Imaging of diffuse HI absorption structure in the SSA22 proto-cluster region at z = 3.1

0.99 MB·

by  Ken Mawatari

Mon.Not.R.Astron.Soc.000,1–13(2016) Printed11January2017 (MNLATEXstylefilev2.2)
i
Imaging of diffuse H absorption structure in the SSA22
proto-cluster region at z = 3.1
7
1 Ken Mawatari,1⋆ Akio K. Inoue,1 Toru Yamada,2 Tomoki Hayashino,3
0
2 Takuya Otsuka,4 Yuichi Matsuda,5 Hideki Umehata,6,7 Masami Ouchi8

n
and Shiro Mukae8,9
a
J 1College of General Education, OsakaSangyo University,3-1-1, Nakagaito, Daito, Osaka, 574-8530, Japan
0 2Institute of Space Astronautical Science,Japan Aerospace Exploration Agency,Sagamihara, Kanagawa 252-5210, Japan
1 3Research Centerfor NeutrinoScience, Graduate School of Science,Tohoku University,Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
4Astronomical Institute,Tohoku University,Aoba, Aramaki, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
] 5National Astronomical Observatory of Japan, Osawa 2-21-1, Mitaka, Tokyo181-8588, Japan
A 6The Open Universityof Japan, 2-11 Wakaba, Mihama-ku, Chiba-shi, Chiba, 261-8586, Japan
G 7Institute of Astronomy, The Universityof Tokyo, 2-21-1 Osawa, Mitaka, Tokyo181-0015, Japan
8Institute for Cosmic Ray Research, The Universityof Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan
h. 9Department of Astronomy, Graduate School of Science,The Universityof Tokyo, 7-3-1Hongo, Bunkyo, Tokyo, 113-0033, Japan
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AcceptedXXX.ReceivedYYY;inoriginalformZZZ
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[ ABSTRACT
Using galaxies as background light sources to map intervening Lya absorption is a
1
novel approach to study the interplay among galaxies, the circum-galactic medium
v (CGM),andtheintergalacticmedium(IGM).Introducinganewmeasureofz=3.1Hi
2 Lya absorptionrelativetothecosmicmean,D NB497,estimatedfromphotometricdata
6
ofstar-forminggalaxiesat3.3.z.3.5,wehavemadetwo-dimensionalD NB497maps
4
2 inthez=3.1SSA22proto-clusterregionandtwocontrolfields(SXDSandGOODS-N
0 fields) with a spatial resolution of ∼5comoving Mpc. The D NB497 measurements in
. the SSA22 field are systematically largerthan those in the controlfields, and this H i
1
absorptionenhancementextendsmorethan50comovingMpc.Thefield-averaged(i.e.,
0
∼50comoving Mpc scale) D NB497 and the overdensity of Lya emitters (LAEs) seem
7
to be correlated, while there is no clear dependency of the D NB497 on the local LAE
1
: overdensity in a few comoving Mpc scale. These results suggest that diffuse H i gas
v
spreads out in/around the SSA22 proto-cluster. We have also found an enhancement
Xi ofD NB497ataprojecteddistance<100physicalkpcfromthenearestz=3.1galaxies
atleastinthe SSA22field,whichisprobablydue toHigasassociatedwiththeCGM
r
a of individual galaxies. The H i absorption enhancement in the CGM-scale tends to
be weaker around galaxies with stronger Lya emission, which suggests that the Lya
escape fraction from galaxies depends on hydrogenneutrality in the CGM.
Keywords: galaxies:high-redshift—intergalacticmedium—cosmology:largescale
structure of Universe
1 INTRODUCTION and stellar component of galaxies are the most com-
mon observable and routinely studied (e.g., Santiniet al.
Galaxy formation occurs through assembly of gaseous mat-
2009;Daddiet al.2010;Genzel et al.2010;Smit et al.2012;
terfollowedbystar-formationinthedarkmatterlarge-scale
Madau & Dickinson 2014). On the other hand, the assem-
structure (“Cosmic Web”). The dark matter structure for-
bly of gaseous matter from the“Cosmic web”of the inter-
mation, which is strictly governed by theory of the gravity,
galactic medium (IGM) onto galaxies is still a rarely ex-
has been well predicted in the many theoretical and nu-
plored territory. The kinetic, radiative, and chemical feed-
merical works (e.g., White& Rees 1978; Daviset al. 1985;
backsfromgalaxiesplayanimportantroleintheIGMmetal
Springelet al. 2005; Mo et al. 2010). The star-formation
enrichment, as well as in the formation of galaxies them-
selves (e.g., Scannapiecoet al. 2002; Tremonti et al. 2004;
Simcoe et al.2006;Aguirre & Schaye2007;Kobayashiet al.
⋆ E-mail:[email protected]
2 K. Mawatari et al.
2007; Cen & Chisari 2011). Understanding the interplay of lected Distant Red Galaxies (DRGs) and Submilimeter
gas between galaxies and the“Cosmic Web”, especially be- Galaxies (SMGs) were also reported (Tamuraet al. 2009;
havior of gas in the circum-galactic scale (circum-galactic Uchimotoet al. 2012; Kuboet al. 2013; Umehataet al.
medium; CGM), is essential to develop a complete galaxy 2014),whichwereconfirmedspectroscopicallyinthecentral
formation and evolution theory. small(.20arcmin2)area(Kuboet al.2015;Umehataet al.
The relation between galaxies and neutral hydrogen 2015). This suggest that assembly of massive galaxies al-
(H i) gas in the IGM/CGM has been investigated spectro- ready proceeded at least in the central region of the z=3.1
scopically with the Lya absorption imprinted in spectra of porto-cluster.
backgroundQSOs(e.g.,Adelbergeret al.2003;Rudieet al. In the SSA22 field, we conducted a deep spectroscopic
2012; Rakicet al. 2012; Turneret al. 2014; Crighton et al. survey of LBGs using the VLT/VIMOS (LeF`evre et al.
2015; Mukaeet al. 2016) and star-forming galaxies (e.g., 2003), and found a good positive-correlation between the
Adelbergeret al. 2005; Steidel et al. 2010; Lee et al. 2016; LBG numberdensity andthe IGMH i absorption in a red-
Mawatari et al. 2016). Some authors recently discovered shiftrangeof2.5.z.3.5(Hayashinoetal.inprep).While
an enhancement of the H i absorption associated with a prominent H i absorption enhancement was confirmed at
proto-clusters at z = 2 – 3 by using QSO sight-lines the proto-cluster redshift we could not resolve the H i ab-
(Cai et al. 2016) or by stacking multiple galaxies’ spectra sorptionstructurespatially,becausewestackedbackground
(Cucciati et al.2014;Hayashinoetal.inprep),whichisalso LBGspectratoincreaseasignal-to-noiseratio(S/N).While
expected from numerical simulations (Starket al. 2015). the majority of the previous studies for the interveningH i
More generally, Mukae et al. (2016) found a weak correla- absorptionarebasedonspectroscopy,wecanidentifytheab-
tion between the strength of the IGM H i absorption and sorptionphotometricallybyafine-tunednarrow-bandimag-
the galaxy number density by analysing QSO spectra as inginprinciple.IfwefocusonHigasatz=3.1,afilterwith
background light sources and large number of photo-z ob- acentral wavelength of ∼4980˚A can beused to captureits
jects as foreground galaxies. Lee et al. (2014, 2016) estab- Lya absorption. A custom narrow-band filter NB497 has a
lished a novel approach to resolve the H i gas structure on central wavelength of 4977˚A and a width of 78˚A in Full
Mpc scales by analysing the Lya forest in individual spec- Width Half Maximum (FWHM) (Hayashinoet al. 2004),
tra of background star-forming galaxies. They applied this whichlimitsthespatialresolutionforHigasstructurealong
three-dimensional H i reconstruction scheme (IGM H i to- line-of-sight of ∼60comoving Mpc in the z=3.1 Universe.
