We use a friends-of-friends algorithm to identify loose groups from the northern CfA2 survey covering the region 8h<={alpha}_(1950)_<=17h and 8.5{deg}<={delta}_(1950)_<=44.5{deg}. There are 406 groups; 149 of these contains five or more members within the survey. Geometric simulations guide our choice of the selection parameters; {delta}{rho}/{rho}=80 is the limiting density contrast and V0=350km/s is the fiducial velocity linking parameter. The geometric simulations are particularly important for evaluating the impact of large-scale structure (e.g., the Great Wall) on group selection. The physical parameters of this large sample are coincident with our earlier results [126 groups in Ramella et al. (1989ApJ...344...57R)]: the median velocity dispersion in 192 (156; 229)km/s and the median blue log(M/L) is 2.38 (2.20; 2.52). The mass-to-light ratio (M/L) is in units of Msun/Lsun for an assumed Hubble constant, H0=100km/s/Mpc. The numbers in parentheses are 99% confidence limits. This group catalog provides a substantially larger sample for statistical studies than has been previously available. For example, it provides a more substantial sample for estimation of the distribution of group velocity dispersions and of the group-group correlation function. (Copyright) 1997 American Astronomical Society.
The catalog contains statistically homogeneous and physically well graunded groups of galaxies based on the CfA2 redshift survey (Cat. J/ApJS/121/287) in the area of space 1000km/s<=cz<=15000km/s, |bII|>=20{deg}. For identification of groups we used a modification of a friends of friends (FoF) method. Principles of friendship and definition of values of presented there free parameters described in Mahtessian (1988Afz....28..255M, 1997Ap.....40..285M). There are 1971 groups with 2 or more members, for a total of 6787 members (46.3%); 765 of the groups have 3 or more members with 4375 galaxies (28.1%). The others 8790 (56.4%) galaxies make a sample of "single" galaxies. The catalog includes group numbers, numbers of members, equatorial coordinates, Virgo-centric radial velocities, line-of-sight-velocity dispersions, integrated group luminosities, and relative quantity of false members.
The catalog contains statistically homogeneous groups of galaxies based on the Harvard-Smithsonian Center for Astrophysics (CfA) redshift survey. Groups in the catalog are all density enhancements in redshift space of a factor greater than 20. All groups contain at least three members. There are 176 groups in the catalog and 102 groups have been identified in one or more previous studies. The catalog includes group numbers, numbers of members, equatorial coordinates, mean flow-corrected galactocentric velocities, line-of-sight-velocity dispersion, integrated group magnitudes, crossing times for the groups, and mean harmonic radii of the groups.
The catalog contains nearby groups of galaxies with outer number density enhancement greater than 20. The groups were searched using a whole sky catalog of 1312 galaxies brighter than mag 13.2 (B) with complete redshift information (Huchra et al. =1983ApJS...52...89H). Only groups containing more than two members are included. The catalogue includes equatorial coordinates, average radial velocities, and velocity dispersions for 92 nearby groups in the first file. A second file contains the results of a comparison between this catalog and de Vaucouleurs' (1975) catalog of nearby groups The Hubble constant was assumed 100km/s/Mpc.
We present a large catalog of galaxy loose groups in the Southern Galactic Hemisphere, selected from the Perseus-Pisces redshift Survey (PPS). Particular care is taken in order to obtain group samples as homogeneous as possible to previously published catalogs. Groups are identified with the adaptive Friends-of-Friends (FoF) algorithm of Huchra & Geller (1982ApJ...257..423H), with suitable normalizations V_0_=350km/s and D_0_=0.231h.Mpc. As a necessary ingredient of FoF algorithms, we obtain the galaxy luminosity function (LF) for PPS. Its Schechter parameters ({alpha}=-1.15+/-0.15, M_*_=-19.3+/-0.1) are in good agreement with similar LF estimates from samples previously used to select groups. The LF normalizations {phi}_*_=0.02h^3^/Mpc^3^ appropriate for PPS yields a density threshold {delta}n/n~180 for the adopted D_0_, apparently rather different from the desired {delta}n/n~80 used in previous studies. We then consider several other link normalizations, and briefly discuss their effect on group properties. We suggest to replace the customarily adopted {delta}n/n parametrization with the more direct D_0_ parametrization. All our catalogs contain N_G_~200 groups, significantly more than in most previous studies where group samples were obtained from galaxy data sets of comparable quality to (but smaller extent than) PPS. The group properties are rather sensitive to the adopted D_0_ and V_0_, but vary little with different redshift corrections, redshift cut-off, and galaxy LF. Loose groups in PPS nicely trace the large scale structure (LSS) in the parent galaxy sample. Physical properties of groups in PPS and in other directly comparable samples are in good agreement. There seems to be a complex interplay among LSS features, FoF grouping procedure, and group properties.
