ReginaSchulteLadbeck 042104

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Information about ReginaSchulteLadbeck 042104
Science-Technology

Published on August 29, 2007

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The Resolved Stellar Content of Nearby “Young” Galaxies:  The Resolved Stellar Content of Nearby 'Young' Galaxies Regina E. Schulte-Ladbeck University of Pittsburgh Slide2:  Cosmology Adapted from Dekel 2003 Observational Cosmology:  Observational Cosmology Study the global properties of the Universe e.g. Ho, m Study the local properties of the Universe which are significantly affected by the global properties e.g. large-scale-structure and galaxy formation from primordial density fluctuations Dwarfs, dwarfs, dwarfs ...:  Dwarfs, dwarfs, dwarfs ... The substructure problem of CDM Formation of dwarf galaxies Dwarf galaxies, DLA systems, and the chemical evolution of the Universe The Dwarf Galaxy Crisis or Searching for Stars in High Velocity Clouds:  The Dwarf Galaxy Crisis or Searching for Stars in High Velocity Clouds The Issue: Substructure:  The Issue: Substructure MWG's virial radius 6 0 0 kpc Font et al. 2002 CDM Predictions vs Local Group Dwarfs:  CDM Predictions vs Local Group Dwarfs Proposed Solutions:  Proposed Solutions Particle physics (e.g. Spergel andamp; Steinhardt 2000, Colín et al. 2000) Astrophysics (e.g. Bullock et al. 2001, Somerville 2002) Observational Bias Dwarf galaxies have been overlooked High Velocity Clouds are candidates (Blitz et al. 1999) High Velocity Clouds:  High Velocity Clouds Are concentrations of neutral hydrogen Have high radial velocities inconsistent with Galactic rotation models Origins (e.g. Wakker andamp; van Woerden 1997) Galactic Fountain Magellanic Stream 'Others' =andgt; Missing satellites if at extragalactic distances (Blitz et al. 1999) =andgt; Search for stars Slide10:  Our Approach:  Our Approach Search for stars in Compact HVCs Deep V, I imaging with the VLT centered on the highest column density HI (from Effelsberg). Small FOV of FORS 6.8’x6.8’, but reach even faint stellar populations throughout the entire Local Group (RGB to 2 Mpc). 2MASS archival data in J, H, K. Appropriate, 2o fields, adjacent fields used for galactic foreground contamination, data sensitive to RBG/AGB within 300 kpc. K-band Position Plots of 2o Fields centered on dSphs:  K-band Position Plots of 2o Fields centered on dSphs Sensitivity of 2MASS Data :  Sensitivity of 2MASS Data MS stars to 125 kpc =andgt; none are seen RGB and AGB to 300 kpc =andgt; simulations used Sculptor (80 kpc) RGB, KS test on LFs could add up to 8 times the Sculptor RGB V of 21.4 arcsec-2 such a high-surface brightness galaxy would have been seen on POSS plates (cf. Simon andamp; Blitz 2002) The Optical CMD of a “Transition Dwarf”:  The Optical CMD of a 'Transition Dwarf' The Optical CMDs of Four CHVCs:  The Optical CMDs of Four CHVCs Sensitivity of VLT Data:  Sensitivity of VLT Data MS stars to 1 Mpc =andgt; none are seen RGB stars to 2 Mpc =andgt; simulations used Phoenix (450 kpc) RGB, KS test on LFs could add up to 70 Phoenix RGB stars 1.5 RGB stars arcmin-2 at 0.5 Mpc V of 29 mag arcsec-2 Mv of -5.8 Statistics:  Statistics If all CHVCs contain stars, then null detection of stars in 5 CHVCs can occur by chance with a probability of andlt;10-8. There is a 50-50 chance that we missed the stars in 5 CHVCs if only 13% of CHVCs have formed stars. Papers on No Stars in HVCs:  Papers on No Stars in HVCs Hopp, Schulte-Ladbeck andamp; Kerp 2003, MNRAS, 339, 33 Simon andamp; Blitz (2002) - POSS plates Willman et al. (2003) - SDSS ERD Lewis et al. (2002) - one HIPASS cloud Irwin et al. (2003) - the M31 HVC No stars=andgt; need to look for gravitational lensing The Formation of Dwarf GalaxiesorExtremely metal-poor star-forming dwarfs in the present epoch:  The Formation of Dwarf Galaxies or Extremely metal-poor star-forming