Laura Hoppmann

Bio: Laura Hoppmann is an academic researcher from University of Western Australia. The author has contributed to research in topics: Active galactic nucleus & Galaxy. The author has an hindex of 5, co-authored 6 publications receiving 154 citations. Previous affiliations of Laura Hoppmann include European Southern Observatory.

A blind HI Mass Function from the Arecibo Ultra-Deep Survey (AUDS)

Abstract: The Arecibo Ultra Deep Survey (AUDS) combines the unique sensitivity of the telescope with the wide field of the Arecibo L-band Feed Array (ALFA) to directly detect 21cm HI emission from galaxies at distances beyond the local Universe bounded by the lower frequency limit of ALFA (z=0.16). AUDS has collected 700 hours of integration time in two fields with a combined area of 1.35 square degrees. In this paper we present data from 60% of the total survey, corresponding to a sensitivity level of 80 micro-Jy. We discuss the data reduction, the search for galaxies, parametrisation, optical identification and completeness. We detect 102 galaxies in the mass range of log M_HI/M_sun-2log h=5.6-10.3. We compute the HI mass function (HIMF) at the highest redshifts so far measured. A fit of a Schechter function results in alpha=-1.37+-0.03, Phi=(7.72+-1.4)*10^3 h^3/Mpc^3 and log M_HI/M_sun=9.75+-0.041+2log h. Using the measured HIMF, we find a cosmic HI density of Omega_HI=(2.33+-0.07)*10^-4/h for the sample z=0.065. We discuss further uncertainties arising from cosmic variance. Because of its depth, AUDS is the first survey that can determine parameters for the HI mass function in independent redshift bins from a single homogeneous data set. The results indicate little evolution of the co-moving mass function and Omega_HI within this redshift range. We calculate a weighted average for Omega_HI in the range $0

From star-forming galaxies to AGN: The global HI content from a stacking experiment

Abstract: We study the atomic neutral hydrogen (H I) content of ∼1600 galaxies up to z ∼ 0.1 using stacking techniques. The observations were carried out with the Westerbork Synthesis Radio Telescope (WSRT) in the area of the SDSS South Galactic Cap (SSGC), where we selected a galaxy sample from the SDSS spectroscopic catalog. Multi-wavelength information is provided by SDSS, NVSS, GALEX, and WISE. We use the collected information to study H I trends with color, star-forming, and active galactic nuclei (AGN) properties. Using near-UV (NUV) − r colors, galaxies are divided into blue cloud, green valley and red sequence galaxies. As expected based on previous observations, we detect H I in green valley objects with lower amounts of H I than blue galaxies, while stacking only

An accurate low-redshift measurement of the cosmic neutral hydrogen density

Abstract: Using a spectral stacking technique, we measure the neutral hydrogen (H I) properties of a sample of galaxies at z = 0.066, consistent with measurements from blind H I surveys and other H I stacking experiments at low redshifts. The combination of the small interferometer beam size and the large survey volume makes our result highly robust against systematic effects due to confusion at small scales and cosmic variance at large scales. Splitting into three sub-samples with = 0.038, 0.067, and 0.093 shows no significant evolution of the H I gas content at low redshift.

From star-forming galaxies to AGN: the global HI content from a stacking experiment

Abstract: We study the atomic neutral hydrogen (HI) content of $\sim$1600 galaxies up to $z \sim 0.1$ using stacking techniques. The observations were carried out with the Westerbork Synthesis Radio Telescope (WSRT) in the area of the SDSS South Galactic Cap (SSGC), where we selected a galaxy sample from the SDSS spectroscopic catalog. Multi-wavelength information is provided by SDSS, NVSS, GALEX, and WISE. We use the collected information to study HI trends with color, star-forming, and active galactic nuclei (AGN) properties. Using NUV-r colors, galaxies are divided into blue cloud, green valley and red sequence galaxies. As expected based on previous observations, we detect HI in green valley objects with lower amounts of HI than blue galaxies, while stacking only produces a 3-$\sigma$ upper limit for red galaxies with M$_{\rm HI}$ $<$ (5 $\pm$ 1.5) $\times$ 10$^{8}$ M$_{\odot}$ and M$_{\rm HI}/\rm{L}_r$ $<$ 0.02 $\pm$ 0.006 $\rm M_{\odot} / \rm L_{\odot} $. We find that the HI content is more dependent on NUV-r color, and less on ionization properties, in the sense that regardless of the presence of an optical AGN (based on optical ionization line diagnostics), green-valley galaxies always show HI, whereas red galaxies only produce an upper limit. This suggests that feedback from optical AGN is not the (main) reason for depleting large-scale gas reservoirs. Low-level radio continuum emission in our galaxies can stem either from star formation, or from AGN. We use the WISE color-color plot to separate these phenomena by dividing the sample into IR late-type and IR early-type galaxies. We find that the radio emission in IR late-type galaxies stems from enhanced star formation, and this group is detected in HI. However, IR early-type galaxies lack any sign of HI gas and star formation activity, suggesting that radio AGN are likely to be the source of radio emission in this population.

