1 / 17

The Dirt on Dry Mergers

The Dirt on Dry Mergers. Vandana Desai (Spitzer Science Center) Arjun Dey (NOAO), Emma Cohen (Caltech), Tom Soifer (SSC, Caltech), Emeric Le Floc’h (Saclay). How and when did elliptical galaxies form?. Naive Expectation: Most massive galaxies form last, and should be young. Reality:

ava-wynn
Download Presentation

The Dirt on Dry Mergers

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. The Dirt on Dry Mergers Vandana Desai (Spitzer Science Center) Arjun Dey (NOAO), Emma Cohen (Caltech), Tom Soifer (SSC, Caltech), Emeric Le Floc’h (Saclay)

  2. How and when did elliptical galaxies form? Naive Expectation: Most massive galaxies form last, and should be young. Reality: Most massive galaxies have old stellar populations. Solution: Form stars early, assemble them late in dry mergers. time Wechsler et al. 2002

  3. Do dry mergers really happen? Surely we can find examples somewhere in 9 square degrees. Bootes field

  4. van Dokkum et al. 2005 NDWFS+MUSYC Red, luminous, early-type, nearby 61 Dry merger Candidates 25 Control Galaxies

  5. Dry Merger Candidates van dokkum 2005

  6. van dokkum et al. 2005 71% of early-type galaxies are morphologically disturbed Most of today’s field ellipticals formed via (major) dry merger.

  7. Are they really dry? van dokkum 2005

  8. Look in the Infrared

  9. Look in the Infrared PAH? Significant Infrared excess over stellar blackbody.

  10. Spitzer-8 indicates heating by star formation!

  11. Look in the Infrared Chary & Elbaz 2001 Excess can be (mostly) accounted for by star formation.

  12. The NDWFS Bootes Sample < 1 Msun/yr Spitzer MIPS-24 detected undetected

  13. Spitzer-24 reveals residual star formation in ~25% of sample.

  14. Dare we infer gas masses? After extrapolating, etc: Gass mass~108 Msun Moist major merger or accretion of dwarf galaxy?

  15. This star formation frosting is likely triggered by mergers. No tidal features Weak features Number Strong features Ongoing mergers SFR (Msun/yr)

  16. Summary • One quarter of dry merger candidates have enough gas to fuel SFR > 1 Msun/yr. • This corresponds to residual star formation on top of a massive old stellar population. • Dry mergers or minor mergers? • This residual star formation is linked to signatures of merger activity.

  17. Spitzer-8 indicates heating by star formation!

More Related