Transcript EROs and submm galaxies: Expectations for FMOS in the

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
S850>4mJy
Borys et al. (2003)
 ~10σconfusion
SCUBA-2 (2007)
will cover ~3 deg2
per week to this
limit.
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 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 3/7
?/7 targets.
SMGs: LE 850.3 at z=2.120
[OII] Balmer jump
Hβ [OIII]
[OII]/Hβ~3 (predicted) so the absence of Hband lines is not unexpected. The continuum
break is well-fit by a 250 Myr starburst.
SMGs: N2 850.2 at z=2.453
[OII]
Hβ [OIII]
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]
Hβ [OIII]
[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 opticalinfrared 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