P. Vanden Bout

The Evolution of Interstellar Medium Mass Probed by Dust Emission: ALMA Observations at z = 0.3-2

The use of submm dust continuum emission to probe the mass of interstellar dust and gas in galaxies is empirically calibrated using samples of local star forming galaxies, Planck observations of the Milky Way and high redshift submm galaxies (SMGs). All of these objects suggest a similar calibration, strongly supporting the view that the Rayleigh-Jeans (RJ) tail of the dust emission can be used as an accurate and very fast probe of the ISM in galaxies. We present ALMA Cycle 0 observations of the Band 7 (350 GHz) dust emission in 107 galaxies from z = 0.2 to 2.5. Three samples of galaxies with a total of 101 galaxies were stellar mass-selected from COSMOS to have M∗ ≃ 10 11 M⊙: 37 at z∼ 0.4, 33 at z∼ 0.9 and 31 at z= 2. A fourth sample with 6 IR luminous galaxies at z = 2 was observed for comparison with the purely mass-selected samples. From the fluxes detected in the stacked images for each sample, we find that the ISM content has decreased a factor ∼ 6 from 1−2×10 10 M⊙ at both z = 2 and 0.9 down to ∼ 2×10 9 M⊙ at z = 0.4. The IR luminous sample at z = 2 shows a further ∼ 4 times increase in MISM compared to the equivalent non-IR bright sample at the same redshift. The gas mass fractions are ∼ 2 ± 0.5,12 ± 3,14 ± 2 and 53 ± 3 % for the four subsamples (z = 0.4, 0.9, 2 and IR bright galaxies). Subject headings: cosmology: observations — cosmology: galaxy evolution ISM: clouds

The Black Hole-Bulge Relationship for QSOs at High Redshift

We examine the black hole mass-galaxy bulge relationship in high-redshift QSOs. Black hole masses are derived from broad emission lines, and the host galaxy stellar velocity dispersion σ* is estimated from the widths of the radio CO emission lines. At redshifts z > 3, the CO line widths are narrower than expected for the black hole mass, indicating that these giant black holes reside in undersized bulges by an order of magnitude or more. The largest black holes (MBH > 109 M☉) evidently grow rapidly in the early universe without commensurate growth of their host galaxies. CO line widths offer a unique opportunity to study AGN host galaxy dynamics at high redshift.

ENHANCED DENSE GAS FRACTION IN ULTRALUMINOUS INFRARED GALAXIES

We present a detailed analysis of the relation between infrared luminosity and molecular line luminosity, for a variety of molecular transitions, using a sample of 34 nearby galaxies spanning a broad range of infrared luminosities (1010 L ☉ < L IR < 1012.5 L ☉). We show that the power-law index of the relation is sensitive to the critical density of the molecular gas tracer used, and that the dominant driver in observed molecular line ratios in galaxies is the gas density. As most nearby ultraluminous infrared galaxies (ULIRGs) exhibit strong signatures of active galactic nuclei (AGNs) in their center, we revisit previous claims questioning the reliability of HCN as a probe of the dense gas responsible for star formation in the presence of AGNs. We find that the enhanced HCN(1-0)/CO(1-0) luminosity ratio observed in ULIRGs can be successfully reproduced using numerical models with fixed chemical abundances and without AGN-induced chemistry effects. We extend this analysis to a total of 10 molecular line ratios by combining the following transitions: CO(1-0), HCO+(1-0), HCO+(3-2), HCN(1-0), and HCN(3-2). Our results suggest that AGNs reside in systems with higher dense gas fraction, and that chemistry or other effects associated with their hard radiation field may not dominate (NGC 1068 is one exception). Galaxy merger could be the underlying cause of increased dense gas fraction, and the evolutionary stage of such mergers may be another determinant of the HCN/CO luminosity ratio.

The essential signature of a massive starburst in a distant quasar.

Observations of carbon monoxide emission in high-redshift (z > 2) galaxies indicate the presence of large amounts of molecular gas. Many of these galaxies contain an active galactic nucleus powered by accretion of gas onto a supermassive black hole, and a key question is whether their extremely high infrared luminosities result from the active galactic nucleus, from bursts of massive star formation (associated with the molecular gas), or both. In the Milky Way, high-mass stars form in the dense cores of interstellar molecular clouds, where gas densities are n(H2) > 105 cm-3 (refs 1, 2). Recent surveys show that virtually all galactic sites of high-mass star formation have similarly high densities. The bulk of the cloud material traced by CO observations, however, is at a much lower density. For galaxies in the local Universe, the HCN molecule is an effective tracer of high-density molecular gas. Here we report observations of HCN emission from the infrared-luminous ‘Cloverleaf’ quasar (at a redshift z = 2.5579). The HCN line luminosity indicates the presence of 10 billion solar masses of very dense gas, an essential feature of an immense starburst, which contributes, together with the active galactic nucleus it harbours, to its high infrared luminosity.

