Search

We combine the recent determination of the evolution of the cosmic density of molecular gas (H2) using deep, volumetric surveys, with previous estimates of the cosmic density of stellar mass, star formation rate and atomic gas (H i), to constrain the evolution of baryons associated with galaxies averaged over cosmic time and space. The cosmic H i and H2 densities are roughly equal at z ∼ 1.5. The H2 density then decreases by a factor to today's value, whereas the H i density stays approximately constant. The stellar mass density is increasing continuously with time and surpasses that of the total gas density (H i and H2) at redshift z ∼ 1.5. The growth in stellar mass cannot be accounted for by the decrease in cosmic H2 density, necessitating significant accretion of additional gas onto galaxies. With the new H2 constraints, we postulate and put observational constraints on a two-step gas accretion process: (i) a net infall of ionized gas from the intergalactic/circumgalactic medium to refuel the extended H i reservoirs, and (ii) a net inflow of H i and subsequent conversion to H2 in the galaxy centers. Both the infall and inflow rate densities have decreased by almost an order of magnitude since z ∼ 2. Assuming that the current trends continue, the cosmic molecular gas density will further decrease by about a factor of two over the next 5 Gyr, the stellar mass will increase by approximately 10%, and cosmic star formation activity will decline steadily toward zero, as the gas infall and accretion shut down. [ABSTRACT FROM AUTHOR]

We present IRAM Plateau de Bure Interferometer observations of the CO(3-2) and CO(5-4) line transitions from an Lyα blob at z ∼ 2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emissions are detected at the location of a strong MIPS source that is offset by ∼1.″5 from the Lyα peak. Neither of these emission components is resolved with the 1.″7 beam, showing that the gas and dust are confined to within ∼7 kpc from this galaxy. No millimeter source is found at the location of the Lyα peak, ruling out a central compact source of star formation as the power source for the Lyα emission. Combined with a spatially resolved spectrum of Lyα and He II, we constrain the kinematics of the extended gas using the CO emission as a tracer of the systemic redshift. Near the MIPS source, the Lyα profile is symmetric, and its line center agrees with that of the CO line, implying that there are no significant bulk flows and that the photo-ionization from the MIPS source might be the dominant source of the Lyα emission. In the region near the Lyα peak, the gas is slowly receding (∼100 km s–1) with respect to the MIPS source, thus making the hyper-/superwind hypothesis unlikely. We find a sub-thermal line ratio between two CO transitions, ICO(5-4)/ICO(3-2) = 0.97 ± 0.21. This line ratio is lower than the average values found in high-z submillimeter galaxies and QSOs but is consistent with the value found in the Galactic center, suggesting that there is a large reservoir of low-density molecular gas that is spread over the MIPS source and its vicinity. [ABSTRACT FROM AUTHOR]

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 × 108L☼, 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 × 1011L☼, respectively. For the lensed galaxy MACS0647-JD, one of the highest-redshift galaxy candidates to date with , we put an upper limit in the [C II] emission of <1.36 × 108 × (μ/15)–1L☼ and an upper limit in the FIR luminosity of <6.1 × 1010 × (μ/15)–1L☼ (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). [ABSTRACT FROM AUTHOR]

We present a study of the cosmic infrared background, which is a measure of the dust-obscured activity in all galaxies in the Universe. We venture to isolate the galaxies responsible for the background at 1 mm; with spectroscopic and photometric redshifts we constrain the redshift distribution of these galaxies. We create a deep 1.16 mm map (mJy) by combining the AzTEC 1.1 mm and MAMBO 1.2 mm data sets in the Great Observatories Origins Deep Survey North (GOODS-N) region. This combined map contains 41 secure detections, 13 of which are new. By averaging the 1.16 mm flux densities of individually undetected galaxies with flux densities Jy, we resolve 31-45 per cent of the 1.16 mm background. Repeating our analysis on the SCUBA map, we resolve a higher percentage (40-64 per cent) of the background. A majority of the background resolved (attributed to individual galaxies) at both wavelengths comes from galaxies at . If the ratio of the resolved submillimetre to millimetre background is applied to a reasonable scenario for the origins of the unresolved submillimetre background, 60-88 per cent of the total 1.16 mm background comes from galaxies at . [ABSTRACT FROM AUTHOR]

We present a 1200-μm image of the Great Observatories Origin Deep Survey North (GOODS-N) field, obtained with the Max Planck Millimetre Bolometer array (MAMBO) on the IRAM 30-m telescope. The survey covers a contiguous area of 287 arcmin2 to a near-uniform noise level of . After Bayesian flux deboosting, a total of 30 sources are recovered (≥3.5σ). An optimal combination of our 1200-μm data and an existing 850-μm image from the Submillimetre Common-User Bolometer Array (SCUBA) yielded 33 sources (≥4σ). We combine our GOODS-N sample with those obtained in the Lockman Hole and ELAIS N2 fields ( Scott et al. 2002 ; Greve et al. 2004 ) in order to explore the degree of overlap between 1200- and 850-μm-selected galaxies (hereafter SMGs), finding no significant difference between their distributions. However, a noise-weighted stacking analysis yields a significant detection of the 1200-μm-blank SCUBA sources, , whereas no significant 850-μm signal is found for the 850-μm-blank MAMBO sources . The hypothesis that the distribution of SCUBA sources is also representative of the MAMBO population is rejected at the ∼4σ level, via Monte Carlo simulations. Therefore, although the populations overlap, galaxies selected at 850 and 1200 μm are different, and there is compelling evidence for a significant 1200-μm-detected population which is not recovered at 850 μm. These are submillimetre dropouts (SDOs), with , requiring very cold dust or unusual spectral energy distributions , unless SDOs reside beyond the redshift range observed for radio-identified SMGs, i.e. at . [ABSTRACT FROM AUTHOR]

