Engineering topics

Pisano, D. J.

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

10 records

DOE OSTI2023

The MeerKAT Fornax Survey: II. The rapid removal of H I from dwarf galaxies in the Fornax cluster

We present MeerKAT Fornax Survey atomic hydrogen (H I) observations of the dwarf galaxies located in the central ~2.5 × 4 deg 2 of the Fornax galaxy cluster (R vir ~2°). The H I images presented in this work have a 3σ column density sensitivity between 2.7 and 50 × 10 18 cm –2 over 25 km s –1 for spatial resolution between 4 and 1 kpc. We are able to detect an impressive M HI = 5 × 10 5 M ⊙ 3σ point source with a line width of 50 km s –1 at a distance of 20 Mpc. We detected H I in 17 out of the 304 dwarfs in our field, with 14 out of the 36 late-type dwarfs (LTDs) and three out of the 268 early-type dwarfs (ETDs). The H I-detected LTDs have likely just joined the cluster and are on their first infall as they are located at large clustocentric radii, with comparable MHI and mean stellar surface brightness at fixed luminosity as blue, star-forming LTDs in the field. By contrast, the H I-detected ETDs have likely been in the cluster longer than the LTDs and acquired their H I through a recent merger or accretion from nearby H I. Eight of the H I-detected LTDs host irregular or asymmetric H I emission and disturbed or lopsided stellar emission. There are two clear cases of ram pressure shaping the H I, with the LTDs displaying compressed H I on the side closest to the cluster centre and a one-sided, starless tail pointing away from the cluster centre. The H I-detected dwarfs avoid the most massive potentials (i.e. cluster centre and massive galaxies), consistent with massive galaxies playing an active role in the removal of H I. We created a simple toy model to quantify the timescale of H I stripping in the cluster by reproducing the observed M r' –M HI relation. We find that a M HI = 10 8 M ⊙ dwarf is stripped in ~240 Myr. The model is consistent with our observations, where low-mass LTDs are directly stripped of their H I from a single encounter and more massive LTDs can harbour a disturbed H I morphology due to longer times or multiple encounters being required to fully strip their H I. This is the first time dwarf galaxies with M HI ≲ 1 × 10 6 M ⊙ have been detected and resolved beyond the local group and in a galaxy cluster.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2021

Commissioning the H i Observing Mode of the Beam Former for the Cryogenically Cooled Focal L-band Array for the GBT (FLAG)

We present the results of commissioning observations for a new digital beam-forming back end for the Focal plane L-band Array for the Robert C. Byrd Green Bank Telescope (FLAG), a cryogenically cooled Phased Array Feed (PAF) with the lowest measured T {sub sys}/η of any PAF outfitted on a radio telescope to date. We describe the custom software used to apply beam-forming weights to the raw element covariances to create research-quality spectral-line images for the new fine-channel mode, study the stability of the beam weights over time, characterize FLAG’s sensitivity over a frequency range of 150 MHz, and compare the measured noise properties and observed distribution of neutral hydrogen emission from several extragalactic and Galactic sources with data obtained with the current single-pixel L-band receiver. These commissioning runs establish FLAG as the preeminent PAF receiver currently available for spectral-line observations on the world’s major radio telescopes.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2019

Large-scale Structure in CHILES Using DisPerSE

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 deep fields. Here we analyze the use of DisPerSE to identify structure in observational data. We apply DisPerSE to the distribution of galaxies in the Cosmic Evolution Survey (COSMOS) field and find the best parameters to identify filaments. We compile a catalog of 11,500 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 H i survey covering redshifts of z = 0–0.45, the COSMOS H i Large Extragalactic Survey (CHILES). In addition we present the predicted H i 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 of z = 0.1–0.45.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

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, 1667.359, and 1720.53 MHz frequencies with a spectral resolution of 357 Hz (approximately 0.06 km s{sup −1}). At the time of the observation, ‘Oumuamua was at topocentric distance and velocity of 1.07 au and 63.4 km s{sup −1}, respectively, or at heliocentric distance and velocity of 1.8 au and 39 km s{sup −1}, respectively. Based on a detailed data reduction and an analogy-based inversion, our final results confirm the asteroidal origin of ‘Oumuamua with an upper bound OH production of Q[OH] < 0.17 × 10{sup 28} s{sup −1}.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2018

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 the Focal L-band Array for the GBT (FLAG) project. Commissioning observations of calibrator radio sources show that this receiver has the lowest reported beam-formed system temperature (T {sub sys}) normalized by aperture efficiency (η) of any phased-array receiver to date. The measured T {sub sys}/η is 25.4 ± 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 {sub sys}/η at ∼4′ (required for Nyquist sampling) and ∼8′ offsets from the boresight is, respectively, ∼1% and ∼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 the boresight, qualitatively agrees 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 H ii 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 inflows and searches for fast radio bursts.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