mography) to star-forming galaxies in the COSMOS field Such a coarse resolution is still enough to investigate the
and found a correlation between galaxy onverdensity and SSA22large-scalestructurebecauseitisexpectedtospread
H i absorption enhancement (Leeet al. 2016). The CGM out &50comoving Mpc.
structure has also been investigated by analysing the H i In this paper, we introduce our new scheme to charac-
absorption as a function of the projected distance between terize the z=3.1 H i absorption strength photometrically,
thebackgroundsight-lineobjectandthenearestforeground and show the results of its application to the multi-band
galaxy. An H i absorption enhancement was detected out imaging data available in theSSA22and two control fields.
to∼2physicalMpcfromLymanBreakGalaxies(LBGs)at WebrieflydescribethedatausedinthisstudyinSection2,
z=2– 3(Rakic et al. 2012; Rudieet al. 2012;Turneret al. and introduce our method to measure the z=3.1 H i ab-
2014). The CGM gas kinematics were also investigated by sorption strength in Section 3. We show the results in Sec-
combining properties of the H i and metal absorption (e.g., tion 4, and discuss them in Section 5. We use theAB mag-
Turneret al. 2016), which suggest theclumpy and outflow- nitude system (Oke& Gunn 1983) and adopt a cosmology
ing nature(Steidelet al. 2010; Crighton et al. 2015). with H0=70.4 km s−1 Mpc−1, W M=0.272, and W L =0.728
Investigating a relation between galaxies and H i gas (Komatsu et al. 2011).
in an extremely high density region is interesting in the
context of both the large-scale structure formation and
the environmental dependency of CGM properties. The
SSA22 field, which we focus in this paper, contains one of 2 DATA
the largest high density structures observed so far at high
2.1 Imaging data
redshift. We previously performed a very wide-field imag-
ing of z=3.1 Lya emitters (LAEs) with Subaru/Suprime- We collected multi-band imaging data available in the
Cam (Miyazaki et al. 2002) seven contiguous field-of-views SSA22 field to measure the strength of Lya absorption
(FoVs),showingthattheprominentlyhighdensitystructure caused by the H i gas at z=3.09. Yamada et al. (2012a)
ofLAEsisstretchedover∼50comovingMpc(Yamadaet al. conducted B, V, and NB497 imaging observations with the
2012a).Even at >50comoving Mpc far from theLAE den- Suprime-Cam equipped on the Subaru telescope. Among
sity peak, the LAE density averaged over a Suprime-Cam their wide survey coverage, 7 contiguous Suprime-Cam
single FoV scale is larger than that estimated in control FoVs,wefocusonthecentralFoV(SSA22-Sb1)whereback-
fields. Spectroscopy of the “proto-cluster” member galax- ground sight-line galaxies at z&3.2 are available from rich
ies revealed that the SSA22 large-scale structure seems to spectroscopicsurveys(section2.2).Thereisthedensitypeak
be a complex of filamentary structures and distinct clumps of z=3.09 LAEs in the SSA22-Sb1 field, and also the sig-
ofgalaxiesinthree-dimensionalspace(Matsudaet al.2005; nificant density excess of DRGs and SMGs was reported
Toppinget al. 2016). These geometrical properties sug- (Tamuraet al. 2009; Uchimoto et al. 2012; Kuboet al.
gest that the SSA22 porto-cluster is an ancestor of local 2013; Umehataet al. 2015). We also used following im-
superclusters or Great Wall (Yamadaet al. 2012a). Sig- agesavailableintheSSA22-Sb1:Subaru/Suprime-CamR,i′,
nificant number density excesses of photometrically se- andz′ bandimages(Hayashinoet al.2004;Nakamuraet al.
Imaging of H i absorption structure at z=3.1 3
2011) and the UKIRT/WFCAM K band image (UKIDSS the public catalog colours (V−R, V−i′, and V−z′) to the
DXSDR10;Casali et al.2007;Lawrence et al.2007).These V band magnitudes that we measured. All the magnitudes
images are smoothed so as to match the point spread func- were corrected for the Galactic extinction (Schlegel et al.
tion(PSF)sizeofbrightstarstotheFWHMof1.′′1.Forthe 1998): AB =0.085/0.077/0.093, ANB497=0.075/0.067/0.082,
smoothedimages,wemeasured5s limitingmagnitudeswith AV = 0.066/0.059/0.072, AR = 0.056/0.052/0.062, Ai =
2.′′2diameterapertures,resultinginB=27.1, NB497=26.4, 0.044/0.040/0.048,andAz=0.031/0.029/0.034fortheSXDS-
V =26.8,R=26.5,i′=26.3,z′=25.6,andK=22.9.Wethen 1C/2N/3S field, respectively.
constructed a muliti-band photometry catalog for i′ band
detectedobjects.Objectextraction wasperformed onthei′
band image usingSExtractor (Bertin & Arnouts1996) ver- 2.2 Background light sources at z≈3.4
sion 2.5.0. The 2.′′2 aperture magnitudes were measured in
Lya absorption by the z=3.1 H i gas is imprinted in the
the all band images, where each aperture was centred on
spectrumofeverygalaxy behindthegasat wavelength l ≈
the i′ band object position. We corrected these magnitudes
4980˚A intheobserver’s rest-frame(hereafter, theobserver-
for the Galactic extinction with AB=0.246, ANB497=0.215, frame). This is in the NB497 filter wavelength coverage. In
AV=0.190,AR=0.154,Ai=0.124,Az=0.090,andAK=0.023.
thiswork,weusedonlygalaxieswithaspectroscopicredshift
These correction values were estimated for the centre of
of 3.296z63.54 as background light sources to isolate the
the SSA22-Sb1 (a =22h17m33s,d =+00◦15′08′′ in J2000.0)
z=3.1HiLya absorptionfrominterstellarabsorptionlines
based on thework by Schlegel et al. (1998), assuming RV =
AV/E(B−V)=3.1.AspatialvariationofD E(B−V)∼0.03in oNfBt4h9e7bfialtcekrg(r4o9u3n7d.5g−a5la0x1i5e.s7t˚Aheinmtsheelvoebs.seWrvaevre-flreanmgteh)sshoifftthtoe
the SSA22-Sb1 area may make at most ∼0.1mag system-
atic offsets in our estimates of the H i absorption strength aportionofl =1087−1170˚Ainthez=3.29−3.54galaxy’s
(D NB497;seethesection3.2),howeverwhichissmallerthan rest-frame,whereNiil 1084andCiiil 1178aswellasbroad
wings of Lya and Lyb of the galaxies themselves do not
an excess of the D NB497 measured in the SSA22-Sb1 field
contaminate.
