H2O emission in high-z ultra-luminous infrared galaxies

0.58 MB·English

by  A. Omont

Astronomy & Astrophysics manuscript no. ms (cid:13)cESO 2013
January 29, 2013
z ⋆
H O emission in high- ultra-luminous infrared galaxies
2
A. Omont1,2, Chentao Yang3,1,2,4, P. Cox5, R. Neri5, A. Beelen6, S. Bussmann7, R. Gavazzi1,2, P. van der
Werf8, D. Riechers9,28, D. Downes5, M. Krips5, S. Dye10, R. Ivison11, J.D. Vieira28, A. Weiß20, J.E.
12 13 14 15 18 16 21
Aguirre , M. Baes , A.J. Baker , F. Bertoldi , A. Cooray , H. Dannerbauer , G. De Zotti , S.A.
Eales17, H. Fu18, Y. Gao3, M. Guélin5, A.I. Harris19, M. Jarvis24,34, M. Lehnert1,2,31, L. Leeuw36, R. Lupu12,
K. Menten20, M.J. Michałowski13,11, M. Negrello21, S. Serjeant22, P. Temi23, R. Auld17, A. Dariush25,17, L.
Dunne26,27, J. Fritz13, R. Hopwood35, C. Hoyos27, E. Ibar32,33, S. Maddox26,27, M.W.L. Smith17, E.
Valiante17, J. Bock28,29, C.M. Bradford28,29, J. Glenn30, and K.S. Scott12
3
1
(Affiliations can be found after the references)
0
2
January 29, 2013

n
a
ABSTRACT
J

8 UsingtheIRAMPlateaudeBureinterferometer(PdBI),wereportthedetectionofwatervaporinsixnewlensedultra-
2 luminous starburst galaxies at high redshift, discovered in the Herschel Astrophysical Terahertz Large Area Survey
(H-ATLAS). The sources are detected either in the 202–111 or 211–202 H2O emission lines with integrated line fluxes
O] ranging from 1.8 to 14 Jy km s−1. The corresponding apparent luminosities are µLH2O ∼ 3−12x108L⊙, where µ is
thelensingmagnification factor (3<µ<12). TheseresultsconfirmthatH2Olinesareamongthestrongest molecular
C lines in high-z ultra-luminous starburst galaxies, with intensities almost comparable to those of the high-J CO lines,
. and similar profiles and line widths (∼200-900 km s−1). With the current sensitivity of the PdBI, the water lines can
h therefore easily be detected in high-z lensed galaxies (with F(500µm)>100mJy) discovered in the Herschel surveys.
p
- oCnortrheectiinnfgratrheedlulummininoosistiiteys,fvoarryaminpgliafisca∼tLio1n.2,.usTinhgiserxeilsattiniognl,enwshinicghmnoededelss,toLHb2eOciosnffiorumndedtowhitahvebaetstterronstgatdiestpiecns,demnacye
o IR
r indicate a role of radiative (infrared) excitation of the H2O lines, and implies that high-z galaxies with LIR&1013L⊙
t tend to bevery strong emitters in water vapor, that have noequivalent in the local universe.
s
a Key words. Galaxies: high-redshift – Galaxies: starburst – Galaxies: active – Infrared: galaxies – Submillimeter: galaxies – Radio
[
lines: galaxies

1
v
81. Introduction H O+ and isotopologues. Together with high-J CO lines,
2
1 these lines provide an important diagnostic of the warm
6Water plays an important role in the warm dense inter-
dense cores of nearby ULIRGs.
6stellar medium of galaxies. First, after CO, H O is the
2
1.most abundant oxygen-bearing molecule, and, second, it In the cases of Mrk231 and Arp220, water emission
0can be an important coolant of the warm gas. Due to the linesuptoenergylevelsofE /k=642Karedetectedwith
up
3Earth’s atmosphere, bulk gas-phase water can only be de- strong line fluxes that reach 25%–75% of the neighboring
1tectedfromspaceorfromthegroundtowarddistantobjects CO emission line fluxes. Spectral surveys made with Her-
v:with redshifts that move the H2O lines into atmospheric schel show that low-z ULIRGs always exhibit bright H2O
windows.
i lines, whereas, only one third of the sample of luminous
X Thestudyofwateremissionlinesinnearbygalaxieshas
infrared galaxies (LIRGs) displays luminous H O emission
2
recentlymadesignificantprogressthankstotheavailability
r lines (van der Werf et al. in preparation [prep.]), indicat-
aoftheirinfrared/submillimeterspectrausingthespectrom-
ing that the strength of the water lines and the infrared
eter mode of the Herschel Spectral and Photometric Imag-
luminosity, L , must be related. The analysis of the H O
IR 2
ingREceiver(SPIRE,Griffinetal.2010)andthePhotode-
emission lines in Mrk231 shows that the excitation of the
tecting Array Camera and Spectrometer (PACS, Poglitsch
watermoleculesresultsfromacombinationofcollisionsand
et al. 2010). The spectra of local ultra-luminous infrared
infraredexcitationthroughfar-infraredlinesinwarmdense
galaxies(ULIRGs) andcomposite AGN/starburstssuch as gas (≥ 100K, ≥ 105cm−3). Moreover, the far-infrared ra-
Mrk231 (van der Werf et al. 2010), Arp220 (Rangwala
diationfielddominatestheexcitationofthehighlevelsand
et al. 2011; González-Alfonso et al. 2012), and NGC4418
their emission lines (González-Alfonso et al. 2010). Pre-
(González-Alfonso et al. 2012) reveal a wealth of water
liminary evidence from the comparison of the spectra of
linesandthepresenceofassociatedmoleculessuchasOH+,
Arp220,Mrk231 and NGC4418 shows that the properties
⋆ Herschel(Pilbrattetal. (2010)isanESAspaceobservatory of the water emission lines in their nuclear regions vary as
with science instruments provided by European-led Principal afunctionofchemistry,nucleosynthesis,andinnermotions
Investigator consortia and with important participation from (outflow/infall)- see Rangwalaet al. (2011)and González-
NASA. Alfonso et al. (2012).
