arXiv subjects

Kelley M. Hess

Publications and source records attributed to Kelley M. Hess.

52 records · Page 3Linked to original sources

arXiv2019

Large Scale Structure in CHILES

We demonstrate that the Discrete Persistent Source Extractor (DisPerSE) can be used with spectroscopic redshifts to define the cosmic web and its distance to galaxies in small area deepfields. Here we analyze the use of DisPerSE to identify structure in observational data. We apply DisPerSE to the distribution of galaxies in the COSMOS field and find the best parameters to identify filaments. We compile a catalog of 11500 spectroscopic redshifts from the Galaxy and Mass Assembly (GAMA) G10 data release. We analyze two-dimensional slices, extract filaments and calculate the distance for each galaxy to its nearest filament. We find that redder and more massive galaxies are closer to filaments. To study the growth of galaxies across cosmic time, and environment, we are carrying out an HI survey covering redshifts z = 0 - 0.45, the COSMOS HI Large Extragalactic Survey (CHILES). In addition we present the predicted HI mass fraction as a function of distance to filaments for the spectroscopically known galaxies in CHILES. Lastly, we discuss the cold gas morphology of a few individual galaxies and their positions with respect to the cosmic web. The identification of the cosmic web, and the ability of CHILES to study the resolved neutral hydrogen morphologies and kinematics of galaxies, will allow future studies of the properties of neutral hydrogen in different cosmic web environments across the redshift range z = 0.1 - 0.45.

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arXiv2018

CHILES: HI morphology and galaxy environment at z=0.12 and z=0.17

We present a study of 16 HI-detected galaxies found in 178 hours of observations from Epoch 1 of the COSMOS HI Large Extragalactic Survey (CHILES). We focus on two redshift ranges between 0.108 <= z <= 0.127 and 0.162 <= z <= 0.183 which are among the worst affected by radio frequency interference (RFI). While this represents only 10% of the total frequency coverage and 18% of the total expected time on source compared to what will be the full CHILES survey, we demonstrate that our data reduction pipeline recovers high quality data even in regions severely impacted by RFI. We report on our in-depth testing of an automated spectral line source finder to produce HI total intensity maps which we present side-by-side with significance maps to evaluate the reliability of the morphology recovered by the source finder. We recommend that this become a common place manner of presenting data from upcoming HI surveys of resolved objects. We use the COSMOS 20k group catalogue, and we extract filamentary structure using the topological DisPerSE algorithm to evaluate the \hi\ morphology in the context of both local and large-scale environments and we discuss the shortcomings of both methods. Many of the detections show disturbed HI morphologies suggesting they have undergone a recent interaction which is not evident from deep optical imaging alone. Overall, the sample showcases the broad range of ways in which galaxies interact with their environment. This is a first look at the population of galaxies and their local and large-scale environments observed in HI by CHILES at redshifts beyond the z=0.1 Universe.

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arXiv2018

The Arecibo Legacy Fast ALFA Survey: The ALFALFA Extragalactic HI Source Catalog

We present the catalog of ~31500 extragalactic HI line sources detected by the completed ALFALFA survey out to z < 0.06 including both high signal-to-noise ratio (> 6.5) detections and ones of lower quality which coincide in both position and recessional velocity with galaxies of known redshift. We review the observing technique, data reduction pipeline, and catalog construction process, focusing on details of particular relevance to understanding the catalog's compiled parameters. We further describe and make available the digital HI line spectra associated with the catalogued sources. In addition to the extragalactic HI line detections, we report nine confirmed OH megamasers and ten OH megamaser candidates at 0.16 < z < 0.22 whose OH line signals are redshifted into the ALFALFA frequency band. Because of complexities in data collection and processing associated with the use of a feed-horn array on a complex single-dish antenna in the terrestrial radio frequency interference environment, we also present a list of suggestions and caveats for consideration by users of the ALFALFA extragalactic catalog for future scientific investigations.

