alx-ai/arxiv_papers · Datasets at Hugging Face

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1. Introduction
It hasbeenobservedthat galaxypropertieschangeas a funct ion
of galaxyenvironment;the morphology-densityrelation re ports
that fractionof elliptical galaxiesis largerat highergal axyden-
sity(Gotoetal.,2003);thestarformationrate(SFR)ishig herin
lower galaxy density (G´ omezet al., 2003; Tanakaet al., 200 4)
. However, despite accumulating observational evidence, w e
⋆This research is based on the observations with AKARI, a JAXA
project withthe participationof ESA.
⋆⋆Based on data collected at Subaru Telescope, which is operat ed by
the National Astronomical Observatory ofJapan.
⋆⋆⋆JSPSSPDfellowstill do not fully understand the underlying physics govern ing
environmental-dependentevolutionofgalaxies.
Infrared (IR) emission of galaxies is an important
probe of galaxy activity since at higher redshift, a sig-
niﬁcant fraction of star formation is obscured by dust
(Takeuchi,Buat,&Burgarella, 2005; Gotoetal., 2010).
Although there exist low-z cluster studies (Baiet al., 2006 ;
Shimet al., 2010; Tranetal., 2010), not much attention has
been paid to the infrared properties of high redshift cluste r
galaxies, mainly due to the lack of sensitivity in previous I R
satellites such as ISO and IRAS. Superb sensitivity of recen tly
launched Spitzer and AKARI satellites can revolutionize th e
infraredviewofenvironmentaldependenceofgalaxyevolut ion.2 Gotoet al.:Environemental dependence of 8 µm luminosity functions ofgalaxies atz ∼0.8
Fig.1.Restframe 8 µm LFs of cluster RXJ1716.4 +6708 at
z=0.81 in the squares, and those of the AKARI NEP deep
ﬁeld in the triangles. For RXJ1716.4 +6708, only photometric
and spectroscopic cluster member galaxies are used. For the
NEP deep ﬁeld, galaxies with photo-z/specz in the range of
0.65< z <0.9are used. The dot-dashed lines are 8 µm LFs
of RXJ1716.4 +6708, but scaled down for easier comparison.
Thethindottedlinesarethebest-ﬁtdoublepowerlaws.Vert ical
arrows show the 5 σﬂux limits of deep/shallow regions of the
cluster (red) and the NEP deep ﬁeld (blue) in terms of L8µmat
z=0.81.
In this work, we comparerestframe8 µm LFs between clus-
ter and ﬁeld regions at z=0.8 using data from the AKARI.
Monochromaticrestframe 8 µm luminosity ( L8µm) is important
since it is known to correlate well with the total IR luminosi ty
(Babbedgeet al., 2006; Huanget al., 2007), andhence,with t he
SFR of galaxies (Kennicutt, 1998). This is especially true f or
star-forminggalaxiesbecausethe rest-frame8 µm ﬂuxare dom-
inatedbyprominentPAHfeaturessuchasat6.2,7.7and8.6 µm
(Desert,Boulanger,&Puget, 1990).
ImportantadvantagesbroughtbytheAKARIareasfollows:
(i) At z=0.8, AKARI’s 15 µm ﬁlter (L15) covers the redshifted
restframe 8 µm, thus we can estimate 8 µm LFs without using
a large extrapolation based on SED models, which were the
largest uncertainty in previous work. (ii) Large ﬁeld of vie w of
the AKARI’smid-IRcamera(IRC, 10’ ×10’)allowsustostudy
wider area including cluster outskirts, where important ev olu-
tionary mechanisms are suggested to be at work (Gotoet al.,
2004; Kodamaet al., 2004). For example, passive spiral gala x-
ies have been observed in such an environment (Gotoet al.,
2003). Unless otherwise stated, we adopt a cosmology with
(h,Ωm,ΩΛ) = (0.7,0.3,0.7)(Komatsuet al., 2009).
2. Data & Analysis
2.1. LFs ofclusterRXJ1716.4 +6708
The AKARI is a Japanese infrared satellite (Murakamiet al.,
2007), which has continuous ﬁlter coverage in the mid
IR wavelengths ( N2,N3,N4,S7,S9W,S11,L15,L18Wand
L24). The AKARI has observed a massive galaxy cluster,Fig.2.Restframe 8 µm LFs of cluster RXJ1716.4 +6708 at
z=0.81, divided according to the local galaxy density ( Σ5th).
Thestars,circlesandsquaresareforgalaxieswith logΣ5th≥2,
1.6≤logΣ5th<2,andlogΣ5th<1.6,respectively.
RXJ1716.4 +6708, in N3,S7andL15(Koyamaetal., 2008).
RXJ1716.4 +6708 is at z=0.81 and has σ= 1522+215
−150km s−1,
LXbol= 13.86±1.04×1044ergs−1,kT= 6.8+1.0
−0.6keV.Mass
estimate from weak lensing and X-ray are 3.7 ±1.3×1014M⊙
and 4.35 ±0.83×1014M⊙, respectively (see Koyamaet al.,
2007, forreferences).
An important advantage of the AKARI observation is L15
ﬁlter, which corresponds to the restframe 8 µm at z=0.81. With
15 (3) pointings, L15reaches 66.5 (96.5) µJy in deep (shal-
low) regions at 5 σ. Here ﬂux is measured in 11” aperture,
and coverted to total ﬂux using AKARI’s IRC correction table
(2009.5.1)1.ClusterstudieswiththeSpitzerareoftenperformed
in 24µm and thus needed a large extrapolation to estimate ei-
therL8µmor total infrared luminosity ( LTIR,8−1000µm).
Note that we do not claim the L8µmis a better indicator of
thetotalIRluminositythanotherindicators(Brandlet al. ,2006;
Calzetti et al., 2007; Riekeet al., 2009), but it is importan t that
theAKARIcanmeausureredshifted 8µmﬂuxdirectlyinoneof
theﬁlters.
Thanks to the AKARI’s wide ﬁeld of view (10’ ×10’), the
total area coverage around the cluster is 200 arcmin2, which
cover larger area than previous cluster studies with the Spi tzer,
allowingustostudyIRsourcesintheoutskirts,whereimpor tant
galaxyevolutiontakesplace(e.g.,Gotoet al.,2003).Prev iously,
Koyamaet al. (2008) reporteda high fractionof L15sourcesin
the intermediatedensity regionin the cluster,suggesting a pres-
enceofenvironmentaleffectintheintermediatedensityen viron-
ment.
Thissameregionwasimagedwith Suprime-Camin VRi′z′
and has a good photometric redshift estimate (Koyamaet al.,
2007).Usedinthisworkare54 L15-detectedgalaxieswhichare
well identiﬁedwithopticalsourceswith 0.76≤zphoto≤0.83.
With the L15ﬁlter covering the restframe 8 µm, we simply

