"Fri Apr 26"

The Column Density Distribution and Continuum Opacity of the Intergalactic and Circumgalactic Medium at Redshift <z>=2.4

Gwen C. Rudie, Charles C. Steidel, Alice E. Shapley, Max Pettini
(Submitted on 24 Apr 2013)

We present new high-precision measurements of the opacity of the intergalactic and circumgalactic medium (IGM, CGM) at <z>=2.4. Using Voigt profile fits to the full Lyman alpha and Lyman beta forests in 15 high-resolution high-S/N spectra of hyperluminous QSOs, we make the first statistically robust measurement of the frequency of absorbers with HI column densities 14 < log(NHI) < 17.2. We also present the first measurements of the frequency distribution of HI absorbers in the volume surrounding high-z galaxies (the CGM, 300 pkpc), finding that the incidence of absorbers in the CGM is much higher than in the IGM. In agreement with Rudie et al. (2012), we find that there are fractionally more high-NHI absorbers than low-NHI absorbers in the CGM compared to the IGM, leading to a shallower power law fit to the CGM frequency distribution. We use these new measurements to calculate the total opacity of the IGM and CGM to hydrogen-ionizing photons, finding significantly higher opacity than most previous studies, especially from absorbers with log(NHI) < 17.2. Reproducing the opacity measured in our data as well as the incidence of absorbers with log(NHI) > 17.2 requires a broken power law parameterization of the frequency distribution with a break near log(NHI) ~ 15. We compute new estimates of the mean free path (mfp) to hydrogen-ionizing photons at z=2.4, finding mfp = 147 +- 15 Mpc when considering only IGM opacity. If instead, we consider photons emanating from a high-z star-forming galaxy and account for the local excess opacity due to the surrounding CGM of the galaxy itself, the mean free path is reduced to mfp = 121 +- 15 Mpc. These mfp measurements are smaller than recent estimates and should inform future studies of the metagalactic UV background and of ionizing sources at z~2-3.

Comments: Accepted to ApJ
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1304.6719 [astro-ph.CO]
(or arXiv:1304.6719v1 [astro-ph.CO] for this version)

ALMA follows streaming of dense gas down to 40 pc from the supermassive black hole in NGC1097

Kambiz Fathi, Andreas A. Lundgren, Kotaro Kohno, Nuria Piñol-Ferrer, Sergio Martín, Daniel Espada, Evanthia Hatziminaoglou, Masatoshi Imanishi, Takuma Izumi, Melanie Krips, Satoki Matsushita, David S. Meier, Naomasa Nakai, Kartik Sheth, Jean Turner, Glenn van de Ven,Tommy Wiklind
(Submitted on 24 Apr 2013)

We present a kinematic analysis of the dense molecular gas in the central 200 parsecs of the nearby galaxy NGC1097, based on Cycle 0 observations with the Atacama Large Millimeter/sub-millimeter Array (ALMA). We use the HCN(4-3) line to trace the densest interstellar molecular gas, and quantify its kinematics, and estimate an inflow rate for the molecular gas. We find a striking similarity between the ALMA kinematic data and the analytic spiral inflow model that we have previously constructed based on ionized gas velocity fields on larger scales. We are able to follow dense gas streaming down to 40 pc distance from the supermassive black hole in this Seyfert 1 galaxy. In order to fulfill marginal stability, we deduce that the dense gas is confined to a very thin disc, and we derive a dense gas inflow rate of 0.09 Msun/yr at 40 pc radius. Combined with previous values from the Ha and CO gas, we calculate a combined molecular and ionized gas inflow rate of 0.2 Msun/yr at 40 pc distance from the central supermassive black hole of NGC1097.

Comments: Accepted for Publication in the ApJ Letters
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1304.6722 [astro-ph.CO]
(or arXiv:1304.6722v1 [astro-ph.CO] for this version)

On the redshift evolution (0 < z < 4) of dust attenuation and of the total (UV+IR) star formation rate density

D. Burgarella, V. Buat, C. Gruppioni, O. Cucciati, S. Heinis, S. Berta, M. Bethermin, A. Cooray, J.S. Dunlop, D. Farrah, A. Franceschini, E. Le Floc’h, D. Lutz, B. Magnelli, R. Nordon, S.J. Oliver, M.J. Page, P. Popesso, F. Pozzi, L. Riguccini, M. Vaccari, M. Viero
(Submitted on 25 Apr 2013)

Using new homogeneous LFs in the FUV and in the FIR Herschel/PEP and Herschel/HerMES, we study the evolution of the dust attenuation with redshift. With this information in hand, we are able to estimate the redshift evolution of the total (FUV + FIR) star formation rate density SFRD_TOT. By integrating SFRD_TOT, we follow the mass building and analyze the redshift evolution of the stellar mass density (SMD). This letter aims at providing a complete view of star formation from the local universe to z = 4 and, using assumptions on earlier star formation history, compares this evolution to what was known before in an attempt to draw a homogeneous picture of the global evolution of star formation in galaxies.
The main conclusions of this letter are: 1) the dust attenuation A_FUV is found to increase from z = 0 to z \sim 1.2 and then starts to decrease up to our last data point at z = 3.6; 2) the estimated SFRD confirms published results up to z = 2. At z > 2, we observe either a plateau or a small increase up to z = 3 and then a likely decrease up to z = 3.6; 3) the peak of A_FUV is delayed with respect to the plateau of SFRD_TOT and a likely origin might be found in the evolution of the bright ends of the FUV and FIR LFs; 4) using assumptions (namely exponential rise and linear rise with time) for the evolution of the star formation density from z = 3.6 to z_form = 10, we integrate SFRD_TOT and find a good agreement with the published SMDs.

Comments: Submitted to A&A
Subjects: Cosmology and Extragalactic Astrophysics (astro-ph.CO)
Cite as: arXiv:1304.7000 [astro-ph.CO]
(or arXiv:1304.7000v1 [astro-ph.CO] for this version)
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