(section 4.1).
Wegatheredgalaxiesatz=3.29–3.54fromthefollow-
For a comparison, we also constructed similar multi-
ing spectroscopic redshift catalogs. In the SSA22-Sb1 field,
band photometry catalogs in the Great Observatory Opti-
weusedthecatalogsfromSteidelet al.(2003),Nestor et al.
cal Deep Survey North (GOODS-N; Dickinson et al. 2004)
(2013), Saezet al. (2015), and our own observations us-
field and the Subaru/XMM−Newton Deep Survey (SXDS;
ing the VLT/VIMOS and Keck/DEIMOS (Faberet al.
Furusawa et al. 2008) field. In the GOODS-N field, we col-
2003): VIMOS06 (Kousai 2011), VIMOS08 (Kousai 2011;
lected Subaru/Suprime-Cam B,V, and NB497 band images
Hayashinoetal.inprep),VIMOS12(Umehataetal.inprep;
from Yamadaet al. (2012a) and R, i′, and z′ band images
Mawatarietal.inprep),DEIMOS08(Otsukaetal.inprep),
from Capak et al. (2004). These images are smoothed so as
and DEIMOS15 (Mawatari et al. in prep). In the GOODS-
to match the PSF (FWHM =1.′′2), and their 5s limiting N field, we used the 3D-HST catalog1 (Momchevaet al.
magnitudes are B=26.8, NB497=26.7, V =25.9, R=26.3,
2016). In the SXDS field, we used the catalogs from the
i′=25.7,andz′=25.4with2.′′4diameterapertures.Wecon- UDSz project2 (Bradshaw et al. 2013; McLureet al. 2013),
structed a multi-band photometry catalog for these images
the3D-HST(Momcheva et al.2016),andtheprojectledby
inthesamemannerastheSSA22-Sb1catalog,wheretheob-
Akiyama, Simpson, Croom, Geach, Smail and van Breuke-
jects were detected in theV band image and 2.′′4 apertures len3 (hereafter, we call the UDS-AGN project; Smail et al.
were used for the photometry. The Galactic extinction cor-
2008; Simpson et al. 2012; Akiyamaet al. 2015). Since red-
rections, AB=0.048, ANB497=0.042, AV =0.037, AR=0.030, shifts in the 3D-HST catalog which were determined from
Ai = 0.024, and Az = 0.018, were applied, which are es- the combination of the HST grism spectra and multi-band
timated at (a ,d ) =(12h37m22s,d =+62◦11′33′′) in J2000
photometryhaverelativelylargeuncertaintyweforcedthem
(Schlegel et al. 1998).
to satisfy zmin>3.29 and zmax63.54, where zmin and zmax
In the SXDS field, Subaru/Suprime-Cam B, V, and
arethelowerandupper68%confidencelimitsforthegrism
NB497 images are available from Yamadaet al. (2012a).
redshifts (Momchevaet al. 2016). We collected 77, 96, and
They observed three contiguous Suprime-Cam FoVs,
80backgroundgalaxies at z=3.29−3.54 in theSSA22-Sb1,
SXDS-1C (a =2h18m00s,d =−5◦00′00′′), SXDS-2N (a =
GOODS-N,andSXDSfields,respectively.Thecoloursofthe
2h18m00s,d =−4◦34′59′′), and SXDS-3S (a =2h18m00s,d =
background galaxies in the SSA22-Sb1 field are systemati-
−5◦25′01′′). Yamadaet al. (2012a) matchedtheirPSFsizes
callybluerthanthoseinthetwocontrolfields,whichisdue
to FWHM ≈1.′′0 and measured 5s limiting magnitudes as
tothedifferenceinthespectroscopictargetselections.Inthe
B≈27.5,NB497≈26.2,andV≈27.1with2.′′2diameteraper-
SSA22-Sb1field,almostallsurveystargetedtheUV-selected
tures. We performed object extraction on the V band im-
LBGsandnarrow-bandselectedLAEswhichgenerallyhave
ageandmeasured2.′′0diameteraperturemagnitudesinthe
blue UV slope. In the other two fields, however, majority
B, V, and NB497 images. For the R, i′, and z′ band pho-
ofthebackgroundgalaxieswerecollected from the3D-HST
tometry, we used a public catalog (Furusawa et al. 2008).
survey which is based on the near-infrared (HST/WFC3)
Their 5s limiting magnitudes are R≈27.0, i′ ≈26.9, and
slitless spectroscopy and can detect more dusty red galax-
z′≈25.8 with 2.′′0 diameter apertures. We merged our own
ies.
V band detection catalog and the public catalog using a
matching radius of 1.′′0. Here,V band photometry included
in the public catalog were used to correct the photometry 1 http://3dhst.research.yale.edu/Data.php
scheme differencebetween Furusawa et al. (2008) and ours: 2 http://www.nottingham.ac.uk/astronomy/UDS/UDSz/
we corrected the R, i′, and z′ band magnitudes by adding 3 http://www.nottingham.ac.uk/astronomy/UDS/data/data.html
4 K. Mawatari et al.
10000 twoeffects.Ourphotometryusingthefixedaperturesisvery
3 sensitivetotheimagesmoothingwhichwasadoptedsothat
2 thePSFsizesarematchedtoeachother(section2.1);there
K
z- 1 might be systematic offsets in the photometric zero-points
0 amongfieldsbecausetheimagingdatausedinthisworkare
1000
-1 basedontheseveralobservationsandreductionsbyindepen-
mber 0 1 2B- z3 4 5 dent research groups. In this section, we adopt corrections
u forbandphotometrysothatthecolourdistributioninevery
N
field is matched to that in theSXDS-1Cfield.
100
Using extragalactic objects is desirable to investigate
anydifferenceincolourdistributionsamongthetargetfields,
because it is difficult to know the accurate amount of the
Galactic dust extinction for each galactic star without its
10
21 22 23 24 25 three-dimensional location. We investigated the fraction of
B [mag] starsinall objectsintheSSA22-Sb1field,wherestars were
selected in theB−z versusz−K two colour diagram by the
Figure 1. Number counts of all objects detected in the i′ band
witha3s significance(blackdashedhistogram),objectsdetected samemannerasDaddiet al.(2004).Thetwocolourdiagram
in all of i, B, z, and K bands with a 3s significance (cyan dot- and the numbercounts of the selected stars and all objects
dashedhistogram),andstarsselectedinthez−KversusB−ztwo are shown in Figure 1, which shows that at B>24mag the
colourdiagram(magentasolidhistogram)intheSSA22-Sb1field. fraction of stars is at most ∼10% and the stars are not
Sub-panel shows objects detected in i, B, z, and K bands (cyan likelytochangecolourdistributionssignificantly.Thestellar
points) and stars (magenta points) in the z−K versus B−z two fractionamongallobjectsshouldbesmallerintheGOODS-
colour diagram, where black line corresponds to the boundary N and SXDSfields because these control fields are oriented
betweengalaxiesandstars(Daddietal.2004). towards outer parts of the Milky Way compared with the
directionoftheSSA22-Sb1field.Fromthese,weneglectthe
stellar contribution to colour distributions of faint objects
2.3 Galaxies at z=3.1
with &24mag in all thefields.
