Search

Submillimetre galaxies (SMGs) are some of the most extreme star-forming systems in the Universe, whose place in the framework of galaxy evolution is as yet uncertain. It has been hypothesized that SMGs are progenitors of local early-type galaxies, requiring that SMGs generally reside in galaxy cluster progenitors at high redshift. We test this hypothesis and explore SMG environments using a narrow-band VLT/HAWK-I+GRAAL study of H  |$\alpha$| and [O  iii ] emitters around an unbiased sample of three ALMA-identified and spectroscopically confirmed SMGs at |$z \sim 2.3$| and |$\sim 3.3$|⁠ , where these SMGs were selected solely on spectroscopic redshift. Comparing with blank-field observations at similar epochs, we find that one of the three SMGs lies in an overdensity of emission-line sources on the |$\sim 4$| Mpc scale of the HAWK-I field of view, with overdensity parameter |$\delta _{g} = 2.6^{+1.4}_{-1.2}$|⁠. A second SMG is significantly overdense only on |$\lesssim 1.6$| Mpc scales and the final SMG is consistent with residing in a blank field environment. The total masses of the two overdensities are estimated to be |$\log (M_{h}/{\rm M}_{\odot }) =$| 12.1–14.4, leading to present-day masses of |$\log (M_{h,z=0}/{\rm M}_{\odot }) =$| 12.9–15.9. These results imply that SMGs occupy a range of environments, from overdense protoclusters or protogroups to the blank field, suggesting that while some SMGs are strong candidates for the progenitors of massive elliptical galaxies in clusters, this may not be their only possible evolutionary pathway. [ABSTRACT FROM AUTHOR]

We present a high-resolution study of the cold molecular gas as traced by CO(1-0) in the unlensed z ∼ 3.4 submillimeter galaxy SMM J13120+4242, using multiconfiguration observations with the Karl G. Jansky Very Large Array (JVLA). The gas reservoir, imaged on 0.″39 (∼3 kpc) scales, is resolved into two components separated by ∼11 kpc with a total extent of 16 ± 3 kpc. Despite the large spatial extent of the reservoir, the observations show a CO(1-0) FWHM linewidth of only 267 ± 64 km sâˆ'1. We derive a revised line luminosity of L CO (1 âˆ' 0) ′ = (10 ± 3) Ă— 1010 K km sâˆ'1 pc2 and a molecular gas mass of M gas = (13 ± 3)Ă— 1010 (α CO/1) M ⊙. Despite the presence of a velocity gradient (consistent with previous resolved CO(6-5) imaging), the CO(1-0) imaging shows evidence for significant turbulent motions that are preventing the gas from fully settling into a disk. The system likely represents a merger in an advanced stage. Although the dynamical mass is highly uncertain, we use it to place an upper limit on the CO-to-H2 mass conversion factor α CO of 1.4. We revisit the SED fitting, finding that this galaxy lies on the very massive end of the main sequence at z = 3.4. Based on the low gas fraction, short gas depletion time, and evidence for a central AGN, we propose that SMM J13120 is in a rapid transitional phase between a merger-driven starburst and an unobscured quasar. The case of SMM J13120 highlights how mergers may drive important physical changes in galaxies without pushing them off the main sequence. [ABSTRACT FROM AUTHOR]

We study the molecular gas content of 24 star-forming galaxies at z = 3–4, with a median stellar mass of 109.1M⊙, from the MUSE Hubble Ultra Deep Field (HUDF) Survey. Selected by their Lyαλ1216 emission and HF160W-band magnitude, the galaxies show an average Å, below the typical selection threshold for Lyα emitters (Å), and a rest-frame UV spectrum similar to Lyman-break galaxies. We use rest-frame optical spectroscopy from KMOS and MOSFIRE, and the UV features observed with MUSE, to determine the systemic redshifts, which are offset from Lyα by 〈Δv(Lyα)〉 = 346 km s−1, with a 100 to 600 km s−1 range. Stacking 12CO J = 4 → 3 and [C i ]3P1 → 3P0 (and higher-J CO lines) from the ALMA Spectroscopic Survey of the HUDF, we determine 3σ upper limits on the line luminosities of 4.0 × 108 K km s−1pc2 and 5.6 × 108 K km s−1pc2, respectively (for a 300 km s−1 line width). Stacking the 1.2 mm and 3 mm dust-continuum flux densities, we find a 3σ upper limits of 9 μJy and 1.2 μJy, respectively. The inferred gas fractions, under the assumption of a "Galactic" CO-to-H2 conversion factor and gas-to-dust ratio, are in tension with previously determined scaling relations. This implies a substantially higher αCO ≥ 10 and δGDR ≥ 1200, consistent with the subsolar metallicity estimated for these galaxies (). The low metallicity of z ≥ 3 star-forming galaxies may thus make it very challenging to unveil their cold gas through CO or dust emission, warranting further exploration of alternative tracers, such as [C ii ]. [ABSTRACT FROM AUTHOR]