Article number,page 1 of 13
First detections of H O megamasers at high redshift sourcesatz >3toshifttheH Olinesinthe lowfrequency
2 2
were reported in objects at z = 0.66 and 2.64 by Bar- bands that are easier to observe. Finally, we chose sources
vainis & Antonucci (2005) and Impellizzeri et al. (2008), spanningawiderangeinintrinsicinfraredluminositiesfrom
while further searches have failed since then (McKean et ∼ 5×1012 to ∼ 2×1013L⊙.
al. 2011). Following initial attempts to detect H O rota- In this paper, we report the first results of this survey
2
tionalemissionlinesfromhigh-zgalaxies(Waggetal.2006; and describe the properties of the H O emission for six
2
Riechersetal.2006,2009)andtentativedetectionsinIRAS new sources. The sample includes (see Table 1 for IAU
F10214+4724 at z = 2.23 (Casoli et al. 1994) and in the names of the sources) i) sources reported in the initial H-
Cloverleaf at z = 2.56 (Bradford et al. 2009), a series of ATLASScience DemonstrationPhase paperby Negrelloet
robustdetectionsofnon-maserH Oemissionlineswerere- al. (2010) - SDP.9 and SDP.81, together with SDP.17b,
2
cently reported in high-z sources. The sources detected in which was discussed in Omont et al. (2011); ii) two other
H O emission lines include a strongly lensed galaxy, HAT- well-studied sources from the H-ATLAS equatorial fields
2
LAS J090302.9−014127 (SDP.17b) at z = 2.3 (Omont et - G12.v2.30 (Fu et al. 2012) and G15.v2.779 (Cox et al.
al. 2011), which was uncovered in the Herschel Astrophys- 2011; Bussmann et al. 2012); iii) two sources from the H-
ical Terahertz Large Area Survey (H-ATLAS) (Eales et al. ATLASNGPfield,NA.v1.144andNB.v1.78,forwhichCO
2010); the gravitationally lensed quasar APM08279+5255 observations(Harrisetal.2012;Riechersetal.inprep.;and
at z = 3.9 (van der Werf et al. 2011; Bradford et al. thispaper)andsubmillimeter imaging(Bussmannetal. in
2011; Lis et al. 2011); HLSJ091828.6+514223, a lensed prep.) are available. Table 1 provides details on the H O
2
submillimeter galaxy at z = 5.2 in the field of Abell 773 observationsofthesevenH-ATLASlensedgalaxies,Table2
(Combes et al. 2012), which was found in the Herschel lists their submillimeter and infrared properties together
Lensing Survey (Egami et al. 2010), IRAS F10214+4724 withthe estimatedamplificationfactors(see Sects.3.2and
(Riechers et al., in prep.). For most of these sources, only 4.1), and Table 3 gives their CO properties available from
one water emission line was reported, with the exception recent measurements using the PdBI.
ofAPM08279+5255,wherea totalofatleastfive emission The redshifts of the seven selected galaxies range from
lineswithEu/k=101to454Kweredetected(vanderWerf 1.58 to 4.24, with the majority in the range 2.0<z <3.3.
etal.2011;Lis etal.2011;Bradfordetal.2011). These re- In the sample, G15.v2.779 is the only source at z > 4
sults underline the unique and powerful diagnostic power and, for the time being, the highest redshift lensed galaxy
of H2O emission lines, which give better insight into lo- spectroscoptically confirmed in the H-ATLAS survey. For
cal conditions in distant galaxies than may be obtained by eachsource,atleastoneofthetwostrongestlow-excitation
othermeans. AsinMrk231,theyrevealthepresenceofex- H O lines is in an atmospheric window observable with
2
tended, warmanddense gaslocatedintheinfrared-opaque thePdBI,eitherH O(2 –2 )withν =752.033GHzand
2 11 02 rest
regions of the galactic cores. E =137K, or H O(2 –1 ) with ν =987.927GHz and
up 2 02 11 rest
Thisnewwindowinthe explorationofhigh-z sourcesis E =101K. As both lines have comparable intensities in
up
based on the combined availability of new instrumentation Arp220 and Mrk231 (see Sec. 4), in the rare cases where
withimprovedsensitivitiesatkeyfacilitiesandtheincreas- both lines are observable, we chose the line at the lower
ing number of gravitationally lensed sources discovered in frequency that is easier to observe, except in the case of
the Herschel andSouthPoleTelescope (SPT) cosmological SDP.17b(Omontetal.2011),where the line H O(2 –1 )
2 02 11
surveys (see, e.g., Negrello et al. 2010; Vieira et al. 2010). wasselectedtoconfirmthetentativedetectionthatwasre-
Following the results reported by Omont et al. (2011), we portedbyLupuetal. (2012). Notethatthesetwoobserved
present here a new study of water emission in six high-z lines are both para-H O and they are adjacent lines in the
2
lensed ULIRGs, which were selected from the H-ATLAS H O level diagram.
2
survey. The data, which were obtained using the IRAM The H O observations were conducted in the compact
2
Plateaude Bure Interferometer(PdBI), clearlyshowwater D-configurationfromDecember2011toMarch2012incon-
emissionlines inallthe sources. Basedonthese results,we ditions of good atmospheric phase stability (seeing of 1′′)
derive a clear relation between the H2O and the infrared and reasonable transparency (PWV ≤ 1mm). Except for
luminosities in high-z ULIRGs. SDP.81, which was observed with five antennas, all other
Throughout this paper, we adopt a cosmology with sources were observed with the six antennas of the PdBI
H0 = 71kms−1Mpc−1, ΩM = 0.27, ΩΛ = 0.73 (Spergel array. The total on-source integrationranges from ∼1 to 2
et al. 2003). hours (Table 1). We used Bands 2, 3 and 4, which cover
the frequencyranges129–174GHz, 201–267GHz and277–
371GHz,andthebandcentersweretunedtotheredshifted
2. Sample selection and observations
frequency of the selected H O emission line using the red-
2
The detection of strong H O emission in the lensed H- shifts estimated from CO observations (Table 3). The cor-
2
ATLAS galaxy SDP.17b by Omont et al. (2011) suggested relator (WideX) provided a contiguous frequency coverage
that the H-ATLAS survey offered a unique opportunity of3.6GHzindualpolarizationwithafixedchannelspacing
to select an homogeneous sample of bright lensed galax- of 1.95 MHz, allowing us to detect the continuum as well
ies spanning a broad range in luminosity and redshift to as any additional emission lines, if present. In the com-
further study the properties of water emission in the early pact configuration, the baselines extend from 24 to 179m,
universe. We selected from the H-ATLAS catalog, sources resulting in synthesized beams of ∼ 1.5′′ x 1.0′′ to ∼ 4′′ x
with strong flux densities (with F >150 mJy) that 3′′ (Table 1). Only SDP.81, G12.v2.30 and NB.v1.78 are
500µm
werewellcharacterized,i.e. hadCOredshiftmeasurements, resolvedat this angular resolution (Fig. 2).
