[tel-00726959, v1] CaractÃ©riser le milieu interstellaire ... - HAL - INRIA

More documents

Recommendations

Info

H. S. Liszt and J. Pety: Imaging diffuse clouds: bright and dark gas mapped in COTable 3. Components with weak CO emission toward the continuum target.Target V τ(1−0) T ∗ RdN(CO)/dV T exc (1−0) p(H 2 ) n(H 2 ) akm s −1 K 10 15 cm −2 (km s −1 ) −1 K 10 3 cm −3 K cm −3∫τ(HCO + )dv/totalB0212 –10.3 0.49 0.40 0.65 3.4–3.6 1.9–2.5 75–100 0.122–0.05 0.95
A&A 541, A58 (2012)tel-00726959, version 1 - 31 Aug 2012As examples of the application of this notion, we note:– For a typical line with τ(1−0) = 1.5 and a Rayleigh-Jeansbrightness above the CMB of 1.5 K, T exc (1−0) = 5.04 K andp(H 2 )/k = 5 × 10 3 cm −3 Korn(H 2 ) = 200 cm −3 at T K = 25 K.– For the strongest absorption line component toward B0355(−17.8 km s −1 ), τ(1−0) = 3.1 andT exc (1−0) ≈ 6K,sothatp(H 2 )/k ≈ 5 × 10 3 cm −3 K once more.– The ≈4.5 K lines observed at the peak positions in severalof the simple fields discussed in Sect. 3 require p(H 2 )/k > ∼8.5 × 10 3 cm −3 Kor> ∼ 15 × 10 3 cm −3 Kforτ(1−0) = 3or1,respectively. Such a heavy over-pressure must be transient.– The very bright 10−12 K lines seen near B0528+134 andB2200+420 require excitation temperatures of 15 K or moreand lie somewhat beyond the range where W CO and N(CO)can be shown to be linearly proportional. They will be discussedseparately in a forthcoming publication based on observationsof HCO + , HCN, and CS.8.5. Failing to detect H 2 when CO emission is weakThere are cases where the brightness of the 1−0 line is well below1 K even when the CO optical depth is appreciable, as summarizedin Table 3; unfortunately we do not have a CO absorptionprofile toward B1928+738 in whose field CO emission wasnot detected, see Sect. 3.4. The regions of very low p(H 2 )towardB0212 and B0224 somehow manage to produce appreciableamounts of CO without exciting it to detectable levels butother lines represented in Table 3 do not arise in regions of especiallylow pressure.In Sect. 2.7 we showed that, on the whole, molecular gasis not underrepresented by CO emission in the collection ofsightlines comprising this work and earlier we showed that thesame is true of the larger sample of absorption-cloud sightlinesfrom which the current sample was drawn (Liszt et al. 2010).Moreover, CO emission from all of the components representedin Table 3 is detected (usually quite strongly) elsewhere in themapped fields except around B1928. However, the fraction ofmolecular gas that is detectable in CO along individual sightlinesvaries substantially. To quantify this we derived the H 2 columndensity from the integrated optical depth measured in HCO +(Lucas & Liszt 1996), see the right-most column in Table 3.With H 2 calculated in that way, the fraction of molecular gasthat is missed by failing to detect CO emission from particularindividual components in four directions is 12% toward B0212,16% toward B0224, 8% toward B0528+134 and 100% towardB1928. Overall the fraction of molecular gas represented bythe weakly-emitting CO summarized in Table 3 is 8% towardB0528, 16% toward B0224, 22% toward B0212, 43% towardB0355 and 100% toward B1730 and B1928.9. DiscussionEven at E B−V = 0.1−0.3 mag, the CO emission traced in thiswork runs the full gamut from undetectable to having brightnesscomparable to that seen in fully-molecular dark clouds.CO emission may be undetectably weak (≪1 K)whenmoleculargas is present in absorption (including that of CO itself) butin other directions it may be so bright that the N(H 2 )/W CO ratiois 4−5 times smaller than the typical CO-H 2 conversion factor2 × 10 20 cm −2 (K km s −1 ) −1 . Under the conditions encounteredin diffuse clouds, CO emission is foremost an indicator of theCO chemistry, secondarily an indicator of the rotational excitation(which reflects the partial thermal pressure of H 2 ) and onlyA58, page 18 of 23peripherally a measure of the underlying hydrogen column densitydistribution as discussed in Sect. 8. Indeed, the simulationsof CO emission from the interstellar medium by Shetty et al.