arXiv subjects

D. J. Pisano

Publications and source records attributed to D. J. Pisano.

At least 73 records · Page 4Linked to original sources

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

Science with an ngVLA: Neutral Atomic Hydrogen in the Local Universe

One of the outstanding questions in astronomy today is how gas flows from the circumgalactic medium (CGM) onto the disks of galaxies and then transitions from the diffuse atomic medium into molecular star-forming cores. For studies of the CGM, the Next Generation Very Large Array (ngVLA) will have the sensitivity and resolution to measure the sizes of the neutral atomic hydrogen (HI) disks of galaxies and complete a census of the HI content around galaxies. Within galaxies, the ngVLA will be able to resolve HI clouds in large numbers of galaxies beyond the Local Group providing measurements of the physical conditions of gas across a wide range of galaxy types. Finally, within our own Milky Way, the ngVLA will provide a dense grid of HI absorption spectra in the cold and warm neutral medium constraining the temperature and density of atomic gas as it transitions into molecular gas. Combined with radio continuum and molecular line data from the ngVLA plus multi-wavelength data from other planned facilities, ngVLA will have a key role in understanding star-formation in the local universe while complementing future studies with the Square Kilometer Array.

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arXiv2018

Early Observations of the MHONGOOSE Galaxies: Getting Ready for MeerKAT

We present early observations of 20 galaxies in the MHONGOOSE survey galaxies using KAT-7, the GBT, and MeerKAT. We present the best calibrators for five of the MHONGOOSE galaxies observed with the KAT-7, and search for signs of gas accretion in the GBT data, down to $3σ$ column density levels of $\rm 2.2\times10^{18}\, cm^{-2}$ over a $\rm 20\, km\, s^{-1}$ linewidth, but identify none. Using the KAT-7 and MeerKAT data, we have derived rotation curves and mass models for NGC 3621 and NGC 7424 out to an unprecedented extent. As a precursor to the SKA, the MeerKAT telescope combines both a high spatial resolution and a large field of view, necessary to map the extended neutral hydrogen in local galaxies. The mass models of the two galaxies were constructed for both the Dark Matter (DM) models (the pseudo-isothermal model and the Navarro-Frenk-White model) and MOND. Overall, we find that the DM models provide a better fit than MOND to the galaxies' rotation curves. Furthermore, the pseudo-isothermal model is found to be the most consistent with the observations.

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arXiv2018

A GBT Survey of the HALOGAS Galaxies and Their Environments I: Revealing the full extent of HI around NGC891, NGC925, NGC4414 & NGC4565

We present initial results from a deep neutral hydrogen (HI) survey of the HALOGAS galaxy sample, which includes the spiral galaxies NGC891, NGC925, NGC4414, and NGC4565, performed with the Robert C. Byrd Green Bank Telescope (GBT). The resulting observations cover at least four deg$^2$ around these galaxies with an average 5$σ$ detection limit of 1.2$\times$10$^{18}$ cm$^{-2}$ over a velocity range of 20 km s$^{-1}$ and angular scale of 9.1$'$. In addition to detecting the same total flux as the GBT data, the spatial distribution of the GBT and original Westerbork Synthesis Radio Telescope (WSRT) data match well at equal spatial resolutions. The HI mass fraction below HI column densities of 10$^{19}$ cm$^{-2}$ is, on average, 2\%. We discuss the possible origins of low column density HI of nearby spiral galaxies. The absence of a considerable amount of newly detected HI by the GBT indicates these galaxies do not have significant extended diffuse HI structures, and suggests future surveys planned with the SKA and its precursors must go \textit{at least} as deep as 10$^{17}$ cm$^{-2}$ in column density to significantly increase the probability of detecting HI associated with the cosmic web and/or cold mode accretion.

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arXiv2018

Search for OH 18-cm radio emission from 1I/2017 U1 with the Green Bank telescope

This paper reports the first OH 18-cm line observation of the first detected interstellar object 1I/2017 U1 (`Oumuamua) using the Green Bank Telescope. We have observed the OH lines at 1665.402 MHz, 1667.359, and 1720.53 MHz frequencies with a spectral resolution of 357 Hz (approximately 0.06 km-s^{-1}). At the time of the observation, `Oumuamua was at topocentric distance and velocity of 1.07 au and 63.4 km-s^{-1}, respectively, or at heliocentric distance and velocity of 1.8 au and 39 km-s^{-1}, respectively. Based on a detailed data reduction and an analogy-based inversion, our final results confirm the asteroidal origin of `Oumuamua (as discussed in Meech et al., 2017) with an upper bound of OH production of Q[OH] < 0.17 x 10^{28} s^{-1}.

