HI Detections Research Articles

The feasibility of weak lensing and 21cm intensity mapping cross-correlation measurements

ABSTRACT One of the most promising probes to complement current standard cosmological surveys is the H i intensity map, i.e. the distribution of temperature fluctuations in neutral hydrogen. In this paper we present calculations of the two-point function between HI (at redshift $z\lt 1$) and lensing convergence ($\kappa$). We also construct HI intensity maps from N-body simulations, and measure two-point functions between HI and lensing convergence. HI intensity mapping requires stringent removal of bright foregrounds, including emission from our Galaxy. The removal of large-scale radial modes during this HI foreground removal will reduce the HI-lensing cross-power spectrum signal, as radial modes are integrated to find the convergence; here we wish to characterize this reduction in signal. We find that after a simple model of foreground removal, the cross-correlation signal is reduced by $\sim$50–70 per cent; we present the angular and redshift dependence of the effect, which is a weak function of these variables. We then calculate S/N of $\kappa$HI detection, including cases with cut sky observations, and noise from radio and lensing measurements. We present Fisher forecasts based on the resulting two-point functions; these forecasts show that by measuring $\kappa \Delta {T}_\mathrm{HI}$ correlation functions in a sufficient number of redshift bins, constraints on cosmology and HI bias will be possible.

A highly sensitive and selective Cd-MOF fluorescent probe for the detection of His, NB, TC and PTH and its applications in real samples

A novel metal–organic framework (MOF) with the formula of [Cd(CIA)(4,4′-BB)·H2O]·H2O (Cd-MOF) (H2CIA = 5-methoxyisophthalic acid, 4,4′-BB: 4,4′-bis((1H-imidazol-1-yl)methyl)-1,1′-biphenyl) has been designed and synthesized through solvothermal reaction. The structure was characterized by TG, IR, PXRD, elemental analysis, single-crystal X-ray diffraction and XPS. The coordination pattern of the fully deprotonated ligand (CIA) in Cd-MOF is μ2-к1: к0: к2. The complex is found to be a three-dimensional reticular material with good thermal stability. Further study revealed that Cd-MOF has good fluorescence performance and can be used as a fluorescent probe for sensitive detection of histidine (His), nitrobenzene (NB), tetracycline (TC) and pyrimethanil (PTH) in water. Four cycles experiments can be achieved with a low detection limit. The detection limits were 0.3 µM (His), 0.05 µM (NB), 0.2 µM (TC) and 0.01 µM (PTH), respectively. To verify the feasibility of detecting PTH in real samples, we further explored it in water samples and apple peels. The spiked recoveries were 95.3–99.4 % and 97.2–101.2 %, respectively. Finally, the fluorescence quenching mechanism of Cd-MOF in His, NB, TC and PTH detection is discussed in detail.

18β-Glycyrrhetinic acid derivative-based metallo-hydrogels with highly selective and sensitive for histidine detection

Quantitative detection of His has aroused great interest in disease diagnosis since abnormal histidine (His) metabolism would cause a variety of serious diseases. However, exploiting a strategy with facile, highly selective, sensitive sensing and low-cost to monitor His remains a challenge. In this study, a series of novel metallo-hydrogels were successfully constructed, which were composed of 18β-glycyrrhetinic acid (GA) derivative (GA-O-09) with rare earth metal ions (Ce3+, Tb3+, Eu3+ and La3+). In addition, these metallo-hydrogels possessed excellent thermodynamics stability with the gel melting temperature (Tgel) ranging from 62.4 ± 0.49 °C to 67.4 ± 0.49 °C and remarkable pH stability over a range of pH values of 3–10. Interestingly, the Histidine (His)-loaded GA-O-09/Eu3+ hydrogel and the His-loaded GA-O-09/La3+ hydrogel displayed extraordinary fluorescence enhancement, in which the lowest fluorescence response concentrations (LODs) of the His-loaded GA-O-09/Eu3+ hydrogel and the His-loaded GA-O-09/La3+ hydrogel were 1.14 × 10-8 and 1.07 × 10-8 M, respectively. Therefore, the result showed that the study of the GA-O-09/Eu3+ and GA-O-09/La3+ hydrogels could provide a potential application for highly selective and sensitive detection for His.