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

We present a deep search for H I 21 cm emission from the gaseous halo of Messier 31 as part of Project AMIGA, a large Hubble Space Telescope program to study the circumgalactic medium of the Andromeda galaxy. Our observations with the Robert C. Byrd Green Bank Telescope 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≲ρ≲340 kpc (0.1≲ρ/R{sub vir}≲1.1). We do not detect any 21 cm emission toward these AGNs to limits of N(H I)≈4×10{sup 17} cm{sup −2} (5σ; per 2 kpc-diameter beam). This column density corresponds to an optical depth of ∼2.5 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{sub c}<0.051 (at 90% confidence) for ρ⩽R{sub vir}. Although 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 H I absorption about an ensemble of galaxies at z≈0.2 show significantly higher covering factors within ρ≲0.5R{sub vir} at the same N(H I), although the metal ion-to-H I ratios appear to be consistent with those seen in M31.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

The resolve survey atomic gas census and environmental influences on galaxy gas reservoirs

We present the H i mass inventory for the REsolved Spectroscopy Of a Local VolumE (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{sup 9} M{sub ⊙}. This first 21 cm data release provides robust detections or strong upper limits (1.4M {sub H i} < 5%–10% of stellar mass M {sub *}) 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 {sub h}, central/satellite designation, relative mass density of the cosmic web, and distance to the nearest massive group. We find that at fixed M {sub *}, satellites have decreasing G/S with increasing M {sub h} starting clearly at M {sub h} ∼ 10{sup 12} M{sub ⊙}, 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 {sub h} ≤ 10{sup 12} M{sub ⊙}, 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 {sub h} < 10{sup 11.4} M{sub ⊙}) halos primarily located within ∼1.5× the virial radius of more massive (M {sub h} > 10{sup 12} M{sub ⊙}) 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.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

THE SEARCH FOR Hi EMISSION AT z ≈ 0.4 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 report the first attempt to use gravitational lensing to detect Hi line emission from three gravitationally lensed galaxies behind the cluster Abell 773, two at redshifts of 0.398 and one at z = 0.487, using the Green Bank Telescope. We find that a 3 σ upper limit for a galaxy with a rotation velocity of 200 km s{sup −1} is M{sub Hi} = 6.58 × 10{sup 9} and 1.5 × 10{sup 10} M {sub ⊙} at z = 0.398 and z = 0.487. The estimated Hi masses of the sources at z = 0.398 and z = 0.487 are factors 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 wideband 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 contain RFI. These techniques can be used to study Hi in highly magnified distant galaxies that are otherwise too faint to detect.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

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 the accretion, processing, and removal of gas across cosmic time. The next generation of radio telescopes will image the neutral hydrogen (H i) in galaxies over large volumes at high redshifts, which will provide key insights into these processes. We are conducting the COSMOS H i Large Extragalactic Survey (CHILES) with the Karl G. Jansky Very Large Array, which is the first survey to simultaneously observe H i from z = 0 to z ∼ 0.5. Here, we report the highest redshift H i 21 cm detection in emission to date of the luminous infrared galaxy COSMOS J100054.83+023126.2 at z = 0.376 with the first 178 hr of CHILES data. The total H i mass is (2.9 ± 1.0) × 10{sup 10} M {sub ⊙} and the spatial distribution is asymmetric and extends beyond the galaxy. While optically the galaxy looks undisturbed, the H i distribution suggests an interaction with 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) × 10{sup 10} M {sub ⊙}. This is the first study of the H i and CO in emission for a single galaxy beyond z ∼ 0.2.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2016

SENSITIVE 21 cm OBSERVATIONS OF NEUTRAL HYDROGEN IN THE LOCAL GROUP NEAR M31

Very sensitive 21 cm H i measurements have been made at several locations around the Local Group galaxy M31 using the Green Bank Telescope at an angular resolution of 9.′1, with a 5σ detection level of N{sub H} {sub i} = 3.9 × 10{sup 17} cm{sup −2} for a 30 km s{sup −1} line. Most of the H i 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 a H i mass of 10{sup 5}M{sub ⊙}. Their velocities in the Local Group Standard of Rest lie between −100 and +40 km s{sup −1}, comparable to the systemic velocities of M31 and M33. The clouds appear to be isolated kinematically and spatially from each other. The total H i mass of all nine clouds is 1.4 × 10{sup 6}M{sub ⊙} for an adopted distance of 800 kpc, with perhaps another 0.2 × 10{sup 6}M{sub ⊙} in smaller clouds or more diffuse emission. The H i 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 H i 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 H i measurements on a coarse grid find emission that may be associated with an extension of the M31 high-velocity cloud (HVC) population to projected distances of ∼100 kpc. An extension of the M31 HVC population at a similar distance to the southeast, toward M33, is not observed.

79 ASTRONOMY AND ASTROPHYSICS↗