INFRARED PROPERTIES OF STAR FORMING DWARF GALAXIES

1
INFRARED PROPERTIESOF STAR FORMING DWARF
GALAXIES

• Ovidiu Vaduvescu
• Postdoc, UKZN SAAO, South Africa
• My Canadian PhD
• Sep 2000 Nov 2005
• Defended on 18 Nov 2005
• York University, Toronto, Ontario Canada
• Presented on July 17th, 2006
• ESO, Vitacura, Chile

2

• What is a dwarf galaxy?
• Any galaxy MBgt-16 (Tamman 1994) or MVgt-18 (Grebel
  2000)
• Three to five types of dwarf galaxies
• Dwarf Irregulars (dIs)
• Blue Compact Dwarfs (BCDs)
• Dwarf Ellipticals (dEs) / Dwarf Spheroidals
  (dSphs)
• Dwarf Spirals (dSs)?
• Any evolutionary relations?
• dIs BCDs dEs ?
• Dwarfs Giants ?

3

• Why star forming dwarf galaxies?
• They trace the early stages of galaxy evolution
• There is no agreement yet about the evolutionary
  connection between dIs, BCDs and dEs
• The closed box model can be checked against the
  three
• From about 450 galaxies in the Local Volume (lt 10
  Mpc), there are about 380 dwarfs (85)
• Why prefer the near infrared (NIR)?
• Need a better gauge of mass via the old stellar
  population
• The extinction is very low (about 10x lower than
  in visible)
• Prefer J and Ks versus H

4

• Three major requirements
• Deeper NIR imaging (?K ? 23 mag/arcsec2)
• Accurate distances (Cepheids, TRGB)
• Precise abundances (OIII ?4363 line)
• Observing samples 90 dwarfs!
• 43 dIs in the Local Volume
• 34 observed by us
• 9 from 2MASS (larger brighter).
• 16 BCDs in the Virgo Cluster by us
• 31 dEs from Virgo Cluster and Local Group
• 22 in Virgo from GOLDMine
• 9 in the Local Group, from the literature.

5

• Seven observing runs
• CFHT, Hawaii
• Direct Imaging (2 runs)
• 2002 (3 nights)
• 2004 (3 nights).
• 29 dIs in the LV
• CFHT Presenting

• WARNING
• Any unauthorized interpretation of this picture
  strictly prohibited!

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• Seven observing runs (continued)
• OAN-SPM 2.1m, Mexico
• Direct Imaging (21 nights)
• 2001 (4 nights)
• 2002 (4 nights)
• 2003 (7 nights)
• 2004 (6 nights)
• 16 BCDs in Virgo
• 6 dIs in the LV
• Special thanks to Dr. Michael Richer!

7

• Seven observing runs (continued)
• Gemini-North, Hawaii
• 2003 (one night).
• Spectroscopy of
• 4 BCDs in Virgo
• The Crux besides Gemini North courtesy of my
  Nikon ?

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• Strategies for NIR observing and reduction
• In NIR, the background noise comes from
• The atmosphere (airglow)
• The structure (telescope, dome, etc)
• The camera (detector, filters, etc).
• Two components
• The background level (median of a sky frame)
• The background pattern (structure, sky frame
  next sky frame )
• We studied the rate of change of the two in
• (Vaduvescu McCall, PASP 116, 2004)

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How often to sample the sky?

• Observing sequences
• sky-gal-sky--sky-gal-sky
• sky-gal-gal-sky-
• sky-gal-gal-gal-sky-
• etc
• Markarian 209
• 10 galaxy frames
• combined using
• - 10 sky frames
• - 6 sky frames
• - 4 sky frames
• - 2 sky frames

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• Conclusions to the background problem
• Background level (associated with the airglow)
• Background pattern (associated with the
  instrument movie).
• To do 1 surface photometry
• Exposures in J must be separated by less than 90
  sec
• Exposures in K must be separated by less than
  120 sec
• Use skygalskygalsky skygalsky sequence.
  

