A sample of faint, southern-hemisphere 60 μm sources

(f_(60) > 100mJy) detected as part of the IRAS Additional Observations has been used, in conjunction with CCD imaging, to produce a list of faint infrared galaxies. Redshifts of this sample of galaxies can be compared

with model predictions for several evolutionary scenarios; the comparisons show an excess of galaxies at higher redshifts (z > 0.1) compared with the predictions of models which assume no evolution of the infrared-galaxy luminosity function

Barrientos, L. F.

Elias, J. H.

Hacking, P.

Neugebauer, G.

Soifer, B. T.

Caltech Authors - Main

1
9
9
3
A
S
P
C
.
.
.
4
3
.
.
1
1
1
E
S/ry Surveys: Protostars to Protogalaxies 
ASP Cotifermce Serles, Vol. 43, 1993 
B. T. Soifer (ed.) 
COSMIC EVOLUTION OF A SAMPLE OF INFRARED-LUMINOUS 
GALAXIES 
J. H. ELIAS and L. F. BARRIENTOS 
Cerro Tololo Inter-American Observatory, National Optical Astronomy 
Observatories, Casilla 603, La Serena, Chile 
P. HACKING, G. NEUGEBAUER and B. T. SOIFER 
California Instituter of Technology, Pasadena CA 91125 
ABSTRACT A sample of faint, southern-hemisphere 60 µm sources 
(!60 > lOOmJy) detected as part of the IRAS Additional Observations has 
been used, in conjunction with CCD imaging, to produce a list of faint 
infrared galaxies. Redshifts of this sample of galaxies can be compared 
with model predictions for several evolutionary scenarios; the comparisons 
show an excess of galaxies at higher redshifts (z > 0.1) compared with the 
predictions of models which assume no evolution of the infrared-galaxy 
luminosity function. 
INTRODUCTION 
The most luminous infrared galaxies detected by IRAS can be seen out to 
cosmologically interesting distances - i.e., distances such that the "look-back" 
time is a significant fraction of the age of the universe (e.g. Harwit et al 1987; 
Rowan-Robinson et al 1991 ). The ability to look back in time - admittedly at 
the limits of the IRAS surveys - allows us to examine whether the propertieti 
of these extremely luminous objects have evolved over time. As a first step, we 
can investigate whether the luminosity function of infrared luminous galaxies 
evolves over time. 
Similar investigations have been carried out previously (e.g. Hacking et al 
1987; Lonsdale and Hacking 1989; Saunders et al 1990; Lonsdale et al 1990). 
However, they have all been limited in one way or another - either by lack of 
depth in flux, incompleteness, or lack of spatial sampling This paper describes 
yet another attempt, in which a sample of adequate depth and spatial sampling 
is studied. 
SAMPLE 
Sources from 25 southern IRAS Additional Observation fields with the following 
characteristics were selected: 
111 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 
1
9
9
3
A
S
P
C
.
.
.
4
3
.
.
1
1
1
E
112 J. ELIAS ET AL. 
• Observed on at least 4 occasions by IRAS (implies completeness to at 
least 100 mJy). 
• Above 40° galactic latitude 
• No more than 10 100 µm sources (to guard against spunous "cirrus" 
sources) 
CCD B and R images were taken of all sources (except for known bright 
galaxies) on the CTIO 0.9-m telescope. Galaxy positions were measured on the 
ESQ and SRC sky survey films, using SAO stars as positional references, or on 
the CCD images, using reference stars whose positions were measured on the 
sky survey films relative to SAO stars. 
The positional accuracy of the co-added AO grids was investigated using: 
• Stars detected at 12 and 25 µm in these AO's and the corresponding 
northern AO's; 
• Stars detected at 60 µm in the same data set (a very small number: 7 
objects); and 
• "Obvious" galaxy identifications (i.e. isolated bright objects) in the 
sample itself. 
These investigations showed the positions to have a 1-u error in the satellite 
in-scan direction of 6 arcsec and in the cross-scan direction of 22 arcsec. The 
positions also showed a small systematic offset (2 arcsec) in the in-scan direction. 
In the larger samples, roughly 5% of the sources showed excessive (non-
gaussian) positional errors. 
REDSHIFTS 
Redshifts for objects in most of the AO fields were taken from the literature 
or were measured using the RC spectrograph on the CTIO 4-m telescope. A 
few of the fields could not be finished, due to lack of time. Within the fields 
that were completely observed, we did not get redshifts for 100% of the IRAS 
sources, for one or more of the following reasons: 
Inadequate signal to noise. This in practice occurred only when the 
candidate did not show emission lines, which in turn makes its identification 
