arXiv subjects

Elizabeth A. K. Adams

Publications and source records attributed to Elizabeth A. K. Adams.

At least 55 records · Page 3Linked to original sources

arXiv2021

The Intrinsic Shapes of Low Surface Brightness Galaxies: a Discriminant of LSBG Formation Mechanisms

We use the low surface brightness galaxy (LSBG) samples created from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP, 781 galaxies), the Dark Energy Survey (DES, 20977 galaxies), and the Legacy Survey (selected via HI detection in the Arecibo Legacy Fast ALFA Survey, 188 galaxies) to infer the intrinsic shape distribution of the low surface brightness galaxy population. To take into account the effect of the surface brightness cuts employed when constructing LSBG samples, we simultaneously model both the projected ellipticity and the apparent surface brightness in our shape inference. We find that the LSBG samples are well-characterized by oblate spheroids, with no significant difference between red and blue LSBGs. This inferred shape distribution is in good agreement with similar inferences made for ultra-diffuse cluster galaxy samples, indicating that environment does not play a key role in determining the intrinsic shape of low surface brightness galaxies. We also find some evidence that LSBGs are more thickened than similarly massive high surface brightness dwarfs. We compare our results to intrinsic shape measures from contemporary cosmological simulations, and find that the observed LSBG intrinsic shapes place considerable constraints on the formation path of such galaxies. In particular, LSBG production via the migration of star formation to large radii produces intrinsic shapes in good agreement with our observational findings.

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arXiv2021

A tight angular-momentum plane for disc galaxies

The relations between the specific angular momenta ($j$) and masses ($M$) of galaxies are often used as a benchmark in analytic models and hydrodynamical simulations as they are considered to be amongst the most fundamental scaling relations. Using accurate measurements of the stellar ($j_\ast$), gas ($j_{\rm gas}$), and baryonic ($j_{\rm bar}$) specific angular momenta for a large sample of disc galaxies, we report the discovery of tight correlations between $j$, $M$, and the cold gas fraction of the interstellar medium ($f_{\rm gas}$). At fixed $f_{\rm gas}$, galaxies follow parallel power laws in 2D $(j,M)$ spaces, with gas-rich galaxies having a larger $j_\ast$ and $j_{\rm bar}$ (but a lower $j_{\rm gas}$) than gas-poor ones. The slopes of the relations have a value around 0.7. These new relations are amongst the tightest known scaling laws for galaxies. In particular, the baryonic relation ($j_{\rm bar}-M_{\rm bar}-f_{\rm gas}$), arguably the most fundamental of the three, is followed not only by typical discs but also by galaxies with extreme properties, such as size and gas content, and by galaxies previously claimed to be outliers of the standard 2D $j-M$ relations. The stellar relation ($j_{\ast}-M_{\ast}-f_{\rm gas}$) may be connected to the known $j_\ast-M_\ast-$bulge fraction relation; however, we argue that the $j_{\rm bar}-M_{\rm bar}-f_{\rm gas}$ relation can originate from the radial variation in the star formation efficiency in galaxies, although it is not explained by current disc instability models.

