Light breeze in the local Universe

1 MB·

by  A. Concas

Astronomy&Astrophysicsmanuscriptno.outflow_SDSS_referee_final_arxiv (cid:13)cESO2017
January25,2017
Light breeze in the local Universe
A.Concas1,P.Popesso1,M.Brusa2,3,V.Mainieri4,G.Erfanianfar1,andL.Morselli1
1 ExcellenceClusterUniverse,Boltzmannstr.2D-85748Garching,Germany
2 DipartimentodiFisicaeAstronomia,UniversitádegliStudidiBologna,V.leBertiPichat,6/2-40127,Bologna,Italy
3 INAF−OsservatorioAstronomicodiBologna,viaRanzani1,I-40127,Bologna,Italy
4 EuropeanSouthernObservatory,Karl-Schwarzschild-str.2,85748Garching,Germany
Received;accepted
7
1
0 ABSTRACT
2
Weanalyzeacompletespectroscopic sampleofgalaxies(∼600,000)drawnfromSloanDigitalSkySurvey(SDSS,DR7)tolook
n
forevidenceofgalacticwindsinthelocalUniverse.Wefocusontheshapeofthe[OIII]λ5007emissionlineasatracerofionizing
a
gasoutflows.Westackourspectrainafinegridofstarformationrate(SFR)andstellarmasstoanalyzethedependenceofwindson
J
thepositionofgalaxiesintheSFRversusmassdiagram.Wedonotfindanysignificantevidenceofbroadandshifted[OIII]λ5007

3 emission linewhich weinterpret asno evidence of outflowing ionized gasin theglobal population. Wehavealso classifiedthese
2 galaxies as star-forming or AGN dominated according to their position in the standard BPT diagram. We show how the average
[OIII]λ5007profilechangesasfunctionofnatureofthedominantionizingsource.Wefindthatinthestar-formingdominatedsource

] theoxygenlineissymmetricandgovernedbythegravitationalpotentialwell.TheAGNorcompositeAGN\star-formationactivity
A
objects,incontrast,displayaprominentandasymmetricprofilethatcanbewelldescribedbyabroadgaussiancomponentthatisblue-
G shiftedfromanarrowsymmetriccore.Inparticular,wefindthatthebluewingsoftheaverage[OIII]λ5007profilesareincreasingly
prominent intheLINERsandSeyfertgalaxies.Weconclude that,inthelow-redshiftUniverse,"pure"star-formationactivitydoes
.
h notseemcapableofdrivingionized-gasoutflows,while,thepresenceofopticallyselectedAGNseemstoplayaprimaryroletodrive
p suchwinds.WediscusstheimplicationsoftheseresultsfortheroleofthequenchingmechanisminthepresentdayUniverse.
-
o Keywords. galaxies:general–galaxies:evolution–galaxies:ISM–galaxies:starformation–galaxies:nuclei–ISM:kinematics
r
t
s
a
1. Introduction energetic to eject the gas away from the galaxy potential well
[
andquenchthe star formation(see for instanceChevalier1977

1ThemoststrikingfeatureofthehistoryofourUniverseisadras- for energy-drivenoutflows, Murrayetal. 2005 for momentum-
vtic decreasein the star formationactivityof thegalaxypopula- driven outflows, and to Hopkinsetal. 2014 for effect of multi-
9tionbyalmostanorderofmagnitudeoverthelast10Gyr,aftera ple stellar feedback in cosmological simulations). Above stel-
6
phaseofhighandratherconstantactivity(e.g.Lillyetal.1996; larmasses of1012 M , instead,morepowerfuloutflowsarere-
5 ⊙
Madauetal.1998;Madau&Dickinson2014,foracomprehen- quiredtoletthegasescapefromthedeepergalaxypotentialwell.
6
sivereview).Whichprocessorwhichcombinationofprocesses, The energyand radiationgeneratedby accretiononto the mas-
0
.so called “queching"ofthe star formationactivity,causessuch siveblackhole(BH),inthemostmassivegalaxies,exceedsthe
1decreaseisstillmatterofanintensivedebate.Itisapparentthat bindingenergyofthegasbyalargefactor(seeFabian2012for
0identifyingthequenchinprocess(es)iscrucialforestablishinga a complete review). Therefore, energetic feedback from active
7
completeviewofhowgalaxiesevolveacrosscosmictime. galactic nuclei (AGN) is believed to provide an important and
1
: Accordingtothemostaccreditedgalaxyformationmodels, effective mechanism to eject the gas away by powerful winds,
vfrom the semi-analytical (SAM) ones to the more recent mass stop the growth of the galaxy and stifle accretion onto the BH
Xiabundance matching models, in the central galaxies, the effi- (DiMatteoetal.2005;DeLuciaetal.2006;Crotonetal.2006;
ciencyinconvertingthegasfractioninstarsreachesamaximum Hopkinsetal.2006;DeBoweretal.2006;Hopkinsetal.2014;
r
aat halo mass ∼ 1012 M with only ∼ 20 % of their baryons Henriquesetal.2016).
⊙
currently locked up in stars (see for example Crotonetal. However,althoughthesemodelsareverysuccessfulinrepro-
2006; Guoetal. 2011 based on the Millennium Simulation, ducing a large variety of observational evidence, in particular,
and Mosteretal. 2010; Behroozietal. 2010; Yangetal. 2012 the evolution of the stellar mass function (e.g. Henriquesetal.
among the mass abundance matching models). The efficiency 2016),theystilllackaclearobservationalconfirmation.Indeed,
drops down steeply towards both sides of this mass threshold a lot of effort has been spent in the last decade from the ob-
(e.g.Madauetal.1996;Baldryetal.2008;Conroy&Wechsler servational point of view to observe the presence of such out-
2009;Guoetal.2010;Mosteretal.2010,2013;Behroozietal. flows at any mass scale and to study their effect on the evolu-
2010, 2013). There is an overall agreement, from the theoreti- tion of the galaxy star formation activity to identify a possible
cal point of view, that below halo masses of 1012 M , the de- relationof cause and effect. Steideletal. (2010) observeblue-
⊙
creasing SF efficiency is likely to be due to gas eating and re- shiftedLyman-αemissioninmostoftheSFgalaxypopulationat
movalassociatedwiththestarformationactivity.Indeed,galac- redshift∼2andassociate suchemissionlinedisturbancetoSF-
ticwindsdrivenbytheenergyandmomentumimprintedbymas- induced outflow (see also Erb 2015 for different emission line
sivestarstothesurroundingISM,arebelievedtobesufficiently study).Atsomewhatlowerredshift,butinalargeredshiftwin-
Articlenumber,page1of13
A&Aproofs:manuscriptno.outflow_SDSS_referee_final_arxiv
dow (0.5 < z < 1.5), Martinetal. (2012) use UV rest-frame
absorption features to identify blue-shifted components as in-
dicationof outflow andfind evidenceof outflowingmaterialin
massive,highlystarforminggalaxies(seealsoRubinetal.2014
2 600
forsimilarstudies).
Powerful AGN-driven outflows are recently observed
500
both at low (e.g. Feruglioetal. 2010; Villar-Martínetal.
