CO excitation in four IR luminous galaxies

The correlation between the CO and far infrared luminosities of spiral galaxies is well established. The luminosity ration, L sub FIR/L sub CO in IR luminous active galaxies is, however, systematically five to ten times higher than in ordinary spirals and molecular clouds in our Galaxy. Furthermore, the masses of molecular hydrogen in luminous galaxies are large, M (H2) approx. equals 10(exp 10) solar magnitude, which indicates the observed luminosity ratios are due to an excess of infrared output, rather than a deficiency of molecular gas. These large amounts of molecular gas may fuel luminous galaxies through either star formation or nuclear activity. This interpretation rests on applying the M (H2)/L sub CO ratio calibrated in our Galaxy to galaxies with strikingly different luminosity ratios. But are the physical conditions of the molecular gas different in galaxies with different luminosity ratios. And, if so, does the proportionality between CO and H2 also vary among galaxies. To investigate these questions researchers observed CO (2 to 1) and (1 to 0) emission from four luminous galaxies with the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope. Researchers conclude that most of the CO emission from these Arp 193, Arp 220, and Mrk 231 arises in regions with moderate ambient densities similar to the clouds in the Milky Way molecular ring. The emission is neither from dense hot cloud cores nor from the cold low density gas characteristic of the envelopes of dark clouds

Massive molecular outflows at high spatial resolution

We present high-spatial resolution Plateau de Bure Interferometer CO(2-1) and SiO(2-1) observations of one intermediate-mass and one high-mass star-forming region. The intermediate-mass region IRAS20293+3952 exhibits four molecular outflows, one being as collimated as the highly collimated jet-like outflows observed in low-mass star formation sources. Furthermore, comparing the data with additional infrared H2 and cm observations we see indications that the nearby ultracompact HII region triggers a shock wave interacting with the outflow. The high-mass region IRAS19217+1651 exhibits a bipolar outflow as well and the region is dominated by the central driving source. Adding two more sources from the literature, we compare position-velocity diagrams of the intermediate- to high-mass sources with previous studies in the low-mass regime. We find similar kinematic signatures, some sources can be explained by jet-driven outflows whereas other are better constrained by wind-driven models. The data also allow to estimate accretion rates varying from a few times 10^{-5}Msun/yr for the intermediate-mass sources to a few times 10^{-4}Msun/yr for the high-mass source, consistent with models explaining star formation of all masses via accretion processes.Comment: 14 pages text, 4 tables, 8 figures, accepted for Ap

Dense Molecular Gas and the Role of Star Formation in the Host Galaxies of Quasi-Stellar Objects

New millimeter-wave CO and HCN observations of the host galaxies of infrared-excess Palomar Green quasi-stellar objects (PG QSOs) previously detected in CO are presented. These observations are designed to assess the validity of using the infrared luminosity to estimate star formation rates of luminous AGN by determining the relative significance of dust-heating by young, massive stars and active galactic nuclei (AGN) in QSO hosts and IRAS galaxies with warm, AGN-like infrared colors. The HCN data show the PG QSO host IZw1 and most of the warm IRAS galaxies to have high L_IR / L'_HCN (>1600) relative to the cool IRAS galaxy population for which the median L_IR / L'_HCN ~ 890(+440,-470). If the assumption is made that the infrared emission from cool IRAS galaxies is reprocessed light from embedded star-forming regions, then high values of L_IR / L'_HCN are likely the result of dust heating by the AGN. Further, if the median ratio of L'_HCN / L'_CO ~ 0.06 observed for Seyfert galaxies and IZw1 is applied to the PG QSOs not detected in HCN, then the derived L_IR / L'_HCN correspond to a stellar contribution to the production of L_IR of ~ 7-39%, and star formation rates ~ 2-37 M_sun/yr are derived for the QSO hosts. Alternatively, if the far-infrared is adopted as the star formation component of the total infrared in cool galaxies, the stellar contributions in QSO hosts to their L_FIR are up to 35% higher than the percentages derived for L_IR. This raises the possibility that the L_FIR in several of the PG QSO hosts, including IZw1, could be due entirely to dust heated by young, massive stars. Finally, there is no evidence that the global HCN emission is enhanced relative to CO in galaxies hosting luminous AGN.Comment: LaTex, 31 pages, including 9 postscript figures, AJ, in press (December 2006