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arXiv2021

The baryonic specific angular momentum of disc galaxies

(Abridged) Specific angular momentum is one of the key parameters that control the evolution of galaxies. We derive the baryonic specific angular momentum of disc galaxies and study its relation with the dark matter specific angular momentum. Using a combination of high-quality HI rotation curves and HI/near-IR surface densities, we homogeneously measure the stellar ($j_{\rm *}$) and gas ($j_{\rm gas}$) specific angular momenta for a large sample of local disc galaxies. This allows us to determine the baryonic specific angular momentum ($j_{\rm bar}$) with high accuracy and across a very wide range of masses. The $j_{\ast}-M_\ast$ relation is an unbroken power-law from $7 \lesssim$ log($M_\ast$/$M_\odot) \lesssim 11.5$, with slope $0.54 \pm 0.02$. For the gas component, we find that the $j_{\rm gas}-M_{\rm gas}$ relation is also an unbroken power-law from $6 \lesssim$ log($M_{\rm gas}$/$M_\odot) \lesssim 11$, with a steeper slope of $1.02 \pm 0.04$. Regarding the baryonic relation, our data support a correlation characterized by single power-law with slope $0.60 \pm 0.02$. Our most massive spirals and smallest dwarfs lie along the same $j_{\rm bar}-M_{\rm bar}$ sequence. While the relations are tight and unbroken, we find internal correlations inside them: At fixed $M_\ast$, galaxies with larger $j_\ast$ have larger disc scale lengths, and at fixed $M_{\rm bar}$, gas-poor galaxies have lower $j_{\rm bar}$ than expected. We estimate the retained fraction of baryonic specific angular momentum, finding it constant across our entire mass range with a value of $\sim 0.6$, indicating that the $j_{\rm bar}$ of present-day disc galaxies is comparable to the initial specific angular momentum of their dark matter haloes. These results set important constraints for hydrodynamical simulations and semi-analytical models aiming to reproduce galaxies with realistic specific angular momenta.

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arXiv2021

Galaxy Properties at the Faint End of the HI Mass Function

The Survey of HI in Extremely Low-mass Dwarfs (SHIELD) includes a volumetrically complete sample of 82 gas-rich dwarfs with M_HI~<10^7.2 Msun selected from the ALFALFA survey. We are obtaining extensive follow-up observations of the SHIELD galaxies to study their gas, stellar, and chemical content, and to better understand galaxy evolution at the faint end of the HI mass function. Here, we investigate the properties of 30 SHIELD galaxies using Hubble Space Telescope imaging of their resolved stars and Westerbork Synthesis Radio Telescope observations of their neutral hydrogen. We measure tip of the red giant branch (TRGB) distances, star formation activity, and gas properties. The TRGB distances are up to 4x greater than estimates from flow models, highlighting the importance of velocity-independent distance indicators in the nearby universe. The SHIELD galaxies are in under-dense regions, with 23% located in voids; one galaxy appears paired with a more massive dwarf. We quantify galaxy properties at low masses including stellar and HI masses, SFRs, sSFRs, SFEs, birthrate parameters, and gas fractions. The lowest mass systems lie below the mass thresholds where stellar mass assembly is predicted to be impacted by reionization. Even so, we find the star formation properties follow the same trends as higher mass gas-rich systems, albeit with a different normalization. The HI disks are small ( <0.7 kpc) making it difficult to measure the HI rotation using standard techniques; we develop a new methodology and report the velocity extent, and its associated spatial extent, with robust uncertainties.

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arXiv2021

A search for radio emission from double-neutron star merger GW190425 using Apertif

Detection of the electromagnetic emission from coalescing binary neutron stars (BNS) is important for understanding the merger and afterglow. We present a search for a radio counterpart to the gravitational-wave source GW190425, a BNS merger, using Apertif on the Westerbork Synthesis Radio Telescope (WSRT). We observe a field of high probability in the associated localisation region for 3 epochs at 68, 90 and 109 days post merger. We identify all sources that exhibit flux variations consistent with the expected afterglow emission of GW190425. We also look for possible transients. These are sources which are only present in one epoch. In addition, we quantify our ability to search for radio afterglows in fourth and future observing runs of the gravitational-wave detector network using Monte Carlo simulations. We found 25 afterglow candidates based on their variability. None of these could be associated with a possible host galaxy at the luminosity distance of GW190425. We also found 55 transient afterglow candidates that were only detected in one epoch. All turned out to be image artefacts. In the fourth observing run, we predict that up to three afterglows will be detectable by Apertif. While we did not find a source related to the afterglow emission of GW190425, the search validates our methods for future searches of radio afterglows.