as the IRAS source somewhat dubious (unless it was visually very bright). It 
is possible, but also not likely, that the absence of emission lines was due to a 
redshift high enough to shift Ha outside the coverage of the spectra (z > 0.5), 
leaving only relatively weak lines in the observable spectrum. 
No suitable candidate. In some cases, all the objects in the field were 
very faint. This may be because the IRAS source is at high redshift, that is, 
an object with extreme far-ir/visible ratio, or it may reflect a bad source (e.g. 
cirrus contamination). 
Missed candidate. In some cases only some candidates in the vicinity of 
the IRAS source were measured, usually because the revised positions on the 
CCD image moved new objects inside the 3-u error ellipse, and in some of these 
cases none of the objects measured appeared to be the correct identification. 
In cases where several candidate objects existed, the identification as the 
IRAS source was based on a mix of three criteria: 
•Positional match (IRAS and optical positions). 
• Visual brightness (visually brighter object is more probable identifica-
tion). 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 
1
9
9
3
A
S
P
C
.
.
.
4
3
.
.
1
1
1
E
EVOLUTION OF INFRARED-LUMINOUS GALAXIES 113 
• Appearance of spectrum (ir luminous galaxy more likely to have emission 
lines). 
Fields with more than one or two "missing" sources were omitted from 
the analysis. Those with only one or two missing were included. It was felt 
that these could be safely included, as the unidentified sources were either (a) 
unbiassed with respect to redshift or (b) high-redshift, high-luminosity sources. 
Since the purpose of this study is to look for an excess of high-redshift sources, 
(and since such an excess is found), missing a few such sources will not prejudice 
the main goal of the study. 
6000 
z 4000 
2000 
0 
-3 
100-200 mJy 
I 
I 
, ______ 
-2 
log 
---· 
-1 
(z) 
I 
I , __ _ 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
L--
0 
Figure 1: Plot of observed number vs. redshift distributions for sample 
galaxies with 60 µm flux densities between 100 and 200 mJy. The data are 
shown as a heavy dashed line. The predictions of three different models, 
derived from Hacking et al 1987, are also shown. The thin solid line is for 
a model without evolution, the dashed line is a simple density evolution 
model, while the dotted line is a luminosity evolution model. 
A histogram of number vs. redshift is shown for each of two flux density 
intervals, compared with model predictions. The data are shown as heavy 
dashed lines. The a model with no evolution is shown as a solid line. A model 
with density evolution (proportional to (1 + z) 4 ) as a dashed line, and a model 
with strong luminosity evolution (proportional to (1 + z)3 ) is shown as a dotted 
line. 
The data show a clear deficit at moderate redshifts (z = 0.01-0.1) relative 
to the model predictions. This is likely to be due to a genuine deficiency of 
galaxies in that distance range, but the model normalization may be in error 
somewhat as well. A similar effect was also seen in the south galactic cap by 
Lonsdale et al (1990). 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 
1
9
9
3
A
S
P
C
.
.
.
4
3
.
.
1
1
1
E
114 J. ELIAS ET AL. 
The data also show a clear excess over the predictions of the "no-evolution" 
model, and in fact suggest that even the weaker evolution models are insufficient 
to account for the excess. The situation would be accentuated if the model in 
fact requires re-normalization. 
3000 
200-400 mJy 
2000 I r..----
z 
I 
I 
I 
I 
I 
1000 I ---· I 
I 
I 
I 
I 
I 
I :------. 
I 
I 
I 
I 
0 
-3 -2 -1 0 
log (z) 
Figure 2: Data for observed number vs. redshift for galaxies between 
200 and 400 mJ y at 60 µm, plotted as in Fig. 1. 
ACKNOWLEDGEMENTS 
This program has been partially supported, both at Caltech and CTIO, by 
NASA under the ADP program. 
REFERENCES 
Hacking, P., Condon, J. J., and Houck, J. R. 1987 Ap.J., 316, L15. 
Harwit, M., Houck, J. R., Soifer, B. T., and Pulumbo, G. G. C. 1987, Ap.J., 
315, 28. 
Lonsdale, C. J., and Hacking, P. B. 1989, Ap.J., 339, 712. 
Lonsdale, C. J., Hacking, P. B., Conrow, T. P., and Rowan-Robinson, M. 1990, 
Ap.J ., 358, 60. 
Rowan-Robinson, M., et al 1991, Nature, 351, 719. 
Saunders, W., Rowan-Robinson, M., Lawrence, A., Efstathiou, G., Kaiser, N., 
Ellis, R. S., and Frenck, C. S. 1990 MNRAS, 242, 318. 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 


