Extragalactic abstracts - IRSA - California Institute of Technology

Spitzer_Approved_Extragalactic
Mar 25, 10 16:24 Page 229/742
Spitzer Space Telescope − Directors Discretionary Time Proposal #250
Mid−IR observations of z=2, BzK selected galaxies
Principal Investigator: Emanuele Daddi
Institution: NOAO
Technical Contact: Emanuele Daddi, NOAO
Science Category: high−z galaxies (z>0.5
Observing Modes: MipsPhot
Hours Approved: 10.2
Abstract:
The cosmic epoch at redshifts between 1.5 and 2.5 appears to be the time of
major formation and assembly of massive galaxies. Results from the K20 and other
surveys have shown that massive galaxies with seemingly large star−formation
rates are common at these epochs. We showed that massive z=2 objects can be
readily isolated using photometry in only B, z and K bands. As a part of the
Spitzer Fellowship program, we propose to obtain deep 24 micron observations
with Spitzer+MIPS of a 350 arcmin square region where about 500 z=2 massive
galaxy candidates have been selected through their BzK colors, and for many of
which spectroscopic redshifts are being measured from VLT+VIMOS spectra. A large
fraction of these galaxies have very red optical colors that suggest severe dust
reddening. Measuring the 24 micron emission of massive z=2 galaxies will be
crucial to trace the presence of dust, thus constraining their star−formation
rates and contribution to the z=2 star−formation rate density. Coupled to the
optical−IR photometry and optical spectra that are already available, these
observations will allow to better understand the role of BzK selected objects in
galaxy formation and assembly at z=2.
Spitzer_Approved_Extragalactic
Printed_by_SSC
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Spitzer Space Telescope − General Observer Proposal #50512
Mid−IR Spectroscopy of gas−rich disk galaxies at z=1.5
Principal Investigator: Helmut Dannerbauer
Institution: MPIA
Technical Contact: Helmut Dannerbauer, MPIA
Co−Investigators:
Emanuele Daddi, CEA
David Elbaz, CEA
Mark Dickinson, NOAO
Glenn Morrision, UH−IfA Hawaii
Daniel Stern, JPL, Caltech
Science Category: high−z galaxies (z>0.5)
Observing Modes: IrsMap
Hours Approved: 15.2
Abstract:
We have recently obtained the first detection of CO in two ordinary massive z=2
galaxies. These massive disk galaxies were observed with the IRAM Plateau de
Bure Interferometer, selected to lie in the mass−star formation rate correlation
at z~1.5, thus being representative massive high−z galaxies. The CO detection
implies that giant molecular gas reservoirs are present in these sources, with
gas fractions reaching 50−70% of the total galaxy masses. With an infrared
luminosity of L(FIR)~10^12 L(sun), these BzK disk−like galaxies are borderline
ULIRGs but with star formation efficiency similar to local spirals, and an order
of magnitude lower than in submm galaxies, unveiling a new formation mode
previously unknown in the distant universe. We propose here IRS spectroscopy of
these two CO detected galaxies at z=1.5 in order to unveil their mid−IR rest
frame spectral properties and measuring the equivalent widths of PAH features at
6.2, 7.7, 8.6 and 11.3 micron and of the 9.7 micron silicate absorption. The
extreme richness in molecular gas in these sources should affect their mid−IR
spectral properties, and we will investigate how the diversity in gas/star
ratios in distant galaxies is important for the interpretation of mid−IR
luminosities of the high−z populations. In particular, the fact that these
ULIRGs behave like scaled up spiral galaxies in their star formation properties
could be reflected in their mid−IR spectral properties. Obtaining the PAH ratios
will be crucial to constrain better the CO to H2 mass conversion ratio Xco.
These observations will represent a legacy from Spitzer for the years to come
for the interpretations of mid−IR properties of distant star forming galaxies.
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