Carboxyl group bearing iridium(III) solvent complex as photoluminescence and electrochemiluminescence probe for the detection of histidine

• A new carboxyl group bearing iridium(III) solvent complex [Ir(pbz) 2 (DMSO)Cl] was successfully synthesized. • Two “signal on” PL and ECL methods were developed for the detection of histidine. • The coordination interaction of [Ir(pbz) 2 (DMSO)Cl] with histidine was studied. • 1:1 of binding stoichiometry and (2.31 ± 1.43) × 10 9 M −1 of binding constant were obtained for the interaction between [Ir(pbz) 2 (DMSO)Cl] and histidine. Histidine (His), as the essential amino acid in human body, plays crucial roles in many biological activities. Here, a new carboxyl group bearing iridium(III) solvent complex [Ir(pbz) 2 (DMSO)Cl] (pbz = 3-(2-pyridyl)benzoic acid, Ir1-DMSO) was synthesized as photoluminescence (PL) and electrochemiluminescence (ECL) probe for the detection of His. Ir1-DMSO exhibits weak PL and ECL emissions. In the presence of His, the coordination interaction of the Ir1-DMSO with His led to the enhancement of PL and ECL emissions. Two “signal on” PL and ECL methods were developed for the selective and sensitive detection of His. The detection limit of His is calculated to be 100 nM and 7 nM via PL and ECL methods, respectively. The coordination interaction between Ir1-DMSO and His was investigated. 1:1 of binding stoichiometry and (2.31 ± 1.43) × 10 9 M −1 of binding constant were obtained for the interaction of Ir1-DMSO and His. This work demonstrates that carboxyl group bearing Ir1-DMSO is an alternative “signal on” PL and ECL probe for the detection of histidine with high sensitivity, good selectivity and larger binding ability, which can be extended in the assay of His-related molecules.

Turn-on and blue-shift fluorescence sensor toward L-histidine based on stable CdII metal-organic framework with tetranuclear cluster units.

A novel CdII-based two-fold interpenetrated metal-organic framework (MOF), namely {[Cd2(BTDB)2(4,4-bpy)]·DMF}n (JXUST-14), (H2BTDB = 4,4'-(benzo[c][1,2,5]thiadiazole-4,7-diyl)dibenzoic acid and 4,4-bpy = 4,4-bipyridine), has been prepared and characterized. Single-crystal structure determination reveals that JXUST-14 has a tetranuclear cluster based 6-connected pcu topological network with Schlafli symbol {412·63}. When soaked in common organic solvents and aqueous solutions with diverse pH values of 2-12 for 48 h, JXUST-14 remains stable. JXUST-14 is a highly selective and sensitive luminescent sensor for L-histidine (His) with a detection limit of 11.1 ppm. JXUST-14 is the first CdII-based MOF for the detection of His via turn-on and fluorescence blue-shift effects. Experimental study and theoretical calculation suggest that the sensing process can be mainly attributed to a charge transfer and energy transfer mechanism. More interestingly, LED lamps of JXUST-14 and JXUST-14@His were successfully developed, which endowed efficient sensitivity for His detection and thus provide great potential for future applications.

Highly selective histamine assay via SERS: Based on the signal enhancement of carbon dots and the fluorescence quenching of gold nanoparticles

Fluorescent background is a major obstacle in surface-enhanced Raman scattering (SERS) and limits its application in various fields of science. This research developed a novel strategy by combining the advantages of the carbon dots (CDs) and gold nanoparticles (AuNPs) to increase the SERS signal for histamine (His) detection. The β-cyclodextrin (β-CD) decorated N,Zn co-doped carbon dots (N,Zn-CDs/β-CD) was prepared, which has both highly selective fluorescence (FL) sensitization and selective Raman signal enhancement for His derivatives (D-His). The prepared AuNPs not only could be used to enhance SERS signal, but also could quench 76% of the FL background at 544 nm, which is conducive to suppress the FL interference caused by carbon dots. Interestingly, the SERS signal increased with the gradual quenching of FL through the energy transfer between the fluorophore and the AuNPs. The combination of AuNPs and N,Zn-CDs/β-CD shows a detection limit of His around 10 μM, and a selectivity and anti-interference capability for His detection in the present of metal ions, sugar and other biogenic amines. This work exhibits the potential for anti-interference, sensitive and selective detection of His in practical SERS applications.

A metal-free fluorescent probe for selective detection of histidine

A highly selective fluorescent probe has been discovered for the recognition of L-histidine (His) without the need to use a metal cation. Mechanistic studies including 1D and 2D 1H and 13C NMR analyses and DFT calculation have revealed that the 2-formyl group of the 1,1′-binaphthyl-based probe reacts with His to form a multicyclic product and the structural rigidity of this product should have contributed to the greatly enhanced fluorescence. The reactions of all the other amino acids with the probe cannot generate such a structurally rigid product and thus exhibit no or much smaller fluorescence enhancement. This probe can also be easily modified to allow the selective detection of His to be conducted in aqueous or fluorous solution.