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arXiv2016

HI Observations of Galaxies in the Southern Filament of the Virgo Cluster with the SKA Pathfinder KAT-7 and the WSRT

We map the Hi distribution of galaxies in a $\sim 1.5^\circ \times 2.5^\circ$ region located at the virial radius south of the Virgo cluster using the KAT$-$7 and the WSRT interferometers. Because of the different beam sizes of the two telescopes, a similar column density sensitivity of $\rm N_{Hi} \sim 10^{18}\,cm^{-2}$ was reached with the two observations over 16.5 km/s. We pioneer a new approach to combine the observations and take advantage of their sensitivity to both the large and small scale structures. Out to an unprecedented extent, we detect an Hi tail of $\sim 60$ kpc being stripped off NGC 4424, a peculiar spiral galaxy. The properties of the galaxy, together with the shape of the tail, suggest that NGC 4424 is a post-merger galaxy undergoing a ram pressure stripping as it falls towards the centre of the Virgo Cluster. We detect a total of 14 galaxies and 3 Hi clouds lacking optical counterparts. One of the clouds is a new detection with an Hi mass of $\rm 7\times10^7\, M_\odot$ and a strong Hi profile with $W_{50} = 73$ km/s. We find that 10 out of the 14 galaxies present Hi deficiencies not higher than those of the cluster's late spirals, suggesting that the environmental effects are not more pronounced in the region than elsewhere in the cluster.

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arXiv2016

HI in Group Interactions: HCG 44

Extending deep observations of the neutral atomic hydrogen (HI) to the environment around galaxy groups can reveal a complex history of group interactions which is invisible to studies that focus on the stellar component. Hickson Compact Group 44 (HCG 44) is a nearby example and we have combined HI data from the Karoo Array Telescope, Westerbork Synthesis Radio Telescope, and Arecibo Legacy Fast ALFA survey, in order to achieve high column density sensitivity (N_HI < 2x10^18 cm^-2) to the neutral gas over a large field-of-view beyond the compact group itself. We find the giant HI tail north of HCG 44 contains 1.1x10^9 M_Sun of gas and extends 450 kpc from the compact group: twice as much mass and 33% further than previously detected. However, the additional gas is still unable to account for the known HI deficiency of HCG 44. The tail likely formed through a strong tidal interaction and HI clouds in the tail have survived for 1 Gyr or more after being stripped. This has important implications for understanding the survival of neutral clouds in the intragroup and circumgroup medium, and we discuss their survival in the context of simulations of cold gas in hot halos. HCG 44 is one of a growing number of galaxy groups found to have more extended HI in the intragroup and circumgroup medium than previously measured. Our results provide constraints for simulations on the properties of galaxy group halos, and reveal a glimpse of what will be seen by future powerful HI telescopes and surveys.

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arXiv2016

ALFALFA and WSRT Imaging of Extended HI Features in the Leo Cloud of Galaxies

We present ALFALFA HI observations of a well studied region of the Leo Cloud, which includes the NGC 3227 group and the NGC 3190 group. We detect optically dark HI tails and plumes with extents potentially exceeding 600 kpc, well beyond the field of view of previous observations. These HI features contain approximately 40% of the total HI mass in the NGC~3227 group and 10% in the NGC~3190 group. We also present WSRT maps which show the complex morphology of the extended emission in the NGC~3227 group. We comment on previously proposed models of the interactions in these groups and the implications for the scale of group processing through interactions. Motivated by the extent of the HI plumes, we place the HI observations in the context of the larger loose group, demonstrating the need for future sensitive, wide field HI surveys to understand the role of group processing in galaxy evolution.

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arXiv2016

Highest Redshift Image of Neutral Hydrogen in Emission: A CHILES Detection of a Starbursting Galaxy at z=0.376

Our current understanding of galaxy evolution still has many uncertainties associated with the details of accretion, processing, and removal of gas across cosmic time. The next generation of radio telescopes will image the neutral hydrogen (HI) in galaxies over large volumes at high redshifts, which will provide key insights into these processes. We are conducting the COSMOS HI Large Extragalactic Survey (CHILES) with the Karl G. Jansky Very Large Array, which is the first survey to simultaneously observe HI from z=0 to z~0.5. Here, we report the highest redshift HI 21-cm detection in emission to date of the luminous infrared galaxy (LIRG) COSMOS J100054.83+023126.2 at z=0.376 with the first 178 hours of CHILES data. The total HI mass is $(2.9\pm1.0)\times10^{10}~M_\odot$, and the spatial distribution is asymmetric and extends beyond the galaxy. While optically the galaxy looks undisturbed, the HI distribution suggests an interaction with candidate a candidate companion. In addition, we present follow-up Large Millimeter Telescope CO observations that show it is rich in molecular hydrogen, with a range of possible masses of $(1.8-9.9)\times10^{10}~M_\odot$. This is the first study of the HI and CO in emission for a single galaxy beyond z~0.2.

