Atomic Carbon and CO at redshift 2.5

A. Weiss IRAM , D. Downes IRAM, C. Henkel MPIfR & F. Walter MPIA

Introduction:

Atomic Carbon:

Investigating the dense interstellar medium in high redshift galaxies is of fundamental importance forour understanding of the early phase of galaxy formation and evolution. Recent studies have revealedthe presence of huge molecular gas reservoirs (>10 SM) in distant objects, which show that thereservoirs for powerful starbursts are present in the early universe. So far, molecular gas has beendetected in about 25 sources at z>2, out to redshift z=6.4 (Walter etal 2003, Bertoldi etal 2003).

The brightest and most common tracer for molecular gas in CO. Multi transition studies of CO can beused to constrain the physical properties of these early gas reservoirs. Observations of CO only,however, do not allow to solve the ambiguity between gas temperature and density in radiative transfermodels. The classical approach to use optically thin CO is not feasible in high-z sources given currenttelescope sensitivity limits.

Observations of neutral carbon (CI) can help to circumvent these problems. Because the 3P fine-struc-ture system of carbon forms a simple three-level system, detections of both optically thin carbon lines,CI(1-0) (492GH) and CI(2-1) (809GHz) allow us to derive the excitation temperature and neural carbonmass independently of any other information (Weiss etal. 2003). Recent studies in the local universe haveshown, that CI is closely associated with CO emission independent of the environment (e.g.Gerin &Phillips 2000, Israel & Baas 2002). Since the critical density for the CI lines and CO(1-0) are similar,this finding suggests that the transitions arise from the same volume and share similar excitationtemperatures (e.g. Ikeda 2002). Therefore the excitation temperature determined from the carbon linescan also be used to solve the ambiguity between the gas temperature and density from CO observationsand thus allow to pin down the physical properties of the molecular gas.

Here we present an in depth study of the molecular properties using CI and CO in the three brightestCO emitters know today at redshift z>2: the Cloverleaf Quasar (z=2.56), IRAS F10214 (z=2.28) and theScuba submm source SMMJ14011 (z=2.57)

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The Cloverleaf QSOThe Cloverleaf is a Broad-Absorption Line (BAL) QSO and is the brightest and best-studied high-z COsource. We detected both carbon fine structure lines using the 30m telescope (CI(1-0) and Bure (CI(2-1) .The data is shown in Fig.1. Our new 30m spectrum agrees well with the first detection of the C(1-0) line by

) )

Barvanis etal. (1997). Note that the Cloverleaf is only the second extra galactic source where both carbonline have convincingly been detected. Our analysis shows that both carbon lines are optically thin. Theirline luminosity ratio is about 0.5 which results in an excitation temperature of T = 30 K. The total mass

of atomic carbon adds up to 7.6 10 SM (using a concordance cosmology and correcting for a magni-fication of m=11 (Venturini & Solomon 2003)).

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IRAS F10214:is a QSO We detected

carbon fine structure line using the 30m telescope

The data is shown in Fig. 3. TheCI redshift is in agreement with the CO redshift. So far we did notobtain observations of the upper fine structure line. The total massof neutral carbon corrected for the magnification of 15 is 1.8 10 SM.

Together with the lower carbon line we observed the CO(3-2),CO(4-3) and the CO(7-6) transitions. The spectra and the measuredfluxes are shown in Fig. 4. Similar to the CO lines in the Cloverleaf,the CO line SED in F10214 is described by a single gas component.Since we do not have an estimate on the excitation temperature ofCO via CI, we can not solve the ambiguity between gas temperatureand density. The turnover of the CO line SED occurs at the CO(6-5)line. This sets a lower limit to the H density of log(n(H )) > 3.5 cm . Temperatures range between 20K

and 80 K. Since the density is not well constrained also the total molecular gas mass is unconstrainedin the LVG models. The models, however, do constrain the CO(1-0) line luminosities. Using a ULIRGconversion factor of 0.8 SM (K km/s) the total H mass adds up to 6.2 10 SM. The size of the

molecular emission region is also fairly well constrained resulting in a radius between 400pc and800pc. The line luminosity ratio between the CI(1-0) / (CO(1-0) of 0.2 suggests that also for F10214the molecular gas properties are similar to those found in local galaxies. This is supported by ourestimate of the carbon abundance of X[CI]X[H ] = 4.9 10 – similar to the Galactic carbon abundance.

F10214 Type II narrow line at z=2.28. thelower , CI(1-0), .Our new spectrum does not confirm the claimed CI(1-0) detectionby Brown & Vanden Bout (1992).

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CI(1-0) 30m

Fig 3: Spectrum of the CI(1-0) ine inF10214 obtained at the 30m telescope.

References:Barger A.J. Cowie, L.L., Smail, I. etal. 1999 AJ, 117, 2656Barvainis, R., Maloney, P., Antouncci, R., & Alloin, D. 1997, ApJ, 484, 695Bertoldi, F., Cox, P., Neri, R., etal. 2003, A&A, 409, L47Brown, R.L., & Vanden Bout, P.A. 1992, ApJ, 397, L11Downes, D., & Solomon, P.M. 1998, ApJ, 507, 615Downes,Frayer, D.T., Ivision, R., Scoville, N.Z., Etal. 1999, ApJ, 514, L13Frerking, M.A., Keene, J., Blake, G.A., & Phillips, T.G. 1989, ApJ, 344, 311Gerin, M., & Phillips, T.G. 2000, ApJ, 537, 644