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arXiv2018

Performance of a highly sensitive, 19-element, dual-polarization, cryogenic L-band Phased Array Feed on the Green Bank Telescope

A new 1.4 GHz 19-element, dual-polarization, cryogenic phased array feed (PAF) radio astronomy receiver has been developed for the Robert C. Byrd Green Bank Telescope (GBT) as part of FLAG (Focal L-band Array for the GBT) project. Commissioning observations of calibrator radio sources show that this receiver has the lowest reported beamformed system temperature ($T_{\rm sys}$) normalized by aperture efficiency ($η$) of any phased array receiver to date. The measured $T_{\rm sys}/η$ is $25.4 \pm 2.5$ K near 1350 MHz for the boresight beam, which is comparable to the performance of the current 1.4 GHz cryogenic single feed receiver on the GBT. The degradation in $T_{\rm sys}/η$ at $\sim$ 4 arcmin (required for Nyquist sampling) and $\sim$ 8 arcmin offsets from the boresight is, respectively, $\sim$ 1\% and $\sim$ 20\% of the boresight value. The survey speed of the PAF with seven formed beams is larger by a factor between 2.1 and 7 compared to a single beam system depending on the observing application. The measured performance, both in frequency and offset from boresight, qualitatively agree with predictions from a rigorous electromagnetic model of the PAF. The astronomical utility of the receiver is demonstrated by observations of the pulsar B0329+54 and an extended HII region, the Rosette Nebula. The enhanced survey speed with the new PAF receiver will enable the GBT to carry out exciting new science, such as more efficient observations of diffuse, extended neutral hydrogen emission from galactic in-flows and searches for Fast Radio Bursts.

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arXiv2018

Resolved H I observations of local analogs to z ~ 1 luminous compact blue galaxies: evidence for rotation-supported disks

While bright, blue, compact galaxies are common at $\rm z \sim 1$, they are relatively rare in the local universe, and their evolutionary paths are uncertain. We have obtained resolved H I observations of nine $\rm z \sim 0$ luminous compact blue galaxies (LCBGs) using the Giant Metrewave Radio Telescope and Very Large Array in order to measure their kinematic and dynamical properties and better constrain their evolutionary possibilities. We find that the LCBGs in our sample are rotating galaxies that tend to have nearby companions, relatively high central velocity dispersions, and can have disturbed velocity fields. We calculate rotation velocities for each galaxy by measuring half of the velocity gradient along their major axes and correcting for inclination using axis ratios derived from SDSS images of each galaxy. We compare our measurements to those previously made with single dishes and find that single dish measurements tend to overestimate LCBGs' rotation velocities and H I masses. We also compare the ratio of LCBGs' rotation velocities and velocity dispersions to those of other types of galaxies and find that LCBGs are strongly rotationally supported at large radii, similar to other disk galaxies, though within their half-light radii the $\rm V_{rot}/ σ$ values of their H I are comparable to stellar $\rm V_{rot}/ σ$ values of dwarf elliptical galaxies. We find that LCBGs' disks on average are gravitationally stable, though conditions may be conducive to local gravitational instabilities at the largest radii. Such instabilities could lead to the formation of star-forming gas clumps in the disk, resulting eventually in a small central bulge or bar.

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arXiv2017

Commissioning of FLAG: A phased array feed for the GBT

Phased Array Feed (PAF) technology is the next major advancement in radio astronomy in terms of combining high sensitivity and large field of view. The Focal L-band Array for the Green Bank Telescope (FLAG) is one of the most sensitive PAFs developed so far. It consists of 19 dual-polarization elements mounted on a prime focus dewar resulting in seven beams on the sky. Its unprecedented system temperature of$\sim$17 K will lead to a 3 fold increase in pulsar survey speeds as compared to contemporary single pixel feeds. Early science observations were conducted in a recently concluded commissioning phase of the FLAG where we clearly demonstrated its science capabilities. We observed a selection of normal and millisecond pulsars and detected giant pulses from PSR B1937+21.

