Line Luminosity Ratios Research Articles

ALMA imaging of SDP.81 – II. A pixelated reconstruction of the CO emission lines

Abstract We present a sub-100 pc-scale analysis of the CO molecular gas emission and kinematics of the gravitational lens system SDP.81 at redshift 3.042 using Atacama Large Millimetre/submillimetre Array (ALMA) science verification data and a visibility-plane lens reconstruction technique. We find clear evidence for an excitation-dependent structure in the unlensed molecular gas distribution, with emission in CO (5–4) being significantly more diffuse and structured than in CO (8–7). The intrinsic line luminosity ratio is r8–7/5−4 = 0.30 ± 0.04, which is consistent with other low-excitation starbursts at z ∼ 3. An analysis of the velocity fields shows evidence for a star-forming disc with multiple velocity components that is consistent with a merger/post-coalescence merger scenario, and a dynamical mass of M(<1.56 kpc) = 1.6 ± 0.6 × 1010 M⊙. Source reconstructions from ALMA and the Hubble Space Telescope show that the stellar component is offset from the molecular gas and dust components. Together with Karl G. Jansky Very Large Array CO (1–0) data, they provide corroborative evidence for a complex ∼2 kpc-scale starburst that is embedded within a larger ∼15 kpc structure.

COLDz: KARL G. JANSKY VERY LARGE ARRAY DISCOVERY OF A GAS-RICH GALAXY IN COSMOS

The broad spectral bandwidth at mm and cm-wavelengths provided by the recent upgrades to the Karl G. Jansky Very Large Array (VLA) has made it possible to conduct unbiased searches for molecular CO line emission at redshifts, z > 1.31. We present the discovery of a gas-rich, star-forming galaxy at z = 2.48, through the detection of CO(1-0) line emission in the COLDz survey, through a sensitive, Ka-band (31 to 39 GHz) VLA survey of a 6.5 square arcminute region of the COSMOS field. We argue that the broad line (FWHM ~570 +/- 80 km/s) is most likely to be CO(1-0) at z=2.48, as the integrated emission is spatially coincident with an infrared-detected galaxy with a photometric redshift estimate of z = 3.2 +/- 0.4. The CO(1-0) line luminosity is L'_CO = (2.2 +/- 0.3) x 10^{10} K km/s pc^2, suggesting a cold molecular gas mass of M_gas ~ (2 - 8)x10^{10}M_solar depending on the assumed value of the molecular gas mass to CO luminosity ratio alpha_CO. The estimated infrared luminosity from the (rest-frame) far-infrared spectral energy distribution (SED) is L_IR = 2.5x10^{12} L_solar and the star-formation rate is ~250 M_solar/yr, with the SED shape indicating substantial dust obscuration of the stellar light. The infrared to CO line luminosity ratio is ~114+/-19 L_solar/(K km/s pc^2), similar to galaxies with similar SFRs selected at UV/optical to radio wavelengths. This discovery confirms the potential for molecular emission line surveys as a route to study populations of gas-rich galaxies in the future.

A SURVEY OF ATOMIC CARBON AT HIGH REDSHIFT

We present a survey of atomic carbon (C i) emission in high-redshift (z > 2) submillimeter galaxies and quasar host galaxies. Sensitive observations of the C i (3P1 → 3P0) and C i (3P2 → 3P1) lines have been obtained at the IRAM Plateau de Bure interferometer and the IRAM 30 m telescope. A total of 16 C i lines have been targeted in 10 sources, leading to a total of 10 detected lines—this doubles the number of C i observations at high redshift to date. We include previously published C i observations (an additional five detected sources) in our analysis. Our main finding is that the C i properties of the high-redshift galaxies studied here do not differ significantly from what is found in low-redshift systems, including the Milky Way. The C i (3P2 → 3P1)/C i (3P1 → 3P0) and the C i (3P1 → 3P0)/12CO(3–2) line luminosity (L') ratios change little in our sample, with respective ratios of 0.55 ± 0.15 and 0.32 ± 0.13. The C i lines are not an important contributor to cooling of the molecular gas (average LC i/LFIR ∼ (7.7 ± 4.6) × 10−6). We derive a mean carbon excitation temperature of 29.1 ± 6.3 K, broadly consistent with dust temperatures derived for high-redshift star-forming systems, but lower than gas temperatures typically derived for starbursts in the local universe. The carbon abundance of X[C i]/X[H2] ∼ (8.4±3.5)×10−5 is of the same order as found in the Milky Way and nearby galaxies. This implies that the high-z galaxies studied here are significantly enriched in carbon on galactic scales, even though the look-back times are considerable (the average redshift of the sample sources corresponds to an age of the universe of ∼2 Gyr).