In this Letter, we analyze the radial ultraviolet-optical color distributions in a sample of low redshift green valley galaxies, with the Galaxy Evolution Explorer (GALEX)+Sloan Digital Sky Survey (SDSS) images, to investigate how the residual recent star formation is distributed in these galaxies. We find that the dust-corrected u-r colors of early-type galaxies (ETGs) are flat out to R_90_, while the colors monotonously turn blue when r>0.5 R_50_ for late-type galaxies (LTGs). More than half of the ETGs are blue-cored and have remarkable positive NUV-r color gradients, suggesting that their star formations are centrally concentrated. The rest have flat color distributions out to R_90_. The centrally concentrated star formation activity in a large portion of ETGs is confirmed by the SDSS spectroscopy, showing that ~50% of the ETGs have EW(H{alpha})>6.0 {AA}. Of the LTGs, 95% show uniform radial color profiles, which can be interpreted as a red bulge plus an extended blue disk. The links between the two kinds of ETGs, e.g., those objects having remarkable "blue-cores" and those having flat color gradients, are less known and require future investigations. It is suggested that the LTGs follow a general model by which quenching first occurs in the core regions, and then finally extend to the rest of the galaxy. Our results can be re-examined and have important implications for the IFU surveys, such as MaNGA and SAMI.
Stellar bars are known to gradually funnel gas to the central parts of disk galaxies. It remains a matter of debate why the distribution of ionized gas along bars and in the circumnuclear regions varies among galaxies. Our goal is to investigate the spatial distribution of star formation (SF) within bars of nearby low-inclination disk galaxies (i<65deg) from the S4G survey. We aim to link the loci of SF to global properties of the hosts (morphological type, stellar mass, gas fraction, and bar-induced gravitational torques), providing constraints for the conditions that regulate SF in bars. We use archival GALEX far- and near-UV imaging for 772 barred galaxies, and for a control sample of 423 non-barred galaxies. We also assemble a compilation of continuum-subtracted H{alpha} images for 433 barred galaxies, 70 of which we produced from ancillary photometry and MUSE and CALIFA integral field unit data cubes. We employ two complementary approaches: i) the analysis of bar (2D) and disk (1D) stacks built from co-added UV images (oriented and scaled with respect to the stellar bars and the extent of disks) of hundreds of galaxies that are binned based on their Hubble stage (T) and bar family; and ii) the visual classification of the morphology of ionized regions (traced from H{alpha} and UV data) in individual galaxies into three main SF classes: A) only circumnuclear SF; B) SF at the bar ends, but not along the bar; and C) SF along the bar. Barred galaxies with active and passive inner rings are likewise classified. Massive, gas-poor, lenticular galaxies typically belong to SF class A; this is probably related to bar-induced quenching of SF in the disk. The distribution of SF class B peaks for early- and intermediate-type spirals; this most likely results from the interplay of gas flow, shocks, and enhanced shear in massive centrally concentrated galaxies with large bar amplitudes (the latter is supported by the lack of a dip in the radial distribution of SF in non-barred galaxies). Late-type gas-rich galaxies with high gravitational torques are mainly assigned to SF class C; we argue that this is a consequence of low shear among the faintest galaxies. In bar stacks of spiral galaxies the UV emission traces the stellar bars and dominates on their leading side, as witnessed in simulations. Among early-type spirals the central UV emission is ~0.5mag brighter in strongly barred galaxies, relative to their weakly barred counterparts; this is probably related to the efficiency of strong bars sweeping the disk gas and triggering central starbursts. On the contrary, in later types the UV emission is stronger at all radii in strongly barred galaxies than in weakly barred and non-barred ones. We also show that the distributions of SF in inner-ringed galaxies are broadly the same in barred and non-barred galaxies, including a UV and H{alpha) deficit in the middle part of the bar; this hints at the effect of resonance rings trapping gas that is no longer funneled inwards. Distinct distributions of SF within bars are reported in galaxies of different morphological types. Star-forming bars are most common among late-type gas-rich galaxies. Bars are important agents in the regulation of SF in disks.
