Measuring Baryon Acoustic Oscillations Along the Line of Sight with Photometric Redshifts: The PAU Survey
Benítez, N.; Gaztañaga, E.; Miquel, R.;Castander, F.; Moles, M.; Crocce, M.;Fernández-Soto, A.; Fosalba, P.; Ballesteros, F.;Campa, J.; Cardiel-Sas, L.; Castilla, J.;Cristóbal-Hornillos, D.; Delfino, M.; Fernández, E.;Fernández-Sopuerta, C.; García-Bellido, J.;Lobo, J. A.; Martínez, V. J.; Ortiz, A.; Pacheco, A.;Paredes, S.; Pons-Bordería, M. J.; Sánchez, E.;Sánchez, S. F.; Varela, J.; de Vicente, J. F.. Measuring Baryon Acoustic Oscillations Along the Line of Sight with Photometric Redshifts: The PAU Survey. The Astrophysical Journal. 2009, Vol. Volume 691, Issue 1, pp. 241-260 (2009)., p. -2009.
of known
physical length, making it one of the most promising probes of the
nature of dark energy (DE). The detection of BAOs as an excess of power
in the galaxy distribution at a certain scale requires measuring galaxy
) BAOs measure the
angular size of this scale projected in the sky and provide information
) BAOs require
very precise redshifts, but provide a direct measurement of the Hubble
parameter at different redshifts, a more sensitive probe of DE. The main
goal of this paper is to show that it is possible to obtain photometric
redshifts with enough precision (σ<SUB> z </SUB>) to measure BAOs
along the line of sight. There is a fundamental limitation as to how
much one can improve the BAO measurement by reducing σ<SUB> z
</SUB>. We show that σ<SUB> z </SUB> ~ 0.003(1 + z) is sufficient:
a much better precision will produce an oversampling of the BAO peak
without a significant improvement on its detection, while a much worse
precision will result in the effective loss of the radial information.
This precision in redshift can be achieved for bright, red galaxies,
featuring a prominent 4000 Å break, by using a filter system
comprising about 40 filters, each with a width close to 100 Å,
covering the wavelength range from ~4000 to ~8000 Å, supplemented
by two broad-band filters similar to the Sloan Digital Sky Survey u and
z bands. We describe the practical implementation of this idea, a new
galaxy survey project, PAU<SUP>16</SUP>Physics of the Accelerating
Universe (PAU): <A
>http://www.ice.cat/pau</A>., to be carried
out with a telescope/camera combination with an etendue about 20
m<SUP>2</SUP> deg<SUP>2</SUP>, equivalent to a 2 m telescope equipped
with a 6 deg<SUP>2</SUP> field of view camera, and covering 8000
deg<SUP>2</SUP> in the sky in four years. We expect to measure positions
and redshifts for over 14 million red, early-type galaxies with L > L
<SUB>sstarf</SUB> and i<SUB>AB</SUB> lsim 22.5 in the redshift interval
0.1 < z < 0.9, with a precision σ<SUB> z </SUB> < 0.003(1
+ z). This population has a number density n gsim 10<SUP>–3</SUP>
Mpc<SUP>–3</SUP> h <SUP>3</SUP> galaxies within the 9
Gpc<SUP>3</SUP> h <SUP>–3</SUP> volume to be sampled by our
survey, ensuring that the error in the determination of the BAO scale is
not limited by shot noise. By itself, such a survey will deliver
precisions of order 5% in the dark-energy equation of state parameter w,
if assumed constant, and can determine its time derivative when combined
with future cosmic microwave background measurements. In addition, PAU
will yield high-quality redshift and low-resolution spectroscopy for
hundreds of millions of other galaxies, including a very significant
high-redshift population. The data set produced by this survey will have
a unique legacy value, allowing a wide range of astrophysical studies.
of known
physical length, making it one of the most promising probes of the
nature of dark energy (DE). The detection of BAOs as an excess of power
in the galaxy distribution at a certain scale requires measuring galaxy
) BAOs measure the
angular size of this scale projected in the sky and provide information
) BAOs require
very precise redshifts, but provide a direct measurement of the Hubble
parameter at different redshifts, a more sensitive probe of DE. The main
goal of this paper is to show that it is possible to obtain photometric
redshifts with enough precision (σ<SUB> z </SUB>) to measure BAOs
along the line of sight. There is a fundamental limitation as to how
much one can improve the BAO measurement by reducing σ<SUB> z
</SUB>. We show that σ<SUB> z </SUB> ~ 0.003(1 + z) is sufficient:
a much better precision will produce an oversampling of the BAO peak
without a significant improvement on its detection, while a much worse
precision will result in the effective loss of the radial information.
This precision in redshift can be achieved for bright, red galaxies,
featuring a prominent 4000 Å break, by using a filter system
comprising about 40 filters, each with a width close to 100 Å,
covering the wavelength range from ~4000 to ~8000 Å, supplemented
by two broad-band filters similar to the Sloan Digital Sky Survey u and
z bands. We describe the practical implementation of this idea, a new
galaxy survey project, PAU<SUP>16</SUP>Physics of the Accelerating
Universe (PAU): <A
>http://www.ice.cat/pau</A>., to be carried
out with a telescope/camera combination with an etendue about 20
m<SUP>2</SUP> deg<SUP>2</SUP>, equivalent to a 2 m telescope equipped
with a 6 deg<SUP>2</SUP> field of view camera, and covering 8000
deg<SUP>2</SUP> in the sky in four years. We expect to measure positions
and redshifts for over 14 million red, early-type galaxies with L > L
<SUB>sstarf</SUB> and i<SUB>AB</SUB> lsim 22.5 in the redshift interval
0.1 < z < 0.9, with a precision σ<SUB> z </SUB> < 0.003(1
+ z). This population has a number density n gsim 10<SUP>–3</SUP>
Mpc<SUP>–3</SUP> h <SUP>3</SUP> galaxies within the 9
Gpc<SUP>3</SUP> h <SUP>–3</SUP> volume to be sampled by our
survey, ensuring that the error in the determination of the BAO scale is
not limited by shot noise. By itself, such a survey will deliver
precisions of order 5% in the dark-energy equation of state parameter w,
if assumed constant, and can determine its time derivative when combined
with future cosmic microwave background measurements. In addition, PAU
will yield high-quality redshift and low-resolution spectroscopy for
hundreds of millions of other galaxies, including a very significant
high-redshift population. The data set produced by this survey will have
a unique legacy value, allowing a wide range of astrophysical studies.