(2011) agree with observations for the dense gas. However, a detailedcomparison with our results on the diffuse material showsthat the brightness per CO molecule is correct but there are up to4 orders of magnitude difference in N(H 2 )/N(CO). This is linkedto the poorly-understood polyatomic chemistry in the diffuse gas(see Shetty et al. 2011, their Sect. 4.3).The over-arching issues most relevant to diffuse cloudCO emission are three-fold: 1) how it may be identified for whatit is, originating in relatively tenuous gas that is unassociatedwith star formation; 2) whether it makes a substantial contributionwhen CO emission is used as a surrogate for N(H 2 )incircumstanceswhere emission contributions from diffuse and denseheavily-shielded gas may be blended; 3) how it is related to theso-called “dark” gas discovered by and Fermi (Abdo et al. 2010)and Planck (Planck Collaboration 2011) that is most prominentat moderate extinction where the transition from atomic tomolecular gas occurs and is claimed to host 50−120% of thepreviously-known CO emitting gas in the solar neighbourhood.As for the identification of diffuse gas, the W CO /W13 CO ratiois the most acessible and direct probe. When diffuse cloud COis excited to detectable levels it is generally in the regime whereW CO ∝ N(CO) and W13 CO ∝ N( 13 CO) so that the brightness ratioW CO /W13 CO will be much larger than the values 3−5 thatareseen when emission arises from optically thick lines from densergas where the rotation ladder is close to being thermalized.Fractionation progressively lowers the N( 12 CO)/N( 13 CO) columndensity ratio in diffuse gas at larger N(CO) (Liszt & Lucas1998; Sheffer et al. 2007) but not below about 15. Intensity ratiosW CO /W13 CO of 8−10 or higher are a strong indicator thatthere is a major contribution from diffuse material.Regarding the contribution of diffuse gas we recently assessedit in the case where an outside observer looked downon the Milky Way disk in the vicinity of the Sun (Liszt et al.2010). We compared the mean emission for the ensemble oflines of sight from which the current background targets weredrawn with the vertically-integrated emission expected for thegalactic disk component at the Solar Circle drawn from galacticplane surveys. The ensemble mean in our dataset, expressedas an equivalent to looking vertically through the galactic layer,was 2 〈W CO sin(|b|)〉 = 0.47 K km s −1 . The galactic disk contributionwas inferred from galactic plane surveys that findA(CO) = 5Kkms −1 (kpc) −1 and an equivalent disk thicknessof 150 pc, implying an integrated intensity through the disk of5Kkms −1 (kpc) −1 × 0.15 kpc = 0.75 K km s −1 .Even if viewed as entirely distinct (because it originatesat galactic latitudes well above those typically sampled ingalactic plane surveys) the diffuse gas contribution to the totalseen looking down on the Milky Way from outside wouldbe 0.47/(0.47+0.75) = 38%, a surprisingly high fraction giventhe supposed absence of molecular gas and CO emission athigher galactic latitudes. The alternative, that the diffuse gas isalready incorporated in galactic plane surveys, makes the majorityof the gas (0.47/0.75) in the galactic plane diffuse. Thisis an even more radical proposition, but is consistent with findingthat the preponderance of the molecular gas seen toward theheavily-extincted line of sight toward B0355+508 at b = −1.6 ◦is actually diffuse.In fact, the extent of the diffuse and/or high-latitude contributionto the local CO emission remains to be determined by widefieldCO surveys whose detection limit is substantially betterthan 1 K km s −1 and perhaps no worse than even 0.25 K km s −1 .