1
2011; Rupke&Veilleux 2011, 2013; Greeneetal. 2012; yr] 400
Mullaneyetal. 2013; RodríguezZaurínetal. 2013; M/O •
C20ic1o2n;eTeretmalo.nt2i0e1t4a)l.2a0n0d7;hBigruhsareedtsahl.if2t01(5e.;gP.erMnaaieotlainl.o2e0t1a5l;. R) [ 0 300ensity
F D
Crescietal. 2015). However, it is not clear yet if the AGN S
feedback,intheformofgalacticflows,isaspecificpropertyof og( 200
l -1
thebulkoftheAGNpopulationorifitconcernsonlyasubclass
100
of these objects Brusaetal. (2015). In addition, it is unclear if
they cause a quenching or an enhancement of the galaxy SF
-2 0
activity(e.g.Crescietal.2015).
9.0 9.5 10.0 10.5 11.0 11.5 12.0
Furthermore,new observationare revealingthe ubiquity of
log(M/M )
O •
SFinducedoutflowsinveryactivelystar-forminggalaxiesatall
cosmicepochs(seeVeilleuxetal.2005andErb2015foracom- Fig.1.SFR-M⋆planeforDR7SDSSgalaxies.Theblacksboxesrepre-
prehensiveoverview).Theyusuallyareassociatedwithenergetic sent the fine grid used for the stacking of the total sample.The white
line shows the position of the so-called "Main-Sequence" (MS) of
starburst phenomena (e.g. Heckmanetal. 1990; Pettinietal.
star−forminggalaxies.TheMSiscomputedasthemodeandthedisper-
2000; Shapleyetal. 2003; Rupkeetal. 2002, 2005a,b; Martin
sionoftheSFRdistributioninstellarmassbinsfollowingtheexample
2005, 2006; Hill&Zakamska 2014), while their impact in the
of(Renzini&Peng2015).
normal star-forming galaxies (Chenetal. 2010; Martinetal.
2012;Rubinetal.2014;Ciconeetal.2016)andtheirglobalef-
fectonthebaryoncycleisstilldebatedSteideletal.(2010). 2015; Carnianietal. 2015). Also, [OIII]λ5007 emission is
These studies have traditionally been carried out with rel- expected to lie in spectral regions free from strong stellar
atively small samples of galaxies. The availability of large atmosphericabsorptions.Intheserespect,itisexpectedthatthe
spectroscopic data sets such as the SDSS Yorketal. (2000), [OIII]λ5007 emission line can be used with great success to
allows to extend such studies dramatically in size. Signifi- identifyorconfirmgalacticwinds.Weexplorehowtheemission
cant improvement has been recently made in this regard (e.g. line profile changes as a function of key physical parameters:
Greene&Ho 2005; Chenetal. 2010; Mullaneyetal. 2013; stellar mass, SFR and primary photoionization processes (SF,
Ciconeetal. 2016). However, all these resent works have fo- AGN). In doing, we analyse both the presence of a second
cused only on a particular category of galaxies. For exam- broader Gaussian component and non-parametric variation of
ple, the optically-selected AGN in Mullaneyetal. (2013) and theline-profile.
Greene&Ho(2005)andthestar-forminggalaxieswithoutAGN
Thisworkis organizedasfollows.InSection2, we present
contributioninChenetal.(2010)andCiconeetal.(2016).
our sample selection and physical properties. In Section 3 we
The aim of this paper is to explore the global propri- describethemethodusedtoextractandanalyzethe[OIII]λ5007
eties of galactic winds in the local Universe a) by analyzing
emissionline fromourstackedspectra.We presentanddiscuss
their incidence in the galaxy population, b) by identifying themainresultsinSection4andfinallywesummarizeourfind-
the powering mechanism: star formation, AGN or a mixed ingsinSection5.Throughoutthispaper,weassumethefollow-
contribution of the two, and c) by clarifying what impact ingcosmologicalparameters:H =70kms−1Mpc−1,Ω =0.3
0 M
they might have on the galaxy SF activity. For this purpose andΩ =0.7
Λ
we investigate the outflow signatures in a large sample of
optical spectra at redshift z < 0.3, drawn from the Sloan
DigitalSkySurvey(SDSS;Abazajianetal.2009),byusingthe
2. Datasample
ionized gas as traced by the [OIII]λ5007 emission line. The
[OIII]λ5007 emission line is one of the strongest features in 2.1.SDSSspectra
the rest-frame optical 1D spectrum of both active star-forming
and AGN dominated galaxies. This line is produced through The galaxy sample analyzed in this paper is drawn from the
a forbidden transition emitted by low-density and warm gas SloanDigitalSkySurvey,(SDSS, Yorketal.2000).Inparticu-
(T∼ 104K). Thus, any disturbed kinematic, such as a broad- lar,weusethespectroscopiccatalogcontaining∼930,000spec-
ening and asymmetry of the [OIII] line, is only due to the trabelongingtotheseventhdatarelease(DR7,Abazajianetal.
presenceofstrongbulkmotionsofionizedinterstellargas(e.g. 2009). We use only objects includedin the Main Galaxy Sam-
for local galaxies Heckmanetal. 1990; Veilleuxetal. 1995; ple(MGS,Straussetal.2002)whichhavePetrosianmagnitude
Lehnert&Heckman1996;Sotoetal.2012;Westmoquetteetal. r < 17.77 and redshift distribution extends from 0.005 to 0.30
2012; Mullaneyetal. 2013; RodríguezZaurínetal. 2013; , with a median z of 0.10. The spectra cover a wavelength
Bellocchietal. 2013; Rupke&Veilleux 2013; Liuetal. range from 3800 to 9200 Å. They are obtained with 3′′ diam-
2013; Harrisonetal. 2014; Zakamska&Greene 2014; eteraperturefibersthat,intheadoptedcosmology,corresponds
Cazzolietal. 2014; Arribasetal. 2014; Ciconeetal. 2016, to≈0.31−13.36kpcfortheredshiftrangez=0.005−0.3.The
and at high redshift Shapiroetal. 2009; Newmanetal. 2012; instrumentalresolutionisR ≡ λ/δλ ∼ 1850−2200andamean
Harrisonetal. 2012; Cano-Díazetal. 2012;Genzeletal. 2014; dispersionof 69 km s−1 pixel−1. Further details concerningthe
FörsterSchreiberetal. 2014; Brusaetal. 2015; Pernaetal. DR7spectracanbefoundathttp://www.sdss.org/dr7/.
Articlenumber,page2of13
A.Concas etal.:LightbreezeinthelocalUniverse
subsample number percent NBins
TOT 621990 100% 148
SF 128258 20.6% 88
Sy
SF-AGN 46081 7.4% 81
1.0
AGN-SF 69421 11.2% 119
LINERs 34640 5.6% 99
TYPE2 10679 1.7% 77
β) 0.5 unClass 332911 53.5% 132
H
OIII]/5007 0.0 Table1.Basicdataaboutthesubsamplesdiscussedinthetext.
g([
o
l SF AGNSF LINERs more exhaustivedetails). The SFR measurementsare based on
−0.5
the Brinchmannetal. (2004) approach.They use the Hα emis-
sionlineluminositytodeterminetheSFRs forthestarforming
galaxies.Forallothergalaxies,thathaveemissionlinescontam-
−1.0 SFAGN
inated by AGN activity or not measurable emission lines, the
−1.5 −1.0 −0.5 0.0 0.5 SFRsareinferredbyD4000-SFRrelation(e.g.Kauffmannetal.
log([NII] /Hα) 2003b). All SFR measures are corrected for the fiber aperture
6584
followingtheapproachproposedbySalimetal.(2007).
