An investigation of the line of sight towards QSO PKS 0237-233

We present a detailed analysis of absorption systems along the line of sight towards QSO PKS 0237-233 using a high resolution spectrum of signal-to-noise ratio (SNR) ~ 60-80 obtained with the Ultraviolet and Visual Echelle Spectrograph mounted on the Very Large Telescope. This line of sight is known to show a remarkable overdensity of CIV systems that has been interpreted as revealing the presence of a supercluster of galaxies. A detailed analysis of each of these absorption systems is presented. In particular, for the z_abs = 1.6359 (with two components of logN(HI) = 18.45, 19.05) and z_abs = 1.6720 (logN(H I) = 19.78) sub-Damped Ly-alpha systems (sub-DLAs), we measure accurate abundances (resp. [O/H] = -1.63(0.07) and [Zn/H] = - 0.57(0.05) relative to solar). While the depletion of refractory elements onto dust grains in both sub-DLAs is not noteworthy, photoionization models show that ionization effects are important in a part of the absorbing gas of the sub-DLA at z_abs = 1.6359 (HI is 95 percent ionized) and in part of the gas of the sub-DLA at z_abs = 1.6359. The CIV clustering properties along the line of sight is studied in order to investigate the nature of the observed overdensity. We conclude that despite the unusually high number of CIV systems detected along the line of sight, there is no compelling evidence for the presence of a single unusual overdensity and that the situation is consistent with chance coincidence.Comment: Accepted for publication in MNRAS. 23 pages, 16 figures, 12 table

Deep Hubble Space Telescope Imaging on the Extended Lyα\alpha Emission of a QSO at z=2.19z = 2.19 with Damped Lyman Alpha System as a Natural Coronagraph

Recent observations suggest that proximate damped Ly$\alpha$ (PDLA) systems can be used to study the host galaxies of Quasi-stellar objects (QSOs), because the PDLAs can block the bright point-spread-function (PSF) from central QSOs. Using six-orbits of narrowband imaging with $\it{HST}$/WFC3, we present the first high resolution narrowband image of the Ly$\alpha$ emission in the PDLA trough of the QSO SDSSJ115432.67-021537.9 . We detect one major component and one minor component in the narrowband imaging. Combining the $\it{HST}$/WFC3 imaging with deep Magellan/MagE spectra, we measure that the Ly$\alpha$ flux F$_{\rm{Ly\alpha}}$ = 1.56$\pm0.10 \times10^{-16}$ $\rm{erg\ s^{-1}\ cm^{-2}}$, which is among the luminous ($\approx$ 2.7 L$^{\star}_{\rm{Ly\alpha}}$) Ly$\alpha$ emitters at $\it{z} =$ 2.19. The $\rm{Ly\alpha}$-based star formation rate (SFR) is $\sim$ 7 \textrm{M_{\sun} \ yr^{-1}}. These observational results favor that the star formation from the host galaxy could be the main mechanism to power the Ly$\alpha$ emission. This new method sheds new light on the study of the kinematic structure and the spatial distribution of the extended Ly$\alpha$ emitting regions around the QSO host

Near- infrared spectroscopic observations of high redshift C-I absorbers

We study a sample of 17 z>1.5 absorbers selected based on the presence of strong CI absorption lines in SDSS spectra and observed with the ESO-VLT spectrograph X-shooter. We derive metallicities, depletion onto dust, and extinction by dust, and analyse the absorption from MgII, MgI, CaII and NaI that are redshifted into the near infrared wavelength range. We show that most of these CI absorbers have high metallicity and dust content. We detect nine CaII absorptions with $W$(CaII$\lambda$3934) >0.23 \AA out of 14 systems where we have appropriate wavelength coverage. The observed equivalent widths are similar to what has been measured in other lower redshift surveys of CaII systems. We detect ten NaI absorptions in the 11 systems where we could observe this absorption. The median equivalent width ($W$(NaI$\lambda$5891) = 0.68 \AA) is larger than what is observed in local clouds with similar HI column densities but also in z<0.7 CaII systems detected in the SDSS. The systematic presence of NaI absorption in these CI systems strongly suggests that the gas is neutral and cold, maybe part of the diffuse molecular gas in the ISM of high-redshift galaxies. Most of the systems (12 out of 17) have $W$(MgII$\lambda$2796) > 2.5 \AA and six of them have log N(HI) < 20.3, with the extreme case of J1341+1852 that has log N(HI) = 18.18. The MgII absorptions are spread over more than $\Delta v$ $\sim$ 400 km s$^{-1}$ for half of the systems; three absorbers have $\Delta v$ > 500 km s$^{-1}$. The kinematics are strongly perturbed for most of these systems, which probably do not arise in quiet disks and must be close to regions with intense star-formation activity and/or are part of interacting objects. All this suggests that a large fraction of the cold gas at high redshift arises in disturbed environments.Comment: 26 pages, 49 figures, 3 tables, accepted by Astronomy & Astrophysics (A&A

