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Submm galaxies and EROs: Expectations for FMOS in the light of OHS observations

Submm galaxies and EROs: Expectations for FMOS in the light of OHS observations. Chris Simpson (University of Durham). Further reading…. SMGs: Simpson, Dunlop, Eales, Ivison, Scott, Lilly, & Webb EROs: Cotter, Simpson, & Bolton

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Submm galaxies and EROs: Expectations for FMOS in the light of OHS observations

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  1. Submm galaxies and EROs: Expectations for FMOS in the light of OHS observations Chris Simpson (University of Durham)

  2. Further reading… • SMGs: Simpson, Dunlop, Eales, Ivison, Scott, Lilly, & Webb • EROs: Cotter, Simpson, & Bolton • Both papers in advanced draft stage and soon to be submitted to MNRAS.

  3. Why FMOS is better than OHS • Multiplexing • Can observe targets for an entire night (or longer) • Higher spectral resolution • More sensitive to emission and absorption lines • More extensive wavelength coverage • Increased probability of measuring redshifts or useful diagnostics • Increased throughput • Better sensitivity

  4. SMGs: introduction • The extragalactic submillimetre background has been resolved into submillimetre galaxies (SMGs) which appear to be dusty vigorous star-forming galaxies. • Half the total extragalactic background is in the submm, while SMGs make up more than half the extragalactic submm background • >25% of all stars since the Big Bang have formed in SMGs.

  5. SMGs: scientific motivation • The strong k-correction for SMGs biases an 850μm flux-limited sample to high redshifts. • if 25% of SMGs have z<2 (Chapman et al. 2003), then ~70% of stars formed at z<2. • FMOS studies of SMGs are motivated to • measure redshifts where optical spectroscopy fails • make alternative measurements of the SFRs

  6. Map production and source extraction by Susan Scott for the SHADES consortium SMGs: number density • SMGs have a sky density of 200/FOV with a flux of S850>4mJy • ~10σconfusion • SCUBA-2 (2007) will cover ~3 deg2 per week to this limit. Borys et al. (2003)

  7. SMGs: redshift distribution • Chapman et al. (2003) find a broad redshift distribution for SMGs, with a median redshift ‹z›=2.4. • The spectroscopic completeness is uncertain.

  8. SMGs: star formation rates • Galaxies with S850~8mJy have SFRs ~1000MΘ/yr. • This is a sensitive function of the assumed dust temperature (T6 for z<3). • Optical spectroscopy gives ~10-20MΘ/yr on average.

  9. SMGs: May 2002 OHS observations • Five nights (19-23 May 2003) shared 60-40 with a second proposal. • Several hours lost to weather and technical problems, so seven targets were observed • selected from the 8mJy survey and CUDSS 14h field • chosen to be too faint for optical spectrographs • Each target was observed for 8x1000s exposures with a 1” slit in ~0.6” seeing.

  10. SMGs: summary of results • Reliable redshifts were obtained for ?/7 targets. • Reliable redshifts were obtained for 3/7 targets.

  11. [OII] Balmer jump Hβ [OIII] SMGs: LE 850.3 at z=2.120 • [OII]/Hβ~3 (predicted) so the absence of H-band lines is not unexpected. The continuum break is well-fit by a 250 Myr starburst.

  12. SMGs: N2 850.2 at z=2.453 • The OHS redshift of z=2.453±0.006 agrees well with the optical redshift of z=2.443 and CO redshift z=2.442. [OII] Hβ [OIII]

  13. SMGs: N2 850.12 at z=2.425 • [OII] is expected in the least sensitive region of the spectrum, so the absence of a formal detection is not inconsistent with [OII]/Hβ~3. [OII] Hβ [OIII]

  14. SMGs: simulated FMOS spectrum of ELAIS N2 850.12 • A simulated 7-hour spectrum produces lines and continuum with sufficient S/N to do science! • The vast majority of SMGs should provide redshifts with FMOS.

  15. SMGs: the IR redshift desert • Our 3σ line flux sensitivies correspond to star formation rates ~10MΘ/yr (cf. Lyα fluxes). • At 2.6<z<3.0: • Hβ is between H & K • [OII] is between J & H • Hα is beyond K • This is the IR “redshift desert”.

  16. EROs: introduction • Extremely Red Objects (EROs) have red optical- infrared colours: • R-K>6, R-K>5, I-K>4, I-H>3, etc. • Such colours can be caused by either an old stellar population, or a younger, dust-reddened population at high redshift (z>1).

  17. EROs: scientific motivation • The “passive” EROs suggest an early epoch of galaxy assembly and an even earlier epoch of star formation. • The starbursting EROs are sites of extreme star formation at moderate redshifts • identification with submm sources below SCUBA confusion limit? • sites of major mergers?

  18. EROs: number density • A surface density of 200/FMOS FOV corresponds to K~19-20, depending on one’s definition of ERO. • around the UKIDSS DXS limit. Yan & Thompson (2003)

  19. EROs: photometric classification • Pozzetti & Mannucci (2000) suggest that ellipticals and dusty starbursts can be distinguished in a colour-colour diagram. E SB

  20. EROs: photometric classification • Mannucci et al. (2002) find approximately equal numbers of Es and SBs. • The distribution of galaxies is not bimodal, and photometric uncertainties are large.

  21. EROs: morphological classification • Yan & Thompson (2003) find more disks than spheroids from their analysis of HST/WFPC2 F814W images.

  22. EROs: spectroscopic classification • Cimatti et al. (2002) took optical spectra of EROs from the K20 sample and found roughly equal numbers of Es and SBs. • K20 galaxies have R-K>5 and the average colour is R-K=5.2.

  23. EROs: Jun 2001 OHS observations • One night (11 June 2001), hampered by poor seeing and the telescope oscillation problem. • Three targets were observed in the field of the wide-angle quasar pair PC 1643+4631A,B (which includes HR10 at z=1.44). • These were selected to have R-K>5.5 from the optical/infrared data of T. Haynes et al. (2002).

  24. EROs: summary of results • Two objects displayed featureless continua with no evidence of spectral breaks, while one (object #09 in the Haynes et al. catalogue) showed a prominent emission line at 15373Å.

  25. ERO J164504.5+462551: spectroscopic properties • The emission line is identified as Hα at z=1.34. • [OII] at z=3.12 is ruled out from the absence of a continuum break and the extreme continuum luminosity it would imply. • The line is unresolved, implying little [NII] emission. • The emission is powered by star formation, rather than an AGN. • The inferred SFR is ~20 MΘ/yr.

  26. ERO J164504.5+462551: morphological properties • TH09 looks like a bulge-dominated passive galaxy.

  27. ERO J164504.5+462551: photometric properties • The near-infrared photometry of TH09 is not very precise, but the object lies close to the line which separates Es from SBs. • TH09 has MB=-21.0 • ~M*

  28. ERO J164504.5+462551: SED • The optical-IR SED can be fit with a combination of old (5Gyr) and young, reddened stellar populations. • The young pop has Av~3 and an SFR of ~80MΘ/yr, consistent with the Hα flux and 8-GHz radio flux limit.

  29. EROs: FMOS simulated spectrum of ERO J164504.5+462551 • A 7-hour observation of this ERO would detect Hβ • get reddening from Balmer decrement • It would resolve Hα and [N II] • importance of AGN contribution

  30. Summary • EROs and SMGs both have number densities appropriate for FMOS observations. • EROs: K < 20 • SMGs: S850 > 5 mJy • Single-night FMOS observations should be sensitive enough to • measure redshifts and accurate line fluxes • study the stellar continuum

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