Fig. 2. The distribution of the galaxies in our sample in the BPT
line-ratio diagram. The solid curve is the theoretical demarcation of Weapplyastellarmasscutatlog(M/M⊙) ≥ 9.0tolimitthe
Kewleyetal. (2001) , that separates star-forming galaxies and com- incompletenessin thelow massregime(seealso Morsellietal.
posites from AGN. The dashed (Kauffmannetal. 2003a ) and dotted 2016). In this way, we ended up with a global sample of ∼
Stasinskaetal. (2006) curves indicate the empirical division between 600000galaxies.
composite SF-AGN and AGN-SF and the pure star-forming galax-
The galaxy sample is shown in the SFR-stellar mass plane
ies, respectively (seetext for more details).The horizontal lineat log
in Fig.1. The color code is according to the number density of
([OIII]/Hβ) = 0.5 is the demarcation criteria between TYPE 2 (or
galaxiesper bin of SFR and stellar mass. We overplotalso the
Seyfert,Sy)andLINERsgalaxiesshowedinKewleyetal.(2006).
Main Sequence od star forming galaxies (MS hereafter), esti-
matedasthepeak(mode)ofthedistributioninthestarforming
galaxyregion,similarlytoRenzini&Peng(2015).
2.3.BPTclassification
2
SF
Emission line diagnostic diagrams are a powerful way
SFAGN
to probe the nature of the dominant ionizing source in
1 AGNSF
galaxies. Baldwin,Phillips,&Terlevich(1981, BPT) and after
r] LINERs
y themVeilleux&Osterbrock (1987) demonstrate that it is pos-
M/O • Sy sible to distinguish normal star-forming from AGN dominated
) [ 0 galaxiesby considering two pairs of emission lines ratios. The
R
F MPA-JHU catalog also includes, for each single spectrum, the
S
( flux measurements of [OIII]λ5007, Hβ, Hα and [NII]λ6584
g
lo -1 emissionlines.Asshowedin Stasinskaetal.(2006),thegalax-
ies that lie in the left side of the Kauffmannetal. (2003a) de-
marcation line includes also objects that have an AGN con-
-2 tamination.In order to better segregatethe purely star-forming
9.0 9.5 10.0 10.5 11.0 11.5 12.0 galaxies from AGN hosts, we refine the BPT classification of
log(M/M ) our sample instead to using the selection criteria performed
O •
by Brinchmannetal. (2004). By using the two optical line
Fig.3.LocationofSF,SF−AGN,AGN−SF,LINERs,TYPE2(orSy) ratios:[OIII]λ5007/Hβand[NII]λ6584/Hα,then,wedefinenew
galaxiesintheSFR-M plane.Fromoutsidetoinsidethecontoursen-
⋆ galaxiessubsamples on the basis of the prevalence of different
compass25,50and75percentofthedatapoints.Theblacklineshows
photoionization processes. All galaxies with no or very weak
themodeanddispersionoftheMS.
emissionlines(S/N < 4)arenotclassifiedintheBPTdiagram
andwecalltheseobjects"unClass".ForthelineswithS/N >4,
2.2.Starformationratesandstellarmasses weadoptedthefollowingclassesofemissionlinenebulae:
Weadoptthestarformation-stellarmassplane(hereafterSFR-
SF Pure star-forminggalaxies,objectswith emission line ratio
M ) in order to classify galaxies in their fundamental proper-
⋆ belowtheStasinskaetal.(2006)curve.
ties. Inordertodefinethepositionforeachgalaxyinthe SFR-
M plane, we use the SFR and M measurements taken from
⋆ ⋆
the MPA-JHU catalog1. Thestellar massesare obtainedfroma SF−AGN The objects whose emission lines are due primarily
fit tothe spectralenergydistribution(SED) byusingthe SDSS to star formationactivity but thathave also a secondminor
broad-bandopticalphotometry(seeKauffmannetal.2003bfor componentduetoAGNpresence.Theyarelocatedbetween
theStasinskaetal.(2006)andKauffmannetal.(2003a)de-
1 http://www.mpa-garching.mpg.de/SDSS/DR7/ markationlines.
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AGN−SF The composite transition region objects that lying
inside the region defined by Kauffmannetal. (2003a) and
Kewleyetal.(2001)curves. EQW Å S/N
0.0 0.5 1.0 1.5 2.0 2.5 3.0 5 10 15 20 25 30
Type2(orSeyfertgalaxy,Sy)AGNandLINERs All the ob-
jectslocatedabovethediagnosticsoutlinedofKewleyetal.
(2001) and separated in Seyfert galaxies and and low- 1
ionization nuclear emission-line regions (LINERs) with M/yr]O •
tlhoeg([dOeImIaI]r/cHatiβo)n=c0r.i5te.ria showed in Kewleyetal. (2006), R) [ 0
F
S
The corresponding diagnostic diagram is shown in Fig. 2. og( -1
l
Wesplitthetotalsampleinsixclasses:SF,SF−AGN,AGN−SF,
-2
LINERs,TYPE2andunClass(cf.Table1).InFig.3wereport
9.0 9.510.010.511.011.512.09.0 9.5 10.010.511.011.512.0
the contourlevelsat25%,50%and75%of thedistributionfor log(M/M ) log(M/M )
O • O •
thefiveBPTclasses,labeledindifferentcolors,intheSFR-M Fig.6.EQW(leftpanel)andtotallinesignal-to-noiseratio,SNR(right
⋆
plane. panel) in the SFR-M⋆ diagram for the total sample. The white line
Throughoutthe paperwe willalso comparethe aboveBPT showsthemodeanddispersionoftheMS.Thegalaxybinswhittotal
emissionlineSNR<8areplottedingreycolor.
classeswiththeTYPE1AGNdefinedinMullaneyetal.(2013).
Due to the dominating AGN contribution, a measurement of
the SFR and stellar mass derived from the spectra and optical
broadbandphotometryisnotavailableforsuchclassofgalax- each bin. However, we check the the error is very stable from
ies. Therefore, they can not be placed in the SFR-stellar mass themostpopulatedbins(∼4000galaxyspectra)tothelesspop-
plane. ulatedones(50galaxies).