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arXiv2017

An Overview of the MHONGOOSE Survey: Observing Nearby Galaxies with MeerKAT

MHONGOOSE is a deep survey of the neutral hydrogen distribution in a representative sample of 30 nearby disk and dwarf galaxies with HI masses from 10^6 to ~10^{11} M_sun, and luminosities from M_R ~ -12 to M_R ~ -22. The sample is selected to uniformly cover the available range in log(M_HI). Our extremely deep observations, down to HI column density limits of well below 10^{18} cm^{-2} - or a few hundred times fainter than the typical HI disks in galaxies - will directly detect the effects of cold accretion from the intergalactic medium and the links with the cosmic web. These observations will be the first ever to probe the very low-column density neutral gas in galaxies at these high resolutions. Combination with data at other wavelengths, most of it already available, will enable accurate modelling of the properties and evolution of the mass components in these galaxies and link these with the effects of environment, dark matter distribution, and other fundamental properties such as halo mass and angular momentum. MHONGOOSE can already start addressing some of the SKA-1 science goals and will provide a comprehensive inventory of the processes driving the transformation and evolution of galaxies in the nearby universe at high resolution and over 5 orders of magnitude in column density. It will be a Nearby Galaxies Legacy Survey that will be unsurpassed until the advent of the SKA, and can serve as a highly visible, lasting statement of MeerKAT's capabilities.

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arXiv2017

Project AMIGA: A Minimal Covering Factor for Optically Thick Circumgalactic Gas Around the Andromeda Galaxy

We present a deep search for HI 21-cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large program Hubble Space Telescope program to study the circumgalactic medium of the Andromeda galaxy. Our observations with the Robert C. Byrd Green Bank Telesope target sight lines to 48 background AGNs, more than half of which have been observed in the ultraviolet with the Cosmic Origins Spectrograph, with impact parameters $25 \lesssim ρ\lesssim 330$ kpc ($0.1 \lesssim ρ/ R_{\rm vir} \lesssim 1.1$). We do not detect any 21-cm emission toward these AGNs to limits of $N({\rm HI}) \approx 4 \times10^{17}$ cm$^{-2}$ ($5σ$, per 2 kpc diameter beam). This column density corresponds to an optical depth of $\sim2.5$ at the Lyman limit, thus our observations overlap with absorption line studies of Lyman limit systems at higher redshift. Our non-detections place a limit on the covering factor of such optically-thick gas around M31 to $f_c < 0.051$ (at 90\% confidence) for $ρ\leq R_{\rm vir}$. While individual clouds have previously been found in the region between M31 and M33, the covering factor of strongly optically-thick gas is quite small. Our upper limits on the covering factor are consistent with expectations from recent cosmological "zoom" simulations. Recent COS-Halos ultraviolet measurements of \HI\ absorption about an ensemble of galaxies at $z \approx 0.2$ show significantly higher covering factors within $ρ\lesssim 0.5 R_{\rm vir}$ at the same $N({\rm H I})$, although the metal ion-to-H I ratios appear to be consistent with those seen in M31.

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arXiv2016

The RESOLVE Survey Atomic Gas Census and Environmental Influences on Galaxy Gas Reservoirs

We present the HI mass inventory for the RESOLVE survey, a volume-limited, multi-wavelength census of >1500 z=0 galaxies spanning diverse environments and complete in baryonic mass down to dwarfs of 10^9 Msun. This first 21cm data release provides robust detections or strong upper limits (1.4M_HI < 5 to 10% of stellar mass M_stars) for 94% of RESOLVE. We examine global atomic gas-to-stellar mass ratios (G/S) in relation to galaxy environment using several metrics: group dark matter halo mass M_h , central/satellite designation, relative mass density of the cosmic web, and distance to nearest massive group. We find that at fixed M_stars, satellites have decreasing G/S with increasing M_h starting clearly at M_h = 10^12 Msun, suggesting the presence of starvation and/or stripping mechanisms associated with halo gas heating in intermediate-mass groups. The analogous relationship for centrals is uncertain because halo abundance matching builds in relationships between central G/S, stellar mass, and halo mass, which depend on the integrated group property used as a proxy for halo mass (stellar or baryonic mass). On larger scales G/S trends are less sensitive to the abundance matching method. At fixed M_h < 10^12 Msun, the fraction of gas-poor centrals increases with large-scale structure density. In overdense regions, we identify a rare population of gas-poor centrals in low-mass (M_h < 10^11.4 Msun) halos primarily located within 1.5 times the virial radius of more massive (M_h > 10^12 Msun) halos, suggesting that gas stripping and/or starvation may be induced by interactions with larger halos or the surrounding cosmic web. We find that the detailed relationship between G/S and environment varies when we examine different subvolumes of RESOLVE independently, which we suggest may be a signature of assembly bias.