Page 1 and 2:
UNIVERSITÉ PIERRE ET MARIE CURIEHA
Page 3 and 4:
tel-00726959, version 1 - 31 Aug 20
Page 5 and 6:
Table des matières1 Rapport de sou
Page 7 and 8:
Rapport après soutenanceHabilitati
Page 9 and 10:
Chapitre 2Curriculum vitaetel-00726
Page 11 and 12: 2.7 ANIMATION ET DIFFUSION DE LA CU
Page 13 and 14: 2.8 PARCOURS 131992-1993 ÉCOLE NOR
Page 15 and 16: Chapitre 3Copyright: IRAM/PdBIIntro
Page 17 and 18: tel-00726959, version 1 - 31 Aug 20
Page 19 and 20: 4.2 ETUDES DIRECTES EN ÉMISSION 19
Page 21 and 22: 4.4 LA LUMINOSITY CO PAR MOLÉCULE
Page 23 and 24: 356 E. Falgarone et al.: Extreme ve
Page 37 and 38: A&A 518, A45 (2010)1001010⌠⌡ τ
Page 39 and 40: A&A 518, A45 (2010)If X HCO + is as
Page 41 and 42: A&A 518, A45 (2010)tel-00726959, ve
Page 45 and 46: A&A 518, A45 (2010)Table E.2. Data
Page 51 and 52: A&A 541, A58 (2012)0.08 0.10.20.12
Page 53 and 54: A&A 541, A58 (2012)b=240.11 0.1 0.1
Page 55 and 56: 0.080.09 0.1A&A 541, A58 (2012)0.14
Page 57 and 58: A&A 541, A58 (2012)43˚00'0.3 0.44
Page 59 and 60: A&A 541, A58 (2012)68˚00'1.1 0.91.
Page 61: A&A 541, A58 (2012)α(J2000)-19H57m
Page 65 and 66: A&A 541, A58 (2012)Jenkins, E. B.,
Page 67 and 68: A&A 541, A58 (2012)Galactic Latitud
Page 71 and 72: 5.2 UNE PHYSIQUE BIEN CONTRAINTE ET
Page 73 and 74: 5.3 PERSPECTIVES : DES RELEVÉS DE
Page 75 and 76: A&A 435, 885-899 (2005)DOI: 10.1051
Page 79 and 80: J. Pety et al.: Are PAHs precursors
Page 91 and 92: 566 J. R. Goicoechea et al.: Low su
Page 109 and 110: J. R. Goicoechea et al.: Low sulfur
Page 111 and 112: L42J. Pety et al.: Deuterium fracti
Page 113 and 114:
L44J. Pety et al.: Deuterium fracti
Page 115 and 116:
772 J. R. Goicoechea et al.: The io
Page 117 and 118:
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
Page 125 and 126:
Page 127 and 128:
A&A 494, 977-985 (2009)DOI: 10.1051
Page 129 and 130:
M. Gerin et al.: HCO mapping of the
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Table 1. Observation parameters for
Page 139 and 140:
A&A 534, A49 (2011)tel-00726959, ve
Page 141 and 142:
A&A 534, A49 (2011)tel-00726959, ve
Page 143 and 144:
A&A 534, A49 (2011)tel-00726959, ve
Page 145 and 146:
tel-00726959, version 1 - 31 Aug 20
Page 147 and 148:
tel-00726959, version 1 - 31 Aug 20
Page 149 and 150:
tel-00726959, version 1 - 31 Aug 20
Page 151 and 152:
tel-00726959, version 1 - 31 Aug 20
Page 153 and 154:
tel-00726959, version 1 - 31 Aug 20
Page 155 and 156:
tel-00726959, version 1 - 31 Aug 20
Page 157 and 158:
¡¢£¤¥¢¦¢ §¨ ©
Page 159 and 160:
tel-00726959, version 1 - 31 Aug 20
Page 161 and 162:
7.2 MODE INTERFÉROMÉTRIQUE 161tel
Page 163 and 164:
7.3 LE FUTUR DE LA RADIO-ASTRONOMIE
Page 165 and 166:
CLASS evolution: I. Improved OTF su
Page 167 and 168:
CLASS evolution: I. Improved OTF su
Page 169 and 170:
A&A 526, A47 (2011)DOI: 10.1051/000
Page 171 and 172:
S. Maret et al.: Weeds: a CLASS ext
Page 173 and 174:
S. Maret et al.: Weeds: a CLASS ext
Page 175 and 176:
IRAM-30m EMIR time/sensitivity esti
Page 177 and 178:
IRAM-30m EMIR time/sensitivity esti
Page 179 and 180:
IRAM-30m HERA time/sensitivity esti
Page 181 and 182:
¬þ«ðZñÛùþ˜ï³þ«ðWMõÑ
Page 183 and 184:
¨-A¨-, #f¡§¨\¤qŠ’‹¼€(
Page 185 and 186:
¤H F!";
Page 187 and 188:
#O.u\J0$!&%©ÉQ©6¦©¨-.u& (HÌ>
Page 189 and 190:
¨*.G©6E¦cÇ¦©¨&ẗØn¨"!-‡
Page 191 and 192:
¢¡¤£¦¥¨§ P© ¡ £¦¥¨§
Page 193 and 194:
'¥0vB"(-7£O.'¥!5#&(-7)7)(:9.*d#J
Page 195 and 196:
¥¤¡ b@‚¥_ƒO@02,.(-EFJbe O@#V
Page 197 and 198:
02J$#J+'10-ï 3 02EFJ+')EKJ5L5†R(
Page 199 and 200:
A&A 517, A12 (2010)tel-00726959, ve
Page 201 and 202:
A&A 517, A12 (2010)tel-00726959, ve
Page 203 and 204:
A&A 517, A12 (2010)tel-00726959, ve
Page 205 and 206:
A&A 517, A12 (2010)tel-00726959, ve
Page 207 and 208:
A&A 517, A12 (2010)tel-00726959, ve
Page 209 and 210:
A&A 517, A12 (2010)tel-00726959, ve
Page 211 and 212:
A&A 517, A12 (2010)tel-00726959, ve
Page 213 and 214:
A&A 517, A12 (2010)tel-00726959, ve
Page 215 and 216:
A&A 517, A12 (2010)tel-00726959, ve
Page 217 and 218:
Table C.1. Definition of the symbol
Page 219 and 220:
IRAM Memo 2011-2WIFISYN:The GILDAS
Page 221 and 222:
WIFISYN3. practiceWIFISYN3. practic
Page 223 and 224:
WIFISYNA. implementation planWIFISY
Page 225 and 226:
tel-00726959, version 1 - 31 Aug 20
Page 227 and 228:
8.3 PERSPECTIVES 227tel-00726959, v
Page 229 and 230:
3 REQUIREMENTS 44 CHANGES FOR END-U
Page 231 and 232:
5 CHANGES FOR PROGRAMMERS 125 CHANG
Page 233 and 234:
A EXHAUSTIVE DESCRIPTION OF THE CHA
Page 235 and 236:
Chapitre 9Copyright: Stéphane Guis
Page 237 and 238:
9.3 ACTIVITÉS 2008-2011 237tel-007
Page 239 and 240:
Contribution de l'Action Spécique
Page 241 and 242:
A. des multi-pixels à bure : une s
Page 243 and 244:
5. besoins en services annexes, bé
Page 245 and 246:
Articles publiés dans des revues
Page 247 and 248:
ARTICLES PUBLIÉS DANS DES REVUES
Page 249 and 250:
Mémos IRAM et ALMAtel-00726959, ve
Page 251 and 252:
Actes de colloques nationaux et int
Page 253 and 254:
ACTES DE COLLOQUES NATIONAUX ET INT
Page 255 and 256:
tel-00726959, version 1 - 31 Aug 20
show all

[tel-00726959, v1] CaractÃ©riser le milieu interstellaire ... - HAL - INRIA

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?