additional sub/millimeter imaging and available deflector During the observations, the phase and bandpass were
identification (see, e.g., Negrello et al. 2010; Bussmann et calibrated by measuring standards sources that are regu-
al. in prep.). In the selection, we also somewhat preferred larlymonitoredattheIRAMPdBI,including3C84,3C279,
Fig. 1. Spectra of the H2O and CO emission lines observed at PdBI toward the seven lensed high-redshift ultra-luminous
galaxiesdiscussedinthispaper. TheH2Oemissionlinesaredisplayedintheleftcolumn(showingthe(211−202)orthe(202−111)
transition;thetransitionsareidentifiedineachbox. TheCOspectraaredisplayedintherightcolumn(showing3–2,4–3,5–4and
7–6 rotational transitions - for G15.v2.779, the[CI] emission line is included in the band). The transitions are indentified in each
box. Allspectraincludethecontinuum,andtheH2OfrequenciescorrespondingtothezerovelocityaregiveninTable4. Thered
lines trace the Gaussian fits to the H2O and CO line profiles and the fit to the continuum emission level. In all cases, the match
between theH2O and CO spectra is excellent both in redshift and in the details of theline profile - see text.
MWC349, CRL618, and 0851+202. The accuracy of the SDP.17b,NA.v1.144,andG15.v2.779. Thethreeremaining
flux calibration is estimated to range from ∼10% at 2 mm sourcesareextended anddisplay distinct lensedmorpholo-
to ∼20% at 0.8 mm. gies including two-image configuration system (SDP.81), a
To complement the H O data, we include in this pa- complex elongatedstructure (G12.v2.30),and anextended
2
per new results on the CO emission for the seven sources. structure (NB.v1.78). Each source is described in detail
For five of them, the CO data were obtained in 2011 and below.
2012 using the PdBI in the A-configuration. Those data Table4reportsthevaluesoftheH Ovelocity-integrated
2
wereacquiredintheframeofasurveyoflensedULIRGsto fluxdensity(lineflux)detectedatthepeakofthesourcein
maptheirCOanddustcontinuumemissionathigh-angular one synthesized beam, I pk, and the velocity-integrated
H2O
resolution (Cox, Ivison et al. in prep.) and a full descrip- line flux integrated over the source size, I . In most
H2O
tion of the results will be given in that paper. For two of cases, the ratio I /I pk is lower than 1.5, except for
H2O H2O
the sources, NB.v1.78 and G12.v2.30, the CO data were the extended sources G12.v2.30 and NB.v1.78. For the
obtained in August 2012 in the D-configuration with five other sources studied in this paper, except for SDP.81, it
antennas. The observations were made in good weather is thus unlikely that significant flux is missed. This is also
conditions and more details are provided in Table 3. In confirmed when comparing our total spatially integrated
this paper, we only present the global CO spectra (i.e., in- continuum flux density S with measurements published
ν
tegratedoverthe source’sextent)withthe goaltocompare elsewhere at the nearby frequency of 250 GHz, using the
thecharacteristicsoftheH2OandCOemissionlineprofiles. bolometer MAMBO camera at the IRAM 30-meter tele-
Adetaileddiscussionofthemorphology,thedynamics,and scope (Negrello et al. 2010; Dannerbauer et al. in prep.).
the lensing of these sources will be given in Cox, Ivison et NA.v1.144 and SDP.81, which were observed at the PdBI
al. (in prep.). close to 250GHz, agree very well with MAMBO observa-
tions. For SDP.9 andSDP.17b, whichwereobservedatthe
PdBI close to 300GHz, the comparison is more difficult;
3. Properties of the H2O emission lines however, S is somewhat higher than the values expected
ν
fromextrapolationsoftheMAMBOvalues. Althoughthere
3.1. General properties
is no MAMBO observation for NB.v1.78, S agrees fairly
ν
Thesevenlensedhigh-z ULIRGsarealldetectedwithhigh well with the flux density measured at 880µm using the
signal-to-noiseratios(S/N>∼6,exceptSDP.81,eitherinthe Smithsonian Millimeter Array (SMA) (Bussmann et al. in
2 –1 orthe2 –2 H Oemissionline(seeFig.1),aswell prep.). Finally, the continuum flux density measured at
02 11 11 02 2
as in the underlying redshifted submillimeter continuum 143GHz for G15.v2.779 is in excellent agreement with the
emission (S/N>20). The water emission lines are strong, value reported by Cox et al. (2011) at 154GHz.
with integrated fluxes ranging from 1.8 to 14 Jy km s−1 The 3.6GHz bandwidth covered by the PdBI receivers
(Fig.1andTable4). Thisindicatesthatinhigh-zULIRGs, (and correlator), which was generally centered on the red-
they are the strongest molecular submillimeter emission shifted frequency of the H O emission line, encompasses
2
lines after those of high-J CO (see Sec. 4.3; note, however, otherpotentialemissionlinesofinterest,includingi)13CO,
that2mmand3mmCOlinesdisplayedinFig.1mayhave H18O, H17O, H O+ in the vicinity of H O(2 –1 ); and
2 2 3 2 02 11
weaker intensity than the 1mm H2O lines). ii) H2O+(202–111,J3/2,3/2 and J5/2,3/2) in the vicinity of
900Tkmhes−H12(OTablilneew4)i.dtThshe(FlinWesHhMa)veraanvgaerieftryomof p14ro0filteos Hsp2eOct(r2a11i–s2t0o2o))l.owHtoowdeevteerc,ttthheeseculirnreens,twshenicshitaivrietynootfsoeeunr
including single Gaussian profiles (NA.v1.144, NB.v1.78), in the Herschel spectra of Mrk231 and Arp220 except for
double-peaked profiles (G12.v2.779), or asymmetrical pro- the two H O+ lines, which are present in the spectrum of
2
files (SDP.9, SDP.17b, SDP.81). The H2O and CO line Arp220(Rangwalaetal.2011). Apartfromthe H2Oemis-
profiles share similar properties (shape, linewidth) in all sion lines, no other emission line is detected at the S/N
sources,suggestingthat there is no strong differential lens- ratio of the spectra of the seven high-z galaxies studied in
ing effects between the CO and the H2O emission lines. this paper.
