)

A program of measuring star formation histories from resolved stars in disk galaxies out to ~10 Mpc will provide an exciting and unique perspective on galaxy formation!

Photometry with ground-based adaptive optics on current and future large telescopes are excellent tools to allow us to measure the star formation histories in the bright components of massive galaxies.

Spatial resolution is the most critical capability needed to measure the star formation histories of massive galaxies; we are just beginning to probe these galaxies.

Resolved stellar populations can be used to measure the entire star formation and chemical enrichment histories of galaxies.

The age and metallicity distributions of stars in bulges and disks are sensitive indicators of galaxy formation physics.

Closing ThoughtsClosing ThoughtsClosing ThoughtsClosing Thoughts

Can we trust star formation histories derived from only

evolved stars?

Can we trust star formation histories derived from only

evolved stars?

•Compare star formation histories derived from 2MASS J-K, K CMD of the LMC Bar (Olsen, in prep.) to that derived from HST/WFPC2 (Dolphin 2002)

J-K

An NGC 3379 Survey: 20-m




Jarrett et al. (2002)

Name r() K Klim Time(s)Re 30 17.0 24.6 1973Re 90 19.3 27.2 22620Rtot 190 22.5 31.1

KHB~29, KMSTO~32.5






Name r () K Klim Time(s)Re 30 17.0 25.7 282 3Re 90 19.3 28.5 47200 Rtot 190 22.5 31.6

KHB~29, KMSTO~32.5







KHB~29, KMSTO~32.5

the star formation histories of disk galaxies

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