The Atacama Large Millimeter/submillimeter Array (ALMA) Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS) Band 6 scan (212–272 GHz) covers potential [C ii ] emission in galaxies at 6 ≤ z ≤ 8 throughout a 2.9 arcmin2 area. By selecting on known Lyα emitters (LAEs) and photometric dropout galaxies in the field, we perform targeted searches down to a 5σ [C ii ] luminosity depth L[C II ] ∼ 2.0 × 108L⊙, corresponding roughly to star formation rates (SFRs) of 10–20 M⊙ yr−1 when applying a locally calibrated conversion for star-forming galaxies, yielding zero detections. While the majority of galaxies in this sample are characterized by lower SFRs, the resulting upper limits on [C ii ] luminosity in these sources are consistent with the current literature sample of targeted ALMA observations of z = 6–7 LAEs and Lyman-break galaxies (LBGs), as well as the locally calibrated relations between L[C ii ] and SFR—with the exception of a single [C ii ]-deficient, UV-luminous LBG. We also perform a blind search for [C ii ]-bright galaxies that may have been missed by optical selections, resulting in an upper limit on the cumulative number density of [C ii ] sources with L[C II ] > 2.0 × 108L⊙ (5σ) to be less than 1.8 × 10−4 Mpc−3 (90% confidence level). At this luminosity depth and volume coverage, we present an observed evolution of the [C ii ] luminosity function from z = 6–8 to z ∼ 0 by comparing the ASPECS measurement to literature results at lower redshift. [ABSTRACT FROM AUTHOR]

We present an ALMA 1.3 mm (Band 6) continuum survey of lensed submillimeter galaxies (SMGs) at z = 1.0 to ∼3.2 with an angular resolution of ∼0.″2. These galaxies were uncovered by the Herschel Lensing Survey and feature exceptionally bright far-infrared continuum emission (Speak ≳ 90 mJy) owing to their lensing magnification. We detect 29 sources in 20 fields of massive galaxy clusters with ALMA. Using both the Spitzer/IRAC (3.6/4.5 μm) and ALMA data, we have successfully modeled the surface brightness profiles of 26 sources in the rest-frame near- and far-infrared. Similar to previous studies, we find the median dust-to-stellar continuum size ratio to be small (Re,dust/Re,star = 0.38 ± 0.14) for the observed SMGs, indicating that star formation is centrally concentrated. This is, however, not the case for two spatially extended main-sequence SMGs with a low surface brightness at 1.3 mm (≲0.1 mJy arcsec−2), in which the star formation is distributed over the entire galaxy (Re,dust/Re,star > 1). As a whole, our SMG sample shows a tight anticorrelation between (Re,dust/Re,star) and far-infrared surface brightness (ΣIR) over a factor of ≃1000 in ΣIR. This indicates that SMGs with less vigorous star formation (i.e., lower ΣIR) lack central starburst and are likely to retain a broader spatial distribution of star formation over the whole galaxies (i.e., larger Re,dust/Re,star). The same trend can be reproduced with cosmological simulations as a result of central starburst and potentially subsequent "inside-out" quenching, which likely accounts for the emergence of compact quiescent galaxies at z ∼ 2. [ABSTRACT FROM AUTHOR]

