the environment of mambo galaxies in the cosmos field
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The Environment of MAMBO Galaxies
in the COSMOS field
Manuel Aravena
F. Bertoldi, C. Carilli, E. Schinnerer, H. J. McCracken, K. M. Menten, M. Salvato
NRAO postdoc symposium. Socorro 2009
Outline
Introduction
From starburst to QSOs
Starburst galaxies in the early Universe
The MAMBO 1.2 mm imaging survey of the COSMOS field
Environment of submillimeter galaxies
Conclusions & Prospects
Introduction: Evolutionary sequence
What is the relation between typical ULIRGs and optically bright QSOs? • Observations (e.g. Sanders et al. 1988) and Simulations (Gerritsen 1997).
Morphology Spectral Energy Distribution (SED)
Flux de
nsity (arbitrary units)
Wavelength (m)
Starburst and QSOs in the early Universe
SCUBA
MAMBO
Hubble Deep Field North
SCUBA map
Hubble Deep Field North
Optical image
Submillimeter blank-field surveys discovered a population of dusty high-redshift galaxies in which a significant fraction of the stars in the Universe were created.
Submillimeter galaxies (SMGs): Mstar ~ 1011 Msun , L ~ 1013-14 Lsun, at z~2
Scoville et al. (2007)
• Total area of 2 square degs.
• Deep exposures:
I~26.5 (mag), (1.4 GHz) ~ 7 Jy
• Sensitive census of galaxies, their evolution and density growth up to z=1.5 (a third the age of the Universe, 4.3 Gyr after the Big Bang)
The COSMOS field
The COSMOS field
MAMBO imaging of COSMOS
MAMBO = Max-Planck Millimeter Bolometer array on the IRAM 30 m telescope in Granada, Spain
An area of 20’x20’ mapped to an rms noise level of 1 mJy per 11’’ beam
AzTEC 1.1 mm survey (Scott et al. 2008)
Bolocam 1.1 mm survey(Aguirre et al., in prep.)
MAMBO 1.2 mm survey(Bertoldi, et al. 2007)
Optical coverage
Spitzer – shallow coverage
MAMBO imaging of COSMOS
Detected:
15 sources >4significance, 11 of which have radio counterparts
10 sources 3 – 4 significance based on a radio identification
Figure. MAMBO 1.2 mm final map. Detected sources are marked with a circle and their respective ID number.
Figure. MAMBO 1.2 mm rms noise map.
Environment of submillimeter galaxies
What is the ‘fate’ of sub-mm galaxies?
Will they end up in the most dense environments ?
Massive radio galaxies are typically found in very dense environments up to redshift of ~ 4.
Figure. Galaxy cluster. X-rays (blue). Optical view taken with the HST. Radio (red).
• Small survey areas and low-density of sources (Blain et al. 2002)• The largest surveys cover ~ 30’ x 30’ • Little is known about their relation with environment (isolated?, in dense environments? )
Environment of submillimeter galaxies
• To date, few studies has been done to investigate the high-redshift environment of SMGs
• It is possible to study the local environment of sub-mm galaxies at high-redshift.
• Need to select objects at redshift similar to that of MAMBO galaxies (redshift ~ 1.5-2.5)
Study the environment of MAMBO galaxies
Starburst QSO QSO in dense environment
Starburst/QSO transition scenario
If sub-mm galaxies evolve into elliptical galaxies in dense environments, they would show signs of clustering in the epoch they were most abundant (redshift ~ 1.5-2.5)
Environment of submillimeter galaxies
• New deep K-band imaging of COSMOS
(McCracken et al., submitted)
• K-band selected catalogue
• Use BzK criterion to split the sample into:
• sBzK + pBzK (redshift ~1.4-2.5)
• nBzK (redshift <~ 1.4)
Efficient method to select galaxies at redshifts 1.5-2.5 : BzK color-color criterion (Daddi et al. 2004)
Figure. BzK color-color criterion.
Projected density maps of low- and high-redshift BzK galaxies
• Densities computed using the 7th nearest neighbour estimator (Dressler, 1980):
, where d7 is the distance to the 7th nearest neighbour.
Density map of low-redshift BzK galaxies Density map of high-redshift BzK galaxies
Consistency check
Reliability of our maps
Both maps trace mostly the same structures, supporting the reliability of our map.
Figure.
Background: Density map computed from the K-band selected catalog.
Red contours: Density map computed by Scoville et al. (2007) from the COSMOS I-band catalog.
Results
• Some MAMBO galaxies are located in regions with enhanced density of low-z galaxies
• Consistent with lensing by foreground galaxies
Figure. Distribution of densities at the position of MAMBO galaxies (filled) compared with the field (open).
Four MAMBO galaxies are located in overdense environments at high-z.
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Environment of submillimeter galaxies
Figure. BzK true color image of the fields of the four MAMBO galaxies embedded in the most overdense regions of high-redshift galaxies.
How likely is that the association of MAMBO galaxies with these overdensities is produced by chance?
Poisson probability of chance association that a significant density peak is found by chance within a distance d from a millimeter source (Downes et al., 1983) :
P(d) ~ 1 – exp( -d2 n ),
where n number density of peaks in the area of the COSMOS MAMBO field (~20’x20’).
Answer:
Very unlikely.
For COSBO-1, P(20”) = 10.4% For COSBO-3, P(20”) < 1e-3%
For COSBO-6, P(20”) = 0.25% For COSBO-16, P(20”) = 2.5%
Photometric redshifts
Further evidence:
Photometric redshifts for galaxies within 20” from the MAMBO galaxy position.
K-band selected
Figure. Histograms represent the redshift distribution for :
• High-redshift BzK galaxies (dark-gray )
• All galaxies (light-gray)
• MAMBO galaxies (black entry)
Peaks in redshift distribution. Most galaxies at high redshift
More evidence
Plateau de Bureau Interferometer in its D-configuration
Higher resolution of ~3”
Better sensitivity
Tentative detection (3) of 2 continuum sources with the PdBI at 1.3 mm toward COSBO-6
Integrated 1.3 mm flux over the whole area is 3.7 +\- 0.3 mJy, consistent with the MAMBO 1.2 mm flux of 5.2+\- 1.0 mJy.
The flux derived for the central source is consistent with its radio emission, assuming it has a starburst-like SED.
Conclusions & Prospects
• MAMBO survey of the COSMOS field.
• We studied the density of high-redshift BzK galaxies around MAMBO galaxies.
• Four MAMBO sources appear to be located in strong overdensities of red galaxies
at high-redshift.
• Photometric redshifts and millimeter continuum imaging support these results.
• Spectroscopy with the Keck telescope will be crucial to confirm groups around SMGs• Millimeter imaging of the MAMBO sources to locate possible multiple sources • Similar studies in other deep fields for statistical analyses (e.g. CDF-S)
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