A search for Ly-alpha emitters around a concentrated-region of strong Ly-alpha absorbers at z=2.3 [GA]


In order to investigate the physical relationship between strong Ly-alpha absorbers (logN_HI>20.0 cm^-2) such as damped Ly-alpha absorption systems (DLAs) and young star-forming galaxies at high redshift, we have conducted narrow-band observations of Ly-alpha emitters (LAEs) in a concentrated region of strong Ly-alpha absorbers at z= 2.3, the J1230+34 field. Using a catalog of Ly-alpha absorbers with logN_HI>20.0 cm^-2 based on the baryon oscillation spectroscopic survey (BOSS), we found 6 fields where 3 or more absorbers are concentrated within a (50 Mpc)^3 cubic box in the comoving scale. Among them, we focus on the J1230+34 field, where 2 DLAs and 2 sub-DLAs present. Our narrow-band imaging observations with Subaru/Suprime-Cam using a custom-made filter, NB400 (lambda_c=4003 A and FWHM=92 A) yield a sample of 149 LAEs in this field. In the large scale (~50 Mpc), we have found no differences between the obtained Ly-alpha luminosity function and those in the blank fields at similar redshifts. We also compare the frequency distribution of the Ly-alpha rest-frame equivalent width (EW_0) in the target field and other fields including both overdensity region and blank field, but find no differences. On the other hand, in the small scale (~10 Mpc), we have found a possible overdensity of LAEs around a DLA with the highest HI column density (N_HI=21.08 cm^-2) in the target field while there are no density excess around the other absorbers with a lower N_HI.

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K. Ogura, T. Nagao, M. Imanishi, et. al.
Fri, 17 Mar 17

Comments: 15 pages, 15 figures, Accepted for publication to PASJ

Effects of dust absorption on spectroscopic studies of turbulence [GA]


We study the effect of dust absorption on the recovery velocity and density spectra as well as on the anisotropies of magnetohydrodynamic turbulence using the Velocity Channel Analysis (VCA), Velocity Coordinate Spectrum (VCS) and Velocity Centroids. The dust limits volume up to an optical depth of unity. We show that in the case of the emissivity proportional to the density of emitters, the effects of random density get suppressed for strong dust absorption intensity variations arise from the velocity fluctuations only. However, for the emissivity proportional to squared density, both density and velocity fluctuations affect the observed intensities. We predict a new asymptotic regime for the spectrum of fluctuations for large scales exceeding the physical depths to unit optical depth. The spectrum gets shallower by unity in this regime. In addition, the dust absorption removes the degeneracy resulted in the universal $K^{-3}$ spectrum of intensity fluctuations of self-absorbing medium reported by Lazarian & Pogosyan. We show that the predicted result is consistent with the available HII region emission data. We find that for sub-Alfv\’enic and trans-Alfv\’enic turbulence one can get the information about both the magnetic field direction and the fundamental Alfv\’en, fast and slow modes that constitute MHD turbulence.

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D. Kandel, A. Lazarian and D. Pogosyan
Fri, 17 Mar 17

Comments: N/A

An X-ray/SDSS sample (I): multi-phase outflow incidence and dependence on AGN luminosity [GA]


Multi-phase fast, massive outflows have been postulated to play a crucial role in galaxy evolution. The aim of this work is to constrain the nature and the fraction of outflowing gas in AGNs, as well as the nuclear conditions possibly at the origin of such phenomena.
We present a large spectroscopic sample of X-ray detected SDSS AGNs at z <0.8. X-ray and optical flux ratio diagnostics are used to select the sample. Physical and kinematic characterisation are derived re-analysing optical (and X-ray) spectra.
We derive the incidence of ionised (~40%) and atomic (< 1%) outflows covering a wide range of AGN bolometric luminosity, from 10^42 to 10^46 erg/s. We also derive bolometric luminosities and X-ray bolometric corrections to test whether the presence of outflows is associated with an X-ray loudness, as suggested by our recent results obtained studying high-z QSOs.
We study the relations between the outflow velocity inferred from [O III] kinematic analysis and different AGN power tracers, such as black hole mass (M_BH), [O III] and X-ray luminosity. We show a well defined positive trend between outflow velocity and L_X, for the first time over a range of 5 order of magnitudes. Overall, we find that in the QSO-luminosity regime and at M_BH>10^8 Msun the fraction of AGNs with outflows becomes >50%. Finally, we discuss our results about X-ray bolometric corrections and outflow incidence in cold and ionised phases in the context of an evolutionary sequence allowing two distinct stages for the feedback phase: an initial stage characterized by X-ray/optical obscured AGNs in which the atomic gas is still present in the ISM and the outflow processes involve all the gas components, and a later stage associated with unobscured AGNs, which line of sight has been cleaned and the cold components have been heated or exhausted.