Improved SOT (Hinode mission) high resolution solar imaging observations

We consider the best today available observations of the Sun free of turbulent Earth atmospheric effects, taken with the Solar Optical Telescope (SOT) onboard the Hinode spacecraft. Both the instrumental smearing and the observed stray light are analyzed in order to improve the resolution. The Point Spread Function (PSF) corresponding to the blue continuum Broadband Filter Imager (BFI) near 450 nm is deduced by analyzing i/ the limb of the Sun and ii/ images taken during the transit of the planet Venus in 2012. A combination of Gaussian and Lorentzian functions is selected to construct a PSF in order to remove both smearing due to the instrumental diffraction effects (PSF core) and the large-angle stray light due to the spiders and central obscuration (wings of the PSF) that are responsible for the parasitic stray light. A Max-likelihood deconvolution procedure based on an optimum number of iterations is discussed. It is applied to several solar field images, including the granulation near the limb. The normal non-magnetic granulation is compared to the abnormal granulation which we call magnetic. A new feature appearing for the first time at the extreme- limb of the disk (the last 100 km) is discussed in the context of the definition of the solar edge and of the solar diameter. A single sunspot is considered in order to illustrate how effectively the restoration works on the sunspot core. A set of 125 consecutive deconvolved images is assembled in a 45 min long movie illustrating the complexity of the dynamical behavior inside and around the sunspot.Comment: 15 pages, 22 figures, 1 movi

Constraining the Gap Size in the Disk around HD 100546 in the Mid-infrared

We refine the gap size measurements of the disk surrounding the Herbig Ae star HD 100546 in the N band. Our new mid-infrared interferometric (MIDI) data have been taken with the UT baselines and span the full range of orientations. The correlated fluxes show a wavy pattern in which the minima separation links to a geometrical structure in the disk. We fit each correlated flux measurement with a spline function, deriving the corresponding spatial scale, while assuming that the pattern arises interferometrically due to the bright emission from the inner disk and the opposing sides of the wall of the outer disk. We then fit an ellipse to the derived separations at their corresponding position angles, thereby using the observations to constrain the disk inclination to i = 47° ± 1° and the disk position angle to PA = 135⁰0 ± 2⁰5 east of north, both of which are consistent with the estimated values in previous studies. We also derive the radius of the ellipse to 15.7 ± 0.8 au. To confirm that the minima separations translate to a geometrical structure in the disk, we model the disk of HD 100546 using a semianalytical approach taking into account the temperature and optical depth gradients. Using this model, we simultaneously reproduce the level and the minima of the correlated fluxes and constrain the gap size of the disk for each observation. The values obtained for the projected gap size in different orientations are consistent with the separation found by the geometrical model

Gas Accretion Traced in Absorption in Galaxy Spectroscopy

The positive velocity shift of absorption transitions tracing diffuse material observed in a galaxy spectrum is an unambiguous signature of gas flow toward the host system. Spectroscopy probing, e.g., NaI D resonance lines in the rest-frame optical or MgII and FeII in the near-ultraviolet is in principle sensitive to the infall of cool material at temperatures ~ 100-10,000 K anywhere along the line of sight to a galaxy's stellar component. However, secure detections of this redshifted absorption signature have proved challenging to obtain due to the ubiquity of cool gas outflows giving rise to blueshifted absorption along the same sightlines. In this chapter, we review the bona fide detections of this phenomenon. Analysis of NaI D line profiles has revealed numerous instances of redshifted absorption observed toward early-type and/or AGN-host galaxies, while spectroscopy of MgII and FeII has provided evidence for ongoing gas accretion onto >5% of luminous, star-forming galaxies at z ~ 0.5-1. We then discuss the potentially ground-breaking benefits of future efforts to improve the spectral resolution of such studies, and to leverage spatially-resolved spectroscopy for new constraints on inflowing gas morphology.Comment: 21 pages, 7 figures. Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