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arXiv2021

VLA Imaging of HI-bearing Ultra-Diffuse Galaxies from the ALFALFA Survey

Ultra-diffuse galaxies have generated significant interest due to their large optical extents and low optical surface brightnesses, which challenge galaxy formation models. Here we present resolved synthesis observations of 12 HI-bearing ultra-diffuse galaxies (HUDs) from the Karl G. Jansky Very Large Array (VLA), as well as deep optical imaging from the WIYN 3.5-meter telescope at Kitt Peak National Observatory. We present the data processing and images, including total intensity HI maps and HI velocity fields. The HUDs show ordered gas distributions and evidence of rotation, important prerequisites for the detailed kinematic models in Mancera Piña et al. (2019b). We compare the HI and stellar alignment and extent, and find the HI extends beyond the already extended stellar component and that the HI disk is often misaligned with respect to the stellar one, emphasizing the importance of caution when approaching inclination measurements for these extreme sources. We explore the HI mass-diameter scaling relation, and find that although the HUDs have diffuse stellar populations, they fall along the relation, with typical global HI surface densities. This resolved sample forms an important basis for more detailed study of the HI distribution in this extreme extragalactic population.

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arXiv2020

Chromatic periodic activity down to 120 MHz in a Fast Radio Burst

Fast radio bursts (FRBs) are extragalactic astrophysical transients whose brightness requires emitters that are highly energetic, yet compact enough to produce the short, millisecond-duration bursts. FRBs have thus far been detected between 300 MHz and 8 GHz, but lower-frequency emission has remained elusive. A subset of FRBs is known to repeat, and one of those sources, FRB 20180916B, does so with a 16.3 day activity period. Using simultaneous Apertif and LOFAR data, we show that FRB 20180916B emits down to 120 MHz, and that its activity window is both narrower and earlier at higher frequencies. Binary wind interaction models predict a narrower periodic activity window at lower frequencies, which is the opposite of our observations. Our detections establish that low-frequency FRB emission can escape the local medium. For bursts of the same fluence, FRB 20180916B is more active below 200 MHz than at 1.4 GHz. Combining our results with previous upper-limits on the all-sky FRB rate at 150 MHz, we find that there are 3-450 FRBs/sky/day above 50 Jy ms at 90% confidence. We are able to rule out the scenario in which companion winds cause FRB periodicity. We also demonstrate that some FRBs live in clean environments that do not absorb or scatter low-frequency radiation.

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arXiv2020

A Demonstration of Extremely Low Latency $γ$-ray, X-Ray & UV Follow-Up of a Millisecond Radio Transient

We report results of a novel high-energy follow-up observation of a potential Fast Radio Burst. The radio burst was detected by VLA/realfast and followed-up by the Neil Gehrels Swift Observatory in very low latency utilizing new operational capabilities of Swift (arXiv:2005.01751), with pointed soft X-ray and UV observations beginning at T0+32 minutes, and hard X-ray/gamma-ray event data saved around T0. These observations are $>10$x faster than previous X-ray/UV follow-up of any radio transient to date. No emission is seen coincident with the FRB candidate at T0, with a 0.2s fluence $5σ$ upper limit of $1.35\times10^{-8}$ erg cm$^{-2}$ (14-195 keV) for a SGR 1935+2154-like flare, nor at T0+32 minutes down to $3σ$ upper limits of 22.18 AB mag in UVOT u band, and $3.33\times10^{-13}$ erg cm$^{-2}$ s$^{-1}$ from 0.3-10 keV for the 2 ks observation. The candidate FRB alone is not significant enough to be considered astrophysical, so this note serves as a technical demonstration. These new Swift operational capabilities will allow future FRB detections to be followed up with Swift at even lower latencies than demonstrated here: 15-20 minutes should be regularly achievable, and 5-10 minutes occasionally achievable. We encourage FRB detecting facilities to release alerts in low latency to enable this science.