We gathered z = 3.1 galaxies from literature to investi- Then, we compared various colours corrected for the
gate the relation between H i gas and galaxies in the Galactic extinctions among the SSA22-Sb1, GOODS-N,
z = 3.1 Universe. We first collected photometrically se- SXDS-1C, SXDS-2N, and SXDS-3S fields. We carefully se-
lected LAEs. Yamadaet al. (2012a) used the NB497 fil- lected the magnitude range of objects used for each colour
ter to construct a homogeneous sample of LAEs with the distribution; fainter than 24mag for rejection of stars and
rest-frame equivalent width of EW0 & 50˚A at z = 3.06 muchbrighterthanthe5s limiting magnitudefor thesam-
– 3.13 in the three our target fields. We also collected plingcompleteness.Weestimatedcorrectionmagnitudesfor
spectroscopically confirmed galaxies at z=3.06 – 3.13. In the photometric zero-points of the all band images in the
the SSA22-Sb1 field, we used the spectroscopic redshift all fields to match the R−i, i−z, R−z, B−R,V−R, B−V,
catalogs from Steidel et al. (2003), Matsuda et al. (2005), NB497−R, B−NB497, and NB497−V colour distributions
Matsuda et al. (2006), Yamadaet al. (2012b), Nestor et al. to those in the SXDS-1C field. The correction values are
(2013), Saez et al. (2015), and our own observations: VI- typically <0.1mag, and 0.16mag at maximum. The colour
MOS06, VIMOS08, VIMOS12, DEIMOS08, DEIMOS15, distributionsafteradoptingthephotometriczero-pointcor-
and the Magellan/IMAX (Dressler et al. 2011) observation rections are shown in Figure 2.
(P.I.: M. Ouchi; hereafter, oIMACS). In the GOODS-N
Since the colour differences in the all fields relative to
field, we used the 3D-HSTcatalog (Momchevaet al. 2016).
thereference field (theSXDS-1Cfield) are minimized, rela-
In the SXDS field, we used the catalogs from the UDSz
tivephotometricuncertaintiesamongthefieldsareexpected
project(Bradshaw et al.2013;McLure et al.2013),the3D-
to be at most 0.04mag (corresponding to two bins shifts in
HST (Momcheva et al. 2016), and the UDS-AGN project
Figure2).Ontheotherhand,weheremention thattheset
(Smail et al. 2008; Simpson et al. 2012; Akiyamaet al.
of the correction magnitudes adopted in this work is not a
2015).Forthe3D-HSTcatalogobjects,weappliedthesame
uniquesolution,andtheremaybeothersetsyieldingagood
mannerasadoptedintheselectionofthebackgroundgalax-
matchinthecolourdistributionsamongthefields.Further-
ies (section 2.2). These spectroscopically confirmed z=3.1
more,thereferencecolourdistributionintheSXDS-1Cfield
galaxysamplescontainsomeofthephotometricallyselected
maybeslightlydifferentfromtheactualdistributions.Inthe
LAEs.
absolute sense, typically ∼0.1mag systematic uncertainty
still remains in each band photometry in each field.For ex-
ample, if we observe galaxies with the same intrinsic SEDs
3 ANALYSIS ineveryfield,theobservedSEDsarepossiblydifferentfrom
the intrinsic one by ∼0.1mag but the difference of the ob-
3.1 Careful calibration of photometric colours
servedSEDsrelativetothatinthereferencefieldshouldbe
In order to characterize the z=3.1 H i absorption strength .0.04mag.Theseabsoluteandrelativeuncertaintiesinthe
photometrically,weneedtocalibrate photometricmeasure- photometry in theobserved fields may cause systematic er-
ments carefully. There may be &0.1mag systematic uncer- rorsinourestimatesoftheHiabsorptionstrength(D NB497;
tainties on magnitudes and colors caused by the following see thefollowing section).
Imaging of H i absorption structure at z=3.1 5
24.0<R<24.5 24.0<R<24.5 24.0<i<24.5
0.1 0.06 0.12
0.09 SXDS1C
ction 00..0078 GSSOXXODDDSSS23NNS ction 00..0045 ction 0 .00.81
mber Fra 0000....00003456 SSA22 mber Fra 00..0023 mber Fra 00..0046
u u u
N 0.02 N 0.01 N 0.02
0.01
0 0 0
0 0.5 1 0 0.5 1 1.5 0 0.5 1
R-i [mag] R-z [mag] i-z [mag]
24.0<B<25.0 24.0<V<25.0 24.0<B<25.0
0.06 0.1 0.12
0.09
n 0.05 n 0.08 n 0.1
ctio 0.04 ctio 0.07 ctio 0.08
a a 0.06 a
mber Fr 00..0023 mber Fr 000...000345 mber Fr 00..0046
u u u
N 0.01 N 0.02 N 0.02
0.01
0 0 0
0 0.5 1 1.5 0 0.5 1 0 0.5 1
B-R [mag] V-R [mag] B-V [mag]
24.0<B<25.0 24.0<NB497<25.0 24.0<NB497<25.0
0.08 0.08 0.07
0.07 0.07 0.06
er Fraction 000...000456 er Fraction 000...000456 er Fraction 000...000345
b 0.03 b 0.03 b
um 0.02 um 0.02 um 0.02
N N N
0.01 0.01 0.01
0 0 0
0 0.5 1 0 0.5 1 0 0.5 1 1.5
B-NB497 [mag] NB497-V [mag] NB497-R [mag]
Figure 2. Various colour distributions inthe SSA22-Sb1 (redsolidhistogram), SXDS-1C (green solidhistogram, reference), SXDS-3S
(blackdashedhistogram),SXDS-2N(magentadot-dashedhistogram),andGOODS-N(bluesolidhistogram)fields.Themagnituderange
oftheobjectsusedareshowninthetopofeachpanel.WeadoptedcorrectionstotheB,V,R,i,andNB497magnitudessothatallcolour
distributionsbecomeconsistentamongthefields.
Table 1.Summaryofbackgroundlightsourcenumbers. icance), and NB497 (with more than 1s significance) band
images.
