arXiv subjects

Robert Minchin

Publications and source records attributed to Robert Minchin.

At least 19 recordsLinked to original sources

arXiv2026

High resolution observations of 'dark' neutral hydrogen clouds in the Virgo cluster with the Very Large Array

We have observed six `dark' neutral hydrogen (HI) clouds discovered in the Virgo cluster by the Arecibo Galaxy Environment Survey (AGES) with the Karl G. Jansky Very Large Array (VLA), giving higher angular and velocity resolution than the original AGES observations. We detected compact HI emission in two of the sources, AGESVC1 231 and AGESVC1 274, allowing us to firmly associate them with faint ($m_g > 18.5$), blue ($g-i < 0.1$) optical counterparts with high $M_{HI}/L_g$ ratios. In a further two sources, we detected low column-density extended HI emission, consistent with these being dispersing clouds from ram-pressure stripping or tidal interactions. The final two sources were not detected with the VLA, allowing us to set low column-density limits on the HI detected by AGES that are consistent with these clouds also being formed from HI that is dispersing into the intra-cluster medium. The four HI sources not associated with optical counterparts thus appear likely to be relatively short-lived objects. No evidence was found for either pressure-supported turbulent spheres or stable dark galaxies.

astro-ph.GA↗

arXiv2026

Ultra Diffuse Galaxies in clusters : the peculiar gas loss of VCC 1964

Context : Ultra Diffuse Galaxies are low surface brightness systems which have been detected in HI in the field, where their line widths sometimes indicate significant dark matter deficits. They are rarely detected in HI in clusters, making their dynamical properties difficult to assess. The relation between field and cluster populations is unclear. Aims : Detecting UDGs entering a cluster could give important clues to their evolution, both in terms of their dynamics but also as to whether they are structurally similar - i.e. if cluster UDGs are generally the same as field UDGs except with less gas and an older stellar population. Methods : We use data from two deep Arecibo surveys, the Arecibo Galaxy Environment Survey and the Widefield Arecibo Virgo Environment Survey, to measure the gas content of the UDG-candidate VCC 1964. Optical properties are quantified from the Sloan Digital Sky Survey and DESI Legacy Surveys. Results : We find a significant 9 kpc offset between the HI and optical components of VCC 1964, no evidence of asymmetry in the HI, and only a modest deficiency level. This suggests a wholesale displacement of the gas content. The line width is 4-5 sigma deviant from the baryonic and over 6 sigma deviant from the optical forms of the Tully-Fisher relation. The optical component is blue and smooth. Conclusions : VCC 1964 is consistent with a UDG experiencing gas displacement due to ram pressure as it enters the cluster for the first time. Intriguingly, its dynamics imply a significant dark matter deficit, however we cannot rule out that this may be due to the gas being displaced out of equilibrium.

astro-ph.GA↗

arXiv2024

Joint Optical and Infrared Observations of N and O Reveal the Dust-Obscured Gas in Haro 3

Accurate chemical compositions of star-forming regions are a critical diagnostic tool to characterize the star formation history and gas flows which regulate galaxy formation. However, the abundance discrepancy factor (ADF) between measurements from the "direct" optical electron temperature ($T_e$) method and from the recombination lines (RL) represents $\sim0.2$ dex systematic uncertainty in oxygen abundance. The degree of uncertainty for other elements is unknown. We conduct a comprehensive analysis of O$^{++}$ and N$^+$ ion abundances using optical and far-infrared spectra of a star-forming region within the nearby dwarf galaxy Haro 3, which exhibits a typical ADF. Assuming homogeneous conditions, the far-IR emission indicates an O abundance which is higher than the $T_e$ method and consistent with the RL value, as would be expected from temperature fluctuations, whereas the far-IR N abundance is too large to be explained by temperature fluctuations. A two-phase analytical model reveals that differential dust obscuration associated with temperature inhomogeneity is likely required to explain all the emission line ratios, and that the total oxygen metallicity of two phases is consistent with the RL metallicity. Our findings underscore the critical importance of resolving the cause of abundance discrepancies and understanding the biases between different metallicity methods. This work represents a promising methodology, and we identify further approaches to address the current dominant uncertainties.