1. Introduction

It hasbeenobservedthat galaxypropertieschangeas a funct ion

of galaxyenvironment;the morphology-densityrelation re ports

that fractionof elliptical galaxiesis largerat highergal axyden-

sity(Gotoetal.,2003);thestarformationrate(SFR)ishig herin

lower galaxy density (G´ omezet al., 2003; Tanakaet al., 200 4)

. However, despite accumulating observational evidence, w e

⋆This research is based on the observations with AKARI, a JAXA

project withthe participationof ESA.

⋆⋆Based on data collected at Subaru Telescope, which is operat ed by

the National Astronomical Observatory ofJapan.

⋆⋆⋆JSPSSPDfellowstill do not fully understand the underlying physics govern ing

environmental-dependentevolutionofgalaxies.

Infrared (IR) emission of galaxies is an important

probe of galaxy activity since at higher redshift, a sig-

niﬁcant fraction of star formation is obscured by dust

(Takeuchi,Buat,&Burgarella, 2005; Gotoetal., 2010).

Although there exist low-z cluster studies (Baiet al., 2006 ;

Shimet al., 2010; Tranetal., 2010), not much attention has

been paid to the infrared properties of high redshift cluste r

galaxies, mainly due to the lack of sensitivity in previous I R

satellites such as ISO and IRAS. Superb sensitivity of recen tly

launched Spitzer and AKARI satellites can revolutionize th e

infraredviewofenvironmentaldependenceofgalaxyevolut ion.2 Gotoet al.:Environemental dependence of 8 µm luminosity functions ofgalaxies atz ∼0.8

Fig.1.Restframe 8 µm LFs of cluster RXJ1716.4 +6708 at

z=0.81 in the squares, and those of the AKARI NEP deep

ﬁeld in the triangles. For RXJ1716.4 +6708, only photometric

and spectroscopic cluster member galaxies are used. For the

NEP deep ﬁeld, galaxies with photo-z/specz in the range of

0.65< z <0.9are used. The dot-dashed lines are 8 µm LFs

of RXJ1716.4 +6708, but scaled down for easier comparison.

Thethindottedlinesarethebest-ﬁtdoublepowerlaws.Vert ical

arrows show the 5 σﬂux limits of deep/shallow regions of the

cluster (red) and the NEP deep ﬁeld (blue) in terms of L8µmat

z=0.81.

