The quasar Q0957+561: Lensed CO emission from a disk at z~1.4?

In recent years large efforts have been made to detect molecular gas towards high redshifted objects. Up to now the literature reports on only two cases of CO-detection in quasars at a redshift between 1 and 2 - Q0957+561, a gravitationally lensed system at z=1.41 (Planesas et al. 1999), and HR10 at z=1.44 (Andreani et al. 2000). According to Planesas et al. (1999), 12CO(2-1) emission was detected towards both the lensed images of Q0957+561 with the IRAM Plateau de Bure Interferometer (PdBI). In contrast to the optical spectra of the two images which support the idea that they are images of one and the same object, the CO-spectra were surprisingly different: the southern image (named CO-B) shows a single blueshifted line whereas a double-peaked line profile with a blue- and a redshifted part appears towards the northern image (CO-A). Based on the observations and on simulations with a gravitational lens program, we are tempted to argue that the line profile traces the presence of molecular gas of a disk in the host galaxy around the quasar. We have now new observations with the PdBI providing the necessary sensitivity to corroborate our disk model.Comment: 4 pages, 1 figure, to appear in "Proceedings of the 4th Cologne-Bonn-Zermatt-Symposium", ed. S. Pfalzner, C. Kramer, C. Straubmeier, and A. Heithausen (Springer Verlag

ECO AND RESOLVE: GALAXY DISK GROWTH IN ENVIRONMENTAL CONTEXT

We study the relationships between galaxy environments and galaxy properties related to disk (re)growth, considering two highly complete samples that are approximately baryonic mass limited into the high-mass dwarf galaxy regime, the Environmental COntext catalog (data release herein) and the B-semester region of the REsolved Spectroscopy Of a Local VolumE survey. We quantify galaxy environments using both group identification and smoothed galaxy density field methods. We use by-eye and quantitative morphological classifications plus atomic gas content measurements and estimates. We find that blue early-type (E/S0) galaxies, gas-dominated galaxies, and UV-bright disk host galaxies all become distinctly more common below group halo mass $\sim {10}^{11.5}\;{M}_{\odot }$, implying that this low group halo mass regime may be a preferred regime for significant disk growth activity. We also find that blue early-type and blue late-type galaxies inhabit environments of similar group halo mass at fixed baryonic mass, consistent with a scenario in which blue early-types can regrow late-type disks. In fact, we find that the only significant difference in the typical group halo mass inhabited by different galaxy classes is for satellite galaxies with different colors, where at fixed baryonic mass red early- and late-types have higher typical group halo masses than blue early- and late-types. More generally, we argue that the traditional morphology–environment relation (i.e., that denser environments tend to have more early-types) can be largely attributed to the morphology-galaxy mass relation for centrals and the color–environment relation for satellites

The Void Galaxy Survey

The Void Galaxy Survey (VGS) is a multi-wavelength program to study $\sim$60 void galaxies. Each has been selected from the deepest interior regions of identified voids in the SDSS redshift survey on the basis of a unique geometric technique, with no a prior selection of intrinsic properties of the void galaxies. The project intends to study in detail the gas content, star formation history and stellar content, as well as kinematics and dynamics of void galaxies and their companions in a broad sample of void environments. It involves the HI imaging of the gas distribution in each of the VGS galaxies. Amongst its most tantalizing findings is the possible evidence for cold gas accretion in some of the most interesting objects, amongst which are a polar ring galaxy and a filamentary configuration of void galaxies. Here we shortly describe the scope of the VGS and the results of the full analysis of the pilot sample of 15 void galaxies.Comment: 9 pages, 6 figures. This is an extended version of a paper to appear in "Environment and the Formation of Galaxies: 30 years later", Proceedings of Symposium 2 of JENAM 2010, eds. I. Ferreras, A. Pasquali, ASSP, Springer. Version with highres figures at http://www.astro.rug.nl/~weygaert/vgs_jenam_weygaert.col.pd

The morphologies of massive galaxies at 1 < z < 3 in the CANDELS-UDS field : compact bulges, and the rise and fall of massive discs

