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

SMGs: number density SMGs have a sky density of 200/FOV with a flux of S 850 >4mJy  ~10σ confusion SCUBA-2 (2007) will cover ~3 deg 2 per week to this limit. Borys et al. (2003) Map production and source extraction by Susan Scott for the SHADES consortium

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 S 850 ~8mJy have SFRs ~1000M Θ /yr.  This is a sensitive function of the assumed dust temperature (T 6 for z<3).  Optical spectroscopy gives ~10-20M Θ /yr on average.

SMGs: May 2002 OHS observations Five nights (19-23 May 2003) shared 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.

SMGs: LE 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. [OII]HβHβ[OIII]Balmer jump

SMGs: N 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= [OII]HβHβ[OIII]

SMGs: N 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][OIII]HβHβ

SMGs: simulated FMOS spectrum of ELAIS N 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 ~10M Θ /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 A,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 J : 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 M Θ /yr.

ERO J : morphological properties TH09 looks like a bulge-dominated passive galaxy.

ERO J : 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 M B =-21.0  ~M*

ERO J : 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 ~80M Θ /yr, consistent with the Hα flux and 8-GHz radio flux limit.

A 7-hour observation of this ERO would detect Hβ EROs: FMOS simulated spectrum of ERO J  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: S 850 > 5 mJy Single-night FMOS observations should be sensitive enough to  measure redshifts and accurate line fluxes  study the stellar continuum