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INFRARED PROPERTIES OF STAR FORMING DWARF GALAXIES

INFRARED PROPERTIES OF 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. What is a dwarf galaxy?

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INFRARED PROPERTIES OF STAR FORMING DWARF GALAXIES

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  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 MB>-16 (Tamman 1994) or MV>-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 (dS’s)? 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 (< 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!

  6. 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 

  8. 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)

  9. 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

  10. 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 sky–gal–sky–gal–sky– … –sky–gal–sky sequence.

  11. 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

  12. 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/ro+e-r/ro) (Vaduvescu et al., AJ 130, 2005)

  13. Surface photometry of BCDs: Sech for the old extended component: IS = I0S sech(r/r0S) plus Gaussian for the young starburst: IG=I0G exp[-1/2 (r/r0G)2] (Vaduvescu, Richer & McCall, AJ 131, 2006) I = IS + IG

  14. Surface Photometry – tool for dI and BCD distinction: NGC 1569 – dI or BCD? Sech fitting (dI?) Sech plus Gaussian fitting (BCD?)

  15. Stellar Photometry – CMDs of dIs: Selected star catalogue (stars from galaxy) Stars in the field (from Milky Way)

  16. 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

  17. 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

  18. 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)

  19. Structural properties of dIs Scale length correlates with absolute magnitude. r0=(-0.810.24)+(-0.070.01)MS

  20. Structural properties of dIs (continued) Semimajor axis correlates with absolute magnitude. r22=(-5.340.40)+(-0.380.02)MS

  21. Structural properties of dIs (continued) Central surface brightness shows a trend with absolute magnitude.

  22. Structural properties of dIs (continued) Total colour has a trend with the absolute magnitude.

  23. Structural properties of dIs (continued) The Tully-Fisher relation for dIs solid fit – our data; dashed – P&T The “dI Fundamental Plane” (Vaduvescu et al., AJ 130, 2005)

  24. Structural properties of BCDs Scale length has a trend with the absolute magnitude. (dashed line shows the dI fit)

  25. Structural properties of BCDs (continued) Central surface brightness has a trend with the absolute magnitude. (dashed line shows the dI fit)

  26. BCDs on the dI Fundamental Plane BCDs appear to lie on the dI FP (Vaduvescu, Richer & McCall, AJ 131, 2006)

  27. 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)

  28. Structural Properties of dEs (continued) Semimajor axis correlates with absolute magnitude (dashed line shows the dI fit)

  29. Structural Properties of dEs (continued) Central surface brightness correlates with absolute magnitude (dashed line shows the dI fit)

  30. Structural properties of dEs (continued) Tully-Fisher relation for dEs is scattered dEs lie on the dI FP (Vaduvescu & McCall, IAU Colloquium 198, 2005)

  31. Spectroscopy of HII regions of BCDs • Determine the oxygen abundance, 12+log(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)

  32. Spectroscopy of HII regions of BCDs (continued) Reduced combined spectrum of VCC 459 (Gemini-N GMOS data)

  33. Chemical properties of dwarf galaxies Luminosity-metallicity relation for dIs 12 + log(O/H) = (-0.13  0.01) MK+ (5.77  0.21)

  34. Chemical properties of dwarf galaxies (continued) Luminosity-metallicity relation for BCDs 12 + log(O/H) = (-0.24  0.03) MK+ (3.88  0.53)

  35. 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)

  36. 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)

  37. Chemical properties of dwarf galaxies (continued) Gas fraction-metallicity relation for dIs & BCDs  = Mgas/(Mgas+Mstars) Closed-box model Lee, 2001 (dotted line) dIs and BCDs appear to fit the closed box model

  38. Conclusions: • In dIs from the LV (D<5 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);

  39. 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;

  40. Conclusions (continued): dIs, BCDs & dEs on the dI Fundamental Plane

  41. 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.

  42. 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 

  43. Thank you ! • Also we’d 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 you’ve wondered: • Background image: NGC 1569 at CFHT 2002

  44. In preparation for an observing night  (La Silla, 2 July 2006, courtesy of my Nikon D50)

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