In this work, we comparerestframe8 µm LFs between clus-

ter and ﬁeld regions at z=0.8 using data from the AKARI.

Monochromaticrestframe 8 µm luminosity ( L8µm) is important

since it is known to correlate well with the total IR luminosi ty

(Babbedgeet al., 2006; Huanget al., 2007), andhence,with t he

SFR of galaxies (Kennicutt, 1998). This is especially true f or

star-forminggalaxiesbecausethe rest-frame8 µm ﬂuxare dom-

inatedbyprominentPAHfeaturessuchasat6.2,7.7and8.6 µm

(Desert,Boulanger,&Puget, 1990).

ImportantadvantagesbroughtbytheAKARIareasfollows:

(i) At z=0.8, AKARI’s 15 µm ﬁlter (L15) covers the redshifted

restframe 8 µm, thus we can estimate 8 µm LFs without using

a large extrapolation based on SED models, which were the

largest uncertainty in previous work. (ii) Large ﬁeld of vie w of

the AKARI’smid-IRcamera(IRC, 10’ ×10’)allowsustostudy

wider area including cluster outskirts, where important ev olu-

tionary mechanisms are suggested to be at work (Gotoet al.,

2004; Kodamaet al., 2004). For example, passive spiral gala x-

ies have been observed in such an environment (Gotoet al.,

2003). Unless otherwise stated, we adopt a cosmology with

(h,Ωm,ΩΛ) = (0.7,0.3,0.7)(Komatsuet al., 2009).

2. Data & Analysis

2.1. LFs ofclusterRXJ1716.4 +6708

The AKARI is a Japanese infrared satellite (Murakamiet al.,

2007), which has continuous ﬁlter coverage in the mid

IR wavelengths ( N2,N3,N4,S7,S9W,S11,L15,L18Wand

L24). The AKARI has observed a massive galaxy cluster,Fig.2.Restframe 8 µm LFs of cluster RXJ1716.4 +6708 at

z=0.81, divided according to the local galaxy density ( Σ5th).

Thestars,circlesandsquaresareforgalaxieswith logΣ5th≥2,

1.6≤logΣ5th<2,andlogΣ5th<1.6,respectively.

RXJ1716.4 +6708, in N3,S7andL15(Koyamaetal., 2008).

RXJ1716.4 +6708 is at z=0.81 and has σ= 1522+215

−150km s−1,

LXbol= 13.86±1.04×1044ergs−1,kT= 6.8+1.0

−0.6keV.Mass

estimate from weak lensing and X-ray are 3.7 ±1.3×1014M⊙

and 4.35 ±0.83×1014M⊙, respectively (see Koyamaet al.,

2007, forreferences).

An important advantage of the AKARI observation is L15

ﬁlter, which corresponds to the restframe 8 µm at z=0.81. With

15 (3) pointings, L15reaches 66.5 (96.5) µJy in deep (shal-

low) regions at 5 σ. Here ﬂux is measured in 11” aperture,

and coverted to total ﬂux using AKARI’s IRC correction table

(2009.5.1)1.ClusterstudieswiththeSpitzerareoftenperformed

in 24µm and thus needed a large extrapolation to estimate ei-

therL8µmor total infrared luminosity ( LTIR,8−1000µm).

Note that we do not claim the L8µmis a better indicator of

thetotalIRluminositythanotherindicators(Brandlet al. ,2006;

Calzetti et al., 2007; Riekeet al., 2009), but it is importan t that

theAKARIcanmeausureredshifted 8µmﬂuxdirectlyinoneof

theﬁlters.

Thanks to the AKARI’s wide ﬁeld of view (10’ ×10’), the

total area coverage around the cluster is 200 arcmin2, which

cover larger area than previous cluster studies with the Spi tzer,

allowingustostudyIRsourcesintheoutskirts,whereimpor tant

galaxyevolutiontakesplace(e.g.,Gotoet al.,2003).Prev iously,

Koyamaet al. (2008) reporteda high fractionof L15sourcesin

the intermediatedensity regionin the cluster,suggesting a pres-

enceofenvironmentaleffectintheintermediatedensityen viron-

ment.

Thissameregionwasimagedwith Suprime-Camin VRi′z′

and has a good photometric redshift estimate (Koyamaet al.,

2007).Usedinthisworkare54 L15-detectedgalaxieswhichare

well identiﬁedwithopticalsourceswith 0.76≤zphoto≤0.83.

With the L15ﬁlter covering the restframe 8 µm, we simply