| 21. |
- Simpson, J. M., et al.
(författare)
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THE SCUBA-2 COSMOLOGY LEGACY SURVEY: ALMA RESOLVES the BRIGHT-END of the SUB-MILLIMETER NUMBER COUNTS
- 2015
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Ingår i: Astrophysical Journal. - 1538-4357 .- 0004-637X. ; 807:2
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Tidskriftsartikel (refereegranskat)abstract
- We present high-resolution 870 μm Atacama Large Millimeter/sub-millimeter Array (ALMA) continuum maps of 30 bright sub-millimeter sources in the UKIDSS UDS field. These sources are selected from deep, 1 degree2 850 μm maps from the SCUBA-2 Cosmology Legacy Survey, and are representative of the brightest sources in the field (median SSCUBA-2= 8.7 ± 0.4 mJy). We detect 52 sub-millimeter galaxies (SMGs) at >4σ significance in our 30 ALMA maps. In 61-15+19% of the ALMA maps the single-dish source comprises a blend of ≥2 SMGs, where the secondary SMGs are Ultra-luminous Infrared Galaxies (ULIRGs) with LIR ≳ 1012 L⊙. The brightest SMG contributes on average 80-2+6% of the single-dish flux density, and in the ALMA maps containing ≥2 SMGs the secondary SMG contributes 25-5+1% of the integrated ALMA flux. We construct source counts and show that multiplicity boosts the apparent single-dish cumulative counts by 20% at S870 > 7.5 mJy, and by 60% at S870 > 12 mJy. We combine our sample with previous ALMA studies of fainter SMGs and show that the counts are well-described by a double power law with a break at 8.5 ± 0.6 mJy. The break corresponds to a luminosity of ∼6 × 1012 L⊙ or a star formation rate (SFR) of ∼103 M⊙ yr-1. For the typical sizes of these SMGs, which are resolved in our ALMA data with Re = 1.2 ± 0.1 kpc, this yields a limiting SFR density of ∼100 M⊙ yr-1 kpc-2 Finally, the number density of S870 ≳ 2 mJy SMGs is 80 ± 30 times higher than that derived from blank-field counts. An over-abundance of faint SMGs is inconsistent with line-of-sight projections dominating multiplicity in the brightest SMGs, and indicates that a significant proportion of these high-redshift ULIRGs are likely to be physically associated.
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| 22. |
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| 25. |
- Xu, C. K., et al.
(författare)
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ALMA observationsof warm dense gas in NGC 1614-breaking of the star formation law in the central kiloparsec
- 2015
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Ingår i: Astrophysical Journal. - : American Astronomical Society. - 1538-4357 .- 0004-637X. ; 799:1
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Tidskriftsartikel (refereegranskat)abstract
- We present ALMA Cycle-0 observations of the CO (6-5) line emission and of the 435 mu m dust continuum emission in the central kiloparsec of NGC 1614, a local luminous infrared galaxy at a distance of 67.8 Mpc (1 '' = 329 pc). The CO emission is well resolved by the ALMA beam (0.'' 26x0.'' 20) into a circumnuclear ring, with an integrated flux of f(C O(6-5)) = 898 (+/- 153) Jy km s(-1), which is 63(+/- 12)% of the total CO (6-5) flux measured by Herschel. The molecular ring, located between 100 pc
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| 26. |
- Aalto, Susanne, 1964, et al.
(författare)
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H3O+ line emission from starbursts and AGNs
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 527:8
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Tidskriftsartikel (refereegranskat)abstract
- Context. The H3O+ molecule probes the chemistry and the ionization rate of dense circumnuclear gas in galaxies. Aims. We use the H3O+ molecule to investigate the impact of starburst and AGN activity on the chemistry of the molecular interstellar medium. Methods. Using the JCMT, we have observed the 3(2)(+)-2(2)(-) 364 GHz line of p-H3O+ towards the centres of seven active galaxies. Results. We have detected p-H3O+ towards IC 342, NGC 253, NGC 1068, NGC 4418, and NGC 6240. Upper limits were obtained for IRAS 15250 and Arp 299. We find large H3O+ abundances (N(H3O+)/N(H-2) greater than or similar to 10(-8)) in all detected galaxies apart from in IC 342 where it is about one order of magnitude lower. We note, however, that uncertainties in N(H3O+) may be significant due to lack of definite information on source size and excitation. We furthermore compare the derived N(H3O+) with N(HCO+) and find that the H3O+ to HCO+ column density ratio is large in NGC 1068 ( 24), moderate in NGC 4418 and NGC 253 ( 4-5), slightly less than unity in NGC 6240 ( 0.7) and lowest in IC 342 ( 0.2-0.6). We compare our results with models of X-ray and photon dominated regions ( XDRs and PDRs). Conclusions. For IC 342 we find that a starburst PDR chemistry can explain the observed H3O+ abundance. For the other galaxies, the large H3O+ columns are generally consistent with XDR models. In particular for NGC 1068 the elevated N(H3O+)/N(HCO+) ratio suggests a low column density XDR. For NGC 4418 however, large HC3N abundances are inconsistent with the XDR interpretation. An alternative possibility is that H3O+ forms through H2O evaporating off dust grains and reacting with HCO+ in warm, dense gas. This scenario could also potentially fit the results for NGC 253. Further studies of the excitation and distribution of H3O+-aswell as Herschel observations of water abundances - will help to further constrain the models.
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