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arXiv2015

KAT-7 Science Verification: Cold Gas, Star Formation, and Substructure in the Nearby Antlia Cluster

The Antlia Cluster is a nearby, dynamically young structure, and its proximity provides a valuable opportunity for detailed study of galaxy and group accretion onto clusters. We present a deep HI mosaic completed as part of spectral line commissioning of the Karoo Array Telescope (KAT-7), and identify infrared counterparts from the WISE extended source catalog to study neutral atomic gas content and star formation within the cluster. We detect 37 cluster members out to a radius of ~0.9 Mpc with M_HI > 5x10^7 M_Sun. Of these, 35 are new HI detections, 27 do not have previous spectroscopic redshift measurements, and one is the Compton thick Seyfert II, NGC 3281, which we detect in HI absorption. The HI galaxies lie beyond the X-ray emitting region 200 kpc from the cluster center and have experienced ram pressure stripping out to at least 600 kpc. At larger radii, they are distributed asymmetrically suggesting accretion from surrounding filaments. Combining HI with optical redshifts, we perform a detailed dynamical analysis of the internal substructure, identify large infalling groups, and present the first compilation of the large scale distribution of HI, and star forming galaxies within the cluster. We find that elliptical galaxy NGC 3268 is at the center of the oldest substructure and argue that NGC 3258 and its companion population are more recent arrivals. Through the presence of HI and on-going star formation, we rank substructures with respect to their relative time since accretion onto Antlia.

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arXiv2014

Variation of galactic cold gas reservoirs with stellar mass

The stellar and neutral hydrogen (HI) mass functions at z~0 are fundamental benchmarks for current models of galaxy evolution. A natural extension of these benchmarks is the two-dimensional distribution of galaxies in the plane spanned by stellar and HI mass, which provides a more stringent test of simulations, as it requires the HI to be located in galaxies of the correct stellar mass. Combining HI data from the ALFALFA survey, with optical data from SDSS, we find a distinct envelope in the HI-to-stellar mass distribution, corresponding to an upper limit in the HI fraction that varies monotonically over five orders of magnitude in stellar mass. This upper envelope in HI fraction does not favour the existence of a significant population of dark galaxies with large amounts of gas but no corresponding stellar population. The envelope shows a break at a stellar mass of ~10^9 Msun, which is not reproduced by modern models of galaxy populations tracing both stellar and gas masses. The discrepancy between observations and models suggests a mass dependence in gas storage and consumption missing in current galaxy evolution prescriptions. The break coincides with the transition from galaxies with predominantly irregular morphology at low masses to regular disks at high masses, as well as the transition from cold to hot accretion of gas in simulations.

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arXiv2013

Evolution in the H I Gas Content of Galaxy Groups: Pre-Processing and Mass Assembly in the Current Epoch

We present an analysis of the neutral hydrogen (HI) content and distribution of galaxies in groups as a function of their parent dark matter halo mass. The Arecibo Legacy Fast ALFA survey alpha.40 data release allows us, for the first time, to study the HI properties of over 740 galaxy groups in the volume of sky common to the SDSS and ALFALFA surveys. We assigned ALFALFA HI detections a group membership based on an existing magnitude/volume-limited SDSS DR7 group/cluster catalog. Additionally, we assigned group "proximity" membership to HI detected objects whose optical counterpart falls below the limiting optical magnitude--thereby not contributing substantially to the estimate of the group stellar mass, but significantly to the total group HI mass. We find that only 25% of the HI detected galaxies reside in groups or clusters, in contrast to approximately half of all optically detected galaxies. Further, we plot the relative positions of optical and HI detections in groups as a function of parent dark matter halo mass to reveal strong evidence that HI is being processed in galaxies as a result of the group environment: as optical membership increases, groups become increasingly deficient of HI rich galaxies at their center and the HI distribution of galaxies in the most massive groups starts to resemble the distribution observed in comparatively more extreme cluster environments. We find that the lowest HI mass objects lose their gas first as they are processed in the group environment, and it is evident that the infall of gas rich objects is important to the continuing growth of large scale structure at the present epoch, replenishing the neutral gas supply of groups. Finally, we compare our results to those of cosmological simulations and find that current models cannot simultaneously predict the HI selected halo occupation distribution for both low and high mass halos.