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arXiv2016

HI4PI: A full-sky HI survey based on EBHIS and GASS

Measurement of the Galactic neutral atomic hydrogen (HI) column density, NHI, and brightness temperatures, Tb, is of high scientific value for a broad range of astrophysical disciplines. In the past two decades, one of the most-used legacy HI datasets has been the Leiden/Argentine/Bonn Survey (LAB). We release the HI 4$π$ survey (HI4PI), an all-sky database of Galactic HI, which supersedes the LAB survey. The HI4PI survey is based on data from the recently completed first coverage of the Effelsberg-Bonn HI Survey (EBHIS) and from the third revision of the Galactic All-Sky Survey (GASS). EBHIS and GASS share similar angular resolution and match well in sensitivity. Combined, they are ideally suited to be a successor to LAB. The new HI4PI survey outperforms the LAB in angular resolution (16.2', FWHM) and sensitivity (RMS: 43 mK). Moreover, it has full spatial sampling and thus overcomes a major drawback of LAB, which severely undersamples the sky. We publish all-sky column density maps of the neutral atomic hydrogen in the Milky Way, along with full spectroscopic data, in several map projections including HEALPix.

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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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arXiv2016

The Search for HI Emission at z $\approx0.4$ in Gravitationally Lensed Galaxies with the Green Bank Telescope

Neutral Hydrogen (HI) provides a very important fuel for star formation, but is difficult to detect at high redshift due to weak emission, limited sensitivity of modern instruments, and terrestrial radio frequency interference (RFI) at low frequencies. We the first attempt to use gravitational lensing to detect HI line emission from three gravitationally lensed galaxies behind the cluster Abell 773, two at redshift of 0.398 and one at z=0.487, using the Green Bank Telescope. We find a 3 sigma upper limit for a galaxy with a rotation velocity of 200 km/s is M_HI=6.58x10^9 and 1.5x10^10 M_solar at z=0.398 and z=0.487. The estimated HI masses of the sources at z=0.398 and z=0.487 are a factor of 3.7 and ~30 times lower than our detection limits at the respective redshifts. To facilitate these observations we have used sigma clipping to remove both narrow- and wide-band RFI but retain the signal from the source. We are able to reduce the noise of the spectrum by ~25% using our routine instead of discarding observations with too much RFI. The routine is most effective when ~10 of the integrations or fewer contains RFI. These techniques can be used to study HI in highly magnified distant galaxies that are otherwise too faint to detect.

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arXiv2015

Sensitive 21cm Observations of Neutral Hydrogen in the Local Group near M31

Very sensitive 21cm HI measurements have been made at several locations around the Local Group galaxy M31 using the Green Bank Telescope (GBT) at an angular resolution of 9.1', with a 5$σ$ detection level of $\rm{N_{HI} = 3.9 \times 10^{17}~cm^{-2}}$ for a 30 $\rm{km~s^{-1}}$ line. Most of the HI in a 12 square degree area almost equidistant between M31 and M33 is contained in nine discrete clouds that have a typical size of a few kpc and HI mass of $10^5$ M$_{\odot}$. Their velocities in the Local Group Standard of Rest lie between -100 and +40 $\rm{km~s^{-1}}$, comparable to the systemic velocities of M31 and M33. The clouds appear to be isolated kinematically and spatially from each other. The total HI mass of all nine clouds is $1.4 \times 10^6$ M$_{\odot}$ for an adopted distance of 800 kpc with perhaps another $0.2 \times 10^6$ M$_{\odot}$ in smaller clouds or more diffuse emission. The HI mass of each cloud is typically three orders of magnitude less than the dynamical (virial) mass needed to bind the cloud gravitationally. Although they have the size and HI mass of dwarf galaxies, the clouds are unlikely to be part of the satellite system of the Local Group as they lack stars. To the north of M31, sensitive HI measurements on a coarse grid find emission that may be associated with an extension of the M31 high-velocity cloud population to projected distances of $\sim 100$ kpc. An extension of the M31 high-velocity cloud population at a similar distance to the south, toward M33, is not observed.