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arXiv2020

Robust HI kinematics of gas-rich ultra-diffuse galaxies: hints of a weak-feedback formation scenario

We study the gas kinematics of a sample of six isolated gas-rich low surface brightness galaxies, of the class called ultra-diffuse galaxies (UDGs). These galaxies have recently been shown to be outliers from the baryonic Tully-Fisher relation (BTFR), as they rotate much slower than expected given their baryonic mass, and to have baryon fractions similar to the cosmological mean. By means of a 3D kinematic modelling fitting technique, we show that the HI in our UDGs is distributed in "thin" regularly rotating discs and we determine their rotation velocity and gas velocity dispersion. We revisit the BTFR adding galaxies from other studies. We find a previously unknown trend between the deviation from the BTFR and the disc scale length valid for dwarf galaxies with circular speeds < 45 km/s, with our UDGs being at the extreme end. Based on our findings, we suggest that the high baryon fractions of our UDGs may originate due to the fact that they have experienced weak stellar feedback, likely due to their low star formation rate surface densities, and as a result they did not eject significant amounts of gas out of their discs. At the same time, we find indications that our UDGs may have higher-than-average stellar specific angular momentum, which can explain their large optical scale lengths.

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arXiv2020

The HI mass function of group galaxies in the ALFALFA survey

We estimate the HI mass function (HIMF) of galaxies in groups based on thousands of ALFALFA (Arecibo Legacy Fast ALFA survey) HI detections within the galaxy groups of four widely used SDSS (Sloan Digital Sky Survey) groups catalogues. Although differences between the catalogues mean that there is no one definitive group galaxy HIMF, in general we find that the low-mass slope is flat, in agreement with studies based on small samples of individual groups, and that the 'knee' mass is slightly higher than that of the global HIMF of the full ALFALFA sample. We find that the observed fraction of ALFALFA galaxies in groups is approximately 22 per cent. These group galaxies were removed from the full ALFALFA source catalogue to calculate the field HIMF using the remaining galaxies. Comparison between the field and group HIMFs reveals that group galaxies make only a small contribution to the global HIMF as most ALFALFA galaxies are in the field, but beyond the HIMF 'knee' group galaxies dominate. Finally we attempt to separate the group galaxy HIMF into bins of group halo mass, but find that too few low-mass galaxies are detected in the most massive groups to tightly constrain the slope, owing to the rarity of such groups in the nearby Universe where low-mass galaxies are detectable with existing HI surveys.

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arXiv2019

Baryon dominated ultra-diffuse galaxies

By means of interferometic 21-cm observations and a 3D kinematic modeling technique, we study the gas kinematics of six HI-rich ultra-diffuse galaxies (UDGs). We derive robust circular velocities and baryonic masses, that allow us to study the position of our UDGs with respect to the baryonic Tully-Fisher relation (BTFR). Somewhat surprisingly, we find that these galaxies are strong outliers from the BTFR, rotating too slowly for their baryonic mass. Moreover, their position in the circular velocity--baryonic mass plane implies that they have a baryon fraction inside their virial radii compatible with the cosmological mean, meaning that they have no "missing baryons". Unexpectedly, the dynamics of our galaxies are dominated by the baryons, leaving small room for dark matter inside their discs.

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arXiv2019

Off the baryonic Tully-Fisher relation: a population of baryon-dominated ultra-diffuse galaxies

We study the gas kinematics traced by the 21-cm emission of a sample of six HI$-$rich low surface brightness galaxies classified as ultra-diffuse galaxies (UDGs). Using the 3D kinematic modelling code $\mathrm{^{3D}}$Barolo we derive robust circular velocities, revealing a startling feature: HI$-$rich UDGs are clear outliers from the baryonic Tully-Fisher relation, with circular velocities much lower than galaxies with similar baryonic mass. Notably, the baryon fraction of our UDG sample is consistent with the cosmological value: these UDGs are compatible with having no "missing baryons" within their virial radii. Moreover, the gravitational potential provided by the baryons is sufficient to account for the amplitude of the rotation curve out to the outermost measured point, contrary to other galaxies with similar circular velocities. We speculate that any formation scenario for these objects will require very inefficient feedback and a broad diversity in their inner dark matter content.