dwarfs in the present epoch Slide20:  Adapted from Dekel 2003 Dwarf Galaxy Building Blocks:  Dwarf Galaxy Building Blocks Halo formed early – stars formed early (overcooling?) Non-merged remnants – old (+ young) stellar population Halo formed early – SF suppressed/delayed Non-merged remnants – dark or intermediate-age (+young) population Halo formed late – stars formed late =andgt; young today Isolated dwarf galaxies – young stellar population cf. Roukema 1998, Babul andamp; Ferguson 1996, White andamp; Springel 2000 Blue Compact Dwarf Galaxies:  Blue Compact Dwarf Galaxies Each square is 5 kpc on the side. Gil de Paz, Madore andamp; Pevunova , 2003 Primary N => Primeval BCDs?:  Primary N =andgt; Primeval BCDs? Izotov andamp; Thuan (1999) interpret BCDs with low N/O at low O/H as 'primeval' galaxies. O is produced in massive stars only. N could be produced in massive stars or in intermediate-mass stars; it is primary if there are no 'seeds' for the CNO cycle. What about DLAs? Slide24:  Co-Is on BCDs/SFHs Regina Schulte-Ladbeck Ulrich Hopp Igor Drozdovsky Laura Greggio Mary Crone Claus Goessel Jan Snigula SFRs in the Izotov&Thuan sample:  SFRs in the Izotovandamp;Thuan sample Note the absence of any local BCDs with SFR andgt; 0.1 M⊙/yr in the 'primordial He' sample. (Hopkins, Schulte-Ladbeck andamp; Drozdovsky 2002) CMD Morphology:  CMD Morphology Aparicio et al. 1996 Simulation of an OLD Galaxy with continuing star formation CMD Morphology of Distant, BCD:  CMD Morphology of Distant, BCD ---- VII Zw 403 from the Ground with the 48” (1.2m) DSS Telescope:  VII Zw 403 from the Ground with the 48' (1.2m) DSS Telescope VII Zw 403 DSS FOV: 4’x 4’ VII Zw 403 from the Ground with the 140” (3.5m) Calar Alto Telescope:  VII Zw 403 from the Ground with the 140' (3.5m) Calar Alto Telescope VII Zw 403 DSS Hopp andamp; S-L 1995 Prime-focus R-band image 256'x160' S is up VII Zw 403 with the 95” (2.4m) Hubble Space Telescope:  VII Zw 403 with the 95' (2.4m) Hubble Space Telescope VII Zw 403 HST Slide31:  The CMD of VII Zw 403:  The CMD of VII Zw 403 Spatial Distribution of the Stellar Populations:  Spatial Distribution of the Stellar Populations Resolving the Core-Halo Structure:  Resolving the Core-Halo Structure How We Derive the Star-Formation History:  How We Derive the Star-Formation History Slide36:  Slide37:  Slide38:  Slide39:  Slide40:  Slide41:  Slide42:  The Star-Formation History:  The Star-Formation History HST/NICMOS CMDs:  HST/NICMOS CMDs HST CMDs of BCDs :  HST CMDs of BCDs More distant BCDs exhibit shallower WFPC2 CMDs. In all cases, stars with ages as old as the limiting magnitudes of the data are seen. Extremely Metal-Poor SFGs:  Extremely Metal-Poor SFGs Increasing metallicity: I Zw 18, Leo A, SBS 1415+437, VII Zw 403 Increasing distance: Leo A VII Zw 403 SBS 1415+437 I Zw 18 Leo A SBS 1415+437 I Zw 18 VII Zw 403 DLAs Extreme SFGs HII regions andamp; galaxies HST WFPC2 over Wendelstein Fields :  HST WFPC2 over Wendelstein Fields GO 5915 Tolstoy et al. 1998 SFH core andlt; 2 Gyr GO 8575 Schulte-Ladbeck et al. 2002 SFH 'halo' ≥9 Gyr Wendelstein 0.8 m Hopp et al. 2004 Cepheids and other variable stars Distance, metallicity, age:  Distance, metallicity, age We find a distance modulus of 24.5 or 795 kpc using the TRGB method. Globular cluster ridgelines indicate the metallicity (Fe/H) of RGB stars is extremely low, 1% Solar, smaller than that of the ionized gas. But if we assume that the ISM of Leo A indicates the metallicity of the RGB stars, then their age is only 5 Gyr. What have we learned? :  What have we learned? All of the candidate 'young' galaxies studied, even those in extremely underdense regions, contain old stars. They are old. If there are still any 'new' galaxies coming into being, we have not identified them yet. The 'leftover' building blocks have had a complex star-formation history of their own, but strong bursts