D., & Solomon, P.M. 2003, ApJ, 528, 37

Ikeda, M., Oka, T., Tatematsu, K., etal. 2002, ApJS, 139, 467Ivison, R.J., Smail, I., Barger, A.J., etal. 2000, MNRAS, 315, 209Israel, F.P., & Baas, F., 2002, A&A, 383, 82Solomon, P.M., Downes, D., & Radford, S.J.E. 1992, ApJ, 398, L29Venturini, S., & Solomon, P.M. 2003, ApJ, 590, 740Walter, F., Bertoldi, F., Carilli, C.L., etal. 2003, Nature, 424, 406Weiss, A., Henkel, C., Downes, D., & Walter, F., 2003, A&A, 409, L41Weiss, A., Downes, D., Henkel, C., & Walter, F., 2004, submitted to A&A

Together with the CI(1-0) transition we obtained spectra of the CO(3-2), CO(4-3), CO(5-4), CO(6-5) andCO(8-7) transitions (Fig 2). The CO(6-5) and CO(8-7) lines have been detected for the first time in theCloverleaf QSO. The CO line SED (flux density vs rotational quantum number) is shown in Fig. 2. TheCO SED turns over at the CO(7-6) line - which shows that the gas is fairly dense. All line fluxes can bereproduced with a single component LVG model. Using the excitation temperature of carbon as T of the

CO(1-0) line pins down the LVG solutions to T = 30K and dense gas with log(n(H )) = 4.2 cm .

This LVG model is shown as yellow line in the CO line SED. The LVG model allows us to predict theline intensity of the CO(1-0) transition. The CI(1-0)/CO(1-0) luminosity ratio is 0.2 - similar to valuesound in local galaxies (Gerin & Phillips 2000).

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f The absolute flux of the CO lines allow us to constrain theangular size of the CO emission region and therefore the size of the molecular toroid surrounding theQSO. The LVG fit in Fig. 2 implies a source radius of 1Kpc. The total H mass is 3.3 10 SM. Comparing

this number to the total carbon mass in the source yields the neutral carbon abundance of X[CI]/X[H ] =

3.8 10 . This value is similar to the CI abundance found in the Galaxy (2.2 10 Frerking etal 1989).

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SMM J14011Our CI(1-0) detection (Fig. 5) in SMM14011 (z=2.58) is the first CIdetection reported in any high-z Scuba sub-mm galaxy. Theabsence of AGN characteristics in optical spectra (Berger etal. 1999)together with the non detection of hard x-rays (Fabian etal. 2000)implies that the gas is mainly heated by starformation.The CI redshift and width is in agreement with values derived fromCO. So far we did not obtain observations of the upper fine structureline. The total mass of neutral carbon corrected for the magnificationof 25 (Downes & Solomon 2003) is 1.6 10 SM.

Our CO(3-2), CO(4-3) and CO(5-4) spectra observed simultaneouslyto CI(1-0) are shown in Fig. 6. The CO line SED in SMM14011 showstwo gas components (Fig. 6) similar to the CO line SED in M82(Weiss etal. 2004). Without the temperature constrain via CI thetemperature – density ambiguity is similar to what we show forF10214 in Fig. 4 (for both components). The total CO flux implies that the high excitation componentis fairly compact (r~400pc ) while the low excitation gas extends over a much larger area (r ~ 2Kpc).The H mass is of order 3 10 SM. The carbon abundance is slightly higher than in the two QSOs:

X[CI]/X[H ] ~ 8 10 .

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Fig 5: Spectrum of the CI(1-0) ine inSMM14011 obtained at the 30m.

Fig 2: CO spectra obtained by us at the IRAM 30m telescope towards the CloverleafQSO. The line flux is show as red squares in the CO line SED plot. The red triangle isthe Bure CO(3-2) flux shown in Fig.1. Other data: CO(1-0): Barvani 1995, CO(4-3):Barvainis etal. 1997 (30m), CO(7-6): Yun etal 1997 (green, OVRO) & Alloin etal 1997(blue, Bure). The yellow line is the LVG solution.

CO in the Cloverleaf Quasar

Fig 4: CO spectra obtained at the IRAM 30m telescope towards the F10214. The line flux is showm as redsquares in the CO line SED plot. Other data: CO(1-0): Tsuboi etal 1992, CO(3-2): Solomon etal. 1992 (Bure),CO(4-3): Brown & Vanden Bout 1992, CO(6-5) Solomon etal 1992, (black, Bure) & Downes etal 2004 (red, Bure).The colored lines are different possible LVG solutions (parameters are given in the plot, m denotes themagnification, is the angular size of the source in arcsec).α

CO in the IRAS F10214 (z=2.28)

Fig 6: CO spectra obtained at the IRAM 30m telescope towards the SMM14011. The line flux is show as redsquares in the CO line SED plot. Other data: CO(3-2): Frayer etal 1999 (green OVRO) & Downes & Solomon2003 (black Bure), CO(7-6): Downes & Solomon 2003. The CO line SED reveals two components. The red line is aLVG model for the high excitation component with Tkin=45K and log(n(H2)) = 3.9 cm-3, the blue line is a fit to thelow excitation medium with Tkin =30K and log(n(H2))=3.0 cm-3. For simplicity we do not plot possible density –

temperature combinations.

CO in the SMM J14011 (z=2.57)

Fig. 1: Atomic Carbon fine structure lines towards the Cloverleaf QSO. Left: Integrated intensity map of the uppercarbon fine structure line, CI(2-1), obtained at Bure. Center: Spectra of the CI(2-1) (red) and CO(3-2) (blue) line.The CO(3-2) was observed simultaneously to the CI(2-1) line. Bottom left: Spectrum of the CI(1-0) line observed atthe 30m telescope.

Atomic Carbon in the Cloverleaf Quasar

CO(6-5)

CI(2-1) Bure CI(2-1) & CO(3-2) BureCI(2-1) Bure

CI(1-0) 30m

CO(7-6)

CO(5-4)