We present new H{alpha}+[NII] imaging data of late-type galaxies in the Herschel Reference Sample aimed at studying the star formation properties of a K-band-selected, volume-limited sample of nearby galaxies. The H{alpha}+[NII] data are corrected for [NII] contamination and dust attenuation using different recipes based on the Balmer decrement and the 24um luminosities. We show that the H{alpha} luminosities derived with different corrections give consistent results only whenever the the uncertainty on the estimate of the Balmer decrement is [C(H{beta})]<=0.1. We use these data to derive the star formation rate of the late-type galaxies of the sample, and compare these estimates to those determined using independent monochromatic tracers (FUV, radio continuum) or the output of spectral energy distribution (SED) fitting codes. This comparison suggests that the 24um based dust extinction correction for the H{alpha} data might be non universal, and that it should be used with caution in all objects with a low star formation activity, where dust heating can be dominated by the old stellar population. Furthermore, because of the sudden truncation of the star formation activity of cluster galaxies occurring after their interaction with the surrounding environment, the stationarity conditions required to transform monochromatic fluxes into star formation rates might not always be satisfied in tracers other than the H{alpha} luminosity. In a similar way, the parametrisation of the star formation history generally used in SED fitting codes might not be adequate for these recently interacting systems. We then use the derived star formation rates to study the SFR luminosity distribution and the typical scaling relations of the late-type galaxies of the HRS. We observe a systematic decrease of the specific star formation rate with increasing stellar mass, stellar mass surface density, and metallicity. We also observe an increase of the asymmetry and smoothness parameters measured in the H{alpha}-band with increasing SSFR, probably induced by an increase of the contribution of giant HII regions to the H{alpha} luminosity function in star-forming low-luminosity galaxies.
H{alpha} imaging survey of the 40% ALFALFA HI LSBGs
Short Name:
J/ApJS/242/11
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a narrow H{alpha}-band imaging survey of 357 low surface brightness galaxies (LSBGs) that are selected from the spring sky region of the 40% Arecibo Legacy Fast Arecibo L-band Feed Array (ALFALFA) HI Survey. All the H{alpha} images are obtained from the 2.16m telescope, operated by the Xinglong Observatory of the National Astronomical Observatories, Chinese Academy of Sciences. We provide the H{alpha} fluxes and derive the global star formation rates (SFRs) of LSBGs after the Galactic extinction, internal extinction, and [NII] contamination correction. Compared to normal star-forming galaxies, LSBGs have a similar distribution in the HI surface density ({Sigma}HI), but their SFRs and star formation surface density ({Sigma}SFR) are much lower. Our results show that the gas-rich LSBGs selected from the ALFALFA survey obviously deviate from the Kennicutt-Schmidt law, in the relation between the star formation surface density ({Sigma}SFR) and the gas surface density ({Sigma}gas). However, they follow the extended Schmidt law well when taking the stellar mass of the galaxy into consideration.
We present the Hamburg/RASS Catalogue (HRC) of optical identifications of X-ray sources at high-galactic latitude. The HRC includes all X-ray sources from the ROSAT Bright Source Catalogue (RASS-BSC) with galactic latitude |b|>=30{deg} and declination DE>=0{deg}. In this part of the sky covering ~10 000 deg^2^ the RASS-BSC contains 5341 X-ray sources. For the optical identification we used blue Schmidt prism and direct plates taken for the northern hemisphere Hamburg Quasar Survey (HQS) which are now available in digitized form. The limiting magnitudes are 18.5 and 20, respectively. For 82% of the selected RASS-BSC an identification could be given. For the rest either no counterpart was visible in the error circle or a plausible identification was not possible. With ~42% AGN represent the largest group of X-ray emitters, ~31% have a stellar counterpart, whereas galaxies and cluster of galaxies comprise only ~4% and ~5%, respectively. In ~3% of the RASS-BSC sources no object was visible on our blue direct plates within 40" around the X-ray source position. The catalogue is used as a source for the selection of (nearly) complete samples of the various classes of X-ray emitters.