3. Method 3.2.Fittingthestellarcontinuum
In this section, we describe how we measure the properties of Inordertomeasurereliablyalso theweakemission linesemit-
the[OIII]λ5007emissionline. ted by the ionized gas, the stellar continuum must be properly
removed. To this purpose, we use the penalized pixel-fitting
(pPXF)algorithm,whichisapubliclyavailableIDLcode,devel-
3.1.Stackedspectra
opedby Cappellari&Emsellem (2004) to find the best fit stel-
Theauroral[OIII]λ5007emissionlinecanbeveryfaintandtyp- lar continuum and separate the nebular emission lines in each
icallyundetectableinmostSDSSgalaxyspectra.Toreducethe stacked spectrum. In brief, pPXF is able to parameterized the
contribution of random fluctuations in the measured flux and line-of-sight velocity distribution (LOSVD) through a Gauss-
then improve the signal-to-noise ratio (SNR) we perform our Hermite expansion of the absorption-line profile by fitting the
analysisinstackedopticalspectra.Inparticular,weusetheme- stellarcontinuumwithasetoflinearcombinationofsimplestel-
dian stacked spectra taken from Concas et al. in prep. In brief, larpopulation(SSP) inputmodelspectra.InthepPXFanalysis
we dividethe SFR-M parameterspace into small bins,shown weadoptalibraryoftemplatespectrabasedonthestellarpopu-
⋆
in Fig.1. The boundaries of this grid together with the abun- lation models from Bruzual&Charlot (2003), hereafter BC03.
dance of sources per bin, are chosen to provide a fine sam- BC03 models are available at a resolution of 3 Å FWHM in
pling of the SFR-M plane and at the same time to have good the wavelength range between 3200 − 9500 Å, which is very
⋆
statisticsineachbin.Weadoptbinsof∆log(M/M ) = 0.2and similar to the one of SDSS spectra (≈ 1800 − 2000 between
⊙
∆log(SFR) = 0.2 dex for the total sample and larger bins for 3800 to 9200 Å). Our templates include simple stellar popula-
the analysis of the individual BPT classes, where the statistics tion with age 0.01 ≤ t ≤ 14 Gyr and four different metallic-
is reduced. We request a minimum of 50 galaxies in each bin. ity, Z/Z = 0.2,0.4,1,2.5by assuming a Chabrier (2003) ini-
⊙
ThegalaxyspectraarefirstcorrectedfortheforegroundGalactic tial mass function (IMF). We perform the pPXF analysis for
reddeningusingtheextinctionvaluesfromSchlegeletal.(1998) eachstackedspectruminthewavelengthrange:[4800,5050]Å,
then they are transformedfromvacuumwavelengthsto air and wheretheHβ,[OIII]λ4959,5007emissionlinesarelocated.The
shiftedtotherestframe.Wenormalizeeachspectrumtothestel- results are a best-fit stellar continuum.For each galaxy bin we
larcontinuumwiththemeanfluxfrom6400Åto6450Å,where subtractthebest-fitstellarcontinuumfromtheobservedstacked
thespectrumisfreeofstrongemissionandabsorptionlines.Fi- spectrum. This "residual" spectrum is used for any analysis of
nally,the rest-framespectra in each bin are stacked togetherto [OIII]λ5007 emission line features. An example of the fitting
produceasinglemedianspectrum.Weobtain148galaxystacked procedureresultisshowninFig.4,whichshowstheverygood
spectraforthetotalsampleand88,81,119,99,77and132for agreementoftheobservedandthemodelcontinuumoveralarge
thesubclassesdescribedinsection2.3.Thedifferentnumbersof wavelengthrangeinthe[OIII]emissionlineregion.Inorderto
stackedspectrabetweenthetotalsampleandthesubsamplesis checkthestabilityofthefittingprocedureandtoestimatetheer-
due to the fact thattowardsthe quiescenceregionless and less roroftheresidualspectrum,weapplyabootstrappingtechnique
galaxiescanbeclassifiedintheBPTdiagram.Insuchregionof by performing the fit on the sample of bootstrapped stacked
the SFR-M plane we analyze the [OIII]λ5007 profile only in spectra in each SFR-stellar mass bin (see previous paragraph).
⋆
thestackedspectrumofthetotalsample. The stability of the procedureis confirmed by the fact that the
Theerrorofthestackedspectraisobtainedthrougha boot- erroroftheresidualspectrumisconsistentoronlyslightlylarger
strappinganalysis.Thestatisticalerrorobtainedinthiswayde- (atmaximum30%)withrespecttotheerrorofthestackedspec-
pendsonthenumberofspectrausedinthestackinganalysisin tra. As an example, the panel a) of Fig. 5 shows the residual
Articlenumber,page4of13
A.Concas etal.:LightbreezeinthelocalUniverse
11..11
Hβ [OIII]4958 [OIII]5007
11..00
x
u
fl

e
00..99
v
ti
a
el
r 00..88 obs
best−fit model
00..77
0.5
0.4
al 0.3
u
d
0.2
si
e
0.1
r
0.0
4800 4850 4900 4950 5000 5050 5100
wavelength [Å]
Fig.4.ExampleofourcontinuumfitandsubtractionperformedforthestackedspectrumwhitSFR=100.2M yr−1 and M = 1010.5M .Thetop
⊙ ⋆ ⊙
panelshowstheobservedstackedspectrum(blackline)andourbest-fitstellarcontinuummodel(redline).Thelightgrey-shadedregionsindicate
thewavelengthrangewheretheHβ,[OIII]λ4959and[OIII]λ5007emissionlinesarelocated.Thebottompanelshowstheresidualspectrum(cyan
line)andtheleveloffluctuationsinthefitresiduals(dashedline).
spectruminthe[OIII]λ5007emissionlineregion.Thequalityof 3.3.1. Profilefitting
ourcontinuumfitisguaranteedbythelowlevelof fluctuations
inthefitresiduals(dashedlinesinFig.5).Theerroroftheresid- We fit the [OIII] line profile in the residual spectrum with one
ualspectrumis,then,usedtoestimatetheSNRoftheemission and two Gaussian components by using an IDL MPFIT fitting
code.Inbothcaseswefitthelinecenter,widthandamplitude.
lineintheresidualstackedspectra.
The single Gaussian fit allows to estimate the global line
For comparison we show also the result of the continuum width,σ[OIII] andtheSNRoftheline.Theobservedσobs ofthe
subtraction method applied by Mullaneyetal. (2013) on the lineis the convolutionof the realwidth ofthe emitted line and
TYPE1 AGN sample ( Fig. 5, panel b). They use, in particu- the instrumental resolution. To remove the instrumental effects
lar, the single continuum subtracted spectra , provided by the wecorrecttheσ whitσ = σ2 −σ2 ,whereσ2 is
obs [OIII] q obs inst inst
SDSSpipeline.Whilethismethodturnsouttobereasonablefor the instrumentaldispersion. For SDSS data the σ change as
inst
AGNspectrawheretheemissionlinehasaveryhighSNRwith a function of wavelength, and it varieswith the location of the
respect to the continuum, it is not applicable to galaxy spectra objectontheplateandthetemperatureonthenightoftheobser-
withlowerSNRemissionlines,asintheconsideredcase. vations.Therefore,inordertousethecorrectσ foralltheour
inst
stackedspectra,weusetheinstrumentalresolutionmeasuredfor
eachsinglespectrumfromtheARClampsprovidebytheMPA-
JHU group. The mean σ in the [OIII] wavelength range for
3.3.Measuring[OIII]λ5007emissionlineprofiles inst
oursampleis∼60kms−1.
The double Gaussian fit allows to estimate the significance
Weanalyzetheoxygenlineshapewithtwodifferentapproaches: of a secondcomponentand its line profile. We take the double
a)byfittingthelinewithasingleandadoubleGaussiantoiden- Gaussianprofileasthebestfitforthe[OIII]lineprofilewhenit
tify a possible second broader component with respect to the leadstoareductionoftheχ2valuebymorethan30%.Thisisto
systemicone,andb)byadoptinganon-parametricanalysis.The avoidamisidentificationofasecondcomponentwhenthedou-
twomethodsarecomplementary.Thefirstoneallowsustostudy ble Gaussian fit provides two Gaussian components with con-
separately the variouscomponentsthat determine the observed sistentwidthandcenteranddifferentamplitude.Indeed,inthis
line,whilethesecondprocedureisindependenttotheparticular casethesumofthetwoGaussianwouldleadanyhowtoasingle
fittingfunctionanditisrelativelyinsensitivetothequalityofthe Gaussiancomponent.Wecheckthatareductionoftheχ2 value
data(seePernaetal.2015,Zakamska&Greene2014,Liuetal. byatleast30%isagoodthresholdtodistinguishtheneedofa
2013). doubleGaussianfit.