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M. Perna, G. Lanzuisi, M. Brusa, et. al.
Fri, 17 Mar 17

Comments: 16 pages, 13 figures, Accepted for publication in A&A

Dark-ages reionization and galaxy formation simulation XI: Clustering and halo masses of high redshift galaxies [GA]


We investigate the clustering properties of Lyman-break galaxies (LBGs) at $z\sim6$ – $8$. Using the semi-analytical model {\scshape Meraxes} constructed as part of the Dark-ages Reionization And Galaxy-formation Observables from Numerical Simulation (DRAGONS) project, we predict the angular correlation function (ACF) of LBGs at $z\sim6$ – $8$. Overall, we find that the predicted ACFs are in good agreement with recent measurements at $z\sim 6$ and $z\sim 7.2$ from observations consisting of the Hubble eXtreme Deep Field (XDF), the Hubble Ultra-Deep Field (HUDF) and Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) field. We confirm the dependence of clustering on luminosity, with more massive dark matter haloes hosting brighter galaxies, remains valid at high redshift. The predicted galaxy bias at fixed luminosity is found to increase with redshift, in agreement with observations. We find that LBGs of magnitude $M_{{\rm AB(1600)}} < -19.4$ at $6\lesssim z \lesssim 8$ reside in dark matter haloes of mean mass $\sim 10^{11.0}$- $10^{11.5} M_{\rm \odot}$, and this dark matter halo mass does not evolve significantly during reionisation.

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J. Park, H. Kim, C. Liu, et. al.
Fri, 17 Mar 17

Comments: 14 pages, 10 figures, submitted to MNRAS

Optical Thickness, Spin Temperature, and Correction Factor for Density of the Galactic HI Gas [GA]


A method to determine the spin temperature of the local (Vlsr=0 km/s) HI gas using saturated brightness temperature of the 21-cm line in the radial-velocity degenerate regions (VDR) is presented. The spin temperatures is determined to be Ts= 146.2 +/- 16.1 K by measuring saturated brightness in the VDR toward the Galactic Center, 146.8 +/- 10.7 K by chi^2 fitting of expected brightness distribution to observation around the VDR, and 144.4 +/- 6.8 K toward the local arm. Assuming Ts=146 K, a correction factor Gamma for the HI density, defined by the ratio of the true HI density for finite optical thickness to that calculated by assuming optically thin HI, was obtained to be Gamma~1.2 (optical depth tau~0.3) in the local HI gas, ~1.8 (~1.3) toward the arm and anti-center, and as high as ~3.6 (~2.7) in the Galactic Center direction. It is suggested that the HI density and mass in the local arm could be ~2 times, and that in the inner Galaxy ~3.6 times, greater than the currently estimated values.

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Y. Sofue
Fri, 17 Mar 17

Comments: 10 pages, 13 figures, accepted for MNRAS

Accurate recovery of HI velocity dispersion from radio interferometers [GA]


Gas velocity dispersion measures the amount of disordered motions of a rotating disk. Accurate estimates of this parameter are of the utmost importance because it is directly linked to disk stability and star formation. A global measure of the gas velocity dispersion can be inferred from the width of the atomic hydrogen HI 21 cm line. We explore how several systematic effects involved in the production of HI cubes affect the estimate of HI velocity dispersion. We do so by comparing the HI velocity dispersion derived from different types of data cubes provided by The HI Nearby Galaxy Survey (THINGS). We find that residual-scaled cubes best recover the HI velocity dispersion, independent of the weighting scheme used and for a large range of signal-to-noise ratio. For HI observations where the dirty beam is substantially different from a Gaussian, the velocity dispersion values are overestimated unless the cubes are cleaned close to (e.g., ~1.5 times) the noise level.

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R. Ianjamasimanana, W. Blok and G. Heald
Fri, 17 Mar 17

Comments: Accepted for publication in the Astronomical Journal, 14 pages, 12 Figures, 2 Tables

The predicted luminous satellite populations around SMC and LMC-mass galaxies – A missing satellite problem around the LMC? [GA]


Recent discovery of many dwarf satellite galaxies in the direction of the Small and Large Magellanic Clouds (SMC and LMC) provokes questions of their origins, and what they can reveal about galaxy evolution theory. Here, we predict the satellite stellar mass function of Magellanic Cloud-mass host galaxies using abundance matching and reionization models applied to the Caterpillar simulations. Specifically focusing on the volume within 50 kpc of the LMC, we predict a mean of 4-8 satellites with stellar mass $M_* > 10^4 \, \mathrm{M_\odot}$, and 3-4 satellites with $80 < M_* \leq 3000 \, \mathrm{M_\odot}$. Surprisingly, all $12$ currently known satellite candidates have stellar masses of $80 < M_* \leq 3000 \, \mathrm{M_\odot}$. Reconciling the dearth of large satellites and profusion of small satellites is challenging and may require a combination of a major modification of the $M_* – M_{\rm{halo}}$ relationship (steep, but with an abrupt flattening at $10^3 \, \mathrm{M_\odot}$), late reionization for the Local Group ($z_{\rm{reion}} \lesssim 9$ preferred), and/or strong tidal stripping. We can more robustly predict that $\sim 53\%$ of satellites within this volume were accreted together with the LMC and SMC, and $\sim 47\%$ were only ever Milky Way satellites. Observing satellites of isolated LMC-sized field galaxies is essential to placing the LMC in context, and to better constrain the $M_* – M_{\rm{halo}}$ relationship. Modeling known LMC-sized galaxies within $8$ Mpc, we predict 1-6 (2-12) satellites with $M_* > 10^5 \, \mathrm{M_\odot}$ ($M_* > 10^4 \, \mathrm{M_\odot}$) within the virial volume of each, and 1-3 (1-7) within a single $1.5^{\circ}$ diameter field of view, making their discovery likely.

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G. Dooley, A. Peter, J. Carlin, et. al.
Fri, 17 Mar 17

Comments: Submitted to MNRAS, 15 pages, 7 figures