The Tully-Fisher relations of the Eridanus group of galaxies

The Tully-Fisher (TF) or the luminosity-linewidth relations of the galaxies in the Eridanus group are constructed using the HI rotation curves and the luminosities in the optical and in the near-infrared bands. The slopes of the TF relations (absolute magnitudevs log2V _flat) are −8.6 ± 1.1, −10.0 ±1.5, −10.7 ±2.1, and −9.7 ±1.3 in the R, J, H, and K bands respectively for galaxies having flat HI rotation curves. These values of the slopes are consistent with those obtained from studies of other groups and clusters. The scatter in the TF relations is in the range 0.5-1.1 mag in different bands. This scatter is considerably larger compared to those observed in other groups and clusters. It is suggested that the larger scatter in the TF relations for the Eridanus group is related to the loose structure of the group. If the TF relations are constructed using the baryonic mass (stellar +HI + Helium mass) instead of the stellar luminosity, nearly identical slopes are obtained in the R and in the near-infrared bands. The baryonic TF (baryonic massvs log2V _flat) slope is in the range 3.5–4.1.     

TheHI content of the Eridanus group of galaxies

The HI content of galaxies in the Eridanus group is studied using the GMRT observations and the HIPASS data. A significant HI deficiency up to a factor of 2–3 is observed in galaxies in the high galaxy density regions. The HI deficiency in galaxies is observed to be directly correlated to the local projected galaxy density, and inversely correlated to the line-of-sight radial velocity. Furthermore, galaxies with larger optical diameters are predominantly in the lower galaxy density regions. It is suggested that the HI deficiency in Eridanus is due to tidal interactions. In some galaxies, evidences of tidal interactions are seen. An important implication is that significant evolution of galaxies can take place in the group environment. In the hierarchical way of formation of clusters via mergers of groups, a fraction of the observed HI deficiency in clusters could have originated in groups. The co-existence of S0s and severely HI deficient galaxies in the Eridanus group suggests that tidal interaction is likely to be an effective mechanism for transforming spirals to S0s.     

Radio continuum and far-infrared emission from the galaxies in the Eridanus group

The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L _20cm > 10²³ W Hz⁻¹) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L _20cm ∼ 10²² W Hz⁻¹) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters.     

A high galactic latitude HI 21 cm-line absorption survey using the GMRT: II. Results and interpretation

We have carried out a sensitive high-latitude (|b| > 15°) HI 21 cm-line absorption survey towards 102 sources using the GMRT. With a 3σ detection limit in optical depth of ∼ 0.01, this is the most sensitive HI absorption survey. We detected 126 absorption features most of which also have corresponding HI emission features in the Leiden Dwingeloo Survey of Galactic neutral Hydrogen. The histogram of random velocities of the absorption features is well-fit by two Gaussians centered at V_1sr ∼ 0 km s⁻¹ with velocity dispersions of 7.6 ± 0.3 km s⁻¹ and 21 ± 4 km s⁻¹ respectively. About 20% of the HI absorption features form the larger velocity dispersion component. The HI absorption features forming the narrow Gaussian have a mean optical depth of 0.20 ± 0.19, a mean HI column density of (1.46 ± 1.03) × 10²⁰ cm⁻², and a mean spin temperature of 121 ± 69 K. These HI concentrations can be identified with the standard HI clouds in the cold neutral medium of the Galaxy. The HI absorption features forming the wider Gaussian have a mean optical depth of 0.04 ± 0.02, a mean HI column density of (4.3 ± 3.4) × 10¹⁹ cm⁻², and a mean spin temperature of 125 ± 82 K. The HI column densities of these fast clouds decrease with their increasing random velocities. These fast clouds can be identified with a population of clouds detected so far only in optical absorption and in HI emission lines with a similar velocity dispersion. This population of fast clouds is likely to be in the lower Galactic Halo.     

ATLAS, and Wide-Angle Tail Galaxies in ATLAS

Using the Australia Telescope Compact Array (ATCA), ATLAS (Australia Telescope Large Area Survey) is imaging two fields totalling 7 square degrees down to 10 μJy beam^− 1 at 1.4 GHz. We have found 6 wide-angle tail galaxies (WATs), 4 of which have sufficient data to identify associated galaxy overdensities. The largest WAT, at a red-shift of 0.22, appears to be associated with an overdensity of galaxies that is spread over an unusually large extent of 12 Mpc, with a velocity range of 4500 km s^− 1. Here we present the WATs in ATLAS and discuss the implications of these observations for future large-scale radio surveys such as ASKAP-EMU.     