From the spatially integrated H O line flux, I , the
2 H2O
apparent H O luminosity, µL where µ is the lensing
2 H2O
magnification factor, can be derived using the relations 3.2. Individual sources
given in, e.g., Solomon, Downes & Radford (1992). µL
H2O The following describes the properties of the individual
varies by only a factor of ∼4 from SDP.81 to NB.v1.78 or
lensed galaxies.
G12.v2.30 (Table 4). Fig. 3 displays the relation between
µL and µL , including the values for local ULIRGs
H2O IR
(Yang et al. in prep.). The infrared and H2O apparent 3.2.1. SDP.81 at z = 3.040
luminosities are one or two orders of magnitude higher in
these high-z galaxies than in local ULIRGs. However, the The source SDP.81 is at the highest redshift among the
ratiosL /L aresimilar,althoughslightlyhigherforthe SDP lensed galaxies of Negrello et al. (2010). It displays
H2O IR
high-z galaxies. twoarcsintheSMA880µmdata,whicharealsoseeninthe
Figure 2 displays the images of the H O emission line HST (Negrello et al. in prep.) and the PdBI CO imaging
2
and the corresponding submillimeter continuum emission results (Cox, Ivison et al. in prep.). Preliminary lensing
for the seven lensed high-z ULIRGs. The relatively low modelingindicatedaveryhighlensingmagnificationfactor
angular resolution (at best ∼ 1′′) of the current data lim- of µ=19 (Negrello et al. 2010), but this value has been
its for most of the sources a detailed study of the spa- reviseddownwardtoµ=9.5±0.5basedonrecentHSTdata
tial properties of their signal. Four of the sources re- (Dyeetal. inprep.). ThisisconfirmedbytheSMA880µm
main unresolved at the present angular resolution: SDP.9, imaging results which yield µ = 9.5± 0.8 (Bussmann et
Fig. 2. Images of the submillimeter continuum (left panel) and H2O line emission (right panel - see Fig. 1 and Table 4 for the
identification ofthetransitions) fortheseven high-z lensed ultra-luminousgalaxies studied inthispaper(sources areidentifiedin
theleftpanels). Synthesizedbeamsareshowninthelowerleftcornerofeachmap. Themapcenterscorrespondtothecoordinates
given in Table 1 and are indicated by a cross. For thecontinuum maps, thecontours start from 3σ in steps of 3σ for SDP.81 and
G12.v2.30, andinstepsof6σ fortheothersources; for theH2Olineemission maps, thecontoursstart from 3σ instepsof1σ (for
SDP.81) and2σ for theothersources. Foreach source,the1σ continuum(mJy/beam)and emission line(Jykms−1/beam) noise
levels are as follows: SDP.81 (0.60 / 0.18), NA.v1.144 (0.35 / 0.31), SDP.9 (0.50 / 0.59), NB.v1.78 (0.28 / 0.30), G12.v2.30 (0.28
/ 0.28), G15.v2.779 (0.11 / 0.24), and SDP.17b (0.73 / 0.56). Four sources remain unresolved at the current angular resolution,
whereasSDP.81,NB.v1.78, andG12.v2.30displaycomplexlensingmorphologiesbothinthecontinuumandlineemissionthatare
revealed even at thepresent low angular resolution. Detailed comments on the sources are given in the text (Section 3).
al. in prep. – hereafter B13). As discussed in Sec. 4.1, profileoftheH Oemissionlineisalsodominatedbyamain
2
we adopted the values of µ derived from the 880 µm SMA redcomponent (peaking at ∼+200kms−1 with a width of
databyB13asbasicreferenceforthelensingmagnification ∆v = 140kms−1). Due to the low S/N ratio of the H O
2
factors listed in Table 2. spectrum,theblueemissioncomponentoftheprofile(peak-
The CO line profile is asymmetrical with a red com- ingat−100kms−1)thatisclearlyseenintheCOspectrum
ponent that is much stronger than the blue one. The line isonlybarelyvisibleintheH2Oemissionspectrum(Fig.1).
Table 1. Observation Log
IAUName ID RAa Deca Date Frequencyb Beam(′′) ton(h)c
HATLASJ090311.6+003906 SDP.81 09:03:11.61 +00:39:06.7 2011Dec 244.890 2.8×1.8 1.2
HATLASJ133649.9+291801 NA.v1.144 13:36:50.00 +29:17:59.6 2012Mar 235.330 1.6×1.1 0.8
HATLASJ090740.0−004200 SDP.9 09:07:40.05 −00:41:59.5 2011Dec 292.550 3.3×1.6 1.4
HATLASJ133008.4+245900 NB.v1.78 13:30:08.56 +24:58:58.3 2012Jan&Mar 240.802 1.4×1.0 2.3
HATLASJ114637.9−001132 G12.v2.30 11:46:37.99 −00:11:32.0 2011Mar 232.734 2.0×1.0 1.2
HATLASJ142413.9+022303 G15.v2.779 14:24:13.90 +02:23:04.0 2011Dec 143.940 4.2×3.1 1.7
HATLASJ090302.9−014127 SDP.17b∗ 09:03:03.02 −01:41:26.9 2011Jan 298.148 2.9×1.1 0.6
a: J2000 coordinates of thecenters of the mapsdisplayed in Fig. 2.
b: Central observed frequency (GHz).
c: Total on-source integration time for thePdBI array with six antennas.
*: The observations of SDP.17b are reported in Omont et al. (2011).