Reliability of parental assessment of auditory skills in young children: a cross-sectional study in Italian language

ObjectiveHearing impairments (HIs) that progress or have later onset may have specific effects on language and cognitive development, but are difficult to suspect during routine primary care visits. Family concern...

Giant Metrewave Radio Telescope Detection of Hi 21 cm Emission from Star-forming Galaxies at z ≈ 1.3

Abstract We report a ≈400 hr Giant Metrewave Radio Telescope (GMRT) search for Hi 21 cm emission from star-forming galaxies at z = 1.18–1.39 in seven fields of the DEEP2 Galaxy Survey. Including data from an earlier 60 hr GMRT observing run, we co-added the Hi 21 cm emission signals from 2841 blue star-forming galaxies that lie within the FWHM of the GMRT primary beam. This yielded a 5.0σ detection of the average Hi 21 cm signal from the 2841 galaxies at an average redshift 〈z〉 ≈ 1.3, only the second detection of Hi 21 cm emission at z ≥ 1. We obtain an average Hi mass of 〈M HI 〉 = (3.09 ± 0.61) × 1010 M⊙ and an Hi-to-stellar mass ratio of 2.6 ± 0.5, both significantly higher than values in galaxies with similar stellar masses in the local universe. We also stacked the 1.4 GHz continuum emission of the galaxies to obtain a median star formation rate (SFR) of 14.5 ± 1.1 M⊙yr−1. This implies an average Hi depletion timescale of ≈2 Gyr for blue star-forming galaxies at z ≈ 1.3, a factor of ≈3.5 lower than that of similar local galaxies. Our results suggest that the Hi content of galaxies toward the end of the epoch of peak cosmic SFR density is insufficient to sustain their high SFR for more than ≈2 Gyr. Insufficient gas accretion to replenish the Hi could then explain the observed decline in the cosmic SFR density at z < 1.

HI detection of J030417.78+002827.4 by the Five-hundred-meter Aperture Spherical Radio Telescope

We present the first HI 21 cm spectroscopy detection of J030417.78+002827.4, which is an active galactic nucleus (AGN) with an intermediate-mass black hole (IMBH) in the center. The observations were carried out with the Five-hundred-meter Aperture Spherical Radio Telescope (FAST) last year. We relied on the ON-OFF observing approach with the 19-beam receiver covering 1.05 – 1.45 GHz. Within a total integration time of about 20 min, the root mean square (RMS) of our data reaches 1.2 mJy beam−1, at a velocity resolution of 1.6 kms. Radio frequency interference (RFI) is checked and excluded during the data analysis. The detected HI spectroscopy shows a dual-horned profile with a line width of 223.5 kms, indicating gas rotation around this AGN. The redshift of this galaxy derived from our HI observation is 0.0447. We calculate the atomic gas mass by the integrated flux of the HI emission line. The total gas mass in this galaxy is estimated to be 1.8 × 1010 M ⊙. We find the fraction of gas-to-stellar mass ratio in J030417.78+002827.4 is more than 50%. This ratio is much higher than the typical value found in other AGNs with supermassive black holes (SMBHs), and is comparable to some star-forming galaxies recently observed by FAST.