The Ks-band Tully-Fisher Relation — A determination of the Hubble parameter from 218 ScI galaxies and 16 galaxy clusters

The value of Hubble parameter (H₀) is determined using the morphologically type dependent Ks-band Tully-Fisher Relation (K-TFR). The slope and zero point are determined using 36 calibrator galaxies with ScI morphology. Calibration distances are adopted from direct Cepheid distances, and group or companion distances derived with the Surface Brightness Fluctuation Method or Type Ia Supernova. It is found that a small morphological type effect is present in the K-TFR such that ScI galaxies are more luminous at a given rotational velocity than Sa/Sb galaxies and Sbc/Sc galaxies of later luminosity classes. Distances are determined to 16 galaxy clusters and 218 ScI galaxies with minimum distances of 40.0 Mpc. From the 16 galaxy clusters a weighted mean Hubble parameter of H₀ = 84.2 ± 6 km s⁻¹ Mpc⁻¹ is found. From the 218 ScI galaxies a Hubble parameter of H₀ = 83.4 ± 8 km s⁻¹ Mpc⁻¹ is found. When the zero point of K-TFR is corrected to account for recent results that find a Large Magellanic Cloud distance modulus of 18.39±0.05, a Hubble parameter of 88.0 ± 6 km s⁻¹ Mpc⁻¹ is found. Effects from Malmquist bias are shown to be negligible in this sample as galaxies are restricted to a minimum rotational velocity of 150 km s⁻¹. It is also shown that the results of this study are negligibly affected by the adopted slope for the K-TFR, inclination binning, and distance binning. A comparison with the results of the Hubble Key Project (Freedman et al. 2001) is made. Discrepancies between the K-TFR distances and the HKP I-TFR distances are discussed. Implications for Λ-CDM cosmology are considered with H₀ = 84 km s⁻¹ Mpc⁻¹. It is concluded that it is very difficult to reconcile the value of H0 found in this study with ages of the oldest globular clusters and matter density of the universe derived from galaxy clusters in the context of Λ-CDM cosmology.     

GMRT observations of interstellar clouds in the 21cm line of atomic hydrogen

Nearby interstellar clouds with high (|ν|≥10km s⁻¹) random velocities although easily detected in NaI and CaII lines have hitherto not been detected (in emission or absorption) in the HI 21cm line. We describe here deep Giant Metrewave Radio Telescope (GMRT) HI absorption observations toward radio sources with small angular separation from bright O and B stars whose spectra reveal the presence of intervening high random velocity CaII absorbing clouds. In 5 out of the 14 directions searched we detect HI 21cm absorption features from these clouds. The mean optical depth of these detections is ∼0.09 and FWHM is ∼10km s⁻¹, consistent with absorption arising from CNM clouds.     

The expansion field: the value of <Emphasis Type="Italic">H</Emphasis><Subscript>0</Subscript>

Any calibration of the present value of the Hubble constant (H ₀) requires recession velocities and distances of galaxies. While the conversion of observed velocities into true recession velocities has only a small effect on the result, the derivation of unbiased distances which rest on a solid zero point and cover a useful range of about 4–30 Mpc is crucial. A list of 279 such galaxy distances within v < 2,000 km s⁻¹ is given which are derived from the tip of the red-giant branch (TRGB), from Cepheids, and/or from supernovae of type Ia (SNe Ia). Their random errors are not more than 0.15 mag as shown by intercomparison. They trace a linear expansion field within narrow margins, supported also by external evidence, from v = 250 to at least 2,000 km s⁻¹. Additional 62 distant SNe Ia confirm the linearity to at least 20,000 km s⁻¹. The dispersion about the Hubble line is dominated by random peculiar velocities, amounting locally to <100 km s⁻¹ but increasing outwards. Due to the linearity of the expansion field the Hubble constant H ₀ can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of 78 galaxies above this limit give H ₀ = 63.0 ± 1.6 at an effective distance of 6 Mpc. They compensate the effect of peculiar motions by their large number. Support for this result comes from 28 independently calibrated Cepheids that give H ₀ = 63.4 ± 1.7 at 15 Mpc. This agrees also with the large-scale value of H ₀ = 61.2 ± 0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of H ₀ = 62.3 ± 1.3 is adopted. Because the value depends on two independent zero points of the distance scale its systematic error is estimated to be 6%. Other determinations of H ₀ are discussed. They either conform with the quoted value (e.g. line width data of spirals or the D _n −σ method of E galaxies) or are judged to be inconclusive. Typical errors of H ₀ come from the use of a universal, yet unjustified P–L relation of Cepheids, the neglect of selection bias in magnitude-limited samples, or they are inherent to the adopted models.     