We have used high-resolution, Hubble Space Telescope, near-infrared imaging to conduct a detailed analysis of the morphological properties of the most massive galaxies at high redshift, modelling the WFC3/IR H-160-band images of the similar or equal to 200 galaxies in the CANDELS-UDS field with photometric redshifts 1 10(11)M(circle dot). We have explored the results of fitting single-Sersic and bulge+disc models, and have investigated the additional errors and potential biases introduced by uncertainties in the background and the on-image point spread function. This approach has enabled us to obtain formally acceptable model fits to the WFC3/IR images of > 90 per cent of the galaxies. Our results indicate that these massive galaxies at 1 2 the compact bulges display effective radii a factor of similar or equal to 4 smaller than local ellipticals of comparable mass. These trends also appear to extend to the bulge components of disc-dominated galaxies. In addition, we find that, while such massive galaxies at low redshift are generally bulge-dominated, at redshifts 1 2 they are mostly disc-dominated. The majority of the disc-dominated galaxies are actively forming stars, although this is also true for many of the bulge-dominated systems. Interestingly, however, while most of the quiescent galaxies are bulge-dominated, we find that a significant fraction (25-40 per cent) of the most quiescent galaxies, with specific star formation rates sSFR < 10(-10) yr(-1), have disc-dominated morphologies. Thus, while our results show that the massive galaxy population is undergoing dramatic changes at this crucial epoch, they also suggest that the physical mechanisms which quench star formation activity are not simply connected to those responsible for the morphological transformation of massive galaxies into present-day giant ellipticals

Structural parameters of galaxies in CANDELS

We present global structural parameter measurements of 109,533 unique, H-F160W-selected objects from the CANDELS multi-cycle treasury program. Sersic model fits for these objects are produced with GALFIT in all available near-infrared filters (H-F160W, J(F125W) and, for a subset, Y-F105W). The parameters of the best-fitting Sersic models (total magnitude, half-light radius, Sersic index, axis ratio, and position angle) are made public, along with newly constructed point-spread functions for each field and filter. Random uncertainties in the measured parameters are estimated for each individual object based on a comparison between multiple, independent measurements of the same set of objects. To quantify systematic uncertainties, we create a mosaic with simulated galaxy images with a realistic distribution of input parameters and then process and analyze the mosaic in an identical manner as the real data. We find that accurate and precise measurements-to 10% or better-of all structural parameters can typically be obtained for galaxies with H-F160W < 23, with comparable fidelity for basic size and shape measurements for galaxies to H-F160W similar to 24.5

A population of luminous accreting black holes with hidden mergers

Major galaxy mergers are thought to play an important part in fuelling the growth of supermassive black holes. However, observational support for this hypothesis is mixed, with some studies showing a correlation between merging galaxies and luminous quasars and others showing no such association. Recent observations have shown that a black hole is likely to become heavily obscured behind merger-driven gas and dust, even in the early stages of the merger, when the galaxies are well separated (5 to 40 kiloparsecs). Merger simulations further suggest that such obscuration and black-hole accretion peaks in the final merger stage, when the two galactic nuclei are closely separated (less than 3 kiloparsecs). Resolving this final stage requires a combination of high-spatial-resolution infrared imaging and high-sensitivity hard-X-ray observations to detect highly obscured sources. However, large numbers of obscured luminous accreting supermassive black holes have been recently detected nearby (distances below 250 megaparsecs) in X-ray observations. Here we report high-resolution infrared observations of hard-X-ray-selected black holes and the discovery of obscured nuclear mergers, the parent populations of supermassive-black-hole mergers. We find that obscured luminous black holes (bolometric luminosity higher than 2x10^44 ergs per second) show a significant (P<0.001) excess of late-stage nuclear mergers (17.6 per cent) compared to a sample of inactive galaxies with matching stellar masses and star formation rates (1.1 per cent), in agreement with theoretical predictions. Using hydrodynamic simulations, we confirm that the excess of nuclear mergers is indeed strongest for gas-rich major-merger hosts of obscured luminous black holes in this final stage.Comment: To appear in the 8 November 2018 issue of Nature. This is the authors' version of the wor

An Ultra Deep Field survey with WFIRST

Studying the formation and evolution of galaxies at the earliest cosmic times, and their role in reionization, requires the deepest imaging possible. Ultra-deep surveys like the HUDF and HFF have pushed to mag \mAB$\,\sim\,$30, revealing galaxies at the faint end of the LF to $z$$\,\sim\,$9$\,-\,$11 and constraining their role in reionization. However, a key limitation of these fields is their size, only a few arcminutes (less than a Mpc at these redshifts), too small to probe large-scale environments or clustering properties of these galaxies, crucial for advancing our understanding of reionization. Achieving HUDF-quality depth over areas $\sim$100 times larger becomes possible with a mission like the Wide Field Infrared Survey Telescope (WFIRST), a 2.4-m telescope with similar optical properties to HST, with a field of view of $\sim$1000 arcmin$^2$, $\sim$100$\times$ the area of the HST/ACS HUDF. This whitepaper motivates an Ultra-Deep Field survey with WFIRST, covering $\sim$100$\,-\,$300$\times$ the area of the HUDF, or up to $\sim$1 deg$^2$, to \mAB$\,\sim\,$30, potentially revealing thousands of galaxies and AGN at the faint end of the LF, at or beyond $z$\,$\sim$\,9$\,-\,$10 in the epoch of reionization, and tracing their LSS environments, dramatically increasing the discovery potential at these redshifts. (Note: This paper is a somewhat expanded version of one that was submitted as input to the Astro2020 Decadal Survey, with this version including an Appendix (which exceeded the Astro2020 page limits), describing how the science drivers for a WFIRST Ultra Deep Field might map into a notional observing program, including the filters used and exposure times needed to achieve these depths.

