A Survey of Local Group Galaxies Currently Forming Stars

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A Survey of Local Group GalaxiesCurrently
Forming Stars
Phil Massey Lowell Observatory April 14, 2003
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The Team

• Paul Hodge, Univ. of Washington
• Shadrian Holmes, Univ. of Texas
• George Jacoby, WIYN
• Nichole King, Lowell Observatory
• Phil Massey (PI), Lowell Observatory
• Knut Olsen, CTIO/NOAO
• Abi Saha, KPNO/NOAO
• Chris Smith, CTIO/NOAO

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Overview

• We are imaging all of the galaxies of the Local
  Group that are currently forming stars
• broad-band (UBVRI)
• narrow-band (H?, OIII, SII)
• with the KPNO and CTIO 4-m telescopes and
  Mosaic CCD cameras.

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Motivation Our Science

• The galaxies of the Local Group serve as our
  laboratories for studying star formation and
  stellar evolution as a function of metallicity,
  Z. (Z varies by a factor of 17 from WLM to M31.)

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Why should the metallicity matter?

• Star Formation
• Lower metallicity gas should have a lower cooling
  rate, and hence higher temperatures ?larger
  Jeans mass, leading to a top-heavy IMF (Larson
  1998).
• But over the limited metallicity range (3x)
  SMC?LMC?MW this effect isnt seen!

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IMF Slope in OB Associations

• From Massey (2003)

Z0.018
Z0.008
Z0.004
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IMF

• Variations that are seen in the IMF slope are
  statistical, not physical (Massey 1998, Kroupa
  2001)
• But what would happen if we extended this to
• one-tenth solar (WLM) to 2x solar (M31)???
• The answer is important for understanding the
  integrated properties of galaxies at large
  look-back times.

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Star Formation/metallicity (cont)

• Some expect that the upper mass limit will vary
  as a function of metallicity
• True only if radiation pressure acting on grains
  is the limiting factor in determining the mass of
  the highest mass star that can form.
• So far we find that the upper mass limits are
  purely statistical, and not physical. What ever
  it is that limits the ultimate mass of a star we
  have yet to encounter it in nature (cf. Massey
  Hunter 1998 ApJ 493, 180).

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Why should the metallicity matter ? (continued)

• Massive Star Atmospheres and Evolution
• Stellar winds are driven by radiation pressure
  through highly ionized metal lines. Mass-loss
  rates will depend upon Z?, where ? ? 0.5-1.0
• This mass-loss has a profound effect on the
  evolution of high-mass stars.

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Relative number of red supergiants (RSGs) and
Wolf-Rayet stars (W-Rs)
log Number RSGs/WRs
From Massey 2003, ARAA 41 (in press)
log (O/H) 12
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Relative number of red supergiants (RSGs) and
Wolf-Rayet stars (W-Rs)
log Number RSGs/WRs
From Massey 2003, ARAA 41 (in press)
log (O/H) 12
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Need good observational database

• New generation of high mass evolutionary models
  are becoming available, which include the
  important effects of rotation (mixing introduced
  by meridional circulation and shear
  instabilities).
• Need solid observational database to help guide
  the theorists.

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Our Science (continued)
Along the way well find The most massive
supergiants. Luminous Blue Variables and other
luminous stars with H? emission. Star formation
rates for massive stars. Distribution and
numbers of evolved massive stars (RSGs, WRs).
HII regions, SNRs, PNe, and the extent of the
diffuse emission.
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Your Science

• This survey will provide the source list
  (finding charts) for spectroscopy with 8-10-m
  telescopes for decades to come. Our data
  products include
• Stacked images (UBVRI, H?, OIII, SII)
• Individual dithered images (suitable for
  photometry).
• Calibration
• Catalog of UBVRI photometry of roughly 300
  million stars

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What Were Doing The Sample

• M31 (10 fields) Pegasus Dwarf
• M33 (3 fields) Phoenix
• IC 10 IC 1613
• NGC 6822 Sextans A
• WLM Sextans B

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How Are We Doing?

• ?M31 (10 fields) ? Pegasus Dwarf
• ?M33 (3 fields) ? Phoenix
• ? IC 10 ? IC 1613
• ? NGC 6822 ? Sextans A
• ? WLM ? Sextans B

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What Were Doing (continued)

• Aiming for a S/N of 3 at UBVRI25,
• in 1 seeing.
• Also imaging in H?, OIII, SII
• Each field 5 ditherings, then stacked.