astro-ph.GA↗

arXiv2024

Reply to: Effects of density and temperature variations on the metallicity of Mrk 71

In Chen et al., 2023 (C23; arXiv:2304.09898), we introduced a new method to directly measure temperature fluctuations and applied it to a nearby dwarf galaxy, Mrk 71, finding a temperature fluctuation parameter $t^2 = 0.008\pm 0.043$. This result is lower by $\sim 2σ$ than the value required to explain the abundance discrepancy (AD) in this object. In the Matters Arising article submitted by Mendez-Delgado et al. (arXiv:2310.01197), the authors claim that using the same data presented in C23 in a different way, it is possible to conclude that the measurements are consistent with a larger $t^2 \simeq 0.1$ inferred indirectly from recombination lines (RLs). However, this requires a higher density such that the infrared [O III] 52 $μ$m and [O III] 88 $μ$m lines -- which form the basis of the direct measurement method -- are mutually inconsistent. Moreover, to reach agreement between the direct $t^2$ measurement and the larger $t^2$ value inferred from RLs requires systematically varying four parameters by $\sim 1σ$ from their best-determined values, which collectively amount to a $\sim2σ$ difference, consistent with the significance ($\sim 2 σ$) originally reported in C23. Therefore, we conclude that the results of C23 hold, and that the combined optical and infrared [O III] data disfavour $t^2 \simeq 0.1$ at the $\approx2σ$ level in Mrk 71. Future work is nonetheless warranted to better understand the AD associated with both optical and infrared emission line analysis.

astro-ph.GA↗

arXiv2023

Shock enhanced [CII] emission from the infalling galaxy Arp 25

We present SOFIA observations with HAWC+ and FIFI-LS of the peculiar galaxy Arp 25, also known as NGC 2276 or UGC 3740, whose morphology is deformed by its impact with the intra-group medium of the NGC 2300 galaxy group. These observations show the first direct proof of the enhancement of [CII] emission due to shocks caused by ram pressure in a group of galaxies. By comparing the [CII] emission to UV attenuation, dust emission, PAH, and CO emission in different regions of the galaxy, we find a clear excess of [CII] emission along the impact front with the intra-group medium. We estimate that the shock due to the impact with the intra-group medium increases the [CII] emission along the shock front by 60% and the global [CII] emission by approximately 25% with respect to the predicted [CII] emission assuming only excitation caused by stellar radiation. This result shows the danger of interpreting [CII] emission as directly related to star formation since shocks and other mechanisms can significantly contribute to the total [CII] emission from galaxies in groups and clusters.

astro-ph.GA↗

arXiv2023

Characterization and Absolute Calibration of the Far Infrared Field Integral Line Spectrometer for SOFIA

We present the characterization and definitive flux calibration of the Far-Infrared Field Integral Line Spectrometer (FIFI-LS) instrument on-board SOFIA. The work is based on measurements made in the laboratory with an internal calibrator and on observations of planets, moons, and asteroids as absolute flux calibrators made during the entire lifetime of the instrument. We describe the techniques used to derive flat-fields, water vapor column estimates, detector linearity, spectral and spatial resolutions, and absolute flux calibration. Two sets of responses are presented, before and after the entrance filter window was changed in 2018 to improve the sensitivity at 52um, a wavelength range previously not covered by PACS on Herschel. The relative spectral response of each detector and the illumination pattern of the arrays of the FIFI-LS arrays are derived using the internal calibrator before each observational series. The linearity of the array response is estimated by considering observations of bright sources. We find that the deviation from linearity of the FIFI-LS arrays affects the flux estimations less than 1%. The flux calibration accuracy is estimated to be 15% or better across the entire wavelength range of the instrument. The limited availability of sky calibrators during each observational series is the major limiting factor of the flux calibration accuracy.

