Probing the reioniza.on epoch with ALMA Laura Pentericci INAF - Osservatorio Astronomico di Roma in collaboration with S. Carniani, A. Fontana, M. Castellano, et al. Physical characteris.cs of Normal Galaxies at z>2 Lorentz Center Workshop 19/10/2016
Why do we want to observe [CII]with ALMA? It is the strongest cooling line of the Interstellar medium (ISM) up to 1% of total FIR luminosity is emined in this line. It is not subject to neutral hydrogen absorp.on thus detectable in the reioniza.on epoch when Lyαα emission is increasingly suppressed for the majority of galaxies (LP +2014,2011,Schenker+2012,Ono+2012 etc ) It is a direct tracer of SFR (De Looze+2014, Sargsyan +2014) and not effected by dust as UV emission and Lyα ( but depends on metallicity ) It probes the systemic redshiz of the galaxies (important to determine ou\lows, modeling Lyα shape etc) Probes dynamical mass of the galaxy
Up to redshiz 5.5-6 [CII] is detected in many LAEs and LBGs and the [CII]- SFR rela.on seems consistent with the low redshiz one (Capak +2015, WilloN+2015, Knudsen+2016) Early ALMA & PdBI searches at z> 6.5 lead to non- detec>ons Ouchi et al 2013 Himiko z=6.6 (LAE) Ota et al. 2014 IOK- 1 z=6.96 (LAE) Kanekaer et al 2014 HCM6A z= (LAE) Maiolino et al 2015 - - BDF3299/BDF521/SDF45 (LBGs) Schaerer et al. 2015 - - A1703- zd1/a1703- zd1 (LBGs) Gonzalez Lopez+2014 - - 2 SDF LAEs Knudsen+2016 - - MS0451- H z=6.7 (LAE) Watson+2015 - - A1689- zd1 no [CII] but con.nuum detec.on Inoue+2016 - - SXDF- NB1006-2 (LAE) [OIII] detec.on but no [CII] Also a deep non- detec.on is obtained from stacking all z 7 sources (cf Ouchi - discussion)
Previous ALMA observa.ons at z 7 focussed on LAEs or LBGs with strong Lyα emission Our sample à we selected bright (in UV) galaxies but with weaker Lyα emission. This was possible thanks to CANDELSz7 an ESO Large program with FORS2@VLT that allowed us to confirm the redshiz of high- z galaxies with Lyα EW as low as 3Å 7 galaxies at z>6.5 Only 4 observed during Cycle 3 EW/Å 3 44 10 6 27 15 15
Previous ALMA observa.ons at z 7 focussed on LAEs or LBGs with strong Lyα emission Our sample à we selected bright (in UV) galaxies but with weaker Lyα emission. This was possible thanks to CANDELSz7 an ESO Large program with FORS2@VLT that allowed us to confirm the redshiz of high- z galaxies with Lyα EW as low as 3Å 7 galaxies at z>6.5 Only 4 observed during Cycle 3 EW/Å 3 44 10 6 27 15 15
We obtain detec.ons for all 4 observed targets with S/N >4.5 *The detec.ons are marginally resolved. *We observed significant spa.al offset (>0.1 ) in 2 cases. *NTTDF6563 was observed on two separate runs (Cycle 2&3) and confirmed on both sets None of the galaxy is detected In the con.nuum SFR dust = 1.73 10 10L IR [L ] 6-7 M yr - 1 à SFR TOT SFR UV
Spa.al offsets are observed in many other cases: do we have an issue with ALMA astrometry or is this a physical effect? our 4 galaxies From lez to right: BDF3299@z=7.109 (Maiolino+2015), A383-5.1 @z=6.027 (Knudsen+2016), RXJ1347:1216@z=6.765(Bradac+2016) Some of the z 5.5 galaxies in Capak+2015 Cumula.ve distribu.on of radial separa.on between 16 ALMA sources and their HST near- IR counter- parts. Blue line is azer shizing the HST frame (Dunlop+2016)
Velocity offset Contrary to the Lyα emission line, the [CII] traces the systemic redshiz of the galaxies à We can measure the ΔV=z Lyα z systemic Values are 100 km/s à quite small for objects with MUV =- 21.5 compared to lower redshiz galaxies of similar brightness
Velocity offset vs M UV Compila.on of Δv Lyα at various redshizs z=7 LP+2016,[CII], Inoue+2015 [OIII], Sobral+2016 [HeII], Stark+2015 CIII] Maiolino+2015[CII], Bradac+2016[CII] For a given M UV the z 7 galaxies tend to have lower ΔV=z Lyα z systemic although the sta.s.cs is limited especially for faint sources z=6 Willot+2015,Knudsen+2016 [CII] z=3.8 Schenker+2013 z=3 LBGs and LAEs Erb+2014 z=3 deep stacks of VUDS sources Guaita+in prep. z=2 LAEs and LBGs Erb+2014
Offset vs Lyα EW Offset vs redshiz z=7 bright objects
Possible origin of smaller offset In shell models (Verhamme+2015,Gronke+2015) this is related to smaller neutral hydrogen gas column densi.es (N HI <10 20 cm - 2) and to reduced ou\low veloci.es Gallerani+2016 find evidence for ou\lowing gas gas with v out =180 km/s at z 5.5 by stacking the[cii] spectra by Capack+2015 and modelling the broad wing residuals (not yet doable with z 7 data) In many recent models connec.ng Lyα to LyC proper.es, small velocity offsets (of the Lyα line compared to systemic) are one indica.on of possible LyC leakers (Dijkstra+2016, Verhamme +2015). In galaxies with low neutral hydrogen column density and/or low covering factor there are some special routes that facilitate the escape of both Lyα and ionizing photons