Articlenumber,page5of13
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1.0
a) b)
x
u 0.5
fl

e
v
ti
a
el
r 0.0
−0.5
4990 5000 5010 5020 4990 5000 5010 5020
wavelength [Å] wavelength [Å]
Fig.5.Average[OIII]λ5007profileofthegalaxysubsamplewhitSFR=100.2M yr−1 and M =1010.5M .Inpanela)weshowtheemissionline
⊙ ⋆ ⊙
derivedwithourmethod.Inpanelb)weshowtheemissionlineforthesameSFRand M galaxiesobtainedbythemethodof(Mullaneyetal.
⋆
2013).Theblacksymbolsaretheobservedflux.Themagentalinesillustratesthetwo-Gaussiancomponentandthebluecurveshowsthecombined
fit.Thelevelofscatterintheresidualsofourfitisshownwiththehorizontaldashedlines.Theverticalgraylinemarktherest-framepositionof
the[OIII]line.
When the doubleGaussian fit is retained as the best fit, we
useittoestimatea)theSNRofthesecondcomponenttocheck
its significance, b) to compare the flux percentage of the sec- SNR II gaussian % flux II gaussian
ond componentwith respect to the systemic contribution,c) to 0.0 0.5 1.0 1.5 2.0 2.5 3.00.0 0.1 0.2 0.3 0.4 0.5
estimatethevelocityshiftofthecentroidwithrespecttothesys-
temic redshift and d) to estimate the line width of second and
systemiccomponent. yr] 1
The errors on all measured quantities are obtained with a M/O •
bootstrappingtechnique.Thefitisrepeatedonthebootstrapping R) [ 0
sample (see previousparagraph)to obtainedthe distribution of F
S
all measured quantities and so the dispersion as an estimate of g( -1
o
theerror. l
-2
9.0 9.510.010.511.011.512.09.0 9.5 10.010.511.011.512.0
3.3.2. Non-parametricanalysis log(M/MO •) log(M/MO •)
Fig. 7. Signal-to-noise ratio, (SNR) and flux enclosed in the second
To have a model independent measurement of emission broaderGaussiancomponent(rightandleftpanel)intheSFR-M dia-
⋆
line profiles we also apply a non-parametric approach. gramforthetotalsample.Thewhitelineshowsthemodeanddispersion
This approach is commonly used in AGN outflows studies oftheMS.ThegalaxybinswhittotalemissionlineSNR<8areplotted
ingreycolor.
(Liuetal. 2013; Rupke&Veilleux 2013; Zakamska&Greene
2014;Harrisonetal.2014;Brusaetal.2015;Pernaetal.2015).
Briefly, we construct the cumulative flux of the line as a func-
tion ofvelocity: F(v) = v f(v′)dv′, in the observedspectrum W80 = v90 − v10, where v90 and v10 are the velocities
R−∞
withoutusinganyparticularfittingfunction.Then,wedescribe at which 90% and 10% of the line flux accumulates, re-
thevelocitywidth,asymmetryandthewingsprominenceofthe spectively. For a purely Gaussian velocity profile the W80
[OIII]linebyusingthefollowingnon-parametricquantities: is proportionalto the standard deviation (σ) and full width
athalfmaximum(FWHM),asshowninthefollowingequa-
1. Velocity width.The velocity width, W80 , is the velocity tion,W80=2.563×σ=1.088×FWHM.ValuesofW80are
range that encloses 80% of the total flux. It is defined by giveninkms−1.
Articlenumber,page6of13
A.Concas etal.:LightbreezeinthelocalUniverse
B/T
0.1 0.2 0.3 0.4 0.5 0.6
22 22 22
yr] 11 yr] 11 yr] 11
/MO • /MO • /MO •
R) [ 00 R) [ 00 R) [ 00
F F F
S S S
g( --11 g( --11 g( --11
o o o
l l l
--22 --22 --22
99..00 99..55 1100..00 1100..55 1111..00 1111..55 1122..00 99..00 99..55 1100..00 1100..55 1111..00 1111..55 1122..00 99..00 99..55 1100..00 1100..55 1111..00 1111..55 1122..00
log(M/M ) log(M/M ) log(M/M )
Fig.10.Leftpanel:σ /σO • intheSFR-M⋆plane.AthighstellarmassthO •egaskinematicsfollowsthevelocitydispersionO •ofthestellarcom-
[OIII] ⋆
ponent.CentralpanelB/TmedianvaluesintheSFR-M⋆diagram.Thebulge-diskdecompositionistakenfromSimardetal.(2011)catalogue.
Weusethevalues calculatedwithther filter.Right panel: σ distributionintheSFR-M⋆plane. Atlow stellarmassestheσ isbelow tothe
⋆ ⋆
instrumentalresolution.Inallpanels,thewhitelineshowsthemodeanddispersionoftheMS.
Line wings r9050
v75−v25.InaGaussianprofiler9050isequalto2.4389,the
2.6 2.8 3.0 3.2 3.4
22 r9050increasesinprofileswithmoreextendedwings.
Theerroroneachquantitiesisestimated,asintheprevious
11 case, via bootstrapping analysis. Each quantity is measured in
yr] the bootstrapping sample related to each residual spectrum in
M/O • ordertoestimatethedispersionofthedistributionasameasure
R) [ 00 oftheerror.Thisisdone,inparticular,tocheckifeachquantity
SF deviatesmorethen3σfromthevaluecorrespondingtoaGaus-
og( sian distribution with the same width of the observed line. For
l --11
this purpose, we use the measure of the global line width esti-
matedwith thesingle Gaussianline profile,asexplainedin the
--22 previousparagraph.
99..00 99..55 1100..00 1100..55 1111..00 1111..55 1122..00
log(M/M )
O •
4. Results
Fig.8.Prominenceofthelinewingsr9050intheSFR-M diagramfor
⋆
thetotalsample.Thewhitelineshowsthemodeanddispersionofthe In this section we show our results for the total sample and
MS.ThebinsbelowM =1010.5M⊙haver9050valuesconsistentwith
⋆ forthefiveBPT classes:SF, SF−AGN,AGN−SF, LINERsand
2.44within3σ.ThegalaxybinswhittotalemissionlineSNR< 8are
TYPE2 AGNs. We show also the comparison with the TYPE1
plottedingreycolor.
AGNsampleofMullaneyetal.(2013).