Table 2. Submillimeter and infrared properties of the lensed ultra-luminous galaxies
SourceID F250 F350 F500 µLIR µ LIR
(mJy) (mJy) (mJy) (1013L⊙) (1012L⊙)
SDP.81 129±20 182±28 166±27 5.8 9.5±0.8 6.1
NA.v1.144 295±45 294±45 191±31 5.7 5.3±2.9 11
SDP.9 485±73 323±49 175±28 4.4 8.5±1.8 5.2
NB.v1.78 273±42 282±43 214±33 11 10.5±1.4 10
G12.v2.30 323±49 378±57 298±45 15.7 9.6±0.9 16
G15.v2.779 115±19 192±30 204±32 8.5 4.1±0.2 21
SDP.17b 328±50 308±47 220±34 6.9 4.3±1.2 16
Note: F250, F350, and F500 are the SPIRE flux densities at 250, 350, and 500µm; µLIR is the apparent total infrared luminosity
(8-1000µm); µ is the adopted lensing magnification factor derived from lensing modeling of 880µm continuum, mostly from
Bussmannetal.inprep. (seetextSec.3fordetails); LIR istheintrinsicinfrared luminosity,derivedfrom theliterature(Harriset
al. 2012; Lupu et al. 2012; Fu et al. 2012; Bussmann et al. 2012) except for NB.v1.78, for which an approximate value is inferred
from scaling thevalueof G12.v2.30 with theratio of the350µm fluxdensities.
Table 3. Observed parameters of theCO emission lines
Source ID z CO line ICO ∆Vco OtherCO data
(Jy.km/s) (km s−1)
SDP.81 3.040 5-4 7.0±0.4 560±40 Harris et al. (2012)
NA.v1.144 2.202 4-3 12.3±0.6 210±10 Harris et al. (2012)
SDP.9 1.574 3-2 9.2±0.3 420±10 Iono et al. (2012)
NB.v1.78 3.111 3-2 3.3±0.5 560±70 Riechers et al. (in prep.)
G12.v2.30 3.259 3-2 7.8±1.7 650±160 Fu et al. (2012)
G15.v2.779 4.244 7-6 7.5± 0.6 840±50 Cox et al. (2011)
SDP.17b 2.305 4-3 9.1±0.3 320±10 Harris et al. (2012)
Note: z is the redshift measured from the PdBI CO spectra (Fig. 1); ICO is the integrated flux of the CO line; ∆Vco is the CO
linewidth (FWHM); references to other CO measurements from theliterature are given in thelast column.
Despite the low angular resolution, the dust continuum to the western arc. Due to the low S/N ratio of the data,
image is clearly resolved (Fig. 2), showing both gravita- the H O emission is seen only in the eastern arc, consis-
2
tional arcs of the 880µm image of Negrello et al. (2010), tent with the only clear detection of the red part of the
with a stronger emission in the eastern arc. This struc- spectrum.
ture is also seen in the CO map of Cox, Ivison et al. which TheH OlinefluxI andtheapparentL luminos-
2 H2O H2O
indicates that the stronger red emission traces the bright ity, which are given in Table 4, take into account the total
eastern arc, whereas the weaker blue emission corresponds emissionincluding the redandblue components. However,
Table 4. Observed parameters of theH2O emission lines and continuum emission
Source Linea νobsb Sνpkc Sνc SνH2Opkd ∆VH2O IH2Opkd IH2Od µLH2Oe
[GHz] [mJy/beam] [mJy] [mJy/beam] [kms−1] [Jykms−1/beam] [Jykms−1] [107L⊙]
SDP.81 2 244.5000 12.5 27.0±1.2 10.7±1.9 140±50 1.6 1.8±0.5 32±9
NA.v1.144 1 234.8343 9.4 16.4±0.7 22.8±1.7 200±50 4.9 7.5±0.9 57±7
SDP.9 1 292.1425 17.4 21.7±0.9 20.3/37.8±2.9f 410±50 11.3 14.4±1.1 60±5
NB.v1.78 2 240.2896 15.4 36.9±0.4 5.0±0.8 510±90 2.7 6.7±1.3 122±24
G12.v2.30 2 231.9458 4.9 21.0±0.8 4.5/4.5±0.7f 690±80 2.7 6.5±1.2 128±24
G15.v2.779 1 143.3837 5.9 7.3±0.2 3.2/6.6±0.5f 890±140 3.4 4.1±0.6 94±9
SDP.17b 2 298.8646 28.6 37.9±1.1 22.9±2.6 300±30 7.2 7.8±0.9 85±10
a: Lines 1 and 2 correspond to theH2O (211−202) (νrest =752.03GHz, Eup =137K) and (202−111) (νrest =987.93GHz,
Eup =101K) transitions, respectively.
b: νobs is the frequency corresponding to thezero of thevelocity scale of thespectra of Fig. 1.
c: Sνpk corresponds to thepeak continuumflux density(mJy/beam); Sν refers to thetotal spatially integrated continuum flux
density (mJy).
d: SνH2Opk corresponds to thepeak H2O fluxdensity (mJy/beam); IH2Opk is thepeak H2O velocity-integrated fluxdensity
(fluxin one beam, in Jy kms−1/beam) and IH2O thespatially integrated H2O line flux (in Jy kms−1). The values derivedfor
SDP.81 and G12.v2.30. are underestimated (see text).
e : µLH2O is theapparent luminosity of theobserved H2O line using therelations given in,e.g., Solomon, Downes & Radford
(1992).
f : In thecases of SDP.9, G12.v2.30 and G15.v2.779, theH2O emission lines are double-peaked and theparameters in thetable
refer todouble Gaussian fits.
duetothelowS/NratiooftheH Odata,thesenumbersare theSMA880µmvaluefromB13,µ=8.5±1.8,whichagrees
2
lessaccuratethanformostothersourcesinoursample. Be- with the HST value and also with µ =11.