Observations of molecular hydrogen in quasar host galaxies at high redshifts provide fundamental constraints on galaxy evolution, because it is out of this molecular gas that stars form. Molecular hydrogen is traced by emission from the carbon monoxide molecule, CO; cold H[SUB2] itself is generally not observable. Carbon monoxide has been detected in about ten quasar host galaxies with redshifts z > 2; the record-holder is at z = 4.69 (refs 1-3). Here we report CO emission from the quasar SDSS J114816.64 + 525150.3 (refs 5, 6) at z = 6.42. At that redshift, the Universe was only 1/16 of its present age, and the era of cosmic reionization was just ending. The presence of about 2 ×10[SUP10] M&Odot; of H[SUB2] in an object at this time demonstrates that molecular gas enriched with heavy elements can be generated rapidly in the youngest galaxies. [ABSTRACT FROM AUTHOR]

We report interferometric imaging of [C II](2P3/2→2P1/2) and OH(2Π1/2J = 3/2→1/2) emission toward the center of the galaxy protocluster associated with the z = 5.3 submillimeter galaxy (SMG) AzTEC-3, using the Atacama Large (sub)Millimeter Array (ALMA). We detect strong [C II], OH, and rest-frame 157.7 μm continuum emission toward the SMG. The [C II](2P3/2→2P1/2) emission is distributed over a scale of 3.9 kpc, implying a dynamical mass of 9.7 × 1010M☼, and a star formation rate (SFR) surface density of ΣSFR = 530 M☼ yr–1 kpc–2. This suggests that AzTEC-3 forms stars at ΣSFR approaching the Eddington limit for radiation pressure supported disks. We find that the OH emission is slightly blueshifted relative to the [C II] line, which may indicate a molecular outflow associated with the peak phase of the starburst. We also detect and dynamically resolve [C II](2P3/2→2P1/2) emission over a scale of 7.5 kpc toward a triplet of Lyman-break galaxies with moderate UV-based SFRs in the protocluster at ∼95 kpc projected distance from the SMG. These galaxies are not detected in the continuum, suggesting far-infrared SFRs of <18-54 M☼ yr–1, consistent with a UV-based estimate of 22 M☼ yr–1. The spectral energy distribution of these galaxies is inconsistent with nearby spiral and starburst galaxies, but resembles those of dwarf galaxies. This is consistent with expectations for young starbursts without significant older stellar populations. This suggests that these galaxies are significantly metal-enriched, but not heavily dust-obscured, “normal” star-forming galaxies at z > 5, showing that ALMA can detect the interstellar medium in “typical” galaxies in the very early universe. [ABSTRACT FROM AUTHOR]

We present ALMA observations of the [C II] line and far-infrared (FIR) continuum of a normally star-forming galaxy in the reionization epoch, the z = 6.96 Lyα emitter (LAE) IOK-1. Probing to sensitivities of σline = 240 μJy beam–1 (40 km s–1 channel) and σcont = 21 μJy beam–1, we found the galaxy undetected in both [C II] and continuum. Comparison of ultraviolet (UV)-FIR spectral energy distribution (SED) of IOK-1, including our ALMA limit, with those of several types of local galaxies (including the effects of the cosmic microwave background, CMB, on the FIR continuum) suggests that IOK-1 is similar to local dwarf/irregular galaxies in SED shape rather than highly dusty/obscured galaxies. Moreover, our 3σ FIR continuum limit, corrected for CMB effects, implies intrinsic dust mass Mdust < 6.4 × 107M☼, FIR luminosity LFIR < 3.7 × 1010L☼ (42.5-122.5 μm), total IR luminosity LIR < 5.7 × 1010L☼ (8-1000 μm), and dust-obscured star formation rate (SFR) < 10 M☼ yr–1, if we assume that IOK-1 has a dust temperature and emissivity index typical of local dwarf galaxies. This SFR is 2.4 times lower than one estimated from the UV continuum, suggesting that <29% of the star formation is obscured by dust. Meanwhile, our 3σ [C II] flux limit translates into [C II] luminosity, L[C II] < 3.4 × 107L☼. Locations of IOK-1 and previously observed LAEs on the L[C II] versus SFR and L[C II]/LFIR versus LFIR diagrams imply that LAEs in the reionization epoch have significantly lower gas and dust enrichment than AGN-powered systems and starbursts at similar/lower redshifts, as well as local star-forming galaxies. [ABSTRACT FROM AUTHOR]