We investigate the CO excitation and interstellar medium (ISM) conditions in a cold gas mass-selected sample of 22 star-forming galaxies at z = 0.46–3.60, observed as part of the ALMA Spectroscopic Survey in the Hubble Ultra Deep Field (ASPECS). Combined with Very Large Array follow-up observations, we detect a total of 34 CO transitions with J = 1 up to 8 (and an additional 21 upper limits, up to J = 10) and 6 and transitions (and 12 upper limits). The CO(2–1) and CO(3–2)-selected galaxies, at and 2.5, respectively, exhibit a range in excitation in their mid-J = 4, 5 and high-J = 7, 8 lines, on average lower than (-brighter) BzK-color- and submillimeter-selected galaxies at similar redshifts. The former implies that a warm ISM component is not necessarily prevalent in gas mass-selected galaxies at. We use stacking and Large Velocity Gradient models to measure and predict the average CO ladders at z < 2 and z ≥ 2, finding and , respectively. From the models, we infer that the galaxies at z ≥ 2 have intrinsically higher excitation than those at z < 2. This fits a picture in which the global excitation is driven by an increase in the star formation rate surface density of galaxies with redshift. We derive a neutral atomic carbon abundance of , comparable to the Milky Way and main-sequence galaxies at similar redshifts, and fairly high densities (≥104 cm−3), consistent with the low-J CO excitation. Our results imply a decrease in the cosmic molecular gas mass density at z ≥ 2 compared to previous ASPECS measurements. [ABSTRACT FROM AUTHOR]

We compare the extent of the dust, molecular gas, and stars in three star-forming galaxies, at z = 1.4, 1.6, and 2.7, selected from the Hubble Ultra Deep Field based on their bright carbon monoxide (CO) and dust-continuum emission as well as their large rest-frame optical sizes. The galaxies have high stellar masses, , and reside on, or slightly below, the main sequence of star-forming galaxies at their respective redshifts. We probe the dust and molecular gas using subarcsecond Atacama Large Millimeter/submillimeter Array observations of the 1.3 mm continuum and CO line emission, respectively, and probe the stellar distribution using Hubble Space Telescope observations at 1.6 μm. We find that for all three galaxies the CO emission appears ≳30% more compact than the stellar emission. For the z = 1.4 and 2.7 galaxies, the dust emission is also more compact, by ≳50%, than the stellar emission, whereas for the z = 1.6 galaxy, the dust and stellar emission have similar spatial extents. This similar spatial extent is consistent with observations of local disk galaxies. However, most high-redshift observations show more compact dust emission, likely because of the ubiquity of central starbursts at high redshift and the limited sensitivity of many of these observations. Using the CO emission line, we also investigate the kinematics of the cold interstellar medium in the galaxies, and find that all three have kinematics consistent with a rotation-dominated disk. [ABSTRACT FROM AUTHOR]

We present an Atacama Large Millimeter/submillimeter Array observation of the Submillimeter galaxy ID 141 at z = 4.24 in the [N ii ] 205 μm line (hereafter [N ii ]) and the underlying continuum at (rest-frame) 197.6 μm. Benefiting from lensing magnification by a galaxy pair at z = 0.595, ID 141 is one of the brightest SMGs. At the angular resolutions of –1.″5 (1″ ∼6.9 kpc), our observation clearly separates and moderately resolves the two lensed images in both continuum and line emission at a signal-to-noise ratio >5. Our continuum-based lensing model implies an averaged amplification factor of ∼5.8 and reveals that the delensed continuum image has a Sérsic index and Sérsic radius of ∼0.″18 (∼1.24 kpc). Furthermore, the reconstructed [N ii ] velocity field in the source plane is dominated by a rotation component with a maximum velocity of ∼300 km s−1 at large radii, indicating a dark matter halo mass of ∼10. This, together with the reconstructed velocity dispersion field being smooth and modest in value (<100 km s−1) over much of the outer parts of the galaxy, favors the interpretation of ID 141 being a disk galaxy dynamically supported by rotation. The observed [N ii ] /CO (7−6) and [N ii ] /[C ii ] 158 μm line-luminosity ratios, which are consistent with the corresponding line ratio versus far-infrared color correlation from local luminous infrared galaxies, imply a delensed star formation rate of (1.8 yr−1 and provide an independent estimate of the size of the star-forming region kpc in radius. [ABSTRACT FROM AUTHOR]

ABSTRACT We report results from a large molecular line survey of luminous infrared galaxies (LIRGs; [ABSTRACT FROM AUTHOR]