Field Nbkg a Nbright b Nuse c WeperformedaSpectralEnergyDistribution(SED)fit-
SSA22-Sb1 77 74 60 tingforB,R,i,andzmagnitudesofeachbackgroundgalaxy
GOODS-N 83 47 40 with a public code, Hyperz (Bolzonella et al. 2000). TheV
SXDS 70 53 33 band photometry was not used because the Lya line of the
aNumberofgalaxiesataspectroscopicredshift3.296z63.54as background galaxies themselves contributes to the V band
backgroundlightsourcesforz=3.1Hiabsorption. flux,whichishardtobeexpectedduetoscatteringandab-
bNumberof thebackground galaxies whicharebrightenough to sorptionbysurroundingHigasanddust.Spectraltemplates
bedetected intheB,NB497,R,i,andzbandimages. consistofthestellarsynthesismodelsofBruzual & Charlot
cNumber of the background galaxies used for our discussion, (2003) with an exponentially declining star formation rate
whose SEDsare wellfit bythe Bruzual&Charlot(2003)model (SFR; t =1Gyr) and a fixed metallicity (Z=0.004). The
templates withareduced c 2 valuelessthanorequalto2. IMF was fixed to a Chabrier IMF (Chabrier 2003) with
the mass range of 0.1M⊙ – 100M⊙. The template redshift
was fixed to the spectroscopic redshift of each background
3.2 D NB497 as a tracer of z=3.1 H i absorption galaxy.Model ages areforced to beless than theage of the
Universe at the galaxies’ redshift. Dust attenuation AV was
Inthissection,weintroduceourschemetocharacterizeLya changed from 0 to 3, where the Calzetti et al. (2000) dust
absorption by z=3.1 H i gas photometrically. Among the attenuation law was adopted.In theHyperzcode, the tem-
background galaxies at z=3.24 – 3.59 in the SSA22-Sb1, plate flux at a wavelength shorter than Lya is attenuated
GOODS-N, and SXDS fields, we here focus on the 74, 57, by a mean IGM absorption at a given redshift according to
and61objectsbrightenoughtobedetectedintheR,i(with Madau(1995).WehaveconfirmedthatthemeanIGMatten-
more than 3s significance), B, z (with more than 2s signif- uationatawavelengthrangebetweentheLya andtheLyb
6 K. Mawatari et al.
RReesstt−−ffrraammee wwaavveelleennggtthh[[ÅÅ]]]] plate NB497 magnitudes (D NB497=NB497obs−NB497temp),
990000 11000000 11110000 11220000 11330000 11440000 11550000 which is expected to reflect strength of the z=3.1 H i Lya
8800
VIMOS08−1427 absorptionrelativetotheaverageinthez=3.1Universe.An
Best−fit temp
00..88 example of our method is shown in Figure 3. In the follow-
6600 ingdiscussions,weuseD NB497estimatesofthebackground
%]%] galaxieswhoseSEDarewellfitbyatemplatewithareduced
Jy]Jy] 00..66 4400 ponce[ponce[ Qc 2SO(csn2,)an<d2o.tIhnerotehxeortiwcotrydpse,swoefegffaelacxtiiveeslywhreomseovSeEADGs Narse,
mm[[ 00..44 eses
ffnn er rer r very different from the star-forming model templates from
FiltFilt oursample.Thenumbersofthebackgroundgalaxiesthatwe
00..22 2200 finallyusedare60,47,and40intheSSA22-Sb1,GOODS-N,
and SXDS fields, respectively. Table 1 is a summary of the
00 numbersof thegalaxies.
00 As mentioned in the section 3.1, theD NB497 may have
44000000 44550000 55000000 55550000 66000000 66550000
OObbsseerrvveedd wwaavveelleennggtthh[[ÅÅ]] systematicerrorswhicharepropagatedfromthoseinthein-
dividualbandphotometry.Wehereassumethatthepossible
Figure 3.Anexampleofourmethodtocharacterizethez=3.1 systematicerrorsassociatedwiththeD NB497is∼0.1magin
H i absorption. The observed B, NB497, and R magnitudes are theabsolutesenseand∼0.04maginarelativesenseamong
shownbyblackcircles,whereeachfilterresponsecurveisshown
the three fields. While in the following we do not include
byblackcurves.Thebluespectrumisthebest-fittemplateforthe theseestimatesofsystematicerrorsintheD NB497measure-
B,R,i,andzbandphotometry.Theobservedspectrumandnoise
ments,weshould always beaware of thesepossible system-
forthisobjectareshownbyredandgreycurves,whichwereob-
atic uncertainties.
tainedintheVIMOS08observations.Blackcrossesandtriangles
arethe filterconvolved magnitudes forthebest-fittemplate and We checked the reliability of our D NB497 scheme us-
observedspectrum.Rbandfilterconvolvedmagnitudefortheob- ing spectra of some background galaxies in the SSA22-Sb1
servedspectrumisnotshownbecausethespectralcoveragedoes fields. Our previous VLT/VIMOS observations (VIMOS06
notincludethewholeRbandwavelengths. andVIMOS08;Kousai2011;Hayashinoetal.inprep)allows
us to investigate H i Lya absorption for individual spectra
of some background galaxies. Wemeasured the EWs of the
1 z=3.1 H i Lya absorption in the available VIMOS spec-
tra, where the absorption flux was estimated in the NB497
wavelength range and the continuum was estimated by av-
eragingfluxintheDArangeexceptfor theNB497 coverage
g] in the observer-frame. The relation between D NB497 and
a
97 [m 0.5 oabssDerNvBe4r-9f7ra=m−e2E.5Wlogc(a1n−bEeWde/s7c8rA˚ib)e,dwihneraenwaenaalsystuicmael ftohramt
4
NB only z=3.1 H i absorption deviates from the cosmic aver-
D age in the redshift range corresponding to the NB497 filter
coverage (FWHM =78˚A). Figure 4 shows the comparison
between the z=3.1 H i absorption EWs measured spectro-
0 scopicallyandtheirD NB497.Inspiteofthelargeuncertain-
tiesespeciallyinthespectroscopicEWs,abettercorrelation
−40 −20 0 20 40 60 80
spec EW [Å](obs) canbeseenforthebackgroundgalaxies whosespectrahave
abs
ahigherS/N(&10). Weconfirmedthattheweighted mean
Figure 4.ComparisonoftheD NB497estimatedfromthemulti- values for subsamples divided by the spectral S/N are con-
sistentwiththeexpectedrelationexceptforthelowest S/N
band photometry and the absorption EW in the observer-frame
measured from the spectroscopic data. We used the spectra of subsample.Thesesuggeststhatwereasonablytracetheab-
23 galaxies at z=3.29−3.54, which were obtained in the VI- sorption strength with the NB497 photometry and the con-
MOS06 and VIMOS08 observations. Symbol types are divided tinuum level with the best-fit model templates as shown in
by the S/N in the DA region of each spectrum (S/N <3: black Figure 3.
crosses;3<S/N<7:cyantriangles;7<S/N<10:yellowsquares; The background sight-line galaxies in the SSA22-Sb1
S/N >10: magenta circles), where big filled symbols correspond
field have bluer SEDs than those in the two control fields
to the weighted mean values. Black solid curve shows the ex-
as mentioned in the section 2.2, which possibly causes a
pectedrelation:D NB497=−2.5log(1−EW/78A˚).Redcrossshows biasintheD NB497measurements.Weconstructedaz≈3.4
theweightedmeanvalueofthe23galaxiesused.