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Surface photometry of dIs KILLALL at work!
KILLALL (Buta McCall, 1999) kill 10,000
stars in five steps (a) Ks image of NGC 1569
(b) Unresolved component, after
KILLALL Resolved/Total flux ratios less than 5
in Ks and 10 in J
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Surface photometry of dIs
Exponential, de Vaucouleurs, and Sersic laws do
not fit dIs. Sech law does I Io sech(r/ro)
Io/cosh(r/ro) 2Io/(er/roe-r/ro) (Vaduvescu et
al., AJ 130, 2005)
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Surface photometry of BCDs
Sech for the old extended component IS I0S
sech(r/r0S) plus Gaussian for the young
starburst IGI0G exp-1/2 (r/r0G)2 (Vaduvescu,
Richer McCall, AJ 131, 2006) I IS IG
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Surface Photometry tool for dI and BCD
distinction
NGC 1569 dI or BCD?
Sech fitting (dI?)
Sech plus Gaussian fitting (BCD?)
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Stellar Photometry CMDs of dIs
Selected star catalogue (stars from galaxy)
Stars in the field (from Milky Way)
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Stellar Photometry CMDs of dIs

• Two details in most CMDs
• Blue finger (J Ks ? 1 mag) O-rich RGB stars
• Red tail (1 ? J Ks ? 2.5 mag) TP-AGB stars

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Surface Photometry

• dIs three magnitudes
• Isophotal MI unresolved, measured from
  ellipses
• Sech MS modeled from sech law applied to the
  unresolved component (no giant stars, thus mostly
  old populations)
• Total MT add the resolved stars from selected
  star catalog.
• BCDs four magnitudes
• Isophotal MI measured from ellipses
• Sech MS model of the outer component (old
  populations)
• Gaussian MG model of the inner starburst (young
  stars)
• Total MT include MS and MG

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Fraction of light from a starburst
Fraction of light of a burst of star formation
contributed by stars brighter than MK 7.5 mag
with respect to the total flux from all stars,
as a function of stellar age. For bursts
younger than 3 Gyr, most of the light comes
from stars brighter than MK 7.5
Based on population synthesis (Girardi et al,
2000, 2002)
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Structural properties of dIs
Scale length correlates with absolute
magnitude. r0(-0.81?0.24)(-0.07?0.01)MS
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Structural properties of dIs (continued)
Semimajor axis correlates with absolute
magnitude. r22(-5.34?0.40)(-0.38?0.02)MS
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Structural properties of dIs (continued)
Central surface brightness shows a trend with
absolute magnitude.
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Structural properties of dIs (continued)
Total colour has a trend with the absolute
magnitude.
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Structural properties of dIs (continued)
The Tully-Fisher relation for dIs solid fit our
data dashed PT
The dI Fundamental Plane (Vaduvescu et al., AJ
130, 2005)
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Structural properties of BCDs
Scale length has a trend with the absolute
magnitude. (dashed line shows the dI fit)
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Structural properties of BCDs (continued)
Central surface brightness has a trend with the
absolute magnitude. (dashed line shows the dI
fit)
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BCDs on the dI Fundamental Plane
BCDs appear to lie on the dI FP (Vaduvescu,
Richer McCall, AJ 131, 2006)
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Structural Properties of dEs
Fit SBPs of dEs using the exp I I0
exp(-r/r0) Scale length correlates with
absolute magnitude (dashed line shows the dI
fit)
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Structural Properties of dEs (continued)
Semimajor axis correlates with absolute
magnitude (dashed line shows the dI fit)
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Structural Properties of dEs (continued)
Central surface brightness correlates with
absolute magnitude (dashed line shows the dI
fit)
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Structural properties of dEs (continued)
Tully-Fisher relation for dEs is scattered
dEs lie on the dI FP (Vaduvescu McCall, IAU
Colloquium 198, 2005)
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Spectroscopy of HII regions of BCDs

• Determine the oxygen abundance, 12log(O/H),
  using
• Direct OIII ?4363 (Osterbrock, 1989)
• given a temperature and density
• The bright-line method R23 (Pagel et al., 1979)
• R23( I(OII ?3727) I(OIII ??4959,5007) ) /
  I(H?)
• Data reduction performed with
• INTENS to fit lines
• (McCall Mundy, 1980)
• SNAP to measure lines
• (Krawchuck, et al, 1997)