CO
causetheemissionisveryextended,thespatiallyintegrated The H O intensity of SDP.9 is by far the largest of our
2
H2OlinefluxIH2O isprobablyunderestimated,asindicated sample, due to the low redshift of the source. The corre-
bytheabsenceofsignificantH2Oemissionseeninthewest- sponding apparent H2O luminosity is among the highest
ern arc, and the very small difference between IH2O and found so far. The emission line profiles in H2O and CO
IH2Opk compared to the continuum ratio Sν/Sνpk=2.2. aresimilar,includingthe strongredemissionspikeandthe
weaker, broader blue emission (Fig. 1). The high angular
CO data from Cox, Ivison et al. (in prep) as well as the
3.2.2. NA.v1.144 at z = 2.202
HST/WFC3 imaging data (Negrello et al. in prep.) show
The narrow H O linewidth of NA.v1.144 is the same as is that SDP.9 is a good example of an Einstein ring, with a
2
seen in the CO emission line (∆v ∼ 200kms−1). It is the clearasymmetrybetweenthe eastandwestarcs. However,
narrowestCO linewidth of our sample (Table 3). our angular resolution is not high enough to resolve the
The estimate of the lensing magnification factor from emission.
detailed modeling based on the SMA image of the 880 µm
continuum emission indicates a low value of µ ∼ 4.6±1.5 3.2.4. NB.v1.78 at z = 3.111
(B13). However, the SMA imaging of this object has lim-
ited uv coverage(only the extended arraywas used) which This source has one of the highest redshifts and highestt
might compromise the measurement of the lensing magni- apparent luminosities in our sample. The intermediate
fication factor. The corresponding values for the IR and linewidth of the CO and H O lines (∆v ∼ 550kms−1) is
2
CO luminosities appear to be surprisingly high compared consistentwith those measuredin the mid-J CO lines used
to the narrow linewidth. Indeed, the uncertain derivation to initially determine the redshift with CARMA (Riechers
of µ from the CO linewidth and luminosity (Harris et al. et al. in prep.). The H O line is indeed the brightest line
2
2012) yields µCO ∼ 23±15. Therefore, we have doubled measured in this source so far and thus provides the best
the uncertainty on the SMA value of µ and adopted the constraints on the line profile. The moderate CO intensity
rms2-weightedaverageofthe estimate fromthe SMAdust- andlinewidthindicatesintermediateCO,H Oandinfrared
2
continuum and the CO line, i.e. µ = 5.3±2.9. intrinsic luminosities, LIR≈1013L⊙.
This bright submillimeter galaxy is clearly unresolved Thelensingmagnificationfactor,derivedfromtheSMA
with our present angular resolution, a result that is con- 880µm imaging results, is µ = 10.5±1.4 (B13), a value
firmed by the small extension observed in the SMA results whichisadoptedinthispaperandisconsistentwithµ =
CO
(B13). 12 (inferred from the CO data of Table 3).
The source is resolved and shows a relatively complex
3.2.3. SDP.9 at z = 1.574 morphology in the H2O and continuum maps. The peak
value in a single beam, I pk, reported in Table 4, is
H2O
The galaxy SDP.9 is the brightest 250µm and lowest red- lower than the spatially integrated value I by a fac-
H2O
shiftofthefivelensesdiscussedinNegrelloetal. (2010). Its tor ∼2.5. The ratio is similar for the 240 GHz continuum,
lensing magnification factor is estimated to be µ=8.7±0.7 wherethe peak value is 15.4mJy/beamandthe integrated
from HST imaging (Dye et al. in prep.). We adopted here flux density is 36.9 mJy (see Table 4). In addition to the
southeast main peak, there are northern and southwestern (Bussmannet al. 2012),which makes it the most luminous
extensions (Fig. 2). This morphology is also seen in recent H-ATLAS source, with LIR = 2×1013L⊙. This is con-
SMA 880µm imaging results (Bussmann et al. in prep.). sistent with the broad CO lines, the widest of our sample
However, the southwest peak is very strong in H O com- (760−890kms−1), which would imply µ ∼8. The H O
2 CO 2
pared to the main southeast peak and the peak ratio in line has one of the largest S/N thanks to good observing
the continuum. This could suggest that the H O emitting conditions in the 2mm window.
2
region is more compact than the continuum. The width and the characteristics of the complex,
double-peakedH Oline agreewellwith thoseofthe CO(7-
2
6) and [CI] lines (Fig. 1). G15.v2.779 has the highest in-
3.2.5. G12.v2.30 at z = 3.259
trinsic H O luminosity of our sample by a factor ∼2. This
2
implies that both should have very large H O luminosities
G12.v2.30 is another prominent source among the H- 2
if the two components corresponded to two galaxies.
ATLASbrightestlenses. Itscomplexdifferentiallensinghas
At the present angular resolution G15.v2.779 remains
beenanalyzedbyFuetal. (2012),showingthatthelensing
unresolved, in agreement with the compactness of the CO
is very different in the near-infrared compared to the sub-
(Cox, Ivison et al. in prep.) and the 880µm continuum
millimeter or CO emission. The various estimates of the
emissions (Bussmann et al. 2012).
lensingmagnificationfactorbasedonsubmillimeter images
or the CO linewidths are comparable: µ=7.6±1.5 for the
dustsubmillimeterand6.9±1.6forCO(1−0)imagingbyFu 3.2.7. SDP.17b at z = 2.305
etal.;9.6±0.9forthesamesubmillimeterdatabyB13(the
valueadoptedhere);µCO=7±2byHarrisetal.(2012)from The detection of the H2O emission line in SDP.17b was
CO(1−0) linewidth and luminosity. These values confirm reportedanddiscussedinOmontetal.(2011). ItsH2Oline
thatG12.v2.30isoneofthemostluminousinfraredgalaxies profileis inperfectagreementwiththe COemissionprofile
in H-ATLAS with an estimated LIR ∼1.6×1013L⊙. -seeFig.1fortheCO(4–3);alsoHarrisetal.(2011)forthe
CO(1–0)andIono et al. (2012)and Riecherset al. in prep.
TheH Oprofileappearstobedoublepeakedwithato-
2 for the CO(3–2) profiles - including the asymmetry with
talwidth of ∼700km/s. Due to the shortintegrationtime
the distinct blueshifted emission wing. The source is not
of the observations, the CO results for G12.v2.30 are the
resolved in the present data and higher angular resolution
noisiest of our sample andthe details of the profile, in par-
dataindicatethatthesourceremainscompactanddisplays
ticular, its double-peaked nature remain unclear. Within
a velocity gradient (Cox, Ivison et al. in prep.).
the noise, the CO profile is compatible with the H O emis-
2 AgaintheµvaluederivedbyB13,µ=4.0±0.6,ismuch
sion, although additional observations are needed to con-
lower than approximately expected from the CO linewidth
firm this result.
and luminosity, which yields µ = 18±8 (Harris et al.
