alx-ai/arxiv_papers · Datasets at Hugging Face

text stringlengths 0 44.4k
convert the observed ﬂux to 8 µm monochromatic luminosity
1http://www.ir.isas.jaxa.jp/ASTRO-
F/Observation/DataReduction/IRC/ApertureCorrection 090501.htmlGotoet al.:Environemental dependence of 8 µm luminosity functions ofgalaxies atz ∼0.8 3
Table 1.Best doublepower-lawﬁt parametersforLFs
Sample L∗
8µm(L⊙)φ∗(Mpc−3dex−1)α β
NEPDeepﬁeld 6.1 ±0.5×10100.0010±0.0003 1.1 ±0.3 5.7 ±1.2
RXJ1716.4 +67082.5±0.1×10100.74±0.04 2.6 ±0.1 5.5 ±0.4
(L8µm) using a standard cosmology. Completeness was mea-
sured by distributing artiﬁcial point sources with varying ﬂux
withinthe ﬁeld andby examiningwhat fractionofthem wasre-
coveredasafunctionofinputﬂux.Sincewehavedeepercover -
age at the center of the cluster, the completeness was measur ed
separately in the central deep region and the outer regions o f
the ﬁeld. More detail of the method is described in Wada et al.
(2008).
Oncetheﬂuxisconvertedtoluminosityandcompletenessis
takenintoaccount,it is straightforwardto construct L8µmLFs,
which we show in the squares in Fig.1. Errors of the LFs are
assumedtofollowPoissondistribution.Here,wetakeanang ular
distance of the most distant source from the cluster center a s
a cluster radius ( Rmax= 6.2Mpc). We assumed4
3πR3
maxas
the volume of the cluster to obtain galaxy density ( φ). This is
only one of many ways to deﬁne a cluster volume, and thus, a
cautionmustbetakentocompare absolute valuesofourLFsto
other work such as Shimet al. (2010). This cluster is elongat ed
inangulardirection(Koyamaet al.,2007),andthus,thevol ume
mightnotbespherical.Yet,comparisonofthe shapeoftheLFs
isvalid.
2.2. LFs inthe AKARI NEP Deepﬁeld
Our ﬁeld LFs are based on the AKARI NEP Deep ﬁeld
data. The AKARI performed deep imaging in the North
Ecliptic Pole Region (NEP) from 2-24 µm, with 4 pointings
in each ﬁeld over 0.4 deg2(Matsuharaet al., 2006, 2007;
Wada etal., 2008). The 5 σsensitivity in the AKARI IR ﬁlters
(N2,N3,N4,S7,S9W,S11,L15,L18WandL24) are 14.2,
11.0, 8.0, 48, 58, 71, 117, 121 and 275 µJy (Wada etal., 2008).
Flux is measured in 3 pix radius aperture (=7”), then correct ed
tototal ﬂux.
AsubregionoftheNEP-Deepﬁeld(0.25deg2)hasancillary
datafromSubaru BVRi′z′(Imaiet al.,2007;Wada etal.,2008),
CFHTu′(Serjeant et al. in prep.), KPNO2m/FLAMINGOs J
andKs(Imaietal., 2007), GALEX FUVandNUV(Malkan
et al. in prep.). For the optical identiﬁcation of MIR source s,
we adopt the likelihood ratio method (Sutherland&Saunders ,
1992).Usingthesedata,weestimatephotometricredshifto fL15
detectedsourcesintheregionwiththe LePhare (Ilbertet al.,
2006; Arnoutset al., 2007).Themeasurederrorsonthephoto -z
against 293 spec-z galaxies from Keck/DEIMOS (Takagi et al.
in prep.) are∆z
1+z=0.036 at z≤0.8. We have excluded those
sourcesbetterﬁt with QSO templatesfromtheLFs.
To construct ﬁeld LFs, we have selected L15sources at
0.65< zphotoz<0.9. There remained 289 IR galaxies with
a median redshift of 0.76. L15ﬂux is converted to L8µmus-
ing the photometric redshift of each galaxy. LFs are com-
puted using the 1/ Vmaxmethod. We used the SED templates
(Lagache,Dole,&Puget, 2003) for k-corrections to obtain the
maximumobservableredshiftfromtheﬂuxlimit.Completene ss
of theL15detection is corrected using Pearsonet al. (2009b).
Thiscorrectionis25%atmaximum,sincewe onlyusethesam-
plewherethecompletenessisgreaterthan80%.
The resulting ﬁeld LFs are shown in the dotted line and tri-
angles in Fig.1. Errors of the LFs are computed using a 1000Monte Caro simulation with varying zand ﬂux within their er-
rors. These estimated errors are added to the Poisson errors in
eachLFbinin quadrature.
We performed a detaild comparison of restframe 8 µm
LFs to those in the literature in Gotoetal. (2010). Brieﬂy,
there is an oder of difference between Caputiet al. (2007) an d
Babbedgeetal. (2006), reﬂecting difﬁculty in estimating L8µm
dominatedbyPAHemissionsusingSpitzer24 µmﬂux.Ourﬁeld
8µm LF lies between Caputi etal. (2007) and Babbedgeet al.
(2006). Compared with these work, we have directly observed
restframe 8 µm using the AKARI L15ﬁlter, eliminating the un-
certaintlyinﬂuxconversionbasedonSEDmodels.Moredetai ls
andevolutionofﬁeldIRLFsaredescribedinGotoet al.(2010 ).
3. Results& Discussion
3.1. 8µmIRLFs
In Fig.1, we show restframe 8 µm LFs of cluster
RXJ1716.4 +6708 in the squares, and LFs of the ﬁeld re-
gion in the triangles. First of all, cluster LFs have by a fact or
of∼700 higher density than the ﬁeld LFs, reﬂecting the fact
the galaxy clusters is indeed high density regions in terms o f
infraredsources.
Next, to compare the shape of the LFs, we normalized the
cluster LF to match the ﬁeld LFs at the faintest end, and show
in the dash-dottedline. In contrast to the ﬁeld LFs, which sh ow
ﬂattening of the slope at log L8µm<10.8L⊙, the cluster LF
maintainsthesteepslopeintherangeof 10.0L⊙<logL8µm<
10.6L⊙.Thedifferenceissigniﬁcant,consideringthesizeofer-
rorsoneachLF.
Weﬁtadouble-powerlawtobothclusterandﬁeldLFsusing
thefollowingformulae.
Φ(L)dL/L∗= Φ∗/parenleftbiggL
L∗/parenrightbigg1−α
dL/L∗,(L < L∗) (1)
Φ(L)dL/L∗= Φ∗/parenleftbiggL
L∗/parenrightbigg1−β

