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Rapid star formation in the presence of active galactic nuclei

Astrophysical Journal 646:II (2006) L37-L39

Authors:

C Lintott, S Viti

Abstract:

Recent observations reveal galaxies in the early universe (2 < z < 6.4) with large reservoirs of molecular gas and extreme star formation rates. For a very large range of sources, a tight relationship exists between star formation rate and the luminosity of the HCN 7 = 1-0 spectral line, but sources at redshifts of z ∼ 2 and beyond do not follow this trend. The deficit in HCN is conventionally explained by an excess of infrared radiation due to active galactic nuclei (AGNs). We show in this Letter not only that the presence of AGNs cannot account for the excess of IR over molecular luminosity, but also that the observed abundance of HCN is in fact consistent with a population of stars forming from near-primordial gas. © 2006. The American Astronomical Society. All rights reserved.

Sinfoni integral field spectroscopy of z ∼ 2 UV-selected galaxies: Rotation curves and dynamical evolution

Astrophysical Journal 645:2 I (2006) 1062-1075

Authors:

NM Förster Schreiber, R Genzei, MD Lehnert, N Bouché, A Verma, DK Erb, AE Shapley, CC Steidel, R Davies, D Lutz, N Nesvadba, LJ Tacconi, F Eisenhauer, R Abuter, A Gilbert, S Gillessen, A Sternberg

Abstract:

We present ∼0″5 resolution near-infrared integral field spectroscopy of the Hα line emission of 14 z ∼ 2 UV-selected BM/BX galaxies, obtained with SINFONI at the ESO Very Large Telescope. The average Hα half-light radius is r1/2 ≈4 h70-1 kpc, and line emission is detected over ≳20 h70-1 kpc in several sources. In nine galaxies, we detect spatially resolved velocity gradients, from 40 to 410 km s-1 over ∼10 h70 -1 kpc. The kinematics of the larger systems are generally consistent with orbital motions. Four galaxies are well described by rotating clumpy disks, and we extracted rotation curves out to radii ≳10 h 70-1 kpc. One or two galaxies exhibit signatures more consistent with mergers. Analyzing all 14 galaxies in the framework of rotating disks, we infer mean inclination- and beam-corrected maximum circular velocities of vc ∼ 180 ± 90 km s-1 and dynamical masses from ∼0.5 to 25 × 1010 h70-1 M ⊙ within r1/2- The specific angular momenta of our BM/BX galaxies are similar to those of local late-type galaxies. Moreover, the specific angular momenta of their baryons are comparable to those of their dark matter halos. Extrapolating from the average vc at 10 h 70-1 kpc, the virial mass of the typical halo of a galaxy in our sample is 1011.7±0.5 h70-1 M ⊙. Kinematic modeling of the three best cases implies a ratio of vc to local velocity dispersion vc/σ ∼ 2-4 and, accordingly, a large geometric thickness. We argue that this suggests a mass accretion (alternatively, gas exhaustion) timescale of ∼500 Myr. We also argue that if our BM/BX galaxies were initially gas-rich, their clumpy disks would subsequently lose their angular momentum and form compact bulges on a timescale of ∼1 Gyr. © 2006. The American Astronomical Socieity. All rights reserved.

Rapid Star Formation in the Presence of Active Galactic Nuclei

ArXiv astro-ph/0606157 (2006)

Authors:

Chris Lintott, Serena Viti

Abstract:

Recent observations reveal galaxies in the early Universe (2

Anglo-australian telescope imaging and microslit spectroscopy in the southern bubble deep field

Astronomical Journal 131:5 (2006) 2383-2393

Authors:

K Glazebrook, A Verma, B Boyle, S Oliver, RG Mann, D Monbleau

Abstract:

We present a deep photometric (B- and R-band) catalog and an associated spectroscopic redshift survey conducted in the vicinity of the Hubble Deep Field-South. The spectroscopy yields 53 extragalactic redshifts in the range 0 < z < 1.4, substantially increasing the body of spectroscopic work in this field to over 200 objects. The targets are selected from deep Anglo-Australian Telescope prime-focus images complete to R < 24, and the spectroscopy is 5 0% complete at R = 23. There is now strong evidence for a rich cluster at z ≃ 0.5 8 flanking the Wide Field Planetary Camera 2 field, which is consistent with a known absorber of the bright QSO in this field. We find that photometric redshifts of z < 1 galaxies in this field based on Hubble Space Telescope data are accurate to σ z/(1 + z) = 0.03 (albeit with small number statistics). The observations were carried out as a community service for Hubble Deep Field science in order to demonstrate the first use of the nod-and-shuffle technique with a classical multiobject spectrograph and to test the use of microslits for ultrahigh multiplex observations along with a new volume phase holographic grism and deep-depletion CCD. The reduction of this new type of data is also described. © 2006. The American Astronomical Society. All rights reserved.

Determining the cosmic ray ionization rate in dynamically evolving clouds

Astronomy and Astrophysics 448:2 (2006) 425-432

Authors:

CJ Lintott, JMC Rawlings

Abstract:

The ionization fraction is an important factor in determining the chemical and physical evolution of star forming regions. In the dense, dark starless cores of such objects, the ionization rate is dominated by cosmic rays; it is therefore possible to use simple analytic estimators, based on the relative abundances of different molecular tracers, to determine the cosmic ray ionization rate. This paper uses a simple model to investigate the accuracy of two well-known estimators in dynamically evolving molecular clouds. It is found that, although the analytical formulae based on the abundances of H 3+, H2, CO, O, H2O and HCO + give a reasonably accurate measure of the cosmic ray ionization rate in static, quiescent clouds, significant discrepancies occur in rapidly evolving (collapsing) clouds. As recent evidence suggests that molecular clouds may consist of complex, dynamically evolving sub-structure, we conclude that simple abundance ratios do not provide reliable estimates of the cosmic ray ionization rate in dynamically active regions. © ESO 2006.