The Stellar Populations and Evolution of Lyman Break Galaxies

Using deep near-IR and optical observations of the HDF-N from the HST NICMOS and WFPC2 and from the ground, we examine the spectral energy distributions (SEDs) of Lyman break galaxies (LBGs) at 2.0 < z < 3.5. The UV-to-optical rest-frame SEDs of the galaxies are much bluer than those of present-day spiral and elliptical galaxies, and are generally similar to those of local starburst galaxies with modest amounts of reddening. We use stellar population synthesis models to study the properties of the stars that dominate the light from LBGs. Under the assumption that the star-formation rate is continuous or decreasing with time, the best-fitting models provide a lower bound on the LBG mass estimates. LBGs with ``L*'' UV luminosities are estimated to have minimum stellar masses ~ 10^10 solar masses, or roughly 1/10th that of a present-day L* galaxy. By considering the effects of a second component of maximally-old stars, we set an upper bound on the stellar masses that is ~ 3-8 times the minimum estimate. We find only loose constraints on the individual galaxy ages, extinction, metallicities, initial mass functions, and prior star-formation histories. We find no galaxies whose SEDs are consistent with young (< 10^8 yr), dust-free objects, which suggests that LBGs are not dominated by ``first generation'' stars, and that such objects are rare at these redshifts. We also find that the typical ages for the observed star-formation events are significantly younger than the time interval covered by this redshift range (~ 1.5 Gyr). From this, and from the relative absence of candidates for quiescent, non-star-forming galaxies at these redshifts in the NICMOS data, we suggest that star formation in LBGs may be recurrent, with short duty cycles and a timescale between star-formation events of < 1 Gyr. [Abridged]Comment: LaTeX, 37 pages, 21 figures. Accepted for publication in the Astrophysical Journa

New Observations and a New Interpretation of CO(3--2) in IRAS F10214+4724

New observations with the IRAM interferometer of CO(3--2) from the highly luminous galaxy IRAS F10214+4724 show the source is 1.5'' x <= 0.9'' ; they display no evidence of any velocity gradient. This size, together with optical and IR data that show the galaxy is probably gravitationally lensed, lead to a new model for the CO distribution. In contrast to many lensed objects, we have a good estimate of the intrinsic CO and far IR surface brightnesses, so we can derive the CO and far IR/sub-mm magnifications. The CO is magnified 10 times and has a true radius of 400 pc. and the far IR is magnified 13 times and has a radius of 250 pc. The true far IR luminosity is 4 to 7e12 Lsun and the molecular gas mass is 2e10 Msun . This is nearly an order of magnitude less than previously estimated. Because the far IR magnification is lower than the mid and near IR magnification, the intrinsic spectral energy distribution now peaks in the far infrared. That is, nearly all of the energy of this object is absorbed and re-emitted in the far infrared. In CO luminosity, molecular gas content, CO linewidth, and corrected far IR luminosity, 10214+472 is a typical, warm, IR ultraluminous galaxy.Comment: 18 pages, including 3 figures, of gzipped, uuencoded postscript. To be published Ap.J. Letter

Petrography and Geochemistry of Metals in Almahata Sitta Ureilites

Ureilites are ultramafic achondrites, predominantly composed of olivine and pyroxenes with accessory carbon, metal and sulfide. The majority of ureilites are believed to represent the mantle of the ureilite parent body (UPB) [1]. Although ureilites have lost much of their original metal [2], the metal that remains retains a record of the formative processes. Almahata Sitta is predominantly composed of unbrecciated ureilites with a wide range of silicate compositions [3,4]. As a fall it presents a rare opportunity to examine fresh ureilite metal in-situ, and analyzing their highly siderophile element (HSE) ratios gives clues to their formation. Bulk siderophile element analyses of Almahata Sitta fall within the range observed in other ureilites [5]. We have examined the metals in seven ureilitic samples of Almahata Sitta (AS) and one associated chondrite fragment (AS#25)