English

Cosmic Evolution of a Sample of Infrared Luminous Galaxies

19
93
AS
PC
..
.4
3.
.1
11
E
S/ry Surveys: Protostars to Protogalaxies 
ASP Cotifermce Serles, Vol. 43, 1993 
B. T. Soifer (ed.) 
COSMIC EVOLUTION OF A SAMPLE OF INFRARED-LUMINOUS 
GALAXIES 
J. H. ELIAS and L. F. BARRIENTOS 
Cerro Tololo Inter-American Observatory, National Optical Astronomy 
Observatories, Casilla 603, La Serena, Chile 
P. HACKING, G. NEUGEBAUER and B. T. SOIFER 
California Instituter of Technology, Pasadena CA 91125 
ABSTRACT A sample of faint, southern-hemisphere 60 µm sources 
(!60 > lOOmJy) detected as part of the IRAS Additional Observations has 
been used, in conjunction with CCD imaging, to produce a list of faint 
infrared galaxies. Redshifts of this sample of galaxies can be compared 
with model predictions for several evolutionary scenarios; the comparisons 
show an excess of galaxies at higher redshifts (z > 0.1) compared with the 
predictions of models which assume no evolution of the infrared-galaxy 
luminosity function. 
INTRODUCTION 
The most luminous infrared galaxies detected by IRAS can be seen out to 
cosmologically interesting distances - i.e., distances such that the "look-back" 
time is a significant fraction of the age of the universe (e.g. Harwit et al 1987; 
Rowan-Robinson et al 1991 ). The ability to look back in time - admittedly at 
the limits of the IRAS surveys - allows us to examine whether the propertieti 
of these extremely luminous objects have evolved over time. As a first step, we 
can investigate whether the luminosity function of infrared luminous galaxies 
evolves over time. 
Similar investigations have been carried out previously (e.g. Hacking et al 
1987; Lonsdale and Hacking 1989; Saunders et al 1990; Lonsdale et al 1990). 
However, they have all been limited in one way or another - either by lack of 
depth in flux, incompleteness, or lack of spatial sampling This paper describes 
yet another attempt, in which a sample of adequate depth and spatial sampling 
is studied. 
SAMPLE 
Sources from 25 southern IRAS Additional Observation fields with the following 
characteristics were selected: 
111 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 
19
93
AS
PC
..
.4
3.
.1
11
E
112 J. ELIAS ET AL. 
• Observed on at least 4 occasions by IRAS (implies completeness to at 
least 100 mJy). 
• Above 40° galactic latitude 
• No more than 10 100 µm sources (to guard against spunous "cirrus" 
sources) 
CCD B and R images were taken of all sources (except for known bright 
galaxies) on the CTIO 0.9-m telescope. Galaxy positions were measured on the 
ESQ and SRC sky survey films, using SAO stars as positional references, or on 
the CCD images, using reference stars whose positions were measured on the 
sky survey films relative to SAO stars. 
The positional accuracy of the co-added AO grids was investigated using: 
• Stars detected at 12 and 25 µm in these AO's and the corresponding 
northern AO's; 
• Stars detected at 60 µm in the same data set (a very small number: 7 
objects); and 
• "Obvious" galaxy identifications (i.e. isolated bright objects) in the 
sample itself. 
These investigations showed the positions to have a 1-u error in the satellite 
in-scan direction of 6 arcsec and in the cross-scan direction of 22 arcsec. The 
positions also showed a small systematic offset (2 arcsec) in the in-scan direction. 
In the larger samples, roughly 5% of the sources showed excessive (non-
gaussian) positional errors. 
REDSHIFTS 
Redshifts for objects in most of the AO fields were taken from the literature 
or were measured using the RC spectrograph on the CTIO 4-m telescope. A 
few of the fields could not be finished, due to lack of time. Within the fields 
that were completely observed, we did not get redshifts for 100% of the IRAS 
sources, for one or more of the following reasons: 
Inadequate signal to noise. This in practice occurred only when the 
candidate did not show emission lines, which in turn makes its identification 
as the IRAS source somewhat dubious (unless it was visually very bright). It 
is possible, but also not likely, that the absence of emission lines was due to a 
redshift high enough to shift Ha outside the coverage of the spectra (z > 0.5), 
leaving only relatively weak lines in the observable spectrum. 
No suitable candidate. In some cases, all the objects in the field were 