Detection of Emission from the CN Radical in the Cloverleaf Quasar at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $z=2.56$ \end{document}

We report the detection of CN(N = 3 → 2) emission toward the Cloverleaf quasar (z = 2.56) based on observations with the IRAM Plateau de Bure Interferometer. This is the first clear detection of emission from this radical at high redshift. CN emission is a tracer of dense molecular hydrogen gas [n(H2) > 104 cm-3] within star-forming molecular clouds, in particular, in regions where the clouds are affected by UV radiation. The HCN/CN intensity ratio can be used as a diagnostic for the relative importance of photodissociation regions (PDRs) in a source and as a sensitive probe of optical depth, the radiation field, and photochemical processes. We derive a lensing-corrected CN(N = 3 → 2) line luminosity of L = (4.5 ± 0.5) × 109 K km s-1 pc2. The ratio between CN luminosity and far-infrared luminosity falls within the scatter of the same relationship found for low-z (ultra-) luminous infrared galaxies. Combining our new results with CO(J = 3 → 2) and HCN(J = 1 → 0) measurements from the literature and assuming thermal excitation for all transitions, we find a CO/CN luminosity ratio of 9.3 ± 1.9 and a HCN/CN luminosity ratio of 0.95 ± 0.15. However, we find that the CN(N = 3 → 2) line is likely only subthermally excited, implying that those ratios may only provide upper limits for the intrinsic 1 → 0 line luminosity ratios. We conclude that, in combination with other molecular gas tracers like CO, HCN, and HCO+, CN is an important probe of the physical conditions and chemical composition of dense molecular environments at high redshift.

Dense molecular gas in a sample of LIRGs and ULIRGs: The low-redshift connection to the huge high-redshift starbursts and AGNs

The sample of nearby LIRGs and ULIRGs for which dense molecular gas tracers have been measured is building up, allowing for the study of the physical and chemical properties of the gas in the variety of objects in which the most intense star formation and/or AGN activity in the local universe is taking place. This characterisation is essential to understand the processes involved, discard others and help to interpret the powerful starbursts and AGNs at high redshift that are currently being discovered and that will routinely be mapped by ALMA. We have studied the properties of the dense molecular gas in a sample of 17 nearby LIRGs and ULIRGs through millimeter observations of several molecules (HCO+, HCN, CN, HNC and CS) that trace different physical and chemical conditions of the dense gas in these extreme objects. In this paper we present the results of our HCO+ and HCN observations. We conclude that the very large range of measured line luminosity ratios for these two molecules severely questions the use of a unique molecular tracer to derive the dense gas mass in these galaxies.