astro-ph.CO↗

arXiv2013

Comparison of HI and optical redshifts of galaxies - The impact of redshift uncertainties on spectral line stacking

Accurate optical redshifts will be critical for spectral co-adding techniques used to extract detections from below the noise level in ongoing and upcoming surveys for HI, which will extend our current understanding of gas reservoirs in galaxies to lower column densities and higher redshifts. We have used existing, high quality optical and radio data from the SDSS and ALFALFA surveys to investigate the relationship between redshifts derived from optical spectroscopy and neutral hydrogen (HI) spectral line observations. We find that the two redshift measurements agree well, with a negligible systematic offset and a small distribution width. Employing simple simulations, we determine how the width of an ideal stacked HI profile depends on these redshift offsets, as well as larger redshift errors more appropriate for high redshift galaxy surveys. The width of the stacked profile is dominated by the width distribution of the input individual profiles when the redshift errors are less than the median width of the input profiles, and only when the redshift errors become large, ~150 km/s, do they significantly affect the width of the stacked profile. This redshift accuracy can be achieved with moderate resolution optical spectra. We provide guidelines for the number of spectra required for stacking to reach a specified mass sensitivity, given telescope and survey parameters, which will be useful for planning optical spectroscopy observing campaigns to supplement the radio data.

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arXiv2013

A Pilot for a VLA HI Deep Field

High-resolution 21-cm HI deep fields provide spatially and kinematically resolved neutral gas maps at different redshifts, which are key to understanding galaxy evolution across cosmic time and testing predictions of cosmological simulations. Here we present results from a pilot for the COSMOS HI Large Extragalactic Survey (CHILES) done with the Karl G. Jansky Very Large Array (VLA). We take advantage of the newly expanded capabilities of the telescope to probe the redshift interval 0<z<0.193 in one observation. We observe the COSMOS field for 50 hours, which contains 413 galaxies with optical spectroscopic redshifts in the imaged field of view of 34' x 34' and the observed redshift interval. We have detected neutral hydrogen gas in 33 galaxies in different environments spanning the probed redshift range, including three without a previously known spectroscopic redshift. The detections have a range of HI and stellar masses, indicating the diversity of galaxies we are probing. We discuss the observations, data reduction, results and highlight interesting detections. We find that the VLA's B-array is the ideal configuration for HI deep fields since its long spacings mitigate RFI. This pilot shows that the VLA is ready to carry out such a survey, and serves as a test for future HI deep fields planned with other SKA pathfinders.

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arXiv2012

Fresh Activity in Old Systems: Radio AGN in Fossil Groups of Galaxies

We present the first systematic 1.4 GHz Very Large Array radio continuum survey of fossil galaxy group candidates. These are virialized systems believed to have assembled over a gigayear in the past through the merging of galaxy group members into a single, isolated, massive elliptical galaxy and featuring an extended hot X-ray halo. We use new photometric and spectroscopic data from SDSS Data Release 7 to determine that three of the candidates are clearly not fossil groups. Of the remaining 30 candidates, 67% contain a radio-loud (L_1.4GHz > 10^23 W Hz^-1) active galactic nucleus (AGN) at the center of their dominant elliptical galaxy. We find a weak correlation between the radio luminosity of the AGN and the X-ray luminosity of the halo suggesting that the AGN contributes to energy deposition into the intragroup medium. We only find a correlation between the radio and optical luminosity of the central elliptical galaxy when we include X-ray selected, elliptically dominated non-fossil groups, indicating a weak relationship between AGN strength and the mass assembly history of the groups. The dominant elliptical galaxy of fossil groups is on average roughly an order of magnitude more luminous than normal group elliptical galaxies in optical, X-ray, and radio luminosities and our findings are consistent with previous results that the radio-loud fraction in elliptical galaxies is linked to the stellar mass of a population. The current level of activity in fossil groups suggests that AGN fueling continues long after the last major merger. We discuss several possibilities for fueling the AGN at the present epoch.