A new probe of dense gas at high redshift: detection of HCO+ (5-4) line emission in APM 08279+5255

We report the detection of HCO+ (5-4) emission from the broad absorption line quasar APM 08279+5255 at z = 3.911 based on observations conducted with the IRAM Plateau de Bure Interferometer. This represents the first detection of this molecular ion at such a high redshift. The inferred line luminosity, uncorrected for lensing, is L = (3.5 ± 0.6) × 1010 K km s-1 pc2. The HCO+ J = 5-4 source position coincides within the errors with that reported from previous HCN J = 5-4 and high-J CO line observations of this quasar. The HCO+ line profile central velocity and width are consistent with those derived from HCN. This result suggests that HCO+ (5-4) emission comes roughly from the same circumnuclear region probed by HCN. However, the HCN (5-4)/HCO+ (5-4) intensity ratio measured in APM 08279+5255 is significantly larger than that predicted by simple radiative transfer models, which assume collisional excitation and equal molecular abundances. This could imply that the [HCN]/[HCO+] abundance ratio is particularly large in this source, or that the J = 5 rotational levels are predominantly excited by infrared fluorescent radiation.

Detection of HNC and tentative detection of CN at z = 3.9

Accepted for publication in Astronomy and Astrophysics Letters (A&ALetters). Acceptance date: 7th December 2006.

The Star Formation Rate-Dense Gas Relation in Galaxies as Measured by HCN(3-2) Emission

We present observations made with the 10 m Heinrich Hertz Submillimeter Telescope of HCN(3-2) emission from a sample of 30 nearby galaxies ranging in infrared luminosity from 1010 to 1012.5 L☉ and HCN(3-2) luminosity from 106 to 109 K km s−1 pc2. We examine the correlation between the infrared luminosity and HCN(3-2) luminosity and find that the best-fit linear regression has a slope (in log-log space) of 0.74 ± 0.12. Including recently published data from Gracia-Carpio et al. tightens the constraints on the best-fit slope to 0.79 ± 0.09. This slope below unity suggests that the HCN(3-2) molecular line luminosity is not linearly tracing the amount of dense gas. Our results are consistent with predictions from recent theoretical models that find slopes below unity when the line luminosity depends on the average gas density with a power-law index greater than a Kennicutt-Schmidt index of 1.5.

Energetics of molecular clouds. III. The S235 molecular cloud

The molecular cloud associated with the S235 H II region has been studied by means of molecular lines and near-infrared observations. The cloud consists of two components, one of which partly surrounds the S235 H II region. The other component contains a dense, hot region of active star formation, marked by self-reversed CO profiles, compact H II regions, masers, and infrared sources. From the molecular line data, the size and mass of the two components are estimated to be 6--8 pc and 3--4 x 10/sup 3/ M/sub sun/. More detailed studies near the region of active star formation yield estimates of density (approx.2--5 x 10/sup 5/ cm/sup -3/) and the abundances of H/sub 2/CO, HCO/sup +/, HCN, and /sup 13/CO. Analysis of the energetics suggests that the cloud is heated by the exciting star of S235 and by the exciting stars of the compact H II regions. Assuming that the gas is heated by collisions with warm dust grains, the far-infrared luminosity has been predicted. The observations of far-infrared emission are in reasonable agreement with predictions.

Simultaneous ultraviolet, optical, and X-ray observations of the X-ray source Vela X-1 (HD 77581)

Ultraviolet spectra of HD 77581, associated with the binary X-ray source Vela X-1, taken with the International Ultraviolet Explorer satellite (IUE) show a spectrum typical of an early B-type supergiant. However, the P Cygni profiles of strong resonance lines show substantial variations with orbital phase. These variations can be ascribed to the changing ionization state in the stellar wind caused by the X-ray emitting companion as suggested by Hatchett and McCray. The mass loss of the supergiant primary is determined to be approx.1 x 10/sup -6/ M/sub sun/ yr/sup -1/. X-ray and spectroscopic and photometric optical observations, simultaneous with the IUE measurements, indicate behavior consistent with previous epochs. The interstellar spectrum shows strong, relatively broad lines of highly ionized Si IV and CIV which may result from the effects of X-rays upon the interstellar material neighboring the source.

Evolution of Interstellar Medium, Star Formation, and Accretion at High Redshift

ALMA observations of the long wavelength dust continuum are used to estimate the interstellar medium (ISM) masses in a sample of 708 galaxies at z = 0.3 to 4.5 in the COSMOS field. The galaxy sample has known far-infrared luminosities and, hence, star formation rates (SFRs) and stellar masses (M∗) from the optical–infrared spectrum fitting. The galaxies sample SFRs from the main sequence (MS) to 50 times above the MS. The derived ISM masses are used to determine the dependence of gas mass on redshift, M∗, and specific SFR (sSFR) relative to the MS. The ISM masses increase approximately with the 0.63 power of the rate of increase in SFRs with redshift and the 0.32 power of the sSFR/sSFRMS. The SF efficiencies also increase as the 0.36 power of the SFR redshift evolution and the 0.7 power of the elevation above the MS; thus the increased activities at early epochs are driven by both increased ISM masses and SF efficiency. Using the derived ISM mass function, we estimate the accretion rates of gas required to maintain continuity of the MS evolution (> 100 M⊙ yr^(−1) at z > 2.5). Simple power-law dependencies are similarly derived for the gas accretion rates. We argue that the overall evolution of galaxies is driven by the rates of gas accretion. The cosmic evolution of total ISM mass is estimated and linked to the evolution of SF and active galactic nucleus activity at early epochs.