[en] We report the detection of CO(J = 3 $\to <!--\; ???\; -->$ 2) line emission in the strongly lensed submillimeter galaxy (SMG) SMM J0939+8315 at z = 2.221, using the Combined Array for Research in Millimeter-wave Astronomy. SMM J0939+8315 hosts a type-2 quasar, and is gravitationally lensed by the radio galaxy 3C220.3 and its companion galaxy at z = 0.685. The 104 GHz continuum emission underlying the CO line is detected toward 3C220.3 with an integrated flux density of S_cont = 7.4 ± 1.4 mJy. Using the CO(J = 3 $\to <!--\; ???\; -->$ 2) line intensity of I_CO(3-2) = (12.6 ± 2.0) Jy km s⁻¹, we derive a lensing- and excitation-corrected CO line luminosity of $L_{\mathrm{C}\mathrm{O}(1-<!--\; ???\; -->0)}^{\mathrm{\prime <!--\; ???\; -->}}$ = (3.4 ± 0.7) × 10¹⁰ (10.1/μ_L) K km s⁻¹ pc² for the SMG, where μ_L is the lensing magnification factor inferred from our lens modeling. This translates to a molecular gas mass of M_gas = (2.7 ± 0.6) × 10¹⁰ (10.1/μ_L) M_⊙. Fitting spectral energy distribution models to the (sub)-millimeter data of this SMG yields a dust temperature of T = 63.1${}_{-<!--\; ???\; -->1.3}^{+1.1}$ K, a dust mass of M_dust = (5.2 ± 2.1) × 10⁸ (10.1/μ_L) M_⊙, and a total infrared luminosity of L_IR = (9.1 ± 1.2) ×10¹² (10.1/μ_L) L_⊙. We find that the properties of the interstellar medium of SMM J0939+8315 overlap with both SMGs and type-2 quasars. Hence, SMM J0939+8315 may be transitioning from a starbursting phase to an unobscured quasar phase as described by the “evolutionary link” model, according to which this system may represent an intermediate stage in the evolution of present-day galaxies at an earlier epoch.

[en] We report the detection of luminous CO(J = 2→1), CO(J = 3→2), and CO(J = 4→3) emission in the strongly lensed high-redshift quasars B1938+666 (z = 2.059), HE 0230-2130 (z = 2.166), HE 1104-1805 (z = 2.322), and B1359+154 (z = 3.240), using the Combined Array for Research in Millimeter-wave Astronomy. B1938+666 was identified in a ^blindCO redshift search, demonstrating the feasibility of such investigations with millimeter interferometers. These galaxies are lensing-amplified by factors of μ_L ≅ 11-170, and thus allow us to probe the molecular gas in intrinsically fainter galaxies than currently possible without the aid of gravitational lensing. We report lensing-corrected intrinsic CO line luminosities of L'_CO = 0.65-21x10⁹ K km s^-1 pc², translating to H₂ masses of M(H₂) = 0.52-17 x 10⁹ (α_CO/0.8) M_sun. To investigate whether or not the active galactic nucleus (AGN) in luminous quasars substantially contributes to L_FIR, we study the L'_CO-L_FIR relation for quasars relative to galaxies without a luminous AGN as a function of redshift. We find no substantial differences between submillimeter galaxies and high-z quasars, but marginal evidence for an excess in L_FIR in nearby low-L_FIR AGN galaxies. This may suggest that an AGN contribution to L_FIR is significant in systems with relatively low gas and dust content, but only minor in the most far-infrared-luminous galaxies (in which L_FIR is dominated by star formation).