Spitzer number counts of active galactic nuclei in the goods fields

We present mid-infrared observations of AGN in the GOODS fields, performed with the Spitzer Space Telescope. These are the deepest infrared and X-ray fields to date and cover a total area of ~0.1 square degrees. AGN are selected on the basis of their hard (2-8 keV) X-ray emission. The median AGN infrared luminosity is at least 10 times larger than the median for normal galaxies with the same redshift distribution, suggesting that the infrared emission is dominated by the central nucleus. The X-ray to infrared luminosity ratios of GOODS AGN, most of which are at 0.5<z<1.5, are similar to the values obtained for AGN in the local Universe. The observed infrared flux distribution has an integral slope of ~1.5 and there are 1000 sources per square degree brighter than ~50 uJy at 3-6 microns. The counts approximately match the predictions of models based on AGN unification, in which the majority of AGN are obscured. This agreement confirms that the faintest X-ray sources, which are dominated by the host galaxy light in the optical, are obscured AGN. Using these Spitzer data, the AGN contribution to the extragalactic infrared background light is calculated by correlating the X-ray and infrared catalogues. This is likely to be a lower limit given that the most obscured AGN are missed in X-rays. We estimate the contribution of AGN missed in X-rays, using a population synthesis model, to be ~45% of the observed AGN contribution, making the AGN contribution to the infrared background at most ~2-10% in the 3-24 micron range, depending on wavelength, lower than most previous estimates. The AGN contribution to the infrared background remains roughly constant with source flux in the IRAC bands but decreases with decreasing flux in the MIPS 24 um band, where the galaxy population becomes more important.Comment: ApJ Accepted, 24 pages, 7 figures, author list modifie

Hubble Space Telescope imaging in the Chandra Deep Field-South. I. Multiple active galactic nucleus populations

We present preliminary results from imaging three Hubble Space Telescope (HST) Wide Field Planetary Camera 2 fields in V and I within the Chandra Deep Field-South (CDF-S). HST Is sensitivity and resolution are sufficient to reveal optical counterparts for 24 of the 26 CDF-S X-ray sources detected in the 300 ks X-ray catalog and determine the morphologies of most of these. We find that the X-ray sources comprise two apparently distinct populations of optical candidates : one optically faint (I greater than or similar to 24), with V-I colors consistent with the I>24 field population, and the other significantly brighter (I less than or similar to 22), with colors redder than the I < 22 field population. More than two-thirds of the X-ray source counterparts are resolved galaxies. The brighter sources are mostly active galactic nuclei (AGNs) based on their high X-ray luminosity. The optically resolved sources in the brighter population have a very narrow range of V-I color and appear to be a mix of both late- and early-type morphologies at low to moderate redshift. We show that the second population, with fainter optical counterparts, can be explained as higher redshift type 2 AGNs

Lower mass black holes in the Great Observatories Origins Deep Survey?Off-nuclear X-ray sources

We have identified a sample of 10 highly reliable off-nuclear (greater than or similar to2 kpc) X-ray sources at z=0.03-0.25 in late-type host galaxies within the two Great Observatories Origins Deep Survey (GOODS) fields (i.e., the two Chandra Deep Fields). The combination of the superb spatial resolution and great depth of the Hubble Space Telescope Advanced Camera for Surveys and Chandra ACIS coverage in the GOODS fields is critical to the identification of these sources. We extend the study of this enigmatic population up to higher redshifts and larger look-back times than has been possible before, finding that the fraction of optically luminous galaxies exhibiting luminous off-nuclear sources at zapproximate to0.1 is larger than at the current time (approximate to36% vs. approximate to8%). The X-ray luminosities of the GOODS off-nuclear X-ray sources are comparable to or slightly greater than the integrated point-source X-ray luminosities of nearby galaxies, providing a possible constraint on the X-ray luminosity function at higher star formation rates. X-ray variability demonstrates that several of these sources are likely single accreting black holes; for the majority, however, the number of X-ray counts is too low for X-ray variability studies