A blind ATCA HI survey of the Fornax galaxy cluster

We present the first interferometric blind HI survey of the Fornax galaxy cluster, which covers an area of 15 deg2 out to the cluster virial radius. The survey has a spatial and velocity resolution of 67″ × 95″(∼6 × 9 kpc at the Fornax cluster distance of 20 Mpc) and 6.6 km s−1 and a 3σ sensitivity of NHI ∼ 2 × 1019 cm−2 and MHI ∼ 2 × 107 M⊙, respectively. We detect 16 galaxies out of roughly 200 spectroscopically confirmed Fornax cluster members. The detections cover about three orders of magnitude in HI mass, from 8 × 106 to 1.5 × 1010 M⊙. They avoid the central, virialised region of the cluster both on the sky and in projected phase-space, showing that they are recent arrivals and that, in Fornax, HI is lost within a crossing time, ∼2 Gyr. Half of these galaxies exhibit a disturbed HI morphology, including several cases of asymmetries, tails, offsets between HI and optical centres, and a case of a truncated HI disc. This suggests that these recent arrivals have been interacting with other galaxies, the large-scale potential or the intergalactic medium, within or on their way to Fornax. As a whole, our Fornax HI detections are HI-poorer and form stars at a lower rate than non-cluster galaxies in the same M⋆ range. This is particularly evident at M⋆ ≲ 109 M⊙, indicating that low mass galaxies are more strongly affected throughout their infall towards the cluster. The MHI/M⋆ ratio of Fornax galaxies is comparable to that in the Virgo cluster. At fixed M⋆, our HI detections follow the non-cluster relation between MHI and the star formation rate, and we argue that this implies that thus far they have lost their HI on a timescale ≳1−2 Gyr. Deeper inside the cluster HI removal is likely to proceed faster, as confirmed by a population of HI-undetected but H2-detected star-forming galaxies. Overall, based on ALMA data, we find a large scatter in H2-to-HI mass ratio, with several galaxies showing an unusually high ratio that is probably caused by faster HI removal. Finally, we identify an HI-rich subgroup of possible interacting galaxies dominated by NGC 1365, where pre-processing is likely to have taken place.

Phos-Tag Fluorescent Gel Staining for the Quantitative Detection of His- and Asp-Phosphorylated Proteins.

We describe a standard protocol for phosphate-affinity fluorescent gel staining that uses a fluorophore-labeled dizinc(II) complex of a derivative of the phosphate-binding tag molecule Phos-tag to detect His- and Asp-phosphorylated proteins separated by SDS-PAGE. The procedure permits the quantitative monitoring of phosphorylated histidine kinases (His-phosphoproteins) and their cognate phosphorylated response regulators (Asp-phosphoproteins) in bacterial two-component signaling transduction systems. The total time required for each gel staining operation is about 2h at room temperature.

Highly selective impedimetric determination of Haemophilus influenzae protein D using maze-like boron-doped carbon nanowall electrodes

This study reports a novel impedimetric immunosensor for protein D detection in purified and bacterial (Haemophilus influenzae, Hi) samples. The detection was based on antigen recognition by anti-protein D antibodies (apD) immobilised at the maze-like boron-doped carbon nanowall electrodes (B:CNW). The B:CNW electrodes were synthesised, and their surface was characterised by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. The sensor was prepared in a two-step procedure: apD were covalently linked on the previously modified B:CNW electrodes using diazonium salt. Modification steps were controlled by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) measurements. The immunosensor exhibited excellent electrochemical performance, stability, satisfactory sensitivities, and linear ranges for antigen detection. Protein D was detected down to 2.39 × 102fg/mL with a linear range extending from 3.37 × 10−11to 3.37 × 10−3μg/mL (in purified sample). Next, Hi's LOD was 5.20 × 102CFU/mL with a linear range of 8.39 × 101–8.39 × 103CFU/mL. Selectivity studies showed no reaction with negative samples as Streptococcus pyogenes, Streptococcus pneumoniae or Bordetella parapertussis bacteria. Therefore, the new approach is suitable for rapid and quantitative detection of Hi, and is a good candidate for further tests on clinical samples.

Quantitative monitoring of His and Asp phosphorylation in a bacterial signaling system by using Phos-tag Magenta/Cyan fluorescent dyes.

In the bacterial signaling mechanisms known as two-component systems (TCSs), signals are generally conveyed by means of a His-Asp phosphorelay. Each system consists of a histidine kinase (HK) and its cognate response regulator. Because of the labile nature of phosphorylated His and Asp residues, few approaches are available that permit a quantitative analysis of their phosphorylation status. Here, we show that the Phos-tag dye technology is suitable for the fluorescent detection of His- and Asp-phosphorylated proteins separated by SDS-PAGE. The dynamics of the His-Asp phosphorelay of recombinant EnvZ-OmpR, a TCS derived from Escherichia coli, were examined by SDS-PAGE followed by simple rapid staining with Phos-tag Magenta fluorescent dye. The technique permitted not only the quantitative monitoring of the autophosphorylation reactions of EnvZ and OmpR in the presence of adenosine triphosphate (ATP) or acetyl phosphate, respectively, but also that of the phosphotransfer reaction from EnvZ to OmpR, which occurs within 1min in the presence of ATP. Furthermore, we demonstrate profiling of waldiomycin, an HK inhibitor, by using the Phos-tag Cyan gel staining. We believe that the Phos-tag dye technology provides a simple and convenient fluorometric approach for screening of HK inhibitors that have potential as new antimicrobial agents.