Cold gas stripping in satellite galaxies: from pairs to clusters

Abstract: In this paper we investigate environment driven gas depletion in satellite galaxies, taking full advantage of the atomic hydrogen (HI) spectral stacking technique to quantify the gas content for the entire gas-poor to -rich regime. We do so using a multi-wavelength sample of 10,600 satellite galaxies, selected according to stellar mass (log M$_{\star}$/M$_{\odot}$ $\geq$ 9) and redshift (0.02 $\leq$ z $\leq$ 0.05) from the Sloan Digital Sky Survey, with HI data from the Arecibo Legacy Fast ALFA (ALFALFA) survey. Using key HI-to-stellar mass scaling relations, we present evidence that the gas content of satellite galaxies is, to a significant extent, dependent on the environment in which a galaxy resides. For the first time, we demonstrate that systematic environmental suppression of gas content at both fixed stellar mass and fixed specific star formation rate (sSFR) in satellite galaxies begins in halo masses typical of the group regime (log M$_{h}$/M$_{\odot}$ < 13.5), well before galaxies reach the cluster environment. We also show that environment driven gas depletion is more closely associated to halo mass than local density. Our results are then compared with state-of-the-art semi-analytic models and hydrodynamical simulations and discussed within this framework, showing that more work is needed if models are to reproduce the observations. We conclude that the observed decrease of gas content in the group and cluster environments cannot be reproduced by starvation of the gas supply alone and invoke fast acting processes such as ram-pressure stripping of cold gas to explain this.

Host galaxies of AGN

Abstract: The relationship of an AGN to its host galaxy is a crucial question in the study of galaxy evolution We perform stellar population synthesis in the central regions of galaxies of different activity levels A large number of stellar features are measured both in the optical and near-infrared We find the nuclear stellar population to be related to the level of activity These differences are no more conspicuous further away in the bulge of the galaxy

WALLABY – an SKA Pathfinder H i survey

Abstract: The Widefield ASKAP L-band Legacy All-sky Blind surveY (wallaby) is a next-generation survey of neutral hydrogen (H i) in the Local Universe. It uses the widefield, high-resolution capability of the Australian Square Kilometer Array Pathfinder (ASKAP), a radio interferometer consisting of 36 \times12-m dishes equipped with Phased-Array Feeds (PAFs), located in an extremely radio-quiet zone in Western Australia. wallaby aims to survey three-quarters of the sky (-90^{\circ} < \delta< +30^{\circ}) to a redshift of z \lesssim0.26, and generate spectral line image cubes at ∼30 arcsec resolution and ∼1.6 mJy beam$^{−1}$ per 4 km s$^{−1}$ channel sensitivity. ASKAP’s instantaneous field of view at 1.4 GHz, delivered by the PAF’s 36 beams, is about 30 sq deg. At an integrated signal-to-noise ratio of five, wallaby is expected to detect around half a million galaxies with a mean redshift of z \sim0.05 (∼200 Mpc). The scientific goals of wallaby include: (a) a census of gas-rich galaxies in the vicinity of the Local Group; (b) a study of the H i properties of galaxies, groups and clusters, in particular the influence of the environment on galaxy evolution; and (c) the refinement of cosmological parameters using the spatial and redshift distribution of low-bias gas-rich galaxies. For context we provide an overview of recent and planned large-scale H i surveys. Combined with existing and new multi-wavelength sky surveys, wallaby will enable an exciting new generation of panchromatic studies of the Local Universe. — First results from the wallaby pilot survey are revealed, with initial data products publicly available in the CSIRO ASKAP Science Data Archive (CASDA).

The ALFALFA H i mass function: a dichotomy in the low-mass slope and a locally suppressed ‘knee’ mass

Abstract: The authors acknowledge the work of the entire ALFALFA collaboration in observing, flagging, and extracting the catalogue of galaxies that this paper makes use of The ALFALFA team at Cornell is supported by NSF grants AST-0607007, AST-1107390 and AST-1714828, and by grants from the Brinson Foundation MGJ also acknowledges support from the grant AYA2015-65973-C3-1-R (MINECO/FEDER, UE) We also acknowledge helpful comments from A Robotham concerning the satellite and central MFs We thank the referee for their thorough reading of the manuscript This work made use of SDSS data products Funding for the SDSS IV has been provided by the Alfred P Sloan Foundation, the US Department of Energy Office of Science, and the Participating Institutions SDSS acknowledges support and resources from the Center for High-Performance Computing at the University of Utah The SDSS web site is wwwsdssorg

The Many Routes to AGN Feedback

Abstract: The energy released by Active Galactic Nuclei (AGN) in the form of radiation, winds, or radio plasma jets, is known to impact on the surrounding interstellar medium. The result of these processes, known as AGN (negative) feedback, is suggested to prevent gas, in and around galaxies, from cooling, and to remove, or at least redistribute, gas by driving massive and fast outflows, hence playing a key role in galaxy evolution. Given its importance, a large effort is devoted by the astronomical community to trace the effects of AGN on the surrounding gaseous medium and to quantify their impact for different types of AGN. This review briefly summarizes some of the recent observational results obtained in different wavebands, tracing different phases of the gas. I also summarize the new insights they have brought, and the constraints they provide to numerical simulations of galaxy formation and evolution. The recent addition of deep observations of cold gas and, in particular, of cold molecular gas, has brought some interesting surprises and has expanded our understanding of AGN and AGN feedback.