mock galaxy sample to investigate the dependency of the
D NB497 on the background galaxy SEDs. The mock galaxy
(socalledDArange)isconsistentwithamorerecentmodel SEDsweregeneratedfromtheredshiftedBruzual & Charlot
(Inoueet al. 2014). We obtained the best-fit template for (2003) model templates with different R−z colours. Each
each background galaxy, from which the NB497 magnitude modeltemplatespectrumwasnormalizedsothattheRband
was estimated (NB497temp). Uncertainty in the NB497temp magnitude becomes the typical value of the observed back-
wasestimatedfromthe1s confidenceinterval(D c 262.3)in ground galaxies (R=25mag), and the each band magni-
thefittingparameterspace(AV versusmodelage).Wemea- tude was randomly extracted from a Gaussian probability
sured the magnitude offset between the observed and tem- distribution with the normalized model magnitude as the
Imaging of H i absorption structure at z=3.1 7
1 tematically larger than those in the GOODS-N and SXDS
fields, which suggests an H i gas excess in the SSA22-Sb1
field. Weighted mean D NB497 values, where we used the
inverse of the uncertainty as the weight, are 0.22±0.02,
0.5 −0.01±0.03, and −0.07±0.04 in the SSA22-Sb1, GOODS-
g] N,andSXDSfields,respectively,whereweadoptlargerone
a
m betweentheinternaland externalerrors astheuncertainty.
7 [
49 Evenaftertakingaccountofthepossiblerelativesystematic
B
N uncertainties of ∼0.04mag among the three fields (see the
∆ 0
section3.2),theexcessoftheD NB497intheSSA22-Sb1field
comparedtotheotherfieldsisstillsignificant.Thenegative
D NB497 values in the SXDS field is less significant, and we
−0.5 SGSOA2O2D−SS−bN1 cannotclaimfromonlythecurrentdatathattheHiabsorp-
SXDS tion is suppressed in the SXDS field relative to the cosmic
25 26 27 28 0 5 10 15 20 25 average.Thebackgroundsight-linegalaxiesintheGOODS-
B [mag] Number NandSXDSfieldsaresystematically fainterintheBband,
Figure5.LeftpanelshowstheD NB497valuesasafunctionofthe whichcauseslargerD NB497uncertaintiesbutislesslikelyto
causetheD NB497differenceamongthefields.Figure6shows
BbandmagnitudesintheSSA22-Sb1(redopencircles),GOODS-
N (blue open triangles), and SXDS (green open squares) fields. cumulative histograms for the D NB497 values in the three
Bigfilledsymbolscorrespondtotheweightedmeanvalueineach fields. We found a clear difference of the SSA22-Sb1 from
field. Right panel shows the number histogram of the D NB497 theothertwofields.WeappliedaKolmogorov-Smirnov(K-
(SSA22-Sb1:redsolidhistogram;SXDS:greendashedhistogram; S) test to check the difference of the D NB497 values. Resul-
GOODS-N:bluedot-dashedhistogram). tantK-Sprobabilitiesare6.7×10−7intheSSA22-Sb1versus
GOODS-N,2.6×10−8 in the SSA22-Sb1 versus SXDS, and
0.69intheGOODS-NversusSXDS.A nullhypothesisthat
1 theD NB497valuesintheSSA22-Sb1fieldareextractedfrom
the same mother sample as those in the other two fields is
significantly rejected,while theD NB497 distributionsin the
0.8
GOODS-Nand SXDSfields are veryconsistent.
n
ctio Since we used faint star-forming galaxies as the back-
Fra 0.6 ground light sources, we achieved a high spatial resolution
ve ofsight-linesforz=3.1Hiabsorption:meanseparationsof
urati 0.4 the background sight-line galaxies are ∼2′ – 3′ or ∼4.1 –
um 5.5comovingMpcatz=3.1.Wevisualizedtwo-dimensional
C skymapsof thez=3.1 Hiabsorption strength,whereeach
0.2 D NB497issmoothedbyaGaussiankernelwiths =3′anddi-
SSA22-Sb1
SXDS videdby thesmoothed sight-line numberdensity.Figures 7
GOODS-N showthetwo-dimensionalsmoothedD NB497mapsaswellas
0
-0.5 0 0.5 1 1.5 sky distributions of the background sight-line galaxies. We
D NB497 [mag] onlyshow thesmoothed D NB497 mapswherethesmoothed
Figure 6.Cumulative fractionhistogram forthe D NB497values number density of background sight-line galaxies is more
than150degree−2.InFigures7,contourlinesshowthelocal
inthethreefields.
numberdensityofphotometricLAEs(Yamada et al.2012a)
obtained after being smoothed by a Gaussian kernel with
mean and the typical photometric uncertainty (∼0.1mag) s =1′.5. We can see the large scale D NB497 excess in the
as the standard deviation. We performed the SED fitting SSA22-Sb1 field, which extends to ∼50comoving Mpc in
for the mock galaxies and estimated the D NB497 with the the z=3.1 Universe. On the other hand, no clear spatial
samemannerasdescribedabove.TheresultantD NB497val- alignment between the smoothed D NB497 and z=3.1 LAE
ues distribute around zero and show no dependency on the numberdensitycanbeseenatleast byeyesinallthefields.
inputSEDcolours,whichsupportsthatourD NB497scheme
properlyevaluatesthestrengthofz=3.1Hiabsorptionrel-
ativeto thecosmic average. 4.2 D NB497 as a function of environment
Inthissection,weinvestigatestrengthofthez=3.1Hiab-
sorption,D NB497,asafunctionofenvironmentaroundeach
4 RESULT sight-line.Photometric LAEsareconsideredtobetraceen-
4.1 H i absorption enhancement over the entire vironment although it may deviate from the real shape of
underlying dark matter structure due to a small duty cy-
SSA22-Sb1 field
cle of LAEs (∼1%; Ouchiet al. 2010). We estimated the
First, we investigate field-to-field variance in the D NB497 LAEoverdensity,dLAE=(nLAE−n)/n,atthepositionofeach
measurements.Figure5showstheD NB497valuesasafunc- background sight-line, where we adopted the average LAE
tion of the B band magnitudes of thebackground sight-line number density in general fields reported by Yamadaet al.
galaxies.TheD NB497valuesintheSSA22-Sb1fieldaresys- (2012a)ofn=0.2arcmin−2 andtheLAElocalnumberden-
8 K. Mawatari et al.
Comoving scale at z=3.1 [Mpc]
-30 -20 -10 0 10
SSA22-Sb1 -20
c]
p -0.4 -0.2 0 0.2 0.4
0.4 M DD NNBB449977
-10 1 [
3.
=
eg] 0.3 0 at z
ec.[d cale -2C0omov-i1n0g scale 0at z=3 .110 [Mpc] 20
D s -4.9
10 g
0.2 n
vi -30
o
m
SXDS
20 Co -5
0.1 -20
c]
p
334.6 334.5 334.4 334.3 334.2 M
R.A.[degree] -5.1 -10 1 [
3.