[en] We report interferometric imaging of CO(J = 3→2) emission toward the z = 2.846 submillimeter-selected galaxy SMM J04135+10277, using the Combined Array for Research in Millimeter-wave Astronomy (CARMA). SMM J04135+10277 was previously thought to be a gas-rich, submillimeter-selected quasar, with the highest molecular gas mass among high-z quasars reported in the literature. Our maps at ∼6× improved linear resolution relative to earlier observations spatially resolve the emission on ∼1.''7 scales, corresponding to a (lensing-corrected) source radius of ∼5.2 kpc. They also reveal that the molecular gas reservoir, and thus, likely the submillimeter emission, is not associated with the host galaxy of the quasar, but with an optically faint gas-rich galaxy at 5.''2, or 41.5 kpc projected distance from the active galactic nucleus (AGN). The obscured gas-rich galaxy has a dynamical mass of M_dyn sin² i = 5.6 × 10¹¹ M_☉, corresponding to a gas mass fraction of ≅21%. Assuming a typical M_BH/M_* ratio for z ∼> 2 quasars, the two galaxies in this system have an approximate mass ratio of ∼1.9. Our findings suggest that this quasar-starburst galaxy pair could represent an early stage of a rare major, gas-rich/gas-poor (^wet-dry⁾ merger of two massive galaxies at z = 2.8, rather than a single, gas-rich AGN host galaxy. Such systems could play an important role in the early buildup of present-day massive galaxies through a submillimeter-luminous starburst phase, and may remain hidden in larger numbers among rest-frame far-infrared-selected quasar samples at low and high redshift.

[en] We report observations of CO(J = 2 → 1) and $\mathrm{C}\mathrm{O}(J=3\to <!--\; ???\; -->2)$ line emission toward the quadruply-lensed quasar RXS J1131−1231 at z = 0.654 obtained using the Plateau de Bure Interferometer (PdBI) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). Our lens modeling shows that the asymmetry in the double-horned CO(J = 2 → 1) line profile is mainly a result of differential lensing, where the magnification factor varies from ∼3 to ∼9 across different kinematic components. The intrinsically symmetric line profile and a smooth source-plane velocity gradient suggest that the host galaxy is an extended rotating disk, with a CO size of $R_{\mathrm{C}\mathrm{O}}\sim <!--\; ???\; -->6$ kpc and a dynamical mass of $M_{\mathrm{d}\mathrm{y}\mathrm{n}}\sim <!--\; ???\; -->8\times <!--\; ??\; -->{10}^{10}$ M _⊙. We also find a secondary CO-emitting source near RXS J1131−1231, the location of which is consistent with the optically-faint companion reported in previous studies. The lensing-corrected molecular gas masses are M _gas = (1.4 ± 0.3) × 10¹⁰ M _⊙ and (2.0 ± 0.1) × 10⁹ M _⊙ for RXS J1131−1231 and the companion, respectively. We find a lensing-corrected stellar mass of M _* = (3 ± 1) × 10¹⁰ M _⊙ and a star formation rate of SFR_FIR = (120 ± 63) M _⊙ yr⁻¹, corresponding to a specific SFR and star formation efficiency comparable to z ∼ 1 disk galaxies not hosting quasars. The implied gas mass fraction of ∼18 ± 4% is consistent with the previously observed cosmic decline since z ∼ 2. We thus find no evidence for quenching of star formation in RXS J1131−1231. This agrees with our finding of an elevated $M_{\mathrm{B}\mathrm{H}}/M_{\mathrm{b}\mathrm{u}\mathrm{l}\mathrm{g}\mathrm{e}}$ ratio of >0.27${}_{-<!--\; ???\; -->0.08}^{+0.11}$% compared to the local value, suggesting that the bulk of its black hole mass is largely in place while its stellar bulge is still assembling.