The Evaporation Regime in a Confined Flare

We studied the evolution of a small eruptive flare (GOES class C1) from its onset phase using multi-wavelength observations that sample the flare atmosphere from the chromosphere to the corona. The main instruments involved were the Coronal Diagnostic Spectrometer (CDS) aboard SOHO and facilities at the Dunn Solar Tower of the National Solar Observatory/Sacramento Peak. Transition Region and Coronal Explorer (TRACE) together with Ramaty High-Energy Spectroscopic Imager (RHESSI) also provided images and spectra for this flare. Hα and TRACE images display two loop systems that outline the pre-reconnection and post-reconnection magnetic field lines and their topological changes revealing that we are dealing with an eruptive confined flare. RHESSI data do not record any detectable emission at energies ≥25 keV, and the observed count spectrum can be well fitted with a thermal plus a non-thermal model of the photon spectrum. A non-thermal electron flux F ≈ 5 × 10¹⁰ erg cm⁻² s⁻¹ is determined. The reconstructed images show a very compact source whose peak emission moves along the photospheric magnetic inversion line during the flare. This is probably related to the motion of the reconnection site, hinting at an arcade of small loops that brightens successively. The analysis of the chromospheric spectra (Ca II K, He I D₃ and Hγ, acquired with a four-second temporal cadence) shows the presence of a downward velocity (between 10 and 20 km s⁻¹) in a small region intersected by the spectrograph slit. The region is included in an area that, at the time of the maximum X-ray emission, shows upward motions at transition region (TR) and coronal levels. For the He I 58.4 and O v 62.97 lines, we determine a velocity of ≈−40 km s⁻¹ while for the Fe XIX 59.22 line a velocity of ≈−80 km s⁻¹ is determined with a two-component fitting. The observations are discussed in the framework of available hydrodynamic simulations and they are consistent with the scenario outlined by Fisher (1989). No explosive evaporation is expected for a non-thermal electron beam of the observed characteristics, and no gentle evaporation is allowed without upward chromospheric motion. It is suggested that the energy of non-thermal electrons can be dissipated to heat the high-density plasma, where possibly the reconnection occurs. The consequent conductive flux drives the evaporation process in a regime that we can call sub-explosive.     

Additional members of the local group of galaxies and quantized redshifts within the two nearest groups

Galaxies of redshiftz ≲ 1000 km s⁻¹ are investigated. In the South Galactic Hemisphere there are two large concentrations of these galaxies. One is in the direction of the centre of the Local Group, roughly aligned with M 31 and M 33. The other concentration is centred almost 80 degrees away on the sky and involves the next nearest galaxies to the Local Group, NGC 55, NGC 300 and NGC 253. The large scale and isolation of these concentrations, and the continuity of their redshifts require that they are all galaxies at the same, relatively close distance of the brightest group members. The fainter members of the group have higher redshifts, mimicking to some extent a Hubble relation. But if they are all at the same average distance the higher redshifts must be due to a cause other than velocity. The redshifts of the galaxies in the central areas of these groups all obey a quantization interval of δcz₀ = 72.4 kms⁻¹. This is the same quantization found by William Tifft, and later by others, in all physical groups and pairs which have been tested. The quantization discovered here, however, extends over a larger interval in redshift than heretofore encountered. The majority of redshifts used in the present analysis are accurate to ± 8 km s⁻¹. The deviation of those redshifts from multiples of 72.4 km s^-1 averages ±8.2 km s⁻¹. The astonishing result, however, is that for those redshifts which are known more accurately, the deviation from modulo 72.4 drops to a value between 3 and 4 km s⁻¹! The amount of relative velocity allowed these galaxies is therefore implied to be less than this extremely small value.     

Isolated Shakhbazian compact groups

It is more appropriate to study the dynamics and evolution of compact groups using a sample of isolated compact groups in the nearby vicinity of which there are no accordant redshift galaxies. To look for isolated compact groups we inspected the environment of 78 Shakhbazian compact groups, with known redshifts. We found that 26 of nearby groups with V < 40000 km s⁻¹ are isolated compact groups in the vicinity of which up to a projected distance of 1 Mpc there are no accordant redshift galaxies. For four of them, the redshift of only two members are known, so their being groups is not certain. In the vicinities of eleven distant groups (V > 40000 km s⁻¹) no accordant redshift galaxies are detected as well. The reason for this may be the faintness of galaxies there. These groups may possibly be isolated.     