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arXiv2019

Five Gas-rich Ultra-faint Dwarf Galaxy Candidates Discovered in WIYN Imaging of ALFALFA Sources

We present results from the analysis of WIYN pODI imaging of 23 ultra-compact high-velocity clouds (UCHVCs), which were identified in the ALFALFA HI survey as possible dwarf galaxies in or near the Local Group. To search for a resolved stellar population associated with the HI gas in these objects, we carried out a series of steps designed to identify stellar overdensities in our optical images. We identify five objects that are likely stellar counterparts to the UCHVCs, at distances of $\sim 350$ kpc to $\sim 1.6$ Mpc. Two of the counterparts were already described in Janesh et al. (2015) and Janesh et al. (2017); the estimated distance and detection significance for one of them changed in the final analysis of the full pODI data set. At their estimated distances, the detected objects have HI masses from $2 \times 10^4$ to $3 \times 10^6$ Msun, $M_V$ from -1.4 to -7.1, and stellar masses from $4 \times 10^2$ to $4 \times 10^5$ Msun. None of the objects shows evidence of a young stellar population. Their properties would make the UCHVCs some of the most extreme objects in and around the Local Group, comparable to ultra faint dwarf galaxies in their stellar populations, but with significant gas content. Such objects probe the extreme end of the galaxy mass function, and provide a testbed for theories regarding the baryonic feedback processes that impact star formation and galaxy evolution in this low-mass regime.

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arXiv2019

The Enigmatic (Almost) Dark Galaxy Coma P: Distance Measurement and Stellar Populations from HST Imaging

We present Hubble Space Telescope (HST) observations of the low surface brightness (SB) galaxy Coma P. This system was first discovered in the Arecibo Legacy Fast ALFA HI survey and was cataloged as an (almost) dark galaxy because it did not exhibit any obvious optical counterpart in the available survey data (e.g., Sloan Digital Sky Survey). Subsequent WIYN pODI imaging revealed an ultra-low SB stellar component located at the center of the HI detection. We use the HST images to produce a deep color-magnitude diagram (CMD) of the resolved stellar population present in Coma P. We clearly detect a red stellar sequence that we interpret to be a red giant branch, and use it to infer a tip of the red giant branch (TRGB) distance of 5.50$^{+0.28}_{-0.53}$ Mpc. The new distance is substantially lower than earlier estimates and shows that Coma P is an extreme dwarf galaxy. Our derived stellar mass is only 4.3 $\times$ 10$^5$ $M_\odot$, meaning that Coma P has an extreme HI-to-stellar mass ratio of 81. We present a detailed analysis of the galaxy environment within which Coma P resides. We hypothesize that Coma P formed within a local void and has spent most of its lifetime in a low-density environment. Over time, the gravitational attraction of the galaxies located in the void wall has moved it to the edge, where it had a recent "fly-by" interaction with M64. We investigate the possibility that Coma P is at a farther distance and conclude that the available data are best fit by a distance of 5.5 Mpc.

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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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arXiv2018

A Search for Molecular Gas in the Host Galaxy of FRB 121102

We present SMA and NOEMA observations of the host galaxy of FRB 121102 in the CO 3-2 and 1-0 transitions, respectively. We do not detect emission from either transition. We set $3σ$ upper limits to the CO luminosity $L_{CO} < 2.5 \times 10^7\,{\rm K\,km\,s}^{-1} {\, \rm pc^{-2}}$ for CO 3-2 and $L_{CO} < 2.3 \times 10^9\, {\rm K\,km\,s}^{-1} {\, \rm pc^{-2}}$ for CO 1-0. For Milky-Way-like star formation properties, we set a $3σ$ upper limit on the $H_2$ mass of $2.5 \times 10^8 \rm\ M_{\odot}$, slightly less than the predictions for the $H_2$ mass based on the star formation rate. The true constraint on the $H_2$ mass may be significantly higher, however, because of the reduction in CO luminosity that is common forlow-metallicity dwarf galaxies like the FRB host galaxy. These results demonstrate the challenge of identifying the nature of FRB progenitors through study of the host galaxy molecular gas. We also place a limit of 42 $μ$Jy ($3σ$) on the continuum flux density of the persistent radio source at 97 GHz, consistent with a power-law extrapolation of the low frequency spectrum, which may arise from an AGN or other nonthermal source.