=
GOODS-6NC2o.3mo-v1in0g scal e0 at z=3 1.10 [Mpc] 3.1 [Mpc] Dec.[deg] --55..32 010 oving scale at z
-10 = m
c.[deg] ale at z -5.4 20 Co
e 62.2 0 c
D s
ng 30
vi
62.1 10 mo -5.5
o 34.6 34.5 34.4 34.3 34.2
189.4 189.2 189 C
R.A.[degree]
R.A.[degree]
Figure 7. Sky distributionof the background sight-linegalaxies inthe SSA22-Sb1, GOODS-N, and SXDSfields are shown by circles,
wherethesymbolcoloursindicatetheD NB497values(D NB497>0.2:red;−0.2<D NB497<0.2: green;D NB497<−0.2:blue).Colourmap
shows the D NB497 distribution; the D NB497 values for every background sight-line galaxy were smoothed by a Gaussian kernel with
s =3′ anddividedbythesmoothedsight-linenumberdensity.Blackcontoursshowthesmoothedandnormalizednumberdensityofthe
photometricLAEs:0.5×(dashed), 1×(thick), 2×,3×,4×,and5×theaveragedensity(0.2arcmin−2;Yamadaetal.2012a).
sity (nLAE) smoothed with a s =1′.5 gaussian kernel. Fig- D NB497 value in the SSA22-Sb1 field is significantly larger
ure8shows theD NB497valuesas afunction ofdLAE forthe than thosein theothertwo control fields.
backgroundsight-linesinallthefields.SSA22-Sb1fieldcon- Theresolution scale on environmenttracedbyLAEsis
tains high density regions with dLAE &2compared with the roughly equal to the mean separation of the LAEs, which
other two control fields. The weighted mean values for the is ∼3 comoving Mpc in the z=3.1 Universe. The strength
threefields(bigcrossesinFigure8)suggestatrendthatthe of H i absorption may be more sensitive to a smaller scale:
average D NB497 becomes higher with a larger average LAE H i gas abundance in the CGM. We selected the nearest
overdensity.Thenegativevalueof theD NB497intheSXDS galaxy at z=3.1 from each background sight-line and mea-
field may beexplained by thenegative LAEoverdensity,as sured their projected distance (impact parameter: b). Fig-
well as by possible systematic errors (see the section 4.1). ure 9 shows the D NB497 values as a function of the impact
However, such a trend between the LAE overdensity and parameter.Wealso took everyfivedatapointsin each field
the D NB497 cannot be found if we look at only the data of along the impact parameter and calculated their weighted
the SSA22-Sb1 field. We took every 10 data points in the mean D NB497 (filled symbols in Figure 9). We only look at
SSA22-Sb1 field along the LAE overdensity and calculated thedistance less than 430physical kpc,which is an average
their weighted mean D NB497 values (filled circles in Fig- impactparameterforstar-forminggalaxieswithMUV <−20
ure 8). The binned D NB497 averages flatly distribute along at 3.06<z<3.13 expected from UV luminosity functions
theLAEoverdensity,andevenatthesmallest dLAE bin,the ofReddy& Steidel(2009)andSawicki & Thompson(2006).
Imaging of H i absorption structure at z=3.1 9
5 DISCUSSION
1
5.1 What drives the large-scale difference in the
H i absorption?
g] 0.5 We obtained the notable result that the Lya absorp-
ma tion by the H i gas at z = 3.1 over the entire SSA22-
7 [ Sb1 field is stronger than that in the control fields. In-
49 terestingly, the D NB497 estimates are not correlated with
B
N 0 the local (∼ 3comoving Mpc scale) LAE overdensity or
D the impact parameter if > 100physical kpc. A remark-
SSA22-Sb1 able difference between the SSA22 and the two control
GOODS-N fields is that the former field contains the prominent den-
-0.5 SXDS
sity excess of various types of galaxies (Steidelet al. 1998;
-1 0 1 2 3 4 5 Hayashinoet al. 2004; Uchimoto et al. 2012; Kuboet al.
LAE overdensity 2013; Umehata et al. 2015). Since an expected average im-
pact parameter between random sight-lines and z = 3.1
Figure 8. D NB497 as a function of the LAE overdensity. Red galaxiesinsuchahighdensityregionshouldbesmallerthan
circles, blue triangles, and green squares show the sight-lines in
that in the normal density region (∼430physical kpc), the
the SSA22-Sb1, GOODS-N, and SXDS fields, respectively. Big D NB497excessatb&200physicalkpcintheSSA22-Sb1field
crossescorrespond totheweighted meanvalueineach field. Big
might be explained by the CGM H i of unobserved galax-
filledcirclesaretheweightedmeanvaluesforevery10datapoints
ies. If the H i absorption enhancement is completely dueto
alongtheLAEoverdensityintheSSA22-Sb1field.
the individual galaxies’ CGM, the D NB497 is likely to cor-
relate with the local overdensity of galaxies, which is, how-
ever, inconsistent with our result (Figure 8). A simple and
plausible interpretation of our results is that the extended
1.5 SSA22-Sb1 H i gas, which is different from H i gas clouds associated
GOODS-N
SXDS with eachgalaxy CGM, distributesonlyin theSSA22field.
Yamadaet al. (2012a) argued that the belt-like LAE over-
1
g] densestructureisanancestoroflocalsuperclustersor“Great
ma Wall”ratherthanasinglecluster.Inthelocalsuperclusters,
7 [ 0.5 there is the warm-hot intergalactic medium (WHIM) with
49 T=105.5–107K(Zappacosta et al.2005;Buote et al.2009).
B
N TheseWHIMisexpectedtobeformedbytheshockheating
D 0 of baryonic matter infalling to the dark matter large-scale
structure, where galaxies are also formed. The diffuse H i
-0.5 gasstructurerevealedbythisworkmaybeinthepre-heated
phaseof theWHIM.
0 100 200 300 400 No correlation between the D NB497 and the local LAE
Impact parameter [physical kpc] overdensity in the SSA22-Sb1 field (Figure 8) can be ex-
plained, at least in the LAE highest density region (LAE
Figure 9. D NB497 as a function of distance from the nearest overdensity&3;seethe4×theaveragenumberdensitycon-
z=3.1object.Redcircles,bluetriangles,andgreensquaresshow
tour in Figure 7), by a scenario that radiation from galax-
the sight-lines in the SSA22-Sb1, GOODS-N, and SXDS field,
ies in the overdense region ionizes the gas and reduces the
respectively.Bigfilledsymbolscorrespondtotheweightedmean
H i amount. Otherwise, hydrogen gas amount is indepen-
valuesforeveryfivedatapointsineachfield.Themagentadashed
curve shows the b –D NB497 relation estimated from the H iab- dent of the galaxy local overdensity. Lee et al. (2016) also
sorptionEWsofRakicetal.(2012),whereweassumedthesimple found a compact (spatial extent .5comoving Mpc) galaxy
analyticformasD NB497=−2.5log{1−EWabs×(1+3.1)/78A˚}. overdensitystructureatz=2.3withnoIGMHiabsorption
rest
enhancement in their three dimensional tomographic map.
