Intense look at Virgo Southern Extension

International Astronomical Union Colloquium

We present the preliminary results of a search for new blue compact dwarf (BCD) galaxies in the Virgo cluster. Our search is based on the automated selection of compact galaxies from digitised scans of UK Schmidt plates and is designed to put quantitative limits on the luminosity function of compact galaxies in Virgo.We have selected a sample of 310 candidate BCD galaxies and have obtained radial velocities for 177 of them using the UK Schmidt FLAIR-II multi-object fibre spectrograph. We have confirmed two new members of the cluster. One is classified as a member (but without velocity) in the Binggeli, Sandage and Tammann (1985) catalogue (VCC) and the other does not appear in the VCC and is therefore probably a new BCD. The other 175 galaxies are background objects at higher redshift, including one classified as ”BCD or background“ in the VCC which we now confirm to be a background object.

The Astrophysical Journal Supplement Series

Virgo is the nearest galaxy cluster; it is thus ideal for studies of galaxy evolution in dense environments in the local universe. It is embedded in a complex filamentary network of galaxies and groups, which represents the skeleton of the large-scale Laniakea supercluster. Here we assemble a comprehensive catalog of galaxies extending up to ∼12 virial radii in projection from Virgo to revisit the cosmic-web structure around it. This work is the foundation of a series of papers that will investigate the multiwavelength properties of galaxies in the cosmic web around Virgo. We match spectroscopically confirmed sources from several databases and surveys including HyperLeda, NASA Sloan Atlas, NASA/IPAC Extragalactic Database, and ALFALFA. The sample consists of ∼7000 galaxies. By exploiting a tomographic approach, we identify 13 filaments, spanning several megaparsecs in length. Long >17 h –1 Mpc filaments, tend to be thin (<1 h –1 Mpc in radius) and with a low-density contrast (...

Astronomy and Astrophysics Supplement Series, 2000

Optical spectroscopy of 76 galaxies, 48 of which are projected in the direction of the Virgo cluster and 28 onto the Coma-A1367 supercluster, is reported. Adding these new measurements to those found in the literature, the redshift completeness in the Virgo region becomes 92% at B T ≤ 16.0 and 68% at B T ≤ 18.0. The one of CGCG galaxies in the direction of the Coma-A1367 supercluster becomes 98%. The Virgo cluster membership estimates obtained on morphological grounds by Binggeli et al. (1985) are confirmed in all cases. However, several "possible members" classified as BCD (if in the cluster) are found instead to be giant emission-line galaxies in the background of the Virgo cluster

Arxiv preprint astro-ph/9811464, 1998

We draw a quantitative comparison of the distribution of the galaxies and the intra-cluster gas in the Virgo cluster by extending the morphological analysis by Binggeli et al. (1987) to the intra-cluster gas. We use the Virgo Cluster Catalog in combination with data from the ROSAT All-Sky Survey. The galaxy distribution and the gas distribution are relatively similar. The steep density gradient southwest of M87 previously observed in the optical is also seen in the X-ray emission. In both wavebands the irregular structure of Virgo can be decomposed into three major subclusters centred on M87, M49, and M86. A new statistical method of subcluster decomposition is applied. Radial galaxy and X-ray density profiles of the three subclusters are fitted with β-models, allowing analytic deprojection. Comparison of these profiles reveals no significant difference between the galaxy number density and the smoothed galaxy luminosity density if the inner part is excluded (r < 60 , dominated by the central giant galaxy), i.e. there is no general luminosity segregation in the cluster. The gas density profile is steeper than the galaxy density profile in the inner part (again excluding the central galaxy), while this trend is reversed in the outer part. The turning point is around 300 kpc. A comparison among the subclusters shows the poorer the subcluster the steeper its radial profile, i.e. the more compact it is, both in the optical and the X-rays. This is in general agreement with recent N-body simulations by Navarro et al. (1997). The subcluster profiles for different Hubble types confirm the well-known result that the distribution of the late-type galaxies is more extended than the early types. Differential and integrated mass density profiles of the different components in the M87 and M49 subclusters are presented. The total, gravitating mass (dominated by dark matter) is inferred from the distribution of the X-ray gas assuming hydrostatic equilibrium. In the M87 subcluster the gas mass is about three times the mass in galaxies (assuming a constant M/L = 20 for the single galaxies), while it accounts only for 8% to 14% of the total mass at 0.4 and 1 Mpc, respectively. In the M49 subcluster there is more mass in the galaxies than in the gas and the gas-to-total mass fraction is only 1%, which is unusually low for a cluster. The profiles of the projected mass-to-light ratio show relatively constant values around 500M /L ,B .

The Astrophysical Journal, 2012

We present three-dimensional space velocities of stars selected to be consistent with membership in the Virgo stellar substructure. Candidates were selected from SA 103, a single 40 × 40 field from our proper-motion (PM) survey in Kapteyn's Selected Areas (SAs), based on the PMs, Sloan Digital Sky Survey (SDSS) photometry, and follow-up spectroscopy of 215 stars. The signature of the Virgo substructure is clear in the SDSS color-magnitude diagram (CMD) centered on SA 103, and 16 stars are identified that have high Galactocentric-frame radial velocities (V GSR > 50 km s −1) and lie near the CMD locus of Virgo. The implied distance to the Virgo substructure from the candidates is 14 ± 3 kpc. We derive mean kinematics from these 16 stars, finding a radial velocity V GSR = 153 ± 22 km s −1 and proper motions (μ α cos δ, μ δ) = (−5.24, −0.91) ± (0.43, 0.46) mas yr −1. From the mean kinematics of these members, we determine that the Virgo progenitor was on an eccentric (e ∼ 0.8) orbit that recently passed near the Galactic center (pericentric distance R p ∼ 6 kpc). This destructive orbit is consistent with the idea that the substructure(s) in Virgo originated in the tidal disruption of a Milky Way satellite. N-body simulations suggest that the entire cloud-like Virgo substructure (encompassing the "Virgo Overdensity" and the "Virgo Stellar Stream") is likely the tidal debris remnant from a recently disrupted massive (∼10 9 M) dwarf galaxy. The model also suggests that some other known stellar overdensities in the Milky Way halo (e.g., the Pisces Overdensity and debris near NGC 2419 and SEGUE 1) are explained by the disruption of the Virgo progenitor.