The Molecular Interstellar Medium in Ultraluminous Infrared Galaxies

We present CO observations of a large sample of ultraluminous IR galaxies out to z = 0.3. Most of the galaxies are interacting, but not completed mergers. All but one have high CO(1-0) luminosities, log(Lco [K-km/s-pc^2]) = 9.92 +/- 0.12. The dispersion in Lco is only 30%, less than that in the FIR luminosity. The integrated CO intensity correlates Strongly with the 100 micron flux density, as expected for a black body model in which the mid and far IR radiation are optically thick. We use this model to derive sizes of the FIR and CO emitting regions and the enclosed dynamical masses. Both the IR and CO emission originate in regions a few hundred parsecs in radius. The median value of Lfir/Lco = 160 Lsun/(K-km/s-pc^2), within a factor of two of the black body limit for the observed FIR temperatures. The entire ISM is a scaled up version of a normal galactic disk with densities a factor of 100 higher, making even the intercloud medium a molecular region. Using three different techniques of H2 mass estimation, we conclude that the ratio of gas mass to Lco is about a factor of four lower than for Galactic molecular clouds, but that the gas mass is a large fraction of the dynamical mass. Our analysis of CO emission reduces the H2 mass from previous estimates of 2-5e10 Msun to 0.4-1.5e10 Msun, which is in the range found for molecular gas rich spiral galaxies. A collision involving a molecular gas rich spiral could lead to an ultraluminous galaxy powered by central starbursts triggered by the compression of infalling preexisting GMC's.Comment: 34 pages LaTeX with aasms.sty, 14 Postscript figures, submitted to ApJ Higher quality versions of Figs 2a-f and 7a-c available by anonymous FTP from ftp://sbast1.ess.sunysb.edu/solomon/

Observations on the Formation of Massive Stars by Accretion

Observations of the H66a recombination line from the ionized gas in the cluster of newly formed massive stars, G10.6-0.4, show that most of the continuum emission derives from the dense gas in an ionized accretion flow that forms an ionized disk or torus around a group of stars in the center of the cluster. The inward motion observed in the accretion flow suggests that despite the equivalent luminosity and ionizing radiation of several O stars, neither radiation pressure nor thermal pressure has reversed the accretion flow. The observations indicate why the radiation pressure of the stars and the thermal pressure of the HII region are not effective in reversing the accretion flow. The observed rate of the accretion flow, 0.001 solar masses/yr, is sufficient to form massive stars within the time scale imposed by their short main sequence lifetimes. A simple model of disk accretion relates quenched HII regions, trapped hypercompact HII regions, and photo-evaporating disks in an evolutionary sequence

Executive performance on the preschool executive task assessment in children with sickle cell anemia and matched controls

Executive deficits are commonly reported in children with sickle cell anemia. Earlier identification of executive deficits would give more scope for intervention, but this cognitive domain has not been routinely investigated due to a lack of age-appropriate tasks normed for preschool children. In particular, information relating to patient performance on an executive task that reflects an everyday activity in the classroom could provide important insight and practical recommendations for the classroom teacher at this key developmental juncture as they enter the academic domain. The performance of 22 children with sickle cell anemia was compared to 24 matched control children on the Preschool Executive Task Assessment. Findings reveal that children with sickle cell anemia are performing poorer than their matched peers on this multi-step assessment. In particular, children with sickle cell anemia required more structured support to shift focus after a completed step, as reflected by poorer scores in the quantitative Sequencing and Completion domains. They also required more support to stay on task, as seen by poorer ratings in the qualitative Distractibility domain. ABBREVIATIONS: PETA: Preschool Executive Task Assessment; SCA: Sickle Cell Anemia; EF: Executive Functioning