astro-ph.IM↗

arXiv2023

Accurate Oxygen Abundance of Interstellar Gas in Mrk 71 from Optical and Infrared Spectra

The heavy element content ("metallicity") of the Universe is a record of the total star formation history. Gas-phase metallicity in galaxies, as well as its evolution with time, is of particular interest as a tracer of accretion and outflow processes. However, metallicities from the widely-used electron temperature ($T_e$) method are typically ~2x lower than the values based on the recombination line method. This "abundance discrepancy factor" (ADF) is well known and is commonly ascribed to bias due to temperature fluctuations. We present a measurement of oxygen abundance in the nearby (3.4 Mpc) system, Mrk 71, using a combination of optical and far-IR emission lines to measure and correct for temperature fluctuation effects. Our far-IR result is inconsistent ($> 2 σ$ significance) with the metallicity from recombination lines and instead indicates little to no bias in the standard $T_e$ method, ruling out the long-standing hypothesis that the ADF is explained by temperature fluctuations for this object. Our results provide a framework to accurately measure metallicity across cosmic history, including with recent data reaching within the first billion years with JWST and the Atacama Large Millimeter Array (ALMA).

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arXiv2022

The Arecibo Galaxy Environment Survey XII : Optically dark HI clouds in the Leo I Group

Using data from the Arecibo Galaxy Environment Survey, we report the discovery of five HI clouds in the Leo I group without detected optical counterparts. Three of the clouds are found midway between M96 and M95, one is only 10$^{\prime}$ from the south-east side of the well-known Leo Ring, and the fifth is relatively isolated. HI masses range from 2.6$\times$10$^{6}$ - 9.0$\times$10$^{6}$M$_{\odot}$ and velocity widths (W50) from 16 - 42 km/s. Although a tidal origin is the most obvious explanation, this formation mechanism faces several challenges. For the most isolated cloud, the difficulties are its distance from neighbouring galaxies and the lack of any signs of disturbance in the HI discs of those systems. Some of the clouds also appear to follow the baryonic Tully-Fisher relation between mass and velocity width for normal, stable galaxies which is not expected if they are tidal in origin. Three clouds are found between M96 and M95 which have no optical counterparts, but have otherwise similar properties and location to the optically detected galaxy LeG 13. While overall we favour a tidal debris scenario to explain the clouds, we cannot rule out a primordial origin. If the clouds were produced in the same event that gave rise to the Leo Ring, they may provide important constraints on any model attempting to explain that structure

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arXiv2022

The Arecibo Galaxy Environment Survey (AGES) XI: the expanded Abell 1367 field. Data catalogue and HI census over the surveyed volume

Many galaxy properties are known to correlate with the environment in which the galaxies are embedded. Their cold, neutral gas content, usually assessed through 21cm HI observations, is related to many other galaxy properties as it is the underlying fuel for star formation. With its high sensitivity and broad sky coverage the blind Arecibo Galaxy Environment Survey (AGES) survey brings significant improvement to the census of HI properties of galaxies in a wide range of environments, from voids to the core of a massive cluster. Here we present an HI census over a volume of ~44000 Mpc$^{3}$ towards the merging cluster Abell 1367 and the large-scale structure (LSS) surrounding the cluster out to cz = 20000 km/s. The survey is sensitive down to a column density of N$_{HI}$ = 1.5 x 10$^{17}$ cm$^{-2}$ for emission filling the beam and a line width of 10 km/s. As an approximate mass sensitivity limit, a member of A1367 (at a distance of 92 Mpc), containing M$_{HI}$ = 2.7x10$^{8}$ M$_{\odot}$ distributed over a top-hat profile of 50 km/s width would be detected at 4$σ$. The results are analysed in combination with optical spectroscopy data from SDSS which we use to estimate the local galaxy density based on the Voronoi-Delaunay method. In total we detect 457 HI sources, 213 of which are detected for the first time by the AGES survey, 134 of which are presented in this article for the first time. 225 of the detections are in the cluster and 232 in the remaining volume surveyed. Here we present the full catalogue of HI detections and their basic properties, including optical ones. We concentrate on the difference between the cluster and the foreground and background LSS, revealing a continuous correlation of HI detected fraction (and HI deficiency) with local galaxy density, independent of global environment.