Gas Accretion and Star Formation Rates

Cosmological numerical simulations of galaxy evolution show that accretion of metal-poor gas from the cosmic web drives the star formation in galaxy disks. Unfortunately, the observational support for this theoretical prediction is still indirect, and modeling and analysis are required to identify hints as actual signs of star-formation feeding from metal-poor gas accretion. Thus, a meticulous interpretation of the observations is crucial, and this observational review begins with a simple theoretical description of the physical process and the key ingredients it involves, including the properties of the accreted gas and of the star-formation that it induces. A number of observations pointing out the connection between metal-poor gas accretion and star-formation are analyzed, specifically, the short gas consumption time-scale compared to the age of the stellar populations, the fundamental metallicity relationship, the relationship between disk morphology and gas metallicity, the existence of metallicity drops in starbursts of star-forming galaxies, the so-called G dwarf problem, the existence of a minimum metallicity for the star-forming gas in the local universe, the origin of the alpha-enhanced gas forming stars in the local universe, the metallicity of the quiescent BCDs, and the direct measurements of gas accretion onto galaxies. A final section discusses intrinsic difficulties to obtain direct observational evidence, and points out alternative observational pathways to further consolidate the current ideas.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by Springe

A coronagraphic absorbing cloud reveals the narrow-line region and extended Lyman α emission of QSO J0823+0529

International audienceWe report long-slit spectroscopic observations of the quasar SDSS J082303.22+052907.6 (z_{C IV}} ∼ 3.1875), whose broad-line region (BLR) is partly eclipsed by a strong damped Lyman α (DLA; logN(H I) = 21.7) cloud. This allows us to study the narrow-line region (NLR) of the quasar and the Lyman α emission from the host galaxy. Using CLOUDY models that explain the presence of strong N V and P V absorption together with the detection of Si II* and O I** absorption in the DLA, we show that the density and the distance of the cloud to the quasar are in the ranges 180 H -3 and 580 > r0 > 230 pc, respectively. Sizes of the neutral (∼2-9pc) and highly ionized phases (∼3-80pc) are consistent with the partial coverage of the C IV BLR by the C IV absorption from the DLA (covering factor of ∼0.85). We show that the residuals are consistent with emission from the NLR with C IV/Lyman α ratios varying from 0 to 0.29 through the profile. Remarkably, we detect extended Lyman α emission up to 25 kpc to the north and west directions and 15 kpc to the south and east. We interpret the emission as the superposition of strong emission in the plane of the galaxy up to 10 kpc with emission in a wind of projected velocity ∼500 km s-1 which is seen up to 25 kpc. The low metallicity of the DLA (0.27 solar) argues for at least part of this gas being infalling towards the active galactic nucleus and possibly being located where accretion from cold streams ends up

A ghostly damped Ly α system revealed by metal absorption lines

We report the discovery of the first 'ghostly' damped Ly$\alpha$ absorption system (DLA), which is identified by the presence of absorption from strong low-ion species at $z_{\rm abs}=1.70465$ along the line of sight to the quasar SDSSJ113341.29$-$005740.0 with $z_{\rm em}=1.70441$. No Ly$\alpha$ absorption trough is seen associated with these absorptions because the DLA trough is filled with the leaked emission from the broad emission line region of the quasar. By modeling the quasar spectrum and analyzing the metal lines, we derive log$N$(HI)(cm$^{-2}$)$\sim$21.0 $\pm$ 0.3. The DLA cloud is small ($\le$ 0.32 pc) thus not covering entirely the broad line region and is located at $\ge$ 39 pc from the central active galactic nucleus (AGN). Although the DLA is slightly redshifted relative to the quasar, its metallicity ([S/H]=$-$0.41$\pm$0.30) is intermediate between what is expected from infalling and outflowing gas. It could be possible that the DLA is part of some infalling material accreting onto the quasar host galaxy through filaments, and that its metallicity is raised by mixing with the enriched outflowing gas emanating from the central AGN. Current DLA surveys miss these 'ghostly' DLAs, and it would be important to quantify the statistics of this population by searching the SDSS database using metal absorption templates.Comment: Accepted for publication in MNRAS Letter, 5 pages, 3 figures, 2 table