A consequence of the smaller offsets (either for lower ou\lows or column densi.es) is that less neutral hydrogen in the IGM would be needed to explain the drop in the visibility of Lyα emission from z 6 to z 7 N H The fraction of Lyα photons, f trans, transmitted through a fully neutral IGM at z=10, as a function of outflowing velocity v sh for N H i = 10 20 cm 2 (red) and N H i =10 21 cm 2 (blue). Outflows of 50 km s 1 boost f trans (Dijkstra+2009) Comparison between observed Lyα EW distribu.on at z=7 and model predic.ons assuming v=200 km/s implies ΔΧ HI 0.51 (LP+2014)
The SFR- [CII] rela.on: do we see a [CII] deficit (or not)? Our galaxies(+bradac) are a factor of 3 less luminous in [CII] compared to local and z 5.5 galaxies with similar SFR. Is this (combined with the many undetec.ons) a solid indica.on of [CII] deficit? Some points to consider 1)SFR is the total of uncorrected UV + dust obscured SFR. Some objects could be shizing along the x- axis 2) Galaxies compactness: should we use surface brightness instead of [CII] luminosi.es? (cf Herrera- Camus+2015) 3) [CII] could be broader than ini.ally predicted - - early es.mates on limits where done using a width of 40-50km/s (e.g. Gonzalez- Lopez +2014, Ota+2014). Our highest S/N line has FWHM=250km/s 4)Metallicity effect
Supposing the deficit is confirmed what causes it? Model by Vallini+2015 (improved version of Vallini+2013) Emission from cold and warm neutral medium + PDR regions Constant distribu.on of metallicity in the gas/ metallicity scales with density Very high spa.al resolu.on (60 pc) Includes increased effect of CMB on the [CII] Lines Emission from PDR regions dominate Possible explana.ons of the observed [CII] deficit are 1) Nega.ve stellar feedback: the molecular clouds in the central parts of primordial galaxies (sites of strong star forma.on) are rapidly disrupted by stellar feedback. As a result [CII] emission arises only from more external accre.ng/satellite clumps of neutral gas. This effect can explain the spa.ally offset emission in some galaxies between the center of SF and that of CII emission. 2) Low gas metallicity 3) A combina.on of the above
Simulation of a primeval galaxy at z = 7.1 with SFR similar to BDF3299. (a) The distribution of column density of ionized gas (which emits Lyα) is shown in colours The black points show the distribution of young stars (UV continuum, which dominates the Y-band emission in our images). The contours show the emission of [C ii] tracing the neutral gas (distributed in clumps orbiting/accreting the primary galaxy). (b) Same as the top panel but the ionized gas has been convolved with the angular resolution of ground based images (0.5 arcsec) and the [C ii] map has been convolved with the ALMA beam of our data. a b (c) Integrated [C ii] spectrum from the whole simulation. c Maiolini+2015, Vallini+2015
Do we see a trend in terms of galaxy proper.es? Lyα eminers have limits that point to lower [CII] emission The 3 red dashed lines are models from Vallini+2015 with different metallici.es (0.2 Z /0.1 Z 0.05Z ) Blue points: low Lyα EW à Z 0.1 Z (including the new Bradac+2016 lensed galaxy) Green points intermediate EW à Z<0.1 Z Red points: high Lyα EW> 50 Å à Z<0.05Z Lyα eminers are believed to have lower metallicity compared to the general LBG popula.on LAEs at z 2.5 have average 0.2 Z with some of the faintest being consistent with 0.02-0.05 Z (Trainor+2016) (see also Erb+2014,Erb+2016 Also consistent with the recent detec.on of [OIII]88μm in the LAESXDF- NB1006-2, at z=7.215 and with high Lya EW (>75 Å). This galaxy shows no [CII] emission implying high [OIII]/[CII] ra.o (Inoue+2016). Such high ra.os are observed in local metal poor dwarf galaxies (Cormier+2015)
Can we use [CII] efficiently to determine the redshiz when the Lyα line is not present e.g. during the reioniza.on epoch for the large majority of galaxies? From CANDELSz7 we have selected the 9 brightest confirmed i- drop (z=5.81-6.35) (DeBarros+in prep) with visible con.nuum + Lyman break (or very weak Lyα) such that the redshiz is constrained to bener than 0.14. Approved for Cycle 4 observa.ons For these galaxies we don t need spectral scanning since the redshiz is already reasonably well constrained by our ultra- deep spectra.
New ALMA observa.ons of BDF3299@z=7.109 the [OIII]88μm emission is detected with S/N=5.5 spa.al and 6.5 spectral 0.3 The [OIII] line is offset both spa.ally (0.3 compared to near- IR emission) and in velocity (+400 Km/s compared to Lyα) The [OIII] and [CII] emission are offset compared to the HST image but also not co- spa>al between them. In the inset the emission from a bright nearby serendipitous source showing the good alignment between the [CII] and [OIII] maps à the offset is real (Carniani et al. in prepara.on)