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The NGC 2841 Group

The NGC 2841 Group. February 6, 2007 Tim Dolch, Bridget Falck, Mike Specian. Huchra & Geller Group Members. Columns: Name, Velocity, Apparent Magnitude, Morphological Type, Galactic Longitude, Galactic Latitude. H&G Members. NGC 2681. NGC 2756. H&G Member Determination (Friends of Friends).

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The NGC 2841 Group

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  1. The NGC 2841 Group February 6, 2007 Tim Dolch, Bridget Falck, Mike Specian

  2. Huchra & Geller Group Members Columns: Name, Velocity, Apparent Magnitude, Morphological Type, Galactic Longitude, Galactic Latitude

  3. H&G Members NGC 2681 NGC 2756

  4. H&G Member Determination(Friends of Friends) 1. Choose a galaxy not previously assigned to a group. 2. Search for other nearby galaxies within a certain projected radius and within a certain velocity window. 3. If no nearby galaxies are found, that galaxy is considered isolated. If other galaxies are found, they are added to the group. 4. For each galaxy added to the group, repeat step 1.

  5. Did H&G Capture Them All? Probably not…

  6. Did H&G Capture Them All?

  7. Did H&G Capture Them All?

  8. Did H&G Capture Them All?

  9. Did H&G Capture Them All?

  10. Did H&G Capture Them All?

  11. What are We Missing?

  12. What are We Missing?

  13. Query w/ SDSS • Many objects with photometry are lacking spectroscopy. • All photometric objects have photometric redshifts, but these are inaccurate, especially for these purposes. • Sample query: SELECT s.bestObjID, s.ra, s.dec, s.z as redshift, p.u, p.g, p.r, p.i, p.z FROM SpecObjAll s, PhotoObjAll p, fGetNearbyObjEq(140.511,50.977,143.25) as N WHERE n.objID = s.bestObjID and n.objID = p.objID and s.z < 0.00426 and s.Objtype = 0 and p.type = 3

  14. Query Results • Using photometric redshifts ~22,000 potential galaxies are returned. • Using actual redshifts, 22 objects are returned within 500 kpc.

  15. Query Results

  16. Query Results

  17. Summing Up the Sloan Query • 2841 10.68 r-band mag • 2756 12.44 r-band mag • 2681 11.02 r-band mag • Of the spectroscopic objects found, average r-band mag was 16.96 • This amounts to 2 orders mag difference in luminosity, therefore “dwarf” classification not unreasonable

  18. NGC 2841 • Sb in Ursa Major, 14.1 Mpc away • LINER nucleus • Triaxial bulge • Retrograde bulge in outer radii • Polar ring orthogoal to galactic plane • Mdisc = 5 x 1010 Msun • Vc = 317 km s-1 • M/L ~ 0.7 L. Portinari, J. Sommer-Larsen, R. Tantalo (2004) MNRAS 347 (3), 691–719.

  19. NII shows spiral arms (shaded areas) • Halpha shows elongated loci (contour arms) • velocity splitting in NII evidence of shock front

  20. An X-Ray View • ROSAT observations with halo velocity of • Infall of gas produces x-ray bremsstrahlung as dominant cooling mechanism • This gas infall is inconsistent with SFR

  21. NGC 2814 in 24 microns from SINGS • Dust not in spatial proximity to stars, so smooth distribution of dust emission expected • 2.1 micron observations show dust emission up to 500 pc above plane A. J. Benson, R. G. Bower, C. S. Frenk, S. D. M. White (2000) MNRAS 314 (3), 557–565.

  22. Unanswered Questions on NGC 2841 Itself • Merger history - Afanasiev et al. speculate that mergers may be necessary to explain dynamical montage - not done to date • GALEX data (not yet released) - NGC 2841 is “remarkable” • Why is the X-ray emission (Lx ~ 1041 erg s-1) too small (theory => 8 times this) to account for accreted SF history? Perhaps could have formed surprsingly early - similar examples at high z?

  23. Properties: Bulge-dominated S0/a galaxy Two concentric, misaligned bars and third inner bar Nucleus is a LINER Underwent starburst ~1Gyr ago? Hosts a supermassive BH? Ref: Cappellari, M. et al. 2001, ApJ, 551, 197 NGC 2681

  24. Recent Starburst • Strong Balmer absorption lines indicative of relatively young (1-2 Gyr) stellar component • Consistent with relative absorption-line strengths of Mg II and Mg I, which are indicative of late A-type main sequence • Stellar M/L for central population is 0.7-1, appropriate for 1-2 Gyr old solar metallicity stellar population

  25. Dynamics difficult, but… Kinematics require presence of central BH only provides upper limit on the mass: MBH < 6 x 107 MSun LINER property suggests a slow, steady feeding of a central BH Two stellar and two gas velocity dispersions, and model with (solid) and without (dashed) assumption of central BH Central Black Hole

  26. Evidence for Interactions • Both presence of supermassive BH and evidence for recent starburst support hypothesis of recent interactions with a neighbor… • However, no clear signatures of recent accretion of gas-rich dwarf, such as morphological distortions or duplicity of the nucleus • Still open questions about group interactions

  27. Future Possibilities • Measurements of stellar kinematics using long slit STIS spectra will remove modeling degeneracy, allow pinpointing of BH mass • H I survey would shed light on whether NGC 2681 underwent a tidal interaction with another galaxy

  28. Type Ia Supernova 1999by • Observed in NGC 2841 • Type Ia SNe are useful as distance indicators • One of the least luminous type Ia events, belonging to a group of “peculiar” subluminous SNe Ia

  29. Why special? • Host has minimal dust extinction and a Cepheid distance has been obtained • Allows independent estimate of Hubble parameter using “peculiar” SNe, since most SNe calibrated with Cepheids are of “normal” type • Found to be consistent, suggesting no systematic error due to selection bias of calibrated SNe Ref: Garnavich et al. 2004, ApJ, 613, 1120

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