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Dwarf Galaxies

Ovidiu Vaduvescu ING and IAC Associated ING+NOT+Mercator Seminar 31 May 2012, La Palma. Dwarf Galaxies. Abstract. Brief overview about science interests of studying star forming dwarf galaxies: dwarf irregulars ( dIs ) and blue compact dwarfs (BCDs);

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Dwarf Galaxies

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  1. OvidiuVaduvescu ING and IAC Associated ING+NOT+Mercator Seminar 31 May 2012, La Palma Dwarf Galaxies

  2. Abstract Brief overview about science interests of studying star forming dwarf galaxies: dwarf irregulars (dIs) and blue compact dwarfs (BCDs); Strategies for NIR imaging of extremely faint targets. Our smart algorithm to subtract the highly variable NIR sky; Our new sech law to fit SBPs of dIs and BCDs; Our new “dwarf fundamental plane” (FP) fitting dIs, BCDs and dEs. Some physical fundamentals of this FP; Chemical evolution of dIs and BCDs in clusters and isolated; Future projects and search for students/collaborators at ING/NOT/IAC/etc.

  3. Why dwarf galaxies and NIR? Because this was my proposed subject for my Canadian PhD (2000-2005) at York University in Toronto (Prof. Marshall McCall); Because dwarf galaxies are the most numerous galaxies in the Universe! Because they should be the most simple to study, believed to be the first galaxies to form, from which the larger ones evolved; Because they are little studied, being very difficult to observe (requiring large telescopes and long time), due to their extremely faint brightness! Why observing in Near Infrared (NIR) and not in visible? - Because NIR light traces better the stellar mass of a galaxy; - Because NIR is more transparent to dust (internal or Galactic).

  4. Observing runs: 2-8m telescopes • OAN-SPM Camila (10n, 2001 & 2003) • CFHT CFHTIR (6n, 2002 & 2004) • Gemini North GMOS-N (12h spec, 2003) • Gemini South GMOS-S (50h Ha img & spec, 2007-2012) • NTT SOFI (5n, 2006 & 2008) • Blanco ISPI (10n, 2006-2009) • VLT HAWK-I (6h, 2008) • TNG NICS (4n, 2010) • INT WFC (10n Ha img, 2009 & 2010) • SAAO IRSF SIRIUS (collab, 2005 & 2006) • CFHT WIRCAM (collab, 2005 & 2006)

  5. Observing in the NIR:The problem with the rapidly variable sky (in level and structure) More difficult than in visible! It is very important HOW we observe in the NIR (how often sample the sky to be subtracted every ~minute). Movie showing Mauna Kea sky and CFHT environment variations in Ks band during 2 min step (timelapse 20 min). Variations across the 3.6' CFHT-IR chip about 1% of the sky level are visible. (Vaduvescu & McCall, 2004)

  6. Observing faint galaxies in the NIR Giving the sequence: sky-gal-sky-gal-sky-.... If one combines the sky observed less frequently, the final combined galaxy gets worse. Thus, a so-called “superflat” in the NIR destroys the temporal sky variation! We invented a smart algorithm to “build” and subtract the sky “under” the galaxies in the NIR.

  7. Our algorithm to reduce NIR images How to build and subtract the sky “under” the galaxy assuming the observing sequence sky1-gal1-sky2-gal2-.... Step 1: raw sky Step 2: Subtract sky1-sky2 (to see all stars) Step 3: find all stars (daofind) Steps 4-6: mask stars (imedit or daophot/PSF) Step 7: add back raw sky2 (to fill back all black holes) Step 8: do these again for sky2-sky1 and average the final reduced sky to interpolate time Remember first raw sky/step1?

  8. Our algorithm to reduce NIR images How an extremely faint galaxy shows up following accurate sky subtraction Step 1 gal: raw galaxy (can you find it? :) Step 2 gal: galaxy sky subtracted (sky built like before) Step 3 gal: combined galaxy (some black hole residuals due to bright stars, background galaxies in the sky field or insufficient large dithering) Step 4 gal: mask residuals (manual imedit or other) – final reduced galaxy image Remember first raw galaxy (step1)?