OUP accepted manuscript

We present the photometric properties of 2210 newly identified dwarf galaxy candidates in the MATLAS fields. The Mass Assembly of early Type gaLAxies with their fine Structures (MATLAS) deep imaging survey mapped $\sim$142 deg$^2$ of the sky around nearby isolated early type galaxies using MegaCam on the Canada-France-Hawaii Telescope, reaching surface brightnesses of $\sim$ 28.5 - 29 in the g-band. The dwarf candidates were identified through a direct visual inspection of the images and by visually cleaning a sample selected using a partially automated approach, and were morphologically classified at the time of identification. Approximately 75% of our candidates are dEs, indicating that a large number of early type dwarfs also populate low density environments, and 23.2% are nucleated. Distances were determined for 13.5% of our sample using pre-existing $z_{spec}$ measurements and HI detections. We confirm the dwarf nature for 99% of this sub-sample based on a magnitude cut $M_g$ = -18. Additionally, most of these ($\sim$90%) have relative velocities suggesting that they form a satellite population around nearby massive galaxies rather than an isolated field sample. Assuming that the candidates over the whole survey are satellites of the nearby galaxies, we demonstrate that the MATLAS dwarfs follow the same scaling relations as dwarfs in the Local Group as well as the Virgo and Fornax clusters. We also find that the nucleated fraction increases with $M_g$, and find evidence of a morphology-density relation for dwarfs around isolated massive galaxies.

Low Surface Brightness Galaxy catalogue selected from the α.40-SDSS DR7 Survey and Tully–Fisher relation

We present a catalogue of an HI-selected sample of 1129 low surface brightness galaxies (LSBGs) searched from the alpha.40-SDSS DR7 survey. This sample, consisting of various types of galaxies in terms of luminosity and morphology, has extended the parameter space covered by the existing LSBG samples. Based on a subsample of 173 LSBGs which are selected from our entire LSBG sample to have the 2-horn shapes of the HI line profiles, minor-to-major axial ratios (b/a) less than 0.6 and signal-to-noise ratio (S/N) of HI detection greater than 6.5, we investigated the Tully-Fisher relation (TFr) of LSBGs in the optical B, g and r bands and near-infrared J, H and K bands as well. In optical bands, the LSBG subsample follows the fundamental TFr which was previously defined for normal spiral galaxies. In NIR bands, the TFrs for our LSBG subsample are slightly different from the TFrs for the normal bright galaxies. This might be due to the internal extinction issue. Furthermore, the mass-to-light ratio (M/L),disk scale length (h) and mass surface density (sigma) for our LSBG subsample were deduced from the optical TFr results. Compared with High Surface Brightness Galaxies(HSBGs), our LSBGs have higher M/L, larger h and lower sigma than HSBGs.

Bivariate luminosity-HI mass distribution function of galaxies based on the NIBLES survey

We present a new optical luminosity-HImass bivariate luminosity function (BLF) based on HIline observations from the Nançay Interstellar Baryons Legacy Extragalactic Survey (NIBLES). NIBLES sources lie within the local universe (900 ≤ cz ≤ 12 000 km s−1) and were chosen from SDSS DR5 such that the optical luminosity function was sampled as uniformly as possible. The HImass function (HIMF) derived from our raw-data BLF, which is based on HIdetections only, is consistent with the HIMFs derived from other optically selected surveys in that the low-mass slope is flatter than those derived from blind HIsurveys. However, spanning the entire luminosity range of NIBLES, we identify a highly consistent distribution of the HIgas mass to luminosity ratio (gas-to-light ratio) with a predictable progression in the meanMHI/Lrratio as a function ofLr. This consistency allows us to construct plausible gas-to-light ratio distributions for very low-luminosity bins which lie outside the NIBLES sample. We also identify a ∼10% decrease in detection fraction for galaxies fainter than log(Lr) = 9.25, consistent with the expected decrease due to distance and sensitivity effects. Accounting for these trends, we reconstruct plausible gas-to-light distributions spanning luminosity bins down to log(Lr) = 5.25, thus producing a corrected BLF. This corrected BLF is in good qualitative agreement with optical luminosity-HImass distributions from the ALFALFA survey and is able to accurately reproduce blind survey HIMFs, lending credibility that this two dimensional optical luminosity-HImass distribution is an accurate representation of the volume density distribution of galaxies in the local universe. We also note that our agreement with HIMFs from other surveys is dependent on accounting for all systematic differences such as selection method, Hubble constant and HIflux scale.