The Astrophysical Journal, 2012

We present new stellar age profiles, derived from well-resolved optical and near-infrared images of 64 Virgo cluster disk galaxies, whose analysis poses a challenge for current disk galaxy formation models. Our ability to break the age-metallicity degeneracy and the significant size of our sample represent key improvements over complementary studies of field disk galaxies. Our results can be summarized as follows: first, and contrary to observations of disk galaxies in the field, these cluster galaxies are distributed almost equally amongst the three main types of disk galaxy luminosity profiles (I/II/III), indicating that the formation and/or survival of Type II breaks is suppressed within the cluster environment. Second, we find examples of statistically significant inversions ("U-shapes") in the age profiles of all three disk galaxy types, reminiscent of predictions from high-resolution simulations of classically truncated Type II disks in the field. These features characterize the age profiles for only about a third (36%) of each disk galaxy type in our sample. An even smaller fraction of cluster disks (∼11% of the total sample) exhibit age profiles that decrease outward (i.e., negative age gradients). Instead, flat and/or positive age gradients prevail (50%) within our Type I, II, and III subsamples. These observations thus suggest that while stellar migrations and inside-out growth can play a significant role in the evolution of all disk galaxy types, other factors contributing to the evolution of galaxies can overwhelm the predicted signatures of these processes. We interpret our observations through a scenario whereby Virgo cluster disk galaxies formed initially like their brethren in the field but which, upon falling into the cluster, were transformed into their present state through external processes linked to the environment (e.g., ram-pressure stripping and harassment). Current disk galaxy formation models, which have largely focused on field galaxies, fail to reproduce these results, thus calling for adequate hydrodynamical simulations of dense galaxy environments if we are to understand cluster disks. The current paper highlights numerous constraints for such simulations. In the Appendix, we confirm the claim by Erwin et al. that Type II breaks are absent in Virgo cluster S0s and discuss the detection of Type III breaks in such galaxies.

The Astrophysical Journal Supplement Series, 2012

Astrophysics and Space Science Proceedings, 2007

Dark Matter supposedly dominates the extragalactic, yet no totally dark structure of galactic proportions has ever been convincingly identified. Earlier we suggested that VIRGOHI 21, a 21-cm source we found in the Virgo Cluster at Jodrell Bank using single-dish observations , was probably such a dark galaxy because of its broad line-width (∼ 200 km s −1 ) unaccompanied by any visible gravitational source to account for it. Now we have managed to image VIR-GOHI 21 in the neutral-hydrogen line, and indeed we find what appears to be a dark, edge-on, spinning disc with the mass and diameter of a typical spiral galaxy. Moreover the disc has unquestionably interacted with NGC 4254, a luminous spiral with an odd one-armed morphology, but lacking the massive interactor invariably responsible for such a feature. Published 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 completely independent evidence for the massive nature of VIRGOHI 21.

2008

We present distance estimates for eleven peculiar Virgo cluster spiral galaxies based on measurements of the stellar kinematics of their central 2 kpc. Stellar circular velocities were obtained using two-integral dynamical models. Distances were obtained by comparing, at each radius, the stellar circular velocities with synthetic H_alpha rotation curves derived from NIR Tully-Fisher relations.The results show that most of our galaxies are located within 4 Mpc of the core of the cluster. Three of these galaxies, previously classified as &quot;low rotator galaxies&quot; or with &quot;Truncated/Compact&quot; H_alpha radial distributions, have stellar kinematics-based distances that are discrepant with HI-based distances by at least 60%, and are likely to be located within the virial radius of the cluster. These discrepancies appear due to very truncated gas distributions plus non-circular gas motions or gas motions not in the plane of the stellar disk, perhaps as the result of gravitat...

The Astrophysical Journal, 2014

An observational evidence is presented for the alignment between the cosmic sheet and the principal axis of the velocity shear field at the position of the Virgo cluster. The galaxies in and around the Virgo cluster from the Extended Virgo Cluster Catalog recently constructed by Kim et al. are used to determine the direction of the local sheet. The peculiar velocity field reconstructed from the Sloan Digital Sky Survey Data Release 7 is analyzed to estimate the local velocity shear tensor at the Virgo center. Showing first that the minor principal axis of the local velocity shear tensor is almost parallel to the line of sight direction, we detect a clear signal of alignment between the positions of the Virgo satellites and the intermediate principal axis of the local velocity shear projected onto the plane of the sky. Furthermore, the dwarf satellites are found to appear more strongly aligned than the normal counterparts, which is interpreted as indication of the following: (i) The normal and the dwarf satellites fall in the Virgo cluster preferentially along the local filament and the local sheet, respectively. (ii) The local filament is aligned with the minor principal axis of the local velocity shear while the local sheet is in parallel to the plane spanned by the minor and the intermediate principal axes. Our result is consistent with the recent numerical claim that the velocity shear is a good tracer of the cosmic web.