  9. KILLALL, an IRAF software to remove stars from an image NGC 1569 (our most complicated studied dwarf): There are about 5000 stars in the first image, including some 2500 on top of the galaxy! They can be removed semi-automatically in 5 steps using KILLALL (DAOPHOT/PSF based script) one day work Buta & McCall, 1999 (UNIX) Vaduvescu & McCall, 2001 (ported in Linux)

  10. Dwarf Irregular Galaxies (dIs) They have surface brightness profiles (SBPs) linear in the outer part and bounding horizontal at the centre. We invented a new “sech” law to fit SBPs of dIs (Vaduvescu et al, 2005): Why is this? Not known. Could be investigated (modeling – collaborators?)

  11. The dIs Fundamental Plane (FP) The linear Tully-Fisher relation does not appear to hold for dIs. Instead, three physical parameters link dIs in a Fundamental Plane (FP) (Vaduvescu et al., 2005, Vaduvescu & McCall, 2008): - Sech absolute mag MS - Central surface brightness o - Hydrogen line width W20 (radio) This FP can be used as a new distance indicator (for dwarfs or others): if we measure o and W20, then we can calculate M, thus the galaxy distance modulus and distance!

  12. Fundamentals of the dwarf FP The baryonic potential plane assuming fixed M/L (left) and individualized virial conditions (right). Standard deviations are 0.29 mag, similar to that of TF relation for giants! (McCall, Vaduvescu et al., 2012)

  13. NIR CMDs of dIs Near Infrared (NIR) Color-Magnitude Diagrams (CMDs) for the stars resolved in two dwarf irregular (dIs) galaxies. Two main details can be seen: the main bulk and a “finger” (Vaduvescu et al 2005). Is the tilt metallicity-dependent? Is the “whole” real? Again, collaborators welcomed!

  14. Blue Compact Dwarf Galaxies (BCDs) BCDs have surface brightness profiles linear at the outer parts and growing then bounding horizontal at the centre. Fitted with the “sech” law to count the outer regions (dashed line) plus a Gaussian to model the central BCD starburst (dotted line) - Vaduvescu, Richer & McCall, 2006:

  15. BCDs and the dIs FP Blue Compact Dwarfs (BCDs) seem to be located on the FP defined by dIs. This probes a physical link between the two dwarf classes. The FP stands as a distance indicator for BCDs, also. (Vaduvescu, Richer & McCall, 2006)

  16. Dwarf Ellipticals (dEs) and the dIs FP Dwarf Elliptical galaxies (dEs) stand on the dIs FP, suggesting a physical link between the three dwarf classes (dIs, BCDs and dEs) (Vaduvescu & McCall 2005). In comparison (left), Tully Fisher relation shows larger scatter (Vaduvescu et al, 2005). New dE NIR data available to probe this (collaborators welcomed)!

  17. Chemical evolution of dIs and BCDs Chemical properties in star forming dwarf galaxies can be measured via spectroscopy, namely the oxygen abundance. Best results are achieved via [OIII] 4363 line (“direct method”), but this is very faint to observe, requiring ~8-10m class telescopes (=> GTC !) Alternatively, use other bright line methods (less accurate) (Vaduvescu, McCall & Richer, 2007)

  18. Chemical evolution of dIs and BCDs Oxygen abundance correlates with absolute sech magnitude in both dIs and BCDs, and in the NIR the relation is tighter than in visible 12+log(O/H)=5.58-0.14log(MS) (rms=0.10)! (Vaduvescu, Richer & McCall 2007)

  19. Chemical evolution of dIs and BCDs In a closed box model, metallicity is expected to correlate with the gas fraction, μ = Mgas/(Mgas+Mstars) BCDs and dIs appear to obey this model (although we need to improve the sample), suggesting a chemical relation. (Vaduvescu, Richer & McCall 2007)

  20. Dwarf evolution in clusters To compare star forming galaxy isolated evolution (Local Volume d<10 Mpc) with the evolution of dwarf galaxies in nearby galaxy clusters (d<100 Mpc) and higher redshift. • Virgo (14 Mpc) • Fornax (17 Mpc) • Hydra (49 Mpc) • Antlia (35 Mpc) • Perseus (5 Mpc) • Abell 779 (92 Mpc) • Abell 1367 (90 Mpc) • Others with WHT, GTC, etc.