astro-ph.GA↗

arXiv2022

Environmental effects in Herschel observations of the ionized carbon content of star forming dwarf galaxies in the Virgo cluster

We use archival Herschel data to examine the singly ionized carbon ([CII]) content of 14 star forming dwarf galaxies in the Virgo cluster. We use spectral energy distribution (SED) fits to far infrared, mid infrared, near infrared, optical and ultraviolet data to derive the total infrared continuum (TIR) for these galaxies. We compare the [CII]/TIR ratio for dwarf galaxies in the central part of Virgo to those in the southern part of the cluster and to galaxies with similar TIR luminosities and metallicities in the Herschel Dwarf Galaxy Survey (DGS) sample of field dwarf galaxies to look for signs of [CII] formation independent of star formation. Our analysis indicates that the sample of Virgo dwarfs in the central part of the cluster has significantly higher values of [CII]/TIR than the sample from the southern part of the cluster and the sample from the DGS, while the southern sample is consistent with the DGS. This [CII]/TIR excess implies that a significant fraction of the [CII] in the dwarf galaxies in the cluster center has an origin other than star formation and is likely to be due to environmental processes in the central part of the cluster. We also find a surprisingly strong correlation between [CII]/TIR and the local ram pressure felt by the dwarf galaxies in the cluster. In this respect, we claim that the excess [CII] we see in these galaxies is likely to be due to formation in ram pressure shocks.

astro-ph.GA↗

arXiv2021

The Widefield Arecibo Virgo Extragalactic Survey: Early Results on Known Dark Sources

The Widefield Arecibo Virgo Extragalactic Survey (WAVES) was an ongoing HI survey of the Virgo Cluster with the Arecibo Observatory's 305m William E. Gordon Telescope at the time of its structural failure. The full 20 square degrees of the southern field and 10 of the planned 35 square degrees of the northern field had been observed to full depth, adding to 25 square degrees observed to the same depth in the cluster by the Arecibo Galaxy Environment Survey. We here review what WAVES reveals about four optically dark HI structures that were previously discovered in the survey area, including two that are not seen despite being well above our detection limit.

astro-ph.GA↗

arXiv2020

Faint and fading tails : the fate of stripped HI gas in Virgo cluster galaxies

Although many galaxies in the Virgo cluster are known to have lost significant amounts of HI gas, only about a dozen features are known where the HI extends significantly outside its parent galaxy. Previous numerical simulations have predicted that HI removed by ram pressure stripping should have column densities far in excess of the sensitivity limits of observational surveys. We construct a simple model to try and quantify how many streams we might expect to detect. This accounts for the expected random orientation of the streams in position and velocity space as well as the expected stream length and mass of stripped HI. Using archival data from the Arecibo Galaxy Environment Survey, we search for any streams which might previously have been missed in earlier analyses. We report the confident detection of ten streams as well as sixteen other less sure detections. We show that these well-match our analytic predictions for which galaxies should be actively losing gas, however the mass of the streams is typically far below the amount of missing HI in their parent galaxies, implying that a phase change and/or dispersal renders the gas undetectable. By estimating the orbital timescales we estimate that dissolution rates of 1-10 Msolar/yr are able to explain both the presence of a few long, massive streams and the greater number of shorter, less massive features.