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arXiv2018

The contribution of HI-bearing ultra-diffuse galaxies to the cosmic number density of galaxies

We estimate the cosmic number density of the recently identified class of HI-bearing ultra-diffuse sources (HUDs) based on the completeness limits of the ALFALFA survey. These objects fall in the range $8.5 < \log M_{\rm{HI}}/\rm{M_{\odot}} < 9.5$, have average $r$-band surface brightnesses fainter than 24 mag arsec$^{-2}$, half-light radii greater than 1.5 kpc, and are separated from neighbours by at least 350 kpc. We find that HUDs contribute at most 6% of the population of HI-bearing dwarfs, have a total cosmic number density of $(1.5 \pm 0.6) \times 10^{-3}$ $\rm{Mpc^{-3}}$, and an HI mass density of $(6.0 \pm 0.8) \times 10^{5}$ $\rm{M_{\odot}\,Mpc^{-3}}$. We estimate that this is similar to the total cosmic number density of UDGs in groups and clusters, and conclude that the relation between the number of UDGs hosted in a halo and the halo mass, must have a break below $M_{200} \sim 10^{12}$ $\rm{M_{\odot}}$ in order to account for the abundance of HUDs. The distribution of the velocity widths of HUDs rises steeply towards low values, indicating a preference for slow rotation rates. These objects have been absent from measurements of the galaxy stellar mass function owing to their low surface brightness. However, we estimate that due to their low number density, their inclusion would constitute a correction of less than 1%. Comparison with the Santa Cruz SAM shows that it produces HI-rich central UDGs that have similar colours to HUDs, but these are currently produced in much great a number. While previous results from this sample have favoured formation scenarios where HUDs form in high spin parameter halos, comparisons with the results of Rong et al. 2017, which invokes that formation mechanism, reveal that this model produces an order of magnitude more field UDGs than we observe in the HUD population.(Abridged)

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arXiv2018

The Enigmatic (Almost) Dark Galaxy Coma P: The Atomic Interstellar Medium

We present new high-resolution HI spectral line imaging of Coma P, the brightest HI source in the system HI 1232$+$20. This extremely low surface brightness galaxy was first identified in the ALFALFA survey as an "(Almost) Dark" object: a clearly extragalactic HI source with no obvious optical counterpart in existing optical survey data (although faint ultraviolet emission was detected in archival GALEX imaging). Using a combination of data from the Westerbork Synthesis Radio Telescope and the Karl G. Jansky Very Large Array, we investigate the HI morphology and kinematics at a variety of physical scales. The HI morphology is irregular, reaching only moderate maxima in mass surface density (peak $σ_{\rm HI}\sim 10$ $M_{\odot}$ pc$^{-2}$). Gas of lower surface brightness extends to large radial distances, with the HI diameter measured at 4.0$\pm$0.2 kpc inside the 1 $M_{\odot}$ pc$^{-2}$ level. We quantify the relationships between HI gas mass surface density and various types of star formation by considering GALEX far ultraviolet observations and H$α$ nondetections. We describe Coma P's complex HI kinematics using spatially resolved position-velocity analysis and three-dimensional modeling. Both methods of analysis suggest that Coma P's kinematics show signatures of either the collision of two HI disks or a significant infall event. Coma P is just consistent (within 3$σ$) with the known M$_{\rm HI}$ -- D$_{\rm HI}$ scaling relation. It is either too large for its HI mass, has too low an HI mass for its HI size, or the two HI components artificially extend its HI size. Coma P lies within the empirical scatter at the faint end of the baryonic Tully--Fisher relation, although the complexity of the HI dynamics complicates the interpretation. The collective HI characteristics of Coma P make it unusual among known galaxies in the nearby universe. [Abridged]

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