We present a new catalog of galaxies in the wider region of the Virgo cluster, based on the Sloan Digital Sky Survey (SDSS) Data Release 7. The Extended Virgo Cluster Catalog (EVCC) covers an area of 725 deg 2 or 60.1 Mpc 2 . It is 5.2 times larger than the footprint of the classical Virgo Cluster Catalog (VCC) and reaches out to 3.5 times the virial radius of the Virgo cluster. We selected 1324 spectroscopically targeted galaxies with radial velocities less than 3000 km s −1 . In addition, 265 galaxies that have been missed in the SDSS spectroscopic survey but have available redshifts in the NASA Extragalactic Database are also included. Our selection process secured a total of 1589 galaxies of which 676 galaxies are not included in the VCC. The certain and possible cluster members are defined by means of redshift comparison with a cluster infall model. We employed two independent and complementary galaxy classification schemes: the traditional morphological classification based on the visual inspection of optical images and a characterization of galaxies from their spectroscopic features. SDSS u, g, r, i, and z passband photometry of all EVCC galaxies was performed using Source Extractor. We compare the EVCC galaxies with the VCC in terms of morphology, spatial distribution, and luminosity function. The EVCC defines a comprehensive galaxy sample covering a wider range in galaxy density that is significantly different from the inner region of the Virgo cluster. It will be the foundation for forthcoming galaxy evolution studies in the extended Virgo cluster region, complementing ongoing and planned Virgo cluster surveys at various wavelengths.Subject headings: catalogs -surveys -galaxies: clusters: general the spectroscopic data for refined classification of galaxies in the Virgo cluster region.We organize this paper as follows. Section 2 describes the definition of the EVCC region and the selection of galaxies. In section 3, we introduce two schemes of galaxy classification based on the SDSS imaging and spectroscopic data. Galaxy photometry is described in section 4 and the final EVCC catalog is presented in section 5. In section 6, we present a comparison between the EVCC and VCC. Finally, we summarize our results in section 7. SELECTION OF GALAXIES DataThe construction of the EVCC is based on the SDSS Data Release 7 (DR7) (Abazajian et al. 2009). The SDSS DR7 provides reduced and calibrated images taken in the u, g, r, i, and z bands with an effective exposure time of 54s in each band (see also Stoughton et al. 2002). The pixel scale of 0.396 arcsec and the average seeing of 1.4 arcsec correspond to a physical size of 32 pc and 112 pc, respectively, at a Virgo cluster distance of 16.5 Mpc (i.e., a distance modulus m − M = 31.1; Jerjen et al. 2004;Mei et al. 2007). The SDSS spectroscopic survey covers nominally all galaxies brighter than r ≤ 17.77 and r-band Petrosian half-light surface brightnesses µ 50 ≤ 24.5 mag arcsec −2 (Strauss et al. 2002). It provides fiber spectra with a wavelength coverage between 380...

We have analysed JHKL observations of the stellar population of the ≈9 Myr‐old η Chamaeleontis cluster. Using infrared (IR) colour–colour and colour‐excess diagrams, we find that the fraction of stellar systems with near‐IR excess emission is 0.60 ± 0.13 (2σ). This result implies considerably longer disc lifetimes than found in some recent studies of other young stellar clusters. For the classical T Tauri (CTT) and weak‐lined T Tauri (WTT) star population, we also find a strong correlation between the IR excess and Hα emission. The IR excesses of these stars indicate a wide range of star–disc activity: from a CTT star showing high levels of accretion to CTT–WTT transition objects with evidence for some on‐going accretion and WTT stars with weak or absent IR excesses. Of the 15 known cluster members, four stars with IR excesses Δ(K−L) > 0.4 mag are likely experiencing ongoing accretion owing to strong or variable optical emission. The resulting accretion fraction (0.27 ± 0.13; 2σ) shows that the accretion phase, in addition to the discs themselves, can endure for at least ∼10 Myr.