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Spectroscopy of HII regions of BCDs (continued)
Reduced combined spectrum of VCC 459 (Gemini-N
GMOS data)
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Chemical properties of dwarf galaxies
Luminosity-metallicity relation for dIs 12
log(O/H) (-0.13 ? 0.01) MK (5.77 ? 0.21)
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Chemical properties of dwarf galaxies (continued)
Luminosity-metallicity relation for BCDs 12
log(O/H) (-0.24 ? 0.03) MK (3.88 ? 0.53)
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Chemical properties of dwarf galaxies (continued)
Gas mass-metallicity relation for dIs BCDs dI
fit (solid line) 12 log(O/H) (5.26 ? 0.46)
(0.32 ? 0.06) log(Mgas) Lee, 2001 (dotted line)
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Chemical properties of dwarf galaxies (continued)
Mass-metallicity relation for dIs BCDs dI fit
(solid line) 12 log(O/H) (5.04 ? 0.44)
(0.34 ? 0.05) log(Mbary) Lee, 2001 (dotted
line)
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Chemical properties of dwarf galaxies (continued)
Gas fraction-metallicity relation for dIs
BCDs ? Mgas/(MgasMstars) Closed-box
model Lee, 2001 (dotted line) dIs and
BCDs appear to fit the closed box model
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Conclusions

• In dIs from the LV (Dlt5 Mpc) observed at CFHT we
  resolved
• stars as faint as MK 7.5 mag (giants younger
  than 8.5 Gyr)
• Resolved/Total flux ratios in dIs in K are less
  than 5 (10 in J)
• Correlated with population synthesis, the
  unresolved component
• can be regarded as old
• Surface brightness profiles of dIs can be fitted
  with sech function
• Surface brightness profiles of BCDs can be fitted
  with sech (to
• model the underlying extended old component)
  plus Gaussian (to
• model the inner young starburst)

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Conclusions (continued)

• Sizes of dIs and BCDs correlates with brightness
• Central brightness of dIs and BCDs correlates
  with brightness
• Colours of dIs correlate with brightness
• CMDs of resolved stars in dIs show two details a
  blue finger
• (O-rich intermediate-age and old AGB bright
  stars), and a red tail (TP-AGB stars)
• BCDs and dIs are similar, structurally and
  dynamically
• dEs follow the structural correlations of dIs,
  matching closely
• the dI Fundamental Plane, suggesting an intimate
  link between
• the two systems

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Conclusions (continued)
dIs, BCDs dEs on the dI Fundamental Plane
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Conclusions (continued)

• Metallicity (oxygen abundances) of dIs and BCDs
  correlates with stellar mass, gas mass, baryonic
  mass, and the gas fraction
• (dIs only). More massive systems contain more
  metals
• BCDs align with dIs on the metallicity baryonic
  mass relation,
• suggesting similar evolutionary connections
  between the two
• Overall, BCDs appear to be dIs observed in a
  bursting phase
• Based on the metallicity gas fraction relation,
  it seems that dIs and BCDs obey the closed box
  model
• dEs appear to represent the final outcome of dIs
  (or BCDs),
• after all the gas is removed from the system.

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Future Projects

• Publish Chapters 7 8 (chemical properties of
  dwarfs) -Vaduvescu, McCall and Richer, AJ 2006b
  to be sent soon
• Enhance the sample later (spectroscopy needed)
• Study the dI Fundamental Plane at the bright end
  based on
• 2MASS (Vaduvescu, 2006c in work)
• Add new dIs data at the faint end two runs at
  SAAO/IRSF, CFHT/WIRCAM, two new runs at ESO/NTT
  and CTIO/Blanco Fingerhut, McCall, Vaduvescu,
  Rekola, et al (in work)
• Study L-Z and mass-Z relation for dwarfs in
  clusters Vaduvescu, Vilchez, Iglesias-Paramo,
  Kehrig, et al (in work)
• Get a job ?

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Thank you ! Also wed like to thank ESO for
granting us time to observe on the NTT. For me,
observing at La Silla was a dream which came
true! In case youve wondered Background
image NGC 1569 at CFHT 2002
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In preparation for an observing night ? (La
Silla, 2 July 2006, courtesy of my Nikon
D50)