or long gaps are not seen. They are quite different from the building blocks that merged into large galaxies at early times. Star-forming Galaxies, Lyman Alpha Absorbers,andThe Chemical Evolution of the Universe:  Star-forming Galaxies, Lyman Alpha Absorbers, and The Chemical Evolution of the Universe SFGs causing Ly absoprtion:  SFGs causing Ly absoprtion With Co-I Rao, Turnshek, Pettini, et al.:  With Co-I Rao, Turnshek, Pettini, et al. Study the chemical evolution of the universe. Study the relation between emission-line and absorption-line diagnostics. Study the relation between ionized phase and neutral phase ISM in galaxies giving rise to DLA systems. Study the nature of DLAs. Slide53:  Hopkins et al. 2001 Slide54:  Lilly et al. 2002 Lilly et al. 2002 SFGs Data from Pettini et al. 2001, Jansen et al. 2000, Kulkarni andamp; Fall 2002 Slide55:  SBS1543+593/HS1543+5921:  SBS1543+593/HS1543+5921 This is a unique system. QSO (z=0.807) impact parameter is small, close to the center of the foreground type Sm dwarf galaxy (z=0.0096). Galaxy previously 'misclassified' as a Seyfert – chance alignment discovered by Reimers andamp; Hagen (1998) during the HS QSO survey. They found the galaxy contains an HII region. HST spectrum shows Ly line is damped (Bowen et al. 2001). Slide57:  Slide58:  Slide59:  Star-Formation Rate:  Star-Formation Rate H luminosity of #5 -andgt; 9.1h70 -2 x 10-4 M⊙yr-1 For total SFR, scale R-band luminosity of the 33 HII regions = 4.4 times that of #5. Total SFR about 0.006 M⊙yr-1 SFR per unit area about 1.4 x 10-4 M⊙yr-1 kpc-2 Slide61:  12 + log (O/H) = 8.2±0.2 or about 1/3 solar MB – 5logh70 = -16.8 ± 0.2 A “normal” dwarf:  A 'normal' dwarf The galaxy is quite normal when compared with other local dwarfs, e.g., in terms of: Absolute magnitude, surface brightness, color, number of HII regions, brightness of the first ranked HII region, metallicity-luminosity relation, neutral gas There is as yet very little known about the nature of galaxies causing DLAs. This DLA has a logarithmic HI column density (20.35) which is at the low end of the observed range. It demonstrates a dwarf disk can cause a DLA locally. Interesting testcase for understanding O/H in galaxies/DLAs:  Interesting testcase for understanding O/H in galaxies/DLAs From OI 1302.17 and assuming the line is optically thin, we get O/H andgt; 1/135 of solar. This is about 40 times lower than the value derived in the HII region. The velocity paramter, b, of the gas must be several hundred km s-1. But if O/H in the neutral phase were the same as in the ionized one, then b⋲32 km s-1, in agree-ment with 21 cm profile, cf. Bowen et al. (2001). Resolve ==andgt; new Cycle 12 data by Bowen et al. Slide64:  Llog (N/O) = -1.4 (+0.2, -0.3) Slide65:  Models from Twarog 1998 Pei et al. 1999 Somerville et al. 1999 Cen andamp; Ostriker 1999 Lilly et al. 2003 I Zw 18, the “most metal poor” galaxy:  I Zw 18, the 'most metal poor' galaxy In the ionized gas: [O/H]NW = -1.52 ± 0.03 [O/H]SE = -1.51 ± 0.03 [N/H] = -2.36 ± 0.07 [Fe/H] = -1.96 ± 0.09 In the neutral gas: Aloisi: [O/H] = -2.06±0.28 [N/H] = -2.88±0.11 [Fe/H] = -1.76±0.12 Lecav: [O/H] = -1.39±0.08 [N/H] = -3.07±0.08 Aloisi et al. (2003) find N/O in the neutral phase is about 2x higher than in the ionized phase. Lecavalier des Etangs (2003) derive N/O a factor of 10 lower than Aloisi et al. (2003). Slide67:  In the case of BCDs, where the ionizing cluster is used as a background source, the line of sight must include some ionized gas. The test is much cleaner in SBS1543+593, where there is a background QSO. Once the question of the validity of assumptions is resolved, we can again turn to the issue of understanding the differences in metallicities of disk galaxies and DLA systems. See Schulte-Ladbeck et al. 2004 Future Work (Cycle 13):  Future Work (Cycle 13) Slide69: 

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