4.1.[OIII]lineintheglobalsample
W80 [km/s] σ [km/s] Weanalysethelinefluxandshapeofthetotalsampleasafunc-
[OIII]
300 400 500 600 0 50 100 150 200 250 tion of position in the SFR-M⋆ diagram. Fig. 6 show the dis-
tributionofthe[OIII]λ5007equivalentwidth(EQW,leftpanel)
and corresponding signal-to-noise ratio (right panel), SNR, of
1
yr] the total emission line in the SFR-M⋆ plane. As expected, the
M/O • MS region is populated by the higher EQW values and higher
R) [ 0 SNR, while towards the passive region, the line is intrinsically
SF weak, with EQW ≤ 1 Å and low SNR, SNR≤ 8. In order to
g( -1 ensurearobustandaccuratemeasurementofthetotalemission
o
l
lineshape,weimposeaSNRlimitonthe[OIII]lineof8.Inlater
-2
figuresofthepaper,allbinswhittotalemissionlineSNR<8are
9.0 9.510.010.511.011.512.09.0 9.5 10.010.511.011.512.0
log(M/M ) log(M/M ) plottedingraycolorandtheyarenotconsideredintheanalysis.
O • O •
Fig. 9. Non-parametric w80 and σ (left and right panels, respec- WeusetheresultsofthebestGaussianfit,singleordouble,
[OIII]
tively), in the SFR-M diagram for the total sample. The white line to check the significance of the second Gaussian component.
⋆
showsthemodeanddispersionoftheMS. When a single Gaussian turns out to be the best fit, we set the
SNRofthesecondcomponentequaltozero.Whenthebestfitis
providedbyadoubleGaussian,weestimatetheSNRofthesec-
2. Asymmetry.ThedimensionlessparameterR=((v95−v50)− ondcomponentand the percentageof line flux encapsulatedin
(v50−v05))/(v95−v05)givesameasureoftheasymmetry thatcomponent.ThisisdoneineachbinoftheSFR-stellarmass
of the velocity profile relative to the median velocity. In a plane.TheleftpanelofFig.6showtheSNRofthesecondGaus-
perfectsymmetricprofileRisR=0 sian component,while the rightpanel shows the percentageof
fluxencapsulatedinit.DespitetheveryhighSNRofthe[OIII]
3. Linewings.Theprominenceofthelinewingsintheprofile line, the second broad Gaussian componentis only marginally
is the non-parametric analog of the kurtosis, with r9050= detectedwithaSNR∼2.5-3atmassesabove∼ 1010M andina
⊙
W90/W50, where W90 and W50 are the width comprising largerangeofSFR.Allowermasses,the[0III]lineisperfectly
90% and 50% of the flux, W90 = v95 − v05 and W50 = consistentwith a single Gaussian andnoadditionalcomponent
Articlenumber,page7of13
A&Aproofs:manuscriptno.outflow_SDSS_referee_final_arxiv
Thus, we conclude that there is only marginalevidence for
abroadcomponentinthe[OIII]λ5007emissionlineprofileand
!!""((
onlyinaspecificlocusoftheSFR-stellarmassplane.Whende-
!!""’’
tected,suchcomponentis centeredatthe systemicredshiftand
2
2 !!""&& thereisnoevidenceofablue-shift,asindicationofwind,asin
-
1 Mullaneyetal.(2013).MostofMSregioniswellrepresentedby
0 !!""%%
.*//* !!""$$ gpaolnaexnietswwitihthno[OaIsIyIm]pmroefitrlyeawnedllwfiittthedlobwykausritnogsliesvGaaluusessi.aOnncloyma-t
-
)*+, !!""## highmasses (1010.5−1011M⊙) we observea marginallyhigher
kurtosisandsothepresenceoflinewings.However,wedonot
!!""!!
find for these galaxies an excess of the line [OIII] width with
!!!!""## respecttothegalaxyvelocitydispersionprovidedbythestellar
SF SFAGN AGNSFLINERsTYPE2TYPE1 component.Indeed,onlyasmallpercentageofthe[OIII]fluxis
encapsulatedin the wings. This indicatesthat likely a low per-
centageofthegasinthesegalaxiesismovingawayinaverylow
velocitywind.
Fig. 12. Mean values of the flux percentage enclosed in the second
Gaussian component for all the BPT classes: SF,SF-AGN, AGN-SF, 4.2.TrendswithAGNandSFactivity
LINERs,TYPE2and TYPE1. Thefluxincreasing withtheincrease
of theAGNcontribution. Theerror barsshown thedispersion around The absence of significantoutflow signature in the globalpop-
themeanvalues. ulationdoesnotexcludethepossibilitythatstrongwindsmight
beobservedinspecificclassesofobjects.Inordertoinvestigate
thispossibilityin thissectionweanalyzethe[OIII]line profile
in the BPT subclasses, and so as a functionof differentioniza-
isneededtofitthelineprofile.Thefluxencapsulatedinthesec-
tion sources. As described in Section 2 we split oursample in:
ond broad component,though, is less than 10% in most of the
SF, SF−AGN, AGN−SF, LINERs, TYPE 2 and unClassgalax-
MSregion,withtheexclusionsofthehighestmassbins,whereit
ies. We perform a first analysis on the stacked spectra of each
reachesavalueof20%.Itreachesasimilarpercentage(20-25%)
subclassand,then,westudythestackedspectraasafunctionof
alsointheregionbelowtheMS,thesocalledgreenvalley.
thepositionintheSFR-M planeforeachsubclassseparately.
⋆
This is also confirmed by the non-parametricanalysis. The
Fig. 11 shows our multicomponent emission line fit to the
vaules of the line wings parameter, r9050, as a function of the
stacked [OIII] line profile of each subclass. It is immediately
position in the SFR-M⋆ plane, is shown in Fig. 8. The r9050
apparent, that the significance of a second broad and blue-
parameter is consistent with the value of a Gaussian function
shifted component is remarkably increasing with the increase
(r9050 ∼ 2.44)alongandaroundthe MSrelation,upto stellar
of the AGN contribution.While the star forminggalaxiespop-
massesof1010.5M .Thekurtosisisexceeding,withpoorsignif-
⊙ ulation show a symmetric Gaussian [OIII] line profile, the in-
icance(∼ 2σ),theGaussianvalueuptovaluesof2.9−3inthe
creaseofthenuclearactivityintheSF-AGNandAGN-SFleads
massrange1010.5−11 M ,wherethepercentageoffluxencapsu-
⊙ to the raise of significant line wings. LINERs, TYPE 2 and
lated in the broader componentis of 20-25%. For comparison,
TYPE1AGN,inparticular,showalsoaslightblue-shiftofthe
the kurtosisof a Lorentzianprofile, with strong wings, is 6.31.
broader component ( characterized by a velocity dispersion of
Inallbins,the[OIII]lineappearstobesymmetrical,withtypical
470.1±110.0,363.1±14.0and363.1±14.0km/s,respectively)
Rvaluesalwaysconsistentwith0within3σofsignificance.
withrespecttothesystemicvelocity(∆V < 70km/s)andcorre-
Fig.9showsthedistributionofthelinewidthintheSFR-M⋆ spondingnegativevaluesintheasymmetryparameter.Theflux
plane, estimated either with the dispersionσ[OIII] or the analo- enclosed in the second Gaussian component goes from 0% in
gousnon-parametricW80(rightandleftside,respectively).We the SF galaxies 48% in the TYPE 1 AGN, consistently with
observeaprogressiveincreaseofthelinewidthwiththegalaxy Mullaneyetal.(2013),asshowninFig.12.