[en] We report the detection of CO(J = 1 → 0) emission toward the lensed L ^*_UV Lyman-break galaxies (LBGs) MS 1512-cB58 (z = 2.73) and the Cosmic Eye (z = 3.07), using the Expanded Very Large Array. The strength of the CO line emission reveals molecular gas reservoirs with masses of (4.6 ± 1.1) x 10⁸ (μ_L/32)^-1 (α_CO/0.8) M _sun and (9.3 ± 1.6) x 10⁸ (μ_L/28)^-1 (α_CO/0.8) M _sun, respectively. These observations suggest ∼30%-40% larger gas reservoirs than previously estimated based on CO(J = 3 → 2) observations due to subthermal excitation of the J = 3 line. These observations also suggest gas mass fractions of 0.46 ± 0.17 and 0.16 ± 0.06. The CO(J = 1 → 0) emission in the Cosmic Eye is slightly resolved on scales of 4.''5 ± 1.''5, consistent with previous studies of nebular emission lines. This suggests that the molecular gas is associated with the most intensely star-forming regions seen in the ultraviolet (UV). We do not resolve the CO(J = 1 → 0) emission in cB58 at ∼2'' resolution, but find that the CO(J = 1 → 0) emission is also consistent with the position of the UV-brightest emission peak. The gas masses, gas fractions, moderate CO line excitation, and star formation efficiencies in these galaxies are consistent with what is found in nearby luminous infrared galaxies. These observations thus currently represent the best constraints on the molecular gas content of 'ordinary' (i.e., ∼L* _UV) z ∼ 3 star-forming galaxies. Despite comparable star formation rates, the gas properties of these young LBGs seem to be different from the recently identified optical/infrared-selected high-z massive, gas-rich star-forming galaxies, which are more gas-rich and massive, but have lower star formation efficiencies, and presumably trace a different galaxy population.

[en] We report the detection of surprisingly strong HCN(J = 6→5), HNC(J = 6→5), and HCO⁺(J = 6→5) emission in the host galaxy of the z = 3.91 quasar APM 08279+5255 through observations with the Combined Array for Research in Millimeter-wave Astronomy. HCN, HNC, and HCO⁺ are typically used as star formation indicators, tracing dense molecular hydrogen gas [n(H₂) >10⁵ cm^-3] within star-forming molecular clouds. However, the strength of their respective line emission in the J = 6→5 transitions in APM 08279+5255 is extremely high, suggesting that they are excited by another mechanism besides collisions in the dense molecular gas phase alone. We derive J = 6→5 line luminosities of L'_HCN = (4.9 ± 0.6), L'_HNC = (2.4 ± 0.7), and L^'_HCO⁺= (3.0±0.6)x10¹⁰ μ^-1_L K km s^-1 pc² (where μ_L is the lensing magnification factor), corresponding to L' ratios of ∼0.23-0.46 relative to CO(J = 1→0). Such high line ratios would be unusual even in the respective ground-state (J = 1→0) transitions, and indicate exceptional, collisionally and radiatively driven excitation conditions in the dense, star-forming molecular gas in APM 08279+5255. Through an expansion of our previous modeling of the HCN line excitation in this source, we show that the high rotational line fluxes are caused by substantial infrared pumping at moderate opacities in a ∼220 K warm gas and dust component. This implies that standard M_dense/L' conversion factors would substantially overpredict the dense molecular gas mass M_dense. We also find a HCN(J = 6→5)/HCN(J = 5→4) L' ratio greater than 1 (1.36 ± 0.31)-however, our models show that the excitation is likely not 'super-thermal', but that the high line ratio is due to a rising optical depth between both transitions. These findings are consistent with the picture that the bulk of the gas and dust in this source is situated in a compact, nuclear starburst, where both the highly active galactic nucleus and star formation contribute to the heating.

[en] We present the search for the [C II] emission line in three z > 6.5 Lyα emitters (LAEs) and one J-dropout galaxy using the Combined Array for Research in Millimeter-wave Astronomy and the Plateau de Bure Interferometer. We observed three bright z ∼ 6.5-7 LAEs discovered in the Subaru Deep Field (SDF) and the multiple imaged lensed z ∼ 11 galaxy candidate found behind the galaxy cluster MACSJ0647.7+7015. For the LAEs IOK-1 (z = 6.965), SDF J132415.7+273058 (z = 6.541), and SDF J132408.3+271543 (z = 6.554) we find upper limits for the [C II] line luminosity of <2.05, <4.52, and <10.56 × 10⁸ L _☉, respectively. We find upper limits to the far-IR (FIR) luminosity of the galaxies using a spectral energy distribution template of the local galaxy NGC 6946 and taking into account the effects of the cosmic microwave background on the millimeter observations. For IOK-1, SDF J132415.7+273058, and SDF J132408.3+271543 we find upper limits for the FIR luminosity of <2.33, 3.79, and 7.72 × 10¹¹ L _☉, respectively. For the lensed galaxy MACS0647-JD, one of the highest-redshift galaxy candidates to date with z_ph=10.7_−0.4^+0.6, we put an upper limit in the [C II] emission of <1.36 × 10⁸ × (μ/15)^–1 L _☉ and an upper limit in the FIR luminosity of <6.1 × 10¹⁰ × (μ/15)^–1 L _☉ (where μ is the magnification factor). We explore the different conditions relevant for the search for [C II] emission in high-redshift galaxies as well as the difficulties for future observations with the Atacama Large Millimeter/submillimeter Array (ALMA) and the Cerro Chajnantor Atacama Telescope (CCAT).