  21. Dwarf evolution in clusters Compared with the LV (isolated objects), star forming dwarfs in Virgo appear to obey the same FP, while Hydra appear to suffer some enviromental effects. Fornax sample is insignificant for any conclusions, and needs increased. (Vaduvescu, Vilchez, Kehrig, et al, 2011).

  22. Dwarf evolution in clusters Apparently, the chemical evolution looks similar in Virgo, Fornax and Hydra, as seen through the closed box model. New GMOS spectroscopic data was acquired recently in Antlia cluster. (Vaduvescu, Kehrig, Smith-Castelli, Richtler 2011 & 2012) – in reduction.

  23. Collaborators • Prof. Marshall McCall, York Univ, Canada; • Dr. Robin Fingerhut, York Univ, Canada; • Dr. Michael Richer, OAN-SPM, Mexico; • Students Francisco Pozo and Angie Barr, UCN Chile -> Bochum Univ; • Prof. Dr. Eduardo Unda-Sanzana, UCN -> UA, Antofagasta, Chile; • Dr. Marcus Albrecht, UCN -> Univ. Bonn, Germany; • Dr. Analia Smith-Castelli, La Plata, Argentina; • Dr. Lidia Makarova, SAO, Russia; • Prof. Dr. Jose Vilchez, IAA, Granada, Spain; • Dr. Carolina Kehrig, IAA, Granada, Spain; • Dr. Jorje Iglesias-Paramo, IAA, Granada, Spain; • Drd. VasilikyPetropoulou, IAA, Granada, Spain; • Dr. Daniel Reverte, GTC La Palma.

  24. Future work • Improve the dwarf FP using new radio data (Paolo Serra + new HI surveys) and deeper NIR data to study further the phsyical link between dIs and BCDs; • Enlarge the dE NIR sample (Blanco 2009 run, Peletiercollab, first release of VISTA, etc) and study their relation with star forming dwarfs; • Approach the relation of our dwarf FP with other classic FPs for giants, in the attempt to constraint their physical evolution. • Due to my present busy support job and other science interests (and also because I became a father!) I need students or collaborators to continue these line of research. Eventually I could co-supervise one PhD student together with another thesis director (from IAC, ULL or others from abroad).

  25. References http://www.ovidiuv.ca/papers/ Vaduvescu, O. and McCall, M., 2004, PASP 116, 640 Strategies for Imaging Faint Extended Sources in the Near-Infrared Vaduvescu, O. et al, 2005, AJ 130, 1593 Infrared Properties of Star-Forming Dwarf Galaxies. I. Dwarf Irregular Galaxies in the Local Volume Vaduvescu, O., Richer, M., and McCall, M., 2006, AJ 131, 1318 Infrared Properties of Star-Forming Dwarf Galaxies. II. Blue Compact Dwarf Galaxies in the Virgo Cluster Vaduvescu, O. and McCall, M., 2005, Proc. IAU No. 198 dEs and the dI fundamental plane Vaduvescu, O., McCall, M. and Richer, M., 2007, AJ 134, 604 Chemical Properties of Star-Forming Dwarf Galaxies Vaduvescu, O. and McCall, M., 2008, A&A 487, 147 The fundamental plane of dwarf irregular galaxies Vaduvescu, O., et al. 2011, A&A 553, 95 Searching for Star Forming Galaxies in Fornax and Hydra Clusters McCall, M., Vaduvescu, O., et al. 2012, A&A 540, 49 Fundamentals of the Dwarf Fundamental Plane

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