We determine star formation rates (SFRs) in a sample of color-selected, star-forming (sBzK) galaxies (KAB < 21.8 in the Extended Chandra Deep Field-South. To identify and avoid active galactic nuclei, we use X-ray, IRAC color and IR/radio flux ratio selection methods. Photometric redshift-binned, average flux densities are measured wit stacking analyses in Spitzer-MIPS IR, BLAST and APEX/LABOCA submillimeter, VLA and GMRT radio, and Chandra X-ray data. We include averages of aperture fluxes in MUSYC UBVRIz JHK images to determin UV-through-radio spectral energy distributions. We determine the total IR luminosities and compare SFR calibrations from FIR, 24µm, UV, radio, and X-ray wavebands. We find consistency with our best estimator SFRIR+UV, to within errors for the preferred radio SFR calibration. Our results imply that 24 µm only and X-ray SFR estimates should be applied to high-redshift galaxies with caution. Average IR luminosities are consistent with luminous infrared galaxies. We find SFRIR+UV for our stacked sBzKs at median redshifts 1.4, 1.8, and 2.2 to b 55 ± 6 (random error), 74 ± 8, and 154 ± 17Mʘ yr-1, respectively, with additional systematic uncertainty of factor of ~2. [ABSTRACT FROM AUTHOR]

A correction to the article "The Molecular Gas in Luminous Infrared Galaxies. II. Extreme Physical Conditions and Their Effects on the X co Factor," which appeared in a 2012 issue of the journal.

In this work, we conclude the analysis of our CO line survey of luminous infrared galaxies (LIRGs: LIR ≳ 1011L☼) in the local universe (Paper I) by focusing on the influence of their average interstellar medium (ISM) properties on the total molecular gas mass estimates via the so-called Xco = M(H2)/Lco, 1-0 factor. One-phase radiative transfer models of the global CO spectral line energy distributions (SLEDs) yield an Xco distribution with 〈 Xco〉 ∼ (0.6 ± 0.2) M☼ (K km s–1 pc2)–1 over a significant range of average gas densities, temperatures, and dynamic states. The latter emerges as the most important parameter in determining Xco, with unbound states yielding low values and self-gravitating states yielding the highest ones. Nevertheless, in many (U)LIRGs where available higher-J CO lines (J = 3-2, 4-3, and/or J = 6-5) or HCN line data from the literature allow a separate assessment of the gas mass at high densities (⩾104 cm–3) rather than a simple one-phase analysis, we find that near-Galactic X co ∼ (3-6) M ☼ (K km s–1 pc2)–1 values become possible. We further show that in the highly turbulent molecular gas in ULIRGs, a high-density component will be common and can be massive enough for its high Xco to dominate the average value for the entire galaxy. Using solely low-J CO lines to constrain Xco in such environments (as has been the practice up until now) may have thus resulted in systematic underestimates of molecular gas mass in ULIRGs, as such lines are dominated by a warm, diffuse, and unbound gas phase with low Xco but very little mass. Only well-sampled high-J CO SLEDs (J = 3-2 and higher) and/or multi-J observations of heavy rotor molecules (e.g., HCN) can circumvent such a bias, and the latter type of observations may have actually provided early evidence of it in local ULIRGs. The only way that the global Xco of such systems could be significantly lower than Galactic is if the average dynamic state of the dense gas is strongly gravitationally unbound. This is an unlikely possibility that must nevertheless be examined, with lines of rare isotopologues of high gas density tracers (e.g., H13CN, high-J13CO lines) being very valuable in yielding (along with the lines of the main isotopes) such constraints. For less IR-luminous, disk-dominated systems, we find that the galaxy-averaged Xco deduced by one-phase models of global SLEDs can also underestimate the total molecular gas mass when much of it lies in an star-formation-quiescent phase extending beyond a central star-forming region. This is because such a phase (and its large Xco) remains inconspicuous in global CO SLEDs. Finally, detailed studies of a subsample of galaxies find ULIRGs with large amounts (∼109M☼) of very warm (⩾100 K) and dense gas (≳105 cm–3), which could represent a serious challenge to photon-dominated regions as the main energy portals in the molecular ISM of such systems. [ABSTRACT FROM AUTHOR]