WALLABY early science – I. The NGC 7162 galaxy group

We present Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) early science results from the Australian Square Kilometre Array Pathfinder (ASKAP) observations of the NGC 7162 galaxy group. We use archival HIPASS and Australia Telescope Compact Array (ATCA) observations of this group to validate the new ASKAP data and the data reduction pipeline ASKAPsoft. We detect six galaxies in the neutral hydrogen (HI) 21-cm line, expanding the NGC 7162 group membership from four to seven galaxies. Two of the new detections are also the first HI detections of the dwarf galaxies, AM 2159-434 and GALEXASC J220338.65-431128.7, for which we have measured velocities of $cz=2558$ and $cz=2727$ km s$^{-1}$, respectively. We confirm that there is extended HI emission around NGC 7162 possibly due to past interactions in the group as indicated by the $40^{\circ}$ offset between the kinematic and morphological major axes for NGC 7162A, and its HI richness. Taking advantage of the increased resolution (factor of $\sim1.5$) of the ASKAP data over archival ATCA observations, we fit a tilted ring model and use envelope tracing to determine the galaxies' rotation curves. Using these we estimate the dynamical masses and find, as expected, high dark matter fractions of $f_{\mathrm{DM}}\sim0.81-0.95$ for all group members. The ASKAP data are publicly available.

The Nançay H i Zone of Avoidance survey of 2MASS bright galaxies

To complement the 2MASS Redshift Survey (2MRS) and the 2MASS Tully-Fisher survey (2MTF) a search for 21cm HI line emission of 2MASS bright galaxy candidates has been pursued along the dust-obscured plane of the Milky Way with the 100m Nancay Radio Telescope. For our sample selection we adopted an isophotal extinction-corrected K-band magnitude limit of $K_s^o = 11.25$mag, corresponding to the first 2MRS data release and 2MTF, for which the 2MASX completeness level remains fairly constant deep into the Zone of Avoidance (ZoA). About one thousand galaxies without prior redshift measurement accessible from Nancay (Dec > -40\deg) were observed to an rms noise level of ~3 mJy for the velocity range -250 to 10'600 km/s. This resulted in 220 clear and 12 marginal detections of the target sample. Only few detections have redshifts above 8000 km/s due to recurring radio frequency interference (RFI). A further 29 detections and 6 marginals have their origin in non-target galaxies in the telescope beam. The newly detected galaxies are on average considerably more \HI-rich (mostly $10^9 - 10^{10}$M$_\odot$) compared to systematic (blind) HI surveys. The HI detections reveal various new filaments crossing the mostly uncharted northern ZoA (e.g. at $\ell \sim 90\deg, 130\deg, 160\deg$), whilst consolidating galaxy agglomerations in Monoceros and Puppis ($\ell \sim 220\deg, 240\deg$). Considerably new insight has been gained about the extent of the Perseus-Pisces Supercluster through the confirmation of a ridge ($\ell \sim 160\deg$) encompassing the 3C129 cluster that links Perseus-Pisces to Lynx, and the continuation of the second Perseus-Pisces arm ($\ell \sim 90\deg$) across the ZoA.

The dwarf galaxy population as revealed by ALFALFA

AbstractThe combination of sensitivity and large sky coverage of the ALFALFA HI survey has enabled the detection of difficult to observe low mass galaxies in large numbers, including dwarf galaxies overlooked in optical surveys. Three different, but connected, studies of dwarf galaxies from the ALFALFA survey are of particular interest: SHIELD (Survey of HI in Extremely Low-mass Dwarfs), candidate gas-rich ultra-faint dwarf galaxies, and the (Almost) Dark population. SHIELD is a systematic multiwavelength study of all dwarf galaxies from ALFALFA with MHI < 107.2M⊙ and clear optical counterparts. Candidate gas-rich ultra-faint dwarf galaxies extend the dwarf galaxy population to even lower masses. These galaxies are identified as isolated HI clouds with no discernible optical counterpart but subsequent observations reveal that some are extremely faint, gas-dominated galaxies. Leo P, discovered first as an HI detection, and then found to be an actively star-forming galaxy, bridges the gap between these candidate galaxies and the SHIELD sample. The (Almost) Dark sample consists of galaxies whose optical counterparts are overlooked in current optical surveys but which are clear detections in ALFALFA. This sample includes field gas-rich ultra-diffuse galaxies. Coma P, with a peak surface brightness of only ∼26.4 mag arcsec−2 in g’, demonstrates the sort of extreme low surface brightness galaxy that can be discovered in an HI survey.