stellar mass M⋆ at any SFR. This is expected since the [OIII] The study of the [OIII] line profile of the individual BPT
emissiontracesthegalaxypotentialwell.Wecomparethevalue classesasafunctionofthelocationintheSFR-stellarmassplane
of σ[OIII] in any bin of the plane with the mean galaxy veloc- showsthefollowingaspects:
itydispersion,estimatedfromtheabsorptionfeaturesduetothe
stellarcomponentprovidedbytheMPA-JHUpubliccatalog.The - SF galaxies, dominating the MS region up to masses of
leftpanelofFig. 10showsthatathighstellar masses, the ratio 1010.8M ,arecharacterizedbyapurelyGaussian[OIII]line
⊙
betweenσ[OIII] andthegalaxyvelocitydispersionisconsistent profile with no evidence of a second broader component.
with1.Onlyatlowermasses(<1010.5 M⊙)theratioincreasesto This is confirmed by the fitting procedure and by the non-
highervalues.Howeverinthisregionnoneofthepreviousindi- parametric method that indicates values of asymmetry and
cators(fluxenclosedinthesecondbroadercomponent,asymme- linewingsconsistentwiththeGaussianvalueswithin1.5σ.
tryR or thekurtosisr9050)showssignatureofa nonGaussian
lineprofile.Thus,weascribesuchincreasetotwofactors:a)the - SFgalaxieswithasmallcontributionfromthecentralAGN
galaxies in this region tend to be pure disks, as shown by the (SF-AGN) show evidence of a second broader component
meanB/Tof∼ 0.1asderivedfromSimardetal.(2011,central only at the 2σ level. Such galaxies,as shownin Fig. 3, are
panelofFig.10),thusthegascouldshowadifferentkinematics mainlylocatedintheMSregionatstellarmasses>1010M .
⊙
thanthestellarcomponent;b)inthisregionofthediagram,the
MPA-JHU public catalog provide values of the stellar velocity - galaxies with a dominating AGN contribution (AGN-SF)
dispersionlowerthantheSDSSresolutionof70km/s,whichwe show evidence of a second broadercomponentat more the
assumeasalowerlimit.(rightpanelofFig.10). 3σonlyonandabovetheMS.
Articlenumber,page8of13
A.Concas etal.:LightbreezeinthelocalUniverse
Velocity Offset [km s−1] Velocity Offset [km s−1] Velocity Offset [km s−1]
−1000 −500 0 500 1000 −1000 −500 0 500 1000 −1000 −500 0 500 1000
11..00 11..00 11..00
SF SFAGN AGNSF
% flux II gauss = 0.00 % flux II gauss = 0.12 % flux II gauss = 0.23
00..88 00..88 00..88
R = 0.01+−0.02 R = 0.06+−0.03 R = −0.01+−0.04
e flux 00..66 rw98005 0= =2 6 25..4974+ [−km0. 0s4−1] e flux 00..66 rw98005 0= =3 7 20..7098+ [−km0. 0s7−1] e flux 00..66 rw98005 0= =4 6 21..9409+ [−km0. 0s8−1]
ativ 00..44 ativ 00..44 ativ 00..44
el el el
r r r
00..22 00..22 00..22
00..00 00..00 00..00
44999900 44999955 55000000 55000055 55001100 55001155 55002200 55002255 44999900 44999955 55000000 55000055 55001100 55001155 55002200 55002255 44999900 44999955 55000000 55000055 55001100 55001155 55002200 55002255
wavelength [Å] wavelength [Å] wavelength [Å]
Velocity Offset [km s−1] Velocity Offset [km s−1] Velocity Offset [km s−1]
−1000 −500 0 500 1000 −1000 −500 0 500 1000 −1000 −500 0 500 1000
11..00 11..00 11..00
LINERs TYPE 2 TYPE 1
% flux II gauss = 0.27 % flux II gauss = 0.29 % flux II gauss = 0.48
00..88 00..88 00..88
R = −0.05+−0.04 R = −0.04+−0.01 R = −0.04+−0.06
e flux 00..66 rw98005 0= =5 7 26..9139+ [−km0. 1s0−1] e flux 00..66 rw98005 0= =4 9 25..9598+ [−km0. 0s2−1] e flux 00..66 rw98005 0= =6 4 38..1322+ [−km0. 1s4−1]
ativ 00..44 ativ 00..44 ativ 00..44
el el el
r r r
00..22 00..22 00..22
00..00 00..00 00..00
44999900 44999955 55000000 55000055 55001100 55001155 55002200 55002255 44999900 44999955 55000000 55000055 55001100 55001155 55002200 55002255 44999900 44999955 55000000 55000055 55001100 55001155 55002200 55002255
wavelength [Å] wavelength [Å] wavelength [Å]
Fig.11.Emission-lineprofilefitstocompositespectraindifferentclassesofphotoionizationprocesses:SF,SF−AGN,AGN−SF,LINERs,TYPE2
andTYPE1.Theblacksymbolsaretheobservedflux.Thefluxerrors,ineachpoint,areshowedinred.Thegreenlineshowsthesingle-Gaussian
fit.Themagentalinesillustratesthetwo-Gaussiancomponentandthebluecurveshowsthecombinedfit.Thelevelofscatterintheresidualsofour
fitisshownwiththehorizontaldashedredlines.Thesignificanceofasecondbroadandblue-shiftedcomponent(magentacurves)isremarkably
increasingwiththeincreaseoftheAGNcontribution.IneachpanelweshowthederivedvaluesoffluxenclosedinthesecondbroaderGaussian
component,asymmetryR,prominenceofthelinewingsr9050andw80.
Velocity Offset [km s−1] Velocity Offset [km s−1] Velocity Offset [km s−1]
−600 −400 −200 0 200 400 600 −600 −400 −200 0 200 400 600 −600 −400 −200 0 200 400 600
11..00 SUPMS MS SUBMS
SF
00..88 SFAGN
x AGNSF
u
e fl 00..66 LINERs
v TYPE 2
ati 00..44
el
r 00..22
00..00
44999955 55000000 55000055 55001100 55001155 44999955 55000000 55000055 55001100 55001155 44999955 55000000 55000055 55001100 55001155
wavelength [Å] wavelength [Å] wavelength [Å]
Fig.13.Variationoftheobserved[OIII]emissionlineprofileasafunctionoftheSFendAGNcontributionforgalaxieslocatedindifferentSFR
bins.Intheleft,middleandrightpanelsweshowthegalaxybinslocatedabove(SUPMS),inside(MS)andbelow(SUBMS)theMS,respectively
with∆SFR=0.4,0.0and−0.4dex.ThegalaxybinsshowedhaveM⋆=1010.5M⊙.The[OIII]emissionlineappearatanyM⋆andSFR
- LINERsandTYPE2galaxiesshowahighSNR(>3)second in the SFR-stellar mass plane. As shown in Fig. 14, SF-AGN
broader component independently on their location on the arepreferentiallylocatedathighSFRandstellarmasses,while
SFR-stellar mass plane. See Fig. 3 for their distribution in AGN-SFandLINERsdominatethegreenvalleyregion.Indeed,
theplane. afterremovingsuchgalaxiesfromtheglobalsample,thevalueof
thelinewingsparameterbecomesconsistentwiththeGaussian
- theresultsareconfirmedbythenon-parametricmethod.The
value all over the plane. This indicates that the deviation from
analysisoftheasymmetryRshowsthatfortheSFobjectthe
thepureGaussianbehaviorobservedinFig.8isduetogalaxies
linetendtobesymmetrical(R∼0)whileintheLINERsand
dominatedbytheAGNcontribution.Inturn,thissuggeststhat,
TYPE2weobserveR∼ −0.1,consistentwiththeresultsof
ifthe secondbroadercomponentis interpretedasanindication
Zakamska&Greene(2014)forasampleofSDSSobscured
ofgalacticwind,such windislikelydrivenbythe AGN,while
quasars.