They argued that no excess of the H i absorption is due
to a lack of the IGM hydrogen gas in/around the galaxy
There may be nearer but unobserved galaxies at z=3.1 for overdensity,whileapossibility of suppressionof theHiab-
the background sight-lines with large impact parameters of sorption by galaxy feedback or a hot intra-cluster medium
b>430physicalkpc.InFigure9,theD NB497seemstobeen- (ICM)wasalsomentioned.Theyexpectedthatthiscompact
hanced at the smallest impact parameter (b<100physical galaxy overdensity evolves to a galaxy group at z=0, not
kpc) at least in the SSA22-Sb1 field, which can be inter- toacluster.SincethegalaxyoverdensityfoundinLee et al.
preted as the effect of H i gas halos associated with these (2016)andtheLAEhighestdensityregionintheSSA22-Sb1
nearest galaxies. In the control fields, such a D NB497 en- field are different in thespatial size and the galaxy popula-
hancementat b<100physicalkpcisunclear dueto asmall tion, it is difficult to compare them directly. However, the
number of the data points. At a larger impact parameter, non-zero H i absorption and large-scale galaxy overdensity
the D NB497 values in the SSA22-Sb1 field seem to be con- in the SSA22-Sb1 field seems to support a picture that the
stant and significantly above zero, which is contrast to the LAE highest density region, which eventually grows into a
D NB497 distribution in thetwo control fields. massive cluster at z=0, contains a significant amount of
10 K. Mawatari et al.
Foreground galaxies w/ Lya Foreground galaxies w/o Lya 2
SSA22-Sb1
1.5 SGSOA2O2D-SSb-N1 1.5 mag] GOOSDXSD-NS
SXDS s [ 1.5
e
n
1 1 ht-li
ag] d sig 1
m n
7 [ 0.5 0.5 ou
NB49 ackgr 0.5
b
D 0 0 or
7 f 0
9
4
B
N
-0.5 -0.5
D -0.5
0 100 200 300 400 0 100 200 300 400 -2 -1 0 1 2 3
Impact parameter [physical kpc] Impact parameter [physical kpc] BV-NB497 of z=3.1 galaxies [mag]
Figure 10. Same as Figure 9, but we divide the sight-linedata Figure 11. D NB497 as a function of BV−NB497 colour of the
pointsbytypesofthenearestz=3.1galaxies:leftpanelforLAEs nearest z=3.1 object, where only sight-lines with distance from
(EWem &50˚A)astheforegroundandrightpanelforgalaxieswith- thenearestz=3.1objectlessthan100physicalkpcareused.
rest
out strong Lya emission (EWem .50A˚) as the foreground. Big
rest
yellow crosses correspond to the weighted mean value for every
fivedatapoints,wherewedonotdividethesamplebythefields.
between the D NB497 and the impact parameter. Especially,
LAEsareexpectedtohavedifferentHigaspropertiesfrom
otherpopulationsof galaxies because thehydrogendensity,
the hydrogen gas which is partially ionized by the galaxy neutrality, and the Lya photon escape fraction are com-
feedback.
plicatedly connected each other.Wedivided thegalaxies at
The size of the H i gas overdensity structure in the z=3.1intotwosubsamples:LAEsreportedinYamadaet al.
SSA22-Sb1fieldrevealedbythisworkis&50comovingMpc
(2012a)andotherspectroscopicallyconfirmedgalaxies.The
becausethepositiveD NB497valuesaredetectedovertheen- LAEs of Yamadaet al. (2012a) were selected basically by
tire survey area. This size seems to be larger than that of the BV−NB497 colour, where the BV is magnitude mea-
LAE overdensity (∼50 comoving Mpc from Yamadaet al. sured in the (2B+V)/3 composite image. The colour crite-
2012a). The H i structure may generally be extended more rionofBV−NB497>1roughlycorrespondstoEWem &50˚A.
rest
than the galaxy structure, because galaxies formed in the Galaxieswhicharespectroscopicallyconfirmedasz=3.1but
middle of the gas structure. The size of the SSA22 H i not selected in Yamadaet al. (2012a) are expected to have
large-scalestructure,&50comovingMpc,islarge,butthere weak or no Lya emission (EWem .50˚A). In the left panel
rest
are some further larger structures in the lower-z Universe. of Figure 10 we show the D NB497 of the background sight-
A traditionally famous large-scale structure is CfA2 Great line galaxies for which the nearest z=3.1 galaxies are the
Wall, which extends at least ∼200Mpc (Geller & Huchra LAEs, while those for which the nearest galaxies are the
1989).Thelargeststructureatz=0istheSloanGreatWall, weak Lya emission galaxies are shown in the right panel.
whichextendsover400Mpcandcontainsseveralsuperclus- We also show the weighted mean values for every five data
ters consisting of tens of galaxy clusters (Gott et al. 2005). points independent of the fields in Figure 10. In the case
Atz∼1,alargerstructuretracedbyQSOshavebeenfound thatthenearestgalaxyhaveastrongLya emission line,we
(Clowes et al.2013),whichreaches>500Mpcinlength.Fu- cannot see the increment of the D NB497 at b.100physical
tureapplicationsofourD NB497methodtomuchwiderarea kpc, while the number of the data points is still limited. A
dataareneededtodeterminetheactualextentoftheSSA22 flat D NB497 distribution above zero is seen in the SSA22-
super-structure and to reveal the relation between it and Sb1field,whichcanbeduetothelarge-scalediffuseHigas
theselow-zlargest structures.Ifthestructureislargerthan uniquein theoverdensityenvironment(section 5.1).Noex-
the upper limit in the scale for cosmological homogeneity cess of the D NB497 at the impact parameter <100physical
(e.g.,370comovingMpcfromYadavet al.2010),thislargest kpcfrom theforeground LAEsisincontrastwith anexcess
structure ever found in the z=3.1 Universe may challenge there for the weak Lya emission galaxies. This difference
thecosmological principle. suggests that LAEs have thiner H i absorption halos than
otherstar-forming galaxies likeLBGs.
5.2 H i absorption halos around z=3.1 galaxies We further investigated the relation between strength
of the Lya emission line from the z=3.1 galaxies and the
The D NB497 estimates are also useful to investigate the ra- Lya absorption by the surrounding H i halos. Figure 11
dial profile of the H i absorption halo in the galaxy CGM. shows the D NB497 as a function of the BV−NB497 colour
We found an excess of the D NB497 at the impact param- of the nearest z=3.1 galaxy, where we used only the back-
eter <100physical kpc as shown in Figure 9, while it is groundsight-linesforwhichthenearestforeground galaxies
less significant in the control fields. Not only a large scale lieswithinb<100physicalkpc.Wecanseeatrendthatthe
integration of H i absorption along sight-line (the NB497 H i absorption in the CGM is weaker for foreground galax-
FWHM corresponds to ∼60comoving Mpc at z=3.1) but ieswithalargerBV−NB497orstrongerLya emission.This
alsodifferenttypesofgalaxies couldobscurethecorrelation trendmaybeduetothesmallhalomassoftheLAEs.Since