The source is resolved with the present angular resolu- CO
2012) - note that this latter value is uncertain because of
tion of 2.0′′×1.0′′ and shows a complex structure that is
the asymmetric CO line profile. However, the image sep-
most clearly seen in the continuum map (Fig. 2): an elon-
arations are at the limit of what can be resolved by the
gatedarctothesouthshowstwopeaksandemissionisseen
SMA.Therefore,wehaveagaindoubledtheuncertaintyon
about 2′′ to the north. Due to the low S/N ratio, only the
theSMAvalueofµandadoptedtherms2-weightedaverage
southern component is detected in the H O emission line.
2 ofthe estimate fromthe SMA dust-continuumandthe CO
G12.v2.30 appears to be a complex source. The dust and
line, i.e. µ = 4.3±1.2. However, the line of sight toward
gasemissionsaswellasthestellaremissionhaveverydiffer-
SDP.17b could include an intervening system, as indicated
entmorphologies,whichindicatesthatthelensingpotential
by a CO line at z = 0.942 reported by Lupu et al. (2012)
is unusual (Fu et al. 2012). Estimating the total intensity
based on Z-Spec data, in addition to the z = 2.3 line seen
of the H O line remains difficult for G12.v2.30. The peak
2 bytheGBT(Harrisetal.2012)andthePdBI(Fig.1). But
valueinasinglebeam,I pk,reportedinTable4,islower
H2O this CO line at z = 0.942 was not confirmed by Omont et
than the spatially integrated value I by a factor ∼2.4.
H2O al. (2011) and more observations are needed to clarify this
The situation is similar for the 240 GHz continuum, where
question. Iftherewassuchadustyobjectatz =0.942,the
the peak value is 4.9 mJy/beam and the integrated flux
lensmodelderivedfromtheSMAdataofthisverycompact
density is 21.0 mJy (see Table 4). This latter value is itself
source would have to be revised.
much lower than the flux density of ∼36mJy measured at
1.2mmusing MAMBO at the 30-metertelescope (Danner-
bauer et al. in prep.). However, the reported value for the 4. Discussion
spatially integrated line flux I is less accurate than for
H2O
most other sources in our sample. Because the emission is 4.1. Lensing
very extended, the spatially integrated H O line flux I
2 H2O Themainpurposeofthis paperistoinvestigatetheimpor-
is probably underestimated, similarly to the continuum, as
tance of the H O emission in high-z ULIRGs, but not to
indicated for the latter by the factor ∼1.5 lower compared 2
studyitsspatialstructurebyseparatingitfromlensingim-
to the MAMBO value.
ages. This is the reason why the observations were carried
out with the most compact configurationof PdBI to maxi-
3.2.6. G15.v2.779 at z = 4.244 mize the sensitivity for detection. Detailed lensing model-
ing is thus out of the scope of this paper. However,a good
With a redshift higher than 4 and F =204±32mJy, control of lensing effects is mandatory for various reasons:
500µm
G15.v2.779(alsoreferedtoasID.141)remainsuniqueinthe i)Asseenabove,theH Oemissioncouldberesolvedoutin
2
H-ATLAS survey (Cox et al. 2011). Its lensing magnifica- sourcesthat are extended, even with the limited resolution
tionfactor has recentlybeen estimatedto be only 4.1±0.2 of the observations reported in this paper. ii) Differential
Table 5. Properties of the dust continuumand theH2O line emission
SourceID lineaobs LIR LH2O−1m LH2O−1a LH2O−2m LH2O−2a
(1012L⊙) (107L⊙) (107L⊙) (107L⊙) (107L⊙)
SDP.81 2 6.1 (1.5)b (2.3) 3.3 3.3
NA.v1.144 1 11 9.7 9.7 (25) (16)
SDP.9 1 5.2 7.0 7.0 (16) (10)
NB.v1.78 2 10 (5.1) (7.9) 12 12
G12.v2.30 2 16 (5.8) (9.0) 13 13
G15.v2.779 1 21 23 23 (55) (34)
SDP.17b 2 16 (8.7) (14) 20 20
a: Line 1 is H2O(211−202) 752.03GHz and line 2 is H2O(202−111) 987.93GHz;
b: Luminosityvaluesfor unobservedlines arewritten in parenthesis,theyareinferred from theotherobserved linesassuming the
line intensity ratio from Mrk 231 (Gonza´lez-Alfonso et al. 2010, subscript m) or Arp220 (Rangwala et al. 2011, subscript a). As
detailed in thetext,we consider that these valuessignificantly underestimate theH2O luminosity for SDP.81 and G12.v2.30.
of µ inferredfrom submillimeter imaging rather than near-
infrared HST imaging, since H O emission should be more
2
relatedtosubmillimeterdustemissionthantonear-infrared
stellar emission, and submillimeter and near-infrared lens-
ing can be very different as examplified in the case of
G12.v2.30 (Fu et al. 2012). As discussed in Sec. 3.2, the
lensing magnification factor µ is thus determined from ex-
isting lensing models based on 880µm SMA imaging re-
sults(B13;seealsoBussmannetal.2012). Fortwosources
thesevalueswereslightlycorrectedbyalsousingthevalues
of µ derived following a method described in Harris et al.
(2012), which uses the relation bewteen the CO linewidth
and luminosity. As the low angular resolution and limited
S/N ratio of our H O data do not allow us to trace pos-
2
sible differential effects of lensing, we adopted a minimum
uncertainty of ±20% for all values of µ.