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arXiv2015

Nearby Clumpy, Gas Rich, Star Forming Galaxies: Local Analogs of High Redshift Clumpy Galaxies

Luminous compact blue galaxies (LCBGs) have enhanced star formation rates and compact morphologies. We combine Sloan Digital Sky Survey data with HI data of 29 LCBGs at redshift z~0 to understand their nature. We find that local LCBGs have high atomic gas fractions (~50%) and star formation rates per stellar mass consistent with some high redshift star forming galaxies. Many local LCBGs also have clumpy morphologies, with clumps distributed across their disks. Although rare, these galaxies appear to be similar to the clumpy star forming galaxies commonly observed at z~1-3. Local LCBGs separate into three groups: 1. Interacting galaxies (~20%); 2. Clumpy spirals (~40%); 3. Non-clumpy, non-spirals with regular shapes and smaller effective radii and stellar masses (~40%). It seems that the method of building up a high gas fraction, which then triggers star formation, is not the same for all local LCBGs. This may lead to a dichotomy in galaxy characteristics. We consider possible gas delivery scenarios and suggest that clumpy spirals, preferentially located in clusters and with companions, are smoothly accreting gas from tidally disrupted companions and/or intracluster gas enriched by stripped satellites. Conversely, as non-clumpy galaxies are preferentially located in the field and tend to be isolated, we suggest clumpy, cold streams, which destroy galaxy disks and prevent clump formation, as a likely gas delivery mechanism for these systems. Other possibilities include smooth cold streams, a series of minor mergers, or major interactions.

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arXiv2015

Observations of the Intergalactic Medium and the Cosmic Web in the SKA era

The interaction of galaxies with their environment, the Intergalactic Medium (IGM), is an important aspect of galaxy formation. One of the most fundamental, but unanswered questions in the evolution of galaxies is how gas circulates in and around galaxies and how it enters the galaxies to support star formation. We have several lines of evidence that the observed evolution of star formation requires gas accretion from the IGM at all times and on all cosmic scales. This gas remains largely unaccounted for and the outstanding questions are where this gas resides and what the physical mechanisms of accretion are. The gas is expected to be embedded in an extended cosmic web made of sheets and filaments. Such large-scale filaments of gas are expected by cosmological numerical simulations, which have made significant progress in recent years. Such simulations do not only model the large scale structure of the cosmic web, but also investigate the neutral gas component. To truly make significant progress in understanding the distribution of neutral hydrogen in the IGM, column densities of NHI=10^18 cm-2 and below have to be probed over large areas on the sky at sub-arcminute resolution. These are the densities of the faintest structures known today around nearby galaxies, though mostly found with single dish telescopes which do not have the resolution to resolve these structures and investigate any kinematics. Existing interferometers lack the collecting power or short baselines to achieve brightness sensitivities typically below NHI=10^19 cm-2. Reaching lower column densities with current facilities is feasible, however requires prohibitively long observing times. The SKA will for the first time break these barriers, enabling interferometric observations an order of magnitude deeper than current interferometers and with an order of magnitude better linear resolution than single-dish telescopes.

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arXiv2014

A low HI column density filament in NGC 2403: signature of interaction or accretion

Observed HI accretion around nearby galaxies can only account for a fraction of the gas supply needed to sustain the currently observed star formation rates. It is possible that additional accretion happens in the form of low column density cold flows, as predicted by numerical simulations of galaxy formation. To contrain the presence and properties of such flows, we present deep HI observations obtained with the NRAO Green Bank Telescope of an area measuring 4 by 4 degrees around NGC 2403. These observations, with a 5 sigma detection limit of 2.4 x 10^18 cm^-2 over a 20 km/s linewidth, reveal the presence of a low-column density, extended cloud outside the main HI disk, about 17' (~16 kpc or ~2R25) to the NW of the center of the galaxy. The total HI mass of the cloud is 6.3 x 10^6 Msun, or 0.15 percent of the total HI mass of NGC 2403. The cloud is associated with an 8-kpc anomalous-velocity HI filament in the inner disk, previously observed in deep VLA observations by Fraternali et al. (2001, 2002). We discuss several scenarios for the origin of the cloud, and conclude that it is either accreting from the intergalactic medium, or is the result of a minor interaction with a neigbouring dwarf galaxy.

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