Lyman Break Galaxies as Markers for Large Scale Structure at z=5

Elizabeth Stanway - Obergurgl, December 2009

Lyman Break Galaxies as Markers for Large Scale

Structure at z=5

Elizabeth StanwayUniversity of Bristol

With Malcolm Bremer, Luke Davies, Matt Lehnert, Mark Birkinshaw, Chris Carilli, Alain Omont


The ESO Remote Galaxy Survey

VRI image of CL1037-1243

• Targets the 10 EDisCS Survey cluster fields (VRIJK)

• Adds Z band imaging and 100hrs of spectroscopy

• Also Spitzer/IRAC photometry

• 20 VLT/FORS2 Slitmasks

• Targets R-drops with R-I>1.3, IAB<26.3, z~5

• R~660, ~6500-10000Å

(Douglas et al, 2009, 2010)


• Better than 80% spectroscopic completeness for dropout candidates

• Reasonable S/N on continuum

• 68 Confirmed Redshifts at 4.4<z<6.4 including:

• 35 Lyman- emission lines

• 33 redshifts determined from Lyman breaks (18 class A, 13 B)

The ESO Remote Galaxy Survey


Tip of an Iceberg?

• These structures may extend beyond the limits of the imaging fields

• One of the fields shows evidence for spatial as well as redshift clustering

• Redshift precision is better than 0.002

• The redshift spikes are not in skyline-free wavelength regions

500 kpc

Examples of Lyman Break galaxy spectra in the z=5.00 field

Overdensities at z=5.00 and z=5.15


Moving to Longer Wavelengths

High Redshift Galaxies at Millimetre Wavelengths

• At z=5, 850m is close to the dust emission peak (i.e. negative K-correction starting to break down in sub-mm)

• Molecular gas is traced at all redshifts by CO emission

• The fundamental rotational transition of CO is at 115.271 GHz

• CO(1-0) at z=5 is in the 12mm/K band

• CO(2-1) emission at z=5 and CO(3-2) at z=8 are both in the 7mm/Ka band

• CO(5-2) emission at z=5 is in the 3mm band

Also - [CII] is a promising emission line, particularly in low metallicity systems, and can be observed in the 1mm band at z=5-6


Cool Gas at High Redshift

• Pilot test– Single pointing at

ATCA– 24 hours at 12mm– 44 hours at 7mm– Bandwidth

z~0.03 (240 MHz)

•Limiting Sensitivity– 0.11 mJy/Beam at 12mm, 0.10 mJy/Beam at 7mm (in 30 km/s)

•Angular Resolution–16x10’’ at 12mm, 7x5’’ at 7mm



(Stanway et al, 2008)



• No detection from LBGs in field

=> MH2<2x109 Msun

BUT• Strong line emission

from optically-faint source at 37.64GHz

• Likely CO(2-1) at z=5.1245±0.0001

MH2=2x1010 Msun


Confirming the Line

• Reobserved at the NRAO Green Bank Telescope in May 2009

• Observations shallower than planned

• Source redetected at 3

• Flux and velocity width consistent with ATCA values


LABOCA Observations

• APEX/Laboca Observations• 11hrs, June-July 2009, Image r.m.s. = 2.8 mJy• No significant detections of CO Emitter source• No detections of LBGs in field

Intensity Coverage

5 arcmin


Dust Limits on Cluster LBGs

• Laboca image covers 4x4 arcmin2 at 90% depth

• Can obtain a limit on the dust mass for spectroscopically confirmed z=5 Galaxies in this field

• Mstars ~ few x 109 M

in these sources

• MH2 < few x 109 M

(2), based on CO line non-detection

• Mdust < few x 108 M

(2 limit) at reasonable temperatures


Dust Limits on the CO Source

• Mdust < 5 x 108 M

(2 limit) at 30K from LABOCA

• Mdust < 2 x 108 M

(2 limit) at 30K from MAMBO

• 1.2mm and 850m limits consistent except at high temperatures (T≈100K)

Mgas/Mdust > 100


MAMBO Observations

• IRAM 30m MAMBO Observations in April 2009 (4hr)

• S1mm = -0.278 ± 0.438 mJy

• Implies L’CO/LFIR ratio more akin to lower redshift star-forming galaxies than ULIRGs/SMGs/QSO hosts

Figures modified from Solomon & vanden Bout (2005)


Constraints on the SED

• SED rules out gas-to-dust ratios typically seen in ULIRGs and QSO hosts at high z.

• More like local star-forming galaxies - Normal not exceptional SF galaxy.

• ALMA will be able to do this work trivially


Constraints on the SED

• SED rules out gas-to-dust ratios typically seen in ULIRGs and QSO hosts at high z.

• More like local star-forming galaxies - Normal not exceptional SF galaxy.

• ALMA will be able to do this work trivially


Our 2009 ATCA Survey

• Targeted second LBG over-density covering 3 times as much area at 37Ghz and 2 GHz bandwidth

• Encompasses 7 LBGs in z~0.1 range (around z~4.95), and 1 other z=5.2 source.

• Observed each pointing for 2 nights using the ATCA with two 2GHz IFs and 1MHz resolution (at 37GHz).

• Redshift coverage of ~4.23-5.34 at 19GHz and ~4.81-5.44 at 37GHz.

• RMS limits ~0.2mJy/beam at 19GHz

~0.3mJy/beam at 37GHz

(in 1 MHz channels)


Preliminary Results

• 6 Possible detections within the ATCA primary beams.

• Three detected at 19GHz and three at 37GHz.

• One has possible 19 and 37GHz detection.

• 3 would fall within the redshift of the over-density.

• Two are closely separated in redshift at z~4.6.

• Gas masses (H2) ~ 3-6 x109M for 37GHz detection and ~ 3-6 x1010M

for 19GHz detections.

• FWHM ~50-120kms-1. Comparable to previous detection.


• z=4.92

• 3x109 Msun in H2

• May be detected in two CO transitions

• Peak flux 0.4 mJy

• v = 50 km/s

Preliminary Results


Limits on LBGs in the Field

• All LBGs are not detected at 19GHz or 37GHz.

• Image R.M.S. Noise ~ 0.16mJy/beam (at CO(1-0) line)

~ 0.37mJy/beam (at CO(2-1) line)

• Gives 2 detection limit ~ LCO< 2.8x1010 K kms-1 pc2

~ LCO< 1.7x1010 K kms-1 pc2

For an unresolved 200 kms-1 emission line at the redshifts of the galaxies.

Can constrain molecular gas in LBGs in the field to:

M(H2)<2.2x1010 M (2, CO(1-0))

M(H2)<1.4x1010 M (2, CO(2-1))

Total observed mass in stellar component and H2 ~1.3x1011 M in 33.8Mpc3


Conclusions

• Lyman Break Galaxies clearly mark out underlying structure at very high redshifts

• Regions overdense in LBGs are perfect for follow-up at over wavelengths

• Molecular Gas may contribute a substantial fraction of the the baryon mass at z=5

• CO emission lines are currently the most accessible probe of this

• Searches for dust and gas dominated galaxies at high z are possible with current instrumentation with several promising candidates already identified

• ALMA will enable more complete surveys of the baryon distribution in high z large scale structure


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Lyman Break Galaxies as Markers for Large Scale Structure at z=5