astro-ph.GA↗

arXiv2019

The Arecibo L-band Feed Array Zone of Avoidance (ALFAZOA) Shallow Survey

The Arecibo L-band Feed Array Zone of Avoidance (ALFAZOA) Shallow Survey is a blind HI survey of the extragalactic sky behind the northern Milky Way conducted with the ALFA receiver on the 305m Arecibo Radio Telescope. ALFAZOA Shallow covered 900 square degrees at full sensitivity from 30° ${\leq} l {\leq} $75° and |b|$ {\leq}$ 10° and an additional 460 square degrees at limited sensitivity at latitudes up to 20°. It has an rms sensitivity of 5-7 mJy and a velocity resolution of 9 - 20.6 km s$^{-1}$, and detected 403 galaxies out to a recessional velocity of 12,000 km s$^{-1}$, with an angular resolution of 3.4' and a positional accuracy between 0.2' and 1.7'. The survey is complete above an integrated line flux $F_{HI}$ = 2.0 Jy km s$^{-1}$ for half the survey, and above $F_{HI}$ = 2.8 Jy km s$^{-1}$ for the other half. Forty-three percent of the ALFAZOA HI detections have at least one possible optical/NIR counterpart in the literature, and an additional 16% have counterparts that only included previous HI measurements. There are fewer counterparts in regions of high extinction and for galaxies with lower HI mass. Comparing the results of the survey to the predictions of Erdogdu et al. (2006), and using their nomenclature, ALFAZOA confirms the position and extent in the ZOA of the C7, C$ζ$, Pegasus, Corona Borealis and Delphinus structures, but not of the Cygnus void. Two new structures are identified, both connected to the C7 overdensity; one extends to 35°, and the other crosses the ZOA.

astro-ph.GA↗

arXiv2019

Survey of Ionized Gas of the Galaxy, Made with the Arecibo telescope (SIGGMA): Inner Galaxy Data Release

The Survey of Ionized Gas of the Galaxy, Made with the Arecibo telescope (SIGGMA) provides a fully-sampled view of the radio recombination line (RRL) emission from the portion of the Galactic plane visible by Arecibo. Observations use the Arecibo L-band Feed Array (ALFA), which has a FWHM beam size of 3.4 arcmin. Twelve hydrogen RRLs from H163$α$ to H174$α$ are located within the instantaneous bandpass from 1225 MHz to 1525 MHz. We provide here cubes of average ("stacked") RRL emission for the inner Galaxy region $32 \le \ell \le 70$ degrees, $|b|\le1.5$ degree, with an angular resolution of 6 arcmin. The stacked RRL rms at 5.1 km/s velocity resolution is $\sim0.65$ mJy beam$^{-1}$, making this the most sensitive large-scale fully-sampled RRL survey extant. We use SIGGMA data to catalogue 319 RRL detections in the direction of 244 known HII regions, and 108 new detections in the direction of 79 HII region candidates. We identify 11 Carbon RRL emission regions, all of which are spatially coincident with known HII regions. We detect RRL emission in the direction of 14 of the 32 supernova remnants (SNRs) found in the survey area. This RRL emission frequently has the same morphology as the SNRs. The RRL velocities give kinematic distances in agreement with those found in the literature, indicating that RRLs may provide an additional tool to constrain distances to SNRs. Finally, we analyze the two bright star-forming complexes: W49 and W51. We discuss the possible origins of the RRL emission in directions of SNRs W49B and W51C.

astro-ph.GA↗

arXiv2016

The Structure of Halo Gas Around M33

Understanding the distribution of gas in and around galaxies is vital for our interpretation of galaxy formation and evolution. As part of the Arecibo Galaxy Environment Survey (AGES) we have observed the neutral hydrogen (HI) gas in and around the nearby Local Group galaxy M33 to a greater depth than previous observations. As part of this project we investigated the absence of optically detected dwarf galaxies in its neighbourhood, which is contrary to predictions of galaxy formation models. We observed 22 discrete clouds, 11 of which were previously undetected and none of which have optically detected counterparts. We find one particularly interesting hydrogen cloud, which has many similar characteristics to hydrogen distributed in the disk of a galaxy. This cloud, if it is at the distance of M33, has a HI mass of around 10^7 Msun and a diameter of 18 kpc, making it larger in size than M33 itself.