[en] We report the detection of 23 OH⁺ 1 → 0 absorption, emission, or P-Cygni-shaped lines and CO(J = 9→8) emission lines in 18 Herschel-selected z = 2–6 starburst galaxies with the Atacama Large Millimeter/submillimeter Array and the NOrthern Extended Millimeter Array, taken as part of the Gas And Dust Over cosmic Time Galaxy Survey. We find that the CO(J = 9→8) luminosity is higher than expected based on the far-infrared luminosity when compared to nearby star-forming galaxies. Together with the strength of the OH⁺ emission components, this may suggest that shock excitation of warm, dense molecular gas is more prevalent in distant massive dusty starbursts than in nearby star-forming galaxies on average, perhaps due to an impact of galactic winds on the gas. OH⁺ absorption is found to be ubiquitous in massive high-redshift starbursts, and is detected toward 89% of the sample. The majority of the sample shows evidence for outflows or inflows based on the velocity shifts of the OH⁺ absorption/emission, with a comparable occurrence rate of both at the resolution of our observations. A small subsample appears to show outflow velocities in excess of their escape velocities. Thus, starburst-driven feedback appears to be important in the evolution of massive galaxies in their most active phases. We find a correlation between the OH⁺ absorption optical depth and the dust temperature, which may suggest that warmer starbursts are more compact and have higher cosmic-ray energy densities, leading to more efficient OH⁺ ion production. This is in agreement with a picture in which these high-redshift galaxies are “scaled-up” versions of the most intense nearby starbursts.