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arXiv2012

NGC 4656UV: A UV-selected Tidal Dwarf Galaxy Candidate

We report the discovery of a UV-bright tidal dwarf galaxy candidate in the NGC 4631/4656 galaxy group, which we designate NGC 4656UV. Using survey and archival data spanning from 1.4 GHz to the ultraviolet we investigate the gas kinematics and stellar properties of this system. The HI morphologies of NGC 4656UV and its parent galaxy NGC 4656 are extremely disturbed, with significant amounts of counterrotating and extraplanar gas. From UV-FIR photometry, computed using a new method to correct for surface gradients on faint objects, we find that NGC 4656UV has no significant dust opacity and a blue spectral energy distribution. We compute a star formation rate of 0.027 M_sun yr^-1 from the FUV flux and measure a total HI mass of 3.8x10^8 M_sun for the object. Evolutionary synthesis modeling indicates that NGC 4656UV is a low metallicity system whose only major burst of star formation occurred within the last ~260-290 Myr. The age of the stellar population is consistent with a rough timescale for a recent tidal interaction between NGC 4656 and NGC 4631, although we discuss the true nature of the object--whether it is tidal or pre-existing in origin--in the context of its metallicity being a factor of ten lower than its parent galaxy. We estimate that NGC 4656UV is either marginally bound or unbound. If bound, it contains relatively low amounts of dark matter. The abundance of archival data allows for a deeper investigation into this dynamic system than is currently possible for most TDG candidates.

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arXiv2011

The Arecibo Legacy Fast ALFA Survey: The alpha.40 HI Source Catalog, its Characteristics and their Impact on the Derivation of the HI Mass Function

We present a current catalog of 21 cm HI line sources extracted from the Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) survey over ~2800 square degrees of sky: the alpha.40 catalog. Covering 40% of the final survey area, the alpha.40 catalog contains 15855 sources in the regions 07h30m < R.A. < 16h30m, +04 deg < Dec. < +16 deg and +24 deg < Dec. < +28 deg and 22h < R.A. < 03h, +14 deg < Dec. < +16 deg and +24 deg < Dec. < +32 deg. Of those, 15041 are certainly extragalactic, yielding a source density of 5.3 galaxies per square degree, a factor of 29 improvement over the catalog extracted from the HI Parkes All Sky Survey. In addition to the source centroid positions, HI line flux densities, recessional velocities and line widths, the catalog includes the coordinates of the most probable optical counterpart of each HI line detection, and a separate compilation provides a crossmatch to identifications given in the photometric and spectroscopic catalogs associated with the Sloan Digital Sky Survey Data Release 7. Fewer than 2% of the extragalactic HI line sources cannot be identified with a feasible optical counterpart; some of those may be rare OH megamasers at 0.16 < z < 0.25. A detailed analysis is presented of the completeness, width dependent sensitivity function and bias inherent in the current alpha.40 catalog. The impact of survey selection, distance errors, current volume coverage and local large scale structure on the derivation of the HI mass function is assessed. While alpha.40 does not yet provide a completely representative sampling of cosmological volume, derivations of the HI mass function using future data releases from ALFALFA will further improve both statistical and systematic uncertainties.

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arXiv2009

Anomalous HI in NGC 2997

We present deep HI observations of the moderately inclined spiral galaxy, NGC 2997. The goal of these observations was to search for HI clouds in the vicinity of NGC 2997 analogous to the high velocity clouds of the Milky Way and gain insight into their origins. We find evidence for the presence of a galactic fountain as well as the accretion of intragalactic material, however we do not identify any large clouds of HI far from the disk of the galaxy. NGC 2997 has a thick, lagging HI disk that is modeled with a vertical velocity gradient of 18-31 km/s/kpc. Anomalous velocity HI clouds with masses of order 10^7 Msun, which cannot be explained by galactic fountain models allow us to estimate a lower limit to the accretion of extragalactic gas of 1.2 Msun/yr. The number and mass of these clouds have implications for cosmological simulations of large scale structure and the presence of dark matter halos. We have used values from the the literature to estimate a star formation rate of 5 +/- 1 Msun/yr and to derive a new distance to NGC 2997 of 12.2 +/- 0.9 Mpc using published Tully-Fisher relations.

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