Investigation of the new Local Group galaxy VV 124

We present the results of our stellar photometry and spectroscopy for the new Local Group galaxy VV124 (UGC4879) obtainedwith the 6-m BTAtelescope. The presence of a fewbright supergiants in the galaxy indicates that the current star formation process is weak. The apparent distribution of stars with different ages in VV 124 does not differ from the analogous distributions of stars in irregular galaxies, but the ratio of the numbers of young and old stars indicates that VV 124 belongs to the rare Irr/Sph type of galaxies. The old stars (red giants) form the most extended structure, a thick disk with an exponential decrease in the star number density to the edge. Definitely, the young population unresolvable in images makes a great contribution to the background emission from the central galactic regions. The presence of young stars is also confirmed by the [OIII] emission line visible in the spectra that belongs to extensive diffuse galactic regions. The mean radial velocity of several components (two bright supergiants, the unresolvable stellar population, and the diffuse gas) is υ _h = −70 ± 15 km s⁻¹ and the velocity with which VV 124 falls into the Local Group is υ _LG = −12 ± 15 km s⁻¹. We confirm the distance to the galaxy (D = 1.1 ± 0.1 Mpc) and the metallicity of red giants ([Fe/H] = −1.37) found by Kopylov et al. (2008). VV 124 is located on the periphery of the Local Group approximately at the same distance from M31 and our Galaxy and is isolated from other galaxies. The galaxy LeoA nearest to it is 0.5 Mpc away.     

GMRT detection of HI 21 cm-line absorption from the peculiar galaxy in Abell 2125

Using the recently completed Giant Meterwave Radio Telescope, we have detected the HI 21 cm-line absorption from the peculiar galaxy C153 in the galaxy cluster Abell 2125. The HI absorption is at a redshift of 0.2533, with a peak optical depth of 0.36. The full width at half minimum of the absorption line is 100 km s⁻¹. The estimated column density of atomic Hydrogen is 0.7×10²²(T _s /100) cm⁻². The HI absorption is redshifted by ∼400km s⁻¹ compared to the [OIII] emission line from this system. We attribute this to an infalling cold gas or to an out-flowing ionised gas, or to a combination of both as a consequence of tidal interactions of C153 with either a cluster galaxy or the cluster potential.     

Pitch angles of distant spiral galaxies

We have studied the pitch angles of spiral arms for 31 distant galaxies at z ∼ 0.7 from three Hubble Deep Fields (HDF-N, HDF-S, HUDF). Using the pitch angle-rotation velocity relation calibrated from nearby galaxies, we have estimated the rotation velocities of galaxies from the deep fields. These estimates have a low accuracy (∼50 km s⁻¹), but they allow low-mass and giant galaxies to be distinguished. The Tully-Fisher relation constructed using our velocity estimates shows satisfactory agreement with the actually observed relations for distant galaxies and provides evidence for the luminosity evolution of spiral galaxies.     

Nearby galaxies. IV. The global Hubble parameter and the dispersion of the Hubble relation

Using a spherically symmetric model of the Virgo flow the global Hubble parameter has been estimated from the observed radial velocities and the photometrically measured distances of nearby galaxies. Adopting the observed recession velocity of the Virgo Cluster to about 1000 km s⁻¹ and the infall velocity of the Local Group to 350 km s⁻¹ the global Hubble constant results to 73 ± 10 km s⁻¹ Mpc⁻¹. This value corresponds with the distance of the Virgo Cluster of 18 ± 2 Mpc. The cosmic dispersion of the galaxies around the Hubble relation is of order of 35 km s⁻¹.     

