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Towards an HI census of the Local Universe: further adventures in NIBLES

Towards an HI census of the Local Universe: further adventures in NIBLES. Tana Joseph. Overview. What is NIBLES? The HI data The optical data Some curious results Re-analysis of the photometry Implications. What is NIBLES?.

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Towards an HI census of the Local Universe: further adventures in NIBLES

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  1. Towards an HI census of the Local Universe: further adventures in NIBLES Tana Joseph

  2. Overview • What is NIBLES? • The HI data • The optical data • Some curious results • Re-analysis of the photometry • Implications

  3. What is NIBLES? • NIBLES: Nançay Interstellar Baryonic Legacy Extragalactic Survey • Quantify HI content of galaxies in the Local Universe • 4000 SDSS galaxies with • 900< cz < 12 000 km/s (Local Universe) • -10m > Mz > -24m • All morphological types

  4. The HI data • Preliminary HI data for 600 galaxies • Compared to NHICAT data (Wong et al., 2006) • Velocities agree well with NHICAT data • HI data reliable

  5. Some curious results • Preliminary results: very high mass to light ratios

  6. What could the problem be? • Are these data points real? • No other systems found with such high MHI/L (Warren et al., 2006, van Zee, 2001) • Highest: MHI/LB = 22 M/L • Since HI data ok, photometry probably at fault • Incorrect magnitudes due to circular aperture? • But Strauss et al., 2002 find no problems for highly inclined systems

  7. What could the problem be? • Optical “confusion” sources? • E.g. SDSS012206+005616 and SDSS012213+005731 (MB=-13m,MHI/LB = 367 M/L) are part of NGC0493 (MB=-20m,MHI/LB = 0.5 M/L) • Not enough to account for all high MHI/L values

  8. Re-analysis of the photometric data • Individual photometry performed on • a subsample of 403 galaxies out of 1385 (g band) • All galaxies in range -10m > Mz > -14m (i band) • Using Source Extractor and JPK’s pipeline

  9. The g band photometry • mSE - mSDSS vs. Petrosian radius • g band magnitude comparison

  10. The I band photometry • i band magnitude comparison • mSE - mSDSS vs. Petrosian radius

  11. Re-analysis of the photometric data • Galaxies with RP < 8’’ have underestimated magnitudes in both g and i bands • Excising sources with RP < 8” gives much better agreement between SDSS and SE data

  12. Re-analysis of the photometric data • MHI/Lg re-determined using SDSS magnitudes for RP > 8” and SE magnitudes for RP < 8”

  13. Re-analysis of the photometric data • MHI/Li re-determined using SDSS magnitudes for RP > 8” and SE magnitudes for RP < 8”

  14. Implications • No galaxies with Mg > -13m and Mi > -12m remain when using SE data for sources with RP < 8” ! • Implications for various studies using SDSS photometry: • The Luminosity function of the Local Universe • Galaxy formation and evolution theories and models

  15. Thank you

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