[en] We report observations of dense molecular gas in the star-forming galaxy EGS 13004291 (z = 1.197) using the Plateau de Bure Interferometer. We tentatively detect HCN and HNC $J=2\to <!--\; ???\; -->1$ emission when stacked together at $4\mathrm{\sigma <!--\; ??\; -->}$ significance, yielding line luminosities of $L_{\mathrm{H}\mathrm{C}\mathrm{N}(J=2\to <!--\; ???\; -->1)}^{\mathrm{\prime <!--\; ???\; -->}}=(9\pm <!--\; ??\; -->3)\times <!--\; ??\; -->{10}^9$ K km s⁻¹ pc² and $L_{\mathrm{H}\mathrm{N}\mathrm{C}(J=2\to <!--\; ???\; -->1)}^{\mathrm{\prime <!--\; ???\; -->}}=(5\pm <!--\; ??\; -->2)\times <!--\; ??\; -->{10}^9$ K km s⁻¹ pc², respectively. We also set 3σ upper limits of <7–8 ×10⁹ K km s⁻¹ pc² on the ${\mathrm{H}\mathrm{C}\mathrm{O}}^{+}(J=2\to <!--\; ???\; -->1)$, ${\mathrm{H}}_2\mathrm{O}(3_{13}\to <!--\; ???\; -->2_{20}$), and HC₃N(J = 20 → 19) line luminosities. We serendipitously detect CO emission from two sources at $z\sim <!--\; ???\; -->1.8$ and $z\sim <!--\; ???\; -->3.2$ in the same field of view. We also detect CO($J=2\to <!--\; ???\; -->1$) emission in EGS 13004291, showing that the excitation in the previously detected CO($J=3\to <!--\; ???\; -->2$) line is subthermal ($r_{32}=0.65\pm <!--\; ??\; -->0.15$). We find a line luminosity ratio of $L_{\mathrm{H}\mathrm{C}\mathrm{N}}^{\mathrm{\prime <!--\; ???\; -->}}$/$L_{\mathrm{C}\mathrm{O}}^{\mathrm{\prime <!--\; ???\; -->}}$ = 0.17 ± 0.07, as an indicator of the dense gas fraction. This is consistent with the median ratio observed in $z><!--\; >\; -->1$ galaxies ($L_{\mathrm{H}\mathrm{C}\mathrm{N}}^{\mathrm{\prime <!--\; ???\; -->}}$/$L_{\mathrm{C}\mathrm{O}}^{\mathrm{\prime <!--\; ???\; -->}}$ = 0.16 ± 0.07) and nearby ULIRGs ($L_{\mathrm{H}\mathrm{C}\mathrm{N}}^{\mathrm{\prime <!--\; ???\; -->}}$/$L_{\mathrm{C}\mathrm{O}}^{\mathrm{\prime <!--\; ???\; -->}}$ = 0.13 ± 0.03), but higher than that in local spirals ($L_{\mathrm{H}\mathrm{C}\mathrm{N}}^{\mathrm{\prime <!--\; ???\; -->}}$/$L_{\mathrm{C}\mathrm{O}}^{\mathrm{\prime <!--\; ???\; -->}}$ = 0.04 ± 0.02). Although EGS 13004291 lies significantly above the galaxy main sequence at $z\sim <!--\; ???\; -->1$, we do not find an elevated star formation efficiency (traced by $L_{\mathrm{F}\mathrm{I}\mathrm{R}}$/$L_{\mathrm{C}\mathrm{O}}^{\mathrm{\prime <!--\; ???\; -->}}$) as in local starbursts, but a value consistent with main-sequence galaxies. The enhanced dense gas fraction, the subthermal gas excitation, and the lower than expected star formation efficiency of the dense molecular gas in EGS 13004291 suggest that different star formation properties may prevail in high-z starbursts. Thus, using $L_{\mathrm{F}\mathrm{I}\mathrm{R}}$/$L_{\mathrm{C}\mathrm{O}}^{\mathrm{\prime <!--\; ???\; -->}}$ as a simple recipe to measure the star formation efficiency may be insufficient to describe the underlying mechanisms in dense star-forming environments inside the large gas reservoirs.

[en] We report the detection of spatially resolved CO(J = 1→0) emission in the z ∼ 3.4 submillimeter galaxies (SMGs) SMM J09431+4700 and SMM J13120+4242, using the Expanded Very Large Array (EVLA). SMM J09431+4700 is resolved into the two previously reported millimeter sources H6 and H7, separated by ∼30 kpc in projection. We derive CO(J = 1→0) line luminosities of L'_CO(1-0) = (2.49 ± 0.86) and (5.82 ± 1.22) x 10¹⁰ K km s^-1 pc² for H6 and H7, and L'_CO(1-0) = (23.4 ± 4.1) x 10¹⁰ K km s^-1 pc² for SMM J13120+4242. These are ∼1.5-4.5 times higher than what is expected from simple excitation modeling of higher-J CO lines, suggesting the presence of copious amounts of low-excitation gas. This is supported by the finding that the CO(J = 1→0) line in SMM J13120+4242, the system with the lowest CO excitation, appears to have a broader profile and more extended spatial structure than seen in higher-J CO lines (which is less prominently seen in SMM J09431+4700). Based on L'_CO(1-0) and excitation modeling, we find M_gas = 2.0-4.3 and 4.7-12.7x10¹⁰ M_sun for H6 and H7, and M_gas = 18.7-69.4x10¹⁰ M_sun for SMM J13120+4242. The observed CO(J = 1→0) properties are consistent with the picture that SMM J09431+4700 represents an early-stage, gas-rich major merger and that SMM J13120+4242 represents such a system in an advanced stage. This study thus highlights the importance of spatially and dynamically resolved CO(J = 1→0) observations of SMGs to further understand the gas physics that drive star formation in these distant galaxies, which is possible only now that the EVLA is rising to its full capabilities.