Submm galaxies and eros expectations for fmos in the light of ohs observations
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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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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

  • Both papers in advanced draft stage and soon to be submitted to MNRAS.

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

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.

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

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)

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.

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.

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.

SMGs: summary of results

  • Reliable redshifts were obtained for ?/7 targets.

  • Reliable redshifts were obtained for 3/7 targets.


Balmer jump


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.

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.



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.



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.

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”.

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).

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?

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)

EROs: photometric classification

  • Pozzetti & Mannucci (2000) suggest that ellipticals and dusty starbursts can be distinguished in a colour-colour diagram.



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.

EROs: morphological classification

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

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.

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).

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.

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.

ERO J164504.5+462551: morphological properties

  • TH09 looks like a bulge-dominated passive galaxy.

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*

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.

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

  • 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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