very faint. This may be because the IRAS source is at high redshift, that is, 
an object with extreme far-ir/visible ratio, or it may reflect a bad source (e.g. 
cirrus contamination). 
Missed candidate. In some cases only some candidates in the vicinity of 
the IRAS source were measured, usually because the revised positions on the 
CCD image moved new objects inside the 3-u error ellipse, and in some of these 
cases none of the objects measured appeared to be the correct identification. 
In cases where several candidate objects existed, the identification as the 
IRAS source was based on a mix of three criteria: 
•Positional match (IRAS and optical positions). 
• Visual brightness (visually brighter object is more probable identifica-
tion). 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 
19
93
AS
PC
..
.4
3.
.1
11
E
EVOLUTION OF INFRARED-LUMINOUS GALAXIES 113 
• Appearance of spectrum (ir luminous galaxy more likely to have emission 
lines). 
Fields with more than one or two "missing" sources were omitted from 
the analysis. Those with only one or two missing were included. It was felt 
that these could be safely included, as the unidentified sources were either (a) 
unbiassed with respect to redshift or (b) high-redshift, high-luminosity sources. 
Since the purpose of this study is to look for an excess of high-redshift sources, 
(and since such an excess is found), missing a few such sources will not prejudice 
the main goal of the study. 
6000 
z 4000 
2000 
0 
-3 
100-200 mJy 
I 
I 
, ______ 
-2 
log 
---· 
-1 
(z) 
I 
I , __ _ 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
I 
L--
0 
Figure 1: Plot of observed number vs. redshift distributions for sample 
galaxies with 60 µm flux densities between 100 and 200 mJy. The data are 
shown as a heavy dashed line. The predictions of three different models, 
derived from Hacking et al 1987, are also shown. The thin solid line is for 
a model without evolution, the dashed line is a simple density evolution 
model, while the dotted line is a luminosity evolution model. 
A histogram of number vs. redshift is shown for each of two flux density 
intervals, compared with model predictions. The data are shown as heavy 
dashed lines. The a model with no evolution is shown as a solid line. A model 
with density evolution (proportional to (1 + z) 4 ) as a dashed line, and a model 
with strong luminosity evolution (proportional to (1 + z)3 ) is shown as a dotted 
line. 
The data show a clear deficit at moderate redshifts (z = 0.01-0.1) relative 
to the model predictions. This is likely to be due to a genuine deficiency of 
galaxies in that distance range, but the model normalization may be in error 
somewhat as well. A similar effect was also seen in the south galactic cap by 
Lonsdale et al (1990). 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 
19
93
AS
PC
..
.4
3.
.1
11
E
114 J. ELIAS ET AL. 
The data also show a clear excess over the predictions of the "no-evolution" 
model, and in fact suggest that even the weaker evolution models are insufficient 
to account for the excess. The situation would be accentuated if the model in 
fact requires re-normalization. 
3000 
200-400 mJy 
2000 I r..--
--
z 
I 
I 
I 
I 
I 
1000 I ---· I 
I 
I 
I 
I 
I 
I :------. 
I 
I 
I 
I 
0 
-3 -2 -1 0 
log (z) 
Figure 2: Data for observed number vs. redshift for galaxies between 
200 and 400 mJ y at 60 µm, plotted as in Fig. 1. 
ACKNOWLEDGEMENTS 
This program has been partially supported, both at Caltech and CTIO, by 
NASA under the ADP program. 
REFERENCES 
Hacking, P., Condon, J. J., and Houck, J. R. 1987 Ap.J., 316, L15. 
Harwit, M., Houck, J. R., Soifer, B. T., and Pulumbo, G. G. C. 1987, Ap.J., 
315, 28. 
Lonsdale, C. J., and Hacking, P. B. 1989, Ap.J., 339, 712. 
Lonsdale, C. J., Hacking, P. B., Conrow, T. P., and Rowan-Robinson, M. 1990, 
Ap.J ., 358, 60. 
Rowan-Robinson, M., et al 1991, Nature, 351, 719. 
Saunders, W., Rowan-Robinson, M., Lawrence, A., Efstathiou, G., Kaiser, N., 
Ellis, R. S., and Frenck, C. S. 1990 MNRAS, 242, 318. 
© Astronomical Society of the Pacific • Provided by the NASA Astrophysics Data System 


https://authors.library.caltech.edu/74631/1/1993ASPC___43__111E.pdf

Cosmic Evolution of a Sample of Infrared Luminous Galaxies

Abstract

Similar works

Full text

Available Versions

Caltech Authors - Main

Caltech Authors - Main