Atomic carbon at redshift ~2.5

Using the IRAM 30 m telescope we detected the lower fine structure line of neutral carbon (CI( 3 P 1 → 3 P 0 ), ν rest = 492 GHz) towards three high-redshift sources: IRAS FSC 10214 (z = 2.3), sMMJ14011+0252 (z = 2.5) and H1413+117 (Cloverleaf quasar, z = 2.5). SMM J14011+0252 is the first high-redshift, non-AGN source in which Cl has been detected. The C I( 3 P 1 → 3 P 0 ) line from FSC 10214 is almost an order of magnitude weaker than previously claimed, while our detection in the Cloverleaf is in good agreement with earlier observations. The C 1( 3 P 1 → 3 P 0 ) linewidths are similar to the CO widths, indicating that both lines trace similar regions of molecular gas on galactic scales. Derived C I( 3 P 1 → 3 P 0 ) masses for all three objects are of order few ×10 7 M ○. and the implied CI( 3 P 1 → 3 P 0 ) 12 CO(J = 3 → 2) line luminosity ratio is about 0.2. This number is similar to values found in local galaxies. We derive a C abundance of 5 x 10 -5 which implies significant metal enrichment of the cold molecular gas at redshifts 2.5 (age of the universe 2.7 Gyr). We conclude that the physical properties of systems at large lookback times are similar to today's starburst/AGN environments.

Starburst activity in the host galaxy of thez$\mathsf{=2.58}$ quasar J1409+5628

We report the detection of CO emission from the optically luminous, radio-quiet quasar J140955.5+562827 (hereafter J1409+5628), at a redshift . We also present VLA continuum maps and VLBA high spatial resolution observations at 1.4 GHz. Both the CO(32) and CO(76) emission lines are detected using the IRAM Plateau de Bure interferometer. The 32/76 line luminosity ratio is about 1/3, indicating the presence of warm and dense molecular gas with an estimated mass of 6 1010 . The infrared-to-CO luminosity ratio (K km s-1 pc2)-1, comparable to values found for other high-z sources where CO line emission is seen. J1409+5628 is detected using the VLA with a 1.4 GHz rest-frame luminosity density of 4.0 . The rest-frame radio to far-infrared ratio, q, has a value of 2.0 which is similar to the values found in star forming galaxies. At the 30 mas resolution of the VLBA, J1409+5628 is not detected with a 4σ upper limit to the surface brightness of 0.29 mJy beam-1. This implies a limit to the intrinsic brightness temperature of 2 at 8 GHz, typical for nuclear starbursts and more than two orders of magnitude fainter than typical radio-loud active galactic nuclei. Both the properties of the CO line emission and the radio emission from J1409+5628 are therefore consistent with those expected for a star forming galaxy. In J1409+5628 young massive stars are the dominant source of dust heating, accounting for most of the infrared luminosity. The massive reservoir of molecular gas can sustain the star formation rate of a few implied by the far-infrared luminosity for about 10 million years.

Gas and dust in the Cloverleaf quasar at redshift 2.5

We observed the upper fine structure line of neutral carbon, C I( 3 P2! 3 P1 )( rest = 809 GHz), the 12 CO(J= 3!2) line (rest= 345 GHz) and the 1.2 mm continuum emission from H1413+117 (Cloverleaf quasar, z= 2:5) using the IRAM inter- ferometer. Together with the detection of the lower fine structure line (Barvainis et al. 1997), the Cloverleaf quasar is now only the second extragalactic system, besides M 82, where both carbon lines have convincingly been detected. Our analysis shows that the carbon lines are optically thin and have an excitation temperature of Tex 30 K. CO is subthermally excited and the observed line luminosity ratios are consistent with n(H2) 10 3 4 cm 3 at Tkin= 30-50 K. Using three independent methods (C I, dust, CO) we derive a total molecular gas mass (corrected for magnification) of M(H2) 1.2 0.3 10 10 M. Our observations suggest that the molecular disk extends beyond the region seen in CO(7-6) to a zone of more moderately excited molecular gas that dominates the global emission in C I and the low J CO lines. described by a 3-level system. This allows us to derive its ex- citation and to constrain the physical gas conditions by obser- vations of the C I( 3 P1! 3 P0) and C I( 3 P2! 3 P1) transitions only. We compare our results from C I with estimates based on ther- mal dust emission and CO. We use H0= 75 km s 1 Mpc 1 and q0= 0:5.