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Hasnt All This Been Done Before?

• Yes, but not with our depth, area, photometric
  accuracy and resolution!
• Photographic plates had the area coverage and
  (usually) the resolution, but neither the
  photometric accuracy nor depth.
• CCD studies had the depth and accuracy but not
  always the resolution and certainly not the area
  coverage.
• Wal Sargent story...

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Comparison of M31 CCD Surveys
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Basic Processing

• Generally following the Valdes IRAF pipeline
  but with some enhancements.
• Better flat-fielding techniques.
• Better determination of sky and scaling in the
  stacking process (via scripts using aperture
  photometry).
• Details, and software, can be found at our web
  site http//www.lowell.edu/massey/lgsurvey

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Photometry

• For the purposes of photometry, we treat each
• Mosaic camera as 8 separate instruments
• PSF variations within a single chip modest
  compared to chip-to-chip variations.
• Different DQE-wavelength dependence for each chip
  means different color terms and even different
  zero-points (despite flat-fielding efforts).

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U flat divided by I flat
Variations ?30
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Photometry software

• Its a factor of 40 times more work (8 chips x 5
  ditherings) but at least when were done we have
  1 photometry.
• Weve developed a series of IRAF scripts and
  FORTRAN programs that allow us to do the
  photometry automatically, chip-by-chip,
  dither-by-dither.
• All of this is freely available from our web
  site
• http//www.lowell.edu/massey/lgsurvey

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How weve solved the calibration problem
Lowells dark-sky site at Anderson Mesa
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External Calibration using Lowell s 1.2-m Hall
Telescope

• Can use only the most pristine, photometric
  nights.
• Select the best calibrated Landolt standards
  covering a complete range of colors
• Investigate gravity effects on the U-band filter

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U solution always squirrelly near U-B0.
U-B
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Its a matter of some gravity....
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Progress Report---How are We Doing?

• All images for M31 (10 fields), M33 (3 fields),
  NGC 6822, IC10, WLM, Phoenix, Sextans A, and
  Sextans B are now released, and sitting in the
  NOAO NSA archive, as well as our own dedicated
  ftp site (which makes bulk downloads easier).
• Poor weather in early September prevented us from
  completing the project still need IC1613 and the
  Pegasus dwarf, plus repeat of poor seeing frames.
• Calibration in progress and catalog should be
  complete on schedule, release Jan 2004.

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Did We Achieve our 1.0 seeing goal?

• Not really...

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(No Transcript)
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1.3
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0.76
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1.3
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0.76
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Poor seeing matters!

• To redo the images with seeing gt 1.3 would
  require only a few additional nights.

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Sadly...

• Weve been told that our time has run out, and we
  arent eligible for additional time via the
  survey TAC.
• So, weve made our best case to the standard TAC
  and well see what happens.
• (Wal Sargent Cautionary Tale)

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M31 in 10 fields
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M31 in 10 fields
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M31 Fields 2 3
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M33-North
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M33-Center
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NGC 6822
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Phoenix
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WLM
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Whats Next?

• Spectroscopy!

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M31
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N206 in M31
ob78-231
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HST/ FUV ob78-231

• Bianchi, Hutchings, Massey (1996, AJ, 111, 2303)

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To take high S/N optical spectra at B19 requires
a really big telescope...
The 6.5-m MMT
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Optical (blue) spectrum ob78-231
Spectrum in collaboration with Kathy Eastwood
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OB78-231 at H?
Spectrum in collaboration with Kathy Eastwood
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Meanwhile, these data are already being used...

• Ben Williams PhD thesis (Univ Washington)
• Williams MNRAS 340, 143 based up a bootstrap
  calibration.
• Forms optical basis for identifying super-soft
  Chandra counterparts (DiStefano et al., in prep)
• Images have been featured in
• APOD 27 Sept 2001
• Astronomy Magazine (Sky Gem feature), Dec 02
• Upcoming Mercury article on super star clusters
  (Hunter, Elmegreen, Massey 2003, in press)

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Real Science

• ...will come once the calibrated photometry is
  complete this summer. (Catalog will be released
  at the AAS meeting in Jan 2004).

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Follow-up Work In Progress

• Well be pushing our studies of stellar winds to
  high metallicities (M31) using Cycle 12 time on
  HST (40 orbits 80 parallels just awarded)
• We also hope to begin extending our studies of
  the IMF to the more distant galaxies of the Local
  Group using DEIMOS on KeckII.