convert the observed ﬂux to 8 µm monochromatic luminosity

1http://www.ir.isas.jaxa.jp/ASTRO-

F/Observation/DataReduction/IRC/ApertureCorrection 090501.htmlGotoet al.:Environemental dependence of 8 µm luminosity functions ofgalaxies atz ∼0.8 3

Table 1.Best doublepower-lawﬁt parametersforLFs

Sample L∗

8µm(L⊙)φ∗(Mpc−3dex−1)α β

NEPDeepﬁeld 6.1 ±0.5×10100.0010±0.0003 1.1 ±0.3 5.7 ±1.2

RXJ1716.4 +67082.5±0.1×10100.74±0.04 2.6 ±0.1 5.5 ±0.4

(L8µm) using a standard cosmology. Completeness was mea-

sured by distributing artiﬁcial point sources with varying ﬂux

withinthe ﬁeld andby examiningwhat fractionofthem wasre-

coveredasafunctionofinputﬂux.Sincewehavedeepercover -

age at the center of the cluster, the completeness was measur ed

separately in the central deep region and the outer regions o f

the ﬁeld. More detail of the method is described in Wada et al.

(2008).

Oncetheﬂuxisconvertedtoluminosityandcompletenessis

takenintoaccount,it is straightforwardto construct L8µmLFs,

which we show in the squares in Fig.1. Errors of the LFs are

assumedtofollowPoissondistribution.Here,wetakeanang ular

distance of the most distant source from the cluster center a s

a cluster radius ( Rmax= 6.2Mpc). We assumed4

3πR3

maxas

the volume of the cluster to obtain galaxy density ( φ). This is

only one of many ways to deﬁne a cluster volume, and thus, a

cautionmustbetakentocompare absolute valuesofourLFsto

other work such as Shimet al. (2010). This cluster is elongat ed

inangulardirection(Koyamaet al.,2007),andthus,thevol ume

mightnotbespherical.Yet,comparisonofthe shapeoftheLFs

isvalid.