astro-ph.GA↗

arXiv2015

The Arecibo Galaxy Environment Survey X: The Structure of Halo Gas Around M33

As part of the HI Arecibo Galaxy Environments Survey (AGES) we have observed 5$\times$4 degrees of sky centred on M33, reaching a limiting column density of $\sim 1.5 \times 10^{17}$ cm$^{-2}$ (line width of 10 km s$^{-1}$ and resolution 3.5\arcmin). We particularly investigate the absence of optically detected dwarf galaxies around M33, something that is contrary to galaxy formation models. We identify 22 discrete HI clouds, 11 of which are new detections. The number of objects detected and their internal velocity dispersion distribution is consistent with expectations from standard galaxy formation models. However, the issue remains open as to whether the observed velocity dispersions can be used as a measure of the HI clouds total mass i.e. are the velocities indicative of virialised structures or have they been influenced by tidal interactions with other structures in the Local Group? We identify one particularly interesting HI cloud, AGESM33-31, that has many of the characteristics of HI distributed in the disc of a galaxy, yet there is no known optical counterpart associated with it. This object has a total HI mass of $1.22 \times 10^{7}$ M$_{\odot}$ and a diameter of 18 kpc if at the distance of M33 ($D_{M33}=840$ kpc). However, we also find that there are numerous other HI clouds in this region of sky that have very similar velocities and so it is plausible that all these clouds are actually associated with debris from the Magellanic stream.

astro-ph.GA↗

arXiv2010

Deep 21-cm HI Observations at z~0.1: The Precursor to the Arecibo Ultra Deep Survey

The "ALFA Ultra Deep Survey" (AUDS) is an ongoing 21-cm spectral survey with the Arecibo 305m telescope. AUDS will be the most sensitive blind survey undertaken with Arecibo's 300 MHz Mock spectrometer. The survey searches for 21-cm HI line emission at redshifts between 0 and 0.16. The main goals of the survey are to investigate the HI content and probe the evolution of HI gas within that redshift region. In this paper, we report on a set of precursor observations with a total integration time of 53 hours. The survey detected a total of eighteen 21-cm emission lines at redshifts between 0.07 and 0.15 in a region centered around ra~0:00h, dec= 15:42deg. The rate of detection is consistent with the one expected from the local HI mass function. The derived relative HI density at the median redshift of the survey is rho_HI[z=0.125]=(1.0+/-0.3)*rho_0, where rho_0 is the HI density at zero redshift.

astro-ph.CO↗

arXiv2007

21-cm synthesis observations of VIRGOHI 21 - a possible dark galaxy in the Virgo Cluster

Many observations indicate that dark matter dominates the extra-galactic Universe, yet no totally dark structure of galactic proportions has ever been convincingly identified. Previously we have suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster using Jodrell Bank, was a possible dark galaxy because of its broad line-width (~200 km/s) unaccompanied by any visible gravitational source to account for it. We have now imaged VIRGOHI 21 in the neutral-hydrogen line and find what could be a dark, edge-on, spinning disk with the mass and diameter of a typical spiral galaxy. Moreover, VIRGOHI 21 has unquestionably been involved in an interaction with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor normally linked with such a feature. Numerical models of NGC 4254 call for a close interaction ~10^8 years ago with a perturber of ~10^11 solar masses. This we take as additional evidence for the massive nature of VIRGOHI 21 as there does not appear to be any other viable candidate. We have also used the Hubble Space Telescope to search for stars associated with the HI and find none down to an I band surface brightness limit of 31.1 +/- 0.2 mag/sq. arcsec.

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