SF seems notcapable of drivingany wind at any mass or SFR
An example of the AGN effect on the [OIII] line profile is value.
showninonemassbinabove(leftpanel),on(centralpanel)and Inordertobettercomparethe[OIII]linewidthwiththere-
below(rightpanel)theMSinFig.13. specttothegalaxyvelocitydispersioninthedifferentsubclasses,
The location of the AGN-SF, LINERs and TYPE2 AGNs weshowinFig.15the[OIII]linewidth,measuredbythestan-
perfectly matches the location of the plane where we observe darddeviationσ asafunctionofstellarvelocitydispersion
[OIII]
in the global population a line wings value slightly larger than σ foralltheionizationclasses:SF,SF−AGN,AGN−SF,LIN-
⋆
the Gaussian value. This is confirmed also by the BPT analy- ERsandTYPE2.Giventhatthemedianinstrumentalresolution
sis applied to the stacked spectra, as a function of the location of SDSS spectra is ∼ 70 km s−1 we restrict the analysis to the
Articlenumber,page9of13
A&Aproofs:manuscriptno.outflow_SDSS_referee_final_arxiv
UnClass SF SF+AGN AGN+SF TYPE 2 LINERs
22
11
yr]
/MO •
R) [ 00
F
S
g( SF
o --11
l SF+AGN
AGN+SF
LINERs
--22
TYPE 2
99..00 99..55 1100..00 1100..55 1111..00 1111..55 1122..00
log(M/M )
O •
Fig.14.BPTclassificationforthetotalsampleintheSFR−M⋆plane.
Fig.15.σ plottedagainstσ MPA-JHUmeanvaluesforthefive
[OIII] ⋆
binswithσ abovethislimit.Forclarity,wecollectourσ ionizationclasses(SF,SF−AGN,AGN−SF,LINERsandTYPE2).We
⋆ [OIII]
valuesinbinsofσ⋆,with∆σ⋆ = 20kms−1.Thedifferention- showthemediananddispersionvaluesofσ[OIII]andσ⋆inbinsofσ⋆,
ization sources are indicated with differentcolors as labeled in with∆σ⋆ = 20kms−1.FilledsymbolsaretheobjectsinthemainSF,
thefigure.Atfixedσ ,wefindthatthevelocitydispersionsmea- SF−AGN,AGN−SF,LINERsandTYPE2subsamples.Opentriangles
⋆ aretheunClassobjects.Thesolidblacklinedenotesσ =σ .
suredfortheionizedgasincreaseswiththeincreaseoftheAGN [OIII] ⋆
activityfromthe"pure"SFtotheTYPE2galaxies.
mass plane. A marginaldetection, at the ∼ 2σ level, is ob-
tainedonlyatstellarmasses> 1010.5M in alargerangeof
4.2.1. TheunClassobjects ⊙
SFR. This is confirmed by the observation of a line width
As mentioned in section 2.3, the unClass subsample includes parameter slightly larger (again at the ∼ 2σ level) than the
a large amount of galaxies that are impossible to classify indi- valuepredictedfora pureGaussianline profileinthe same
vidually using the BPT diagram. In order to take into account region of the plane. The line profile appears to be always
these large fraction of galaxies, we decide to performthe BPT symmetric, even when a second broader component might
analysisinthe medianstackedspectra.Followingthe approach contribute.Thefluxpercentageenclosedinthebroadercom-
of Concas et al. in prep. we use a combination of the publicly ponent,whendetected,isoftheorderto10%inmostofthe
availablecodespPXFCappellari&Emsellem(2004)andGAN- plane and it reaches values of 20-25% at very high masses
DALF Sarzietal. (2006) to fit and remove the stellar contin- andSFRandinthegreenvalley.
uumandtoderiveemissionlinefluxesofthefouremissionlines
used in the BPT diagram(i.e. Hβ, [OIII]λ5007,[NII],Hα). As – Thecomparisonofthelinewidthofthe[OIII]withtheveloc-
expected, the majority of the stacked spectra show very weak ity dispersion obtained from the absorption stellar features
emissionlines.Thesegalaxiesaremainlylocatedinthesocalled reveals a good agreement in most of the plane, indicating
quiescentregion.AthigherSFRvalues,alltheunClassstacked thatthe[OIII]tracestheunderlyinggalaxypotentialwellas
spectrashowallthefouremissionlines(Hβ,[OIII]λ5007,[NII] the stellar component. Only in few very low SFR and stel-
andHα)withS/N> 4toclassifythemintheBPT diagram.We lar mass bins we observed a disagreement, that we ascribe
checkthatthesegalaxiesfollowthesametrendshownbytherest tospectralresolutionissuesanddifferencesinthestellarand
ofthesample,withtheprominenceofthesecondbroadercom- gaskinematicsinpurelydiskgalaxies.
ponentincreasinginparalleltoinincreaseofthenuclearactivity
– The analysis of the [OIII] line profile as a function of the
contribution.
BPTclassificationrevealsthatforthe"pure"SFgalaxies,the
ionizedinterstellargastracedbythe[OIII]λ5007linenever
5. DiscussionandConclusions appearsto be outflowing.The line profile is perfectlyfitted
by a single Gaussian without need of a second component.
In this work we investigate the presence of galactic winds in a This holds in all the regions of the SFR-stellar mass plane
large spectroscopic sample of ∼ 600000 local galaxies drawn dominatedbySFgalaxies,suchastheMS.
from the spectroscopic SDSS DR7 database. In particular, we
usethedeviationoftheforbidden[OIII]λ5007emissionlinepro- – The significance of a second broader Gaussian component
filefromaGaussianasaproxyforthegalacticwinds.Weusethe increases with a clear trend with the increase of the AGN
spectral stacking technique to increase the SNR of the spectra contributiontothegalaxyspectrum,withamaximumforthe
and to determine how the average [OIII]λ5007profile changes AGN TYPE1 of Mullaneyetal. (2013). The flux enclosed
asafunctionofthekeygalaxyphysicalparameters,suchasSFR in thesecondcomponentrisessteadilyfrom0%in pureSF
andM .Wealsoexplorehowthelineprofilesrelatetothepartic- galaxyto∼48%intheTYPE1AGNs.
⋆
ularphotoionizationmechanisms:SForAGNactivity.Weana-
– The analysis of the [OIII] line profile of each BPT class in
lyzetheoxygenemissionlineprofilebyperformingalinefitand
theSFR-stellarmassdiagramshowsthatgalaxieswithanin-
anon-parametricanalysis.Ourmainresultscanbesummarized
creasingAGNcontributionoccupypreferentiallytheregion
asfollows:
ofthediagramwheretheglobalpopulationshowamarginal
– Intheglobalgalaxypopulation,wefindnoevidenceofasec- deviation from the Gaussian line profile: at high mass and
ondGaussianbroadercomponentinmostoftheSFR-stellar SFR and in the green valley. If AGN hosts are removed
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