2.2. LFs inthe AKARI NEP Deepﬁeld

Our ﬁeld LFs are based on the AKARI NEP Deep ﬁeld

data. The AKARI performed deep imaging in the North

Ecliptic Pole Region (NEP) from 2-24 µm, with 4 pointings

in each ﬁeld over 0.4 deg2(Matsuharaet al., 2006, 2007;

Wada etal., 2008). The 5 σsensitivity in the AKARI IR ﬁlters

(N2,N3,N4,S7,S9W,S11,L15,L18WandL24) are 14.2,

11.0, 8.0, 48, 58, 71, 117, 121 and 275 µJy (Wada etal., 2008).

Flux is measured in 3 pix radius aperture (=7”), then correct ed

tototal ﬂux.

AsubregionoftheNEP-Deepﬁeld(0.25deg2)hasancillary

datafromSubaru BVRi′z′(Imaiet al.,2007;Wada etal.,2008),

CFHTu′(Serjeant et al. in prep.), KPNO2m/FLAMINGOs J

andKs(Imaietal., 2007), GALEX FUVandNUV(Malkan

et al. in prep.). For the optical identiﬁcation of MIR source s,

we adopt the likelihood ratio method (Sutherland&Saunders ,

1992).Usingthesedata,weestimatephotometricredshifto fL15

detectedsourcesintheregionwiththe LePhare (Ilbertet al.,

2006; Arnoutset al., 2007).Themeasurederrorsonthephoto -z

against 293 spec-z galaxies from Keck/DEIMOS (Takagi et al.

in prep.) are∆z

1+z=0.036 at z≤0.8. We have excluded those

sourcesbetterﬁt with QSO templatesfromtheLFs.

To construct ﬁeld LFs, we have selected L15sources at

0.65< zphotoz<0.9. There remained 289 IR galaxies with

a median redshift of 0.76. L15ﬂux is converted to L8µmus-

ing the photometric redshift of each galaxy. LFs are com-

puted using the 1/ Vmaxmethod. We used the SED templates

(Lagache,Dole,&Puget, 2003) for k-corrections to obtain the

maximumobservableredshiftfromtheﬂuxlimit.Completene ss

of theL15detection is corrected using Pearsonet al. (2009b).

Thiscorrectionis25%atmaximum,sincewe onlyusethesam-

plewherethecompletenessisgreaterthan80%.

The resulting ﬁeld LFs are shown in the dotted line and tri-

angles in Fig.1. Errors of the LFs are computed using a 1000Monte Caro simulation with varying zand ﬂux within their er-

rors. These estimated errors are added to the Poisson errors in

eachLFbinin quadrature.

We performed a detaild comparison of restframe 8 µm

LFs to those in the literature in Gotoetal. (2010). Brieﬂy,

there is an oder of difference between Caputiet al. (2007) an d

Babbedgeetal. (2006), reﬂecting difﬁculty in estimating L8µm

dominatedbyPAHemissionsusingSpitzer24 µmﬂux.Ourﬁeld

8µm LF lies between Caputi etal. (2007) and Babbedgeet al.

(2006). Compared with these work, we have directly observed

restframe 8 µm using the AKARI L15ﬁlter, eliminating the un-

certaintlyinﬂuxconversionbasedonSEDmodels.Moredetai ls

andevolutionofﬁeldIRLFsaredescribedinGotoet al.(2010 ).

3. Results& Discussion

3.1. 8µmIRLFs

In Fig.1, we show restframe 8 µm LFs of cluster

RXJ1716.4 +6708 in the squares, and LFs of the ﬁeld re-

gion in the triangles. First of all, cluster LFs have by a fact or

of∼700 higher density than the ﬁeld LFs, reﬂecting the fact

the galaxy clusters is indeed high density regions in terms o f

infraredsources.

Next, to compare the shape of the LFs, we normalized the

cluster LF to match the ﬁeld LFs at the faintest end, and show

in the dash-dottedline. In contrast to the ﬁeld LFs, which sh ow

ﬂattening of the slope at log L8µm<10.8L⊙, the cluster LF

maintainsthesteepslopeintherangeof 10.0L⊙<logL8µm<

10.6L⊙.Thedifferenceissigniﬁcant,consideringthesizeofer-

rorsoneachLF.

Weﬁtadouble-powerlawtobothclusterandﬁeldLFsusing

thefollowingformulae.

Φ(L)dL/L∗= Φ∗/parenleftbiggL

L∗/parenrightbigg1−α

dL/L∗,(L < L∗) (1)

Φ(L)dL/L∗= Φ∗/parenleftbiggL

L∗/parenrightbigg1−β