Fig. 3. Apparent H2O luminosity versus apparent infrared
luminosity of high-redshift sources, for H2O Line 1 (211 −202,
752.03GHz) with the Arp220 H2O line ratio (see text), com- 4.2. Relation between H O and infrared luminosities
pared to local ULIRGs (µLIR<4 ×1012L⊙, Yang et al. in 2
p6.r8epx.1).0−T6haenddas2h.6edx1d0ia−g6o,neaqlulainletsohtahvoesecoonfsAtarnpt2L20H2aOn/dLMIRrkra2t3io1s. TfahcteoirnstrliinstseicdHin2OTalubmlein2o,siatriees,rebpaosretdedonfotrheeamcahgnsoifiucracetioinn
Because of their peculiarities, values for SDP.81 and G12.v2.30
Table 5. The information on the H O emission is limited
(underestimated by factors possibly up to ∼1.5-2 because they 2
bytheobservationofasingleemissionlinepersource. This
areveryextended,seetext),andthoseofAPM08279+5255and
prevents us from comparing the H O excitations between
Mrk231 (type 1 and type 2 QSOs, respectively) are printed in 2
blue. different sources. It is nevertheless interesting to compare
theirH Olineluminosityandtochecktheirdependencyon
2
other properties, such as the infrared intrinsic luminosity,
L , since infrared excitation is thought to play a key role
IR
lensingeffectsmustbecontrolledforcomparisonwithemis- in the excitation of the H O levels.
2
sion from other H2O lines or other molecules or dust. As In addition, the H2O lines that were observed differ
discussed, e.g., by Serjeant (2012), the importance of dif- from source to source: three sources were measured in the
ferential lensing is enhanced for the highest magnifications H O(2 –2 ) emission line (’Line 1’) and four sources in
2 11 02
whichtakeplaceclosetocaustics,and,especially,forblank the H O(2 –1 ) emissionline (’Line 2’) To deal with this
2 02 11
fields,suchasH-ATLASwherethedeflectorsareeithersin- disparity, we approximated the integrated line flux, I ,
H2O
gle massive galaxiesor small groups of galaxies. A striking ofthe emissionline thatwasnotobserved,byadoptingthe
example is the large difference observed in lensed images valueofthelineratioof’Line2’to’Line1’measuredeither
in the near-infrared compared to the submillimeter or CO in Arp220, r =3440/2970=1.16 (Rangwala et al. 2011)
21
emission of G12.v2.30 (Fu et al. 2012). iii) Lensing magni- orinMrk231,r =718/415=1.73(González-Alfonsoetal.
21
fication must be corrected for deriving intrinsic properties 2010), listed as ’a’ and ’m’ in Table 5. The correspond-
of the sources such as luminosities or line ratios. ing values of L are reported in parenthesis in Table 5.
H2O
To infer intrinsic infrared and H O luminosities of our Finally, the full set of values of the intrinsic luminosities
2
sources,a first approximationis to derive a (mean) lensing L forlines 1 and2 andthe line ratios ofArp220or
H2O−1/2
magnification factor µ. We systematically preferred values Mrk231 are reported in Table 5.
Fig. 4. Relation of the intrinsic H2O luminosity with the infrared luminosity for the seven ultra-luminous infrared galaxies
reported in this paper, other well-known high-z sources taken from the literature, and local ULIRGs (LIR<4 ×1012L⊙, Yang et
al. in prep.). The luminosity is reported to the H2O (211−202, 752.03GHz) emission line (referred to as ’line 1’ in this paper),
where we adopted an Arp220 H2O line ratio when another H2O line (’line 2’) was measured (see text). The solid line shows a
best-fit power-law, LH2O =LαIR, where α=1.17±0.08. Error bars are defined in the following way: i) for LIR, they combine the
uncertainties on the values of µLIR and the uncertainties on µ given in Table 2; ii) for LH2O, they include the errors on IH2O of
Table 4, and the same uncertainties on µ except that when the latter is <20% it is replaced by 20% (see Sec. 4.1). Because of
theirpeculiarities, values(inblue)for SDP.81andG12.v2.30 (bothunderestimatedbyfactors possibly upto∼1.5-2becausethey
are very extended, see text), and those of APM08279+5255 and Mrk231 (type 1 and type 2 QSOs, respectively) are not taken
into account for thefit.
Thereareseveralargumentstofavortheconversionfac- α=1.22±0.10 and 1.28±0.12 for the Arp220 and Mrk231
tor of Arp220 rather than Mrk231: for all galaxies,except line ratios, respectively. Independent of the selected lines
G12.v2.30,theCOexcitationseemssignificantlylowerthan orratios,these results indicate thatL increasesrapidly
H2O
inMrk231(Lupuetal.2012);usingtheMrk231conversion with L , possibly faster than linear. We note, however,
IR
factor seems to yield anomalously low values for the line 1 that since systematic errorswere not taken into accountin
luminosity of sources only observed in line 2 (Table 5). this analysis, adding the statistical and systematic errors
Therefore, keeping all uncertainties in mind, the rela- could result in a relation that is closer to being linear. A
tionship between L and L is displayed in Fig. 4 for steepincreaseisconsistentwithasignificantroleofinfrared
H2O IR
LH2O−1a (line 1 with Arp220 line ratio). This relation- radiationintheexcitationofthewatervaporlines. Itisin-
shipisinferredfromallsourcesstudiedinthispaper-with teresting to note that a similar behavior with the infrared
theexceptionofSDP.81andG12.v2.30whoseH Ointensi- luminosity has been found for the intensity of local H O
2 2
ties are uncertain and probably underestimated by factors and OH megamasers, which could be interpreted as a re-
possibly up to ∼1.5-2because they are very extended - to- sultoftheimportanceofinfraredpumpingonthesemasers
getherwithHLSJ0918fromCombesetal.(2012),andlocal (e.g. Lo 2005).
ULIRGs (LIR<4×1012L⊙)from Yang etal. (in prep.). A However, it is important to stress that, as shown e.g.
best-fit power-law to this relation following
bythemodelingofH OexcitationinMrk231byGonzález-
2
Alfonso et al., the intensity of (optically thick) H O lines
2
L =Lα (1) results from a complex interplay between various parame-
H2O IR
ters that includes gastemperature anddensity, H O abun-
2
yields α=1.17±0.0.10 using ’line 1’ and the Arp 220 dance, infrared radiation field, spatial distribution of H O
2
line ratio. Using the Mrk231 line ratio would and dust, etc. The present data, with only one H O emis-
2
yield α=1.11±0.10, whereas using ’line 2’ would give sion line per source, prevents us for constraining the water