The isolated dSph galaxy KKs3 in the local Hubble flow

We present SALT spectroscopy of a globular cluster in the center of the nearby isolated dSph galaxy KKs3 situated at a distance of 2.12 Mpc. Its heliocentric radial velocity is 316 ± 7 km s^–1 that corresponds to V_LG = 112 km s^–1 in the Local Group (LG) reference frame. We use its distance and velocity along with the data on other 35 field galaxies in the proximity of the LG to trace the local Hubble flow. The following basic properties of the local field galaxies are briefly discusse: morphology, absolute magnitudes, average surface brightnesses, specific star formation rates, and hydrogen mass‐to‐stellar mass ratios. Surprisingly, the sample of the neighboring isolated galaxies displays no signs of compression under the influence of the expanding Local Void. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Intrinsic Redshifts and the Tully–Fisher Distance Scale

The Tully–Fisher relationship (TFR) has been shown to have a relatively small observed scatter of ∼±0.35 mag implying an intrinsic scatter < ±0.30 mag. However, when the TFR is calibrated from distances derived from the Hubble relation for field galaxies scatter is consistently found to be ±0.64 to ±0.84 mag. This significantly larger scatter requires that intrinsic TFR scatter is actually much larger than ±0.30 mag, that field galaxies have an intrinsic TFR scatter much larger than cluster spirals, or that field galaxies have a velocity dispersion relative to the Hubble flow in excess of 1000 km s⁻¹. Each of these potential explanations faces difficulties and contradicted by available data and the results of previous studies. An alternative explanation is that the measured redshifts of galaxies are composed of a cosmological redshift component predicted from the value of the Hubble constant and a superimposed intrinsic redshift component previously identified in other studies. This intrinsic redshift component may exceed 5000 km s⁻¹ in individual galaxies. In this alternative scenario a possible value for the Hubble constant is 55–60 km s⁻¹ Mpc⁻¹.     

Quantized redshifts: A status report

The current status of a continuing programme of tests for redshift periodicity or ‘quantization’ of nearby bright galaxies is described. So far the redshifts of over 250 galaxies with high-precision HI profiles have been used in the study. In consistently selected sub-samples of the datasets of sufficient precision examined so far, the redshift distribution has been found to be strongly quantized in the galactocentric frame of reference. The phenomenon is easily seen by eye and apparently cannot be ascribed to statistical artefacts, selection procedures or flawed reduction techniques. Two galactocentric periodicities have so far been detected, ∼ 71 .5km s^-1 in the Virgo cluster, and ∼37. 5km s^-1 for all other spiral galaxies within ∼ 2600km s^-1. The formal confidence levels associated with these results are extremely high.     

Surveying the Local Supercluster Plane

We investigate the distribution and velocity field of galaxies situated in a band of 100 by 20 degrees centered on M87 and oriented along the Local supercluster plane. Our sample amounts 2158 galaxies with radial velocities less than 2000 km s^?1. Of them, 1119 galaxies (52%) have distance and peculiar velocity estimates. About 3/4 of early-type galaxies are concentrated within the Virgo cluster core, most of the late-type galaxies in the band locate outside the virial radius. Distribution of gas-rich dwarfs with M_HI >M_* looks to be insensitive to the Virgo cluster presence. Among 50 galaxy groups in the equatorial supercluster band 6 groups have peculiar velocities about 500–1000 km s^?1 comparable with virial motions in rich clusters. The most cryptic case is a flock of nearly 30 galaxies around NGC4278 (Coma I cloud), moving to us with the mean peculiar velocity of ?840 km s^?1. This cloud (or filament?) resides at a distance of 16.1 Mpc from us and approximately 5 Mpc away from the Virgo center. Galaxies around Virgo cluster exhibit Virgocentric infall with an amplitude of about 500 km s^?1. Assuming the spherically symmetric radial infall, we estimate the radius of the zero-velocity surface to be R₀ = (7.0±0.3) Mpc that yields the total mass of Virgo cluster to be (7.4 ± 0.9)× 10¹⁴M_⊙ in tight agreement with its virial mass estimates. We conclude that the Virgo outskirts does not contain significant amounts of dark mater beyond its virial core.     

A Catalogue of Galaxies within 10 MPC

A catalogue is given of the 179 known galaxies within 10 Mpc. The inclusion of a galaxy depends on its redshift (v₀ ≤ 500 km s⁻¹) or, in the case of 7 dwarf galaxies, on the fact that their distances are known to be small. The catalogue contains in addition 52 more distant galaxies with v₀ ≤ 500 km s⁻¹: 50 are bona fide Virgo cluster members and 2 are members of the Leo group. Positions, types, absorption-corrected luminosities, and velocities are given for the catalogue galaxies. The catalogue is believed to be nearly complete for galaxies brighter than ∽ – 18^m.5, but it contains also many considerably fainter galaxies. The galaxies within 10 Mpc form the Local Group with 28 members and seven additional groups with a total of 92 known members. 59 galaxies (33%) do not seem to belong to any group.