In this paper, we introduce the Local Volume TiNy Titans sample (LV-TNT), which is a part of a larger body of work on interacting dwarf galaxies: TNT (Stierwalt et al. 2015). This LV-TNT sample consists of 10 dwarf galaxy pairs in the Local Universe (< 30 Mpc from Milky Way), which span mass ratios of M * ,1 /M * ,2 < 20, projected separations < 100 kpc, and pair member masses of log(M * /M ) < 9.9. All 10 LV-TNT pairs have resolved synthesis maps of their neutral hydrogen, are located in a range of environments and captured at various interaction stages. This enables us to do a comparative study of the diffuse gas in dwarf-dwarf interactions and disentangle the gas lost due to interactions with halos of massive galaxies, from the gas lost due to mutual interaction between the dwarfs. We find that the neutral gas is extended in the interacting pairs when compared to non-paired analogs, indicating that gas is tidally pre-processed. Additionally, we find that the environment can shape the HI distributions in the form of trailing tails and that the gas is not unbound and lost to the surroundings unless the dwarf pair is residing near a massive galaxy. We conclude that a nearby, massive host galaxy is what ultimately prevents the gas from being reaccreted. Dwarf-dwarf interactions thus represent an important part of the baryon cycle of low mass galaxies, enabling the "parking" of gas at large distances to serve as a continual gas supply channel until accretion by a more massive host.

We revisit the filamentary structures of galaxies around the Virgo cluster, exploiting a larger dataset based on the HyperLeda database than previous studies. In particular, this includes a large number of low-luminosity galaxies, resulting in better sampled individual structures. We confirm seven known structures in the distance range 4 h −1 Mpc < SGY < 16 h −1 Mpc, now identified as filaments, where SGY is the axis of the supergalactic coordinate system roughly along the line of sight. The Hubble diagram of the filament galaxies suggests they are infalling toward the main-body of the Virgo cluster. We propose that the collinear distribution of giant elliptical galaxies along the fundamental axis of the Virgo cluster is smoothly connected to two of these filaments (Leo II A and B). Behind the Virgo cluster (16 h −1 Mpc < SGY < 27 h −1 Mpc), we also identify a new filament elongated toward the NGC 5353/4 group ("NGC 5353/4 filament") and confirm a sheet that includes galaxies from the W and M clouds of the Virgo cluster ("W-M sheet"). In the Hubble diagram, the NGC 5353/4 filament galaxies show infall toward the NGC 5353/4 group, whereas the W-M sheet galaxies do not show hints of gravitational influence from the Virgo cluster. The filamentary structures identified can now be used to better understand the generic role of filaments in the build-up of galaxy clusters at z ≈ 0.

Using SDSS-DR7 and NASA/IPAC Extragalactic Database spectroscopic data, we identify 166 galaxies as members of the Ursa Major cluster with M r < −13.5 mag. We morphological classify all galaxies by means of carefully inspecting g−, r−, i−band colour and monochromatic images. We show that the Ursa Major cluster is dominated by late-type galaxies, but also contains a significant number of earlytype galaxies, particularly in the dwarf regime. We present further evidence for the existence of several subgroups in the cluster, consistent with previous findings. The early-type fraction is found to correlate with the mass of the subgroup. We also investigate environmental effects by comparing the properties of the Ursa Major early-type dwarf galaxies to those of the Virgo cluster. In contrast to the Virgo, the red sequence of the Ursa Major cluster is only sparsely populated in the optical and ultraviolet colour-magnitude relations. It also shows a statistically significant gap between −18 < M r < −17 mag, i.e. the Ursa Major cluster lacks early-type dwarf galaxies at the bright end of their luminosity function. We discover that the majority of early-type dwarf galaxies in the Ursa Major cluster have blue cores with hints of recent or ongoing star formation. We suggest that gravitational tidal interactions can trigger central blue star forming regions in early-type dwarfs. After that, star formation would only fade completely when the galaxies experience ram pressure stripping or harassment, both of which are nearly absent in the Ursa Major cluster.